Quality Amplifier with Tetrodes

JAN. 194 81

TETRODES 1flh 5 TE IS HIGH- QUALITY AMPLIFIER WITH

Vol. LIV. No. I 15 www.americanradiohistory.comwww.americanradiohistory.com Advertisements Wireless World January, r948

Compression moulding press output can often be increased by t00% using high frequency pre- heating. For phenolic type powders thorough pre- heating gives a great degree of plas- ticity and makes possible the rapid production of flaw -free mouldings. Lower moulding pressures are possible with pre -heated powder, tool wear is reduced and curing time can be cut by as much as two -thirds. B.I.Callender's offer a range of high frequency pre- heaters sufficient to meet the needs of most compression moulders. They are robustly built for factory use, fully screened to con- form with Post Office requirements and incorporate safety devices to protect operators. Write for Publication No. 2X9 which gives full information on all B.I.Callendcr's High Frequency Heating Equipment.

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www.americanradiohistory.comwww.americanradiohistory.com wireless World JANUARY RADIO AND ELECTRONICS 1948 3 7 t h YEAR O F PUBLICATION

Proprietors : ILIFFE & SONS LTD In this Issue Managing Editor : HUGH S. POCOCK,

Editor : H. F. SMITH EDITORIAL COMMENT .. .. I -- HIGH -QUALITY AMPLIFIER DESIGN. By P. J. Baxandall 2 PUSH-PULL INPUT CIRCUITS. By W. T. Cocking 7 Editorial, Advertising and Publishing Offices: SHORT-WAVE CONDITIONS. By T. W. Bennington Io DORSET HOUSE, STAMFORD STREET, LONDON, S.E.I. GOVERNMENT HEARING AID .. I1

Telephone : Telegrams : CLANDESTINE RADIO .. 13 Waterloo 3333 " Ethaworld, Sedist, (60 lines). London." AMATEUR RADIO EQUIPMENT .. .. 14 TELEVISION PICTURE SIZE. By " Cathode Ray " 16

WHAT IS GOOD REPRODUCTION ? .. .. 20 PUBLISHED MONTHLY WORLD OF WIRELESS .. .. 21 Price : 1/6 MORE LOW -POWER TRANSMISSION. By 25 (Publicatirn date 26th of preceding month) W. Oliver OUTPUT TRANSFORMER EFFICIENCY. By A. E. Falkus 26 Susscription Rote : 20/- per annum. Home and Abroad AIR -LINE RADIO ...... z8 _ BOOK REVIEWS .. .. 3o UNBIASED. By " Free Grid " Branch Offices : 32 Birmingham : King Edward House, New Street, 2. LETTERS TO THE EDITOR.. 33 Coventry : 8-10, Corporation Street. RANDOM RADIATIONS. By " Diallist " . . 36 Glasgow : 26B, Renfield Street, C.2.

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www.americanradiohistory.com 22 Advertisements Wireless World January, 1948

VALVES AND THEIR APPLICATIONS

By M. G. SCROGGIE, B.Sc., M.I.E.E. No. 13: Mullard HIGH -SLOPE R.F. PENTODE EF42

diameter. The fact that the structure it supports IT is well known that for television and other is much smaller in itself makes it more rigid. But wide -band v.h.f. purposes the important the exceptional feature is a metal gauze cylinder characteristic is high slope (gm). Since the enclosing the whole electrode system and welded to load impedance is necessarily small, making the it at top and bottom - only 14 mm. apart. The slope large is the only way of obtaining a useful result is so firm that there is no need for mica stage gain. spiders or other supporting contacts with the glass One also expects a modern valve to be miniature bulb, and microphony from that cause is absent. and single -ended. As a screen, the position of the cylinder inside Achieving a design that fulfils these requirements the bulb excludes a certain type of noise associated is less than half the job. However attractive the with bulb charges. specification, it is worth little if the valve is difficult Mechanical distortion or strain that would to produce in large quantities, or is inconsistent. impair consistency is minimized in two ways : the The EF42 is interesting on account of its per- cylinder enables the electrodes to be more formance, but perhaps more so because it is at the uniformly heated during outgassing; and the bulb same time a good valve to manufacture. That is is " soldered " to the base by means of a low - why I am leaving until next month its characteristics temperature sealing cement. and applications (except to say the the slope is very Other details of the base are the silver plating of nearly 10 mA/V) and dealing first with its the pins to minimize contact resistance, the absence construction. of spigot (optional in the B8A), and the side boss to ensure correct and visible location. GRID Summarizing: the EF50 technique has been COOLING developed several stages further in the EF42 with PLATES the following beneficial results :- (1) Higher slope, with improved v.h.f. performance. (2) Miniature size. (3) In spite of (1) and (2), remarkable consistency of production. WELDS GAUZE (4) Exceptional rigidity and absence of micro - SCREEN phony. (5) Freedom from bulb charge noise.

LOCATI NG BOSS SEAL This is by G. GLASS BASE the thirteenth of a series written M. Scroggie, B.Sc., M.I.E.E., the well-known Consulting SILVER PLATED PINS Radio Engineer. Reprints for schools and technical To maintain the close spacing necessary for such colleges may be obtained free of charge from the a high slope, the electrode structure must be strong address below. Technical Data Sheets on the and rigid. Several features make for this in the EF42 and other valves are also available. EF42. Firstly, the structure is supported directly on the contact pins set in a ring around the pressed - THE MULLARD WIRELESS SERVICE CO. LTD., glass " button " base. This base, the new British TECHNICAL PUBLICATIONS DEPARTMENT, standard B8A, is like the EF50 type reduced in CENTURY HOUSE, SHAFTESBURY AVE., W.C.2

4dvertisement of The Mullard Wireless Service Co. Ltd. (M.V.M. 50)

www.americanradiohistory.com wireless World RADIO AND ELECTRONICS

Vol. LIV. No. 1 January 1948

Post Office Control EVERYTHING touching on the technical use even more remotely connected with the " trans- of radio communication channels demands mission of messages or intelligence? " However, the closest and most detailed regulation by a more mature consideration. leads to the conclusion national authority, working in its turn within a that, if only as a matter of expediency, the national framework decided upon by international agree- radio authority must at least be responsible for the ment. On that there can be no argument ; a " free- allocation of radar frequencies. We assume that for-all " radio spectrum would soon be free for responsibility for detailed administration of radar nobody. There will be almost equal unanimity will remain with the Ministries of Transport and on the proposition that there should be unified Civil Aviation, depending on the application. control of all forms of radiation, whether for com- Another aspect of Post Office control that has munication or not. recently given us concern is what we have termed Here we come to one of the weaknesses of restrictive uses of the authority vested in the British wireless legislation, which for all practical P.M.G. In the August, 1947, issue of Wireless purposes is confined to the Wireless Telegraphy Act World we suggested that neither the broadcast of 1904. Those responsible for that archaic docu- licence or any other form of licence available to ment can have had no conception of the ramifi- the public conferred authority to listen to trans- cations of radio in later years, and it is not sur- missions such as calibrated frequencies, time sig- prising that the Act, in spite of its supplement of nals, weather reports, scientific test signals and the 1925, fails to provide means for dealing with like when transmitted by stations in the " special modern developments. In exercising the monopoly service " category. Most of these transmissions are conferred on him by the Act, the Postmaster in fact directed either specifically or by implication General has gradually extended his powers to cover to the public, and it seems highly restrictive that such developments as radio telephony, picture any barrier should be placed in the way of their transmission and television. But the P.M.G. has, reception. in general, shown some diffidence-presumably on What is a legal grounds-on assuming control of radio Station? developments less directly concerned .with com- Broadcasting munication. Except under powers conferred on The Post Office does not confirm or deny our him by wartime Orders, we believe he claims no interpretation of the regulations governing the issue legal right to control potential sources of radio of broadcast licences but now offers us a new interference such as, to take an extreme case, R.F. definition of the term " broadcasting station " (on heaters. Until recently, there has been no indica- which the matter largely depends). This definition tion that the latest non -communication radio device reads :- communication service of -radar-has been considered as coming within his . " a station in a radio purview. Indeed, reasoned arguments have been transmissions radiated for direct reception by the adduced in this journal that it does not do so. general public on frequencies assigned to such But now we learn that legal opinion has been services." taken, and it has been decided that " radar appara- It would perhaps be unwise to attempt a re- this new tus is apparatus for wireless telegraphy within the examination of the problem in the light of meaning of the Wireless Telegraphy Acts." Ac- definition, into which it is at least possible to read cordingly, the P.M.G.'s licence is required before a more favourable interpretation. We will content issue of a radar installation can be set up and worked. ourselves by expressing the hope that the At first sight this assumption of control seems the new definition betokens a desire on the part of arbitrary and unjustified, being quite out of keep- the Post Office to allow the public to make use, ing with the wording and spirit of the 1904 Act. without cumbersome formalities, of services that P.M.G. can sweep radar into his net at a are clearly intended for the benefit of all. There If the inter- stroke of the pen, cannot he do the same with the matter must rest until the findings of the any other application of radio technique that is national conferences are adopted.

www.americanradiohistory.com 2 Wireless World January, 1948 High - Quality Amplifier

Advantages of Tetrodes in the signals, and to permit the lowest possible hum level to be ob- Output Stage tained.' The solution to the problem of B.sc. (Hons.) applying a large amount of By P. J. BAXANDALL, feedback over the output trans- (Telecommunications Research Establishment) former was found to lie in the use of a very ingenious design ' of IN the April and May issues of reasonably low non -linearity dis- transformer, developed by C. G. Wireless World a design for tortion. Mayo, of the B.B.C. Engineering an audio amplifier was (3) To reduce non -linearity Research Department, in conjunc- described using triodes in all distortion to a given level, it is, tion with Messrs. Tanner and stages and giving an output of of course, necessary to apply con- Ellis.' Unfortunately space does about 14 watts, the non -linearity siderably more negative feedback not permit a full account of the distortion and hum being reduced with tetrodes and pentodes than design principles of this type of to a very low level by the applica- with triodes, but this has great transformer, which has a speci- tion of about 20 db of negative advantages from the point of view ally positioned third winding feedback over all four stages. of reducing hum.' It allows one for negative feedback, but the The present article describes an to use less smoothing of the H.T. basic idea may be explained as amplifier employing tetrodes in supply, and also the output trans- follows. the output stage, with high -slope former can be mounted closer to Fig. r (a) shows a circuit in pentodes in the one previous the mains transformer for a given which an output valve feeds a re - stage. The output power is rather N' I over ro watts, and the non - PRIMARY WINDING + H.T. AND STRAY CAPACITY LEAKAGE linearity distortion and hum-level INDUCTANCE are of the same order as in the previously described amplifier. L' The input voltage for maximum output is approximately 4 volts ANODE R.M.S., and it is intended that the unit shall constitute the ANODE CURRENT r =gm x VIN i LOAD N ' ` main amplifier " section of an y a installation involving a radio receiver unit, gramophone and perhaps microphone preamplifiers. Most high -quality radio receiver NEGATIVE units will provide an output of well FEEDBACK over 4 volts, and this level is also FEEDBACK (b) a convenient level for feeding (a) through a cable from a multi- channel preamplifier and mixing Fig. r (a). Circuit with negative feedback from secondary of output unit. transformer. (b). Approximate equivalent circuit at high frequencies. Considerable economies can be effected by avoiding the use of amount of hum output due to sistive load through an output triodes, for the following magnetic coupling between these transformer, negative feedback reasons :- components. being taken from across the load. When (r) The power efficiency of out- contemplating building a Fig. r (b) shows the approximate ro -watt amplifier of very low dis- equivalent circuit applicable at 4 put tetrodes or pentodes, in Class tortion, the writer therefore " A " operation, is greater than de- high frequencies, the transformer cided to use tetrodes, with high- having first been replaced by one for triodes in Class " A," result- slope pentodes ing in economies in power -supply in the pre -output of unity turns ratio with a suit- stage, provided that it proved ably modified secondary load im- components for a given output possible power. to apply an adequate pedance. The effects of the main amount of feedback with com- winding inductance, the core (2) \The input grid -swing re- plete stability. It was considered losses and the winding resistance quired by output tetrodes or essential to include the output may be neglected to a first ap- pentodes is less than with triodes transformer inside the feedback proximation at high frequencies. for a given output power, so that chain to enable the feedback to Assuming a low secondary im- even with high -slope pentodes in reduce the non -linearity distortion pedance, the secondary winding the pre -output stage, this grid - caused by the transformer on capacity may also be neglected.3 swing can be supplied with large - amplitude low - frequency With this arrangement, it wane

www.americanradiohistory.com January, 1948 f'irrless World 3 ings, arid by adopting the right arrangement it is possible to make L'a very small relative to L'b Design and L'0. If L'a is zero, then, provided AMPLIFIER CHARACTERISTICS no appreciable current flows in Output power ro watts into r5 -ohm load. L'0, the feedback voltage will be Input voltage Approx. 4 volts R.M.S. for ro watts output. always in phase with the anode Working frequency range .. 3o c/s to 16,000 c/s. voltage. The current in L'0 can Low -frequency response .. Less than o.r db down at 3o c/s. be made negligibly small by High -frequency response .. Less than r db down at 16,000 c/s on of loudspeaker load. Less than 2 db arranging that the impedance down at 16,000 c/s on r5 -ohm the circuit connected to the feed- resistive load. back winding is very high com- Non -linearity distortion Less than o.r per cent. at ro watts output. pared with the impedance of this Output impedance .. Approx. o.8 ohms in series with roo -µH. winding. In practice, with the Hum .. 8o db below ro watts output (roo db winding arrangement used, L'a is with extra care). slightly negative. This gives the feedback voltage a slight phase lead at high frequencies and does seen that the feedback voltage means the feedback voltage could not adversely affect the stability. will lag in phase relative to the be taken from a point equivalent The simplest winding arrange- anode current by an angle tending to the anode as far as phase shifts ment which achieves the above to 180 deg at very high fre- are concerned, though actually result is a concentric one, with quencies, or more than 18o deg derived from a secondary wind- the primary winding between the if there is appreciable capacity ing, then stability would be main secondary winding and the across the load. Since the rest readily obtainable and the advan- feedback winding. Though an of the amplifier circuit will in- tages of including the transformer amplifier using such a simple de- evitably produce slight phase lags inside the feedback loop also sign could be made quite stable, at high frequencies, the circuit secured. the frequency response, on load, will be unstable if too much This result is obtained if the would fall off more at high fre- feedback is applied, for, as the feedback is derived from a quencies than is desirable, owing frequency is raised, the total separate secondary winding cor- to the rather large leakage in- phase shift will then reach 18o rectly positioned on the bobbin ductance between the primary deg before the loop -gain has fallen relative to the other windings. and output windings. The feed- to unity. The approximate equivalent cir- back would not correct this, be- It is, of course, possible to raise cuit at high frequencies for such cause the effect of the feedback the frequency at which the trans- a three -winding transformer, is only to make the response from former phase shifts become serious by sectionalizing the trans- Fig. 2 (a). Circuit with feedback from N :1 BETWEEN I AND 2 former windings and thereby re- third winding on output transformer. (b). Approximate equivalent circuit at ducing the leakage inductance. high frequencies. If provision is also made in the amplifier circuit to reduce the for- PRIMARY WINDING ward gain to a low value, with AND STRAY CAPACITY small phase shift, at a frequency lower than that at which the transformer shifts become serious, then a fairly large amount of feedback ANODE may be applied with stability, especially when the amplifier is ANODE CURRENT feed an inductive always used to gm z VIN IA load such as a loudspeaker. This sectionalizing, however, increases the constructional difficulties of the output transformer, and in diffi- NEGATIVE NEGATIVE any case it will be found very FEEDBACK FEEDBACK cult to obtain good stability with such a transformer if as much as (a) (b) qo db of negative feedback is applied in .an amplifier intended to again with the transformer re- the amplifier input to the feed- operate with low distortion over a duced to unity ratio, is shown in back winding nearly flat, whereas frequency range as wide as 3o c /s Fig. '2 (b), the actual circuit being if L'b is too large there will be a to r6,000c/s. as shown in Fig. 2 (a). The considerable voltage drop across The phase of the anode voltage values of L'a, L'b and L'0, which it at high frequencies, due to the in Fig. r (b) can never lag by are due to the leakage inductance load current. more than 90 deg relative to the between windings, depend on the In the transformer designed for anode current, so that if by some relative positioning of the wind - this amplifier and nescrihed in the

www.americanradiohistory.com 4 Wireless World January, 1948

High -Quality Amplifier Design- put. voltage at the lowest working response is produced by having Appendix, the primary is divided frequency, taken as 3o c/ s, with- suitably small values for the screen into two sections, with the output out requiring too large a peak bypass condensers for V, and V2 ; winding between them and the magnetizing current for the out- as the frequency is lowered, the feedback winding in two sections, put valves to supply without over- phase lead due to these condensers one at the inside of the bobbin loading. Space does not permit a reaches a maximum, and then and the other at the outside. This full discussion of the factors tends back to zero again at the gives a response which is less than governing the choice of core very low frequencies, where the 2 db down at r6,000 c/ s with a material, core size and winding inter -stage coupling condensers r5 -ohm resistive load, and less turns, but by using a Radiometal give a large phase lead. By cor- than r db down when feeding a core, working with a peak flux rect proportioning of these time r5 -ohm loudspeaker. These density of about 9,000 gauss for constants, it has been possible to figures could be improved by ro watts output at 3o c/ s, the out- ensure that the total phase -shift further sectionalizing the wind- put transformer made for this is comfortably less than i8o deg at ings, but this seems quite unneces- amplifier fulfils the requirements all frequencies for which the loop - sary for practical purposes. of high efficiency, low leakage in- gain is greater than unity, and In designing the output trans- ductance and reasonably small hence good low -frequency stability former from the point of view of size and weight. is secured. its low -frequency performance, no The complete circuit diagram is The condenser and resistor account was taken of the low- shown in Fig. 3. A " see -saw " joined in series across the anode level primary inductance value, phase -inverter is used-otherwise load of V, cause the forward gain since even if this were so low as called " floating paraphase " or of the amplifier to fall off as the

Fig. 3. Circuit diagram of amplifier. All resistors are i -watt, ± zo per cent unless otherwise marked.

6 to cause the response without " anode - follower." 4, 5, The frequency is raised, ultimately feedback to be several db down coupling condensers between the reaching a level of about -20 db at 5o c/ s, the response would be two stages have been made excep- relative to the response at medium made almost dead level down to a tionally large, to ensure that as frequencies, with a very small much lower frequency than this the operating frequency is lowered phase -shift. Stability is then when a large amount of negative the output transformer produces a assured at high frequencies, since feedback was applied. The im- large attenuation before the the remaining 20 db or so of loop portant factor was rather to en- coupling circuit phase -shift (a gain is lost largely in the output sure that the transformer was lead) becomes large. Additional stage, with well under 18o deg capable of delivering the full out- attenuation of the low -frequency total phase -shift. The loop gain

www.americanradiohistory.com January, 1948 Wireless World 5 drops to unity at a frequency of ing. The amplifier will give an and Fig. 4 shows the variation of the order of 600 kc /s. output of over ro watts at 3o c / s 3rd harmonic distortion with out- The condensers and resistors without serious distortion. put power, using the maximum across the primary of the output In building the amplifier, the amount of feedback-about 36 db. transformer are mainly for the interstage coupling condensers r purpose of preventing the produc- (0.5 uF) should be mounted on an 1 tion of destructively high instan- insulating support well clear of the taneous voltages in the event of chassis, to minimize stray capa- 0.2 drastic overloading of the ampli- cities. Very good quality conden- fier. If the amplifier is feeding a sers should be used, as their leak- 40c sl moving -coil loudspeaker or re- age resistance should not fall f corder cutting head, which have below about roo megohms. a high inductive impedance at Dubilier " Nitrogol " condensers high frequencies, these resistors are very suitable. 0' I t and condensers ensure that the Meter jacks have been included output valves work into a reason- for checking the D.C. circuit con- ably constant load fre- at all ditions. Only three of these, 400c s quencies, so that even if, due to representing the minimum require- / an excessive input signal, one out- ments, have been shown in Fig. 3. s put valve is cut off and the other J2 and J3 permit the output valve driven into grid current, the cur- currents to be set up to 64 mA 03 4 5 6 7 8 9 10 II 12 rent turned into the transformer each, or a little less if desired. The OUTPUT POWER (WATTS) primary will not be able to currents are first equalized by develop too high a voltage across means of the 5o -ohm potentio- Fig. 4. Variation of third har- it. If, for some special purpose, meter, and then set to the collect monic with output power. Feed- the amplifier is to be used for feed- absolute value by adjusting the back at maximum (36 db). ing a pure resistance load, these roo -ohm potentiometer. They condensers and resistors should be should be reset whenever it is These measurements were made disconnected, as their presence found that they are different by with a r5 -ohm resistive load, as will prevent the amplifier from more than 5 mA. A milliammeter it was found that if a loudspeaker delivering its full output voltage (preferably o-5 mA) inserted into load was used, a several times J, serves as a very sensitive over- increase in the distortion of the load indicator, for as soon as any output voltage occurred, due to grid current flows in the output non-linearity distortion in the cur- valves, this biases back the grid rent drawn by the loudspeaker; of V2, thus reducing its cathode this was, of course, a fault of the current. Quite a large reduction loudspeaker and not of the ampli- occurs before the amplifier output fier, and emphasizes the fact that waveform becomes visibly dis- a normal present-day loudspeaker torted, so that if the programme gives much more non -linearity level is kept down to such a value distortion than an amplifier such that only slight movements of the as this. It would seem desirable needle occur on loud passages, no to devote much attention to im- serious audible distortion will proving loudspeakers from the result. non -linearity distortion point of The potentiometer across the view. feedback winding of the output The hum -level, with full feed- transformer may be omitted if back, is about 8o db below maxi- desired, as the amplifier is per- mum output. This is just audible fectly stable with the maximum in a quiet room at about ift from feedback of 36 db. Its presence, the loudspeaker, and is therefore however, enables one to demon- quite negligible for normal pur- 50 cis MAINS strate easily the improvement in poses. It can be reduced to distortion and hum reduction roo db below maximum output obtained by applying the feed- (a) by replacing the ro -k12 resis- at high frequencies without over- back, and may also be useful in tor feeding the H.T. supply to the loading. The amplifier is per- cases where the gain of the ampli- first stage by two 4.7-kSl resistors fectly stable without them, even fier is not quite high enough, since in series, with an additional 8-µF on open circuit. the gain may be increased by ten condenser to earth from their The output valves are operated times by means of this control, junction, and (b) by connecting at a higher anode current than is still leaving about zo db of feed- a roo -ohm " hum-dinger " across necessary for delivering full out- back. The distortion will still be the heater winding, with its slider. put power at medium frequencies, under r per cent at ro watts out- taken to about ro volts D.C. posi- so that they can supply the neces- put, which is tolerable for many tive with respect to earth. Good sary peak magnetizing current for purposes, such as P.A. screening and layout of the input the output transformer at very The non -linearity distortion pro- circuit to V, is also essential, and low frequencies without overload- duced is mostly 3rd harmonic, a valve specimen should be chosen

www.americanradiohistory.com b Wireless World January, 1948

High -Quality Amplifier Design- No trace of self -oscillation could +H.T. OUTPUT ANODE having low hum characteristics.' be detected with any value of N.F.B. The output transformer should be capacitance. With an amplifier mounted at right angles to the having negative feedback from the 'WI BMW mains transformer and smoothing main secondary winding, shunt- choke, but there is no need for ing this winding with capacity wide spacing between these com- would increase the phase -shifts at 2 5 ponents. high frequencies, and produce A quick method of investigat- oscillation if too much feedback was in use. ing the performance of an ampli- 200Vel MCII fier from the point of view of fre- The characteristics of the ampli- quency and transient response, is fier described are summarized in the table at the head of this to observe the output voltage 3 6 waveform with a square input article. APPENDIX voltage waveform. The accom- 44 panying oscillograms show very OUTPUT TRANSFORMER Core convincingly the improvement in 1}in. stack of Type 4o4A Radiometal l performance due to the applica- laminations, o.or5in. thick. (Telegraph S.F. B. tion of a large amount of negative - Construction and Maintenance Co.) T's and U's inserted in bobbin in +H.T. OUTPUT ANODE feedback. (a) shows the 5o -c/s groups of 8, in alternate directions. (To square-wave input, (b) shows the reduce tendency to saturate near joints.) with Tests amplifier output waveform, Bobbin Total primary resist- a 15 -ohm resistance load and no To suit core, with i/16in. central ance =16o ohms approx. division, and slotted to take inter- Total primary induct- connections. ance, measured at Windings (see diagram) 2,000 c/s on low- =6o henrys Section (s). 24 S.W.G. enam. io turns level A.C. bridge approx. each side of division, uniformly spaced Leakage inductance; out across bobbin. zo turns total. measured across Section (2). 32 S.W.G. enam. 800 turns whole primary, total, layer -wound with 0.00rin. trans- with output wind- millihenrys former paper between layers. 12 layers, ing shorted approx. approx. 70 turns per layer. The last layer should be spaced out uniformly to REFERENCES occupy full width of one side of bobbin. 1" Negative Feedback and Hum," by Section (3). As z, but wound in reverse " Cathode Ray." Wireless World, May direction. 1946. Section (4). Three layers of zo S.W.G. 2 British Patent Number 514,729, enam., paper interleaved, total 128 turns Mayo, Tanner and Ellis. for both sides of bobbin. Multiply turns 8 " Electric Circuits and Wave Filters," by for impedance Z other than by A. T. Starr (Pitman). See Chapter I V. Square -wave test signal (a), and /5 " The See -saw Circuit," by M. G. output into 15 ohm load, (b) with- 15 ohms, and choose suitable wire size. Scroggie. Wireless World, July 1945. out, and (c) with negative feedback. All layers should occupy full bobbin " The Anode-Follower," by B. H. width, to avoid excessive leakage Briggs, R.S.G.B. Bulletin, March 1947. inductance: s Introduction to Circuit Techniques feedback, and (c) shows the out- Section (5). As (2). for Radiolocation, by F. C. Williams. put waveform with 36 db of feed- Section (6). As (3). J.I.E.E., Part IIIA, No. i, 1946, p. 289. back. The sloping shape of wave- Section (7). As (i). " Hum in High -gain Amplifiers," by Wireless World, (b) Note.-Three layers of o.005in. Empire P. J. Baxandall. form indicates an imperfect to inserted between all sections. February 1947. low -frequency response-actually cloth be nearly 3 db down at 3o -c / s as measured by normal sine -wave methods. The clearly visible lines Books issued in conjunction with " Wireless World " at the changeover positions indi- Net By cate that the high -frequency re- Price post sponse is also not ideal. The out- WIRELESS DIRECTION FINDING. By R. Keen, M.B.E., -F ... 45/- put waveform with 36 db of feed- B.Eng. (Hons.), Fourth Edition, XII 1,059 pages ... 45/9 TELEVISION RECEIVING EQUIPMENT, by W. T. Cocking, back is, however, almost identical M.I.E.E., Second Edition ...... 12/6 12/11 to the input waveform, and the FOUNDATIONS OF WIRELESS. Fourth revised Edition, by fact that there is no overswing at M. G. Scroggie, B.Sc., M.I.E.E...... 7/6 7/10 WIRELESS SERVICING MANUAL, by W. T. Cocking, M.I.E.E., the changeover positions, which ...... Seventh Edition ...... 10/6 t0/10 has been checked with a faster HANDBOOK OF TECHNICAL INSTRUCTION FOR WIRELESS time -base, shows that the high - TELEGRAPHISTS, by II. M. Dowsett, M.I.E.E., F.Inst.P., and L. E. Q. Walker, A.R.C.S., Eighth Edition ...... 30/- 30/8 frequency stability is also excel- BASIC MATHEMATICS FOR RADIO STUDENTS, by F. M. lent. Colebrook, B.Sc., D.I.C., A.C.G.I. 10/6 10/10 A further verification of the GUIDE TO BROADCASTING STATIONS, Third Edition ... 1/- 1/1 stability of the amplifier was RADIO WAVES AND THE IONOSPHERE, by T. W. Bennington 6/- 6/3 obtained by shunting the output Obtainable from all leading booksellers or from terminals with a capacitance, London, S.E.1. which was continuously varied up ILIFFE & SONS LTD., Dorset House, Stamford Street, to a value of several microfarads.

www.americanradiohistory.com January, 1948 Wireless World 7 Push -Pull Input Circuits Part 1.-General Principles is one very simple system possible when conditions are such that no part of the input By W. T. COCKING, M.I.E.E. source need be earthed. These conditions sometimes occur with THE use of push-pull ampli- phase, so that E12 = - E32. No a gramophone pickup, and it is fication is now widespread specific relation between the ampli- A I in high -quality apparatus. tude and phase of EAB and E12 is An amplifier working on this necessary. principle requires an input voltage Before proceeding, a word about which is balanced to earth or, to the double subscripts used above put it another way, it requires in two describing the voltages may be ;C input voltages of equal amplitude advisable. The full meaning of but of opposite phase. E12 is that terminal r is positive Most sources of input voltages with respect to terminal 2 by the .f:cl are two -terminal devices, how- magnitude of voltage E ; E21 ever, and most of them have one means that terminal z is positive B of their terminals earthy, so that with respect to terminal r and is, Fig. 3. The basic in many cases the voltage pro - of course, same resistance phase - the as saying that split terminal r is negative with respect ter. to terminal 2. Hence E12 = E21. then possible to use This double - the arrange- -subscript method of ment of Fig. 3, in which the OUTPUTS specifying voltages is very con- inevitable stray capacitances are venient because it avoids any ambiguity. shown dotted. In order that E12 may equal Transformer coupling is not Fig. 1 Diagrammatic representation E38, it is necessary only to have being dealt with in this article, - of an unbalance -to -balance trans- 121 = R2 and C1 = C2 ; the value former. but it is well to show how it fits into of C, any capacitance directly the box of Fig. r. It is a very across the input terminals, does vided by the source is unbalanced simple case and is illustrated in not affect the balance. Under this to earth. Some device which will Fig. 2. If the transformer has a condition E12 = EAB/2 = - E32. turns ratio of i : n between ter- transform an unbalanced voltage The capacitances thrown on i, 2 minals A, B and 3, E12 to a balanced one then becomes i, then = and 3, 2 by the following push-pull necessary to connect the input EAB n/z and E32 = : EABn/2. amplifier will usually be very source and the amplifier. nearly equal, for the two sides of One of the oldest of such devices Fig. 2. T h e the amplifier will be alike. Any is a push-pull transformer, but push -pull discrepancy between C1 and C2, arrangements embodying RC- transformer is therefore, comes chiefly from coupled valves are now more one form of different stray capacitances to common and are known by various phase -splitter. earth from two sides of the pickup names, such as phase splitters, or other input source. phase reversers, phase inverters, The accuracy of balance between With some equipment this may paraphase amplifiers, see -saw the two depends mainly on the be large, while with other appar- circuits. transformer and is usually good, atus it may be negligibly small. Although much has been written although it generally falls off at It is, however, always posible to on these circuits there is sur- the higher prisingly little published material frequencies on on the degree of balance obtain- account of wind- able over a wide frequency range. ing capacitances. While general information about It is to be them is plentiful, detailed informa- noted that the tion is scarce. primary winding Whatever its actual nature, the can be earthed general unbalance -to -balance or not as the transformer can be represented by requirements of the box of Fig. r. The output the rest of the voltage EAB of the source is circuit may applied to terminals A, B, and dictate. there are developed at terminals Turning now I, 2 and 3, 2 voltages E12 and E32 to resistance Fig. 4. Here the phase-splitter of Fig. 3 is shown of equal amplitude and opposite methods, there applied to a diode detector.

www.americanradiohistory.com 8 Wireless World January, 1948

Push -Pull Input Circuits- These circuits have been previ- amplifier must in some degree. equalize the capacitances by ously described,' but they are depend on the characteristics of adding to the smaller, but it is included here since they do not the valve used. Consequently, it rarely convenient to do so. seem to be very well known, and is less easy to maintain balance The circuit is not much used although they are not often useful, over a wide range of frequencies because it raises difficulties in there are occasions when they are or over long periods of time than obtaining a simple volume control convenient. They have one great with phase-splitters in which the and in- most practical cases it is merit, which is that if the compo- balance is independent of valve desired to have one input terminal nents are carefully matched the - characteristics. balance can be This should not be taken to R1 perfect at all mean that phase -reversers are, in Li A frequencies. practice, greatly inferior to phase- F Circuits of this splitters. They are not, and with type, including good design they can give an (.5= 1 some others of adequate performance. Some great practical types are widely used.

i0 ¡ 2 importance, are Before we start to consider in usually termed detail the various circuits of both phase-splitters to categories which find considerable C,= 4 distinguish them practical application it may be as Cl C, from another well to treat one more phase- 3 group known as splitter of a type not often used.

C6 phase - reversers. We shall consider this because it R2, T h e essential is very similar to the well-known thing about a cathode -follower type phase- phase-splitter is splitter and its analysis will serve that the output to clarify the action of the latter. Fig. 5. A modified form of Fig. 4 permitting one voltages are de- The circuit diagram is shown terminal of the tuned circuit to be earthed. veloped by the in Fig. 7 (a) and its equivalent at passage of the (b) and it will be assumed that the earthy. This basic method can also same current through two equal bias resistance Rb is adequately be used with diode detector, and impedances in series. Thus in by-passed by Cb, so that at all one way of doing this is shown in Fig. 3, ignoring stray capacitances, frequencies in which we are Fig. 4. For balance it is necessary an input voltage EAB drives interested these components can to have R, = R2, R, = R4, a current i through R, and R2, be regarded as short-circuited. R5 =- Re, C, = C2, and C, = C4. so that i = EAB/ (R, R2). For the moment it will also be In addition stray capacitance to The output voltages are assumed that the decoupling capa- earth from A should equal that Ell = iR, and E22 = - iR2. citance Cd is large enough to be from B, and capacitances to earth Because they are developed by the considered a short-circuit. from r and 3 should also be equal. same current, equality of the out- Now suppose the input voltage The floating R.F. input circuit puts requires only equality of the EAB increases ; that is, suppose is often inconvenient and can be resistances. These are static terminal A becomes more positive avoided by the arrangement of elements which are easily made than terminal B. This changes Fig. 5. Here again, R1 = R2, equal in practice and which retain the grid potential with respect to R, = R4, C, = C2, C3 = C4, their equality over long periods. the cathode by the same amount C5 = C,, L1 = L2. The circuit The second group-the phase- and the anode current increases looks unbalanced because earth reversers-depend on the use of a thus increasing the voltage drops is connected to one side of the valve amplifier of unity gain. across Ra and R The increase R.F. coil instead of to a centre - They are illustrated diagrammati- of current through R, makes its tap, but in all ordinary cases the cally in Fig. 6. The input ter- cathode end more positive to of the tuned circuit is impedance minals are common with one pair A negligible at audio frequencies, of output terminals so that EAB and it is unnecessary to complicate and E1, are actually identical. B matters by tapping the coil. ES2 is provided by applying EAB Suitable values of components also to an amplifier, represented are : R, = 5o k SZ, R2 = 2 M SI, by the box, giving phase reversal C, = C, = ioo pF, C5 = o.orµF, and unity amplification so that L, = suitable R.F. choke for the E22 = - EAB = - E12. input radio frequency. It is obvious that perfect balance This circuit is more convenient is obtainable only if the amplifier Fig. 6 Unbalance -to -balance than the gramophone one, because is perfect over the whole range of achieved by a phase -reverser. volume control can easily be frequencies required. It is also carried out in the pre -detector obvious that the gain of the earth and the change of voltage circuits. As in the other circuits, is positive -going ; thus, the stray capacitances from A and B " Push -Pull Input Systems," by cathode output E32 is positive. to earth must be equal, and also W. T. Cocking. Wireless World, The increased voltage drop those from r and 2 to earth. September esst, 1934, Vol. 35, p. 245. across Ra makes the anode end

www.americanradiohistory.com January, 1948 Wireless World 9 more negative with respect to a perfect balance is not possible quadrature and of only o.8 per positive H.T. and so less positive because the impedance of the cent of its amplitude. with respect to earth. The change H.T. supply system is in series This phase unbalance can be at the anode is thus negative - with Rd. It cannot readily be reduced as desired by increasing going and the output at the anode taken into E12 is negative. Terminals r and 3 account and its thus vary in potential in opposite effect is small directions with respect to 2. over the A.F. The magnitudes of the changes range. are iaRo and iaRa where is is the When C4 and change of anode current ; and so Rd are large for equal magnitudes of output enough for effec- we must have Ra = R 0. tive decoupling The circuit is one which lends their effect on the itself to a simple mathematical balance is small. analysis and the relevant equa- Their effect on the amplitudes of the output Fig. 8. The equivalent circuit for high frequencies voltages is of Fig. 7 (a) is shown here. negligible, but Cd alters the phase of one output Cd and if otherwise possible it is voltage slightly relative to the helpful to use large values for other, and it is this phase Ra, R. and Rd. angle which is responsible for the At high frequencies the equiva- major part of the unbalance. lent circuit has the form of As an example of the sort of Fig. 8 in which Cga, C00 and Ca. thing encountered represent the inter -electrode capa- in practice citances of the valve and C1 and C2 consider a stage are the capacitances in shunt with ° using the follow - Ra and R0. They are mainly the input capacitances of the following stage. If the circuit is Fig. 7. A triode balanced and the outputs are phase - splitter based on Fig. equal Ca, can be replaced by two 3 is shown at capacitances in series each of (a) and its capacitance 2Cao. This junction equivalent will always be at earth potential circuit for low and so can be connected to 2 and middle without affecting matters. frequencies When the circuit is balanced, at (b). (a) (b) therefore, and this means Ra= R0, CI = C2, the effect of Ca, can be fions are given in the Appendix. ing typical values :- µ= z8, ra assessed by replacing it by 2Cac The degree of unbalance is ex- = 18k12,Ra = Rc = Rd=5okfà in shunt with C1 and C2. pressed by U = (E81 - E32)/E32 Cd = 8 µF. When Cd is of The grid-cathode capacitance _ (Aa - A.)/A.. Its physical negligible reactance Za = R0 and C00 comes in shunt with the meaning is most easily seen by Equations (r) and (2) give input voltage and has no effect on considering the currents in the z8 x 50 the balance and this is also the anode circuit following A. Aa rr.8 of a ideal 18+50+50- case with the grid leak R9. There push-pull stage. The individual remains the anode -cathode capa- alternating anode circuits are At 5o c/s, wC4R4 = 6.z8 x 50 citance Cga. The input voltage is proportional to A. and A the x 8 x ro-O x 5 x ro4 = 125.6 responsible for driving a current amplifications between grid and and the approximate formulae round the circuit including Cqa and the anode and cathode outputs (7) and (8) are sufficiently both anode and cathode imped- respectively, and the current in accurate. From (8) U2 = 1/125.6 ances and it is in opposition to the the common H.T. lead to their _ - 0.008 and from (7) U1 =- anode current. As it flows difference. The unbalance is ex- 0.000064. The amplitude un- through both impedances and pressed by the ratio of this out -of - balance is clearly negligible and these are equal it has no effect on balance current in the H.T. lead the phase unbalance is small the balance. to one of the anode currents. enough to be ignored for most The voltage acting to drive The condition for balance is purposes. What this means is current through Cpa is EAB -}- clearly Za = R0. On account of that the anode output consists of -{- E32 and so the input current the decoupling components Cd two component voltages one of E21 is i1 -1- E21 and Rd this condition can never be which is negligibly different in = iwCga(EAB + E32). The input impedanceis Z;,a = met exactly. It is, of course, amplitude from the cathode out- possible tò insert a similar circuit put and in phase opposition to it EAB/il r/r9 wCra(1 +E21+ Eß9>] in the cathode lead, but even then and the other of which is in phase = EAB

www.americanradiohistory.com TO Wireless U 'orid January, 1948

Push -Pull Input Circuits- time working frequencies as low as E32 µR` Now E32/EAB = Ae, the amplifi- (I) 7 Mc/ s may have to be used over EAB ya I R, -)- Z. some paths, though over those pass- cation between input and the E12 µZa cathode output, and E18/EAB _ -Ao- - (2) ing in southerly directions higher EAB ya R, -i- Za Aa, be- frequencies than this should remain = - the amplification The unbalance usable tween input and the anode out- throughout the night. Ae_Za Below are given, in terms of the put ; also, Ae = Aa. UAa- A, R, I .. (3) broadcast bands, the working fre- Hence Zin = 1/jwCya(2 -F zAe) ; quencies which should be regularly that is, the input capacitance due =o when Za=R usable during January for four long- to feedback in I + zAe times the At low frequencies distance circuits running in different grid -anode capacitance. This is Rd directions from this country. In Za = R, addition a figure in brackets is given the well-known Miller effect. + 1 + jc0C4Rd will be seen from for the use of those whose primary It that the Therefore, interest is the exploitation of certain point of view of balance this stage Rd/R, frequency bands, and U = .. (4) this indicates is not far from ideal, for the only } jwCaR4 the highest frequency likely to be disturbing effect is that of Cd and Rd I - jrC4Rd usable for about 25 per cent of the time during it is not hard to keep this very + w2Cd2Rd2 the month for com- small. For most applications, munication by way of the regular This represents an in -phase amplitude layers. Times throughout are in however, there is the serious draw- unbalance of back that neither input terminal G.M.T. R./R, Mont eal : 0000 9 Mc/s (14 Mc/s) be earthy, and it is for Ul = .. (5) can this 4- 0300 7 (12 ) 0900 9 or 11 Mc/s (16 ) reason that the circuit is rarely and a quadrature unbalance of used. 1100 17 or21 Mc/s (26 ) Rd wCdRd 1300 26 (38 1800 21 The time that has been spent U 2 = R, 1 w2Cd2R42 (6) 2000 17 or 15 Mc/s (22 ) on it is far from wasted, however, 2200 11 (18 ) When r w2C42Rd2 2300 for one of the most widely used < 9 (15 ) Buenos Aires: 0000 11 Mc/s circuits is very similar to it and Ai (16 Mc/s) U1 I/w2Cd2R,Rd 0500 9 much of the analysis still applies. U2/wC,R4) 0700 11 (_ - (7) (18 ) will 0800 21 This circuit be dealt with in U2 - 1/ruCaR, .. (8) (28 ) 0900 26 (40 ) Part II. In practice R, and Rd are usually 1900 21 2000 17 or 15 Mc/s APPENDIX I of ; if (22 the same order of magnitude 2200 11 Referring to Fig. 7(b) and assuming then U2 is small U1 will be very small (18 ) Cape Town : 0000 11 Mc/2 Cb is (16 M/cs) that large enough for its and the total unbalance will be 0300 9 (15 ) reactance to be negligible negligibly different from U2. 0500 11 (290 0600 17 ) 0700 26 (40 ) 21 1700 or 17 Mc/s (29 ) 2000 15 2200 11 Short - wave Conditions (18 ) Chungking : 0000 7 Mc/s (12 Mc/s) in : 0400 9 November Retrospect Forecast for January ) 0500 11 (16(14 0600 17 or 21 Mc/s (23 ) (Engineering Division, B.B.C.) 0800 26 By T. W. BENNINGTON , ) 1200 17 or 15 Mc/s 1700 11 or 9 Mc/s (2415 ) a 7 >. was very interest- activity. On undisturbed days ex- 2300 (13 , ) NOVEMBERing month in the short-wave ceptionally high frequencies were world-a month during which therefore usable, and many trans- January is not usually a particu- several significant events oc- atlantic amateur contacts of go Mc / s larly disturbed month, though iono- curred. The first of these was the were made. Night-time working sphere storms which do occur are fact that a decrease-the first since frequencies were such that, on un- often particularly troublesome at 1944-occurred in the running aver- disturbed occasions, frequencies this time of year over dark trans- age sunspot number, indicating, lower than 9 Me/ s were seldom mission paths. At the time of though not certainly, that the maxi- really necessary. writing it would appear that dis- mum in the current sunspot cycle Conditions were less disturbed turbances are more likely to occur may be past. than has been the case during the within the periods 3rd/ nth, 8th/ The second was that predictions past few months, though some iono- loth, 13th/ 14th, 18th, 24th, and that the ionisation of the regular sphere storms did occur. The most 3oth/31st than on the other days of F2 layer would reach values capable disturbed periods were 9th/ 12th, the month. of sustaining fairly frequent com- 13th/ 16th, 19th, 24th and 3oth. munication on frequencies as high Forecast.-There should not be Ships' Electrical Gear as go Mc / s proved true, such com- much change in either daytime or munication providing valuable in- night-time M.U.F.s as between De- SUPPLEMENT containing formation as to the peak frequencies cember and January. Daylight alterations and additions to the for long-distance communication working frequencies during January current " Regulations for the Elec- during the winter day of an excep- will therefore be relatively high and trical Equipment of Ships " has tionally high sunspot maximum those for night-time relatively low. recently been issued by the Institu- year. The 28-Mc/s amateur band should tion of Electrical Engineers, Savoy During the month the maximum be regularly usable over daylit Place, London, W.C.2 (Price is). usable frequencies continued to in- paths, and, if conditions should It covers matters regarded as need- crease by day and to decrease by prove favourable, contacts on higher ing urgent attention that have night, in accordance with the amateur frequencies may become arisen since the issue of the 3rd seasonal trend and the high solar possible on odd occasions. Night- edition in 1939.

