BUILD A MOVING -COIL LOUD SPEAKER
MODERN.MONTHLY IRIETSS Edited by NORMAN EDWARDS Vol. IX. No. 18. JUNE, 1928.
TUL- ZoMZUR sCIcO Cj oMaE
www.americanradiohistory.com `1vI C:k\ \4lkti.1:.-, June, 1928
WONDIZF ilL Nov VALVI l With the Mullai'd PM FIlament.. .«wil.
Mullard always leads ! Max. Fil. Volts - 4.0 The new Mullard P.M.4D Fil. Amps. _... 0.1 has no equivalent ... it is Max. Anode volts 125 the ideal valve for perfect *Imped. (ohms). 6,000 detection and transformer *Ampli. factor .... 12.5 coupling. *Mut. Conduct. Low impedance. 2.1 mA!volt. Large amplification. *At Anode Volts 100, Grid Volts Zero. Consuming only 0.1 amp. at 4 volts and possessing all the advantages of the wonderful Mullard P.M. Filament. The valve for every four.volt valve user. Obtainable from all radio dealers. PRICE 12/6 EACH In Irish Free State, 13;' Q ùllard THE MASTER VALVE
www.americanradiohistory.com June, 1928 MODERN WIRELESS \\\\\ Vol. IX. No. 18. MODERN WIRELESS JUNE, 1928. Pane Pase Editorial 579 The " Harris " Crystal Set .. 621 Microphones in Music Halls .. .. 580 Radio with tirenfell in Labrador 625 Why I Believe in Radio .. 581 The " Quick-Change " Four .. .. 629 The Sydney Two" de Luxe ., 583 Radio and the Gramophone .. .. 635 Loud -Speaker Positions .. 588 Radio Abroad .. .. 640 Listeners Likes and Dislikes .. .. 58 4 My Broadcasting Diary . 641 What are Cathode Rays? .. .. 591 Operating the " Easy -Tune Four .. 643 A 900,000 -Volt Tube .. .. 593 How Your Broadcast is Provided .. 645 Television by Cathode Rays .. .. 595 Dust-The Enemy ...... 648 A Three -Valve Portable .. 599 Valves for Portables 649 Those Classical Broadcasts . 605 American Views on Home Television 650 A Moving -Coil Loud Speaker 807 In Our Test .Room ...... 651 Questions Answered .. ., 610 What Readers Think ,. 654 That Indispensable Inductance 611 Television Notes of the Month ., 658 A Choke Unit Aerial 613 In Passing ...... , 659 On the Short Waves .. 616 Vampire Valves ...... , 662 Standard Coils ...... 617 Radio Notes and News ...... 666 As some of the arrangements and specialities described in this journal may be the subject of Letters Patent the amateur and trader would be well advised to obtain permission of the patentees to use the patents before doing so.
Edited by NORMAN EDWARDS. Technical Editor: G. V. DOWDING, Grad.I.E.E. Scientific Adviser: J. H. T. ROBERTS, D.Sc., F.Inst.P.
Construct the MAGNUM Construct the STANDARD M.W. LOADING COIL "SYDNEY" TWO " QUICK -CHANGE" FOUR as described in this issue.
1 Mahogany As described in this issue. Cabinet, with 12, Baseboard 1. 5 O as used in the 1 Ebonite Panel, 14" x 7", ready drilled 6 0 £ s. d. 1 Copper Screen for above, as described 2 6 1 Ormond 0005 Condenser, 1 Mahogany Cabinet with 12" Baseboard ... 2 2 0 ' Ouick-Change ' with S.M. Dial 13 6 1 Cyldon Condenser, 00025 ...... 9 6 1 Ebonite Panel, 211 x 7", ready drilled ... 9 0 2 Vibrating Valve Holders . 4 0 2 Magnum Panel Brackets ...... 2 6 Four described 1 R.I.-Vartey Straight Line Transformer .. 1 5 0 4 Magnum Antiphonlo Valve Holders . ... 8 0 1 Magnum Neutralising Condenser ... 5 O 2 Magnum Standard M.W. Loading Coils (as in this issue. 2 Magnum used in the original set described) ...... 15 0 Panel Brackets (small size) 1 6 1 Magnum Terminal - 1 Magnum Condenser ...... 5 0 Panel with 7 Indi Neutralising eating Terminals ...... 2 Magnum H.F Chokes ...... 15 0 Price ... 3 6 1 Magnum Terminal Pal with 3 Indi- 1 Magnum Terminal Strip with 8 Indicating cating ... Terminals ...... 4 O Terminals ...... 1 6 1 Interchangeable Choke with Base 5 0 1 Magnum Terminal Strip with 2 Indicating 2 ...... 1 O 7/6 Lissen Base -Mounting Rheostats .. ... 3 0 Terminals ...... 1 Lissen Grid 2 Condensers, 0005 mfd.... 1 1 0 Leak and Corn binator ... 1 6 Igranic Lokvane 1 Lissen Base Mounting Potentiometer 1 1 Cyldon Reaction Condenser, 0001 ...... 7 6 ... 6 1 Lissen 0003 Fixed Condenser .. ... 1 0 2 Liasen Fixed Condensers, 001 ...... -. 2 0 2 Lissen 0005 Fixed Condensers 1 -0003 ...... 1 O ... 2 0 Lissen Fixed Condenser, 1 Lissen 001 Fixed Condenser ...... 1 1 Lissen Grid Leak, 25 meg...... 1 0 ... 0 1 1 Igranic On -Off Switch 2 6 1 Lissen Grid Leak, 2 meg ...... O 1 Special Coil, ready wound with' Base and ...... 1 0 Specialists in Components and constructional 2 Grid Leak Holders ... . Clips ...... 7 O ...... 7 6 1 Dubilier R.O.C. Unit Connecting Wire and ... 2 Dubilier Mansbridge Condensers, 2 mfd. 7 0 Kits for all sets described in " Modern Wire- Flex ...... 1 0 1 Márconiphone L.F. Transformer (low ratio) 1 5 0 less " and " Wireless Constructor." 3 O 1 British General L.F. Output Choke, 20 £6 henries ...... 130 O Comprehensive range of lists including several 1 Copper Screen, as described ...... 3 6 2 Special Coils with Bases ...... 17 6 new Magnum Products will be sent on receipt MAGNUM Wire and Flex ...... 1 6 H.F. CHOKES Connecting of stamp. These compact and light £11 7 6 II.F. Chokes are used atiüit°ii.: 'Ggeitilit... :4ì''.'.'i ', h..1,'t::... }'» .....i_ . ne; and specified by several recognised designers owing to their amazing efficiency. MAGNUM Made in two ranges:- Standard type, 50 to BUILME-JONE 3,000 metres. MOVING -COIL SPEAKERS :.. u Short-wave type, from ô. CO. LTC., below 10 up to 100 incorporating B.T.H. Rice -Kellogg Units MAGNUM HOUSE metres. are now available. TELEPHONE: HOP 6257-8 Price Prices from 10s. Od. to £9 £45 288,BOROUGH HIGH ST. 7/6 Particulars on application. LONDON. S. E.1 .....; ...:.:K:.::: ...... ¡..¡ . . :..;.:: r :.:.:: . . . r.!r// :: t:/.t.. ¡r:.^.:e:.:.:.:.::: ;:.:r:..,: :v.:.r:::: r.u:.ts: v.:: .t::::r::r.s::.: v..y:::: :::::t.T:..:: .::.... :'r:::.::..t1 ::::.:.:.:. :...... "..._.r..., -_._ ......
577 U
www.americanradiohistory.com MODERN WIRELESS June, 1928
4151.40
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The " Sydney Two De Luxe "-" Regional " Rumours-" Radiotic" Farmers
The " Sydney Two De Luxe " most of the area at present served by the Daventry Experimental station, and a power of at least 25 kw. seems FEW sets have gained such rapid popularity as the indicated. " Sydney Two." Originally designed as a two - Even now, however, it must be remembered that the valve receiver for short-wave reception only, it Regional Scheme, as a whole, has not been sanctioned quickly became a " favourite " circuit, and thousands by the P.M.G. The next twin wave -length high -power of amateurs throughout the country have from time to station may be held up, just as the new North London time testified to the " Sydney Two's "- extraordinary one was, and many years may pass before the ten stations efficiency. are complete. That may seem a pessimistic view to take, Consequently, it is not out of place to give in this issue but experience has shown that when dealing with the of MODERN WIRELESS a de luxe version of this receiver, Post Office it is best and safest to take a pessimistic view. and we feel sure that the improvements made in this if, by some lucky chance, the scheme is proceeded with " M.W." version, together with the high reputation of But without undue delay, then in about four years' time the the set, will make it very welcome to our readers. ten Regional transmitters should be in full working order. This de version of the Sydney Two " has special luxe " meantime, amateurs and listeners-and especially features which should enhance its appeal. For instance, In the Captain Eckersley-will rejoice that at last a definite the de luxe model is suitable for reception of all wave- move can be made. lengths ; the set is not confined to the reception of stations operating only on the short-wave band. Constructors will also notice that the set is agreeably " Radiotic" Farmers free from hand-capacity effects on short-wave adjustments, "RAT." is the latest term used to describe people and that the system of reaction control is extremely who have been badly bitten by the " wireless smooth and free from those " threshold " noises which so bug." It has been coined by Mr. Geoffrey often completely ruin reception on so many short-wave Mitchiner, a young boy formerly of Croydon, Surrey, six sets. . who emigrated with a party of juveniles to Canada Needless to say, we strongly recommend this " Sydney weeks ago. Mr. Mitchiner is a wireless enthusiast, and Two De Luxe "-hence its " starred " position in t his before emigrating asked the Canadian National Railways to make special efforts to place him with a farmer issue ! And as " M.W." is not in the habit of bawling officials exaggerated and super merits for every set it publishes who would co-operate with him in his wireless experiments. (although it must be pointed out that all sets, according He has since written to an official of the company in to their class, have to pass a stringent " O.B." test before London stating that he is now working with Mr. William seeing the light of day), we feel sure that many of our McLaughlin, a " radiotic farmer " of Burketon, Ontario, readers will build this set with pleasure and ultimate and that he hopes to be able to pick up, with a special set profit. We hope they will write to us in due course and he is erecting, short-wave broadcasts from a friend in let us hear how they have fared with the " Sydney Two Croydon each Sunday morning. This is believed to be De Luxe." the first occasion on which the radio has been used by an emigrant to keep in touch with his friends in England. " Regional " Rumours Mr. Mitchiner is a close friend of Mr. H. L. O'Heffernan, THE P.M.G.'s sudden decision in approving the new of 2, Chepstow Road, Croydon, Surrey, an experimental North London regional transmitter came as a wireless amateur broadcasting under the call -sign 5 B Y. great surprise. After something like three years' His is an official contact station for certain radio stations dilly-dallying a definite move has at last been made, and, in the United States. Mr. O'Heffernan broadcasts by short if all goes well, within the next eighteen months the new wave across the Atlantic at certain stipulated times, and twin wave -length high -power station should be operating. Mr. Mitchiner will try to pick up these broadcasts each Various rumours regarding sites for the new station have Sunday morning. circulated from time to time, and Potters Bar has been For this purpose he took with him to Canada a two - a prime favourite, with Barnet a close second. The real valve short-wave set which he built himself. It is especially site is most likely to be ìn the neighbourhood of Brook - arranged for receiving short-wave broadcasts, and on it man's Park, which is nearer to London than the other Mr. Mitchiner, while in England, has picked up Schenec- sites suggested. In any case, the station will have to cover tady and Pittsburg. 579
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his own instrument that had been stolen from him. A horn loud speaker, as the theatre management would have it, failed to ensure a reproduction of sufficient faithfulness to make the recognition of the violin plausible. A compromise was made by placing beside two narrow -plaited loud speakers, mounted on a common base -plate, a dummy horn, thus giving the illusion of a voice coming out of the horn. However, the very faithful rendering of the two loud speakers was purposely impaired to the extent of obtaining some of the timbre characteristic of horn loud- speaker reproduction, while making it still plausible that the violinist's By DR. ALFRED GRADENU"1 TZ. instrument was actually recognised by its owner. TIE general tendency of the ball were used for recording purposes, modern stage' to profit on an the necessary amplifier installations Clear Reproduction ever-increasing scale by the being accommodated on the fifth -floor. The reproduction of the voices resources of twentieth-century en- The machinery for generating the was extremely distinct, and entirely gineering is strikingly exemplified anode current was installed in the free from the characteristic defects ley the recent installation of a compre - engine -room (basement), where jll of the average loud speaker, so that the remaining engines and machines even trained spectators failed to of the house are likewise found. realise whence the voices were coming. Eight Loud Speakers Read Eight narrow -plaited diaphragm POPULAR WIRELESS loud speakers were used on the stage for rendering the singing, and were Britain's Best installed by pairs in the ceiling of Radio Weekly. the auditorium in a ,practically in- Every Thursday. Price 3d. visible position vertically above the orchestra. After this promising be2inuing In another scene of the same opera the same plant is to be used in other the composer desired a broadcast operas in connection with any special transmission to be performed, in effects. connection with which a violinist, The installation was made by the among other things, was to recognise Siemens and Halske people, of Berlin.
One of the pairs of plaited diaphragm loud speakers mounted on a common board. hensive set of loud speakers at the Berlin Municipal Opera House. Elaborate Equipment Though the need for a loud- speaker transmission to the stage was at the time only apparent in exceptional cases, this complete plant was installed at the outset, and was for the first time taken into operation in connection with the recent first night of E. Krenek's popular opera, " Jonny spielt auf " (" Johnny is playing up "). The composer, for instance, in the second act asked for the noise of an avalanche to be represented by a choir. This choir being installed on the third -floor, its singing had to be made audible by loud speakers throughout the auditorium. Band microphones installed in the music- nich are installed on the fifth floor of the Berlin Municipal Opera House 580
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Here the author of the famous "Scarlet Pimpernel" gives strong reasons why she is one of the keenest supporters of broadcasting. THERE was recently an amusing complaint that the Then we are told that the growing habit of decreasing modern general use of wireless was affecting the our allowance of exercise will be so increased by the weather in Great Britain, and causing rainy chance of having our amusements-now almost our only summers and severe winters. How this rumour started means of physical activity in many cases-brought to us I do not know, but the amount of credence it gained in our homes will devitalise the races of the world, leaving proves what an amazing amount of superstition is left in a nerveless, incapable creature in course of time which our natures after all these centuries of civilisation ! will lose the greater part of the use of its limbs, and the Say there is a mystery in a thing whose workings are joy that conies from glowing health. not yet fully understood, and thousands of people will see something akin to witchcraft in the simplest phenomena ! " Immense Potentialities For Good"' There have been more serious criticisms of radio, But all these arguments are, in the first place, quite however, since Senator Marconi gave the fruits of Iris powerless to stop the Juggernaut advance of progress. research to the world. Men and women really qualified Much the same things were said in the advent of railway to judge have thought and said that it is, for example, trains, of aeroplanes, of the telephone and of the motor- killing all that is best in drama all over the world. car. There have been protests against everything calcu- They argue that patrons of the theatre will not go i.o lated to speed up the world. Yet they have not succeeded, the trouble of venturing out of their homes on cold or and the thine- that were complained of have seldom done wet nights when they can be given much harm. In the case of wireless, good music and other forms of enter- I believe its effect will not be merely tainment at home merely by turning passive, but that it has immense a switch. This, they contend, will potentialities for good ! mean the gradual extinction of one In the first place, will it not help, of the noblest arts for the expression rather than harm, drama ? An im- of human emotions, and incidentally mense new public will be interested the throwing out of employment of in the theatre by hearing the broad- thousands of men and women. cast extracts of plays, and the interesting facts about them and the Alleged Damage great players of the past which are Other critics have levelled their frequently given. Employment Will attack on radio because they state be given to a new class of actor, who that it is damaging literature. No will make a specialised study of radio longer are we left with leisure to react drama, which itself has great future widely, and gain the inestimable possibilities. comfort and companionship of good Literature should certainly gain literature. Instead, we are given a from the new interest which will be few fragmentary facts now and again aroused, in it by the introduction of by wireless, and with these we content constant references to it which are ourselves, like travellers who mistake Baroness Orczy, the well-known always made in cultured conversation. mirages for real oases in an arid desert. novelist. Moreover, debates between famous tSE
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battery, no other grid bias is neces- and he intends to take this back with sary. The incoming signals at this him to Kabul. eg GRID BIAS- stage seldom exceed a small fraction How to avoid distortion of a volt. into eeeeeeeeeceeeeeeeeee For the detector valve, the swing A recent investigation the efficiency of school wireless sets shows may rise to 2 or 3 volts, so that THE object of the grid-bias bat- schools of the County of one cell (14 volts), or two cells at that the tery is to keep the grid of the hold the record for satisfactory most, of the biasing battery will be Kent amplifying valve always nega- reception. tive. relatively to the filament. What sufficient. The same amount will * * * is not sometimes borne in mind is usually suffice for the first low -fre- tnat although there may be 3, 44, 6, quency stage, though it may be in- When two of the inhabitants and or even 7-1 negative volts on the grid creased to 44 volts if the high-tension the resident nurse on the island of St. when signals are not being received, is above 80 volts. Kilda were taken ill, a wireless S.O.S. this may not be sufficient to keep the for medical assistance was sent out, a grid negative when the set is in Power -Valve Bias doctor and nurse were despatched to operation. For the power stage, using a plate the island, and the patients were voltage of 120 or more, the grid bias brought to the mainland in the steamer Large Grid Swing may be at least 15 volts (ten dry - lighthouse commissioner's The effect of the incoming signals cell units), if good reproduction and " Hesperus." - * is to swing the normal grid voltage an economical use of the high- * * up and down about its normal or fixed tension batteries are' points worth £4,000 Award setting. In a four -valve set with a consideration. The Royal Commission of Awards power amplifier, the " swing " on the to inventors recently awarded £4,000 last stage may easily rise to between plus royalties to the Metropolitan 15 and 30 volts, or even more if power- Vickers Company, Ltd. (Metro -Vick), ful signals are required. In the 'FROM FAR AND NEAR'; in respect of wireless reception earlier stages the swing is, of course, apparatus. less pronounced.
