RADIO REVIEW (141H Year of Publication)

he rele AN D RADIO REVIEW (141h Year of Publication)

No. 397. WEDNESDAY, APRIL 6TH, 1927. VOL. XX, No. 14.

Assistant Editor: Editor: Assistant Editor: F. H. HAYNES. HUGH S. POCOCK. W. JAMES.

Editorial Offices : 539-40, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone : City 4011 (3 lines). Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. Telephone : City 2847 (13 lines). Telegrams : "Ethaworid, Fleet, London."

COVENTRY : Hertford Street. BIRMINGHAM Guildhall Buildings. Navigation Street. MANCHESTER : 199, Deansgate. Telegrams: " CyeBet Coventry." Telegrams: " Autoprees. Birm- oghnm." Telegrams: "IliYe, Manobeeter." Telephoner 5210 Coventry. Telephone: 2970 and 2971 Midland. Telephone: 8970 sad 8971 City. Subscription Rates : Home, 178. 4d.; Canada, 978. 4d.; other countries abroad, içs. 6d. per annum. As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy themselves that they would not be infringing patents.

THE VALVE. cern should be to make the best use of them, being careful that each type is made to function under conditions most F one asked 1v11at is the most useful component favourable for its best performance. in wireless communication to -day there could The present issue of The Wireless World has been pre- be but one reply -the valve. -From small pared with the object in view of supplying this necessary iI beginnings the valve has grown in a compara- information, anti, in particular, details are given of the tively short period of receiving valves now available to 4-4-4-4-4-4-4-4,4+ 4,4-4-4-4-4- years until to -day it is the public. Looking through this regarded as the formidable list one is almost forced justly CONTENTS. i soul of wireless. Considering the PAGE to the conclusion that there are too unpretentious start which the valve EDITORIAL VIEWS ...... 405 many types made by nearly every made and the fact that wireless at valve manufacturer, and in very that time appeared to be getting MODERN VALVE MANUFACTURE 406 f many cases the characteristics of along quite well without it, it is the By J. J. Gracie. valves are so nearly similar that more remarkable that to -day we are READERS' NOVELTIES ...... 414 the necessity for the two types so in seems might, of completely dependent upoìl it HINTS AND TIPS FOR NEW READERS 415 doubtful. One its various forms and applications. course, go much further with the Not only is the valve used in the CHOOSING THE RIGHT VALVE 417 plea for standardisation, and say actual transmitter or receiver, but By P. K. Turner. that the time has really come when in many auxiliary directions, NEW APPARATUS ... 422 greater attention should be paid to in view especially in connection with CURRENT TOPICS ... 423 this subject, especially of broadcasting and telephone trans- the fact that an association of valve . missions. How To TEST YOUR VALVES ...... 425 manufacturers exists which can do When will the valve reach By W. James. much to facilitate standardisation. finality in its development ? Prob- NEWS FROM THE CLUBS 429 In many directions it is obviously ably at no time in its history impossible to limit the number of will BROADCAST BREVITIES 430 such a stage be reached, for so types, but different classes of fila- many new roads are open to de- RECENT INVENTIONS ... 432 ment voltages must surely be an velopment which have limitless LETTERS TO THE EDITOR 433 exception. Here it would seem that horizons. The possibilities of READERS' PROBLEMS ... 436 it would be possible to dispense multiple electrode valves have been with alternative filament voltages developed only to a small extent, and base our requirements, say, on though there is much to be done in 4 -volt valves and so gradually this field. Substitutes for incandescent filaments will, no eliminate the 2- and 6 -volt types as time goes on. These doubt, he developed in the future to enable us to obtain additional voltage types can have comparatively little in electronic emission, and already we have the valve with an the way of advantages, and yet they account for approxi- indirectly heated cathode, although this is probably only mately two- thirds of the total number of valves which in an early stage of development ; but whilst we look are really required. forward to the future we must not neglect the present, and One final plea, which must not be overlooked, is that the valves we have at our disposal to -day are unlikely to for a standard method of valve nomenclature which is become obsolete for some considerable period. Our con - surely many years overdue. B5

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. ` .' . . ! N11111111111 1111111 11111110 1111.11111111111111111111111111 ! l l l I I Ì I I lÍlÍIÍI ! l I I I I I I I I I I I I I I I l I Ì Ì iiI I I I I I I I I I I I I I I I I I I I I I Ì I .1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Ì I I ! I ! I I I I I I I I I ! I I I I I I I I I I I I I l Ì Í Ì ÌN I I I ' Í I I IIIII.l IIIIInIIiIIIIIIIIIÌÌIi llll!IIIIIIIIIIIIIIIIIIIIIIUIIIIIÌIIIÌIIiIIIII Constructional Details of Receiving and Transmitting Types.- By J. . GRACIE. VENTS move rapidly in the world of wireless, but haust by bombardment, lasting for two hours or more, has it is doubtful if anything has changed more often given way to machine pumps fitted with high- frequency than the design and methods of manufacture of gear to volatilise the " getter," which produce highly t lermionic valves, and more particularly receiving valves, exhausted valves at the rate of 30o an hour or so, and during recent years. It seems only a short time since the what, is perhaps more interesting to the reader is the fact " R " valve was generally accepted for all purposes of that these changes, which tend all the time toward faster reception, and no other type was seriously contemplated ; production and the elimination of the " human element," to -day there are, at a modest estimate, something like tend also to an unmistakable improvement in the quality 150 different kinds of receiving valve on the market, and of the finished article. The fine clearances common enough during this period of approximately four years there have to -day between grids and filaments, the closeness and also been many other valves which have sprung up, had evenness of the grid turns in a modern high " m " valve, a brief existence, and died a natural death. the uniformity of characteristics between valve and valve It can easily be appreciated that the valve manufac- of the same type, could not be approached if one had to turer has had his hands pretty full all this time ; his job depend upon manual labour, however skilled or con- has been twofold, first to improve existing valves and to scientious. develop new ones to give better characteristics, in order Nearly all receiving valves are similar in general con- to meet the public's ever -increasing demand for quality struction, that is to say, they consist of an electrode with power, and secondly to improve his manufacturing system, mounted on support wires which pass through a technique so as to reduce costs and thereby permit a corre- glass seal, the whole arrangement being contained in a sponding reduction in selling prices. glass bulb which is exhausted as completely as possible. Manufacturing Methods -A Comparison. The electrodes are usually three in number -the filament, anode, and grid. The cathode emission is obtained either The " R " valve of four years ago took 21 hours to from the filament itself, as in the case of a bright emitter, make ; the same valve nowadays is made in rather less by raising it to a state of incandescence, or from a coating than half an hour. The old - D.E.R. (then known as on the filament, in which case the filament acts merely as the L. T. i) took about five hours to make, and required a heater of the coating. Quite recently a new type has a high degree of skill in electrode assembly, exhaust, and been marketed in which the cathode is a nickel cylinder electrical treatment; this valve is now made in about one - coated with an emissive substance and heated purely by tenth of the time, and the labour involved can be classed radiation from the filament, which is inside, but not in as unskilled throughout, a result which has been achieved contact with, the cathode. largely by the introduction of automatic machinery and The glass operations are similar to those of lamp - the use of electro-chemical means of creating vacuum, making. A length of glass tube is fed into a machine known as " getters." which simultaneously cuts the tube into short lengths and Anyone visiting a modern valve works would recognise forms a flange at one end, Fig. r (A). This " flange " very few of the operations in use four years ago. Prac- is placed in another machine, together with the exhaust tically everything has been radically altered ; anodes that stem and the requisite number of leading -in wires (B), used to be blanked out and rolled by hand are now turned which may number from four to nine, and the wires are out by automatic machines at several hundreds per hour ; fused into the glass pinch as in (C). During the fusing grids that used to be wound by hand and laced with great operation air pressure applied to the exhaust stem blows are to a damping wire are now wound, spot -welded` at a hole through one side of the pinch, thus leaving an every turn, and cut off continuously at high speed; ex- exit for the gases during exhaust. This is how the s 6

www.americanradiohistory.com .APRIL 6th, 1927. Wfipagoo 107 Wopllo1

LNICKEL WIRE

SUPPOET

PLATINUM U STITUTE AIR -TIGHT SEAL

EXHAUST HOLE ii. COPPER LEADING NICKEL SUPPORT WIRE IN M'IRE

FINE MOLYBDENUM SPIRAL IN SMALL GRID WIRE FILAMENT SURPLUS SUPPORT WIRE CUT OFF HERE AFTER MOUNTING ASSEMBLY OF TYPE D.E.3' FINISHED VALVE READY FOR CAPPING

'R" VALVE BRIGHT EMITTER GLASS BULB BROKEN AWAY SHOWING ELECTRODE FINE SPRING OF SYSTEM. MOLYBDENUM WIRE

STRIP SPRING EXHAUST STEM OF NICKEL SEALED OFF STEEL

O DER." VALVE DULL EMITTER JOINT BETWEEN SEAL R BOLE. H, M ANON

METHODS OF OBTAINING CORRECT GLASS FILAMENT TENSION SURPLUS REMOVED AFTER, SEALING IN

I STANDARD 4 PIN CAP

Fig. 1.-Types of receiving valves and processes In their construction. (A) glass flange ; (B) construction of leading-in "wires; (C) complete assembly of foot with wires fused into " pinch " and exhaust stem attached ; (D) cylindrical anode ; (E) hat or oblate anode ; (F) cylindrical grid with single support wire ; (G) " flat " and with " hairpin " support ; (If) electrode assembly in bright emitter valve, showing spring tension on filament ; (J) .06 filament and support prior to assembly ; (K) electrode assembly of .06 valve (L) low temperature filament supported without spring tension ; (M) method of springing straight horizontal filament ; (N) springing of inverted V filament ; (P) original shape of bulb ; (Q) valve ready for exhausting ; (R) " gettered " valve ready for cementing to standard 4 -pin cap (S). " pipless " effect is obtained, the stem being subsequently consists of a nickel -iron core plated with copper and sealed off below the flange and hidden inside the cap. borax, designed to have the same coefficient of expansion The four external wires are of copper and are subse- as the particular kind of glass of which the tube is made. quently attached to the valve legs ; the inner wires are The whole thing is known as the " seal " or " foot," and usually of nickel and carry one or other of the electrodes; it now remains to assemble the electrodes on it. The the small central portion, which is sealed into the glass, manner of doing this depends considerably on the tvnt B7

www.americanradiohistory.com ¢o8 VIp®Il@oo APRIL 6t11, WopIlol 7927. Modern Valve Manufacture. - Another essential is that the filament should be straight, of valve under consideration. The electrodes may be i.e.,'coaxial with the grid and anode; appreciable sag- cylindrical or oblate, upright or vertical ; the grids and ging tends to distort characteristics, and may even brim anodes may be so large as to require two supports each ; the filament on to the grid. Arrangements have therefore whilst the filament nifty be straight, " V," " N," or even to be made, where necessary, for keeping the filament " W " shaped, requiring two, three, four, and five sup- taut. This would appear to be rather simple, but actu- ports respectively. Some filaments require springing to ally is not. It is impossible, for example, to supply the avoid displacement on to the grid, in which case the right amount of tension to a straight filament running at tension has be to carefully controlled ; too much tension a temperature much over 2,5oo° K., such as a bright - may cause the filament to stretch and break when heated emitting filament of the " R " type. On heating up, the up; too little leaves it loose and liable to sag. In a valve tungsten wire simply stretches and finally breaks, and of the o.o6 ampere class the margin is necessarily very one must rely upon the non -sagging effects of chemical small indeed. additives to preserve a straight wire throughout life. The anodes are usually made from nickel strip o. r to 0.15 mm. thick, fed into a machine which folds it into Microphonic Noise. the required shape, (D) and (E). The overlap can be It is much easier to spring a dull- emitting filament, as joined by welding or riveting. its temperature remains well below the " softening " point The grids can be made in several ways, all of which of the wire, but here another and much more formidable are automatic or semi -automatic. Small cylindrical grids difficulty arises ; a sprung filament has a natural (F) fre- may be made continuously by a machine which winds quency of vibration, and if this frequency is within the the fine molybdenum grid wire round a straight- moving audible range the valve is liable to cause what are known nickel support wire. A roller follows each revolution of as microphonic noises. The modern tendency in design the grid wire and spot -welds each turn as it passes over is always towards lower filament currents, and, unfor- the support wire. Suitable interruption of the spot - tunately, the lower the current the greater is the tendency welding cut rent leaves unwelded gaps along the spiral, towards microphonic noise so long as the filament is so that grids of the correct length are wound in rapid sprung. One solution to this lies in a filament which succession, cut off, and discharged by the machine. Flat operates at such a low temperature that its filament does oval grids are usually made rather differently, as in this not expand or sag and therefore does not require any case there are two support wires (G). A " hairpin " of tension. It will be noticed that the newest types of low - nickel is clipped to a mandrel of the correct shape and consumption receiving valve embody this improvement the grid. wire wound over it and subsequently welded by (L). When a spring is used with a straight filament it a roller. The pitch of the grid turns is regulated by a usually consists of a strip of nickel steel (M), but in the lead -screw, and it is possible by this method to get as case of the vertical " V " filament a shaped hook of many as roo turns to the inch accurately spaced and molybdenum is usually sufficient (N). securely welded. The three electrodes are assembled on to the " foot " Filaments. by means of jigs. The precision of these jigs is of a high order, as exact location is most important, and each There are various ways of making up and mounting seal is carefully inspected before passing on to the next filaments, which vary in size from the D.E.3 class, taking operation. With few exceptions every joint is spot -welded o.o6 ampere, to the L.S.5, which takes o.8 ampere, or by means of a momentary current of 200 to 500 amperes the new K.L.r, which carries as much as 2 amperes. In at very low voltages. During assembly a small quantity general, however, there are certain laws to be observed, of magnesium wire or strip is lightly welded to the anode which govern the method of mounting, which leave very for a purpose which will be described later. little choice as regards any particular valve. In the first place, as much of the hot portion of the filament as Exhausting. possible must be contained inside the grid to prevent the One matter of the utmost importance in the preparation passage of stray electrons from filament to anode outside of all electrodes, whether for receiving or transmitting the control of the grid. The cooling effect of the support valves, is the " gas- freeing " of all metal parts, which wires varies with the current carried by the .filament, so is carried out by cooking both the raw material and the that in the case of a bright emitter such as the " R " finished articles, in a vacuum furnace at about r,000° C. (H) it is possible to allow several millimetres of cold The raw metal contains various gases, such as water (and therefore non -emitting) filament to protrude at each vapour and the oxides of carbon, not only on its surface, end. This has the advantage in manufacture of allow- but internally, and it is essential that these gases be ing plenty of room for spot -welding the filament to its removed before the valve is exhausted, otherwise the pro- supports. At the other end of the scale is the D.E.3 fila- cess cf exhaustion would be unduly prolonged and the ment, which is hot practically throughout its length. In probability of a permanent vacuum very much reduced. this case the whole filament is enclosed in the grid, and Once the " volume gas " has been removed by cooking, special arrangements have to be made for mounting it. it is found that exposure to the atmosphere does not cause Dne method is to form an incomplete loop of nickel with appreciable .reabsorption, even over several days, while he filament mounted in the gap (J). The loop is any fresh " surface gas " can be quickly got rid of by nounted to its supports (K) and cut through at the points the pumping process. indicated by dotted lines in the figure, the loose pieces Once the electrodes are assembléd, the " foot " is )eing then shaken clear. sealed into the bulb (P), the neck of which is melted by Bs

1. www.americanradiohistory.com APRIL 6t1i, 1927. Wfipigh@O WOAA 409 )Iodern Valve Manufacture. - attached to the anode now comes into operation.. In prob- gas flames around the flange and the excess of glass ably the best method an oscillatory circuit is arranged blown clear (Q) ; the valve is now ready for exhausting. so that a coil, carrying a heavy high -frequency current, The machine' usually employed for this purpose con- can be lowered over the valve in one of the final positions sists of a circular manifold carrying up to twenty -four of the pump. This sets up eddy currents in the metal rubber connections into which are placed the stems of parts of the valve, sufficient to raise the anode to a red the valves to be exhausted. The rubbers are connected heat, and so volatilise the magnesium, which leaves the to a system of pumps in such a way that as the manifold anode in the form of vapour and condenses on the coldest

SILICA SEPARATOR BETWEEN FILAMENT SUPPORTS

SIDE SPRINGING SYSTEMS

TUNGSTEN FILAMENT

INVERTED GLASS SEAL,

FI;'. 2.- Constructional details of the electrodes of a 4 kW. " air- cooled " transmitting valve. (A) glass seal for filament leads i (l3) side supports for filament leads ; (C) silica separator for filament leads ; (B) springs and insulators for end filament supports ; (E) filament assembly. moor.; round, each valve is subjected to a more and more surface in its immediate neighbourhood, usually the wall intense process of exhaustion. At the same time, the of the bulb. In doing so it " cleans up " the residual valve passes through a gas oven maintained at a tempera- gas, together with the gas given off by the anode in heat- ture of 4000 C. to 450e C., which has the effect of ex- ing up, leaving a gas pressure of the order of o.000r mm., pelling from the glass parts any gases contained by which constitutes a sufficiently " hard " vacuum for our them, in particular water- vapour, which has disastrous purpose. effects on the emission of most dull emitters. By the The valve is then sealed off below the flange (Q), and time the valve has reached the end of the circuit the gas the four -pin base is fitted by the application of cement, pressure inside is of the order of o.oi mm. of mercury; baked in a small electric oven, fitted over the base (S). there is even at this pressure far too much gas in the The subsequent processes depend upon the nature of valve to permit the formation of a coating of such a the valve. A bright emitter needs only to be run for a substance as thorium, for example, while the gas itself short time at slightly more than normal voltages, whereas would, in the event of any emission being produced, a dull emitter requires a certain amount of electrical become ionised and set up grid currents which would treatment to produce the required standard of emission. reduce the working efficiency of the valve. In order to Thoriated valves, for example, require the thoria in the clear up this remaining gas the magnesium previously filament to be reduced and diffused to the surface of the B9

www.americanradiohistory.com WATshoo 410 APRIL WOpIld. 6th, 7927, Modern Valve Manufacture. - anything up to a kilowatt, and the valve may filament tr form a molecular be called coating of thorium, the upon to handle as much as 15 or 20 tungsten acting then partly kW., of which to as a heater and partly as a may be dissipated at the anode in the reservoir of more form of heat. The thorium. Again, some coated filament anode voltage is often of the valves are order of to,000, but this lit up during the pumping operation to gas -free is by no means the limit, the coated one type of rectifying valve substance and leave a pure uncontaminated being capable of standing up salt of barium to as much as iso,000 volts. or strontium, or whatever the emissive Clearly, then, the running conditions substance may be. of transmitting valves are considerably more severe and must he taken It only remains to test the valve for emission, vacuum, into consideration during manufacture, with the result filament volts and current, and characteristic slope. The that a number of changes in method and design at once vacuum is taken as roughly proportional to the amount appear. of negative grid current due to ionisation of the gas The amount of heat dissipated internally imposes addi- particles, and is measured by applying a fairly high posi- tional restrictions ; the glass bulb in turn has tive voltage to the plate and varying to pass on negative voltages to this energy in the form of thermal radiation, and the grid, with a sensitive galvanometer in the in the grid -fila- high -power valves we soon reach the limit both in ment circuit; a soft valve gives size of a current of the order bulb (for practical purposes) and composition of glass. of microamperes, but a hard one gives practically no Beyond 4 kW. or so it is necessary to use " backlash " at all. some substance such as silica, or, better still, to dispense with the glass Transmitting Valves. envelope altogether and make the anode the outside of the valve, cooled externally by circulating Both in construction and manufacturing water or oil. processes, The last type is generally known as a " water- transmitting valves are a different proposition, cooled," the reason or, more accurately, " cooled- anode," valve, and is being, of course, that whereas in the the receiving valve the type now used in practically all long -range high object is to ensure the best possible reproduction -power of signals transmitting stations, such as Daventry, Rugby, and the consistent with the minimum expenditure of power, the new beam stations. transmitting valve has to deal primarily with power out- In a valve dissipating up to _} kW. it is permissible put. The power used in a receiving to valve is nowadays use nickel anodes, but above this both anodes and grids of the order of half a watt in the filament and anode must be of a less volatile metal, such as molybdenum, circuits ; in a transmitter the filament wattage alone is while tungsten is preferable for support wires in certain cases. The anode of the " water - cooled " valve does not reach a high temperature and can therefore be made .w, of copper or iron. It is impossible to use the ordinary flat glass " seal " common to all receiving valves, because the heavy currents involved, and the high anode voltages used, usually round about I o,000, necessitate a double -ended valve, while the grid lead, for considerations of both insulation and capacity; is usually taken out through the side of the bulb. The size of the anode and grid leads, hitherto unim- portant, now demand consideration, especially on the lower wavelengths, where the grid current is of the order of amperes. The grids of transmitting valves are quite complicated structures. Those of modulators have generally the usual spiral formation, but the grid of an oscillator is, as a rule, of molybdenum mesh, the spacing being closer at the ends than in the middle. In both cases the grid is carried by a rigid framework of molybdenum channel or solid rod, designed to withstand the effects of high temperature. General view of machine pump for The filament is usually in the form are valves exhausting receiving valves. In the foreground waiting their turn for pumping and on the right a valve is about to of " V " or " W "; the tops of the oven. At the other end of the oven the high- enter the pumped valve frequency coil has descended over a loops to liberate the magnesium, and ln the last position a valve has been may be kept in position by sealed off and is being automatically removed from the machine. springs in buttons of insulating B IP

www.americanradiohistory.com APRIL 61/i, 1927. VrApaSE,0 ¢1I WOO 1fid Modern Valve Manufacture.- The filament seal and supports having been prepared, material fixed in the top of the grid, or by vertical rods the filament, which has been previously bent to the correct from the filament seal, but in some rectifying valves a shape, is mounted on the molybdenum strip supports (E). special arrangement is made for springing the filament The grid frame cons%ts of uprights of channel molyb- from an arm through the side of the bulb. denum, carrying bands of molybdenum strip along its It will readily be appreciated that, in view of all these upper half, with lower down a wider spacing ring of the restrictions, the manufacture of transmitting valves does same material, and at the hase a wide band of iron, not at present lend itself to standardisation ; moreover, which is eventually fitted over the outer tube of the fila- methods of production vary considerably with the dif- ment seal and tightened up by means of small bolts and ferent types of valve. nuts. The filament seal thus acts as a support for the We can perhaps take as typical the manufacture of a grid, although the grid lead is taken out elsewhere. The is first cut glass transmitting valve of the 4 kW. input class, and, grid itself consists of molybdenum mesh and later on, a cooled anode valve. to shape and then literally sewn by hand on to the frame-

FILAMENT SUPPORT THIMBLE OF PUCE PLATINUM

CLAMP GLASS TO METAL JOINT

GLASS SEAL FILAMENT WIRE COPPER LEAD

GLASS TO TOP ENO OF FILAMENT METAL JOINT SYSTEM

PLATINUM THIMBLES

COPPER ANODE

FILAMENT CONE GLASS BULB NICKEL IRON SUPPORTS

Flg. 3.- Cooled anode valve. (A) filament seal ; (B) top filament support ; (C) anode seal. In the glass valve there are four " seals " to be made, work with threads of tungsten. Once the grid is mounted, two for the filament leads at one end of the valve, one the filament springs (D) are put in position and the fila- for the anode lead at the other end, and the grid seal at ment correctly adjusted for position and tension, and the side of the bulb. All these seals are of the " in- this part of the valve is now ready for sealing -in. verted " type, i.e., the flat " pinch " is outside the The anode is made from molybdenum sheet and is of valve and supported by a double glass tube, Fig. 2 (A). the usual cylindrical form. Among the mechanical dis- Pure platinum is used in the form of strip in order to advantages of molybdenum is its reluctance to be sppt- bass the heavy current (25 amperes in the filament cir- welded to itself, and so rivets are used throughout. The cuit) without undue heating. The external leads are of anode is mounted on a framework of molybdenum up- stranded copper and inside nickel rod or strip connects rights and clamped by an iron band to its own glass seal, witlr the electrode system. Fig. 2 shows the electrode which is then sealed into one end of the bulb, which system and its supports in detail and is self -explanatory. differs from the ordinary valve or lamp bulb in having a It will be noted that quite a lot of " extras," such as neck at both ends. The grid -filament system is then silica separators (C) and heads (B) are used to secure sealed in at the other end, great care being exercised to adequate insulation and precise spacing, and that great get the two systems truly coaxial; finally, the grid lead trouble is taken to keep .the more susceptible glass parts, is extracted through a hole in the side of the bulb and such as the seal, out of the heat zone. joined to the grid seal, which is then attached to the bulb B II

www.americanradiohistory.com N'n/gnlIepoSS 4r: APRIL 6th, 1927. - World. Modern Valve Manufacture. - be estimated by the fact that at different periods the froni outside. It will be seen that the manufacture of anode has to dissipate from two or three times its normal such a valve as this involves a high degree of skill iñ toss, running at a white heat for many minutes at a glass -blowing, mechanical fitting, and even needlework stretch. The valve is then sealed off and is ready The for exhaust of a valve of this sort is a long job, re- use after the usual beads and sleeving have been attached. quiring several hours' constant attention by skilled ob- servers. In this case, of course, automatic pumps are Cooled Anode Valves. ruled right out, and each valve has its own pump system, Technique of a different character has been developed which consists of a high- quality mercury vapour diffusion ïn the construction of the cooled anode valve. Compared pump backed by a rotary oil pump. The valve is sealed with any type of receiving valve, this might reasonably on to a glass manifold connecting with the pumping be described as a heavy engineering job. The system, " busi- and by means of a change -over tap and a McLeod ness " énd of the valve consists entirely of metal, and gauge readings can be taken of the approximate pressure the work is done by specially trained mechanics. The in the valve at any time. A gas oven is lowered over the filament, grid, and anode systems are built up separately, valve, which is " baked " at 400° C. for half an hour then assembled, sealed in; and exhausted, but the methods to liberate the " glass " gases. The diffusion pump is employed are different from anything so far described. then operated until a good vacuum is obtained. The anode, as has been said, is the outside of the During this time the electrodes have, of course, been valve itself, and must therefore be absolutely non- porous cold, but now first the filament is lit up, and then volts and free from cracks, even at fairly high temperatures. are applied to the anode and grid, and in consequence In the case of single -ended valves it is pressed out from large quantities of gas are given off as the electrodes heat copper sheet into a closed cylinder gin. or rein. long up. The whole of the remaining time is applied to the and tin. thick, with a flange at the open end ; into this removal of this gas as fast as it is evolved, and thé end are fitted first a £one of nickel -iron tapering outwards severity of this " bombardment " of the electrodes may to a very thin edge, which will ultimately receive the glass bulb direct, and next a copper cone, which is virtually an internal extension of the anode and acts as an electrostatic shield to the glass -to -metal joint. In addition there is an external copper flange which acts as a support for the water- jacket when the valve is in use. The anode is usually cylindrical, but in the case of a rectifier is sometimes binocular, to reduce the filament -anode path and also to relieve electrostatic stresses between the , filament limbs. The nickel - iron cone is copper -plated and treated with borax at the edge, after which one end of the glass tube which will ultimately contain the seals and electrode supports is held round it and melted on by carefully controlled gas - flames. The joint thus formed is not only absolutely gas- tight, but mechanically very strong and free from strain. The grid of a " cooled anode " valve is similar to that of a large transmitting valve in general design, but more robust in construction and mounted on bands and Apparatus for pumping medium -power transmitting valves. Noie the mercury vapaw, seals in much the ' same condensation pump and liquid air trap brlow table and gas oven lifted clear of the valves during bombardment. way. B I?

www.americanradiohistory.com WApasoo APRIL 61/i, rg27. Walla 4Ï3 Modern Vaive Manufacture.- by the usual " backlash " method, owing to the high The filament current is usually 5o or 75 amperes, and voltage and currents involved, so a receiving valve of ordinary platinum seals in glass pinches are no longer the L.S.5 type is attached beforehand to the valve by adequate. The method employed is shown in Fig. 3, in glass tubing, and suitable voltages are applied to its which it will be seen that a platinum " thimble " is joined plate and grid, and the reverse grid current is measured, direct to the glass tubing. The external copper lead is exactly as in testing for " backlash " in a finished receiv- pushed up inside the thimble, and a clamp is tightened ing valve. We thus estimate the vacuum in the small up on to the thimble, gripping the copper lead securely valve, which can be taken as approximately equal to the and at the same time passing the current to the filament vacuum in the larger one.

Representative types of receiving valves (A to G) compared with some high -power transmitting valves and their components. The anode and grid of a 4 kW. transmitting valve are shown at H and J. K is a sectional view of a double -ended cooled -anode rectifier, and L is a rectifier specially designed for an anode potential of 150,000 volts. support. The filament itself is, of course, of generous After .exhaustion, a cooled anode valve is fitted with proportions and so are its springs, which are made of stout specially designed caps for the filament and grid leads, tungsten wire. the anode connection being made direct to the anode 'l'he sealing -in of such a valve is made difficult by the itself. fact that the anode is opagge, and it is impossible to' see by eye whether the grid and filament are co -axial with Conclusion. the anode or not. High- precision mechanical devices are In conclusion it -may be said that, owing to the enor therefore used for this operation, no subsequent inspec- mous rush of new development work, the technique of tion of the electrodes being possible, and up to the present valve manufacture is actually further from standardisa- the result has been quite satisfactory. In passing, it may tion to -day than ever before. The constant cry for lower be said that it is actually possible to inspect the electrodes filament current plus better characteristics plus lower by taking X -ray photographs of them, and this process prices, in receiving valves, together with the necessity for is regularly used in " inquests " on valves at the end of increased power in single -valve transmitting units plus their useful life, but obviously does not lend itself readily ability to handle short wavelengths, have combined to to factory usage. make the manufacturer's life " not a happy one." Pre- The exhaust and bombardment of cooled anode valves sumably the thermionic valve, like its more brilliant but lasts for twelve hours or more and is carried out on much less ambitious brother, the electric lamp, will ultimately the same lines as for glass valves, exceptthat much more arrive at something like finality, when the number of power is used and additional technical problems are in- types will be reduced to reasonable proportions and troduced, some of a very interesting nature. In the manufacturer and purchaser alike will have time to tall finished valve it is not convenient to measure the vacuum a " breather." A 13

"iy.firÿ ,o :o-a:;aatx.+r.:.www.americanradiohistory.com e...w a,....+.i.,.-. ,.ö",..tir- Or pa®00 APRIL 6t11, .1927. WOO lt'ilol

A Section Devoted to New Ideas and Practical Devices.

SIDE -PLAY IN CONDENSER The use of ordinary wire paper which should, in turn, be rounded at SPINDLES. clips to hold the ends of the winding the edges to prevent damaging the The system of vernier control, con- before fixing to soldering tags is well paper. sisting of a small friction wheel at known, but this method cannot be The tool is worked round the edge the, edge of a condenser dial, has of the paper with suitable pressure been described in wireless periodicals from the thumb in the position shown. since the earliest times, but the par- No attempt should be made to finish ticular arrangement shown in the dia- the rim " once round " as the paper gram serves another purpose. will be sure to crumple; three or four Side -play, if not already present in circuits should be sufficient. the top bearing of a cheap condenser, The formation of a rim in this way soon develops where the diameter of is useful when constructing double - the spindle is small, resulting in cone diaphragms, as indicated in sec- scratching noises due to the intermit- tion in the diagram, as a much firmer tent contact and to small changes of joint between the cones is thus ob- capacity. By fitting two vernier tained. V. W. E. attachments at points on the edge of Holding wire in position when winding is 0000 interrupted -way through coil. the dial separated by 90° the spindle half SOLDERING HINTS. is continually forced to one side of employed should it be found neces- Faulty connections at soldering sary to interrupt winding operations tags can often be traced to the pres- half way through the coil. The dia- ence of a non -conducting film of gram, which is self -explanatory, resin between the tag and holding- shows how two rubber bands may be applied to hold the wire under these conditions. W. B. 0000 CONE DIAPHRAGM CONSTRUCTION. The formation of a stiffening rim at the edge of a cone loud- speaker diaphragm is greatly facilitated by the use of a small forming tool. This consists of a piece of wood of round section ein. to tin. in diameter and 4in. to 6in. in length. The end is sharpened to a chisel edge and then saw -cut with a fine hack -saw to a depth equal to the width of rim required. The saw -cut should be made slightly to one side of the chisel edge Two vernier control knobs fitted to take Before soldering connection to tag, bend up side-play in the condenser spindle. downwards to prevent flow of flux on to winding. the hearing and no further trouble will he experienced. H. D. H. down screw due to flux gravitating 0000 on to the screw and the end of the COIL WINDING. winding. The art of winding single -layer To avoid this trouble, all that is coils has fallen into abeyance during necessary is to bend the tag down be- the vogue for plug -in coils, but is now fore soldering, as shown in the dia- being revived for the construction of gram. This also directs the flow of H.F. transformers for short wave- solder to the desired point. Forming a rim on the edge of cone loud- lengths. speaker diaphragms. V. W. E.

B 1 4

www.americanradiohistory.com Wilpa@g,0 APRIL 6th, 1927. 415 11-1101

A Section Devoted to the Practical Assistance of the Beginner. PROTECTING VALVES AND ranged to " make " the high- tension amplification factor for a given im- BATTERIES. circuit before the filaments are pedance is always desirable, designers Few of us are entirely guiltless in lighted, and -more important -to are limited by various inherent diffi- the matter of burning out valve fila- break the L.T. before the H.T. is culties, and in any case the figures ments and short- circuiting expensive disconnected. By observing this pre- applying to any of the more efficient H.T. batteries. Good resolutions as caution, risk of damage to such iron - makes are more or less the same. to the observance of such obvious pre- cored inductive windings as those of 'Faking the particular class of valve at cautions as disconnecting the neces- transformers, loud -speakers, etc., is present under consideration as an ex- sary leads are often neglected when avoided. The connections of the ample, we find that an average ampli- making hasty adjustments or experi- switch are shown in Fig. i. fication factor of about zo is obtain- mental alterations, and in the long The simpler device suggested in able, although this is generally run the slight expense and trouble Fig. 2 is not altogether satisfactory. reduced- slightly in the case of those involved in fitting some form of At first sight it may seem that the with z- and 4 -volt filaments, which safety device which compensates for H.T. circuit is broken as well as that are inherently somewhat less efficient, the fallibility of the human element of the L.T. battery ; a moment's con- all other things being equal. will be amply repaid. sideration, however, will show that The modern " 20,000 ohm " valve One of the most certain methods of this is not the case, as the negative is one of the most generally useful, reducing risk of damage is to insert end of the battery is still connected to and its usual title of " H. F. ampli- the filaments through the L.T. and The arrangement is, how- 0 rheostats. H.T.+1 ever, of some utility, if it is always

H T.+2 remembered that the rheostats should be turned to the " off " position when making adjustments. 0000 H. VALVE CLASSIFICATION. 1 1 The amateur would probably do SWITCH SWITCH L+ well to relinquish the idea of men- L.T tally classifying valves under the f arbitrary headings of " H.F.," " L. F.," " power," etc. The present- Fig. 2.- Another me hod of fitting an Fig. 1.- Connections of a D.P.S.T. switch day practice in this respect is liable "on -ofr" switch. Note that the filament arranged to break both L.T. and H.T.'cir- rheostats most be in the " oft " position cuits. It may be connected up externally. to be confusing, and is in any to disconnect the H.T. battery. case hardly helpful as an aid to the a fuse in the junction between H.T. choice of a valve for a specific fier " is apt to be misleading ; indeed, and L.T. batteries, though unfortu- purpose. it has usurped the Majority of the nately the number of fuses which are It would appear to be a better prac- functions of the original " general really satisfactory is at present tice to cultivate the idea of always purpose " type, as it operates satis- strictly limited. It is still better to thinking in terms of anode impedance factorily as a detector or first stage fit separate fuses in each positive (or A.C. resistance). Thus, for the L.F. amplifier in the majority of high- tension lead. majority of modern transformer - circuits. A good alternative method is to fit coupled H.F. amplifiers, a " 20,000 Reference should also be made to a switch in such a way that the nega- ohm " valve, with a filament rating the class including the so- called tive H.T. lead is broken as well as suitable for the L.T. battery in use, " power " valves, of from 5,000 - the L.T. supply to the filaments. The would be chosen. It should be real- ro,000 ohms impedance, generally blades of the switch should be ar- ised that while the highest possible used in the last stage of loud- speaker n r5

www.americanradiohistory.comvfia.:aiolri.;it,icai.[a.:wlíi.ir:raYa.:.wv.íe:-:«nk..=:'ir2tsRS2' 410 Wilpec00 APRIL 6th, 1927. NVOO YIld sets from which no groat volume is 3,500 ohms tends nowadays to become be substituted by one of i8,000 ohms expected, and where cost, both initial less distinct. and equal efficiency. and maintenance, is a consideration. It must not be thought that there The high -amplification, high -im- It must he noted that, if the figures will be a vast difference in perform- pedance valves of from 5o,000- above are taken as truly representa- ance between valves having imped- roo,000 ohms are being produced in tive under working conditions, the ances differing only by some to or 15 increasing numbers, and have several valve with the lower rating will as a per cent., providing the relationship distinct fields of usefulness, notably rule be able to deliver louder undis- between the amplification factors as tuned -anode H.F. amplifiers, and torted signals, but will consume more remains sensibly constant; thus, it as anode rectifiers or L.F. amplifiers high- tension current. The dividing would be a difficult matter to detect with resistance coupling. They must, line between these valves and the any audible difference in signal however, be used with care and only " super power " class of some 2,500- strength were a 20,000 ohm valve to under expert advice.

DISSECTED DIAGRAMS.

Practical Points in Design and Construction. No. 66. -Anode Detector with Two Resistance coupled L.F. Amplifiers. (Continued from last week's issue.) The present series of diagrams is intended to show progressively, and in an easily understandable manner, the various points to which special attention should be paid in the design of typical wireless receivers, and at the same time to assist readers in mastering the art of circuit diagrams. In the skeleton diagrams below are shown some modifications of the receiver discussed in last week's issue. Non -essentials are omitted.

H.T. + v H.T. + H.T,+ C ... H.F.C:

:111. Ill TO TO i GRID GR1D v?8

I° , 011i R '., »

. :¡ ' G.B.- L.T.- L.T.-

(1) (2) (3)

Reaction is added by inserting the neces- By connecting an H.F. choke and the usual Another method of preventing possible sary colt (variably coupled to the aerial by-pass condenser in the manner shown, ill effects due to the passing -on of H.F. inductance) in series with the anode of the H.F. and L.F. currents are more or impulses into the L.F. amplifier. A resist- the detector valve. less separated. ance It is inserted. LTHOUGH reaction control at inductance, may both be mounted in of H.F. impulses to the grid of the its best is not obtainable when a " two -way " holder. L.F. amplifier. The arrangement using a " bottom bend " detector, Selectivity may be improved by in- shown in (3) serves a similar purpose the arrangement shown at (r) will re- serting a fixed condenser of o.000r to and is simpler ; the resistance R, con- sult in a very considerable increase of 0.0003 mfd. in series with the aerial, nected to the grid of V2, may be of range. A No. 3o or 4o reaction coil as indicated at C in (2). In this from o.i to 0.5 megohm. This de- will generally be sufficiently large for diagram is shown one of the many vice may be combined with (r), giv- use on the broadcast waveband, while possible methods of separating H.F. ing the arrangement of the B.B.C. a No. roo should be suitable for and L.F. currents, and of preventing demonstration receiver " B " (see Daventry. This coil, and the aerial (or, rather, reducing) the application TVireless TVorld, March 16th, ßr927). s 16

www.americanradiohistory.com APRIL Gl/r, 1927. VffiTIghoo 417 WO)sbil

Characteristics Required for the Various Stages in a Multi =valve Receiver. By P. K. TURNER.

CHOOSING the right valve is an easy task if you (` ` voltage amplification factor ") and Ra (' ` A.C. anode are not afraid of arithmetic, but a puzzling one resistance " or " slope resistance ") of available valves. for the hazy- minded. Of course, there are two Now, in the case of the power valve, the requirement parts to the problem-first, to work out just what charac- already mentioned- sufficient power -means that there teristics the valve should have ; second, to find which of must be enough " straight " in the characteristic curve. the valves on the British market have these characteristic's. To get reasonable volume from a loud -speaker, there must There are eight distinct functions which the valve may be generated in the anode circuit of the last valve a volt- he called upon to perform, and they fall into the follow- age swing of about 120 for a " 2,000 -ohm " loud- speaker, ing classes :- or about 8o for a " 750- ohm." Now, suppose that (r) " Power," i.e., the last valve in a domestic loud- Fig. r is the curve of a power valve with an amplification speaker set. (2) " Transformer amplifier," i.e., any valve to be followed by a transformer, the ratio of which can be chosen at will. (3) " Voltage amplifier," to be followed by some form of coupling such as resistance, choke, or tuned anode. (}) " Grid detector." (5) "Anode detector." (6) " Super power," i.e., for use in the last stage of hpp a high -power amplifier. (7) Power rectifier for H.T. supply from mains. (8) Valves for A.C. filament feed. I see way the problem - can no better of tackling thane yo to take each position in a multi -valve set in turn, and , see what is required. C The Power Valve. . Here the first essential, of course, is the ability to 1o° put out enough power. It may be as well to begin, with the consideration of this valve, a campaign for the use B of a type of valve curve different from the usual. This E latter, as is \yell known (see Fig. r), shows the anode current for any grid voltage, each curve being for a fixed I yp anode voltage. It may be said at once that curves of this type are practically useless for purposes of design. But if we take the four points A, B, C, D, for zero grid volts and various anode voltages, and plot them as one curve, as in Fig. 2, we have a curve of much greater utility. For the moment, however, I will base my discussion on the type of curve shown in Fig. i, assum- Fig. 1.-Usual form of characteristic curves of a typical paner ing that the reader also has information as to the µ valve. B 21

www.americanradiohistory.com righog APRIL 61 /1, 1927. NVoFlidl Choosing the Right Valve. - with a filament current of 0.25 amps. at 6 volts) can factor of 5. If we are to have 120 volts swing in always be made with two or three times the G. of a 306. the anode circuit there must be 24 volts grid swing. So Again, an extremely high µ valve cannot be made with we must have a " curve " which is straight (or nearly so high a G. as one with a lower l4; and, lastly, there so) between D and E. That is the first requirement, the is in some sense a compromise between long life and high actual grid voltage of E (24 volts in this case) being G.. worked out as shown below. Getting down to brass tacks, a valve with a 525 or 625 filament and Ra of about 3,000 will probably have a p. of something between 3 and 5, and will have a long 5 , enough curve to give the zo -volt grid swing required to get enough output for a 75o -ohni speaker. There are several such valves listed. As between the various ones, see which has the shortest bottom bend : this will need the smallest H.T. supply both for voltage and current. 4 I With this valve in the last holder you can just fill a room with a D.C. supply of ro mA at 120 volts, and do it properly with zo mA at zoo volts. D With a 2,000 -ohm speaker you can go up to, say, 7,000 3 ohms Ra, and get a p of about 8; but you will be wiser to go for 5,000 ohms and a t of 6 or thereabouts. Even with these lower values you will need at least rso volts and zoo or more if you want full volume. C Please do not laugh at this-I know that hundreds of 2 people are connecting loud -speakers to last valves fed with go volts, with about 4 volts bias, and producing very loud noise. But I am talking now about pure reproduction. Under -power is one B of the three great curses of out -of -date wireless. 1 The Transformer Amplifier. first A Let us consider L.F. transformer coupling. As we all know, a transformer will not transform direct currents. Further, an intervalve transformer does not 50 100 150 200 transform the lowest frequencies very well ; but the point ANODE VOLTS where it begins to go on strike is within the user's control. A good, big, expensive transformer will deal with much lower frequencies than a skinny one. You pay Fig. 2 -Anode characteristic curve (for zero grid volts) of the the extra money partly as a reward to the maker for same valve as Fig. t. knowing how, but largely because_ to get -the lower fre- The second requirement is a slope resistance which is quencies you need more wire and more Stalloy, and both not too large for the loud- speaker. The bass notes will cost money. But also -and it is a big but-arty trans- suffer if this slope resistance is much above 3,000 ohms former will get lower and lower frequencies as you use for a .75o -ohm speaker, or 7,000 for a 2,000 -ohm before it a valve of lower and lower Ra; and, considering speaker. This, of course, excludes the case where an various ratios of transformer by,the same maker, the output transformer is used; but it still applies for the lower the ratio the better the low frequencies. modern fashion of choke output to keep the D.C. out So, if you are using a first -class transformer of low of the speaker. ratio, you can use a valve of fairly high Ra, and thus make up for the low transformer ratio by high p. in the The Mutual Conductivity. valve. But if you want to get fair results from a not - Now the of any valve is limited if we put a limit too -good transformer, keep Ra down. You will note that on the Ra. In fact, the ratio p./Ra is the very important Ra is the limiting factor, and that good magnification thing called the " mutual conductivity," and is usually for the whole stage depends on getting a fairly high p. written G. (except by valve makers, who for some unfor a given Ra. In fact, a high G. is the quality wanted known reason often call it r,). G,a is usually given for a transformer amplifier. : as the above ratio multiplied by a million : in other Getting to figures as an example of what can be done words, multiply t by 1,000 and divide by Ra expressed with a transformer, take a Marconi Ideal 2.7 : I after a -ohm in thousands of ohms. . Thus a power - valve with Ra 3,000 valve. The falling -off will be only 10 per of 3,000, p of J.3, has a G. of cent. at 32 cycles -which is for practical purposes all 3.3 x 1,000 3,300 that we need -and the stage magnification about 8. The r, roo " microamps per volt." same transformer, or a Ferranti AF3, with a 20,000 ohm 3 3 valve, will give fine results. With a 40,000 ohm valve Every valve maker tries to get as high a G. as posit will give excellent results if you are clever. Roughly sible Plenty of filament power helps : a 625 valve (i.e., speaking, I feel that the following table indicates the B 22

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WhYdsoo APRIL 6tki, 1927. MpIlcl 410 Choosing the Right Valve. - D.C. supply is practically unaffected. Each has its highest Ra safe to use before a transformer for the ratio own difficulties. named :- In the case of resistance couplings, there is the Ratio : 2: r 3: I 4: r 6: perennial difficulty that if the resistance is low compared Max. Ra:i4o,000 20,000 10,000 5,000. with Ra the amplification is low (Fig.1 5 shows how the Even so, this only applies if the transformer is first stage amplification compares with p. for various ratios class. If it is good second class, cut Ra to half or two - of the resistance to Ra), while if the reverse is the case thirds the above values. If the transformer is not up very little of the H.T. voltage gets to the valve, and to this quality burn it. there is every prospect that the latter will he worked on Having decided the Ra, simply get the valve with the the bottom bend of its curve. highest p, provided that Ra is not. above the settled value. But remember that valves of. very high p. for their Ra- i.e., very high G,,-have a slight tendency towards (a) short life, and (b) irregularity as between different samples. One has to pay for everything. If you are free to choose both transformer and valve, remember that high p. and low transformer ratio will usually give the highest overall amplification. With 512 or similar valves, one should get Gm= r,000 for low µ, falling to G, = Soo at a "µ of zo ; with 2 -volt or 3 -volt valves, half these values. Fig. 4.- Schematic connections of impedance coupling between valves. As practical advice, I suggest that you adopt one of

the two extremes : either arrange, by fairly high H.T. and lowish coupling resistance, that the valve is working on its " straight," or on the other hand use a very high coupling resistance, when it will be found that (although the valve is working on a curved part of its characteristic) the resulting distortion is negligible. +H T. G.B. If you decide on the first alternative, use a valve of Ra 20,000 to 40,000 and p. about zo, make the coupling Flg. 3. -When the +H.T. lead is connected to a tapping on the resistance between t and 2 times the Ra, and use at tuned anode coil the valves are virtually transformer coupled. The system is often referred to as auto- transformer coupling. least 120 volts, preferably 15o -zoo. In the second case use a valve of Ra 50,000 to roo,000 and p. 3o -5o, with H.F. transformer coupling includes such a circuit as coupling resistance o.5 to I megohm. In the first case, Fig. 3, where the tapped " tuned anode " coil is really use a wire -wound resistance. In the second this is probably an auto- transformer. Here the matter of even amplification is not important. The first essential is maximum stage amplification for tuned signals. In the case of telephony there is also a rather complicated matter- that of getting high amplification before the selectivity is so great as to cut the side -hands. With transformer step -ups of the order of 2 : r for broadcast waves, or up to 4: r for longer waves, it will be found that valves with Ra of ro,000 to 20,000 are usually most suitable, and the more the merrier. Voltage Amplifiers. In stages where one endeavours, as in Fig. 4, to insert in the anode circuit such an impedance that the passage of the varying anode current in it sets up a voltage across it which is passed on direct to the next valve, the amplification of the stage can never he quite as much as that of the valve itself. Hence there is a natural inclination to make p. as high as possible. The value of G,a falls off for valves of very high ,u, but this does not have such an important effect with this type of coupling, though it must not by any means he neglected.

These couplings fall into two sub- classes : resistance Fig. 5.- Curves showing the relation between the amplification couplings, where the anode impedance absorbs the D.C. per stage in a resistance- coupled amplifier and the ratio between supply to the valve as well as the A.C. output from it ; the external.anode resistance and the A.C. resistance of the valve. RQ = external anode resistance; Ito = A.C. resistance of valve; and other types such as choke and tuned anode, where the µ' = amplification per stage ; µ = valve amplification factor. B 23

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Wñp®hoo 120 APRIL 6í1a, 1927. WopIldl Choosing the Right Valve. - Remember that both dimming the filament and decreas- inipracticable, so do not use a valve having a lower Ra ing H.T. (or increasing the bias) tend to increase Ra. than that suggested, because anode resistances which are This may be useful. not wire -wound will stand only very low currents. Grid Detector. Do not forget that with the low resistances you should use, say, o.r or 0.25 mfd. coupling condenser and 0.25 or The trouble here is that the essential factor of quality o. r megohm leak ; while with the high resistance you is one that is hard to measure and is never given by should use o.or or o.005 condenser and a 3 to 5 megohm makers. However, if they give curves of grid current against leak. The low resistance will give the purer tone ; the grid volts one can make a guess : efficient grid high, of course, more amplification. rectification depends on having a sharp bend to the grid With L.F. choke coupling the difficulty is that as far current curve. Efficient use of the rectified current is as its coupling properties are concerned, the choke behaves a matter of the µ of the rectifier ; but this is governed like a resistance which varies with frequency. At the by the coupling which follows it, as already explained. higher audio frequencies it will give a stage amplification Generally speaking, valves suitable for resistance of practically theµ of the valve, so that for good results coupling make the best grid detectors. it must be made big enough to give this amplification at Anode Detector. the lowest frequency the loud- speaker can deal with. Here what one wants is a sharp bend at the bottom Working it out numerically I find that if one allows a of the ordinary valve curve, but unfortunately this is drop of 5o per cent., 3o per cent., or ro per cent. in the usually got with , amplification of the lowest frequency valves of low , and thus large values that is to be dealt of grid bias are with, one has the following figures, called for, or else a specially low tap depending on the on the type of loud- speaker anode battery. :- In any ease, the Ra of the valve under working con- 5 o°, 3 o°/0 ro% ditions will be high, even if the same valve used as Rice-Kellog 300 200 100 amplifier has a low Ra. Hence this valve, like the grid Kone 500 300 150 detector, should be followed by resistance coupling, even Horn 2,500 1,600 Soo if_ transformers are used for later stages. In choosing the right valve it is a matter of looking These figures are the ratio Ra/ I, : i.e., slope resistance at valve curves and picking out one with a sharp bottom of valve over inductance of choke ; and they are based bend. Generally speaking, the 2 -volt class is the best on the assumptions that the amplifier must go down to hunting ground for- valves of this type. 32 cycles for the Rice -Kellog, so cycles for the Kone, or 250 cycles for an ordinary horn speaker. Super Power. The figures are for one stage. If you want to use When it is desired to fill a ballroom with dance music more stages, remember that you will get these losses in or to give a demonstration in a room big enough to hold each stage. . fifty people or more, one immediately requires a power Just as an example : if one wants to work a Kane which it is impossible to derive without distortion from from two choke -coupled stages, with 3o per cent. drop the ordinary set. One needs a last stage with; say, zo overall, and the chokes have been bought as 8o henries watts H.T. input. each, one must work for about 15 per cent. drop per If one has A.C. available, it is simplest to get the stage, or, say, Ra /L= 220, or Ra =220 x 80= 17,600. H.T. by rectifying. In this case one uses, sai, 500 This is the highest safe value of Ra : a lower one will volts and puts in 40 mA. if there is only D.C., the give a better performance. labour of getting the necessary batteries makes it easier It is obvious that for first -class results very large chokes to use, say, 300 volts, 7o mA. are necessary. Remember to get them guaranteed to have In each case the valve requirements are rather different ,their rated inductance ith the steady -anode cuTreut. from those of ordinary receiving valves. The essentials In a badly designed choke this may cut the inductance to are : (a) safety under high voltage -this means, as a only a tenth of its rated value. rule, a " bombarded " valve; (b) reasonable life -this Selectivity is the chief aim as a rule when designing Means special filaments; (c) copious emission -this means tuned anode couplings; i.e., one does not want uniform fairly large filament power ; and (d) ability to dissipate amplification, as in L.F. work. You will already have the H.T. watts without getting too hot. gathered that for even amplification valves of low Ra Hitherto the L.S.s and L.S.5A have been the British are always easier to find couplings for. By the same valves par excellence for this work. But I believe there token, valves of high Ra always give increased selec- are some other valves of this type coming along. The tivity for H. F. L.S.s and L.S.5A will safely dissipate ro watts, so are Hence, for single H.F. stages use valves of high Ra usually used two or three in parallel. (and high p). The limit will be found in stability. It is only a well- arranged non -neutralised stage that will Power Rectifiers. stand valves above 20 in ,u. For H.T. from mains. Here high power is the main For neutralised amplifiers one may go up to 30, but thing. If one is going to the trouble of using the mains beware of getting too selective and cutting the side - the thing should be done properly. No " B " eliminator bands. There is especial liability to this on longer can be considered really good unless it can deliver at waves and in supersonics, and in the latter case a µ of least 25 mA to the set, apart from any current used in 15 is about the limit as a rule. an output potentiometer. The rectifier should be able B 24

www.americanradiohistory.com APRIL 6th, 1927. 421

Choosing the Right Valve. Ro, - its heat. Hence, apart from the choice of and IL to to put out at least 45 mA. Here the helium gas tube, suit coupling conditions, choose valves whose filaments with no filament, has some obvious advantages, for a are low -volt, high -current -such as the Weco (type 525), rectifier of the above output will probably take at least and similar valves. 1 amp. at 6 volts for the filament. Of course, the most obvious development is, the use of Valves for A.G. Filament Feed. an indirectly heated cathode. There are now separate cathode valves such as the K.L. s, specially designed for Just one point for those of you who are trying this : A.C. feed. the hum comes in two ways. First, there is the fact that each end of the filament is sometimes positive and Conclusion. sometimes negative. Get over this by bringing all grid I am afraid that this sketch has been devoted to and anode leads back to a potentiometer. Second, the couplings as much as to valves per se ; but I hope I varying filament current causes varying emission. This have shown that the two subjects are so closely inter- can only be decreased by having a thick filament to hold woven that one cannot be considered without the other.

R.C.A. Wavelengths. an input of about 5 watts. Signals from We give below the wavelengths of a ARDI were about R6 -7 on a two -valve few of the experimental stations of the receiver. The whaler at the time was Radio Corporation of America, which TRANSMITTERS' NOTES about 70° 30' S., 176° 10' E., almost will probably be of service to readers exactly antipodean to Mr. Diesen's sta- wishing to calibrate short -wave re- tion, which is situate about 69° 10' N., ceivers :- AND QUERIES. 18° 30' E. It is suggested that when the waves have passed the equatorial 2 Rocky Point, N.Y., 14.1 metres \BC circle of the station the intensity of the 2XS 11 11 11 14.93 16.0 signals increases, and reaches a maxi- 2NT the is reached. WLL 16.6 mum when Antipodes W.IK New Brunswick, N.J., 21.5 1607 on 135 metres, from 1620 to 1632 on 0 0 0 0 105 metres, and from 1645 to 1657 on WIZ 5, 43.5 IP Two -way Working with the Pacific Coast. 0000 95 metres; Sunday, from 1005 to 1017 on Mr. M. E. J. Samuel (G 5HS), 16, 47 metres, and from 1030 to 'L042 on 43 Blenheim Road, London, N.W.8, informs Belgian Amateurs. metres; Wednesday, from 2245 to 2257 In view of the recent issue of Trans- as that at 1915 G.M.T. on Marcel 26th on 20 metres. The signals will consist he succeeded in establishing two -way mitting Licences to Belgian amateurs, it of an ordinary test for eight minutes, will probably interest our readers to know communication with U 7EK, of Everett, followed by a series of five -second dashes Washington, on a wavelength of 22.8 the names of the executive officers of the for three minutes, then a one -minute test Réseau Belge -the Belgian section of the metres. The input was about 120 watts, and a notification of the wavelength- and 7EK reported signal strength as R3, I.A.R. U. -whose headquarters are at e.g., " Ici 145 metres " for three minutes. du Congrès 11, Brussels. while his were received at R3 -4. The Rue These .transmissions will be directed by one of President, M. Paul le Neck, EB 4UU Pacific Coast is always considered Lieut. Vanhay, Rue Braent 122, Brussels. the most difficult places with which to (ex U3). The " Club des 4 " will welcome any establish communication with Great Secretary- Treasurer, M. Marcel Ocre - contributions in the form of books of man, EB 4FU (ex Z8). Britain. reference for their library, which may G 51IS was also in touch with U 6ZAT, Traffic Manager, M. Georges Nulemans, be forwarded to M. R. Destrée, 38, rue 4F'l' (ex 08). of Los Gatos, California, on December EB de Suede, St. Gilles, Brussels. is be- Technical Manager, M. Joseph 0000 12th, 1926, at 1805 G.M.T. This lieved to be the first case of European llussche, EB 4BT (ex C2). I.F.S. Transmitters. Members of the Council, M. Robert two -way working with that district on We are asked to state that QSL cards the 20 metre waveband. The transmis- 4SA (ex P2), M. Léon Hun - Deloor, EB for transmitters in the Irish Free State in Rhodesia. nincks (ex U2). sion was also heard Southern should be addressed to the Irish Radio Mr. Samuels finds that, while it is ex- QSL Section, M. A. John, 88, Bd. Transmitters' Society, Solent Villa, Pacific Lambermont, Brussels. ceedingly difficult to reach the Kimmage Road, Trenure, Co. Dublin. A Coast by the dark path on the 45 or 32 000o mutual arrangement has been made (as metre wavebands, it seems compara- The Club des 4 " is conducting a re- stated, in our 'issue of March 16th) be- tively easy on about 20 metres via the gular series of tests to investigate the tween the I.R.F.S. and the Radio Trans- daylight path. He attributes the diffi- problem of " fading," and ask for the mitters' Union of Northern Ireland, culty of communicating with the Pacific collaboration of all licensed transmitters, whereby QSL cards sent either to Dublin Coast to the shielding effect of the great especially those working- on low power. or Belfast will be forwarded to amateurs mountain ranges, and suggests that the The particular points to be noted are in Northern Ireland and the Irish Free 20 metre waves come down from the the period of recurrence and the influence State, as required. Heaviside layer at a steeper angle than of atmospheric conditions. M. G. Van 0 0 0 0 those of greater length. den Eynde (EB 4GO), 22, Rue du Re- Norwegian Whalers Returning. 0 0 0 0 morqueur, Brussels, is the Hon. Secre- A considerable number of our readers New Call -signs Allotted and Station.; tary in charge of these tests and will have heard signals from AQE, 'and it Identified. to those wishing may be of interest to note that the Nor- furnish full particulars G 5CG and G 6PX D. Shannon, Gothic Cottage, Four to participate. wegian whalers, Sir Janes Clark Ross Oaks Rd., Four Oaks, Birmingham. Amateur listeners who are interested (AQE) and Nielsen Alonso (ARCX), (Change of address.) from Ant- G 610 T. Woodhouse, 31, Tresco Rd., Peckham Rye, in the various short -wave tests conducted are now on their way the S.E.1 S. by the club should communicate with arctic, bound for Europe. 2 APW A. D. Narraway, The School House, Dorring- M. P. E. Leveque, 52, Avenue de Mr. J. Diesen (LA 1A), Moen i Maal- ton, nr. Shrewsbury. Brouchère, Anderghem. selv, Tromsö, to whom we are indebted 2 BLX J. W. Tyrrell, 14, Boundary Rd., Ramsgate. A series of calibrated waves will be for this information, tells us that on 0 0 0 0 transmitted during March and April March 5th he was in two -way communi- QRAs Wanted. from EB 4AI and EB 4AR at the fol- cation, at 8.45 G.M.T., on a wavelength A 6WA, AR SLIT A, C 3AEL, lowing times :- Saturday, from 1530 to of 32 metres, with the whaler C. A. C 3WAB, CS 2YD, EP lAL, FQPM, 1542 G.M.T. on 145 metres, from 1555 to Larsen (ARDI), in the Antarctic, using NU 2RS, NU 7DBE, 0 811A, WAA, %0. B 25

. .:,_ . . , .... www.americanradiohistory.com v. The Manufacturers' Latest Products.

ATLAS A.C. BATTERY ELIMINATOR. Biassing potentials for H.F. or anode There is considerable latitude with re- bend detecting valves should be obtained gard to the equipment which may be pro- from separate cells. vided in a battery eliminator for obtain- Tested on the full load of 28 mA., and ing ample output and liberal smoothing. operating a four -valve set comprising two The only form of L.F. stages, there was an entire absence battery eliminator of which should be tolerated is one in which tween 20 and 150. A multi- contact hum when using two Mullard DT15 economy has not been the foremost con- switch arranged as a potential divider valves as rectifiers. sideration in the design. The dimensions gives the adjustable voltage. 0000 The eleminator (model A.C.2) is rated of the transformer, as well as the capa- BATTERY ELIMINATOR CONDENSER. city of the smoothing condensers and as being suitable for use on supply volt- current- ages between 200 and 250 at frequencies To combine in one unit all of the con- carrying capacity and inductance densers required in a battery eliminator of the smoothing chokes should be liberal. from 30 to 120. Connected to a 240, 50 cycle supply, the potential developed is a good feature, for apart from the con- at the output terminals, which depends, venience of wiring, much less space is of course, largely on the load, was found occupied. to be 250 when bridged with a shunt circuit passing 10 mA. The maximum voltage on a 25 mA. load was found to be 180 volts, while the stated voltage output of 150 was obtained when the total load was adjusted to 28mA. The variable voltage terminal is adjustable in stages of 20 volts when the current taken from the eliminator is 5 mA. The inclusion of terminals for giving grid biassing. potentials is a useful feature, particularly when power valves are 1 I EoRA __ used with the high anode potential which m-HypRA is obtainable. Terminals are fitted marked - 4, -8, -12, and -16 volts. ttn.uNarORCOacsENstIt UNIt These potentials were found to be prac- wiEP PPO tically correct when the rectifier was on I open circuit. With a 5mA. load, how- Tnoh, ever, on the H.T. supply the biassing The Zell potential advanced in the case of the first 4 -volt section to -5.2 volts, with proportional increases on the other tappings. Sectional condenser unit for use in the con- The eliminator is quite suitable for struction of an A.C. battery eliminator. operating a multi -valve receiver, including both high and low frequency ampli- A bank of Hydra condensers (Louis fying stages, and the high anode and Holzman, 109, Kingsway, London, Atlas battery eliminator for use with A.C. biassing potentials which can be obtained W.C.2) is now supplied in a convenient supply. Full-wave rectification is pro- render it suitable for use with a power form incorporating nine separate vided, and grid biassing potentials are capa- obtained as well as a high anode voltage amplifying stage where these potentials cities graduated in value and breakdown suitable for operating a power amplifying are essential in order to obtain good voltage according to the position they stage. quality. The addition of the variable would occupy in the circuit of an voltage control greatly adds to the use- eliminator. All these points have received careful fulness of the eliminator, though the ad- The diagram shows the connections of attention in the A.C. eliminator of H. justment moves in rather large steps. the section within a unit which should Clarke & Co. (Manchester), Ltd., Atlas prove useful for the construction of Works, Old Trafford, Manchester, which almost any form of battery eliminator. is a full -wave rectifier in which provision Two sections of 0.1 mfd. are rated to has been made for using either two half- withstand 1,500 volts. Two sections of way rectifying valves to provide full -wave 2 mfds. together with an 8 mfds. section rectification, or a single full -wave recti- are rated at 500 volts, the test potentials fier may be inserted in one of the valve - presenting the peak voltage on A.C. holders. supply. The four remaining sections are The apparatus is housed in an iron rated as suitable for use at a D.C. . case to which an ebonite panel is fitted potential of 500 volts. carrying the potential controlling switch Tests were applied to the section at and the various output terminals. Three 50 per cent. over the rated voltages with- outputs for H.T. supply are provided, the out breakdown. Wiring would be simpli- approximate voltages developed being 60, Internal connections of the Hydra bank of fied were the connecting tags near 150, and a variable potential range be- condensers. the base of the unit instead of at the top. Et 26

www.americanradiohistory.com APRIL 6111, Wilwgisog WOr ioll

r Brief Review

WORLD RADIO CO TERENCE._ MANY HAPPY RETURNS. DR. J. A. FLEMING. Germany is to be reps esented at the Senatore Marconi has just celebrated Dr. J. A. Fleming, the famous wireless international radio confer mce to be held - his fifty -third birthday. engineer, has been appointed president of at Washington in the e: ly autumn. 0000 the Victoria Institute or Philosophical 0000 A WELSH DELINQUENT. Society of Britain. Great 0000 THE TREACHEROUS SCILLIES. A Government official at Llanelly has been fined £2 for using a wireless re- GERMANS TO BUILD SIAMESE Work is nearing comple . on in the erec- ceiver without a licence. This is believed STATION. tion of a wireless beacon o Round Island, to be the first wireless " piracy " prosecu- The German Telefunken Company has one of the Isles of Scilly. hen in operation in Wales. secured the contract for the erection of tion the beacon will send out continuous 0000 a new wireless station at Bangkok, Siam. signals capable of being icked up at a THE WIRELESS PIANO. English and French companies put for- -range of 500 miles. A private company has been formed, ward quotations, but the German firm's 0000 known as Wireless Piano Players, Ltd., quotation of an inclusive charge of AN IMAGINATIVE CON EMPORARY. for the purpose of acquiring and exploit - £25,000 was considerably lower than that Under the title " N w Terror to ing an invention for the electromagnetic of the nearest competitor. Travel," a contemporary describes the reproduction of wireless reception by 0000 use of a portable wireless set on a train pianos and similar instruments. MUSIC ON A ZEPPELIN. journey from Paddington to Gloucester. 0000 In the new Zeppelin airship now under Considering that the set perated head - HEEDED WARNINGS. construction at Friedrichschafen, says a phones only and could be witched on or The chairman of the Bromley (Kent) Zurich correspondent, broadcast receivers off at will, we fail to ee where the magistrates states that the warnings will be installed so that passengers can " terror " comes in. issued from the bench in regard to the listen to European and American pro- 0000 illicit use of wireless receiving apparatus grammes. The airship is intended for LEVIATHAN'S ATLAN IC 'PHONE have had a good effect. No increase in journeys between Spain and the Argen- CALL. the usual fine of 10s. seems necessary. tine. The Atlantic wireless t ephone service was employed for the first time on board ship last week, when r. Joseph E. Sheedy, European directo of the Mer - chant Fleet Corporation, at a luncheon aboard the Leviathan a Southampton, exchanged greetings with he manager of the company in-New York. The luncheon, attended by a large gat ering, was in honour of the liner's fifty rst crossing of the Atlantic since being a quired by the American merchant marin 0000 PORTABLE SETS IN AUSTRIA. Readers whose travels take them to Austria this year will b interested to learn that foreign visitors aking wireless receiving sets into the c. untry are not required to pay the usual licence fee of 2s. per month, but a speci fee of is. per month, provided their sta does not exceed three months. An a plication form can be secured at any pos' office, and on entry into the country f reigners must deposit a given sum for Cu atoms purposes to cover the set, which is reimbursed on leaving the country. The saving of is. a mon th may not be vital of importance to pt ople who can SIMPLIFIED DIRECTION FINDING. A close -up view of a D.F. installation which is afford the fare to Austria but the con - being installed on forty -four steamers patrolling the Great Lakes in America. The cession will be recognised as a friendly dial shown at the base of the frame aerial, indicates the direction of a tran =matter, while the milliammeter gives a clue to its distance: The apparatus will he invaluable one. for locating vessels in fog. B 35 .-Alt

www.americanradiohistory.com 121 Wbghoo APRIL 6th, 1927. Wo0gi ó WHEN LONDON SCHOOLS MAY satisfying the claims of the hundreds of Postmaster -General why the British LISTEN. American stations which would each. like Broadcasting Corporation was to receive Wireless receiving apparatus has been an exclusive wavelength, but it is now £50,000 in revenue less this year than last installed in 100 London schools, says a realised that Canada, as sovereign in her year ; and how many wireless -listening report issued by the Elementary Educa- own field, can employ wavelengths which licences were in force this year as corn - tion Sub -Committee of the London County may bring confusion to the most carefully pared with last.. Council. It has been decided to permit laid plans. Sir William Mitchell- Thomson said schools to listen on Friday afternoons The desire of the Canadian Govern- that the amount paid to the British from 3 o'clock onwards, subject to certain ment is for a treaty guaranteeing the un- Broadcasting Company last year covered conditions. These conditions include ap- disturbed use of certain wavelengths, but not only the revenue for the service but proval of the programme and the correla- no settlement can be reached until the also the sum required for the repayment tion of the wireless lessons with the rest reassembly of Congress. Meanwhile a of the company's share capital and the of the school work. working arrangement must be discovered. expense of winding up the company. The As the Sub- Committee consider that 0000 revenue of the British Broadcasting Cor- good reception is of paramount import- ADDRESSES, PLEASE I poration during the financial year 1927 -28 ance, arrangements have been made for In connection with their announce- would be substantially greater than the the testing of the sets by B.B.C. ments in our advertisement columns, revenue of the company for the conduct engineers. of the service during the year 1926. 0000 The number of licences in force on Feb- IS YOUR MEDAL WAITING? EASTER HOLIDAYS AND ruary 28th, 1926, was about 1,906,000, and The Air Ministry announces that the SMALL ADVERTISEMENTS. the number in force on February 28th, British War and Victory Medals of a On account of the Easter Holidays 1927, was about 2,235.000, in addition to the Small Advertisement Section in licences for blind persons. large number of ex- officers and ex- airmen the issue of April 20th will close earlier about 4,400 free of the Royal Air Force still remain to be than usual. Cony should reach the issued, despite the efforts made to dis- Advertisement Manager not later than Regional Station Experiments. tribute them by sending communications April 12th. Sir W. Mitchell- Thomson informed Mr. to the latest known addresses of all those Day that the British Broadcasting Cor- concerned. Messrs. J. H. Corbett, of 1, Railway poration had stated that they proposed to Applications from ex- Service personnel Approach, Lewisham, S.E., state that carry out experiments at Daventry at an entitled to medals should be addressed in several cases replies have teen re- early date, and when those had been com- by ex- officers to the Secretary, Air ceived from persons who have omitted pleted they might be in a position to Ministry, Adastral House, Kingsway, to give their address. They would be submit proposals for the establishment oT W.C.2, and by ex- airmen to the Officer - glad if correspondents who have not regional high -power stations. in- Charge, R.A.F. Record Office, Ruislip, would write received acknowledgments Post Office Wireless Cars. Uxbridge, Middlesex. again. 0000 Viscount Wolmer informed Sir H: CANADA AND THE U.S. RADIO Brittain that the use of motor cars for COMMISSION. WIRELESS AT WESTMINSTER. the detection of oscillation was at present A knotty problem is facing the United BY OIIR PARLIAMENTARY CORRESPONDENT. in the experimental stage. The question States Federal Radio Commission with of increasing their number would be con- regard to the wavelengths employed by B.B.C. Income. sidered if experience showed that the Canadian broadcasting stations. The In the House of Commons :ast week results were likely to justify the expense Commission has work enough ahead in Lieut.- Commander Kenworthy asked the involved.