www.americanradiohistory.com January, 1948 Wireless World Government Hearing Aid

FIRST DETAILS OF THE SPONSORED DESIGN

THE Committee' appointed to advise the Medical Re- search Council upon the device is brought into operation. played through high -quality re- sign'of hearing aids has now pub- The first problem was to enun- producing systems, built by the lished its report2 and it is possible ciate the performance which Post Office Research Station and might be expected to fitted with variable â + 20 frequency - 1111113111111_1111111 satisfy the requirements characteristics. Tests were made 111111111111111111111111131I of the majority of the deaf with 228 subjects, representing ( + 10 persons who will benefit all types and degrees of deafness, _ma,1nuareaás by J. the scheme. To this and it was found that a response .a mazursn al end clinical experiments curve with a loss of 12 db per < _11111111e2ii=Z were conducted with the octave from 75o c /s down to 200 aid of specially prepared c / s and Ñ - 10 111111111115%f111113111M11 either a level or a rising .'.51.,11_.. articulation test records response, at 5 db per octave from or7M MAGNETIC 20 -ter II Z111111111111111111 W C 2. 1 13M0 IMO

FREQUENCY (cis)

CA 101 Fig. o. Frequency re- IONE CONTROL sponse characteristic A% (with permissible MO / IM 0 onlpF tolerances). Zero level 45 corresponds to a minimum amplification of 40 db. to disclose the technical specification of the hearing aid which CRYSTAL MICROPHONE it is proposed to dis- rSV tribute when the new T National Health Ser- Fig. 2. Circuit diagrams CRYSTAL of proto- INSERT RECEIVER type amplifiers for 047 Mil use with magnetic or crystal type earpieces. 75o c /s to 4,000 c / s, gave the best results. Permissible tolerances were established and are indicated by the shaded areas in Fig. r. It TONE CONTROL was further established that with IMO ( oOmpF new batteries the acoustic amplification corresponding to o db in the curve should be not less than 4o db, that the acoustic input / output curve at 750 c /s should be linear up to pressures of zoo dynes / cme, and that the noise level with volume control at maximum as expressed by the CRYSTAL ratio of the voltage across the MICROPHONE telephone with and without an

www.americanradiohistory.com 72 Wireless World January, 1948

Government Hearing Aid- and the other for use with an in- parisons were made of the results acoustic input of 200 dynes / cm2 sert receiver of piezo-electric type obtained with the subject's own at 75o c /s should not exceed and of American manufacture. hearing aid, the Committee's two 4o db. American (Raytheon) valves are designs with external and insert When the battery voltages are also recommended pending the earpieces, and an American aid reduced to two thirds (1 .o volt with insert receiver which, in the per cell) the amplification should opinion of the Committee, repre- not be down by more than 6 db sented the best commercial prac- and linearity should be main- tice. Twenty subjects obtained tained up to too dynes/cm'. best results in intelligibility tests Tests to be made at or corrected to a temperature of 27° C on account of the known variability in sensitivity of piezo-electric microphones and receivers with temperature. The report recommends that considerable freedom should be permitted in the development of designs to attain this performance, provided that there is Crystal -type receiver with interchangeable standardization of battery sizes rubber and plug and socket connectors. adaptors. For guidance, circuit diagrams development of equivalent types with one or other of the Com- are given of two prototype aids in this country. The hearing aid mittee's models. All preferred which have been constructed by with piezo-electric insert made use the Committee's models on the the P.O. Research Station, one of a 3o -volt H.T. battery, but a score of quality of reproduction. for use with a lightweight non - 45 -volt battery was needed for the The report deals with the design resonant moving -iron diaphragm magnetic receiver type of circuit. of audiometers, and gives details receiver of a type developed by Both H.T. batteries give a life of in appendices of simple objective the Ministry of Supply and the about r5o hours. The L.T. fila- methods of testing the perfor- Ministry of Aircraft Production, ment cells gave 5o hours on inter- mance of hearing aids. mittent service REFERENCES: and 35 hours on W. G. Radley, C.B.E., B.Sc. (Eng.), continuous ser- Vh.D.. M.I.E.E., Controller of Research, Engineering Department, General Post vice of 15 hours Office (Chairman). per day with the Sir W. Lawrence Bragg, O.B.E., M.C., M.A., D.Sc., F.R.S., Cavendish Professor magnetic receiver of Experimental Physics, University of type of circuit. Cambridge. R. S. Dadson, M.A., National Physical About 5o per Laboratory. cent longer life C. S. Hallpike, M.B., F.R.C.P., F.R.C.S., Medical Research Council. for the L.T. cells Colonel D. McMillan, O.B.E., B.Sc.(Eng.), was A.M.I.E.E., Post Office Engineering Re- obtained search Station. when used with L. C. Pocock M.Sc. (Eng.), A.M.I.E.E., the piezo insert Standard Telephones and Cables, Ltd. T. S. Littler, M.Sc., Ph.D., University of receiver circuit. Manchester (Secretary). Medical Research Council, Special Report Amplifier panel Series, No. 261. ' Hearing Aids and removed from Audiometers." H.M. Stationery Office. moulded case. External dimen- Radio Data Charts " sions are 3¡in. x ANEW edition of 21n. x rin. this publication, which comprises a series To check of Abacs giving in graphical form the most of validity of the essential data required the for receiver design, has now been specification, issued by our publishers. It reduces tests were carried the labour of calculation in upwards out with 27 sub- of 4o design problems. The book, jects with vary- which is now bound in stiff boards, ing degrees of costs 7s 6d from all booksellers, or, deafness, who by post 7s ix d. The subjects possessed and had covered range from the design of R.F. coils and transformers to the several months' calculation of loudspeaker dividing experience of the networks and include problems re- best available lating to parallel-wire, coaxial and commercial hear- quarter - wavelength transmission ing aids. Com- lines.

www.americanradiohistory.com January, 1948 Wireless World 13 Clandestine Radio Some Ruses Adopted by the Dutch

THE secret production of midget complete re- receivers was so well organized ceivers. Although in Holland by the spring of 1944 production could that when a coded request for parts not openly be for a set was received from a Dutch properly organized, prisoner of war in Germany it was personal initiative decided to send him a complete re- was not lacking ceiver concealed in a tin of veget- and it was not ables. The single -valve receiver, long before home employing a triode-hexode as de- construction was tector and A.F. amplifier, was revived on an in- assembled in the empty tin which tensive scale. had been fitted with a special lining Practically all so that it would produce the correct the miniature re- sound if tapped and its weight was ceivers were made The cut-out pages of a prayer book concealed this made up to the proper value. the for operation from receiver. circuit is shown in the accompany- the mains. The ing diagram. anode voltage was This is one of the ruses employed obtained by rectifying the mains denser, comprising two 8µF units, by the Dutch resistance movement voltage with either an " acorn " measuring only r8 mm by go mm and described by a contributor to valve or, as shown in the diagram, long, was used for smoothing. It a selenium will be seen that a condenser was rectifier used as a series impedance in the capable of sup- heater circuit as miniature trans- plying a maxi- formers were not easily obtainable. mum of 10 mA. A valve like the Philips UCH2r, 1 A miniature designed for a small heater current cylindrical elec- and a high heater voltage, was trolytic c o n - specially suitable for use in this circuit. Another circuit which was popular among set makers because of its high sensitivity was a two -valve T- reflex arrangement. Trimming condensers (3 to 3o pF) were used for 1 rJF- tuning, and, with well-chosen coils, the 3o-, 40- and go -metre bands could be satisfactorily received with This s ngle-valve cir- A.C. MAINS a very short aerial. cuit, combining grid In conclusion the article states: detection and A.F. am- i O ' ` Needless to say, this wartime ven- plification, was popular ture had its dangerous side, and among Dutch construc- unfortunately some who took part tors of miniature sets forfeited their lives." during the German occupation. Philips Technical Review, Novem- ber, 1946. Members of the resistance movement used receivers assembled inside a wide variety of articles in everyday use. Two of them, seen at an exhibition of equipment used by the resistance movement, are illustrated on this page. During the German occupation of Holland the Dutch were forbidden to listen to foreign broadcasts. To enforce this order all sets were con- fiscated in 1943. As a result there was a great demand for miniature receivers. The article states that it was primarily the Philips organization which met the demand for com- A baby's powder duster concealed this set. The mains lead was camou- ponents and, in some instances, flaged as a dressing -gown girdle and the earpiece as a baby's rattle.

www.americanradiohistory.com i4 Wireless World January, 1948 Amateur Radio Equipment IT is not surprising that the emphasis was on transmitting equipment at the November Exhibits at the R.S.G.B. Show exhibition held in London by the Radio Society of Great Britain. Of attractive set, covering as it does all the price is £42 plus purchase tax. the fifteen firms participating the the amateur bands from 3.5 Mc/s to Denco were showing a prototype majority had something of interest 28 Mc / s. It is crystal controlled, of a new communications set which contains modulator and power sup- covers 175 kc/s to 36Mc/s in six plies and, assembled in a three-tier ranges. A turret coil assembly is rack, costs £98. It is also available used and band -spread is provided by as a kit of parts. a cam -operated mechanism which Transmitters for the beginner rocks the stator sections of the gang were shown also by Radiocraft, condenser. The set has one R.F. some of their models being very stage, two I.F. amplifiers on 1.6 modestly priced. The model 41 for Mc/s, crystal and audio filters giv- example, which is a combination of ing an 800 -c/s band -width at high tritet oscillator and P.A. of flexible selectivity, noise limiter and B.F.O. design and fitted with plug-in coils, The price is expected to be about costs only ¿7 is 6d or ¿12 los with £48. Miniature valves are used. a self-contained power supply, when Another example of a modern it becomes the model 41 P. communications receiver was shown Receivers of various kinds were by E.M.I. Sales and Service. This well in evidence and they ranged also has an R.F. stage, two I.F. from a simple O -V-1 set to the most amplifiers on 465 kc / s, noise limiter up-to-date communications receiver. and crystal filter. It covers 55o kc / s Some of both varieties were seen on to 3o Mc/s. the Eddystone stand, the simpler Kits of parts sets and converters being assembled for building from the designs given in the firm's small T.R.F. " Short Wave Manual." short-wave re- The Eddystone model 640 is an outstanding example of a communications set designed for the amateur and it embodies all the special fea- Odeon 5o -watt output transmitter tures one expects to find in a set of covering the 3.5- to 28-Mc/s bands this kind. It has an R.F. stage, and including modulator and power two I.F. amplifiers on 1.6 Mc / s, supplies. noise limiter, B.F.O., crystal filter, to the amateur transmitter. Com- plete sets were shown ranging in size from a C.O.-P.A. set of 25 watts rating for the beginner to a large rack -built 15o -watt transmitter E.M.I. transmitting valves : the shown by Odeon Radio and costing TT11 tetrode and DET18 triode, ¿230. Labgear had a multi -tier equivalent to the American 35T. transmitter with a variable -frequency master oscillator, which by ceivers using plug-in coils means of switching provides for and having bandspread operation on to, 14, zo, 4o and 8o are sold by Southern metres. An 813 valve is used in the Radio and Electrical Sup- output stage and the full 15o watts plies; an 0.V.2 kit, for allowed by licence can be employed. example, costs £5 r7s 6d Complete with modulator, all power complete. supplies and a crystal monitor the British equivalents for price is £175. most of the popular types Ib addition to the large trans- Radio craft low - of American transmitter Odeon Radio had a number power transmitter type 41P mitting valves are now of low -power sets, some of which including power pack. available. E.M.I. Sales are designed for the beginner requir- and Service showed a ing an unexpensive set for C.W. provision for headphones and covers range including the TT11 R.F. operation. An intermediate model 1.7 Mc / s to 32 Mc / s. Separate tetrode with top anode connector of 5o watts output proved an band -spread condensers are used and and on an octal base. It is

www.americanradiohistory.com January, 1948 Wireless World Ig rated at 7.5 watts anode dissipation QVO.i-2o, equivalent to the and can be used up to Zoo Mc / s. 815, and the QVO7-4o, equi- There was also the KT8C, a replace- valent to the 829B. The ment for the well-known 807, the former will give a C.W. out- DET18 triode replacing the 35T, put of 40 watts and func- the DA4i, substitute for the TZ4o tions up to zoo Mc/s, while and the DETI9 double triode, an the latter's output is 6o equivalent to the RK34. Mercury watts with a limit frequency vapour and hard vacuum rectifiers of 25o Mc/s. A feature of were also shown. the QVO7-4o is the inclusion Belling -Lee EF5o-type valve holder Mullard had a very comprehensive of a built-in screen by-pass capacitor. and valve retaining ring. range of valves in both transmitting For high -power operation, where and receiving types. The popular a wide range of co -axial plugs and EF5o with its companion V.H.F. sockets also a new EF5o-type valve typés EF54 (RL7), EC52 (RL16) holder and valve retaining ring. were shown together with a new Some well -made coil turrets were valve, the EF55, for us in wide -band seen on Labgear's stand together amplifiers and having a slope of with plain and split -stator conden- 12 mA/ V. A special non -micro - sers, also a special wide -band R.F. phonic pentode for us in early stages coupling unit for transmitter and of modulation amplifiers has been receiver stages. Denco showed a coil turret for use in receivers and many coils and components with polystyrene insulation. A new range of transmitting condensers with ceramic insulation was seen on Eddystone's stand, where, among other items of interest, was key, more Woden Multi -Match modulation a new automatic transformer, type UM2, rated to familiarly known as a " Bug," handle 6o watts of audio. which is priced at 3 17s 6d. Meters of various kinds from single -range pointer instruments to an 813 might be used, Mullard have an equivalent in the QY2-loo, giving 26o watts output up to Mullard VHF double tetrodes ; the 120 Mc /s. In addition QVO7-4o and the QVO4-2o. there is a comprehensive range of audio -frequency developed and is given the type amplifying valves and number EF37. mains rectifiers of the mer- Among the Mullard transmitting cury vapour type. valves is the QVO4-7, a tetrode suit- Aerial equipment was able for use as crystal oscillator, shown by Antiference, doubler or tripler up to r5o Mc/ s. Belling and Lee, and It operates at 300 volts H.T. and Eddystone, with co -axial its anode dissipation is 7.5 watts. and flat -twin feeders by Other Mullard types are the QVO5- the Telegraph Construc- 25, a direct equivalent of the 807, tion and Maintenance Co. and two double R.F. tetrodes, the Belling and Lee showed

List of Exhibitors

Antiference, Ltd., 57, Bryanston Street, Radiocraft, Ltd., II, Church Road, London, W.I. Upper Norwood, London, S.E.19. Eddystone automatic key ; this type Belling and Lee, Ltd., Cambridge Radiomart, Ltd., 48, Holloway Head, is usually described as a bug-key. Arterial Road, Enfield, Middlesex. Birmingham. Denco (Clacton), Ltd., 355-359, Old Southern Radio and Electrical Sup- Road, Clacton -on-Sea, Essex. plies, 85, Fisherton Street, Salisbury, multi -range test sets were shown by E.M.I. Sales and Service, Ltd., Wiltshire. Pullin. Sheraton Works, Hayes, Middlesex. Stratton and Co., Ltd., Eddystone Taylor and Labgear, Willow Place, Fair Street, Works, Alvechurch Road, West Mains and modulation trans- Cambridge. Heath, Birmingham. fdrmers, the latter potted and filled Measuring Instruments (Pullin), Ltd., Taylor Electrical Instruments, Ltd., Avenue, Slough, with pitch to prevent " chatter,' Winchester Street, Acton, London, 419-424, Montrose Woden's stand, while W.3. Bucks. were seen on The Mullard Wireless Service Co., Ltd., The Telegraph Construction and Main- a range of components for receivers Century House, Shaftesbury Avenue, tenance Co., Ltd., 22, Old Broad and transmitters was exhibited by London, W.C.2. Street, London, E.C.z. Co., Ltd., Moxley Odeon Radio, Radiocraft, Radio - Odeon Radio, 56, College . Road, Woden Transformer Eddystone. Harrow, Middlesex. Road, Bilston, Staffs. mart, and

www.americanradiohistory.com l () Wireless World January, 1948 Television Picture Size DEMONSTRATE television} IS were adjusted to make the picture to anyone previously un- WHAT square and the persons on the acquainted with it, and you screen BEST ? appear as if suffering from are almost sure to hear some starvation. This is not necessarily comment about the size of picture. so. As a matter of fact, the worst By " Is that as big as you can have " CATHODE RAY " distortion is usually due to the it ? " or " When will they be viewer what size the screen was so curvature of the tube face; but larger ? " You may reply that long as it was placed at the right this can be overcome by using a television pictures anything up to flat -ended tube. My impression 20 feet by 16 can be obtained now distance to subtend the approved correct angle. (see Fig. 3) is that the fore- (at a price) ; or that the picture shortening effect of viewing a your friend is looking at is really But what is the approved angle? As that is a fairly complicated frame of the standard proportions the ideal size if only he had the (a) at 38° off the axis, where it sense to know it. Anything you question to answer, we will dispose of one or two simpler matters looks like b, makes the viewer say is likely to start a first-class unconsciously compensate for the argument. For there are quite a first. For although 8 is certainly a X number of interesting things in very important factor, it is not this question, and also a good deal the only one. To see that, one of confused thinking, possibly has only to suppose that in order because it is outside the usual radio to save money and room the engineering curriculum. picture is brought very close. Of course we all know that the The most obvious result is to hP price goes up very steeply as the restrict the number of people size of the picture is increased, and who can all comfortably get their L. that in these days most of us will heads at the distance which makes be lucky to have any picture at O right, and at the same time ; within a sufficiently small angle all but taking a more detached Y view, it is interesting to consider from the axis for distortion of the what would determine picture due to the foreshortening Fig. 2. For a given "spread" of the ideal audience, XOY, the largest angle ¢, size of picture, (a) assuming perfect to be tolerable. In Fig. 2 the maximum tolerable angle off the that can be tolerated by them sets definition, and ,(b) with 405 -line or a minimum limit to picture axis (PO) is marked ¢. the distance, any other particular definition. d, from the screen. Given the size of audience, XOY, For a specified Question (a) is an optical and B, the minimum dimensions of psychological one. Obviously the and the angle ck, the shortest the picture then follow. Norm- best size of picture is closely con- possible distance, d, follows. If rk ally ql, is in the horizontal plane, n8o and O vertical, but there is no nected with the viewer's distance is in degrees, d is times the from the screen. 2n96 objection to drawing them on the In fact, the same diagram as here. important quantity is the ratio length of the arc XOY. Inci- of the two, or, what comes to the dentally, in determining the distortion, which he would not do same thing,' the angle subtended length of XOY it cannot always if the picture were .. viewed right at the eye by the screen (Fig. r). If be safely assumed that everyone on the axis and the narrowness will be happiest produced by insufficient amplitude when they're view- of line scanning (c). I have tried ing cheek to cheek. to settle this by viewing the screen The value of as at b through a square mask, but is decided by how it is difficult to ensure fair con- much distortion ditions for testing these subtle d r, viewers are pre- psychological effects, and the pared to put up results were inconclusive. By the with. Anybody way, the top and bottom edges who grumbles at in Fig. 3b, if drawn accurately, 38° ought, in times are not quite straight ; and the Fig. r. The size of a picture to a viewer is not of austerity, to be ratio of the two sides depends on just its own size, but the angle O. Pictures of turned out to make O as well as on #. Here O is different dimensions, h, h and h21 all look the room for someone taken as 14°. same size if viewed at proportionate distances. else. It narrows Accepting 9 = 38° as a working the picture by limit for hard times, _ this ratio or angle were dmin the only 22 per cent, so that its apparent times XOY. So if we knew B, thing to be considered, then it width is about equal to its average we could then work out would make no difference to the height; and one might suppose and wmin (the minimum picture h that the viewer would get the width) is, in the B.B.C. 1 Because 2 tan realm, 2 d same effect as if the width control 5/4 times hmi,,.

www.americanradiohistory.com January, 1948 Wireless World 17

Before tackling- the O question, board know only too well how scene were viewed at a distance there are reasons why even an much more difficult it is to see which would make the batsmen audience of one cannot economize them there, where the O is exces- look as large as they do in the ad lib by viewing a small picture sive, than at a safe distance. As picture held close up, their B's close up. If it is too close, he the eyes are able to exploit only would be very different (Fig. 4b). cannot focus his eyes on it at all. quite a small field at a time, the The effect of taking the photo The minimum distance varies vast extra expense of a television with a telephoto (small O) lens with individuals, and tends to screen to go much beyond that and then looking at the resulting increase with age, necessitating field would be difficult to justify picture close up (large()) is to the use of spectacles; but even make A A look as if it had been with normal sight most people moved to A'A', close to BB. find it difficult to focus much Amateur photographers (or 9` nearer than inches. Even if their victims) . are more familiar possible, it is not desirable to view with the opposite perspective a picture anything like as near as distortion, for their cameras are that. The mere fact of having to (a) (b) (c) most often wide-angle, and the Fig. 3. A frame of the British focus the eyes at close range on a resulting pictures so small that to picture standard ratio of width to height representing something at b view them so as to subtend the (5 : 4) is shown at a; and is the a much greater distance is one same as seen at an angle ¢ of 38° same angle they would have to more thing tending to destroy the (0 = r4°). Although the width of be at the end of one's nose. Seen illusion. Ideally, the picture b is actually slightly less than in at a reasonable distance, the should be at the same distance as c (a square frame), the perspective picture subtends a much smaller ; effect makes seen in the principal object depicted a picture this O than did the camera, with but as the distance increases the way seem less distorted. grotesque results if the photo- focusing becomes less and less In practice there is another grapher had been indiscreet critical. I wouldn't like to consideration-perspective. Any enough to have snapped his dogmatize on this point, but I camera lens-television or other- fiancée with her feet much nearer for typical television suggest that wise-has its own 8. One with a to the camera than her face. scenes, and especially for outdoor large O is described as a wide-angle The relevant factor in television events, there is appreciable loss of lens ; a telephoto lens has a very is of course the 8 of the television illusion on if screen this count the small 8, because d is very large in camera. And that is awkward, is 6 nearer than about feet. The comparison with h. If the result- because in the B.B.C. studio realism of distant outdoor scenes ing picture is of such a size or Emitron it varies from 28° at such as sporting events is un- viewed at such a distance as to infinity to 22° for a close-up. doubtedly much increased, at the make the viewing O different from However, the difference between of close-ups, having expense by the camera 8, there is perspective these and an average of, say, 25° the screen 40 or more feet away, distortion. There are plenty of is not enough to distort the per- as in a cinema. Always granting, examples in newspaper pictures, spective appreciably, so one need of course, that the appropriate B such as those of cricket matches not worry unduly about the is maintained. or battleships ,at sea. Viewed technical problems of providing Now perhaps we are ready for B. Since it is a measure of apparent A picture size-the size as seen by the eye, without reference to its ------e ------distance-it would be just a question of how large we wanted it, if everything else could be made A (a) to meet our choice. Possibly the A Á Fig. 4. (a) Two objects of equal ideal O would be 360°, so that we height AA and BB, at different dist- could see the performers even if ances, have practically the same 8 they moved round behind our gee to a long-range camera C, so appear almost equally long on the resulting chairs ; but the advantage of picture. (b) When this picture is being able to do that would hardly A AB (b) the paper viewed close-up, the nearly equal be worth the miracle that would in the normal way, with (though much larger) 8's make the have to be performed in order to I2-I8 inches from the eyes, the objects appear very close together obtain it. One will have to wait scene looks as if it had been (A'A', BB) ; viewed with the actual a long time for completely realistic squashed flat. Batsmen at both separation (AA, BB) the B's are reproduction of floor shows. ends of the pitch measure the widely different. In most forms even of " live " same height on the paper, because entertainment, as at a theatre or with the telephoto lens their 8's a viewing chair that would shift football match, there are limits to were practically the same (Fig. its distance from the screen in one's field of view-and that 4a). Such a picture looks natural synchronism with the focusing doesn't count the people in front. only when viewed from the other of the camera. What is more This limitation is not altogether side of the street or whatever awkward is that in the cricket a question of economy or con- distance is needed to equal the match type of broadcast the O of venience. Schoolboys asked to very small O of the actual scene B.B.C. uses a camera with a inscribe their answers on the from the site of the camera. If the about 2°. This perspective can

www.americanradiohistory.com Wireless World January, 1948

Television Picture Size- that seats which make B very little force in itself, being only a easily be reproduced by standing large are unpopular, even when guide to the O beyond which one a long way from the television they are right on the axis ; for sees no more detail in the picture. screen. Standing (not sitting), to people have to be bribed by lower Viewers are quite entitled to be ready to rush forward whenever prices to sit in them. The most prefer to sit closer, even though the producer decides to change to popular O is not very clearly they see no more, just because for a long shot ! So, as you see, to defined, but seems to be round a variety of other possible reasons take perspective as the guiding about ro°, say picture distance they may like the picture to look principle lands one into absurdity. 6 times picture height. The larger. If the line structure itself People are quite ready to sacrifice largest C.R. tube size normally is disliked (though in certain types perspective, plus a stiff price for available is the 15 -inch, giving a of drawings, much used in adver- a pair of field glasses, in order to picture join high, so on a cinema tising, it is not only tolerated but gain a close-up view at the races ; basis one would expect people to seems to be highly favoured) it so televiewers can hardly grumble sit about 5 feet away. At that can easily be made almost invisible if the same facility is provided at distance they would have to keep by adjusting the focusing control no extra expense and without within a 64 -foot frontage to con- until the edges of the lines join up. even the trouble of taking their form to the 38° 4, limit. The width of the spot, if circular, hands out of their pockets. Nor So much for a picture with is then about half of one cycle at do the vast number of cinema - perfect or nearly perfect definition. 2.5 Mc/s, so is not a seriously goers grumble about the liberties How does the 405 -line standard limiting factor in horizontal defini- that the film producers take with affect the matter ? It is not very tion. As a matter of fact, most perspective. easy to say, but one would expect televisors suffer from slight astig- there would be little inducement matism ; that is to say, the setting Studio Perspective to come nearer (or have the for sharpest focus in the vertical Just as a matter of interest, picture larger) than the point at direction does not exactly coincide though, let us see where it takes which the lines were clearly with that for the horizontal. My us if we make our screen size distinguishable. At least, that is policy is to adjust for sharpest correct for perspective in studio the theory. My experience doesn't line structure and then defocus scenes.; that is to say, B = 25°. altogether support it, for I find slightly to merge the lines, chopsing Suppose the width of the audience, that when Mr. Philip Harbin that rotation of the control which XOY in Fig. 2, is 8ft, and that it holds out the final result of his improves horizontal definition. tolerates ç = 38°. Then the cookery demonstration I almost distance of the screen must be at have to come to the assistance of Sight and Sound least 6ft. At that distance the the safety glass window in front How about the sound ? One height of the picture must be of the screen. of the earliest gloomy forecasts 32in and its width 4oin. Rather That may be a rather special about television was that it would expensive. case, arousing deep-rooted and be absurd to have a big voice Or consider a lone viewer pre- highly strained instinct ; but the coming from a tiny figure on the pared to have the screen at tendency is there with any very screen. That was a fine example ordinary book distance, say j34in. near close-up, and it is opposite to of the muddled thinking I The screen size for correct per- the appropriate movement for mentioned. The size of a singer to spective is then 6 x 74in, which maintaining right perspective. the onlooker is primarily B, not is what one gets quite economic- However, let us see what happens the number of feet or inches high ally from a gin tube. Moral: if we assume that the viewer in the flesh or on the screen. There don't marry. gravitates to the distance where is no need to have a picture It may be as well to remark he can just detect that the picture millions of miles wide in order to here that if the B.B.C. were not is made up of lines. There are show the sun at the size it appears cramped for studio space they actually 377 of them (the rest to the eye. In normal circum- would probably use a smaller B, being blacked out between frames), stances it is within the capacity like film producers, which would and normal eyesight is unable to of televisors to present to the eye help the perspective -conscious distinguish them if they are and ear the same size and loudness viewer. as they would experience direct What it boils down to, then, is closer than about j minute (= at a performance. If the B.B.C. do that it is nice to have the per- 6o their job properly the televiewer spective right most of the time if So the O for the whole picture, on should not have to adjust his 77 one can, but it is quite im- this basis, would be 360 = 6.3°, volume control as the camera practicable to do so all the time, approaches the performer, or vice and anyway nobody seems to which means that a 9 -inch tube versa. worry about it much, even sub- should not be viewed closer than Because screens are generally consciously, so in the end it is a 44 feet, and a j5 -inch tube closer smaller than they would be if question of what size people like than 74 feet. At 6.3° the per- expense were no object, one does to have the picture and whether spective is wrong for the present tend to sit rather close to them ; they can afford it. studio performances, and (what and the question may well be In a cinema there is a fairly cuts much more ice) the picture raised about the possible loss of wide choice of B, so it is instructive is smaller than most viewers like. illusion when the sound (even to see what people do choose. One The line structure argument, by when adjusted to give the correct thing that seems quite clear is the way, seems to me to have very loudness in the ear) is coming

www.americanradiohistory.com January, 1948 Wireless World 19 from a source at the same short combination of circumstances. larger. The most popular choice, distance. Whether it is another Some people go to the trouble if it were free, would probably case of our illusions having been of making the sound come from make O about io°, but is not at well and truly pre -destroyed in round the edges of the C.R. all critical. At a distance suitable the cinema I wouldn't like to say, tube, instead of just below or to for the average living room, 8 feet, but in practice the question does one side. Presumably with the 1o° would require the picture to not seem to arise. Any readers usual arrangement they find it an be 16 X 20in as provided by at who do feel unhappy with the effort to associate the sounds least one model on the market, loudspeaker close up (again, with the sights. If so, I think using a 4in projection tube. This O assuming correct volume) may they must be in rather a small is wrong for perspective with the care to try a separate loud speaker minority. present studio lenses, but may be at the estimated actual distance While on the subject of sound nearer the mark later on ; anyway, of the performer. Personally I and sight it may be a good oppor- nobody worries. It is also more think that any effect which might tunity to stir up controversy still than close enough to the picture be gained in this way is likely to be further by referring once again to to show up the lack of definition obscured by the acoustics of the what I named " scale distor- in a 405 -line system ; the standard studio, which may or may not be tion " (Wireless World, September ought to go up to about 700 lines, beneficial, depending on circum- 27th, 1937). However perfect the but that is because the public stances. When listening to some- sound reproducer may be in other would like more detail, not thing going on some distance away respects, it fails if the loudness because they are afraid of seeing in an ordinary room or hall, the (as heard by the ear) is not the lines. If the accommodation sound received direct is modified same as if the performance were would run to a longer distance, a by the sound reflected from the being heard direct. Altering the larger picture still would suit the surroundings. Listening close up, loudness inevitably alters the eyes better, for all except close- especially in a room with balance of sound frequencies. A ups, and cinema fans would plenty of upholstery and curtains, quiet voice reproduced loudly tolerate even these. The dis- this added sound is almost neglig- sounds unnaturally deep. There advantages of the present short- ible. Assuming that the studio is some degree of analogy between range viewing are not materially and microphone are arranged to this and the perspective of the increased by the accompanying yield an appropriate ratio of picture. Altering the size (as seen short range of the hearing. And indirect to direct sound, it seems by the eye), that is to say, the B, finally the public can get used to unnecessary, if not actually un- inevitably alters the balance of almost anything, and in these desirable, for the sound to be dimensions, so that (for example) days most of them have to. further modified by the listening a distant scene reproduced close room. So the only objection to up looks unnaturally flat. Most Manufacturers' Literature people will tolerate both effects the close-up loudspeaker is that CATALOGUE " DL " of Drydex bat- the sound all comes from one unless carried to extremes. teries for radio receivers, hearing source, which is what one would My conclusions on the whole aids, etc., from Chloride Electrical listening to what was going matter of picture size are that the Storage Co., Clifton Junction, nr. Man- get by chester. on in the studio through a hole present sizes, even the smallest in the wall. Placing the loud- (gin tube) are perfectly all right Leaflet describing electrical process speaker at a distance, so that for solitary viewers and courting timer, Model TDX-2, from Electro reverberation does come from all couples. On special occasions, Methods, 220, The Vale, N.W.rr. directions, might be helpful if the upwards of 20 people find it Illustrated list of " Somerford " listening -room acoustics fitted the worth while to crowd round a 9in mains transformers (59 types) from scene and studio reverberation screen, but they would enjoy it Gardners Radio, Sotnerford, Christ- were absent-a not very likely better if the screen were much church, Hants. Brochure describing the Type. AL /5 cabinet loudspeaker for indoor P.A. Television Receiver application from Goodmans Industries, "Wireless World" Lancelot Road, Wembley, Middlesex. IT should be pointed out that cer- removed, or with many of the retain electrolytic capacitors are ceiver valves removed. Leaflet describing Model 120o cathode- used in this equipment with normal As the removal of individual ray oscilloscope from Industrial Elec- applied voltages which are only valves is often convenient when tronics, 229, Hale Lane, Edgware, slightly below their rated voltages. testing, there is no objection to the Middlesex. of individual valve It is, therefore, necessary to take removal any Descriptive leaflets from Metropolitan care that the equipment is not mis- other than the line or frame time - Vickers Electrical Co., Trafford Park, used in such a way that an appre- base output valves. With the excep- Manchester, dealing with Oscilloscope ciable voltage rise can occur. tion of these the current taken by any and Test Set for " Seasean " radar, As an extreme example of such other is too small for its removal to Cathode-ray Oscilloscope (Type 253), misuse, the operätion of the power cause any great rise of voltage. Signal Generator (Type 231), Miniature on open -circuit would almost Correction.-An error occurred in Cathode-ray Oscilloscope (Type 244), unit Stabilized Power Unit (Type 215), rise the circuit Fig. 1 of " Television certainly result in a voltage Valve Voltmeter and Test Set, R.F. sufficient to damage the 32-µF elec- Receiver Construction," Part io heater (Type 310A). trolytic capacitor in it. Other con- (Wireless World, December, 1947, ditions likely to result in a less p. 481) in which an EA5o D.C. re- Illustrated catalogue of accumulators serious rise of voltage are the opera- storing diode is shown. This valve in sealed glass boxes from the Tudor tion of the equipment with the line was inadvertently included and Accumulator Co., 5o, Grosvenor Gar- or frame time -base output valves should be entirely omitted. dens, London, S.W.r.

www.americanradiohistory.com 20 Wireless World January, 1948

What is Good Reproduction ?

the Royal Society of Arts by low notes ; where amplitudes on November 21st the Discussion by the were large enough to make this T B.S.R.A. met to discuss serious, it was worth while using the essentials of good reproduc- separate loudspeakers for high tion of sound, and heard a lucid British Sound Re- and low frequencies. and comprehensive exposition of Modifications of the original the problems involved. cording Association sound pattern not usually classed M. G. Scroggie who opened the as distortions included differences discussion said that there were two in the size and position of the possible definitions of good re- sound the engineer. Possibly the high - source, also the effect of production, that which aroused reverberation at both ends of the in the listener the same sensations order odd harmonics such as the 11th, 13th, etc., in small reproducing chain. The apparent as the original sound or which fractions that of one per cent may be the cause, reverberation time could be in- aroused the most pleasurable sen- creased by placing the main loud- sations. Both but, in general, harmonics are involved the subjec- relatively unimportant symptoms speaker at a distance, perhaps in tive opinion of a listener and an adjoining room, and using an quantitative assessment of non -linearity. was diffi- Harmonic distortion was easy extension loudspeaker with volume cult ; it was practically impossible to measure, but the single -tone control near the listener ; an echo to compare results obtained at effect could be produced by an different times and places. input genera 11 y employed was singularly lacking in enter- almost inaudible output from the Attempts had been made over close-up source. the last 25 tainment value and bore little years to substitute relation to normal programmes. In the discussion which followed, objective measurements of re- one speaker thought that the producing equipment, Non -linearity resulted in com- but in spite bination tones by intermodulation effect of room acoustics at the of an enormous variety of tests receiving end could be solved, as well as harmonic distortion ; from which to choose, no reliable given the necessary finance, by system of objective whereas the lower harmonics testing had harmonize with covering one wall with loud- emerged. There seemed to be the original tones, an the intermodulation products do speakers to simulate a full unbridged gulf between the orchestra, switching to a single physical nature of sound waves not. The ear itself is non-linear ; how then does it distinguish central unit for speech, and sub- and the emotional effect they stituting an infinitely absorbing produced. Hence it was externally produced harmonic and necessary labyrinth for the opposite wall ! combination tones ? Possibly to be guided at all times by Denman' had approached this subjective effects and to because the non -linearity is of a continue different kind producing different ideal many years ago when the to try to make objective tests audience virtually sat in the mouth tones ; if so, one would expect agree with them. In correlating of .a it to be more tolerant of high - large experimental horn subjective and objective tests one loudspeaker let into the ceiling should be on guard against hasty than of low-order tones. Mr. Scroggie then dealt with and, together with a thick carpet, conclusions; bad reproducers themselves provided the requisite often created strong harmonics, distortions arising in the loudspeaker and referred to recent sound absorption. Several but it did not follow that all speakers underlined the import- reproducers that created strong measurements of transients which persist after the signal has been ance of reverberation, and all were harmonics would necessarily be agreed that it ranked higher than bad. cut off. He also mentioned the Doppler -effect modulation of high wide frequency response in its On the question of perfect, or emotional effect on the listener. pleasing, reproduction Mr. Scroggie In assessing the merits of a loud- referred to the frequent preference speaker the listener should not of listeners for a restricted fre- OUR COVER allow the effects of reverberation quency range, even when offered to cloud his judgment. As an reproduction which This month's illustration shows was as perfect some of the aerial arrays at G5BY, aid to reaching an appropriate as present knowledge could make the amateur station operated. by psychological frame of mind for it. Recent experiments by Dr. Hilton O'Heffernan at Bolt Tail, the test it was suggested by one Olsen in America, dispensing with South Devon. In addition, there speaker that the loudspeaker electrical reproduction and using are two other multi -element rotat- should be regarded as an aperture direct listening with and without ing beam aerials for the V.H.F. in a wall separating the listeners' acoustic filter screens, showed that bands and a 50-Mc/s rhombic aerial room from the original perform- listeners had no inherent distaste radiating towards N. America. ance in G5BY has been particularly suc- an adjoining studio. for high frequencies. The con- Nine speakers, including W. S. clusion cessful lately on the 50-Mc!s band, to be drawn was that the on which he has worked most Barrell, H. A. Hartley, J. Moir, ear was capable of detecting U.S. districts, South Africa, M. J. L. Pulling and P. G. A. H. distortions too small to be Canada and Egypt. Voigt, took part in the discussion. measured by the instruments of Weeless World, July gist, 1929.

www.americanradiohistory.com January, 1948 Wireless World 21 WORLD OF WIRELESS

B.B.C. Management + Purchase Tax Changes + New Television Gear + Nobel Prize for Ionospherist

B.B.C. CHANGES scopes are not affected by the in- Wedding. Situated opposite West- ABOARD of Management has crease as they are not subject to minster Abbey, it was used to tele- been established at Broadcast- Purchase Tax. vise the procession as it approached ing House under the chairmanship An amendment to the Finance Parliament Square. A Super-Emi- of Sir William Haley, the Director Bill has reduced the Purchase Tax tron then took over while the C.P.S. General. The other five members on batteries and accumulators from Emitron was panned round on to the of the Board are :-Sir Noel Ash - 5o per cent to 33-k per cent. Abbey, door to give close-ups of the bridge, who has been deputy D.G. bridal party and some of the guests since 1943, becomes Director of B.B.C. TELEVISION O.B. alighting from the coaches. This new E.M.I. tube is in- Technical Services; B. E. Nichols, UNIT of the new Director of Home Broad- creased sensitivity and is largely free B.B.C. is to use the Pye from the shadow effects which casting, has been Senior Controller T11E of Programmes since 1944; Maj. Videosonic system of television demand " tilt and bend " correction. for some of its outside broadcasts. Gen. Sir Ian Jacob, who has been The Controller of Service, Corporation has ordered one of PICTURE the European the Pye O.B. units which, it will be TRANSMISSION assumes the control of both the recalled, WHEN completed, the new overseas divisions as is a complete transmitter- and European from camera to aerial-in a " shoot- phototelegraphy equipment now Director of Overseas Services; Air ing brake." being installed by Cable & Wire- Chief Marshal Sir Norman Bottom - One of its main less in Electra House will provide ley is features is its re- to be Director of Administra- duced size compared with the con- for the simultaneous transmission tion ; and a Director of the Spoken voy of vehicles which constitutes and reception of pictures on five Word, who has yet to be appointed. the present O.B. units. radio channels. This arrangement does not alter The Videosonic The company's phototelegraphy position of transmissions, in the the Board of which the sound channel is conveyed equipment was completely de- Governors who are responsible to by width -modulated stroyed when its Central Telegraph the Government for pulses inserted the control of in the line sync pulses, will be re- Station was burnt down by in- the Corporation. ceived at Alexandra Palace where cendiary bombs in 1941. It was Another change affects the television and sound will be separated temporarily re -equipped with Post vision service. Maurice Gorham, before retransmission. Office gear and more recently with who has been head of the television the G.E.C. console phototelegraphy service since it reopened in June, transmitter -receiver. New equip- 1946, has resigned and is succeeded NEW TELEVISION CAMERA ment has also been purchased from by N. Collins, until recently Con- ONE of the new C.P.S. (cathode - Muirhead's, of Eimers End, Kent, troller of the Light Programme. Mr. potential stabilizers) Emitron and Edouard Belin, of Malmaison, Gorham has been with the Corpora- camera tubes was used by the France. tion for 21 years and was at one B.B.C. for televising the Royal The Muirhead equipment, which time Editor of Radio Times. - P.T. ON VALVES AND BATTERIES THE effect of the change in Pur- chase Tax from 33-j; per cent to 5o per cent on valves and cathode- ray tubes is shown in the following selection of prices from the revised schedule issued by the British Radio Valve Manufacturers' Association. The increased purchase tax does not, of course, apply to stocks in retailers' hands on which the lower rate had already been paid. The pre -Budget Purchase Tax is given in brackets. Valse list prise purchase Tax s. d. s. d. 4 9 1 7 (1 1) 9 0 3 0(2 0) 10 0 3 3 (2 2) 11 6 3 9(2 6) 15 0 4 11 (3 3) 17 6 6 9 (3 10) 20 0 6 6 (4 4) C.R.T. list price £9 (9in) 70 3 (46 10) PICTURE TELEGRAPHY. The new Belinographe phototelegraphy £1.2 (12in) 93 8 (62 5) equipment (right) and the G.E.C. consol transmitter -receiver installed by Cathode-ray tubes for oscillo- Cable & Wireless in Electra House.

www.americanradiohistory.com 22 Wireless World January, 7948

World of Wireless- REMINISCENCES Philosophy, Cambridge. He has has yet been installed, is been president of the International not THE Silver Jubilee of the B.B.C. Scientific Radio Union since 1934. basically the same as that fitted in brought forth a spate of articles H.M.S. Vanguard for the Royal in both the specialist and lay press tour of South Africa, to which by old-timers. Some of them in- reference was made in our March cluded interesting reminiscences issue. which are worth recalling. have Two Belinographe- units Arthut Burrows, whose death is already been installed. in reminded of this recorded these pages, With the installation readers of the three -minute interval equipment six additional photo - each seven minutes telegraph services will shortly be which followed with Empire coun- of broadcasting. This was a condi- opened-mainly tion of the B.B.C.'r original licence tries. to avoid possible interference with The -largest volume of traffic ever distress calls. handled by C. & W. was on the occasion of the Royal Wedding. In Sir William Haley, B.B.C. Direc- all 222 pictures were transmitted to tor General, states " Any celebration fifteen countries. of British broadcasting would be in- complete without a tribute to Lord Reith [the B.B.C.'s first general R.S.G.B. STATION manager]. Few men have had opportunity to render so -Hal a service THE headquarters' station of the SIR EDWARD APPLETON, to their generation. No man has G.B.E., K.C.B., F.R.S. R.S.G.B. is expected to be on discharged a great responsibility the air early in the new year. Initi- with more seriousness or higher pur- ally it will operate as a frequency pose." It will be recalled that Sir Edward marker. was recently awarded the U.S. Medal It is proposed to radiate a short of Merit for his wartime contribu- automatically transmitted message NOBEL PRIZE tions to radar and to Anglo-Ameri- at a speed of 12 w.p.m. during the WINNER can scientific collaboration during first two minutes of each hour from SIR EDWARD 'APPLETON, the war. 0600 to 2400, on 3500.25 kc/s. F.R.S., is the first radio The value of the Kobel prize is physicist since the days of Marconi £8,000. to be honoured by the award of the DISC OR TAPE ? Nobel physics prize. In announcing RECEIVER EXPORTS the award the Swedish Academy of THE oft -repeated rumour that the Science stated that it was " for his ALTHOUGH there was a marked gramophone record companies work on atmospherical physics, and decrease in the export of domes- have attempted to restrain the de- especially for his discovery of the tic receivers during October as com- velopment of new methods of re- Appleton layer." pared with the 1946 figure (29,493 cording, such as those on magnetic as against 54,492), the figures for tape and wire, to protect their in- The last radio award was made the period January to October show terests in disc manufacture, have jointly to Marconi and Braun in an increase of nearly 8o,000 sets. been discredited by Sir Ernest Fisk. 1909. The increase in value is consider- In his statement as vice-chairman Sir Edward, who has been Secre- ably greater. The 262,218 receivers and managing director of E.M.I., tary (Administrative Heäd) of the exported during the ten-month Sir Ernest r.nnounced at the annual D.S.I.R. since 1939, started his re- period in 1946 were valued at general meeting that the company search into the existence of the iono- £2,470,220, whereas the value of is energetically developing these sphere whilst in the Cavendish this year's 340,873 sets was new methods of sound recording Laboratory, Cambridge, where from £3,849,920. and reproduction. 1919 he taught physics under Sir The biggest market continued to In defence of the disc he in- J. J. Thomson. From 1924 to 1936 be India, which purchased 92,74o stanced the cheapness and the ease he was Wheatstone Professor of sets during the ten months under of mass production, adding that at Experimental Physics, King's Col- review. The 1938 figure for the present there is no practical method lege, London, and from 1936 until same period was 4,088. The Indian for the mass production of wire and his present appointment he was Government recently decided to tape records. Jacksonian: Professor of Natural place a ban on the import of broadcast receivers.