The Early Stages His Majesty The King of Afghanis- The call -sign of the new German Generally speaking, if the grid of tan recently purchased an eight -valve experimental short-wave transmitter. the H.F. amplifier is connected to the super -heterodyne receiver with a at Goeberitz is A F K, and the wave- negative terminal of the filament gramophone pick-up and amplifier, length 37.8 metres. . from the rolling prairie, may no longer be isolated islands in the grass, but may be given a close link with the WHY I BELIEVE IN RADIO happiness of community spirit from the cities. ß -continued from page 581 More than these, even, is radio a boon to those lonely reßßegeßee..$geeeeeeeeeeeeee white people who are isolated from their kind in the heart of some land where even the colour of the in- writers are arranged, and books of importance so frequently habitants is different from their own. Loneliness- discussed that a new vista will open out before thousands nothing else-has in the past driven such men to drink, who have always previously been accustomed to avoid drugs, and worse. Now they have but to erect a portable the masters of literature in case they should prove boring. mast, switch on a button, and they hear the voices of their The complaint on grounds of harm to physique is kind, dance -music lilting from a ballroom, or the soothing manifestly absurd. The human body demands a certain croon of a violin to steal awaytheir pain. amount of exercise, and that we all give it whenever we can. Besides, it does not need skilful argument to show Boon to the Sick whether the average young man or woman would rather Think alone, I say, of the great boon to the sick and choose to sit and " listen in " if there was an alternative suffering in hospitals and elsewhere, that they can now choice of any such active gaine as cricket, tennis, or hockey ! have music and many other hitherto impossible pleasures Wonderful Advantages brought to them where they lie, so that they may for a while forget their unhappiness and join again in the In addition to all this, of the wonderful new think mirth of the healthy world. which radio has brought to us. Ships can advantages Yet these are but single instances of the great gifts knowledge that they are put out to sea now without the which wireless brings us.. Besides these, there are all the to be off for a space from all human kind. Wrecks cut marvellous utilities of it-the incalculable speeding up of fires ship can now at and there are still, but the stricken world communications, the increased possibilities of inter- fling a of agony crackling across the waves, and least cry national exchange of opinions, and consequent increase from all points be sure that rescuers will immediately turn in trust, and the marvellous future of television and tele- of the compass and come as fast as steam can hurry them photography which as yet are still in their infancy. to the scene of the disaster. Yes, emphatically I believe in radio ! I foresee that it advantage has been brought Imagine what an immense will bring vast advantages to our struggling world. I of our vast Empire'-to people by wireless to the outposts believe that. in time it will be ranked as perhaps the weeks no other human beings, who for days and see greatest of all modern factors that have added to the no of amusement save what perhaps, or have means progress of humanity. they can themselves invent. The Canadian Government is already doing all in its power to stimulate the interest (World Copyright (1928) by The Author's Advisory Service, London. of farmers in radio, so that their little kingdoms, carved All rights reserved. Reproduction in part or whole prohibited.) 582
www.americanradiohistory.com June, 1928 MODERN WIRELESS
A magnificent version of a receiver which in its original ,form achieved xÈá.nev ahFvLIE immense popularity. In its present guise, the set preserves all its efficiency on the short waves, the ease of handling is enhanced, and it can also be used for ordinary
broadcast reception. Designed, built and described by the " M.W ' Research Department. 000s OH.T.4- F you have not yet made for ¢ yourself a short-wave receiver R.F.C.b +0--41H7.+i you are missing one of the few P/aiON 600/ o00.5 b things remaining in radio capable of giving a real thrill to even the most hardened long-distance enthusiast. Until you have tried it, you can have little idea of the intense satisfaction H.T.- to be derived from an experience such as the following. One of the first tests which the writer carried out on the L.T+ " Sydney Two " was when the B.B.C. T way relaying the transmissions from one of the well-known Australian 18 W/TCH stations, and on one of these Sunday afternoons it was noticed that the R.B.C. was having considerable. COMPONENTS AND MATERIALS REQUIRED 11, in. x 1 Ebonite panel, 14 in. 7 in. x 1 or 1 0005 variable condenser (Ormond 2 Pieces of ebonite, 3, in. x
. ', ¡;, in. (Any good branded material, in set. Any good make with a in., for H.F. choke mounting. Becol, Ebonart, Radion. Red Seal, sound positive connection to the 4 Sockets with nuts (Clix or similar Trelleborg, etc.). moving vanes). Note : If you type). type). . . 1 Cabinet, 14 in. x 7 in. x 12 in. deep, intend to use the set only on 4 Standard plugs (Clix or similar with baseboard and brackets (Art - short waves choose a 0003 -mid. (Two for G.B. and two for con- craft, Bond, Cameo, Caxton, Maker - condenser). nections to reaction coil.) e import, Pickett, Raymond, etc.). 1 Vernier dial for above (Must be of a 2 Valve pins for H.F. choke. 1 L.F. transformer (R.I. & Varley really good smooth type. Not 1 Piece of ebonite, 8 in. x 2 in. x 1 in., " Straightline " in set. Any good necessary with some condensers for terminal board. make). which actually incorporate a slow- 1 Piece of ebonite, 3 in. x 2 in. x .', in., 2 Sprung valve holders (Benjamin, motion mechanism). for terminal board. Bowyer -Lowe, Burndept, Burne- 1 00025 variable condenser (miniature 1 Sheet of copper, 12 in. x 6 in. x Jones, B.T.H., Igranic, Marconi - type). (Peto -Scott in original set.) h in. thick. . phone, Pye, Redfern, W.B., etc.). 1 L.T. on -off switch (Benjamin, Igranic, 1 Standard Becol former, 3 in. long, . 2 Baseboard rheostats (Lissen in set. Lissen, Lotus, etc.). for short-wave coil (See text). No. 18 plain ... Any similar type, Igranic, etc.). 1 Baseboard neutralising condenser Small quantity of copper .. 1 Baseboard 400 -ohm potentiometer (Any standard make of fairly large wire for coil, also No. 34 S.W.G. (Lissen in set. Any similar type. capacity. Bowyer -Lowe, Burne- D.S.C. wire for H.F. choke, and 200 ohms will serve). Jones, Igranic, J.B., Peto -Scott, etc.). material for wiring set. ii .. 2 0005 fixed condensers (Clarke, 10 Indicating terminals (Belling & Lee, Cardboard tube for reaction coil. ... Dubilier, Igranic, Lissen, Mullard, Eelex, Igranic, etc.). 3 Spring tapping clips. T.C.C., etc.). 1 2-meg. grid leak and holder (Dubilier, Quantity of single flex, sundry pieces e of wood for coil supports, etc. ... 1 .001 fixed condenser (Clarke, Dubilier, Igranic, Lissen, Mullard, etc.). .. Igranic, Lissen, Mullard, T.C.C.,etc.). 1 Piece of tubing, 2 in. diameter by NOTE.-The extra components and of the set ... 1 0003 fixed condenser (Clarke, 3 in. long, for low-wave H.F. choke materials for the adaptation . Dubilier, Igranic, Lissen, Mullard, (Any good insulating material, on the upper waves are given in the . Pirtoid, Radion, etc.). text. ... T.C.C., etc.). 583
www.americanradiohistory.com MODERN WIRELESS June, 1928
difficulty, conditions apparently being large measure from the fact that a thing about the station being about to very bad at their receiving station. quite small and simple set gives all close down on a fine Australian What was coming out from 2 L O was that is needed, even a one-valver morning, the listener all the time almost unrecognisable and scarcely a being capable of picking up such being aware of the fact that it is, to word could be heard of the Australian transmissions as those of the famous him, a particularly dreary British announcer's remarks. short-wave broadcasting station Sunday afternoon and that the morn- K D K A at Pittsburgh, U.S.A., this ing to which the Australian is referring ! Superiority station being audible practically every is Monday morning ! Again, if you Accordingly, it was thought that it night in the winter, while 2 X A D, can read a little Morse there is the would be interesting to see whether 2 X A F and other American short- never-ending interest of picking up conditions were as bad in the locality where the " Sydney Two " was being tested, and it was therefore connected up to an indoor aerial and search made for the short-wave signals from Australia. Imagine the sense of superiority which resulted when it was found that the station could be picked up quite readily, and received at good strength for considerable periods with little or no interference
or fading ! Of course, one told oneself that it was simply that conditions for short-wave reception vary from one locality to another to an extraordinary degree, but it must be confessed that whatever one tells oneself there is always a sort of sneaking feeling that " those B.B.C. fellows don't know wave broadcasting stations can also signals from amateurs from almost anything about short-wave reception. be heard whenever conditions are at every part of the inhabited globe. My set is a real set." all favourable, often even in summer. Transatlantic reception on the newer With a two -valve set, again, one or wave -lengths of 45 metres and below Fascinating Possibilities other of the Australian stations can is now quite commonplace, and is Seriously though, the fascination of also be picked up on many occasions, easy with even the simplest of short-wave reception is really extra- and one can experience the rather receivers. ordinary, and it must be experienced extraordinary sensation of hearing to be realised. Probably it comes in the Australian announcer say some - A Mistaken Idea It seems that the fascination of short-wave work is at last beginning to be realised by the ordinary broad- cast enthusiast, and short-wave sets are being built in greatly increased numbers. No doubt in the past it was natural that some listeners should rather fight shy of them, probably partly because there were few regular short-wave telephony transmissions and very largely because there was a general impression that short-wave sets were very mysterious and difficult to handle-an idea largely fostered by the more advanced short-wave enthusiast, who made a practice of talking a rather horrible jargon and loved to foster the idea that only the real expert could make and operate a short-wave set successfully. Not Difficult It was only natural that the plain constructor should get the idea that something very special indeed was needed in the way of construction and layout to get any results at all on short waves, especially when he saw This photo was specially taken to show three of the characteristic features of the set. the extraordinary lengths to which (s) Is the special home-made H.F. choke for the short waves, which can be replaced in a the went, moment by an ordinary standard one for longer waves ; (2) indicates the plug and socket enthusiasts sometimes dis- connections to the reaction coil, and (3) is the small series condenser. pensing with a cabinet because of 584
www.americanradiohistory.com June, 1928 MODERN WIRELESS possible losses in the wood, standing are high efficiency resulting from tive letters have be nn received from their skeleton sets on empty bottles certain special features of construc- readers who built the original set, to lift them off the table, and so on. tion, ease of operation resulting from quite a number of these reporting One even seems to have heard of the the fact that by the use of a simple success in receiving the Australian man who had the horrible experience tapping scheme a very wide range of transmissions. of finding that his new short-wave set waves can be covered without coils Wide Wave Range In its original form the -set vas only intended for reception of wave- lengths between about twenty and forty metres, so that it was essentially a short-wave set, but in producing the " De Luxe " edition for publica- tion in l\IoDERS WIRELESS, provision has been made for extending the wave -length range upwards to cover the ordinary broadcast wave -lengths in addition, and thus you can employ the set as a standard equipment for broadcast work likewise. Further- more, quite a number of special refinements have been added, such as the use of a neutrodyne condenser in series in the aerial circuit, so that you efficient Neatly balanced ! The panel layout is unconventional, but produces a very can use this as the series capacity of the wiring. arrangement when desired instead of the home- simply would not give any signs of being changed, and considerable ease made condenser called for in the oscillation or reaction, the reason of construction, chiefly a result of the original design, the provision of metal being that one of the bottles on which use of a very easily-made specia! coil. screening behind the panel to mini- he had placed it was made of glass A really remarkable series of aprecia- mise hand -capacity effects. and so on. containing a high proportion of lead ! (Slightly exaggerated for the sake of effect, perhaps, but we have all heard something like this at one time or another !) :>:,;:,. Combined Sets It has been realised of late that the original idea that a separate special set was needed for short-wave recep- tion was a great drawback from the point of view of the home constructor, who often did not feel that he could afford to build an entirely separate set and keep it going in addition to his usual broadcasting equipment, so that a good deal of ingenuity has been expended of late in devising sets capable both of short-wave reception and of work on the ordinary broadcast waves, a combination which has been shown to be perfectly feasible, thereby exploding one of the earlier shibboleths of the game. The " Sydney Two " de Luxe, for example, the design which we shall be considering in the pages which follow, has been designed primarily as a highly efficient short- wave set, yet by including suitable coils it will also work well as a plain " detector and L.F." receiver for ordinary broadcast purposes. This set in its original form of the " Sydney Two " was first published in " Popultar Wireless," and has Here is a general key to the layout. (i) On -off switch; (z) condenser across transformer proved to be probably the most primary (to be -omitted if R.I.-Varley type not used) ; (3) tuning condenser; (q) H.F. choke popular of all the short-wave receivers socket; (5) reaction condenser; (6) " safety condenser " in reaction circuit; (7) detector valve socket; (8) detector rheostat; (9) series condenser; (io) grid leak and holder; (II) grid published in either that journal or condenser; (Y.2) tuning coil; (i3) condenser across 'phones; (i4) L.F. valve rheostat; (15, 11IouEr,x WIRELESS. Its special points L.F. valve socket; (i6) L.F. transformer. 53,5 X
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In its latest form it probably repre- a combined broadcast and short- for an up-to-date design for use on sents something like the ideal in a wave set, or as a good standard re- the lower waves exclusively. really simple but efficient short - ceiver for the more experienced short- The circuit originally chosen was waver, and it is equally suitable as wave listener who has been looking one of the best of those available for
SOLDERED 70 00025 COPPER SHEET REACT/ONCOHDR
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F/L. RES dÿ%i'//. TÓ1 CO/L
F/L RES.