THE BRITISH WIRELESS DINNER CLUB, Air -Commodore L. F. Mandy presides at the dinne. of the British Wireless Dinner Club. held at the Trocadero Restaurant on Saturday, March 26th, the principal guests being Sir Ernest Rutherford and Sir Evelyn Murray, Secretary to the General Post Office. A number of well -k sow a personalities in wireless circles will be recognised in the photograph. B 36

dA t..;:, ,x -r ..... _t..e5`°.dertx...r:w. www.americanradiohistory.comc,r.n- !ii s".; ie;:.^+Nr''=áil,?%If:i'. .ef+é4`.° APRIT 6111, 7927. WAT@Ilsog Wafficd 425 HOW TO TT YOUR VALVES. Design and Construction of a Simple Test Board. By W. JAMES.

VALVE testing board is one of the most useful the relative merits of the various valves; in fact, com- pieces of apparatus that anyone taking a ,serious parisons of makers' figures are not satisfactory unless interest in the subject of valves and receiving complete data are available. " That this is true is circuits can possess. Valves vary enormously in charac- generally admitted by those competent to form an teristics; even individual valves of the same series differ opinion; hence it is of primary importance for those in- among themselves to an extent sufficient to eroduce notice- terested in the design of receivers very carefully to able effects in reception. Normally the makers, or their attend to this question of a valve's characteristics under publicity. departments, supply characteristic curves and working conditions. data relating to their valves, but it has to be remembered that this information applies to an average valve of each Taking Characteristics. type and may be a very different thing from the specimen Static characteristic curves, fortunately, can easily be secured by a user. Further, the information does not obtained. The illustrations here show a simple testing always relate to the valves as used under normal con- hoard which has been used by the writer for a consider- ditions; anode A.C. resistance, in particular, varies con - able time. A feature which may appeal to the reader siderably with the effective voltage acting to produce is that the four meters shown on the board can be removed anode current. Consequently a comparison of the by undoing the connections and sliding the instrument maker's figures will not, of necessity, serve to indicate forward. The connecting wires are of stranded conductor provided with large connecting tags, and the wires are passed through holes in the board, so that even- when the wires are removed from the instrument - terminals they remain in position ready to be recon- nected again. Instruments of the Weston Electrical Co. are used, and have the following ranges :- Grid Voltmeter. -o - 2.5 - ro - 25 volts. Anode Voltmeter. -o -75 - 3co volts. Filament Voltmeter. -o- 7.5 volts. Filament Ammeter. -o - o. r - r - rip amperes. For the grid circuit a microammeter having a full scale reading of 5o microamperes is used, while anode current is read on a Weston Sub - Standard Ammeter, o - 5 - 5o milliamperes. The latter instruments are so often used for other work that they are not fixed in any way to the board. The average amateur will probably not require the two filament meters, since the maker's filament ratings are usually reliable, and filament voltage can be read on the Fig. 1.-The complete valve testing board. All batteries are connected to terminals, as are the grid and anode ammeters. meter normally used in tli B 37

www.americanradiohistory.com 426 WAp@Il®00 APR1Z 6th, 1927. WOI Dd. How to Test Your Valves. - of the potentiometer. A potentiometer having a resist- grid circuit. A further item included on the board is a ance of about r,000 ohms is suitable. 2 -pole change -over switch; this merely transfers the On the right -hand side of the board are two resist- polarity of the grid bias. With the switch in one posi- ances; one has a fairly high value of resistance and the tion a negative voltage is applied to the grid, while a other a low resistance, the combination being such that the positive bias is given by throwing over the switch. The filament voltage can be carefully set at a given figure. magnitude of the voltage applied depends on the battery Another item of interest is the single -pole change -over ,onnected to the grid bias terminals and to the setting switch mounted on the strip of wood by the side of the

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www.americanradiohistory.com APRIL Gtk, 1927. Nrpagoo 427 WI ?lid How to Test Your Valves.- To find the approximate amplification factor we have filament voltmeter. This merely serves to connect the to set the anode voltage at a given value, say 120, and voltmeter across the filament of the valve or across the the grid bias to a value such as might be used under valve and filament ammeter in series. working conditions. The anode current should be noted.. The usual static characteristic curves are easily obtained Now the anode voltage is reduced by, say, ro volts, and in the following manner. A valve is put in the socket, the anode current is again noted. Next the grid bias is its filament voltage being adjusted to the working value. changed to restore the anode current to its former value. A given anode voltage is applied and readings of anode From the figures obtained the approximate amplifi- current for various grid voltages taken. This is repeated cation factor can easily be found, as it is given by the for a number of anode voltages, and the results are change in anode voltage divided by the change in grid

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Fig. 3.- Wiring diagram. Most of the wires are run below the board and are brought through holes at the Instrument terminals. plotted to give curves after the style of those given in fiias. For the anode A.C. resistance we divide the Figs. 5 and 6. Two valves were chosen and tested for change in anode voltage by the change of anode current. the purpose of illustration, one being of the type having Details of the characteristics of the two valves tested a moderate amplification factor and A.C. resistance, while by way of example are given below the figures. Anode the other has a much lower amplification factor and A.C. A.C. resistance, and to a certain extent the amplification resistance. Naturally the valve with the lowest A.C. factor, is found to vary with the anode voltage, grid resistance has the greater anode current for given grid bias, and filament voltage. To reduce the anode A.C. and anode voltages. resistance it is necessary only to raise the anode voltage,

B 39

www.americanradiohistory.com 7WEp,SIl®00 .128 APRIL 6th, 1927. WoACi be obtained from a receiver the characteristics of which are known. TO GR It will have been noticed that the amplification factor GRID and anode A.C. resistance found by the above method is not, strictly speaking, for the anode voltage of 120, 11 °r$ 1( since the anode voltage was reduced to to volts as plat ox a of the test, but the results are sufficiently accurate for most purposes. This can be tested by finding the value L.! 3i when the anode voltage is raised from 120 to 13o volts. o o NENEr o o ENMMr 3 -0 iiiiiiiiiiiiiiiii°iii Mó,,I/, NEM ,E) II,M.MfI 2-5 Flg. 4.- Wiring of the under side of the two-pole change -over switch. yWM IEWI, o"/h iN reduce the negative grid bias, or to increase the filament EM ,I 2.0 current (if this is below normal). It follows therefore NI that the anode A.C. resistance can be \IÌ%y IM increased by re- EMEr/rA is MI ducing the anode voltage or the filament current, or by NEIEIr1EI,ME/ óIM , iNE 1.5 increasing the negative grid bias. These statements can mMI,g/I.ENNriI.M easily be verified by anyone having a valve testing board, I and a realisation of them will enable the best results to NrII.Mri/EEEI,MN%IM EENNEII.MEUNENNR1UEVI IE 1.0 NEMEI/Ar.NIEr/EII MIENN/MEE%NI.MI.MMIELNI.MI.NN 05 N!NEiENEriE 6'0 NEMN/iNEGMIEMENME MAGAAI9WiE EM%MENEENNEIiEMEIM mfi MiMiANEEMAMAMAMEEEE NNEEI.ME 50 -6 5 4 3 2 1 0 MENLENEE/INEI.MEEI GRID VOLTS I.MMAy.NI IEU 4.0 oiNri Fig. 6.- Curves of a 2 -volt valve having a fairly high anode A.C. ó M 5.I resistance. The actual amplification factor and anode A.C. resist- ego ance were found to be 25 and 37,000 ohms respectively /M ov./R/ for an anode N MNIN voltage of around 120 and a grid bias of nggative 1.5. oo/EI NUNNM% iE 5i E 3'0 v IM= MEM/R/N. .:mow The characteristic curves shown in Figs. 5 and 6 are M applicable r,/Nm, .o.R under. the conditions of the test only, that is, EI/ENIE /NN 5 //NIRA IM 2.0 with no load in the anode or grid circuits. When a load GMIRa ANNE such as a resistance is connected in the anode circuit the iNONI.1 q,0 MN= ENRRERAMME/%NMNRA MEE= anode voltage, as distinct from the voltage of the anode REWNEGMMEN 1.0 battery, will vary with the voltage applied to the grill PLRMEECN.MIMR/ in such a way that a curve drawn to show the relation ENNEEiiRMAMNNMEN between battery volts and anode current will more o extend -14 12 10 9 8 7 6 5 4 3 2 1 0 to the left of the zero grid voltage line than an ordinary GRID VOLTS characteristic curve taken with no load in the anode cir- A cuit. Such a curve will be straight over a greater part of its length than the static curve, and its length will Fig. 5.-Curves of a typical 2-volt valve; the amplification factor depend on the value of the anode resistance as well as and anode A.C. resistance are 9.1 and 17,000 ohms respectively for an anode voltage of around 120 and a grid bias of negative 4.5. the battery voltage.

A. F. Bnlgin and . Co. (9, 10 and 11, London Electrical Co., 1, Sherborne Cursitór Street, Chancery Lane, E.C.4). Lane, King William Street, London, Lists Nos. 110, 111 and 112, dealing with Catalogues Received. E.C.4. Eighty -page catalogue of high - Ueclorem and Conapeta Radio Products class proprietary radio components. and Conapeta Measuring Instruments. Leaflet describing the " Leco-dyne " Re- Chloride Electrical Storage Co., Ltd., J. R. .1\1,n1]-., Imperial House, 15 -19, ceivers. Clifton Junction, near Manchester. Folder Kingsway, London, W.C.2. Folder deal- R.I. Instruments, Ltd., 12, Hyde

No. 5008, dealing with Exid,: " Mass " ing with Columbia dry batteries for wire- Street, New Oxford Street, London, - Type batteries for long, slow discharges. less use, including the Layerbilt No. 4486 W.0 -1. Leaflet dealing with the R.I. Folder No. 5009, relating to Exide WH for heavy duty with neutrodyne and Power Transformer designed for operat- and WJ special " Mass " type batteries. multi -valve sets. ing K.L.1 Type valves from A.C. -Mains. B 40

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CLUB REPORTS A Society in Lancaster. ND himself, at the March meeting of the Society. of a the Kensington Radió Instead The radio club in connection with horn Mr. Child used a baffle board of Storey Institute, Lancaster, has entered TOAPICS on testing it showed meet- three -ply wood, and into a new era of activity, and its no special resonance peaks, as did two ings now include debates, lectures, loud- speakers of the horn type which were demonstrations and morse instruction. put to the same test. The subject of an interesting debate on Secretaries of Local Clubs are invited to The occasion was very unfavourable, Saturday, March 12th, was " Wireless send to for publication club news of general the evening being devoted to a simul- All will be v. Gramophone." All wireless enthu- intere4. photographs published taneous land -line broadcast, but members siasts in the district are cordially invited paid for. heard enough to convince them that, to communicate' with the hon. secretary, As :t result of elections which took especially on the lower notes, Mr. Child Mr. W. Salt, 5, Coverdale Road, Lan- im- place towards the conclusion of the meet - had succeeded in making considerable caster. Experts and beginners are equally provements on the average commercial welcome. ing all the officers were re- elected for an- 0000 other year. type of loud- speaker. Hon. secretary : Mr. G. T. Hoyes, 29, Hon4, secretary : Mr. H. A. Green, 100, New Society in Huddersfield. Pellatt Grove, Wood Green, N.22. Upper Phillimore Place, W.8. The first general meeting of the 0000 0000 Huddersfield New Radio Society was held Irish Transmitters. A Long -wave Receiver. on March 21st at the Central Lads' Club, Transmitters' Society Ramsden Street, The Irish Radio Of particular interest to long -distare Huddersfield. Applica- held a business meeting on March 15th, tions for membership are welcomed and enthusiasts was the lecture given at the when Col. M. J. C. Dennis, C.B. (GW- Tottenham Wireless Society's last meet- rhould he forwarded to the hon. secretary, llB) was elected president, while Messrs. Mr. Frank Simpson, 39, Victory Avenue, ing by Mr. F. E. R. Neale. The lecturer J. J. Dowling and Eric Megaw were demonstrated a long -distance receiver, l'addock, Huddersfield. The entrance elected vice -presidents, and numerous fee is specially constructed by loins for use on Is. and the annual subscription officers were appointed. The com- 2s. 6d. other wavelengths over 900 metres. Up to five 0000 mittee is now arranging lectures, demon- valves were used, and the lecturer showed strations and morse classes. A Survey of Science. that with this equipment he had all the Hon. secretary : Mr. Cyril Fagan, 2, his The Golders Green long -wave continental stations at and Hendon Radio TTpper Leeson Street, Dublin. command. the aid of two tone con- Society departed from the usual channels oooo With of discussion trols Mr. Neale showed how comfortable when on a recent evening A New Hornless Loud-speaker. loud-speaker strength could be obtained they welcomed as lecturer Mr. G. G. \l Blake, r. Maurice Child demonstrated a new from most stations. Owing to the fact M.I.E.E., who took his audience meting coil loud -speaker, by that none of the three H.F. tuned circuits on an imaginary " constructed Journey into the World was highly selective, tuning in was of Science." Mr. Blake dealt with a wide simple, and yet the all -round selectivity range of subjects, touching upon the Einstein Theory FORTHCOMING EVENTS. was sufficient for general purposes. In and the construction of the course of the lecture, mention was the atom, WEDNESDAY, APRIL Eth. ether waves, radiant heat, and made of the system of neutrodyning em- lines of force. He concluded with a short InstihNion of Electrical Engineers, (Wireless 6 ployed by Mr. W. James in his well - history of Clark of Section.-At p.m. (Light Refreshments Maxwell's theory at 5.30). At the Institution, Savoy known receivers, and it was shown that light. Of special interest was an analogy Place. W.C.2. Lecture: "Battern Eli- stability was maintained over entire of a wireless minators or Appliances for the Operation the circuit where the batteries of Radio Receiving Apparatus by Energy tuning range. were replaced by pumps and the wires Desired front Electric Supply Mains," by Hon. secretary : Mr. A. G. Tucker, 42, by water pipes; flow of was Messrs. I'. R. Coursey, B.Sc., and H. the energy At,drewes, B.Sc. Drayton Road, Tottenham, N.17. clearly demonstrated. Tottenham 1i'ireless Society. -At 8 p.m. The Society will hold the third dance At the Institute, 10, Bruce Grove. Busi- 0 0 0 0 ness meeting. Subject: "Summer Pro - of the season in the club ballroom on graennie." Wireless Films Displayed. April 27th at 8 p.m. Dance tickets, price Barnsley and District )Wireless .Association.. -At 8 p.m. At 22, Market Street. Lec- Filins of interest to all wireless en- 3s., together with full particulars of future ture: "The ,Water Analogy," by Mr. field days, etc., can be obtained from the J. S. Gillett. thusiasts were displayed at the Central Ediubiergh and District Radio Society. - Hall, Bristol, under the auspices of the bon. secretary : Lt. -Col. H. A. Scarlett, At 8 p.m. At 117, George Street. Busi- Society, D.S.O., 357a, Finchley Road, N.W.3. ness meeting. Bristol and District Radio on 0000 THURSDAY, APRIL 7th. Wednesday, March 16th. Golders Green and Hendon Radio Society. Thanks to the generosity of Messrs. A Year's Work. -3t 8 p.m. At the Club House, Willi- field )Way, N.W.11. Auction of Surplus The General Electric Co., Ltd., and Twenty -nine meetings, including two Apparatus. Chairman, iii. A. J. Standard Telephones and Cables, a pro- Bremner, B Sc. gramme was provided which lasted two field days and a celebration dinner, was FRIDAY, APRIL 8th. the record of the North Middlesex Wire- Sheffield and District Wireless Society. - and a half hours. In the interval the less Club for 1926, as revealed in the AI the Dept. of :I pntied Science. St. Rt. Hon. the Lord Mayor of Bristol, Mr. George's Square. Lecture by Mr. R. E. secretary's report at the annual general Bounce. E. R, Appleton (director of the Cardiff meeting held on March 16th. The hon. Lerne Radio Sorietn. -At 8 p.m. At Col - B.B.C. Station), and the chairman of the Iirewn'.s rate. Wellington Street. Annual treasurer, Mr. H. A. Crowell, presented gracral muting. society each addressed the meeting, ex- a very creditable balance -sheet showing MONDAY, APRIL 11th. plaining the charitable objects to which a slight increase over the balance of last Nort5ampton. and District A 'tweeter Radio the proceeds of the occasion were to be Soriety. -:I t 8 p.ue. At Cosmo Cafe, The year. Mr. Gartland gave an explanation Drapery. Lecture by Messrs. Shaw and devoted. These were the Lord Mayor's of the Club's Instrument Loaning Scheme, T :ask r. " Wireless for Hospitals " Fund, and the Crab:don li-ireless and Physical Society.- 5WA " Sets for the Sick " Fund. while a short account of the work of the .1r 8 p.ne. At 128A, George Street. Lec- Club Library was given by Mr. F. C. ture: "Quarts," by 1fr. A. Ilieederlieh. Hon. secretary : Mr. S. J. Hurley, 4f, March. Cotswold Road, Bedminster, Bristol. B 4i

www.americanradiohistory.com WApaigEO 430 MTH APRIL 6th, 7927.

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Savoy Hill Topicalities : By Our Special Correspondent. Lord Clarendon on Tour. -" Daventry Junior" and Essential Services. -A Plea from Shetland. - If Summer Comes.- Signals During the Eclipse. -A Soviet Programme.

Histrionics at the Microphone. has been tolerated by the authorities Wanted -100 per cent. Service. Berlin is copying London by opening simply because, being on a wavelength of Heaven forbid a battle royal between 1.600 a school of broadcast dramatic -art. metres, it has not interfered with the Post Office and the B.B.C. anent the essential services. ' But " Daventry 0000- ' plans which have been so conscientiously Junior " and the other stations com- Lord Clarendon on Tour. developed at Savoy Hill during the past prising the regional group will work on few months. Lord Clarendon, the new chairman of With tact and diplomacy the ordinary broadcast band. On the on both sides trouble may be averted, the British Broadcasting Corporation; has assumption (by no means preposterous) paid his first and the B.B.C. may achieve its laudable visits to the Cardiff and that the other regional stations will be object of providing Manchester stations respectively. He is a 100 per cent. ser- situated near London, Cardiff, Man- vice throughout the country. no stranger at Savoy Hill, where the the possibility chester and Glasgow, of According to estimates at Savoy Hill members of the board meet regularly interference with ship signals is not un- every fortnight the present service covers 80 or 85 per to discuss policy. That likely. cent. of the population. his lordship will visit each station in Before licensing a regional station the turn, including the relays, is extremely Post Office will assure itself that essential 0000 aonbtfui, nor does the necessity for such services are not encroached upon. A Tragic Petition. a course appear to be very urgent. Certain districts are badly served at 0000 present, as is shown by the complaints By the Way. received from time to time at headquarters. Among the benighted areas are If I am not mistaken, Lord Clarendon the dales of Cumberland, County is one of the few celebrities associated Donegal, the north of Scotland, and with broadcasting who have never them- Orkney and Shetland. selves used the microphone. Not long ago a tragic petifion against 0000 ship interference, with forty signatures, "Only too Happy." was received from Shetland. 0000 The Soviet Government has issued instructions to " actors, singers and No Complaints. musicians " not to accept any supplemen- One of the few spots from which no tary fee for having their performances complaints have been received is Lundy broadcast. Isle, in the Bristol Channel, but I hear " Artists, as well as authors," runs the that this apparent contentment is due regulation, " should be only too happy to to the fact that the erstwhile sole in- perform the rûle of public educator which habitant of that island is either dead or the science of wireless telephony allows has gone away. them to assume." 0000 Now, if the B.B.C. approached the Return of Rev. H. R. L. Sheppard. music -hall interests in this tactful The address during the service which is fashion . . .! to be relayed from St. Martin- in -the- 0000 Fields on Good Friday evening will be Daventry and the Post Office. given by the former vicar, Rev. H. Il. L. Apropos the test transmissions which Sheppard. " Dick " Sheppard, listeners are shortly to be made from " Daventry will be glad to know, is now much Junior," the powers that be are very improved in health. explicit on the point that these will be of 0000 an experimental nature only. While H Summer Comes.

- there can be little doubt that the new No doubt the brains of Savoy Hill are station will eventually form the first link already engaged in framing a summer in the regional chain, the Post Office, it. THAT SPRING FEELING. Broadcast policy. If they are not . . . well the must be remembered, have a veto in the reception on the river has a fascination sooner they are the better. matter. of its own. The fact is evidently realised by the fair occupant of this up-Thames The type of programme which seems 5XX, with its power of 25 kilowatts; houseboat. graceful and pleasing in winter can on a B 42

www.americanradiohistory.com W'ATcIlmo APRIL Gth, 1927. 431 WopIlc1 day in summer be as flaccid as a pancake. As a suitable summer item a friend suggests that the B.B.C. should take the wireless perambulator round the Tower of London and similar places of interest in company with lecture parties of American tourists. 000.0 Atmosphere. In " tours of this description the guide could supply talk and atmosphere, while the Americans could also supply a little of both in the form of a " running commentary."

Thus :- - Guide : This is the Monument, com- memorating the Great Fire of London, 1666. Tourist : Gee, but Ah guess, bo, that fire wouldn't have come off in our li'1 old town. We got a Niagara. . . . ooi. A Peculiar Piano. A piano built specially for broadcasting purposes has been installed in the studio of the WBBM station, Chicago. The lower tones are specially strengthened, while the middle tones are subdued. The top notes are endowed with additional ring. 0000 A Fresh Start in So'burg. On April 3rd the Johannesburg broad- AN AUTOMATIC RECEIVER. This rather cumbrous piece of apparatus is claimed casting which closed down in to be the first broadcast receiver fitted with automatic tuning. When the mechanism station, has been set it will tune in a dozen different broadcasting stations at predetermined ignominous circumstances recently times during the day.. The instrument has been designed by the United States through la':k of funds, was taken over by Bureau of Standards in Washington. Dr. L. W. Austin, head of the Radio Transmission the new African Broadcasting Company, Research Laboratory, is seen in the photograph. Ltd. This company, which seems to be element seems to predominate, and who built on a surer foundation than the FUTURE FEATURES. shall say that it is superfluous? previous broadcasting enterprise, is to Sunday, April 10th. Here is the " Komintern " programme erect a high power station at Killarney, for a recent Saturday :- to supersede the LONDON.- Matthew Passion, re- 4.00- programme. near Johannesburg, layed from York Minster. 4.!0.- Children's present " J.B." 5.20 -5.45.- Statement by the Central A relay will then operate at BELFAST.- Special Palm Sunday Committee for Workers' station relayed from St. Education. Bloemfontein. Service 5.50-6.15.- Lecture on the Resources of 0000 Anne's Cathedral. the Soviet Union. " Iron." Professor Signals during Solar Eclipse. Monday, April 11th. Federovsky. Probably because it will occur at such LONDON. - Concert by prize 6.15- 7.05. -Workers' Wireless News- an abominably unreasonable hour, the winners of London Musical paper. eclipse of the sun on June 29th is not Competitions. 8.00 -8.30.- Statement by the Central likely to form the subject of a running AseRnEEN.- Scottish Programme. Committee of the Young Communist commentary by the B.B.C. The period Tuesday, April 12th. League. of totality occurs about 5.25 a.m., and at LONDON.-" Polly," an Opera by 8.30 -11.00. -Dance Music. And so to bedski. that time there is a probability that _Mr. Gay. 0000 broadcasting stations within and near the GL,tscow-. -A Railwayman "s Night. An Esthetic Anaesthetic. shadow, such as Liverpool and Man- Wednesday, April 13th. chester, will transmit a .tuning note for The following story, emanating from CAL .DIFF.-Concert by " Women of New Jersey, commands respect if only on the benefit of listeners who are carrying Wales." out experiments on the effect of the eclipse account of its extreme tallness. 1.A:VCIIESTER. Roosters Con- on signal strength. -The It appears that a dear old gentleman 0000 cert Party. who had passed his threescore years and Foundation. Thursday, April 14th. ten was required to undergo a serious Without LONDON.- Spanish Programme. operation. It was feared, however, that There is no truth in the rumour that, GLASGOW.- Scenes from " King an aniesthetic of the ordinary kind might if weather conditions are unpropitious, John " : " The School for have fatal results, so the surgeons cast the B.B.C. programme department will Scandal." about for some other means of saving postpone the event. " In this particular their patient unnecessary pain. They had case," a B.B.C. official is said to have Friday, April 15th. Lor-noN. " The Dream of almost given up the problem in despair remarked, " we shall offer no objections - when the patient himself came forward to the natural course of events." Gerontius " relayed from 0000 Bishopsgate Institute. with a constructive proposal which was BIRa11NCHAM. -Good Friday pro- put into effect. While the operation Soviet Programmes. gramme of Passion Music. lasted the old gentleman wore headphones Typical programmes of the Moscow and listened to broadcast music which stations have been sent me by corre- Saturday, April 16th. took his thoughts off the pain. spondent, and they serve to slim that GLASCdw.- Neapolitan Programme. Considering the sort of music we some- Russian listeners will stomach even more BELFAST.- Idylls of the Hebrides. times have to listen to, I begin to believe talk than the Germans. The educational that the story might be true. B 43

www.americanradiohistory.com WIp@Ilsoo 432 APRIL 1927. WoEIlLil 6th,

NT IrIVEIY'l'IOlY

The following abstracts are prepared, with the permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Patent Office, 25, Southampton Buildings, London, W.C.2, price Is. each. Short -wave Transmission. two valves comprises an ordinary choke - of spurious oscillations. The circuit is (No. 242,653.) control modulation system. Connected claimed to be particularly efficient when in the grid circuit of the Convention date (U.S.A.): Nov. 6th,1924. master oscillator the anode potential is supplied from a valve V, is an arrangement shown at X, source of alternating current. One of the disadvantages of short -wave which is used continuously to vary the 0000 transmission lies in the periodic fading frequency of the oscillations. This may to which the higher frequencies are par- consist of a rotating condenser plate or Short -wave Coil Construction. ticularly susceptible. Briefly, this may some means for altering the value of the (No. 263,259.) be assumed to be due to there being two inductance in the grid circuit of this Application date: October waves, one a ground wave and the other valve. The specification indicates how 21st, 1925. a: wave reflected from the Heaviside this can be done by the use of two E. L. Wildy and the London Electric layer. Owing to variation in the Heavi- valves oscillating at another frequency. Wire Co. and Smiths, Ltd., give details side layer the voltages at the receiving 0000 in the above British patent of a system station, which are a combination of of short -wave coil construction which is those obtained from both waves, are con- Valve Oscillator. illustrated by the accompanying diagram. (No. 258,257.) The coil is of the type comprising a Convention date (Germany) : Sept. 11th, 1925. A valve oscillator is described in the above British patent by Telefunken Gesellschaft für Drahtlose Telegraphie. The particular novel feature of the invention lies in thé use of a positive potential on the grid with respect to the filament. The manner in which the circuit is arranged is shown in the diagram. The oscillatory circuit consists of an inductance L, tuned by a condenser C,. One end of the oscillatory circuit is connected to the anode A, while the other side is connected through a condenser C. shunted by a resistance R to the grid G. A tapping on the inductance L, is connected to a source of positive poten- Variable wavelength transmitter for short- tial wave communication. (No. 242,653.) B, the negative end of which, of course, is connected to the filament F of Insulating supports for short -wave coils. the valve. Here, then, both the anode and (No. 263,259.) stantly changing in magnitude and phase. grid According to the present invention, are given a positive potential with which respect to the filament. Since number of spaced turns of thick wire is due to A. N Goldsmith and Marconi's the grid which is positive, current will flow in the grid are separated by insulating sup- Wireless Telegraph Co., Ltd., the difficulty circuit, and ports provided with transverse holes for is overcome by continuously varying the will occasion a fall of potential along the resistance thereby main- retaining the wire. The novelty of the wavelengtit of the transmitting station, so R invention lies in the construction of the that over a given short interval appreci- insulating supports. In the accompany- able signal voltages will be obtained at any ing diagram the turns of the coil are given instant from one or other of the fre- shown at T. and are spaced by means of quencies of transmission. The accom- ebonite or other insulating spacers X. panying diagram shows a form of trans- The construction of the spacers is shown mitter utilising this principle. The valve in the lower half of the illustration, and V, is provided with a grid inductance will be seen to comprise an outer tubular L a condenser C and an anode in- member 0 and an inner member R. Both ductance L2, the two being coupled so the members O and R are provided with as to produce continuous oscillations of little holes H, and the member R is a very high frequency. The anode circuit slipped into the tubular member 0 so cónt,ins another inductance L which is that the two sets of holes register. The coupled to another inductance L, in the ends of the inner portion R are threaded grid circuit of an amplifying valve V, and provided with nuts N. Thus it will coupled through the usual coils to the Oscillatory valve circuit. (No. 258,257.) be seen that on tightening the one or aerial system. A speech modulation valve other of the nuts against the ends of V, is connected in the usual manner with tanning the grid at a lower positive poten- the outer member O it will cause the the microphone M and transformer T. tial than the anode. It is stated that inner member to be displaced slightly, The anode supply for the valve V, and this particular circuit is conducive to thereby bringing about a locking action V,. shown at B is connected through a the production of gentle oscillations and on the turns of the wire, thus main- 'lioke L, so that the arrangement of the also does not give rise to the generation taining a rigid construction. 44

Ai3ñYiiw www.americanradiohistory.comá*iii2 The Editor does not hold himself responsible for the opinions of his correspondents. and address. Correspondence should be addressed to the Editor, "The Wireless World," Dorset Hoase, Tudor Street, E.C.4, and must be accompanied by the writer's name DIRECTORY OF SOURCES OF SPECIAL INFORMATION. circuits of the valves before I felt justified in complaining by about the matter. Sir, -Just as the practical utility of a book is impaired the point the distortion of knowledge I would also like to emphasise that the want of an index, so the vast aggregation is by no means always There can be little doubt that cases added to present. that has been built up and is in many being is acoustical, most of the studios at Savoy owing to the lack of the trouble entirely day by day is largely lost to mankind Hill being more or less unsuitable for bringing out the finer a master -key to its whereabouts. Throughout this country there like to men- and experience points of piano tone. In this connection I should are numerous centres of specialised knowledge the most natural piano that I have ever heard broad- of of which has only tion that the most varied description, the existence cast has been from the Grotrian Hall. to be known for them to prove of great service to the world. on the light and recording The following passage, which has a distinct bearing It is with the object of bringing these to in question, quote due acknowledgment from their salient features in concise form that the Association of subject I with the Broadcasting Column of a recent issue of The Observer : Special Libraries and Information Bureaux, in collaboration the distinctly bad with the Carnegie Kingdom Trust, has asked me to " Some while ago I drew attention to United rendering of piano music that was sometimes obtained from compile a directory. the London station, and pointed out that a really bad ren- It has been decided to go forward with the printing of a much still dering of a solo might be followed by a good transmission first edition of this directory at midsummer, but given to understand remains to be done. It is recognised that completion in any of a pianoforte accompaniment. I was time. that the fault existed in one particular studio, and that one subject is well -nigh impossible in so short a It made it would not be used however, greatly this end if libraries, organisa- directly arrangements could be would, further of am now sure it is not tions, firms and individuals possessing special information on for this type transmission. I that have one, but two or three of the studios which suffer from the any subject and willing to answer inquiries thereon, which use of not yet been in touch with us, would communicate with me complaint, whatever it is. Perhaps the suspended of the stand -supported pick -up," will at 38, Bloomsbury Square, W.C.1. G. F. BARWICK, microphones, instead " General Editor. make a difference. It is certainly high time that something London, W.C.1. fault is in the March 18th, 1927. was done, since it is no doubt that the transmission." G. F. ROSSITER. Teignmouth. March 1.6th, 1927. RANGE OF ATMOSPHERICS. Sir, -I was interested in your article in the March 16th issue reference to the discussion which has arisen over Rocky on the range of atmo- Sir, -With in reference to a test from Point the transmission of pianoforte music by the B.B.C., I entirely spherics. agree with Mr. Richardson when he states that it is bad. You may be interested to hear that years ago, while working by him to during bad Mr. R. N. Ballard airily dismisses him advising long -range wireless, it was a general practice, look to his set or loud- speaker. Perhaps he would like-to know atmospherics, to repeat any word, without request, whenever the apparatus that I am using. we had a bad " X " this end, as the same disturbance invariably For London I use a D.E.5B as rectifier, using anode bend was heard the other end, thereby mutilating the signal. is through a resistance capacity 1916." rectification. This coupled London, S.E.20. coupling to a L.S.5, which in turn is coupled through a choke 1927. March 19th, (150 henries) to three L.S.5A valves in parallel. The loud- speaker is one I built on specifications of the model used by Dr. McLachlan in his lecture before the R.S.G.B. in B.B.C. TRANSMISSION OF PIANOFORTE MUSIC. January, 1926, namely, a free -edge coil drive. Sir, -In my previous letter in connection with the B.B.C. The result on all music with the exception of the piano is transmission of pianoforte music I described in some detail the perfect. power stage of my receiving set, merely to show that the With the piano there is a blasting effect, although there is receiver should be capable of giving pure results with adequate no actual overloading of the valves, as all the meters remain volume. Mr. Richardson's receiver, from the description he perfectly steady. gave of it in his second letter, should also give very fine results. My theory (I am not an authority) is that the microphone The advice given by one of your correspondents that we should actually picks up the mechanical blow of the hammers on use suitable valves and grid bias was, no doubt, well meant, the strings of the piano. but was hardly necessary. While agreeing with Mr. A. L. If one sits close enough to the piano the same effect is noticed. Royer that it is possible to overload a superpower valve (or I might add that I am using 400 volts H.T. obtained from even two such valves in parallel -which I use), yet I can assure Exide 5 amp. -hour accumulators, with 40 volts grid bias on him that the distortion I complain of is not due to overloading the L.S.5 and 90 volts bias on the L.S.5As. of the valves, being evident on quite soft passages on the I am situated about four miles from 2L0. A. S. BROWN. speaker and in the telephones on two valves. Naturally, too, London, S.E.16. I had made careful tests with a milliammeter in the plate March 22nd, 1927

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www.americanradiohistory.com 434 NVflp@hoo APRIL 6th, 1927 Wore-Ad Sir, -As one of the great majority of your readers who are possibility of microphonic noise due to this cause can then be following with intense interest the progress of your campaign avoided. for good quality in broadcast reception I would like to mention That a microphonic noise of definite pitch can be caused by one way in which the B.B.C. can give invaluable assistance to- other means, however, is shown, .I think, by a further phenom- wards the realisation of this ideal. I refer to a transmission enon I have obtained. Using a valve whose bulb was wound of a series of equally modulated notes covering the whole tightly with shellacked string, which I have found effective in musical scale, the frequency being indicated after each note. preventing vibration of the glass, and in a rigid holder, I ob -. A simple way to do this was shown in a recent R.S.G.B. talk, tained a microphonic noise of about 1,000 cycles which waxed where a piano was used. Thousands of interested listeners must and waned regularly. The waxing and waning occurred with have missed this opportunity of testing their receivers, for the a frequency of 2 to 6 times a second, and this frequency was nature of the talk was not announced in The Radio Times, and controllable by the filament rheostat. I assume, therefore, that 6 p.m. is an inconvenient time for many of us. I had the ex- the filament vibration was beating with another vibration quisite torture of hearing it in a local dealer's shop, for the of nearly equal frequency, arising probably from the holder. result did net flatter his reproducer, and my set was five minutes' Birmingham, March 16th, 1927. G. H. S: walk away, just out of reach. No doubt financial considerations will preclude the use of more accurate methods, but a weekly piano transmission would be very useful. It would not be necessary to trespass on pro- Sir,-Since, in criticising my article on "Microphonic Noises," gramme time, and " 2L0 stand -by transmitter testing " could your correspondent, " Howler," makes certain statements which, be made to have a real meaning for the listener. I venture to suggest, are not scientifically accurate, and may, Teddington, S. J. WALLIS. therefore, lead some of your readers astray, I should welcome March 16th, 1927. this opportunity of replying to his comments. " Howler " suggests that the fault does not lie in the valve holder, and the resonance effect is due to the vibration of the Sir,-With reference to the correspondence anent the B.B.C. electrodes. If " Howler " examines my article he will find that piano transmission, might I put on record the following facts I state in the fourth paragraph that what he calls the resonance which I have not seen mentioned as yet :- effect is due to the vibration of the electrodes. I cannot agree 1. When 2L0 is " distorting," the transmission from 6 BM with " Howler " that the fault does not lie in the holder. or 5IT is perfect -naturally, when 2L0 is S.B. to these stations. Since the electrodes are mechanically connected with the holder, 2. When 2L0 is bad, 5XX is perfect, on the same programme. it follows that if the holder is capable of sustaining oscilla- 3. Up to the time a certain London store started extending tions, then the electrodes will remain in a state of oscillation. their premises, and of necessity erecting large steel cranes and If, however, the holder cannot sustain oscillations, then the using many tons of steel girders and corrugated iron, this dis- electrodes will not remain in this condition. Frankly, I cannot tortion was not noticeable in this district. This store is the see " Howler's" line of argument in suggesting that the holder " base " of the 2L0 aerial. is not responsible. For a considerable time I have, in a very humble way, esperi, " Howler's " experiments of substituting spring holders of mented for perfect reception, and my instrument is a Marconi different natural periods and finding that the note in the tele- Straight 8, with a D.E.5A iri the last L.F. stage, especially phones is not varied are quite inconclusive, and he deduces wired for large grid bias, working a Western L ectric " Kone " therefrom inaccurate conclusions. The natural period of all loud -speaker. spring holders when loaded with the mass of the valve is such I might mention that the facts I have referred to have been that it is capable of shock exciting the electrodes and enabling verified many times in this district. them to remain in a state of vibration. The note which is That distortion is present at times the B.B.C. are the first given is a function of ^the natural period of the electrode system. " Howler " to admit, but if every receiving station were to be only one - suggests that I have generalised from the result tenth as efficient as the B.B.C. transmission I doubt if there of one experiment. I do not think I am guilty of this. The would be so much " grousing." I would like to have had some experiment mentioned was merely given to illustrate my theo- of the " grousers " with me in 1916 when using wireless telephony retical deductions, of which the major portion of my article consists. The cessation of howling from the air ! " LATE CHIEF INSTRUCTOR." due to the substitution of Farnham, March 21st, 1927. a rubber- mounted holder for a spring holder was not a coincidence as suggested, and it seems to me that my article clearly points out how and why this should have occurred. MICROPHONIC NOISES. " Howler " is quite wrong when he states that " acoustic energy is collected by the glass walls of the valve and trans- Sir,-I have recently been subject to low- frequency howling, mitted to the electrodes. . Sound energy by its very due to my using a high- impedance valve as detector with a plate definition is kinetic. Energy which is collected most obviously potential of 90 volts, and leaky grid method of rectification. be potential. Obviously, then, any energy is After trying many ways which collected of curing the trouble I tried those is not in the form of sound. What actually happens is describe l by " Howler," and the one under the heading " Valve this : Of the sound impinging on the wall of the valve, a minute Vibration," in the March 16th issue, but none effected a cure. part is collected or absorbed and converted into heat. The After some further experiment I decided to bind the glass majority of the sound energy, however, walls of the does work on the glass valve with Empire tape, and, giving four layers, wall, causing it to turn about a fulcrum situated in the spring leaving the top exposed, I fastened the tape with a rubber band. holder, This this work overcoming the inertia of the valve and oper- completely cured the trouble. I may add I can now bring ating against the restoring force of the spring and the air the loud -speaker within a few inches of the valve without any resistance. A valve howl in a spring holder is not highly damped whatever. RICHARD C. LE MARE. unless it is of considerable mass. This Stockport, March could only be obtained 19th, 1927. by using a very light spring, insufficient to support the valve, or, alternatively, loading the valve with a heavy mass. Since this is not the case the sound waves cause the valve in the Sir,-In connection with Mr. Tyer's article on " Microphonic holder to remain in a state of oscillation, because the damping Noises " in your March 9th issue, and the reply thereto in your is not sufficiently high, and accordingly the electrodes also issue of March 16th by " Howler," my own experience may be remain in a state of oscillation. However, interest. by mounting the of valve on a block of sponge rubber, the mechanical damping is It is often possible to raise the pitch of a microphonic noise sufficiently high to prevent the valve as a whole from due remaining to an L.F. amplifying valve by lowering the filament tem- in a state of oscillation. " Howler's " suggestion of using a perature, and rice versa. The noise in this case is clearly due lined wooden box over the valve would certainly tend to prevent to a vibration of the filament with a frequency depending on its a large proportion of the sound waves doing tension, any work on the and this may be controlled at will by varying the ther- valve, but if this can be more easily accomplished simply by mal expansion. In fact, in many cases a valve will stand suffi- mounting the valve on a block of rubber I do not see that any cient L.T. voltage to run the filament quite slack, and all advantage is gained. Moreover, the suggested method still does B 50

www.americanradiohistory.com " APRIL 6th, 1927. 435 not protect the filament from any shock excitation which might possibly hear a spot of music above the speech -and, further, be transmitted through the base of the valve and through a there seems no point in a silent period, for, with a modern bench on which the set may be placed. " Howler " can easily properly designed receiver employing four valves, it should prove my statements experimentally by arranging, perhaps, a be perfectly easy to separate such stations, to mention a few, four -valve amplifier in spring holders. If the first valve is given as Stuttgart, Toulouse, Hamburg, Frankfurt, and Brussels. an impact, the amplifier (if it is amplifying properly) will give The trouble at present seems to be that the average receiver, a tremendous noise in the telephones. If, now, he damps the at least in this neighbourhood, is quite incapable of receiving vibrations of the first valve simply by holding the top in two anything but the local station without oscillating, and should fingers, or, alternatively, tying it against a small rigid support, we have another advertised silent period it is perfectly certain with a small block of rubber, rag, or cotton -wool, and then if from what happens every Sunday evening all sets really cap- the valve is once more given an impact he will. find that able of receiving distant stations would be switched off, the practically no noise will be heard at all. This experiment, owners knowing full well that the correct name for such a of course, should be carried out in such a manner that the period would be " The Oscillator's Paradise." first valve and its associated equipment is mechanically isolated South Croydon. GEORGE H. TOZER. from the other valves in order that the other valves are not March 23rd, 1927. affected by the impact given to the first valve. Watford. PAUL D. TYERS. March 22nd, 1927. Sir, -Having read the letter on the subject of the silent period by Mr. Caddick in your issue for March 23rd, I wish. to express my views as a wireless fan who has spent con- money on expensive sets. GAS DISCHARGE RELAYS. siderable time and May I say first that I certainly do not approve of a silent Sir, -On page 262 of your issue for March 2nd there appears period until such time as one can be assured that the air a description of a three -electrode neon tube relay attributed is not rent with squeals and howls, as it is during the silent to Messrs. Richter and Geffcken, of Leipzig. I have already period on Sunday evenings. My experience is that distant constructed and experimented with this arrangement, which I stations are only worth listening to when the local is on the patented" in France on September 30th, 1926 (patent No. air. At such a time those people with out -of -date valve sets 225,835). know perfectly well they cannot cut out the local, and there- The substance of the claims of my patent are :- fore do not try. It is at this moment that the man with the (1) Valve having unilateral conductivity employing neon deeper pocket, if he is up -to -date and has spent his money gas at low pressure, two or more cold electrodes being well, can cut out the local and get the distant stations with located in the valve between which an electrical discharge some degree of comfort. takes place, but having one or more electrode, the purpose For my own part (I am situated within about two miles of of which is to control this discharge. 2L0) I do all my long distance listening whilst the local is on, (2) In one method of constructing this valve the cold as I find it impossible to listen in during the silent period on electrodes take the form of plates and points, or one electrode Sunday evenings. with multiple points erected towards the plates with one I can only suggest that Mr. Caddick should make his set or more control electrode placed between the discharge more selective (not a difficult matter), or, if his set is fairly electrodes in the form of a grid, spiral, perforated selective, to be content with a moderate number of foreigners plate, etc. instead of wanting every station in existence. One of these types, which was constructed for me by the If we had a silent period I guess under present conditions L.S.I., functions with a 250 volts and a discharge current of it would be impossible to listen. B. GLADSTONE. 0.02 amperes, and with this low- frequency amplification has London, W.14, been obtained. March 23rd, 1927. My work in this direction is not complete, and on this account I have not yet communicated the results obtained to any scientific society. Sir, -I have read with considerable interest your Editorial I should appreciate it if you would publish this information concerning the above subject in the March 23rd issue of The in order to draw attention to the probable priority of my Wireless 1Vorld. work over that of Messrs. Richter and Geffcken. Your point was very plainly demonstrated in this district Juvisy -s -Orge, France. M. JOSEPH ROUSSEL. last Sunday evening. It so happened that the Cardiff station March 3rd, 1927. was broadcasting a religious service in Welsh at a time when other B.B.C. stations were silent. A few of us in Carnarvon in possession of selective multi -valve sets are able to receive THE SILENT PERIOD. the Cardiff broadcasts with comparativé ease at almost any interest time. The majority, however, are only able to receive Cardiff Sir, -I have read with your Editorial and the many most conditions. from correspondents on the matter of a silent period under the favourable letters Last Sunday evening Cardiff carne in at good strength, but which it is proposed to institute for the express purpose of who were valve sets to receive owing to the ear- splitting howls caused by people allowing owners of programmes from nothing of the Cardiff transmission, I for foreign countries. As an amateur who has been interested in obviously hearing one was obliged to switch off my receiver, as it was painful long- distance reception for some years, I should like to give in the neighbourhood oscillating you my experience. to listen to a score of sets we now have a silent furiously. First and foremost period from about have of others who experienced the same annoyance, p.m. to 8 p.m. every and of I heard 5.45 Sunday, without fear con- is safe to say that the nett result was that no I say that during that period it is absolutely im- and I think it tradiction one in the town itself received the transmissions satisfactorily. possible to receive distant stations as the air is rent with E. LYON RICHARDS. of " squeal Carnarvon, every conceivable variety cat call " and " " from March 24th, 1927. listeners trying to receive distant stations; this state of affairs commences the moment London switches off and continues until it starts transmitting again. From this experience I am forced to the conclusion that the only use for a silent ALUMINIUM PANELS. period would be -in fact, is -to demonstrate the amount of Sir, -We notice on page 331 of your journal of March 16th interference which can be caused by oscillating receivers. that hints are given by your correspondent, " C. H. R.," for Under present conditions it is only possible to receive distant frosting aluminium. Your readers may not be aware that stations when London is transmitting, and then programmes, frosting is a standard finish with which the metal is obtain preferably orchestral or military band, so that the " wipe out " able through the usual channels. H. COUSINS, is effectual, for the squealers will attempt their distant recep- London, E.C.4, For the British Aluminium Co., Ltd. tion when speech is being transmitted -as then they can March 23rd, 1927. B 5t

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7fiF'e@aT 436 APRIL 1927. Wom1Il4 6th,

" The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply.

H.F. Transformers. windings should be wound over the end Constructing a Moving -coil I ant modifying the H.P. side of my of the secondary connected to the fila- Loud -speaker. receiver to coirespond with that of ment-. The object of this is to reduce Can you tell set, the me where I can obtain the the "Eve.ryman four" and current which passes from the primary iron .stampings in a recent the transformer to to the secondary described find on windin through the capacity of article on moving-cod loud -speakers terminate the .section at a the windings. As is well known by any- by G. 117. Sutton? it means that must one who has conrcnient point I tried the wrong method of A. A. have either 14¡ or 15¡ turns. 16'ill connection, the effect is to weaken signals S: the that use the exact considerably and to broaden These stampings are, we believe, of a fact I cannot the tuning. standard winding as specified adversely affect 0 0 0 0 pattern, and obtainable from \lessrs. Joseph Sankey & Sons, Ltd., results.' Furthermore, I find that H.T. from D.C. Mains. ,t will be necessary to crass the 168, Regent Street, London, W.1. primary and neutralising windings, I lri..h to construct an H.T. battery 0000 reduce the number of turns eliminator for use on my 240 -roil unless I D.C. inairis, and believe Low Loss or High Efficiency. on the former. I should appreciate that an instrument be I ans intending your on this. likely to suitable for my to build a short -ware comments purpose was receiver for reception. of T. C. B. described in February/ wavelengths last year. Please inform me as to the round about 60 metres, but as I have Although the designer's specification exact date of the issue, and if it is by ins a large number of components should be followed closely, the fact that .still available from your publishing such as variable condensers of a very you are using half a turn or so more office. A. C. S. good type, -I wish to know whether I or less will not affect results appreciably, The can use these, or is it essential that I and as long as wires are air- spaced eliminator to which you refer was the described in our purchase low -loss components? where no ill will issue of February 24th, they cross effects be 1926, which is, D. T. S. produced. You are wise, however, to however, now out of print. We reproduce herewith the circuit As has been frequently pointed out in pay special attention to this point, as diagram of the most cases of difficulty with these trans- arrangement in question, this journal, the term " low- loss " is only formers have been traced to incorrect or a synonym for " high- efficiency,' and is partially short -circuited windings. not, as many people would suppose from 000o. a perusal of many catalogues, a synonym for skeleton inductances, condensers, etc. Connecting an " Everyman Four " It is obvious that whether constructing a Coil. wireless receiver or indeed any other piece The selectivity of my " Everyman Four " of apparatus, we shall get better results receiver is not quite so good as I if we employ components of high efficiency have been led to expect, and the tun - than if we use components of low effi- ing range of the secondary circuit is ciency. Because your variable condensers very difftrent from that of the aerial are possibly of conventional appearance circuit. Would you suggest a likely and are not of weird and wonderful trouble? E. C. L. design, it does not necessarily say that ' Lack of selectivity and peculiar tuning they are of low efficiency, and we think is invariably due to the method of con- that in all probability you would obtain necting- the secondary - Fig. 1. -A straightforward eliminator excellent results with them. In any of the high for P.C. mains. frequency transformer. The end of the case, why not put a short -wave receiver secondary winding of the high- frequency from which you will see that lamps are together roughly on a board with the com- transformer over which is wound the used as potential dividers. The chokes ponents you have on hand, and you can primary and balancing windings should may have an inductance of from 30 to 50 soon see whether or no they are suitable. be connected to the filament side of the henries each, while the condensers should If you do not obtain great success on the circuit, while the free end of the second- have capacities of from 2 to 5 mfds., It first trial, do not, however, jump to the ary -that is, the end farthest from that may be added that another, and possibly conclusion that your components are at which carries the two primary windings-- in some cases a superior, arrangement was fault, because the element of skill enters should he connected to the grid. This discussed in the " Hints and Tips " sec- very largely into the successful operation is the correct method of connecting prac- tion of our issue for February 16th, of a wireless receiver, more especially on tically any B.F. transformer; the primary 1927. the short wavelengths. B 52

www.americanradiohistory.com a c. ' .. - .. y f.: .'_. '..

WApigsgo APRIL Oa, 2927. Walt( 437 The First Superheterodyne. successfully receive the ordinary broad- cause, obviously, the L.F. amplifier is casting I understand that the first constructional stations of either this country or perfectly conventional. article dealing with a superhetero- the European continent. We do not mean Referring to Fig. 2, the coils L and dyne receiver was published in this that you could not receive these at any L2 really consist of one continuous wind- country by The Wireless World time, but on very few nights would recep- ing of 75 turns of No. 22 D.C.C. or any tion some tine in 1925, and I shall be likely to be free from interference other approximate gauge of wire wound glad if you can give me the date of due to atmospherics, mush, etc. We on a cylindrical former 3in. in diameter. the issue in which this article assume, therefore, that you are desiring The earth connection is joined in at 60 appeared. P. H. G. to receive long -wave stations mainly, and turns from the grid end, whilst a few in this case the long aerial which you pro- tappings are made at the grid end of The first complete constructional article pose to erect would be of advantage. Of the coil to give a coarse adjustment of dealing with a superheterodyne receiver course, on the shorter wavelengths it the inductance of the grid circuit. The was published in The Wireless World would be a great disadvantage from many last fifteen turns of the combined coil, not in 1925, as you suppose (although cer- points of view, as for one thing it would that is L_, are similarly tapped in order to tainly a seven -valve superheterodyne was greatly mar selectivity. give a variationv of aerial coupling. A described in the issues of March 4th and space of about tin. is left on the former, 11th of that year), but in the issues of 0000 and then the reaction winding is wound November 14th, 21st and 28th, 1923, on in Reinartz Wronged. the same direction. 'This winding although circuit diagrams óf superhetero- may, of course, be of much smaller gauge . dyne receivers had been published in this I have noticed that there seem to be a than the other windings if so desired. journal a good time previous to that date. large number of circuits bearing the The actual number of turns, of course, The receiver was invented in 1917 and was name of " Reinartz " which differ cannot be stated precisely, as it depends in quite common use among amateurs in very greatly from one another. Can on various factors, such as the damping this country very early in the present yaw, therefore, give me the true present in the grid circuit, which may be decade, although it did not become really Reinartz circuit. P. L. S, small or otherwise according to whether popular until the summer of 1925, partly we have used good components and owing to the lack of ready -made compo- It is quite true, as you say, that there whether or no there are leakages due to nents on the market until that period, and are a large number of circuits which are a valve holder, a former, or other com- to the absence of reliable constructional wrongly given the name of Reinartz cir- ponent made of inferior material; usually data and values suitable for British valves. cuit, and it appears to have become an 15 to 18 turns are ample. The H.F. choke obsession with certain people to give this may consist of any of the commercial name t3 0000 any circuit in which reaction is chokes upon the market, or a simple home- Modernising a Receiver. + Could you tell me how best to bring up o to date the receiver of which the H.T circuit diagram is shown on the at- + tached sheet? T. W. T. As your circuit comprises the now obsolete arrangement of a direct- coupled aerial with tuned anode H.F. amplification, we is a are afraid it difficult matter to sug- 1 mfd gest how it may be remodelled without 0.0003 mfd considerable alteration. In all probability -H the best method of effecting a real im- HT? provement is to rebuild the H.F. and de- f tector circuit to approximate closely to the arrangement of the " Everyman E Three " receiver described in our issue o of November 3rd and 17th. ó 0000 An Unknown Locality. I am building a six -valve wireless receiver, and wish to ask your advice concerning the question of erecting an 0.0003 rn fd aerial. 1 have ample space at my disposal, and find that I can erect an aerial of over 200ít. in length. L3 Should I obtain much greater effi- o ciency than by the use of a standard p 100ít. aerial? Not being on British territory I am not restricted to the - standard length of aerial. . Fig. 2. -The original Reinariz circuit with one stage of L.F. amplification. L. Q. K. controlled by means of an ordinary vari- made choke. The remainder of the cir- You omit to state in your letter whether able condenser. We give in Fig. 2 a cuit is perfectly conventional. you expect to receive the stations of the diagram of the original Reinartz This original circuit is open to much British Broadcasting Corporation, long - circuit with the addition of an ordinary criticism, such as, for instance, the losses wave telephony stations, or the very many stage of L.F. amplification for the pur- introduced by the switching arrangement long -wave C.W. morse stations which are pose of loud- speaker operation. It must at the high potential end of' the grid coil,` in existence. Moreover, it is somewhat be remembered, of course, that strictly and has been improved and modified from difficult for us to deduce this point defi- speaking the Reinartz is a single -valve time to time by the original author, nitely from your letter, since you omit circuit, and it is not really correct to whilst at the same time other experi- to put your address, but judging from speak of a three -valve Reinartz circuit menters have made certain alterations the postage stamp on your envelope we when we mean a Reinartz circuit followed and have even in many cases changed the should say that you are too far away to by two stages of L.F. amplification, be- name 'of the circuit. B 53

www.americanradiohistory.com MpegaT 438 W0rfli APRIL 6/ /l, rg27. An " Everyman " Alteration. A Tuning Problem. A Schnell Snag. i ant building an "Everyman Pour" I have a two -valve set consisting of a de- 7 am constructing the Schnell circuit, receiver, but wish to know if 1 can tector followed by a choke- coupled which has been published from tinte use two 0.0005 mid. variable con- amplifier. I find that When con- to time in your journal, and wish to densers which I have by me, in place vected up in the usual manner to a know if I may follow the detector of the 0.0003 mid. 'specified. standard aerial and to a water pipe valve with a stage of resistance - D. V. R. earth, signals are very faint 'in the coupling, using an 80,000 -ohne valve as The first effect- of using .0005 mfd. loud-speaker, whilst if I connect the detector, and a 1- megohnt anode variable condensers would be to raise earth lead to the wiring of the electric resistance. M. F. O. both the maximum and the minimum of bell system signals come in at. great It is not possible to follow the detector the tuning range of the receiver. Pro- strength. I shall be gild if you can with this form of resistance -coupling, as vided the condensers were of modern assist me in my trouble. you desire, owing to the fact that you type, however, the minimum range would H. M. V. desire reaction effects. Indeed, this is not be greatly increased, and you could The trouble is probably due to the fact true with all regenerative detector re- still tune well down with the receiver. that your earthing system is of very high ceivers, namely, that if the ordinary It might be thought that the increase in resistance. You do not say whether or smooth control of reaction is desired, then the maximum of the tuning range would, no you make use of reaction, but we pre- a stage of resistance coupling using a be a great advantage, but it must be sume you do not, as we observe from very high value of anode resistance, can- remembered that the receiver would be your address that you are very close. to not be used. You must use either a trans- considerably less sensitive on the upper 2LO. The use of the electric 'bell system former - or a choke, or you may use -st énd of the scale. You could, however, as a rough counterpoise probably results stage of resistance- coupling employing a Use the condensers as 0.0003 mfd. instru- in a great decrease in damping. Pos- 100;000 to 150,000-ohm anode resistance ments, by utilising only the lower half of sibly, also, your aerial is of somewhat shunted by a 0.0001 mfd. fixed condenser, the scale, but it would be obvious to you high resistance, and the set might work this being used in conjunction with a that you would have a more crowded con- all right with your -existing earth system valve of about 30,000 ohms impedance, denser dial, since the same number of if your aerial were of smaller size, as and, moreover, one having the highest stations which would have to be spread possibly the aerial is exerting a great possible amplification factor for this im- over 180 degrees of scale in a 0.0003 mfd. damping effect. You could with advantage pedance, such as the D.E.5B or other condenser will be crowded in a less por- completely overhaul your aerial and earth similar valve. tion of scale. Provided, however, that system, shortening the aerial, making 0000 you use good slow motion dials, this dis- sure that all soldered joints are in order advantage will not be so great as itmight and that you are earthed on to the main Three or Four ? at first seem. 0000 water pipe. As a temporary measure, I hare 'only recently heard of your we would suggest that you reverted to " Everyman Three " and " Every- your earth system and connected a small man Four" valve receiver, and I A Superfluous Condenser ? fixed condenser in serie1.with the aerial shall be glad if you can tell me in I am building an A.G. mains, bgttery lead -in, the capacity of which may be which issues of The Wireless World eliminator, and I should be glad if 0.0002 mfd. Another cause of the trouble these were published, so that I may you would tell me whether it is neces- might be that fundamental wavelength obtain sante front you. Could you sary for me to use a fixed condenser of the aerial and earth system may differ also indicate which receiver you con- in the earth lead of ney receiver in considerably when the bell system is sider to be the best for all -round order to avoid Short- circuiting of used, compared with when the proper work solely on the normal broadcast- mains, since, of course, the mains will earth is used. Therefore the tuning ing wavelengths. T. L. A. be entirely isolated front the set by range when the proper earth is used may The " Everyman Three " receiver was the transformer, as naturally the be such that your local station does not printery and described with full constructional details secondary windings are lie within the tuning range of your coil in issues of November 3rd and 17th, not in our electrical contact. A. C. B. and condenser, and you might therefore 1926, and these two back numbers may As a measure of safety we would advo- try the effect of merely changing the still he obtained from our publishers. cate that a condenser be used in the earth value bf the aerial tuning coil. The " Everyman Four " was described in lead even although the mains are isolated our issues of July 28th, August 4th, from your receiver as you state. There September 8th and October 13th, 1926, is always a possibility of a sudden break- but some of these are now out of print ; down of the insulation between the BOOKS ON however, we have published a book en- primary and secondary of the transformer THE WIRELESS VALVE titled the " Everyman Four," giving full with possible resultant disaster. Indeed, constructional details both theoretical and we would advocate that as a measure of Issued in conjunction with "The Wireless World." practical wiring diagrams, and all other safety a large -size fixed condenser be particulars, and this book may be ob- " WIRELESS TELEPHONY," by R. D. used in the earth lead of the set irre- BANGAY. Price 2/6 net. By Post, s /9. tai.ned from our publishers at a cost of spective of whether the mains are A.C. ls. 2d., post free. " THE OSCILLATION VALVE -THE or D.C. and irrespective of whether ELEMENTARY PRINCIPLES OF ITS The " Everyman Three " and the in the case of D.C. the positive or APPLICATION TO WIRELESS TELE- " Everyman Four " both make use of one negative main is earthed. This GRAPHY," by R. D. BANGAY. Price 6t- net. stage of a similar type. In the con- By Post, 6/3 ILF. denser should be of as large a former case, however, a leaky grid recti- capacity " WIRELESS VALVE RECEIVERS stage as possible (preferably not- less AND CIRCUITS IN PRINCIPLE AND fier was used, followed by a single than 1 mfd.) in order not to upset the PRACTICE," by R. D. BANGAY and N. of transformer -coupled L.F. . amplification, tuning. An important point ïs that the AsnnalnGE, B.Sc. Price 2'6 net. By Post, 2 /ro. whilst in the latter case an anode bend condenser dielectric should be one which .n THE THERMIONIC VALVE AND ITS rectifier was used followed by a resistance. is guaranteed to withstand a voltage DEVELOPMENT IN RADIO TELE- coupled stage and then a transformer greatly exceeding the mains GRAPHY AND TELEPHONY," by Dr. stage of L.F. amplification. For gc:.eral voltage, J. A. FLEMING. Price r5 /- net. By Post, 15/9. since obviously it would be of little use loud- speaker work probably the " Every- " CONTINUOUS WAVE WIRELESS instru- employing a 1 or 2 mfd. condenser whose TELEGRAPHY," Part r, by W. H. ECCLES, man Four " is the most suitable dielectric would break down immediately D.Sc. Price 25/- net. By Post, 25/9. ment, the other being more for the ntan the mains voltage was thrown across as who desires to search for very distant it with order) from a result of a breakdown of the insulation Obtainable by fias! (remittance stations on the telephones, although, of between the ILIFFE & SONS LIMITED course, it will operate a loud- speaker at primary and secondaryof Dorset House, Tudor St., London, E.C.4 power it great strength from it large number of your transformer, as would then Bookstalls be no safeguard at all. or of Booksellers and the less distant stations. B 54

www.americanradiohistory.com í AN D RADIO REVIEW (J5th Year of Pubhcation) » I

No. 398. WEDNESDAY, APRIL 13TH, 1927. VOL. XX. No. 15.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

Editorial Offices : 139-40, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone : City 4011 (3 lines). Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4.

Telephone : City 2847 (x3 tines). Telegrams : " Ethaworld, Fleet, London." COVENTRY: Hertford Street. BIRMINGHAM Guildhall Buildings, Navigation Street. MANCHESTER: 199, Deansgate. Trle rang e "Cyclist Coventry." Telegmer, : " Antopress, Birmingham." Tetepranu '1110e, Me.nchester." Telephone: 5210 Coventry. l'elephores: 2970 and 2971 Midland. Tetepmne: 8979 and 8971 City. Subscription Rates: Home, 175. 4d.; Canada, 17s. 4d.; other countries abroad, los. 6d. per annum. :Ls many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy themselves that they would not be infringing patents.