REGISTER OF TAXI RADIO.- MANUFACTURERS Two-way radiotele- AMONG the 4,500 British manu- phony gear installed facturing organizations listed in by Pye in one of a the first post-war edition of the Vet of sixteen taxis " F.B.I. Register of Manufacturers " in Cambridge. Its which has just been published, are a use, to give orders considerable number in the radio in- to taxis, accounts dustry. This 1947 / 48 edition of the for a considerable Register, which is published jointly reduction in " dead by Kelly's Directories and Iliffe and mileage". Sons, is the only complete guide to the members of the Federation of British Industries. One section of the volume classi-

www.americanradiohistory.com January, 1948 Wireless World 23 fies the manufacturers under 5,250 the Telecommunication Research that we might have to record super- headings of their products or ser- Establishment, Malvern, the 40 - sonic frequencies in order to ensure vices. Reference facilities are given minute film is available from the complete realism of reproduction. in French and Spanish. Information Branch, Ministry of Comments on this apparent para-

Distribution . is being handled by Supply, Shell Mex House, London, dox will be found on p. 36. Kelly's Directories, Ltd., 186, W.C.2. Strand, London, W.C.2, from whom Two films featuring marine radar PERSONALITIES copies are available, price £2 2s. have been produced by Metrovick. There are special terms for F.B.I. One, " Radar Goes to Sea," shows Air Cmdre. L. Dalton -Morris, C.B.E., members. the production and use of the Sea - is relinquishing the post of Director of scan equipment and the other, Signals, Air Ministry, on his appointment as commandant of the Central INDUSTRIAL BURSARIES " Radar Record," includes a photo- Signals Establishment at Watton, graphic record of the P.P.I. picture THE British Council has inaugu- Norfolk. The C.S.E. provides flying taken during a trip up the Firth of facilities for the calibration and testing rated a scheme for awarding Clyde. of radar and radio navigational aids short-term bursaries to enable tech- The successful use of Decca in and is the training station for operating nical workers from overseas to see speeding the passage of colliers dur- crews for all ground control approach something of industrial techniques ing last year's fuel crisis is featured installations. in this country. Although so far in the film " The Decca System of Air Cmdre. E. H. Richardson, there have not been any applications Navigation." This 16 mm sound C.B.E., who has been Director of Radio from workers in the radio industry film, which runs for 3o minutes, can at the Air Ministry since August, 1946, is to become Director of Signals in it is included in the list of trades be borrowed from the Decca Navi- covered by the scheme. succession to Air Cmdre. L. Dalton - gator Co. Morris (see note above). In his present The bursary will cover travelling position he is responsible for the tech- expenses and a maintenance grant nical direction of the R.A.F. signals during the three or four months' SUPERSONIC HIGH service; he will in future be responsible stay in this country. Candidates FIDELITY ? for signals policy, planning and should apply to the offices of the AT a meeting of the Royal Society organization. British Council in their own of Arts on November 19th, S. H. Capon has been appointed country. under the chairmanship of Sir Noel Sales Engineer of T.C.C. He was Ashbridge, a paper was read by Sir formerly senior production officer in the Ministry of Aircraft Production. MARINE RADAR Ernest Fisk on the " Development of Soµnd Recording and Reproduc- C. A. Ingram, B.A.(Cantab), has THE original date fixed for the tion." In it he disclosed that been appointed secretary of the Radio termination of the agreement E.M.I. had been successful in re- Section of the I.E.E. in succession to whereby Admiralty radar equipment cording frequencies as high as K. W. T. Brown, who held the post Type 268 is fitted in merchant ships for a few months. Prior to joining the 20,000 c / s on lateral -cut discs. In I.E.E. in 1946, Mr. Ingram was a Naval as an interim measure was June, the discussion which followed radar officer. 1949. This was extended to Decem- several speakers, including Sir Mal- Leslie McMichael, director of ber and has again been extended as, colm Sargent, expressed the opinion McMichael Radio and past president of so far, no commercial equipment the- Brit.I.R.E., is visiting Australia has been submitted to the Ministry and New Zealand for a few months of Transport for approval. during the early part of 1948. Some 26o ships of the Merchant Navy have been fitted with Type OBITUARY 268 radar and the arrangements for maintenance in this country and It is with regret we record the death overseas have been extended to of Arthur Burrows at the age of 65. cover the continued use of the gear. " Uncle Arthur," as he became known to thousands in the early days of the B.B.C., was a pioneer of broadcasting. NAVIGATIONAL FILMS In 192o he radiated a daily programme from a liner during her trip across the RADAR is featured in the latest North Atlantic. The transmissions, of the " Britain Can Make It " radiated from the ship's 3 -kW set, were series of films sponsored by the Cen- received at 1,2oo miles. Burrows left tral Office of Information. This am, the B.B.C. in 1925 to become general No. 6, which has been produced secretary of the International Broad- jointly by the Ministry.. of Transport casting Union, a position he held until and the C.O.I., shows the produc- early in the war, when he rejoined the equipment and its B.B.C. He became Director of Broad- tion of radar casting at the Ministry of Information application to marine navigation. in 1942. Available on both 16 and 35 mm film, this 10 -minute sound reel can. IN BRIEF be borrowed from the Central Film Office of the C.O.I., London, W.r, Car Radio Licences.-Motorists can or in the case : of overseas readers obtain a refund, at the rate of is 8d

from the . Information Officer per month, on the unexpired portion attached to the British Embassy in of their car radio receiving licences their own country. where a car has been laid up because of the withdrawal of the basic petrol Another radar film (16 mm sound) ration. Application should be made is aväilable from the Ministry of to the nearest Head Postmaster, en- Supply. " R.D.F. to Radar," as its ARTHUR BURROWS, whose death closing a formal signed notification title implies, traces the history of is announced on this page, broad- stating that the car had been with- radar from the early experiments of casting from 2L0 in 1922. He was drawn from service. Watson-Watt to its latest applica - Director of Programmes of the Preparatory to the All-American ions to air navigation. Produced by original B.B.C. wavelength allocation conference to be

www.americanradiohistory.com 24 Wireless World January, 1948

World of Wireless- been transferred to 23, Dalkeith Place, D. M. Heller and L. C. Stenning, on held next year in Canada, a meeting Kettering. January 14th. of the signatories to the Havana Treaty Radio and Radar are featured in the Discussion on " To what Extent does of 1937 was held in Havana in Novem- " Highways of the Air " exhibition Distortion Really Matter in the Trans- ber. The original Havana wavelength staged by the Royal Geographic mission of Speech and Music? " on treaty was extended in 1946 for a Society at its headquarters in Kensing- January loth; opener, P. P. Eckersley. further two years. The allocations will ton Gore, London, S.W.7 (December Informal Meeting.-Discussion on cover all wavelengths for North and 22nd -January 15th). The Ministry of " The British Patent System and Pro- South America in the medium -wave Civil Aviation is exhibiting Consol, cedure " on January 26th; opener, band. Gee and I.L.S. equipment. The ex- C. S. Parsons, B.Sc. The An increase of 2,80o television receiv- hibition is open on weekdays, except above meetings will be held at ing licences during October is recorded Christmas Day and Boxing Day, from 5.3o at Savoy Place, London, W.C.z. by the G.P.O. The total number was II.0 to 5.0. Cambridge Radio Group.-Address by C. E. Strong, O.B.E., Radio Section 27,850. I.B.S. Conference.-The I.E.E., in chairman, collaboration with the British on January 13th at 6.o at A.F.N. Aerial.-The introduction of National the Cambridgeshire Technical College. a new aerial for the American Forces Committee for Scientific Radio, is plan- Sec.: ning to hold a J. E. Curran, M.Eng., University Network transmissions from Munich - conference on radio of Engineering, Trumpington Street, Stuttgart on 240 metres was marked physics, radio noise, propagation and Cambridge. by a special programme during which the standard of measurement. The North-Western proposed dates are April 7th Radio Groub.- the switchover took place. The old and 8th. " Triodes for Very Short Waves," by aerial was directed to this country for J. Bell, B.Sc., M. R. Gavin, " Lord Haw-Haw's " broadcasts. The M.B.E., INDUSTRIAL NEWS M.A., B.Sc., E. G. James, Ph.D., new installation is intended to give B.Sc., and G. W. Warren, B.Sc., on better coverage in Southern Germany. January zest at 6.3o at the Engineers' There was no noticeable break in the Baird.-The office of John Logic Club, Albert Square, Manchester. transmission during the switchover and Baird, Ltd., has been transferred from Asst. Sec.: Upper Grosvenor A. L. Green, 244, Branting - no apparent diminishing in signal Street, London, W.r, ham Road, Chorlton-cum-Hardy, Man- strength in the home counties. to 466, Alexandra Avenue, Rayners chester, 21. Lane, Pinner, Mddx (Tel.: Pinner Scottish Consol.-Because of the possible 2051). Centre.-" Speech Com- closing down of the North Atlantic munication under Conditions of Deaf- chain of Loran stations with the re- Cintel.-To introduce the new range ness or Loud Noise," by W. G. Radley, allocation of frequencies consequent of Cintel electronic apparatus manufac- C.B.E., Ph.D.(Eng.), on January 27th upon the Atlantic City decisions, the tured by Cinema -Television, Ltd., the at 6.15 at the Societies' Rooms, The International Civil Aviation Organiza- company has arranged a trade exhibi- Royal Technical College, George Street, tion has been urged to erect Consol tion at Brettenham House, Lancaster Glasgow. Sec.: R. B. Mitchell, 154. stations in Norway, N. Ireland, Ice- Place, Strand, London, W.C.2, from West George Street, Glasgow, C.z. land, the Azores, Newfoundland and January zoth-31st. Admission to the North-East Scotland Sub -Centre.- Bermuda. exhibition, which will be open from " The Design of a High-Fidelity Disc 9.30 to 5.o daily, except Sunday, will Recording Equipment," by H. Davies, Aircraft Relay Stations.-To ensure be the reception of the hourly weather re- by ticket obtainable from Cinema - M.Eng., on January 7th at 7.30 at the ports from aircraft on the North Television, Ltd., Worsley Bridge Road, Caledonian Hotel, Aberdeen, and on Atlantic route when adverse conditions London, S.E.z6. January 8th at 7.o at the Royal Hotel, for H.F. transmission prevail, air Foire de Paris.-The 1948 Paris Inter- Union Street, Dundee. Sec.: P. liners are now operating as E.H.F. national Trade Fair will be held from Philip, c/o Electricity Supply Dept., relay stations. A constant watch in May 1st to 17th. Some zoo of last Dudhope Crescent Road, Dundee. the E.H.F. band is kept by radio year's 9,000 exhibitors were British. South Midland Radio Group.-" The officers in aircraft belonging to mem- The London representative of the fair Cavity Magnetron," by H. A. H. Boot, bers of the International Air Transport is Miss Lambert, 14-15, Rugby Cham- Ph.D., and Professor J. T. Randall, Association, who will pass on reports bers, l ugby Street, W.C.r, from whom D.Sc., F.R.S., on January 26th at 7.0 from one to another until they are details may be obtained. at the James Watt Memorial Institute, Great Chatles Street, Birmingham. within range of a ground station. Manchester Radio Industries' Club. Sec.: -The Manchester Radio E. May, Birlec, Ltd., Tyburn Phototelegrams.-A phototelegraphy and Electrical Road, Birmingham, 24. circuit between the U.K. and Bermuda Club, which has a membership of was recently opened by Cable and nearly 200, has become affiliated to the Royal Society of Arts Wireless. The usual Empire charges Radio Industries' Club, and will in " Recent Progress in the Making of future bear the above name. Precision Instruments," by A. J. apply for a picture measuring up to Philpot, 24 sq in :-commercial, £5; Press, £3. C.B.E., M.A., B.Sc., on January z8th at 2.3o at the R.S.A., Amateurs' Course. - Prospective CLUBS John Adam Street, Adelphi, London, amateur transmitters in the Southport W.C.2. area may be interested to learn that Barnet.-Non-members will British the be wel- Sound Recording Association Southport Technical College has come at the next meeting of the Barnet " The Significance of the Amplifier arranged a course covering the syllabus Group of the R.S.G.B., which will in- in High-Fidelity Recording and Repro- for the City and Guilds' examination clude a sale of surplus gear. will duction," by H. for a licence. It J. Leak, on January transmitting be held at 7.30 on January 17th at the 23rd at 7.o at the Royal Society of Pakistan.-The administrative head- Millicent Café, Lytton Road, New Arts, John Adam Street, Adelphi, quarters of the Pakistan Broadcasting Barnet. Sec.: R. Walker, G6QI, 7, London, W.C.z. Sec.: R. W. Lowden, Service has been established in Potter's Lane, New Barnet, Herts. Wayford, Napoleon Avenue, Farn- Karachi, where a new station is to be Burnham (Som.).-The first meeting borough, Hants. built. It is to be equipped with two of the Burnham and Highbridge Radio Society of Great Britain 50-kW American transmitters. At Amateur Radio Society, which is in " The Design and Construction of present Pakistan has only three course of formation, will be held in Amateur Transmitters," stations, all medium -wave, by J. N. at Lahore, January. Interested amateurs in the Walker (G5JU), on January 9th at 6.3e Peshawar and Dacca. Burnham area of Somerset should at the I.E.E., Savoy Place, London, Society of Relay Engineers.-We communicate with the acting secretary, W.C.z. Sec.: J. Clarricoats, New have received from the Society of A. D. Taylor, G8PG, c /o P.O. Radio Ruskin House, Little Russell Street, Relay Engineers a copy of the consti- Station, Highbridge, Som. London, W.C.r. tution under which the society was British (Cinematograph Society formed in 1945. Among the objects Newcastle Section.-" The Cathode - are the improvement of, the status and MEETINGS Ray Tube," by G. Parr, on January efficiency of those engaged in relay en- 6th at Io..3o in the Neville Hall, Neville gineering. T. H. Hall, A.M.Brit.I.R.E., Institution of Electrical Engineers Street, Newcastle-on -Tyne. Sec E. has been appointed secretary of the Radio Section.-" Reference-Crystal - Turner, 30, Ettrick Grave, Sunderland, society. The society's offices have Controlled V.H.F. Equipnients," by Co. Durham.

www.americanradiohistory.com January, 1948 Wireless World Advertisements 25 THE BELLING -LEE PAGE Providing technical information, service and advice in relation to our products and the suppression of electrical interference (2) The elimination of interference is dealt with in two ways. (a) By the production and en- couragement in the use of better radio connections typified by terminals, plugs and sockets, and valveholders of many kinds. (b) We claim to be the first firm to specialise in the suppression of electrical interference. This is dealt with both at the listener's end and at the source. All the work we have done on the This type of suppressor is usually recom- subject, supported by the findings mended by the Post Office, for fitting at of the Post Office, the B.B.C. and the meter board or across the brushes of The illustration shows the " WINROD ' the Electrical interference -creating motors and genera- aerial L.581. Price I9/6. It is neat, inex- Research Association, tors, etc. List No. L.I1113/CT. Price 27/6. pensive and easy to fix. An outdoor aerial emphasises that suppression must this type will improve signal to liners, Belling -Lee do the work. of always be a co-operative effort. A reasonable noise ratio in relation to indoor types. They are also to serve the (Note to dealers at foot of page.) aerial at the listener's end, and a honoured fishing fleets of home waters and We re-established our " short reasonable amount of care taken in have those operating in distant deep sea run to enable us to the design of the appliance, or the " department fisheries. undertake " special " work for cus- suppression of the interference it A soldering tip tomers, including Universities and creates. The use of polythene insulant Government Research Establish- When we started this work we were in plugs and sockets with particular ments from whom suggestions are alone. Many firms have since reference to our coaxial range, welcome for the modification of joined in the fight against inter- raises ones or two points. Firstly, Belling -Lee components, and the ference by offering vertical aerials, official technical opinion is against consideration of development con- matching transformers, window any attempt being made to solder tracts within our sphere of activities. aerials, etc. The more firms manu- to the screen of cable with polythene We appreciate that many research facturing and advertising such insulant. More harm than good is establishments are three to five years appliances the better for the cause. likely to follow. ahead of commercial practice and Provided always that the products Parts to which you are likely to only by the closest co-operation are technically worthy. It is possible solder are silver-plated to ensure with them in the earliest stages can to introduce losses in an aerial easy and quick " wetting." See we hope to reap the full benefit. system that may give rise to much that the iron is at the correct The policy behind the activities disappointment. temperature. If it is running cool of this Company can be summarised Suppression at the source is a through electrical " load -shedding " as (r) Safety, (2) The elimination of tricky subject. There are few and allowed to lie for a considerable interference with radio. secrets in the design of suppressors. time on the part to be heated, (r) Safety is provided by the It may truthfully be said that any heat will 'travel to the polythene, adequate fusing of electronic circuits fool can make suppressors, but it with the result of a distorted plug calling for fuses of considerable takes craftsmen with experience or socket. accuracy. It is possible for a radio to use them efficiently. Much the receiver or any other appliance to same may be said of aerials. Perhaps *WINROD AERIALS cause fire before the blowing of a that is why we get so many of CAN NOW BE SUPPLIED normal 5 amp. house fuse. In the difficult cases, e.g. those on the spheres other than radio and elec- outer fringe of the range of Alexan- EX STOCK tronics, we assist protection by a dra Palace, etc. Probably it also FROM YOUR WHOLESALER comprehensive range of thermal accounts for our being called upon (See illustration above) switches which many manufacturers to suppress interference on the Royal fit to motors used in refrigerators, Train on the occasion of Their etc. These obviate burnt out motors Majesties' visit to South Africa. BELLING & LEE LTD by cutting off current if excessive heat When great shipping companies CAMBRIDGE ARTERIAL ROAD. ENFIELD. MIDDX is generated by a fault. require suppression on the largest

www.americanradiohistory.com 26 Advertisements Wireless World January, 1948

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www.americanradiohistory.com January, 1948 Wireless World 25 More Low- Power Transmission PRE-WAR readers of the Present-day Results Wireless World may re- Analysis of member an . article headed on 7 Mc/s ` Low-power Transmission-Long Ranges on One Watt," which appeared in the issue dated Sep- By W. OLIVER (G3XT) tember 14th, 1939. This contained of results during a corresponding five -month For this latter investigation a detailed analysis the three different transmitters have obtained with a very low -power period recently shows that the transmitter at G3XT over a low -power performance of this been used, and all have given and the station häs proved to be even broadly similar results, although period of five months, they differed considerably in performance of this set, with an more successful than before. one from The analytical tables accom- design, layout and power. The input averaging watt is similar to was shown to be con- panying this article give a com- first transmitter that batteries, used in 1939 and the input, too, good under all conditions parative record of the results sistently is the one in the overcrowded 7-Mc/s wave- obtained during the two periods, same-approximately band and at times little short of pre-war and post-war. One can watt. see at a glance that the 1947 The second and third trans- amazing. are single -valve sets and Strangely enough, an analysis results are far superior in all mitters at G3XT respects. are pentode crystal oscillators. of results obtained Among the valves tried in the the 2220, ANALYSIS OF RST REPORTS ON SIGNALS second transmitter are FROM G3XT PMzzA and 105, with inputs OVER A PERIOD OF 5 MONTHS IN 1947 ranging from I to 3 watts. The third transmitter is a rather un- conventional mains set with a Readability (R) Strength 22A6 as the oscillator, and an (S) 5 4 3 2 1 Totals input of 4 to 5 watts. 9 6 6 Although the mains transmitter 8 21 21 is the most powerful of the three, 7 99 7 106 in actual practice the average 6 154 13 167 reports are much the same irres- 5 98 35 8 I I 143 45 pective of which one is in use. 4 14 25 6 In fact, experience has shown that 3 4 8 6 19 3 other amateurs who were familiar 2 2 1 with the signals from this station 1 were quite unable to tell which of Totals 398 89 20 2 510 the transmitters was on the air at any particular time.

ANALYSIS OF COMPARATIVE RESULTS Aerial FOR A CORRESPONDING PERIOD IN 1939* The present transmitting aerial is a 66ft. end -on type and is a few Strength Readability (R) 5 4 3 2 1 Totals feet higher than those generally (S) used before the war. It is also a 9 1 1 little more in the open relative to 8 11 11 surrounding trees and buildings, 7 57 1 2 2 62 otherwise it shows little improve- 6 74 8 4 1 87 ment over the earlier ones. It is 5 83 18 3 1 105 obvious, therefore, that the 4 17 8 4 - 29 14 immense improvement in results 3 5 2 7 cannot be attributed to any 2 1 2 3 2 1 3 increase in the efficiency of the 1 transmitter, aerial or power. Totals 249 39 22 5 ' 0 315 The most plausible explanation of the superior results now ob- probably lies in a great * " Low -power Transmission," by W. Oliver (G3XT), W reless World, tained September 14th, 1939. improvement in the receiving

www.americanradiohistory.com 26 Wireless World January, 1948

More Low-Power Transmission- Recent experience has shown that end activities with signals fully technique at the other stations it is possible to get as many as readable, despite interference, contacted by G3XT. Many fifteen or twenty contacts on throughout a conversation lasting amateurs have undoubtedly gained 7 Mc/s during the height of week- ten or fifteen minutes. a great deal from the training and experience they had as radio operators in the Services, and the majority seem to have better receiving sets now than they did Output Transformer before the war. The fact that so many ex -Service operators are at A Simple Method present working exclusively in Efficiency C.W. may also be a contributory of Measurement factor. By On one occasion a station in 1 HE problem of measuring A.E. FALKUS,B.Sc. (Eng.), A.M.I.E.E. Holland reported the overall efficiency of (Chief Engineer, R. & A. Ltd.) G3XT's one -watt 1 small audio - frequency signals remaining transformers, such as the output voltage could be brought into steady around S9 transformer of a domestic radio phase, and their product would set, offers certain difficulties then give a true value for the in- as the power concerned is put watts. This condenser must, too small to be measured of course, absorb some energy, accurately with the usual but in practice the error is quite type of wattmeter. negligible. Transformer efficiency is If various values of condenser normally specified working are connected across a transformer into a pure resistive load, working into a constant load, one nd the output watts may value of capacity can be found therefore be easily obtained which will give a minimum for the from a voltmeter reading product of input volts and amps across this load. Measure- for a constant output. A prac- ment of the input power is, tical way of determining the right however, more difficult. capacity is to connect a resistance Owing to the leakage induc- in series with the transformer tance in the transformer, primary and to connect this resis- which may be , quite appre- tance and the transformer primary ciable, the input current to the X and Y plates of a will be out of phase with the cathode-ray tube, as shown in the applied voltage, and the figure. Care must be taken to product of input current make direct connection to the and input voltage will give plates, as if this is made through a falsely high value for the an amplifier an unknown amount input watts. of phase shift may be introduced. It occurred to the writer The trace on the screen will be that if the right value of an ellipse. If the capacity in One of the low -power transmitters capacity were shunted across shunt across the transformer is at G3XT. The aerial tuner is the transformer input to com- now varied the ellipse will be seen mounted on top of the metal pensate for the inductance, to swell or shrink in width, and a cabinet. in the manner of the nor- value is easily found for which mal power factor correction the ellipse becomes a throughout a QSO straight line. which lasted condenser, the input current and This occurs when the volts across for an hour. Only three out of the six " top -score " reports were obtained with the mains transmitter, using a power of 4 to 5 watts. It will be seen that the S8, S7 and S6 signal reports are roughly double their 1939 total, whereas the reports of lower strength signals have remained round about the same as before the war. This is the most convincing proof of an all-round improvement. An even more encouraging point is the number of successful contacts which have been made by G3XT Cathode-ray tube connections for resonance indication in test for small during periods of heavy QRM. A.F. transformer efficiency.

www.americanradiohistory.com 27 January, 1948 Wireless World the series resistance are in phase effective leakage inductance may involves an analogous problem with the volts across the trans- be calculated from the value of C due to Doppler effect; the receiver former, that is, the input current required to bring the input current acceptance band, has to be kept and voltage are in phase. and voltage into phase. It can trained on a shifting frequency. If the value of the series resist- be shown that the leakage induct- The shift can be pre -calculated, ance is R2 and the voltage as ance in henrys is : however, and in this-as in the - complex measured across it by a valve V32 C calculations of space voltmeter is V2, then the input navigation-electronic computors V E would no doubt be used to give (V3 w C)E + current is RE. If V, is the voltage CRE)z quick and accurate answers. The z Doppler effect would be of the across the transformer primary, Where : C is in farads. V2 V, in volts. utmost value for enabling the RE and are then the input power is V, x' R is in ohms. speed of approach at landing to be z w is err x frequency of test. indicated. The sensitivity of this If the load resistance is R, and the method was strikingly demon- output volts the output power In practice it will be found a V good plan to choose a value for strated at Radiolympia, where. movement as slow as o. r metre / . R2 smaller than the The overall efficiency is somewhat sec is RER,r impedance of the lit the indicator lamp. nominal input Although weight aboard a therefore :- transformer. The value of C for space V12 Rz mea- ship would be at such a premium x roo per cent. a small output transformer as a frequency of 40o to allow only essential equip- V, V, R1 sured at c/s ment to be carried, there would is the is likely to be about 0.015 µF. It of interest to note that be no such restrictions on land, where electronics could be given a free hand in simulating conditions of flight in the trainers that would Electronics and Space Flight be necessary to enable prospective pilots to make their initial mis- takes without suffering the New Uses for Radio ? drastic penalties that would follow in IT is not many years since flight for a few absorption bands the actual space flight. outside the earth's atmos- range from ro to ro9 Mc / s is avail- Mr. Clarke discussed possible phere was entirely visionary ; able. Owing to the great sensi- navigational aids. Celestial ob- fit for fantastic fiction, but not a tivity of photo -electric devices, servations, with electronic com- subject for practical engineering. and the compactness of high- putors, would probably serve Although space flight has not yet power radiators, it might well be most requirements in manned been developed to the point at that light waves would be superior ships ; but telemetering and con- which cruises round the moon or to radio for communication from trol equipment would be required planets can be advertised, that is space ships. for pilotless craft. He mentioned an extension in detail, rather than The power required for radio the value to radio research of ob- in principle, of what has already communication was tabulated for servations from outside the iono- been accomplished. So when typical cases. For example, using sphere, transmitted by rocket - Arthur C. Clarke spoke to the Bri- a zoo sq metre radiator on the propelled ballons sondes, which tish Interplanetary Society* on earth and r sq metre on the ship should be well within the scope of the uses of electronics in this far- at the distance of the moon, a known techniques. flung activity, he did not have to power of only 16 watts would be Any hopes that radar might be begin by apologizing for the sub- sufficient, ideally, for speech com- used to give space pilots warning ject matter. So far from being munication on a wavelength of when to take anti-meteor evasive pure speculation, his lecture rocm. If the large radiators were action were completely de- naturally included present-day used at both ends, morse com- molished by the lecturer. The practice in such initial ventures as munication to Jupiter at 400 amount of power needed for giving the V2 and moon radar, and pro- million miles would be within the even a few seconds notice of ceeded to quantitative examina- capabilities of present-day equip- normal -sized meteors was fantas- tion of more ambitious projects ment. But there would be an in- tic-probably enough to volatilize for the future. convenient time lag, due to pro- all the said meteors in its beam ! The word " electronics " in the pagation, of more than an hour Nor would it be easy, in the was used, for lack of a better between dispatch of the message moment or two available, to scan title out from one, to include not only valve and and the reply ! the relevant space, pick devices but possible appli- Communication with reasonable the numerous meteors present circuit would collide cations in the entire electromag- power depends on two things : a therein any that netic spectrum. It was pointed narrow beam, and a narrow band- with the ship, and compute the out that the longer radio waves width. The first presents the evasion that would dodge it with- hand, and ultra-violet problem of keeping the aerials out running into another. In on the one the risk of collision on the other, are stopped by the trained on their targets ; a prob- actual fact, earth's atmosphere, but except lem which wartime development was one that could be faced fairly of " lock -follow " has gone a long calmly, being of the order of once million years per ship. M. G. S. 8th November, 1947. way towards solving. The second per

www.americanradiohistory.com 223 Wireless World January, 1948 Air -line Radio Equipment for Operation on Long Routes

AGOOD idea of the radio J. A. McGillivray, radio super- Bendix roo -watt sets with crystal equipment of a large intendent of B.S.A.A., makes control of 8 channels per set. modern air -liner is given by some interesting comparisons be- Though crystal control is in itself the accompanying photograph, tween the present gear and that an advantage, the 16 channels which shows the gear installed in installed in the earlier Tudor I. provided by the two sets are in- one of the Tudor- IV aircraft of That aircraft carried, for main sufficient for all the requirements British South American Airways. communications, two American of B.S.A.A.'s long route, which extends to Santiago, Chile. Consequently, the R.A.F.-type TRr 154 /1155 40 -watt equipment has been chosen. This gear, with its master oscillator control, has the disadvantages of low power and a tendency towards frequency drift, which have to be overcome by operating skill. The advantages are a large saving of weight plus standardization : the TRr 154 / r 155 is widely used in B.S.A.A. aircraft. For short-range work, the two American SCR274 sets with three receivers, as fitted in the Tudor I, have been replaced by a second TR1r54/r155, again with a saving in weight, but also with the sacrifice of the simplicity of crystal control. Avoidance of duplication in equipment is another gain. The D.F. installation, comprising a manually operated loop working with the R1155 receiver, plus a Marconator set providing direct readings of true bearings. Mr. McGillivray points out that automatic direction finders suitable for aircraft use are expected to be available soon in this country, and it is hoped before long to replace the manual gear by automatic. A.S.V. radar equipment was installed in the earlier aircraft, but this has been replaced by Rebecca -Eureka equipment, for which the appropriate ground beacons have been installed by B.S.A.A. along its routes. This substitution makes a small saving in weight. The radio Radio installation on altimeter and blind one of the latest Tudor IV aircraft of British South approach gear are as originally American Airways. A, aerial leads-in; B, approach beam receiver (ro8- planned. rrr Mc/s); C, shert-range transmitter; D, D.F. receiver; E, inter -com- Unfortunately, the fail- munication box; F, fuses; G, glide -path receiver (332-335 Mc/s); H, H.T. ure-as yet-to attain standardi- generator; J, L.T. generator; K, morse key; L,. loop control; M, Mar- zation of ground equipment conator; N, aerial ammeters; O, loop lead-in; P, L.T. generator; Q, H.T. makes it necessary to carry receiv- generator; R, main communication receiver; S, standard beam approach ing equipment for both the Stan- receiver (33-40 Mc/s); T, main communication transmitter; V. V.H.F. dard Beam Approach and the transmitter -receiver. I.L.S. system.

www.americanradiohistory.com January, 1948 Wireless World 29 Radio Amateurs' Examination Report on Results for 1947 OF the 326 candidates who 3.-What is understood by the term " C.W." and what special method is needed Dependability sat for the Radio Ama- to detect C.W. signals? Describe a circuit teurs' Examination in arrangement which could be used for this purpose, illustrating your answer by a dia- May, 1947, only 120, or 37 per gram. cent, obtained a pass. This is a 4.-What is meant by modulation? De- scribe a method of modulating a typical low - very much lower percentage than power R.F. amplifier. 1946 398 during when 295 out of 5.-What are the relative advantages and entrants passed. disadvantages of a variable -frequency master oscillator over a crystal -controlled oscillator The comments of the City and for use in an amateur transmitter? Describe Guilds of London Institute on the a variable -frequency oscillator of good frequency -stability. Inc papers submitted at the last ex- ehe is 6.-Describe, with the aid of a diagram. amination instructive and the circuit arrangement of a low -power should be of value to those in- crystal -controlled transmitter for the 58.5 to tending to enter for future exam- 60 Mc /s frequency band. 7.-Describe FOUR types of aerial com- GRAMO -RADIO inations in order to qualify for an monly used for amateur transmission and amateur transmitting licence. how they may be coupled to the transmitter. AMPLIFIERS What are their relative advantages and dis- In the examiners' opinion the advantages? Several models are available falling off in the percentage of en- 8.-Condition 8 of the Postmaster -General's incorporating 3o watt or 15 trants obtaining a pass is licence to establish an amateur wireless watt Amplifier combined attributed to the fact that a large station stipulates:- with gramophone player or " Where the sending apparatus is not number apparently sat for the crystal -controlled there should be kept at the automatic record changer examination without adequate station ... a reliable frequency meter of the and radio receiver with piezo-electric crystal type or other type ap- preparation. One passage in the proved by the Postmaster -General, for monitor speaker. A.C./D.C. report is worth quoting in this re- measuring the frequency to an accuracy of models also available. not less than ±0.1 per cent." spect ; it states that . . . ' ` From Describe an apparatus to meet the fore- Write for illustrated list of full the phraseology and vocabulary going requirement. Illustrate your answer Sound Equipment Range for every used, and the general way in by a diagram and explain how the apparatus type of installation. which the answers were given, it is used. Model R.G.A. 633E/RC. is apparent that a large number Examiners' Comments of entrants, unused to sitting for examinations had received little Question 1.-Comparatively few or no coaching for the Radio candidates attempted this ques- Amateurs' Examination. The tion ; of those who did less than use of abbreviated and corrupt half did so correctly. English, such as is commonly Questions 2, 3 and 4.-Fairly used by amateur radio operators, well done by the better candi- is to be deprecated for examina- dates. tion purposes." Question 5.-The essential In order fully to appreciate the points in the design of a variable following detailed comments of frequency oscillator of good fre- the Institute the questions are quency stability were not at all given in full below. well understood. Question 6.-Many incorrect Amateurs' Examination Paper, answers given 14th, 1947. were concerning the May required frequency of the crystal Candidates should attempt as many ques- and the methods of multiplication tions as possible. Use should be made of diagrams where applicable. suggested to obtain the required final 1.-An alternating voltage of 10 volts at a frequency showed little re- 100 gard to efficient operation. frequency of Mc/s is applied to a cir- -2R Question well 7.-Not done in cuit consisting of the following elements con- particular the methods of coup- nected in series:- 1 (i) an inductance of 10 microhenrys. ling to the transmitter were dis- (ii) a capacitance of 10 picofarads. cussed very briefly. (iii) a resistance of 10 ohms. Question 8.-Very poorly done (a) What current flows through the circuit? by comparatively few entrants S6' (b) What voltage appears across the in- who attempted the question. ductance? They seemed to have a hazy idea THE TRIX ELECTRICAL CO. LTD. 2.-What is meant by the "selectivity" of of what a frequency meter of the 1-5 MAPLE PLACETOTTEMNAM COURT ROAD. LCD. DON, W.1 a tuned circuit? On what circuit constants 7f/URY041:MUSEUM 5817 CR1M$uCABILL''n11EADID.WE$DO.LONDON. does it depend? piezo-electric type really is, and Why is this quality necessary in a receiver? how to use it.