386
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June, 1928 MODERN WIRELESS short-wave work, and no alteration Securing the start and finish of the taken as before to a couple of has been made here in producing the winding is quite easy ; the wire is sockets in a wooden cross -piece. " De Luxe " edition. quite stiff, and will be firmly held if The arrangements for the H.F. It will be seen that by connecting the end is passed through a small choke are also a characteristic feature the aerial to one of the alternative hole drilled in one of the ribs and the of the " Sydney Two " de Luxe. For terminals a neutrodyne condenser end turned up, half an inch being the short waves a special choke is is brought into circuit in series left projecting for the attachment of used- consisting of a winding of 75 with the aerial lead, and a suitable the clips. turns of No. 34 D.S.C. wire on the adjustment here is very helpful in The mounting of the coil is very piece of tube mentioned in the list getting proper reaction effects on simple, since all connections are made of components. In one end of this the short waves (it is not intended by means of clips and there is thus tube a wooden cross -piece is fitted, for use on the longer waves, of no need to arrange for any plug and and to this is screwed an ebonite course). socket base. A wooden cross -piece is base -piece in which are mounted two fixed inside one end of the former by valve pins or plugs such as the Clix The Short -Wave Coil means of two small brass screws and Felex types, to which the ends passing inward through holes in the of the winding are taken. These The short-wave coil is wound with walls of the tube, and to this is pins are placed 4- in. apart and they spaced bare wire, and three flex screwed a wooden upright piece; 3 are to be inserted in two corre- leads with tapping clips are provided in. long. The lower end of this sponding sockets in another piece of for making connection to it. Of latter is arranged to fit tightly ebonite screwed down upon the these leads (T2 on wiring diagram), between two wooden strips screwed baseboard. one comes from the grid condenser, down upon the baseboard. The coil and one (T3) from a point on the can thus be pulled out and replaced The Long -Wave Choke these wiring of the earth terminal, and with one for the broadcast waves in For work on the ordinary broad- are normally attached to the extreme a few moments. cast waves you will need to. replace ends of coil. The practical the This latter coil is to be wound on this www.americanradiohistory.com MOW.RN WIRELESS June, 1928 4`1 4 ef34,-mge eGeG causes a partial reflection back on LOUD -SPEAKER to the diaphragm and may even OVERSEAS RADIO cause very serious distortion. 2 c73 POSITIONS In some of the newer houses built ffi ITEMS How you should place the instru to -day, in which thin slate asbestos 2 get results. 3 ment to good over a wooden framing is used as 1_P By J. R W. D Using a power of only four watts, dividing walls, it may often be found three Dublin amateurs recently got that the whole wall tends to vibrate into two-way touch with Victoria, when the loud passages are being VVHEN a large orchestra is to be Australia. This is claimed to be the broadcast special precau- reproduced ; in this case the loud first two-way amateur communication tions have to be taken so speaker should be placed in the corner between the Irish Free State and the that each instrument will sound at on a firm pedestal and some form of Antipodes. fairly heavy drapery located at the its best. The cornet player must , rear of the speaker. It is remarkable not sound as though he and he alone Part of the celebrations marking constitutes the band. The players the effect that this drapery has on any tendency to wall vibration. the tenth anniversary of the Republic are so arranged that the microphone of Czecho-Slovakia will take the form is in a position to pick up each instru- of a wireless exhibition to be held at ment at its correct strength. Easily Tested Should the room have an extra Brunn from June 3rd to September At the receiving end the loud 30th. speaker must be placed so that friends high ceiling, place the speaker a little higher than usual. It is surprising listening to the programme do not first how distance from the floor effects Denmark's short-wave broad- appear some to be in the orchestra has results. Rough tests may easily be casting station recently been stalls and others at the farthermost on 78.5 on Mondays, carried out in this direction with a testing metres heights of the gallery. It is a good Wednesdays and Fridays, between pair of steps placed against the wall, plan, once the most suitable position 11 p.m. and -1 a.m. for the loud speaker has been found when by placing the speaker on each always to step in turn the most suitable height in any particular room, The Copenhagen station recently place on spot and may easily be found. it this particular installed a new transmitter for broad- to point it in the saine direction. Very good results can be obtained by employing two loud speakers casting its regular daily programmes Vibrating Objects placed at different heights. One, upon 327 metres. Sometimes it is noticed that on perhaps, very near the ceiling and the . particular nights the loud speaker other rather lower than usual. This Wireless signals from American appears to be very tinny on certain scheme gives an excellent sound amateurs were first received direct by notes, yet at other times results are distribution. the amateurs of Great Britain in 1921. quite O.K. Very often this is due to placing the speaker upon an object THE G.O.M. OF RADIO which also carries porcelain or glass- ware. These peculiar sounds are not always due to the loud speaker, but to the vases, dishes, or whatever they may he, responding to a certain note issuing from the loud speaker. Humming can be exceedingly irri- tating and can spoil many excellent programmes. But frequently, after careful search, it will be traced to the loud -speaker extension leads running parallel 'to electric light mains, especially if alternating cur- rent is in the house. Mysterious clicks every few minutes is another fault which can be traced to a similar source, and is due to the sudden surge which takes place in the mains when a circuit is made or broken, i.e. on closing a switch. A Peculiar Effect If the room in which the loud speaker is giving trouble is much longer than it is broad, point the loud speaker so that it is facing the longer The above is one of the latest photographs of Sir Oliver Joseph Lodge, who celebrates the way of the room. ' In certain types 77th anniversary of his birthday, on June 12th. Everyone knows that Sir Oliver is our of loud speakers, notably the cone greatest living scientist, and the radio public in particular has learnt to appreciate type, a peculiar effect is often set up the fine radio pioneer work carried out by Sir Oliver long before Marconi was the speaker has heard of. The coherer and the first tuning apparatus for radio are but two of his due to the fact that many contributions to the science of wireless. We are sure our readars will join with been placed so as to face close to an us in wishing him hearty congratulations and many happy returns on his 77th birthday.- opposite wall of the room. This The Editor. 588 www.americanradiohistory.com June, 1928 MODERN WIRELESS LISTENERS' LIKE DISL1KIS An article all should read. I iuTIcism of the broadcast programmes is so easy and are diversified, and hundreds of high - so general that it is not surprising if we come to tastes extremely would be required if we were cherish the fond delusion that we could vastly power transmitting stations what we want. improve the programmes if their selection were put into all to be given exactly hands. our "One Man's Meat . . ." we should no And, indeed, undoubtedly have difficulty Naturally we find it difficult to realise that our own in making them suit our own individual tastes much favourite items mar be other peoples pet aversions, better than can the B.B.C. But there our success would and that what we dislike intensely mar be giving pleasure probably end ; and when it came to compiling, week in, to thousands. And vet that is undoubtedly the fact, week out, programmes which the public as a whole however catholic our tastes may be. would appreciate, most of us would, I fear, soon have to There is one particular feature in recent programmes confess to ignominious failure. which seems to me to be uttelr stupid and inane. Yet I am told. and I fully believe it to be true, that after every broadcast of this item hundreds of appreciative letters are received from every part of the country. I do not doubt The Earl of Drogheda is particularly fitted to write an article upon the likes and dislikes of listeners, for since the inception of The Wireless League he has been closely identified with its work. He has had a distinguished career in the Foreign Office and served in the Irish Guards. The Earl of Drogheda. It is very easy to expect too much from broadcasting. Science and organization hare enabled us to listen during the greater part of the day and evening to a continuous programme brought into .our, own homes. And, having accepted this miracle as part of our everyday life, it is but a short step farther to demand that at whatever hour we care to switch on our set we shall hear something that will give us pleasure, or entertainment, or instruction, or for at the moment. whatever we happen to be in thenmood DON'T NEGLECT THE ON-OFF SWITCH. A good deal of That is, of course, asking for too much. It might be criticism arises from what the author aptly terms " the unpleasant practicable if we all thought alike, but fortunately our habit of keeping one's set continually switched on." 5S9 www.americanradiohistory.com MODERN WIRELESS June, 1928 that everyone who made inquiries would have the same whilst not ignoring the claims of the various sections of experience. the minority. Nor should it be forgotten that a good deal of programme To what extent the B.B.C. has succeeded in doing this criticism arises from what, for want of a better phrase, it must be very difficult for the authorities themselves, and I can only call indiscriminate listening. By that I mean it is next door to impossible for any private individual, to the casual switching on of one's set without taking the estimate. For the immense audience-running into many trouble to refer to the paper to see what is being broadcast millions-of which we are all a part is, in the main, a at the moment, or the unpleasant habit of keeping one's silent audience. It is a very small minority which set continually switched on. troubles to express its views on the entertainment offered In the first case one is liable to hit upon a time when to it, and one can only guess at what the dumb majority something of no interest to oneself is being broadcast, to is thinking. switch off with or without an imprecation, and often to miss a particularly pleasing item which may be following Join a Society immediately afterwards. The result may well be that the vocal minority gets In the second case, apart from laying oneself open to what it wants in opposition to the wishes of the majority. justifiable homicide by other members of the household, But one presumes that the B.B.C. is well aware of this one is completely deadening one's powers of appreciation. danger, and, after all, it is a risk which silent majorities Admittedly it is nobody else's business what use one always run, and a result for which they have only them- makes of one's set, but in either case one is not giving the selves to blame. programmes a fair chance. The moral of all this seems to be that the only way in One of the most popular items in the programmes-Jack Payne and his B.B.C. Dance Band. Let us assume, however, that we use our wireless sets which we as individual listeners can attempt to improve with a reasonable amount of thought and moderation. the programmes-or perhaps I should say, can attempt The question still remains, " Do the programmes need to make them more representative of the wishes of the improvement and, if so, what can we as individuals do public as a whole-is to take the trouble to express our to improve ? them " views on them more often. How are we to do so ? To the first part of this question most people will return Well, the most obvious way is to write to Savoy Hill an unhesitating affirmative. How far that affirmative is letters of praise or denunciation, as the case may be, justified it is hard to say, for, as I have already explained, whenever an item particularly pleases or displeases us. it is impossible to judge the matter in the light of our That is the most direct, but rather a troublesome method. own private feelings. Another way-and a very good one-is to take part in any ballots on the subject organised by the Press. A B.B.C. Still Learning third, and perhaps the best, way is to join one of the Still, it is a fair assumption that, even after several societies formed to promote the interests of listeners. years' experience, the staff of the B.B.C. have probably By this one gains the advantage of consultation and con- not achieved a perfect interpretation of the wishes of the certed action with others. public. I do not think that they would themselves lay The largest of these societies is the Wireless League, claim to any such achievement. Rather would they, I which has its head office at 7, Southampton Street, imagine, admit that they are still learning, in the same Holborn, London, and an enquiry addressed to the way that the listening public itself is still learning what to Secretary of the League at that address would no doubt ask of broadcasting. elicit any information desired as to its numerous activi- The business of the broadcasting authorities is obviously ties, aihongst which is the frequent submission to the to strike a balance between conflicting opinions, and to B.B.C. of programme reports based on correspondence compile their programmes in accordance with what they from its members and on suggestions received from believe to be the wishes of the majority of their public, its representatives throughout the country. 590 www.americanradiohistory.com MODERN WIRELESS -72,'. This easy -to -understand article makes clear the nature of these extremely interesting rays which figure so largely in the latest scientific developments of to -day. By Dr. J. H. T. ROBERTS, F.Inst.P. describing the nature of cathode or fundamental negative particles of The raising of a substance to a of IN rays I suppose most scientific electricity. . - high temperature has the effect men would begin by outlining Súppose that owing to some violent producing ionisation, and the hot gases what takes place in a nearly evac- shock or disturbance an atom of drawn from the neighbourhood of uated glass vessel when a high- matter loses one of the electrons from flames or incandescent substances are tension electric discharge is passed its electronic system, then there is an very strongly ionised. through it. This is, no doubt, because unbalanced positive charge equal to Without, however, discussing cathode rays were first discovered in the negative charge which has been further the various methods by which some such way, and also because, carried away by the escaping electron. ionisation is produced, let us now strictly speaking, cathode rays must The result is that the atom as a whole deal particularly with the ionisation necessarily (as their naine implies) be has become positively charged. In which takes place in a vessel which is associated with the discharge from a the same way, in certain circumstances nearly evacuated and through which cathode. an atom may acquire an additional an electric discharge is passed. Tubes electron from outside, in which case Abe the atom becomes negatively charged CATHODE FUORESCENT SCREEN as a whole. CATHODE 4f--p 'á./ RAYS Causing Ionisation Now let us see in what circum- F/G. stances atoms of matter (and with t PERFORATED A3oo atoms I include, of course, combina- SCREEN CATHODE RAY BEAN molecules) f GZ OR PENCIL 1/NY/SIRLE) This simple diagram illustrates the motion of atoms called may tionsmay c_ C of electrons away from the cathode and gain or lose electrons and so become BRioHT.Svur HEwhvo POINT of IA//0ACr of pgsitive ions away from the anode in a negative or positive ions. Showing how cathode rays are produced, discharge tube. There are a considerable variety and may be allowed to shoot through a of so-called " ionising agencies." For perforated screen, producing a bright spot on fluorescent screen. I think, however, that it will be example, if X-rays or ultra-violet a much simpler, especially as my readers light, or for that matter even ordinary of this kind are probably familiar to are radio experimenters, to begin at sunlight, fall upon matter, there is almost everyone, some of the earliest a different point in the story and to usually some degree 'of ionisation forms being known as Geissler tubes. state at once that cathode rays are produced ; in other words, some of If we have an almost completely none other than our old friends the the atoms exposed to the radiation exhausted glass tube through which electrons which perform such useful have their electronic systemss upsyMeenupset. two metal electrodes are sealed, and service in their passage between - sually the ions produced in this we apply to' these electrodes the out- the filament and anode in a wire- way are positive ions, but in certain put from a high -voltage generator less valve. In other words, you circumstances the electrons so set (such as the secondary of an induc- know now that in dealing with free may wander about and eventu- tion coil), the following effect takes cathode rays you are dealing with ally attach themselves to other normal place : First of all there will be a none other than the familiar electrons atoms, so forming negative ions. few wandering ions present in the 591 www.americanradiohistory.com MODERN WIRELESS June, 1928 small amount of residual gas in the of electrons in another part of the beam will be subjected to a rapidly - tube (there are always a few ions tube. Electrons produced in this way varying shifting influence and the present even in the atmosphere, these are known as cathode rays, and owing faithfulness with which the bright being probably produced by the to their exceedingly small mass they spot on the screen will follow the effect of sunlight and other weak are susceptible to rapidly -changing fluctuations in the transverse or dis- ionising agencies), and under the electric and magnetic fields. - placing electric field will depend upon powerful electric field between the the lightness in weight (smallness in electrodes in the discharge tube the Exceedingly Light mass) of the particles of the cathode negative ions will be driven away As to the actual velocity of stream, and also, upon the quick- from the negative electrode and the cathode rays, this, of course, depends ness with which they reach their towards the positive, whilst the posi- upon the potential difference or vol- objective. tive ions will be driven in the opposite We have already seen that the direction. tage between the electrodes, but in a fairly high vacuum the cathode rays cathode particles are exceedingly light, If the electric field is sufficiently may attain a velocity of 100 million. and we have further seen that in the intense the few residual ions initially feet per second, or about 20,000 miles conditions under consideration they present in the gas will acquire may attain a velocity of - a second, which is approximately one - about one considerable velocities and in their tenth of the velocity of light. tenth of the velocity of light, which is progress they will collide with sonic The mass of the electron or cathode exceedingly