ANOTHER CRITIC OF BROADCASTING. places these instruments beyond the reach of a very large proportion of the population. H E latest addition to the ranks of the critics " But, sooner or later," says Mr. Wells, " boredom of broadcasting is Mr. H. G. Wells, who, and disappointment with these poor torrents of insignifi- in a recent edition of one of the Sunday cant sounds must ensue. Are there, indeed, any inde- papers, occupied the greater part of a page fatigable listeners who have stuck to this amusement since to tell us why broad- the beginning? If so, I think they casting is a farce and 4+S I I..I+ are probably very sedentary per- why its decline and CONT ENTS. sons, living in badly lit houses or eventual fading out is inevitable. PAGE otherwise unable to read, who have At the ronclusion of the article the EDITORIR.L VIEWS .. 439 never realised the possibilities of Editor promises that " another COIL-DRIVEN DIAPHRAGBI LOUD- the gramophone and the pianola,

vigorous article by H. G. Wells SPEAKER DESIGN (concluded) ... 440 T and who have no capacity nor op- will appear on Sunday week." By N. W. McLachlan. portunity for thought or conver- When we had reached that edi- PRACTICAL HINTS AND 'rips ...... 447 sation." torial appendix after having labori- CRYSTAL- CONTROLLED TRANSMITTER 449 lj A Phantom Army of ously read through Mr. Wells's By R. W. H. Bloxam. Listeners. entire article, we could not help wondering whether the Editor had ACC CMLTLATOR SULPHURIC ACID ... 451 Mr. Wells makes it quite clear not been a little careless in his INVENTIONS OF WIRELESS INTEREST 453 that he himself has no use for choice of an adjective, for we can- READERS' NOVELTIES ... 455 present -day broadcasting, but it is not remember having read any- CURRENT- TOPICS ... 456 surprising that he, whom we are thing by Mr. \\Tells previously OSCILLATPNG CRYSTALS 458 accustomed to regard as having an Avhere the use of this adjective extraordinarily NEWS FROM THE CLUBS 459 complete know- would not have been more appro- ledge of human nature, should BROADCAST RECEIVER -- l r: RAMC priate than in describing his article now be " at a loss to imagine any on broadcasting. We had hoped NEUTROSONIC SEVEN 461 sort of person becoming addicted BROADCAST BREVITIES when we came to read the article 465 j to listening -in as a frequent enter - that at least we should have been NEIV APPARATUS ... 467 tainment," when, if Mr. Wells given some strong points against LETTERS TO THE EDITOR 470 would go to the trouble of look -

broadcasting sufficient to provoke 11 FADERS' PROBLEMS ... 472 ing up the facts, he would find a desire on our part to argue, but that the number of listeners is perhaps the strongest case which steadily increasing, and the :\[r. Wells makes out is that music in the home can be copies of the wireless programmes sold weekly and obtained equally as well from a gramophone or pianola the correspondence received at the R.B.C. headquarters as from broadcasting, and that in the former case you can are alone a guarantee that the future of broad - make your own selection of the music you wish to hear. casting will not present the amusing picture which In our opinion, it is so difficult to compare these two he draws of the service continuing to operate foi that the point is scarcely worth discussing, even if we the entertainment of a phantom army of listeners, omit the consideration of cost, which in the case of the " the last living listeners having dispersed and gone to pianola and gramophone, with the addition of records, other things." B 5

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WA P@ÌlMO ¢0 Warild. APRIL r 3th, 7927. C DkilitIrragnm LOUD-SPEAKER DESIGN. Constructional Details of Diaphragm, Moving Coil and Electro= magnet. (Continued from page 377 of the issue of March 30th, 1927.) By N. W. McLACHLAN, D.Sc., M.I.E.E., F.lnst.P. WE have dealt, in the previous article, with the strength in the air gap of about S.000 to 9,000 lines per theoretical side of the subject in a somewhat square centimetre. For working from a D.C. supply extensive, though by no means exhaustive, circuit the magnetising coil is wound in manner, one section of because it is imperative that the experimenter 19,000 turns or in two sections, each of 9,500 turns of should know exactly the foundations upon which the No. 34 D.S.C. The resistance of each section is just over design is evolved. When unexpected results are obtained S5o ohms. For a too -volt supply the coils are connected he will have more chance of arriving at the reason, and in parallel', whereas for a zoo -volt supply they are con- greater possibility of rectifying defects. nected in series. The circuit diagram is shown in Fig. rr. The Electro- magnet. Owing to the large inductance of the coil (bordering on 90 henries), it is imperative to connect a buffer resistance So far as actual construction is concerned, it is pro- across it to prevent undue sparking at the switch and posed to describe a coil -driven loud -speaker in detail, voltage rise on the winding when the current is switched but there are minor points of construction which can be off. The value of this resistance is 4,000 to 6,000 ohms, left to the conception of the reader. Dealing with the and it must he capable of withstanding the mains across electro- magnet, this is shown dimensionally in Fig. to. it without undue heating. In addition there may be a The winding depends upon the voltage to be used, but series resistance for regulating the current in the winding is designed to dissipate about 25 watts. This gives a field of the electro- magnet. For continuous work some of this resistance may be required to reduce the heating of the pot, more particularly for a 240 -volt supply, where the loss will exceed 25 watts. T However, this is really a matter for experiment. It w may be useful to paint the outside of the pot with a dull. black paint, thereby giving a high coefficient of emissivity to promote cooling. The coils should be carefully insulated. Impregna- tion and baking with suitable varnish, e.g., Bakelite, 5 is recommended, the whole coil being well taped with silk. This is very important to avoid any chance of breakdown to the metal clue to voltage rises. The ends of the winding must be brought out at the middle of the coil, and not at the inside or outside, so that there is no chance of the insulation being rubbed off when the coil is put in the pot. To get the coil comfortably into the pot, the latter should be rubbed carefully inside with Pig 10.-Leading dimensions of electro-magnet. The winding for 200 to 240 volts may consist A single coil of larger wire of one system as shown or two sections if desired, as indicated In the text. There should be a thin ring of insulating material at the bottom of the pot and the lower lead should be well to dissipate 25 watts can be insulated. used for 100 volts. 6

www.americanradiohistory.com WtEP@Ilsto. APRIL 13th, 1927. 441 WoOptCo'l Coil- driven Diaphragm Loud -speaker Design. - where low tones abound, the shrillness of the upper paraffin wax. Where the leads come up inside the coil register is counterbalanced. near the central pole and at the bottom they should be Attention should be paid to the insulation of the inner well protected with cistoflex. A slight space should be surface of the coil to avoid the wire touching the central left above the.winding to allow the leads to be brought pole and short -circuiting the mains as described previously. out readily. Various precautions can be taken. In Fig. 12, if a short - Moving Coil. circuit occurs, the lamp lights, and this is possibly better than using a fuse. This point, however, can be settled So far as this item is concerned, the reader must by the constructor himself. A partial short- circuit determine for himself whether he uses a high- Or a low - occurred on my own set, due to the field winding earthing ,resistance unit. I should advise him to try both, making quite sure that the diaphragms for each coil are as alike as possible. A high- resistance coil zin. in diameter can he wound with 800 to 1,200 turns of No. 46 enamelled wire. It must be varnished and baked to get good insulation between turns and to secure the necessary mechanical rigidity. A wire of smaller diameter will give a lighter coil, but is more

t : g. 1 1.-Connections of difficult to wind and niore magnet winding showing butler or quencning resis- liable to burn out. This, tance to absorb back E.M.F. however, can be left to the of magnet winding. reader's discretion. He ought to remember that more turns mean reduced upper and lower tones, but a greater output. The greater the diameter of the wire, the greater the mass, but the lower the resistance and the better the mechanical rigidity. With the above coil the internal A.C. resistance of the power valves can vary from 4,000 ohms to 1,000 ohms. The quality, of course, changes, but the alteration is not serious. The output increases as the valve resistance decreases, due to the augmented alternating current in the coil. For example, with a r,000 -turn coil the D.C. resistance is about goo ohms, and with a valve having p =4,000 9 ohms the output would be proportional to 4,90 Putting another valve of the same class in parallel would I '' make the output proportional to I ) Thus the (\ 2,90o ' z -gz ratio of the outputs would be -900) This is \5 76 ('2,900 I readily detected by ear, especially when the intensity is appreciable. With this coil, a valve impedance of 1,300 ohms and a set operated from zoo -volt mains, the low tones of the grand organ are sufficiently powerful to make objects in a room of average size vibrate appre- \ ciably, whilst an orchestra is more pleasant in the next \ FLAT SEATING FOR room. In other words, the intensity is considerable, hut COIL ABOUT .8 WIDE

Fig. 13.- Dimensions and constructional details of diaphragm. The cuts in the rim are spaced } in apart. to the pot. When the coil touched the pot it made a inHlN;i FEED TO valiant effort to drive the diaphragm across the room. VALVE A low- resistance coil can be wound with 4o to 5o turns T of No. 32 or 34 D.S.C., the construction being identical o o with that of the high- resistance moving coil. The transformer can be a Marconiphone Ideal core with 3,600 turns on the primary and 36o turns on the secondary. The Fig. 12.-Safety lamp connected in H.T. feed to reduce damage through a short- circuit between moving coil and electro -magnet. primary is wound in three sections, and the secondary in B7

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Wil.p@IlWO APRIL 13171, r927. WaOPi 1101 Coil- driven Diaphragm Loud-speaker Design. - forceful at frequencies lower than loo. At 5o cycles two or four. The latter is preferable to reduce leakage. the by- passing action of L is roughly double that at The terminals should be such as to allow a ratio of Io0 cycles. 3,60o 3,600 but the whole of the secondary should 360 or 180 The Diaphragm. always he used, i.e., for 1So turns the two halves are The shape chosen for the diaphragm is a right circular connected in parallel.- The Windings should have the cone. Its central angle is probably more a matter of lowest possible resistance. No spacing pieces are needed experiment than calculation. The projected diameter is to separate the coils. The wire for the primary is No. a question depending upon the conditions of operation

38 enamelled or No. 4o D.S.C., the latter being pre- and the personal taste of the experimenter. From the. - ferable, unless the No. 38 is well varnished and baked. fat disc theory we saw that the larger the disc the weaker The coils should be wound closely, or they may not fit the high tones, and after a certain point the low tones on the core. It is advisable to make a check calculation decreased, owing to the " accession to inertia effect." to make sure that, according to the winding method em- Then on top of all this we must consider the low- ployed, the live or seven sections will fit on the core. As f requency motional and high- frequency inductive react- a first approximation the primary of an 6 Ideal has about the correct number of

2 0, 000 turns, viz., 3.30o. This wind- 6 - ing, with a secondary of 17o and 340 turns of No. 22 D.S.C., will make quite a good first attempt. The inductances of the windings can be calculated approximately for small alternating currents as used with an \.I bridge at Soo cycles, from the knowledge that r,000 turns are equivalent to r henry. Thus 3,300 turns - r 1 henries. The inductance depends, of course, on the value of the alternating current, and increases therewith up to a point.' At low frequencies, where the magnetising current of the transformer is greatest, the inductance will exceed r r henries. The permeability of the iron for this value of inductance is 26o. The permeability steadily increases with the magnetising current, and the latter will depend upon the frequency and the signal strength. Thus we have a further distortion from the transformer, which Rear view of loud -speaker movement.* showing ought to have been cited previously. If clamp for electro-magnet. we assume that the magnetising current of the transformer is to per cent. of the total current at too cycles when antes of the coil. Also there are cone resonances, which that total is to milliamperes, the R.M.S. magnetising may spoil all our schemes unless care is taken to reduce force is approximately 0.23 C.G.S. unit. From curves them to a minimum. Taking various factors into account for Stalloy we find that the permeability exceeds r,000, and including balance of the musical scale, spatial dis- so that the inductance will exceed .}o henries, which is tribution, and efficiency, I have found the diaphragm of quite a large value. Fig. 1,3 to give satisfactory results. But I think the experi- So long as the inductance with small currents is fairly menter should discover for himself the result of increasing large, the increase in inductance does not alter the quality or decreasing the diameter of the diaphragm. A 6in. dia- to the extent indicated by this calculation. For the best phragm is somewhat lacking in bass, and usually makes results, the intensity should not be too weak, or the the letter " s " whistle, but, apart from focussing, a rein. magnetising current will be an appreciable fraction of diaphragm should give fair results, provided always that the whole. In this way the coil would be robbed of the real result is not masked by strong resonances. This current by the transformer, or.. in other words, the value diaphragm will have a noticeable focussing at high fre- of L, in Fig. 8 (b)4 would be small enough t0 by -pass quencies, hut the low- frequency register should be good. coil current. Obviously this argument becomes more The paper portion is cut to the dimensions given in Fig. 13. No reinforcing cone is used at the apex, but 2 A 3,600 : 240 (15 : 1) ratio can be used if desired. a is has See " Intervalve Transformer (ores," 7'he Wireless World. circle drawn which a projected diameter on the .July 14th, 1926, p 45. diaphragm equal to that of the coil. The apex is pushed The Wireless World, March 30th, 1927. inwards, starting at the point and gradually advancing e 8

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.4PRIL i3th, 1927. WfipsIlwo 443

Coil -driven Diaphragm Loud -speaker Design. - diaphragm over and rum round the inside with the tube with care until the diameter at the base is that of the to make a flat seating for the coil. Now invert it to coil,. i.e., to the circle line. check whether the flat seating lies in a horizontal plane. A piece of cardboard i4in. square is cut with a central Place the paper flange of the coil on the seating and see hole about rtin. diameter and smeared with Seccotine. that the axis of the coil is vertical and that it sits pro- A piece of sheet rubber (5 to 8 mils. thick; a rubber perly. apron will probably serve the purpose) is stretched Before proceeding further a decision must be made -just taut-over the sheet and pasted down with a roller regarding the leading -in wires to the coil. Various faced with rubber as for photographic work, or a rolling courses are open, but it is always essential to avoid pin. This is allowed to dry. The serrated edge of the resonance due to leading -in wires. The wires will diaphragm is painted with seccotine, and the diaphragm vibrate audibly if care is not taken. One method is to then put centrally on the rubber. The various paper stick them to the diaphragm and bring them to terminals flaps round the edge are pressed down on to the rubber, on the wooden frame. Another- is to take them part -way and a light weight put on the top of the diaphragm until along the diaphragm and bring then) up to terminals the adhesive is dry. A better but more tedious way is mounted on the cradle for the pot. In any case, the to apply a little french chalk to the rubber and place free portions should be flexible, short, and of greater the diaphragm centrally on it before applying the ad- diameter than the wire of the coil (see Fig. 16). hesive. This, under the action of a pressure by hand Having settled the mode of leading -in, the coil flange on the vertex, allows the periphery of the diaphragm to is smeared with seccotine and pressed on to the diaphragm slide over the rubber and take a more circular shape. seating. Then a number of strips of silk (say eight) Having got a good seating on the rubber, four flaps go° are used for additional strength to connect the flange to apart are lifted and painted with Seccotine, using a small the cone (see Fig. 14). This mode is, of course, not brush, each flap being pressed down. Meanwhile, pres- unique, and other methods will occur to the experimenter. sure is maintained at the top of the diaphragm, and The pip or re- entrant cone has not been decapitated to avoid circulation pressure. A centering device can be used, in which case the pip is removed. Care must he taken to avoid appreciable constraint due to this device, or the amplitude may be curbed at low frequencies. On the other hand, there is the possibility of introducing sufficient elasticity to cause resonance. With a wide air gap the centering device -for an experimental model -is unnecessary. Sometimes centering can be done with three threads at 12o° on the flange of the coil, but care must LEADS THIN CARDBOARD be avoid resonating. Elastic might serve 5 " taken to these RING 32 WIDE the purpose. The mounting of the diaphragm and pot are shown clearly in one of the photographs. The back of the cone should be as free as possible of obstructions to allow the sound to he freely radiated.

Influence of Diaphragm Mass. For efficient working it is necessary to reduce the mass of the diaphragm as much as possible. There is 8 PIECES THIN SILK TAPE a limit to the reduction in mass beyond which the acoustic is fear /2 WIDE SECCOTINED performance alters appreciably, but there little of that being approached with present -day materials of construction, using a diaphragm Bin. to loin. in diameter. 14.- Method of mounting coil on diaphragm. As against this we might enquire what happens when the mass of the diaphragm and coil are increased beyond other flaps treated similarly. A light weight is left on the values given in Table I.' Euppose we double the diaphragm whilst the adhesive dries. the mass of the disc. The total mass is now The rubber at the front is now cut away with a sharp 20 + 5 + 3..5=28.5 grants. The value of the motional knife or scissors, which can be dipped in watnr to make capacity C, is . But C2 is unaltered, as we have not cutting more facile. The cardboard is then mounted in C2 a wooden frame -unless it is stiff enough to he self - changed the coil, whereas os is increased in the ratio Supporting a piece of multi -ply wood was used in 25.5 -or 1.5. This means a per cent. increase in the first instance, as in Fig. 15. The frame is put on 18.5 5o a horizontal table and the circle at the vertex adjusted Thus the low - frequency motional reactance will decrease until its plane is horizontal. This ensures that the axis considerably, thereby giving a larger current. This in- of the coil will also he horizontal. Take now a piece of crease, combined with the lesser relative importance of ebonite tube of external diameter equal to that of the coil and the wall thickness of which is 3 -32in. Turn the ' The Wireless T'orlrl, March 30th, 1927. B 9

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WfinIl@g0 444 APRIL 13111, íg27. WOO pild Coil-driven Diaphragm Loudspeaker Design. - ous shapes of baffle made out of cardboard. A size 4ft. the air inertia at low frequencies -3.5 is a much smaller to Eft. square is suggested for experimental work. A proportion of 28.5 than of 18.5 -means augmented out- wide, short, conical horn (say, aft. long), made out of put at low frequencies. But-the inevitable price we cardboard, should be tried in addition to the flat board pay -tlie radiation resistance at all frequencies is re- to investigate the problem. As a permanent fitting, a piece of multi -ply board 4ft. square and gin. thick will duced in the ratio ( I) 2 = , i.e., the output is f.5, 2.25 be found satisfactory, although to get the very low tones halved, except at low frequencies, to get an improved of the organ properly it should be larger. Perhaps we bass register. In practice it is imperative to ensure that should mention that there must be no air space through the conditions under which the above statements are which pressure waves can leak in the vicinity of the

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519. 15.- Adjustable frame for supporting edge of diaphragm formulated do not suffer violation due to pronounced diaphragm. The baffle should bed well on the diaphragm diaphragm resonances. frame, and a thin piece of felt at the rear of the baffle would accomplish this comfortably. The Baffle. We have seen that the motional capacity and the acces- The function of this accessory is to reduce interference sion to inertia are responsible for reduced low -tone out- between the two sides of the diaphragm. To avoid inter- put. Also we know that acoustic output can be enhanced ference absolutely, the two sides of the diaphragm should by reducing the solid angle into which the diaphragm be completely isolated. A box construction does this, but discharges. Thus we should expect a baffle shaped after generally introduces additional effects and should be the form of a short, wide, double hollow pyramid of avoided if possible. To prevent a loss in output, square section would assist the lower frequencies. This is especially below the middle of the pianoforte, a baffle easily made for experimental purposes with cardboard. is necessary to reduce the solid angle into which the Comparative tests can be made with a flat baffle, but these diaphragm discharges. It is an easy matter to try vari- tests should be conducted when there are low tones to

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www.americanradiohistory.com APRIL r,,th. 1n27. WIp@Il®go 445 Worlld! Coil- driven Diaphragm Loud -speaker Design. - in air consists of three components, namely, (a) that re- reproduce, e.g., full orchestra, grand organ, military quired to overcome the mass inertia of the diaphragm, band with bass drum. (b) that required to overcome the " accession to inertia Amplifiers. of the diaphragm in virtue of the air moved, (c) that required to overcome the pressure due to the generation It is not intended to discuss the question of amplifiers of sound. or amplifier design. Obviously the amplifier character- (2) Both (b) and (c) vary istic be should uniform from 5o to 7,000 cycles or more with the frequency and the in order to do the loud- speaker justice.' The amplifier described by Mr. Haynes in The Wireless TV NV for February 16th, 1927, suits the purpose quite well. Some experimenters may prefer to use resistance- capacity coupling for the last two valves. On this score I hold no hard- and -fast views. If a '7 transformer is used, the H.T. voltage with a D.E.5, L.S.5, or similar valve should not exceed 15o volts, to avoid saturating the core and reducing the low- frequency inductance. In the maiority of cases 120 volts will be ample. The ampere - turns per centimetre can be checked, knowing that the turns per centimetre are about 400. Thus with a feed current of 6 niA. the ampere -turns per centimetre are 6 x ro -' x 400 =2.4. The variation in value of the differential permeability at Soo cycles is indicated by the curve of Fig. 3, " Intervalve Transformer Cores. " ' The inductance will be reduced in value, however, if the iron has previously been magnetically saturated by too large a feed current through the primary. Summary. Owing to the extensive nature of the subject, it is- well to epitomise the situation in general. (r) The force required to make a diaphragm vibrate

A rise in the lower register would be beneficial to counteract the effect of motional capacity. ' The Wireless World, loc. cit.

The complete loud -speaker with 4 ft. battle B of multi -ply wood. C, cradle for holding magnet; D, cone diaphragm; F, felt for damping ; Fr, supporting frame for diaphragm ; M, field magnet; MC, magnet control rheostat and multi- sparking resistance; S, diaphragm suspension; T, input transformer ; W, leads from moving coil.

LEADS STUCK DOWN size of the diaphragm. (b) is greatest AND TAKEN TO TERMINAL ON FRAME at low frequencies, and increases with the size of the diaphragm. At low frequencies it is proportional to the cube of the diameter of the diaphragm. Since the mass of the diaphragm de- LEADS PASSING THROUGH the of the diameter, DIAPHRAGM TO TERMINALS pends on square ABOVE MAGNET the accession to inertia increases more rapidly than the mass of the diaphragm. For diaphragms of average size the magnitude of (c) is almost negligible in comparison with (a) and (b). (3) The distribution of acoustic radiation from a diaphragm depends upon its shape. With a flat disc (and a cone) there is a reduced output at high frequencies, owing to interference of the radiation from different parts of the diaphragm. With a cone the reduced Fig. 16.- Alternative methods of firing leads from moving coil. solid angle at the concave side and the

www.americanradiohistory.com _rT4A-'T'4«gi

i ' ' - .. - WAp®Il®20 APRIL 73/11, 7927. WOifIlC1 Coil- driven Diaphragm Loud -speaker. Design. - quencies and the inductive reactance at high frequencies. increased angle at ;he convex side mean a greater and a (8) The ail pressure on the axis of a flat disc at points lesser H.F. outpui respectively. exceeding about eight diameters distant is directly pro- (4) Apart from resonance, the larger the diaphragm, portional to the acceleration of the disc and inversely the less the high -frequency radiation. proportional to the distance from the disc. (5) When a diaphragm is driven by a moving coil the (9) The acceleration of the disc depends upon the motion of the coil in the magnetic field induces a.back current in the coil and upon the total equivalent mass E.M.F. which reduces the operating current. This of the moving parts. The latter is greatest at low fre- means that the coil has a motional impedance. For sim- quencies. whereas the current tends to fall away at both plicity this impedance can he regarded as a resistance, high and low frequencies. Thus the acceleration of the equal to the acoustic radiation resistance, in series with disc, and therefore the axial air pressure, falls off at a condenser. The impedance (owing to the condenser) both extremities of the acoustic register. increases as the frequency decreases. (ro) The air pressure at a point distant from the disc (6) The current is also reduced at high frequencies whose radius vector (see Fig. 6, March 3oth issue) makes due to the coil inductance. At a certain frequency the an angle B with the axis, is equal to that at a point on the inductance and motional capacity yield electromechanical axis, equi- distant from the disc, multiplied by a factor resonance. depending upon H and the frequency. The factor decreases (7) To prevent the current being reduced appreciably with increase in f and H. At high frequencies there are at the upper and lower extremities of the acoustic register. values of 19 where the air pressure is zero, and in general the internal valve resistance plus that of the coil should the radiation is confined to a beam whose angular width be somewhat greater than the capacity reactance at low fre- is 20, where H, decreases as the frequency increases.

" History of Radiotelegraphy and Radio- extensive additions have been made telephony." By G. G. Blake, throughout the text to keep it up to date M. I. E. E., A. Inst. P. (Radio Press, during the publication period, and the in- Ltd., London, pp. xix -425. 1926. Book RevIlewo clusion, for example, of reference to the Price 25s.) Transatlantic Telephone is evidence of Although the science of radio commu- the author's success in this direction. It nication in the sense that we know it to- action as an introduction to the history. nray be added, also, that this history is day may be said to be only thirty years and this is followed by a sketch of the a particularly welcome one in that it gives old, the first discoveries relating to this development of electrical signalling an account of radio development from the method of transmitting intelligence were systems and of the telephone, before elec- scientific aspect rather than from the made more than fifty years ago. Prior tromagnetic waves and their production necessarily biassed view -point of commer- even to this date many suggestions and and detection are discussed. Subsequent cial application. experiments had been made in connection chapters deal with various practical radio PiIII.Ir ll. Cor"RSEY. Í with electrical communications both with transmitting appliances in use to -day -- and without connecting wires between the Spark, Arc, Alternator, Valve, etc. -with two stations, and descriptions of many of details of their development from early these early experiments and apparatus ideas. The applications of radio to make curious reading in the light of direction -finding, radio control, photo- BOOKS AND modern knowledge. graphic transmission, television, broad- The invention, and more particularly casting, short -wave and "beam" trans- CATALOGUES the practical development of the ther- missions are dealt with in considerable de- mionic valve, has probably been responsi- tail, while in Chapter RV is a particularly RECEIVED. ble for a more intensive and revolutionary full account of the many applications of development of radio methods than has the thermionic valve to the numerous re- taken place at any other period of its his- ceiving and amplifying circuits in use Ward and Goldstone, Ltd., Frederick tory. As a result of the more powerful to -day. Road', Manchester. List RW /51, relating methods of research thus made available. An entire chapter is devoted to the de- to all types of wire for radio purposes. the realisation or development of several velopment of the microphone as applied to D P. Battery Co., Ltd., Bakewell, of the earlier arrangements or methods be- radiotelephone transmission as distinct Derbyshire. Brochure dealing with D.P. comes more practicable and may have from ordinary telephony ; while frequency Kathanode batteries for locomotives. valuable results. The possibility of such raisers, radio " calling -up " devices and " The Inner by developments by the bringing to light recording apparatus also find a place. Number," F. Chenhalls A story based upon again of almost forgotten and in- To produce a complete history of the Williams. wireless schemes and mental Pp. 274. ventions is one of the reasons which have growth and advance telepathy. 'Pub- of radio appliances lished by Longmans, Green and Co., led to the production of history, in from their embryonic is a of Ltd., this states task London. Price 7s. net. which accounts are given of the develop- encyclopedic magnitude, and the author 6d. ment of radio communication and of many of the work under review must have ex- "Bildfunk." Anleitung zum Selbstbau of the devices and appliances associated perienced considerable difficulty in eines Bildempfängen (Wireless Transmis- with it. To assist the experimenter and arriving at a decision as to what to in- sion of Pictures with Instruction for Con- research worker full references are include and what to omit. The selection structing a Receiver). By R. Hell. Pp. cluded in the bibliography attached to that has been made, however, provides a 114, with 80 illustrations and diagrams. the end of the volume so that fuller de- very interesting historical story, and one Published by R. C. Schmidt and Co., tails of any apparatus mentioned can be that will doubtless also be of considerable Berlin. Price Rm. 3.50. found if desired. value to all workers in this field of investi- " Rundfunktechnisches Handbuch," The work is divided into sixteen chap- gation. Part II., by Dr. Heinrich Wigge. Pp. ters with four appendices, and is pro- The book is well printed and produced, 314, with 417 illustrations and diagrams. fusely illustrated throughout. A résumé and the diagrams and illustrations are Published by M. Krayn, Berlin. Price is given of modern views of electrical very clear. There is evidence also that mk. 12. B I2

www.americanradiohistory.com WpgIl®20. APRIL 13111, 1927. MAO 147

-_ -P=CTICÄ- _ -- i ( AND

Aids to Better Theoretical Diagrams Reception. Simplified.

PREPARING LITZ WIRE. lowing this plan, the risk of omitting audible L.F. oscillation is not pro - The high- frequency resistance of a essential leads, or introducing errors, duced. coil wound with multi -stranded cable is redu'el very considerably. The resistance will naturally he of may he increased appreciably if even 0000 the grid -leak type, and, if possible, a single conductor is broken, so great various values should be tried experi- MODIFYING THE " NUCLEUS " he in the mentally. An H.F. choke of small care should taken baring RECEIVER. wire. It is recommended that, after physical dimensions and low self - unlaying the outer silk coverings, the When an extra low -frequency am- capacity may be substituted for it; ends should be laid on a piece of plifying stage is added to the this is likely to be even more effective paper, when the individual wires may Nucleus " receiver (described in on the longer wavelengths, where the he lightly scraped with a knife - The Wireless World for December difficulties of separating the L.F. and which should not be too sharp -or a 1st, 1926), trouble may occasionally H.F. components are more pro- be caused by the action of H.F. cur- nounced. piece of emery cloth. It will then 0000 to see if any of rents in the L.F. circuits. This will be an easy matter REACTION ADJUSTMENTS. the strands are broken off. probably manifest itself by the pro- best size of reaction coil in It is hardly necessary to test each duction of a " howl," which can The be found only conductor, although it is not a very generally be prevented by connecting almost any receiver can error, as difficult matter to do so; one end a resistance of from a quarter to half by the method of trial and on amount of should he bared and soldered, and a megohm in series with the grid of so much depends the in the and on then connected to a terminal of a the first L.F. valve, as shown in Fig. damping present circuit, The separate strands r. This arrangement, which has been other factors which can hardly be testing circuit. The at other end should be scraped included in several receivers described allowed for by the designer. the with and frayed out, when they may be recently in this journal, is applicable constructor who is disappointed from his set counted and the continuity of each to any circuit in which a stage of re- the results obtained make experimen- tested in turn. should accordingly 0 0 0 0 tal adjustments to the number of turns in this coil, always hearing in WIRING PROCEDURE. mind the fact that the smallest in- When wiring up a receiver, it is as ductance which allows oscillation to well to adopt a methodical and be produced over the whole tuning systematic plan. While no method range is likely to be the best. can be said to be definitely right or 0000 wrong, it will be found convenient to start with the negative 'bus -bar TESTING " EVERYMAN " COILS. (common to both L.T. and H.T.). Before connecting up the H.F. Whatever kind of conductor is used transformers used in the " Everyman for the main wiring, this lead should Four," the " Wireless World Five," be of bare wire, as a considerable and several other receivers recently number of connections will eventually described in this journal, the amateur Fig. 1. -The insertion of a resistance (R) is advised to assure himself that the be made to it. to prevent the development of H.F. po- The filament circuits of all the tentials across the first L.F. grid circuit fragile primary and neutralising valves should now be completed, after windings are intact and not short- which the aerial -earth leads and con- sistance coupling follows the detector .circuited. The connection between nections of the grid circuit associated valve. Room can almost invariably the two screws, which will ultimately with the first valve should be wired. be found for the necessary resistor, be joined to H.T. +, should be re- One should now proceed with the grid and the plan is one which should moved temporarily, as by doing so it circuit of the succeeding valve, and always be tried when the reproduction will be possible to make a more con- so on to the output stage. By fol- seems to be lacking in quality, even if clusive continuity and insulation test. B 13

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WiT@Il@go WOrIld APRIT_ 1311t, 1927. DISSECTED DIAGRAMS. The present series of diagrams is intended to show progressively, and in an easily Practical Points in Design understandable manner, the various points to which special attention should be paid in the design of typical wireless receivers, and al the sanie time to assist readers in and Construction. mastering the art of circuit diagrams. The arrangement shown below, with the addition of a suitable L.F. amplifier (lo No. 67. -A Modern H.F. Amplifier be shown in next week's issue), represents the best modern practice, and is, in essentials, that of the popular " Everyman Four" receiver. with Anode Detector.

(1) (2 The filament circuits of the valves are completed in the usual The negat've L.T. is generally connected manner. The tuned secondary of an "untuned aerial" to earth as shown, thus former is trans- tying down all the batteries to earth potential. The anode circuit connected between grid and filament of the H.F. valve, of the I1.F. salve is completed through the transformer primary a negative bias battery being interposed. and H.T. battery.

The tuned secondary of the H.F. transformer. with parallel, condenser in A neutralising winding, coupled to the primary, is connected back is connected between grid and filament of the detector to the H.F. grid a valve. An adjustable bias battery through balancing condenser. The anode circuit for rectification is inserted In of the detector is completed through telephones or an L.F coupling the low potential end of the circuit. device.

THE majority of modern H.F. made appreciably positive. may he design used in the receiver already transformers are designed to eliminated altogether. mentioned ; it has a low- resistance pork with a valve of, very roughly, The detector valve will usually be secondary, tuned by a o.0003 mfd. 20,000 ohms impedance, so one of of the high -magnilication, high - condenser, and a space -wound pri- this pattern will he chosen as an H.F. impedance type, if it is to be resist- mary of extremely line wire to keep amplifier, except where, due to the ance-coupled to the L.F. amplifier. down capacity between the windings. proximity of a powerful local trans- The aerial -grid transformer may Referring to (3), when the two cir- mitter, extreme selectivity is neces- he of the type used in the " Every- cuits are brought into tune, oscilla- sary. In such cases an efficient man Four," and several other re- tion would be produced. This is pre- " high amplification " valve, of not ceivers recently described in this vented by feeding back opposing volt- much more than 50,000 ohms, may he journal, with a low- resistance second- ages developed across the added chosen with advantage. ary and a spaced aerial winding of neutralising winding shown in (4) Grid bias is applied to this valve fine wire. To cover the normal through a balancing condenser (N.C.). both to economise in anode current broadcast waveband, for which the The prevention of interaction be- and to prevent damping. With the set under discussion is primarily de- tween the two transformers is a matter high magnification valve mentioned signed, a 0.0003 mfd. tuning con- of the greatest importance ; to over- above, this must be reduced, or, in denser is suitable. come this difficulty an earthed metal- the case of valves where such cur- The high- frequency transformer lic screen is usually interposed be- rents do not flow until the grid is may also with advantage be of the tween the two coils. B 14

www.americanradiohistory.com MpdS00, APRIL 13111, 1927. 149 WOO 1FIlA

CRYS '.s 11L-CON1 ROLLEDalI ,ED 'J1'RANSMITTJ1.11\,0 Practical Details of a 50 watt Installation Working on 45 Metres. By B. W. H. BLOXHAM (5LS). UCH has Keen t\riticu in the technical journals a crystal with a fundamental frequency equal to that of regarding the piezo- clectriç properties of quartz the final output, and the second to employ a crystal oscil- A" , crystals and the application of such crystals for lating at a harmonic of the final output frequency. t le purpose of providing resonators giving a frequency The first method is very difficult to put into operation, standard, or for the stabilisation of transmitters. although the amplification per stage is somewhat higher It is not proposed, therefore, to go over this ground, and than that obtained by the harmonic method. The difficulty the reader is referred to the issues of Experimental is to prevent self-oscillation immediately the plate circuit IPireless for March 1926, December 1926, and January of any valve is tuned to the same frequency as the grid 1927, where a very full exposition of the theory of opera- circuit. tion and practical working details of crystal oscillators and crystal- controlled transmit- Keying. ters is given by Messrs. Keying is the next _problem requiring solution, and the Goyder and Hinderlich. usual method generally involves the stoppage of oscilla- It is therefore the object tions in the final amplifier. If all the valves are supplied of the present article to with H.T. front a common supply (with the voltage suit- record a few practical de- ably reduced by resistances for the various stages) the start- tails regarding the setting ing and stopping of oscillations in the valve taking most up of crystal- controlled .current will cause very considerable fluctuations of H.T. transmitters, which are the voltage applied to the other valves. 'Phis regulation will result of much experiment immediately upset the adjustment of the intermediate ;Intl the trying out of vari- amplifying stages, if not the crystal oscillator itself, and ous schemes, ami also to de- self- oscillation sets in, the balance of the whole system scribe a set which has been .)eing affected. made to give excellent re- This can, of course, be overcome in two ways. Firstly, -41.1 sults, and is a: the same the set may be keyed at some point in the aerial circuit, -LT. time economical in the although this is not easy to arrange where large R.F. cur- amount of apparatus re- rents are present in the station portion of the antenna quired. leads. Also, unless the final amplifier is of very generous Fig. 1 .- Crystal -controlled valve oscillator with " parallel" H.T Fig. i shows the contra dimensions for the power it has to handle, trouble will be feed. lional circuit arrangement Itlun(l to occur through heat in of the anode, since when of a crystal oscillator valve ; in this case shown with " parallel " H.T. supply. When the circuit LC is tuned to the fundamental frequency of the crystal the valve will oscillate. As is \veil known, the oscillations are absolutely constant in frequency, and resist any tendency to frequency changes; so much so that, even with an unsmoothed rectified A.C. high -tension supply, a practically pure C.V. output is obtained. Since it is not possible to apply a voltage exceeding 400 to the crystal oscillator valve, on account of the danger of cracking the crystal, it becomes necessary to employ amplifying stages if the input to the aerial is to exceed 5 or 8 watts. Two alternative systems are available, the first being to employ General %iew of the 45 metre, crystal -controlled transmitter at 5LS.

13 17

iiltnt.riek www.americanradiohistory.com 150 `wffT@Ilsoo Wopc APRIL 13th, 7927, Crystal -controlled Transmitter. - reduce the amplitude of the oscillations. the If the amplifiers key is up there is no opportunity for it to dissipate the are to work atthe fundamental frequency energy generated. of the crystal, Secondly, the difficulty of the voltage it is usually sufficient toconnect a grid leak in series with regulation due to the keying of the final amplifier may he an R.F. choke across the grid -filament circuit of the oscil- overcome entirely by arranging a separate H.T. supply lator valve. Where harmonic amplification is to be em- for this valve, the crystal oscillator and any intermediate ployed, the grid leak should be replaced by a bias amplifiers being fed from one common but entirely separate battery. source. It will be found that the grid may be made very con- This is, however, an expensive system, since in the case siderably negative without cutting down the output, and of stations employing A.C. as a source of power, two at the same time the high bias tends to produce a strong separate H.T. transformers, with their attendant recti- harmonic in the output at double the frequency of the rvstal oscillation. It will be obvious that in order to secure the greatest output possible from the small available grid swing given by the crystal, it is necessary to employ a valve having a high amplification factor. At the same time it must he capable of giving. full output power with the available 400 volts maximum w H.T. o Fig. 2 shows the circuit 0 and details of the transmitter at 5LS. This arrangement gives an input power to the amplifier of 54 watts, with an input of 8 watts to the crystal oscillator valve. FILAMENT The crystal has a funda- TRANSFORMER mental of 91.6 metres and rests between two steel plates ground dead fiat, each t sin. square by ¿in. thick. The crystal is tin. square. This Fig. particular crystal requires no 2.- Circuit diagram of 50 watt crystal -controlled transmitter. R F choke[ 3 -inch windings of No 30 D.S.C. on ;in. die. formers; R.F. choke_,, 100 turns No 30 S.W.G. random wound 1din. reaction. The circuit L, C, long, tin. dia.; C, 0.00025 mfd. C2, ; 0.0001 mfd., double spacing ; C3, C4, C.5, 0.0005 mfd. ; 0.002 mfd. ; C7, C,, 0.01 is tuned to 90 metres. The mfd., C;,, 0.002 mfd. ; L,, 25 turns No. 16 S.W.G., 3in, dia, ; L2, 18 turns No. 16 spaced Un. S.W.G., spaced 5 turns per inch. ; 1,3, 10 turns No. 12 S.W.G. 4 in. dia., spaced crystal valve at present in in.; B1, 45 volts; B,, 120 volts; M.T., microphone transformer; S, battery switch; X, key provided with shorting switch for telephony. use is an American type U. X. 2 to, which is rated at fying arrangements, are ne essary, besides smoothing 7', watts and has an amplification factor of 30. A Milliard apparatus for each supply. D. F.A.6 has been found quite suitable as acrystal oscillator 1Vith harmonic operation the regulation trouble does not valve. In accordance with the remarks previously made, a make itself nearly so apparent, and it is possible to key fairly high negative bias is used, in order to strengthen the amplifier in the usual manner and to work crystal oscil- the 45 metre harmonic produced in L, C,. lator and amplifier from one H.T. source. There is also The resistance R for reducing the H.T. for the crystal very little tendency to self -oscillation of the amplifier, and valve has a value of 12,000 ohms. This resistance is of any such tendency is fairly easily overcome. the well -known " Zenite " non - inductive type. It has been The Crystal Oscillator. found that these resistances possess some slight residual inductance which falls near the frequency corresponding to Half the secret of getting proper control lies in working 45 metres, and it is quite impossible to tune the set without the crystal oscillator valve at full output. Referring to the shunt condenser. the value of which may be anything Fig. r, it will be noted that no reaction arrangement is over 0.002 mfd. shown. If reaction is necessary, it may be applied in the The amplifier valve V, is a Nullard type V.O.5o, and usual manner, as explained fully by Mr. Hinderlich in the filament supply for this valve is obtained from a trans- Experimental TVirless (January 1927). former. The input to the grid of this valve is regulated Full output from the crystal valve could not be obtained by the position of the tap on L1. The tap is usually set with the grid circuit arrangement as shown in Fig. r. one or two turns below the anode tap of V,. It should, of The crystal itself is a fairly good insulator, and the grid course, be as near to this tap as possible, consistent with of the valve Nvould become so negatively charged as to the prevention of self -oscillation. B 18

www.americanradiohistory.com WApeIlsoo APRIL 13tki, 1927. ¢sr Wolf licl but Crystal-controlled Transmitter.- valve would undoubtedly upset the whole system, offered by The circuit L C, is tuned to 45 metres. It is important, owing to the resistance to frequency changes is practicable in this case. Also, owing of course, that both L1 and L; be of ' ` low- loss " construc- the crystal it quite tion, and in tuning a large number of turns with a small to this property, it is possible to obtain good quality with amount of parallel tuning capacity are desirable -par- grid circuit modulation. ticularly in the case of Li C. Tuning Adjustments. It is necessary to restrict the fields of the various chokes should first employed as much as possible, and those used consist of To adjust the transmitter the crystal valve to the amplifier 4 in. lengths of - in. diameter ebonite tube, wound for a be got working properly. The H.T. adjusted length of Sin. with No. 3o S.W.G. D.S.C. wire. The should be cut off, and L, C1 and the grid bias at the maxinìum winding is " spaced " at three places for hin., in order to until an absorption wavemeter lights reduce the self-capacity as much as possible. possible distance from L1. . the These chokes are visible in the photograph. The three The H.T. may now be put on the amplifier, and by means chokes seen in the photograph at the extreme left are in the circuit L2 C2 adjusted for maximum oscillations of C1 will filament transformer secondary leads. of C., and adjustment of bias. Slight retuning then be Keying is performed in the grid bias circuit of the be necessary, of. course. The aerial circuit may valve at X. This method allows the amplifier to -coupled to L; and tuned in the usual manner. amplifier and continue oscillating weakly when the key is up, although The difficulties in building such a set are not great, how not enough to give a strong spacing wave. there is great satisfaction in knowing that no matter steady Being out of the radio -frequency portion of the circuit, much the aerial may be swinging -the wave remains the induct- key leads may be made as long as is desired. at the other end -even putting your hands near the hundred For telephony it has been found best to modulate into ances will not make the wave shift more than a few impos- the grid circuit of the crystal oscillator valve, thus making cycles, and provided it is properly adjusted it is the perpe- use of the amplifying properties of this valve. With an sible for a crystal -controlled transmitter to be ordinary master- oscillator system the introduction of the trator of those " chirpy " notes, than which there is nothing modulation transformer into the grid circuit of the master more dreadful to try to " copy." ACCUMULATOR SC,_,PIHICR._.0 AC!lDol Simple Chemical Tests for Purity of Water and Acid. \IPURITIES are often present in eater and acid, tube. Add one drop of pure concentrated sulphuric acid and decrease the life and efficiency of storage and one drop of pure concentrated nitric acid, then batteries. two drops of potassium sulphocyanide solution. If but not The most common impurities are chlorine, nitrates, it remains clear and colourless, it may be used, arsenic, ammonia, iron and lime. otherwise. be Drinking water is not always suitable for batteries. Lime Test. -Clean a test tube with the water to and add ten Before water is used for maintaining the level of the tested, half fill the tube with the water, ; mixture. electrolyte in the cells, it should be tested as follows :- drops of ammonium oxalate solution shake the lamp flame Water. Hold the test tube in a Bunsen or spirit for about half a minute. Allow the tube to cool for five Test. clean a test tune with the Chloride -Carefully minutes. The water should remain clear. water to be tested ; half fill the tube with uu ater, add a of pure nitric acid and five drops of silver Acid. few drops ought nitrate. The water should remain clear, or show a very Acid before being filled into storage batteries faint opalescence only. to be subjected to the following tests. than 5.220, Test. -Carefully clean a test tube with the If the acid be of á higher specific gravity Ammonia and proceed as - figure, or thereabouts, water to be tested ; thereafter half fill the tube with reduce it to that water, and add five drops of Nessler's solution ; shake follows :- water should remain colourless. Chlorine Test. -Clean a test tube with the acid to be the mixture. The of half a test tube of the water add tested, half fill the tube with acid, add three drops Nitrate Test. -To nitrate four drops of brucine sulphuric solution. The pure nitric acid, then add five drops of silver three to chlorides shaking must remain colourless. solution. If the acid becomes milky, it contains water on faint opalescence Nitrite Test. -To half a test tube of the water add in excess. If, however, there is only a -diamine sulphuric solution. Water it may be used. 5 c.c. of metaphenylene and brown discolouration. Ammonia Test. -Clean a test tube with the acid, must not show a must a porcelain evaporating basin with fill it a quarter full with acid. The acid in the tube Iron Test. -Clean potash tested, and pour roo c.c. of the water be neutralised ; in order to do so add caustic the water to be full, then shake into the clean basin. Evaporate the water down to about solution. until the tube is three -quarters by means of red 20 C.C. Allow to cool, then pour it into a clean test the mixture. Test for neutralisation which should just turn blue when immersed Co., litmus paper, 1 Abstract from a pamphlet issued by the D.P. Battery in solution. -- Lid., Bakewell, Derbyshire. the B 19

www.americanradiohistory.com _52 Wffll'®Il®00 WorIl4 APRIL zit /r, x927. Accumulator Sulphuric Acid. - Alternative Arsenic Test. -Put a few pieces of zinc Add three drops of Nessler's solution, when the mix- in the arsenic test bottle, moisten a small piece of filter ture ought to be of a light lemon colour. If the colour paper with a few drops of mercuric chloride solution, approaches that of dark yellow, the acid contains too place this paper upon the end of the glass tube (into much ammonia, and must not be used. which another piece of filter paper has been inserted Nitrate Test. -Clean a test tube with the acid, and about half -way up), and hold it in position by means pour acid into the clean tube until it is about half full. of a rubber ring, the other end of the glass tube being Add three drops of indigo sulphuric solution; shake the attached to test bottle by means of rubber stopper. Add mixture. Pour half of the mixture into another clean acid to bottle, insert stopper, and leave for fifteen test tube, and heat one of the tubes in a Bunsen or minutes. If more than a faint yellow tinge is imparted spirit lamp flame for about two minutes, holding to the paper, too much arsenic is present. 'the tube in the flame by means of the test tube holder; NOTE. -The prepared filter paper in the tube must be do not allow the mixture to boil and spurt out of the moistened with water before using the apparatus, and if tube. it gets black, remove and moisten another - Compare .piece with the colour of the acid in the two tubes. lead acetate solution and insert into tube. If the colour of the acid in the .tube that has been heated is much lighter than that in the other, the acid MATERIALS REQUIRED FOR THE TEST. contains an excess of nitrates, and must be rejected. I Spirit lamp and stand. Confirm by brucine sulphuric tests given under water I \Vire gauze. analysis, or this test aloñe is sufficient. r 4in. diameter porcelain evaporating basin. Iron Tcst. -Clean a test tube as before, and half fill r \Vood test tube holder with test tubes. it with the acid to be tested ; add five drops of potas- T Vulcanite and rubber test tube cleaner. sium ferrocyanide solution, and shake the mixture. The i Test tube holder. colour of the acid ought not to change beyond a light loo Filter papers. blue. If it changes to a dark blue, iron is present in r so c.c. graduated glass measuring cylinder. excess, and the acid must not, therefore, be used. r Small bottle of pure granulated zinc, free from Confirm the iron test by cleaning another test tube, arsenic. and half fill it with the acid as before. Now add five 2 Litmus books -red and blue. drops of potassium sulphocyanide solution, and shake Arsenic testing bottle, with glass tube and rubber the mixture. If the acid changes to a light red colour stopper. it may be used ; should it change to a blood -red colour r Bottle of zo per cent. caustic potash solution. the iron present in the acid is in excess of what is per- Bottle of pure sulphuric acid. missible; such acid must not, therefore, be used. i Bottle of pure nitric acid. Arsenic Test. -Clean a test tube as before, and half r Bottle potassium sulphocyanide solution. fill it with the acid. Moisten a small piece of filter r Bottle potassium ferrocyanide solution. paper, of a size sufficient to cover the mouth of the tube, r Bottle ammonium oxalate solution. with two drops of silver nitrate. I Small bottle silver nitrate solution. Drop a piece of pure granulated zinc (guaranteed r Small bottle Nessler's solution. free from arsenic) into the tube, and cover the mouth with Small bottle lead acetate solution. the moistened filter paper. Allow the tube to stand I Small bottle metaphenylene- ciiamine. for half an hour. Small bottle brucine sulphuric solution. Examine the damp filter paper; if a dark brown r Small bottle mercuric chloride solution. colouration has formed, allow a drop of pure nitric acid Small bottle indigo solution. to fall on the discolouration. Should this colouration en- NOTE. -It is highly important that all apparatus and tirely disappear, is arsenic absent; if, however, it still the hands be perfectly clean before making the tests, remains, arsenic is present in the acid. The acid may otherwise false results may be obtained. be used if there is not more than a very faint yellow Suitable sized bottles of the above chemicals would colouration be left on the filter paper. roo c.c. and so c.c.

L.F. TRANSFORMER CONNECTIONS. f HE majority of manufacturers of low- frequency This arrangement is correct for probably the majority IL transformers include with their products definite of instruments, though it is as well to try experimental instructions a :. to how these components should be con- reversals of both primary and secondary in turn. nected in circuit. These should be followed implicitly, Comparatively few makers give recommendations as to as a reversal will affect adversely the performance of a the capacity of the condenser, which is normally shunted well -designed instrument. Failing any definite recom- across the primary winding of the first transformer ; this mendations on the subject, however the transformer is, nevertheless, a matter of some importance, and should be connected up as follows :- the effect of various capacities should be carefully O. P to plate, I.P. to H T +, O.S. to grid, I.S. to noted. A value of 0.0003 or o.000s mfd. is generally grid bias negative. sufficient.

B 20

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The following abstracts are prepared, with the permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Patent Office, 25, Southampton Buildings, London, W.0 2, price 11- each. are connected across Toroidal Coil. in a receiver by mechanically coupling the of the potentiometer tuning control with some arrangement two variable tappings XY on a resistance (No. 257,564.) so such as a potentiometer. The specifica- connected across the filament battery, : Aug. 314, of the potential Convention date (U.S.A.) t ion points out that the amount of re- that accurate adjustment 1925. generation existing in a high -frequency drop along the windings can easily be ob- A form of toroidal coil suitable for amplifier may be dependent upon the tained. By mechanically linking the con- high- frequency circuits is described by l,:)sition of the tuning condenser. As the densed shaft with the potentiometer arm the Coto -Coil Co. and E. F. Parks in the condenser is varied so must the reaction the positive potential applied to the grids above British patent. In the diagram M "mtrol be appropriately adjusted. The is increased as the condenser is decreased. particular invention utilises a potentio- Unfortunately, however, the setting of meter method of controlling the reaction the condenser and the potentiometer does by damping the grid circuit by applying not follow a straight -line law, which wind a a positive potential. In the diagram the means that it is necessary to aerial circuit AE is coupled to the input potentiometer so that the resistance drop circuit L, C, of the first valve V,. This across it is not constant. In order to is coupled to the next valve V, by means overcome this difficulty the desired law is of a lrigh- frequency transformer H.F.,, obtained by connecting in parallel with the secondary of which is tuned. A the potentiometer BCD auxiliary resist- similar transformer H.F.., is used be- ances P, Q and R. The effect of this is tween the second valve V, and the de- equivalent to winding the potentiometer tutor valve V,. The lower end of the in sections having different ohmic resist- input circuit of the valve V, and the ances. The specification also provides for secondary winding of the transformer linking the condenser with a filament H.F., are connected to the slider arm C rheostat for the purpose of dimming the ,f a potentiometer BCD. The ends BD filament instead of using a potentiometer.

Toroidal coil winding. (No. 257,564.) represents a mandrel or axially rotated spindle of the winding machine on which the wire W is wound, the turns being spaced in a similar manner to those of a honeycomb or duolateral coil. The wire is wound along the mandrel with a constant pitch until it reaches the point X, when the direction is reversed, the wire returning at Y. A number of layers may be wound in a similar manner, so that a nntltilayer coil is obtained. The winding is then removed from the mandrel, and the coil is bent into a ring so that a toroidal winding results leaving an appearance similar to that shown in the diagram. 0000 Controlling Reaction. (No. 253,072.) Contention date (U.S.A.) : June 4th, 1925. The Lovejoy Corporation and D. R. described in the above British Lovejoy 253,072.) patent a method of controlling reaction Potentiometer control of reaction in a H.F. amplifier. (No.

13 21

www.americanradiohistory.com APRIL 73111, 1927. Electrical Gramophone Reproducer. can also be .used for .broadcast reception, through a condenser C, to the anode, the (No. 253,096.) when an aerial and earth system AE- is filament centre point being taken included, to the Conrention dette (U.B._I.): June 2nd, and a toaster switch S is used two condensers C, and C,. The output 1925. to connect the detector valve either to the of the oscillator is coupled to the first aerial system or to . the oscillator valve high A system comprising an electric grànw- -frequency amplifier V, through a associated with- the pick -up arrange- coupling condenser C, and a grid - phone reproducer and an ordinary wire- ment. choke less receiving L,. The output circuit of the valve V, system is described- by oovo comprises Marconi's Wireless Telegraph Co., Ltd., an inductance L, which is and coupled through a condenser C, to the J. Weinberger in the above British An Auto-coupled Transformer. patent. The electric pick arrange- grid circuit of the main amplifying valve -up which includes ment from the record comprises a needle (No. 264,910.) V a grid choke and or stylus N, which works Application resistance L, R.,. The last valve V, is on the sound date: October 23rd, 1925. coupled trace of the record, and is E. A. Graham and L. in the usual manner to the aerial connected to H. Paddle de system a balanced electromagnetic system con- scribed in the aboye British patent speci- AE. A microphone M is consisting of an armature A pivoted fication a particular nected to the primary winding of a spécial about form of auto -coupled transformer its centre point, and working between a transformer. The amplifying having two secondaries S, valve V, is and S,. The pair of poles at each end. A valve V, first secondary S, is con- Is arranged as an oscillator, the anode nected to the grid- filament circuit of the circuit containing an inductance L, and modulator valve V the anode of which the grid circuit an inductance L part is connected to the source of supply B of which is tuned by a condenser C,. through a modulation choke Z, this valve The windings W of the electromagnetic modulating the output of the last valve system are also included in the anode in the normal manner. The other circuit of the valve, and are shunted by secondary S, is connected to the input a condenser C, to pass the high- frequency circuit of a valve V which is normally oscillations existing in that circuit. A 'provided with a large negative bias, battery B, supplies both filament and thereby making the internal resistance anode voltages, the filament current being very high. This valve, however, is in controlled by a resistance R,. Movement series with the anode supply to the first of the needle N will cause the armature amplifying valve V,. When there are no to move in the magnetic field, thereby speech currents the valve V, will offer a causing a considerable change in flux, Auto -transformer valve coupling circuit. very high impedance, and, consequently, which will cause potentials to be produced (No. 264,910.) the output of the amplifying system will across the winding W. be very small, so small, in fact, This will mean provided with input terminals T, and that the that the anode voltage of the oscillator whole system will hardly radiate. As valve will vary, the anode circuit contains the primary AB soon as speech potentials thereby modulating its of an are applied to output. The output auto -coupled transformer. This the valve V however, they will of the oscillator winding AB is shunted by a resistance overcome valve, however, is transferred through R,. The secondary winding of the trans- an inductance L. and a condenser C, to former AC is connected to the L, another tuned circuit L, C, grid circuit which is of the next valve through a stopping condenser K to prevent the posit:re potential 03 t;," -C2 Ca Lz from the anode battery being applied to H HI the grid of the next valve. Owing to the presence of this condenser a grid leak R_ has to be employed, and is shown connected in series with a low- frequency choke L. The output of the second valve

is shown at O, and can be connected to 2 another similar auto -coupled transformer. Alternative systems are given in the spe- L4 cification in which the transformer is provided with tappings, so that the degree of amplification can be varied, while, in another modification, the secondary or I It-Li1l full winding is shunted by a. potentio- s2 meter, the 1t1/ slider arm of which is con- s nected to the coupling condenser, in this 111i 1 way controlling the potential applied to the grid of the next valve. v4 0oo0 14 Quiescent Telephony. (No. 252,027.)

Convention. date (U.S.A.) : May lltb, 1925. A system of quiescent telephony Circuit of quiescent telephony transmitter. contrd (No. 252,027.) suitable for duplex work is described by Circuit for electrically reproducing the British Thomson- Houston Co., Ltd., the negative bias and allow the valve V, gramophone records. (No. 253,096.) and I. F. Byrnes in the above British to pass sufficient current, and, therefore, patent. The circuit should make the cause the system to amplify and radiate coupled to the input L, C, of a. detector invention quite clear. The transmitting considerably. Since, however, speech valve V,. When both the valves are system is of the drive or master oscillator voltages will be applied by the secondary functioning a portion of the output of type, an intermediate amplifier being used S, to the modulator valve, it will, there- the oscillator will be rectified by the between the master oscillator and the fore, modulate the output of the system. detector valve. However, since this out- final valves connected to the aerial circuit. In this manner a quiescent -system is ob- put is modulated, the modulation will be The drive valve V, is provided with a tained; i.e., there is only appreciable detected by the valve V thereby work- tuned circuit L, C, C,, one end being radiation when microphone potentials are ing the telephone receivers. The system connected to the grid and the other actually existent. B 22

www.americanradiohistory.com .. _... .. _ . .. .. : _ . WApeism APrt IT. I,, 1927. WopIl

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A Section Devoted to New Ideas and Practical Devices.

to the soldering tags of fixed con - ing a skeleton framework. After densers and other components. trimming up with a file and carefully V. G. flattening it should be replaced in the 0000 condenser, when it will be found that the full movement of the vernier knob VERNIER CONDENSER IMPROVE- will be equivalent to about one degree MENT. EXPERIMENTAL CONNECTIONS. on the dial of a 0.0003 mfd. con - l3efore vernier dials became avail- When trying out new circuits it is denser J. N. it vvas customary to fit variable 0000 collection of flexible able useful to have a condensers with an auxiliary vane of various lengths H.F. CHOKE FORMER. connecting wires operated independently of the main the various components for joining up condenser vanes by a small knob. lliscaoled photographic Jilin spools whirls may be screwed to a temporary with a centre core constructed of wood baseboard and panel. can he used to support the windings The use of spade terminals at the of a H.F. choke. ends of the connecting wires has been First obtain two pieces of fibre or suggested, but with this system diffi- other suitable material about Sin. long culties are likely to arise when adding and dn. wide and saw out each piec . a new wire to a terminal already for half its length so that the two may loaded with three or four other leads. be interlocked. One metal end -piece In the system shown in the diagram of the spool, which should be of the small brass clips are substituted for quarter -plate size, is cut off, and two the spade terminals, by means of

Vernier condenser vane with central portion removed to give smaller rate of change of capacity. For short -wave work the variatir,n rC raluicity provideil by the single - plate vernier is frequently found to be greater than is required for accurate tuning. In these circumstances it will he found an advantage to dismantle the auxiliary condenser and to remove the central shaded portion of the vane, as shown in the diagram, leav-

Terminal clips for experimental connecting wires. Valves for Readers. Photographic film spool used as H F. choke former. which it will be possible to make any made in number of connections to a terminal saw cuts at right angles are For every practical idea sub- about ÿin. by fixing a short strip of brass as the wooden core to within accepted pieces are then shown in the diagram. Connections mitted by a reader and of the base. The fibre the wooden may be added to or removed from this for publication in this section the fitted into the slots in strip without in any way interfering spool and secured with a trace of glue Editor will forward by post a is wound with the remainder of the clips. or shellac varnish. The wire of British make. edges Another advantage of this method receiving valve on in sections in steps cut in the A. A. H. is that clips can he connected directly of the fibre supports. D 23

www.americanradiohistory.com WAp®Ilo,,To WalIld APRII 13th, 7927.

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INP011111 111 Ì II+ IIIINIII Cal SRJ un II'!qr..l¡ = ï CU1FNT.'d` - 111 !.... INÌÌñIIIY TOPIC,J' Events of the Week in Brief Review.

WIRELESS EXHIBITION. RUSSIA'S NEW STATION. We are able to munication with other aerodromes and state that the annual The new Moscow station, "Great with aeroplanes Wireless Exhibition held under the aus- Komintern," in flight. which will work with a The installation will pices of the N.A.R.M.A.T. will open at power of consist of a group 40 kW., will certainly enable of four 3 kW. transmitters Olympia on September 21st and continue the voice of Moscow operated in to be heard through- conjunction with a direction until October 1st. out Europe. It has -finding re- 0 0 00 been constructed ceiver. Independent drive circuits according to plans prepared by will NEW STATION DIRECTOR FOR Professor maintain constancy of frequency and Bonch Brouevitch, and was lately offi- wavelength. BOMBAY. cially -opened. The new wireless D.F. re We are able to show a ceiver is so arranged We understand that Mr. Leslie B. general view of the building that, if required. Page, with one two or three circuits can be operated on who was well known as the station of the huge lattice masts in the fore- director at the TIull Broadcasting Sta- ground different wavelengths for the reception and another more distant. of telephony tion, has been appointed to a similar post and telegraphy on the same under the Indian Broadcasting Company aerial. for their Bombay Station. The masts and transmitters will be o o o o erected two or three miles from the Aero- SO NEAR, AND YET SO FAR! drome, and operated by remote control. It is expected The freakish nature of short that this new station waves will be in operation sometimes causes remarkable and curious before the end of 1 be coming season, vagaries in the transmission of messages. A story reaehes us from California that 0 0 0 0 an amateur in San José, wishing to com- AN OBLIGING MILKMAN. municate with a friend in Carmel, about Amateur wireless in America is con- 50 miles distant, found himself unable ducted on more commercial lines than to get : into touch with him t his he in this country and is recognised ascribed as n. to the habit of short waves convenient way of transmitting public visiting the upper atmosphere before messages. Even being eavesdroppers join ill reflected back to earth. However, the game. We hear that at Hartford. he determined not to be beaten, and, re- Connecticut, a milkman listening on his membering that his friend kept a regular broadcast receiver schedule with another chanced to pick up a amateur in Singa- message from an amateur station pore, he relayed his message via Asia intended for Mr. K. B. Warner, the secre- ,and received an answer by the sane tary of the route, each message A.R.II.L., who happened b, having to travel be one of his regular customers. over 1,600 miles to bridge a 50 -mile gap. The 0 0 0 0 message was duly delivered with the morning milk. NORTHERN LIGHTS NOT TO BE BLAMED. 0 0 0 0 AN It is often supposed that wireless re- EXAMPLE WORTH FOLLOWING. ception is adversely affected by the Aurora Listeners in Denmark are congratulat- Boreztlis, but Lieut. H. Holten Moller. the ing themselves on the fact that, since engineer in charge of Godhavn Station in the number of licences of valve receivers Greenland. disagrees with this theory. has exceeded that estimated in the His station is said budget, the authorities have to be the most northern s. decided to in the world, and throughout the winter dt" reduce the fee from 15 to 10 kroner, thus !lla3 e I Íf) 11111 l,\G.;e.. the sun is not seen. The Danish Govern- löf'!Ilji bringing it down to the level of crystal -.; II set ment has instructed him to carry out a owners. number of tests to investigate* the effect, A kroner is equivalent to about eleven pence, so if any, of the Northern Lights, but, so Russia's " Daventry," the Great Komintern it will be seen that the Danes far, he cannot find that they are respon- Broadcasting Station in Moscow. will now pay even less for their enter- sible for fading, weakness of signals or tainment than we do in Great Britain. It is also stated poor reception. He states, in fact, that "CROYDON CALLING " -WITH A that' the Danish though he has had eleven years experience NEW VOICE. Broadcasting authorities will transmit a special late programme of wireless in all parts of the world Ile The new station, from Soro on has never before experienced which is to be 1,153 metres for the benefit of their coup such ideal erected for the Air Ministry by the Mar- trynuen resident conditions -presumably only from a wire- abroad. This transmis- coni Co., will replace the one that has sion will probably be given between less point of view -as in his present done duty for micl station. the last seven years and night and 2 a.m., so that it may not considerably extend the range of com- interfere with other European stations. B 24

www.americanradiohistory.com APRI .T, r ,th, 7927. hrll® WzoOpIlCt 457 THE BRITISH LEGION'S WIRELESS SHADRACH, MESHACH AND ABEDNEGO. WIRELESS AT WESTMINSTER. PRIZES. The apparent paradox of " cold heat BY OUR PARLIAMENTARY CORRESPONDENT. 'The Birmingham No. 1 branch of the is exemplified by electric furnaces such as In British Legion, of which H.B.H. the that used in the research laboratory of answer to Mr. Johnston. who asked Prince of Wales is Patron and Field the General Electric Co. in Schenectady. whether he had any complaints from owners of wireless Marshal Earl Haig President, is en- Men thrust their hands casually into a sets in arluoath deavouring to enlist the sympathies of fmnece which melts metal with ease, and regarding difficulties of listening in to wireless enthusiasts in the scheme for white mice will stay in it even though the the program III es of the Dundee broad- giving 500 children a day's outing in current is tot, but it is a simple matter casting station since the recent altera- the country. Contributors of 6d. to their for them to run out if they so desire. tions in the wavelength, Sir W. Children's Outing Fund will be entitled It should be noted, however, that the Mitchell -Thomson said he had received to participate in the draw for a complete Wren are careful to remove any rings from no. such complaints, but he had no doubt 3 -valve set which is being offered as a their fingers and the metal drinking cup the British Broadcasting Corporation prize. The drawing will take place on for the mire is outside the furnaces. world be ready to investigate the matter. Friday. July 15th, and will be performed The explanation of the apparent mystery 0 0 0 0 by Mr. J. Smedley Crooke, M.P. Do- is that the high frequency furnace beats Daventry and Crystal Users. nations may he sent to the No. 1 Branch electrical conductors only. Mr. Day asked the Postmaster- General Headquarters at the " Hope and 0 0 0 0 whether, in view of the PERSONALLY fact that the Anchor," New Canal Street, Birming- CONDUCTED. licence fee iparíd by owners of ham. wireless The Royal Mail Steam Packet Co.'s crystal sets was the same fee as that 0000 motor vessel " Asturias." now on a paid by owners of wireless valve cruise round the is BROADCASTING IN ELEMENTARY world, fitted with all sets. and that the London transmit - SCHOOLS. the latest wireless luxuries. Loud - ting station 2L0 shut down some nights speakers are installed in various positions at 11 p.nr., The educational he would arrange for the pro- value of broadcasting on the promenade deck, and one of the gramme sent out from Daventry is now recognised by the L.C.C., whose after this officers on the bridge can direct the atten li,,nr. and obit!, was only available to Education Committee has sanctioned, as an experiment, the reception of broadcast talks from three o'clock onwards on Friday afternoons in their elementary schools. The experiment is to be tried for a year, and it will be interesting to see whether the scholars will profit by this recreative form of instruction. it is understood that in one hundred of the Council's schools wireless apparatus has been installed without expense to the Ccnmittee, the sets being either free gifts from the teachers and others, or paid for out of the school funds. Judging from the letters in the daily Press there is a vast number among grown -up listeners who resent any attempt on the part of the B.B.C. to impart useful knowledge -they don't. know and they don't want to know - but the youthful mind is generally of a more inquiring nature and more eager For information. especially if it can be ,assimilated in a pleasant manner.

0 0 0 0 THE AUSTRALIAN BEAM SERVICE. The Anglo- Australian Beane Service. which was opened for public service on -April 8th, establishes for the first time in History a direct line of public communication between Australia and London, and is the longest direct telegraph service of RECOMMENDED BY THE B.B.C. the world. Secrecy of communication is ensured by the speed at which In next week's issue will appear full constructional details of the two- and three -valve messages receivers recommended by the B.B.C. for good quality broadcast reception. The will be transmitted. The automatic aap- circuit systems of these receivers which have already been described in the pages of patatus is capable of transmitting and this journal have created considerable interest and it will be remembered that specimen from sets were demonstrated by the B.B.C. on their stand at the recent Ideal Home Exhi- receiving 500 to 2,000 letters per bition held at Olympia minute. The change -over periods during which communication is at present some- tion of the passengers to objects of in- valve -set owners, to be relaid from the what uncertain occur, fortunately, be terest in the passing scenery in the same Loudon station so as to give owners of tween 9 p.m. and midnight and between planner as the conductor of a char -a -bane crystal sets the same benefits as owners 9 a.m. and noon (by Australian time) - instructs his flock. The vessel is also of valve sets? that is, during the time when nearly all supplied with a Marconi " baud repeater " Sir W. Mitchell -Thomson said that this business houses in one country or the equipment so that reproduction of music was a natter within the discretion of the other are closed. and talks may be turned on whenever the British Broadcasting Corporation. He A second beam station is now being passengers seem to need cheering up. understood that at times when Daventry completed in Australia for direct service The ordinary programmes broadcast was working and London was not most to Montreal. from land stations can. of course, be persons using crystal sets in London or Messages for the beam service can be picked up and relayed to various parts of other places within a radius of 100 miles in handed at any postal telegraph office in the vessel. The Saturday evening pro - of Daventry could receive the Daventry the cities. suburbs, or country towns of gramme from WGY was clearly heard programmes with little alteration of their Australia. while in harbour at Durban. sets. B 25

www.americanradiohistory.com wmat APRIL 13th, 1927. OSC LArJL 7/16 CRYSTALSO Recent Research wit,. Low= frequency Oscillations.