www.americanradiohistory.com 30 %%'ireli s% World January, 1948 BOOK REVIEWS

Fundamentals of Radio. By Jor- to mean both " mega- "" and effects of reflections from local dan, Nelson, Osterbrock, Pum- " milli-." After all, they differ sources. The author suggests that phrey and Smeby. Edited by only by the factor of ro'! the solution of this vital problem W. L. Everitt. Pp. 400 + xiii. Some of the terms whose tech- may be found in the use of micro- Constable & Co., Ltd., ro, Orange nical significance is by no means waves or short -pulse radar systems. Street, London, W.C.2. Price easy to grasp at first are introduced It is evident that the final aim of als 6d. without explanation. For example, designers of such systems is to make THE writing of a comprehensive " unstable " ; the reader has to it possible to achieve fully auto- basic book on radio, especially guess that on p. 133 it means matic blind landings. Already for readers " oscillating" and on p. 167 " un- many successful landings of this who lack the power of have sustained abstract thought, is a steady." What is called a quarter - type been made with appara- problem. It resembles a game of wave matching section is actually tus linked to the automatic pilot of patience in that the author is under a stub, not what is generally under- the aircraft, but these have shown an obligation to deal with each sub- stood by that term. that the reaction of even slight ject in In dealing with wave -forms it is beam -bends is serious and that the such an order as not to have root of the to use terms or ideas he has not yet desirable that the student should be problem lies in com- familiarized with the sine form pletely stable and reliable guide explained. Whatever standard of paths. intelligence readers are assumed to wherever it occurs, instead of being shown triangular waves or semi- In the chapter dealing with radio have should be maintained con- altimeters perhaps mention should sistently. There is the need to circular waves in lieu, as in Fig. ro -6, etc. On the other hand, have been made of the application avoid continuing theory too long at of the radio instrument to pressure a time without practical applica- where the purpose of a diagram is to show a departure from sine shape pattern flying. The only reason for tion. Above all, there is the prob- a civilian aircraft requiring an indi- lem of combining accuracy, clarity, (due to F.M.), the form actually shown (Fig. 14-4) is apparently cator which reads high altitudes is and conciseness. So it is not diffi- so as to be able to use the normal cult to criticize a book that sinusoidal; and the text gives the impression that merely making the aneroid instrument for the detection attempts such a task. of changes in atmospheric pressure " Fundamentals of Radio " scores wave " slimmer or fatter " necessarily renders it non -sinusoidal. whilst in flight. full marks for keeping theory closely Much of the book is concerned related all the time to practical If such details as these could be tidied up, " Fundamentals of with descriptions of radar systems, issues. Although the mathematical but it would be a mistake for the standard is kept within very ele- Radio " would be an excellent book for the practical man who wants to reader to imagine that it is with mentary algebra (which is given these that the world's aircraft in Chapter know how radio equipment works, r) and the necessary obtain their navigational aid ; basis of electrical theory is included without going too deeply into mathematics. M. indeed the majority still use C.W. (Chapters 2 and 3), the book suc- G. S. methods established before the war, ceeds in covering a remarkably and the airlines and authorities wide range-almost everything one Radio Aids to Navigation. By responsible for the safety of flying can think of except radar and R. A. Smith. Pp. 1 ro + xiv ; 37 appear to be slow in adopting new centimetre-wave techniques. In- figures. Cambridge University techniques. Shipping, on the other evitably, in one moderate -sized Press, zoo, Euston Road, Lon- hand, has already taken full advan- volume, some of the topics are don, N. W. r. tage of wartime developments both treated only superficially ; but the THIS is another of the mono- in the field of anti -collision radar working of transmitters and re- graphs of the " Modern Radio and radio position -fixing systems. ceivers (F.M. as well as A.M.) is Technique series ; it outlines the This book will appeal to radio explained fairly fully. principles underlying radio and engineers and aviators alike, as it It is on the ground of clarity - radar navigational aids, with paris clear that the author has a cum -accuracy that the book is most ticular reference to their application thorough knowledge of the airborne open to criticism, because some of to aviation. as well as the chairborne aspects of its shortcomings in this respect The treatment of the subject is the subject upon which he has seem to be avoidable. The various non - mathematical but technical written so lucidly. C. B. B. distinct uses of symbols-for knowledge is assumed, and sufficient generalizing arithmetic, for indicat- detail is given for any of the sys- Electronics and Their Application ing mathematical operations, for tems described to be. clearly under- in Industry and Research. Edited abbreviation, and for reference in a stood. There is also enough by Bernard Lovell, O.B.E., diagram-are all confused in one explanation of practical and opera- B.Sc., Ph.D., F.Inst.P. Pp. paragraph ; and what clear idea can tional problems for the reader to be 66o+xvi, with 404 illustrations. the beginner derive from the state- able to form his own opinion of the The Pilot Press, Ltd., 45, Great ment that " Mathematics packs relative merits of devices designed Russell Street, London, W.C.x. much meaning into one symbol to to perform the same role, such as, Price 42s. make the symbol useful where for instance, C.W. and radar omni- ONE of the effects of modern words or numbers would not directional ranges. research has been to dissolve serve"? Incidentally, a collected The two chapters devoted to aids the artificial divisions that had table of letter symbols, to match to instrument landing give an excel- been erected between the sciences. that provided for graphical circuit lent summary of what has been Another has been to expand know- symbols, would have been helpful. accomplished in this field to date, ledge far beyond the grasp of any The reviewer, for one, failed to find but it is disturbing to realize that individual. So just when seeing the any key to the symbols " f " and even now there is no completely field as a whole is more than ever " ff " after many of the references satisfactory system, due to the diffi- desirable, it has become impos- in the index. The usual American culties involved in producing guid- sible. But although it is no longer practice is followed of using " m " ance beams which are free from the practicable, as it once was, for a

www.americanradiohistory.com January, 1948 Wireless World 31 person to have a fair grasp of all in Medicine; XII, Electronics in the arts and sciences, this should Physiology ; XIII, The Betatron; be no excuse for concentrating so XIV, Electron Microscopy and exclusively on our own job that Electron Diffraction. we cannot see even our corner of Most books on electronics are too The following figures the wood for one particular twig. superficial or too specialized. This A pleasant and profitable correc- one strikes a very happy medium. tive for radio workers suffering The first chapter is perhaps a little from excessively restricted field of concentrated for readers who have are the pass figures vision is the volume under review. no harkground in physics, and the Pleasant, because on the whole it is treatment of servo -mechanisms and so well written and produced; and to some extent R.F. heating and profitable because it is so likely to radar, is mathematical, but not on final test for stimulate thought and ideas. excessively so. The chapter by Neuro -physiology, for example, J. D. McGee on television is might seem a forbidding and irre- an excellent review of electronic levant subject for the radio engi- camera tubes, and contains much Model QA12/P neer. But Dr. Pumphrey's chap- hitherto unpublished information. ter, on just this, is not only a " Radar," by R. A. Smith, is lively piece of writing but his final also a clear and well-balanced sur- AMPLIFIER section might well appeal to the vey. The statement that the term most practical -minded radio man. " radar " is now associated with " The physiology of the mammalian pulse technique rather than with ear is necessarily largely based on echoes is misleading, however, for work with experimental animals, it has never been so used in cats, guinea -pigs, and so forth, America, where the term origin- whose auditory spectrum extends ated, and the tendency to do so in far up into the supersonic range. this country is to be deprecated. But there is literally no equipment It would he far better to widen the available for reproducing or record- redundant term " radiolocation " ing sound in the range ro -roo (which was never used by radar kc/s. . There is a crying need workers themselves- " R.D.F." for a high -gain low -noise amplifier was their name) to cover all with a pass band of the order of systems for location by radio, in r cycle-ro kilocycles per minute, contradistinction" to radio com- but none exists and its develop- munication. ment would require work for which Each chapter is well referenced few physiologists have the com- for the assistance of those who RANGE c.P.s. petence or time." And so on. want to pursue the subject further. FRFREQUENCY db 20 ' Illustrations are good, and there 0.3 output The man whose work lies, say, in r1S1T1V11}óocoscslr are Eu1l author and subject indexes. output valve or circuit design, can hardly for f(u11 produce the most effective device, It is a pity that the symbols and mdhvolts abbreviations are not British 5 s. or even know what device to pro- 1,NicCONTf

www.americanradiohistory.com 32 Wireless World January, 1948 Unbiased

up to the maximum in order to Now I am not suggesting that we Designers Forward enable me to continue listening are on the verge of a dictatorship amid the racket of the childish from the extreme Left or the ex- Please prattle which passes muster for con- treme Right, but there is un- OF all the trends of modern versation among the offensive doubtedly a very grave danger of a design in the field of radio re- females whom Mrs. Free Grid insists dictatorship of another sort. Judg- ceivers and other electronically on bringing home from time to time. ing by the activities of Mrs. Free operated apparatus intended for Grid and her friends, we may easily providing entertainment, I deem the wake up one fine morning to find most important to be the appear- By a matriarchy firmly established. ance of one or two makes of mag- Mr. Churchill, Sir Stafford Cripps netic -tape home recorder giving a FREE GRID and myself would then be seen continuous run of entertainment busily engaged in pledging each without record changing. other in a Loving Cup of watery I think so not because, in my Actually, of course, it wouldn't cocoa during a brief respite from opinion, they are likely in the fore- be a lot of good merely to be able our enforced floor -scrubbing activi- seeable future to take the place of to switch on the recorder in the ties. disc machines; indeed, for ordinary middle of a play or other continuous entertainment I much prefer the programme, as when it came to the discs as they enable one to select time when I was able to resume very quickly any particular item of listening to it I should have for- music without tediously wading gotten the first part. What is through a lot of extraneous matter. wanted is for the magnetic -tape re- Nor, do I welcome the tape recorder corder to be in action all the time. because of its possibilities in the It could be easily run through the way of recording my voice and that " wipe out " coil afterwards unless of Mrs. Free Grid. That can be it were desired to preserve the pro- done equally well on a disc and, in gramme for future use. any case, anybody who has ever A programme clock could be in- possessed a home ciné camera will cluded so that it would be possible know that, for most people, that to bottle any item that happened sort of thing has little more than to be due on the air at a time when A Loving Cup. novelty value. the listener was out. We should No, the real scope of the tape then have the complete home radio If this sort of thing does happen recorder is for it to be incorporated entertainer. we shall be in a far sorrier plight as an integral part of a domestic than if it had occurred twenty years radio receiver so that it can be ago. The listening public having switched on to bottle any pro- A Grave Menace been spoonfed with factory-built re- gramme desired. Most people have ceivers, instead of having to make experienced the great annoyance of THE great argument against a do and mend as we pioneers did a being interrupted by casual visitors wire broadcasting system has quarter of a century ago, home con- when listening to a broadcast play; always been a political rather than struction is almost a lost art. more especially if it be a serial. a technical one, it being said in There is only one remedy and some quarters that it would play that is for the Editor to publish directly into the hands of any immediately a comprehensive series home-grown Hitler who might arise of articles in which real austerity in these islands. The absence of home construction is taught. De- ordinary domestic wireless sets scribing variable condenser vanes would, of course, prevent listeners hewn out of old biscuit tins and hearing the uplifting voices from coils made from old picture wire, the British freedom stations beyond the articles must take nothing for the seas. granted and even include home- This is so, but all the same I made valves and the construction could not help thinking that there of the necessary pumping gear to was a lot in the remark made by create a vacuum. P. P. Eckersley in his article in the I would also suggest that a December issue that if a dictator- Defence Regulation should be in- Offensive females. ship came, broadcasting by any voked making it impossible for technique would be cut off. This anybody to buy a factory-built set is no argument for a wire system until he had demonstrated Many I his a time would have gladly of broadcasting, but a challenge to capabilities in austerity home con- given up my nightcap of the real us to be up and doing to devise struction. I know that the manu- McCoy in exchange for the ability some scheme whereby every listener facturers will be against me, but to switch my set over to " record- has the technical knowledge to im- they always have been and I would ing " on the unexpected entry of provise some method of overseas remind them if Free that my fears prove Mrs. Grid and some of her listening after the political police well founded they, too, will find friends. As it is, I have had to have descended upon him and taken themselves in the floor -scrubbing be content with turning the wick away his receiver. fatigue party.

www.americanradiohistory.com January, 1948 Wireless World LETTERS TO THE EDITOR[ Now to Output Transformers and Feedback Avoiding the "Single Point" Sound Source WIN SALES High -Quality Amplifiers stantially discrete elements such YOUR journal publishes from as resistances and condensers, by time to time some excellent making use of the relationship and circuits of high-performance audio that exists between frequency amplifiers and the more recent characteristic and phase change. ones are based on the application All this is familiar to many of of a considerable degree of nega- your readers but what is not tive feedback. In many instances always remembered is that Bode's Influence people this feedback is applied over a simplification fails when the cir- portion of the circuit containing cuit includes distributed elements an iron -cored audio transformer or such as in a transmission line or choke. The specification of this when at some high frequency cer- component thereby becomes contain components such as valves siderably altered and hardly or transformers cease to act as would it be fair to condemn a nor- lumped constants. It follows mally good transformer because of from this that when a transformer the inadequacy of its performance is included in a feedback loop its in such a circuit. It is to this I phase change characteristic must would like the attention of your be known over a band consider- readers drawn. ably wider than the normal audio In circuits where the trans- band before the performance with former is not included in a feed- regard to stability can be pre- back loop, this component would dicted. This characteristic can be judged according to its prop- only be determined by experiment erties (level frequency character- and it is usually easier to connect istic, low harmonic distortion, the transformer in circuit, adjust- level phase change and frequency ing the amount of feedback to the characteristic, optimum loading maximum giving unconditional Lesson number one in selling is to of the valves, high frequency, etc.) stability with a margin allowed within the desired frequency range for component value variations. present your product attractively. For a production job the margin which might be from zo to 20,000 We are specialists in this field. c /s in the very highest fidelity allowed must be adequate to cover the inevitable variations, especi- equipment. The uSe of negative We design and build cases that additional really of distributed constants, of feedback introduces transformers. quirements which have no direct not cnly fit the job but do a job- bearing on the fidelity of repro- To sum up : if a transformer duction but are demanded merely giving a performance beyond re- of hard selling. And we work by stability considerations. These proach over the audio spectrum is additional requirements are ob- found to account for instability in fast -7 days from rough sketch a circuit with high negative feed- tained from the well-known to finished product, if necessary. Nyquist Regeneration Theory back, it would be unfair from this published in 1932 in the Bell to conclude that it is a bad com- System Technical Journal and ponent, a conclusion which might IMPOSSIBLE? BUT IT'S TRUE lightly referred to by E. Jeffery be derived from the wording of TRY US AND SEE in your August issue. Major Jeffery's article (vide p. 276, col. 3, The condition for stability is August, 1947). that the feedback loop must not TREFOR WILLIAMS. introduce a phase change as great Partridge Transformers, Ltd., as 18o deg at any frequency at London, S.W.r. which the gain of the loop (forward and return) has ,not fallen B.B.C. Services by n db where n db is the amount PRECISION BUILT of applied negative feedback. ]f¡TITH reference to Thomas H. W. Bode* has later simplified v v Roddam's article, " Short INSTRUMENT CASES this for design purposes, in cases Waves for Pleasure," published in where the loop contains only sub- Wireless World for October, 1947, ST., may I draw attention to the 112-116, NEW OXFORD Bell System Technical Journal, Vol. XIX. - Muse,n,5944. JulY, 1940, PP. 421-454. fact that the B.B.C.'s " Over LONDON, W.C.I.

www.americanradiohistory.com 34 Wireless World January, 1948

Letters to the Editor- I find that this is best achieved be awarded only on examination. seas " Services are not primarily by the judicious placing of large By so doing all radio amateurs intended for listeners in Europe, reflecting surfaces in front of the would be technically qualified who must not perfect re- loudspeaker in such a way as to and so expect the chaotic`Etheris conditions ably ception when they happen on increase the air loading on the forecast by ' " would be transmissions directed to Africa, diaphragm and to function to avoided. " AMRAD." Asia, Australia or America. some extent as a very large There is, however, a " Euro- folded horn. If this is properly F.M. and Monopoly pean " Service in the B.B.C., and done the increase in realism and this includes transmissions both " presence " is quite remarkable, THEE only really important ad- in Swedish and English which are but unfortunately this solution is, vantage of a frequency - received well in most parts of the generally speaking, only practic- modulated national broadcasting country. Details of our Swedish able in a fairly large room, though system would be that it enabled transmissions are regularly in smaller rooms it is sometimes domestic listeners to receive pro- printed in the official Swedish possible by placing the loud- grammes without interference radio paper, and full details of all speaker in a cupboard to make from badly maintained and un - our European Service transmis- use of the door (if suitably solid), suppressed electrical apparatus in sions are contained in a bulletin set at the correct angle, as the their vicinity. A very secondary which is at present sent on re- first reflector. claim by F.M. partisans is that quest to listeners in Europe. I have no doubt at all that reproduction can be more faithful GORDON WINTER, high audio frequencies are neces- to the origin than with A.M. ; this European Publicity Officer, sary, and can be nice, but only claim is and has always been B.B.C. when properly presented. weakened by the facts that (a) R. MARKER. the improvement can only be H.F.: Necessary and Nice ? Honiton, Devon. slight under the best conditions, IAM quite sure the average and (b) the great majority of the listener restricts high -fre- Amateur Operator's listening public do not like or quency response in an effort to Qualifications want " super -high-fidelity " re- improve reproduction. production. This horrifying statement is the HAVE read with interest the Against these advantages must result of a number of experiments I letter from " Etheris " in your be put the facts that (a) only long I have carried out with a view December issue, and in particular overdue legislation (already exist- to increasing the illusion of noted the number of licences ing in certain European countries) " presence in reproduced sound. issued each month and the pos- prevents a selfish minority from The reproduction provided by sibly disastrous outcome. being obliged to keep offending the usual loudspeaker working Apparently the large number apparatus in good order and fit through a hole in a baffle is quite of licences issued per month is en- suppressors-the cost of which unrealistic. It badly lacks the tirely due to those applicants would be quite small : (b) the cost " roundness " of the original per- who are exempted by virtue of of setting up a nation-wide net- formance, and this is caused by some qualification-among many work of F.M. transmitters would the fact that much of the repro- others, those who hold the Post - be enormous and would have to duced sound (particularly the Master -General's " Special " Cer- come out of the pockets of al- high audio frequencies) reaches tificate. ready well -taxed citizens ; (c) the the ear in the form of a narrow The examination for the listening public would be forced beam from a relatively small " Special " Certificate does not in- to buy F.M. receivers (or, pos- point of origin. clude theory, and it is well known sibly, in a negligibly small number The average listener finds that that a large majority of those who of cases, " adaptors,") (d) a vast he can make things sound more possess that Certificate have no amount of material and labour natural by reducing his H.A.F. theoretical knowledge. I am con- would be required for the change- response (which reduces the fident they could not pass the over, and both- are not only in beaming), and he also boosts the technical examination for the short supply but urgently re- bass in an effort to achieve amateur licence. quired for export activities rather greater depth and roundness. The It would appear to be an un- than for domestic use ; (e) except resulting " mellow tone," while justified assumption that because for freak and very erratic chances, anathema to you and me, un- an individual has acted in a reception by the mass of non- doubtedly pleases the average wireless capacity in some branch technical listeners would be con- ear. of the Services he has in every fined to that of the national F.M. If, on the other hand, steps are case a sufficient knowledge of the network, with the consequent loss taken to reduce the " beam subject to justify his exemption of the ability and liberty to listen effect " by more legitimate means from the examination. And to what the rest of the world had which also give the illusion of a those who have the requisite to say on important controversial far larger point of origin, I have knowledge would assuredly not issues-a deprivation which should proved to my satisfaction that an hesitate to sit for the examina- be fully appreciated in the danger- extended H.A.F. response, far tion. ous times ahead of us in regard from being disliked, is welcomed Accordingly, I suggest that it to social developments. with enthusiasm by the unin- is in the interests of all radio W. H. CAZALY. itiated. amateurs that the licence should London, N.W.

www.americanradiohistory.com January, 1948 Wireless World 35 Miniature F.M. Transmitter - Receiver

AS an outstanding example of Portable Radio -telephone miniaturization it would be difficult to find an equal to the Use V.H.F. portable radio telephone for Pedestrian RECORD by Tele-Radio Development, made When it is realized that this 177, Edgware Road, London, W.2. REPRODUCER x lin x equivalent of an eight -stage super- This set measures gin into an weighs approximately 81b heterodyne is compressed 34ín, and of approximately Tin including batteries. overall space is designed for x 4in x tin it will be appreciated The equipment word miniature on a fixed frequency in that the use of the operation in describing this equipment is fully the 70- to 95-Mc/s band and dif- frequencies can be used for justified. ferent Despite so much in so small a send and receive. receiver are Crystal control is used in both space all parts of the receiver and the accessible, a point of no little im- the transmitter and from the maintenance two circuits are virtually indepen- portance feature aspect. Needless to say, the trans- dent, the one common with its fewer stages, being that the receiver's audio mitter section, as a microphone is equally accessible and the work- stages are used a very high standard. amplifier for the transmitter. This manship is of is a There are two models of this has three valves, the first noise available ; in one the This amplifier with special attention to low oscillator tripling radio telephone low crystal -controlled receiver and transmitter are level, good response (30-18,000 cps.) and the frequency in its anode circuit, harmonic distortiop (I per cent. at IO watts). chassis assembled one switch for the second combines the functions of separate Suitable for any type of pick-up with other and a separate bat- compensation, double negative feedback frequency doubler and reactance above the record tery box is employed. In the other, circuit to minimise distortiongenerated modulator and the third is a push- speaker. Has fitted plug to supply 3 ra 3 amp. is the more recent develop- a mixer or feeder pull Class C amplifier delivering which L.T. and 300 v. 30 m/A. H.T. to ment, receiver and transmitter are unit. Complete in metal cabinet and extra 700 milliwatts to a quarter - 2.9. gns. about on one chassis with the batteries microphone stage. As illustrated. Price vertical aerial. A deviation in case without extra 4microphonehe wave accommodated in the lower part of Complete of plus or minus 15 kc / s is em- stage ployed. The microphone is a the case. Chassis only, without extra microphonePstagg for send or re- . -coil type. The switching moving ceive is effected by a multi -contact relay on the receiver chassis, which " SUPER FIFTY WATT " is actuated by a press switch in the handle of the microphone. A AMPLIFIER head -set is separate telephone This Amplifier has a response of 30 cps. to normally used but it could be re- 25,000 cps., within } db., under 2 per cent. 15 watts, placed by a combined hand -tele- distortion at 40 watts and I per cent. at including noise and distortion of pre -amplifier and phone and microphone. microphone transformer. Electronic mixing for Despite the relatively large microphone and gramophone of either high or number of valves for a portable set low impedance with top and bass controls. L.T. consumption is Output for 15/250 ohms with generous voice coil the H.T. and feedback to minimise speaker distortion. New not heavy. The transmitter takes style easy access steel case gives recessed controls, mA 1.4 volts and 23 mA at making transport safe and easy. Exceedingly well 650 at Amplifier complete in 90 volts, while the receiver accounts ventilated for long life. steel case, with built-in 15 ohm mu -metal shielded for 35o mA L.T. and 15 mA H.T. microphone transformer, tropical finish. Only one of the two units is Price 361 gns. operating at any time. There are many uses for a handy AD/47 10 -VALVE TRIODE It falls r adio telephone'of this kind. CATHODE FOLLOWER AMPLIFIER \v ithin a similar category to the telephones des- For this recording and play-back Amplifier we mobile V.H.F. radio claim an overall distortion of only 0.01% as cribed in this journal from time to measured on a distortion factor meter at middle time but it is a pedestrian's or frequencies for a 10 -watt output. The output crystal transformer can be switched from 15 ohms to Tele -Radio miniature Y.H.F. patrolman's equivalent. 2,000 ohms, for recording purposes, the measured controlled F.M. transmitter -receiver. damping factor being 40 times in each case. Full details upon request. Export Agents The receiver is a super -hetero- "DEFLECTOR COIL Dealers and dyne with one R.F. amplifier a should write for special terms to :- single -valve frequency changer with EFFICIENCY": A CORRECTION oscillator, the crystal -controlled In this article, Wireless World, VORTEXION LTD. sixth harmonic of which is applied 257-261, THE BROADWAY, grid. There are two December, 1947, P 460:- to the mixer ' ' S.W.19 working at 4.7 Mc/s For ' kilowatts ' read kilovolts WIMBLEDON, LONDON, I.F. amplifiers ' 3. to Eqn. (5). For da2' Telefhsnes : LIBerty 2814 and 6242, (the second acts as a limiter) a dis- just prior in- the denominator of : VORTEXION, WIMBLE, LONDON." criminator with two Germanium read d2 ' Telegrams " crystals and two A.F. amplifiers. Eqn. (iz).

www.americanradiohistory.com 3(, R'ïrelcss World January, 1948

Don't you often feel, after watching RANDOM a studio item, that the results as RADIATIONS entertainment scarcely repay the hard work which all concerned have By "DIALLIST" put into its production? If the V.I.P.s of television broadcasting can realize these things they'll see Televised News which you'd have liked to see tele- to it that the fifteen minutes vised pictures last once FOR years I've been urging in night. And why a week of the Teleciné Review be- stop at home news? Many Euro- comes first these columns that the tele- pean fifteen minutes a day and vision capitals are within 3-4 hours' then thirty minutes or more a day. service should include illus- flight. The evening trated news bulletins and I am glad illustrated news The more television concerns itself bulletin could certainly include with actualities, the sooner to see that something of the kind events which happened will it is at last to be started. Within on the same be on the road to becoming as much day in France, Belgium, Switzer- a part of our daily the next few days a weekly feature land, Holland, lives as some called " B.B.C. Teleciné Review Denmark and prob- broadcasting now is. " ably Norway, Sweden and the Wes- is to be inaugurated. It will run tern parts of for a Germany. Pictures quarter of an hour. That is from the rest of Europe at any rate a beginning and I would need be ` ... But Those Unheard are only one day stale; we could have not mind making a modest bet that those from Sweeter" it receives America and India and a very hearty welcome much of Africa two days from viewers-provided, of course, after the AT a recent meeting of the Royal event; even from Australia the Society of Arts Sir Ernest Fisk that it's well done. My feeling has delay would be less than a always been that television can week. announced that E.M.I. had been make one of its biggest appeals by successful in recording frequencies presenting pictures of current A Big Show up to 20,000 c / s on wax discs. In view of the fact events. You can't, of course, ex- Naturally all of this would call that even the lissom pect highlights every day for a large ears of the human young can re- on a par and expensive organiza- spond to with the Royal Wedding, the Boat tion. A score or nothing above about more of mobile r.6,000 c/ s, whilst Race, the Derby, the Cup Final or ciné units would be needed in those of aged the fight for a boxing championship various parts dodderers like myself have norm- of this country and ally a cut-off in the neighbourhood title. Even if you could, such events the air transport would have to be often of ro,000-r2,000c/s, your comment take place at times which pre- maintained. Abroad the system on vent a considerable proportion of could be this statement might be a ribald expanded gradually from " So what? " But television set owners from watching comparatively small beginnings- when Sir Mal- direct broadcasts. But say a mobile colm Sargent and others who know interesting ciné recorder in Paris both their musical and their acoustic events are happening all day and to start with. The position would every day. be onions maintain, as maintain they They can be recorded by eased to no small extent by the did, that even the ciné camera and I am sure growth of higher frequencies that national-and later inter- may have to be recorded in order an illustrated news bulletin made up national-relay links. As, for in- to obtain complete of ciné films, accompanied by stance, these realism in repro- a good began to cover more duction you begin to do some think- running commentary, would prove and more of our own country the ing. need At first blush the idea seems an enormously popular daily feature for the physical conveyance of utter nonsense: how if sent out at a convenient the films to London can what we time each would diminish. hear be affected by the presence or evening. The originals could be transmitted absence from the of frequencies that we can't nearest television centre hear? And then something at the Immense Scope and relayed over the linking net- back of your mind whispers work. The more I that think of it the f, in other words, two super- A really live B.B.C. department, surer do I become that the real job -f3=f3: not stinted in the matter of finance, sonic frequencies may produce an of television is to bring pictures of audible could make bulletins of this kind current events beat frequency. It seems into our homes either quite possible that when an orches- such a success that the television as they occur or soon after they would rapidly become almost as in- tra is in action the supersonic upper have happened. I don't believe that harmonics of certain instruments dispensable a piece of domestic there is much future for entertain- do equipment as the broadcast receiv- produce such beats. If they are ment produced in the studio speci- absent from an electro -mechanical ing set is now. The combination of ally for television purposes. Plays? ciné camera and emitron-controlled reproduction, it doesn't sound quite Certainly ; but let's have them real. vision transmitter opens up almost straight from the theatres at which unlimited possibilities. Existing If the original supersonic frequen- air they are running. Concerts should cies are, say, rg,000 transport facilities should enable come from and 21,000c/s a real concert hall, dance the beat will be at the audible fre- films of daytime events in pretty music from ballroom, restaurant or well any part of quency of 2,000 c/s. Assuming that this country (de- " palais." The studio stuff is far there is such a veloped and processed en route, if beat and that I re- too artificial in its atmosphere- cord and reproduce up to, perhaps, need be) to be in London in ample television should show the real time for the evening transmission. 6,000c/s, why should not the beat thing-and far too limited in its frequency of 2, 000 And is there a day between one end c / s be adequately possibilities. Can you, frankly, raise brought out, even though the and the other of any year on which any enthusiasm over shots first of dozens of interesting events generating frequencies are removed are not a dance band as a group and then by the cut-off at 6,000 c/s? taking place somewhere in these of individual performers on various islands? Look at the headlines The answer is that non -linearity in instruments? Are you at all thrilled is required somewhere in the system this morning's papers and ask your- by the sound -and -vision presenta- to produce the self whether there were not yester- beats. If the record- tion of a studio singer or other solo- ing microphones, amplifiers and cut- day all sorts of goings on in Eng- ist? Do you find the studio plays ting heads land, Scotland, Ireland are free from non - or Wales of as satisfying as they should be? linearity distortion the beat frequen-

www.americanradiohistory.com 37 January, 1948 Wireless World

ties will not be generated as such in the record, nor will they be present in the reproducing equipment if it Resistors is similarly free from ` amplitude Power distortion." Not until the original supersonic frequencies reach the non-linear device known as the ear will the audible beat frequency emerge. So if you cut off at t6 kc / s in recording you must do your mixing and introduce some non -linearity before or in the cutter head if you want to record those beats. Which poses the question: If one records only the whole gamut of audible sounds how much non -linearity distortion should be introduced for realistic reproduction?

'Phone Lines and Television AT first blush he pair of wires which connects your telephone and mine to the exchange, or those which connect one exchange with For all uses .. . another, might not seem to offer a very promising means of conveying the wide range of frequencies needed for television modulation. The former run 64 lb to the mile, the latter to lb or 20 lb. In ordinary use pairs are not called upon to handle frequencies higher than BULGIN high-grade resistors, made in 10, 20, 3,000-4,000 cycles a second-and the full range of vision frequencies 40 and 60 watt sizes with ratings from 25- radiated from A.P. goes up to 2.7 megacycles a second. Yet during 150,000 ohms, have been still further im- there ma'y be as outside broadcasts proved in design and materials. The highest quality much as eight miles of ordinary telephone line in use. It is true that obtainable, oxidised non -corrodible resistance wire they are normally made to carry frequencies only up to 2 Mc / s ; but is now helically wound on a braided core of glass - that is sufficient for a pretty good picture and, if it were thought to fibres, obviating any possibility of acid -attack on there be worth the extra expense, the wire. This cord is wound on an unglazed re- would be comparatively little difficulty about raising the limit to the fractory former, and held by terminating clamp full 2.7 Mc / s. An article in a recent issue of the B.B.G. Quarterly de- bands, for lashed and/or soldered connections. For ex- scribes how it is done. Briefly, from 60°F. periment showed that the main use at up to 450°F. surface temperature snags were heavy attenuation of the ambient-adequate ventilation to be provided. very high modulation frequencies and considerable phase distortion. the high frequençies is Maintaining V. to earth, 1,000. Max. V. across just a matter of using plenty of re- Max. wkg. peaters in the lines. Telephone lines terminals, 750. Max. test -V. to E., 1;500 PEAK. have ordinarily a repeater at every 20-25 miles ; for television frequencies a repeater every ij miles is needed. It has been found that phase distortion can be avoided by the use of suitable equalizers, so transportable repeater - equalizer units, weighing less than 15o lb apiece, were designed and brought into use. With these any telephone pair can readily be adapted for television purposes. The radius of in the London area has been O.B.s g LTD. BYE -PASS RD. BARRING greatly increased without the ex- A.F.BULGIN CO. of laying numerous branches pense lines) of coaxial cable. Telephone: RlPpleway 3474 (5

www.americanradiohistory.com 38 Wireless World January, 1948 RECENT INVENTIONS RADAR AERIAL SYSTEM A Selection of the THE oscillation centre of a dipole More Interesting A B, diagram (a), coincides with the common focus of two elliptical re- Radio Developments flectors, C, D. Radiation from the of right-hand limb of the dipole is col- the target, even at low angles of (P.P.I.) that is produced by the echo lected by the mirror C and passed to elevation. The outer cone serves to signals from the pulsed exploring beam. its conjugate focus S; whilst radiation reduce the time that would be required R. A. R. Tricker, A. Tutchings, from the left-hand limb is first reflected to explore a given field of observation, J. C. C. Stewart and C. S. if Wright. by the mirror D on to its conjugate the sweep were confined to the inner Application date, April 14th, 1943. focus P, and is then concentrated by cone alone. No. 584848. a back mirror 111 on to the first focus S. H. M. Dowsett, Application date From this point the energy diverges in September 24th, 1940. No. 576941. TRANSMISSION LINES the form of two hollow concentric cones, DISPLAY SYSTEM FOR TWO wires of equal diameter are one having a wider angle than the laid in close proximity but separ- other, is shown at N and O in RADAR ately from diagrams each other, to form a single - (b) and (c). The field strength IF the fluorescent screen of a cathode layer coil, which may have a magnetic is at a maximum along the interior ray tube is replaced by one coated or dielectric core angle of of constant or graded each cone, the relative ampli- with an alkaline halide, the trans- characteristics. The arrangement is tudes of the echo signals from a distant parency of the coating is momentarily such that when the currents in both wires are in phase -opposition 20 ñ their respectiv fields neutralize 9% X each other, so that the coil has practically no inductance, though .-15/5 Ä-4-4F--- 4 X when the currents are in phase its inductance is high. The coil can be used, for instance, to feed a push-pull amplifier from a coaxial line or other source that is unbalanced to earth, since any undesired in - i phase currents are automatically choked out, AA S and only a symmetrical r load is put on the line. The device can also be used as an arti- M ficial line for matching and other purposes, and can be given any desired / value of surge impedance by suitably selecting the nature or shape of the (a) core. Patelhold Patentverwertungs and Elehtro-Holding A.G. Convention date (Switzerland) October 8th, 1942. No. W 585995. ANTI -RADAR DEVICES IT is known that / the position of 1 aircraft in flight can to some extent be camou- flaged against the scrutiny of radar devices by releasing strips of metal foil Radar aerial with segre- or W metal - coated gated go and return paths. (b) paper from the varied by the scanning beam in such (C) craft. These reflect target, due to each a way that the screen will modulate the exploring pulses beam or cone, being the rays of light and so indicated at W and T. The receiving projected through it confuse the observer. from an external lamp on to an ex- Such strips are not very effective aerials (not shown) are located one ternal viewing screen, when behind and one in front of the trans- thereby permit- used against centimetre waves. ting the reproduction of images of a According to the invention, they mitting dipole, in the radiation -free size that is are axis of the outgoing signals. not limited by the dimen- replaced by " floats " made of several sions of the receiving tube. sheets of metallized paper, The arrangement is stated to be free This known arrangement which are from earth -reflection effects, and to is referred so hinged together that they can be to as a " skiatron," and, according to folded flat for storage, give a direct indication of the bearing the invention, but which open it used to obtain a large- out under spring pressure, when re- scale reproduction of the " picture " leased, to form a many -cornered (P.P.I.) that is given on the C.R. in- " balloon " The British abstracts published dicator with a slow rate of descent here are prepared with the of radar equipment of the type through the air. The corners act as permission of the Controller of in which an exploring beam is rotated efficient reflectors of short-wave energy, H.M. Stationery Office, from in synchronism with a radial time over a wide angle of incidence, specifications obtainable at the base. A scale and map or graticule of the so, provide false echo signals of con- Patent Office, 25, Southampton terrain under observation is also separ- siderable intensity. Buildings, London, W.C.2, price ately projected 1/- each. on to the viewing Marconá s Wireless Telegraph Co., scree', to facilitate the identification Ltd., and J. and correlation C. Barton. Application of the positional data date December 6th, 1944. No. 586904.

www.americanradiohistory.com JaKuary, 1948 Wirelesr World Advertisernen:s I

rF -41 =. . , I<

" Avo ' nstrun.nts available 'rom :cc ck: VALVE TE;raR TEST BRIDGE The "Ay," Vale Teste gives relic-de arc definite D.C. A' "PMI "IOR indicotior of the. state End effic ercy of some 2,000 English. American and Contir enlrl MOMS under actual working :Dnditioas. It it a_em)amed by a compreheTsive Va ve Da a Book ar.c s E tiplcal example of the higa stanc'ard of acru.aq associated with ali 'Avo" E.ectricd Testirg us:rurnerts. Fully descriptis , literatl.re ava table am apprccticn. Ze/r_,:q:e,n;y

THE ALTONATIC CO L WINDER & ELECTRICAL EQUIPMENT CO., LTD.

o l S E 1 1 C _ S S E E T N D V N D E R H D U O 7 A T R :O O N S 1 TELEPHONE. VIrrOR/A3,04I9 A

www.americanradiohistory.comwww.americanradiohistory.com 2 .ldverlienfcni., Wirciess World January, fytS des'q5 LET US BRING THEM TO ¿ /FE c

Made in Three Principal Materials FREQUELEX PERMALEX TEMPLEX An insulating material of Low A High Permittivity Material. A Condenser material of med- Di- electric Loss, for Coil For the construction of ium permittivity. For the Formers, Aerial Insulators, Condensers of the smallest construction of Condensers Valve Holders, etc. possible dimensions. having a constant capacity a: all temperatures.

the most difficult problems solved by .. . Hullers BULLERS LOW LOSS CERAMICS

BULLERS LTD., 6, LAURENCE POUNTNEY HILL, LONDON, E . C . 4 (Telephone: Mansion House 9971 13 lines) Telegrams: "Bullern, Cannon. London" WE are all familiar with shortages -material shortages -but there is one shortage that nothing on this earth can put right -and that is TIME. On every hand, one hears such remarks as " I haven't had the time." Radio amateurs are no exception -in fact, it is true to say that radio amateurs lack time more than most -to build or modify equipment -erect new aerials -actually work " on the air " -and the host of other complications which attend a radio amateur's life. In the " good old days," there was little option but to build one's own equipment. Today, we say good luck to the man who still prefers to build his own gear -there is nothing like some practical experience. Many " hams " will have learnt that, whilst " straight " sets are not difficult to make, even then many snags crop up and it is not easy to obtain a good performance over the wide range of high frequencies allotted to amateurs. Few will question the necessity of using a highly selective superheterodyne receiver in these days of congested bands. Those who have actually attempted to build one will know that a lot of time is taken up in the actual construction and usually even more in making adjustments. getting rid of the " bugs " and obtaining adequate performance on all the usual bands ! Some amateurs (usually those with a professional background) have the knowledge, and test equipment, to build an excellent receiver. To others we say buy an Eddystone " 640 " Receiver. Commercial interests aside, we can assure you in all sincerity that you will be well satisfied with its performance -many receivers are now in use and by every post we receive testimonials to the excellent results obtained. You will get excellent value for your money -the receiver is a solid engineering job, entirely British made, and costs E42 : 0 : 0, which, judged by modern standards, is anything but dear. Space does not permit the discussion of the finer points of the " 640 " and of their relative importance but we hope to do so in future advertisements. If you are not already familiar with the receiver, you are invited to get into touch with one of our agents, or with us direct. With a first -class communications receiver sitting on your operating table, your problems on the receiving side will be at an end, and you will have more of that infinitely precious if abstract commodity-TIME -to devote to your many other interests. !EDDYSTONE

www.americanradiohistory.comwww.americanradiohistory.com January, 194SS Wireless World Idrlir;,rcn1

jOFDERN MASTERS REPRODUCTION

HERE are speakers that go higher and speakers that go lower : other speakers 50% shallower and 40% lighter ; a pickup which can reproduce up to 20,000 c.p.s. ; another pickup giving moving -coil quality with

I volt output ; public address speakers for all occasions - designed and made by men with eighteen years' practical experience.

Write for full technical details -a postcard will do I1Uvox TRUVOX ENGINEERING CO. LTD., TRUVOX HOUSE, EXHIBITION GROUNDS, WEMBLEY, MIDDLESEX

www.americanradiohistory.comwww.americanradiohistory.com 4 Advertisements Wireless World January, ¡948 loto 310 Ines.

Light Weight 36 lbs. Negligible Stray Field. Frequency

Calibration I "." Modulation 30% sine wave 1,000-. and pulsed 50.50 square wave at 1,000. Attenuation Max. error at 300 mcs.±2dB Precision Slow- Motion Dial. Wide Range. 10 -310 mcs. Compact 121in. x 131in. x7fin.

Dual -Power Supply 200-250v., 40 -100 80-v., 40 -2000 "Advance" Signal Generator jroiriiuj type D.1. This " ADVANCE " Signal Generator is of entirely new design and embodies many novel constructional features. It is compact Judieuce in size, light in weight, and can be operated either from A.C. Power Supply or low -voltage high-frequency supplies. An RL18 valve is employed as a colpitts oscillator, which may MORE AND MORE people are enjoying be Plate modulated by a 1.000-cycle sine wave oscillator, or grid modulated by a 50'50 square wave. Both types of modulation are good radio entertainment through internal, and selected by a switch. The oscillator section is triple the shielded and external stray magnetic and electrostatic fields are negligible. Six coils are used to cover the range, and they are smooth power provided by Pertrix accu- mounted in a coil turret of special design. The output from the R.F. oscillator is fed to an inductive slide wire, where it is monitored by mulators. Every Pertrix product a an EA50 diode. The slide wire feeds a 75-ohm 5 -step decade gives attenuator of new design. The output voltage is taken from the end of a 75-ohm matched transmission line. consistently high performance -just a The instrument is totally enclosed in a grey enamelled steel ease with a detachable hinged lid for use during transport. little more than the promise. For trouble - Price £80 free listening choose the accumulator Delivery ex Stack. in the red and yellow pack. Most good Write for descriptive Leaflet. dealers stock them. ADVANCE COMPONENTS, LTD. BACK ROAD, SHERNHALL STREET, WALTHAMSTOW, LONDON, E.17. H O L S U N B A T T E R I E S LTD. Telephone Larkswood 4366 -7. 137 Victoria Street, London. S.W.:

www.americanradiohistory.comwww.americanradiohistory.com January, t948 Wireless World Advertisements 5 METALLISED CERAMICS There's a size for every job in the S.P. range of metallised bushes

Recent additions to the range : IO x 4 mms. 117 x 25 mms.

For full information and prices please write to : STEATITE & PORCELAIN PRODUCTS LTD. STOURPORT -ON-SEVERN, WORCS. Telephone: Stourport llll. Telegrams: Steatain, Stourport. S.P.44

www.americanradiohistory.comwww.americanradiohistory.com . tiverli.srul,nrs Wireless Wes rlel

The leading radiograms are fitted with Coodmans 12` loudspeakers.

Type No. T2/1205, 15

CO O H MA NS

ExcECLEN°. GOODMANS INDUSTRIES LTD LANCELOT ROAD. WEMBLEY, MIDDX

FOR THE RADIO SERVICEMAN DEALER AND OWNER The man who enrols for an I.C.S. Radio Course learns radiothoroughiy, completely, practically. When he earns his Diploma, he will KNOW radio. We are not content merely to teach the principles of radio, we want to show our students how to apply that training in practical, evary -day radio service work. We train them to be successful. Write to the I.C.S. Advisory Dept. stating your requirements. Our advice is tree. MODEL 44 You may use this coupon SUBSTANDARD METER INTERNATIONAL CORRESPONDENCE SCHOOL Ltd Widely used for standardizing first DEPT. 38, INTERNATIONAL BUILDINGS, KINOSWAY, LONDON, W.C 2 Please explain fully about your instruction in the subject marked X. grade single and multi -range meters. Complete Radio Engineering Radio Service Engineering Radio Service and Sales Elementary Radio 44 ranges. 6 in. mirror scale. Moving coil cut-out. And the following Radio Examinations: - British Institution of Radio Engineers P.M.G. Certificates for Wireless Operators City and Guilds Telecommunications Wireless Operators and Wireless Mechanics, R.A.F. I.C.S. students for Examination are coached till successful. Nome. Age ELECTRONIC INSTRUMENTS LTD Address 'Cs 17 Paradise Road, Richmond, Surrey

www.americanradiohistory.comwww.americanradiohistory.com f tlIRIrUI'. I1f 'írtI N11'urld lt(<,crlisculcnts 7 1`,n/tAICChl tt'DIPLItZ _ Jï _-rlifier designers

watts'. require- many ends on the capable ments óeiágstsualln) cam 30 broc castlreceiveF from outputut Power nominal amplifiers o wattsl anda power ents (assuming large to watts dependent somee 2 to 15 power. ut ' is of ram up tudio P ooutput avail- ' watts is of t° Kilowatt useful recd' choice watts up ed that only by remembered input from not deliveredY ustb e Ppower limited adequate D.C.' and current an voltage It from by the e oweY also to ablable P but rectifier. h as KÇ66 output or is advantageous unit, tetrad¢ Withit larger eo th e power and the desirable.to es and Is properly tdith voltage stabilisation a PrOPlode screen AC a constant f screen DC than some form such is better some circuit voltages tetrade of valve lowe l H? or tYPtypes pentode different designed from of output circuit. the ranges Grief data on below is giyen

CATHODE RAY TUBES VALVES

The General Electric Co., Ltd., Magnet House, Kingsway, W.C.2.

www.americanradiohistory.comwww.americanradiohistory.com I'', .-I it, 4'l'liclllr'Nlì irelews VI'urld /,iiru,r ll i

CO SISTENTLY

Pullin Miniature Instruments are charac- terised by their robust construction, good damping, excellent finish and pleasing appearance. The square types enhance the appearance of rectangular switchpanels. A complete series of square flush type instruments with styled covers is now available in 2 ", 4" and 3V' dial sizes.

Complete range includes Moving Coil ; Rectifier ; Thermo -couple, for all sizes ; and Moving Iron AC /DC types in the Series 35.

SERIES 20 2" DIALS NEW TYPES FOR MIDGET RECEIVERS THE SCIENTIFIC HEARING AIDS METEOROLOGICAL VALVE INSTRUMENTS BRITISH MADE ETC SERIES 25 IiIVAC Greenhill Crescent, Phone. HARROW DIALS LIMITED Harrow on the Hill.Middx. 0895

SERIES 35 31," DIALS

We can give early delivery -write for PULLIN details. MINIATURE INSTRUMENTS AMBASSADOR 4756 Chassis * * AN ENTIRELY NEW RECEIVER WITH * * * * * * QUALITY REPRODUCTION SPECIFICATION: This is a chassis which will appeal to w±ipa the Short -Wave enthusiast who also appreciates quality reproduction. A 5 valve A.C. superhet with six wave bands, all coil ranges, with electrical bandspread on principal S.W. INSTRUMENTS (PULLIN) LTD bands. Available with or without L.W. band. Address all enquiries to Dept. 1, Electrin Works, Immediate Delivery can be given. Winchester Street, Acton, London, W.3. Telephone: Acorn 4651 -4 WRITE FOR FULL IETAILS TO AMBASSADOR RADIO WORKS HUTCHINSON LANE, BRIGHOUSE, YORKS.