high as compared with the of the uncharged normal gas mole- particle is also exceedingly small, velocities attained by mechanical cules or atoms. If the collisions with and is only about 1/1,800 of the mass of objects with which we ,are ordinarily the atoms or molecules are sufficiently the hydrogen atom, which is the familiar. violent, an electron (or electrons) may lightest of all atoms. Therefore, the cathode stream be shaken out from atoms or mole- represents virtually a " weightless " cules which are struck in this way, or " massless " beam, and is eminently with the result that a further supply INDUCTION ELECTRIC Paco CATHODE RAY BEAM adapted for following and indicating COIL FOR of ions immediately becomes available. FOR DEFLECT/NO DISPLACED SPor D/SCNAReE /Aye exceedingly rapid variations in electric These newly -born ions will instantly Fc j voltage. In the same way, if a mag- proceed to move in their appropriate netic field be applied to the rays during directions under the influence of the their passage towards this fluorescent electric field and will again strike screen the rays will follow exceedingly normal molecules or atoms of the rapid variations in the characteristics gas and produce still further ions. OR/O/NRL SPOT of the magnetic field. If both electric R3o2 and magnetic fields are used the rays " Ionisation By Collision " will similarly give an extremely faith- This figure illustrates how a cathode-ray ful indication of the combined or The negative electrons, as you stream may be projected between metal know, are of very small mass as plates at different electrical potentials and resultant of the effects due to the compared with the positive ions, so deflected by the electric field. two fields. and consequently they acquire a Finally, a word or two as velocity under the influence of the to the The Oscillograph way in which a electric field which is enormously cathode-ray system Instead of the fluorescent screen, as exceedingly greater than the velocity acquired may be used an delicate which is comparatively insensitive, a by the positive ions. The negative indicator of electric or magnetic highly sensitive photographic plate. If we look electrons in the discharge tube will variations. at the diagrams may be used, in which case a per- we see proceed away from the negative herewith that if the cathode manent record of the movement of stream is allowed* electrode (or cathode). We may to pass between the point of impact of the cathode two across which a regard them as proceeding from the plates transverse beam with the screen may be ob- cathode and as striking the anode, electric field is set up, the stream will tained. be deflected from Original course, and as a matter of fact the impact of its One of the most successful uses to the negative particles upon the anode since the cathode particles, being whiéh the cathode-ray beam has been negatively electrified, will be repelled sets free further supplies of positive put is_ in the so-called " cathode-ray ions, whilst the impact of the positive by the negative plate and attracted oscillograph," which gives a very ions upon the cathode sets free further by the positive plate. If the cathode faithful record of exceedingly rapid supplies of electrons. Thus, although stream is falling at its destination variations such as the characteristics upon a fluorescent screen, it will mark the presence of a certain amount of of telephone speech currents, high - gas in the discharge tube is necessary a bright spot at the place where it frequency oscillatory currents, and impinges on screen ; to give the discharge a start, the the therefore so on. supply of electrified particles to carry any shift of the point of impact (due, Owing to the enormously rapid on the discharge may come also for instance, to the application of a " response " of .cathode-ray devices, (once the discharge has started) from transverse electric field, as just men- attempts are being made to apply the electrodes themselves. tioned above) will be immediately this principle to television, and I by a in of We have seen, then, that there is a evident shift the position hope that the foregoing explanation stream of rapidly -moving electrons the bright spot on the screen. of the nature and general properties proceeding from the cathode and of cathode rays will enable readers to striking the anode. If we drill a small Can be Rapidly Controlled understand, in a general way, why hole through the anode as shown in If the electric field through which cathode rays are being tried for over- the figure, some of the rapidly-moving the rays are shooting is one which is coming some of the tremendous electrons will shoot through this hole varying in its voltage characteristics mechanical and manipulative ob- and will form a pencil or tiny beam with great rapidity, the cathode-ray stacles of television. 592 www.americanradiohistory.com June, 1928 MODERN WIRELESS Producing a high-speed electron stream by means of vacuum tubes. From a Special Correspondent. of 175,000 miles Two years ago very considerable We were told of acetylene gas being incredible velocity interest was evinced in the transformed into a solid yellow mass per second ! when subjected to a short exposure; remarkable results achieved The New Tube b} Dr W. D. Coolidge, of the General of bacteria withering under the influence of the rays ; of small animal The new tube is a sort of three -in - bodies being disintegrated without one arrangement of the first. After sign of burning or charring. These his work with the 300,000 -volt tube and other wonders were effected by a he commenced to build larger indi- tube operating on 300,000 volts. vidual tubes, but he soon discovered that there were limitations to the A True Prophecy voltage which could be applied. He Dr. Coolidge at that time declared then conceived the notion of adopting that, he had by no means said his last the cascade arrangement, whereby word in regard to this tube or its the rays from one tube could be fed possibilities. He has just now an- into another, which would speed nounced a development which in its them up and feed them along farther way is as remarkable as his first to still another tube. The plan discovery. For he has produced worked, and in this way Dr. Coolidge a triple -cascade cathode-ray tube succeeded in applying the 900,000 operating not on 300,000 volts, but volts. on no less than 900,000 volts, and The electrons expelled from the capable of sending out into the air tube appear as in the previous case a stream of electrons at the almost as a purplish haze ball. The velocity Dr. W. D. Coolidge. Electric Company of America, with a Cathode Ray Tube. It will be recalled that the tube was said to be a vacuum in which it was possible to generate as much electricity or as many electrons in one second as it was calculated could be produced by one ton of radium. Peculiar Effect The word " calculated " was then used advisedly, because the pro- ductivity then, as now, of a ton of radium was a matter of theoretical multiplication rather than of practical proof. there being, so far as we now know, only about a pound of radium in the world. In any case, in the cathode ray we had t hat bombard- ment of.the atmosphere which caused crystals of mineral calcite to assume the appearance of red-hot coals and remain a glowing mass of incan- descence whilst being perfectly cold. A double sectional cathode-ray tube employed by Dr. Coolidge during his researches. 593 www.americanradiohistory.com MODERN WIRELESS June, 1928 of their expulsion is so stupendous The Cathode Ray Tube itself is tubes for voltages appreciably in that it can only be comprehended by about 95 in. long, and has three excess of 250,000, we have seemed to a trite comparison. The figure of bulbs, each 12 in. in diameter. The be continually contending with and 175,000 miles per second, probably window from which the electrons limited by the ` cold cathode ' effect," the fastest speed ever attained, is arc emitted is of thin metal foil but Dr. Coolidge said. about three hundred and fifty one ten -thousandth of an inch, or one More recently we have found that thousand times faster than the speed quarter that of au ordinary piece of we can remove this limitation by of a bullet shot from an army rifle. writing paper, in thickness. subdividing the total potential This is absolutely holeproof, and is difference applied to the tube between What Use Are They ? so constructed as to withstand a total different pairs of tubular electrodes. Naturally enough everyone in- atmospheric pressure of more than 100 The electrons are then given successive terested is now asking : " What will pounds, the difference between the accelerations as they pass between be the use of the high-speed waves or outside air and the almost perfect successive pairs of electrodes. particles thus projected ? " Dr. vacutun within the tube. A heated Coolidge himself is not prepared to tungsten filament, originally used by . dogmatise in the matter. He is Dr. Coolidge in his X-ray tubes, . "Acetylene gas. is transformed into . content to declare his intention of . a solid yellow mass, while small .. furnishes the supply of electrons. . animal bodies are disintegrated .. experimenting with them in the .. The glass tube is shielded with a without sign of burning or charring." . convinced belief that they will before copper tube so that the stream of . long be used for therapeutic, chemical, electrons cannot strike the glass and bactericidal and other practical pur- cause punctures. " This, in effect, divides the tube poses. That they will assist our up into sections, each of which may knowledge of radiation laws and of Harder Rays be good for as much as 300,000 volts. the atomic nucleus is tolerably " In our earlier attempts to build We have already successfully operated certain. experimental X-ray and cathode-ray such a cathode-ray tube with three sections on 900,000 volts. " This cascade or multi -sectional system promises to let us build vacuum discharge tubes for as high voltages as we can produce. This applies as well to an X-ray tube as to a cathode-ray tube, as the latter may be converted into the former by the addition of a suitable target. It also applies equally well to a high -voltage kenotron. " This opens a vista of alluring scientific possibilities. It has tanta- lised us for years to think that we could not produce in the laboratory just as high-speed electrons as the - highest velocity beta rays of radium, and just as penetrating radiations as the shortest wave -length gamma rays from radium. Powerful Penetration " According to Sir Ernest Ruther- ford, we need only a little more than twice the voltage which we have employed already to produce X-rays as penetrating as the most penetrat- ing gamma rays from radium and three million volts to produce as high- speed beta rays. The intensity factor would be tremendously in our favour, as with twelve milliamperes of current we would have as many high-speed electrons coming from the tube as from a ton of radium in equilibrium with its decomposition products. " Another factor in our favour would he the control which we would have of the output. This would be quite different from our position with respect to radium, in which case no physical or chemical agency at our command in any way affects either the The triple tube from which the high-speed electrons are shot out into space. quality or the quantity of the output." 591 www.americanradiohistory.com June, 1928 MODERN WIRELESS The power to " see at a distance" has for long been one of the greatest desires of scientists, and the author of this informative article was one of the pioneers in the search for television. As early as 1897 he was devising schemes for the use of the cathode ray in this connection. No less an authority than Sir means of instruments working on this was, in fact, to employ two of Braun's Oliver Lodge has recently cathode -Tay principle, and, in arder oscillographs, one at the transmitting given his considered opinion to study the matter, I obtained from and the other at the receiving stations, that, for really efficient television, Germany one of Braun's tubes, with the two cathode-ray beams to be mechanical contrivances are likely to which I made many experiments simultaneously and synchronously de- fail, for the reason that they are showing the rapidity and precision flected by the varying fields' of two already about at the end of their with which the cathode-ray bawl electro -magnets placed at right angles tether from the point of view of could be deflected both magnetically to one another, and energised by the rapidity and accuracy of movement, and electrostatically. same two alternating electric currents and that for real success still more is of widely different frequencies, so necessary of them. that the moving extremities of the two would be caused to sweep Sir Oliver Lodge goes on to men- beams again, tion cathode rays or moving elec- synchronously, over and over over the whole of the required sur- trons as " the only things likely to be faces at the transmitting and sufficiently docile and controllable to both receiving each complete be used as the agents for television. stations, sweeping being within the small No material things are likely to be fraction of a second required tó take able to move quickly enough, but advantage of visual: persistence. electrons respond so instantaneously that if devices can be invented for A Real Difficulty utilising them the theoretical diffi- All this being laryanged, so far as culties with the required rapidity of the receiving apparatus was con- motion would begin to disappear cerned, it is evident that the moving both from the sender and the receiver, extremity of the. cathode-ray beam especially as photo -electric response had only to be allowed to impinge on is almost infinitely rapid.:' a sufficiently sensitive fluorescent screen, and given from the transmitter Early Investigations at the right moments suitable varia- Sir Oliver ends by mentioning that tions in its intensity,- to produce the suggestions to the sane effect were Alan A. Campbell Swinton, F.R.S., required picture. made long ago by me on several occa- M.Inst.C.E., M.I.E.E. The real difficulty, however, lay sions, and gives reference to some of in devising an efficient transmitter these. Under the circumstances., it The idea had occurred to me that which, under the combined influence has been -proposed that I should give with two similar cathode-ray beams, of the impact of the transmitting some account, not only of my sag ges- controlled and deflected simultane- cathode-ray beam on a suitable tions of the past, but also of my ously by magnetic or electric forces screen, and the effect of light and present views and my ideas as to the due to the same electric currents it shade in the picture to be transmitted, future. should be possible to obtain absolute thrown on the same screen by a lens, It was only a very few years after synchronism in the motions of the should sufficiently vary a transmitting the introduction of the Cathode Ray two cathode beams at speeds how- electric current to produce the neces- Oscillograph, by Braun, in 1897, that ever rapid, and with a degree of sary tined alterations in the intensity I first thought of the possibility of accuracy that could not be expected of the cathode-ray beam of the producing practical television by front any material objects. My plan receiver. 595 www.americanradiohistory.com MODERN WIRELESS June, 1928 Some actual experiments were tried leading authority on the subject of the Russian, Boris Rosing, applied in this direction abcut the years light-sensitive electric cells, in pre- for on December 13th, 1907, N.,. 27570, 1903-1904, in which I was helped paring the selenium -covered plate. which suggested a cathode-ray oscillo - by my then assistant, Mr. J. U. M. It must he remembered, however, graph as a television receiver, but Stanton. What was tried was based that at that time, which was more used mechanically rotating mirrors on the known variability of the elec- than twenty years ago, the application for transmitting, was not accepted and trical resistance of selenium under of heated cathodes were unknown, and light. -A metal plate, one surface of these latter could only be obtained which was covered with selenium, for operation by very high voltages was mounted in a vacuum tube, so which were very difficult to obtain that the end of a cathode-ray beam in a steady form, while thermionic from a suitably placed electrode amplifiers and such -like devices were could, by electro -magnetic deflection, also quite unknown. be caused to traverse the coated Further experiments were therefore plate, while, at the same time, the for the time abandoned, and when I bright image of an electric arc was published in " Nature " for June 18th, thrown on the selenium surface by 1908, what is believed to be the first means of a lens. published suggestion of the use of cathode rays for television, no par- The Complete Scheme ticular method as to how the cathode- It was hoped that the variation in ray transmitter was to be constructed Mr. J. L. Baird, the television experimenter, the resistance of the selenium under was suggested ; while later, when, who has received much publicity of late. the influence of light would cause the in 1911, my paper was read before the electric current passing in the circuit Rontgen Society, in which was given published till after the publication of the coated plate and the cathode a complete scheme for a cathode-ray of my letter in " Nature " for June rays to vary to an extent that could television system, what was proposed 18th, 1908, suggesting the use of be shown on a sensitive galvanometer was the adoption of a transmitting cathode-ray oscillograpbs both for or electrometer suitably connected. screen, not covered with resistance - transmitting and for receiving, and It was found, however, that with the varying selenium, but one made of that no one else, except myself, apparatus used no reliable results a fine mosaic of photo -electric cells, appears to have published the idea could be obtained, and this in spite which would probably prove a more of both transmitter and receiver being of the fact that we received the per- sensitive and efficient arrangement. worked by synchronously-heating sonal assistance of the late Professor Here attention should be drawn to cathode rays, as described above, till G. M. Minchin, who was the then the fact that the British patent of long after my detailed and illustrated account in my paper to the Rontgen Society of November 7th, 1911, which was printed in full in the Rontgen Society's own journal, and very fully reported in " The Times " for Nov- ember 15th, 1911. Drawback of Mechanical Devices Now, if the use of cathode-ray electrons, in place of mowing material parts, is to be the method by which successful television is ultimately to be obtained, it seevis clear that this will best come about with electrons used both in the transmitting and in the receiving apparatus, as if mechanical devices are still retained for transmitting, the final result must be governed by the speeds obtainable with the material moving parts of these devices, and it is only by avoid- ing altogether the use of material mechanism that the extreme mobility and tractability of electrons can fully be taken advantage of. Then, again, if electrons can be adopted as the only objects in motion, both for transmitting and receiving, they can also be used in suitable triode thermionic oscillating valves to supply, from batteries, or from a public electricity supply, the two of largely differ- Carrying out experiments in M. Edouard Belin's laboratory, where oscillating mirrors alternating currents are employed to cause a beam of light to traverse the picture. ent frequencies required to actuate 