ESEARCHES upon piezo- electric crystals, which tector in Fig. 3, taken by Dr. Seidl, we see that the de- can be excited into mechanical oscillations by tector also has a falling characteristic, and therefore a means of H.F. oscillations, as well as those upon negative resistance, over a certain range and that it can the oscillating crystals of I.ossev, have already been be made to oscillate thereby. The detector which fur- dealt with several times in this journal. In both cases, nished the characteristic in Fig. 3 consisted of zincite however, high -frequency oscillations are dealt with, and a steel point. For steel points certain gramophone whereas new experiments of Dr. Franziska Seidl at needles prove satisfactory, and various other known de- Vienna show that with a crystal detector relatively slow tecting substances can be used as crystals. It is, how - oscillations pf audible frequency can be generated. Such ever, always important to adjust extremely carefully the a detector might almost be termed a " diaphragmless telephone." 'I'he arrangements in Dr. Seidl's experiments are apparently just the same as with the " singing arc " discovered about 25 years ago by Duddell. Duddell noticed that an electric arc -lamp in mA Fig. 1.- Circuit of Duddell's parallel with which a con - 60 50 40 30 20 10 10 20 30 40 50 60 " singing arc." denser and inductance are connected is excited into oscillations which can be heard as a loud note if they are within the range of audibility. For purposes of comparison Duddell's circuit is given in Fig. I. The part played by this circuit in wireless telegraphy is well known, for it is possible to attain quite high frequencies by this means and to excite an aerial directly. The reason for the arc's capability of oscillating lies in its falling characteristic, which is diagramatic- ally represented in Fig. 2. Contrary to the usual Fig. 3.-Characteristic of the oscillating crystal used by Dr. Seidl. " ohmic 'i resistance the terminal voltage of the arc falls if the current increases, i.e., the arc has a " negative pressure with which the steel point is pressed against resistance " just as in the case of a triode valve provided the crystal. Further,' Fig. 3 shows that the character- with regenerative coupling. istics for the two possible directions of current are of If we now look at the characteristic of a crystal de- similar form but with different slopes, i.e., it is easier to make the crystal oscillate in one direction than in the other. The circuit in which the crystal is made to oscillate at audio frequency is given in Fig. 4. Contrary to the experiments of Lossev, in which a small biassing potential is used on the crystal,. a fairly high potential is employed with the low -frequency oscillations of Seidl, as indicated in Fig 3. It is necessary also to adjust the potential w carefully, preferably with a 0 potentiometer, P, placed somewhere in the current o > supply lead. In parallel with the detector D there may be a condenser C of o.3 mfd. and an inductance L of o.i henry. In the lead to the oscillatory circuit is an iron -cored choke -coil CURRENT which is useful but not absolutely necessary. The similarity of the FIg, 4.- Oscillating crystal circuit for audio frequencies. fig 2.-Falling characteristic of the Duddell arc oscillations in this circuit 13 26

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APRIL 13t11, 7927. WAp@Ilsog Wosllí 459 Oscillating Crystals. - that the potential across the crystal falls at the same time to the oscillations of the " singing arc " is brought out to 3 volts. If the capacity was altered the periodicity by the fact that the frequency of the circuit C L D is not of the oscillations changed and, in fact, the smaller the determined solely by the capacity and inductance but capacity the more rapidly the oscillations followed each depends to a considerable extent upon the pressure of the other. steel point against the crystal. With the above- mentioned The similarity of this phenomenon to the known values, a potential of 59 volts and a current of 25 milli- arrangement for producing oscillations by means of a amperes a frequency of 853 was produced, while with a glow- discharge lamp suggested to Dr. Seidl the circuit potential of 47.8 volts and 12 milliamperes the frequency in Fig. 5, where only the condenser C is in parallel with the detector D, a high resistance R being placed in series with these. The resistance was roo,000 ohms, while the condenser could be adjusted between o.00s and 1.0 mfd. This circuit gave a pure and constant musical frequency depending upon the voltage and the size of the condenser. It Was even possible to short-circuit the resistance R completely ; a clear and steady note was still obtainable by careful adjustment of the detector. In this case, however, the potential across the crystal must not he too great-about 8 volts was enough on the average - in order to make the detector oscillate. Surprising as it may seem, it was even possible to do away with the con- Fig. S. Modified circuit Fig. 6.-Simple crystal cir- dispensing- with induc- cuit which has been made denser :rs Well, thus simply supplying the detector with tance L. to produce oscillations. a D.C. potential across a potentiometer (Fig. 6). It was could often be made to oscillate. was 795. Once the crystal is set neither frequency nor found that the detector current vary over a long period of time (two hours, for though not very easily: a high- pitched note was pro - instance). duced, but the conditions for oscillation were unstable Sometimes it is found that the oscillation of the crystal and made the further investigation of the problem a starts and stops periodically. In such a case it is found matter of considerable difficulty. -H. K.

i CLUB ; t , ,. REPORTS Am- t r of A Satisfactory Report. ND D.F. stations due to deflection the waves layer, was also of the City by the Heaviside The fourth annual meeting dealt with. Mr. Atkinson concluded with of Belfast Y.M.C.A. Radio Club was lehl TOAPIC S The hot. the methods used in counteracting these on the 29th March, 1927. effects. secretary in his résumé of the club's Hon. secretary : Mr. J. Levy, 19, activities during the year mentioned that Secretaries of Local Clubs are invited to Landsdowne Road, West Didsbury. a licence the club had now transmitting send in for publication club news of general 0 0 0 0 and experimental work was being carried interest. All photographs published will be out at the week -ends. A Morse class paid for. A Champion of R.C.C. had been run during the winter season Speaking in favour- of resistance for those interested, and a course of A Talk on Direction Finding. capacity coupling in a lecture before the monthly lectures had been given during On Friday, April 1st, Mr. S. .Atkinson, Bristol and District Radio Society on the same period, principally by members B.Sc., Tech., gave the members of the March 25th, Mr. John Rhee, of Messrs. of the club. The hon. treasurer reported Radio Experimental Society of Man- Mulland Wireless Service Co., Ltd., said that there was a substantial balance in chester a most interesting talk on that the advantages of this form of hand. notwithstanding the outlay on the " Direction Finding." -The speaker coupling were simplicity, compactaass, transmitter, which included DET valve, graphically illustrated the directional light weight, small consumption of high - and a three -valve short -wave receiving properties of the frame aerial, and pro - tension current, and uniform amplifica- set. :eeded to show nmthematically how the tion at all frequencies. The chief disad- The following officers and committee induced E.M.F. in the frame for a given vantages were that the amplification per were appointed to conduct the affairs of signal strength varies, and can be calcu- stage would never exceed the amplifica the club for the year 1927 -28 :- President. lated, as the frame rotates. He then tion factor per valve, and there was a Mr. J. S. B. Shaw ; `ice- presidents, explained how to allow for and also how serious danger of rectification taking Messrs. C. Allen, J. B. Dolphin, J. For to overcome " vertical effect " in place in the low- frequency amplifier. The sythe, J. Lockhart and J. White ; hon. ordinary frame reception, and how to lecturer gave recommendations as to the secretary, Mr. J. J. Cowley ; hon utilise the " vertical effect " in D.F. values of coupling condensers and grid - treasurer, Mr. E. G. Diamond; commit- work. The " Robinson System " as used leaks. tee, Messrs. E. Beat, W. C. Haddick, R. in the Air Force was next described and This was the final meeting of the winter Holden, S. Johnston and G. Kirkwood. fully explained, and the speaker followed session and an interesting summer pro- Hon. secretary : Mr. John J. Cowley, with the " Bellini -Tosi system," with the gramme is now being arranged. Y.M.C.A. Radio Club, 4, St. Paul's dual fixed frames. The problem of night Hon. secretary : Mr. S. J. hurley, 46, Street, Belfast. effect and fading of signals in coastal Cotswold Road, Bedminster, Bristol. a 27

Fi,T.íigib:'.,ïv111: . .F _... www.americanradiohistory.com 460 WAptlisog APRIL 13th, 1927.

Quality in Reproduction. its size. If it were too small the set At the meeting of the Muswell Hill & FORTHCOMING EVENTS. would distort very badly, and practically District Radio Society, held March 30th, all the lower tones would be cut out. WEDNESDAY. APRIL 13th. Mr. L. Hirschfeld, B.Sc., brought a three - Edinburgh and District Radio Society. -At The higher notes, also, would not be valve set of his own make, worked en- 117, George Street, Edinburgh. "Elec- amplified to any extent, for the circuit trical :Measuring Instruments," by W. D. capacities would tirely off the mains. A 20,000 ohm wire - Oliphant. A t 8 p.,n. provide a leakage path wound tapped resistance was used for 3lnswell Hill and District Radio Societ?t.- of lower impedance. The same At T'ollington School, Tat It, "The " snags " were encountered if one in- H.T., while the valves were feel through Genera/ Design of Broadcast Receivers," a 60 -watt lamp. The set was resistance - by F. H. Haynes. .l t 8 pant. creased the anone resistance unduly. coupled and gave pure reproduction of THURSDAY. APRIL 14th. They liad found that a three to five Northampton and District Radio Society. tuegohm anode resistance gave the best London, Daventry and Radio Paris. The -At 8 p.m. "The Fe,ranti Trans- most surprising fact was that Mr. Hirsch- former," by Mr. Garrick (of Ferranti, results. The most suitable size for the feld had entirely eliminated all ripple; Ltd.). coupling condenser was 0.0003 infd. the final slight hum being excluded by WEDNESDAY, APRIL Roth. Curves were shown which gave the Edinburgh and District Radio Society.- fitting a potentiometer across the detector " Sonie Methods of Measuring Signal amplification at varions frequencies, and valve filament. A small variable condenser Strength and Application," by J. 13. it was noted that these appeared to be Davidson. extremely good. (neutrodyne type) was inserted between Tolu.nhana Wireless Society. -at The In- the grid of the detector valve and the stitute, Bruce Grove, Tottenham. Lecture: Suitable values of H.T. were discussed "It (nark: Receive, s," by T. rickety. .4 t plate of the 1st L.F. valve. s p.m. and demonstrated on the receiver. Grid Hon. secretary, Mr. Gerald S. Sessions. bias was an important question, and ex- 20, Grasmere Road, Muswell Hill, N.10. periments were conducted to show the effect of an alteration from the recom- o o o o repaid the labour and time expended by mended values. Suitable values of grid A New Continental Receiver. members of the Society. The case of the leaks were given. If these were mounted An interesting talk was given by 11ír. blind person who is also partially deaf on ebonite of poor quality or proper A. W. Knight before the members of has also received attention, but fortu- mounts which were dirty or dusty, it the Croydon Wireless and Physical nately it has been discovered that such might be found that the set would Society on a new type of radio receiver cases are very few. function equally well without a grid embodying resistance- capacity coupled 0ooc leak. This was obviously due to the fact high frequency amplifiers now being that the leakage path across the ebonite Grid Leaks and Condensers. was acting as a grid leak. marketed on the Continent. Unsuccess- A most interesting lecture ful attempts at high -frequency amplifica- was given Some interesting facts were given to the Tottenham Wireless Society on regarding the construction ,,f the grid tion by means of resistance- capacity Wednesday, March 30th, by Mr. coupling have been tried for some time, Parr, leaks used by Messrs. Ediswan. The of the Ediswan Valve Co. He took as method of manufacture was explained and only recently has any real progress his subject " Resistance capacity been achieved in this direction. The amplifi- anti result- of life tests sicen. Tt was lecturer gave an account of the Loewe duplex and triplex valves and how they f functioned, and brought with hint for demonstration purposes a three -valve set, ,vhich he had just received from abroad. consisting of detector and two stages of !ow- frequency amplification. Although the set was tried out on an indoor aerial, yet good amplification was obtained sufficient to work a loud- speaker on the local broadcast, and members heard items from the 2L0 programme. The three valves were enclosed in a nickel -plated container, which acts as a protection for the valves and also as a holder for the other components, and this container was opened in order that members could inspect the valves and lay -out and compare the latest Continental practice of radio assembly with that in vogue over here. Much interest was aroused in the construction of the receiver and valves. Mr. Knight was heartily thanked for his very interesting talk and demonstration, and for giving the members au opportunity of seeing the form of receiver A COMPACT STATION. U 3AHL is a station often picked up on this side of the Atlantic. that might become popular on these shores It is owned and operated by Messrs. F. F. Priest and C. B. Knight at 903, Hanover Avenue, in the near future. Norfolk, Virginia. Tne smaller set uses one 203A valve with 150 watts input and works on 80 metres. The larger set transmits on 40 metres with a single 250 watt valve. Hon. secretary, Mr. H. T. P: Gee, 51-52, Chancery Lane, W.C.2. cation. He explained very fully the noted that these seemed to be extremely 0000 theory and practice of the subject, and good. They had been tested with 200 Service for Blind Listeners. demonstrated most of his points on a volts across them. Curves showed that

Several months ago Capt. Ian Fraser ' R.C. Threesome " receiver. Valves after several thousand hours they sud- broadcast an appeal for wireless receivers (laving any impedance desired could be denly gave out. The old type of grid for the use of. the blind. The project constructed, but after a point any in- leak gradually varied in use until its was taken up with enthusiasm by the e:rease was not beneficial. In theory, to resistance was infinity. The new grid Tottenham Wireless Society with the connect to the grid one only required a leaks used in the set remained perfectly result that in nearly 30 cases blind people condenser ; any condenser would do pro- constant during the whole of their useful in the locality have been provided with vided it had a high degree of insulation; life. a service of set construction and main- in practice, however, while not being very Hon. secretary, Mr. A. G. Tucker, 42, tenance. In every case the pleasure given critical. there were points which governed Drayton Road, Tottenham, N.17. 13 28

www.americanradiohistory.com APR /T, r;th, 102 7. VrtigIlcgoI -sr

VVOU:..1I -

Semizportable Set for Long= distance Reception with Loud= speaker or Phones.

AS the name implies, the Neutrosonic Seven is a lilament current of r..} amp. is drawn from the 2 -volt, supersonic heterodyne receiver employing seven 40- ampere -hour accumulator, chich is of the unspillahle valves in which the well -known principle of " neu- type. trodyning " or balancing out stray capacities has been The lid of the battery box is readily detachable, and applied to the H.F. and intermediate amplifying valves. contains the frame aerial. This can be mounted to rotate It is designed for long- distance reception on a frame on a pivot fixed to the top of the battery compartment, aerial, and can be used either as a permanent receiver in and is connected to the set through flex leads spaced the home or as a por>rtble set. It is not, however, a apart with ebonite cleats. Incidentally, we found that portable set per se-that is, no quality of performance these cleats caused a certain amount of trouble when shut- has been sacrificed to the end of portability ; but, the ting down the lid of the battery box unless they were all design having I ,een perfected, the makers have very wisely lying flat. in future models this trouble will no doubt decided to build it in portable form, thereby greatly ex- be overcome by allowing a little more space inside the lid. tending its utility. Although rather too heavy to he A switch on the frame aerial box gives three wavelength carried far without fatigue it seems to us an ideal set ranges, and the reader should not forget to move this for motoring or boating expeditions. switch into the appropriate position when changing the tuning units in the set. Durable Finish. Before leaving the topic of batteries a word of praise There will be few who will object to the workmanlike is due to the " Springmore " wander plugs, which give appearance of the set, but if it is thought in certain a firm electrical contact in H.T. and grid bias battery circumstances that it does not quite conform to " period sockets. They have been adopted also for the frame ideas in furnishing or interior decoration, it can he aerial and loud- speaker connections to the set, and are housed in a suitable cabinet and used in conjunction with nnuh superior to the ordinary type of wander plug. the Igranic folding frame aerial. Where A.C. supply mains are available, it is a good plan to make use of Constructional Details of Receiver. the Igranic H.T. supply units in order that the dry cell TI1a receiver case is well designed. The front panel batteries may he conserved for outdoor use. is detachable, and slides into a recess under the panel, The full equipment is contained in two black thus serving as a convenient rest for the hand while leatherette- covered cases complete with carrying straps making tuning adjustments or for spreading out the cali- and handles. The photographic illustrations to this bration charts for examination. Special fittings are pro- article give a good idea of the general appearance of the vided inside the lid for carrying the spare tuning unit set and show it packed for transport and opened up for and a pair of telephones. use. The seven valves function as follow : -First valve One of the boxes contains the H.T. and I,.T. batteries. (Cosmos S. P. r8I R) : H. F. amplifier for incoming signals which are connected to the receiver through a multiple from frame. Second valve (S. P. 16 /R) : Oscillator. cable terminating in a six -way plug. A central spigot Third valve (S.P.181B) : 1 irst detector. Fourth and and keyway ensure that the plug is always correctly in- fifth valves (S.P.r8; B) : Intermediate frequency ampli- serted. The H.T. batteries are of the small -capacity fiers. Sixth salve (S.P.18 /B) : Second detector. type supplying 8.5 milliamperes at 162 volts. A total Seventh salve (S. P. i 8 1 Hrow n) : Power output valve. B '-9

www.americanradiohistory.com WIlm@iluz APRIL r3th, 1927. 46 WaiIle Broadcast Receiver-Igranic Neutrosonie Seven. - Both detectors are mounted in rubber - sprung holders, the remaining valve holders being rigid. The valves behaved themselves very well indeed, and no trouble was experienced from microphonic noises unless the balancing condenser were thrown out of adjustment to obtain reaction

- effects. Manipulation of the balancing condenser in this way, although mentioned in the'iristruction book, is hardly necesmry; all the results mentioned later in the article were obtained with the balancing condenser in the normal position. Tuning coils for the oscillator and H.F. amplifier are boxed in neat moulded units which fit into a well at the extreme left of the valve panel. The top of one of these units in situ can be seen in the photograph of the open receiver; the same photograph shows the long -wave unit in the lid of the case. From left to right the three main tuning controls are

Front cover removed from battery box, showing compartments for cable connector and L.T. and H.T. batteries..

as follow : " Frame," " H.F. tuner," and " Oscilla- tor.'' In the top left- hand - corner is the balancing-condenser which; once set, does not require further adjustment. The corresponding knob- in the tip right -hand

corner operates a filament rheostat. - At the - bottom of -the panel immediately below the H.F. tuner dial is a volume

control. On the left - of this is a filament switch, . and on the right a telephone jack which automatically cuts out the loud - speaker. All controls are mounted on a metal panel which effectively -screens the circuits in the interior of the set from hand capacity effects. The manipu ?ation of three tuning controls calls for considerable skill, which can only be acquired by practice. The single- control receiver is, of course, the ideal to which alI manufacturers aspire, but receivers of this type are generally suitable only for local station reception. The battery box and frame a..»0 na they appear lin use. Note and the ebonite cleats separating the frame aerini leads. The manipulation of two controls is soon mastered, B.30

www.americanradiohistory.com 31'7; R _ . . .-r ;--, . ,- . . . -

Mp@R®oo APRIL r_ltde, 1.027. 463 GV®TIld Broaücast Receiver- Igrsniie Neutresonic Seven. - controls are experienced only when " searching " at it is probable that in the future sets with two controls random for distant stations. Tuning charts drawn with will predominate. The addition of a third tuning control great precision on squared paper are issued with each set greatly adds to the difficulties of tuning, and the differ- showing the settings of all three dials for any wave- ence in this respect between two controls and three con- length. These certainly give sufficient data to get some - trols is much wider than that between one and two. Add where near the required station, but that is all. We found to this the fact that rotation of the '" Indigralsh " dials the accuracy of draughtsmanship to be justified only in in a clockwise direction results in a decrease in the scale the case of the " oscillator " settings; the other two reading, and the confusion of a humble beginner is com- curves were by comparison unreliable, due no doubt to plete. Still we cannot have it all ways, and three controls variations in the capacity of the leads to the frame and is the inevitable price we pay for the unquestionable ad- of the balancing condenser. vantages- increased sensitivity, selectivity, and freedom On the subject of tuning the instruction book is brief. from low- frequency interference conferred by the use The reader is referred to the calibration charts for dial of a high - frequency stage preceding the first detector. In settings, and the only useful hint regarding the niceties any case, the tuning difficulties associated with three of tunin; is in connection with the sequence in which the three main adjustments should be made. The order given is as follows : (r) "Oscillator," (2) "Frame," (3) "H.F. Tuner." To anyone whose previous experience has been with simple " straight " receivers, this order will seem strange, and they will wonder why the frame should not be tuned first to get some strong signals on to the grid of the first valve before playing about with the subsidiary process of hetero- dyning the signals by means of the oscillator. The sequence recommended by the makers immediately becomes logical, however, when it is realised that we have in the local oscillator a first - class heterodyne wavemeter, the calibration of which is much more likely to remain constant than the frame aerial circuit with its flexible leads. The H.F. circuit is tuned last because its tuning, due to the shunting resistance of the anode current of the valve, is probably somewhat flatter than that of the frame circuit. Alternative Oscillator Settings. The frequency of the local oscillator always differs from the frequency of the incoming signal by a fixed number of cycles per-second, this number being the frequency to which the intermediate amplifier valves are tuned. It is immaterial whether the frequency of the oscillator is higher or lower than the incoming signal (frame and H.F. tuner circuits) provided that the differenci in frequency between the two groups, of circuits is the same. Consequently, it will be found that any station can be tuned in at two distinct settings on the oscillator dial, one above and one below the frequency to which the other two dials are tuned. (Tire numbering of the graduations is arbitrary, and, it must not be assumed that the oscillator dial Grneral view cf the receiver opened up for use. Battery, frame aerial and loud- settings will he numerically above and speaker connections are made te a socket and terminals on a small panel situated at the back of the cabinet. below those of the other two dials.) E 31

www.americanradiohistory.com tot Wpg®00 APRIL 13th, 7927. NVoOpilt Broadcast Receiver- Igranic Neutrosonic Seven. - tant stations tuned in without a trace of the local station ; Only one of the two possible series of oscillator settings but it is as well to know the little tricks of which the local has been plotted on the calibration chart, which seems a station is capable in trying to bluff the listener into - pity, as the alternative settings are often invaluable in believing that nothing else is to be heard within ten metres eliminating interference from other stations adjacent in or ten miles. Further observation will show that the ci-avelength. However, the reader can easily -plot the two spurious local station oscillator settings always occur missing curve by taking a few points on well -known at the same points, whatever the settings of the " Frame ' stations. It will be as well to take the wavelength for and " H.F. Tuner " dials, and the reader should have these new points from the existing " oscillator " curve no difficulty in avoiding these if he follows the maker's rather than from the official value assigned to the station, advice in setting the " Oscillator " dial first; it is only which may he temporarily off its wavelength. when searching at random in the wavelength vicinity of the local station that confusion is likely to arise. Selectivity. With a thorough mastery of the niceties of tuning, an An excellent example of the value of the alternative exploration of the wavelength range of the receiver will oscillator setting was afforded while listening in to Cardiff yield a rich harvest of stations. During the course of a on the lower (353 metres) at a distance of only 1¡ miles from 2L0 single evening 4o stations were received (361.4 metres). With the recommended oscillator setting wavelength range, 30 on the loud- speaker, and the re- of 40.5 (according to the chart), the Cardiff station came mainder at good telephone strength. There must be few in at loud- speaker strength, but with a slight background European stations outside the range of this receiver, frün 2L0, which could only be eliminated by turning the though the reception of low -power stations at great dis- frame to the minimum position for the London station, tances will naturally he subject to atmospheric conditions. :i manoeuvre which naturally resulted in a decrease in Long -wave Stations. signal strength from Cardiff, and would have entirely extinguished the latter if the two stations happened to On the long -wave range the following stations were re- have the same bearing at the receiver. On the alterna- ceived at loud -speaker strength : Radio -Paris (1,759 tive oscillator setting of 48 no trace of the London station metres), Daventry (1,600 metres), Moscow (1,45o metres), could be heard, even though the frame were deliberately Karlsborg (1,375 metres), and Hilversum (1,o6o metres). pointed in its direction. Anyone who has tried to cut out A further test of the receiver was carried out in Fleet London at this distance, and has noticed how the emana- Street, where considerable interference is usually experi- tions from the Oxford Street transmitter seem to permeate enced from telegraphic lines and instrunients. Very into a set in spite of the most careful precautions, will little noise was picked up, and several stations were re- realise that this performance is a high tribute to the selec- ceived in spite of the -fact that the receiver was being tivity of the Neutrosonic Seven. It seems a pity to think used underground in a basement. What little interfer- that someone may be deprived of this wonderful per- ence there was entered the receiver through the frame formance through not knowing the use of the alternative aerial, and it was found possible to eliminate the series of oscillator settings. extraneous noise completely by making use of the directional properties of the frame. Incidentally, it may be Tuning Out the Local Station. mentioned that throughout the tests no trouble was While on the subject of oscillator settings it may be experienced through interference from long -wave C.W. as well to refer to a phenomenon which may mystify the stations which are frequently picked up by the inter- beginner while searching for distant stations on wave -' mediate circuits in superheterodyne receivers. close to that of the local station. Let us assume lengths General Impressions. that the " Frame and " H.F. Tuner" dials have been set to a wavelength, say, 5 metres above that of the local The whole equipment gives an impression of soundness station. On swinging the " Oscillator " dial the usual and utility, and, during the period it has been in our two positions at which the set becomes sensitive Neill he hands, behaved with consistent reliability. The several observed and will be characterised -by strong signals from details we have felt it our duty to criticise are unimpor- the local station. If the " Frame " and " H.F. Tuner " tant when compared with such qualities of performance circuits are now reset so that they are, say, 8 metres as sensitivity, selectivity, and freedom from interference, different from the local station, the same effect will he and on these points the Neutrosonic Seven scores full observed on rotating the " Oscillator " control. The mat ks. prima facie conclusion is that one is handling a most un- The price of the receiving set, inclusive of valves, selective receiver, and that it is useless to attempt to phones, and spare long -wave unit, is .44o, to which must receive anything within to metres of the local station. be added £5 17s. 6d. for royalties which the Igranic Phis conclusion, though natural, is quite false; the two Company pay to the Marconi Company and Standard positions at which the local station is received are spurious Telephones and Cables, Ltd. The battery box complete " sensitive spots," and are caused by the oscillator beat- with H.T. and L.T. batteries, multiple cable connector, ing- with the forced oscillations in the frame and H.F. and frame aerial costs ,10 ros. A special battery box 'circuits induced by the strong signals from the local incorporating also a loud- speaker can be supplied to station. The true " sensitive spots " where the oscillator order. beats with the resonant frequency of the frame and H.F. The manufacturers are the Igranic Electric Co., Ltd., circuits must be looked for between or just outside the Bedford, the London office being at 147, Queen Victoria spurious settings. They will he easily found, and dis- Street, E.C.4. B 32

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NEWS FROM ALL QUARTERS.

Melody and Muscle. The " Dream of Gerontius " will he re- The commentators for the Cup Final layed front the Bishopsgate Institute at at the Stadium, Wembley, on April 23 8.15, conducted by the composer, Sir Edward are to be Mr. G. F. Allison and Mr. Elgar, and I can imagine no more suitable Derek McCulloch. There will be com- work for concluding a .Good Friday programme. munity singing before the game and 0000 during the interval. A Frivolous Interlude. 0 0 0 0 The Saturday programme is, of course, Old and New Favourites. of an hilarious nature, the chief attraction Miss Fay Marbe will appear in the being the revue " Advanced Sparks," variety programme from 2L0 on April written by the well -known "L. G." of 18. Other artists taking pact are Elsie By Our Special Correspondents. Punch. This contains what is said to be Carlisle and Bobby Alderson (at the the first " Petrol " song ever written, and piano), Jock Glen (Scotch comedian), and is entitled " Honk, Honk." The cast in- Ann Penn in impersonations. cludes Miss Jean Alliston, whose stage FUTURE FEATURES. e. 0 0 0 experience began at the early age of Sunday, April 17th. eleven, when, as a child actress, was England and Wales Contribute. she LONDON.- Religious Service front engaged at His Majesty's Theatre by the The oratorio, " Emmaus," by Sir Her- Carlisle Cathedral. late Sir Herbert Tree. The difficulty of bert Brewer, organist of Gloucester BousNEMouTx.- Afternoon Concert giving her an efficient school training Cathedral, will be performed at Cardiff relayed from King's Hall during this period was surmounted by the station on April 24th. Sir Herbert will Rooms. provision of a school room under the dome conduct, and the will artists be Hilda Monday, April 18th. of the building, where, in addition to ex Blake and Parry Jones. cellent general instruction, the LONDON. Band Concert. children -Military often enjoyed of 0000 MANCHESTER.- and Lulla- the advantage reading Serenades lessons given by Tree himself. A Royal Broadcast. bies. hard work most have been the order of the day, for The speech of H.M. The King will be Tuesday, April 19th. when lessons in the dome were over it broadcast from Cardiff on April 21st mi LoxDoN.- Symphony Concert S.B. was generally time for a rehearsal in the the occasion of the formal opening of the from Liverpool. theat re. National Museum of Wales. He will be CARDIFF. -" An S.O.S. Announce- The remainder of the evening pro- accompanied by the Queen and will be ment." played by Station Radio gramme will include Mr. Bransby received by Lord Kenyon, the President Players. Williams in his impersonations of Dickens' of the Museum. In addition to the MANCHESTER. -" The Sultan of characters, Messrs. Hatch and Carpenter, speeches a descriptive commentary will be Mocha," Comic Opera by Al- Miss Marie Dainton, and the ever -popular relayed to Daventry of the arrival of fred Cellier. Toni Clare. Their Majesties 0000 and of others parts of Wednesday, April 20th. the ceremony that would not otherwise Easter Services. be distinguishable if the sounds only were LONDON. -" The Spell," a Comedy in one act by Bernard Duffy. Bach's great Passion Music will be. broad- broadcast, such as the Inspection of the cast during the afternoon of Sun- CARDIFF. Madrigal, with ex- Easter huard of Honour and the reception by -The day from York Minster. The interpreta- the President and officials of the Museum. amples by the Cymric 3ladri- galists. tion of this noble work, descriptive of the A programme of music lias been narrative taken from St. Matthew's Gos- arranged by Sir Walford Davies. I under- Thursday, April 21st. pel, will, without doubt, be most ably stand that the fine buildings have already LONDON. -" Violoncello Recital by rendered by the notable choir of the cost over a quarter of a million pounds. Luigi Gasparini with Minnie Minster. Hamblett (pianoforte). The North Country will also contribute Eastertide Programmes. BIRMINGHAM. - " The Constant the evening service, which will be relayed Lover," by St. John Hankin. front Carlisle Cathedral. The B.C.C. has, as usual, given careful 0 0 0 0 attention to the provision NEWCASTLE.-" Q " Farce in one of excellent pro- act by Stephen Leacock and More Laughter and Jollity. grammes during Easter On the holiday. Basil Good Friday, a Children's Service, suitable MacDonald Hastings. Of the programme for Easter Monday to the occasion, will begin at 4.30 p.m., Friday, April 22nd. little need be said beyond the fact that the general tone will be one of variety and will be conducted by St. Christopher's LONDON. - " The Merchant of Training College. This will be followed Venice " (Shakespeare). and light entertainment suitable to the prevalent holiday atmosphere. at 5.0 p.m. by unaccompanied evensong CARDZFF.- Organ. Recital by Arthur 0000 relayed from Christ Church, Oxford, where M. Sims from Central Hall, the choir is perhaps unequalled in the Newport. A Hair -raising Programme? artistic rendering of unaccompanied Mr. A. J. Alan, the mystery story- music. At 6.0 p.m. the Aeolian Chamber Saturday, April 23rd. teller whose broadcasts of hair- raisers Orchestra will play, and at 7.15 p.m. a LONDON. -Press Club Concert. were a feature of 2L0's programmes some service will be broadcast front St. Mar- CARDIFF. - Concert by the St. time ago, will reappear before the micro- tin's in the Fields with an address by our George's Society, relayed from phone on April 20th, when he will make good friend and " wireless vicar " the Whitehall Rooms. contribution to the " My Programme Rev. " Dick " Sheppard. series. B 33

. www.americanradiohistory.com 466 Wilpcdgzo APRIL ,;th, 1927. WOírld " He Knows Me, Like the Cuckoo, by the L.C.C. in the preparation of suitable A Reminiscence of Wagner. the Bad (2) Voice." talks and instructions for the Friday after- Richard Wagner, the father of the con- Mr. Glyn Eastman, wlio is broadcast- noon broadcasting to the Council schools. ductor at the concert on April 7, him- ing from Bournemouth on April 17th, Probably the whole of Friday afternoon self conducted a series of six concerts was with his regiment in a wood behind will be devoted to broadcast lessons and at the Albert Hall in 1877. Richard the lines one night during the war when not merely the last school hour. The Wagner's orchestra " worked zealously some of the men got up an impromptu B.B.C. will give advice and time benefit front beginning to end," according to the concert. Mr. Glyn Eastman's contribu- of their wide experience in the choice of critics. During these concerts Wagner tion to the entertainment was the Torea- suitable installations and their upkeep. I in spite of his strong objections to repe- dor's song from "Carmen." As he was understand that the course of instruction titions of auy passages from his works, singing a party of mounted men carne will begin directly after the Easter holi- allowed encore after encore. Many royal down the road, and, on hearing the song days and will include school concerts by personages were present. coming from the wood, one of them the People's Concert Society, bright de- o o o 0 jumped off his horse and ran towards the scriptions of travel and foreign countries, singer. The rides was Mr. Glyn East- explanations concerning the making of A Whiff of Fresh Air. man's brother, tvho had recognised the English laws and their necessity for the I understand that during the coming singer's voice. The coincidence was the well -being of a civilised nation, the mean- summer the experiment of broadcasting more remarkable because the brothers ing of the British Constitution, talks on sounds from seaside places will be re- had not met for more than a year, and English folk music, dancing, etc., and peated, and probably extended. Last neither knew that the other was at that other subjects tending to broaden the year the noise of the sea and other cheery time in France. minds of the rising generation and en- sounds from Eastbourne, Brighter, 0 0 0 0 courage them to take a pride in their Dover, Ramsgate, Bexhill, Yarntoutlt Apropos the " Variety " War. citizenship and a wider view of their and Felixstowe were brought to the jaded ears in cities, and Experience is said to show that the " duty towards their neighbour " than of listeners our great broadcasting of excerpts from they might otherwise be able to acquire in it is thought that they will again wel- plays and, tends to increase the box office receipts, Iheir, possibly, narrow surroundings. come these heartening perhaps, up in big provides a means of super -publicity for 0000 reminiscent sounds when shut any play, and reaches the public ear Opinion on the National Concerts. towns on hot summer evenings-assum- more effectively than ing, of course, that we get any real any other kind of A mistaken impression has been gain- summer this year. advertisement. Having listened out of ing ground that the National Concerts 0000 curiosity to the broadcasting of a popu- have not been considered a success. The A Tentative Change of Programme. lar actor and heard the laughter and ap- idea was probably engendered by the plause with which his by -play is greeted, sparse attendances at the Albert Hall, Do listeners want dance music iupre- a listener is probably fired with a desire but the t'ecence to talks, variety or orchestral the B.B.C. are confident that performances? The B.B.C. to to see the play of which he has only attendances are not a true criterion. propose heard a small part, and that without the put this to the test by introducing a Incidentally, the audience at these eon - slight action which may he even more in- certs has never dropped below 3,000, but variation in their programme triguing than the bare words. with timings on Tuesday evenings. Dance 0000 the Albert. Hall looks half empty music has hitherto been given between double ! that number Thus it exhibits 10.30 and midnight, after the regular Training the Youthful Mind. opposite characteristic u the to that of studio transmissions. It is now intended I understand that the B.B.C. will co- pint pot which, alas, always appears to to broadcast dance music from 9.30 to peraie with of hold more is case. the Education Committee than actually the 11.0 p.m., and transfer that part of the programme which is at present given between 9.30 and 10.30 to follow on from 11.0 p.m. until midnight. This later part of the programme will provide a distinct contrast to the dance music, being probably confined to light classical music. Dancers will so doubt appreciate the evident desire of the B.B.C. to satisfy their wishes, even at the expense of keeping their announcers and musicians from their needful slumbers for an extra hour and a half. 0 o c The Queen's Hall. At the moment of writing nothing has bourgeoned forth in the shape of an arrangement between the B.B.C. and Messrs. Chappell regarding the future of the Queen's Hall. From a broadcasting,. if not from a musical, point of view, the matter is not vitally urgent. The summer season will soon be upon us, and few folks will fret if large orchestral concerts are missing from tit; programmes during the " dog days. ' As winter approaches, however, the B.B.C. will be seeking a successor to the Albert Hall, which will not be used to the same extent as hitherto. If negotia- Jotts for the use of the Queen's Hall full through the Corporation will not be at the THE GLOUCESTER REPEATER STATION. This almost unknown link in the end of its resources. Covent Garden simultaneous broadcast system of the B B.C. cunt rois the bridging together of stations giving the saine programme as well as providing the intermediate amplification Opera House has been mentioned in con - necessary when working over long distance land lines. nection with some interesting proposals. B 34

www.americanradiohistory.com WAp®Il,sgo APRIL 1311r, ¡927. Myra ah;

TURERS 9 TUS

A Review of the Latest Products of the Manufacturers.

SIMPLE REMOTE CONTROL UNIT. _1 relay control unit is obtainable from windings. It is advisable, however, to It is now becoming common practice Bally. Grundy & Barrett, Ltd., 2, Saint use an additional series resistance for to distribute leads from receiving sets so Mary's Passage, Cambridge, which can voltages over 150 to restrict the current that telephone or loud -speaker reception lie easily introduced into the outgoing in the relay circuit to about 2 mA. The can be obtained in various points remote loud -speaker leads, so that the actual lower limit of voltage required to operate from the set. Many systems have been control is obtained by a switch placed the relay was found to be about 80, so devised for controlling the receiver from in a loud- speaker circuit. When the that the unit also serves to give warning distant listening points, and although the circuit is completed through a loud- when the H.T. battery requires renewing most obvions system would make use of speaker the relay pulls over, closing the or recharging, similar to the arrangement local circuit controlling the filament cur- described in a recent issue entitled " An rent. Circuit arrangements are shown in Automatic Receiver." ` The unit retails - _---- the accompanying diagrams, one of which at a moderate price, and can be relied provides for connecting the loud- speaker upon to give trouble -free service. directly in the plate circuit of the out- 0 0 0 0 put valve, and the other where the loud- SCREENED WIRE. speaker is fed through a condenser. A carefully considered layout must be adopted in constructing a battery elimina tor in order to prevent the leads carrying alternating current taking paths near to or parallel with wires connected in the smoothed D.C. output circuit. It is sometimes recommended that the output leads should be screened in metallic The distant control unit of Messrs. sleeving, though the wire available for Baily, Grundy & Barrett, Ltd. No addi- this purpose is usually very difficult to 3ional leads are required to those feeding the loud -speakers handle and occupies considerable space. Messrs. Ward & Goldstone, Ltd., a pair of wires additional to those oper- Frederick Road, Pendleton, Manchester, ating the loud -speaker, a controlling have recently placed on the market arrangement is required in which the screened wire carrying a covering of metal wires carrying the speech currents also foil. The wire, which is No. 18 tinned control the relay connected to the cur- copper, carries a double covering of rent supply to the receiving set.

A modified circuit arrangement for remote control in which the loud -speaker is fed through a condenser. In this instance a single wire is used for both controlling the relay and conveying the speech or music. The introduction of the relay unit into the output of receiving set was found to have no effect on either the volume or the quality, which is not surprising in view of the very high impedance of the Wire carrying metallic covering for screen- of a ing is useful in the construction of battery relay windings. The relay is similar eliminators. This view is enlarged, the pattern to a telephone switchboard relay, copper conductor being No. 18 S.W.G and is, consequently, robust and entirely reliable in operation. The unit is in- cotton, and after treatment with wax is tended for use with a normal H.T. poten- spirally wrapped with moderately thick Circuit connections of the remote control tial of 120 volts when the operating cur- tin foil. Leads carrying alternating unit when the loud -speaker is connected directly in the plate circuit of the last rent is 2 mA., though voltages as high valve as 200 can be used without injury to the June 9th, 1926, page 756. n 35

4 www.americanradiohistory.com WAp6Ilsoo :168 APRIL 13th, 7927. /nOIfilZ current can, with advantage, 1.)e connected The scale reading as marked reads to wires near the surface of the baseboard. in pairs and bound together along their 5 mA, and by means of a rotating switch In bringing the end of the wire from length, and in spite of the adoption of the maximum range .s extended to read the top of the spool to one of the ter- screened wire should be kept apart from minals a slot is provided down the edge the leads carrying the rectified output. of the spool which on reaching the bottom Screened D.C. leads may also be hound section is held in position by making a together with a bare copper wire and turn round the surface of the winding connected to an earthing terminal. of the bottom section. The undesirable 0000 stray capacity presented between the two ends of the spool by this arrangement INSTRUMENT SCREWDRIVERS. of the connecting leads is, however, quite The amateur is often handicapped by small, owing to the fineness of the wire, possessing few working tools, and even but it would be an improvement were with the most modest workshop equip- this wire to be taken down the centre ment the possession of a góod screw- of the former or connected to a stiff wire driver is essential. To use an inferior slightly spaced from the winding. The screwdriver often results in the spoiling spool measures about 3in. in height and of good components and mars the appear- the circular base covers an area 2in. in ance of an otherwise good set by d iameter. damaging the screw heads. 0000 An attractive range of screwdrivers NEW M.H. SWITCHES. particularly handy for wireless work are Not only in radio- frequency circuits, obtainable from Atalanta, Ltd., 1 -3, but also in circuits associated with audio - Brixton Road, London, S R .9. Three frequency currents is it necessary when sizes are available, the largest being pro- 'three -range miiliammeter useful for plate current using switches to ensure that only very vided with a moulded Bakelite handle. determinations. small stray capacities are introduced. It either 10 nr 25 mA. As the scale of the is no longer considered safe to make use instrument lias been individually calibrated the reading can be relied upon to be accurate to within small limits. The movement pointer is dead beat coming to rest quickly when taking readings. The aim of the manufacturers has been to provide the amateur with an instrument useful for making measurements in connection with wireless receiving sets and a saving of expense is effected by combining three scales in a single instrument. 0000 HIGH-FREQUENCY CHOKE. A useful form of high frequency choke coil, designed for baseboard mounting, is manufactured by the Premier Supply Stores, 20 -22, High Street, Clapham, London, S.W. It is of simple yet reliable construction, the winding being sectioned and A useful series of screwdrivers and box wound into grooves in aai ebonite pillar. M.H. low capacity switch. The tags being spanners suitable for wireless con- near the surface of the baseboard provide structional work The ebonite pieces are turned and for neat wiring while their distribution on either side of the ebonite bar will be found generally convenient for making the A milled ring which can be set at any circuit connection. convenient position along the handle gives an easy turning movement, whilst the of the ordinary Dewar key for switching handle which presses into the palm of the an L.F. amplifier so that although the hand is arranged to revolve. The blade practice of introducing switches into high is well shaped and does not slip out of frequency circuits may be declining, and the slot of the screw, while the advan- the need for a really low capacity switch tages gained by the particular form of for use in L.F. circuits has arisen. handle are quickly appreciated when To meet the demand L. McMichael. using this form of driver. Ltd., Wexham Road, Slough, Bucks. The smallest of the three types is ob- have recently designed a novel form of tainable with a set of three box spanners switch possessing several points of merit. for turning B.A. nuts. The spanners The contacts lie in grooves along the merely fit over the blade of the driver, sides of an ebonite piece in the centre and not only are they useful for turning of which is an insulating spindle carry- nuts in otherwise inaccessible positions but ing a brass sleeve. The knob, which is there is less chance of injuring the faces operated like a plunger, moves the sleeve of the nuts as compared with the use of so as to make connection between the pliers or other forms of spanner. various contacts and the rubbing move- 0000 ment, together with a liberal area of contact ensures reliable connection without THREE RANGE MILLIAMMETER. The Premier baseboard mounting H.F. danger of noise being created in a re- To meet the requirements of the choke coil ceiving circuit by intermittent or high amateur particularly when testing valves, polished and made from ebonite sheet resistance connection with the springs. A. IL Hurt, Ltd., H. A. H. Works, and rod, a pair of terminals being accom- The switch is arranged for either one Tunstall Road, Croydon, have introduced modated on the ebonite base piece to hole panel mounting or for screwing down a three -range miiliammeter. facilitate the running of the connecting to a baseboard, and the position of the s 36

r.aa.,:. , ->- www.americanradiohistory.com.d...;ti as- WIp®hoo APRIL 13111, 1927. Wald 449 tags near the surface of the board is a hectors of coils differing in length. The mount, is an air -spaced winding carried great convenience when connecting up. coils are of No. 16 enamelled wire on ebonite rods. The switch moves with a snap action, rigidly supported between ebonite strips, An unusual and attractive feature is the spindle being supported by'substan- and although only a minimum of solid that of employing a glass panel for tial brass bearing plates. The metal dielectric material is used in the construc- carrying the controls, which, as well as parts are nickel- plated, and the operating tion the coils are perfectly durable and displaying a well- finished interior, permits knob polished and engraved. This new robust. Coils and coil holder are obtain- of the tuning coils being viewed so that component can be safely employed in able if required as separate components. the tuning range can be estimated. practically any circuit system where it is The high -frequency choke coil connected In addition to the reaction condenser desired to produce changes in the circuit in the plate circuit of the detector valve a control of self -oscillation is provided by arrangement by means of switching. is also of special construction, and as a potentiometer connected to the grid It is supplied as a single or two -pole two- well as being provided with a two -pin leak. If the size of the reaction coil is position switch, and can probably be ex not suitably chosen tended to include any number of contacts some degree of over- according to requirements. lap may occur when adjusting the reac- o o 0 o tion condenser close RECEIVER. to the oscillating A SHORT -WAVE point, and the There are comparatively few short- potentiometer will be wave receiving sets on the market, and found useful for pro although amateurs interested in short- viding a critical ad- wave reception usually construct sets' for justment under such themselves, there is a considerable demand circumstances, though for a made -up short -wave set. a slight falling off in A complete two -valve short -wave re- signal strength receiver is manufactured by Stratton & Co.. sults when the valve I.td., Balmoral Works, Bromsgrove becomes an anode Street, Birmingham. The circuit band detector b} arrangement employed is that most b e i n g negatively universally adopted by amateurs and biased. comprises an aerial coil, inductively This receiver is coupled to a tuned closed circuit with a suitable for the re variable capacity reaction. ception of amateur To cover a w_de range of wavelengths transmissions, and interchangeable plug -in coils must be on test both 2XAh adopted, and the simple form of coil and KDKA were mount which is fitted is a feature of the readily tuned in at 'a. set which will recommend it to the short- satisfactory telephone wave enthusiasts. It comprises a series strength, signals be- of sockets arranged along an ebonite ing easily separated Eddystone short -wave receiver. Plug-in coils provide a wide from heterodyned strip, some of which are connected across wave range. Reaction is controlled by potentiometer and variable the in order to accommodate the pin eon- condenser. carrier wave.

" Radio for the Million." London Guide for Motor Owners. " Radio for the Million," Vol. 1, Nu. 2, A booklet which should prove of con - issued by the Mallard Wireless Service TRADE NOTES. riderahie àervice and interest to private Co., Ltd., maintains the standard set by motor owners in the London district has the first issue. Constructional details aie been issued by the Hart Accumulator Co.. äve11 in connection with the "Drake " Ltd., of Marshgate Lane, London, E.15. Nearest Garage i,. M. and " Columbus " P. M. receiving B.T.H. Constructors' Sets. It is known as the " sets. while an illustrated article deals Guide " (London district). The booklet Messrs. The British Thomson- Houston provides useful information regarding with the Mollard P.M. speaker and its Co., Ltd., of Coventry, have produced an abilities in the reproduction of instru- railway stations, theatres, hotels, etc., and attractive booklet giving complete details an ingenious system of classification pro- mental and vocal music. We understand for the home construction of " Resistor " copies may be obtained free of charge vides instant information as to the that B.T.H. constructors' sets. of on application to the Editor, 63, Lincoln's garages nearest to the various places The building of each set is carefully importance and interest. Inn Fields, London, EX'.. or by filling described with the aid of diagrams and 0000 in a coupon obtainable from local dealers. photographs. The reader is also in- " The Brown Budget." - 0000 structed in the assembly of the " Re- The Brawn Budget for March in- B.B.C. Ideal Receivers. sistor " amplifier intended fc,r use with cludes an interesting contribution entitled crystal receivers. We understand from the General 0000 " Bringing the Loud- speaker to -the Masses," and describes the " Brown " Electric Co., Ltd., of Magnet House, Telephony. Kingsway, W.C.2, that the valves used Holland and Java Ideal wireless set, which consists of a in the B.B.C. Ideal receiving sets on Wireless telephonic communication has combined amplifier and crystal receiver. show at the Daily Mail Ideal Home Ex- been established for the first time The issue is of greater interest to the between Messrs. Philips' Laboratories, than to the amateur. hibition were the (arme types DE5. wireless dealer 0000 DE5a, DE5b, and LS5. Eindhoven, Holland, and Bandoeng. 0000 Java, Dutch East Indies. Messrs. Loewe Valves. -A Correction. Philips Lamps, Ltd., 145, Charing Cross In our issue of March 9th last it was New Address. Road, London, W.C.2, state that a tele- stated that the London agency for Loewe A rapid increase in business has led gram was received in reply from the valves had been secured by Mr. J. Dorn. Messis. The Electron Co., Ltd., manu - Dutch East Indian Government con- We now learn from the manufacturers, facturers of the Six -Sixty valves, to seek gratulating Messrs. Philips on their Messrs. Loewe -Radio G.m.b.H., Wiesen - fresh fields and pastures new. Their new splendid transmission, which was carried weg 10. Steglitz, Berlin, that the state- address is 122 -124, Charing Cross Road, out on a wavelength of about 30 ment was incorrect, and we regret the London, W.C.2. metres. error.

B 37

www.americanradiohistory.com VTApdsog APRIL_ r,,tb, WopIlcI 1927.

The 'Editor does not hold himself responsible for the opinions of his correspondents. Correspondence should be addressed to the Editor, "The Wireless World," Dorset House, Tudor Street E.C.4, and must be accompanied by the writer's name and address. B.B.C. HIGH -POWER STATIONS. capped than that the vast majority of London listeners should Sir,Being one of the earliest advocates of a system of five be deprived of an alternative programme? high-power broadcast stations for Great Britain, even in the I have been a listener for over three years, and have longed days of the mushroom growth of the relay stations, I note with for the time when 2L0 would be moved outside London. I alarm in Capt. Eckersley's letter, published in your issue of live about a mile from 2L0's aerial, and it is impossible to cut March 30th, that what the B.B.C. really mean is ten trans- then out unless one uses a very expensive set. mitters, two at each point, radiating London, W.8. (MISS) A. M. J. SHORTER. on apparently widely dif- April ferent wavelengths with equal power. Both in my own Opinion 4th, 1927. and from a study of a recent article by Dr. A. N. Goldsmith in the Proceedings of the I.R.E. on the interference caused by the American 50 kW. station at Boundbrook, I am sure that AMATEUR INTERNATIONAL PREFIXES. live or six 50 to 100 kW. stations located in suitable spots midway between populated areas would only cause less than half Sir, -I have been following with interest the discussions by the interference of the present multiplicity of stations mostly your correspondents and your editorial comments iú The Wire- located in towns. less 1Vorld on thesubject of the new amateur international inter- This new proposal, however, of five double -wave stations is - mediates launched by the I.A.R.U. on February 1st. There worse almost than the existing system, and would tend to seems to be quite a tempest on this topic in your country. The limit most listeners to the two alternative programmes of the discussion in your columns has now sufficiently crystallised to nearest station by blocking both ends of the wavebands with a indicate the existence of several fundamental misconceptions, transmission of high field strength. The original scheme, how- and I beg enough space in your valuable pages to comment on ever, which some of these subjects in the hope that the misunderstanding is sane practicable policy, is for, say, six single - wave transmitters spread equally as regards frequency over the nnny be cleared away. present broadcast wave -band to all broadcast alternative pro- It seems to be a common impress ions in England that the new grammes every day of the week. This would give two alter- amateur intermediates were drawn up hastily, without due con- native programmes to the crystal set from the nearest town, and sultation with other people, and that in general " the Yankee practically unlimited choice to the valve user. A good while in his usual high -handed manner pushed the new inter- back when the N.A.R.M.A.T. were inviting suggestions as to mediates on us." At Paris in April of 1925 the first Inter- improvements on the present system, I drew up the following national Amateur Congress was held, with representatives present from twenty -odd nations, schedule of operation over a period of a week for six high - including a substantial repre- power stations. It brings out very prominently the value of sentation frown the British Isles second in number to the French the scheme representatives only. It was at this Congress thht the Inter- national Amateur Radio Union was formed, its constitution STATION. adopted, and many subjects studied involving international DAY. 1 2 :3 4 5 ti amateur co- operation. The questions on which action was not taken by the Union itself at this Congress were referred to the Mon. A F E D C B Executive Committee of the Union for action. As a result the question of international intermediates was studied by the Tues. P A F E 1) C Execu- tive Committee for something over a year and a half, views Wed. C B A F E D exchanged between the various members, and several alterna- Thurs. D C B A F E PROGR:\TIb1E. tive schemes for intermediates discussed. The scheme even- Fri. D C B A F tually determined upon was adopted by a vote of the Execu- tive Committee of the Union. As this Committee has five Sat. F C but E D B A members, there were many nations not directly represented Sun. c,r G2 G1 t>a G, G, upon it, but England was, in the person of the Vice- president of the Union, Mr. Gerald Marcuse, who, with A, dance music; B, variety and the reservation light entertainment; that British adoption of the new system was dependent upon C, opera and symphony concerts ; D, talks and educa- the approval of tine General Post Office, voted in favour of the tional matter ; E, military bands and orchestral music; action. The new system was F,. vocal announced on November 30th, and instrumental solos; G G G,, etc., 1926, to go into effect February 1st, 1927, and complete Sunday programmes, all different, informa- of appropriate type. tion on it was immediately forwarded to all sections and This at one blow practically solves the programme difficulties, officers of the I.A.R..U., to all national amateur societies, and as, while the crystal user has a better service than at present, to every amateur magazine whose- address was known to the a set with probably only two valves can choose at least four headquarters of the Unions. I submit that this actions was con- alternatives and a modern selective type the whole six. Hence stitutional, that rather than being a hasty plan it was the result every night a listener may have his talks, his dance music, or of long and careful study, and that rather than being an his symphony concert as the mood takes him merely by tuning American idea perpetrated by Americans and fitted only for in the scheduled station, which, using high power, would come Americans, it represents the best thought of a representative in from anywhere in Great Britain. W. J. RANDALL. international group. Nottingham, Mardi 31st, 1927. Your correspondents also make it quite clear that it is believed that it was quite untactful of the Union to announce a system of intermediates without ascertaining the views of the Sir, -In your issue of March 2nd you are sorry for those Governments concerned, that members in many countries run a a ho will live under the aerial of the new regional London risk of trouble with'their authorities by adopting the new plans, station, surely it is better that a few people should be handi- and in general that it was another Yankee mistake to- think B 38

www.americanradiohistory.com W11pcdis@@ APRIL 13th, 1927. t71 Wait cd that because such a system was acceptable in the United States makes no difference what the call is, and this comment is part it would be acceptable in all other Governments. In the con- of the same mistaken assumption commented upon above, that sideration of this question I believe there is a truly fundamental the intermediate is part of the call. misconception of the nature and status of an intermediate. I It is perhaps worthy of comment that practically all of the am very strongly of the opinion that the matter of international British stations that are heard regularly in the United States amateur intermediates is no concern of any Government. It is are employing this new plan of intermediates. I sincerely the inalienable right of _a Government to assign its colts in any trust that as time wears on and British amateurs appreciate fashion it sees fit, but the intermediate is not part of the call. that they were represented in the adoption of the new plan, One of the alternative plans considered when intermediates and that it does not conflict with the system of calls of the were under discussion was a proposal to get the co-operation of General Post Office, they will think better of the plan and the Governments of the world in the assigning of calls that abandon their position as the only group in the world which is would be so constructed as to indicate in themselves the protesting against it. K. B. WARNER, nationality of the sending stations. The Union abandoned Hartford, International Secretary -Treasurer. this proposal for the very reason that it (loes not believe that Conn., U.S.A. it is any concern of the amateurs how the Governments assign March 21st, 1927. their calls -that is the business of the various Governments. On the other hand, the Governments having assigned calls, it is very much the business of the amateur to arrange for his international identification. Imagine an amateur in Czecho- LOUD- SPEAKER REPRODUCTION. Slovakia, with a call assigned by his Government. That Sir, -In connection with the article in the March 23rd issue amateur can get on the air and operate with that call and then by Dr. N. W. McLachlan, may I suggest a little more atten- laboriously say, " I am in Czecho -Slovakia," if he pleases. tion to what our U.S.A. brothers call the " orthophonie " horn. On the other hand, if he is assured that all of his fellows will About a year ago I carne across a report of work carried out understand hirn, he may simplify this practice by transmitting on sound by the " U.S.A. Army School of Sound," and was the letters "ec" before his call, thus shortening his labour. misguided enough to calculate (not a very difficult matter with It is to be emphasised that the " ec " is not a part of the the help of a mathematically inclined friend) the figures for a call, and is not a prefix to the call, as your General Post Office 6ft. horn on the exponential curve to fit a three -guinea. has seemed to view it. The British Postmaster -General has " Ampliou " gramophone attachment I had in use. stated, in connection with his disapproval of the new amateur The plan was handed to a carpenter and the horn produced intermediates, that prefixes have already been allocated by in tin. cypress at a cost of 25s. The total cost was therefore agreements between the various Governments concerned. It is £4 8s to be presumed that he is referring to the international agree- I have a special two -valve receiver for the local station, ment for the assignment of the initial letters of calls for com- 2ZY, on a good outside aerial, and believe I can amplify all mercial stations amongst the various nations of the world, as frequencies transmitted, although I do not claim that the now managed by the Berne Bureau. Of course, this is quite speaker does actually give the very lowest notes. proper and binding amongst calls of this nature, but the The loud -speaker has many times been compared with other amate-ir calls of most nations, including Great Britain, are not speakers costing as much or more and of standard manufacture, so derived. The new intermediates are not part of the call, in every case beating them hollow in every way. in call itself, and they may they do not involve a change the The orthophonie horn 6ft. long transmits vibrations of 100 not even be considered as a prefix to the call. They must be to 5,000 per second, covering practically all musical notes. a new series of abbreviations, co-opera- considered as amateur Middle C is, of course, 256, and an octave lower is 128, the tively agreed upon by the amateurs of the world, through their fourth octave above is 4,096 vibrations second. The of per average co-operative associations, for the purpose indicating horn -type speaker transmits vibrations of 275 to 2,500, and call which a nationality regardless of the Government assigns. the average cone type 150 to 600 vibrations approximately. It was because it was so clearly established in the minds of In my opinion cone speakers will disappear, especially when was a the officers of the Union that the intermediate not part means are found of fitting a Eft. or longer orthophonie horn no effort was made by the Union to secure the into of the call that a comparatively small compass nations in- assent of the Governments of the various before My only trouble during the last twelve months has been the new system. On the contrary, it was regarded the augurating varying amount of modulation (under -modulation) put on the as one of those strictly co- operative amateur problems for the was organised. carrier wave of 2ZY, my best results always being obtained solution of which the I.A.R.U. It is to be when the set has some power to handle. noted that in all the world the only Government agency that Timperley. ARTHUR F. WILLIAMS. is with the matter is the British thinks it concerned General March 25th, 1927. Post Office. The Headquarters Office of the Union hopes that it will become apparent to the officials of your Post Office Department that there is nothing in the intermediates which the agreement to which operates contrary to international Great WOOD STAIN AND POLISH. Britain is a party, and that the scheme was, in fact, planned to avoid such embarrassment. Sir, -I read with interest your article on " Wood Stains and There are many criticisms of the system itself : that it is Polish," and also your correspondent's letter in March 30th a muddleheaded system, that the " e " for Europe is no good issue. May I state that the best mahogany stain obtainable - and won't get through, that the system is not adaptable to and the cheapest--is made from bichromate of potash dissolved Swedish calls, etc. No man -made scheme for anything is ever in water to the strength required ? I say this is the best simply perfect, and it is not pretended that this is a perfect system. because I have found it so myself, having made and polished It is merely the best proposal that has been advanced, consider- a large number of wireless cabinets and other furniture, that ing the varying needs and conditions around the world. There being my trade. will doubtless some day have to be some small adjustments and It is easy to use, being just wiped on with a small piece of some additions to the list. There have been various little diffi- sponge or rag, and left to dry. Garnet polish is the best all - culties occurring in its inauguration, based for the most part round polish to use, but if a " red " mahogany is wanted a on petty national jealousies, but I am glad to say that now little red polish can be worked in, but too much red does not amateur radio around the world is generally settling down into look well. an acceptance and a practical use of the system, which has The first and second coat of polish can be applied with the already demonstrated its merit. The practical use of the brush, but after that, to get a good finish, use a rubber of system has demonstrated that there is no difficulty about the cottonwool covered with a piece of rag soaked in the polish, letter " e " in the intermediate for European countries -it does with just a touch of oil on the face to prevent it from sticking. get through entirely satisfactorily ; in fact, this was demon- This process is quite easy and gives a good finish, which a strated before the new system by the use of the single letter good set deserves. W. R. N. KING. " e " by Spain for some years previous. As to the new system Eastbourne. not being adantable to Swedish calls, of course it is, t.r it March 31st, 1927. B 39

www.americanradiohistory.com " The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply.

A Matter of Taste. lengths at maximum efficiency. We eon - use of your volante control, or otherwise I notice that in the. diagram of the R.B.C. sider, however, that it would be unwise desensitise the set, because with the local three -valve set, there is a fixed con- to recoutnneud you to attempt to modify station going at full blast with your set in denser having a value of 0.01 mid. either of the receivers mentioned. We its most sensitive state, signals would be connected between the bottom end of think you would he well advised to wait far too loud for comfort. Having thus for the tuned grid circuit of the detector the published description of a. fout- desensitised the set, you pick up only va.lve all -trave calve and. L.T. -whereas tae the dia- cet which will appear in the transmission from the local station gram published by you on page 318 this journal at a very early date. without any concomitant hissing. When of your [March 16 issue this is 0000 trying to receive a distant station, how- omitted. Can you tell cue whethe, Tantalum Rectifiers. ever, at full loud- speaker strength, it is th-is condenser is not absolutel y essen- obvious that your set must be put into /' /rase gicr; ,ne fall details of the opera- tial? D. N. C. its most sensitive state, and it is unfor- tion 0/ It tantalum rectifier, and also tunately unavoidable that these noises ate 'l'he purpose of this condenser is to (l, tails for - the construction of suit picked up. Indeed, if you will listen to conduct all H.F. energy direct to the e b apparatus for charging a 4-volt your local station with the set in its most negative side of the filament of the valve aecunrulatar frown. 240 -volt sensitive state, we think that you will rid this condenser, instead of leading it 111 a1.115. N. C. E. readily hear this hissing noise, although over to the wander plug inserted in the We are grid afraid that it would be quite of course the signals will be much louder. bias battery and thus forcing it to beyond the scope of a letter to treat this get hack to filament as it were Even on a local station receiver the viâ the subject adequately. We think you would noise grid bias battery. In the case of hissing can be heard at those times be well advised to read a very practical when speech or music is not being actually receivers employing an H.F. stage in article on the subject which appeared in which tra,ismitted. the H.F. valve is given a negative the November, 1925, issue of our com- o 0 0 0 bias from a grid bias battery at the oppo- panion journal, Experimental Wireless. site end of the receiver, this condenser is 0000 Transmitting Licences. very desirable to avoid setting up instab- Music or Mush. 1 have been a keen wireless enthusiast ility by leading H.F. currents right and a reader of your paper .since across the set to the grid battery. When 1 hare built a five -valve receiver using two 1919, and should stow like to try my a receiver employs no H.F., however, no B.F. stages which is giving ate hand at very good transmitting. Unfortunately, such trouble should be caused, and we results indeed, and an however, I have no knowledge en,,rmous of as to doubt if any difference would be perceived number distant stations the procedure to be adopted in ob- between a receiver built with tonne in on the loud- speaker. I taining the this con- notice, necessary Poet Office denser and a similar one built without it. however, that when receiving licence. I pride myself that I hart any local station at good loud -speaker 0000 IC fair theoretical knowledge of the strength reception is all that could .subject. K. L. F. be desired, but I find that although While there seem to be no hard -and- An " All- wave " Receiver. 1 can easily pick up eitel tune in fast rules governing the issue of amateur 1 have decided to construct either the distant Continental stations on the transmitting - " Everyman Four " receiver loud- speaker at fully the licences, the Postmaster or the same General requires that applicants should " Winless World Five." Would -nolame as my local station, there is it a have sufficient knowledge to satisfy him be possible to use interchangeable continuous background of a kind of transformers for both hissing and that they are capable of doing serious long and short rushing noise. lV/ty is experimental work. .Ability to read weaves, either home -made or of pro- this, and how can I eliminate it? and prietary manufacture? transmit horse signals is essential, and In this S. D. H. the prospective transmitter must have locality 1 find that there is frequent The noise which you hear is possibly Morse interference come definite line of research in view. on every w2ee- due to a large extent to what is known as Should your application (which should 1-_-With except that of Darentry. mush from high power arc stations, but he addressed to the Secretary, G.P.O., D. S. N. the broadcasting station to which you are London, E.C.) not be admitted, you may We agree with you that on the South listening also contributes greatly towards nevertheless be able to secure an arti- Coast it is almost essential to have a set it. Now when you are receiving your ficial aerial permit, and later to obtain designed for working on the long wave- local station obviously you make drastic the full transmitting licence. B 40

www.americanradiohistory.com +ILT. .17 .. i!17=TATI--Tr'll , -- " WApgmo APRIL z,3t1i, 1927. WofIl 473 Crystals that Oscillate. H.F. valve and incidentally acts as a 0.0003 mfd. being a better size, although I .wish to build an " oscillating crystal form of volume control. The use of this we admit that 0.1005 mfd. has frequently rheostat, been used The is receiver," cod shall be glad if you would be possible, but control successfully. point could give vie the necessary details would be very critical, due to the con- this : a good 0.0005 mfd. variable con- for constructing this. T. G. L. siderable variation of filament current re- denser of modern type has a very low We sulting from a small movement of the minimum and reaction feed back is prac- think that by far the best advice we tically can give you is to refer you to our issue control knob. Indeed, it is possible that cut off when the condenser is at a 30 its dated September 1925, where you -ohm rheostat might have an excessive minimum setting, but we think you 2nd, well will find full constructional details, to- minimum value, and you would be will find that many mica dielectric con- 10 densers gether with the usual photographs, wiring advised to use one of, say, ohms. have an exceedingly high mini- diagrams both 0000 mum; in fact, in some we have tested the practical and theoretical, minimum of an instrument such as you desire. An Ambitious Project. capacity has been almost 50- per cent. of the maximum. The of on, considering the construction of a state 0000 I affairs is then similar to that which would speech amplifier having five or six exist if you used a good 0.0005 High or Low ? valves, which is to be used for both modern 1 inn in possession of Iwo loud- speakers, mfd. air dielectric condenser, and owing gramophone and broadcast reproduc- to some one Of a high. re %Monee type, and mechanical effect were unable. to tion. Please let me have a circuit move the other of a loll resistance type. the dial more than about half -way diagram of a suitable arrangement. round towards the minimum 1 should like if possible to arrange F.P.W. position. to throw either of these instruments It should be stated emphatically that 0000 into circuit instantaneously by means the construction of an ambitious instru- of a simple switch. Needless to ment of this sort is not to be undertaken " Free " Grid Bias. say, am using a proper step -down I lightly, and the subject is certainly too I hrice diridccl to niu/cc Ito the "Every- transformer for my low ir.wstance in- in a large a one to be dealt with letter. man Four receiver, fund intend strument, T. P. to U. It would, of course, be an easy matter ude tivo -colt mires throughout. It It will be quite in order for you to to give you a circuit diagram, but with- seems to ni.e that certain modifica- fix up the arrangement you desire by out a discussion as to valve lengthy tions will be necessary, and should following the arrangement we and I give in impedance, coupling components, appreciate information on this point. Fig. 1. It will be seen that the primary anode voltages, we should probably be A. L. C. of the step -down transformer is used as doing you a disservice by doing so. If a choke when using the high resistance you will give us a few further indica- When using two -volt valves throughout. instrument. You can, as is shown in tions as to your requirements, and the it will no longer" be possible to take Fig. 1, make use of the single wire loud- I-1.T. voltage available, we will endea- " free " grid bias for the detector from speaker extension system, which was de- vour to suggest modifications of one or the drop in voltage across one of the fixed scribed in full in an article entitled other of the descriptions published in resistors. These should accordingly be " Music without Muffling " in our issue recent back numbers. omitted, and, instead of returning the 0000 The " Everyman Three " on Long Waves. I have just completed the " Everyman. Three" receiver, from which results are all that could be desired. There is, however, a good deal of interference and fading on the broadcast waveband in this locality, and I should like to modify it for the reception of Daventry. T. R. L. This receiver may be modified for long - wave reception in the same way as the " Everyman Four." This subject was discussed in the " Hints and Tips " section of The Wireless World for Decem- ber 8th last ; but at your very consider- Fig. Modifying the " Everyman Four." able distance from the transmitting 2.- Fig. 1 -A high or low resistance output. station we are fairly confident that you would low -potential end of the tuned circuit to not obtain good results. the junction between them, it should be of February 10th, 1926, or, alternatively, 0000 taken to a suitable negative tapping point instead of returning the loud -speaker Air or Mica? on the common bias battery. The neces- earth, you can return wire to a separate I have built a modified Reinartz receiver sary modifications are shown in Fig. 2. or any of the A it to the earth terminal in which. I have used a commercial large condenser, of from mfd- receiver. Thus, 0.01 up- battery terminals of your choke of very good make, but I fiord wards, may with advantage be connected either a high or low resistance loud- that even with the reaction condenser as shown at C, in order to restrict the to the speaker may be connected output at minimum position the set will not circulation of H.F. currents. terminals of your set, the two -way switch stop oscillating. you tell Although we have stated above over to the relevant Can me that the being thrown where I have gone wrong? I might filament resistors may be omitted, it position. 0 0 0 0 mention that the reaction condenser should be remembered that the detector is 0.0005 mfd. mica dielectric con- valve has a high resistance in its anode "Everyman Four." denser. It does not appear that the circuit ; thus the full emission is not re- I am constructing the " Everyman Four " trouble is due to choke resonance, or quired, and in the interests of economy, a receiver, and intend to use 2 -volt due to too many turns on the reaction resistor of some five ohms or more may valves throughout. Tlrill the rheostat coil; actually I have only 15 turns be inserted as shown at R. If your de- as specified by the designer be suit- on the reaction coil. M. T. N. tector valve normally takes only 0.1 amp., able? P. A. J. It appears to us that your trouble lies a ten -ohm resistor will be suitable. At The 2 -ohm master rheostat can cer- in your reaction condenser. Of course, in the same time, it would be desirable to tainly be used, but 30 ohms is rather a any case 0.0005 mfd. is rather a large con- replace the rheostat R. by one having, a high value for R which controls the denser to use as a reaction condenser, maximum resistance of 10 or 15 ohms. B 41

www.americanradiohistory.com WipgIlwo APRII. ¡3111, 474 World. 1927. Beware of Big Aerials. An Important Precaution. energy would be forced along to the grid I hare constructed a straightforward I ant contemplating the substitution of of the L.F. valve, not only robbing the reaction detector and 2 -L.F. receiver with a resistance- coupled stagee, to my circuit of H.F. energy, but also the ordinary type of reaction, and 1 existing two -valve Reinartz receiver causing instability and bad quality by am experiencing the following curious in place of the transformer coupling introducing H.F. energy into the L.F. phenomena with it, which 1 should be now used. Will you indicate the cor- part of the receiver. glad if you could assist me to rect connections? H. L. 0000 unravel. At a point which is mid- In order to effect this change it is A Reason for Everything. way between London and Daventry I only necessary that the anode resistance find that 1 can get very powerful I should be glad if you will explain why, be put in the place previously occupied in your " Everyman" signals from both stations, the aerial by the transformer primary, series of re- the grid ceivers, you have matte it a habit used being only about 50ft. in total leak be put in the place previously occu- length. In a locality, however, which of mounting your valve holders on pied by the transformer secondary, with four small is considerably nearer to London, but the coupling ebonite pillars, and condenser uniting their re- whether it is passible to obtain the _ further from Daventry, and where spective high potential ends, as is shown sanie results the aerial used is of a generous in Fig. with the sit without 3. Be very careful to connect adopting this procedure. C. H. 101 ft. length, I find that Daventry is up the coupling R. condenser in the position The excellent, and is practically as loud as shown. Obviously, if the coupling con- principal reason for our mounting before, 'whilst London only comes in the valve holders was in order to raise comparatively feebly and I cannot get the valves more clear of the wiring on the set to oscillate on London. One the level of the baseboard in order to would have expected, of course, that facilitate the insertion and withdrawal of London signals would have been the valves without coming into contact, increased and Daventry decreased. with any of the wiring. Doubtless, of Why is this? R. H. T. course, by the exercise of a little ingenuity, it would be possible to use . The cause of your trouble is not hard ordinary valve holders, and still avoid to see. On the point midway between this trouble. the two stations, both of them come in at 0 0 0 G excellent strength, even though the aerial be a small one, as one would normally Reaction Facklash. expect. The vital clues is given by your The reaction. control in my receiver is not statement that in the locality nearer to nearly as smooth as it might be. The London the aerial is of a generous 100 ft. circuit is of the Hartley type, with. This will be all to the good on Daven- a centre -tapped frame aerial, and try's wavelength, but on London's wave- comprises a detector with tiro stages length the aerial damping is probably far of transjotvner- coupled LE'. amplifi- too high, which accounts for your failure cation. I have cluays understood to make the set oscillate. We are of the Fig. 3.- Coupling condenser connections. that this arrangement of rapacity opinion that you will not get the set to reaction should give -eery smooth. oscillate no matter how large a reaction denser were connected direct to the de- regeneration. M. A. E. coil you use ; probably, in fact, if you tector valve plate, that is, on the other Although ihis method of controllin attempt to use a large coil you will ob- side of the H.F. choke, the reaction con- reaction can be extremely satisfactory, it tain some very curious phenomena. If trol would be wiped out, since, of course, will only give good results when the vnlnes you had a shorter aerial at your second a wire runs from this side of the H.F. of the various components associated, with locality we think things would be normal. choke to the reaction coil and condenser, the detector valve are carefully chosen, We advise, however, that you try the the H.F. energy being forced round this and --most important of all -when the experiment of simply connecting a 0.0002 path by the H.F. choke; whereas, if you working voltage of the grid is suitably mid. fixed condenser in series between were-.to make a wrong connection such as chosen with regard to the leak resistance. the aerial lead -in and the aerial terminal we have mentioned, part of the H.F. Instead of returning the lower end of of your set. This will have the effect of the grid leak to the positive side of Um greatly reducing aerial damping, and you filament or to the positive L.T.. battery will find that the set will oscillate readily lead, you are strongly recommended to BOOKS FOR "I HE and receive London at great strength ; join it to the slider of a potentiometer. whilst in spite of the small capacity of the windings HOME CONSTRUC I OR of which will be joined the condenser, you will find that Daventry across the low tension battery. By adopt- will still come in at great strength as Issued in cantunction with" The Wireless World." ing this plan it will he possible to find before. It may be possible for you to an adjustment which gives both good de- " THE . HOME CONSTRUCTOR'S use the same aerial coil in the case of EASY -TO -BUILD WIRELESS SETS,' tection and smooth control of reaction. both London and Daventry, although your by F H. HAYNES. Price r/6 net. By Post, r,o. Al, the same time you should experiment tuning condenser. setting will be greatly "TUNING COILS AND METHODS OF with various values of H.T. voltage. but we should advise also TUNING,' by W kiss. Price si6 net. different, that By Post, s /1o. 0oo0 you try the effect of using a size larger coil "HOW TO BUILD AMATEUR VALVE Multi- stranded Cable. in each case when using this small con- STATIONS," by P. R COURSEY. B.Sc. denser. In all cases of reaction troubles Price 1/6 net. By Post, 1/8. bare same Litz wire with 27 strands al caused by high -resistance earth connec- "THE CONSTRUCTION OF AMATEUR .Vo. 42 gauge wire, each strand being tions, unduly long aerials, multi -wire VALVE STATIONS" by Alan L M. DOUGLAS. enamelled, with a double silk cover - aerials, or aerials running parallel to or Price 1/6 net. By Post. 1/8. ing over all. This, except for the fart in close proximity to walls, it is advis- " THE HOME CONSTRUCTOR'S that individual strands are silk WIRELESS GUIDE," by W. JANES. Price covered, is similar to able that trial be made of this simple 3/6 net. By Post, that specified 3/9. in eeveral of your recent cure. In most cases, of course, such "MAST AND AERIAL CONSTRUC- articles, and causes as we have mentioned will bring TION FOR AMATEURS," by F. J I.should lie -dad to know if it is likely about these troubles only on the normal AINSLEY, A.M.1.C.E. Price rt6 net. By Post, 1/8. to give satisfactory results. S. S. G. This wire broadcasting wavelengths, while Daven- Obtainable by past (remittance with order) from should be fairly satisfactory, try reception and other long -wave recep- ILIFFE & SONS LIMITED, although its use is not recommended by tion will be perfectly normal, which Dorset House, Tudor St., London r.C.4, several designers, due to the possibilities accounts for the puzzlement of many or of Booksellers and Bookstalls of short circuits between individual con- readers on this point. ductors.