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements q

INDUCTANCES I. WEARITE I.F. Transformer Nos. 501/2. Size (Coding as for Denco interchangeable coils also 1 g in. sq. by 3j- in. high, 450 -470 Kc /s. No. 501 has shown in this advertisement). critical coupling with flying lead. No. 502 has close " Maxi Q " unwound formers with cores .. .. 2 3 coupling for diode input flying lead. Both types to o -no 9. EDDYSTONE No. tots U.H.F. Choke 120/25 2 & 20. EDDYSTONE No. 959 6 -pin interchangeable Mc /s. Inductance 5.6 microhenries .. .. i 9 coils. Three winding coils adaptable to most circuits. 10. EDDYSTONE 1010 S.W. Choke. 6o/1.5. Tuning range with 16o p.f. allowing for average circuit No. capacities :- Mc /s. Inductance 1.25 millihenries .. .. 2 6 II. EDDYSTONE No. 1022. Transmitting S.W. 6 BB 33.3 to 21.4 Mc /s 5 o 6 W 3.95 to 1.8 Mc /s 5 3 Choke. 60/1.5 Mc s. Inductance 1.5 millihenries 16 LB 25 to 11.5 Mc /s 5 o 6 P 2000 to 924 Kc /s 5 9 carries 25o milliamps ...... 3 o 6 Y 13.6 to 6.4 Mc /s 5 0 6 G 1153 to 590 Kc /s 5 9 16 R 7.3 to 3.2 Mc /s .. 5 3 6 BR 612 to 300 Kc/s 6 6 12. DENCO 2.6 millihenry general purpose S.W. 6 GY 300 to 150 Kc /s 6 6 Choke on polystyrene former ...... 2 3 3, 21 & 22. DENCO interchangeable coils on low -loss 13. WEARITE Coil pack series 600. Three ranges, ribbed polystrene formers tin. x t } in. dia. Superhet coil assembly. Range 1. 1 to 2 Mc 's (tuned too pf) In two types : 2. 2 to 4.5 Mc / s (tuned loo pf) Type No. 6o5B. 16 5o metres, zoo; 550 metres, 8o0 /2,000 3. 4 to 9 Mc s (tuned too pf) metres. 4. 7 to 19 Mc /s (tuned too pf) Type No. 6o5B. 13/35 metres, 34/120 metres, 200/550 5. t6 to 34 Mc /s (tuned too pf) metres. Both types, price each .. .. £2 2 o 6. 3o to 6o Mc /s (tuned 5o pf) 14. VARLEY No. BP26. " Nicore " H.F. Choke, 7. 5o to 90 Mc /s (tuned 5o pf) screened general purpose H.F. Choke .. .. 7 6 8. to 125 Mc /s (tuned 5o pf) 70 15. EDDYSTONE No. 645 I.F. Transformers. 45o/ -Full details on request. 465 Kc /s. Litz wound and permeability tuned, plated 4. BU LG I N " Skeleton " general purpose H.F. Choke. brass case gives efficient screening. Band -width for a MI-wave type ...... 6 6 pair of transformers is 5 Kc /s at zo dB down. Two gives band -width of 5 ì. EDDYSTONE No. 1o66 All -wave Choke. One stages (three transformers) dB 19 6 Iole fixing. Inductance 17.9 millihenries.. .. 4 o Kc /s at 3o down...... 16. DENCO Midget I.F. Transformers, available in B U LG I N Quench coil. Two winding unit for super for 465 Kc /s and 3 Mc /s each to o egeneration ...... 5 6 frequencies .. 17. WEARITE I.F. Transformers, available in '. & 8. DENCO "Maxi -Q" Plug -in coils (Octal based). Midget ro 6 n eight ranges covering from 85o Kc /s to 130 Mc /s. frequencies 465 Kc /s, 1.6, 2.1 and 4.8 Mc /s each.. Each range available in four types for all purposes. 18. LABGEAR I.F. Midget Transformers, 465 Kc /s Blue," 4/- ; " Yellow," 4/ -; " Red," 4/ -; " Green," 5/o. each 9 6

14, SOHO STREET, OXFORD STREET, LONDON, W.I

Telephone : GERrard 2089. Shop hours : 9 a.m. -5.15 p.m. Sots. 9 a.m. -1 p.m. s

www.americanradiohistory.comwww.americanradiohistory.com io Advertisements Wireless World January, 1948 YOUR CHOICE for QUALITY Manutacturers of high quality Broad- cast Receivers and Radiograms designed for Home and the Export Market. The Expert Models have fully tropicalised components, achieving unsurpassed short -wave performance. CHAIRSIDE MODEL A450 The housing of this Receiver is unique in that it is contained in a bevelled plate -glass mirror cabinet, fitted to a wrought iron frame- Special dials supplied for any country work finished in Cream enamel. It embodies all the latest technical developments for easy handling, range and clarity of reception, and PRICES AND FULL PARTICULARS ON REQUEST provides not only a first -class radio but an attractive piece of furni- ture which can replace a Chairside Table and will harmonise with any surroundings.

SYMPHONY MODEL A420 This new Receiver embodies the very latest technique in construction. The cabinet is richly veneered in Walnut with a cross banding of Macassar Ebony. Clearly readable edge -lit dial with an 8 in. traverse magic eye and 2 -gear control. Instant unerring selection of the required frequency range. Automatic volume control and an I.F. trap are incorporated in the circuit. Sockets are provided for gramophone pick -up and extension speaker.

ALLANDER INDUSTRIES LTD. 48, Avenue St. Bridgeton, Glasgow, Scotland.

You

e get years of RESISTANCE TUNED OSCILLATOR. Model LO 63 -B. THIS is a precision audio oscillator faultless having a harmonic content of less than 1% and a frequency stability of better than .25 %. The circuit employs an entirely service because they are :- INDIVIDUALLY DESIGNED new principle. The frequency calibration RIGOROUSLY TESTED is direct reading over the entire range. A .. . MECHANICALLY SOUND calibrated attenuator and output meter frorst ELECTRICALLY PERFECT are incorporated. Standard range 30 cycles to 33,000 cycles. Other models available from 1 cycle to 100,000 cycles.

For particulars of this and our full range of measuring instruments, write to :- BRITISH PHYSICAL LABORATORIES SI, NORTHGATE STREET, DEVIZES. Phone 536 Houseboat Works, : 12113A Radlett, Herts. 'Phone Radlett 5674-5 -6

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements ix

Both are T.C.C. Capacitors. The little fellow has been widely known and used for very many years -but the big boy makes you

think ! It is just one of the many T.C.C. special transmitting types, which are used almost exclusively in all the big radio broadcast transmitters. This particular example is a o.003µf oil -filled, mica dielectric job, it handles 20 amperes of carrier frequency, plus to Kv Audio " Mod " and 16 Kv D.C. Despite the disparity of size and function, there is one important factor common to these, and indeed, to all T.C.C. Capacitors. It is the engineering skill in design and manufacture which established and has maintained T.C.C. leadership in every branch of the capacitor field. Whether your capacitor problems are " little fellows " or " big boys," submission to T.C.C. technicians will always provide the solution.

NORTH ACTON LONDO. V1/3 TELEPHONE.' ACORN O O 61

www.americanradiohistory.comwww.americanradiohistory.com 12 Advertisements Wireless World January, 1948

\ This Vibratorpack developed by Specialists will enable users of battery SMALLER sets to operate from a 6 -volt car than a H.T. Battery. accumulator, thus eliminating ex- Size : 7 5f >: 3 pensive H.T. battery replacements. * A.F. ATTENUATOR, TYPE I358 Careful design has eliminated all Frequency Range, zero to 20Kc,'s. Input Impedance, Interference. Consumption is less than 600 ohms. Attenuation, 0 -110 dB in steps of I dB, 3 amp. ± I% nominal voltage ratio. Internal Termination of 600 ohms at option. Dissipation t watts. JJiìs Ie,iu/io V I B R A T O R P A C K MASTERADIO LTD., Sales Dept., 319 /321, Euston Road, London, N.W.I

* DIODE VOLTMETER, TYPE 281 0.1 -I50 volts, 50 c /s. to 250 Mc, s. ± 2% of F.S.D. Stable zero setting. Alternative model having additional d.c. voltage ranges available.

5,000 S, W STATIONS In a letter recently received by us from Mr. H. R. Ldge, of Worthing. Susses, he says: With further reference to the S W list of Stations heard on my ONE Valve Receiver * HIGH DISSIPATION the famous S. G. Brown using your TYPE A' Headphones, I have Type "A " Headphones pleasure in reporting that I have now tinted RESISTANCE BOX, TYPE I752 give highest possible effi- 5,000 S W Stations mostly 40 and 20 metres with a few on 10 metres, with 130 Territories ; is 0-1 meg. in 5 decades. 6 watts per resistor, 60 watts ciency this attained by represented. the Adjustable Reed Move- "Among the O Stations recorded were four per decade, except last decade which is 20 watts. ment which replaces the working on low power. Henley -on- Thames flat ONE watt. Falmouth 3 watts, Lines 5 watts. Accuracy 5 Voltage 1,000 usual diaphragm. + %. limit volts. S. Wales R watts. Price and 60 - per pair "Am now out for ten thousand I but each PRICES FROM YOUR LOCAL DEALER additional thousand now Is hard work; hut, ON APPLICATION careful listening with these sensitive headphones should eventually secure the target. Yours saner ly.

rrleficll LA'iORATORIES LTD. Phone ACOrn 5021 bs eOREMAM WOOD HfRTS g .S4,67X-TOWL,15 TEllPNONE ltSTa[F 11I7 < VICTORIA RD., NORTH ACTON, LONDON, W.3

www.americanradiohistory.comwww.americanradiohistory.com lazuary. 194.8 Wireless, World .4dverti.:ements 13

THE EDISON SWAN ELEC-R1C CO. LTD., 155 CHARING CF.05S ROAD, LONDON, W.0 2

www.americanradiohistory.comwww.americanradiohistory.com 14 Advertisements Wireless World January, 1948 f h THE COMPLETE SERVICE FOR SOUND RECORDING AND REPRODUCTION

* Mobile, static and specialised r...ording units. * Complete Wire Recorders, Recording and Wipe - off Units. * Recording Amplifiers. * Moving Coil and Crystal Microphones. * Sapphire cutting and reproducing stylii. * Blank recording discs from Sin. to 17ín., Single or Double sided. * Lightweight, moving iron, permanent sapphire and moving coil pick -ups. * A comprehensive range of accessories to meet every requirement cf the sound recording engineer. Portable Dual Channel ** And our latest development (of special interest to Recording and Replay Outfit. users of sapphire and delicate pickups) -THE SIMTROL. This is a controlled micro-movement easily fitted for use with any type of pick -up.

OUR WELL- EQUIPPED WORKSHOPS ARE AVAILABLE FOR THE DEVELOPMENT OF EQUIPMENT TO MEET SPECIAL NEEDS.

SIMON SOUND SERVICE, Recorder House, 48/50, George St., Portman Square, London, W.1.

CABLES : Simsale, London. TELEGRAMS : Simsale, Wesd,, London, TELEPHONE Welbeck 2371/2. Wharfedale LOUDSPEAKER ACCESSORIES

TRUQUAL Volume Control

10 Watts 9/6 20 Watts II/6 With Escutcheon L.S. SEPARATOR Also CHOKE Crossover 1000 c.o.s.. 3 27/5 3 -15 ohms 30 watts, for use with cleaner reproduction, SEPARATOR. improved "top . I. Set speaker only. SPEAKER 2. Extension speaker only. SWITCH 3. Both speakers. With escutcheon and 9/6 back plate for fixing. Maie and Guaranteed by WHARFEDALE WIRELESS WORKS BRADFORD ROAD, IDLE, BRADFORD relephon,e:- WOOLWICH 1422 Telephone: IDLE 461. Telegrams: Wharfdel, Idle. Bradford CAMBRIDGE ROW WCOLWICH SE I8

www.americanradiohistory.comwww.americanradiohistory.com January, r948 Wireless World Advertisements 15

DUBI LIE CONDENSEN CO . (1925) LTD. WHERE HIGH STABILITY IS ESSENTIAL For operation in certain special conditions, a high degree of stability is the chief characteristic required of fixed resistors. For example, in television, electronic and instrument applications where maintenance of maximum stability is desired over long periods of continuous use high stability in resistors must be the primary qualification. The particular process of manufacture to which Dubilier High Stability Resistors are subjected ensures this great stability of resistance value, coupled with a low temperature coefficient of resistance, a negligible voltage-coefficient and a low " noise level ". In all conditions where high stability is vital, a selection from this specially designed range of Dubilier High Stability Resistors type R should be made. Full technical details and prices will be sent upon receipt of your enquiry.

DUBILIER CONDENSER CO. (1925) LTD., DUCON WORKS, VICTORIA ROAD, NORTH ACTON, W.3 'Phone : Acorn 2241. 'Grams : l-licoltcon, Phone, London. Cables : Hivoltcon, London. Marconi International Code. DII

www.americanradiohistory.comwww.americanradiohistory.com 16 Advertisements Wireless ürorld January, 1998 M. R. SUPPLIES Ltd. offer from stock the following first- class, brand new Laboratory and Electrical Material. Our discriminate buying is your safeguard. All prices nett. GERMANIUM CRYSTAL RECTIFIERS (G.E.C.). We are pleased to be able to offer I bese new remarkable rectifiers from stock. Only 13 mm. long, wire-ended. Frequency range : 50 c/s to 45 Mc /s. Capacitance, 0.3 mid. Many uses, including discriminator and limiting circuits, In F/M receivers, as second detectors, meter rectifiers for A.F. and R.F. Numerous other applications where diodes are normally used -valve voltmeters, etc. 27/6 each. THERMO-COUPLES (ex- Govt.) by Cambridge Instrument. 5 ma. and 10 m.a. only. New, boxed, either 7/6. INSTRUMENT RECTIFIERS (full wave) 1 m.a. and 5 ma., either 5 / -. THERMOSTATIC SWITCHES (es-Air Ministry, new), Switch capacity, L5 amp. Switch on at 32° F. and off at 59° R, and therefore right for many applications in frost protection. Operating temperature can be considerably adjusted. 4/6 each, 45/- dozen. RESISTANCE BOXES. (Decade type) by best precision makers. Units 0/10, tens 0 /100, with additional 100 ohms (can be altered to multiplier). Fitted Turner mica' Galvo. Switching for Wheatstone Bridge and other testa. In portable case, 16 x 71 x tin., 65 /- (des. 2/ -). VARIAC TRANSFORMERS. Input, 200 /240 v. 50 e. ; output, 220 v. 50 e. (infinitely variable In these limits). Loading, 1.85 kva. ; weight, 22 lbs. Oil filled. Essential for correcting mains fluctuations. £7 10s. (des. p. train, 3/6). E.H.T. VOLTMETERS, m /coil, by best makers. 0/3,500 volts, 311n. dia. Projection 41n. With internal series resistance, 47/6. STAGE DIMMERS, best fully enclosed pattern with worm drive and handwheel, fitted carbon -break flicker switch and "off" position. Rated to control stated load from full- bright to blackout at 220/240 v. 500 watts, £3 18s. 86. ; l000 watts, £7 2e. 6d. ; 1200 watts, £8 12s. 66. ; 2500 watts, £9 15s. (carr. 5/- any one). MOVING COIL MICROPHONES (It esto). Special offer of senior model with cushion mount. Black oast housing with plated motif. Really fine response -folly recommended, £4 10s. MICROPHONE FLOOR STANDS to suit, all chrom. Collapsible model. 52/6; heavy 3 -claw foot model, 65/ -. Also Table Stands, 2 -draw, all chrom., 29/6. LARGE ALARM BELLS, operation 50/100/240 v. A.C. Fitted twin gongs each tin. din. Overall: height, 12ín.; width, 121in. P.O. type. completely weatherproof, loud note, 29/6. ELECTRO-MAGNETIC COUNTERS. Counting up to 9999, operating from 12/24 v. L.C. (or mains voltage A.C.). We offer only brand new ones with cover and window at 7/6 each. CENTRIFUGAL BLOWERS. Fine new offer of G.E.C. machines, operating from 6/12 v. D.C. or 12/15 v. A.C. Intake, 211n.; outlet, lain.; height overall, glen. Very powerful suction and blast, 57/6 (des. '2/ -). H.T. RECTIFIERS (S.T.C.- Selenium). D.C. delivery up to 350 v. 120 m.a. in half - wave or voltage doubler (two can be bridged for 300 ma.). Very special offer, 7/6 each. SMALL UNIVERSAL L.V. MOTOR/1,12/24 v. A.C. /D.C. Length, lin. ; width, 21ín. ; }in. shaft. Ball bearing. Many uses in lab. and home, 17/6. "FUZIT" WIRE JOINTERS. Exceptional offer of this useful S.T.C. product. Electrically welds all wires (res, or copper) from 50 to 30 s.w.g. Operation, 200/250 v. A.C. With portable transformer (Sec. 45 v. 4 amps. tout.). Hand-tool, etc., ready for use, 65/- (des. 2/ -). (Please include sufficient for packing and despatch.) If your radio Ai M. R. SUPPLIES Ltd., 68, New Oxford Street, London, W.C.1 Telephone: MUSeum 2958 his been letting \mn\\\111lmmtlyiI// iM you down p ONE a-1 P%ouR `HAVE -A-GO' ßACAO

1P'AAí/////,/l r zr ii II I I I Now that Stentorian Exten- with sion Speakers are coming back to the shops the pleasure of listening again becomes complete. Just plug in one of these superb permanent magnet speakers to your set and you can enjoy its clear, pure tone anywhere in the house, sitting -room, kitchen bed- PRICES room, wherever you happen SENIOR MODEL to be. Ask your local dealer Type SC with Universal about them. Transformer £5 15 6 Type BX minus Universal U } A T u R s PRICES: BABY MODEL Transformer .. £5 2 6 Type BC with Univer- JUNIOR MODEL sal Transformer £2 19 0 Type JO with Universal AND Type BC minus Uni- Transformer £5 0 0 versal Transformer £2 13 6 Type JE mines Universal MINOR MODEL Transformer .. ... £4 10 6 Type MC with Univer- CADET MODEL 'type CC with Universal sal Transformer . £2 5 6 l'ype MX minus Uni- Transformer . £4 10 0 versal Transformer £1 19 6 Type CIC minus Universal Transformer .. .. £4 0 0

BAT TEA rfS CII)Stentorian ISSUED BY THE PERFECT EXTRA SPEAKER FOR ANY SET THE CHLORIDE ELECTRICAL STORAGE COMPANY LTD. WHITELEY ELECTRICAL RADIO CO. LTD., MANSFIELD, NOTTS. aDE84

www.americanradiohistory.comwww.americanradiohistory.com January. r948 Wireless World Advertisements 17 401k. CINTE A ENTIRELY NEW ELECTRONIC INSTRUMENTS CINEMA -TELEVISION LIMITED INDUSTRIAL STANDARD ELECTRONIC ELECTRONIC METAL DETECTOR COUNTER

An automatic inspection equipment A high speed electronic counter of for the detection of ferrous and particular appeal to the indus- non -ferrous metal particles of all trialist. Facilities are provided kinds in non - metallic substances for batching, selective counting such as foodstuffs, plastics, textiles, etc., the maximum counting -speed tobacco, timber, pharmaceutical for the equipment being 30,000 products, etc. per minute.

UNIVERSAL LABORATORY OSCILLOSCOPE A unique instrument meeting fully OSCILLOSCOPE the requirements of the serious users ...a... A high grade 6' screen oscilloscope of oscilloscopes for laboratory and industrial purposes, arranged to expressly designed for laboratory permit readily the assembly of use, incorporating hard valve linear suitable units to fulfil every applica- time base, 3 megacycle "Y" ampli- tion. Complete range of units is fier and I megacycle "X" amplifier. available, e.g. stabilised time base. + `t Cupboard and trolley are available A.C. and D.C. amplifiers, 5 beam 4 switch unit etc. if required.

1)EMONSTRATION OSCILLOSCOPE PROCESS TIMER , Demonstrator and student alike will A compact instrument, acclaim the features of (tom the "CINTEL" this equipment - 15" tube with glare re- range, providing simple moving filter, 2 beam switch for simultane- and accurate electrical ous delineation of two control for scientific and recurrent wave forms, or their "addition" to industrial processes cf produce a single re- every kind. The timing sultant trace. Provi- sion is made for setting range extends from 0.25 up from rear of in- to 90 seconds strument, inspection windows permitting rear view of trace. CINEMA -TELEVISION LTD, INCORPORATING BAIRD TELEVISION LIMITED WORSLEY BRIDGE RD., LONDON, S.E.26 Telephone : HiTher Green 4.600 Suppliers to ADMIRALTY, MINISTRY OF AIRCRAFT PRODUCTION, MINISTRY OF SUPPLY, ARMAMENT RESEARCH, etc. Manufacturers of Scientific Instruments and Photo -electric cells.

www.americanradiohistory.comwww.americanradiohistory.com i8 Advertisements Wireless World January, 1948 REA

REPRODUCERS

We have pleasure in announcing an entirely new range of R. & A. reproducers, the " 700 " series. The outcome of three years' design, development and testing under the most exacting conditions and the installation of special purpose machine tools and jigs, the " 700 " series represents an outstanding advance in the design of sound reproducers. Further particulars of this series will appear in future announce- ments, and our Technical Staff will be pleased to supply any other information you may require.

Reproducers & Amplifiers Ltd., Frederick Street, Wolverhampton

A New Line in- TRANSMITTING CONDENSERS RAYMART has pleasure in introducing the following NEUTRALISING AND TUNING CONDENSERS, the former having ceramic insulation and aluminium vanes, and the latter polystrene insulation and aluminium vanes. All remaining metal parts are brass,. either nickel plated or " natural," machined from the bar, ensuring the greatest accuracy. Bearing and housing are the same as used on our well -known VC and MC range. Type No. of Vanes NCS ... 2fixed and I moving NCIO 3 fixed and 2 moving NCI3 4 fixed and 3 moving TCSBO 4 fixed and S moving (I section only)

Note. -The NCS, NCIO and NCI3 make ideal tuning condensers for P.A. stages in UHF Transmitters as they can be ganged to make split stator n V types. Flash over voltage : TCS, 2,000 volts ; NC, 5,000 volts. NCI3 Max. Min. Air 19 Type No. 22 Type No. Type Cap Pf. Cap Pf. Gap PRICE NCS ... 5.5 2.9 .190" 5/- NCIO... 9.4 3.8 .190" 6 13 NCI3 ... 13.3 5.0 .190" 7/6 TCS80 79.5 7.8 .070" 25/-

Supplies limited owing to shortage of raw materials. RAYMART I,Y S.BIRD J SY Dgl X. 48 HOLLOWAY HEAD, BIRMINGHAM, I ARTERIAL Á Enfield. Telephone: Midland 3254. CAMBRIDGE -2 'Grams: Capacity, 'Phone: Enfield 207f

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 19

PEEP AT THE BUSY END OF YOUR RADIO .

Many people are still not convinced that a Radio owes much of its performance to the Transformer inside In a world whose tempo is governed it. Slowly we are our proving to by the radio wave, it is necessary to friends, the Radio Manufacturers, that a Parmeko Transformer makes a very think quickly and to think ahead. real and lasting contribution and like Marconi engineers have an advantage most people - who rely on our extensive Research and Design Departments - they in this the advantage of a technical are wisely beginning to forget that - silly old word 'Transformer' and think background that takes in the whole 'Parmekot instead and to use properly history of wireless communications. the many services it is our specialist job to give. In the reconstitution of old services and the development of new ones, that Do think over the fact that we make only Transformers - not Radios, experience will be vital. On land, on Refrigerators, etc., plus Transformers. in the future as Surely it follows that with sea and in the air, specialization we produce a better in the past, communications will be Transformer cheaper. linked with Marconi - the greatest name PARMEKO OF LEICESTER. in wireless. MAKRS OF TRANSFORMERS. Marconi the greatest name in wireless

MARCONI'S WIRELESS TELEGRAPH COMPANY LTD

THE MARCONI INTERNATIONAL MARINE COMMUNICATION COMPANY LTD e MARCONI HOUSE, CHELMSFORD, ESSEX

www.americanradiohistory.comwww.americanradiohistory.com 20 Advertisemenis Wireless World January, 1948

aid to better

Ceramic Lead-through Capacitors are small in dimensions and can be directly connected to the chassis, thereby keeping series induct-

ance and resistance to an absolute minimum. Full technical data furnishec on request.

CERAMIC -... a 1 4' 0h CAPACITORS

\x4s, v 44

UNITED I NSIL LATOR CO. LTD., OAKCR OFT RD., TOLWORTH, SURBITON, SURREY.1

Telephone : Elmbridge 5241 (6 Imes) Telegrams Colonel, Surbitor.

vt_AA.)14-3- cl.7o ck I v\._ C c.

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 23

THE 6B5 comprises two triode units in cascade, whilst type 42 is a pentode. Both valves have 6 pin bases so connected that replacement is possible without change of wiring. Type 6BJ develops its bias internally and it will be necessary to include a bias resistor and condenser in the cathode lead of the 42 valve. w Reprints of the earlier sheets in this series are available for those who aY have not a complete set, so let us know which numbers you still require. w _ RATED CHARACTERISTICS G2 GI 6B5 42 6B5 w Heater Voltage 6.3 6.3 volts J Heater Current 0.8 0.7 amp. o A Anode Voltage 300 285 volts _ Anode Current 43 38 mA. Bias Resistor - 400 ohms _ H H Optimum Load 7000 7000 ohms Power Output 5.0 4.2 watts u TYPE 685 TYPE 42 z CHANGE SOCKET CHANGE CONNECTIONS a OTHER WORK PERFORMANCE TYPE NECESSARY CHANGE FROM FROM OLD TO NEW TO SOCKET SOCKET

Insert Bias Resistor (400 ohms I watt) and by -pass con - 42 U.X. 6 -PIN NO CHANGE NO CHANGE denser (25 F.. 25 NEGLIGIBLE Volts) in series with the cathode lead to pin 5 of socket

A scheme repair IZING . k ee ßRIMb BRIMAR to especially y This is devised everyone flolMAfi the on lines hristmas and not useful VALVES his Set at home RADIO wantsshelf waiting for spares. e

STANDARD TELEPHONES AND CABLES LIMITED, FOOTSCRAY,SIDCUP, KENT. 10 A SERVICE PLAN FOR PLANNED SERVICE

www.americanradiohistory.comwww.americanradiohistory.com 24 Advertisements Wireless World JnnrQ rrt', tq4S MeThree Instruments-in-One PORTABLE RECEIVER TESTER (TF.888) dAUe,i>e/ s,,,e.s. y sa/kes.,ae

Here is one of the new "Measurtest" Instruments, versatile, compact and portable. Designed to obviate the laborious use of groups or pairs of bench -type instruments, the Portable Receiver Tester successfully combines a signal generator, output power meter and crystal calibrator. In the servicing or manufacture of radio receivers, therefore, it is a pocket laboratory in itself - all for the price of one orthodox instrument. For complete operational convenience, the Portable Receiver Tester is fitted alternatively with either mains unit or dry battery. It is fully guaranteed and available to you for demonstration at any convenient time. Further particulars freely available.

MARCONI INSTRUMENTS LTD.

ST. ALBANS, HERTS. Telephone: St. Albans 6161/5 Northern Office: 30 ALBION STREET, HULL.. Hull 16144 8615 Western Office: 10 PORTVIEW ROAD, AVONMOUTH. Avonmouth 438 Southern Office: 109 EATON SQUARE, S.W.I. Sloane H. T. RECTIFIERS for broadcast receivers A range of rectifiers is now available which will meet manufacturers' general requirements for broadcast radio receivers. These units are very much smaller in bulk and weight, have a high efficiency and good regulation.

I, dimensions Output Max. input Overall Type Volts Volts j mA Length Width Height

14A118 600 120 275 41¿ 21 21 14A79 400 120 210 31 21 21 14A79 400 75 210 31 21 21 14A59 300 75 170 21;?,. 21 21 4A79* 245 120 250 31 21 21 14A46* 270 60 250 2q 21 21 15846* 270 30 250 116 1; 11 5D281' 120 20 108 1 25/32

* For AC /DC receivers. t For battery eliminators. Write for full details to Dept. W.W., WESTINGHOUSE BRAKE & SIGNAL CO. LTD., 82 York Way, King's Cross, London, N. WE: s;rrNG OUSE METAL EMIL TE RECTIFIERS

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 25 THE BELLING-LEE PAGE Providing technical information, service and advice in relation to our products and the suppression of electrical interference (z) The elimination of interference is dealt with in two ways. (a) By the production and en- - couragement in the use of better radio connections typified by terminals, plugs and sockets, and valveholders of many kinds. (b) We claim to be the first firm to specialise in the suppression of electrical interference. This

is dealt . with both at the listener's end and at the source. All the work we have done on the This type of suppressor is usually recom- subject, supported by the findings mended by the Post Office, for fitting at of the Post Office, the B.B.C. and the meter board or across the brushes of The illustration shows the " WINROD ' the Electrical Association, interference- creating motors and genera- aerial L.581. Price 19/6. It is neat, inex- Research tors, etc. List No. L.1118 /CT. Price 27/6. pensive and easy to fix. An outdoor aerial emphasises that suppression must type will always improve signal to liners, Belling -Lee do the work. of this be a co- operative effort. A reasonable noise ratio in relation to indoor types. They are also honoured to serve the (Note to dealers at foot of page.) aerial at the listener's end, and a fishing fleets of home waters and We have re- established our " short reasonable amount of care taken in those operating in distant deep sea run " to enable us to the design of the appliance, or the department fisheries. undertake " special " work for cus- suppression of the interference it A soldering tip tomers, including Universities and creates. The use of polythene insulant Government Research Establish- When we started this work we were in plugs and sockets with particular ments from whom suggestions are alone. Many firms have since reference to our coaxial range, welcome for the modification of joined in the fight against inter- raises one or two points. Firstly, Belling -Lee components, and the ference by offering vertical aerials, official technical opinion is against consideration of development con- matching transformers, window any attempt being made to solder tracts within our sphere of activities. aerials, etc. The more firms manu- to the screen of cable with polythene We appreciate that many research facturing and advertising such insulant. More harm than good is establishments are three to five years appliances the better for the cause. likely to follow. ahead of commercial practice and Provided always that the products Parts to which you are likely to only by the closest co- operation are technically worthy. It is possible solder are silver -plated to ensure with them in the earliest stages can to introduce losses in an aerial easy and quick " wetting." See we hope to reap the full benefit. system that may give rise to much that the iron is at the correct The policy behind the activities disappointment. temperature. If it is running cool of this Company can be summarised Suppression at the source is a through electrical " load -shedding " as (s) Safety, (2) The elimination of tricky subject. There are few and allowed to lie for a considerable interference with radio. secrets in the design of suppressors. time on the part to be heated, (s) Safety is provided by the It may truthfully be said that any heat will travel to the polythene, adequate fusing of electronic circuits fool can make suppressors, but it with the result of a distorted plug calling for fuses of considerable takes craftsmen with experience or socket. accuracy. It is possible for a radio to use them efficiently. Much the raceiver or any other appliance to same may be said of aerials. Perhaps *WINROD AERIALS cause fire before the blowing of a' that is why we get so many of CAN NOW BE SUPPLIED normal 5 amp. house fuse. In the difficult cases, e.g. those on the sphères other than radio and elec- outer fringe of the range of Alexan- EX STOCK tronics, we assist protection by a dra Palace, etc. Probably it also FROM YOUR WHOLESALER upon comprehensive range of thermal accounts for our being called (See illustration above) switches which many manufacturers to suppress interference on the Royal fit to motors used in refrigerators, Train on the occasion of Their etc. These obviate burnt out motors Majesties' visit to South Africa. BELLING &LEE LT by cutting off current if excessive heat When great shipping companies CAMBRIDGE ARTERIAL ROAD. ENFIELD. MIDD is generated by a fault. require suppression on the largest

www.americanradiohistory.comwww.americanradiohistory.com 26 Advertisements Wireless World January, 1948

HERE IS THE WAY TO BETTER SOUND DISTRIBUTION The Multicellular type of horn his been developed to facilitate quality sound reproduction in auditoria by providing satisfactory distribution of the higher audio frequencies essential for intelligibility. Vitavox Multicell horns are available in two types having lower cut -off frequencies of 220 and 95o c.p.s. respectively and in a wide range of cell combinations to suit particular combinations.

MULTICELL HORNS

Obtainable from your VITAVOX Dealer but do not hesitate to Consult us in cote of difficulty or if you require further details.

Vitavox Limited, Westmoreland Road, London, N.W.9 Telephone : Col indale 8671- 3

=_ = N s GG 9tr 9 ß FlEC1RO O . ot P55° ONN 'P f The Correspondence and College Courses provided by E.M.I. Institutes which cover recognised 1c= es o ty atVenero diplomas such as the City and Guilds, etc. are OV6ttoes t written and supervised by E.M.I. * scientists who are Gp 4e specialists in Electronic Science. 1 vo" e `tele,vetty Courses are in ..000.1,1Cetv, Zeo already available such subjects as tbe Basic Radio, Basic Television, etc. and the prospectus obLva_ tvto 4Ntaetl two. is being constantly extended. vg,ttg With E.M.I. basic training you can eventually become a 1 01/`() 9?0 4' specialist in Television, Radio Communication, Radar, 4,00-. Navigational Aids, Audio Frequency, Medical and various ee For full details apply to: The Electronic applications. Principal: ProfessorH.F.Trewman M.A. (Can tab ), M.I.Mech.E., M.Brit.I.R.E. E..I. I%flhIIJItI lED Dept. 16, 43, Grove Park Road, Chiswick, London, W. 4 * The E.M.I. Group includes " H.M. V." Marconiphone and other important electronic interests. F..19

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 lVircless World Advertisements 27

1998 ACKNOWLEDGED THROUGHOUT eget-4-4 THE WORLD

RESISTORS CERAMICONS Hi -K CERAMICONS POTENTIOMETERS SUPPRESSORS VITREOUS ENAMELLED WIRE -WOUND RESISTORS Erie Resistor Ltd., The Hyde, London, N.W.9, England O N Telephone : COLindale 8011 -4. Cables : RESI STO R, L DON. Factories : London & Qt. Yarmouth, England Toronto, Canada Erie, Pa., U.S.A.

www.americanradiohistory.comwww.americanradiohistory.com 28 Advertisements Wireless World January, 1948

t`ta t` HIGH "Q" CIRCUITS In response to the growing demand for HIGH QUALITY CIRCUITS o 1;U our Technical staff have designed A SPECIAL RANGE OF CIRCUITS to meet the need of all DISCERNING AMATEURS. Suitable for all types of sound measurement rang- * All -dry Short wave receivers. ing from the volume of * Mains A.C. or AC DC TRF and noise of a whisper to that of a factory hooter. Simple Superhet receivers. to operate ; completely * Transmitters. self -contained ; rugged and portable. * Communication receivers. WIDE RANGE -34 to 130 decibels. * Amplifiers and Mains packs. NON -DIRECTIONAL SOUND -CELL TYPE Whatever your requirements, MICROPHONE - removable for special applications. please let us know. SLOW -FAST METER. INTERNAL CALIBRA- free. TION SYSTEM. Illustrated catalogue 6d. post THREE WEIGHTING NET- WORKS ONLY BRAND NEW COMPONENTS IN STOCK. COMPLETE P BSENCE OF INDUCTANCES in construction enables accurate readings in presence of

magnetic fields. BERRY' (SHORT WAVE) LTD. DAWE INSTRUMENTS LTD HARLEQUIN AVE., GT. WEST ROAD, BRENTFORD, MIDDX. Phone: EALING 1850 25, HIGH HOLBORN, LONDON, W.C.1 (Opp. Chancery Lane). Tel.: HOLborn 6231. am

Realism in Resistors produced Sound Recording by the cracked car- l bon process remain stable to ± I% of initial value. *Tolerance ± t% f2%i5% L o w temperature co-efficient.

%%4eIwyia mmOoom resistor WELWYN ELECTRICAL LABORATORIES LTD. Welwyn Garden City. Herts Telephone Welwyn Garden 18168

To the exclusive range of sound equipment produced by B.S.R. is now added the D.R. 33 Direct QUALITY ! ! ! Disc Recorder. The D.R. 33 incorporates the latest developments Come and hear the LOWTHER -VOIGT radiograms, in recording technique and is the finest direct recording instrument available. It is supplied in an electrograms and loudspeakers or let us demonstrate attractive carrying case and is completely portable. them to you in your own home. No charge for this, of We sho:ild be pleased to send you further par- course, but we don't think you'll be able to do without ticulars of this latest production of the B.S.R. Research Laboratory. one of your own. We are always glad to see you, or if Amplifiers, microphones, loudspeakers and acces- you can't call, drop us a postcard. We needn't say, of sories. course, that all this equipment is designed to give best DIRECT DISC RECORDER possible reproduction from radio and records, and the reproduction is UNSURPASSED ! ! ! ELMSLEIGH RADIO CO., BIRMINGHAM SOUND REPRODUCERS LTD. 1102 London Road, LEIGH -ON -SEA, Essex. Claremont Works, Old Hill, Staffs. Phone Cradley Heath 6212/3. London Office: 115, Gower Street, W.C. 1. Phone Euston 7515. Phone 75168.

www.americanradiohistory.comwww.americanradiohistory.com Advertisements 29 January, 1948 Wireless World

REPRODUCTION PERFECT EVERYTHING THAT OPENS AND SHUTS . .

the ideal communications receiver - the receiver which fits into any given set of conditions - is a rare bird. Some have this facility, some that, but it has remained for Rediffusion to provide them all in the latest addition to their range of radio equipment, the Redifon " R -50 ". Consider these features and weigh them up for yourself . . . .

B R I E F S P E C I F I C A T I O N Frequency Range - sj.; feels - 26 kris; 93 ko /s - jz Mel s; in eight bands. 2 stages. Selectivity - - - - Five positions - j I.F. and Crystal Sensitivity - - - - Constant between r -z micro -volts over the entire range. Image Protection - Ranges from go db. at highest frequency to over roo db. Tuning So: r slow motion drive, coarse and fine tuning together with logging teak for accurate resetting, Maintenance it greatly simplified by virtue of the fact that R.F., (.F., and A.F. sections are in separate, demountable units. ...With complete 1/ediloi, "R-50" dependability R E C E I V E R

For all installations,

inc!uding P U B L I C ADDRESS, either indoors or out CAIIONEIIS OUTPUT TRANSFORMERS COUPON Please send the leaflets marked 'Sorrerford" Output Transformer NAME C "Sarrerford" Auto Transformer RESS D "Sarr:erford" Mains Transformer Radio ADC édifon [ "Samerford " Smoothing Chokes [. "Samerford" Driver Transformer Radio Communications Division E.H.T. Transformer L, "Samerford" REDIFFUSION LIMITED, BROOMHILL ROAD, S.W.18 RADIO I.T D., SONIERFORID, CHRISTCHURCH, HANTS. GARDNERS Designers and Manufacturers of Radio Communication and Industrial Electronic Equipment FOR RADIO INDUSTRY LABORATORY Seien. RC 103

www.americanradiohistory.comwww.americanradiohistory.com 3o WIRELESS WORLD CLASSIFIED ADVERTISEMENTS January, r948 Rate 8/- for 2 lines or lees and 3,- for every additional) line or part thereof, average lines 6 -8 words. Boa CHARLES AMPLIFIERS -Announcing a Numbers 2 words plus 1r -. Press Day: February 1948 new version of their famous HFA1 ampli- issue, first poet Wednesday, January 7th. No responsibility fier -the HFA3 incorporating a pre -amplifier accepted for rrrors. to enable the use of moving coil pick -ups direct; this amplifier in conjunction with the Lexington moving coil pick -up and the WARNING B.A.E.C. twin 'matters cone speaker provides the are warned that Government surplus highest obtainable fidelity of reproduction; components which may be offered for sale the complete range now comprises amplifier through our columns carry no manufacturer', HFA1 7 watt cathode follower output for guarantee. Many of these components will have crystal pick -ups; HFA2 single -ended 3 watt been designed for special purposes making for crystal pick -up; the HFA3 for them coil pick moving unsuitable for civilian use, or may have de- -ups; full constructional blueprints, teriorated as a 2/6 each; full kits or separate components result of the conditions under available or supplied which they have been stored. We cannot ready assembled; stamp for comprehensive catalogue. -Charles Ampli- undertake tc deal with any complaints regarding fiers, le, Palace Gate, any such components Kensington, W.8. purchased. Tj.P. RADIO SERVICES, Ltd., offer Air- NEW RECEIVERS AND AMPLIFIERS 11 master 5 -valve 4- waveband de luxe, A.C. chassis, with Goodman 12in P.M. moving UNIVERSAL ELECTRONIC PRODUCTS, speaker, £2415; coil 36, Marylebone High St., London, W.1. our amazingly popular 10- watt twin channel 3 -valve A.C. amplifier, com- Tel. Wel. 4058. plete with valves, £8/18/6; OUR U.E.7 amplifier is designed for the the amazing Peter connoisseur Pan midget radio, A.C, /D.C., 2 waveband, in who requires the best possible highly polished jazz reproduction together with the highest finished cabinet; a qual- standards ity product, 12gns; ex -Army type 9- of workmanship and materials; ai hA, valve receivers operate write for descriptive leaflet. We invite you from A.C. mains or to hear this amplifier 12v accum. frequency range, 17 to 1.2 me /s, demonstrated in con- all in perfect condition, 16gns, carr. paid; junction with the Wilkins & Wright pick -up art photographs and the latest type speakers, of the above goods available including the to all genuine enquiries; satisfaction always new Wharfedale corner cabinet model. We guaranteed; we specialise in high fidelity thank our many customers for sound reproduction their support & wish all readers of Wireless for the home, clubs, concert halls, etc., and World " a will undertake PARTRIDGE Happy and Prosperous New Year. the design and construction of H.P. RADIO SERVICES, Ltd., 55 County equipment to meet your own requirements. Rd., Liverpool, 4. (Estab. 1935.) ' 18958 )EGALLIER'S, Ltd., will re -open for the RECEIVERS, AMPLIFIERS -SECOND -HAND LL sale of American receivers when restric- TROPHY 8 Comm. 11.7, 550m, perfect ' tions permit.- Degallier's, Ltd., BCM /DEG.9, dition, con- London, W.C.1. £12. -Box 4498. [8902 [8883 RCA AR -88 (with speaker), very good con- RECEIVER type R.3170Á radar, used for MANUAL dition. -Write Box 4464. [8858 anti -jambing devices, radio counter FOR sale, AR88D in excellent condition with measure; contains 14 modern a.n. valves, in- manual; £60. -Box 4466. [8860 cluding 8 Mallard EF50; all perfect and new; 358X, 9 colts, 90kc -31mc power pack, price 50/- each, plus 4/- carriage. Containing : -Many useful circuits as new; offers UNCLE TOM'S RADIO over £30_ Box 4495. CABIN, 5, Seven including New 15 watt high quality R1155 receiver, excellent condition, £14.- Stars Court, Manchester, 4. [8965 Osborne, 53, amplifier with 40 Montague Rd., Dalston, E.8, ribbon and armature pick -ups. db of negative ONE B.B.R. P.A.20 amplifier, 2 F.I LS7 BRIERLEYfilters, amplifiers and pre -amplifiers. feedback over three stages. units with 40in horns; £58. 4521. Arrangements are being made for -Box the demon- Also TELEVISION Console G.E.C. receiver, 10x8 stration of these products by agents throughout :- Design of Electrical Equip- picture, £90.- Hare, Westholt, Henlow, the British Isles. Where arrangements for thi: ment including Power Supply Units. Beds. [8887 have not so far been completed It is possible R1155. -Customers assure us that our for our sales representative to demonstrate is Articles on Negative feedback fully modified version is the best all- your own home when next in your district.- - and Volume expansion, Acoustical round set available to -day. J. H. Brierley, Ltd., 46, Tit.hebarn St., Liver Problems, Sound Reinforcing COMMUNICATION results with local station pool, 2. [8266 and quality; 10 valves, 16-4.000 metres, d.f. re- Super de luxe five -waveband feeder Public Address. An appendix con- moved, new front panel, PX4 -pull unit, with tuned R.F. stage and push quality 1948 sisting of six selected design charts. amplifier, bass and treble boost (separate con- magic eye, 15inx55L,in station-named scale, 10/ trols), gram input, other refinements, com- 17, 16/35, 34/100, 200/550, 800/2,000 metres. Cross -over network circuits, etc., plete with speaker; £35. communication type coil pack, high " Q " I.F. WRITE for full details, or call transformers, completely assembled and aligned etc, stration for demon- and ready to connect to audio amplifier. -Send R1155 circuit and values, 1/6 post free. 21/2d stamp for full details to the sole distri- + + + WE can offer to modify your R1155 in the butors, Couiphone Radio, 58, Derby St., Orma- At last the completely revised post- same way, or to your special require- kirk, Lancs. [8959 war ments; re- alignment, calibration and repairs `PECIAL offer : Midget communication re- edition for which you have to all communication and quality receivers; tJ miner and power pack (M.C.R.I,), 5- been waiting. first-class work with first -class instruments valve superhet, complete with aerial and experts. by equipment, lightweight -R.T.S., Ltd., 8, Gladstone Rd., Wim- earth headphones; bledon, S.W.19. Liberty 3303. [8795 range 20 -3,000 metres in four bands, operates We regret the delay and advise IJ'CRAFTER on any voltage between 97 and super Skyrider SX -28, crystal 250 A.C. or early application as the issue is phasing, S meter, 42 -0.Smc 115 -230v, as D.C.; £9/10; send for one now before stocks new; what offers are special offer, slow limited. ?-Box 4496. [8899 exhausted; another C.A. AR.77E 540kc /s to 31mc /s, 10 motion drives by Muirhead," 50 -1 ratio, 10 /- valves Xtal, £30 or highest offer. -Har- ea, postage 6d; also milliameters, 0 -1 15/- ea; man, Pentlands, Pentland send for 6 -page list; trade supplied.-L. Wil- PRICE 5/- POST FREE Rise. Portchester. kinson, Wholesalers, 204, Lower Addisrombe HAMMARLUND HQ129X, 11 valve, latest Rd., Croydon. Add. 2027. [8264 1947 communication receiver, with speaker, 6 wavebands, crystal filter and GOODSELL, Ltd., 40, Gardner St., Brighton phasing, band spread, " S amplifier " " meter, noise -The Williamson to W.W." limiter, 115 -250 volts, A.C.; £120. -Dr. S. specification fitted with best quality compon- COUPON Melling, 50, Greatorex St., E,l. [8813 enta, Partridge transformers and oil condensers OVERWHELMING demand for some of our on 425volt line, price £21; with voltage sta- Please send me post free a copy lines has caused bilised power pack (valve delay in replying to our controlled) ensuring of the customers and has also cleared out some of no volts in excess of 350 for the pre -amp and new Partridge Manual. our however, complete stability where disposal bargains; there are, still high gain required, I enclose P.O. /Cheque value 5/ -. a number of attractive items of appeal to the super amplifier, 26gns; pre -amp, including amateur enthusiast, but remember stocks are E.F.37 with 4- position bass boost and 4- position limited, treble control and E.F.37 as straight so don't delay; R.A.F. radar ampli- triode for fier, mode, 1124, complete 6 -stage U.H.F. amp- Hi -Fi pickups, for use with above, £414; a Name. complete new range lifier with 6 valves, 3 Westectors, 3 I.F. stages, of feeder units using the 6 pre -set R.F. setting, makes an ideal base new Denco 5 and 10-band turrets, improved for television or F/M experiments, compo- I.F.T.s and large attractive glass dials with Address nents alone worth £10, magic eye. available shortly; send for our price £4/10 ea.; details. class D. No. 1 wavemeter a few left only, ASUPERHET which will bring you hun- complete with all spares and crystal check dreds of shortwave stations just as soon unit at £5/5; aerial couplers, type D, com- as batteries and 'phones are connected, 6 to plete, at £1 /15; R.A.F. dinghy sets, 9mes, 4 2volt valves, slow motion drive, size we have only a small quantity of these portable transmit- 6inx5inx91/2in, guaranteed O.K., price Telephone.. Abbey 2244 ters, ideal for amateur field day work when 29/6, postage and insurance 2/6; suitable modified, hand double headphones fitted with plug in jack, driven -generator gives 6 volts other and 400 volts, 6J7 and 6v6 valves, neon in- 6/6; interesting bargains: 12 assorted dicator, our price, £2/5; 3 -stage instrument switches, price 10/ -; 12 assorted amplifier magnetic relays, price panels for 1T4 type valves complete with con- 11/ -; 17 -range ac /dc PAR °,MIDGE densers, resistors and vol. control, can be made multi -meter for all radio sets, price £7; thermo couple H.F. into midget portable by adding tuning device meter, price 4/6; nuts, (20/- worth of components), to clear at 7/6 bolts and washers, small sizes for model mak- TRANSFORIVIERS each; send stamp for complete ing, three gross assorted, price 7/6; all post LTD bargain list; free. -The Instrument terms, cash with order or c.o.d. over £2.- Co., Ltd., 244, Harrow 76 -8, PETTY FRANCE. LONDON, S.W.I Orders to Dept. W.W., Ariel Trust, Ltd 188, Rd., W.2. [8864 Vauxhall Bridge Rd. London, S.W.1. [8106