596 www.americanradiohistory.com June, 1928 MODERN WIREI.Fcc the two deflecting magnetic or electro- tection, it varies the strength of the Mr. G. J. Blake and Mr. H. J. Spooner static systems at both the sending receiving cathode-ray beam, which, describe a television transmitter using and at the receiving stations, used in turn, affects the brightness of that cathode rays, with a selenium resist- for the purpose of causing the syn- particular portion of the fluorescent ance arrangement designed on exactly chronous combined oscillating and screen on which the end of the cathode the same lines as I had tried, the traversing movements of the two beam is at that instant impinging. other details of both transmitter and cathode-ray beams, while the exact receiver being the same as that which 'synchronisation of these could be Selenium Too Slow I described in my Rontgen Society 'maintained by special wireless signals Thus on the receiving fluorescent paper of 1911, but with the addition ón a ware -length different from that screen a replica of the picture thrown of thermionic amplifi.rs and wireless -of the main transmission. by the lens on the transmitting arrangements, such as I suggested in screen is reproduced. my Radio Society paper of March 26th, A Great Improvement Very possibly with modern know- 1924, which appears to have been This would obviously be a great ledge and arrangements the trans- published prior to Messrs. Blake and improvement on the mechanically mitting method in which selenium is Spooner's patent specification, which Moving alternate -current dynamos used might be got to work, though was not accepted till May 26th, 1925. suggested -for this purpose in my paper probably it would be- too sluggish for of 1911, and in a further fully illus- showing rapid movements in the Colour Television trated paper on " The Possibilities picture transmitted. It is, however, Possibly, however, another trans- of Television " I read before the interesting to note that many years mitting arrangement employing cath- Radio Society of Great Britain on after my experiments and publication, ode rays, still better than either the March 26th, 1921. It would get in their British patent applied for on one using selenium or the particular rid of all mechanical motion whatever, February 28th 1924 (No. 234,882), class of photo -electric cells_ described and the whole of the transmitting and receiving apparatus would become reduced to instruments with nc, material moving parts whatever, not much more complicated than those now used for modern wireless broad- casting and receiving. The diagram shows my appara- tus, both for transmitting and for receiving, as figured in my paper of 1924, but modified as employing triode thermionic oscillators instead of rotating dynamo machines. For those who have not my paper of 1924 before them, it may be well to give a short description of how the apparatus is designed to operate. At both ends the two cathode-ray beams impinge on screens, which they are caused by the deflecting systems to sweep over rythmically and in complete synchronisation in parallel lines backwards and forwards from end to end. The Photo -Electric Screen In the transmitter the screen is composed of a very large number of minute photo -electric cells which are each activated, more or less, by the amount of illumination each receives from the image thrown upon the whole screen by the lens. The end of the transmitting cathode beam explores each of these cells in turn, and as to whether it finds it illuminated and thus activated or not, an electric impulse of varying intensity, propor- tional to the amount of local illumin- ation, is transmitted to the neigh- bouring gauze grid. - The varying electric current thus originated, after amplification and into wireless waves, is conversion One of the most nearly successful attempts at practical television has been made by Dr. transmitted to the receiver, where. E. W. Alexanderson, of the American G.E.C., but here again mechanical methods put a after further amplification and de- definite limit upon the detail with which pictures can be transmitted. www.americanradiohistory.com MODERN WIRELESS June, 1928 in my papers of 1911 and 1924, is what Now, to consider the chances Of results may be obtained. The chief is described in V. K. Zworykin's British television by cathode rays being matter to be settled is probably the patent specification No. 255,057 of 1925. perfected, it must be remembered best form of photo -electric sensitive This is a patent applied for by the that since its original invention more transmitting screen which will produce Westinghouse Electric & Manufac- than thirty years ago, and particularly the required momentary electric im- turing Company', of the U.S.A., the during the past nine years, great pulses under the combined effect of contention date of which is July 13th, practical improvements have been the lights and shades of an image 1923, and the complete specification made in the cathode-ray oscillograph, thrown upon the screen by a lens, of which was accepted on March 31st, which originally, in its " hard " form, when swept backwards and forwards, 1927. In this, where a gauze grid is was very intractable. or in .spirals, by the oscillating and employed, and a large number of very traversing, or - the spirally moving, small photo -electric cells, similar to my Further Research Needed end of the cathode-ray beam. suggestions of 1911 and 1924, the cells Such oscillographs are now com- High-speed synchronous deflecting are composed of minute globules of mercial instruments in practical use, systems, worked by oscillating valves, specially prepared potassium hydride but even now they are probably will also require working out, and it in an atmosphere of argon. capable of much still further improve - cannot be pretended but that to get TiooE '/000^- PERSEC: OSC/LLATORS PER SEC. PER SEC: VAPOUR CHAMBER J LENS L TANSM/TTEk /31-CE/l/E"R V60 The specification, which is a very ment, more especially as regards the good results many and arduous interesting one, gives full particulars, luminosity. of the fluorescent screens, investigations are likely to be found and should be studied in detail by which should be arrived at by more necessary, such as may well occupy anyone who wishes to understand experimental investigation, which a skilled researchers for considerable Zworykin's ideas. Further, it con- large demand would no doubt bring time, and require much money. tains the 'new suggestion that, by about. So far as existing mechanical inserting both in the transmitter and At present, so far as appears, it is methods of television are concerned, in the receiver mosaic three -colour only for reception that cathode rays I agree with Sir Oliver Lodge's view screens, like those used in autochrome have so far actually been used in that these have. probably already colour photography, coloured pictures television experiments. Cathode-ray reached about the limits of perfection could be transmitted and reproduced, transmitters, though suggested, and that are obtainable, and that for this extra complication increasing the even patented, as mentioned above, so general purposes these are unsatis- difficulty of success by three timei, far as my information goes, have not factory. inasmuch as three times the number been exhibited or even claimed as Indeed, it was my opinion that of granulations would be required to actually having been made to function. this would prove to be the case form die received- image of any Several workers are, however, now that led me, nearly thirty years ago, desired quality in colour instead of in said to be at work upon the subject, to consider other than mechanical monochrome. and it may be hoped that successful methods. 598 www.americanradiohistory.com June, 1928 MODERN WIRELESS This receiver, which is completely self-contained and embodies a frame aerial and loud speaker, weighs only 20 lb. It employs a remarkably sensitive circuit and is capable of really useful ranges of reception. By J. ENGLISH. THERE is no doubt that the couraged by quite a number of find that, with a little patience, it is popularity of the portable re- manufacturers. Several firms are possible to build yourself quite a ceiver is increasing consider- producing compact , four- and five - respectable lou_l-speaker portable foc ably, chiefly among those people who valve sets which are, however, some- one-third the cost of the commercial are interested in radio solely as a what ponderous in weight. article. Of course, some sacrifica' in the effective range of th , set has to be Inexpensive and Efficient made in order to reduce expense and COMPONENTS even the Apart from the listening public it weight so considerably, but :: 1 0003 variable condenser with vernier:: type of portable I have in mind is is probably the ambition of every :: dial (Ormond in set. Any compact:: not so very inferior to the commercial good make). amateur to own at some time or other fi ve -val ver. 1 Potentiometer, 400 ohms (Igranic:: is -a loud -speaker portable set, but many - . or similar type). are deterred from acquiring one by :S 1 On -off switch (Ormond in set. Ben-:: jamin, Igranic, Lissen, Lotus, etc.).:: the high cost of commercial sets. Where Constructors Score :: 2 L.F. transformers (Mullard P.M. in:: When you come to look into things This is because the amateur con, set). you find that a good five-valve set structor is able to take advantag( :: 3 Valve holders (Benjamin in set. Any:: making foi good sprung type). costs about thirty guineas and weighs of technical developments, :: 1 0003 fixed condenser (Clarke,:: nearly as many pounds. greater efficiency with less weight, :: Dubiliet, Igranie, Lissen, Mullard,:: However, if you are keen on con- which the manufacturers are unable T.C.C., etc.). structing wireless sets, you will soon as yet to incorporate in their sets. :: 1 Semi -fixed resistor, 30 ohms (Any:: standard make, Lissen, etc.). :: 1 Cone loud -speaker unit (" Beco " in :Y X318 h! .+i set. A little rearranging will per-:: .2 mit other types such as Amplion:: and Mullard to be used). :: 'Phone terminals ' (Eelex in set.:: 3 Belling -Lee, Clix, Igranic, etc.). ó: :: A. & E. terminals (as above). ó: L. S :: 7 Plugs (as above). :: 4 Spade terminals (as above). :: Quantity single rubber -covered flex:: (24 D.C.C., 36 D.C.C., Eureka:: :: Resistance Wire, 30 S.S.C.). :: Materials and wood for carrying case:: and skeleton former. C> A c)b .0003 of entertainment. The com- means 411042, pletely self-contained portable re- C> ceiver capable of loud-speaker re- production at some distance from the E local station is one of the most popular models, and the demand for err this type of portable is being en- 599 www.americanradiohistory.com WVIODERN WIRELESS Jùne, 1928 Because the loud -speaker portable the entire contents of the case in aerial will increase the loud -speaker is such an attractive proposition for order to hear the loud speaker in range of the set considerably, and the man who builds his own set, I operation. good daylight results should be pos- have been tempted to design a _port- The built-in frame aerial, which, sible up to 50 miles or so from your able for loud -speaker working on a by the way, is specially wound for local station. Up to 20 miles or so built-in frame aerial, using all the high efficiency as described below, is lond-speaker reproduction is very latest devices for high efficiency with designed to receive on the normal strong. the minimum of weight. The result- wave -length band which includes You can get much more fun out of ing three -valve receiver is illustrated such stations as 2 L 0 and 5 G B. the set by running it on the frame in these pages, and you will see that it is reasonably compact and un- obtrusive in appearance. In full working order it weighs about twenty pounds, which is more than I should have liked, but it is possible to reduce this weight as I shall explain later. in any case, the total weight is not excessive in view of the results obtainable, which are about the average for a three -valve portable. Design of the Set One side of the case has two doors, the upper one g iving access to the The controls are mounted on a small panel, the components being tuning controls and thr,e lower to fixed to a baseboard the which forms part of a convenient and easy -to -make internal framework filament, grid bias and H.T. batteries. assembly. The cone loud speaker is built in The London station is audible at aerial, because you are not tied down behind a grille opening on the other very good loud -speaker strength at a to one spot as with the home receiver. side of the case, the reason for doing distance of 15 miles, and the set Because of this the portable very goon this being that, once the set is tuned should have a loud -speaker range of demonstrates the versatility and fas- in, it can be closed up and carried at least 20 miles from a main broad- cination of radio reception in a way about while working. This method casting station. At 12 ruiles from that the fixed receiver can never do. of mounting the loud speaker also 2 L 0 the full loud -speaker volume is In order to make the set as adaptable preserves the unobtrusive appearance more than sufficient for comfortable as possible, provision is made for of the outfit, in that loud -speaker audition in the average living-room, using 'phones in place of the loud reproduction can be enjoyed without and signal strength has to be reduced. speaker for reception of stations the entrails of the set being in full 5 G B comes in at good strength up to beyond loud -speaker range. view. 100 miles away. A Novel Circuit X319 Now; in order to obtain the results mentioned above with only three r- valves, it is obviously necessary to SKELETON use a combination giving high am- plification and sensitivity with pure reproduction, and requiring the least number of controls. The _ best com- PANEL bination is undoubtedly a regenera- tive detector followed by two stages RECESS FOR \ r I 6" M/OOL E- RA /L of L.F. amplification, the control of reaction requiring to be particularly JJII 11I1 smooth for easy operation, especially - M/POLE RAIL -2r- " /4- BASEBOARO where a frame aerial is used. From long experience of the regen- KJLETOiv SKELETON erative detector valve with frame - ---... aerial unput, I know that there is not /8 - much to choose between various conventional circuits provided reaction is quite smooth. However, the recent SKELETO development of a new application of . the ubiquitous Filadyne circuit for F/0.2 aETA/LS OP CASE frame - aerial reception provided me with just the type of detector I - I am a I,,liuvcr in construct- Provision is ìnade for the connec- required for this set. This particular ing a porta t hat it 'does not tion of an external aerial so that the Filadyne circuit is highly sensitive look like a wireless set when in set may be used either on the, home and stable, and requires very few operation, and I never- feel satisfied aerial or 'on a temporary one when components for its construction. with the appearance of some com- taking the set with you on a country I have described this Filadyne- mercial portables which must reveal ramble. Quite a modest external frame combination in some detail in a 600 www.americanradiohistory.com June, 1928 MODERN WIRELESS previous article, but for the sake of valve for the same degree of amplifica- Coining now to practical details, completeness let me give you a brief tion and power output. there is nothing in the design of the outline of its features. First of all, 1 f we were using three -electrode set that should prove difficult to the two frame aerials are used, each valves in this set it would be necessary average constructor, although there forming one of the tuned filament to apply at least 100 volts to both L.F. is somewhat more constructional work coils, a smaller winding between the valves for good results. But the two than is met with in the usual fixed two being the reaction coil L3 of tctrodes provide full loud -speaker receiver. Most of the constructional Fig. 1, the theoretical circuit of the volume on only GO volts H.T., so that work is involved in the making of the receiver. there is no loss of efficiency while the carrying case and the skeleton frame- saving in weight makes the receiver work and in the winding of the double a much more portable proposition. frame. TO SEM/f/XED RESISTOR Use of Tetrodes FRON7 OF L2 L3 Li It should be understood that in a SET is all to' gain portable receiver there TO+TÉRMN )o To L.T- and nothing to lose _by using tetrodes VALVENOLDER GRID r -7ö¿ TERM/NA[- in, place of the ordinary välve. Apart ALVE OF //OLDER-- fróm the use -of tet_rode valves there. is TRANS FR nothing out of the oïdinary'about the 4 AND Z3 WOUND /N L.F. stages, as you will see from the SAME Di ECT/ON of Fig. 1. Note, ho«=ever, Fic.4 diagram g268 that the fixed resistor 112 is common to both L.F. valves, which do not A working knowledge of carpentry require separate or critical adjustment will carry you through this quite of filament voltage. easily, but if you do not wish to do The more technical of my readers the woodwork yourself any reputable may query the efficiency of the frame firm of cabinet makers will undertake 'l'he two frame aerials are wound in aerial where, as in this receiver, the the work for a reasonable charge. opposite directions, as I have found whole of the receiver and batteries are After all, the construction of the case in previous experiments that less wire inside the frame itself. But with a is quite simple as will be seen from is required to cover a given wave-band frame of this description the magnetic the diagrams of Fig. 2, which will when the two filament coils are wound field is concentrated fairly close to the provide all the information required side by side in opposition. Also the windings so that if the latter are only by the constructor. H.F. resistance of the tuned circuits an inch or so from the nearest com- is reduced by this method of winding, ponent parts no serious loss of energy The Original Case would and where the two filament coils are will arise. In this receiver, as you I may mention here that it design in the form of frame aerials the will see from the photographs, the have been possible to the double loop seems to have better frame windings are entirely air -spaced outfit -to fit into a smaller case, but 'pick-up qualities -than the usual single and not near enough to any metal by allowing more room we have the winding. In this receiver the high parts to cause appreciable H.F. losses. ad, I Tonal advantage of a. larger and efficiency of the Filadyne detector is largely due to the employment of the special double opposition -wound frame aerial. Smooth Reaction Control The degree of reaction is controlled as in the normal Filadyne circuit by the variation of anode Totential, which is controlled within fine limits by the potentiometer P. This pro- vides a remarkably simple yet very effective control of reaction, and when you have such smooth control the receiver is more easily operated at optimum efficiency. After the Filadyne detector two stages of transformer-coupled L.F. amplification are used in order to obtain súfficient volume to operate the loud speaker satisfactorily. Here again I have been able to make use of a new development which has helped considerably in keeping down the weight of the -set. This is the recent introduction of improved forms of the you are tetrode valve, which, as As will be seen, when the upper door is dropped open both the controls and the majority doubtless aware, requires a lower of the components become visible. The back of the small cone -type loud speaker can be anode voltage than the three -electrode seen between two of the valves. 