B 4 2

www.americanradiohistory.com AN D RADIO REVIEW (15'f Year of Publication)

16. No. 399. WEDNESDAY, APRIL 20TH, 1927. Vol,. XX. No.

: F. H. HAYNES. Editor : HUGH S. POCOCK. Assistant Editor - - Editorial Telephone : City 4011 (3 lines). Editorial Offices : 539-40, FLEET STREET, LONDON, E.C.4 LONDON, E.C.4. Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, Ethaworld, Fleet, London." Telephone : City 2847 (13 lines). Telegrams: " Street. MANCHESTER: 199, Deansgate. COVENTRY: Hertford Street. BIRMINGHAM: Guildhall Buildings, Navigation Coventry." Telegrams: " Autoprees. Birmingham." an Telegrams: "Cyclist 2971 Midland. Telex net 8970 andd hEy." Telephone: 1210 Coventry. Telephone: 2970 and annum. Subscription Rates: Home, 17s. 4d.; Canada, 17s. 4d.; other countries abroad, 19s. 6d. per advised, before making use of them, to satisfy themselves that they As many of the circuits and apparatus described in these pages arere cooveredypat, would not be infringingeaders are

the point of view of the scientific tackling of the problem, TELEVISION. the most interesting of the methods recently discussed the fascinating subject of is no doubt that of Dr. Alexanderson, of America. Dr. N contemplating of one is very soon brought to the Alexanderson appears to have a very thorough grasp television series point of wondering just how far we have the problems involved, and he has undertaken a of the actually succeeded along the path of solu- of experiments to ascertain what al;e the limitations our disposal where- tion of this problem. apparatus at with must be tackled.. one goes solely by the problem If expect that if Dr. the popular reports We fully CONTENTS. continues his re- are published at frequent Alexanderson which PAGE searches with the unrivalled intervals, one is led to suppose EDITORIAL VIEWS ...... 475 resources which are at his dis- that television is already accom- PHOTOTELEGRAPHY AND TELEVISION ... 476 posal, developments of first -rate plished, and that there only remain By A. Dinsdale. importance are likely to result. matters of minor detail to be at- 481. tended to before a living cine- COUPLING CONDENSERS AND LEAKS 0000 L. M. Sowerby. matograph becomes a reality. By A. THE B.B.C. RECEIVERS. We cannot help feeling regret NOVELTIES FROM OUR READERS 484 O much interest has been that in a matter of this kind, Two AND THREE VALVE RECEIVING shown in the three wireless which is of such scientific interest, 485 S receivers demonstrated by the those who are working on the prob- CURRENT TOPICS 492 at the Ideal Home Exhi- lem do not seem to realise the ex- R.B.C. MANUFACTURERS' NEW APPARATUS ... 494 at Olympia that we decided tent to which confidence in their in- bition PRACTICAL HINTS AND TIPS ...... 495 the circuits of these re- ventive efforts, however humbly to give OF TRANS- in The Wireless World, they may regard them themselves, THE CONSTANCY B.B.C. ceivers were published in our is shaken when the inventor gives us ii MISSIONS ...... 497 1 and they issue of March róth. Since those a gilded story through the medium By W_ H. F. Griffiths. appeared there has been a of an over -imaginative and per- ... 501 circuits BROADCAST BREVITIES ... for constructional haps wholly unscientific journalist keen demand NEWS FROM THE CLUBS ... 503 j these sets. It who is far more concerned in being articles on building LETTERS TO THE EDITOR ...... 505 that the able to justify startling headlines is, of course, understood PROBLEMS 506 not be de- in giving the bare, and per- READERS' actual B.B.C. sets could than for the reason haps somewhat dry, facts with scribed in this way, not prepared which he is supplied. We believe that the B.B.C. was used in that, although a good deal of interesting work is being to disclose the make of the various components in the direction of solving the problem of television, building the sets. We have, therefore, taken the B.B.C. clone up receivers up to the present little of real practical value has circuits with the values indicated and built yet are achieved. It is true that crude representations of using components of our own choice, and these sets been are objects have been reproduced over a distance by one or now being described. The two- and three -valve sets four -valve receiver will two different systems, but we have no proof as yet that dealt with in this issue, and the issue to appeal any one of these systems is likely to produce results form the subject of an article in an much beyond their present stage of development. From shortly. H 5

www.americanradiohistory.com Wpagog 476 APRIL loth, 1927. Was' Ild

An Account of Dr. E. F. W. Alexanderson's Experiments. By A. DINSDALE.

There is no reason why such an apparently impossible dream should not come true, and come true within a relatively short space of time. It is not so many years ago since Owen D. Young, of the Radio Corporation of ' America, expressed, at a banquet, the hope that radio would soon give us visual means of communication. This idea seemed rather far- fetched to several technical men who were present, but work upon these lines was immediately started, and to -day there is a commercial wireless picture service in regular operation between London and New York. It takes about twenty minutes to transmit one of these pictures across the Atlantic, whereas Bernard CONTEMPLATION of the works Shaw's of great imagina- imaginative scene foretells the direct vision tive authors inevitably leads one to of distant the conclusion moving objects. Our experience of the cinematograph that the really great discoveries and inventions of indicates that in order to portray a scene in such a our modern civilisation are first visualised by them long manner before that all movement is faithfully reproduced, six- they become accomplished facts. Jules Verne's teen descriptions complete pictures per second must be flashed upon the of submarines and aircraft are cases in point. screen. Under the stimulus of such imaginative writings it would Retentivity of Vision. appear that scientists then set about the business of making the author's dreams come true. Each succeeding picture is slightly different from its In the realm of television many fiction stories have predecessor, and, due to the phenomenon known as been written in which television, in some form or another, " retentivity of vision," has been the observer sees, not sixteen brought in as an accomplished fact. An out - separate pictures, standing but one single picture full of smoothly example of this is to be found in George Bernard flowing movement. Shaw's well -known play, " Back to Methuselah," in Thus, in order to achieve television, we must which is described a scene taking place speed up in the year 217o, our phototelegraphy system so that a single picture where the head of the British Government can holds confer- be transmitted in one -sixteenth of a second instead ences with his Cabinet ministers several of hundred miles twenty minutes. From twenty minutes to one -sixteenth away. At his desk is a switchboard, and in the back- of a second is a tremendous stride, but one which Dr. ground is a screen upon which, when he selects the right Alexanderson has set about trying to make, starting with key at the switchboard, a life -size picture appears of the phototelegraphy as the art is already known to -day. man to whom he is talking, a picture which portrays There is nothing particularly novel in Dr. Alexander - faithfully all the movements of the distant minister. son's phototelegraphy apparatus, which is of the well - Work Based upon Phototelegraphy. known revolving cylinder type. His researches in this direction have tended rather Taking this to investigate and solve- the incident in Shaw's play as his " text," problems involved in the transmission Dr. E. F. W. Alexanderson, of the picture im- of the General Electric pulses over great distances by wireless. Company, Schenectady, N.Y., The accom- has embarked upon a line panying photographs, which were made at Schenectady of experimental research to see if he cannot make Shaw's at a rate of sixteen square inches per minute, will vision an actual demonstrable fact. serve to give some idea of the degree of success which has e 6

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WApSIl®s0 477 APRIL 20111, .1927. tiopika Phototelegraphy and Television. Although better results appear to have been obtained - that attended his efforts. They were made as a preliminary by the modulation method, Di-. Alexanderson states the study of the commercial transmission of photographs by his researches have tended to make him consider to wireless over long distances. adaptation of the telegraphic method of communication The recording instrument used in making the originals picture transmission as one of the essential problems. deleterious effects of, these pictures is a standard General Electric oscillo- Only in this way, he thinks, can the and he - has devised graph, with some adaptations. of fading and static be eliminated, a method of sending half -tones which takes advantage of The Radio Link. the more efficient methods used in radiotelegraphy. It is distort or Up to the present radio communication has been carried obvious that fading and static would seriously sent by wireless over a great out by means of two distinct methods of signalling : by mutilate a picture being the modulation and by interruption. The older of these two distance. Dr. Alexanderson's method makes use of methods, and by far the more sensitive and economical, is latest devices of long -distance, high -speed radiotele- that of interruption, and it has been developed to a high graphic practice, wherein it is equally important to pre- the automatic degree of efficiency, as is evident from the example shown vent mutilation of signals in order that signal recording apparatus shall be able to produce un- below. raphic signals. The modulation method, on the other hand, is corn- blemished records of the transmitted tele

[Courtesy C.E.C. of America. Comparison between pictures transmitted (left) by the modulation method and (right) by the interruption method. paratively new, and not nearly so sensitive and economi- Briefly put, radiotelegraph engineers overcome fading to produce a cal. It is the method employed by our broadcasting by using at all times sufficient amplification fading. stations, and for a given power the effective range of the readable signal during the worst intervals of a pre- modulated signal is only about one -third or one -quarter The output signal is prevented from rising above that of the interrupted signal. determined value, sufficient for recording, during periods Picture transmission by wireless has been tried by both of strong incoming signals, by throttling it down by a limiting valve. these methods of modulation. The transatlantic picture means of a circuit arrangement employing remains constant service is operated by the interrupted method of The output signal of the receiver thus introducing a signalling. at all times. Static is taken care of by has experimented with both methods, threshold value of signal into the receiver, so that nothing Dr. Alexanderson In this page is shown a comparison of the results is received unless the signal exceeds this value. this and on of the On the left is a picture clipped from a news- way, so long as the signal strength exceeds that obtainable. from paper and transmitted by means of a modulated signal. prevailing static, the effects of static are eliminated right is the same picture transmitted by inter- the signal record. On the devices rupted, or telegraph, signal. The other pictures repro- Thus far it has not been possible to adapt these so that for duced here were transmitted by the modulated method, a to modulation methods of communication, long distances the modulation frequency of 3,000 being employed. This picture transmission by wireless over is obviously better frequency was superimposed upon a carrier wave, just as interruption, or telegraphic, method is done in broadcasting. fitted to give unblemished results. s7

www.americanradiohistory.com 478 WApaseo APRIL 20111, WmIld1 r927. Phototelegraphy and Television. - Producing Half tone Effects. Dr. Alexanderson obtains half -tone effects by causin his transmitting mechanism to analyse the picture int o five or more separate shades, such as white, light grey medium grey, dark grey, and black. This is done auto matically, and the receiving mechanism also reassembles the shades automatically. Various methods can be designed for translating these different light values into radio signals. One method is to use a separate wavelength for each shade, requiring, in this case, five wavelengths. The pictures shown here, however, were made by a process which employs only one wavelength. This is accomplished by causing the transmitting mechanism, at every moment, to select automatically the shade that comes nearest to one of the five shades. A telegraphic signal is then sent out which selects the corresponding shade in the receiving machine. This process is not so complicated as it sounds, for the telegraphic code by which the various shades are selected depends upon the synchronism of the two machines, which synchronism is necessary under all circumstances. Thus black areas in the picture at the transmitting end are reproduced at the receiver by exposure of the sensitive paper to the recording light spot during four successive revolutions of the paper -carrying cylinder. Light grey is produced by a single exposure during one revolution only, and no exposure during the three succeeding revolutions. It will be seen, therefore, that the receiving cylinder must be run at four times the speed of the transmitting cylinder, but with the same speed of axial movement. [Courtesy G.E.C. of America.] Picture transmitted by wireless with the modulated system. The The overlapping exposure is modulation frequency was 3,000 and the time taken for trans- progressive and the whole mission four minutes thing is a continuous process, tending to graduate evenly the various degrees of light and shade in the picture. The relative difference in definition between these pictures is due, according Speed Limitations in Television. to Dr. Alexanderson, to the effect of the sluggishness of the tuned Turning now transmitting aerial. The to the question of television, Dr. Alexan- two- minute picture was not nearly derson queries whether the medium so sharp as the eight - with which we are minute picture, but was, nevertheless, sufficiently dealing is capable of functioning at the so to enormous speeds be acceptable for ordinary television purposes, supposing of signalling required in television work. Necessary such a degree of definition could be obtained at television units in the system are the photoelectric cell, the amplifier, speeds of transmission. the aerial and the wireless wave. Of these, the first two Since there is so much sluggishness on a wavelength.of employ the medium of the electron, which is extremely 12,000 metres, let us examine the effect of reducing the fast; but the use of wireless waves imposes certain speed wavelength limitations to 12 metres, equivalent to a frequency of on account of the limited number of wave- 25,000 k.c. If the photoelectric lengths available. cell, amplifier and the light control can keep up with The lines upon this enormous frequency, which Dr. Alexanderson is working the wireless wave will perform appear to indicate that, its task and transmit a in order to obtain high quality single picture, the definition of which reproduction of a television will be equal to the image, it will be necessary to two- minute picture as transmitted make use of several on the longer wave, in wavelengths, each carrying an imper- one -thousandth part of two fect image. At minutes, i.e., in approximately the receiving end all these imperfect or one-eighth of a crude second. This is not equivalent to cine- images will be combined to produce a single image matograph speed, of high but it is sufficiently close to give us a quality definition. fairly good picture. This conclusion has been reached as a result of some Another difficulty, experiments where a life -size television image is made in the transmission of single pictures required, as suggested at different by Bernard Shaw, is in sufficiently speeds on a single wavelength of 12,000 illuminating the metres, screen at the receiving end in the ex- or 25 kilocycles. Pictures sent in two minutes tremely limited amount were reproduced of time available. somewhat crudely ; those sent in four In any television receiver minutes very much better, so far developed or suggested, and when the time of transmis- the incoming picture impulses control sion was extended to eight minutes the degree of bril- for the same picture liancy of a source of light which is focussed the reproduction was well -nigh perfect. upon the screen and caused, by optical means, to sweep rapidly up B 8

- www.americanradiohistory.comAi pl'I1F-.. c.M.1.i.xr:hriMiifiYl Wpd®@o 479 APRIL loth, 1927. Wofficl Phototelegraphy and Television. wide, around which are mounted twenty -four mirrors - inches by four. This drum and down and across the screen, gradually covering it all each measuring about eight intensities of light. In order to give the is direct -coupled to a high -speed electric motor. with varying reflected of a complete picture this traversal When the drum is stationary a spot of light is observer the impression square, and must be arranged to take place practically on to the screen, which is about four feet of the screen As instantaneously; otherwise the observer would see what this spot of light is the brush that paints the picture. vertically across actually occurs spot of light gradually crossing the the drum revolves the light spot passes -a set at a slightly as it swings rapidly up and down. the screen, and then, as a new mirror, screen light spot passes In order to get an image of fair quality the least we different angle, comes into line, the on a track closely adjacent to can be satisfied with is ten thousand different values of across the screen again, but on until the light intensity. This may mean that the spot of light that of its first traversal. This action goes mirror mechanisms will pass' across the screen in roo parallel paths, each entire screen has been covered. Such workers, and there is path being subdivided into roo different light values. have been used by several television particularly novel in- If this process is repeated over and over again at the nothing about this one which is of moving ,speed of sixteen separate pictures per terest. picture lies in it means that r6o,000 changes of light value, or The novelty of Dr. Alexanderson's experiments second the difficulty picture impulses, are required per second. Such a speed the method being tried by him to overcome of sufficiently illuminating a large screen in the extremely short period of time available. is impossible to do this by means 5C IIEN As explained above, it r- of a single spot of light, using any known methods of MULTIPLE illumination and optical distribution of the light beam, uGHT -SPOT so Dr. Alexanderson has been experimenting with seven light spots instead of one, for by so doing 49 times as Mleaoz ozu:ñ much useful illumination can be obtained. first glance it is not easy to see why the gain in light 5oue o D2ING At SCVEN LIGHT MOTOR. should be as the square of the number of light spots used, BEAMS but on consideration it will be seen that, with one light spot in use, and a drum carrying 24 mirrors, the spot of light will pass over the screen 24 times. If seven light sources and seven spots of light are used, however, there will he a total of 168 light -spot passages over the screen LENSES for every revolution of the drum. Multiple Light -spots. The advantage of using seven beams of light in this gain I) fashion is two -fold. First of all there is a direct of illumination of 7 to i. Secondly, there is the further the light beam must Arrangement of Dr. Alexanderson's experimental television advantage that the speed at which projector. travel over the screen can be reduced approximately one - for each individual light spot now has only 24 Moreover, a good seventh, seems, on the face of it, inconceivable. cover instead of i68. basis of more than tracks to picture really requires an elemental Although the light itself may travel at any conceivable speed for the light im- loo lines, so that a more suitable speed, there are limitations to the speed at which the pulses would be somewhere about 300,000 per second ! This also holds good for of mirror 'drum can be driven. Not only must we employ wireless waves capable method of causing a light beam to also any other mechanical such an enormous speed of signalling, but we must The mirror drum used by Dr. Alexan- brilliancy that it will traverse a screen. employ a source of light of such derson has already been designed to run at the highest even though it has only illuminate the screen effectively, possible speed. to illuminate any one 1- 3oo,000th of a second in which The only way to speed up the movement of the light given spot. would be to reduce the diameter of the the most brilliant beam, therefore, Dr. Alexanderson admits that, given also the size of the mirrors, but mirrors one - design the opti- drum and arc lamp we know of, no matter how we as large as those at present in use would only across the screen, we seventh cal system for sweeping this light one -seventh as much light and thus neutralise the brilliancy to illuminate a large reflect cannot obtain sufficient advantage gained by using seven light spots instead of of light. screen with a single spot one. Dr. Alexanderson's Experimental Television Projector. There is another advantage arising out of the use of each individual light-spot For the purpose of examining this particular problem the multiple light beam. Since of the speed necessary and attempting to solve it, Dr. Alexanderson has built an need only move at one -seventh cover the entire screen, experimental television projector consisting of a source of when a single spot only has to impressions to be made on the light, a lens and a revolving drum carrying a number of the total number of light amongst the seven beams. mirrors. The drum is built after the style of a flywheel, screen can also be divided up necessary, for a well- defined about 4ft. in diameter, with a flange about ten inches As described above, it is 139

www.americanradiohistory.com - rce,>F.nn1G.té dad ¢8o WBTsIl@oo %pIld APRIL zot11, 1927.. Phototelegraphy and Television. - ary upon the screen, shows seven points of light arranged picture, to make at least 300,000 light impressions on the like the end section of a piece of seven -stranded wire. screen per second. If only one light -spot is employed it Tests have been made with this model television pro- must be capable of handling this enormous number of jector to demonstrate the method of covering the screen light changes. By using seven light- spots, however, each with individual seven beams working simultaneously in parallel. beam need handle only 43,000 impressions per As the mirror second. drum revolves, these seven beams trace seven lines at once on the screen, and then pass over another A modulation speed of 43,000 per second is high, ac- adjacent cording track of seven lines until the entire screen has to our present radio practice, but it is more within been covered. reason than 300,000, being only about ten times as high In a complete television as the speed apparatus, of course, each of we use in broadcasting. the seven light -spots There is would have to be independently con yet another point in favour of the multiple trolled by the beam system. distant transmitter, so that each traced its own individual crude picture. For this purpose seven It is easy to design a television system that will give photoelectric something cells would have to be arranged in a cluster like 40,000 picture units per second, but the at the transmitter, results would each cell controlling one channel of a be so crude as to have no practical value, multiplex radio system. for work already done on phototelegraphy has shown that at least 300,000 units per second will be necessary to Seven Channels Required. give satisfactory results for television purposes. For this purpose Dr. Alexanderson suggests that a This speeding -up process, unfortunately, is one of Hammond multiplex system could be used with seven in- those cases where the difficulties increase as the square termediate carrier waves, which, as he puts it, are of the speed, and the main cause of the trouble is the " scrambled " and sent out by a single transmitter, and fact that we have to depend upon moving mechanical unscrambled apparatus. at the receiving station so that each controls If sòme means were available for sweeping one of the seven a beam of light beams. light across a screen at ultra -high speed with- He further suggests that out the use seven television carrier waves of mechanical apparatus, the problem would may be spaced too kilocycles he easier apart, so that a complete of solution. But such means are not available television wave -band at present, should be 700 k.c. wide. Such a so the ideal picture on a large screen, contain- radio channel might ing at be placed between 20 and 2 r metres. least 300,000 picture units, cannot be obtained by and he is of the means opinion that if the use of such a wave- of mechanical apparatus and a single light -beam. band will enable Dr. Alexanderson's us to see across the ocean it will be way out of the difficulty, then, con- assigned to a worthy sists of purpose. reproducing on the screen seven crude pictures, No details of Dr. Alexanderson's containing only 40,000 transmitting mechanism picture units each, and so inter- are available, and he lays no claim lacing them optically that to having completely the combination effect is that solved the problem of television. He merely of a single good picture containing states that 300,000 units. " Our work has, however, already proved that In his experimental projector Dr. the expec- Alexanderson has tation of television is not unreasonable, and that it may arranged his seven light sources close together in star be accomplished with means that are in our possession at formation, so that the multiple beam, when seen station- the present day."

Electric Furnaces. A New Battery Eliminator. The subject of electric furnaces may seem only indirectly connected with wire- TRADE NOTES. The use of battery eliminators is daily less, but, as they are used becoming more and more popular, the to a consider- ordinary able extent in the manufacture of valves dry H.T. battery having the and in research work generally, the obvious defect of gradual deterioration description of the Wild- Barfield small A Portable Frame Aerial. and sometimes letting one down at an awkward and electric furnaces for laboratories and Now that " summer is y -comen in " unprepared moment. works, lately issued by Messrs. Auto- the thoughts of wireless enthusiasts Messrs. Radio Instruments, Ltd., 12, matic and Electric Furnaces, naturally turn to Hyde Street, New Oxford Street, Lon- Ltd., 173- portable receivers. A don, 175, Farringdon Road, E.C.1, will prob- useful adjunct to these is the W.C.1, have sent us a descriptive " Climax leaflet of their new ably interest many of our readers. This Folding Frame Aerial " manufactured by H.T. battery elimina- well -illustrated pamphlet describes the Messrs. Climax Radio Electric, Ltd., tors for either A.C. or D.C. supply, giving alternatively the price various furnaces and temperature-con - Quill Works, Putney, S.W.15. Two models for the trolling apparatus supplied by are made standard complete apparatus and of the com- the firm -the type suitable ponents necessary and covers a wide range. for wavelengths of 250 to 750 metres, for those preferring and to build up their own 0000 the series -parallel model for 300 to 750 H.T. eliminators. and 750 to 1,650 metres. The leaflet is entitled " The RIght Coils for Constructors. Mains Supply Unit, " and will be sup- 0000 plied in quantities to interested From Messrs. Collinson's Precision dealers. Screw Co., Ltd., Macdonald Rd., Lon- The Helping Hand. 0000 don, E.17, we have received a descriptive Messrs. Leslie McMichael, price list of Ltd., have their " Colvern Coils for issued a convenient little booklet describ- Change of Address. Every Modern Radio Circuit," the six- ing their well.known wireless components The Automatic Coil Winder teen pages of which are devoted to useful and giving useful and Elec- data covering their information concerning trical Equipment Co., Ltd., to " Winder various coils, formers their use to the best advantage. The and condensers, with practical notes House," Rochester Row, S. W.1. They on contents include their latest H.F. chokes ask us to state suitable circuits. and multiple that they still retain their switches. old telephone number -Victoria 4350. B IO

-:aa .:..-4r,.a.wYi i www.americanradiohistory.com nr.' 9Et- eo-:,rM.iF?rx^rriOYÍ-.^f=ÖWiI"r1 1927. VfiwsIl®@g 481 APR1T, 2ot1a, Wo1eIld COCPi[ d.INC CONDENSERS AND LEAKS. How to Calculate the Correct Values for Any Frequency.

By A. L. M. SOWERBY, M.Sc.

N the matter of the coupling condensers and grid leaks grid of the valve in such a circuit is exactly that of the inter- to be used in choke and resistance coupled low -fre- grid bias battery, even if a to-megohm resistance quency amplifiers, there are at present two distinct venes between the battery and the grid. schools of thought, resulting in the recommendation of So far as the D.C. aspect of the circuit is concerned, utterly different values from these small but important com- then, the resistance of the grid leak is of no significance ponents. It is the purpose of the present article to trace whatever ; it remains to consider it from the standpoint the reasons for the older views, and to define clearly the of the signals themselves. values actually desirable. Fixing the Grid ¡leak Resistance. The old values that have been accepted unquestioningly I will show until recently are, roughly speaking, 0.05 to 0.25 mfd. Reference to the skeleton diagram of Fig. A.C. for the coupling condenser, and 0.25 to 0.5 megohm for that the leak is connected between a point of high and the leak. Two reasons are usually given for these values. (signal) potential (namely, the grid of the valve) will flow First, that if 'a grid leak of higher resistance is used earth, so that a certain small alternating current assists any charge that may appear on the grid will leak away through it. This alternating current in no way by only slowly, and that until this charge has leaked away in the operation of the amplifier ; on the contrary, source the amplifier will be " choked," or at least will deliver tending to lower the potential of the grid it is a signals of poor quality. Further, it is commonly believed of loss, and must therefore be kept sufficiently small to a high- resistance that a low- resistance leak is necessary to " allow the grid he negligible. This implies, of course, bias to get to the grid." Secondly, the high value of a leak, which, as we have already seen, is perfectly suited coupling condenser is explained by stating that since it is to the D.C. conditions of the circuit. necessary to pass, more or less equally, signals of all frequencies down to, say, 5o cycles per second, a large condenser is required, for a small one would have too high an impedance, and so would prevent the lower musical notes from reaching the grid of the valve, resulting in partial suppression of the lower notes. Two Common Fallacies. Let us analyse these statements a little more closely and try to see exactly how far they are justified. Evidently, if a charge collects on the grid of the valve during reception, and then leaks away again through the grid leak, grid current is flowing. In the early days of expen- broadcasting, when power -valves were ruinously Fig. 1.- Schematic diagram of resistance -capacity coupling sive, and very little used by the ordinary amateur, valves between two valves. were habitually overloaded, so that grid current was To fix on a suitable value for this leak we must take almost inevitable. Moreover, it was then of no great into consideration the fact that it is more or less in consequence, because the early loud -speakers gave such with the anode resistance or choke, which is also poor quality that a little grid -current distortion more or parallel between a point of. high signal potential and made no audible difference. Nowadays, however, connected less earth. (Note that " H.T. + " is, if we neglect the re- conditions have changed ; we use power valves in place of the H.T. battery, at the same signal potential of R- valves to operate our excellent modern loud -speakers, sistance as the filament, despite the difference in D.C. potential.) and no avoidable distortion, no matter how small, can he then, to make the resistance of the grid tolerated. It will suffice, high with that of the anode circuit ; if the Since in any modern amplifier grid current is elimin- leak compared grid has not less than ten times the resistance of the ated by proper adjustment of grid bias, in conjunction leak resistance we can regard any losses produced by it with high H.T. voltage, and an avoidance of overloading, anode A higher resistance than this, though it coupling condenser will never acquire a charge. The as negligible. the increase the overall amplification, grid leak, then, need not on this account he made of low may not appreciably way detrimental. resistance. And further, if no grid current flows, the will not be in any case, if the anode resistance has a value of the grid leak need not be low " to allow the To take a concrete 150,000 ohms, as recommended by the makers grid bias to get to the grid," for in a circuit where no value of type valves, the grid leak should current flows there is no voltage drop across even the for use with D.E.5B of not less than if- megohm, and any highest. resistance, as a moment's consideration of Ohm's have a resistance Law will show. The grid bias actually applied to the value above this may be used. B II

www.americanradiohistory.com sé WIp@11®2g Woelid APRII, 2oth, r927. Coupling Condensers and Leaks.- (r) shows the same thing; high values either of C or of If a choke is used in place of an anode resistance, the R tend to make n equal to unity, when E, equals E. calculation of a minimum value for the grid leak is not Since, however, both R and C must be very large indeed easy, in even the rare case when the inductance of the to make n actually equal to unity (the ideal case) we must choke is known. However, this is of no importance set some arbitrary lower limit to n at some arbitrarily whatever, since a 5- megohm resistance is not likely to be chosen frequency. too small for even the most massive choke, and may be The writer has taken, as a basis for calculation, the used in all cases. condition that the voltage E, shall not less Having be than qo dealt with the question of the grid leak, con- per cent. of E at a frequency of 5o cycles per second. sideration of suitable values for the coupling condensers On this basis we shall lose in our amplifier not more than is our next concern. It has been stated, by those who advo- LOWEST NOTE HIGHEST cate the use of coupling condensers of PIANO NOTE OF MI OF PIANO the order of 0.0005 mfd., that it is only necessary to use a condenser of capacity e C" C"' i large compared with the grid -filament 1 o capacity of the succeeding valve. Actu- ally, it will be seen that the capacity o required is chiefly determined by re- "/ % the SWWAN/.fl sistance of the grid leak, and that when n o e./-' MIll the grid -filament capacity of the succeed- 0 4 ing valve is large, the capacity of the _ ,fi coupling condenser must be reduced to 0 keep the general tone of the music at _ normal level. 32 64 128 258 512 1 n2a o nea Calculating Capacity of Coupling FREQUENCY Condenser for a Given Grid Leak. In effect, as can be seen from Fig. 2, Fig. Curves 3.- showing effect on frequency characteristic of a single stage due to which is a simplified version variations in the coupling capacity. Curve (1) is any of the rele- table, the for of the co.ubinations in the other fractions showing the ratio of the other condenser values to the capacity vant part of Fig. r, the coupling con- chosen, the grid leak remaining constant. denser and grid leak are connected in series between ro per cent. per stage of notes of this frequency, which a point of high A.C. potential (the plate of V,), and is just less than an octave above the lowest note of the earth. An alternating current then flows through the piano. circuit,.and we have to choose such a value for C that the The value of capacity necessary voltage -drop to give any predeter- E, across R shall be nearly equal to E, the mined value of n at any desired frequency output voltage, for all frequencies. is given by the formula : A simple calculation, given in the appendix, shows that the ratio n between n E, and E for various frequen- C= . (2) cies is given by the formula : wRSn$ Fr R which is simply formula (r) rearranged. É =n= (I) VR2 Some Representative Values. + w2C2 If we now put n = 0.9 in formula (2) we find that in which w 27r = x frequency, and the remainder of the if R = 5 megohms (which is the most generally useful symbols have meanings the implied by Fig. 2. value, since ro- megohm leaks are not easy to obtain), C must have a value of not less than o.00r3 mfd. to satisfy this condition. Corresponding capacities are given in GRID OF V2 4 the Table for all usual values of grid leaks. Grid leak. Coupling condenser. (Megohms) (:llicrofarads) E, 0.25 ...... 0.026 0.5 ...... 0.013 1.0 ... 0.0065 2.0 0.0033 FILAMENT 3.0 0.0022 5.0 0.0013 10.0 0.00065 Fig. 2.-Equivalent current to Fig. 1. Those who read the apperdix will observe that in this Clearly, the higher the resistance of R, and the greater treatment of the subject the effect of valve and other the capacity of C, the greater will be the voltage drop stray capacities has been neglected. The plate -filament across R, the and smaller the drop across C, as can be capacity of V and the grid -filament capacity of V2. seen from Fig. 2. without any calculation. Equation together with stray capacities due to the resistances and B 12

www.americanradiohistory.com Medsoo 483 APRIL loth, 1927. Wora Coupling Condensers and Leaks. - any switches their holders, the wiring, and HIGHEST NOTE NOTE that may be used, are all shunted across LOWEST OF PIANO OF PIANO MIDDLE t the grid leak, so that the voltage de- C. 1 C,,. C C, C veloped across it will be less for high frequencies than for low. Since this results lo in a lowering of the tone of the music, I -..011Ìi- while we are at the moment concerned o with finding the capacity large enough to ilfi 06 avoid undue raising of the tone by cutting 111_ -- - notes, our momentary neglect ___ off the low o WIE-IAIN of this effect of stray capacities is justi-

fied. o The use of capacities above those given G noticeably alter the %-' in the table will not 1 .,._,. .... wo 32 --- tone of the music ; capacities below those given will raise the tone by cutting out FREQUENCY the lower notes. In view of the fact that lessen the amplification of stray capacities for various coupling capacities -two stages. the higher frequencies, the writer has Fig. 4.-Frequency characteristics found it advisable, in a resistance ampli- interesting, perhaps, are Figs. 4 and 5, which fier, to use condensers of little more than half the capacity More in a similar manner the tone of music after 2 given, in order to keep the general tone of the music at represent stages. The ordinates in these figures are about the right level. In the final output, of course, and 3 such the cube respectively of the corresponding both high and low tones are missing to quite a consider- the square and Fig. 3. able extent, but the quality nevertheless appeals to the ordinates of the writer would like to point out that ear as being excellent. In conclusion, there is only one difficulty likely to be met with in using condensers and leaks LOWEST NOTE HIGHEST NOTE of the values herein suggested. That PIANO OF PIANO MIDDLE OF is, that perfect insulation in the coupling iC,., C C, C C' C" C"' t condenser is even more essential than r in amplifiers of standard pattern, owing ° _... to the high resistance of the leak. o I/. ///i' NOW___ DvIIAll APPENDIX. II/ In the circuit of Fig. 2, if 0 I = current flowing EI_-_._-- then, taking the circuit as a whole, o 4-I E ,_-C(i I . VRa 32 64 12 1024 2,0' + WzCa ' ' FREQUENCY Also, for the resistance only, I_ Fig. 5.- Curves equivalent to Figs. 3 and 4 for three stages. if Equating these two values tor 2, we get In passing, it is amusing to recall the oft- repeated Et E equally amplified in a R / I statement that " all notes are Ra resistance amplifier," and to compare this glib nonsense + with the real facts. = n, the equation becomes Some idea of the effect on the tone of changing the Now putting -t 3, coupling condenser is given by the curves of Fig. n ] The verti- which have been calculated from formula (i). R 1 cal scale represents n, or signal strength, while the hori- + a,aC'a plotted on the zontal scale represents frequency, or C of the logarithmic or " musical " scale. Each " " It piano is marked. n (1) in the 1 The curve r represents the capacity prescribed + (,af,`a any given grid -leak value ; z, ¡, etc., represent table for by a little rearrangement, we can get capacities of double, half, etc., this value. It will be From this, that the lower frequencies fall off rapidly as the C= (2) seen (ORA/ capacity is reduced. I - ns B r3

www.americanradiohistory.com 484 WIp® hog Waili& APRIL 2011/, 1927.

NOVELTIES FROM OUR READERS

MIND A Section Devoted to New Ideas and Practical Devices.

VALVE CONTACT. H.F. CHOKE. or dials, get chipped and are thereby Faulty contacts between valve legs A rubber grip such as is used for spoilt for use on a panel. Such clips and sockets is a frequent cause of cycle handle -bars, and procurable for may easily be filled in with black failure in receiving sets, and can be a a few pence, makes an excellent for- sealing -wax. Plenty of wax should source of great annoyance when try- mer for an air -cored choke. The best be used, the excess being removed ing out a new set for the first time. type has a length of about 4in. with with a fine -cut file. The repair may To make quite certain that all valve a maximum diameter of I4in. There be finished by polishing with some contacts are perfect, a small piece of fine abrasive, such as french chalk, coil spring may be inserted in each on a wash -leather pad. -F. P. socket. Three or four turns cut from 0000 a spring taken from a petrol lighter will be found quite satisfactory. - A SCREW -DRIVER HINT. T. H. W. Screws in awkward and obscure 0 0 0 0 corners of receiving sets require long screw -drivers for tightening up. CLI ' CONNECTIONS. Often there is difficulty in engaging The spring clips illustrated in the Rubber handle-bar grip used as 11.F. the end of the screw -driver in the sketch are constructed from safety choke former. screw slot, particularly when the pins by removing the metal cap screw -driver is inclined to the axis of and bending to the shape shown. are about zo grooves in the centre, the screw. The direction of the screw The point should also be cut off and wide, and if the grooves are fitted with fine wire HEAD the end of the wire bent upwards to such as No. 47 SLOTTED prevent the connector from being D.S.C. an efficient choke will result. accidentally pulled off. It takes up but little room, and, If difficulty is experienced in open- the wire being well spaced, has a low self- capacity. J. F. F. 0000

REPAIRING MOULDINGS. It sometimes happens that bakelite or ebonite mouldings, such as knobs

VALVES FOR IDEAS. Readers are invited to submit brief Indicating mark to show direction of details, with rough sketches, where grinding on the end of a screw -driver. necessary, of devices of experi3 Spring connectors constructed from safety mental interest for inclusion in this slot can be seen, but it is difficult to pins. section. A dull emitter receiving tell which way the grinding on the valve will be despatched to every screw -driver is pointing if the lighting ing the connector with the fingers, reader whose idea is accepted for in the interior of the set is poor. i.e., if the connector twists sideways publication. To overcome this difficulty, a slot when pressure is applied, thin metal Letters should be addressed to the Editor, should be cut in the head of the plates may be soldered to each wire, "Wireless World and Radio Review,' Dorset coinciding with House, Tudor Street, London, E.0 4, and handle the direction as indicated by dotted lines, to afford marked " Ideas." of grinding, as shown in the sketch. a better grip. -A. B. -A. G. E. B 14

_--- erir,Y4:Y::..411.41u.-aí, Jttlaeittr7a,m.:>www.americanradiohistory.com l..,r ,z+,aler.lwwoia.- r Design and Construction of Simple Loud = speaker Sets. the designs, CONSIDERABLE interest has been created by operated. Certain considerations lie behind at the recent " Ideal for although each of the three sets shown were intended B.B.C. demonstrations has which showed types of sets to be used as local station receivers, one of the aims Homes " Exhibition, without com- for home reception. As a result of the been to provide a high degree of selectivity recommended is evidenced by the B.B.C. having entered into the field of set designing, plicating tuning. An aim at selectivity fixed condensers in the lead is not surprising that many listeners are diligently con- introduction of the small it the use of a parallel the designs put forward. The circuit systems between aerial and aerial inductance, forming to capacity, as well as of the three sets which were exhibited are entirely ortho- tuning condenser of large maximum dox, and rather take one back to the type of receiver used by the provision of reaction. in the early days of broadcasting. Novel features have 0000 been avoided, but the principal merit of the sets is the TWO -VALVE B.B.C. RECEIVER. arrangement by the use of interpretation of the circuit up to, perhaps, ten miles and new types of valves correctly For loud -speaker reception modern components from a main broadcasting station and assuming the use of reaction, this receiver can scarcely be improved upon. As it is usually a question of cost that limits one to the use of two valves, extravagance has been carefully avoided in making up this set, though where the merit of a particular component has a bearing on the results which will he obtained the quality of that component has been the first consideration. Material Required. The fixed aerial condensers are of the small mica dielectric type. For aerial tuning it is immaterial whether the variable condenser follows the S.L.F. law, as shown, and almost any type of aerial tuning con- , Details the front Eia3j32 in. dia. denser will be suitable, C, 3/16 a nl dia. D 1¡8 inndiát,y countersunk tor ZNo 4hwood acre/ws

13 17

www.americanradiohistory.com VIp@Dago APRIL 2011,, WoucIl0 1927. 2 and 3 Valve Receiving Sets. - though in allowing space for the sweep of the moving plates of the condenser actually fitted in this instance, sufficient room has been pro- J `S-.. vided so that other condensers can be fitted without modification of the panel lay- j out. A geared dial is em- 3 4 _"J ployed which is convenient, ----¡ - .-J 22 though not essential, for . ' 73/4

aerial tuning. The two -coil . ¡ 4 holder is L.-.;._L.-.; geared, and of a ! r, 34 °: i:i _. ;a, {. =`.. r-- -4 type that causes the reaction .- 'r - . } 11», -t t.., coil to drop away from the front of the panel. The cir- L t

:------cuit requires the grid con- ""t denser and leak to be sepa- < ' Ea.; rately mounted. As a high- tension 2Y2 battery of Izo volts 23/4 3Y; 4 has to be used a 15 -volt grid 14. bias battery must be fitted, and it should be provided Positions for securing the components to the with tappings at every r baseboard (2 -valve set). volts. No bridging condenser is provided across the H.T. fore on the left, which rather lengthens the terminals wiring and -a permissible economy. A cabinet of high prevents the layout of the parts following the positions quality has been selected, as this adds much to the value shown in the theoretical diagram. The operating dial ;s of the receiver. The cost of the necessary parts and balanced on either side by the " on and off " switch and materials given on page 489 is 15s. £4 the coil- holder knob, while the output terminals are con- Layout. veniently arranged for connecting to telephone or loud. speaker leads at the centre or lower edge of the panel. It is essential with only a single tuning to dial locate On the baseboard practically all the components fall on it in the centre of the comparatively small panel. The two lines, which is preferable to merely distributing them coil holder, also associated with the aerial circuit, is there- uniformly over the area, and actually facilitates wiring. For ease of construction the terminal strip is mounted hori- zontally, the connecting wires being passed through holes in the hack of the cabinet. The panel is not supported by brackets, and is secured to the fillets provided at the ends of the cabinet. Working Instructions. All components should be to hand before the construction is commenced, so that should anv minor differences from those specified above exist, the necessary changes can be made before drilling is commenced. A great deal of trouble is saved by pur- chasing the cabinet fitted with panel and baseboard, and these should be carefully fitted together with three No. 4 x ¡in. brass screws. The reader is reminded that nickel -plated screws are available and look well. Interior view of the finished two-valve set. After locating the positions a 18

www.americanradiohistory.com 487 APRIL 20111, 1927. Wpe®00 WOpIld. 2 and 3 Valve Receiving Sets. - for the holes on the panel small in. holes should be drilled through, taking care that the point of the drill does not wander, and subsequently enlarged to the size specified in the drawing. Many small hand braces will not accommodate the large twist drills required for clearing the bushes of the one -hole fixing components, and the holes can either be enlarged with a small rat -tail file, working to a line,- or with a large twist drill held in a pair of grips and following a guide hole. A polished panel finish is probably more durable than a matt surface, while a line finish, such as is obtained by rubbing from end to end of the panel with fine carborundum cloth, looks well. Before screwing the components down to the baseboard all tags should be scraped and tinned. To facilitate making connections with the aerial and battery terminals a row of suitably spaced holes should he made in a piece of thin tin plate and then cut to form a series of tags with ends about ein. in length, so that when mounted on the under side of the strip the ends project along the edge of the ebon- Practical wiring diagram. It may be necessary to reverse the leads connecting to the reaction. coil. ite, shown in the practical as iring diagram. Tinned copper wire, No. 18 S.W.G., straightened by stretch- ing, is used for wiring up. Operation and Results. A No. 5o coil or its equivalent inserted in the aerial circuit gives a tuning range of about 245 to 535 metres. A 15o coil should be used for tuning to Daventry, and it may be mentioned that, to provide critical reaction control, the reaction coil should have fewer turns than the grid coil. The effect of reversing the leads to the reaction coil holder should be tested before completing the wiring. If the aerial' consists of less than Soft. of wire, the aerial sKould not connect to the tuning coil through either of the con - densers. It -is only when better selectivity is required, or when the aerial is rectification Circuit diagram of the B.B.G. two -valve receiver making use of grid a full rooft. in length, that the series with reaction, series connected aerial condensers and transformer L.F. coupling. B 19

www.americanradiohistory.com 488 Mpg@g0 .APRIL zotla, rgzg: , o tlllc

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valve set. Sizes of holes : A, 3r8 ; in. dia. B, 7/32 in. dia.; C, 1 8 in. dia, countersunk for wood screws; D, 118 in. dia. countersunk for No. 6B.A. screws. No. 4 condensers are brought into circuit. At II miles from stages, and in the P.I., B.T.H., Osram, or Marconi 2L0, using a short loft aerial, this set gave signals of good series may be selected valves giving an amplification of strength in a normal sized room with a sensitive loud- from 5 to 7. For good local station reception speaker of the horn type. Using an L.F. telephone receivers and valve such as a D.E.5, B.4, P.M.6, or S.T.62 by critically adjusting reaction other may be B.B.C. and Contin- used in the detector stage, followed by a D.E.5A, ental stations were easily tuned in. B.1 1, Daventry at about P.M.256, or S.T.63, using 120 volts, H.T. and 7o miles was appreciably weaker than 2L0 a grid at II miles, bias of perhaps somewhere between 7.5 and 15 volts. though its signals could he easily followed from a loud- 0000 speaker without concentration. On a good outdoor aerial THREE -VALVE B.B.C. SET. Daventry not only came in at ample strength, but Radio - Local station reception is again the intention with Paris could be tuned in on a loud- speaker. the three -valve receiver put forward. What has been said in Any good general purpose valves may be used in the two the case of the two -valve set concerning aerial tuning and

The simplicity in the arrangement of components for the threevalve set is shown in the above rear view.

9 20

www.americanradiohistory.com 71pggoo . 489 APRIL loth, 1927. WopH

B.B.C. TWO -VALVE SET. 8 Nickel -plated terminals A, E, Al, A2, H.T. -i-, -, L.T. -1-, 1 S.L.F. condenser, 0.0005 mfd., with friction control, lin, dial - (Belling & Lee). (Ormond). P -{-, P (Belling & Lee). 0.0003, No. 610 type (Dubilier). 2 Ebonite sh ouded terminals, - 2 Fixed condensers, and off" switch (Wright & Weatre). Fixed condensers, 0.0001, No. 610 type (Dubilier). 1 "Wearite" "on 2 battery " Ever-ready " (Portable Elec. Light Co.). I Grid leak. 2 meg., Dumetohm and holder (Dubilier). 1 -16 volt G.B. mahogany, 14 x 7 X 8in. deep (W. and T. Lock). I Two -coil holder. 1 Cabinet, 1 Ebonite panel, 14 X lttt. I "Ideal" transformer, 2.7 to 1 (Marconi). & 1 Baseboard. 2 "W .B." valve holders (Whiteley, Boneham Co.) Wander plugs, sistoflex, screws, wire, etc. B.B.C. THREE -VALVE SET. mfd. (Brandes). 1 Grid leak, 0.1 meg. (Igranic). 1 Condenser, slow motion, 0.0005 ready" (Portable Elec. Light Co.). Newey " (Pettigrew & Merriman). 1 -16 volt G.B. battery, "Ever- 1 2 -coil holder, " H.T. 1, + 2, H.T. L.T. -i-, 0.0003 and base (Igranic Elec. Co., Ltd.). 9 Terminals, A, Al, A2, E, + -, 1 Fixed condenser, L.T. "Eelex" (J. J. Eastick). 2 Fixed condensers, 0.0001 and bases (Igranic Elec. Co., Ltd.). -, 2 Terminals, L.S. -i-, (Igranic). 2 Fixed condensers, 0.1 mica, (T.C.C.). - cabinet, mahogany, 21 X 7 X 7Lin. deep (Car- condenser, 1 mfd. (T.C.C.). 1 "Cameo" 1 Fixed Co.). holders (Benjamin). rington Man. 3 Valve 91 x 7ín. -off" switch, "Trix" (E. J. Lever). 1 "Cameo" panel, 1 "On- and " brackets. Anode resistance, 150,000 ohms (Varley). 1 pair " Cameo I Baseboard. Anode resistance, 250,000 ohms (Varley). 1 1 Wander plugs, flex, screws, wire, sistoflex, etc. 1 25 -henry choke (R.I.). 2 Grid leaks, 1 meg. (Igranic).

panel and baseboard equally applies in this case. Anode The components are situated on the use of reaction as they appear in the has been substituted in place of the leaky almost in the same relative positions bend rectification the apparatus associated with probably bringing about an improvement theoretical circuit diagram, grid condenser, in a unit alongside of it, pro- quality and giving a very smooth control of self- oscilla- each valve being assembled in wiring with short leads. The detector valve, tion by means of the reaction coil. It is doubtful if reducing simple equipment, and associated aerial terminals occupy course to the use of reaction will be necessary at a distance tuning -hand end, the components being liberally spaced say, 15 miles from a main station, which should prob- the left of, the swinging reaction coil. Most of the ably not be exceeded if the really first -class quality of to accommodate is assembled in line and packed into small reproduction which this receiver is capable of giving is L.F. equipment space, the arrangement' giving a clean, workmanlike ap- to be maintained. set, the telephone terminals are resistance -coupled, using wire - pearance. Like the two -valve The two L.F. stages being supported on and mica coupling condensers. To are in the front, all other terminals wound anode resistances of the baseboard. All of parasitic currents and the ebonite strips attached to the edge prevent the circulating for 5s. in the L.F. amplifier a resistance necessary parts can be purchased £6 setting up of oscillation Details. in the lead to the grid of the second valve. Constructional is inserted and brackets are supplied with the The loud -speaker is operated through the usual choke and Panel, baseboard it is necessary to finish the edges of the condenser. cabinet, although

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assembled (3 -valve set). The setting out of the centre lines on which the components are

13 2 t

www.americanradiohistory.com 490 Wilpacgoo APRIL loth, 1927. Woh1Ilca1 2 and 3 Valve Receiving Sets.- Brackets are obtained for baseboard, which supporting the small fixed in this case is 7-ply and, if desired, condensers, while insulating pieces varnish or polish. will need to be made The brackets also will need to be up to support the grid resistance secured, and for and leaks; sin. ebonite fixing the panel with a view to avoiding is used for this, and the clips attached the appearance of screw together -with con -, heads on the front, 6B.A. screws necting tags with fin. 6B.A. screws should be used, and nuts, -the heads drilling slightly smaller holes nearly being recessed to avoid contact through the with the baseboard. No. r8 panel and forcing the screws home without wire is used for connecting need for tapping. up, and all battery leads are run on the face of theTboard. Small ebonite cleats, with

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Pictorial view of the wiring showing the actual route taken by the leads. It is advisable to slightly elevate the coil holder, and a grooves to engage on the wire, are made up from rain. piece of kin. ebonite should be slipped underneath it before ebonite sheet, and attached at the points screwing shown in the down. A screw should only pass through one wiring diagram. Construction will be found quite of the holes, straight as the holder is primarily held in position by forward, without any trouble as to fitting the `components, its one -hole fixing. To facilitate making connection to the all being simply screwed down to baseboard or panel. The flexible leads the of holder a small piece of kin. ebonite one difficulty that may arise is the fitting of the terminal carrying two pairs of tags is secured to the baseboard strips at the hack of the cabinet. immediately If one so desires the behind the coil holder. cabinet may be ordered with the apertures already made B 22

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Wflp®Ilsoz 497 APRIL 20f1/, 7927. WGIsIlca 2 and 3 Valve Receiving Sets. - for the strips, so that, having o + H. T. 100V carefully filed the ebonite 250,000n to fit the holes, the width of 0 0001 WIRE WOUND O + HT. mfd TO CARRY 180 V the baseboard is adjusted so 1mA 150,000 0 15- 20 HENRIES that the ebonite strips come WIRE WOUND CARRY TO CARRY O-HT. flush at the back. 2 mA L fd Valves and Operation. E E ZrnAt-o L. S. o--- om= oolows As the valves used in the 1 ó \ 0 mfd receiver demonstrated were b o of the Osram type, D.E.5B, D.E.5, and D.E.5A could E', be recommended for use in uY o the three stages. It might ó be found possible, without o impairing quality, to employ L T a D.E.5B as the second valve, with a critical adjustment of grid bias, though the SWITCH D.E.5 will, of course, he entirely satisfactory. A receiver, though similar in tuning arrangements to the two-valve set, employs The three -valve with a choke loud -speaker feed. valve of the L. S.5 or even anode rectification, is resistance coupled, and is provided L.S.5A type may replace the and as to actual range valve in the last stage for operating a large loud- sponds with the two -valve receiver, its to bring in distant speaker, and in this case the grid bias battery should of reception, as indicated by ability not so effective, but for really be increased to two 15 -volt sections. In the P.M. stations, it is perhaps quite station little can better it. series the first valve may be a P.M.5B, with a critical ad- good quality from the local fifteen miles from the local justment of H.T. voltage and r or 3 volts negative on For the listener situated within 25 if he erects a good grid, the second valve a P.M.5X, and the output valve station, or perhaps up to miles the the best possible repro- It would be useful to have a P.M.6 avail- aerial and who needs a set to give a P.M.256. and without a the P.M.5X could be moved into the detector duction with a good grade loud -speaker, able so that recommended. At stage, using the P.M.6 as the first L.F. Alternatively great outlay. this set can be thoroughly reception of Daventry can the P.M.6 could he tested in the place of the. P.M.256. a conservative estimate good loo miles. As to tuning range, the performance of the set corre- be obtained at a radius of

EFFICIENT H.F. AMPLIFICATION ON THE NORMAL AND LONG WAVEBANDS.

This receiver makes use A rear view of the " All -Wave Four," which is to be described ln next week's Issue. of interchangeable H.F. transformers of modern design. B 23

www.americanradiohistory.com 492 WflEpasoo `vJodd. APRIL loth, 7927.

News of the Week in Brief Review.

A BRIGHT IDEA. THE IRISH IMPORT TAX. "HUSH HUSH" The newly appointed STATION IN PARIS. Federal Radio An Anti -Tax Campaign has been Excitement has Commission in America has received been aroused in Paris a initiated by the joint efforts of the lead- over the discovery by the police letter from an enthusiastic listener de- ing wireless interests of a manding that in- Ireland with the secret wireless transmitting station of immediate steps be taken object of securing the removal of the high power, to eliminate atmospherics. present believed to be operated for 0000 import duty on wireless goods. the purpose of communicating Bourse Parliamentary deputies PARIS WIRELESS EXHIBITION. are being re- prices to foreign countries. minded that the tax is having a ruinous But, whatever purpose Paris will hold its Fourth Wireless effect the of the trans- Exhibition on the development of broadcasting missions, nefarious or otherwise, the from October 28th to Novem- in the -Irish Free State. authorities ber 13th at the Grand Palais, under are agreed that the station in- the It is pointed out that under existing fringes the Government telegraphic auspices of the Syndicat Professionnel des conditions the retail mono- Industries Radioelectriques. prices of wireless poly. The two operators, together with 0000 apparatus are beyond the purse of the four foreign bankers, are accordingly average citizen, and, owing to the conse- being charged with CONFUSION WORSE CONFOUNDED. quent restricted committing this The clarification market, there is no possi- offence. of the American bility of establishing a wireless manu- ether, now choked up with Apparently the existence of the station more stations facturing industry in the country, so that was first than it can carry, remains a dream suspected on account of a of the a protective tax is not needed. number of mysterious future, despite the machinery recently set advertisements ask- up by the American 0000 ing for wireless operators. Congress to deal with FOUND. the problem. According to our Washing- 0000 ton correspondent, these The owner of a copy of the 1927 edition THE RANCE OF ATMOSPHERICS, arrangements of The have been rendered practically useless Wireless Amateur's Diary and Members of the Incorporated Radio through the failure of the Senate Notebook which has been found in a Society of Great Britain have received to ap- train is invited an prove the allocation of funds for their to make application invitation to attend a meeting of the operation and the pay for it at the offices of this Journal, giv- Boyal Meteorological of the Commis- ing Society, 49, Crom- sioners. evidence to prove ownership. well Road, South Kensington, S.W.7, at It is considered probable that, pending a settlement of the monetary question. the three commissioners may be willing to serve without pay for eight or nine months. 0000 BY BEAM TO AUSTRALIA. At 6 o'clock on the mbrning of April 8th the official beam wireless service was opened between this country and Australia. On the previous day a preliminary demonstration was given in the Central Wireless Office of the G.P.O., and com- plimentary messages were exchanged between Mr. L. S. Amery, Secretary of State for the Dominions, and Lord Stone - haven, Governor -General of Australia, Mr. Bruce, the Australian Prime Minister, Mr. Hughes, and others. The messages from London are despatched ria land line to Grimsby, whence they travel 10,000 miles to the Australian receiving station at Rockbank, and from there via land line to Melbourne. In the reverse direction signals travel from Mel- bourne, via land line to Bailan, whence they are transmitted to Skegness and conveyed by land line to London. It is expected that the Indian and AUSTRALIAN BEAM SERVICE. The Marconi receiver at Skegness, an important South African beam stations will be link in the new chain linking London and Melbourne. The photograph shows a corner of the receiving room with the land line connections ready for testing within a few weeks. recording instruments. and high speed

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www.americanradiohistory.com a tti?tïE APRIL loth, 1927. Wfipdmo MALI 493 5 o'clock this evening (Wednesday), when an interesting report on " The Range of Atmospherics " will be brought forward and discussed. The opener of the discussion will be Mr. R. A. Watson Watt, B.Sc., of the Radio Research Board. A limited number of tickets of admission will be available for members on application at the offices of the Radio Society. 53, Victoria Street, Westminster, S.W.!'. 0000 WORLD -WIDE AMATEUR TESTS. An international test to be held in \l,c for the purpose of ascertaining the most dependable amateur transmitting stations in each country, and to be participated in by amateurs all over the world, has just been announced by the Communica- tions Department of the American Radio Relay League. The test will start on May 9th, to last for two weeks, and will be open to anyone in any country of the world possessing an amateur transmitting and receiving station. Messages will be filed for delivery in all countries, and the amateur station in each locality showing the quickest, most accurate, and most consistent performance in connection with the forwarding of these messages to their destinations will receive a suitable certificate designating it as an official foreign contact station. TRANSMITTER WHO RECEIVES HIS OWN SIGNALS. Mr. Boyd Phelps (2EB) Readers interested in the test should of Jamaica, New York, with his short-wave transmitter specially designed for work make immediate application for further on 5 metres. In his band is a 5 -metre wavemeter. As he cannot discover an amateur who will receive on such a low wavelength, Mr. Phelps has installed an particulars to the Secretary of the Ameri- automatic transmitting key; he is thus able to tour the country in a car and pick can Radio Relay League, Hartford, Con- up signals from his own station I necticut, U.S.A. 0000 was organised by the American Telephone dance music was being broadcast from " SOME THIN NEW." and Telegraph Company. The experiment Daventry ; and whether, seeing that this Amateur transmitters occasionally get was first performed on the telephone line, annoyance was due to the fact that more than they expect in the direction but subsequently the party witnessed a holders of experimental licences availed of reports, etc. The following string of number of vaudeville " turns " trans- themselves of their privileges on these questions has been received by a Glas- mitted by wireless from the Whippany occasions, he" would take steps either to gow transmitter from an enthusiast in broadcasting station, New Jersey. For forbid any testing to begin until Daventry Rockdale, Texas. the benefit of a large audience, the pic- had closed down, or, alternatively, to " Dear Mr. - -, tures on the small' glass square were pro- terminate the programme from Daventry I saw in the Dallas News where jected on to a screen, and although the at 11 p.m. on Mondays, Wednesdays, and you heard one of our stations over in definition on the screen was not so clear Fridays ? U.S.A. that is some thin new to us. . . it was generally agreed that the demon- Sir W. Mitchell- Thomson said that his I hate to put you to so much truble by stration was a remarkable success. attention had not previously been called asking so maney questions but we are The person whose picture was trans- to this matter. He was surprised to proude that you can get our stations in mitted (says the Times New York corre- learn that there was any appreciable U.S.A. I wish we could get your stations spondent) sat in front of a cabinet con- interference by experimenters with the on what meter do youall broadcast and taining three large photo -electric cells, reception of Daventry programmes, as the what is some of station call letters and each 15in. long. Across the subject's wavelengths which experimenters were what power is your station how maney features ran a beam of light directed to authorised to use were far removed from watt please tell me all aboute your successive points by a rotating reel, with the 1,600 metres wavelength of the radios I have been in the radio buisness 2,500 points pierced in the edge, in such Daventry station. If Sir F. Hall would for aboute four years but we cant learn a manner as to direct the beam to every bring any particular case of which he to much we have to maney stations in part of the feature. The changing might have knowledge to the attention of U.S.A. we have some thing over sixteen currents set up in the photo -electric cell the B.B.C. they would no doubt imme- hundreds stations I guess that is the were amplified 5,000,000,000 times before diately investigate it. reason we cant do much on distens so transmission. So clear was the " pic- I guess my letter is tire some but I hope ture" on the receiving screen that it was 0000 you will ans it and tell me all aboute possible to distinguish the person's teeth stations so I hope to here from you. and the ash on the end of a cigarette. A Cenotaph Broadcast. Yours Truley In reply to Major Cohen, who asked why he had refused the request of the 0000 British Legion to broadcast their annual TELEVISION DEMONSTRATION IN WIRELESS AT WESTMINSTER. Cenotaph service on Whit Sunday, in NEW YORK view of the value of the service to thou- In a square of glass tin. across, a BY OUR PARLIAMENTARY CORRESPONDENT. sands of ex- Service men and widows and group of Press representatives at the Bell dependants of ex- Service men who were laboratories in New York saw the figure Interference by Experimenters ? unable to be in London on that date, of Mr. Hoover, the U.S. Secretary of Sir Frederick Hall asked the Post- Lord Wollner said that no such request Commerce in Washington, speaking on the master- General in the House of Commons had been made to the Póstmaster- telephone 200 miles away. last week whether his attention had been General. The matter fell. within the pro- This successful demonstration of tele- called to the annoyance caused to vince of the First Commissioner of vision was carried out on April 7th and listeners -in on three nights a week when Works. B 25

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A Review of the Latest Products of the Manufacturers.

THE FARRAND LOUD -SPEAKER. working on 300 volts, with signals from a deal of skill and experience are required A loud -speaker of the cone type which local station, there is no tendency to to produce a really attractive finish. has attained considerable popularity in rattle. The demand for aluminium panels is the United States is the Farrand, a pro- The genera] finish is good, and the now being met by White Bros. & Jacobs, duct of the Farrand Manufacturing Co., apearance attractive both as regards the Ltd., 46, Chalk Farm Road, London. Inc., and handled in this country decoration of the cone and the antique N.W.1, bearing an engineturned finish and by Lar- bronze sen de Brey & Co., 14, Brownlow Street, base. covered with a hard transparent lacquer. Holborn, London. 0000 The accompanying photograph does not It is a beautifully finished instrument show the panel to its best advantage, and consisting of a double 14in, cone which, MANDEM DIALS. the small circles, resembling an engine instead turned finish, which are marked with regu- of being constructed of shaped As many vari- cardboard, is of exceedingly thin wood, there are on the market larity over the surface look well when re- and, judging from stiffness, able condensers fitted with small and in flecting light, particularly when in com- the the wood some cases dials, supply used is probably in the form of ply. unattractive the bination with the ebonite tuning dials. of a separate dial McLeod & McLeod, A critical adjustment of the reed is not by Aluminium panels will not be found diffi- required, and it is merely necessary cult to drill, though when the condensers to tighten up the adjusting screw in the of several tuning circuits are assembled centre, which suggests that the movement on the conducting panel . somewhat large is a differential one. The loud- speaker holes must be drilled to accommodate small to - does not work on small input, but when insulating bushes prevent short a second L.F. stage is employed excellent circuiting the grid bias -sing cells. Being reproduction is obtained. Although giv- covered with a hard transparent varnish, the surface can be cleaned down without ing a good response in the base, there is remain no tendency for louder notes to pro- injury to the marking, and will the bright without oxidising or corroding. duce a booming sound, an effect which is 4,4+1444,41010104k f44r4,#e fi 4 ,YS.á+4-+t.Tttioqrt. The new Mandem dial. It is of good design and cleanly finished. M.10**1l1 329, High Holborn, London, W.C.1, will be appreciated by many amateurs who wish to improve the appearance of their sets. The dial which is 4in. in diameter is a really attractive job. It is cleanly moulded in ebonite and carries a 180° scale. The operating ring is liberal in diameter, and the milling is deep and sharp. Examined for trueness the underside was found to be perfectly flat. - Fixing is provided by means of a recessed grub screw. o000

FIGURED ALUMINIUM PANELS. Several attempts have been made by amateurs to replace the usual ebonite The Farrand cone loud- speaker. On the panel A substitute for ebonite panels. An reverse side the cone is open at the by one of aluminium. The diffi- aluminium panel with an engine turned centre. culty usually encountered is to provide surface protected with a hard trans- a good finish for the aluminium surface parent lacquer. sometimes met with in loud- speakers of and the amateur sometimes finds that the The panel supplied for examination was this general type. Both speech and music grade of aluminium he is working will Ain. in thickness, and was quite stiff. are reproduced with a clean crisp sound, not take a bright polish. Aluminium panels of this type are likely and even on heavy input, such as is ob- Attempts bave been made to produce a to become exceedingly popular in the near tained from two L.S.M. valves in parallel figured surface and here again a good future. E 26

www.americanradiohistory.com ?CFfs:* APRIL zoth, r927. Wipigh@o %n01r'l 495 2RACT:CAL hTNIr5 AHD 7-2so A Section Mainly for the New Reader.