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 31 BRAND new Canadian Type R.103 M.K.1 DYNAMOS, MOTORS, ETC. staff car radio, 6 volt, world -wide recep- to AC rotary converter, output kilowat, tion on short and medium wavebands, 7 -valve DCsmooth for radio; £20 or offer. -Gee, 5, superhet, complete with aerial and box of all Riverside Close, Staines. Tel. Staines 883 spares; nearest offer to £30. -Box 6145, U.K. ELECTRADIX BARGAINS after 6 p.m. [8940 Advtg. Co., Ltd., 25, Shaftesbury Av., W,1. chargers for home and export, HALLICRAFTER 8X16, perfect, world com. BATTERY4 models, 2- 6 -12v, 1, 2 or 4amp de, any DYNAMOS. D.C. 50170 volt 10 amps. shunt mains voltage; generous trade terms; write munications bandspread 550m- 61mcs. wound, ball bearing machines, 1,000 r.p.m., E14. Xtal gate, S meter select B.F.O., pitch, tone, for catalogue. -Tel. Hoddesdon 2659. The 5 12 volts 10 vol., R.F. controls, 11 valve 15 watt P.Y. out- 30 volt amps. 1,500 r.p.m., L5. amps., Banner Electric Co., Ltd., Hoddesdon, Herts. put, 4Ogns or near offer; P.M. apkr. in cabinet. E4. types of rotary converters, electric Brown's 'phones, radio parts, -30, Springfield ALLmotors, battery chargers. petrol- electric Gdns., Upminster, Essex. [8903 Resistances. Var. slide vit. enamelled tube with generator sets, etc., rotary transformers, input A.F. type 1124 receivers with 6 valves, laminated brush and slides, 14 ohms 5 amps., 12e dc. output 600v at 250ma; price £4/10 3 I.F. stages, ideal to convert for tele- suitable with 50 70 volt dynamo for charging each nett, post paid; J.A.P. No. 2A engines, vision base, definitely sound, 35/ -; ex -Govt. sur- circuits at 5 amps., 25 - each. As new. 1.2 b.h.p. at 2,600 r.p.m.. complete and ready plus, Radar equipment, receivers, wavemeters, for use, £17 nett, ex works. -Ward Lordscroft rotary transformers, motor generators, indicat- Meters. Ironclad A.C. voltmeters, G.E.C. 4in. Works, Haverhill, Suffolk. Haverhill 253/4. ing units, calibrating units, for sale. -J. Rae, switchboard, 0 -60 volts, 45/ -. Ammeters to SANGAMO synchronous motors, self starting, 200 a.c., 50 cy., consumption 2V2- 39, Penn Rd., Wolverhampton. [8922 -. Frequency -250v match, 0-40 amps., 45/ meter watts, size 23/4inx2in, geared 1 rev. 60 mins., COMMUNICATION receiver, 2 r,f. osc 40/60 cy. Crompton F.G. Ironclad switchboard, MxR, 2 i.f., p.pp. triode output S meter, can be reset to zero by friction drive from noise limiter, a.f.c. control circuits and b.f.d. 50 volts 671in. x 6 1in. x 4in. with lamp on top to front or back shaft, s/sxl /loin, to run clock- 150 k.c. to 26 me /s, £38; Midwest super illuminate dial, ES Ss. Ammeter to match, wise, ideal movements for making electric 0 -50 amps. A.C., 75/-. Voltmeter to match, clocks, time switches, etc., nickel -plated finish, radiogram, triple speakers, new Garrard auto - 0 -75 volts A.C., 65/ -. price 22/6 ea.; 12 to 1 dial trains to fit above g changer; also fitted modern G.E.C. overseas spindle, 216 " 10 " chassis; nearest £110.- G3BNL, 53, per set extra; f/3.5 lenses, 2in D.P. 50 amp. knife switch on Paxolin focus, by well -known makers, ex -Govt. stock, as Old Steine, Brighton. [8783 Switches. new, fitted in oxidised mount, flange, etc., ideal TEST EQUIPMENT panel, 35; -. for projectors, enlargers, cameras, etc., price £9; all wave sig. gen., £6/10; bar- 27/6 each, postage 6d.; to callers only, Bendex AV040,gains. -Box 4311. [8822 Motor Blowers. 24 volt D.C. Keith Blackman type R.A.10 receivers; Selsyn motors, K20, type W1191A, new 3v, Sin. inlet and outlet, E5. aerial cameras, heavy duty 1.f. chokes, change- WAVEMETER,100kc -20mc, 95 / -. -Box 4307. [8815 over relays as used in 1154 transmitter, 1,000v 200 microamp, 31;}ín die., un- TRANSFORMERS. B.T,H, 200/230/250 v. 200ma transformers, multi -way screened cable scaled, -. Shrewsbury. METERS, 25/ -55, Copthorne, 50 cy., 2 volts 2 amps. and 75 volts 6 amps., with and plugs, test sets fitted with C.R. tubes; meter type Sae., £12; advance sig. C.R. 15 taps, 70;- ; carriage paid England and Wales. power units, type 526; performance TAYLORgen., type B.3.C, £12; both perf. -Box 4507. meters, type 53874; a.c. mains wavemeters, Weston E.772, i's new otters. 2.2 K.W. Transformers, 403 220 volts, with equal type W1252; battery wavemeters, type W1095; ANALYSER,-918, Chester Rd., B'ham, 24. Erd. 0712. tappings to 25 volts, L9 IOs. receivers, type 1147; a.c. mains power packs generator B.Y.L. 30mcs-100kcs int. for 1147; indicator modulators, auto trans- SIGNALmod, AC mains, scarcely used, 19gns.- Auto Transformers, 230;110 volts 85 watts, formers; receivers, type 76A; battery driven Caflyns, Ltd., Commercial Rd., Eastbourne. 25 - ; 150 watts, 35/- ; 300 watts, 65j- ; I K.W., amplifiers, large assortments of volt, amp and and resist- " IV-ORMAN " capacity analyser £7 lOs. Transformers double wound for models - milliammetera, neutralising units with R.F. sig -gen or "\ ance bridge; £10; or exch. 230 ;20 volts 2 amps., 30/- ; 12 volts 3 amps., 32/6. meters, metal rectifiers, relays, vibrator packs, Avometer. -Selectest, 108, Oakland St., Widnes. intercom. sets, signal generators d.c. to a.c. OIN thermocouple moving coil milliammeters. converters; 12 and 24v d.c. to 230v a.c. Sun - a at 5/6 MOTORS. Electradix Micro 0- 350m /a, new ex -Gov.; bargain Motors for Instrument work Vic delayed action control, 3,500watts, blower each, £3 per doz.. post free. -J. McMillan. motors, G.E.C. gas -filled mercury relays; and models 2in. x 11 in., weight 5. Oakfield Road, Bristol. 8. Brown's A type headphones; E.M.I. cathode - GM3155B ose., £18; Siemens only 10 ozs., 12;24 volts ; ray tubes; 6 -valve receivers incorporating PHILLIPSmulti -range ac /dc voltmeter, £12; Wheat- work from dry cells or A.C. Clystron unit, etc. -H. Franks, 58, New Oxford stone bridge, £5; TZ40s, 40/- each; all un- Mains through transformer, laminated fields, ball St., W.C.1. Tel. Mus. 9594. [8970 used; Bittorf and Funke valve tester, £15 or bearings, totally enclosed, small vee pulley, VALVES nearest offers. -41. Miller Av., Grimsby. centrifugal relay speed governor on shaft remov- NEW 813 (1), 110 / -; 872A (1), 807 (21, frequency oscillator model 7600, able for second shaft drive. Precision made 25/- each. -Box 4494. [8895 from below 20cps to over new, boxed, RK34s, 6 / BEATrange coverage ex -W.D. stock. Worth 45' -. Price 21/. each. U.S.A., -; 20kcs, a laboratory instrument, full technical BRAND9001s, 10 / -; R.C.A. 8085, 35/ -; R.C.A. details on application; price £28/17/6. -Radio Limited stocks. 8014s, 500w air -cooled triodes, £3.- Sykes, Development Co., Moretonhampstead, Devon. Oldfield Rd., Honley, Huddersfield. [8924 N.UPLANS announce No. 14, their valve - Battery Chargers. Keep your accumulator in LARGEST and most comprehensive range in voltmeter, invaluable on the testbench, condition while the car is laid up. Send for the country, British and U.S.A. types, at measurements at all frequencies, and DC with Special Battery Charger leaflet " W.W." Board of Trade prices; send for lists (valves diode probe for signal tracing, etc. Easily available), free, s.a.e.; valves sent c.o.d.; re- made, easy to use; full plans, details, 2/6; from Headphones. Single low resistance for circuit tailers not supplied. E. Bradley, Whinnie Knowe, Escalls Cliff, with headband and cord, 5 / -, or RANSOM, Bond St.. Brighton. [7223 [8847 testing, etc., GRAMOPHONE AND SOUND EQUIPMENT Sennen, Cornwall. 716 per pair. AVOMINOR, £6; model 40 Avometer, SIMON SOUND SERVICE can supply your £16; Sin voltmeter reading 180, 15/- ea; needs. [8712 5ín ammeter 0/30, 15/- ea; 550ohm 0.25/1 Speed Meters by A.T. Speedometer Co., 1,500 INFINITE Baffle corner deflectors, scienti- amp, shunt regulators, 15/- ea; 2 volt Varley r.p.m., 4ín. dia. black dial, white figures and scale, fically designed acoustic chambers as re- 40 A.H. dry accumulators, 12/6 ea; all goods 20/ -. viewed ' Wireless World" June; send for new and unused.- Capper, Westbourne, Gorse catalogue. -Broadcast & Acoustic Equipment Bank Lane, Baslow, Bakewell, Derbyshire. Relays. 1,000 ohm coil, G.P.O. type, enclosed, Co. Ltd., Broadcast House, - Tombland, Nor- SIGNAL generator model 101a has proved its 2.6 each ; 30 ohms 2 -make 2 -break contacts, wich 26970, [6434 efficiency everywhere, range 100kcs to 50mes, 2 6 each. ROFESSIONAL recording equipment; to individual calibration accuracy better than 1% the trade, recording machines, blank discs, new type scale assembly giving close readings. Spark Coils. Ex- G.P.O., 6/12 volts, to give up cutters, trailer needles, etc., from stock; record- sectionalised attenuator, 12 months guarantee; to Iin. spark, with spark gap, 25/ -. ing amplifiers, matching transformers. ribbon particulars, Radio Develop- and m.c. microphones; full trade terms. -Sound £13/19/6.-Full Discs (Supplies), Ltd., 83a, Bold St., Liverpool. ment Co . Moretonhampstead, Devon. [8877 Battery Superseders, 6 volts D.C. input, AMMETERS, h.f., brand new ex- Govt., -. for Q.11.E.F.I. moving -coil pick -up is now avail - 230 volts 40 m.a. D.C. output, 55/ Send able for both home trade and export; boxed, Weston 2in proj. 0 -350mA m/ coil, leaflet. it 5/6 (48/- doz.) Ferranti 2in prof 0 -200mA combines for the first time high fidelity with m /coil, 7/6 (60/- doz); electrostatic volt- high output voltage, enabling it to directly Switches. I ohm to 0 and meters (Elec.Inst.Co.) 0 -5,000 volt, 31/2in flush Dimmer Rheostat replace normal moving iron pick -ups without m /coil, 30/- (£12 per doz.); hydrometers, un- off up to 3 amps. for regulation of 6 volts, 2 6. any extra amplification; it has an exception- breakable glass, 3/6 (30/- doz.). -Auto Collec- ally clean response with no undesirable reson- Av., W.4. (Chia- Invisible Ray Control. Raycraft Kit with ances, thereby reducing needle scratch. Price, tions, Ltd., 126, St. Albans finish, 40/- wick 1601). [8896 selenium bridge in bakelite case, 10,000 ohm in walnut and black plastic each resistor, valveholder, etc., with retail, including transformer, plus 10/4 pur- NEW LOUDSPEAKERS relay, megostat, chase wholesale enquiries in- HIGH quality, precision -built speakers. instruction booklet, 45; -. tax; and retail Ticonal magnets, detachable dia- vited; illustration sent on request-Brooks & twin cone.- Broad- BohmBohn), Ltd., 90, Victoria St., S.W.I. phragms, die-cast chassis, ; las. Buzzers. The Townsend high you interested in reproducing sound cast & Acoustic Equipment Co., Ltd., Broad- note Wavemeter Test Buzzer, cast House, Tombland, Norwich 26970. (6435 as nearly as possible to the original and LOUDSPEAKERS. SECOND -HAND plat. contacts, 5 / -, G.P.O. doing this at a reasonable cost? If so, we CE (tweeter) unit, with 3- celled double contact blade for invite you to either come to our demonstra- ITITAVOXhorn; £10 /10. -Box 4519. [8936 distant signals (as illustrated), tions or write for full particulars; demonstrn. h.c. corner horn with bass chamber tions daily, 9.30 -10.30 am, 6 p.m. -6.30 pm., TOIGTless unit; offers- -Box 4499. 18904 excepting Sat.- Rogers Developments Co., 12, 12in P.M., in very fine heavy Please include postage for mail orders Macclesfield St., Shaftesbury Ave., W.1. [8743 cabinet, 2ft square, as new; £12 POLYTONE electric gramophone motors, TITAVOXpolished 200 -250 volt ac, induction -drum type, (London).-Box 4508. [8919 auto stop triple convertion, B.T.H. 612 field. loin non -magnetic turntable, and mahog. cabinet resonance ELECTRADIX RADIOS speed regulator, guaranteed, price £6 /18/6; BAKER60W recf; complete with mounting plate, 12inx14iu, in damped; £11/11 -37, Motcombe Rd., East. 214. Queenstown Road, London, S.W.8 bourne. Tel. 2452. [8947 black or grey ripple finish, controls and turn- super quality 12 -inch permanent (Late Queens Road) table polished, with Rothermel crystal pick- cone speaker, Ticonal mag- up fitted £2/17/6 extra; limited supply. - BAKERmagnet triple Telephone : MACaulay 2159 Co., Yew View, Bristol net, 15 ohms, complete with infinite baffle Martuck Eng. Rd., cabinet in the white, new, £6110. -Box 4505. Whitchurch Som. [8798

www.americanradiohistory.comwww.americanradiohistory.com 32 Advertisements Wireless World January, 1948

COMPONENTS-SECOND -HAND, SURPLUS VALLANCE'S FOR GOOD VALUE CHARLES BRITAIN (RADIO), Ltd. If you do not find a transformer to your requirements in the list below, may we quote you for a type wound VIBRATOR pack, size 7inx3inx2%in, black to your own specification? 7 to 14 days delivery. crackle case, 6 volts only, employs a Wearite CRYSTAL PICK -UP DE LUXE MAINS TRANSFORMERS BY WODEN. Stratosil vibrator and gives 250v at 80ma, the £ s. d. output is not rectified but the outfit contains DTM. 11250- O.250v. 60 m /a. 4v. 2.5a. 4v. 4a. 1 19 6 all the necessary filters, etc.; price 27/6, plus 1 / DTM.11A 250 -0-250v. 60m /a. 5y. 2a. 6.3v. 3a. 1 19 6 6 carriage and packing. Components : We DTM, 12275.0 -275v. 120 m,'a. 4v. 2.ha. 4v. 4a. 2 8 6 offer the following selection from our large DTM. 12A275- 0 -275v. 120 m /a. 5v. 2a. 6.3v. 3a 2 8 6 and comprehensive stock : Loudspeakers, Rota DTM13A 350.0 -350v. 120 m /a. 5v. 2a. 6.3v.4a. 2 14 0 loin P.M. less trans, £1; Rola 8in P.M., less PTM.14 425- 0.425v. 150 m /a. 4v. 3a. 4v. 4a, 3 10 0 trans, £1; Page 5in P.M., less trans, 14/6; PTM.19A 425.0.425v. 150 m /a. 5v. 3a. 6.3v. 4a 3 10 0 Goodmans 12in Hi -Fi twin cone (Axiom DTM.15A 500-0-500v. 150 m /a. 5v..3a. 6.3v. 4a 3 15 0 Twelve), £7/10, plus 5/- carriage and packing; UTM.16 650- 0-650v. 200 m /a. .. .. 4 2 6 Goodman's 12in 15ohm speech coil, £5/17/6, DE LUXE FILAMENT TRANSFORMERS BY WODEN, plus 5/- carriage and packing. DTF.12 2.5v. 10 amp- C.T...... 1 18 SPECIAL offers : 36 asstd tubular condensers, DTF.14 5v. 4 amp. C.T...... 1 11 001mfd to -1, 10/6; 72 asstd resistors, DTF.17 7.5v. If amp. C.T. V ...... 1 17 r/4, 1/z and !watt, all new, 100ohms to 6meg, DTF.18 5v. 3 amp. 6.3v. 4 amp. .. .. 1 18 12/6; 72 asstd metal cased condensers contain- Special 5v. 5v. 5v. all C.T. 3 amp. .. 2 12 ing -01, -1 15 and Special 7.5v. 4 amp. C.T. 6.3v. 5 amp. C.T. including 2, 01, 2,500v 2 5 wkg, all new, 27/6; 36 mica condensers, -0001 WITH 'CRYSTAL STOCK LINES FOR THE EXPERIMENTER. to / I6 01, all new, 12/6; 12 volume controls, less U.H.F. Coils by Eddystone. switch, 5,000ohms to 3meg, 3 turns supported by 17/6; 24 valve - frequentite strip, Cat. 601 2 3 holders, Loctal, Octal, 7 4 turns supported by frequentite 5 and -pin, etc., all strip, Cat. 602 2 3 new 10 / -; send for list " W " The ACOS G.P.IO combines 5 turns supported by frequentite strip, Cat. 603 2 4 available. -Charles of other bargains purity of re- 8 turns supported by frequentite strip, Cat. 604 2 6 Britain (Radio), Ltd., Radio production with extreme reliability. A 10 turns supported House, 2, Wilson St, London, E.C.2 Tel. by frequentite strip Cat. 605 2 6 Bis. 2966. unique flexible assembly renders the crystal Frequentite base for above. Cat. 606 1 6 [8961 Suitable Air Dielectric Condensers in the Eddystone W. SMITH k Co. (RADIO), Ltd., offers virtually unbreakable, while a needle - range, for tuning the above inductances. Con- the following: - pressure adjustment Is incorporated In the structed of heavily brass, ends GUARANTEED sound sliver plated the are and perfect: R.A.F. base. Resonance -free response from 50- ceramic, and a sturdy rotor bearing is fitted. The type 39 aerial coupling units with 0 -3 and spindles at the rear. extend for ganging purposes. 0 -6amp thermo coupled meters and 100watt 8,000 cps. Output I.5 v. at 1,000 cps. Needle Dimensions l /In. x llin, x liín. long; im. hole dummy aerial, 17/6 each; 1,000kc crystal pressure I} mounting. units, new and boxed, 10 /6 each; R.A.F. oxs. (adjust- 60 P.F. variable Trimmed Condensers, Cat. 1.82 7 0 R1124 receivers, 41.3mcs, complete with valves able). 15 P.F. Trimmer. Cat. 550. 6 0 very easily adapted for television, Vibra- 25 -25 p.f. Split Stator Condenser, Cat. 583 8 0 limited number only, 59/6 each; Admiralty 1149. 2 tion -free arm 34 -39 p.f. Split Stator Condenser, Cat. 584 8 3 speed dials, very fine job, 4/6 movement. Transmitting Crystal Holders ...... 2 0 sers, each; conden- Bias Condensen. lmfd 5kv working, 10 /- each; .25mfd Screened lead. Flexible coupling A protects 2kv working, 2/6 each; R.A.F. crystal B against 25 mid. 35v. 2 6 50 mid. 50, 3 6 with output testers Price in Great breakage. 25 mid. 50v 3 6 50 mid. 12, 2 4 2volt valves suitable for adapting to 5- (Brit. Pat. 579,524. Pats. Button Base Valve Holden, Ceramic metre receivers, brand new, 19/6 each; E.F.50 Britain 481 (In- pend. abroad). 1 1 valve holders, Licensed by Pyrex Bowl Insulators 9 Pax 6d, ceramic 9d, cluding P.T). Brush Crystal Co. Ltd. 4 mid. 500v. Block Metal case 7 -pin 6d each; I.F.F. receivers, Condensen, 4 6 valves, complete with And all other lines you need or are ever likely to need 29/6; selector 24volt step in relays, Obtainable only from Radio Dealers in radio. Prompt C.O.D. or C.W.O. Semite. 1/6 each; 12volt stater relays, '3/6 each; 18 Please include extra for packing and postage. and 24-way screened cables, 4/6 each; 8volt %amp rectifiers, 3/6 each; 5ma rectifiers, 2/3 COSMOCORD LTD VALLANCE'S each; 60ma L.F. chokes, 2/6 each; 0- 20volt 144 BRIGGATE, LEEDS 1. Phone: 29428/9. ac meters, 21 /sin scale, 10/6 each; plus ENFIELD: MIDDLESEX Staff Call Signe (12111fV, 089X, 02A11V, G3BDD carriage. G3ABD. G. W. SMITH & Co. (RADIO), Ltd., 3, Lisle St., London, W.C.2. Gerrard 8204. PARK RADIO OF MANOR PARK, 676 -8, Rumford Rd.. E.12. Tel. Ilford 2066. TELEVISION kits, £22/10, absolutely complete set of parts with working instructions, LASKY'S RADIO to avoid risk tube supplied to callers only; Pye Co -Ax ping and socket, as used on wartime apparatus, 1/- each; large 12 -pin sockets. NEW YEAR'S 9 around 3 middle, 2/ -; under -pillow extension speakers, play the kids to sleep, or don't dis- turb wife while nAKERs SPECIAL OFFER your you listen to the end, 2/6 each; Tannoy double -button hand mikes. good hardwearing job with muting switch, lead Ex -LM. Test Set, Type 185. Containing six valves, and plug, 10/6; trickle chargers, 230v &sew/14,04.c' charge ac, four VR65's, one 5Z4 (rectifier), and one EA50. 2 or 4v 1/4a, 12/6; transformer and rectifier supplied for making up in 15 minutes, Transformer type 1OK/13257, 8 x 16 mfd. block contact mikes for pianos, RAD O condenser, smoothing violins, guitars, etc., choke, 2 Pot/meters, Yaxley 2/6 each, transformer 6 / -; tungsten contacts -bank 5-position switch, 6 coils iron -cored, toggle for renewing worn vibrators, energising 1/6 pair; self - HIGH FIDELITY SPEAKERS 'witch, red indicator lamp, resistances, condensers, telephones, will work up to 2 miles valveholder. on 1 wire and Mounted on chassis size 12in. x 81n. x earth return, a boon for the Triple 1fin. Totally enclosed in strong metal bedridden, keep in touch with the 12' cabinet, out running patient with- enamelled grey. Overall size, 12in. x SIin, x 681n, up and down stairs, fine also for Cene Model farm outhouses, 2/6 each; who hears New and warmed. Pries 59/6 each. Carriage 2/6 extra. you or grandpa? the radio, Limited quantity only. Let the old folk bear the radio in comfort, modulated output unit with A R headphones, suit any set, 30/ -, cash refunded Ex -A.M. Oscillator Unite. New and unused. Con- if not satisfied; burglar alarms, M taining 1 valve type 6J0, associated 230v ac/dc, E resistances and suitable for shop premises, intruder sets condensen, toggle switch, 16in. 3 -core screened bell alarm cable. ringing. 55/- complete; replacement bob- P Complete unit entirely screened In grey enamel box. bins for Garrard pickups, including C. bers for new rub- Size : 5in. x 5in. x 2 /in. Amazing value. New and reassembling unit, 4/9. [8960 L unused. 7/6 each, postage entra. GANG condensers, escutcheons, transformers E etc., to be sold regardless of cost. -Send Push Button Control Units No. 2. Containing 5 -way stamped addressed envelope for full particulars push button unit, turns. /rec. switch, 2 -pin plug and to Retail Sales, Ltd., 6, Chiltern Parade, Syca- F .socket. New, unused and boxed. 6/6 each. more Rd., Amersham, Bucks. [8670 V W." moulded television coil formers, Special Meter Parcel No. 1. Containing 12 moving with feet and slugs, 9 for 7/6; blocking E coil meters, amp /meters, Ma/meters, Micro /amp- ose. trans., 1 -1, 3/6; 100 ma chokes, cast E meter, thereto /couples, volt/meters. The caso, 8 / -; 5in P.M. speakers, 14/ -; R1155, parcel 6c 60.9.. Taylor, R post free 25/15/0. Guaranteed satisfaction or £12.- 24, Enmore Rd., S.W.15. R money TELEVISION aerial equipment, 5 refunded. types fully waterproofed aerials available, poles, S S lashings, all types of feeder in stock; send for SEND STAMP FOR OUR CURRENT LIST, AND brochures; aerials installed. -Wolsey Television, BULLETIN OF OTHER EX -G0V. BARGAINS, WHICH Ltd., 87, Brixton Hill, S.W.2. Tulle Hill 1240. OWING TO LIMITED SPACE WE CANNOT ADVER- TELEVISION constructors! All your re- PIONEERS OF MOVING COIL SPEAKERS TISE. ALL ENQUIRIES INVITED. quirements: 1.000 valvese; cathode ray tubes : CRM91, CRM191, 9in and 12in rubber NEW 1948 MODELS masks, EHT trans., line and frame output CINEMA Model, 18 inch - 28 19 6 trans, focus and scanning LASKY'S RADIO coils, H.V. conden- AUDITORIUM Model, 12 inch - 86 10 0 sers, %in conformers with iron cores, aerials, Send ltd. now for Illustrated list to: 370, Harrow Road, Paddington, W.9 80ohm feeder, mains trans, etc., etc.; send for lists or state your requirements; all goods BAKERS `SELHURST' RADIO Opposite Paddington Hospital.) 'Phone ' CUE 1979 are new and are sold at manufacturers list - 75-77, Sussex Road, South Croydon, Surrey Hour : 9 a.m. to 6 p.m. Mon. to Sat. Thun. half day nrices. -E. A. Porritt, 13 -27, Wastdale Rd., Forest Hilo, 8.E.23. (8901 Telephone : CROydon 4226.

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 33 7t ADIOGRAPHIC, Ltd., 66, Osborne St., A. RYALL, 65, Nightingale Lane, Lon- IL Glasgow. Tel. Bell 3776. -Crystal holders, don, S.W.12. -Mail order only, postages Type 2, socket with ktin centres, price each extra, c.o.d. £1 or over, please send large en- 6d; ribbed ceramic former, linxlskin, price velope for our full list; U.S.A. make metal each 2/ -; rubber masks suitable for mounting ARMSTRONG cased 500v tubular 0.1mí. 7/6 dozen; Silver of bin C.R. tubes, price each 2/ -. [8879 mica, 200pf, 300Pf, 400 f, 500pf, 4/6 dozen; AXLEY type switch, 3 -bank 1 pole, 6- 500v wkg. Micamoulde dozen; .L way each bank, short spindle; ex-Govt., Mica 0.01mf, 3 -2/ -; d 0,00 d g 1, 4/-d 9/- doz.; 0.000127 telling condensers, 42/- wkg., 3 -2/ -; all condensers guaranteed; Am- doz.; Mazda Octal valve holders, amphenol, phenol type British 5 -pin valve holders, 4/6 3/9 doz., in 500 boxes :-Will Owen, 538a, dozen; U.B.A. paxolin 4 -5 -6 -pin, 3/6 dozen: Mansfield Rd., Sherwood, Nottingham. [8920 volume controls, 10,000 medium spindle, 1/6 METEOR ELECTRONICS. -Midget i/c coils, 250,000ohm shcrt spindle, 1 /6; Bar type 3 midget 2 -wave coils: constructional kits gang, 0.0004mí short spindle, 5 / -; Twin for midget coil -packs and I.F. transformers; ceramic 0.0003mf, 5/6; Bar type 4 gang permeability tuners and S.W. coil units; send 0.0004mí, 5/-; Resistors, i/watt, 1/2watt, 100 21/2d stamp for full lists, including smoothing ohms to 2 meg level assortment, 40 -5/ -; chokes and O P.T.s- Gloucester Row, Wey- Plastic group boards, drilled, less tags, 9w, mouth, [8951 types, 3 -1 /6; Switches 513.211. 6w, 2/ -: 3B.2P. DUAL output mains operated h.t. units, 6w, 2/6; 2B.3P. 3w, 2/3; Res. panels, 5 -way 650v at 400 ma and 300v at 120 ma, with 25mí and three res., 1/3; Twelve -way using separate rectifiers, also incorporated group boards with 9 -lwatt and 1 /2watt res., 2 /-; 12v vibrator -pack, £5; lkw 230v to 115v all new; twenty types in stock; Octal plugs, transformer, £2/10, plus cost of carriage and cap and socket, 3 -2/6 with tags 3 -3/ -; high: packing; send for details.- Barton, 41, Bed- resistance 'phones with sponge earpads, with minster Down Rd., Bristol, 3. [7851 good class microphone all wired into plug, COPPER wires, enamelled, tinned, cotton rubber wadded, plug type 1011/10991, 10/9 and silk covered, all gauges; B.A. screws, pair; Metal boxes, black finish with quarter - nuts, washers, tags; bakelite and ebonite inch paxolin panels, fixing lugs and corner panels, tubes, coil formers; headphones, flexes. sockets, size 81/2x7%X31in deep, 6/9 each solder, etc., list s.a.e.; trade supplied. -Post Model complete; International Octal valve holders. Radio Supplies 33, Bourne Gardens, London, RF103 Paxolin chassis hype. 4/6 dozen; Metal -cased E.4. Tel. Clissold 4688. [8231 tubulars, 0.5mf, 350v, at 7Id C., wire ends, A LARGE quantity of radio components, in- 3 -2'6; Fifteen relays in carrying rack, mounted, eluding condensers, flexible couplings, 3 with cover, 42/6; Centre zero meter pole 3 -way switches, line cord, multi range 10 VALVE ALL -WAVE SUPERHET microamperes, £3. [89280-20 ohms meters. screened wire single and twin, S- MORE bargains for radio men. -Special this core flex., 2- and 4 -way fuse boxes, etc. - plated steel chassis, 131/2inx6inx or call L. Goodman (Radio), 9, month; 'Phone Ltd., RADIOGRAM CHASSIS. 21,1in, punched and drilled 5 -valve set, 7/-; Percy St., Tottenham Ct. Rd., W.I. Mus. 0216. 16x8mf 450v can T.M.C. elect., 6/ -; 25ml KIT sets, superbet A.C. or A.O. /D.C., 25v elect., 1/9; new valves, 6K7G, 6J7G, £7/19/6; amazing results, and easy to p.m. speakers, components 25A6G, 25Y5G, list prices; build without instruments; 61/2in, service kit containing 12 -1w, matched and pre -set; no drilling; equal to any SPECIAL 14/11; FEATURES 12 -1/2w resistors, 12 tub. condensers, assorted commercial receiver; elaborate build- 1 10 VALVE values, 3 trimmers, 1 -25mf 25v, -16x8 450v ing instructions; beautiful cabinets in wal- CIRCUIT. our price 20/ -; re- nut and bird's eve maple. -J, Morgan, 164, can., retail value 38/9, R.F. PRE -AMPLIFIER. sistors, lw 4/ -, 1 /2w 3/-; tub. cond., 4/6 doz; Whvteleafe Rd.. Ce,terham, Surrey. [8831 w.c. CARE ELECTRIC, 15, Little Newport St., transformers chokes, volume controls, v1 W.C.2. Tel. 6794. -Offers WAVE BAND EXPANSION. switches, coils, trimmers, chassis, many other London, Ger. lines all at rock- bottom prices; terms c.w.o., you guaranteed goods at the keenest prices, LARGE GLASS SCALE. large comprehensive stocks of radio c.o.d. (over £1), carr. paid over £1, otherwise from add R. Trading Co., 126, Warwick goods; 6v or 12v car radio vibrator trans- 3 STAGES A.V.C. 6d. -J. formers 75ma 300v II.T., size 3x3x2%, 15/- Rd., Kenilworth, Warwicks. [8797 ea; 7-core 14 -36 multi. -cable, 1/3 per yd; 30ma TREBLE LIFT CONTROL. MARVELLOUS opportunity for laboratory, pentode speaker transformers, small size, 3/3 (Operates on both radio and gramo- oil filled voltage regulating transformer, ea 35/- per dozen; 200ma 20 henries, tropi- phone.) in 180 -260v out., 218 -242v in., 2v steps ±1/.. calised smoothing chokes, 18/6; 120ma ditto., 50 cycles, L6 kVA wt. 5cwt, £25 on site; 12/6; 11in condenser mounting clips, 3/- per PLUS 6 db. BASS LIFT ON GRAMO- cable as Nov. advt.; rotary transformer, dozen; 0 -300v dc moving coil v.meter, 21/2in PHONE. (To restore bass cut on smoothed, in 12v out., 220v Boma, U.S. Army, with shunt, brand suitable for receiver. CCT46145; ex- R.A.F. in dial, complete external some records.) 12.6e 2.6A. L.T., new, 12/6 ea; Bin R. & A. P.M. speakers 24v out., 250v 70ma H.T., dozen; 10 OUTPUT. 12v carbon pile voltage regulators, 5/ -; iron with transformers, 22/6 ea, £12 per WATT PUSH -PULL keys, 2/6; 30 even amount of mixed resistors from 1 watt cored R.F. chokes, 3d; Morse - 20w tapped 0.1 watt, our selection, £2/5 per gross; P.F. condensers, 3d; 3 ohm down to resistors, 1 /6; mie. transformers 2/6, 6 -1 epicyclic reduction drives 1/2in spindle, lin vitreous side tone 1 /6; double pole change -over switch, long, 2/3 each; 2%in drum, drive, and spring, push button, G.P.O. type, 6d; Cord type 2 -pin for slow motion tuning, 2/9 complete; Inter- To export buyers we can confidently sockets 6d; air spaced ceramic trim- holders 1 and 6 (small), national octal valve with pins recommend RF103 to any firm abroad mers, 1 / -; bargain parcels ex- R.A.F., etc., omitted, 5/- dozen; small flexible 1/4in suitable for experimenters, magnificent oppor- spindle couplers, 5/6 dozen; 4 valve T.R.F. who contemplates making a high -grade tunity to secure first class equipment at scrap chassis, 91/2X4%X11/2 heavy gauge steel, Radiogram or Console radio receiver. prices, £1; ex- R.A.F. generators complete sprayed grey, 3/9 each; Pye plug connectors, with ammeter, regulator, cut -out, etc., output ea. 1/- The lively short -wave performance 12 -32v 9A, £7; generators only, £5/10; can 31/2 Gee Scope an oscilloscope of outstanding also be used as 24v 1/2hp motors or as repul- performance, price £35; descriptive leaflet coupled with the excellent quality repro- sion induction motor on 230v A.C. mains; on also a very large selection of money application; duction ensure an outstanding performance. please include postage and packing; valves, condensers, line cord, knobs dials, returned if goods unsuitable. -Moseley, Eler- etc.; special prices for large quantities; s.a.e. trical and Radio, Corse Lawn, Glos. [8905 for all enquiries. [8789 We will gladly make any alterations wireless bargains. selenium rectifiers, f.w. bridge SOUTHERN RADIO'S - NEW STC to the specification to meet individual Latest radio publications : Amateur Conn. dampproof finish, 17v la 12/1, 2a Transmitters' Construction Manual, 2/6; Radio 15/5, 3a 21/6, 4a 25/ -, all p.f.; 36v 2a 28/6, requirements. Repairs Manual, 2/6; Car and Portable Radio 4a 38/ -, 50v 4a 53/8, all post 9d. Heavy Manual, 2/6; Radio Valve Manual, alterna- duty type, Tin sq Al cooling fins: 17v 6a To home buyers demonstration tive and equivalent British and American 34/1, p. 1 / 16v l0a 43/8, p. 1 / -; 33v 6a - model now available to interested valve types, 3/6; Radio Circuits, receivers 63/8, 30v l0a 71/2, 28v 20a 139/3, 54v 6a transmitters, power packs, etc., 2/6; Short "89/6, 90v 65 141/- 110v 6a 166/4, all p. 1/3. callers to hear, and technical specifica- all valve -type chargers avail- Wave Handbook, 2/ -; Ultra Short Wave Hand- Replacements for tion now available on request. book, 2/6; Manual of Direct Disc Recording, able, for Philips 367 by return of post (dealers 2/6; Test Gear Construction Manual, 1/6; note). H.W., push -pull and v. doubler rects. Pocket Book, colour code, formulas, etc., for all duties. Specialised rectifying equipment It is hoped that a number (very limited Radio schools, etc. Kits, trans. rect. and 1 / -; Midget twin ganged condensers, 2inxlinx for labs., unfortunately) will be available for early 11/2in, 5/- each, postage 6d; Midget single gang rheostat for 16v 10a charger, £6 /12/6; 17v condensers, 11/2inxlin, 2/6 each, postage 6d; 6a, £411216; special 16v 5a, £312/6 vent delivery. R.A.F. Morse keys, 2/6 each, postage 4d; in- steel case 7/6 extra; 16v 4a, £3, case 7/6; Morse keys with bakelite 16v 2a 28/6, case 7/6. Transformers: 130w structors pattern for The above model is for A.C. Mains. case, 7/6 each, postage 8d; power packs for 17v 6a 47/6, p. 1/3. 220w 16v l0a M.C.R.I. pattern, input 90/250 A.C. or D.C., 65/ -, p. and 6. 1/6; 790w for lv 4a 35!6, We also have a similar model Type UNI 103 output 90 volts h.t. and 71/2 volts Lt., D.C., p. 1 / - 17v 2/3a 26/ -, P. 1 / -; 150w slider 24/6, p. 8d; 5.5amp lohm s. £2 each, post 1 / -; condensers, 1 plus, 1 plus 1, res., all values for DC /AC Mains. 2/6 each; ex -Army headsets, carbon mikes rotary 7/6, p. 8d. H.D. six -way 15a switches coil ear phones, guaran- 8/6, p. 8d. Fluorescent fittings comp, with and cushioned moving and starter gear: 40w from £6/9/3, * * * teed perfect, post free 12/6; ex -Govt. input tubes 1 mu metal core, 80w from £818, twinlamp £17/2/6, all carr. transformers, ratio :49 4/6, extra. Illus. list 2d stamp. C.o.d, on postal post 1 / -; ratio 1 :7 mu, metal core, 4/6, post 1 / -; Systoflex assorted sizes and co,ours, 2/6 goods only, otherwise c.w.o or pro-forma in 2mm voice. Trade supplied. Special, one only, per dozen lengths; Peribraid cotton petrol direct-coupled ARMSTRONG TELELY1g oN CO. LTD. covered plastic sleeving, 8/6 per 144 yards Delco -Remy 15v 200w (minimum generator with tank volt and ammeter and WARLTERS ROAD, HOLLOWAY, LONDON, N quantity). to run Pearce, 66, Gt. SOUTHERN RADIO SUPPLY, Ltd., 46, Lisle fuses ready £15- 'Phone : NORth 3213 Percy St., Londba, W'.O.L (nr. Angel). 18930 St.. London, W.C.2. Gerrard 6653. [892f