601 www.americanradiohistory.com MODERN WIRELESS June, 1928 more efficient frame aerial. Even pleasing than staining and polishing All wood required is 4 in. thick, here the case is not over-large for a the wood. Also, if you' are not very and the various pieces are cut out loud -speaker portable. skilful at wood -working, it hides up according to the diagram of Fig. 3. The original carrying case weighs any deficiencies in your carpentry. You will require two of each of the about seven pounds, but if you can This cloth covering can be water- three pieces A, B, and C, and four obtain a fibre case of similar dimen- proofed by lightly coating with french of the pieces D to fit between the ends sions it should not weigh more than polish. The leather handle, with B and C. The bottom and top pieces two or three pounds. The wooden case is somewhat heavy, but it is certainly very strong and will stand much hard usage. The four sides of the case of *-in.- thick wood are first joined together, and then the back piece of three-ply nailed and glued into position, the 4 -in. hole for the loud speaker having been already cut out. This is best done with a small fretsaw, finishing the edge with a file and sandpaper. The middle rail, on which the two front doors are hinged, is slightly recessed into the side pieces. This rail, with doors already hinged, is only screwed into position after the receiver proper has been finally placed in the case. A pair of 16 -in. ball - catches at the top of each door is sufficient to prevent them jarring open. fittings, is obtainable from any shop A can have a number of 1 -in. holes A Cloth Covering repairing trunks and suit -cases and is drilled in them to reduce weight, as A very pleasing appearance is im- quite easily fitted. in the bottom board of the original parted to the case by covering it, The next step is to construct the set. The skeleton is then put to- as in the original; with thin book - skeleton former on which the frame gether, gluing each joint, and the cloth, this material being obtainable aerials are wound. Into this skeleton whole bound up with string and laid quite cheaply in á variety of colours. the receiver proper is eventually built, aside .for 24 hours on a flat surface, The cloth is 'put. on with thin glue, and the: batteries accommodated, so so that when the glue is set the and with careful workmanship the that the set, as a whole, is complete skeleton will be truly square on all final surface is more durable and without the case. sides. In the meantime, the panel and baseboard can be prepared. The panel need not be ebonite, because the difference of potential between the panel components is so small that no leakage will occur if well -seasoned wood is used. For the same reason the aerial and earth terminals are mounted on one of the side strips of the skeleton, as you will see from the photographs. I have used for the panel a piece of 1 -in. mahogany, tined and polished, which gives a rentable appearance. Winding the Frame The panel and baseboard are cut to the dimensions of Fig. 5, where the position of mounting the panel on the baseboard is shown in dotted lines. The panel, after drilling the necessary holes, is best glued to the baseboard and held in place by two thin e -in. brass screws, screwed from the underside of the baseboard. When the skeletón is properly set you can wind on the frame aerials, which consist of two closely -wound of 24 The set is built into a simple but robust framework, and on this it is an easy matter to layers 18 turns No. D.C.C., with wind the frame aerial. Note the wood cut away in order to reduce the weight. the smaller reaction winding . of 602 www.americanradiohistory.com June, 1928 MODERN WIRELESS turns No. 36 D.C.C. between them, one. The resistor is simply a 5 -in. is the wiring of the detector -valve as shown in Fig. I. This diagram also length of No. 30 S.S.C. Eureka wire and frame-aerial connections. The indicates the connections for each having a resistance of 8 ohm. The diagrams of Fig;. 4 and 6 should help winding. wire is wound on a small piece of here. In wiring up you will probably use some insulated wire, euch as Notice that the frame winding- wood, which is then screwed in place wire can be nearest the front is tapped at the underneath the baseboard. Glazite, although bare tenth turn from the L.T. battery Although other L.F. transformers used if well spaced. TIM leads to the lengths end, this tapping going to the aerial can be used, I can thoroughly recom- batteries are best made with hoiss terminal. If the wave -length of your mend those specified for this set, of insulated flex, and the small which these local station exceeds 400 metres, it which are just ideal for a portable in the baseboard through would be advisable to make each owing to their small weight and size. Although small compared with the frame winding 20 turns instead of 1S.. This set embodies the novel and highly usual run of good transformers, they 3 ;; The smaller _ tuning capacity then 3 efficient Filadyne circuit which was ;; required adds slightly to the efficiency put up a very excellent performance j; originated by the Technical Editor and ;; subsequently developed by the author. of the receiver on'higher wave -lengths. which cannot be rivalled by other jj small ;j The receiver was thoroughly tested by ;; The winding of the frames is much transformers. ;j the " M.W." Research Department. ;; .. .. simpler than it sounds and actually .... takes less time than winding an Wiring Quite Simple ordinary 60 -turn coil. Notice that With all components in position and other wires pass are indicated in the ends of the windings are passed you can commence wiring up the Fig. 6. Note that the leads to the through small holes drilled in the top panel -baseboard unit as shown in inner grids of the tetrode valves hoard and secured by forcing in small Fig. 6. In this diagram it has been terminate in spade terminals in order pieces of matchstick. necessary to draw the panel, base- to ensure a good connection to the board, and detector valve holder in inner grid terminal on the valve base. Assembling the Woodwork one plane, so that some leads appear The panel and baseboard unit can When you have finished winding longer than they really are. The now be inserted in the skeleton the frames, you will be able to appre- connections to the detector valve formner, and held in place by two small ciate some of the points of the design. holder and to the frame and reaction screws, although these are hardly You will see that all the windings are windings should be left until the rest necessary if it is a reasonably tight well air -spaced at all points, and this adds appreciably to the efficiency of the frame aerials. The panel and baseboard must now be placed ill position, the baseboard resting on pieces of wood glued and screwed to the side -pieces of the skeleton. The panel -baseboard unit should be a nice tight fit, and if the panel is slightly too large, a few shavings'shoulcl be removed from its top edge. When all is in order, re- move the panel and baseboard, and mount the 'components to the layout of Fig. 5. It is very important to adhere to the exact positions indi- cated for every component, as in a portable of this description the final layout is necessarily the result of much thought and consideration. Mounting the Components Notice that the vernier dial is mounted slantwise, in which position it fits with. more clearance near the operating knob. The detector valve holder is also in rather an. unusual position, being mounted upside down on the underside of the top board, its case. You will note reduces the length of several Here you see the complete set ready for use, but removed from as this that there is ample room for batteries of the larger capacity types. connections. The semi -fixed resistor (30 ohms) of the wiring has been completed, fit. The remainder of the wiring for the first valve is mounted under- as it is easier to solder up with the can now be completed, and the neath the baseboard near the panel, panel -baseboard unit out of the receiver is then ready for insertion in as can be seen from one of the photo- skeleton. the carrying case. Before this 'is done, graphs, and the fixed resistor common The wiring of the receiver is by no however, the cone loud speaker must to both L.F. valves is also mounted on means so complicated as it looks ; be fitted to the back of the case over the underside of the baseboard. You there are not many leads, and most the 4 -in. hole already cut out in the can very well make this resistor your - of them are quite short. The only position shown in Fig. 2. The loud 't is not worth while buying thing you want to be careful about speaker used here is a " Beco " unit, 603 www.americanradiohistory.com MODERN WIRELESS June, 1928 which the makers are prepared to four -volt ranges. The valve I found tetrodes were absolutely non -micro - supply without the usual cabinet in a most useful was an old Radio -Micro phonic and, although nearly touching form suitable for portable sets. This 06 dull emitter, which proved to be the loud speaker, neither valve unit is remarkably compact and the least microphonic. suffered from microphonic reaction. rigidly constructed, but not at all The two tetrodes used here are an heavy, so that it is eminently suitable Curing Microphonic Howls A.P.412 H.F. and an A.P.412 fór a portable. The unit handles very This brings me to a most important power for the first and second stages strong signals without distortion, and point, the reaction between the loud' respectively. Both valves have puts up an excellent performance equal speaker and the microphonic detector common voltages for inner grid to that of some larger cone models. Valve. Ina portable, where the two (12 volts) and anode (60 volts). - On When mounting the unit a piece of are so close together, the result of these voltages the first L.F. stage copper gauze 5 in. in diameter is this reaction is generally an uncon- gives a remarkably high degree of placed over the hole,-, then one of the trollable howl. I found this out amplification, and the consequent ring washers supplie& with the unit immediately I put the set in its case large input to the last salve is and; lastly; the unit itself. Two handled and switched On ! Owing to the by the .A.P.412 power 4 B.A. bolts and nuts are sufficient Filadyne valve being more susceptible without any sign - of overloading. to hold the speaker firmly in position, to sound vibrations than the ordinary Au ordinary power valve would the heads of the bolts being 'counter- detector, the problem of curing this require more than 120 volts H.T. sunk into the outside of the back of unbearable howl seemed difficult until for these results. the case. I tried a dodge" first suggested by Mr. Harris. Preliminary Adjustments Suitable Valves This consists of covering the .glass Having inserted th valves and Now, before finally placing the bulb of- the valve with a layer of connected up batteries, switch- on 'the receiver in the Case it is a good idea- Plasticine about 'g in. thick: This set -and .adj ust the semi -fixed resistor to have a trial run on the work bench, cured the howl completely. You will Rl until reaction control on the po- as in this way the set is more access- notice the coating on the valve in tentiometer is quite smooth. For ible if any faults have to be traced. one of the photographs, a small pad the usual Filadyne valves not more First of all a word about valves. of cotton wool being used to prevent than 30 volts H.T. is necessary, and The detector can be one of the usual excessive vibration of the valve in control of reaction is smoother if Filadyne valves, such as the D.E.R., its holder. In very bad cases filling the filament current is kept fairly D.E.2 L.F., D.E.3, etc., choosing up the space around the loud speaker low. In fact, reduce the filament preferably one with a low filament with cotton wool helps greatly. current to the lowest value giving consumption in either the two- or I was glad to find that the two (Continued on page 672.) *. NEAREST1.2 Ì f L3 )1ir NEAREST4 Fic.6. /NNER - 2 W /R/NG Ma*.Oi/TER DIA G RA M. ON-OFF SH'/TCH A L. S. o B C EARTH/NGr TRANS °CORES 'Sent», twillimmommae}symi L.T,- ,s" J.>L.T r.Jt +so VS'ï www.americanradiohistory.com June, 1928 MODERN WIRELESS Those Gassisal Broadcasts MOST listeners are familiar with the procedure of listener to enjoy to a greater extent a particular orchestral publi-hing in musical programmes analytical or pianoforte item broadcast. notes. These notes are provided for the benefit For one thing, to appreciate and understand such of members of the audience who want to know a little notes one must be familiar with the meaning of words about the technical construction of certain orchestral used in the musical vocabulary-words like Andante, etc., etc. Unless one knows items, etc. ; and sometimes a brief note is given in Scherzo, Sostenuto, Adagio, connection with the composer's life, etc. the meaning of such words, music notes of the "analytical " A typical example of these so-called analytical notes- type are more or less unintelligible gibberish to the reader. which are regularly published in the " Highbrow " Items -B.B.C.'s official journal-might read 1s Many listeners who write to the as follows : .. A large section of the listening . '"The first movement opens with .s . newspapers and bitterly complain of maintains that the B.B.C. sustained chords which strike a sombre public . the preponderance of " highbrow " .. broadcasts too much " classical " note, the succeeding slow theme pro- . . music in the B.B.C. programmes do music-and another large section viding the basis, as it were, for the . . so because they listen to some classical . maintains the B.B.C. broadcasts . work as a whole. Innuediately follow- . . composition without the slightest un- too little. But too much or too ing sonorous and majestic chords . .:: derstanding of what it is all. about. the ... little, the man who condemns of the main theme follows a section . ... And therein lies one of the funda- " classical " music misses a good exposition of the .. .. mental differences between so-called in quick time-an .. deal of pleasure because he does .. first and second themes, one in a minor . " jazz " music and " classical " music ; . not know how to enjoy it- . the former requires no intellectual in major . . key and the other the as this article attempts to make lib. ... concentration ; the latter, although etc., etc. And so on ad . clear. .. These " analytical" notes are sup- ... beautiful themes may occur, does posed to help listeners to understand necessitate the use of one's brains -or and appreciate various works of the shall we say, intelligent appreciation, masters, old and new, which appear in the B.B.C. as well as emotional. programmes week by week. There are, of course, many, many so-called classi- cal (i.e. first-class) compositions which are not only Music Notes intellectually first-class, but " tunefully " first-class- Now the experienced and cultured student of music- compositions about which one does not have to the man who has, to some extent, studied the technique have knowledge in order to enjoy listening to them. But of music, and who is generally familiar with most of the there are, as well, many wonderful musical works of first- orchestral and piano " masterpieces " which are broadcast class merit which the average listener would not condemn given an intelligible ' from time to time-may find these notes useful and as " highbrow " if only he were perhaps interesting, because they supply clues to the outline as to the meaning, origin, and general plan of construction and development of musical works, and the work. although he may be fairly familiar with them, these music Many listeners have complained that, for example, notes jog his memory, just as the stage prompter jogs the Bach items in the programmes " leave their cold " ; and memory of an actor reciting lines which, although familiar, although the B.B.C. has done much to encourage and sometimes slip the memory. cultivate a wider appreciation and understanding of But of what good are such notes to the many hundreds classical music-especially in the broadcasting of musical the of thousands of non -technical musical listeners i They talks by Sir «Talford Davis and by broadcasting serve no real purpose, and certainly they do not help the " Foundations of Music " series-the fact remains that 605 www.americanradiohistory.com MODERN WIRELESS June, 1928 when, for example, a big symphony is to be broadcast, branches of mathematics. (I remember once. talking to a there is seldom an intelligible and explanatory broadcast famous mathematician about Einstein's Theory of Rela- preface to the work. Consequently, rnanÿ thousands of tivity. From the mathematical point of view-which was listeners switch on one evening and hear the "bald beyond me-my friend found that theory a sheer joy ! announcement that, say, a Beethoven Symphony will be " It's beautiful," he said. Really, it gave him the same broadcast. sort of pleasure as a beautiful piece of music gives a That one item may last half an hour-and the listener musician.) who is not reasonably familiar with Beethoven music This article, despite its ramblings, aims at suggesting cannot be. expected to sit and listen to a long and com- to the listener who has not studied classical music, and plicated symphony unless he has an innate appreciation of does not understand it, that there are ways of learning classical music. to find great pleasure in so-called " highbrow " music How To without resorting to the lengthy task of studying the Appreciate The " Classics" technique of musical compositions. Some people have the love of good music born in them As a crude example of " semi -classical " music, let us so that, without any study at all, ; they enjoy it to the full take the famous, if hackneyed, piece by Rachmaninoff- others find have they to cultivate the taste for good music ; the Prelude in C Sharp Minor. if they don't they realise they will not enjoy it to the full. The writer knows at least three people who were not There is no reason why a man or woman of average interested in music until they heard that old story that intelligence, who is sufficiently musical to enjoy a good the Prelude was supposed to be a musical representation light opera tune by Sullivan, or Offenbach, should not, of a man buried alive ! by means of a little intelligent application, learn to ap- preciate and greatly enjoy the more classical works of com- " Music With a Story" posers like Bach, Beethoven, Mozart, Wagner, and others. When you listen to the B.B.C. orchestra playing the This article was started with the idea, not of preaching Prelude again, you will notice that the music does fit in or lecturing to the lowbrows, but with the idea of making with this story and even with the story which suggests a few suggestions as to how the listener with no musical the bells of Moscow ringing during the great fire of 1812. training, but who is not without some musical sense-i.e. And Tschaikovsky's " 1812 " is another example of appreciation of beauty in sound, sense of time, etc.