VOLUME CONTROL. seme complex ones which are now It should berealised that there are It is now recognised that one of the obsolescent) in which coils having a two distinct methods of adjustment most effective controls of signal in- high H.F. resistance are used, but whereby the valve may be made to tensity is obtained by varying the it is a matter of considerable import- operate on the lower bend ; either filament current of the H.F. ampli- ance when the detector valve follows the grid or anode voltage may be fying valve. The full benefit of this a modern H.F. transformer. In altered, and thus a correct operating device is, however, felt only when fact, the increased amplification oh- point may be .found with the ar- the rheostat operates smoothly and rangement referred to above, even if when its value is suitably chosen the valve has a sharp bend. In prac- with regard to the valve. It would tice, however, two variables are clearly be a mistake to use a 3o -ohm always inconvenient, and it will be instrument to control a 2 -volt valve found better to keep the plate volt- consuming 0.3 amp., as a movement age fixed and to make finer adjust- of the brush through a few degrees ments of grid bias than are possible would make a very large difference by varying the battery tappings with in emission. For this valve a maxi- the aid of a potentiometer connected mum value of 5 or to ohms would as in Fig. t(b). be better. Still another method of obtaining A 6 -volt valve, consuming fine control of grid bias is shown in 0.1 amp., on the other hand, will Fig. t(c).; this, however, is only ap- continue to emit when a very con- plicable when a 2 -volt detector is siderable resistance is inserted in used in conjunction with 4- or 6 -volt series with its filament ; a maximum valves. One end of a rheostat is con- Fig. 1(b).-Fine adjustment of grid voltage value of 5o ohms is not too great. by potentiometer control. nected to the filament, and a lead 0000 from the negative side of the I..T. tamable tends to offset the reduced ANODE RECTIFICATION. battery is soldered to a suitable point detector efficiency, and, except per- In on the winding. By joining the lower spite of the fact that a valve haps when dealing with a very feeble potential end of .the tuned circuit to acting as a " bottom bend " rectifier input, signals may actually be louder the contact brush, the correct propor- is less sensitive than when function- than when grid detection is used. tion of the total voltage " dropped " ing with the more generally used Generally speaking, a valve with across the resistance, is applied to the leaky grid condenser, the former an amplification factor of 20 or even grid. arrangement is becoming increasingly much more is to be recommended as popular, not only because it is likely an anode rectifier. Many of the modern high- magnification valves are particularly suitable, and some of them have an exceptionally sharp bend on the lower part of their characteristic curves. To obtain the best results on weak signals, it is essential that the steady voltage applied to the grid should be of such a value that it is normally maintained at this point of curvature. When dealing with very large applied H.F. voltages as received from a near -by station, the adjustment of bias is not critical, although it is desirable that the grid Flg. 1(c).-Another method, only applica should be sufficiently negative to ble when there is sufficient voltage drop Fig. 1(a). -The simplest method of adjust in the resistance. ing grid bias. prevent the flow of grid currents. Under such conditions the simple In each of the diagrams a by -pass to introduce less distortion, but be- arrangement shown in Fig. i(a) is condenser C is shown. While not cause it does not damp the circuit adequate. It will be seen that the absolutely essential, its inclusion is across which it is connected. This lower end of the tuned circuit is taken recommended. Any capacity of from feature may not be of much advan- to the negative side of the filament o.ot mfd. upwards may be used for tage with many simple circuits (and through a tapped bias battery. the by -pass condenser. B 27

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DISSECTED DIAGRAMS. The present series of diagrams is intended to show progressively, and in an easily understandable manner, the various points to which special attention should be paid in Practical Points in Design the design of typical wireless instruments, and at the same time to assist readers in and Construction. mastering circuit diagrams. The "mixed" L.F. amplifier circuit shown below is becoming increasingly popular, and is particularly suited for adding to the H F. No. 68.-A Resistance-Transformer amplifier- detector set shown in last week's issue. This combination gives, in essentials, L.F. Amplifier. the circuit of the " Everyman Four" receiver.

(i) The anode circuit of the preceding valve (connected to the input L.F. voltage variations developed across the anode resistance are terminal), is completed through a resistance with shunting con- applied to the grid of the first L.F. valve (V1) through a condenser denser and H.T. battery. Filaments of the L.F. valves are fitted with a leak, through which a negative bias is applied. connected in the usual manner.

The plate circuit is completed through the L.F. transformer The anode circuit of the second valve is completed through a loud- primary and H.T. battery. The secondary is joined across grid speaker. A resistance (Ri) of about 0.5 megohm is Inserted in and filament of V,, with bias battery interposed. the grid circuit of V, to isolate it from H.F. impulses.

IT is intended that this amplifier to the capacity of C2. The insulation better response on the lower frequen- and the detector (with or without of all these components must be of cies. This will give less amplifica- H.F.) preceding it should be fed the highest order. tion and will automatically reduce the from common batteries. Thus a The present tendency is to use as tendency towards overloading. separate set of parallel battery ter- V, a valve of about 20,000 ohms im- The question of cost enters largely minals are generally mounted on the pedance. With the usual 120 volts into the choice of an output valve " input " side. H.T. supply a negative bias of (V2), as it should be emphasised that No attempt will be made to deal 3 volts may be applied to its grid. large power outputs are only obtained with the values of the anode resist- With the valve mentioned above, a by expending a considerable amount ance R the by -pass condenser (C,), low -ratio transformer, with a large of battery power. This valve should or the coupling condenser (CO, as primary, is suitable. Alternatively, accordingly be of the lowest possible this matter has been dealt with else- a valve of lower impedance may be impedance consistent with the H.T. where on several occasions. The grid used with the same transformer and current (and voltage) which can con- leak (R2) will be chosen with regard suitably increased bias, with a still veniently be fed to it. B 28

www.americanradiohistory.com APRIL 20(11, 1927. WñpISh2.0 497 Mitt c1 THE CONSTANCY OF B.B.C. TRANSMISSIONS. Factors Governing the Strength of Received Signals. By W. H. F. GRIFFITHS. N the smoking compartment of however powerful their actual voices, one's City -bound morning train Quite erroneous ideas of the constancy are made to effect roughly the same one often hears some such state- of signal strength obtained from a local mean modulation ratio throughout ment as " 2L0 was frightfully weak broadcast transmission are sometimes their performances, further brief ad- last night." formed through neglecting to take justments having, of course, to be It is, of course, necessarily a account of many variable factors made to suit an increase of power statement of the " man- in -the- present at the receiving end. occurring on certain of the soloist's street " whose only instrument for the notes (characteristic of the particular comparison of signal strength is the singer), in order to prevent brief human ear. Wireless men know how utterly impossible period over -modulation. it is to employ the ear as an instrument for the compari- If it is assumed that the modulation ratio throughout a son of sound intensities even when the interval between given class of musical item is maintained (by control), the sounds to be compared is brief. For any statement always, at the same constant mean value, then the actual of relative signal strengths to be made on two receptions signal strength or audibility will be dependent only upon separated by an interval of twenty -four hours, and, in the amplitude of the radio- frequency carrier -wave, and all probability, with the ears in an entirely different this can be measured at the receiving Station without physical condition brought about by a variety of causes, reference to modulation ratio except for sudden fluctua- among which is the strain of a noisy city, is well known tions, of very brief duration, due to over-modulation to be absurd, especially when the statement has quanti- which can easily be detected and ignored. tative pretentions, such as a definite small percentage difference. Local Variable Factors. To judge the relative signal strengths of a local broad- Even by the use of meters, however, small carrier -wave cast station on successive nights to be, say, zo per cent. variations are not easy to determine unless one has a com- different is therefore an impossibility unless meters are plete knowledge of all the possible variable factors at employed, and yet one would certainly not expect greater the receiving end. If an aerial is simply tuned to reson- variations than this when situated within, say, ro miles ance with an incoming transmission by means of an of the station, assuming the ratio of modulation ampli- inductance L (Fig. r) the " resonance volts " across the tude to carrier -wave amplitude maintained latter may be measured by means of a high - constant by the station engineers ; i.e., great impedance thermiónic detector voltmeter variations of radio- frequency energy are V. The aerial current is proportional to not expected. this voltage, and, if the aerial is exactly in Short -period fading and great signal resonance with the incoming signal wave, strength variations due to radio- frequency the E.M.F. induced in the aerial by the transmission causes are only experienced in potential gradient of the advancing wave- the reception of transmissions from stations front is also proportional to the voltmeter (operating on the 300 -500 metre waveband) reading. at least 7o to 'co miles distant. Quite apart from variations of field strength of the transmission being received Audibility Dependent upon Modu- it is possible to experience variations of lation Ratio. voltmeter readings due to a variety of In the reception of radio -telephony, causes, among which may be enumerated Fig. 1.-Circuit for measuring however, the actual signal strength, as ex- the radio-freq uency E.M.F. the following :- induced across the ends of the perienced by the ear, is not only dependent aerial tuning in ductance by .he I. A slight detuning of the aerial circuit upon the radio- frequency energy, but also transmission fr om the broad - by a mechanical " drift of inductance casting station. " the upon the extent to which this energy is L, by change in disposition of leads or by modulated. In fact, variations of " modulation ratio " swinging aerial. Tuning will be fairly sharp, because (or audio- frequency variations) of the transmitter may the only load on the circuit, that of the voltmeter, is in- produce much greater variations of actual signal strength appreciable. This error is eliminated by careful retuning than those caused by radio -frequency variations. between readings. It is possible, however, to control this modulation ratio 2. Variations of aerial circuit effective resistance due to during transmissions, and, normally, one may assume series resistance changes, such as earth resistance, plugs,

that it is kept fairly constant for any given class of or switches, or other contact surfaces. . musical item. That is to say, the amplification control 3. Variations of aerial circuit effective resistance due is so arranged that, for instance, all contralto soloists, to dielectric losses in aerial insulators, in the insulation 8 29

-. www.americanradiohistory.com.-.. -.- -. .. ._..__..r:o..+.... 11es,.:.at:x.3..,ari¡e..o Wfipshgo APR& zotle, 7927. 498 Woyad. The Constancy of B.B.C. Transmissions. - of the tuning coil or in any solid dielec- 16 tric material between the aerial and earth lead -in wires. 4. Variations of aerial circuit effective 1 1 resistance due to changes of impedance B of another aerial in close proximity to 1.2 the one in use. 5. , Variations of aerial circuit effective resistance due to changes of load, if any, 10 JA-" taken from it. This possibility should (t) J always be eliminated by making sure O 08 that the thermionic voltmeter is the only > load imposed, and this is usually negligible and certainly constant. 06 Misleading Signal Curves. Strength 04 In order to show how important these local variations may become, the reader 02 is referred to the curve of Fig. 2, curve A, showing the signal strength variations of 21.0 at ro miles between o 6 7 8 9 10 11 6 p.m. and 10.45 p.m. on a particular evening, as they would have appeared TIME (P. M) J ANUARY 1927 if the voltmeter readings had been Fig. 2.-Curves showing (A) the apparent vari ation in signal strength during the course of un evening of 2L0 at 10 miles, and (B) after correcting for variations in the effective resis tance of the aerial circuit. possible by a knowledge of the effective -__ . resistance changes of the aerial cir- -` ------z____,- _ - cuit from readings - ., (B) i-- taken at half 12 hourly intervals during the test. After _,..-- these corrections had been made the -- r (A) curve was completely altered, and is 10 I - shown in Fig. 2, curve B. Many of its --G irregularities were entirely smoothed out 8 and the total change, it will be seen, was reduced to ± a -5 o 4.5 per cent. from mean value of 1.37 volts -a variation which 6 a 8 is quite negligible, and which is, in fact, -4 outside the limits of accurate measure- 4 4 ment unless the utmost precaution is -4: exercised. D --- The explanation for the large changes 2 41 in the pseudo -voltage curve A is fairly -31 simple. 31 In the first place, the day, during the 6 7 8 9 10 11 hours prior to the commencement of the TIME (P.M) JANUARY 1927 test, had been very wet, and the D.C. insulation resistance of the aerial (from Fig. 3.- Curves (A) and (B) reproduced from Fig. 2. Curve C shows the improvement of aerial toearth insulation throughout the evening, and curve D earth) at six o'clock was found to be only the effective aerial circuit resistance. 0.5 megohm. At half- hourly intervals throughout the evening the D.C. insula- accepted as an unquestionably true criterion. It will be tion of the aerial was tested and showed a steady im- observed that this curve shows a steady increase of signal provement, until at nine o'clock it reached the value strength as the night progressed, just as one would expect ro megohms, which, from experience, was known to be in the reception of a long- distance station, due to the a good normal value. The curve C of Fig. 3 shows this Heaviside layer and the well -known night effect-the improvement of insulation, which was undoubtedly due total change is seen to be nearly ± 20 per cent. from a to the dry, bright evening. These values of insulation mean value of 1.21 volts. resistance were not in themselves the direct cause of any This was kncwn to he far too great a variation, and appreciable increase of effective resistance of the aerial corrections were applied to the curve -corrections made circuit. The reactance of L at 361.4 metres (the wave- B 30

www.americanradiohistory.com APRIL zoth, 1927. Wipagoo NWEtcol 499 The Constancy of B.B.C. Transmissions.- insensitive low- resistance crystal contact and falls due to length of 2L0) was about 88o ohms, and a resistance of complete catwhisker release from the crystal. The effect r.o megohm shunted across this would only have increased of this absorption is shown as an increase of effective the effective resistance of the aerial circuit by about o.75 resistance in curve D (Fig. 3), and at 7.53 p.m., when ohm. The normal (lowest experienced) aerial circuit the interfering aerial was earthed (and its impedance resistance was known to be 36.5 ohms, and the value therefore tremendously increased), the signal strength (from curve D, Fig. 3), corresponding to a D.C. insulation of r.o megohm (on curve C), is seen to be 46 ohms. It is, however, reasonable to suppose that the improvement of D.C. insulation resistance could be taken as a rough indication of a reduction of dielectric losses of the unclean aerial and lead -in insulators, although the two TWO quantities are not in any way numerically related. CONTACTS Measurements of effective resistance (also made at half - SHORT ED hourly intervals during the test) proved this to be the case, the curve D giving the general steady decrease in TO effective resistance from 46 ohms at six o'clock to 36.5 RECEIVER ohms at 10.3o p.m. It will be noticed that the decrease of A.C. leakage lagged somewhat behind the decrease of D.C. conductance by a period of about an hour-this also is, perhaps, conceivably natural. Fig. 5. -The effective aerial circuit resistance is frequently increased by poor insulation at X due to accumulation of dirt This gradual aerial improvement therefore explains the or moisture in the fibre when the switch is exposed to apparent gradual increase in signal strength of curve A the weather. (drawn also on Fig. 3 for comparison with the curve of was suddenly increased corresponding with a sharp aerial resistance), but the well -defined drop of voltage decrease in aerial resistance. from seen o'clock precisely until 7.53 p.m. was due to energy absorption by a neighbouring aerial. The tuning The Correction of the Signal Strength Curve. of a near -by aerial lower and smaller than the one in use Having ascertained to what causes the local variations has been shown by the present author' to effect a con- were due, and having plotted the curve of effective aerial siderable reduction of signal strength, and, in the present resistance variations, corrections were applied to curve A case, a sudden drop of 5 per cent. occurred at the moment of apparent signal strength by multiplying the voltmeter of opening the earthing switch of an already tuned and reading at any instant by the ratio of augmented effective adjusted crystal receiver. The sudden fluctuations be- resistance at that instant to the normal (lowest experi- tween seven o'clock and 7.5 p.m. indicated a catwhisker enced) value of aerial resistance. This gave the voltage adjustment of the interfering receiver -rises due to that would have been obtained across the aerial tuning

1 The ineeless World, June 3rd and 10th, 1925. inductance hail the effective resistance of the complete aerial circuit not been augmented by any means, but remained constant throughout the test at its normal value of 36.5 ohms, and the resulting curve is therefore a true criterion of field strength fluctuation in the neighbourhood of the receiving station. It is, perhaps, interesting to note that in dry weather, when the insulation remained constant throughout the day of the test, and when local interference was known to be absent, curve E, Fig. 4, of actual resonance volts was obtained. This curve is typical of many obtained under perfect conditions, and has a mean value only r per cent. different from that of the corrected curve of Fig. 2. Curve F of Fig. 4 is typical of signal strength curves obtained from 5XX, 75 miles distant, the maximum variation being ± 3 per cent. The constancy of field strength from a transmission at this distance is largely due, of course, to the much longer wavelength employed. Fig. 4. -Curve E: Variations of signal strength from 2L0 in dry weather without Short- period variations of signal volt- interference from adjacent aerial. Curve F : Signai strength curve for 5XX at 75 miles. age, of course, occur, due to excessive ! B 31

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;no Wfip@11@gg APRIL 2otIi, 1927. Wolelld1 The Constancy of B.B.C. Transmissions.- the aerial as an indication of the changes of total di- modulation, and these should not be taken into account. electric loss at radio -frequencies. There is one fault For this reason the modulation should be observed common to many aerials that may be traced in this way during tests of this kind by coupling a rectifying circuit -the losses which occur in outside earthing switches of with telephone receiver sufficiently loosely to the aerial the double -pole change -over type hsually mounted on inductance so that no change of voltage is detected porcelain bases, as sketched in Fig. 5. The porcelain due to its proximity -this is best accomplished by base is glazed, and so causes very little trouble, even in using a semi -aperiodic coil, of very high inductance, far wet weather, but the insulating piece, X, which bridges removed from L. the two switch blades is usually of fibre, and when this If the moving coil instrument of the thermionic volt- becomes damp when dirty it is a source of loss by no meter is sufficiently (excessively) damped it will not indi- means inconsiderable. cate these sharp over -modulation variations, and if, on the In one case of the writer's experience, although the other hand, the moving system is inclined to excessive D.C. insulation of the aerial system was only increased " over -swing " they will he much exaggerated. from 5 megohms to 13 megohms by the removal of this bridge piece, the effective resistance of the aerial was Conclusion. decreased by 3.5 ohms, which was equivalent to a pure In conclusion the author would emphasise the import- shunt resistance of only 2.2 X ros ohms across a reactance ance of using the D.C. insulation resistance variation of of 88o ohms, the wavelength being that of 2L0.

Reception in India. waveband. He and Mr. E. T. Pethers Mr. R. J. Drudge -Coates (AI DCR), (G 6QC), 3, Conley Street, East Green- Rawalpindi, gives his experiences on re- wich, S.E.10, are transmitting on this ception of European signals. Ile states TRANSMITTERS' NOTES waveband on Mondays, Wednesdays, and that on 45 metres they are just audible Fridays, after 2300 G.M.T., and will be at about 1830 G.M.T., and are best from glad of any reports from ljisteners. about 2000 to 2400 G.M.T., fading out AND QUERIES. 0000 with daylight at 0030. On 32 metres QSL Cards for Belgian Amateurs. signals are good from 1430 to 0030 We are asked by the Reseau Belge to G.M.T., and their strength is better than that. QSL cards for amateur trans- 1500 to state on 45 metres. U.S.A. signals come in 2300, and on Fridays from 1800 mitters in Belgium should be addressed to 2300, G.M.T. well after 2300 G.M.T. 0000 to their headquarters at 11, Rue du Con - Mr. Drudge -Coates also tells us of ah grès, Brussels, and not to 88, Bould, interesting low -power test with the Mr. Gerald Marcuse (G 2NM), Queen's Lambermont, as stated in our issue of American yacht Warrior (KFSX1, Park, Caterham, will be conducting tele- April 6th. then at Colombo, a distance of 1,700 phony tests on 90 metres every Sunday 0000 14.30 miles from Rawalpindi. The H.T. of at and 18.30 G.M.T., commencing New Call Signs Allotted and Stations his receiver was keyed, and a transmis- with 1.5 watts input to aerial and Identified. sion made on 39.8 metres. Signals were gradually increasing the power. He will welcome and acknowledge all reports G 5KH R. H. P. Collings, 144, West Hill, Putney, reported by KFSX as R2. steady. The 0000 S.W. receiver was an 0-v -1 Reinartz using 75 2BAS K. C. Wilkinson, Jnr., 133, Half Moon volts to V24 valves. Mr. T. Woodhouse (G 610), 31, Tresco Lane, Herne Hill, S.E.24. (This call - will welcome co- opera- sign was given incorrectly in our issue 0000 Road, S.E.15, the of March 16th, as 2BHS). ion of any provincial experimenter who AI 2KW L. E. W. Jones, " A " Corps Signals, Shortwave Transmissions. nay still be working on the 150 -200 metre Karachi, India. The American station 2XAF, operated by the General Electric Co. at Schenec- tady, New York, will transmit regularly on Thursdays from 6.0 p.m. to midnight E.S.T. (23.00 -05.00 G.M.T.) in addition to its present transmissions on Tuesdays at 6.0 p.m. and on Saturdays at 6.30 p.m. E.S.T. The wavelength is 32.77 metres, and the station transmits the same programme as WGY. 0000 2XG is also transmitting telephony tests on 15 metres at about 2.0 p.m. on most days. 0000 Another experimental short -wave station of interest to amateurs is PCJJ, owned by the Phillips Lamp Works in Holland, which is working on 30.2 metres. We understand that this station has recently been heard in Sydney. This is claimed as a record distance for shortwave broadcasting. The station was also clearly heard in the Dutch East Indies,' Dutch West Indies, and South Africa. programme is A GERMAN TRANSMITTER. The amateur station EK 4AEO, formally operated A i egular broadcasting and on from under the call -sign K 16, which is owned by Herr Karl Kerger, in Hamburg, now being transmitted Mondays situated on the roof of an eight -story building. The transmitter has an input of 1800 to 2300, Tuesdays from 2000 to 50 watts to a Hartley circuit giving .6 amp. in the aerial and the wavelength used 2400, Wednesdays and Thursdays from is 39 metres. B 32

www.americanradiohistory.com Wbrishoo APRIL 2011?, 1927. Mutt 501

NEWS FROM ALL QUARTERS. By Our Special Correspondent.

Wavelength and Power Tests. -New Long -wave Stations.- Future of the Queen's Hall. - Noise from Trams.- German Broadcasting Handbook. -Coming Events.

The King at Cardiff. waveband can only accommodate comfort- The King's Speech at the formal open- FUTURE FEATURES. ably about a dozen stations. ing of the National Museum of Wales on The problem is not, of course, so acute Sunday, April 24th. as in the case of the April 21 will be broadcast from Cardiff LONDON.- Military Band Concert. ordinary broadcast- and relayed to Daventry. Other stations ing waveband of 300 to 500 metres, but CARDIFF. -" Emmaus," an Ora- it is nevertheless one of considerable of the B.13.C. will pick up the Daventry torio, by Sir Herbert Brewer. diffi- transmission by wireless link for re- broad- culty. Capt. Eckersley is not a man to casting. Monday, April 25th. be beaten in matters of this kind, and 0000 LoxnoN.- Symphony Concert. he is confident that a formula will be GLASGOW. -" The Lesson," a one evolved which will enable mutual inter- Daventry and Son. act Radio Play founded on fact, ference between long -wave stations to be The interest shown in "Daventry by Morland Graham. avoided. Junior " has misled many listeners into ABERDEEN. -Tchaikovsky Concert. 0000- supposing that the new station is now Tuesday, April 26th. New Station for Sweden. This is conducting its preliminary tests. LONDON. Band Concert. Apropos these tests, I understand that is -Military not the case; it Daventry Senior that BOURNEMOUTH. Favourites. the number of prospective long -wave has been busy with tests after the regular -Old ABERDEEN. - " Heart's Desire," stations continues to increase. Italy's broadcast programmes have closed down. Comic Opera in two acts, by new 1,600 -2,000 metre Telefunken station The tests are being conducted with is now testing on 5 kW. ; Holland is talk- various Continental stations, using the Mabel Constanduros. BELFAST. " Madame ing of a 1,850 -metre station near Amster- longer wavelengths, in pursuance of the - Favart," Comic Opera (Offenbach). dam, and Motala, near Stockholm, has mandate given to Capt. Eckersley by the begun testing on 1,320 metres, although 27th. International Broadcasting Bureau in Wednesday, April this is 16 metres longer than the official Geneva last February to investigate the LONDON.- Chamber Music. wavelength allotted by Geneva. This problem of the allocation of long wave- MANCHESTER.- Choral Songs and new Swedish station will relay the pro- lengths among European stations. Instrumental Interludes. grammes from Karlsborg and, it is stated, 0000 Thursday, April 28th. will be the most powerful in Europe, with 5XX Testing. LONDON. -Light Orchestral Con- an input of 120 kW. in the generators The tests have been, and cert. and 40 kW. to the anodes of the oscillat- are still being, ing valves. conducted between Daventry, Radio - GLASGOw.- Orchestral Concert. Paris, Königswusterhausen, Rome, and BELFAsT. -Symphony Concert. The comparative strength of many European stations is somewhat Karlsborg, and the first series consisted Friday, April 29th. often of experiments with varying wavelengths difficult to estimate, as in some cases the LONDON. -" Romeo and Juliet." published figures give the output of the keeping a constant separation of 10 kilo- MANCHESTER. " The Burglar," cycles between each station and keeping - main generators, and in others the power Comedy in one act, by Mar- absorbed by the valves. In the case of the power constant. A second series of garet Cameron. tests followed, in which the wavelengths Daventry the power is, I believe, reckoned Saturday, April 30th. by the output of the transmitter. were kept constant and the power varied, 0000 The value of these experiments may be BnRnssN GUAM. -Popular Favourites. realised when it is recognised that there MANCHESTER.-Concert by Prize- Queen's Hall Concerts. are already upwards of thirty broadcast- winners of Lytham -St. Anne's The question of the future of the ing stations in Europe using wavelengths Musical Festival. Queen's Hall is still under discussion, and between 1,000 and 4,000 metres, which I understand that Messrs. Chappell and s 33

1 www.americanradiohistory.com Whpagglo APRIL zoth, 1927. 502 WorIld

Co. and the B.B.C. have not yet come to " Say when." . The explanation of this A Treat Postponed. terms over the suggestion that the latter unexpected interlude was due, I under- Owing to indisposition, Miss Fay should in future carry on the good work stand, to a slight defect in the trans- Marbé, whose broadcast was announced which Messrs. Chappell feel reluctantly mission line which necessitated a rapid last week would take place on April 18th, compelled to relinquish, and continue change over. These minor mishaps are has been obliged to postpone her first those much appreciated concerts which not unknown to the B.B.C. engineers, but appearance before the microphone until have become almost a necessity to music - as a general rule the actual changing over April 30th. loving Londoners. can be staved off until the interval 0000 In a recently published letter in the between two items. On this occasion the Travelling with a Xylophone. daily Press Messrs. Chappell assure us engineer whose voice broke in upon the flowing melodies was not aware that the The Musical Avalos, the novelty xylo- of their intention of continuing the phone will broadcast from Birming- Queen's Hall concerts, but leave us in microphone was still in action on that trio, refer particular circuit. Misunderstandings ham on April 21st, from Manchester on doubt as to whether these intentions April 22nd, and from Cardiff on April only to the symphony concerts or if the will occasionally happen even in the best regulated undertakings, and, anyhow, 23rd. They are reputed to possess the " proms " are also included. largest xylophone in the world. 0000 the interruption was not long enough to cause any serious inconvenience except, o o o o "The Wandering dew." perhaps, to the telephone staff of the A Quarrel Scene from Shakespeare. A full -sized broadcast programme of B.B.C., who were kept busy for a time Two duologues from Shakespeare are " The Wandering Jew " is to be given in satisfying frenzied enquiries, " What to be broadcast from Birmingham on during the Whitsuntide week with Mr. they were after." 00oo April 25th. One is the quarrel scene from Matheson Lang in his original part as " Julius Ciesar," with Wortley Allen as " Matathias," which many of us will A Useful Handbook. Brutus and Stuart Vinden as Cassius, and recollect when so ably played by him at I have received from Germany a useful the other is the wooing of Lady Anne from the New Theatre in 1920. I understand little guide to the broadcasting stations " Richard III.," with Stuart Vinden as that he will be supported by an exceptionally strong cast, and we may look forward to an entertainment which will enthral alike those who have seen the play and those to whom it is new. 0000 Tramway Interference. I referred a week or two ago to the system adopted in Vienna to cope with the interférence caused to listeners through noises caused by leakages or other defects-from their point of view - in the electric tramway system. This interference does not appear to be confined to Austria, as I hear that a petition has been signed by listeners in Reading asking if the town council can do anything to abate similar interference from the tramway system in that town. I also hear of complaints from Bath, Bristol, Norwich, Ipswich, Leeds, Burn- ley, Bradford, Rotherham, Purley, and many other places. The B.B.C. is always ready and willing to follow up such matters immediately, and in many cases the mere replacing of a defective insulator has been sufficient to overcome the trouble. It is feared, however, that all municipal and other electric traction cor- porations do not always take the interest in the listeners' comfort that they might reasonably do without very much trouble IN A RUSSIAN VILLAGE. Peasants at a village club near Taganrog listening to and expense. a broadcast concert. Towns and villages all over Russia are being rapidly equipped 0 o o 0 with receivers in order that the powerful stations now under erection . may be beard in all parts of the country. Another Royal Broadcast. The speeches following the annual of the world, printed in English, French Richard, Duke of 'Gloucester, and Molly dinner of the Royal Academy should and German. The contents include the Hall as Lady Anne. Stuart Vinden began prove of exceptional interest when broad- names, call- signs, wavelengths and his theatrical career at His Majesty's, cast on the evening of April 30th. power of every public broadcasting sta- London. The president, Sir Frank Dicksee, will tion, with an additional table giving 0000 on that occasion propose the health of fuller particulars of those in Europe, and Pot Pourri. the Academicians' guest, H.R.H. Prince a map showing their geographical posi- " Scraps," a new radio revue, which is Henry, and I feel sure that few listeners tions. to be broadcast from 2L0 on April 30th, will willingly miss either this speech or A brief note gives the times and code will include the following sketch items :- Royal reply.' the 0000 used in the transmission of time " The Reformers," by A. P. Herbert; signals from Nauen and the difference of " Three Ways of Saying It," by Mabel A Curious Contretemps. standard times in various European zones Constanduros ; " Cross Words," by R. Many of those who were enjoying Miss compared with G.M.T. Another useful Guy -Reeve ; " Making the Pudding," by Alice Moxon's singing, relayed from the adjunct is the International Morse code J. Melluish; " Wedding Quartette," by Grand Hotel; Eastbourne, on Sunday, of letters, figures, and punctuation marks. Herbert C. Sargent. The cast includes April 10th, were surprised when the The booklet may be obtained from Harold Clemence, Alma Vane, Harold melodious strains faded ont and were Messrs. Stern -Druckerei, of Magdeburg, Kimberley, Florence Bayfield, Philip replaced by a masculine voice calling and the price is 1 mark. Wade and Mabel Constanduros. B 34

www.americanradiohistory.com WApaigoo APRIL 20111, 1927. Wollli NEWS FROM THE CLUBS: Secretaries of Local Clubs are invited lo .send in for publication club news of general interest. All photographs published will be paid for.

Uncanny Electro- Mechanical Intelligence. relay. This relay switched on the fila- progress made by the few but very keen Major Raymond Phillips recently gave ment of the valves in a room upstairs Morse students. a lecture to the Croydon Wireless and immediately the loud- speaker on the The Secretary then gave a short lec- Physical Society on " Wireless Control ground floor was connected to the circuit. ture on the simple principles of wireless and Its Future," at which the Mayor of Mr. Ostermeyer, who is a short -wave transmission and reception ; this was Croydon presided, and was supported by enthusiast, owns a very neat transmitting illustrated by blackboard diagrams. The Mr. W. Thompson, B.A., B.Sc., president station, and is the fortunate possessor of lecture, which was followed by an earnest of the society. an American Synchrophase receiver, discussion amongst the members, even- An essential piece of apparatus used by which was also demonstrated to the club tually went back to the discovery of Major Phillips was a special form of upon this occasion. This instrument con- lodestone and the interesting laws of coherer which was unaffected by the firmed the fact that several Continental magnetism. explosions from a pistol which valves transmissions are still suffering from The various activities of the club now could not possibly have survived. Such heterodyne, including Langenberg include :- Lectures, debates, demonstra- a coherer had in fact been used without (Cologne). tions, Morse tuition, exchange mart, damage in connection with the firing of a After the demonstration there was dis- " radio " bulletin, construction classes. six -inch gun. cussion on mast erection, the switching Anyone interested in the above club Carrying a small transmitter, controlled on and off of current, and aerial should communicate with the Hon. Secre- by a Morse key, the lecturer walked about screening. tary, Mr. W. Salt, L.S.I.S.A., Lancaster in Hon. Secretary Mr. E. J. Turbyfield, Storey Institute Technical College, Lan- the auditorium and rang- singly or caster chords -a row of bells on the stage. F.L.A.A., 42, Alexandra Road, South (Wireless Section). With the same transmitter, from similar Woodford, Essex. Meetings at 8 p.m. 0000 distances, the Major controlled perfectly weekly. Television Experiments. two toy trains on circular rails laid on the The members of the Hounslow Wireless stage. He started and stopped them at Society are deeply interested in television. will, moved them backwards or forwards FORTHCOMING EVENTS. At a meeting held on March 29th it was together, or in opposite directions. More WEDNESDAY, APRIL 20th. decided that those members interested surprising still was the control exercised Edinburgh and District Radio Society.- and prepared to take part should act in 117, George Street, Edinburgh. "Some collaboration and under the direction of by speaking through a special microphone. Methods of Measuring Signal Strength When the Dlayor and Mr. W. Hussey, at Application," by J. B. Davidson. At Mr. Huntingford, who had kindly con- one of the members of the audience, 8 p.m. sented to superintend the experimental THURSDAY, APRIL 212t. simply said " Stop," the trains obeyed. work ; that the members should be pro- Institution of Electrical Engineers.-Savoy " Back " saw them immediately begin to Place, Victoria Embankment, London, vided each month with a report, and run backwards, and " Ahead " invariably IV.C.2. Kelvin Lecture, "High -Frequency when possible a demonstration showing Currents," by Prof. G. W. Marchant, produced forward movement. These D.Sc. At 6 p.m. the progress made ; that the apparatus three commands were instantly responded Goldens Green and Hendon Radio Society. possessed by the society should be avail- -Wiliifield Wau, Goldens Green. N.W.11. to. To control pure mechanism by only "Principles and Prospects of Television" able for experimental purposes as talking to it created a weird impression. (with experiments), by Prof. J. Denton, required. A.M.LE.E. At 8 p.m. The latter part of the evening was With the same portable transmitter a FRIDAY, APRIL 22nd. motor horn was sounded on the stage. Radio Society of Great Britain. -Informal devoted to an examination of the specifi- The lecturer, by means of the transmitter, Meeting. At 6 p.m. At the Institution cation of a television system as patented of Electrical Engineers, Savoy Place, filed a revolver when fifteen yards or so W.C.2. Discussion on the coming Solar by Mr. Cnarles Baxter. Although mem- away, and then readjusted the receiver Eclipse. bers were impressed by the ingenuity of so that, from the same distance, the MONDAY, APRIL 25th. the invention, some doubt was felt as to off four times in rapid suc- Northampton and District Radio Society. - the definition obtained by the system used revolver went At the Cosmo Cafr.. "The Tropakronke," cession. by Dr. D. D. S. Stewart. At 8 p.m. when transmitting objects illuminated by Visitors will be gladly welcomed to the WEDNESDAY, APRIL 27th. ordinary light. meetings of the society, which are held Radio Society of Great Britain. -At 6 Hon. Secretary : Mr. W. R. Collis, 7, p.m. (tea at 5.30.). At the Institution at 128, George Street, Croydon. Particu- of Electrical Engineers, Savoy Place, Algar Road, Islewortlr. lars can be obtained from the Hon. Sec., W.C.2. Lecture and Demonstration: 0000 "The Internal Action of the Thermionic Mr. H. T. P. Gee, of Staple House, 51, Valve," by Mr. A. C. Bartlett. Wire Telephony. and 52, Chancery Lane, London, W.0.2. The lecture given by Mr. E. Cross before 0000 the members of the Sheffield and District An Energetic Society. Wireless Society at the meeting on the A Remote Control Demonstration. Another well -attended meeting of the 1st inst. was somewhat off the beaten The South Woodford and District Lancaster Storey Institute Students' track and dealt with the closely allied Radio Society met on Monday, March Association Wireless Club took place on subject of wire telephony. The lecturer 28th, at the Experimental Station, 5AR, Wednesday, March 30th. After the first described the use of repeaters for worked by Mr. Ostermeyer, of South minutes had been read the Secretary amplifying- speech currents over long Woodford. The object of the meeting gave his report, and commented on the transmission lines, and showed how the was to witness a demonstration of the wireless debate held on March 12th, use of the thermionic valve had provided distant control unit recently put on the which was attended by over forty a solution of this problem. The latter market by the Lissen Co. The demon - students. portion of the lecture was devoted to a stration showed that when worked on a The report was followed by a few description of the Sheffield automatic filter circuit it was really the high tension remarks by the Morse instructor (Mr. telephone installation, which has recently current which ensured response from the R. Shenton), who spoke highly on the been successfully put into commission. B 35

...,._. sitar.a www.americanradiohistory.com 504 WAg®hoo APRIL zoth, 1927. WOli'a1

At the close of his lecture Ma Cross A Regular Field Day. electrical methods. The ordinary sound - announced that members would be box was discarded, and a headphone enabled to see the plant in operation as Material enough for half a dozen used in its place, the method being he was arranging for a visit to one of lectures was used by Mr. H. Saville siinilar to that used by the B.B.C. for the exchanges at an early date. (61IS) at his demonstration before the the transmission of gramophone records. Hon. Secretary : Mr. T. A. W. Blower, Stretford and District Radio Society on Among other pieces of apparatus 129, Ringinglow Road, Sheffield. Thursday, March 24th. He began by explained to the members were an , 0000 using the Loewe triple valve, which con- improved H.T. eliminator and a Trickle tains most of the elements for making a charger for accumulators, the latter complete three -valve resistance- coupled which Comfort in Coventry. being one of the Tantalum type, set ; in fact, the only other components was also used by Mr. Saville to show The Coventry Trapsinitters' Association used were a condenser and coil. Yet that a chemical rectifier would only pass are again active, after a lapse, owing to excellent loud -speaker reproduction was current one way. their loss of previous headquarters. given from both Manchester and Daventry Finally, the lecturer took about a They are now comfortably situated in without the use of any reaction. score of the party to his house for supper the Ragged Schools, New Buildings, Next Mr. Saville demonstrated the new and to hear a demonstration of a coil - and would welcome any amateur trans- Marconi Osram K.L.1 valve, and as the driven loud-speaker, the tone of which mitter visiting the city, on any alternate club room is fitted with direct current, was very fine, especially on the bass Tuesday upon which the meetings are he converted the supply into alternating notes, the only drawback, from the held, to these headquarters, where they and successfully showed how simple it ordinary person's standpoint, being that will find both lively discussions and was to run a set from the mains direct. considerable power was required to Morse practice in progress. The third item in his repertoire was operate it. Hon. Secretary : Mr. L. W. Gardner, an illustration of the direct broadcasting Hon. Secretary : Mr. J. Chapman, 99, 10, Ludlow Road, Coventry. of gramophone records by means of Cyprus Street, Stretford, Manchester.

Rawalpindi, India. Wakefield, Mass., U.S.A. January- February, 1927. Great Britain : -G 2CC, 2IT, 2KG, England : -G 2DX, 2VR, 2KZ, 2CC, 2JP, 2NH, 2NM, '211G, 2ASW, 2XY, 2GY, 2RG, 20D, 2LZ, 2XP, 2JY, CaIlIla ligarcdo 5AD, 5BA, 5BY, 5DH, 5HX, 5KU, 2QM, 5BY, '5HX, 5WQ, 5UW, 5DH, 5NW, 5OA, SRH, 5UW, 5YA, 5YX, 5MA, 5FQ, 5UP, 5XY, 5VL, 5YV, 6BP, 6FA, 6HZ, 6LR, 611,Y, 6WV, 5LF, 5AD, 5GQ, 5TZ ('phone), 6UZ, Extracts from Readers' 6Y0, 6YP, 6YQ. 6TA, 6B11, 6BD, 6ZM, 6YD. Scot- U lAGS, per H. D. Prince (G 6H1'), land : -GC 2511, 2WL, NW, 6KO, Logs. 12, Hillcrest Road, Sydenham. 6NW. Ireland : -GI, 5WD, 6MU Hampton, Middlesex. ('phone), 6QD. Free State : -GW 11Z, February. 18B. Australia : A 2YJ, 2RT, 2MS, Great Britain : -G 2A0, 2AY, 2CC, 2N0, 2YI, 2IJ, 2TM, 31IL, 3AT, China : -BXY. Denmark : -D 7CY, 2RK, 2UN, 2VG, 2VS, 2WJ, 2X0, 3DC, 3MY, 3OT, 3NB, 3VP, 3AL, 7WW, 7ZG, 7MK, 7DD, 7SS, 7EP, 5FQ, 5GQ, 511K, 5HX, 5JG, 5KH, 3BQ, 3PX, 4AN, 5KN, 5BG, 5HG, 7GN, 7CZ. Dutch Colonies : -PKP, 6FD, 6FT, 6FZ, 6IA, 6IZ, 6KK, PTS. Egypt : 5JA 5LF, 5AR, 6AG ('phone), 6SA, -SUC. France :- Northern Ireland : -GI 2IT, 5M0, 6MU, 7DX, 7CW, 7LA, 7CS, 7BQ, F 8OE0, BEF, 8JN, 8DDH, 8JN t', 5WD, 6MU, 6QD, 6WG, 6YW. Irish 71G. Belgium : -B 411S, 4A11, K44, 8DX, 8FIZ, BAY, 8BRN, 8XIX, Free State :-GW 11B, 11Y, 13C, 14B, 8SM, BYY, 8YA, V33, Bl. Denmark : -D 7MT, 7FJ, 8KP, 8FF, 8PJN, 3AG, 3XC. Belgium : -B BE9, K44, 7ZM, 7BX, 7BD, DNSC, DOXZ. SCN, BFP, 8FK, FW, OCLY, OCDJ, K3, 4AR, P7, 411S, K6, 4UU, Bl, : 2CO3 France : -F 8EI, 8GI, 8UT, 8ZB, OCRU, FUT. Finland -S 1DO, 3XX, Zl, 7EC, 05, H5, S5, D2, 2NM. Britain : 2AY, 8JJ, 8BP, 8GER, 8YO11, 8UDI. Great -G 2WJ, 08, 4QQ, 4XS. Canada : -C 1AD, Germany : -K 4ADB, 4ADI, - 4YAE, 2LZ, 2RG, 2WN, 50Y, 5PM, 5HZ, 1AR, 1DM, 2F0. Denmark :-D 7NI, 5DH, 5MA, SZA, 4YAB, 4ACA, 4SAR. Holland :- MW, 5IV, 5UW, 7J0, 7FJ, 7ZM, 7CH. Spain : -EAR 5TR, 5LB, N OPM, OQQ, OAF, PB7A, OAZ. SKR, 6WG, 6LR, 6UT, 6, 18, 28, 44, 52. France : -F 8TRV, Italy : -I 10E, 1BW, 1NA, 1BD. 6FD, 6ZG, 6VC, 6WV, 6XG, 611,V, 8UDI, BGZ, 8SSW, 8KZ, 8CP, 8ARO, Japan : -J 1PP, 1SR, KZB. Java :- 6KO, 6QH, 6MS, GBM, GBK. Ger- 8LZ, 811IP, 8SST, 80LO, 8VVD, many : EI PK1, PK9. Phillippines : -PI 1H11, -K 44, 4ABR, 4AEU, 4RL, 8ABC, 4BM, 8IU, 8BRI, 8YA, 8SIT, 4ABF, 4YT, 4DBA, 4KBL, 4X11, 1BD, 3AC, 3AB, 7OU, WUCC, 8LB, 8FLM. Italy : -I lAY, 10E, WUAJ. Russia : -R 1NN, 2WD, 4SA, 4DKA, AGB, AGC. Holland 1DI, 1UU. Germany : -K 4XU, 4SA, RCRL. Sweden : -SM, TN, UK, UV, N OUC, ONF, PCA, PCMM. India :- 4AFK, 4AAP, 4ABF, 4GD, 4AEY, VJ, RP, XR, YG, SKTR, SIC. AI DCR. Indo-China : -AF HVA, 1B, 4RM, 4UAO, 4DBA, 4DKA, 4SMR, : 1CY, South Africa : -O A3Z, A3A, A4L, A4Z, HNN. Italy -I 1DR, 1DO, 4QJ,, 4XB, 4WM, 4KA. Norway :- 1DM. A5X, 1811, K. U.S.A. :-U 1AAO, 1SL, 1DO, Irish Free State :- LA 1R. Holland : -N ONM, OPM, 2ATH, 2CVJ 6CKV, SOAP, 9CPU, GW 3XC, 3ZZ. Japan : -JES. Java :- 2PZ, OCX, OST, OWJ, OWF, OLY, Miscellaneous European : ANE, AND, ANF. Luxemburg WIZ. - :- OWM. Austria : -O JZ, HK. Por- BR O L 1SE. Morocco : -FM 8AFA, BRIT, 5AA, 0 HK, HL, 0 KE, 0 TH, tugal : lAW, 3FZ. Sweden : -SM 8J0, 8ST, BPMR. Northern Ireland -P S 2NM, S 2ND, s 7ND, La 1E, La 4X, :- UV. UK, WR. Finland : -S 7NB, GI 5M0, 5NJ, 6MU, 631V. Norway TPAI, IC SN1, CS 2YD, CS 2UN, :- 11vß. Yugo -Sfavia : -YS 7DD, 7WW. 1X, LA1, 1A, 1SE. GF3. Asia : -1DH, SS 2SE, JM 3AB, LA lAD, Portu- U.S.A. :-U 1YB, IAHU, IASU, lAGA, KFSX, KDGL, AE 1BK, FC 8EM, gal : -P 1AE, 1AF. Sweden : -SMUK, 1FN, 1LX, 1AJF, 1BBM, lAKR, FI BFOK, FI 1B, BN SKl, BN SK2, SMRV, SMZN, SMYU, SMVR, lAYX, lACU, 1VW, 1AUR, lASA, WUAT, ORA. SMUA. South Africa :-0 A4X, A3X, lAAP, lATG, 1NV, 1QC, 1BDB, R. J. Drudge -Coates A4Z, A3Z. Spain : -EARI. Tunis := 2AHE, 2DH, 2AUL, 2SZ, 2CDR, (AI -DCR). OCTU. United States : -U 2TP, 8DF, 2HS, 2PV, 3AHL, 3LAR, 3BQJ, 4DD, (0 -v -1) Reinartz. SEX. lIC, lAJ11, IALR, BAJ, 1KP, 4KR, 5JF, 8YOR, 8DCM, 8RP, 8ABG, 2XAF, 8DON, 1CDP, 3CKL, 2PZ, 8AF, 8AMU, 9DR. Various : -FN Tunbridge Wells. 1VB, lID, 1CMF, 1AUR, 2CVR, 8PMR, 8RIT, 8SSR, 8VX, 8AY, Feb. 20th to March 13th. 3BSH, lAGR, WIK, WIZ. Miscel- OIIA, WIZ, WIR, WIK, PCMM, laneous : -PK9, VZDO, 1X11, BIH, Australia : -A 2N0, 5KN. Belgium :- PX1, ET 2XA, ICU, TMU, ER 5AA, B B2, 05, V4, 4AU, K4. Brazil :- LP1, 9XE, BG 2XT, SJM, 9SJ, .AP4, SGT, SUC. BZ lAW, lAC, lAK, lAR, IAA, GBH. W. H. Allen. (0 -v -1). On 40 to 200 metres. 1BW, 2AX, lIB, SQl, SPW, PTR. (0 -v -1 Schnell) on 20 to 50 metres. A. F. Elton Bott.. B 36

www.americanradiohistory.com APRIT, 20171. 1927. Wto hog s.? Walllka

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The Editor does not hold himself responsible for the opinions of his correspondents. address. Correspondence should be addressed to the Editor, "The Wireless World," Dorset House, Tudor Street, E.C.4, and must be accompanied by the writer's name and

SHORT -WAVE TRANSMISSION ROUND THE EARTH. for this naturally does not devolve on the engineer. For a half hour after this we are treated to piano solos, etc., as part Sir,-In your issue of March 23rd, on page 356, there is a of tests from 2L0, and this is closely followed by a shrill brief note referring to the experiments recently made in Berlin whistle, indicating the start of further tests by the stand -by to determine the time taken for a signal to travel round the transmitter. Twelve o'clock is quite a usual time for all this world. From this time the length of path is calculated, and to finish, when I am enabled to listen without interference to thus the height at which the wave has travelled, is deduced. the tail -end of a programme from Madrid or Barcelona. Both The results obtained give a height which your Berlin corre- these transmissions are well worth hearing, but to go for them spondent gives as 350 kilometres, but which Herr Quack, of earlier necessitates the use of reaction to the detriment of the Telefunken Company, states to be 182 kilometres. Nov quality. By reason of limited pockets there must be many these results are based on the, assumption that the waves travel readers who are in similar circumstances to mine, and who with the velocity of light in tacuo, but since the waves travel share my complaint. in an ionised medium they have a phase velocity higher and It should here be emphasised that regular listening at very a group velocity lower than the velocity of light. Since the late hours never reveals a high- powered foreign station or its waves travel around the earth their phase velocity can be esti- stand -by transmitter testing. mated, and from it the group velocity. Making this very neces- Precluding the discount, if any, of the value of daylight test, sary correction, the German observations are consistent with a it would seem that the authorities abroad are not active in height of about 90 kilometres, which agrees very well with the tills direction. Although just praise must be given to the height deduced from other experiments. I had already written British stations for their small percentage breakdown periods, an article discussing this point in detail, which article will I am sure we should all appreciate some official assurance on this appear in the May number of Experimental Wireless -when the matter, which is important. In spite of Captain Eckersley's note in The Wireless World suggested the advisability of remarks, I think you will agree that first -class selectivity to be pointing out at once that the height of several hundred kilo- independent of any interference is still an expensive pro- metres for the ionised layer was the result of a false assump- position. A. F. CADDICK.. tion. G. W. O. HOWE. Croydon, March 30th, 1927. Glasgow, March 26th, 1927.

DISTORTION IN RESISTANCE AMPLIFIERS. STAND -BY TRANSMITTER TESTS. Sir, -I have read with much interest the article by Baron Sir, -Your leading article in the issue of March 23rd, which Manfred von Ardenne on " Sources of Distortion in Resistance summarised the opinions expressed in your correspondence Amplifiers." The report shows theoretically and practically columns has, I observe, elicited an explanation of the Broad- that the high -impedance, high voltage- factor valve introduces casting Corporation's policy from the chief engineer. distortion due to :- As the writer of a letter dealing more with the high power (a) Valve capacity shunting the anode resistance. question than the other matter, may I say that not only is (b) Too small a coupling condenser at the low frequencies. Captain Eckersley's letter a justly deserved compliment to the In order to reduce these forms of distortion to inappreciable activities of The lVireless World, but it also illustrates both values it is obvious that the valve impedance must be kept the efficiency of his department and the genuine interest in small while retaining the voltage factor, the anode resistances listeners' welfare displayed by the gallant Captain. Rather can then be kept small so that the shunting due to valve than maintain the official aloofness which only too often char- capacity is considerably reduced, and finally larger coupling acterises the work of a Government Department, this branch condensers and lower grid leaks can thus be used, thereby cor- of the Corporation evidently is alive to the value of the techni- recting considerably these causes of distortion at the lower cal Press in forming a definite future policy. Such co- operation frequencies. augurs well for the development of the British broadcasting The Cosmos blue type valves with low impedances of 55,000- system. 70,000 ohms are, therefore, a most decided advance in reducing While sharing the fears of your Journal as to the overwhelm- the causes of distortion when used with the Cosmos resistance ing local power of these contemplated stations, it would, per- coupling unit having a low anode resistance and high coupling haps, be as well to withhold our criticisms until they may be condenser value together with a normal value of grid leak wanted. of 5 megohms. I may say that in the course of correspondence with the It is unfortunate that this article considered only the high - B.B.C. on the question of Morse interference and other matters impedance valve, as the use of such a valve will tend to intro- I have found, especially with the chief engineer, an intelligent duce these causes of distortion to a much greater degree. desire to help the listener, and genuine complaints have always The advantages of lower impedance valves are only lightly re- brought very courteous acknowledgments. ferred to in Fig. 5 (3), where the frequency amplification curve In view of this friendly attitude, may I ask Captain Eckersley is superior, but the particular valve used was of low voltage to enlighten us on a further important matter which concerns the factor. late listener very much. Of late there has been greatly increased In conclusion the low- impedance high voltage- factor valve activity in testing from the London station and its auxiliary at is the correcting factor in resistance amplifiers. Marconi House. On Mondays, Wednesdays, and Fridays, now, METROPOLITAN- VICKERS ELECTRICAL CO., LTD., when 2L0 is supposed to close down at 11 p.m., the programme Manchester. N. P. Hinton. is often extended until 11.15 p.m. or after. The responsibility April 7th, 1927 B 37

"d-idritniiii- ,iair-Vra.liAe.rdrtwww.americanradiohistory.com -- -_ 'a:.Ydaa-:ei. .-.¢w.,i:.:JYu... ..í 5o6 WApe®00 APRIL zoth, 7927.. WDEld

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The " Universal Three " Again. at the bottom of the diagram a variable effects of occasional overload, if you allow have had a " Universal Three" receiver condenser of somewhat similar capacity. them to take place, will be serious, and in operation for a considerable time Thus, the Gambrell " Neutrovernia," you could reduce the value of the coup- now with great success. I should which has a minimum of 2 and a maxi- ling condenser to 0.002 mfd. without any like, however, to alter it so as to mum of 40 micro -microfarads, would be noticeable falling off in the reproduction experiment with the Hartley circuit, entirely suitable, or, of course, any other of the lower tones. as I understand that the Schnell cir- neutralising condenser. Reaction is then cuit which this receiver uses can be controlled by this condenser. 0000 readily converted to the Hartley cir- 0000 Selectivity. cuit with the minimum of trouble. T. B. D. Resistance Capacity Values. 1 should be greatly obliged if you would I propose to use a Cossor 2 -volt R.C. give me your advice with regard to This receiver, which was published in the following problem. issues of 18th, 25th, valve as an anode bend detector, which I ant situated our August and Sep- about one mile 1926, was, is to be coupled to the L.F. ampli- from the Glasgow sta- tember 1st, of course, designed tion, and to tune from 20 to 20,000 metres, fier by the resistance method. Please wish to build a receiving set and, therefore, to cover practically all give me your opinion as to the best which will cut it out and bring in as wavelengths values of components. H. A. N. many of the Continental stations as and thus to be a really possible. universal .instrument. It can fortunately From the point of view of high ampli- I am prepared to use up to be converted to the Hartley circuit with- fication combined with good quality, we five valves (two H.F. stages), but out in any way interfering with these doubt if you could better an anode resist- would muele prefer to make up a four - great advantages. Referring to the dia- ance of 0.5 meghom, a coupling condenser valve set if this could be guaranteed to give &. gram in Fig. 1, which we publish below, of 0.005 mfd., and a leak of 3 meghoms. the desired result Taking it is only necessary to remove the variable The capacity of the coupling condenser in the "Everyman Four," and the 0.0005 mfd. condenser marked reaction, conjunction with the leak resistance as " Wireless World Five" sets, which and also to substitute in place of the specified will give an excellent pass -on of do you recommend? A. P. N. 0.00005 fixed feed hack condenser shown the lower audible frequencies, but the Without an intimate knowledge of local receiving conditions, it is always difficult to give a definite opinion on these matters. We do think, however, at the very short distance you mention, one could hardly expect a receiver with only two tuned circuits to give sufficient selectivity ; and to be on the safe side we recommend the " Wireless World Five." 0000 H.T. Accumulator Troubles. I have just tested my accumulator high tension battery, which is an old one, and find that several of the cells are " dead." As it seems to run down very quickly, I am wondering if it is the presence of high resistance in these cells which causes a quick discharge. Would it be advisable to hare then. replaced? H. H. C. We think it is highly improbable that your " dead " cells have a high resistance, and even if they had, the presence of this resistance would tend rather to restrict the discharge of the other cells than to accelerate it. We do consider, however, that it would be highly desirable to have Fig. 1. -A universal Hartley receiver for all wavelengths. the faulty cells replaced. B 38

www.americanradiohistory.com APRIL loth, 1927. WIIpW®go WopIlccl 507 A Correction. being perfectly satisfactory for ordinary locality, it will be necessary for you to 1 have obtained a copy of your purposes. The second method also is take the most sensitive receiver you can " Everyman-F'our " booklet, and am quite good, but the third method is get. You will therefore need to take constructing the receiver described scarcely to be recommended owing to either a multi -valve straight H.F. set, therein. There appears, however, excessive microphonic noises. In any such as the Marconi " Straight Eight," to be a discrepancy between the in- case, however, the input from your or a good super heterodyne, such as the structions given on pages 8 and 9 amplifier to the microphone must be Igranic " Neutrosonic Seven." We men- for making the aerial -grid trans- made via a proper microphone trans- tion these two sets as being fairly repre- former and the illustration on page former. Usually, it is best to purchase sentative of the two main classes of wire- l0. In the farmer case, it would the transformer from the same firm as less receivers in this country, and there appear that the primary winding of the microphone, or a complete tone arm are, of course, a large number of sets this ,transformer is wound in. the should be obtained. Of course, in cases in this country of equal merit. We think same direction as the secondary, of emergency an intervalve transformer it would be as well for you to write namely, in a clockwise direction look- would give results in this position, but round to the various big wireless firms, ing at the transformer from its you should choose an instrument like placing your requirements clearly before bottom end, a tapping being made at the Marconiphone 8 to 1 rather than the them, and arranging to have a demonstra- the eighth turn. In the illustration, Marconiphone 2.7 to 1. tion of the particular receiver they re- however, it would appear that the The complete instrument can be used commend, and afterwards to make up winding is commenced at the ter- as an ordinary speech amplifier, or, your mind upon the matter. We pre- minal marked Al, and wound on the of course, with the substitution of an sume that you will have facilities same direction as the secondary as intervalve transformer in place of the for charging accumulators. It will, far as the tapping in the eighth turn microphone transformer, the instru- of course, not be possible for you to marked A2, but at this tapping it ment can be used after a wireless re- receive the stations of the British Broad- would appear that the winding is reversed and finishes up by being wound in the opposite direction. It would appear to me that the illustration is wrong, and I should be glad if you would confirm this. J. 0. H. You are perfectly correct in your assumption that the illustration wrong, and is unfortunately due to 'a draughtsman's error. A moment's thought will make it clear to you that with the primary winding reversed in this manner at its half -way point, the E.M.F. induced by signals coming down the aerial in the top half of the coil would be counteracted by the reversed E.M.F. set up across the lower half of the winding. In brief, the primary winding would possess negligible inductance, and there would scarcely be any coupling at all between primary and secondary, and in theory no signals should be heard, although doubtless due to stray couplings between the aerial lead -in, etc., a certain amount of Fig. 2.- Connections of a speech amplifier. signals would be heard due to the great sensitivity of this receiver. The wind- ceiver. We gave full details together casting Co., nor stations on the North ing then should be wound on from Al to with a circuit showing the necessary American continent, except under very E in the same direction as the secondary switching arrangement to throw over exceptional conditions, and then only by winding. from wireless to local speech reproduc- a very exceptional freak. 0000 tion, the whole apparatus being very 0000 simple and inexpensive to make, on page An Obsolete Canned Music. 827 of our issue dated June 16th, 1926. Circuit. I wish to build an amplifier suitable for Of course, where absolutely faithful re- In the early days of broadcasting I had a ampli/ying gramophone music, and production of gramophone music is five -valve receiver with two neutral- shall be glad if you will give me a required, an electromagnetic pick -up ised tuned anode H.F. valves stabil- simple and inexpensive circuit dia- device should be used, together with an ised by means of a potentiometer, gram. T. F. L. amplifier such as was described in the with a detector valve and two L.F. We give in Fig. 2 'the circuit diagram special article published in our issue of amplifiers. I have been abroad for which you require. With regard to the January 26th, 1927. th.e last two years, and before my de- pick -up device from your gramophone, 0000 parture disposed of this set. Before you do not state constructing a new one, your opinion exactly what method At the Back of Beyond. you propose to adopt for this. In many as to whether the same circuit (which cases as you know, complete gramophone I ant. at present in London, but shall gave excellent results) is still to be tone arms can be purchased with an shortly be returning to the Tierra recommended would be greatly ordinary typé of microphone incorporated del Fuego region, and ans desirous appreciated. W. B. D. in the tone arm, except, of course, that of taking a wireless set with me. It can be definitely stated that the the microphone is specially adapted I do not wish to construct an instru- of your receiver to the ment circuit is now quite obso- needs of the gramophone. In other cases, myself, but wish to take a lete, and we have no hesitation in saying readers have mounted the microphone commercial receiver, and should like that much greater amplification and your advice on better directly in- front of the loud -speaker horn, this matter. R. C. selectivity would be obtained from a single whilst still another section of experi- The nearest broadcasting stations to stage of modern H.F. amplification. If menters have made use of one of the this desolate spot will probably be Val- you care to write to us again, indicating many microphone buttons which arOE upon paraiso and Buenos Aires, and, since both your requirements more fully, we will the market for this purpose. The first these places will naturally be well out- recommend the most suitable of our recent of these methods can be recommended as side the thousand -mile limit from your designs. B 39

da'.. .. www.americanradiohistory.com ..,1- ,:i:ÿ:K.:-.r.v ai..Nyi : =- , WAT@Ilago soß World APRIL 20111, 7927. A Phantom Fault. supply at a much higher periodicity, ductance here, and we should advise that I have recently built a loud-speaker very namely, 90 cycles. We understand that you connected the primary and secondary carefully in accordance with the in- many of the larger manufacturers are of your 4 to 1 transformer in series and structions given in an article pub- prepared to quote special prices for use it as a choke in a choke coupled lished by you in your issue of August battery eliminators of unusual frequencies stage following the detector, and that 4th, 1926. I notice that this instru- or voltages, and we should advise you to you followed your first L.F. valve by ment appears very sensitive to dis- make enquiry among them. Of course, the 2.7 to 1 instrument, using it as a tortion in the amplifier, a fault which the difficulty in a low periodicity supply normal transformer. is not found in two other horn type is adequate smoothing, and at the same 0000 loud -speakers made by reputable time readers have reported to us excel- firms which I possess. I do not lent results on 25 cycles even with When Bushes are Superfluous. standard eliminators designed mainly for claim by any means that my ampli- I ant constructing the " Everyman fier is of the best type for distor- 40 to 60 cycles. Eventually, of course, as you know, it is intended to abandon Four" receiver, following the in- ttonless reproduction, and, in fact, structions given in your book on am intending to reconstruct it, but the use of D.C. in this country for domestic use, and to standardise all this receiver. I wish to know my hoot type loud -speakers appear whether it would be possible fa me to give less distortion than my home- sources of supply at 220 volts A.C. 50 cycles periodicity, just as in America a to dispense with the ebonite panel made diaphram type. Yet curiously and make use of a panel of three -ply on standard of 110 volts 60 cycles is used. enough, testing them on a friend's wood. I also propose to use 2 -volt amplifier which is built according to This naturally makes for much cheaper mass production of battery eliminators, valves throughout, and ant con- the very latest ideas for distortion - templating actually the Mullard less reproduction my home -made and, indeed, of all electrical devices such as electric cookers, etc. P.M.1 H.F. valve as II.P., detector, loud- speaker sounds extremely pleas- and ing, and 0000 first L.F., with a Mullard my horn type ones give dis- P.11.2 in the output stage. Will you tinctly inferior results. On de- Pitfalls o! Anode Bend Rectification. liberately I au intending to build a four -valve set state whether these valves would be introducing distortion into in order? May a ntr/ amplifier, however, the consisting of an H.F. valve and I also use stud friend's switch to change A, falling off in quality in my home- anode bend detector, and two stages the aerial from to Az or A , in the receiver, instead made loud -speaker appears to be far of L.F. I wish to use two Marconi - greater than in the case of the horn phone transformers in the L.P. of providing separate terminals? type, and that is why I say my home- amplifier which I have on hand, and R. H. F. made instrument appears distinctly I presume that this would be in You can very well use the wooden panel sensitive to distortion in the ampli- order, and that I should use the 2.7 in place of the ebonite one, and you need fier. I shall be extremely obliged to 1 ratio instrument in the first put no bushes on to insulate variable if you will show nie how to correct stage, and the 4 to 1 instrument in condensers, etc., since all parts which are this trouble_ K. O. F. the second stage, as you so fre- in electrical contact with this panel are This symptom far from showing that quently advise in transformer -coupled at earth potential with respect to oscil- your loud- speaker possesses any great amplifiers. L. D. T. latory currents, and therefore no loss of fault, shows that you have built it better In reality, of course, for best results efficiency will take place. With respect than you knew, and that you have con- using anode bend rectification, it is pre- to D.C. currents of course, the low structed a very good instrument indeed. ferable to use one of the new type valves potential end of the variable condensers Naturally, of course, a really good loud- specially produced for this purpose fol- which are in electrical contact with the speaker should be sensitive to faults lowed by a very high anode resistance, wooden panel are actually slightly above however slight in other parts of the re- say, 1 megohm in value. If you follow earth potential owing to the 12 volts grid ceiver. Probably, indeed, the overall your anode bend rectifier with a 2.7 to 1 battery in the case of C, and the fixed reproduction of your other two loud- transformer which has an inductance, we resister in the case of C but, of course, speakers is so bad that any fault in the understand, of 50 henries, you will not this will not matter with respect to H.F. amplifier from the point of view of faith- get very good reproduction, especially on energy, and no leakage is likely to take ful reproduction is swallowed up in the the lower notes, because you must place, and bushing would be superfluous. vast sea of distortion produced by the remember that the valve impedance, Were you using a metal panel, however, loud -speakers, and, therefore, these loud- normally high, will be much higher still it must be remembered that in that case speakers sound no better if moved from a when used as an anode bend rectifier. bushes would have to be fitted to both bad amplifier to an almost perfect one, You want, in fact, a much bigger in variable condensers in order to avoid but at the sanie time they show little or directly short -circuiting the H.F. valve no diminution in quality if moved from grid battery, and the resistance R but an almost perfect amplifier to a ROOKS FOR these bushes, even in this case, need not thoroughly bad one without grid bias or be very large, as they 'only have to with- power valves. You are advised, there- THE WIRELESS STUDENT stand a very small voltage. In the case fore, to leave your home -made instrument Issued in conjunction with The Wireless World." of wood, therefore, you would be per- alone, and to rebuild your amplifier. fectly in order in using it without any 0000 "THE PERRY AUTO TIME MORSE extra bushes. A Periodicity Puzzle. SYSTEM " by F. W. PERRY. Price 6d. net. With regard to valves of the type you By Post. 7d. mention, we would ' suggest Mullard I am about to purchase an H.T. battery " WIRELESS VALVE RECEIVERS eliminator to work off my mains AND CIRCUITS IN PRINCIPLE AND P.M.1H.F. in the H.F. position, a Mul- which are 240 volts 25 cycles, but PRACTICE " by R D. BANGAY and lard P.M.1A. as detector, a Mullard N. ASEBRIDGE, B.Sc. Price zi6 net. By Post P.M.1L.F. in the first L.F. position, and most of the advertised instruments 2 /io. seem to be built for 40 to 60 cycles. a 'P. M.2 in the output position. " THE OSCILLATION VALVE - THE I shall be glad if you can advise nue ELEMENTARY PRINCIPLES OF ITS With regard to the latter part of your in this matter. K. N. R. APPLICATION TO WIRELESS TELE query, it is possible to use this stud Undoubtedly the greater number of GRAPHY " by R. D. BANGAY. Price 6/- net. switch without serious losses being intro- By Post, 6/3. duced, of course, aerial losses are A.C. electrical supplies systems in this i' ELECTRONS, ELECTRIC WAVES as, country operate with 40 to 60 cycles AND WIRELESS TELEPHONY " by Dr. always fairly high in any case, and. the periodicity, and this accounts for prac- J. A. FLEMING, M.A. Price 7/6 net. By Post, St- slight additional loss which is bound td tically all the eliminators being made for Obtainable (remittance be caused in this manner will probably by post with order) from pass unnoticed. Still, if not done care- this periodicity band. There are, how- ILIFFE & SONS LIMITED ever, some' sources of supply having a Dorset House, Tudor St., London, E.C.4 fully, noticeable extra losses would be we much lower periodicity such as 25 as in or of Booksellers and Bookstalls introduced, and on the whole think your case, and some on the contrary, you would find it better to avoid this. B 40

www.americanradiohistory.com AN D RADIO REVIEW (151h Year of Publication)

No. 400. WEDNESDAY, APRIL 27TH, 1927. VOL. XX. No. 17.

: H. HAYNES. Editor : HUGH S. POCOCK. Assistant Editor F. - - Editorial Telephone : City 4015 (3 lines). Editorial Offices : 539-40, FLEET STREET, LONDON, E.C.4 E.C.4. Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, : Ethaworld, Fleet, London." Telephone : City 2847 (13 lines). Telegrams " Deansgate. BIRMINGHAM: Guildhall Buildings, Navigation Street. MANCHESTER: 199, COVENTRY: Hertford Street. Manchester.' Telegrams: " Autopress, Birmingham." Telegrams: " Ililie, Telegrams: "Cyclist Coventry." Telephone: 8970 and 8971 City. Telephone: 5210 Coventry. - Telephone: 2970 and 2971 Midland. Subscription Rates: Home, i7s. 4d.; Canada, 17s. 4d.; other countries abroad, t9s. 6d. per annum. slaking use of them, to satisfy themselves that they As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before would not be in /ringing patents.