www.americanradiohistory.comwww.americanradiohistory.com 34 Advertisements Wireless World January, 1948 KITS of radio receivers from £7/8; 4- and 5- valve, new materials, table models. semi -midget; our latest kit. -Wylwyn Star 1948 has connections for gramophone pick -up, ex- MIDLAND INSTRUMENT Co. tensions to loudspeaker A.V.C., 6 hours average time for constructing; full details, dia- WINDING OFFER grams with each kit; c.w.o. or c.o.d.-Isher- GOVT. SURPLUS STOCK woods, Retne House, 81, Plungington ltd., Preston Tel 3348. Estd. 1936. [6788 R 1N;WINDING VOLTAGE REGULATORS, fitted H.T. rectifier, var. OSCILLOSCOPE units, ex- W.D.C.R. tube resistor, etc., 3/8, 36/- doz. SELECTOR SWITCHES indicator units, less 2áin tube, in steel 12/24 -v. Impulses and borne,, operating yaxley switch case, hinged glass window, removable cover and A ND brand new, 3/6, 30/- doz. CONNECTORS, 5C/430 bottom plate, contain felt -lined tube holder bakelite 2 -way, 4d., boxes of 50, 12/6. STEATITE and socket, tea -way tag strip, condensers and interlocking beads, No. 2, 10/- Ib. ELIMINATORS. resistances, 2 potentiometers 2 heavy duty 200/250 -v. A.C. output 120 -v. 30 -m /A. D.C. fitted keyed 4 -way sockets, one hole only through neon stabilizer, brand new. 40/ -. ATTENUATOR chassis, room for power supply, time base and LOUDSPEAKER units type 17, fitted control knob with pointer, Beale marked amplifier; offered at 10 /- each to clear, postage 0-100, brand new boxed. 3/6, 38/- doz. 1/2; few only keyed 4 -way plugs available at MAGNIFIER units type 2, emulate of transmitting 2/6 ea; s.a.e. for bargain lists.- Amateur Radio var. conde. and tapped plated coils, 2/6, 24/- doz. Service REPAIRS CERAMIC var. coeds. 50 -pf., 1 /-, 10/. doz. VITREOUS G6HP, Canning St., Burnley. [8816 wirewound resistors, 21 ohm. 15 amp., 5 / -, 48/- doz. COULPHONE RADIO, 58, Derby St., Orms- MICROPHONE transformers No. 2, 2,6. 20/- doz. kirk, Lanes. -" The return of post mail BY NO. 18 RECEIVEBScomplete with 4 valve,, 6 to Sm /es., order service." New goods only; post free over 2 -v. and 120 -v. 35/ -. No. BIB RECEIVERS, complete 5/ -; c.w.o. or c.o.d.; everything from a 6BA with 8- valves, 2.4 to 6.7 mks. 6.3 -v. and 250 -v. 60/- washer to a 1,250 volt mains transformer; JONES PLUGS with socket, to fit, 10 -way, 3/6, 36/- we have been told by many clients that we doz. 12 -way, 4/8, 48/- doz. ELECTRIC FANS, carry the most versatile and comprehensive 12 -v. brand new boxed. 30/ -, 215 doz. MOTOR GEN- stock of radio goods in the "TELECRAFT" 4 U.K.; valves, (TRADE ERATORS, type, 12 -v. 500 or 750 watts, 24 -v. speakers, mains transformers, chokes, line cord, MARK; 350 or 500 watts, 30 /- each, plus 5/- carnage. IRON- receiver kits, complete receivers, tuning units, CLAD S-amp. A.C. mains 4-position switches, 5/ -, coil packs, electrolytic's, tuning condensers, 48/- doz. Ex -GoY. ALL -DRY BATTERIES, fully Eddystone armatures, fields, motors, guaranteed by us, as previously advertised, 00 -v. S.W. components, etc., etc.; it will pay you to send 21/.d plus 11.v. 5/- ; sealed carton, of 8 batteries, 30/- stamp for our latest 45 -v. batteries, 55in. x 31ín. x llin., 3/ -, 30/- doz. 24 -page catalogue. [8885 bobbins and solenoids. NO. 19 SET AERIAL VARIOMETERS, 3i6, 36/- duz, SUPREME RADIO, 746b, Romford Rd., ROTARY TRANSFORMERS, easy to convert to Manor Park, London, E.12. -2 gang 000.5 200/260-v. A.C. motors, fitted double ended shaft, condensers with feet, 9/6; line cord, 20/- doz with ineteootione, brand new, 30 /- poet free. D.S. yds; tubular condensers, 0.1, 0.01, 0.05, 5/6 COMPASS variation correcto., brand new boxed, doz; 8mfd can or cardboard, 39/- doz; can 12/6, post 1 / -. SPARK COILS, fitted trembler and type 16mfd, 4/3 ea; 16+8, 7/- ea; 16 +16, condo., 12 -v. approx. 010. spark, brand new, 12/8, 7/3 ea; 8-/-8 +8, 7/3 ea; 24+8, 7/3 ea; Post 9d. AIRCRAFT COMPASSES, type Pll, alcohol 8 }8, 6/- ea; 4mfd can, 15/- doz; condenser float, in wood cases, 40/- poet free. clips, Southern Trade Hundreds of other interesting Radio and Electronic 4/6 doz; resistances, sizes from 22011 items, send for our Nov. /Dec. Bets. 2d. with s.a.e. to 2.21neg t,6w, 3/- doz; assorted W.W. res, Orders over 30/-, po,' free. No C.O.D. under 20/- 1 and 2w, handy sizes, 2/6 doz; volume con- Services Ltd. pleuse. trols, 50k, short spindle, 12/. doz; standard v /cs with sw long spindles, 100k and 50k, 42/- doz; 5k up to 2meg, 4/6 ea; 250k, less 297/299, HIGH STREET Moorpool Birmingham, 17 sw, 2/6 ea; 2,0004 W.W., job line, 12/- doz; Circle, wave all glass dials, 3/6 ea; 1 +1 condensers, CROYDON Tel.: HARborne 1308 or 2664 350v w dc, 250v w ac, 6/- doz; midget knobs, less grub screw, 1/- doz; 4 -pin ux ceramic 'Phone : CRO 4870 valve holders, 1/- doz; Mazda octal holders, 3/6 doz; anchoring tags on Paxolin panel, 3/- gross; grid cap and lead on panel with 574 res attached, 4/- doz; Paxolin panels with tags, 3- 4 -8 -11 way, 3 ways, Id; !watt carbon -res. 27,000, 75,000[2, 4/- doz; 10,000 YOU 5w, 5/- doz; .0005 mica fixed condensers, 2/6 doz; Westectors, 1/8 ea; meter rectifiers, 5ma, 5/6 ea; Coractual plug and socket, 1 /6; earphone insert or mike, 3/- can become ea ; ex-Government meters, calibrated 5,0004 -0 ma range 0 -6, 0 -1.5v and 0 -3v mc, internal resistance, 25012, size 2 %in, flush mounting non -splint glass, £1 ea; everything a first -class for the service engineer. Send s.a.e. all enquiries. 6d extra packing and postage. No c.o.d. [8962 SELENIUM metal rectifiers, H.T. rectifiers, RADIO charger kits, etc., all new stock; adu postage 6d up to 15/ -, 1/- above; circuit and interesting data supplied; S.T.C. 12v 3amp ENGINEER selenium rectifier with 50watt transformer and ballast bulb for 2v to 12v charger, no rheostat or ammeter needed, 45/ -; ditto, witn 2amp rectifier, 36/6; ditto lamp, 34/ -. We are specialists in Home - Transformer, rectifier ballast bulb Inc 2v, 6v Study Tuition in Radio, charger, with 3amp rect, 42/ -; 2amp, 33/ -; wit' mains arem transformer, 75watt size with 12v 4amp Television and Mathematics. rectifier and ballast bulb for 2v to 12v Post coupon now for free charger, 62 / -; 140watt transformer with giant IYFlv fOLOFiP type 12v 6amp rectifier and ballast bulb for tel.s you all about the complete booklet and learn how you 6v, 12v charger, £5; makes a really heavy range of Henley SOLON Electric can qualify for well -paid duty car battery charger; mains transformer Soldering Irons, for the standard voltage employment and 2v 0.5amp rectifier, makes ideal trickle ranges of 200/220 and 230/250 : 65 watt or profitable charger for 2v cell, 13/6; guaranteed one and 125 watt models fitted with oval - spare -time work. year. Heavy duty charger kits for small radio tapered bits or pencil bits and 240 watt store, mains trans, selenium rectifier, ballast models fitted with oval- tapered bits are bulb for one to 20 cells, lamp, 95/ -; ditto available. 2amp, £6/5; ditto 1 to 12 cells, 2amp, 95/ -. Write Today for the new folder ref. Y.lo Rectifiers only, 12v 3amp, 21/ -; 12v 2amp, describing T. & C. RADIO COLLEGE 12/6; 12v 1.5amp, 10/6; 12v 5amp, 28/6; giant' 12v Samp with large aluminium cooling North Road, Parkstone, Dorset fins, 32/6; 24v 2.5amp, 32/6; 24v 4amp, 42/-; also 6v 2amp, 9/6. Slider resistances, 0.5- ohms 10amp, 15/ -; 7.5ohms 5amp, 25/ -; 10- ohms 4amp, 26/ -; ammeters, 0 -3 and 0 -6- (Post zn unsealed envelope, Id. slump) amp, 12/6, H.T. rectifiers, new small suave selenium type for ac /dc sets, 250v 60ma, Please send me free details of your Home - 9/6; full wave bridge; 250v 100ma, 15/6; Study Mathematics and Radio courses. eliminator type, 120v 20ma, 7/ -; ilov 6Oma, 9/ -; 350- 0 -350v 80ma, 13/6. Instrument rectifiers, 5ma for Avo, Avominor, 12/6; NAME "Victor" bell transformers, 5/ -; Rola Bin P.M. speakers, leas trans, 17/6; crystal W. T. HENLEY'S ADDRESS diodes, 2/6; Rothermel Senior bakelite pick- TELEGRAPH WORKS CO. LTD. ups, 52/6; Lustraphone m/c mikes, 65 / -. w.W.87. Uplands (Engineering Dept.) CHAMPION, 43, Way, London, 51 -53 London, E,C.I i N.21. Lab. 4457. [8963 Hatton Garden,

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 35 VALUE! Matt has it. Special offer, head- RADIO components. -50 brand new useful phones with lead and jack plug, 5/6 per components to a list price value of £20 pair (boxed 2 pairs); speakers, P.M. (less for only 50/ -; our assortment includes P.O trans.), 4in 17/6, 5in 15/6, output trans. to standard relays, air dielectric condensers. match, 5/6 each; condensers, 0.1, 0.01, 9/. doz.; selenium rectifiers, wire wound potentio- 2, 4, 8 mid, 16 +8 mfd, 8 +8 canned; line cord, meters, transformers, chokes, electrolytics, 3.3 amp (60 ohms per ft), 2 -way, 1/6 per .\ \II /// jacks, insulators, signal lamps, plugs and yd, 3 -way 2/6 per yd; volume controls (Cen- sockets, tag panels, i.f. transformers, r.f. tralab), various values, L/S 3/6, W/S 4/9; chokes, block condensers, etc., etc.; our put 'rystal pick -ups, Rothermel, De Luxe, £2/16/3 chase of a complete Ministry of Supply store (int. P. Tax); 2 -gang condensers, 0.0005 (not makes this unprecedented offer possible; order midget), 5/6; television cable (aerial lead -in). Laej a sample parcel and come back for more. - 1/6 per yard- large assortment of B.V.A. and MM. O. S. 24, New Rd., London, E.l. [8745 U.8. valves always in stock; let us have your has for mnquiries. AMATEUR giving up experimenting -Matt Radio Service, 29, Castle St.. o 0 sale large quantity components, includ- Kingston -on- Thames, Surrey. Kingston 8353. ing Rothermel 5.12 pick -up, boxed, £2/7/6, SPECIAL ex -Gov. Clearance Offers :-CR Philips crystal do., used £2/7/6; Ferranti tubes 3in and 5in, 50/- ea MC meters, cabinet extension loudspeaker (marked), £2/2; :in flush 0.40 and 0 -20v 7/6 ea; 0 -5ma Ferranti projecting 0- 71/2ma meter (se recti- Dell by Turner, fier type), £1/17/6; ammeters, various ranges, tester 0 -3 or 30v 3in scale. at 5/6 condensers, and 12;6. Vibrator packs, 12v, 200v, 100ma. THE "FLUXITE" QUINS AT WORK each; 400v, 650v 800v smgothed in case, 30/- ea, 6v ditto 30-. working; 1V.W.Q.A, chassis with valvebolders, Rotary transformers, 12v "Look who's there! Televising tonight! 9/6; 470 -0 -470, etc., transformer, 35/-; H.D. 275' 110ma, 500. chokes, 150ma, 17/6 each; large quantity of Soma 12/6, 12v 480v 40ma. 10/6. Ele,s. Why it's 01 demonstrating FLUXITE," valveholders, tubulars, resistors, state 32mfd 450v 4/ -. 50 assorted brand new res etc. rod From within came a cry needs, lists for s.a.e.-15, Bibury Rd., Bir- cons. ceramic, silver mica and tubul;,r. mingham, 28. [8845 and 1/, and 1 watt mounted on panels reail/ "Televising my eye! F1hITH RADIOCRAFT, Ltd., the Leicester to use 9/6 per 50, 16/. per 100. Ceramic I've soldered myself in here tight! specialists, offer from comprehensive stamp trimmers, 15- 29mfd, 3/- doz. Yaxley " their stocks : 20, 40 and 80m Eddystone 4 -pin coils, ype 10 -way selectors, 1/3 ea., 12/- doz. Panel 5/- set of 3; tuning condensers, standard 3- indicator lights, red, blue, green or clear, 1/3 gang, 0.0005 ceramic insulation, grin spindles Bulgin red 1/9. Adjustable bench lamp 12/6 at both ends for clockwise and anti -clockwise ea. 12v vibrator trans. 100ma 9/6. operation, 7/6; standard single -ended 3 -gang 'oloured knobs engraved, brilliance, focus, See that tine FLUX ITE is always by 0;000160, 7/6; 3 -wave band S.M. drive with A. B or (' red, blue yellow and white g -ass and 7inx4in escutcheon, 12/6; epicyclic till circular with knurled edge 1:,in standard you drives. 5 :1, 1 /6; sleeving, 12, 1. 1i /, 2mm, 36 - in the house garage it. 3d ea, 2- doz., 18!- gross. Black push - - - - yds 2/6, 144 yds 10 / -; meters, 3in flush type, ,u lope 4d 3;- doz., doz 6d ea 2in plain %mu A.C., 10- D.C. 1 -0 -1ma D.C., SW and USW chokes, 1/- ea. Dust tuned workshop - wherever speedy 0 -20v 0 -10ma 0 -12A R -F., thermocouple, all at 12/6; ditto, -oils. medium luz. wave, 1/9 each., 15/- 0 0 D.C., 350 -0 -350 millivolts p: tat mutipurpose transformers can be used soldering is needed. Used for -12A D.C.. -20A mains D.C., all at 15/ -; 0 -500 mieroamp Ferranti, is output, chokes, etc., a very useful 25/ 2in square flush 0 -lna. 25/-; Everitt lee,, with 12 -way solder tags on pax, 4/- over 40 years in Government -; Balanced F.dgecumbe 0- 5,000v m /roil, 34:in, 25/ - mains armature phones complete with transformer, 295- 0 -295v BOma. 6.3v 2A, 5v ack plug 6/- set. LR díaphrm. type 4/- set. works and by leading engineers or \IC type with mike 12/6 set. All 2A, 19/6; Stanelco soldering iron 200 250v, brand new. list 21/ -, our price 1.2/6; G.E.C. 0.5 -750v i /ogle MC units 4/6 ea., MC hand mikes 6/6 and manufacturers. Of all Iron - block condensers, 6/- doz.; owing to the im- ma. If.R. earpieces 1760 ohms 1/6 ea. possibility of listing many separate items we Valves, new, 9001 9/6, 6AK5 10 / -, IT4 10/ -. mongers-in tins, 10d., 1 /6 & 3/ offer a special bargain parcel of ex -Govt, com- Mallory 6 or 12v vibrators 8/6. AC power ponents having a retail value of over, £5, for Jacks 230v, 700v 70ma, 12v la, brand new only £1; over 50 useful items, our selection, n ease with valves and smoothing, 55/ -. but satisfaction guaranteed or money refunded; 3uecial 1 doz assorted pots and ves long and latest lists of many other items free on request; ;hart spindles. 500 ohms to 14 meg, 12/ -. trade supplied. 3rand new R1585 12 valves midget receiver TO CYCLISTS ! Your wheels FRITH RADIOCR.AFT, Ltd., 69 -71, Church or 250 mes with valves, £4 /10. S.a.e. for Gate. Leicester. Tel- 58927. [8925 ists please. CLEARANCES, Ltd., 27. Tottenham T. ENGLISH, The Maltings, Rayleigh Rd., will NOT keep round and true RADIOCourt Rd., W.1. Mus. 9188. -Electrolytics, flufton, Essex [8688 8mf 170v 2/3, 8mf 450v 3/3. 16 /24mí 350v unless' the spokes are tied with 4/ -, 25mí 'IF'EAKER trans. tapped output, ultra - 5/6. 16+16mf 350v 5/6. 32mf 350v midget, 5/ -, midget 5/6, standard 8 / -; 25v 2/ -, 50mt I2v 1/9, 100mí 12v 1 / -, 100mf output (6L6 valves, A/A load 6,600- fine wire at the crossings AND 6v 1 / -. Meters 0-30ma 21/2in scale flush Aims), output 7.5 and 15ohms, 21/ -; P.P. mounting 8/6. lma 2'ldn scale flush mounting, nodulation trans. for 807 valves, audio power SOLDERED. This makes a much calibrated 0 -100 15/11, 0 -150ma 2in square 50 watts, 2 -1, at 12/6; chokes, flush 9/6, 0 -200ma 21/2in flush 9/6, 0 -750 ultra- midget scale 3Oma 5/ -, midget 50ma 5/6, standard 100ma stronger wheel. It's simple -with micro amp plug in 21,/in 9/6. for use with thermocouple. 1 /6,, by. duty 15012C'Oma 12/6: "Rues" tun - calibrated ng assembly, assembled and fully wired for FLUXITE -but IMPORTANT. Ex- R.A.F. visual indicators. 2 types still .m,i. waves. On chassis, dial, pointer, I-F.s coils, available, type 3 containing 2 complete ,adders, etc. Series heater wiring for use with Weston 300 micro amp movements 51 -, cross- ìk8g, 6k7g valves, complete, factory tested and over needle type, as used with R1155 with ligaed, with circuit, £5; 5v superhet, fully 2 60 micro amp movements, 5/11. High killed chassis, 111/.,x 5,zx2%in, 7/ -; AVO voltage condensers, 0.1 12,000v test tit filled, 6 / 0.0005 2 gang tuning condensers with rapacity bridge, £11; single core screened The FLUXITE GUN puts -; condensers ;able, per yard 9d; twin ditto 1 / -; nuts/ epicyclic drive, 10 /6; mansbridge ;crews, 4, 6, 8 BA 6/- gross (2 gross in all); 1mí 350v 8d, 1,000v 1/3, 2ml 300v 10d, 4mí 4/6, 0.25mf 2,000v 1/9; 0.25 2,500v 2/ -. 'entralab volume controls with switch, 5,000 - FLUXITE 600v with hhms to 1 meg, 6 / -; English and American all working V. cathode ray indicator units naxolin valveholders, 8/- per doz; slow motion where you want bin tube (non -persistent), 7 valves (4 EF50 and Irons drives, 3/ -; Epicycle drives 3/3; SML 3 EB34) available to callers only at £2/19/6 fiats, 2/ -, 5x51/ 2/6; 2 -gang it by a simple ex-army 38 sets, 5 -valve trans -rec. complete coloured 4x34/ valves and junction box (as used ; ondensers, 0.0005mid 11 /-, ditto Tiny Tim with 5 2v in tanks with 19 seta), 45/ -; 2 section aerials ltted trimmers, perspex dust cover, 2x11/:X pressure. Price carbon .1/2in, 17/6; 2 -gang, 0,0001mfd 6 / -, 2 -gang for same, 7/6: throat mikes, 3/6; with switch in handle, 6 / -: plit stator, 0.00017mfd. 6 / -; 3 -gang, 0.0001 - mikes, power type 1/6, or filled, 2/6. power units with rotary trans., and carbon aid, 7/6; condensers: Electrolytics, 24 plus 300v ;mid, 8mfd. 500v, 4 / -; mfd, pile voltage reg., input 24v, output 350v, 7!6; 8 with 12v in will give 200v '5v, 1 / -; 4 mfd, 12v, 9d; 20 plus 20mfd, ALL MECHANICS WILL VE\ 30ma, 6.5v 3.5a 50v, 7/6; 32mfd, 350v, 5/ -: 25mfd, 25v, 2/6; 30ma, 15/ -; Vit, res. 10w 50052 1/6, 20w with gaper, 2mfd, 1,000v, 3/ -; 4mfd, 100v, 9d; drive clips 2K, 8K, 2/ -; 40w 14K tapped at 2K, 3/ -; square plane M/L with escutcheon. metal rect. 12v 1,lra, bridge, 3/6; mains ssemblies; 2 adjustable ',Jess, pointer etc., 11 /6; ditto full vision, droop) ers 0.2a 1,000í2, 3/6 (with AML 12/6; relays, 400ohm 12v 3/ -, 100-25ohm taps or 12v 3/6; line cord, 3way 0.3amp per yd WANTED, EXCHANGE, ETC. ,/ -; ditto 2 way 2/ -; Weymouth all wave coil URGENTLY wanted, record player for 110 - ack with circuit, brand new, 36/6; Weymouth volts d.c. -Box 4602. [8967 nidget i.e. I-F. trans. 465 Kcs, brand new, IT SIMPLIFIES ALL SOLDERING WTD.- Hallicrafter 8X28 or Hammurland [8859 rr. 18/9; standard I.F. trans., pr. 15/ -; ditto super pro., parties. -Box 4465. each 2/ -; M/L t.r.f. coils EXCHANGE AR88D for SX28A or super .F.s 2Mcs, with for Book on the " eaction, circuit, pr. 7/6; M/L 1..c, t.d.f, pr. Write ART OF " SOFT pro., cash either way. -Box 4467. [8861 0 /6; BML, aer & osc, pr 10 /6; sleeving, all SOLDERING and for Leaflets on CASE- HARTLEY- TURNER " Box Boffle. " -16, Ches. [8844 !olours, I mill, 35/40 yard reels, 1 /6; twin HARDENING STEEL and TEMPERING Banbury, Dr., W. Timperley, resistance, 300 ohm, 1 amo, WANTED, any quantity Litz wire, one wave 'ariable 25/-; 1d. 'axley type, 3 -pole. 2 -way, 2/ -, 4 -pole 3 way TOOLS with FLUXITE. Price each. winder. pref. E.T.A. type W- -Box 4520. / -, 4 -pole 4 -way 3/6; nice type. DPDT, 2/6; WANTED, " W.W.," Feb -, May, July, omprehensive lists monthly; 21/5i stamp en- FLUXITE LTD. August, Sept., Oct., '47; reply stating tuiries; postage extra all orders. prime. -Box 4492. [8891 ), GHEENLICK, Ltd., 34, Bancroft Road, (Dept. W.W.), Bermondsey Street, 5.E.1 SERVICE sheets purchased and cash paid. - 'ambridge Heath Road, London, E.I, Tel. State quantity to Bulls, 246. High St., tepne: Green 1334 1.8799 Ilarlesden, N.W.10- (8857

www.americanradiohistory.comwww.americanradiohistory.com ;G Advertisements ECliPtiti World Ir01:((f1'1'. 101S ANTED. -MSS ED45 recorder, turntable, W cutting head and mechanism- only. -Wade. 29, Clarendon Rd., Leeds, 2. [8935 MORE BARGAINS WIRELESS WORLD," Dec. 1945, Jan. " EX -ARMY RADAR RECEIVER TYPE and Dec. 1946, Feb. 1947, state price. - Bryant, 31, Osborne ltd., Wolverhampton. R.D.F.7, Covers 150 -165 mc's with variable Specialists OUANTITES of ex -Gov. valves, types tuning. 10 valves as follows : 6 type SP41, b6 VR53, VR56 and VT52 or equivalents, 2 type EA50, I type RL7, 1 type RL16. Manu- wanted for cash.- N,R.S., 66, Parkhill Road. factured by R.G.D. BRAND NEW IN London, N.W.3. [8768 ORIGINAL CASES. ONLY 59;6. (Carriage, ALL recording and reproducing equipment in etc., 7/6). and accessories for amateur and profes- 2 VOLT VIBRATOR POWER UNITS. sional work. -Bristol & West Recording Ser- As used on the Canadian 58 set. Fully vice, 79, Old Market 6t., Bristol, 18907 5,001.6890t07,O01Ò to smoothed, 2 v. input, giving output of 1.5 v. LARGE quantity P.O. relays, coil FI,T. 10,000 ohms contacts, 2M, or 2C.O.; L.T. and 90 v. and 180 v. at 35 ma. Size P.O. relays, coil 2,500 to 5,000 ohms contacts, HIGH POWER - HIGH QUALITY Bin. x 3)in. ail in. Operating details supplied. 2B. 3M-Particulars to Box 4463. [8855 ONLY 60/- (carriage, etc., 2, -). Spare 2 v. GW.1'the SMITH & Co. (RADIO), Ltd., require vibrators IS - each. following : new or second -hand radio AMPLIFIERS. A very fine ex- R.A.F. receivers and radiograms; all classes of radio battery amplifier. Easily convertible into test equipment; highest rash prices paid. a loud- speaking telephone or office inter - G. W. SMITH & Co. (RADIO), Ltd.. 2. Cecil PUBLIC ADDRESS communicator, or can be used as amplification Rd.. Southgate, Loudon, N.14. 7'el. Enter- stage for pick -up, etc. Complete with valves prise 5463. [5116 types QP2I and 210LF. Power supply 120 v. URGENTLY needed for export \I.E.A. pat terns 72, 74 and 4a laminations; Scott's V. IN WOODEN H.T.,2 L.T. BRAND NEW pattern 130 and 4a laminations or equivalent 25 /6). SYSTEMS TRANSIT CASE. ONLY -(carriage,etc.,2 in iron; 39s gauge copper wire, enamelled. - ELIMINATORS. Made to Air Ministry Otters to A.W.F. Radio Products, Ltd specification by Atlas & McMichael. 220- Borough Mills, Bradford [8526 250 v. A.C. input, 120 v. D.C. output. ONLY of E.M.G. gramophone unfortu- 55.- (carriage, etc., 3, 6). OWNERnately moved into 220v DC supply area TRANSMITTER KITS. The complete wishes to exchange AC gramophone motor for M.O. unit and the P.A. Output unit used on a universal motor in good condition, or would the famous R.A.F. TI154 TX. Only requires buy outright a new or secondhand motor. - AMPLIFIERS construction of the valve section to Reply to Rourke, 38, Belgrave Court, W.4. the buy for cash, new, used, radio, eleetri- from ISO W IkW complete the TI 154. Circuit details supplied WEcal equipment, all types; especiallç to enabling this to be done, or can be used as a wanted, radios, radiograms, test equipment, basis for any TX. BRAND NEW IN motors, chargers, recording gear, etc. -It you MAKER'S CARTONS. ONLY 49,- (carriage, want to sell at the maximum price call, write etc., 6/6). or 'phone to University Radio, Ltd., 22, Lisle Lists. St., Leicester Sq., W.C.2. Ger. 4447. C.W.O. please. S.A.E. for REPAIRS AND SERVICE MAINS transformers rewound, new trans formers to any specification. W. Bryan Savage Lt THE RADIO CORNER (ç tl. MOTOR rewinds and complete overhauls; first 138, GRAY'S INN ROAD, LONDON, W.C,1 class workmanship, fully guaranteed. WESTMORELAND ROAD, LONDON,N,W. (Terminus 7937) F, M. ELECTRIC Co.,, Ltd., Potters Bldgs, (2 mins. High Holborn, 5 mins. from Warner Gate, Nottingham. Est. 1917. from Tel. 3855. Telephone : Colindale 7131 King's X) repairs, British, American. Open until I p.m. Saturdays. TOUDS'PEAKERany make, moderate prices.- Sinclair Speakers, 12, Pembroke St.,' London, N.' Terminus 4355. [3308 instrument repair?. Electrical test TESTinstruments repaired and recalibrated. Quick service, guaranteed work.- Elettrice, 99, George St., Croydon. [8698 OIIDSPEAKEIIS repaired; transformers, TRANSFORMERS & CHOKES Co-s J J clock coils, chokes, rewound; prompt at- High Quality Vacuum Impregnated tention; prices quoted. -E. Mason, 5, Balham Grove, Ballranr. London, S.W. [7667 L LECTRICAL measuring instruments skil- v 1 fully repaired and recalibrated.- Electrical AUSTIN MILLS LTD. A vi instrument Repair Service, 329, Kilburn Lane, LOWER CARRS R for all purposes I London, W.9. Tel. Lad. 4168, [6935 D EWINDS and conversions to mains and STOCKPORT GREENFORD, MIDDx. 'WAXLOW 2300 1L output transformers, from 4/6; pp equip - Telephone : STO. 3791 Established 20 years. ment a speciality. -N.L. Rewinds, 4, Brecknock Rd., N.7. Tel. Arnold 3390. [6283 SERVICE with a Smile. " -Repairers of all fs7 types of British and American receivers; THESE ARE IN STOCK coil rewinds; American valves, spares, line cord. -- F.R.I., Ltd., 22, Howland St. W.1. kcs. Principles of Radar. By M.I.T. 25s, Museum 5675 [1575 100 Postage 9d. REPAIRS to moving coil speakers, cones. coils fitted field rewound or altered; QUARTZ The Mathematics of Wireless. By R. speaker transformers, clock coils rewound, Stranger. 7s. 6d. Postage 4d. uaranteed satisfaction, prompt service; no CRYSTAL mains trans. accepted. Radio Engineering. By F. E. Terman. L.S. REPAIR SERVICE. 49, Trinity Rd.. UNIT 30s. Postage 8d. Upper Tooting, London, S.W.17. Balham 2359 Classified Radio Receiver Diagrams. STURDY rewinds, mains transformers, chokes and fields; we give prompt delivery Type E. IOs. Postage 5d. By M. Squire. 6d. and guarantee satisfaction; 14 years' experi- Radio Test Instruments. By R. P. Turner. ence; prices an request-Sturdy Electric Co., Q5/100 25s. Postage 6d. l.td.. Dipton, Newcastle -on -Tyne. [4316 mains, output transformers, Wireless Coils, Chokes and Transformers. REWINDS;fields, chokes, etc.; wave- winding and for Secondary Frequency Standard By F. 1. Camm. 6s. Postage 4d. II.F. coil repairs, all makes; 26 years' experience; reasonable charges: prompt delivery. Accuracy better than 0.01";,. * New angle The Wireless World Valve Data. 2s. - * I1. W. Forrest. Shirley, Wham. Shi. 2483. of cut give a temperature coefficient of 2 parts i Postage 2d. of all types of transformers a million per degree Centigrade temperatur REWINDINGchokes, etc.; quick service; motor rewinds change. Vitreous silver electrodes fired direc Radio Valve Equivalents Manual. By new * of all types; replacement bobbins supplied; on to the faces of the crystal itself, giving permar Bernard B. Babani. 2s. 6d. Postage 2d. transformers to any specification, -Radio & Transformer Services, 570, Manchester Rd. ence of calibration. * Simple single valve circui The Practical Radio Reference Book. gives strong harmonics at 100 kcs. intervals up t Ed. by Roy C. Norris. 8s. 6d. Postage 6d. Hollinwood, Lancs. [8638 and transformer repairs 2Q Mcs. * Octal based mount of compact dimer LOUDSPEAKERby return of post we offer the sions. PRICE 45 ¡- Post Fre We have the finest stock of British and " almost "; quickest service in the trade, at competitive Full details of the Q5 /100, including circuit American Radio Books. Complete list prices. Send ld for our monthly service bul- are contained in our leaflet Ql. Send stamp letin, Dept. W.- A.W.F. Radio Products, Ltd.. your on application. Borough Mills, Bradford, Yorks. Tel. 22838. to -day for copy LOUDSPEAKER repairs, any make, reason THE MODERN BOOK CO. able prices, prompt delivery, to the trade THE QUARTZ CRYSTAL Co., Ltc (Dept. Vv30 and quality fans; 25 years' combined expert 63 -71 Kingston Road, ence with Rola, Magnavox, Goodmans, ('ele. NEW MALDEN, SURREY 19 -21, Pracd Street, London, W.2. kn.-Santini Servire Bailin, 80, Nichnnnul Telephone : MALden 0334 Rd., Kingston on Thames Kin 8008 1497.

www.americanradiohistory.comwww.americanradiohistory.com January, rggb' V1'irle*a N'orld Advertisements 37

MAINS transformer rewound and constructed to any specification ; prompt delivery.- Brown. 3, Bede Burn Rd., -Jarrow. [3460 GALPINS AREWIND service which duplicates or ELECTRICAL STORES modifies as required; transformers, loud 408, HIGH STREET, LEWISHAM, speakers, etc; prompt returns.- Raidel Services, LONDON, S.E.I3 49, Lr. Addiscombe Rd., Croydon. Cro. 6537 REWINDS, mains transformers, speaker field Tel. : Lee Green 0309. Near Lewisham Hospital. coil, chokes, high -grade workmanship, 7- TERMS : CASH WITH ORDER. NO C.O.D. day delivery; new transformers constructed to EX- R.A.F. CALIBRATOR UNITS TYPE 18. customers' specification, singly or in quanti- 4040000000 Metropolitan Radio Service Co., 1021, These units consist of 1 -100 k/c Xstal 2 -EF ties.- 50 valves and numerous other components (new Finchley Rd., N.W,11. Speedwell 3000. [3719 *d'F sermerice months' guarantee , any boxed), 35;- each, P; F. HOUv, 24 transforR rewind mains outputs ltlr. anb Uttíloen EX- U.S.A. ARMY HAND DRIVEN GENE- and i.f.s., etc., all types of new trans(., etc., RATORS (as new). Output, 162 volts at supplied to specification; business heading or tuíol) alt rrabrr5 a 60 m /a, 3.1 volts at .3 a., complete with all smooth- service card for trade prices.-Majestic 33 finding .liagram ,35/ -each. Ditto,425 ing Co., Bournemouth. chakesan. circuit 180, Windham Rd., t%iCtrö Cbrí%t11ia>5 volts at 115 n, /a, u.+ volts, 32 m /a, 6.3 volts at 2.5 COIL specialists. -Tuning and oscillator coils, anb amps., 6.3 volts at .43 amps.,at So,/- each. I.F., L.F. and stains transformers re- A SPECIAL LINE OF VOLTMETERS. wohnd and wound to specification; wavewind- #)a}lp)1 PA) pear First -grade Moving Coil 0 to 20 volts, tin. square Log. L.S. repairs.- Electronic Services face, new boxed, 10/- each, in lots of 3, 25/ -. IR.T.R.A.), 17, Arwenack St., Falmouth, Cornwall; and 49, Uxbridge EX- R.A.F, MICROPHONE TESTERS. These Rd.. Ealing, W.5 -UPS, replacement coils for Garrard Td f 'fA' *<\fi 4*-A í0 F-k consist of a Ferranti 21in. m /coil 0 to I m/a meter PICKtype, etc., 5/3; rewinds to clock coils, 00 with Westinghouse Rectifier incorporated, cali- fields, transformers, etc., replacement Marconi, brated at present 0 to 10 volts, microphone trans- I.M.V., mains transformer coils, 18/ -; 48- former, jacks, etc., all contained in polished teak hour service; trade enquiries. Radiocrafts, 10, NOW IN STOCK case, size 61 in. x51in. Condition as new. Price Goodmayes Rd., Goodmayes, Essex. Tel. 32;6 each. Seven Kings 4557. - [8505 MAINS TRANSFORMERS. (New.) Tapped COILS and transformers manufactured to specification single or quantity; rewinds IMMEDIATE DELIVERY 200¡250 50 cys. I ph. Output350 /ujd50 input volts to all types of coils, transformers, etc.; quali- v. 180 m /a, 6.3 v. 4 a., 5 v. 3 a., 4 v. 4 a., 37/0 each, fled consulting engineers available to help SPECIAL I; 6 post. Another 500/0 /500 v.150 m /a.,6.3 v. 4 a., solve your problems; first -class service and 5 v. 3 a., 4 v. 4 a., 41/6, post 1/6, Another 6, 12 delivery. -Millett & Holden, Ltd., 2, Pembury VARIABLE SELECTIVITY I.F. TRANS- and 24 volts, 10/12 amps., 45/- each, post 2/ -. Rd.. Westcliff-on -Sea, Essex. [8480 FORMER Another 141- and 17( volts at 30 amps. (auto REWINDS. -Armatures fields, transformers. 465 kas., giving the choice of three degrees of wound), E4 /15 / -, post 2/6. Another 70J/0/700 v. pickups, vacuum cleaners, gram. motors. selectivity. 1. High Selectivity. 2. Medium. speakers new cones and speech coils, 80 m /a., 12 v. 1 a., 4 v. 2 a., 30/-. Another, 4 refitted 3. High Fidelity. Controlled by three 6.3 v. and 12.6 volts at 12 amps., 45/ -, post 2/6. All guaranteed and promptly executed. New position switch. Iron cored, screened. The vacuum cleaners, most popular makes. Send Another 17( and 20 volts at 30 amps., 95,/ -, post 3/6. second I.F. is centre tapped on both primary TRANSFORMERS (Mains stamped addressed envelope for list of radio AUTO WOUND spares and c.o.d. service. -A.D.S. Co., 261 -3 -5, and secondary to reduce damping. Circuit 6, 10, 19, 175, 220, Boosters), tapped 0, 200, 225, Lichfield Road, Aston, Birmingham, 6. [8238 diagram supplied. l'rice £1 per pair. 240 and 230 volts at 1,500 watts (new ex- Govt.), LOUDSPEAKER repaira.-L. Cottenham, [5 /10 / -, post 5/ -. the leading repair specialist of the North, NEW CIRCUIT AUTO WOUND TRANSFORMERS (Voltage for your loudspeaker repairs; all types re- Changer), tapped 0, 10, 20, 25, 90, 130, 150, 19U, paired, fields rewound to any resistance, field A /C.T.R.F. Nigh Fidelity Receiver. 5 Valves. 210 and 230 volts at 1,000 watts. (It will be seen replacement bobbins, keen competitive prices 2 H.F. stages, infinite impedance detector, that almost any voltage can be obtained from this and quick service; send to L. Cottenham, Triode output. Two wavebands, Medium Loudspeaker Repair Factory, Whetley Lane, and Long. Provision for P.U. and Ext. Transformer.) Price E5/10/-, post 5 / -. Bradford, Yorks; MAINS TRANSFORMERS, EX -GOVT. In- enquiries immed. attention. Loudspeaker. Blue prints, 3/8, two practical NATIONAL RADIO SERVICE & TELE volts 50 cys. I ph. Output, 12} volts and one theoreticaL put, 230 VISION CO. -Trade service engineers; C.T. at 25 amps., 45/. each, carriage 5/ -. immediate service any district; rewinds to all METERS ALL BY WELL -KNOWN types transformers, armatures, motors, loud- 6 -VALVE SUPERHET CIRCUIT MAKERS. Ex- Govt., new boxed 1st Grade speaker cones, speech coils fitted, and British 3 Wavebands. A.C. only. Moving Coil. 0 to I m /a., 21/- ; 0 to 40 volts, American components and valves; enquiries A circuit that will please the most critical. 15/- ; 0 to 10 amps., 15/- ; 0 to 5 mja., 17/6 ; invited for contract trade service; multiple This circuit has been designed to receive all 0 to 20 m /a., 17/6 ; 0 to 50 m /a., 20/- ; all tin. transformer winding. -63, High St., St. John's Wood, N.W.8. worthwhile stations on the medium wave fsd. 0 to 3 m /a., 22/6 ; 0 to 50 m /a., 22/6 ; 0 to Primrose 6725. [6752 band (200 -540 metres) a 200 m /a., 22/6 ; 0 to 4 amp. Thermo Coupled, MISCELLANEOUS with high fidelity SPEECH disability; H. V. Short Waves (16-47 metres) are 30/- 0 to 20 volts A.C., calibrated 50 cys., 25/- ; Mr. Hemery con- output. suits at Wigmore Hall Studios, W.1. as good as obtained on purely 0 to 3,500 volts Electrostatic, 35 / -. All 2 }in, fsd. some short- M.A.-Car aerials, whip type, approximately Australia L.T. RECTIFIERS (new), 6 volts, I} amp., 7/6 wave receivers. and America have 3ft 9in, ball jointed base; our price 3/9. been received regularly by many of our each ; 12 v. 1,1 amp., 10/6 each, 9d. post. Instru- post 6d. at loudspeaker strength. Long ment Rectifiers, S.H., 10 or 20 m/a types, 4/6 each. M.A.- Aerial wire, stranded bronze, reels of customers : The MAINS CHOKES, 9 hy., 100 m /a.,6/6 ; 20 hy., 1004t. with clips; our price 2/3, 8d. Wave few stations now operating are post well received. 120 m /a., 106 each ; 30 by., ISO m /a., 22/6 each. M.A. -Para rubber strip, 15ft reels, zyrin wide, MAINS TRANSFORMERS, 230 volts, 50 cys. our price 1/3, post 6d; black plastic boxes, Blue Prinb. 2 Practical and 1 theoretical with lid, approx 4t/Qx3%x2r %in, our price 10d with detailed priced list of components, 3/6 I ph. input. Output, 500/0 /500 volts at 250 m /a., each. Another with two windings each, post 6d. per set. - 5 v. 3 a., 47/6 M.A. -2 -pint blowlamps, new, unused, give iri- of 6} volts 5 amps., 30/. each ; another with tense blue flame for soldering, etc.; our price v., 180 m /a:, twice three 6.3 volt Windings 350/0/350 29/6. post 1 / -. CIRCUIT No. 20 and two 5 -volt windings, 42/6 each ; -another M.A.- Petrol -electric generators, 6 -12v, 7 amps 50 volts at approx. 50 amps., also a 5 -volt winding, output, single cylinder engine, tools and spares 10 valves, 6 wavebands, 12 watts [3/IS / -, each CIF. All the above Transformers are included, self-contained portable outfit for (undistorted) very large type, so please allow 3/6 for carriage. charging or lighting; our price £24/10, car- EX -NAVAL CATHODE RAY RECTIFIER riage extra; many larger sets in stock. Output Superheterodyne New and unused, sold components M.A. -Full list of surplus goods free on re- UNITS. for quest; wholesale enquiries invited. Receiver of : 2 x.5 mf. 2,500 v., 1 x.1 mf. which consist MARBLE ARCH MOTOR SUPPLIES. Ltd.. This set is noted for its fine quality of 6 2 mf. 800 v., 2 x 8 mf. 800 v. 15 volume 5,000 v., x 286 -302, Camberwell Rd S.E.S; branches at reproduction on radio and gram. We have controls, various values, approx. 100 small con- 133 -5, Edgware Rd. W.2; 26. Goldhawk Rd., much appreciation and congratula- resistance, received densers and smoothing choke and Shepherd's Bush, W.12; 1,156, London Rd., tions from customers on its performance. including 3 EF50 and 1 base. 9 v. holders, tube Norbttry. S.W.16. [8841 A demonstration model is available at our wired and with addition of 'T ARGE quantities of P.V.C. covered cables All components the premises at 307 High Holborn. mains transformer would make a good oscilloscope. L various grades for sale for immediate de- Price 4S -, carriage paid. livery. -Box 4503. [8910 FULL SIZE BLUE PRINTS (2 practical CYSTOFLEX sleevings, 250,000 -GOVT. VARIOMETER for No. 19 sets ; about yds and 1 theoretical) and priced list of com- EX available new. 206 -210, these contain C.T. Westector, .001, 5,000 v., brand -M.M.C., ponents 6/ -. Any component may be pur- Bishopsgate, London E.C.2. [8867 chased separately. condenser, etc., price 7/6 each. Complete in C348Q circuit and alignment data, 3/6; metal case with graduated dial. B CR100 circuit, 3/ -; complete list s.a.e.- We are always pleased to demonstrate Re- SHUNT WOUND D.C. 110 volt motors, B. G. Menden, 10, Alfriston Rd., Liverpool. ceivers built from our blue prints without 1,500 r.p.m. approx. }, h.p., condition as new, 17/6 ALUMINIUM chassis and panels to your obligation, and you are Cordially invited to each, post 2! -. specification or in standard sizes; we can call, see and listen. EX -GOVT. NEW MAINS TRANSFOR- punch for valvehoiders, etc.; sample prices, MERS. Input, 200 /250 volts. Output, 525/0/525 6inx4inx2in 3/9, 10inx6inx2in 4/6. -Mead, One minute's walk from Chancery Lacer v. ISO mla., 5 v. 3 a., 6.3 v. 5 a., 35,'- each, post 13 Bence Lane, Darton, Barnsley. [8830 Underground Station. price lots of half dozen more. REPLACEMENT chassis, 4 waveband,corn- 24. Special for or plete with speaker. 14gns; replacement T.C.C. CONDENSERS (new). 4 mf. 1,000 -volt motor and turntable unit, £6 plus tax; also working, 3/6 each. P; F Mains, Smoothing Chokes speakers, pick -sips, amplifiers from 5 -50-watt; 307, HIGH HOLBORN, 10 hy. 150 m /a., 180 ohm., 8'6 each. Ditto (new), mains or battery; s.a.e. list. -Radio Unlimited. LONDON W.C.I. Phone.- NOL.orn 10 hy. 80 m'a. 200 ohm., 616 each. 16. Carnarvon Rd., Letton. [8937 463/