-could " Programme " music-or music with a story-which has be helped to learn to love works which, to -day, he achieved great popularity. condemns as " dull," or " highbrow." The " Prelude " and " 1812 " are not first-class works, The writer of this article is far from being a " highbrow," but there are many first-class works which, if one knows a but by a peculiar bit of luck he has learnt to enjoy, not little of their history, if one gets the key to the emotions only a rousing musical comedy tune, a " jazz riot," but which gave them birth, cannot fail to arouse one's interest. works by composers like Bach. Beethoven, Mozart, Everyone has heard, or heard about, Beethoven's Brahms, and others. At one time they " bored him stiff " ; " Moonlight " Sonata, but not everyone has heard his to -day they offer a very wonderful and enjoyable treat. " Emperor " Concerto-written because of the composer's Now, the cultivation of a sense of enjoyment of classical one-time admiration of Napoleon. music does not depend upon a technical study of music. When next you hear the B.B.C. broadcast the There are, of course, many people who enjoy Bach purely " Emperor," listen to it, and remember that Beethoven intellectually ; emotionally the genius of Bach " leaves was inspired to compose it because of Napoleon's wonderful them cold," but the almost mathematical precision of victories ; the Concerto gains an added interest and you Back's technique interests them, and arouses their will find your imagination helps you to take a keener enthusiastic admiration just as -a difficult problem arouses interest in the work. the enthusiasm and admiration of a student of the higher (Continued on page 673.) Mr. Percy Pitt conducting the Symphony Orchestra at Savoy Hill. To this group of musicians are due many of those " classical " broadcasts which form the subject of the accompanying article. 606 www.americanradiohistory.com June, 1928 MODERN WIRELESS A MOVING -CO LOUDSPEAKE The cost of the average moving -coil loud speaker has hitherto often been prohibitive, but here is one which is capable of giving excellent results and which costs only £5. By G. V. COLLE. Dviuxe recent months the writer the moving coil, to bring leads away When addre sing enquiries to the has investigated the merits of from the outside surface of the makers, it is necessary to give details so a number of different makes diaphragm, the job can be done with of the mains to be employed, that be of moving -coil loud-speaker parts for a tube of Seccotine, a screwdriver and the correct field coil may included. home assembly. While many of those a little common sense. tested were found to be good, yet it There is no diaphragm to be cut was thought that in most cases their out, nor leather to be fashioned out prices were not low enough to give to the required radius, since this is them a wide appeal, while in others all done by the firm supplying the the difficulties of construction were parts. The moving coil is ready too great. wound and- is provided with tags for Recently the writer has come sticking to the diaphragm. 'across a set of loud -speaker parts conforming to the standards which he Economical had mentally set. These are (1) Lastly, we have a field winding to the " magnet pot," which cheapness ; (2) good quality of repro- energise duction and reasonable sensitivity; should not get unduly hot and which (3) ease of assembly, and (4) low must be economical as regards current Using a choke output with a low -resistance running cost (i.e. low field current consumed. All these contingencies speaker. consumption). are met in the model which forms the In the first case, the cost of the subject of this article, and on test As some readers seem to be in doubt or complete set of parts (including all the current consumption was 130 as to which is the better, a high- milliamperes at 240 volts and 90 milli- a low -resistance moving coil, perhaps a H.T. amperes at approximately 160 volts. few words of explanation will be useful. TO MAINS 25:1> 40. S SUPPLY sL. This photograph gives TO Of S1SO a good idea of how LEAOS SECONDARY 2^-! OUT PUT The simplest method of connecting up a the loud speaker TAAí+tSPORMER low -resistance loud speaker. appears when. com- ú pleted. Note the lugs the minor parts for the diaphragm) is on the front alumin- £4 18s. 6d., with 3s. 6d. extra on the ium ring for attach- field coils for rectified A.C. mains. The ing to the " baffle." quality of reproduction and the Four small bolts and sensitivity to weak inputs without nuts are suitable for having to resort to a very small the purpose. annular gap for the moving coil is, in the writer's opinion, equalled by very few. k Extremely Simple In referring to (3) it can he stated that with the exception of soldering two small pieces of flex to the ends of cc, 7 www.americanradiohistory.com MODERN WIRELESS June, 1928 Apparently the chief objection to and also increase the risk of burning Drop the coil on the apex of the the low -resistance coil has been the out the moving -coil windings. Such diaphragm so that the two wires come lack of a really good transformer coils must be connected to the set each side of the join on the latter. of a suitable ratio. through a choke filter output. Then carefully place a paperweight, aFa7 Lastly, the writer recommends a or any other heavy object having an THIS ARRANGEMENT 4-mfd. Mansbridge type condenser for even weight, on the rim of the moving /S RECOMMENDED WHEN US/NG A use in conjunction with the L.F. coil, so as to force the gummed tags H/CN RES/STANCE and it must be of a type tested on the surface of the paper. MO YANG CO/L. 20H choke, to to at least twice its working voltage, POWER 4MFD VAL VES the latter being the voltage applied to the power valves. The diaphragm and leather strips of the speaker are supplied ready cut, L. S. so there is little to cut except a little piece off bne of the leather strips. The diaphragm is arranged with three projecting .pieces, two on one A good, large choke is essential in this edge and one on the other. The one circuit. on one edge should be carefully few MAGNET NEON LAMPS W/TROUT Fortunately, during the last POT RES/STANCE ELEMEN7A months, two or three good trans- /N THE/R BASES formers having a 25 to 1 ratio have TO SOURCE made their appearance, and among I .i / OF CURRENT these the writer has had experience of (D.CMA/NS is very efer OR A. C the Ferranti. This transformer 0 RECT/F/ER) suitable, provided a current not in 4240 excess of 40 milliamperes is passed through its primary. covered with Seccotine or any other A front view of the assembled unit. Note good adhesive, and the other two on the centre -maintaining device. The lugs on the aluminium ring are for supporting Commencing Assembly the other edge treated similarly unit on the wood " baffle." It is necessary High -resistance moving coils do so that, when the gum has become to make a hole in the baffle equal to the inside diameter of the aluminium ring. not, of course, require a step-down " tacky," they can be overlapped with two on one A wood board 3 ft. by in. thick (ply- transformer, but this does not infer stuck surface of the wood) is recommended. they should be connected directly in cone and one on the other. series with the anodes of the power It does not matter whether the two projections go on the inside While doing this, examine the coil valves, as this will seriously reduce to see if it " sits " level, and, if not, the voltage applied to the anodes surface of the diaphragm or not, so long as they overlap firmly and adjust before the gum sets hard. neatly, and no air spaces show This may sound complicated, but between the flaps. The diaphragm since the constructor will find the can now be left for the gum to "set." hole at the apex of the diaphragm is Now carefully pick up the coil and perfectly level, the latter having been crNtRE MAMTAININC, cut out by the manufacturers with a OfVICf. very gently unroll the few turns of wire which are left for sticking to the special tool, it will be found quite surface of the diaphragm. See that easy in practice. no loose turns are left, as these will FLEX LEADS ARE O/NED TO only cause a nasty vibration if not THE TH/N ENAMELLED WIRE removed. The two leads should be TN/S SERRATED EDGES' arranged to come from the coil at OF MOY/WC COIL SURFACE FORMER GUMMED /S to 1 in. from each other. TO SURFACE OF GUMMED DIA PNRA GM Handle Carefully 346 Do not hold the coil on opposite MOVING .4PPROX CO/L sides of its surface as the tendency C_ will be to make it slightly oval. It is best to hold it between the first finger and thumb on the opposite THE LEADS FROM sides of one wall. With the coil in THE MOV/NC CO/L this position, and its wires neatly ARE STUCK ALONG THE SURFACE OE straightened out, carefully bend each THE DIAPHRAGM UNDER TN/NM-RIP OF PAP gumming tag at a sharp angle (45 /9252 degrees approx.) to the wall of the The assembly of the diaphragm coil in an outwards direction. The The parts shown here are supplied by the coil should " sit on the outside When the coil has ' set " hard on makers, and consist of the cardboard ring surface of the diaphragm at its apex; the diaphragm, remove the weight, for holding the diaphragm, 4 pieces of and to do this carefully gum the inside and then gum the wires from the coil special leather ready " chamfered," the diaphragm, and the centre -maintaining surface of the tags and allow to get down the side of the diaphragm, device. " tacky." the two leads slightly diverging. 608 www.americanradiohistory.com June, 1928 MODERN WIRELESSS The wires can be held in position with With the leather ring in position can 'be pulled on to the cardboard narrow strips of paper (about R in. the diaphragm can be placed on a ring, but not too tightly. the As the pot is supplied with the field wide) up to 4 in. from the periphery flat surface with the leather at of the diaphragm, where they can be bottom. The cardboard ring supplied coil ready fitted, it is only necessary joined to small pieces of light flex by with thef outfit can then be treated with to screw on the four aluminium sup- ports and the back aluminium ring for the diaphragm to the top of these. The last operation is to fit the diaphragm in position, and to do this grasp the assembly by its cardboard ring and drop the moving coil into its gap. Move the cardboard ring about until the coil is practically central in its gap, and while in posi- tion mark through the holes in the aluminium ring underneath the card- board on to the latter with a pencil. Centring the Diaphragm Remove the diaphragm assembly and punch or cut holes- in. diameter round the points marked. The holes will be punched both through the cardboard and leather, since the latter will be covering the ring. After this operation, refit the diaphragm, making certain it is replaced in the frame the same way round. Then drop the top aluminium O IL ring over the cardboard one, also ascer- Dropping the completed diaphragm into position. The centre -maintaining device is taining the holes in this to correspond only fitted when the unit is completely assembled. Holes in the cardboard ring are made bottom alumin- when the moving coil is approximately centred in the annular gap. with the ones in the ium ring. The cardboard ring should soldering and then " gummed off " gum on one of its surfaces, and, when he moved by hand until the coil is with two small pieces of paper, so " tacky," passed over the inverted exactly in the centre of the annular that all strain on the flex is taken up cone diaphragm and on to the rough gap in the pot, when the screws through by these last. side of the leather ring. The leather the aluminium and cardboard rings The next important step is to attach left between the cardboard ring and can be tightened. the leather pieces one at a time, but the diaphragm should be uniform The centring device is fitted on the before doing so mark a light pencil all the way round, so it is as well to spindle, but before doing se, coat the line on the inside surface of the see that the cardboard ring is fitted " legs " of the device with gum, fit up diaphragm, about 33 in. from the centrally in the first place. over spindle, and then tighten periphery all around the edge. Before the gum " sets " the leather with the brass terminal head provided. Gum can then be applied to the inside surface of the diaphragm in the area between the line and the periphery. Do this carefully, making certain no part is omitted. While still " tacky," pick up a piece of the leather with the smooth side upper- most, and apply the rough side to the gummed surface at any portion of the diaphragm, taking care the leather does not go beyond the pencil line. Avoiding Overlap Now smear the chamfered ends of the leather strip already stuck down with gum, and apply one of the other pieces of leather so that the chamfers overlap correctly. Do this for the third piece, which should be applied to the opposite side of the first piece of leather, and then gum down the fourth piece. The whole idea is to form a leather ring, with Showing how the diaphragm is formed. The moving coil is fitted when diaphragm has the strips chamfered together. " set," the leads from the former being arranged each side of the join on the latter. 009 www.americanradiohistory.com MODERN WIRELESS June, 1928 in distant stations with my receiver, which is a det. and two L.F. stages." Cases of this kind cannot, as a rule, be cured by one party only, but the co-operation of both parties concerned is desirable. The trouble generally arises from the use of small sets which necessitate the use of a large amount of reaction, and, as a rule, the only certain cure is for both parties to build larger sets, preferably employing neutralised H.F. stages. Sometimes a cure can be effected by making sure that a different earth is used by each receiver, and sometimes the use of a small condenser in series with each earth lead will improve matters. The only really direct cure is to and then remove fixed Suitable Detector Valve the resistor, separate the aerials to as great a or turn out N. C. (Cardiff).-" I have an L.F. the H.F. valve filament. distance as possible, and to refrain Rotate the neutralising transformer, 3-1 ratio, and the condenser from using reaction even in such a until signals primary winding is stated to have become inaudible. This way as to cause the set almost to an inductance value of approximately point is sometimes a little critical oscillate. 60 henries. The transformer is to be and the procedure is to rotate the employed in a straightforward Det. neutralising condenser very slowly. Aperiodic Aerial Coupling G. and 1 L.F. set. What type of detector Signals gradually fade away and, the P. (Cardiff) has a receiver valve shall I use ? " silent point " having been passed, employing direct aerial coupling, Use a detector valve having an they return again to full strength as consisting of a single plug-in coil impedance of 1.5,000-20;000 ohms. the moving vanes become further in tuned with a 0005 variable condenser With a valve of this type you should mesh. in parallel. He wishes to know how he may increase in obtain good sensitivity and high - selectivity order quality reproduction, provided you Jllli!IIIIIIIIIIIIIIIIIIilllllllllllllllllllllllllllllllllll111111111Ilfl to tune in distant stations free from interference. only use a moderate amount of THE TECHNICAL QUERIES reaction. The use of what is generally termed DEPARTMENT " Aperiodic Aerial Coupling " is often beneficial in increasing H.T. Batteries. Are you in trouble with your set P selectivity. Mount another coil socket by the G. M. (Berwick).-" I have a five - H Have you any knotty little Radio problems = valve set H.F., Det., and 2 = requiring solution 7 side of the existing aerial coil, so that -2 L.F.- = The MODERN WIRELESS Technical Queries H which works perfectly from a I20 -volt Department has been thoroughly reorgan- _ the coupling between the new coil = ised and is now in a position to give H and the existing one will be as tight accumulator H.T. supply. When I = an unrivalled service. The aim of the de- E- attempt to use dry batteries, however, = partment is to furnish really helpful advice as possible. From one of the ter- = In connection with any radio problem, theo- _ the receiver becomes difficult to = retical or practical. _ minals on the new socket take a wire Full details Including the revised and, in to a new terminal on the panel or control, the H.F. stages tending to = cases, considerably reduced scale of charges, _ oscillate, and the L.F. side " motor - = can be obtained direct from the Technical = terminal strip ; this will be the new H Queries Department, MODERN WIRELESS, H boating." Can you tell me why this Fleetway House, Farringdon Street, aerial terminal. Connect the other London, E.C.4. _ ? terminal on this new socket to earth. occurs " H A postcard will do : on receipt of this all the H The trouble is probably produced H necessary literature will be sent to you free = The coil sizes used will- now be E. and post free, immediately. This applica- _ by a coupling effect due to the internal fion will place you under no obligation what- _ slightly different, and, in general, H ever. Every reader of MODERN WIRELESS will be as follow : resistance of the dry battery H.T. = should have these details by him. _ supply. Possibly the current required = An application form is included which will = In the old aerial socket, which now H enable you to ask your questions, so that = to operate your five -valve set is a H we can deal with them expeditiously and = becomes the secondary coil, for the H with the minimum of delay. Having this broadcast band a No. 60 or 75 little too great for the particular form you will know exactly what informa- _ type of dry are = tion we require to have before us in order = coil. For Daventry, a No. 200 or battery you using, with completely to solve your problems. _ the consequence that the internal 250. resistance rises rapidly. Alternatively illllllllllllluIllllllllllllllll111111INllilllllllllllllllllülllllllr In the new socket, for the broadcast band, a No. 25, 35, or 50 will be the battery may be partly run down. After this adjustment vanes the needed, and for Daventry a No. 75 Try one of the " super " batteries are locked in position, in cases where or 100. with large cells. These are specially this is possible, and the H.F. valve designed for such sets as yours. filament is switched on again. The set "Solodyne " Three is then ready for use. D. M. T. (Dublin).-" Will you Neutralising please tell me where I can find J. T. (Brixton) wishes to know how Interaction Between Aerials details of the coils for the " Solodyne " to neutralise a single H.F. stage by S. T. C. (Birmingham).-" I am Three (3rd version), as described in the " silent -point " method. troubled greatly by interference from the April issue of MODERN WIRE- This method of neutralisation is my neighbour's set. The symptoms LESS ? very simple provided some means of are bad fading on the local station Details of these coils will be found switching out the H.F. valve filament and oscillation. This trouble also in the article describing the " Viking is included. Tune in the local station makes it very difficult for me to tune Four, " in the December, 1927, issue. 