Will Holland's Example be Followed ? BROADCASTING. EMPIRE It will be of interest to observe whether this example set OR the second time in the short history of by Holland will be followed by other countries in Europe. broadcasting it has been left to Holland Personally, we should be sorry to see stations established to steal a march on this country and, in in this country to work on wavelengths of that order unless fact, on Europe generally. It Neill be ample notice were given, for the reason that comparatively remembered that few sets in the hands of the some long while public would be capable of before broadcast- listening in to the transmissions. CONTENTS. The only application which ing here . was introduced British PAGE we can see at the moment for amateurs were accustomed to EDITORIAL VIEWS ...... 509 a short -wave broaìi sting .station listen to the Dutch broadcasting TRANSMISSION 510 COMMERCIAL PICTURE would be for; the station at The Hague which, with By A. Dinsdale. in this country of overseas communisa- the call -sign PCGG, sent out regu- PRACTICAL HINTS AND TIPS ... 517 Purpose tion, as we have previously stag - lar Sunday afternoon concerts, ALL WAVE "FOUR" ... 519 i in mainly for the benefit of listeners By H. F. Smith and N. P. gested these columns, here. Now again Holland sets the Vincer :hinter. Not a B.B.C. Affair. ' example by leading the way in CURRENT TOPICS ...... 527 short -wave broadcasting. On the NEW FOUR -ELECTRODE VALVES 529 If such a station were erected it 55th of March the station PCJJ, By A. P. Castellain. might quite possibly fall outside established at the Philips Lamp NEW APPARATUS ...... 530 the scope of the British Broad- Laboratories at Eindhoven, in FIELD WINDINGS FOR MOVING -COIL casting Corporation and conte Holland, -communicated by wire- LOUD- SPEAKERS ... .. 531 under the control of the Foreign less telephony with the Dutch By G. W. Sutton, B.Sc. Office and the Colonial Office. in Dutch BROADCAST BREVITIES ...... 533 station at Bandoeng, the An Opportunity Neglected. East Indies. The transmission BATTERY ELIMINATORS (ABSTRACT) 535 t was carried out on a wavelength of By Philip R. Coursey and H. It is a matter for regret that we approximately 3o metres. Andrews. should so far have neglected to READERS' NOVELTIES ...... 539 take advantage of the wonderful Heard in Australia. LETTERS TO THE EDITOR ...... 540 opportunity which broadcasting Since that initial success fairly READERS' PROBLEMS ...... 542 provides for communication with regular broadcasting has been con- the outlying sections of the ducted. Now, as we go to press, Empire. When we know that comes the announcement that the Sydney station, 213L, wireless sets are be ng bought in places as far distant as has successfully rebroadcast one of the programmes. We India and Iraq, in the hope of being able to pick up congratulate Holland, and the Philips Company in par- the transmissions from Daventry once in a while for, ticular, on the enterprise shown in establishing this broad- perhaps, no more than a few minutes, we can form casting record, more especially so as the purpose is some idea of the enthusiasm which would be created apparently to provide a means for long- distance broad- if a short -wave British station were established in casting, and advantage has been taken of the peculiar this country of sufficient power to be heard more or less suitability of the 3o -metre wavelength. consistently I B5

www.americanradiohistory.com WIp@Il@zo 510 7orlic APRIT, 27th, r927,

rJ NSM

A Technical Description of the Methods and Apparatus Used in America. By A. DINSDALE.

FROM time to tine various systems of phototelegraphy that the principal business of the company which de- have been described in this journal. Many of these veloped it is wire, and not wireless telephony, and it have been purely experimental in character, but desired to put its wire system to a further use. some of them have been practical and ready for com- Another aspect of the problem is that although the mercial exploitatica. Other countries are gradually broad principles of picture transmission have been well taking up the commercialisation of picture transmission known for nearly fifty years, their reduction to successful and making progress. In this country we have scientists practice required, among other things, the perfection of who have developed entirely practical apparatus and apparatus and methods for the faithful transmission of methods, but no move is being made to exploit them electrical signals over long distances, and these develop- commercially. ments have become known to the communication art only In America, where there is no Government monopoly within the last few years. of electrical communications, work on the commercialisa- Prominent among these later developments which have tion of picture transmission has been going on for some facilitated picture transmission are the photoelectric cell. time, having been undertaken by the American Telephone the thermionic valve amplifier, electrical filters, and the and Telegraph Company and the Bell Telephone Labora- use of carrier currents. tories, Inc. Complete success has attended these efforts, and seven " Telephotographic Stations," extending right Picture Transmission Apparatus. across the United States, ale now in regular daily com- Essentially, the process of transmitting a picture from mercial operation. one place to another electrically (i.e., by wire or wire- For the complete details of this extensive system. less) consists of three operations. First, there must be described in -this article, we are indebted to the above - some means for translating the lights and shades of the mentioned companies. picture into some characteristic form of electric current. The seven stations already in operation are Boston; Secondly, there must be a channel, wire or wireless, New York, Cleveland, Chicago, Atlanta, San Francisco, capable of transmitting the characteristic of the electric and Los Angeles. An eighth station is under construc- current faithfully (i.e., without distortion) to the re- tion at St. Louis quired distance. Finally, at the receiving end there must Transmission Over Telephone Lines. be some means for retranslating the received electrical signal into lights and shades, corresponding accurately The system as at present established makes use of the in relative values and positions with those of the original wire transmission lines of the Bell telephone system, picture. which cover the entire country. While the mechanism for Analysed for purposes of electrical transmission, a the transmission of photographs over extensive distances picture consists of a large number of tiny elements, and has been primarily developed for use on these telephone the transmission process necessitates some method of lines, it has been demonstrated experimentally that it can traversing or scanning these elements, which must be be used to send pictures by wireless just as easily when transmitted one at a time in a definite sequence. atmospheric conditions are such that steadiness of trans- The method used in the Bell system is to prepare the mission and freedom from interference prevail. picture as a film transparency, which is bent round a Fading and static are the greatest difficulties en- glass cylinder. The cylinder is then mounted on a car- countered when an attempt is made to transmit pictures riage, which is moved slowly along its axis at the same over great distances by wireless, and these difficulties time that the film cylinder is rotated. may easily cause interruptions in the service. The system A tiny spot of light, focussed upon the film, is thus to he described, therefore, was designed for wire trans- caused to traverse the entire picture area in a long spiral, mission partly for this reason and partly for the reason like the needle of the old -fashioned phonograph. Within B 6

www.americanradiohistory.com WIpISIl@00 APRIT. 27t11, 1927. Woc1 512 Commercial Picture Transmission. - the cylinder is located a photoelectric cell, upon which the spot of light shines after passing through the film and the glass cylinder, and the degree of brilliancy which falls upon the cell at any given moment depends upon the density of the portion of the film through which the light is shining at that moment. The arrangement of this apparatus is shown in Fig. I. know, _ A photoelectric cell, as most readers probably is a device for transforming light impulses into electrical impulses. It is, unlike selenium, practically instantane- ous in its response, but not so sensitive. It consists of a Fig. 2.- Optical system at receiving end. L, light source ; D, cathode of some alkali metal, such as potassium, sealed condensing lens ; V, light valve ; S, projection lens ; C, sensitive film. in a vacuum. When light shines upon the metal it emits electrons, i.e., an electric current, just like the glowing depends upon the variations of the incoming electrical filament of a receiving valve. impulses, which represent values of light and shade in Assuming for the moment that the photoelectric current, the original picture at the transmitter. which is a direct current of varying intensity, is of ade- After passing through the aperture of the light valve, the quate strength for successful transmission, and that the beam of light falls upon the sensitive film bent round transmission circuit is suitable for carrying direct current, the cylinder, which rotates in exact synchronism with the one at the sending end, thus exposing the film to an extent which will vary in exact proportion to the lights and shades of the original picture. Adapting the Scheme to Telephone Line Transmission. In the simple outline of the scheme given above, nothing was said about the transmission ciruit, which in this case is the ordinary telephone line. Since this latter was developed primarily for a purpose other than picture transmission, the picture transmission apparatus must be adapted to suit existing line conditions. As already stated, the output of the photoelectric cell at the sending station takes the form of a very weak Fig. l.- Sectional diagram of optical system at transmitting end. L, light source ; D, condensing lens A, diaphragm ; S, projection lens ; C, transparent picture film ; P, photoelectric cell. we will imagine that the output current from the photoelectric cell has traversed the transmission circuit and arrived at some distant point. The Light Valve." At this distant point we require the third element mentioned above -means for translating the incoming electrical impulses into light and shade. This is accomplished in the system under discussion by means of apparatus illustrated diagrammatically in Fig. 2. A source of light, L, is focussed on to a cylinder, C, which has wrapped round it a piece of unexposed photographic film, and which is rotated and moved axially exactly in step with the cylinder at the transmitting end. Between the light source and the cylinder there is interposed a device known as a " light valve." This device, in 3, is due in its general form to shown in detail Fig. Fig. 3.-Details of light valve. R, ribbon carrying picture current; E. C. Wente. It consists essentially of a narrow ribbon- P, pole piece of magnet ; J, Jaws of aperture behind ribbon. like conductor lying in a magnetic field in such a position The range of fre- as to cover entirely a small aperture. direct current of varying amplitude. The incoming current impulses pass through this quency components in this current varies from zero up -distance which is, in consequence, deflected to one side to a few hundred cycles. Now, commercial long ribbon, transmit direct by the interaction between the polarising field and the telephone lines are not usually designed to so the photo- field set up round the ribbon by the passage of the current currents or very low- frequency currents, through it, thus exposing the aperture beneath. Light electric currents cannot be directly transmitted. passing through, or attempting to pass through, this aper- In order to overcome these difficulties, therefore, the means of low. ture is thus varied in intensity in accordance with the photoelectric currents are first amplified by upon a modu- extent of the displacement of the ribbon, which in turn frequency amplifiers, and then impressed s2

www.americanradiohistory.com í72 Wilp®Il,SW APRII. 27117, 1927. WotCRA Commercial Picture Trans- ' mission.- lator valve jointly with a V carrier wave having a fre- L_ETT,P AM quency of about r,3oo A cycles. What is actually PICTURE CHANNEL -\ transmitted over the telephone line, then, is the carrier wave modulated by the photoelectric current M impulses, so that the line AR OM currents, in frequency range SYNCHRONISING CHANNEL and amplitude, closely re- semble the currents of ordi- Fig. 4.- Diagrammatic representation of nary speech, for which picture and synchronising currents. P. photoe:ectric the cell; AM, amplifier- modulator; A, amplifier; V, light valve; M, phonic wheel motors; circuit is designed. T, tuning forks; AR, amplifier -rectifier. When the carrier current, modulated according to the causes. If an attempt is made lights to control two cylinders and shades of the picture at the sending end, by this method the received picture traverses will, in general, be the ribbon of the light valve At the receiving skewed with respect to the original. end, the aperture is opened and closed with each pulse In the present instance the difficulty was of the alternating current. overcome by The envelope of these pulses controlling the phonic wheel motors at each end by the follows the light and shade the of picture, but the actual same fork, and for this purpose it is necessary to trans- course of the illumination with time shows a fine struc- mit to the receiving end impulses controlled by the fork ture of the same periodicity as the carrier. at the sending end. Thus two sets of impulses must he This effect is shown in the upper part of Fig,. 4, sent along the transmission line, marked viz., the picture impulses " Picture Channel." and the synchronisation impulses. This could How Synchronism is Achieved. be achieved by using two separate transmission circuits, as shown in Fig. 4, but It is fairly this is not obvious that in order to ensure that the economically practical, so the problem has light and shade traced been solved out on the receiving film shall by impressing upon the transmission circuit reproduce an exact copy a second of the picture at the sending carrier wave. This second wave has a frequency of about end of the circuit, it is essential that the cylinders at 400 cycles, and carries the synchronisation impulses. both ends rotate at exactly the same speed. Various Thus the line has two currents to carry, one of them methods of achieving this necessary synchronism of (the picture carrier) having a frequency of 1,300 cycles, motion have been developed from time to time, but the and the other (the synchronisation impulse carrier) having method used in the Bell system consists of phonic wheel, a frequency of 400 cycles. Both these frequencies are or impulse motors, controlled by electrically operated dyell within the frequency limits for which - tuning forks. the long istance telephone lines are designed, and they If it were possible are far for two forks at widely separated enough apart to be separated easily by means of electrical points to vibrate at exactly the same frequency, the prob- filters. lem of synchronisation would immediately be solved, but At the sending end a master fork controls such an the speed of arrangement is not practical, for variations of the phonic wheel motor which drives the speed cylinder me- occur with variations of temperature and other chanism and at the same time impresses control impulses

Fig. 5.- Layout of complete system. B, master fork ; C, control carrier ; mechanism; oscillator CF, control channel filter ; M, motor ; S, starting PC, picture carrier oscillator; PF, picture channel filter; AM, amplifier- modulator; L, lamp; P, photoelectric cell; V, ; light valve A, amplifier ; E, amplifier- rectifier ; G, secondary fork; D, terminal amplifier. B8

www.americanradiohistory.com WIp@IlMO 513 APRIL 271Tk. 1927. Wald and the Modu- Commercial Picture Transmission. characteristics of the amplifying valves. - in the figure by the upon the control carrier wave. At the receiving end the lating valve circuits are shown immediately below these valves. control impulses, after being filtered and amplified, drive diagrams which lie whole extent. a secondary fork which controls the phonic wheel motor They are not linear over the the linear characteristic, which which drives the receiving cylinder. In order to preserve is essential for faithful picture transmission, it becomes The Electrical Circuits. The mechanical and electrical arrangement of the whole system are shown diagrammatically in Fig. 5, in 0---11--rOZW which the various elements previously described are shown in their proper relations to each other. T T Certain portions of the electrical circuits are worthy T One of these is the 0 of somewhat detailed description. o channel, and o I i amplifier- modulator system for the picture SYNCHRONISING CHANNEL FILTER

CARRIER INPUT 6000 -6-635P Gm' Go r-0 Vt 74-2- EG, EG3 ö. _1"3 6 rwwv -I ,a 7'LINE RC Ég 2 T T o 'LINE PICTURE CHANNEL FILTER

Fig. 7(a).-Schematic circuits of picture and synchronising channel NA filters. E3 G in l2 necessary to locate the range of variation of current F each of the latter valves on a linear portion of their 405 characteristic. Ri This is accomplished by appropriate biasing voltages of this method of E2 E E3 (Eg), as shown. As a consequence the straight portions of the valve charac- l, , utilising received at the distant end of the d teristics, the current circuit does not vary between zero and a finite value, but between two finite values. This electrical bias is No4 r exactly matched in the light valve by a mechanical bias E2 of the jaws of the valve opening-an ingenious arrange- 'o ment. form of Na 2 In Fig. 7 (a) is shown diagrammatically the the band pass filters used for separating the picture and Noi synchronising channels. The synchronising channel 4 of b LIGHT E, filter transmits a narrow band in the neighbourhood A Em a too cycles, and the picture channel filter a hand between 600 and 2,500 cycles. Fig. 6.- Schematic circuit diagram of amplitter- modulator with electrical characteristics of each element. another is the filter system employed for separating the picture and synchronising channels. In Fig. 6 (top) is shown a diagram of the D.C. amplifier and the modulator used for the picture channel, together with diagrams (bottom) showing the electrical characteristics of each element of the system. At the extreme left is the photoelectric cell, the current from which passes through a high resistance. The potential tapped off this resistance, of the order of 3o or 4o millivolts, is applied to the grid of the first valve. The second valve is similarly coupled to the first, and the modulator valve follows in order. The relationship between illumination and current in the photoelectric cell is shown in diagram No. r, and highest values of is linear from the lowest to the Fig. 7(b).- Attenuation characteristics of picture (lull line) and illumination. The voltage-current (E versus I) synchronising (dotted line) channel filters. B9

www.americanradiohistory.com S7¢ WATe@00 Wald APRIL 27th, 1927. Commercial Picture Transmission.- line in In the received picture represents a track which has addition to these main circuits arrangements are been followed provided by the light beam in its passage across the for starting the two ends of the circuit simul- original picture. taneously and for the transmission of signals. These functions are performed by the interruption of the picture current working through appropriate relays and detectors. Testing circuits are also provided for adjusting the various parts of the circuit without the necessity for using the actual transmission line. The Structure of Received Pictures. All electrically transmitted pictures have a certain amount of structure, upon the degree of fineness of which depends the excellence or _ otherwise of the picture. This structure may be likened to the dots of which a newspaper reproduction is composed. In order to obtain the reproduction it is necessary to divide the picture up into these dots. The process is the same for reproductions on fine art paper, but the dots can be much smaller, so that they are practically invisible, which results in a picture of very much better quality.

Port:on of transmitted picture of variable width line type, enlarged

When picture transmission is accomplished by the modulation method, as in the present case, there are, in general, two methods by which a transmitted picture may he received. One of these is to form an image of the light valve aperture on the sensitive photographic film. When this is done the resultant picture is made up of lines of constant density but varying width. For a dark part of the picture the lines are all thick and heavy : white portions have very fine lines, and intermediate shades are represented by lines the width of which varies in accordance with the density of the picture at any given spot. An advantage of this form of reception is that the picture (when received in negative form), if the structure is of suitable size (6o to 65 lines to the inch), can be used to print directly on zinc and thus make a typo- graphic printing plate similar to the earlier forms of half -tone, whereby the loss of time usually incident to copying a picture for reproduction is eliminated. TIIe disadvantages of this form of picture are that it does Enlarged section of picture transmitted by the variable density line method. not lend itself readily to retouching or to change of size in reproduction, and the white portions are marred by In electrically transmitted pictures the structure con- fine parallel lines. sists, in most cases, of lines. 'These are caused by the The other method of reception is to let the light from process of scanning by the light beam at the transmitting the light valve fall upon the film in a diffused manner end, as the picture rotates upon its cylinder, and each through an aperture of fixed length, so that lines of B IO

, _ . ' .. ..,.a. .. .-:w .r-4.-,:'uk.`7iib`"3iiiYfïs.t1iNii'www.americanradiohistory.com " WIp,s11@mo 515 APRIL 2711!, ¡927. Wosiid are portraits, such as, for instance, those of Commercial Picture Transmission. - impossible or missing persons ; finger prints ; drawings, constant width (exactly juxtaposed) but of varying criminals such as details of mechanical parts; weather maps, mili- density are produced. representations of transient con- Prints made from negatives received in this manner, tary maps, or other enough (wo lines per inch ditions. provided the structure is fine picture is a similar in appearance to original The fact that an electrically transmitted or more), are very closely a field of usefulness may be reproduced through the faithful copy of the original offers photographic prints and of original messages cross -line screen. The gradations of in connection with the transmission ordinary half -tone form is of significance, in the picture are very much smoother, or documents in which the exact light and shade letters, cheques, legal papers, etc., white portions are unmarred by lines, and the picture such as autographed is of vital importance that these documents may he retouched or subjected to any special photo- and where it graphic procedure which may be desired. Practical Details of Procedure. The photographs reproduced here have all been transmitted electrically by the system under review and received by the variable density line method. Readers May, therefore, judge for themselves as to the excellence of the results. The picture to be transmitted is handed in to the telephoto station, usually in the form of a negative, which is apt to be of any one of a number of sizes. From this a positive film is made, measuring five inches by seven; which is then placed in the cylindrical film - holding frame of the transmitter. Simultaneously an unexposed film is placed on the receiving end. Adjustments of current values for " light " and "'dark " conditions are then made over the line, after which the two cylinders are started simultaneously by a signal from the transmitting end. The time of transmission for a picture sin. x 7in., having too lines per inch, is about seven minutes. This time is a relatively small part of the total time required from the taking of the picture until it is delivered in the form of a print. Most of this total time is taken up with purely photographic processes. When these processes are reduced to a minimum by using the negative and the sending end positive while still wet, and making the prints in a projection camera without waiting for the received negative to dry, the overall time can he reduced to about three -quarters of an hour. Practical Utility of the System. [Courtesy : Bell Teirpkmu Laboratories. Autographed photograph transmitted by the variable density lice The utility of the system under discussion was first method. in America in 1924 during the Republican demonstrated be sent from one place to another in the minimum space and Democratic Conventions (for the Presidential elec- and New York. During these of time. tion) held in Cleveland Whilst the application of the system of news photo- hundreds of photographs were transmitted to conventions the most obvious, NV hereby photographs or to Cleveland and Chicago, graphs is perhaps New York and Chicago, may be transmitted to points hundreds of cities in the afternoon papers. of great events and reproduced in those and reproduced immediately in newspapers of picture news service on a still miles distant A demonstration while the story is still " red hot," there are a thousand was furnished on March 4th, 1925, when larger scale and one commercial applications, as the following pictures of the inauguration of President Coolidge were New examples (which have already occurred) will show. transmitted from Washington simultaneously to by the X -ray appearing in the One field of usefulness is suggested York, Chicago and San Francisco, here. Such pictures as this, or Some typical news photograph reproduced afternoon papers in all three cities. can be transmitted to some herewith. electrocardiographic tracings, illustrations are reproduced a continent so that his diagnosis of the which electrically transmitted pictures specialist across The fields in be flashed back with a minimum of delay. service are those in which it is desired trouble may may he of greatest is suggested by the "reproduction of a information which can only he conveyed Another use to transmit an oil company's stock circular, illustrating if at all, by an appeal to vision. Illustrations copy of effectively, the case of a New York firm which, being interested in of cases where an adequate verbal description is almost

13 IT

www.americanradiohistory.com n:_-b:. ia .r 1. 51n WIp@Il@oo APRIL 271Tz, WOsIl4 1927. Commercial Picture Transmission.- the floating of a new stock issue, was able to save eleven - days and meet a favourable market by flashing telephotos of stock circulars and stock certificates back and forth across the country, thus getting in hours the approvals, revisions, etc., that would otherwise have corisume-d nearly a fortnight, and making certain that printing directions were given in unmistakable form. A street railway company in California desired to show a new type of tramcar at a meeting of its directors in New York City. There had been an unavoidable delay in forwarding the picture, but it got there on time and very satisfactorily in the form of a telephoto. An advertising manager in Nevt York planned to be in Chicago on a certain day, but at the last minute could not make the journey. An important cover illustration for a booklet had to be in Chicago the next morning. The air mail had gone, but in the emergency the telephoto system supplied the picture in less than two hours. (From New York to Chicago is a 22 -hour journey by express train.) These are but a felt, of scores of different examples of the utility of the system which could he given. As regards charges, a picture can now be sent from Boston to New York for $15 (4.3); to Chicago for $25 (ZS); to San Francisco for $5o (Zito); simultaneously to New York, Chicago, and San Francisco for $6o (Zr2); New York- Chicago, $20 (Z4); New York -San Francisco, $45 (Z9) > Chicago -San Francisco, $35 (Z;). There are also other reduced charges, and extra prints can be obtained within the area of reception for $r.5o (6s.) each. During the Christmas season, by special arrange- FCourlesy: !:ell !'elephone Laboraloair,. ment, personal photographs, Example of X ray photograph electrically transmitted by the inscribed with Christmas and variable density line system. New Year greetings and autographed, could be sent f ,tr,,. t,on - SpaeP t30 lino. pro. 4 column.. Bonin. 3 point and hae,line test *mid,' on 40 . Mra,Ire, p,tot by anyone over the telephone blank top, ont rand ono -half picot hotton. All diptar o C..lon aotd. Batanee in ßoo4mao. lines to five centres throughout the country. For thii service a special price of Pantepec oil Company of Veniez uela)4 $15 (Z3) was charged, and L it constituted incorporated under the lawsof Delaware ¡O Qt-, bold an unusual means of greeting rela- Transfer Agent: Registrar: \ lo tives and friends. Tele- h':, u-.coal Bank of Commerce, New York Bankers Trust Company, New Yorkf) 14- photos sent under the i-- akle ¡NGH PAS kt E $ arrangement were printed on ( :APIT:\I..IZA -FION heavy art . paper and were Pt Authorized 10 To be presently Issued and flot ..t acdin; +, enclosed in an attractive 4.14 2,00,000 shares 1,500,000 shares folder. No par value shares I+ It For the purposes of regu- 0.43 lar commercial I t -*

www.americanradiohistory.com Wilp,shoo APRIL 27111, 7927. 517 WoreIlco1

A Section Mainly for the New Reader.

A word of warning should be added very heavy) cells will supply for ex- for the benefit of those who propose tended runs. This limits our choice to add loose -coupling to a receiver of valves, and almost rules out the use which includes a stage of un- neutral- of a loud- speaker. When the current ised H.F. amplification. Sets of this consumed is as low as, say, o. r amp., LOOSE COUPLING. kind are normally stabilised by the comparatively small cells will put up a good performance, so the type of One of the most certain ways of aerial load ; when this is removed or valve with this consumption (at about overcoming (or at any rate reducing) decreased uncontrollable oscillation 2 is to be recommended. caused by induction effects will be produced as the grid and plate volts) one trouble The fact that two or three of them frorn near -by power circuits is to re- circuits come into tune. Obviously, - may be used in the set need not mean place the popular direct-coupled " therefore, before adding the loose a heavier demand on the L.T. battery, aerial system, as shown in Fig. r (a) coupled aerial arrangement, it will be as their filaments may be connected in by loose coupling (Fig. r (b) ). At the necessary to neutralise the high -fre- as shown in Fig. 2. This the selectivity of any requency valve. series, same .time arrangement will necessitate a higher will be improved by the altera- ceiver 0000 battery voltage, but in spite of this it tion. VALVES FOR PORTABLES. has a real advantage, as three comparatively small cells (41 volts) sup - accumulators provide the Although plying o. r amp. are almost certain to source of low- tension most satisfactory have a longer life than two i..,rger cells voltage, it cannot be denied that these (of the same total weight) which batteries have certain disadvantages would be discharged at 0.2 amp. were when used in conjunction with portable receivers, in spite of the fact that extremely compact and almost unspill- able patterns are obtainable commercially. It is largely because the type of set under consideration is not in constant use that sufficient attention is seldom paid to the accumulator, which is allowed to stand- perhaps in an almost discharged condition -for pro- tracted periods, with consequent deterioration. It must be admitted that there is a certain attractiveness about the idea of Fig. 2. -Valve filaments in series. using dry cells, which are the only other really practicable alternative. A the filaments connected in parallel as

Fig. 1.- Direct- and loose-coupled aerial chosen battery, even if it is of usual. . connections. suitably small capacity and consequently of The connections of the grid return The necessary modifications are by light weight and low in cost, will give leads are often a source of difficulty connected means difficult, although it will good service on the intermittent dis- to those who a -e using series- no Except in sometimes be impossible to find room charges likely to be required, and may valves for the first time. rec- for the extra tuning condenser in the be thrown away when exhausted. the case of a leaky -grid condenser however, suffer from tifier, these are always made to the receiver : in such cases it may con- Dry batteries, of the veniently be mounted in a separate several disabilities, the most serious negative side of the filament diagram the wooden box, which will at the same being their inability to provide heavy valve in question. In the filament terminals is time serve as a support for the coil - currents ; 0.3 amp. may he taken as polarity of the holder if required the maximum which even large (and indicated, as a guide. B 13

www.americanradiohistory.comi - n.li;e-i.., 518 7,1p@hoo walld APRIL 27th, 1927. DISSECTED DIAGRAMS. The present series of diagrams is intended to show progressively, and in an easily Practical Points in Design understandable manner, the various points to which special attention should be paid in and Construction. the design of typical wireless receivers, and at the same time to assist the beginner in mastering the art of reading circuit diagrams. The effective and simple method of No. 69. -A Singlevalve " Hartley " obtaining capacitative control of reaction, which is shown Receiver. below, can be recommended.

, It H.F.C. ---- , ---

_" Ici RC H.T.

+ + + L.T. L.T. T. (1) 0 (2), (3) The conventional method of connect!ng One half the valve filament of a centre -tapped coil, the The anode circuit is completed through circuit. Following the whole of which is tuned by a parallel a chose and the H.T. battery, usual practice, t, ,e controlling rheostat is variable condenser, is connected between a portion inserted in the positive low -tension lead. of ti.e H.F. energy being fed back to the grid and filament of the valve. grid circuit through a reaction condenser.

/ 11111 H.F.C. l/ H.F.C. H.F.C.

. _ r . . _ _+ t H.T. H.T H.T.

+ t t LT. LT. LT

(4) (6) (6) The addition of a grid condenser and leak, An aerial is connected to the grid end of An improvement is effected with the insertion of phones in series with the coil (through a by providing the anode, completes detecting eeries condenser). a separate " untuned " aerial winding, tie circuit. The earth connection is added. tightly coupled to the grid.

AS the valve is to operate as a grid tive control. Its capacity must be where interchangeable coils are used. detector, the considerations af- small ; in general a maximum of The series condenser Cs has the effect fecting its choice are in no way dif- 0.00005 mfd. (5o micro -microfarads) of reducing damping and improving ferent from in those applying a more is more than ample, so a " vernier " or selectivity ; its capacity, on the normal conventional circuit. Generally speak- " balancing " type will serve. Again, waveband, may be from 0.0001 to ing, one of not more than 30,000 both sides are at high oscillating 0.0002 mfd., and for the longer waves ohms impedance is recommended. potential, so an extension handle is about 0.0003 mfd. A commercial pattern of centre - again desirable. The inductance of In (6) a still more effective aerial tapped coil may be used ; one with the H.F. choke is not critical, nor is coupling arrangement is shown ; this is from 6o to 75 turns will cover the its efficiency of prime importance. It mainly applicable to the 300 -500 normal wave band, while a No. 25o is should have a restricted external field, metre waveband or to the short waves. for suitable the majority of the long - and thus will be of small size. For the former, the secondary may wave stations. A tuning condenser In (4) the grid condenser (C2) and have a total of 6o turns of wire (Litz (C1) of 0.0005" mfd. is assumed. the grid leak may have the conven- may he used) on a Sin. former. The Both sides of this condenser are at tional values of 0.0003 mfd. and 2 aerial winding, which is preferably high potential ; some form of exten- megohms. This circuit, with the sub- tapped, has about 55 turns of fine sion handle should, therefore, be fitted stitution of a centre tapped frame wire, wound on spacers over that part to minimise hand -capacity effects. aerial for the coil mentioned above, is of the grid section of the coil adjacent In (3) the reaction condenser (R.C.) a complete self -contained receiver and to the centre tapping. Control of re should be carefully chosen, as the sen- may form the basis of a portable set. action is greatly improved by adding sitivity of this circuit depends almost The connections of aerial and earth a potentiometer as shown to regulate entirely on the smoothness of regenera- shown in (5) are the most convenient the mean grid potential. B I4

www.americanradiohistory.com Wipa®AT APRIL 2711e, 1927. Mill& 519 L A I t»

By H. F. SMITH and N. P. VINCER= MINTER.

Interchangeable H.F. Transformers for Long and Short Waves.

` laziness, URING his life the average man is almost certain ' necessity being merely a polite synonym for sooner or later to run up against some of those 'whilst " progress " is a more all-embracing, word than. D fatuous individuals who, in the course of a con- necessity. The exercise of a little not -too -fatiguing versation concerning subjects about which they know thought will speedily reveal the truth of these assertions. nothing, seem impelled by some malignant force to shout as we shall now proceed to demonstrate. their ignorance from the housetops by indulging in such From that dim and distant age, umpteen centuries ago, feeble- minded and hackneyed phrases as " Wireless is when the man -like ape first began to merge almost imper- still in its infancy," " Necessity is the mother of inven- ceptibly into the ape -like man, or from the time when present tion," etc., in a futile effort to cloak their aforemen- Adam fell into his unfortunate sleep up to the ignorance. enlightened age of chewing -gum and chauvinism, and tioned and Now half these phrases, such as the former of the two henceforth up to the final cooling -down of the earth Tuesday, quoted, are inaccurate, and the rest, such as the latter, are consequent disappearance of than (or until only half -truths, which are far worse than honest straight- May 29th, A.D. 1928 (according to a recent broadcast and will forward lies. It is with the latter kind of statement from 2L0), the whole of mankind has been, with a dread that we are most concerned here. This phrase, beloved be, generation after generation, afflicted its way on to the as it was of our grandfathers, is undeniably the truth, disease which has even yet not found universal but it is neither the " whole truth " nor is it " nothing statute book of the B.I.A., namely, the almost course, the great but the truth." To he absolutely true, the phrase should affliction ( ?) of laziness. In reality, of in disguise, con- read " haziness is the mother of progress," the word gift of laziness has ever been a blessing

; C7, Cp, 0.002 mfd. ; Cy, ; Ca, 1 mfd. C;,, 0.1 mfd. C, 0.0001 mfd. Fig. 1.-The circuit diagram. C,, C2. C;,, 0.0005 mid R7, Rg, 3 megohms. 2 mfds. Rl, R2, R7, R4, depending on valves used; R;, Rg, '0.5 megohm ; Rg, 0.25 megohm;

13 17

-°'_- .. www.americanradiohistory.com 520 WAp®hoo Wald APRit 2711f, 1927. All -Wave "Four "- stantly tkrging man to hitch his wagon to the stars, as we shall now indisputably /7" ïuai prove. 'r Talking of wagon hitch- ing, what was it that caused primitive man to hitch his yet more primitive soap box to a particularly docile Brontosaurus and so com- mence the great trek of progress in locomotion, which has culminated in the almost universal Ford ? Laziness, of course : nothing more certain, and so has it been throughout (a) (b) the ages, until in the early days of the present century Fig. 2.- Sectional drawings showing construction and connections of the H.F. transformers. man invented the gramo- The lettering on the various ends of the windings corresponds with that shown in Figs. i and 6. The short- and long -wave transformers phone in order to avoid the are shown at (a) and (b) respectively. necessity for turning out to go to a concert hall or theatre. " But what on earth," writes " Red Hot Enthusiast " But laziness is, always has been, and always will be like from Tristan Da Cunha, " has all this to do with the an insidious drug, insomuch that the more it is indulged four -valve set about to be described. Was laziness the the greater is the desire for indulgence, and so twenty years motive that prompted its production? " Most certainly, later we see mankind, tired of " changing the record," inventing broadcasting in order to avoid this exertion. The Long-wave Problem. Even in the short time that broadcasting has been extant, All last winter, if anybody wished to receive 200- to 600- we see the insidious craving at work, once more bringing metre stations at maximum efficiency he used an " Every- forward the battery eliminator in order to avoid the effect man -Four "; but what happened if he desired long -wave of lugging the old accumulator to the charging station. stations, like Moscow and Königswusterhausen? He had It will be realised, therefore, that laziness, and the fact to change over all his batteries, valves, loud -speaker, etc., is that the more it indulged in the greater is the craving to his long -wave receiver (if he possessed . one), for, of - for it, is responsible for all modern progress. All men course, the " Everyman -Four " lays no claim to DX on are fortunately infected with it, except those few who long waves. Shocking ! What a waste of labour ! boast of rising at unchristian hours of the morning in What unnecessary exertion ! (at least, so the writers to in order indulge strenuous mental or physical exercise thought), and what is the result? Progress once more ! before breakfast. No man, surely, who exercises his A set which is efficient both on the " normal " and on the imagination to this extent can possibly be accused of " long " broadcasting wavelengths. This receiver does, laziness. - however, require that coils and H.F. couplings be

Rear view of the receiver, with coils and ff.F. transformers in position.

F 18

www.americanradiohistory.com WApGtillo co gal APRIL 27th, 1927. WocIlca1 ".Everyman- All -Wave "Four."- cannot be put into the same class as the and selec- changed, but for the moment the writers' appetite for Four " from the point of view of sensitivity not undesirable to profit progress is satiated. Long before the next season com- tivity. It was therefore thought these receivers with mences, however, the old craving will once more arise; by the experience gained from bosh the designers will feel too feeble to go on with this plug - ging-in business, and the result will he the production of a set the operation of which looks less like work. A set, in fact, which will cover the whole wavelength band from an Angstrom unit to a light -year, with one dial and no plugging, switching, or jacking. The present receiver naturally falls considerably short of this ideal, but it may well be asked by those already possessing receivers made up from constructional details provided by this journal during the past year whether

The long-wave transformer. what result the reader must judge after he has read the description of the present receiver, the salient points of which we will now proceed to discuss. The first thing to strike our notice is that two plug -in coils are used in a two -way coil holder, each circuit being fully tuned. In other words, straightforward loose coupling. " Shades of Michael Faraday," cries " Ad- vanced Experimenter, Wigan," " have the writers been

The short -wave transformer. the receiver will be of greater utility to them than their is to existing sets. - The best way to answer "this question briefly review the salient points of one or two typical receivers of the past year. For purposes of comparison, therefore, we will pick out two typical general purpose receivers published in this journal during the past year and discuss how the " All Wave Four " shows a superior- ity or inferiority complex (with apologies to Professor Freud) relative to these two typical receivers. The first of these which we have chosen is the " Everyman- Four," and, as we have already pointed out, this present receiver is superior on the long -wave side, the " Everyman- I+our " never having been intended to receive distant long - wave stations. We will now take another typical receiver which uses an H.F. stage, and which was intended to receive both the " normal " and the " long " broadcast wavelengths, namely, the "Neutralised Tuned Anode Re- ceiver" (W.W., 2olro/26). This particular receiver, wavelength flexibility useful as it was in the matter of Fig. 3.- Dimensions of the screen. It is screwed to small and in its ability to receive stations of medium distance, wooden battens secured to the baseboard, also to the panel.

Ft 19

www.americanradiohistory.com 522 Wilpshoo Woplld APRIL 27th, 1927.

Fig. 4.- Drilling details of the panel. ; A, í'21n. dia. B, l /4in. dia. ; C, 3116in. dia. ; D, 5/32in. dia., screws ; E, 1;8ín. die., countersunk 6 countersunk for 4 B.A. for B.A. screws and No. 4 wood screws ; F, 3/32in. dia., tapped 6 B.A. excavating in Tutankhamen's tomb? ". Not so. Selec- work. It is considered to be a good compromise between tivity is desired, is ? it not What better method than the highest possible amplification and that high selectivity. coupling ? loose " Why not aperiodic coupling ? " replies which is so desirable for distant work. The very Experienced im- " Engineer " (who invariably uses the prac- portant factors of ease and simplicity of construction are tical wiring plan rather than the theoretical diagram when also taken into account. It is not denied that it could studying the principal features of any new circuit). Very possibly be made more efficient by entirely jettisoning nice, too, on all wavelengths not exceeding 600 metres constructional simplicity. Both these transformers are or so; probably, indeed, the only method below ioo mounted in six -pin bases, one pin being " dead." Please metres, possibly the best method on the normal broad- note, however, that, use is made of an efficient type of casting wavelengths (with ordinary tuned loose- coupling mounting, with the pins arranged around the circumfer- a very good second), but on long wavelengths a doubtful ence of the former, so keeping the termination of the starter. This method of aerial coupling, then, is in reality various wires spaced fairly well apart rather than run- the only one to use in order to avoid undue complications. ning them in such a way that, owing to capacity effects, The H.F. Transformers. the H. F. energy is apt to emulate the birds in spring by lightly leaping from twig to twig, and so cause losses The next point of interest is the coupling between H.F. and possible instability. and detector valves. This is of a similar type to that The particular formers and base used do not provide employed in the " Everyman -Four " on the normal broad- a non -reversible mounting, and there- is some slight risk casting wavelengths, the long -wave transformer design of short -circuiting the H.T. battery if the transformer is being the result of a considerable amount of experimental incorrectly inserted. This should not occur, however, if

Fig. 5. -The layout of components on the baseboard. B 20

www.americanradiohistory.com APRIL 27th, 7927. Wfip@hoo 523 WWU& All -Wave " Four. " -. gain in amplification. The stabilising resistance Rs, reasonable care is taken, as the cross -bar acts as a guide. which prevents the application of H.F. voltages to the The maker's trade -mark stamped on one end acts as a L.F. amplifier, should not be omitted, as it is not put register line. It would be better, however, if manufac- there for ornamentation. turers could produce a more fool -proof design from the Three similar tuning condensers are used, mainly to but point of view of elimination of risk of coil reversal with- obtain symmetry in the appearance of the front panel, out sacrificing the efficiency of the present mounting. expense may be reduced by using a plain " semi-circular The next point to claim attention is the potentiometer plate " condenser for aerial tuning. There is no real controlling the grid voltage of the detector valve, which, point in using a S.L.F. instrument for this circuit, and to with modern types of valves produced specially to function its tuning is not particuluarly sharp, due, of course, in this position, is a real necessity, since the correct loca- the heavy damping of the aerial. Semi -fixed filament first L.F., tion of the bottom bend is too critical for the r, -volt resistors are inserted in series with the detector,

AEL o 1, Q

. SWITCH - :'--

: 0 L. 1,--. ¢ \\\ ..Cf) 0 r, ----N----0' G r , 1 C <>> < p .. a , w Cig, 02 O 7

41411.5' 0 --472,-.--472,-.4--- i (1_9. a

T- t G B 2 } ` ' - 0A ,

Fi fb I Q ® Pn.'° In tr o, II al 89 ti®a'.?il II OM V e 7 CiÌ "fp®` ifdóo, 'o.©O : t :e@O ; . a ' ® . i / HFT I G O. 11i _. GB., ® - ®. .. ® k b a p 1 J B I .,q G, Ii ._ O .,.#® fjjf E 8 I _ _ O-.C4d J 0-'CigCa, O d s 10 - - .:.j _-_T - . i a n- O I r i tilta ç o

that is supported at one end only, the clip at the other end being connected to the Fig. 6. -The practical wiring plan. Note R correspond=s to that in Fig. 7. grid of V3 by a flexible wire. The lettering on the wires passing through the baseboard valves. It should be pointed out that, as tapping of the grid battery. [" No, ` Puzzled Pim- and output in their anode lico,' it is no use trying to stir up the manufacturers the two former have a high ohmic resistance the interests produce bias batteries with half -volt tappings. "] circuits, full emission is not required, so in to as We \vill now pass direct to the L.F. amplifier, which, of economy the filament current should be kept down it will be noticed, consists of two resistance -coupled much as possible. This peculiarity accounts for the fact ; in stages. It may well be asked why a transformer is not that the set is extremely economical in upkeep cost first L.F. used in the final stage. Reduction of cost is the primary fact, the H.T. current of the detector and reason; moreover, under moderately favourable conditions valves is almost negligible, while their L.T. consumption the amplification provided by the arrangement as specified is also low. The rheostat R1 controlling the H.F. valve We now come will give adequate loud -speaker volume on most signals should be regarded as a volume control. which are really worth while reproducing in this manner. to the vital constructional details. Those working under unfavourable conditions, or whose A standard panel was chosen, as this, together with primary object is the reception of really distant stations a suitable ready -made cabinet, should be obtainable from at loud- speaker strength, may easily substitute a good dealers. The holder is sunk below the baseboard by sheet transformer for the second resistance with a considerable cutting a hole and screwing it to an ebonite secured B 2J

www.americanradiohistory.com 521 WAp®hoo APRII. 27fh, 7927. Wo ArIld

Fig. 7.- Wiring of the underside of the baseboard. Flexible leads for appropriate points, and then be plaited together and external connections to the batteries should be soldered to the passed out through a single hole in the b *k of the cabinet. The strip measures 81n. by 3 /81n. and is 1;4in. thick. terminal to the underside. This avoids the trouble of obtaining head of a screw passed through a special panel, although one of the ribs. This those readers who desire to is ultimately joined to the pin use coils of unduly large which connects to the diameter must naturally obtain detector valve grid. In deciding the ultimate a panel having an extra -inch connections half in height. It is diffi- of all the ends of the windings, the constructor cult to find a better shock- absorbing should substance than sponge consider Fig. 2 in conjunction with rubber; a strip of this, about Fig. 6 and the in. in thickness and measur- theoretical circuit diagram. The same lettering ing 2111. is adopted in width and Tin. in length, carries the sockets in each case. for detector and L.F. valves, which are fixed by means of screws fitted with large washers to prevent their pulling Primary and Neutralising Windings. through. The nuts on these screws are tightened up until The primary and neutralising sections the heads lift clear are interround of the baseboard, to which the rubber exactly as in the case of the " Everyman Four is attached with solution. " coils, to the description of which the reader is referred for fuller The short -wave H.F. transformer, which covers a details. Each winding has a total of is turns bf No. 4o wave band of from about 200 metres to well over 600 D.S.C. wire, carried on six ebonite strips with 32 grooves metres with the condenser specified, is wound on a to the inch. +in. wide, thin. thick, and r ¡in. long. " Radiax " ribbed former with A a mean diameter of about longitudinal V- shaped depression is filed on their sin. and a length of under Ain. The secondary, with a wind- surfaces, so that they may fit snugly over the angle ing length of formed slightly under sin., is wound with 7o by the secondary winding where it passes over turns of 27/42 Litz, the ribs. the lower end terminating at the The depth of these depressions is such that the spacing appropriate pin, while the top end is soldered to the between windings is about -tin. One of the strips carries

Plan view of the receiver, with coils and transformer removed; note sponge rubber base for the valves. B 22

www.americanradiohistory.com WflE3@h g 525 APRIL 27111, 1927. Woirl01

LIST OF PARTS.

1 Ebonite Panel 24in.x 7in.x liu. 1 Condenser type No. 600 0.0001 mfd. (Dubilier). 1 Two -coil holder (Lotus). I Condenser Mansbridge 0.1 mfd. (T.C.C.). 4 Porcelain grid leak bases. (A. F. Buigin & Co.). 4 Valve holders (Athol). 3 Variable condensers 0.0005 mfd. (Eureka). 3 Semi-fixed resistors (Peerless). 2 Plug -in ribbed formers 31in. (Radiax). 1 Rheostat 35 ohms ( Lissen). 1 Base for above. 1 Potentiometer (Lissen). 1 Condenser 1 mfd. (Dubilier). 1 Single pole On and Off " switch (Benjamin). Indigraph dial (Igranic). 1 Condenser 2 mfd. ( Dubilier). 1 Micro condenser with lin. 2 T -size cells (Siemens). 3 Indigraph vernier dials ( Igranic). 2 Resistances 0.5 meg. (Ediswan). 4 Terminals (Eelex). 2 Resistances 3 meg. (Ediswan). 1 Baseboard 24in.x 7 ¡in. 1 Resistance 0.25 meg. (Ediswan. 20 yards Litzendraht wire 27/42. sponge rubber. 2 Condensers type No. 620 0.002 mfd. (Dubilier). Wire, sleeving, screws, ebonite, aluminium, Approximate cost using the above components but exclusive of cabinet and accessories, IS 15s. article itself. In all other In the " List of Parts" included in the descriptions of THE these components are mentioned in the WORLD receivers are detailed the components cases the constructor can use his discretion as to the choice of com- WIRELESS and that by the designer and illustrated in the photographs ponents, provided they are of equal quality to those listed actually used of the instrument. Where the designer considers it necessary that he takes into consideration in the dimensions and layout of the may use. particular components should be used in preference to others, set any variations in the size of alternative components he

or none at all if the a roB.A. screw at each extremity for the purpose of grid bias voltage being applied to it, " late." A anchoring those ends of primary and neutralising windings valve is of the type where grid current starts a 20,000 which connect to + H.T. (marked B in Fig. 2). The good measure of amplification is obtained from 2o. Financial heads of these screws are deeply countersunk to avoid the ohm valve with a voltage factor of about of valve to be possibility of a short- circuit to the secondary. Two other considerations will largely decide the type ; with as large a voltage strips can y a single scret$ for connection to the top end of used in the output stage one Nowa- the primary winding, and the lower end of the neutralis- handling capacity as possible should be selected. low - ing winding. days the amateur has a wide choice of suitable of The long -wave transformer, which covers a waveband impedance valves which operate well on anode voltages of from under goo to about 2,000 metres, is wound on a about 120. of neutralising similar former. Its secondary, with 265 closely wound It should be pointed out that the type high capacity for this turns of No. 36 D.S.C. wire, is approximately sin. long. condenser used has an unnecessarily fixed plates were Over the lower end is wound the primary, with 45 turns particular receiver ; two moving and two as of No. 4o D.S.C. on similar spacing strips, which here accordingly removed. This plan can be recommended, are zin. in length. Over this, again, is the neutralising a lower maximum capacity makes for easier operation. section, with the same number of turns. The strips sup- Final Adjustments. porting this winding will be held in position by the wire, the final matters are facilitated by securing them with a trace The last .screw having been driven home and but last to the of melted Chatterton's Compound at each end. As in the connection soldered in position, we come at a No. 35 or 40 case of the short -wave coil, the spacers have a depression operating details. For the short waves the greater their under -sides, so that there is a spacing of coil in the (moving) aerial socket will cover filed on most Úin. between windings. All the windings of both part of the " normal " waveband, while. a No. ,75 of about long coils are in the same direction. makes is suitable for the secondary circuit. For.the waves we must substitute Nos. 15o and 25o in these re- Choice of Valves. spective positions, remembering that on . the upper and size larger or is intended that an H.F. valve (V1) of from 20,000. lower limits of the waveband to be.covered a It circuit. to 30,000 ohms should be used, and both transformers are smaller will probably Be necessary in the aerial he stable over the designed with this in view. Greater selectivity, particu- Once neutralised, the receiver will in use ; larly on the short waves, is obtained with a valve of higher. whole of the wave -range covered by the transformer same impedance (which should, incidentally, be accompanied by indeed, favoured by fortune, it is probable that the will hold good for a corresponding increase in amplification factor, or the adjustment of the balancing condenser is actually so sensitivity will be disappointing). As a detector, one of both long - and short -wave couplings. This is an ex- the new high -magnification, valves (impedance 70,00ó- in the set as described. In any case neutralising ` do 100,000 ohms) is recommended. Most of these valves tremely simple matter [" No, Doubtful Durham,' we the balancing condenser as a furtive require about x volts negative on the grid for good de- lzot habitually use in order to bring in (listant stations -the tection ; this is, of course, the maximum provided by the reaction control such adventitious aids, single cell as shown. A 3 -volt battery may be substituted set is capable of doing this without de- neutralisation is admittedly rather if necessary ; two -cell torch refills .are of convenient size. although a little signal. ") It is rather difficult to make a definite statement as to the helpful when receiving a particularly elusive best valve for the first L.F. stage (V3). Where maximum The receiver is sensitive and selective on both the short on the long magnification is desired, the same type as is used for the and long wavebands. Moscow, for instance, volume on the detector will naturally be adopted, a very small negative wave side, was received at very convincing B 23

....._.. www.americanradiohistory.com S26 WAT@Il@OO APRIL 27111, W(9)11(91 í927.

All -Wave "Four. " - - It might be thought that with three tuning controls this loud- speaker without any trouble. As to the selectivity, receiver would be rather difficult to operate, but this is not whilst of course tuning is not so sharp that readers need so because with the aerial moderately. closely coupled the be afraid of cutting themselves on it, it is considerably tuning of this circuit is naturally flat, and searching\can better than that of many receivers having a popular reputa- be carried out over a reasonably broad wavelength tion for band this particular quality. On London it was pos- with the remaining t o condensers, -selectivity being sible to go .down to 385 metres without the faintest trace brought into play and unwanted stations cut out by of that station at a distance of 21' miles. Not the slightest loosening the coupling immediately the desired station is difficulty was experienced in getting Radio -Paris at over- located. This control over the selectivity of the receiver is, powering loud-speaker volume with.no whisper of Daven- indeed, one of its most useful points. It should be remem- try in the background, even during the rather prolonged bered that All three circuits must be kept in tune. The intervals for refreshments which this particular foreign beginner should search carefully until the positions of the station is in the habit of taking. This test was made at controls corresponding to a number of stations have been a distance of just over thirty miles from Daventry. All noted, when it will be an easy matter to find intermediate the worth -while long -wave European stations were received wavelengths. , on the loud -speaker with no trouble. As for the stations This receiver will, it is hoped, fill a long -felt want, . working on the lower wavelengths it is not proposed to since it is neither expensive nor is it difficult to build and waste time and space by printing a lengthy list. Incident- operate; moreover, it does not depend for its success on ally, such lists convey no useful information to the know - the use of certain unalterable components. Results will ledgeable-wireless man unless they are accompanied by a depend largely on the excellence or otherwise of the H. F. lengthy description of receiving conditions and a list of transformers; every care should be taken to see that they stations which can be heard in daylight on some standard are carefully constructed exactly in accordance with the receiver with which he is familiar in order that hemay specification given above, and that the pins make good have a definite basis for comparison. contact with their sockets.

VALVE DATA. The followink amendments and additions should be made to the Valve Data Sheet which accompanied the issue of April 6th, 1927. In order that the information contained in the List may be kept up to date, additions and amendments will given from time to time. be

Ampli- A.C. Filament Make of Valve. Type. fication Resistance Price. Remarl S. Factor. (Ohms). Amps.

(FOUR VOLT.) B.T.H. Substitute B.5 7.0 17,000 0.06 I4 /- British Thomson -Houston Co., Ltd., Delete .. B.6 8.0 12,000 0.12 22/6 Crown House, Aldwych, London, W.C.2.

MARCONI. Add . D.E.H.410 40.0 70,000 0.1 14/- Marconiphone Co., Ltd., 210 -212, Add .. D.E.L.410 13.0 14,000 0.1 14/- Tottenham Court Road, London,W.1. Add D.E.P.410 6.25 6,250 0.1 18/6 MULLARD. Add .. P.M.3A 35.0 63,000 0.1 14/- Mullard Wireless Service Co., Ltd., Substitut,, P. M.4 7.0 7,000 0.1 _ 18 /6 . Mullard House, Denmark Street, - London, W.C.2.

DSRAM..' . - Add .. D.E.H.410 40.0 70,000 0.1 14/- Cieneral Elec. Co., Ltd., Magnet House, Add .. D.E.L.410 13.0 14,000 0.1 14/- Kingswày, London, W.C.2. Add .. D.E.P.410 6.25 . 6,250 0.1 18/6 (SIX VOLT). BENJAMIN. Substitute S.P.55 /B. 35.0 ' 55,000 0.09 14/- Blue Spot Benjamin Elec., Ltd., Tariff Road, Substitute S.P.55 /R. 6.0 3,500 0.25 22/6 Red Spot, Tottenharh, London, N.17.

B.T.H. Substitute B.7 8.0 12,000 0.06 18/6 British Thomson-Houston Co., Ltd., Crown House, ' Aldwych, London, W.C.2.

:OSMOS. Substitute S.P.55'B. 35.0 55,000 0.09 14/- detro -Vick Supplies, Ltd., 145, Charing' Substitute S.P.55'R. 6.0 3,500 0.25 22/6 Cross Road, London, W.C.2.

6 24

www.americanradiohistory.com Wfipahoi3 APRII_ 27111, 1927. Wald 527

--Ó ®® { 1=- j°167 L'l IIIt i ;(,,,.; W il- (lill171 1 1 - r, IIIIIII M nn III ; Illll1_ G1 n, url;: mnian luru.nl' Ì{G l_iri_-'...... :, C U P P F2N T TOPIC.J' Events of the Week in Brief Review.

THE BIG VOICE. BETTER LATE THAN NEVER. GERMAN LICENCE FIGURES. Cologne has been fitted with The Bulgarian Government has decided The number of licensed German Cathedral by 22 loud- speakers. to issue permits to private citizens to listeners increased during March 0000 operate wireless sets. 51,664 to 1,635,728. This figure is still 0000 considerably behind that of Britain. STATION. NEW R.A.F. AN IRISH DEBUT. 0000 has been near Mitcham Land purchased The Cork broadcasting station (60K) LECTURES IN BATTERSEA. Common by the Air Ministry for a wire- Free was officially opened by the Irish in the Battersea district will -less transmitting station. State on Monday last, April Readers Government be interested in an announcement regard- 000o 25th. wavelength is 400 metres. Its ing a new course of wireless lectures ap- ANOTHER SHORT -WAVE BROADCAST. 0000 pearing under " News from the Clubs.' \VLW. the Crossley broadcasting sta- TONGUE TEST BY TELEVISION. 0000 tion at Cincinatti. must be added to the attending the recent tele- The success INDIAN BEAM SERVICE IN JUNE ? list of American stations transmitting on vision demonstration in New York has short wavelengths. WLW now broad- already stimulated the imaginations of Official tests with the beam wireless casts on 52.02 metres in addition to its One genius has station at Poona (Bombay Presidency) are American journalists. are normal wavelength of 422.3 metres. discovered that television would make it expected to begin in May. If they 0000 possible for a physician in New York to successful a public beam service between and this Country and India may be inaugur- WIRELESS IN THE WATER. ring a patient in some other city examine his tongue. ated before the end of June. Otto Kemmerich, the German swimming champion, has set a precedent by swimming for an hour in the North Sea while listening to a broadcast programme from Hamburg. The headphones were secured in a specially constructed cap. He considers that broadcast music is more invigorating than that supplied by tug musicians, who often become seasick ! 0000 D.F. TEST FLIGHT. An aerial voyage from Paris to Dakar. via Tunis and Timbuctoo, has been undertaken by two French officers, Lieutenant Girardot (pilot) and Captain Cornillon (observer), with the object of. testing the efficacy of wireless direction- finding in the air. In the outward and return journeys the airmen will cover a distance or over 4,000 miles. 0000 LISTEN TO -NIGHT FOR PCJJ. The Philips short -wave experimental station PCJJ, which has aroused so much interest by establishing communication with Bandoeng and Sydney and with amateurs in various parts of the globe, has issued a working schedule for the present week. Transmitting on 30.2 metres, the station will work from 7 p.m. to 11 p.m. (G.M.T.) on Wednesday, Thursday and Friday. High power is used, and PCJJ a new destroyer, built on the DESTROYER WIRELESS. H.M.S. " Ambuscade," system should be heard with ease on all short- Clyde, which has just been commissioned at Chatham. A feature of the aerial tolerated in the Navy I wave sets in this country. is the abundance of Insulators ; no power leaks are B 2q

www.americanradiohistory.com Mp®Ilsmo 528 APRIL 27th, 1927.

ALMSHOUSE WIRELESS. by being placed at the bottom of the traction, motor starting and lighting pur- Each of the almshouses associated with waiting list for the crime of seizing poses, together with samples of the raw St. Giles -in- the -Fields Church, Blooms- Canadian wavelengths. materials used in their manufacture. The bury, W.C., has been presented with a 0000 exhibition interested many past and wireless set by Mr. C. Shortland, a LOUD -SPEAKER LAMENTATION. present pupils of the school. warden of the church. 0000 0000 With the approach of warmer weather comes a renewal of the unpleasant prac- The " Polar -three " Envelope. MARCONI CONCESSION IN BOLIVIA. tice of planting the loud -speaker in the From the Radio News Bureau, Ltd., open window so that the world A Decree has been signed granting to all can Br'ownlow House, 50 -51, High Holborn, hear what is going on Marconi's Wireless Telegraph Co., Ltd., at 2L0. W.C.1, we have received a constructors' The correspondence columns in the envelope - the administration of the post, telegraph containing the information daily Press are growing eloquent on the and wireless services in Bolivia for 25 necessary for building the well -known years from April 15th. subject, and one writer cites a case in " Polar -Three " receiver manufactured by 0000 which a raucous loud- speaker produced the Radio Communication Co., Ltd. The nervous prostration and a doctor's bill in envelope contains a full -size blue print BELGIAN -U.S. WIRELESS SERVICE. the house next door. Another complain- wiring diagram, full -size drilling tem- ant recommends Successful experiments in two -way that all loud -speakers plate, photographs, coil chart, and other sold should be wireless communication recently con- incapable of producing a informal inn. greater volume is necessary. 000o ducted between the Belgian station at than The Ruysselede and New York are likely to sensible remedy lies with the A Crime Averted. owners of the loud -speakers. When the lead to the establishment of a public ser-- instrument is placed in the open air the l'he London showrooms of Messrs. vice'in about two months' time. Leslie considerate listener will remember to cut McMichael, Ltd., were recently the 0000 down the volume to the comfortable scene of the exciting arrest of a man subsequently sentenced THE SURPLUS FIVE HUNDRED. minimum. to four years' 0000 penal servitude at the Old Bailey for " From the listener's point of view, out A DRASTIC REMEDY. fraud. The man had attempted to ob- of 733 stations (in the United States) tain by dishonest means a 7 -valve A summary method of dealing with the super- there are about 230 stations that the sonic receiver de luxe, valued at £49, loud -speaker nuisance is described by a listener wants," says the Iowa Radio and the set was to have been correspondent of the New York Times, demon- Listeners' League, in evidence given strated at his flat on the evening of the before the new Federal Radio Commis- who writes :- day in question. The police intervened, sion. For 'the benefit of previous correspondents however, and the man received a surprise may I describe a method of silencing objection- when he returned to 0000 able loud -speakers and getting as much enjoy- the showrooms in the evening to take possession ! FREE RECEIVERS FOR THE BLIND. ment out of doing so as an artilleryman gets out of watching his shells do their stuff? A free receiving licence is an ironical My friend Mike, who is a radio fan when he concession to a blind man who is not delivering ice. has perfected but not cannot patented the process.. afford a receiving set. For the benefit of Now Mike built a set on at board and used CATALOGUES RECEIVED. blind people unable to buy wireless sets= the fatuous ' Carpet of Bagdad " circuit. which blooper of gives it. the Nation il Institute for the Blind is is a " " tue first order. Ile Readers wishing to obtain coptes of s little extia in the way of plate voltage and raising a fund for providing them with then turns his dials and listens for the aiueals the catalogues mentioned below should receivers free of cost. ill the near -by sets. If they detone. he follows apply to the manufacturers direct. Il Persons wishing to contribute them up until they become disgo,ted, and give is advisable to enclose stamps for to the up. it's rare sport: better even than poisoning postage. fund are asked to send tltcir gifts to Mr. howling cats. AL. J. Dyson and Co.. Ltd., 2, Coleman Henry Wagg at tlie offices of the Insti- we wonder why we This is so simple that Street, London, E.C.2. Leaflets describ- tute, 224-228, Great Portland Street, W.1. hadn't thought of it before. ing the - Thornbui-n " and ' Godwines " t c000 lf.'l'. Eliminators, the " ilicrotutre " BRAILLE WIRELESS JOURNAL. variable condenser, and the " Airmax " From the well -known French publishing Low -Loss Coil. house of Etienne Chiron, 40, Rue de NEWS FROM THE TRADE. C. Ede and Co., Ltd., Byfleet, Surrey. Seine, Paris, 6e, we have received a copy, Leaflet describing the C.E. Precision printed in Braille, of the International Floating Valve Holder, Rheostats, Radio Review, specially intended for Cabine's for Every Type of Receiver. Potentiometers, and Grid Leaks. blind readers. C. A. Vandervell and Co., Hume constructors are generally Ltd., Acton, Written in Esperanto, able London, \V.3. Abridged list (Publication the International to make a good and workmanlike job of No. 72) of Radio Review should have a wide appeal the electrical parts of their receivers, but new C.A.V. Broadcast Re- among blind wireless ceivers, Loud- Speakers, and enthusiasts of all may not have the necessary or L.T. and nations. took ex- Accu lators. The editors are Dr. Pierre perience for the superfine cabinet work. Corret M. and E. Aisberg. and the paper For these Messrs. Carrington Manufac- Garnett, Whiteley and Co., Ltd., "Lotus is now in its second year. turing Co.. Ltd., " Cameo " Works, Works," Broadgreen Road, Liverpool. 0000 Sanderstead Road, South Croydon, can Pamphlet No. 1,013, "The Uses of Lotus supply size Jacks, Switches and Plugs," together with THE U.S. BROADCASTING POSITION. any or make of cabinet at a reasonable price. Though they have blue -print showing circuits for use with The new U.S. Federal Radio Commis- recently moved to more extended pre- Lotus jacks and switches. Also blue -. sion has granted temporary permits for 27 mises in South Croydon, their vans still print and directions for Lotie Remote old broadcasting stations to continue make daily deliveries in London. Control House Wiring System. operations on their present wavelengths, 0000 Afa Accumulators Limited, 120, Totten- writes our Washington correspondent. ham Court Road, London, W.1. List Every broadcasting station in the Bart Batteries at School Exhibition. No. 4, dealing with the Varta " Duplex " United States which desired to continue The Hart Accumulator Co., Ltd., Rectifier for charging H.T. and L.T. transmissions after April 24th had to exhibited several types of "Hart " bat- batteries from A.C. supply. secure a temporary permit from the Com- teries at the Commercial Exhibition of Electradix Radios, 218, Upper Thames- mission. At the time of writing it is the Haberdashers' Aske's Hampstead Street, E.C'.4. 68 -page catalogue of wire- doubtful whether all the stations will School held at Westbere Road, N.W.2, less transmitting and receiving experi- secure this coveted privilege. on March 29th. 30th, and 31st. The mental gear, including sets, components, At least 40 stations are being penalised displáy included batteries for wireless, and accessories. B 26

- _ _ .Jrr[a.: slL,r.e. - www.americanradiohistory.com- ..,yt_ -_-- !-¡yy,a.__ ._iiiá., ;

APRIL 27th, 1927. Wflpewo 529 Wacica1 NEW FOUR-EL CTRODE VALVES. High Efficiency on Low =plate Voltage. By A. P. CASTELLAIN, B.Sc., A.C.G.I., D.I.C.

SOME time agog the writer pointed out some of the more efficient than the normal three -electrode owing to possibilities of the four -electrode valve when suitably its peculiar construction, which enables high amplification designed for the work it has to do, instead of being, to be obtained with relatively low resistance, so that it as it was at that time, an even worse compromise than was appears that this type should be among the survivors in the old type " general- purpose " valve. the course of the next few years. Since that time a large amount of research has been The four -electrode valve; designed to operate on low carried out by the writer on four -electrode valves in the plate voltages will have an immediate application in electrical laboratories of East London College, and many country or other districts where main power supplies are experimental valves have been made and tested in the not available, . and also for portable sets, where any course of evolving really efficient designs for H.F., I.. F., economy in batteries is at once appreciated, and will en- and power valves to operate on very much lower plate able a really light portable loud- speaker receiver to be voltages than the three -electrode type of valve. constructed which is capable of receiving many stations The complete results of these experiments will be pub- on its own self -contained frame aerial. lished in due course, but it may be said here that it has been found possible to construct a four -electrode valve to The Neglect of the Four- electrode. have characteristics the same as, or, in some cases, much The four -electrode valve has been sadly neglected, in better than a corresponding three -electrode valve operating this country especially, and probably what has contri- on from twice to three times the plate voltage required buted more to its present unpopularity with most valve . by the four- electrode valve; and that, too, without a manufacturers than anything else is the so- called H.T. - corresponding increase in plate current. Hence the effi- less circuit, to which attention was devoted some time ciency of the four -electrode valve is much greater than ago. that of the more usual type. This scheme was all right for oscillation and detec- In view of the foregoing tion, though, of course, not remarks, it is extremely so efficient as when a high - interesting to see what the tension battery was used, but applications of an efficient when it comes to amplifying four- electrode valve are for loud -speaker results, it likely to be. simply cannot be done with good quality results com- Valves of the Immediate bined with good volume with- Future. out the use of a high- tension The writer is strongly of supply. the opinion that the valve - However, when the valve types of the immediate future is properly designed for low -i,e., those valves the use of voltage (not no voltage) which will extend rapidly - operation, it then compares are three in number, namely : more than favourably with (I) The externally heated the usual type of valve, and cathode or " Mains " valve. valves so designed may be (2) The " Short Path " used in sets formerly employ- A power amplifier for ing three -electrode valves type of valve. 40 volts H.T. (3) The four -electrode with no alterations to the valve. components and With the addition of only one extra lead The " Mains " valve will obviously extend in use in to the high -tension battery, which latter may be reduced those districts where power supplies are available, since to a half or even a third of its orikinal value, thus con- it does away with all batteries, and is capable of dealing siderably reducing the upkeep or maintenance cost of with large volume outputs with very good quality, since the set, while still keeping the same output volume and large plate voltages are obtainable without much bother with probably better quality reproduction. and fuss. It is probable that high amplification valves A two -stage power amplifier, using efficient four -elec- of this kind will be produced which will still further trode power valves, will be described, with full construc- extend the usefulness of this type of valve, but it must tional details, in an early issue. This amplifier (see be remembered that the use of this type is stictly limited photo) is capable of giving an output volume more than to places where main supplies are available. sufficient for the average room on as little as 3o volts The " Short Path " type of valve is, or can be, made H.T., while the volume obtainable using 6o volts H.T. is sufficient for filling a small hall- -these large volumes I The Wireless World, July 21st, 1926 being given with good quality reproduction: B 27

www.americanradiohistory.com Wpcdgag 530 01cí APRIL 2711e, 7927.

A Review of the Latest Products of the Manufacturers.