www.americanradiohistory.comwww.americanradiohistory.com 38 Advertisements reless World January, 1945 sale, large quantities of electric cable FORof all descriptions.- Please send list of HENRY'S POTENTIOMETERS your requirements, together with full details, to Box 4459. [8849 SPARKS' data sheets provide complete con- COMPONENT SPECIALISTS structional details and full -size draughtsman- prepared prints showing drilling, assembly and wiring plans of tested and guaranteed RECTIFIED OUTPUT METER. F.B.D. 1 m /a, 20,000 designs by L. Ormond Sparks. ohms per volt, 4 inch square, Linear graduation, 0 -10. LATEST release. -The Challenger portable an Es- govt., by Taylor Instruments. ac /dc 3.valve (plus rect.) T.R.F. circuit hav- Complete in strong wooden case with two range ing an exceptional performance on med. and switch for 0.20 milnwatte, or 0 -80 milliwatts. Out; long waves, the ideal set for radio in any standing value. 55 /- only. room, no aerial or earth; 6in Stentorian VALVES. We have a large stock of many difficult speaker gives amazing power and quality; no types. at current controlled priers, including IE5, complicated switching or adjustments; data 304, 1T4, I85, 5E4, aT4, 5Y3GT, 68C7G, 68L7(3T, sheet 2/9. 6L6, 305GT, 128,17, 12SE7GT, etc., etc. " Ì[IDOET COIL PACE. Size 3lin. x 2m- x Slit. COMPONENTS can now be supplied; send a It" Comprising 6 ultra midget iron-cored coils on poly - stamp for list giving full details of the 34 designs strene formers, complete trimmers, midget 4 -pole available. 3 -way switch, trimmed ready for use. Coverage, SPARKS' DATA SHEETS (W), 9, Phoebeth 15,5.52 iu., 200.590 m., 800 -2,000 m. Complete with Rd., Brockley, S.E.4. Tel, Lee Green 0220. suitable 5 valve 8'Het circuit. A really remarkable COPPER and resistance wire, silk, rayon, coil pack. 33/ -only. cotton and asbestos covered, 15 to 46 WEARITE "P" COILS. Full range in stock. 4RELIANG swg; each. Litz wire, 27/42, 27/44 and 27/46; 10 tons in stock at 10% under market price. -C. WEARITE I.F. TRANS. Midget 21 / -pair. Standard Leatherbarrow, Ltd., Grand Bldgs., W,C.2. 20/- pair, Iron -cored for 465 ko /s. Whitehall 3948 [8829 CAL PACKS. 3 wave. Weymouth, 36/6. ATKINS. RADIO cabinets (midget), hand made, Iron- cored, with gram position £2. Each polished. ultra modern design complete with circuit. dial cut on TINNED COPPER WIRE. 1s, 20, 22 gauge, I Ill. reels. right 4x3, 12x7x6 internal, chrome speaker 1/6. Type T.W. Wire Wound bare; 32/6 inc. dial to suit, post 1/- extra; c.w.o.; ERSIN MIILTICORE SOLDER. 16 gauge, 40,6o, Rating I' ANGES satisfaction guaranteed.-Burl ans, 64, per carton, of 60ft. 5/3. Also available in 6d. carton. Reighton Rd., London, E.5. [8968 ELECTROLYTICS. We have a large stock of all 5 W. Max. 10. 100,000 Si Max. WORK WANTED types by leading manufacturers. linear (linear) CAPACITY available for assembly, wiring, VALVEHOLDERS. All types, British and American ( ) ( 100- 50,000 L2 Max. testing radio chassis; large or small quan- Ampheaol. 7/6 don. Paxolin IÍ /- dos. Ceramic, B70 !I (graded) tities. -Box 4028, 1/- each. Ceramic EF50 1/6 each, Ceramic, Inter - 3 W. Max. [8755 Octal each. 100. 10,000 Si Non - FACTORY has technical 1/6 Ceramic Acorn type, for 955 etc., staff and capacity 2/- each. (graded) 1 inductive available for manufacturing scientific or other articles RESISTORS. I, I and 1 watt, 6,'- per dos, Large Type S G. Composition in glass. -Box 4462. [8853 range. make wireless and radiogram cabinets CONDENSERS. 2pf- .1mfd., 5/6 per doe. 2,000 ohms 2 WEfor home I W. Max. to and export; immediate ile. PPE P11301 AND SOCKETS. Complete 1, 6 pr. megohms liveries.-Radiac, Ltd., 26, Brondesbury Rd.. London, N.W,6. Maida Vale 8792. [8025 We can meet all your component requirement'. CHARACTE..ISTICS : (both types) linear STOVE enamelling. -We og semi -log.,inverse are now in a posi- log., non -inductive,etc tion to accept orders for plain and crackle Cash with order, or C.O.D. (over £1) FULL finish, specialists DATA FROM : in New Wrinkle - " -W- If. Barrell, Ltd., 68, Portswood Rd., Southampton. A stamp will bring our current list. RELIANCE CABINETS! -Large modern factory now has Manufacturing Co. (Southwark) capacity available for additional radio Ltd., cabinet manufacture; 5, HARROW ROAD, W.2 Sutherland rkd., Higham ill, London, E.17. we have every facility for large-scale productions; let us quote Te /ephone : Larksword 3245 you. - PAD 1008/9 Box 3745. [8645 LET us build that new radio for you; earn receiver is specially designed, under laboratory conditions, to fulfil your most exacting requirements.-For further details D C O . 24 Belmont Circle Harrow. Middx ARGE old -established public company in THE COIL London PICKUP L with extensive experience of mass- production woodwork and exceptional facilities Encourages Even the Best and resources for the production of radio and gramophone cabinets would welcome enquiries Amplifier from the trade. -Enquiries to Box 3900. [8665 and tracing work for radio and 220 D.C. to 220 A.C. DRAW1NGelectrical Deto". t,om- engineering, jig and tool and light engineering, photoprinting; full sets of WILKINS & WRIGHT LTD. BEETHOVEN ELECTRIC EQUIPMENT LTD. drawings undertaken to Holyhead Road, Handsworth, B'ham Beethoven Works, chase Road London. N.W.10 commercial or Minis- 21. try standards.-Drawing & Tracing, Ltd., 456a, Ewell ltd., Tolworth, Surbiton. Tel. Elm bridge 7406. L7703 BUSINESSES FOR SALE OR WANTE3 RIGHTON. -Radio and elec. retail and con- B tracting; shop with basement workshop, good lease exceptional low rent; £1,250 all at; offers; HILL & CHURCHILL LTD. QUARTZ no agents. -Box 4304. [8806 CRYSTAL UNITS LANCASHIRE coast.- Old -established radio and electrical business with excellent liv- BOOKSELLERS ing accommodation included. Sole agent for leading makers; £3,000 plus s.a.v. Vacant possession on completion. -General Business SWANAGE, DORSET Transfer Co. 88, Mosley St., Manchester, 2 WEST End ground floor showrooms and basement, close Oxford Circus; 1,400 sq Available from Stock: ft; ideally suitable for electrical trade; rent Kiver "Television Simplified " - £550 p.a.; premium £750 for good lease. - Sole Agents, Harris & Gillow, 9395, Wardour Glasgow " Principles of Radio En- St., London, W.1. Gerrard 2504 (10 lines). gineering " , WEST Country County town. -Very fine and 2 5 - well -established radio shop and radio en- " Principles of Television gineering business; small flat, fully equipped Engineering " - - - - 27/6 workshops and benches; large turnover, audited accounts; business equipment and leases for Fink " Radar Engineering " - 35/- sale as a going concern; very strongly recom- Shea "Transmission Networks mended. -Apply Jackson -Stops & Staff, Yeovil. SITUATIONS VACANT and Wave Filters " - - 38!- Vacancies advertised are restricted to persons Skilling " Fundamentals of Electric or employments excepted from the provisions Waves " - - - - - 18 of the Control of Engagement Order, 1947. CONTACT sought with specialist able to Schelkunoff '' Electromagnetic Waves " 37 6 advise occasionally on R.F. transmission Simon " Radio Service Trade line problems.-Box 4470. [8871 WORKS manager with extensive experience 17 6 loudspeaker mfr., excellent prospects for Postage extra. really keen energetic and capable man. -Write fullest particulars Box 4473. [8880 SALFORD ELECTRICAL INSTRUMENTS LTD. PRODUCTION- MINDED tester required to take charge of small sub- section engaged PEEL WO.S. Saffo RD on repetition work, electro- acoustic instruments CATALOGUE ON APPLICATION ro,000 . THE GENERAL ELECTRIC Co. Ltd., of Errane Wembley district- -Box 4472. [8875

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 39

ERIE RESISTOR, Ltd., have vacancies in their sales department for capable correspondence clerks. PREMIER RADIO COMPANY a APPLICANTS must possess a fundamental and knowledge of the principles of radio, LTD. a thorough knowledge of the trade, and, above MORRIS & CO. (RADIO) in all, must bave had previous experience ALL POST ORDERS to 167, LOWER dealing with voluminous and varied corre- ES All Goods Offered in Last Issue Still spondence, on either sales or service. CLAPTON ROAD LONDON, Available. APPLY at once, by letter, stating age, quali- 'Pncne : Am':erst 4723 salary required, and, fications. experience, ALL CALLERS to 169, FLEET STREET, when free, to, Sales Manager, Carlisle Rd., The llvde, Hendon, N.W.9. [8825 LONDON, E.C.4. R1155 COMMUNICATION Air Ministry has vacancies in the 'Phcne: Cent. al 2833 THEMeteorological Office organization for a TYPE RECEIVER number of civilian Radio (Meteorological) Terms of Business: Mechanics to maintain radar equipment. Cash with order or C.O.D. over El APPLICANTS must possess a knowledge of the fundamental principles of radio and radar Send 214. stamp for latest list and practical experience in the maintenance and use of electrical, radio and radar instruments including cathode ray oscilloscopes. MIDGET RADIO KIT. Build your own midget radie. PREFERENCE will be given to former A complete set of parts, including valves, loudspeaker Royal Air Force personnel and any other ex- and instructions. In fact, everything except cabinet necessary to build 4 -valve Medium and long Wave Servicemen possessing the requisite qualifica- or WC. to serve T.R.F. radio operating on 200 -250 v.11110118, A/C tions. Staff selected will be required Valve Ilse -up, 6K7, 6J7, 25216, 25 Y5. Wavelength, at any station at home or abroad and in the covered 200 -557 and 700. 2,000. Size 10 x 6 x bin. Con,. case of appointments at house units, will gener- pletely drilled chassis. Price, including tax, £B Os.11d. ally be expected to make their own arrange- kit of Successful appli- SUPERE8T MIDGET RADIO KIT. A complete ments for accommodation. parts for a 5 -valve superhet. Covers 16.50 and '200 -557 cants will be engaged on a non- pensionable 25A6, 25 Y5. being metres, AC /DC 200 -250 v. 6K8, 61(7, 6Q7, basis only, although prospects of later Size, 10 x 6 n 6ro. Completely drilled chassis. Price, placed on the permanent establishment are including tan, £9. wages not ruled out. The commencing weekly An attctivera bronw iwkelite cabinet can be supplied per week Now available with Power Pack and output in the United Kingdom are £6.5 for either kit at a cost of 27/4 (inclusive) for appointees aged 21 and over. stage with 8in.loudspeaker. MAINS TBANSFuiRMERS. All Input, 230 v. 50 c Varying allowances are payable in addition v. Price Complete, as above, E20. Type 30, output 30 v. 4 a., 201- ; Type 31, output 40 to the basic wage for service in most Overseas Type 32, 1155 Receiver only 212. 10. 3 a. and 104 v. 11 a. (auto- wound). 21/- locations. 700 + 700 150 A, 1,000 v. 30 m /A (half wave), 4 v. 1 a. to Air m/ APPLICATIONS should be addressed 4 v. 3-5 a., 40/-1 Type 33, 32, 34, 36, 35 v. at 2 a., 15/ -. Bush House, N.W. Wing, Ministry (S.5(h)), kit of Aldwych, London, W.C.2. [8846 ALL -WAVE SUPERHET KIT. A complete TELEPHONE LINE or required for de- parta to build a 6 -valve short (1.50) medium and long DEVELOPMENT engineer drilled chassis, OP trans work on automatic control gear; wave set, including valves, sign 3/15 ohms and full instructions. Incorporates Wearite B.Sc. standard; previous exp. in electronics and Valve UNISELECTOR SWITCHES [8838 iron-cored coil unit, 5 watts pushpull output. servo systems desirable. -Box 4314. 6K7, 6Q7, 6J7, two 25A6. Operates on Have various vacancies for line up, 6K8, 4- or 6 -bank, 26 contacts. LEYTONIA RADIO. -Have A/C or D/C 200 -260 v. The ideal radiogram chassis. applications including automatic tuning, first -class servicemen, television experience Price, without speaker, £11 lls. Od. etc. Operates on 25 -50v highest rates in London for and circuit selection, an advantage, High Rd.. RADIOGRAM CABINETS. Dignified appearance 4 -bank 28/6 men with pre -war records. -828, Fond workmanship. Size 311in. high, 181in. deep. E.10. d.. veneered walnut. Prise 6 -bank 39' Leyton, some 33in. wide. French polished, JUNIOR laboratory assistant with £28 7s. 3d. Also available complete with electric knowledge of physics and some electrical motor, auto stop and magnetic pick -up, £37 6s. 2d. training. -Write, giving details of experience, Ditto with Rothernel Crystal Pick -up. £38 12s. 7d.. Hunt, Ltd., 8 record -mixer changer. £48 18s. Od. 6 -VALVE SHORT WAVE age, etc., to : A. II. B radon or with Valley, 8.W.18 BUPERHET TUNING PACKS. Completely wired and JUNIOR electronic engineer with experience aligned. 13 -40. 40-120, 190.570 metres. R.F. stage. by design de- Complete with 3 -gang TYPE R208 RECEIVER of sound recording required 465 k /c. ; 9 connections only. work in connection with new condenser, calibrated. engraved Perspex dial, and 8/31. 10 for A.C. 100-250 partment for Range -60 mcs. Suitable -Reply, stating qualifica- drive. Litz wound polystyrene insulation, permeabilit y 6 volt battery. Metal rectifiers, B.F.O., commercial product. bandwidth. Price complete or tions, exp., age, salary req., to Box 4510. tuned I.F.-s, 7 k /c. built -in L;S. Super Slow Motion Dial, pro- laboratory assistant, either sex, £3 17s. Bd. super job in CHEMICAL MOTORS. A few avail- vision for phones, etc. A real 16 to 18 years required for manufacturing ELECTRIC GRAMOPHONE grey metal cabinet complete with valves and concern at Surbiton, matriculation or equiva- able. Write for details. vibrator. 112 . 10 lent standard of education essential. -Write ALUMINIUM CHASSIS. Substantially made of bright and salary required.- aluminium. with four sides. stating age, experience 56 Box 4310. 170%3(s2in. .... 4/6 illo41olin..... laboratory assistant, 20- a 7/- 12 x 9 x 201n..... 7, 9 H.P. A.C. JUNION 16 x8x211n..... 8 6 FRACTIONAL some knowledge of chemistry, prefer2,, with 14 x9x21in..... 8/3 8 10/6 22x 10 x21in. .. 136 up to Inter -B.Sc. standard, for raw material 20 x x 21in..... Write, giving details of MOTORS and process testing.- OFFERS age, etc., to : A. H. Hunt, GOVERNMENT SURPLUS experience, [8353L3 Brush type, 220-250 v., 50 cycles, 5,000R.P.M. Becton Valley. S.W.18. OSCILLOORAPH POWER UNIT KITS. Input 230 v. 1 Edg- voltage doubling Overall length 10in., diam. 4in. + spindle 'TORWEST SERVICES. Ltd., of -3, include transformer, metal rectifiers, Edgware, require Radio extends I in. both ends. 37/6. Post 2/6. warebury Lane, hand smoothing condensers. and Television Service Engineers. Applicants Type 909, output 900 v. 25 - should write giving fullest details of experi- Type 410, output 1,800 v. 25 - ence and salary required. Permanent position METAL EECT3PIERB. ELECTRO MAGNETIC with congenial working conditions. [8840 Output Volta Current Type Price service engineer required, previous 600 ...... 90 m /a. H.W. 5 H.W. or V.D. 5 RADIOexperience on fault location and repairs 280 ...... 40 mla. COUNTERS essential; 44-hour week, 360 75 m /a. H.W. 5 - domestic receivers ...... 1 12 or write for 16 ...... amp. Bridge 6 Owing to short space advert, see last issue. good pay and prospects; 'phone 48 11 Bridge 25:- interview. -Radio Mainten- amp. appointment for consists of a special purpose Ex- G.P.O., every one perfect, electro- ance k Supply Co., Sidcup. Bexleyheath 1874. TEST UNIT TYPE 73 required, Oscilloscopethatrequiree only rewiring and the additiou magnetic, 500 ohm coil, counting to 9,999, senior assembly foreman and resistors to convert into a many area, must be capable of con- of a few condensers operated from 25v.-50v. D.C., RADIOManchester standard Oscilloscope, input 230 v. 50 c. A 3/in. C.R. domestic applications. 5/6 trolling male and female labour, experienced 1 8834, 1 5E4, 3 SP41, 2 EA50, industrial and with tube and 1 8U220A. in assembly belt lay -out and familiar are included. Controls are " Brightness," " Velocity," A.I.D. requirements. -Apply stating age, ex- "X Shift, " "Y Shift," Focus Amplifier, "in /out," perience and salary required to ilox 4474. Calibrate," on /off /TX." Price £8 Bs. Od. Super Quality Heavy Duty SOBELL INDUSTRIES, Ltd., have vacancies Carriage and packing. 20/- in various parts of the country for first - makes Bakelite cases. clean METERS. Beet - class radio and television service engineers, Range Ext. Basic Fitting Type Fri,e TWIN ELEMENT driving licence essential, salary £6 plus allow- Diem. Movement ances, expenses and incentive bonus, equipment 600 M/A 3" - Prol M/C D/C .. 12 6 SLIDING RESISTANCES provided. -Write Service Manager, Langley dA Flush Thermo .. 76 Park, Nr. Slough, Bucks. [8834 21" - Port H. Wire .. 7 6 5.4 ohm at 20 amp 47/6 TECHNICIAN required to take complete 20A . 2" '25 M/A Flush MC/ D/0 .. 7 6 ' 121 M/A Flush M/C D/C .. 76 12 ohm at 10 amp. 39/6 charge of testing department for small 40A 2" 25A 31" 5M /A Flush M/C D/C .. 76 at 5 amp. 35/- of electro- acoustic instruments, 70 ohm manufacturer 26A 31" 25 M/A Prot M/C D/C .. 7,6 Single Element 14 ohm at 5 amp. 13/6 work involves accuracy and close measurement, M/A Flush M/C D/C .. 7/6 to assist with intrumentation I M/A 2" I will be required 150 M/A 31" 150 M/A Flush MC/ D/C .. 12.6 and construction of test equipment. Wembley M/C D/C .. PLEASE NOTE : All Carriage charges relate 200 M/A 31 200 M/A Flush 12.6 [8874 D/C district. -Box 4471. 1 WA 31" I M/A Flush M/C .. 20. - to the British Isles only. Middle East.-Signals Adviser REQUIRED FERRANTI 1 MILLIAMP METERS. 311n. external We do not issue lists or catalogues to Government, preferably single and be- with.self- contalned Westing- of age; should have up -to-date diameter, flush mounting, low 45 years house bridge rectifier. Scale marked 0 -10 volts with knowledge of civil communications and radio fitted in well made wooden box 6 x 5 > traffic control technique; inclu- fifty divisons, LISLE

www.americanradiohistory.comwww.americanradiohistory.com 40 Advertisements Wireless World January, [948 MUST gear maintenance engineer required by radio manufacturers, Erith district, to take charge of calibration and standards; previous experience essential-Apply Box 4493. We cordially invite JUNIOR engineer required for development Precision of radio components by progressive company in Snrbiton area; degree or equivalent Overseas Establishments to electrical engineering essential. Box 3903. woodwork ANUMBER of vacancies exist for research and development engineers in a large interested in firm manufacturing wireless communication FOR equipment in South -East England; candidates EXPORT ORDERS of university degree standard in telecommuni. High - Fidelity Sound cations preferably with previous industrial exp., apply, quoting Ref. 86, to Box 4500. opportunity ; well -known maim- Reproduction to apply EXCELLENTlecturers introducing a. most attractive We are well equipped for novelty article for the electrical trade (just now entering I. he British home market) wish the production of high for Agency terms to io engage representatives for export apd hone market; nmst have drive and personality; grade veneered cabinets yessive position of importance. -ITox 4306. " LOWTHER -VOIGT rr pro F: require some technicians and era It srnen in quantity. We invite for devcloprnent ;tot production of Ilartley- 'turner specialities, essential require- enquiries for Radio -Gram Quality Equipment ments are intelligence, reasonable skill. and desire and ability to use personal initiative Cabinets, Consoles, and and enterprise. -Write fully stating remunera- tion required to 11. A. Hartley Co., Ltd.. 152, other repetition woods Hammersmith Rd., London, W.6. [8972 AMBASSADOR RADIO have a rwacancy for work. THE LOWTHER MANUFACTURING CO. an experienced Mechanical Designer to take full charge of all mechanical designs anti Lowther House, St. Mark's Road, supervise production of mechanical assemblies. Timber Licence required Applicants must apply by post in first instance BROMLEY, KENT. stating experience, present employment and salary requited to R. N. Fitton, Ltd., Radio Ray. 5225. Works, Hutchinson Lane. Brighouse, Yorks. BAXTER STAVRIDI & CRAIES Ltd. required to fake charge 9 Commercial Road, Edmonton, London, SUPERINTENDENTof radar and radio assembly department, N.18 large electronic equipment company, Manches- ter area, must be capable of controlling stale 1155 OWNERS and female labour on track and bench assem- Our original post -war The beet of sets break down, and as it le difficult bly. -Apply giving fullest particulars of age, have met REVISED PLANS to buy spares for 1155's, we suggest that hay plans many to experience, qualifications and salary required man -made setbacks a parcel of 25 spares, including r.F. Transformers, to Box 4528. [8954 are evolving. Please R.F. Cells, R.F.O. Coil, H.F. Choke, etc., etc., is a APPLICATIONS are invited for position of don't write, phone, sound Idea. We can offer such a parcel for 26.6 chief planning engineer for large radar post free, e.g. less than the cost of the I.F. Trans- or call. We will formers. We are able to make this offer became we and electronic equipment company, north Man - bought a big stock of new parts which were not needed cheater area, must have good engineering back- advise when ready. when the Air Ministry contract for 1155 receivers was ground, be fully conversant with all machine completed. All parts are new and exactly as used in shop fitting, and assembly operations. -Apply your set. Order now to avoid disappointment. giving full details of age, experience, career VOIGT BULL'S EX-GOVT. DEPT.,42 -46 WINDMILL HILL, and salary required to Box 4527. -[8953 RUISLIP MANOR, MIDDLESEX. ASSISTANT engineer required for design and PATENTS LTD. development work in the test instru- menta laboratory of Murphy Radio, Ltd. Can- didate should possess a. degree or equivalent qualification, experience is preferable but not essential.-Apply in writing, giving full par. MORSE CODE ticulars to Personnel Department, Murphy Radio, Ltd., Welwyn Garden City, Herts. [8823 This unique handbook TRAINING TRANSFORMER department superintendent shows the easy way to required by radar and radio electronic secure A.M.1.Mech.E. There are Candler equipment company, Manchester area, to take A.M.Brit.I.R.E., A.M.I.E.E., charge of modern transformer shop. be fully City and Guilds, etc. Morse Code Courses conversant with all operations of coil winding, for impregnation and assembly by male and female WE GUARANTEE - labour.- Address replies, giving details of age. PASS BEGINNERS AND experience and salary required to Box 4529. "NO -NO FEE." OPERATORS. TECHNICAL assistants with radio and tele- Details are given of over 150 vision experience wanted in large factory Dipl -ma courses in all Send for this Free in West London, 1 a senior inspector, 1 for branches of Civil, Mach maintenance and precision test gear, 2 for re- Elec., Motor, Aero., Radio, "BOOK OF FACTS" pair and testing of sound amplification equip- Television and Production It gives full details con- ment, 2 for interference investigation work; Engineering, Tracing, Building, salary £6 to £8 per week. -Apply giving age Govt. Employment, R.A.F. cerning all Courses. and particulars of experience, etc., to Box 4525. Maths., Matriculation, etc. REQUIRED, machine shop superintendent Safeguard THE CANDLER SYSTEM CO., by radar and radio manufacturers, large you- future; send factory, Manchester area, most be capable of 'or your copy at once-FREE. (Room SSW), 121 Kingsway, London, W controlling male and female labour engaged on B.i.E.T., 387, SHAKESPEARE HOUSE, Svs'em Co., Denver, Colorado, U.S.A production of components for assembly lines, 17, STRATFORD PLACE, LONDON, W.I. knowledge of machine, press and fitting operations essential. -Apply giving full particulars of experience and salary, etc. to Box 4530. engineers required by light en- PLANNINGgineering company, North Manchester TELEPHONE HANDSETS area. accustomed to radar anti radio equipment production; must have served general en. COVENTRY Made by T.M.C. for Government use, RADIO gineering apprenticeship and be capable of de- COMPONENT SPECIALISTS and incorporate self- energising inserts veloping and planning all machine shop, fitting SINCE 1925. and assembly (permanent magnet balanced operations. -Apply, stating age, arma- experience and salary required, to Box 4603. SPECIAL OFFER ! ture). Ideal for house, office, works, radio manufacturer has vacancy LEADING High Grade Micro- shop for chief design draughtsman used to con - ammeters edge- or house-to -shack communica- trul of staff and operation of up to date draw- wise type 20 -0 -20 IAA, 3 [ ' scale tion. Whilst stocks last, price only ing office system; extensive experience of light electro- mechanical design (straight line). I I /6d. each or 22/6d. pair, with dia- desirable; substantial and progressive position for New Meters, in sealed makers' cartons. gram, plus 2/- packing and postage. man with the right qualifications.-Applica- tions with full details of experience These are offered below half price Fantastic value, dont miss them' and salary required to Box 4309. - [8819 while stocks last. E3 -6 -0 post paid. department of the research lab- PATENToratories of the General Electric Co., Send for latest list of components, 3d. WIRELESS SUPPLIES UNLIMITED Ltd., North Wembley, Middx., require a tech- (Próprs, Unlimitex Radio Ltd.) nival assistant linale or female) with a good honours degree or with similar qualifications, COVENTRY RADIO, 264.266, Old Christchurch Road, and preferably with some experience of patent BOURNEMOUTH, work, to act as assistant to a chartered pat nt DUNSTABLE ROAD, LUTON, BEDS. Hants. agent; apply by letter only to the Direct,', statiee age, exp. and academic qualificati. , .

www.americanradiohistory.comwww.americanradiohistory.com January, 1948 Wireless World Advertisements 41 RADIO machine shop foreman required I), supervise the production of component, for radar and radio equipments, Manchestct ENTERTAINMENT area. -Address particulars of age, experience . RADIO VALVES From recordings, stage, or film, to audiences qualifications and salary required to Box 4504 BULLS of ro to l,000 persons. SENIOR assistant with knowledge of com- 246 Haig HARIESDENtwii ponents required for West Central London and BRIMAR.-10-4 1011, 5ì1250A. 666. 6K6. 1ìK7, retail trade, ability to take charge of 6877, 68117, 6T7, 616, 765, 7137, 768, 7C6. 714, SOUND AMPLIFIERS develop " Ilam " business, good wages and 9D2, 1001, 111)3, 1105, 12867, 25Z4, 15D2. of 8D2, Models for every purpose, with outputs 6, commission to rights man. -Box 4469. [8869 008808. -4TPR, 4T816, 138PA, 13VPA, 4081TA, 20, 25, at prices front component manufacturers require 41MPT, 41MRC, 418TH, 42.OT, to, 15, 35, 45 watts radio engineer to 412(HL, 41MP, 9}r Gns. Domestic, professional p.a. cine LEADINGthe services of a graduate 420T -0D, 42PTB, 202VP, 202 V PB,2o3THA,210DDT, carry oat research and development programmes 2101)(1, 210LF, 21550, 2201IPT, 2200T, 220P, 220PA, projector, recording, high standard, fidelity, /PEN, etc. booster circuits all latest in connection with electronic components, fuses D01,4, MP /PEN. MS'PEN, 2(8/PENB, MV8 Mixing and and suppressors; good background in general 0M4, OM6, O519. 05110, PTIO. refinements incorporated. Twelve designs to physics and some inventive ability essential; XH, XL, XP. X8G, XT, 1 W. Sheet free. Com- HIVAC.-XD, choose from. (Summary salary will be in accordance with qualifications MARCDNII0BRAM. -- CRT -F,4102 /B17, D41, 1)42, plete data sheets, 3d.) and experience bitt will not exceed £500 per D63, DA30, DO2, D16t3, 1'L74M, 1iN41, ()TIC, G1,150, annum; give full details of age, education and H30, 1163, HAI, 111)24. 6L2, HL2K, KT2, KT41, cxperieeee. -Box 4305. [8810 KT44, K1'61, KT63, KT86, KT71, KT74, KTWO1, TRANSFORMERS TEt'HN1('AI, assistant required by large KTW63, KTZ41, KTZ63, KTZ73M, LOI1, 1,63, LP2, Power, audic, outputs and chokes. There are electrical manufacturer; applicants should 1.856, 3(1141, MKT4, ML4, 2(84B, MSP4, 2(140. 77 specifications in our production schedule have had practical experience in the servicing N14, P2, PT2SR. PX25, QP21, 823, U10, U14, U16, is OP4, as illustrated. U17, U18 /20, U31, U50, U52, U74, VMP4G, VM84B. -the latest addition of radio receivers, and be familiar with the 165, 171M, 163, Z22, Z63, 301, 302, (Leaflet T.R. Free upon request.) design and operation of dealer test gear; W21, XU1M, selected candidate would be required to submit 303, 304. books on test MAZDA.-AC2PenDD, AC6PEN, AC5PENDD, reports and compile instruction ACOPEN, AC /P, ACPen, ACP4, ACTB1, Dl, DOP, gear and give practical demonstrations. 'Write, DCSO, DD41, DD101, DD207, DD620, H210, HL21DD, giving full details of age, experience and salary HL23, H1.23DD, 2(1.41, HLIIDD, 11L42DD, required, to Box 4501. [8908 HL133DD, HUE/1320, P41, Pen25, Pen46DD, Pen46, WANT-ED.-Working technicians with ex- Pen453DD, PenDD4020, QP25, QP230, 80215, 8P41, perience in construction, wiring and test- 8P42, 8P2220, TH233, TH2321, TP22, TP25, TP26, ing of radio and/or electronic gear, able to 0403, UÚ7, V914, VP23, VP -11, VP133, VPi322, work from mechanical layout drawings anti ÚY5'300. theoretical circuit diagrams and use own MULLARD: 2D4Á, 2D13C, 5U4, 513, 605, (CO, initiative to produce results during develop- DOD, 637, 6L6, 6477, 667, 1641; AZI, AZ31, CBL31, ment and production stages of manufacture CC1135, CL33, CYl, C110. CY31, DAF91, DF33, of high -grade electronic good wages DF51, DF91, DK91, DL35, I)L9'2, D024, 0026, apparatus; EBC3, EBC33, dud working conditions-Apply to Savage & D030, DW2, DW4/360, EA50, EB34, EBL21, 8052, E0031, ECC52. ECC34, 60036, EC1121, Parsons, By -Pass, Watford. [8957 EF39, 6E30, to assistant ECH35, EFS, EEO, EF22, EF36, EF37, appointment offered EF54, ELI, EL3, EL32, EL33, EL36, EL38, ELIO, LONDONphysicist with a leaning to radio and EM4, EM34, 61135, F013, FC13C, FW4 /500, HLule, ratio output 37 6 ]ectrical circuits; applicants should have ap- 11VR2, HVR2A, 1W4í500, KBC32, KF35, K1(32, OP4. Twelve and not OPI2. Ditto 50w. high -8. 55 - nnpriate theoretical qualifications, 11,35, Pen4VA, Pen428, PenA4, PM2, P2(2H1,, 'r55 than two years' experience, and will PM4DX, PM122( PM22A, PM22C, QP22B, from 26 - each required to develop the electrical aspects 8P4ß, 8P13, 8P13e, TOO, TDD2A, TDD13c, T11411, POWER TRANS ..f plastics evaluation in a large chemical TH300, TT4, U52, VP2, VP2B, VP4, VP4A, VP13A, 15131 You must have our complete ',motoring, manufacturing company ; the work offers pros- VP13C, UBL21, UCH2I, ÚY21, catalogue, send 3d. at tutee. pects for promotion; commencing salary range AMERICAN. -0Z4, 1A4, Aì5. 1B4, 1D7, 1E5, 1E7, £375-£500. -Box 3526. [8560 1F4, 1F5, 1F6, 1F7, 106, 1116, 1I,C6, 1LN5, 185, SITUATIONS WANTED 1T4,1T5,1 -V, 2A8, 2A7, 2136, 287, 212, 3A8, 367/1291, GENERAL LAMINATION PRODUCTS LTD., (released Nov.), radar /fitter. age 22, 3Q5, 5114, 614, 513, 5Z3, 524, OAS, 6A4, (AO, uRA.F.. desires progressive opening in radio field; 6Á137/1853, 6AC7 /1851, BASS, 6AE8, 6AG6, SAGO, Winder House, Broadway. Bexleyheath. possesses keen brain and mechanical aptitude; E407, OAKS, 664, 6137, 668, 6C4, 6C5, 606, 6(18, ODS, 6D6, 6D8, 6E5, 6E6, 6E7, 6F8, OF7, 6E8, 606, able to drive. -Box 4F17. [8934 6116, 615, 677, 6.18, 6K6, OK7, 6K8, 6L6, 61,6, 6L7, DEVELOPMENT engr., 20 yrs. experience, 617, 0Q7, 6P5, 6R7, 68A7, 6807, 68E7, 6807, 88117, C. & G. in radio communication, National 6827, 68K7, 681,7, 68N7, 6887, 6867, 6T7, 6V6, Cert. in El. Eng., requires position with effi- 0X5, 615, 7.06, 7A7, 7B5, 7B6, 7B7, 788, 705, 7C6, cient manufacturer. -Box 4312. [8827 7C7, 7117, 787, 7Q7, 714, 10, 12A, 12A5, 12A6, 1267, de "Hi-Fi" RADIO engineer, 23, C. & G. Radio I & H, 1208, 1275, 12K7, 12%3, 12Q7, 12307, 12887, 128K7, Apropos tech. elec., trans. lines, 7 yrs. exp. h.f. 120Q7, non, 12867, 1225, 14A7, 1466, 14Q7, 15, 20 25A8 2515 25Z4, 26, 27, 2807, 29, 30, 31, have been teased somewhat by our reference transmitters, receivers, p.a., etc.; design, de- 17, 22 We velop, test, mechanical staff control, take 32, 33, 34, 35A.5, 3526, 36, 37, 38, 39/44, 41, 42, 43, to seekers after the truth touring London in charge, drive, seeks progressive position. -Box 46, 48, 49, 50, 53, 55, 57, 59. 77, 79, 80, 81, 83, 04, 89, it. It has been suggested that the truth 807, 832, 066A. 954, 955, 958, 11726, 1299A, 16211, search of 4497. [8900 7193, 9001. 9002. 9003, 9004, 9005, 9106, and 101 will not be found even when they reach Hammer - Cpl. experienced radar mech., seeks RA.F.progressive post, education, metric stan- more types. smith Road. capital Order C.O.D. above listed numbers or equivalents dard, own car, 1947 model, small (subject to stock). Please enquire for any valve you is ? " As if considerable experience To that we ask " What the truth available required, require, even 11 not listed. We may bave it. Obi we feel the need of telling with high quality audio amps, age 23. re- and new types are arriving daily. private enterprisers leased Jan. -Box 4524. [8946 the truth about the things we make and sell. CHIEF engineer (mechanical), 11 years in THIS MONTH'S SPECIALS and Maintenance," 818. They do what they are claimed to do -which radio industry, seeks interesting post, fully " Radio Servicing experienced tool design, operational planning. Trimmer Tool Hite (old price) 301 -. is to reproduce radio and records without adding "Radio- Craft " Library : 10 American Book -.:1e -. assembly, machining, press -work. resistance Oscillator distortion to the reproduction, and if in this STP PRESS : AVO Battery £12. welding, etc., conversant with conveyor methods, Taylor Meters on Easy Terms. direction they fall short of telling nothing but large and small scale production. -Box 4313. Ex -A.M. batteries. inert, 120v. 10.9. the fault is ours because we are not TUITION the truth, Radio School Wishing a Happy New Year. wise, and so we cannot achieve per- THE British National Bulls infinitely (WW.)246, High St., Harlesden, N.W.10 fection. OFFERS you a career who come to see and hear our ideas WRITE to -day for free booklet describing our But those wide range of training courses in radio, Radar,. an " hi -fi " say that what we have achieved is telecommunications, principles, mathematics. so near as not to matter very much. That is physics, and mechanics; correspondence and pleasing to us for we must stand or fall on what day classes for the new series of C. & G. examinations; we specialise in turning " operators " LRSIPIPIPP'IN STOCK we can do, and so far we have stood up very well. into ' engineers and for this purpose on: We will gladly send full details of our products "Four Year Plan " (leading to A.M.I.E.E. au'l AVOMETERS A.M.Brit. 9 C. and G. Certifi- request as possible. Our mailing I.R.E., with Model 7 ...... Cash price £19 10 0 as soon after cates as interim rewards) is unsurpassed; '' our and if we have not so 0 I st is now very extensive guarantee has no strings attached. " -Studies Avominor AC /DC Universal meter... £8 10 far provided all the information we have been Director, B.Sc., A.M.I.E.E., M.Brit. I.R.E. Valve tester, complete ...... £16 10 0 for it is simply due to the fact that we would 66, Addiscombe Rd., Croydon, Surrey. [6811 asked P.M.G. exams. and I.E.E Avominor DC meter ...... £4 4 0 not our friends by sending our scrappy RADIO training.- insult Diploma; prospectus free. - Technical Oscillator, mains S13 0 0 information and the compiling and printing of College, Hull. [0611 Please let us have your enquiry for other good information takes time in these hard days. PROFESSIONAL qualifications, engineer- -L lecturer (B.Sc.Eng. A.M.I.E.E.) will get models our non -political text-book " New oral and corre- Meanwhile you through A.M.I.E.E. exams, All Avometers available on convenient terms `dotes Radio " is now accepted as the standard spondence tuition. -Box 4308. [8818 in correspondence covering work on the subject of " hi -fi " and no enthusiast COMPLETE course Cyldon Door Chimes ...... 49/8 amateur and C. & G.1. exams consisting Far more pleasant than the ordinary door bell should be without a copy. Price 3/8d. Post of 12 lessons, send for particulars.- Every - free. man's Correspondence College, 72, St.. Stephens Illustrated list of any of the above items 1d. House, Westminster. S..W.1. [8839 AGENTS WANTED The LONDON RADIO SUPPLY Co. CO. LTD. representatives H. A. HARTLEY MANL'FAC "rFRER.i require L.R. Supply Co. Ltd.) Est. 1925 152, HAMMERSMITH RD., LONDON, W.6. throughout the U.K. to market their (The RIVerside 7387. special moving coil pick -ups and other speciali- BALCO3ISE SUSSEX FPL 'P.54 ttes.- WI ill. t, Box 4468 [8866

www.americanradiohistory.comwww.americanradiohistory.com 42 Advertisements Wireless World January, 1948 AGENCIES sales manager proceeding to EDDYSTONE '640' TECHNICALNorth America early in 1948 wishes to contact manufacturers regarding agencies. - Please write Box 4491. [8889 An Important We are now booking orders for this PATENT NOTICES first -class communications receiver. BRITISH Patent No. 496441; the proprietors of this patent, which relates to con- TRADE EXHIBITION Demonstration model on view at nectors for electrical conducting wires, are OF prepared to dispose of it, preferably our Show Room. by way of outright sale.-Enquiries should be addressed NEW ELECTRONIC INSTRUMENT in the first place to Andrews & Byrne, 329, EDDYSTONE ' 504' in stock. High Holborn. London, W.C,1. [8807 Developed by CINEMA -TELEVISION LT( TECHNICAL rRAINING 52 Page Catalogue of Components will be held of & AM.I.E.E. City of Guilds, etc., on " No Accessories I /- Post Paid. Pass -No Fee" terms; over 95% successes; for full details of modern courses in all BRETTENHAM HOUSE, branches of electrical technology send for our LANCASTER PLACE, LONDON, W.C.2. B.T.S. 112 -page handbook, free and post free. - B.I.E.T. Dept. 388A), 17, Stratford Place, From JAN. 20th to JAN. 31st inc The Radio Firm of the South. London, W.1 [6270 63 London Road, Brighton i, BOOKS, INSTRUCTIONS, ETC. Further particulars and Tickets of Admission (t EBB'S radio map of the world locates bona -fide Trade only) obtainable on application u Sussex. any station heard, size 40x3Oin, 4/6, CINEMA-TELEVISION LIMITED, poet 6d; on linen, 10 /6, post free. -Webb's Worsley Bridge Road, Lower Sydenhan Radio, 1 -4. Soho St., W.1. Gerrard 2089 [9947 London, S.E.26.

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