M.H. BASEBOARD RHEOSTATS. THE FORMO CONDENSER. PILOT ART DIAL. The practice of using variable filament A condenser of novel construction has Geared condenser dials operating under resistances controllable from the front recently been designed by the Formo Co., a cover and provided with an aperture of the instrument panel is now being Crown Works, Cricklewood Lane, Lon- through which the scale is viewed are now discontinued in favour of the adoption don, N. W.2. practically standard as tuning controls on of adjustable resistances secured to Instead of the usual end plates with American receiving sets. Dials of this the baseboard. New types of valves in- spacing washers and rods, the fixed plates type are now becoming popular in this troduced within the past few months do are held in position by means of a stiff coríntry, though as a rule they are more not require a critical adjustment of fila- metal casting. Support for the fixed costly than the simple form of bevelled ment potential, . and when once suitably disc. adjusted these valves will give good per- An inexpensive dial of American formance in spite of small changes in the manufacture is now voltage obtainable from derived from the accumulator. Messrs. Rothermel Radio Corporation of A new component for controlling fila- Great Britain, Ltd., 24-26, Maddox ment current has just been placed on Street, Regent Street, London, W.1, and the market by L. McMichael, Ltd., is a product of the Pilot Electric Manu- Hastings House, Norfolk Street, Strand, facturing Co., Inc. In spite of its London, W.C. It consists of a turned low price, is well made and possesses, all ebonite former carrying a strip mounted the features to be found in the more resistance winding. The arm rotates expensive types. The cover is a clean over the resistance wire as in the moulding of good design, and two usual form of knob -controlled rheo- scales are provided, advancing in op- stat, and when the best setting has posite directions, so that the dial been found no further adjustment is can be used required. with condensers in which A useful feature is that the capacity increases either in a the rheostat is actually calibrated in clockwise or anti- clockwise direction. ohms, and the resistance introduced into The scales are divided into one hundred the circuit by the rheostat can be read divisions. Gearing is arranged by means off from engraved markings. These base- of a positive friction drive which en- board mounting rheostats are available tirely avoids backlash. The operating in values suitable for use with either knob projects about an inch above the bright or dull emitter valves. The centre surface of the dial cover, spindle revolves so that the in a brass bush, and the hand is well removed from the plate of contact spring makes hard contact on The new Formo condenser. A stout the condenser in the process of tuning. the wire, though giving quite a smooth metal casting supports the fixed plates Covered dials of this type should not be and spacing washers are dispensed with.

plates is obtained by two bolts passing through the frame with stand off insulating washers and to minimise dielectric loss a liberal air space is left between the fixing screws and the holes in the frame. Instead of spacing washers both fixed and moving plates are securely clamped in position on slotted bars. The plates are firmly held in position, making reliable electrical contact. The shape of the plates is a little unusual as they do not truly follow either a straight line wavelength or straight line frequency law The new M.H. baseboard mounting and neither does the increase in capacity The new Pilot dial. adjustable rheostat carrying a scale follow a logarithmic scale. For tuning calibrated In ohms. circuits possessing an appreciable capacity as large as the circular bevelled dial, and when the condenser setting is at zero the this new Pilot dial measures 4in. in movement, while a hard spring reinforced straight line frequency condenser has been height by 38in. in width. The dial is by a stiffening plate picks up contact found a little inconvenient, and the shape easily attached to the condenser shaft by with the spindle. The metal parts are adopted in this case appears to give a use- means of a grub screw, while a nut and plated, and this component possesses a ful spacing between stations over the scale bolt, together with template card, are sup- first -class instrument finish. divisions of the dial. plied for locating the cover. 28 rb ... -liaiih. s. '}.iö: bat w--bddAwìi:akwww.americanradiohistory.com ,.4,11r iik.a.r 1 n¢ 6,liidlf.iLa7i-1GU lúlbe+ .tu:-doóíiiiisH.-rNl;ténFsisS orrat>i WApg@go APRIL 27th, 1927. 5.11 G9`OO 1ll& MVO WINDINGS f®rr Moving-cell L®ui-spealkerao Calculation of the Turns for Different Magnet Cores and Supply Voltages. By G. W. SUTTON, B.Sc.

EVERAL enquiries have recently been received from and radiated from their surface. If the coil is totally experimenters wishing to wind an exciting coil for enclosed, as in the case of the " Magnavox," the whole a moving -coil loud- speaker to. work from some par- of the heat has to traverse such a path. It is, therefore, ticular voltage, such as the too- or zoo -volt D.C. mains. necessary to have the best possible thermal contact between Since the available winding space in such instruments is the surfaces of the coil and the iron on which it is wound. likely to vary with the type of construction adopted in A layer of enclosed air is particularly had in this respect. different cases, it is scarcely sufficient to work out the The coil should be wound on a thin, built -up, leatheroid approximate number of turns and gauge of wire required former, which fits the iron -core both internally and at the in a given instance. A method of estimating these quan- ends as closely as possible. This is a point well worth tities for any voltage and winding space is therefore given attention, as it,directly.affects the possible efficiency of the below, so that experimenters may readily meet their par- finished instrument. ticular requirements. The power which may safely be dissipated in the wind- The governing factor is, of course, the number of ing is estimated in the following manner. The surface ampere -turns (i.e., the product of the turns on the excit- being -normally situated in still air, the power radiated ing coil and the current flowing in it) which it is thought per sq. cm. of surface may be taken to he 0.0012 necessary to employ. This in its turn is determined by watt per degree Centigrade rise in temperature. A rise the air -gap field- density required for satisfactory opera- of about 4o° C. on the outside is allowable so long as tion. If great care is taken in the construction of the the constructional detail mentioned above is satisfactory. moving -coil, so that it may he accommodated in a very The internal temperature should not then he more than short air -gap, say, -hin., 700 -800 ampere -turns will he 65° or 7o° C. The radiating surface is roughly estimated found to give a sufficiently intense field. With longer from the dimensions of the coil and core. In the present gaps a proportionately larger number of ampere -turns case it is 17o sq. cms. will he required. Such proportions result, incidentally, in a field density three or four times as great as can be obtained from an ordinary permanent magnet system. Winding Space. OF 15 The cross -sectional area of the winding will be deter- LENGTH MEAN TURN cros mined by the size of the casting or stampings to be used. If we take, for example, the case of the instrument described in The Wireless TVorld, February 9th, 1927, the area available is 3.5 x 1.9 = 6.65 sq. ems. Allow- ing a space factor of 0.75 for uneven winding and overall insulation the space actually occupied by the winding is approximately 5 sq. ems. In the construction described in that article D.C.C. wire (No. 22 S.W.G.) was used. The thickness of the cotton insulation further reduces the space in that case to about 2.6 sq. ems. of actual copper. The finer the wire the greater would this reduction become, and considerable improvement would obviously result from the use of enamelled wire. and el represent the correct number of turns and If T 1.- Example showing method al arriving at length diameter of wire (copper only -not including insulation) of mean turn. T x d2 = some constant, k, (1) under conditions = 2.6 sq. ems. in above case. The power radiated from the surface of continuous running is therefore 0.0012 x 4o x 170 The second determining factor in our calculation is the = 8.1 watts. allowable temperature rise in the winding. This limits For our second equation we may therefore write the current which may be passed through a given coil V2 /R = k2 = 8.1 watts (2) without charring the insulation on the innermost and therefore hottest turns. A large proportion of the heat The resistance R may be readily expressed in terms of generated in such a construction as the one being con- the number of turns, diameter of wire, length of mean- sidered has to be conducted to the iron stampings turn and specific resistance of copper. R will be directly 29

www.americanradiohistory.com WIp®Ilsoo Wati APRIL 27th, 7927. Fieli Windings for Moving -coil Loud- speakers.- and then from equation (r) the number of turns may proportional to the number also of turns T and inversely pro- be found. The second expression shows that the ampere portional to the square of the wire diameter d, turns which can be obtained in a given winding- space, i. c., R allowing a definite temperature -rise, is independent of the = T X X k3 ohms ... . (3) dz working voltage, provided, of course, the number óf The length of mean turn is estimated from the dimen- turns and gauge of wire are adjusted to the voltage. sions of the bobbin (see Fig. r) to be 15 ems., while the An Example. - specific resistance of copper (hot) may be taken to be 0.02 ohm per metre per sq. mm. If only one turn were In the present case the operating voltage is 6. The wound on in such a way as to fill the whole winding space required wire diameter is found from equation (4) to be the resistance would be 0.069 cm. ; and the turns from equation (r) to be 55o. 15 r Actually 5zo turns of 0.071 cm. (No. 22 S.W.G.) were X X 0.02 = 14.6 x I0 -6 ohm, loo r used. The calculated ampere -turns are 745 ; the instru- -X2.6Xroc) ment 7 4 as wound having ro at 6 volts. As mentioned above, i.e., when T = r, d2 = 2.6 and R = 14.6 x 10 -6; if it is desired to operate the coil from a hence'frorn equation (3) k3 = 38 x ro -s. higher voltage it would be preferable to use enamelled wire so as to avoid In the present case, therefore, k1 = 2.6 sq. cms., k2 = waste of winding -space. 8.1 watts, and k3 = 38 x 10-6 ohm. If, therefore, a coil is required to operate direct from From equations (r), (2) and (3) roo -volt mains, the winding space may be taken as 5.0 sq. cros. instead of 2.6. The diameter of the wire is /k1 k2. k3 found to be V 0.0198 cm., nearly No. 36 S.W.G. ; the d 2 (4) number of turns is 12,700 and the resistance r,roo ohms. and To work straight across 200 -volt mains about 25,000 turns of 38 or 39 S.W.G. would be necessary. The ,kt k2 I T (5) labour of winding such a coil is scarcely worth the ks economy effected, and a preferable arrangement would be The first expression enables the correct diameter of to connect a zoo -volt 40 -watt lamp in series with the wire to be at once obtained for any operating voltage; roo -volt coil mentioned above.

Antwerp. 5TG, 5XD, 5KU, 5ZA, 5WQ, 5SK, Great Britain : -G 2A0, 2 OD, 5BY. 5GO, 511X, 5GQ, 5VL, 5PM, 5KZ, U.S.A. :-NU lAHI, lAJM, 1ALZ, 5UL, 5D11, 5IS, 5LF, 5WH, 5JW, lAMJ, lAMN, lAQT, lASF, lAYX, 5TU, 5W, 5GU, 5SZ, 5TG, 5XH, 1BUX, 1BYV, 1CMX, 1CQ, lIC, 1RD, 5TD, 5RZ, 6UT, 6FT, 6RY, 6Q0, 1RY, 1SW, 1VC, 2ADM, 2AKV, 2GP, Extracts from Readers' 6LL, 6LR, 6BT, (OU, 6DR, 5BD, 20X, 2T13, 2XAD, 3BGG, 4BL, 8AHC, 6YU, 6XP, 6YR, 6QL, 6VP, 6WG, 8AHK, 8ALY, 8AXA, 8BAJ, 80Q, Logs. 6TW 6CL, 6WK, 611Q, 6FD, 600, 8ZG, 98RN, 9CCA, 9SD. Canada :- 6YD, 6MA, 6ZG, 6TG, 6JS, 6YV, NC 2F0. Saigon : -AF 1B. Brazil :- 6ZD, 6HW, 6DA, 6IA, 6R0, 6XL, SB lAD. Jamaica : 2PZ. Chile 6TY, 6AT. GC -NJ :- -NC lAD, lAR, 1DJ, 1DQ, 2AX, 6NX, 6IZ, 6KO, 6MS, 6JS, SC 3AG. South Africa : A5X, 5JD. GI 2IT, -FO 2BE, 2DO, 2F0, 3AEL, 3WAB, 8RG. 5M0, 5WD, 6MU, 6WG, A6N. Norway : -LA1A. Spain : -EAR 6QD. GW 11B, 14 B, 16B, 18B. France : Australia : -OA 2MS, 2N0, 2YI, 3BQ, 41. Sweden : -SMUK. Austria : -EA 8IL, 8FL, 8RV, 3DC, 3HL, 3X0, 5AX, 5JA, 5W11, -F 80UI, 8UT, 8JD, OHK. France : -EF 8JN, 8CT, 8YOR. 8DDH, 8FLM, 8CP, 8I11, 8DS, 8KU, 6WA. Tasmania : -OA 7CW, 7DX, Irish Free State : -GW 18P. Belgium 8VAA, 8GDB, 8CA, :- 7HL. New Zealand OZ 2XA, 8JR, 8HIP, EB 4AU, 4WW, 4ZZ. L. Era. :- 8JRK, 8ESP, 8GER, 8DL, 8YA, 4AA, 4AC. : On 20 metres. (EB South Africa -F0 A3W, 80QA, 4BC). A3X, A5X, A6N, A9A. Argentine 8PJW, 8SSY, BNCX, 81'I, :- FFY. Morocco :-8MB, BRIT, AIN. Wimbledon. SA DB2, DH5, 1101. Uruguay : -SU Belgium : 1BU, 1CD, 1CX, 10A, 1XM, -B 05, 08, K4, K3, K44, Jan. 1st to April 10th. 2AK. C9. 4RE, 4AI, 4BL, 4RK, 4XX, Chile : -SC 2AS. China : U.S.A. :-NU 3ACM, 3ACW, 3AFW, -AC 8FJE 4CB, BAR. Canada 3CF. U.S.A.: 3AHL, 3AJ, 3AJC, 3ANY, 3AUV, ( ?8FJT), BFLO. French Indo -China : -- : - KDKA, WIK, WIZ, U980. Holland : AF 8FOK, 1B, HVA. Siam : 3AY, 3BG, 3BHV, 3BQJ, 3BWT, -AE -N OBX, OM, OGA, ONF, OFK, 1BK. Costa Rica : CTO. Brazil 3CAH, 3CDS, 3CE, 3CKL, 3CKJ, -NR :- OMAR, OLY, OWJ, OBLX, OEC, 3EF, 3GB, 30P, SB lAD, 1AF, lAJ, 1AK, 1AL, 3GX, 3HG, 3J0, PCMM. : lAO, lAR, lAW, 1BK, 1BR, Sweden -SMVR, SMUK, 3KU, 3LD, ZPF, 3QE, 3QF, 3SK, 1BY, S\IZY. Italy :-I 1RE, 1DM, 1('E, 3TE, 3TN, 3VF, 3WID, 3WJ, 3Z0, 1BU, 1CA, lIB, lIC, lID, 2AB, 2AG, 2AJ, 2AR, 1F0 (10E lwatt). Spain : -EACI, 4AAH, 4AA0, 4AK, 4BN, 4CV, 4DD, 2AM, 2AS, 2AV, EAR6, EAR22, EAR28, EAR44, 4DV, 4EC, 4FT, 4GZ, 4HX, 41IY, 2AX, 5AB, 5AE. F. Pemberton. EAR48, EAR50. Denmark : 7WA, On 20 -45 metres (0 -v -1). -D 4I0, 4IT, 4IZ, 4LL, 4NH, 40B, 7MT, 7EC, 7L0, TFJ. Portugal :- 4RM, 4RR, 4RY, 4TE, 4TK, 4TU, Wolverhampton. 1AF, lAO, IAA. Tunis : -OCTU. 4YB, 5EW, 5HE, 5ZAV, 6BZF, 60I, January 23rd to March. Luxemburg :-L 1P. Germany K K4, 7DBE, 9AAO, 9ADN, :- 9AEK, 9ARN, Great Britain : -G 2LJ, 2HQ, 2GF, l6. 4ABF, 4AEM, 4ABK, 4DKA, 9BE, 9BRC, 9BTZ, 9CN, 9CPM, 2WN, 2CS, 2VR, 2VG, 2DL, 2YQ, 4BCE, 4AAP 4DR. Egypt : -SUC2. 9CWN, 9CYW, 9DIH, 9DQR, 9DQW, 2QM, 2WJ, 2PZ, 2DN, 2AY, 2VL, Various : -B Wl, EC lAB, EAKL, 9DR, 9DVG, 9MN. India : -AI 2KX, 2GV, 21IM 2D11 2BI 2DB, 2DX, GBM, GFY. GBZ. W. O. Wigg. DCR. Philippines :-OP 1AU . Canada : 2QC, 2S0, 50C, 5LK, ' 5UW, 5US, On 35 -60 metres (0 -v -0). s 30

www.americanradiohistory.com Wbgilmo APRIL 2711r, 7927. Woc .)33

SAVOY HILL TOPICALITIES.

discussions are taking New Job for the B.B.C. ? tion become that place as to the feasibility of securing There are still people who, to use an further offices somewhere in the Strand. Army expression, " want jam on it." This will involve decentralisation and Among this optimistic throng I am in- will raise mildly invidious questions as to clined to class a celebrated actress whose who can and who cannot be spared from letter appeared in an evening newspaper a H.Q. few days ago. 0000 wrote) in " Could not the B.B.C. (she New Premises Y sending out its SOS messages tell the rela- the time of the next train An alternative to decentralisation would tive concerned By Our Special Correspondent. a new from his or her town to the town where be 'the acquisition or erection of broadcasting building, on the precedent the sick person is? For London people it S O Crowding at Savoy help, too, to be told which ter- S.- set forth by the American National Broad- would be a in which the minus to proceed to." Hill. -Ship Broadcasts. - casting Co. in New York, to spoil the ship for administrative offices would be grouped It would be a pity Regional Scheme Reflections. hall designed, architectur- a ha'porth of tar, and I feel sure that the round a large if asked politely, would gladly -The Music Halls. ally and acoustically, for broadcasting B.B.C., fact, on these supply a fleet of SOS vans equipped with purposes. In something hampers and lines will be almost a necessity in view of camp beds, refreshment Room Only. concerts other aids to comfortable travel. It Standing the public demand for symphony would only entail an addition to the Mention of a larger staff reminds me of on a larger scale. is hardly conceivable that the licence fee. the lamentation poured into my ear by a It 0000 B.B.C. official at Savoy Hill a few days recently concluded series of National Con- ago. certs at the Albert Hall will find no as it Pity tin Poor Announcer. " Enlarging the staff ? " he exclaimed equivalent next winter, particularly or If the B.B.C. had to search for train in reply to a query. " The building is was evident that during the last three of the series the public began to times before distress messages were packed already ! " four broadcast much valuable time would be- There is no doubt that the B.B.C. develop the habit of attending. - lost. A larger staff would also be needed, headquarters are unpleasantly congested, 0000 otherwise awkward gaps in the pro- despite the additional suites of rooms On April 30th. years ago when the old gramme would ensue while the over - obtained two Nelson Keys will broadcast from 2L0 through Savoy Mansions became B.B.C. property. worked announcer rummaged on Saturday next, April 30th. Brad Shaw. So serious has the problem of accommoda- 0000 Launching Ceremony to be Broadcast. The ceremony of the launching of the Commonwealth and Dominion liner Port Gisborne from the shipyard of Messrs. Swan, Hunter and Whigham- Richardson, `Yallsend -on -Tyne, will be broadcast from 2L0 and 5XX on April 30th. The transmission will include the christening ceremony, performed by Mrs. John Boyden Hooper, a speech by Sir G. B. Hunter, and a description of a modern shipyard a ship. and the building of0000 On Board Ship. Dance music from the R.M.S. Majestic, the largest steamer in the world, will be relayed to the Bournemouth station during the evening of May 2nd. The Majestic will be in Southampton Docks on May 2nd, and a ball is to be held on board ship in aid of the Royal South Hospital. Hants and Southampton0000 " Daventry Junior " Still Preparing. The long -delayed experiments from THE COMMUNAL AERIAL. Instead of the usual array of uaslghtly aerial poles, Daventry Junior will probably start early tl.ese new houses of a Bradford estate are provided with the modern " maypole," the engineers are shown in the photograph. ir, May, and I hear that B 31

www.americanradiohistory.com WflmIlsto 534 Wasia qPRIT_ 27th, 7927. fairly confident of success. The main uncertainty associated with high -power transmissions on the short broadcast band is in regard to the question of interference with ship and commercial stations. In this respect it is assumed that Daventry Junior will benefit from its position in the centre of England, far from the shipping routes and other channels of wireless intercourse. If, as is expected, the tests are completed in a shorter time than was originally planned, I should be prepared to wager that the first regional high -power station will be in regular operation much earlier than the time originally mentioned, viz., November. 0000 Choosing Sites. Then (if the B.B.C. has any money left !) we may see the rapid prosecution of the complete 'regional scheme. The big- gest job -a job beside which the picking of winners would be child's play -will be the choice of suitable sites. Of this, more anon. 0000 Community Plays in Belfast. A CALAMITY IN GERMANY. An aerial mast at Königswusterhansen, erected only Community plays, like community sing- a few months ago, which has been blown down in a gate. ing, are on the increase. It is the policy of the Belfast station to assist the growth cession. But I understand that neither of the native drama. To this end the FUTURE FEATURES. Mr. Charles Gulliver nor Sir Oswald Stoll Carrickfergus Players, a band of en- Sunday, May 1st. the leading music hall proprietors, has County have been thusiasts from Antrim, LONDON. -Light Orchestral Con- approached the B.B.C. direct, all the con- asked to produce one of their own plays cert. troversy having been conducted through in the Belfast studio. This is called BIRMINGHAM. - Symphony Con- the Press. Until the B.B.C. are ap- " Miss Clegg's Legacy," and will be given cert. proached directly in the matter no end 'to on May 6th. IANrsESTER. Motor the present ru,poase is likely. 0 0 0 0 - Fodens' Works Band. 0 O 0 0 Russian Exiles at the Microphone. Monday, May 2nd. Broadcasting as an Russian exiles in the home of their LONDON. -Act I of " Der Rosen - Anesthetic. adoption, which is England, are to give kavalier " relayed from Covent Two or three weeks ago I cast doubts a programme from 2L0 during the first Garden. upon the authenticity of a news story week in June. Vladimir Polunin, who Tuesday, May 3rd. from New York concerning an elderly lives in Chiswick, and is the scene painter ABERDEEN.- Variety Programme. man who successfully underwent a surgi- to the Diaghileff Russian Ballet, will take cal operation to the accompaniment BELFAST. - " Handel in oilier of an a leading part in organising the pro- Countries." " anaesthetic " in the form of a broad- gramme, and his children, who are re- cast programme on the headphones. puted to be among 'the most beautiful in Wednesday, May 4th. That the story was not so extravagant England, will sing. A Russian noble who LONDON.- Annual Demonstration of after all is shown by the fact that the was a prominent figure at the Tsar's the Boys' Brigade relayed from wireless programmes are frequently put to Court when Rasputin was killed, will also the Royal Albert Hall. the same use at King's Collage Hospital, take part. Princess Zinovieff is another BouRNEMouTH.- Orchestral Concert Denmark Hip, London, S.E. The Chief of the singers. The compères will be relayed from Winter Gardens. Engineer at the hospital tells nie that A. P. Herbert, of Punch, and L. de G. CARDIFF. - Winners at Bristol patients undergoing painful operations of Sieveking, both of whom will, I hope, Eisteddfod-programme. a minor character are very grateful for make the announcements in English. NEWCASTLE. -A Tyneside Even ing. the distraction afforded by listening to the 0000 Thursday, May 5th. 2L0 programmes. The phones in the operating room are The Music Halls. LONDON.- Tchaikovskv Programme. CARDIFF. A May -Time Revel." connected to the main hospital set -an At the moment of -" writing the air is ABERDEEN. -" At the Nineteenth eleven -valve instrument installed recently thick with rumours anent a proposed sub- Hole," a Golfing Programme. under the Daily News scheme. sidy of the music hall industry by the 0000 B.B.C. in return for permission to employ Friday, May 6th. artists who are in the habit of serving DAVENiRY. -St. George's Dinner contracts with the " halls." Speeches. " Living Composers' " Night. In the case of the B.B.C. subsidy to the BIRMINGHAM.- Popular Orchestral On May 8t .h Birmingham listeners will newspapers' direct service in the shape of Programme. hear a programme of music by living com- news is given for value received ; in sub- Saturday, May 7th. posers, including the " Wand of Youth " sidising the music halls, however, the LONDON. - Augmented Military suite by Sir Edward Elgar, the Concert B.B.C. would reap no direct gain, and Band. Piece for 'Cello and Orchestra by would, of course, have to pay artists in GLASGOW. - Scottish Humour Dohnanyi, in which the soloist will be addition to paying the subsidy. Series. No. 3. Leonard Dennis, a member of the Station An annual sum of £60,000 has been ABERDEEN. -" The Third Degree,' Orchestra, and also the " Bridal Song " mentioned, and although this may seem a play by Frank Bremner. from the cycle of " Sappho " songs by Targe, it can at least form a basis for dis- Granville Bantock. 8 32

..,.,- ,t. - _,s, www.americanradiohistory.com WAp4@00 APRIL 27111, 1927. WOpIld 535

Bd J1r1i9,11ER 11 dliAVllIN Ai ,ORS0 Appliances for the Operation of Radio Receivers by Energy Derived from Electric Supply Mains.

By PHILIP R. COURSEY, B.Sc., M.I.E.E., and H. ANDREWES, B.Sc. (Abstract of Paper read before the Wireless Section of the Institution of Electrical Engineers.)

THE frequent replenishing or recharging of batteries The first essential element of the H.T. appliance is a be or accumulators used to supply radio receiving filter to perform the smoothing action, and this must apparatus with H.T. and L.T. has given rise to combined with a potentiometer or some equivalent device considerable dissatisfaction, and has created :a demand for subdividing the applied voltage into two or more parts. for apparatus which will replace them and provide equiva- For the A.C. supply circuits some rectifying device must lent voltages and currents derived from the public electric also be added. The essential elements of an H.T. supply supply mains. appliance suitable for use on a D.C. supply circuit are These pieces of apparatus used to supply radio receiving sketched in Fig. 2. It comprises two input terminals Ti sets are very commonly termed " battery eliminators," but T2, across which is shunted usually a pair of condensers since some types of apparatus which properly belong to this class still make use of batteries or accumulators this term scarcely seems suitable. For this reason they are referred to herein as " radio supply appliances," with the idea that this term is of broader application than the other. A more suitable and general term that could be universally accepted would, however, he desirable. Theoretical Considerations. A radio receiver customarily requires three sources of energy, viz., L.T., H.T., and grid bias. It should be particularly noted that these three sources of voltage necessarily have a common connection to the valve filaments. This introduces a complication which must not be overlooked when considering the application of radio supply Fig. 2- Simple filter circuit for H.T. supply appliance. appliances, since these necessarily have a further common coil L, is connected. This in the electric supply mains. Fig. i represents C C27 between which a choke connection suppress currents of the the theoretical arrangement rather than a possible actual combination acts as a filter to to allow the lower frequencies and one, and two at least of these appliances are commonly higher frequencies and to pass through. The first combined into one unit, or alternatively batteries or accu- zero frequency (direct current) . a proportion of the ripple fre- mulators are retained for one of the supplies. The precise condenser, C by- passes reactance of the condenser falls for arrangement of apparatus necessary to provide an H.T. quencies, since the The choke L, offers an impedance supply to a radio receiver depends in the first place upon increasing frequencies. with the frequency, thus whether the electric supply system from which the radio to these ripples which increases lower frequencies to pass through to the supply is to be derived is direct or alternating current. In allowing only the a further selective action. the latter case some form of rectification must be provided. second condenser C2. This offers similar to the first condenser C. The general form of this filter is of the well -known " low pass " type. Double Filter Circuits. Frequently a further filtering stage consisting of an additional choke coil L2, and condenser C3 (Fig. 3), is added to improve the filtering efficiency. The full voltage across the last or output condenser C2 (Figs. 2 and 3) is obtained from the terminals A and D, to which the radio set may be connected. With a 220 to 240 -volt supply, at least 200 volts is usually available at these output terminals, the difference being the voltage drop due to the resistance of the choke coil Or coils Lf and L2. Most radio apparatus, however, requires one. or more lower voltages in addition to the full output voltage. These may be obtained by a potentiometer arrangement connected across the output terminals A, D, such as is R in Figs. 2 and 3, with the Fig. I.- Theoretical arrangement of radio supply appliances. indicated by the resistance 5 33

www.americanradiohistory.com WAT®Il@AT Waal APRIL 27th, 1927. Battery Eliminators. - two (or more) tapping points connected to the terminals and C. It is usual and desirable to connect additional condensers -of at least r microfarad capacity- across these additional voltage tapping points, as shown at C,4, and C5. These condensers provide a certain measure of additional smoothing action, but more important is their action in preventing excessive coupling between valves when more than one valve stage is operated from any one tapping point. If the condensers were omitted the varying anode currents drawn by each valve of the radio receiver would be forced to travel through a portion at least of the resistance R, producing across its terminals a volt- Fig. 4.- Alternative arrangement of multiple H.T. voltages. age drop of the same frequency, which would in consequence be communicated to the remaining valves in the drawn by these valves is subdivided through the different receiver. Low - frequency oscillations, or " howling " of resistances. This results, however, in a somewhat greater the receiver, would then be very liable to occur. The low voltage variation of the tapping points B and C with impedance offered by by -pass the condensers C4 and C5 changes in the load current drawn by the valves. to the passage of alternating currents effects a consider- If a potentiometer arrangement is used on the lines of Figs. 2 and 3, the total resistance, R, needs to be high, or it will draw too large a current through the filter. Normally, the resistance of the chokes Lt and L2 is much in excess of i,000 ohms, in order to obtain a large inductance in a small space, and at a reasonable cost, so that only a few milliamperes can be drawn through the filter ithout causing excessive voltage drop. For this reason also the method of Fig. 4 is advantageous, as it makes a smaller demand upon the filter. Convenient values for the resistances of Rt and R2 are generally found to be between ro,000 and roo,000 ohms, depending upon the voltage and the current desired at each of the tapping points. A Fig. 3.- Double filter circuit for H.T. supply appliance. small demand for current will obviously require the use of a high resistance, and any considerable change made in able diminution of the voltages available for producing the output requirements will necessarily involve a change such feed -back effects. It is for this reason also that the being made in the resistance values, unless a considerable capacity of the output condenser C must likewise he large. change in operating voltage is also permissible. A minimum capacity of 2 microfarads is customarily used, but larger values are desirable. Filtar Circuit Design. In lieu of the potentiometer arrangements for tapping It may be said that there are, in the main, three im- the output voltage a very frequently used arrangement portant electrical factors affecting the design of the filter, omits the portion of the potentiometer between the tapping apart from economic considerations. In this, as in most point and the H.T. negative terminal D, so that merely a other apparatus, the commercial design is to a greater or series resistance is used between the H.T. positive terminal less extent a compromise between the considerations of A and the load applied to the tapping terminals B and C. This modification is shown in. Fig. 4, in which these series resistances are indicated at R R. , one being connected in series with each tapping point ]l and C. Two by -pass condensers, C4 and C$7 are shown, connected in the same way as in Figs. 2 and 3. This arrangement is simpler than the potentiometer one, and has the additional advantage of somewhat reducing the coupling between different valves in the radio receiver, since the total H.T. current Fig. 5.-A.C. characteristic of a single filter circuit.

r .34

www.americanradiohistory.com VAT®Il®00 APRJT, 27171, 1927. . 537 ou Rr1 Battery Eliminators. - Other measurements of similar character have also been electrical efficiency and of cost. These three factors are made with other factors of the filter varied in turn, and (r) The internal resistance of the choke winding. similar characteristics plotted out. These enable the (2) The resonance,or " pass " frequency of the filter. appropriate design of the filter for any given conditions (3) The output impedance of the output circuit of the to be arrived at from a consideration of the curves. filter at audio frequencies. The general form of these characteristics shows that Improvement of the desirable qualities of all three fac- for the higher frequencies of 5o cycles and over, particu- tors invariably increases the cost of the apparatus. larly for the larger inductance values for the choke coil, As regards its effect in suppressing ripple frequencies the use of the filter gives a considerable reduction in the from the supply circuit, the simple single filter of Fig. 2 output of the ripple component. A further reduction in these unwanted components is obtained by the use of a second filter circuit, of the form given in Fig. 3. A 18 group of characteristic curves for such an arrangement is reproduced in Fig. 7. 16 3 mfd It may be particularly noted that some of these curves show a subsidiary " hump " which might have a serious 14 effect on the efficiency of the filter, if such a hump should occur near so or roo cycles. The possibility of such _ 1.2 occurrences emphasises the desirability of plotting out the 10 ANNE '',",05mfd 0.8 16 0.6 '1,,,,,' , 14 04 "" 0.2 12 0 20 30 40 `'50 60 70 80 FREQUENCY

0.8 111111 Fig. 6. -Effect of output capacity' on A.C. characteristic. may be regarded as a resonant circuit, consisting of an inductance in series with a condenser, the input being applied across the two in series and the output being taken from across the condenser terminals. This resonant 0.4 circuit is damped by the resistance of the load circuit (radio receiver) which is connected across the condenser terminals. This resonant circuit is independent of the 02 II completely closed circuit consisting of the coil I.,, and the Malt' condensers C1 and C. in series. This has been con- formed experimentally by plotting the characteristics of MEMO such a filter when subjected to applied alternating poten- 10 20 30 40 50 60 70 tials of various frequencies. The characteristic curve of the filter was, under these conditions, found to be totally FREQUENCY unaffected by the capacity of the input condenser C,. A typical characteristic curve of this type taken on the com- a filter as used in an supply Fig. 7. -A group of A.C. characteristics for various arrangements ponents of H.T. appliance of double filter circuits with different capacities and inductances. is reproduced in Fig. 5. The output capacity of the These curves show that a double filter circuit may give worse results than a single filter using the same components unless filter does, however, affect the characteristic, as it alters the correct arrangement is chosen. the resonant or pass frequency (see Pig. 6) in which filter output characteristics are plotted for four different values frequency characteristics of any filter that it is proposed of output capacity for a given choke coil. to use in an H.T. supply appliance. 0 It is suggested that some definite method of rating the Filter Characteristics. output and characteristics of these supply appliances In these curves the ordinates plotted are the ratio of might be formulated on the lines of the three main elec- the output voltage to the input voltage. They therefore trical characteristics of the filter which are mentioned express the effectiveness of the filter to reduce the ampli- above, and that such factors might provide a means of tude of an applied ripple voltage of various frequencies. adequately expressing the performance of the appliance B 35

www.americanradiohistory.com WAp@Ilmo 538 Wayc APRIL 2711!, 7927. Battery 'Eliminators.- L.T. supply is provided by a floating battery connected under working conditions. Probably further experimental across the L.T. circuit, appropriate resistances or rectifiers work is still required before such a scheme could be for- being arranged to provide the requisite magnitude of L.T. mulated completely. supply current, so that the battery across the line is not A commonly adopted arrangement for grid bias supply under discharge, but merely serves to by -pass the un- is to insert a resistance in series with the negative return desired ripple frequencies. The battery acts in this con- lead to the H.T. appliance, so that the negative terminal nection as a very low resistance shunt, or as a condenser of the supply circuit is made more negative than the valve of enormous capacity. A method of L.T. supply, how- filaments of the radio receiver. This resistance should be ever, which is at the same time a true battery eliminator, shunted by an additional by -pass condenser. would be more desirable. To enable filter arrangements of the above type to be At the present time it may be said that the most com- used with an A.C. supply circuit, a number of special monly adopted arrangement for supplying a radio receiver rectifying valves are now marketed. Some of these are is an accumulator for the L.T. supply, with an appro- designed for single -wave, and some for double -wave recti- priate supply appliance, or battery eliminator, for the fication. Several of these have already been described H.T. supply. The L.T. accumulator may be maintained in these pages. charged by means of some form of trickle charger, or by When the available electric supply system is D.C., the ordinary charging means. Doubtless, however, further provision of a L.T. supply to the radio receiver is com- developments in L.T, supply appliances will be made in paratively simple, but is far from economical, since the due course, resulting in the manufacture of apparatus total current required for the L.T. circuit, which is util- having the reliability and efficiency of some of the present_ ised in the receiver at 4 to 6 volts, must be paid for at forms of H.T. supply appliance. With some of these the supply circuit. voltage. This latter may be as much latter more attention to the details of design would result as 240 to 250 volts, in which case the efficiency of the in more effective apparatus, capable of greater output, arrangement cannot exceedabout 2r per cent., while the and it is hoped that some of the methods of testing these remaining 97¡- per cent. of the energy taken from the appliances which are outlined in the paper will be of mains must be wasted as heat in the series resistance. service to manufacturers, and will lead to a better under- Probably the most useful filtering arrangement for standing of their action and design.

TRANSMITTERS NOTAS LT- QUERAND International Relay Contest, May Europe this summer. He expects to be 9th -22nd. in London from August 4th to 10th, and With reference to our note on page 344 IES would like to get into communication of our issue of March 23rd, we are asked with amateurs interested in communica- by the Communications Manager of the tion with Japan. Letters should be sent A.R.R.L. to correct the statement, made c/o Otto Reimers, Alsterdamm 4 -5, Ham- in error, that only one reply might he burg, Germany. During his absence Mr. a British transmitter. He is usually on received from any one country. While S. Osaka will operate KZB, which sends the ether from 2100 to 0000 J the rules of the contest limit amateurs G.M.T., is a regular test every Tuesday, Thursday in U.S.A. and Canada to sending "one also working traffic with U.S.A. from 0130 to and Friday from 0800 to 1300 G.M.T., message per country," each entrant may 0300 G.M.T., and will be glad and on the first to hear from anyone receiving Saturday of every month accept reply test rpessages from several his signals. from 0800 G.M.T. to the next, day. CQ stations in each country, but only one 0000 will he sent for 3 minutes each hour. 20 message may be accepted by each Mr. Collins (NE 8JC), St. Johns, New- and 40 minutes after each hour, during individual from any one foreign station. foundland, will be glad if British and the 24 hours. 0000 Irish amateurs will look out for his sig- 0000 General Notes. nals on 44 to 46 metres. He transmits Mr. Louis Era (EB 4BC), 46, Avenue regularly from midnight (G.M.T.) on- New Call -Signs Allotted and Stations Van Put, Antwerp, city manager of the, wards. Identified. Reseaa Belge, tells us that he has lately 0000 G 5FQ E. H. Capel, 11, Gerrard Road, Harrow, been in two -way (Change of address.) communication with Mr. W. E. J. Moree (OD PK9), 89. G H. D. Cohen (144, West Hill, amateurs in various parts of the world, Nakoelaweg, Bandoeng, Java, was in 5KH Putney. inclnding A5A in Johannesburg and S.W.15. (Correcting the entry on page 500 0 two -way communication on February of our issue of April 20th, when the name FK KTC in Khartoum. The latter 20th, between 2055 and 2145 G.M.T., was incorrectly given as R. H. P. Collins.) station was worked on 32.5 metres with with G 5HY, Mr. Baynham Honri, in G 5NQ A. C. Mercer, Straithgate, 222, Roolev Lane, an input of 50 watts at a time when he London. This he states to be the first Bankfoot, Bradford. (Change of address.) was unable to pick up any Swedish, intercommunication between amateurs in G 5RT R. W. T. Brewer, " Dorchester," Mile End American or Canadian stations on 20 or Road, Colchester. (This call -sign was England and Java. Atmospherics were formerly owned by C. D. M. Hamilton, 40 metres. prevalent and interfered a good at Hull). 0000 deal with the interchange of greetings. G OYU J. Hanson, ' Abbeydore," Wyken Avenue, A correspondent, who claims to he the 0000 Wyken Grange Estate, Coventry. (Change first English amateur to receive signals of address.) on 20 metres from Honolulu, informs us Mr. Yoshio Imaoka (J KZB), of the 2ACQ F. W. Woodward, 5, Portland Gardens, / Harringay, N.4. (Mr. Woodward par- that OH 6AG is working on 19 and 20 research laboratory of the Tokyo Electric ticularly wishes to notify that be no longer metres and wishes to get into touch with Co., in Kawasaki, Japan, is visiting holds the call-sign G 20W). B 36

*arti93.t.wd.rc.k.awváßs:r.Ifiq.:-''.ia.c`.riìF;bg4;Yl..N'6'éláiwww.americanradiohistory.com x. F#tJ~`_+aír* . .et-ss 'tsir_ APRIL 27th,- 1927. WinIlmo 5.79 W01s114

LA19E125 NO l ,'':LTIf S hftuseese

A Section Devoted to New Ideas and Practical Devices.

EARTH PIN. the panel is tightened up by means of porarily screwed down on to the If any wire is left over after erect- a special spanner C supplied with spanner, and will effectively prevent ing an aerial it can be used for an the condenser. the claws from rising out of the holes earth connection in the following in the bush. -j. P. manner :- 0000 A wooden stake, eft. or aft. in length is obtained (a broom handle PORTABLE TESTER.. will serve) and the end pointed to The use of telephones in conjunc- drive into the ground. A lateral hole tion with a dry cell for testing con- is then drilled through the stake from tinuity has been referred to on many side to side about Sin. from the point. previous occasions in these pages, but The end of the surplus wire is then the testing unit has been built in the inserted in this hole and the entire form of a box with terminals to which length of the stake closely wound phones and testing leads are attached. with the wire. To finish off the wind- With this arrangement portability is ing the end of the wire maybe pulled seriously impaired, and one is virtu- into a slot cut in the end of the stake. ally tied down to one place. Use of dial bush of Gecophone condenser The advantage of this method of to keep spanner in position when tignt- ening panel bush.

Two holes are drilled in the flange of this bush on opposite sides of the main spindle S, and into these holes fit the two claws at the end of the spanner. Now a certain degree of downward WOUND WITH pressure is required to keep these claws from slipping out while tighten- / 72 ing up the bush. To get over this COPPER WIRE difficulty, the dial bush A should be brought into use. This may be tern-

VALVES FOR IDEAS. Readers are invited to submit brief details, with rough sketches, where Wire-wound earth pin. necessary, of devices of experi= Portable testing outfit with dry cell mental interest for inclusion iri this attached to headbands. earthing is that a continuous length section. A dull emitter receiving of wire without joints can be used valve will be despatched to every to an old pair between the earth terminal of the set By fixing the dry cell reader whose idea is accepted for in and the ground. -D. R. V. of phones, and connecting as shown publication. the diagram, it is possible to walk

Letters should be addressed to the Editor, about with the headphones in posi- GECOPHONE CONDENSER HINT. "Wireless World and Radio Review" Dorset tion and to carry out tests in any House, Tudor Street, London, E.C.4. and 'l'he main bush B securing the marked " Ideas." part of the room with the two free frame of the Gecophone condenser to telephone tags. -W. D. B 37

'..R.:ieA-....._. www.americanradiohistory.com 540 WApAsoo AP.PRIL 27th, 1927. WOrDci

y,. p_IIIIIIIÌIII 1i,11111,OO1'.w .i ,I,I.IIiIII.Illllili;,llli}IIII

Editor does not hold himself Nisl: :11 The . responsible for the opinions ill III II In I IIIIi i l Ìlgl111.1 I IiÍÌIIIIIIIIIIIÍ;II ii{III I IIII'lllllllllnl1a 1Ï1mmílililllll1' of his correspondents. Corres;ondence should be addressed to the Editor, "The Wireless World, Dorset Hose. Tudor Street, E.C.4, and must be accompanied by the writer's name and address.

B.B.C. HIGH -POWER STATIONS. B.B.C. RELAY TRANSMISSIONS FROM AMERICA. Si % -I have read with great interest two letters, one by Sir,May I be permitted to write and confirm the remarks Mr. W. J. Randall and the other. by Miss A. M. J.. Shorter, in regarding American relays as mentioned by your correspondent your issue of the 13th April. Mr. A. W. Sikes ? As both these correspondents labour under a misapprehension, We are usually informed that we are going to be given more may I be allowed the courtesy of your columns again to make or less " a special treat " by the B.B.C. in the form of a clearer the basic ideas underlying the new Regional Scheme? programme from one of the American broadcasting stations. In Mr. Randall is quite right in stating that the scheme we due course we get it, more or less ; but, really, it can hardly be have in mind is to establish five two -wavelength high- powered called clear enough to be enjoyed. stations, provided Post Office permission is forthcoming. Mr. I am in the habit of tuning in both 2XAF and KDKA very Randall says that this will prevent any possibility of persons frequently, and on nearly every occasion receive the transmis- living near these stations being able to listen to foreign stations, sion with remarkable strength and purity. and he proposes that six central stations, perhaps at Daventry, Possibly this branch of relaying does not lend itself for suc- would solve the whole trouble. cessful results when " boosted up " by the amplifiers of a We have to balance up, however, two factors; first of all, powerful broadcasting station, and if this is the case I stand the strength required for a service area, and secondly, the corrected. E. T. BELL. strength above which we must not go to enable valve set users Southampton. to reach out. At the outset one must indicate that one is March 23rd, 1927. . sympathetic with both claims, but it must be realised that the first claim has priority, B.B.C. TRANSMISSION OF PIANOFORTE MUSIC. radiating I, personally, would like to see a central station (Messrs. idea was, in fact, seriously considered. Sir, -I have read with interest your correspondent's six wavelengths. This in current issue of your Calculation, however, shows that to give anything like a ser- Rossiter & Brown) letters the vice area over tl,e whole of the British Isles, these stations periodical. As an amateur musician of very many years I would strongly would have to be of the order of hundreds of kilowatts. Firstly, their sets or their loud- probably not be allowed by the authorities; secondly, advise these gentlemen to blame either they would of them, before blaming the they would be far too expensive; and thirdly, they would speakers, or perhaps the tuning in case fade " 100 miles whatever their B.B.C. possibly any " at Laffitte, about 17 kilometres power. I live at a place called Maisons of Paris; my receiving set is an 8 -valve it realised these new stations will not be in the centre on the western side Is that superheterodyne made by Mr. F. Plow, of Paris, with a Brunet of large cities, but will be located outside them, so that the say that the pianoforte in general about the same field 2 -tone loud- speaker, and I would like to large city will have strength which receive either from 2L0, Daventry, as it has to -day, which, except very near the transmitter, is transmission I Bournemouth or Manchester is, without any exaggeration, not prohibitive ? For instance, Miss Shorter says she lives a regional perfect, whether from the studio or relayed from other places. mile from 2LO's aerial. She will find when the station am an organist of over 22 years' standing, field from the regional station will Might I add that I is erected that the strength Chapel Royal chorister, and an engineer by profession, be about one -tenth of what she now receives, and that so far an ex with a very delicate and sensitive ear for music of any des - from making it difficult for her to reach out, she will be much R. E. GOUGH. placed. as a of fact, will cause cription. more favourably This, matter Anvers. a good deal of trouble, because a great many people who us April 11th, 1927. listen only to the local station will be crying out for the very loud signal which they have been used to and which they will continue to expect, instead of the sufficiency they will receive. EMPIRE BROADCASTING. Our object is to make Britain a service area with alternative programmes, and it may interest technicians to know that we Sir, -In view of the paragraphs that have appeared in The consider that the " A " service area is bounded by the field TVireless World from time to time concerning the suggestion contour line of about 10 millivolts per metre, while the " B " that 5XX should operate a short -wave station for the enter- service area may be considered to be bounded by 5 millivolts tainment of the Empire, it might interest you to hear that per metre. our old friend PCGG, operating on 30.2 metres, is now being The fears of both your correspondents would appear to me received with remarkable strength in this country. His pro- to be on the whole groundless, since neither of them is likely gramme two nights ago, consisting of English gramophone to live under the shadow of the aerial of any of the new records, was listened to here for two hours (1530 to 1730 G.M.T.), regional transmitters, which will be remotely placed. and although reception was not as perfect as, say, a local London, W.C.2. P. P. ECKERSLEY. broadcast station, it is much more enjoyable to listen to than April 14th. 1927: most Continental stations are in England. Distortion and fading B 38

I , 1. a,-,.stn-,r.: .,,.w < ... , ax.s,it. www.americanradiohistory.com. .. "-L. ..? ira. f.,'.ye^ rf, nl= . -, r:'r . . WkaIlmo APRIL 27111, ¡927. My 1. 541 were much less noticeable than when listening to 2XAF at home, provide two blind people with an endless source of happiness due to greater power being used, it would seem. for the rest of their lives. This demonstrates that good short -wave broadcasting is pos- All sets will be distributed by the National Institute through sible. That the programmes would be appreciated here is the County Associations for the Blind in all parts of the certain, whatever objections may be raised at home. The news country. bulletins alone would be a great boon as even local papers Donations for this purpose should be sent to me at the are one or more days behind, except in the big cities. Also National Institute for the Blind, 224-8. Great Portland Street, a daily Empire news bulletin would surely have an excellent W.1. HENRY T. WAGG. influence everywhere in the world, for our language is not London. Chairman of the Technical and Research confined to the Empire April 12th, 1927. Committee, National Institute By providing such a station the B.B.C. would open a big for the Blind. prospect to British manufacturers. " British Short -wave Sets for British Broadcasting! " would be an effective slogan. VALVE NOMENCLATURE. Meerut, U.P., India. E. J: If. MOI'PETT. March 26th, 1927. Sir,-Your Editorial, " The Valve," in the April 6th issue was of particular interest, especially the final paragraph. This WIRELESS SETS FOR THE BLIND. question of nomenclature should be given more attention, the various symbols used by different writers being confusing. I Sir, -It seems almost impossible that, for a few pounds, a was particularly pleased to find you had not used the terni blind man may be made equal in all respects to a man with " impedance " in your valve supplement. for sight a few hours every day during the rest of his life ! I cannot agree with you that the voltage of 4 should be- Yet it can àe done. Wireless does it. come the standard. The unit for a lead cell being 2, why use The National' Institute for the Blind has already distributed multiples? hundreds of wireless sets, and from experience knows that The case could be made out for three types of user (receiving these have not only brought endless pleasure to blind people, valves only) but have literally :- changed their entire outlook. But there are ( Ton with supply mains to house. thousands still without sets and to provide them funds are (b) Town with no supply. urgently needed. (c) Country. Thanks to Captain Ian Fraser and other members of Parlia- Surely sections (b) and (c) would be in favour ment, of one cell the blind do not have to pay for their wireless licences, provided it was possible to obtain types now made only in the but a free dog kennel is not of great use to one unable to 6 -volt rating. afford a dog! Section (a) have easy access to recharging or A.C. heating, Yet the granting of free licences is one step forward; while and so the voltage would not affect them. : the provision by One other point the National Institute of a Braille Radio Trines you did not mention the important question of cost. Surely is another. And if your readers will help me, the provision of the cost to the public is too high compared with the free wireless cost of sets will soon crown with success our several manufacture! C. E. CHESTER. attempts to bring to the blind poor the inestimable benefits Southampton. of wireless. Will they remember that one £5 note alone will April 14th, 1927. NEWS FROM THE CL BS. Secretaries of Local Clubs are invited to send in for pubitcation club news of general interest. AU photographs published will be paid for. A Visit to Croydon Aerodrome. Summer Wireless in Battersea. Battersea and District Radio Society, By kind permission of the Air Ministry, Wireless enthusiasts in the Battersea which has just started the summer term a party of members of the Muswell Hill district are cordially invited to join the of regular lectures (Tuesdays and Wednes- and District Radio Society paid a visit days, 7.45 to 9.45 p.m.). Enrolment can to the Croydon Aerodrome on April 9th. he made during the present fortnight, the The party were conducted round the FORTHCOMING EVENTS. subscription being is. per term (no extras). hangars and were given the opportunity WEDNESDAY, APRIL 27th. .c Lectures are classified under three head- of closely inspecting the saloon and pilot's Muanril 71111 and District Radio Soriety.- ings, viz., elementary. intermediate, It 8 p.m. At Tollington School, Tether- and cockpit of one of the new German all - down. Demonstration by Mr. II. L. advanced. In the elementary department metal monoplanes. Great interest was Kirke on " Distortionless Reception," 't new beginners' class is being formed Win./ the Rice Kellogg type loud- displayed in the wireless apparatus. speaker. for theory and practice. The intermediate A visit was then made to the wireless Tottenham Wireless Society. -At 8 p.m. department will deal with the theory of At the Institute, 10, Bruce Grow. Lec- transmitter and the operators' room. The ture: "Short il'nre Work," by Mr. S. electricity, magnetism. and wireless recep- transmitter at Croydon is worked by Sin it h. tion. including practical work and Morse. Edinburgh and District Radio Society. - means of remote control from the signal At 8 p.m. .4t 117. George Street. Lec- with field days. Advanced students will tower. Its operation was clearly demon- ture: "The Electrical Recording of experiment in short -wave reception and Gramophone Records," by Mr. J. V. strated by the engineer -in- charge. The l'arnol. transmission, with Morse practice and receiver has been in use for six years and Barnsley and District Wireless Associa- field days. is shortly to be replaced by modern tion. -At 8 p.m. At 22. Market Street. Those interested should at Demonstration on Transmitter. communicate apparatus. North Middlesex Wireless flub. -At 8.30 once with the hon. secretary. Mr. A. F. Full particulars of future meetings and p.m.. At Shaftesbury Hait, N.11. Lec- Hembury, Winstead Street, Battersea, ture': "Electrolytic Rectifiers," by 11r, 4. unen -air events may be obtained from the 1. J. Simpson. S. \\ -.11. hon. secretary. Mr. Gerald S. Sessions, Institute of Wireless Technology -.I t 7 p.m. At the Engineers' Club, C'or- 20. Grasmere Road, N.10. cntry Street, II'. Lecture: "The Visiting 2L0. 0000 Electrical Recording of Gramophone Records." by ,1/r. Marrie J. King. The wireless societies are still privileged Looking Backwards. FRIDAY, APRIL 28th. to visit the B.B.C. stations. At the last --set Radio Experimental Society of Manches - During the veer the Muswell Hill ter.- Au,,unl General Meeting. meeting of the North Middlesex Wire- and District Radio Society has provided MONDAY, MAY 2nd. less Club the hon. secretary announce.' four lantern lectures, twelve ordinary lec- Northampton and District Amateur Radio that he had received an invitation for a Society. --At 8 p.m. At the Cosmo Cafe. tures, nineteen combined lectures and The Dranrry. Annual Exhibition. limited number of members to visit 2L0. demonstrations, two visits to places of Croydon Wireless and Physical Society.- and there was great competition among interest, besides other attractions. Alto- ' At 8 p.m. At 128n. George Street. Lec- those present to be admitted to the party. ture: " What is the Use of ILF'. gether 41 meetings have been held, and Valves?" by Mr. Purkia, This will he the third occasion on which the Society is justly proud of its record. members of the club have visited 2L0. s 39

www.americanradiohistory.com V/Tmg hog APRIL 27th, i927. WopIlcol

The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed " Information Department." Each separate question must be accompanied bÿ a stamped addressed envelope for postal reply. "Litz " or " Litzendraht "? stranded and uninsulated wire under the across the secondary will be more certain 1 ani engaged in the construction of a name of Litz, as of course such wire of stopping the howl, but this would modern type of receiver using the would still come within the scope of the cause serious decrease in volume, and in type of H.F. transformers developed Litzendraht, meaning stranded wire. You any case 4 megohm is quite low enough by you and used in a large number can do nothing, therefore, except to deal to stop all howling. This method, only with reputable of your sets. I purchased the neces- 0000retailers. though usually certain in practice, is a sary Litz wire for winding the palliative rather than a preventative, secondaries, but results were none too A Worrying Whistle. because the proper way to have set to good. A friend informed me that 1 hare built a four-valve receiver con- work in the first place would have been the wire which I was using was not sisting of H.P., detector, and two to design the amplifier properly. Litz at all, but a poor imitation; L.P. stages, using a 4 to 1 ratio 0000 however, on returning the wire to transformer in the first stage, and a Run -down H.T. Batteries. the retailer from whom I purchased 6 to 1 in the output stage. Both 1 have a three -valve set consisting of the it, he assured me that this was Litz these transformers are made by a conventional detector and tu:o L.P. wire. I obtained the proper wire firm of repute, but I get a continuous amplifiers. The set is built mainly from another source, and I at once whistling noise in my loud -speaker for quality, and in the output stage noticed that this wire was in which is unaffected by turning soy I am, using an L.S.5A type of valve appearance vastly different from tuning dials. Is this oscillation? 'with 250 volts on the plate. Both the other wire, crud, moreover, M. C. R. L.P. valves are supplied with H.T. I find that by using it I obtain This is not oscillation in the ordinary from my mains, but I find it better vastly improved results compared accepted sense of the term, which is to supply the detector, which after to my previous efforts. Both wires usually taken to mean oscillation at high all does not consume a great plate were., however, stranded. It is frequency, but the howl is produced by current, by means of an ordinary 60- obvious that unscrupulous retailers L.F. oscillation in the L.F. amplifier. volt dry battery, as I find that a are selling stranded wire of an in- If it were . H.F. oscillation, of course hunt is produced when this valve is feror type as Litz. Can nothing he rotation of your tuning condensers would supplied from the mains. Lately, done to prevent this fraud? A. M. alter the pitch of the note produced. needing a new battery in this you are labouring under posi- Unfortunately The trouble is due, in our opinion, to tion, I made use of an old 100 -volt a delusion that the word Litz is a pro- the use of an excessively high ratio of battery which I had by me, the tected word descriptive of a certain 6 to 1 in the second stage, and you would voltage of which had fallen to 60. of stranded wire. This is not. so, I brand have done far better and at the same found that a bad howl was caused of course, and the word Litz is merely time have obtained ample volume even the English abbreviation for the German in the receiver. On substituting a on distant stations, and better quality new 60 all well: word Litze meaning a strand, and the -volt battery was also by using a 2.7 to 1 in the first German word Draht meaning a wire. stage Evidently the trouble is caused by and your 4 to 1 in the We thus have the combination second stage. To the battery, but I cannot see the word cure your trouble now Litzendraht meaning roughly stranded you should first difference myself between a new 60- wire, the German word Litzen being of see that your components are well spaced volt battery and an old 100 -volt course the plural of Litze. The word out, transformer cores being at right - battery which, tested with a reliable angles even if shrouded so Litz, therefore, is not a trade mark, and that all voltmeter, reads just over 60 volts. can never be adopted as such by any chance of stray coupling is minimised. G. K. M. firm, as it is a colourable iiihitation of a See that the metal covers of your trans- There is, of course, a great deal of normal word occurring in a recognised formers are earthed, and also see that difference between using a new 60 -volt language. By popular consent, of course, you have very large fixed condensers battery and an old 100-volt battery which the word Litz has been taken to mean a across each H.T.+ battery tapping to has run down to this voltage value. In wire built up of a large number of common H.T. -. If this fails to cure the latter case, of course, the battery has strands of a narrow gauge wire, each the trouble we think it best for you to dryed up and its internal resistance is strand being separately insulated, and ap- try the effect of shunting a grid leak probably very high indeed, and even pearing at the centre and the outside of of megohm value across the secondary though you have only one valve running the wire an equal number of times. This of each transformer in turn, as this will from it, this resistance will set up a howl condition is satisfied in true Litzendraht almost certainly cure the trouble, and at such as you mention. In the case of by platting the strands together in groups the same time, provided the leak is not your new battery, of course, the internal of three. Imitation Litz is simply twisted lower than megohm, no perceptible resistance is very low. You might 1 e together. There is nothing, however, to decrease in volume will be experienced. able to use your old battery by putting prevent a firm from selling ordinary Of course, a 100,000 ohm resistance large fixed condensers across that section

15 40

.-=Mh. `7Fié>r.ltcwersiswww.americanradiohistory.com r .';s'ss '-?1; Wfip®Il,som APRIL 27th, r927. WopIl 543 of the H.T. battery you are using, but The Nucleus Receiver. high quality sets prefer to use absolutely it is infinitely preferable to use a new I am making a unit receiver on the straightforward circuits. In any case, battery. You would find that the dif- general lines of the 'Nucleus" set, since your set is a reflex you already havè ference would be accentuated were you but for reasons which. I need not one stage of L.F. amplification incor- running two or more valves off the same enter into leave made up the detector porated in -it, and the addition of an H.T. battery. valve (without an L.F. amplifier) as extra two -valve amplifier is almost bound 0000 the basic unit. It occurs to me that to result in bad quality due to valve over- A Ratio Riddle. the resistance and transformer L.P. load, and also probably trouble will be units, experienced due to L.F. oscillation unless a crystal described in your issue of A friend has built for me set you use exceptionally large con- using catswhisker type March 23rd, would, if made up into fixed the ordinary a single instrument, densers such as two or more microfarads of crystal, followed by a two -valve suit my purpose very well. I should, of course. .e across from each H.T.- tapping to the amplifier using a Marconi 8 to 1 and I the resistance stage first. If r common negative, or alternatively, use a a Marconi 2.7 to 1 transformer. recommend this arrangement, wit separate H.T. battery for the additional notice that he has placed the 8 to 1 you please let me' have a circuit dia - amplifier. - transformer first, and he asserts that gram of the combined amplifier, 0000 this is the correct procedure. If bearing in view the Dear at Any Price. you why you fáct that I wish this is so, can explain to feed the detector H.T. supply am in possession of a four -valve in your articles that I constantly urge from its own terminal, to be able to receiver and make use of dry when using two good transformers eliminate ratio one valve (with automatic batteries as my source of supply. I of different ratios the lower filament control), and to connect the noticed that as the batteries grew instrument should be used first? batteries permanently to the L.F, old crackling noises developed, and V. D. S. unit. P. H. T. a friend told me that if I shunted Your friend is perfectly cn rect in his The arrangement you propose seems to the H.T. battery with a large - assertion that he has built the receiver be quite practicable, and we think that capacity condenser I should eliminate correctly. This is on the face of it an the circuit given in the diagram should be these crackling noises. I conse- apparent contradiction of our usual suitable. The input terminals A and B quently adopters his advice and advice to readers, but it may perhaps be will be connected respectively to plate shunted a condenser of 4 m fds. regarded as the exception that proves and H.T. positive supply of the pre- across with beneficial results, but the rule. Your puzzlement arises prob- ceding detector valve. now I notice that my H.T. batteries ably from a lack of the true understand- A small condenser of about 0.0001 mfd. run down exceedingly quickly. Can ing of the reason why we advise in most may generally be connected with advan- you explain this? I might mention cases that the low -ratio transformer tage across the input terminals ; as to that the condensers were very cheap. comes first, and you are advised to read whether it is mounted in the detector M. R. O. the special article we published in our or L.F. unit will depend on the par- It appears from the symptoms which issue dated May 26th, 1926, entitled ticular use to which you wish to put the you give us that there is a leakage " Coupling L.F. Valves," where the former instrument. either in the dielectric of your con- whole of this matter is fully gone into. Briefly, the impedance of the transformer primary or choke should greatly exceed impedance to which it is o the internal I-H.T. H.T.+ coupled. Now a detector valve is usually a moderately high-impedance valve a high- impedance valve [1" because B M usually gives best results as a detector ó under general conditions, since the valve INPUT impedance is high the external im- A pedance must be much higher. This H.T. ó means a high- inductance primary, which in its turn means a very large number E of turns on the primary among other a things, and consequently there is no room for many secondary turns unless we make the instrument of unwieldy size, which we do not want to do, and in any case. if we attempted to do so, we should H.T. bring in other undesirable effects due to self- capacity. It will be obvious, then, LT. L.T. will to + that this transformer have o + be of low ratio. Probably our first L.F. o valve will be of lower impedance than the detector valve, and therefore, follow- Combining " ing the same train of thought, we do not - the Nucleus " L.F. Units. require so many turns of wire on the primary, so have more room for A Precarious Proposal. densers or a surface leakage between the secondary turns, and therefore get a I am in possession of a one -valve reflex two terminals. At any rate, it would higher ratio of, say, 4 to 1, although in receiver, and am desirous of adding seem to us that you have purchased many cases a high -impedance valve may to it a good two -valve amplifier of inferior condensers in which insulating be used as the first L.F. valve, when it modern design, which will give me material is used which is not above sus- must, however, be followed by a high purity of reproduction, and shall be picion, and that consequently all the impedance, and, consequently, if a good glad of your assistance in this time your batteries are slowly discharg- transformer is used, it must be of low matter in advising nie whether eny ing. We should advise you to connect ratio. The ordinary type of crystal, proposals are quite in order. up a suitable meter in series with your however, is of low resistance, and a rela- N. K. D. H.T. battery and a small choke coil. If tively few number of turns may be used Whilst of couree we should not care you notice that a continuous deflection in the transformer primary following it, to say that it is impossible to build a of the needle takes place, you can then and so we have plenty of room for reflex .set giving purity of reproduction, assume that the condenser under test is secondary -turns and get a high ratio. it is generally found that designers of faulty 8 41

www.americanradiohistory.com WAp@IlWO 51st APRIL 2711t, 1927. WOpIlol Eliminating Waste. fore the 4 -volt one must not be overlooked. coupling, and, in general, it is best not 7 have built a modern type of neutralised If the power valve, however, is of the to use a Reinartz circuit on long wave- receiver, which. gives me most excel- type consuming three -quarters of an am- lengths, but if selectivity is desired to lent results. On turning out the pere or more, then the point is not so use a fully tuned aerial circuit. Daventry H.F. valve I find that the local and Radio Paris, etc., come in much station signals completely disappear, better on the ordinary loose- coupled aerial and I have to use the H.F. valve circuit than on an aperiodic aerial circuit. even for the reception of the local Since aperiodic aerial coupling is one of station, tvltich is distant only a few the main features of the Reinartz circuit, nt?Ze$. Surely this is rather absurd one cannot say that it is therefore an as I often want to listen to the local efficient circuit on the long wavelengths, statiòn programme it seems very and the longer the wavelength the worse wasteful to use the H.F. valve. it is. The other feature of the Reinartz L.V.G. circuit, namely, capacitative control of The magnetic reaction, functions quite fact that the local station is com- efficiently pletely cut out when the on the long wavelengths. In H.F. valve is general, one can only turned out, shows that your set is very use aperiodic well neutralised, aerial coupling efficiently on the long and if the local station waves by did come in, of course, experimenting with the actual then we should aerial on which say that the set was not properly neutra- the set is to be used, lised Unless your and then it will be found that one could local station was excep- not transfer the set tionally close. We would suggest that to an entirely different Filament circuit 3 aerial and still obtain you mounted your neutralising condenser of -valve set using the same good 2- and 6 -volt valves. results in the same mauer one could on on the panel, so that on turning out the the H.F. valve shorter wavelengths. when desiring to serious, because receive the local station you will only the small extra current 0000 have to move the demanded by the other valve will not add neutralising condenser much slightly to bring in this local station at to the load on the 2 -volt accumu- A Misleading Mishap. lator as compared with the load on the excellent strength. You must not forget I have r »eenlly built a four -valve receiver to return the neutralising 4 -volt accumulator. condenser to 00o0 . seeing two L.F. stages, but I notice its original setting when desiring to that, when normally connected up, search for distant stations, or the set will A Long -wave Trouble. very hoar volume and great oscillate. distòr- It would be desirable, there- I have recently seen it stated tion is caused; upon reversing the grid fore, to use a neutralising that the condenser with Reinartz circuit is of little use on bias battery, however, and applying a a clearly defined dial indicator, so that long Can positive potential to the L.F. you could waves. you inform me ralres, return to the original setting whether or no this is remarkably good results are obtained. without having to re- true? neutralise every R. T. C. Can you inform. me Where I have gone time. sarong? 0000 Our answer depends, of course, upon B. H. W. exactly what you mean by long waves, The trouble is undoubtedly that your since certain types of amateurs are rather grid bias battery is wrongly marked, the A Problem of Power. apt to regard even 25 metres as a long positive terminal being marked with a - I am in possession of a three -valve re- wave nowadays. The Reinartz circuit (minus) sign, and vice versa. This is by ceiver employing two stages of trans- is at its best on wavelengths not exceed- no means an uncommon fault with cheap former- coupled L.F. I find, how- ing 600 metres, but above that wave- foreign -made grid batteries, while reports ever, that my output valve is over- length its efficiency commences to fall off have conic to our ears that a few batteries loaded even though it is one of the very rapidly. The Reinartz circuit, as have emanated from the factories of Brit- best 2 -volt power calves upon the you know, employs an aperiodic- coupled ish manufacturers of the highest repute market. If 1 increase the H.T. above aerial circuit, and while it is fairly easy with this defect. One should always look the figure given by the manufacturer to use the same number of turns for an for trouble of this nature when puzzled and increase the grid bias proportion- aperiodic aerial circuit over a com- by the behaviour of a set, while it is just ately, I find that it still overloads paratively large part of the broadcasting, as likely it would occur in an H.T. on loud passages of music, my test band, for instance, the long waves do battery. being ?,tads by means of a milliam- not take kindly to this form of aerial 000:; neeter in the elate circuit. I have therefore determined to use a large A Valve Query. 6 -volt power valve in the last stage, BOOKS FOR I hare in my possession a calve of 80,000 and shall be glad if you will let me ohms impedance with a correspond- know what is the proper method to WIRELESS BEGINNERS ingly large magnification factor, and I connect it up, as I still desire to use was wondering whether I could use my 2 -volt valves in the other stages. Issued in conjunction with "The Wireless World.' this in the H.F. stage of the "Every- Shall I need to buy a separate 6 -volt " YOUR FIRST STEPS IN WIRELESS," man -Four " and so get vastly im- accumulator? M. P. M. by HUGH S. POCOCK. Price od. net. By Post, Ird. proved amplification. P. R. B. It will not be necessary at all for you "WIRELESS TELEPHONY," by Unfortunately, you could not use this R. D. BANGAY. Price 2/6 net. By Post, 2/9. to buy a new 6 -volt accumulator, and we in the H.F. stage of the receiver you men- a "THE WIRELESS TELEPHONE," by advise the purchase of 4 -volt supple- P. R. COURSEY, B.Sc. 2/6 2 tion, as, of course, when considering the mentary Price net. By Post, /9. instrument. The connections " CAPT. ECKERSLEY EXPLAINS," by question of H.F. amplification one must which you will have to make will be as CAPT. P. P. ECKERSLEY. Price 2/- net. By take into consideration also the valve for shown in the diagram. We have, of course, Post, z /2. which the H.F. transformer was designed. only put in the necessary connections, all " UNCLE JACK FROST'S WIRELESS It was designed for a valve of about other connections being normal. It must YARNS ON GOOD RECEPTION AND 30,000 óhms impedance, and to get maxi- HOW TO GET IT," by CArr. C. C. J. FROST. not be forgotten that the filament current Price z / -net. By Post, 2/2. mum amplification one should choose a load of your big power valve will be valve having an impedance of roughly thrown on both the 4 -volt and the 2 -volt Obtainable by post (remittance with order) from 30,000 ohms, and having the highest pos- batteries, while in addition the 2-volt ILIFFE & SONS LIMITED, sible magnification factor for this im- battery will have to supply the remaining Dorset House, Tudor St., London, E.C.4, pedance. Increasing the impedance will two valves. The point that the 2 -volt OP of Booksellers and Bookstalls. increase the selectivity at the expense of accumulator may become discharged be- sensitivity. s 42