610 www.americanradiohistory.com June, 1928 MODERN WIRELESS That indispensable Inductance An article concerning all kinds of coils, and the interesting principle upon which they work. By P. R. BIRD. frequency of the 11E two most fundamental facts happening in that wire. We know, number being the about the workings of any for instance, that if the current is alternating current). But in order to wireless set are capacity and coming from a battery connected to get a grasp on inductance' we have to inductance-capacity being concen- the ends of the wire we can reverse go one step farther than all this. trated in the condensers, and induct- the direction of the current by There is one vital fact of which we never lose sight-tire fact that ance in the coils ; but whereas one reversing the battery. must occasionally comes across a wireless We know that we can increase the every electric current of whatever set which has no condenser in it amount of the current by increasing kind has associated with it a magnetic whatever, one never secs a set that has the voltage of the battery (or by field. This magnetic field lies outside it no coil in it. decreasing the resistance of the wire). the wire carrying the current, but We know that if we insert a switch is just as important as the current, What Is It? we can break the current by breaking jùst as inevitable as the current, and At first glance it would appear that the circuit. just as varied, versatile, and complex whilst we can do without capacity in If, instead of connecting a battery as the current. Between the current the form of condensers, it is impossible across the wire, we connect an flowing in any wire and the magnetic wire to do without inductance in the form alternator across it, we know that we field which appears around that of a coil. What is this inductance shall get alternating current in it- there is a complete. co-operation. and why is it so indispensable ? current which flows first in one I suppose that most wireless en- direction and dies away, and then Current's Counterpart thusiasts have at some time or other reverses and flows again in the other The relationship between these two been interested in this question, and direction, and dies away, repeating is absolutely perfect. As surely as it is safe to say that most listeners this cycle of operations a certain darkness implies light, as inevitably who have looked up inductance in the number of times per second (this as " child " 'suggests " parent," as text -books or who have tried to form a mental picture of what inductance really is from definitions of the word, have been thoroughly bewildered by the explanations ! For to get a good picture of inductance one' must employ not figures and facts, but the faculty of imagination. If we turn away from the 'text -books for a moment, we can, in a flight of fancy, grasp the very essence of the thing. The Vital Fact Starting right at the beginning, let us picture first of all a piece of wire in which a current is flowing. Although Three important points where induct- we have never seen an electric current ance is indispensable : (r) L.F. transformer; (2) high - we have a fair conception of what is frequency choke, and (3) tuning coil. 611 www.americanradiohistory.com MODERN WIRELESS June, 1928 plainly as positive suggests negative, about magnetism. One of the most suddenly, for the force which pre- so certainly does the conception of a interesting facts, you will remember, viously opposed it is now assist- current imply the accompanying" was the fact that if a wire ór any ing it. conception of a magnetic field sur- other conductor is moved whilst in a We have all noticed that a motor- rounding that current. magnetic field, an electric current will car or heavy truck can easily be moved If the current varies, the asso- tend to flow along the wire ; and the over level ground by one man, when ciated magnetic field varies. When same holds true if we hold the wire once the initial difficulty of starting the current starts, the magnetic field stationary and move the magnetic it has been overcome. But all the starts. When the current attains a field itself nearer to or farther from time that it is moving it is saving up maximum, the magnetic field attains the wire. that energy that was applied to start a maximum. If the current falls, the Having got so far let us consider a it, and it will be just as impossible for magnetic field falls. If the current simple coil of wire and the commotion one man to stop it suddenly as it was reverses its direction, the magnetic in and around that coil when a for him to start it. In mechanics this field reverses its polarity. If the current flows in it. Imagine a simple reluctance to budge, and reluctance current fluctuates from any cause, at coil, say only two turns of wire, and to stop when once on the way, is called any speed, in any way, that same assume that the current is racing inertia. The electro -magnetic counter- cause will vary the magnetic field, at around the first turn on its way to part which we have been discussing- a corresponding speed; and to exactly the second turn. Commencirig at the this reluctance of a current to com- the same degree. moment the current commenced, and mence flowing through a coil, followed reaching outwards as the current races by its reluctance to stop when started Field Fluctuations forward, a magnetic field has sprung -is due to the coil's " inductance." So important is this magnetic into being around the first turn of counterpart of the current, so perfect wire. The second turn of wire lies Multiplying Magnetism is the relationship between the field closely by the first turn and right in and the flow, so intensely are these the path of that moving magnetic In all the foregoing we have assumed that the magnetic action is SD v Amur ef2 taking place in air. It is well known, 80000 /141,,,r5 . a+tr however, that iron appears to have a O.P/WORE HT multiplying effect of magnetism, so ABOUT that the magnetic effects of a coil caä ABOUT.IÓ'ISANY3 ZOHENRI!s be greatly increased by providing it .gBoar2001I1Hrs with an iron core. Low -frequency transformers, L.F. chokes, and similar highly -inductive windings are always so provided when low -frequency ffT currents are being dealt with. But, generally, the advantage of iron cores cannot be applied tó high -frequency inductances because the H.F. currents flow much faster than the corre- sponding magnetic changes can take place in iron. _:6-- The fact that inductance opposes a Gß - - w ! change in the current flowing can be of Tt great importance in high -frequency work, because if we use sufficient This diagram of a typical set shows how wide are variations in inductive values. Note inductance, the rapidly changing the great difference between a long straight wire (aerial) and the shorter length of wire wound to form an aerial coil. current will be so hampered by the magnetic monster confronting it that two bound together as it were, that field, and consequently the second it will be choked off from any desire the text -books will completely mislead turn, too, has a:current in it. . to flow that way, and will choose any us if we think of the currents they This second current, for reasons alternative path that is presented to mention as currents only. Alone, which we cannot enter into at the it. Aptly enough we call such electrical currents do not exist. moment, always tends to oppose the inductances " H.F. chokes." Every current has its magnetic first current which created it. But, It is merely for the sake of simplicity counterpart. Every flow has its funnily enough, no sooner does that that circuit explanations are almost fluctuating field, rising when the flow original current cease and die away always given in the form of current rises, steadying when the flow is than the secondary current starts to flow and capacity charges. But the steady, collapsing when the flow fall away, and in reversing it actually purpose of this article will have been ceases ; and this mysterious magnetic assists that first current, which a served if it reminds the reader that counterp. et, this invisible accom- moment before it tended to oppose. no current of any kind ever flows panist, lies at the very root and except to the accompaniment of a essence of inductance. magnetic field, that no condenser ever Haring well and truly grasped the Energy Returns to Roost charges or discharges without a fundamental fact of the matter, the So, because of the magnetic inter - corresponding magnetic commotion, fact that magnetic field is always leakage betwen the coils of wire, the and that every wire inside the set or accompanied by a magnetic field-we current experiences a certain difficulty out of it continually " carries on " to can digress a moment to remind in getting under way ; but once it is the accompaniment of that indis- ourselves of what we were taught fairly under way it cannot be stopped pensable inductance. 612 www.americanradiohistory.com June, 1928 MODERN WIRELESS A1 Choke pJ nit Aerial While comprising all the elements of an efficient output filter, this unit enables one to employ loud -speaker extension leads as an indoor aerial. Excellent results are possible and there is no danger and no complications to face when installing this economical and convenient system. By G. V. DOWDING, Grad.I.E.E. PRACTICALLY everybody who runs character, and it is not essential that It enables the loud -speaker extn- a loud -speaker receiver sooner very strict precautions should be taken sion leads to be used in addition or later instals loud-speaker. in regard to their_ insulation, and so as an aerial. There is no reason at all of wire in- extension leads, but the practice forth. . Nevertheless, for the sake of why these long lengths is dangerous or, at least, there is a permanency it is always as well to stalled in the house should not be grave probability of trouble occurring carry out the wiring carefully, and employed for such a purpose. They unless some efficient H.T. by-pass with good material. have, indeed, quite good pick-up scheme is arranged. If this is not qualities if employed in the right way. " or done it is not only the " sounds Dual -Purpose Leads I originated the idea some two which are led all around the house Now I am going to describe the three years ago, but at that date I to the various loud speakers, but also construction of a loud -speaker by-pass only gave a short theoretical explana- the H.T. current. In a conventional unit which can be connected to any tion of it. This is the first time that straightforward circuit the loud existing receiver. In addition to this the scheme has been brought forward speaker takes its place in series article comprising all the elements in a practical manner. If you glance in the anode circuit of the last valve. of a perfectly good by-pass unit, it at the theoretical circuit of the unit In this circuit is directly connected embodies one or two extra inexpen- you will see that the idea is a per- the H.T. battery or H.T. supply. sive components which give it pro- fectly simple one. There is, first of all, is. employed You will see that in such a case perties of an unusual nature. the L.F. choke, which a loud -speaker extension lead is to take the place of the loud speaker virtually an H.T. positive lead. in the anode circuit of the last valve Remembering that the H.T. negative of the receiver. is invariably taken to earth, the danger of an H.T. battery short- How the Unit Operates circuit with amateur wiring will be In each lead coming away from this apparent. But it is a very simple is a large fixed condenser provided matter to confine the H.T. to the for the purpose of isolating the loud- set itself by means of a choke con- speaker leads in regard to the steady denser by-pass scheme. H.T. current. These fixed condensers, however, offer very low resistances Many Advantages to L.F. impulses such as comprise and so on. Across the usual loud -speaker ter- musical sounds, speech, minals on the set is connected an As a matter of fact, their resistances view L.F. choke. Each side of this choke are so low from this point of that to a fixed condenser and the they can be almost disregarded. But is taken directly other terminals of the fixed condensers instead of being connected to the long loud-speaker to the L.F. extension wires, these are joined joined to leads. An incidental advantage is fixed condensers are then L.F. choke of good make will high -frequency chokes. that an act as have ample impedance at a low ohmic These high -frequency chokes -frequency resistance. The steady H.T. current complete barriers to high in their turn offer will, therefore, be carried without currents, but these trouble, and the loud negligible resistances to the low - saturation to the speaker relieved of the steady current frequency current proceeding receiver. You which can cause, into the bargain, loud speaker from the troubles and so on. will now see that the loud -speaker demagnetising or two ad- Having installed an efficient by-pass The unit comprises only one extension leads get their L.F. im- ditional components of a simple and the slightest of this nature, the extension- which pulses through without scheme inexpensive nature above those impulses lead wiring can be of the flimsiest figure in an ordinary loud -speaker filter. trouble, and that the H.F. 613 www.americanradiohistory.com MODERN WIRELESS June, 1928 picked up by the extension leads In the first place, you will find and should be capable of handling a acting as an aerial can travel only them quite selective, especially when fair current without saturation. Do one route, and that is via the aerial employing the unit, owing to the not try to use one winding of a low - terminal on the unit. There is negli- introduction of that series fixed con- frequency transformer, because it will gible L.F. feed-back owing to the denser. You can compare their pick- not be suitable for the purpose. fact that a 0002-mfd. fixed condenser up qualities with an indoor aerial is placed in series with the aerial. of similar dimensions and arrange- The Parts to Use This fixed condenser offers a com- ments. If the loud -speaker extension Regarding the 2-mfd. fixed con- paratively high resistance to low - leads run along the picture -rails of a densers, these need not be of the large frequency current, although it is au lower room, or to an upper room in sizes employed in H.T. units. They the house, the pick-up will be quite will 12209 0002MF0 not have across them the whole AER/AL good, and, in cases, almost equal to voltage of the H.T., or even a moder- THEORET/CAL 11...sA CIRCUIT that of an outdoor aerial. ate proportion of this. The only other items you will need which I have not Perfectly Safe so far mentioned are five terminals 2MFo R. FC. If the loud -speaker extension leads and a small cabinet. There is no need 73 L. S To L.S run underneath the floor boards and for you strictly to adhere to the dimen- ON L.F. CNOKE EXTENS/ONS lower rooms, then the pick-up will sions and layout that I have given. SET, f 2MF0 fc FC be moderately inefficient, but if you Providing you use satisfactory com- F ---r 0000 use this unit and decided to make ponents and have them correctly double use of your loud -speaker wired up there is really little else that easy path for H.F. Tins circuit pro- leads then you can run these in such matters. vides very interesting study, for it a way that they will answer both ,;bows exactly what H.F., L.F., and purposes equally well. That is, keep 834- the leads high and run them as' L S. 4 AE R/AL 7O SET ordinary direct current can and can- direct _ ® ts_ not do. I want you particularly to from point to point as possible. Also, /448 6 I f note that between the two pairs of keep them away from damp walls -L6' /-; terminals on the left- and right-hand and from large metal objects, pipes, 4 . 1-2814 side of the unit, only L.F. current can and so on. And let me interpolate 38 pass. Steady D.C. current and H.F. here that, by the way, the scheme is a perfectly safe one ; no damage % cannot, for they have barriers raised L.S. ET can be caused either to the set or to r%`t ,t f r47n against them. PANEL its accessories. LAYOUT. R2o7 An Incidental Advantage The cost of the unit is to be going Six g -in. or i -in. bolts and nuts will It is not improbable that a fair the cost of any ordinary loud -speaker be required to hold amount the components of distortion occrirs in some unit, plus that of two high -frequency to the panel. Two at diagonal corners sets owing to H.F. being fed into the chokes and one small fixed condenser. of the L.F. choke will hold it quite L.F. end of the set via the loud- This additional expense will not be securely. The two large fixed con- speaker extension leads. is all It very anything but 'a proportion of that of densers and the H.F. chokes need well to include H.F. stoppers and an outdoor aerial system, and only have only one each. The small fixed R.F. chokes in the middle of a set about equal to that of the cost of an condenser can be held in position by if a path is left open for tliè " per- ordinary indoor aerial. You will see, its own leads. If you desire great nicious H.F. at this of end the therefore, that the scheme has a solidity you can employ screws and receiver. is not ! It improbable, there- financial attraction nuts for all the holes provided fore, that another incidental advan- in the The H.F. chokes can be of any good components, but in the original model tage accrues in the introduction of make, and the same applies to the I employed only half a dozen, and found the result quite satisfactory. TO SET AERIAL Using the Unit C L Only a few words will be needed in FCNOXE 000,">MAO ` , / S respect of the wiring. Use a fairly alee;.--,;; stout gauge of wire for this, Glazite for preference. Providing loops are di° e - 0 made in the ends of the leads, solder- Mo ing is not essential. I C.YOKE There are no difficulties or restric- . tions regarding the use of the device. 1.,tii,- CO C© % 0 O 0 0 It is, however, advisable to keep the o;l o 2iNF0 leads between the receiver and the l unit as short as possible. Place the unit right up against the set, and use `- h: FCHoKE 0 L. S. TO .SET 2 . / two short separate leads for this pur- pose. Do not use a piece of twisted flex. Also keep that single piece of X305 W/R/A/C DIA GRAM. wire which you will use to connect these R.F. chokes. Now regarding the three fixed condensers. The main the aerial terminal of the receiver to efficiency of L.F. extension leads requirements of the L.F. choke are the aerial terminal of the unit as short as an aerial, just a few words. that it should have ample inductance and as straight as possible, and well 614 www.americanradiohistory.com June, 1928 MODERN WIRELESS away from battery leads and the L.F. not matter much, but the higher they can be done. There are no complica- end of the set. go in the house the better the result. tions to fear in putting the scheme If you are already using a small You need not worry about increasing into use in this or in any other way. fixed condenser in series with the their length in order to gain a little .I have tried it with all sorts of sets and aerial terminal of your set, and tins bit of extra height. You will not lose the results have been uniformly good. component is embodied in your re- strength of signals by so doing. The As a matter of fact, in cases I have ceiver, you may find that bringing the result in all probability will be a most dispensed with the. H.F. chokes, but extra fixed condenser in series in the decided gain. this is a practice which I do not unit gives you too sharp tuning. In No Complications advise. this case, one or other of the con- With an efficient by-pass scheme densers can be shorted out of circuit. an extra Having connected up the unit you such as this unit provides 20 or 30 ft. of loud -speaker extension IN OTHER LANDS can proc.eed to run your loud -speaker wire no appreciable difference extension wires from it to any and makes to the L.F. energy whatever. every room in the house. Generally At the Japanese broadcasting speaking, you will find it better to A208 0002MFD AER/AL stations the microphones are placed connect the loud speakers in series. about two or three feet from the ground, owing to the fact that most Tin Loud Speaker Circuit (6ÖÓ00ÓTh of the performers are seated upon the loud- You take a wire from the 1?F.C. floor when broadcasting. terminal on the unit 70 70 speaker extension SET 6EADS to one term final of the first loud speaker R. F. C. Wireless communication has now to be served. From the other terminal (óööó0b` been established across Arabia, one of this loud speaker you take a wire of the stations being placed at Mecca. loud Diagram of a unit for attaching to set round to one of the other speakers already having a choke output in order to and from the other terminal of this make it possible to use the loud -speaker A wireless medical service has been instrument you run a lead either back leads as an aerial. instituted in Belgium and free mes- or to the other terminal on the unit If your set already has a choke - sages describing symptoms and asking on to the next loud speaker, and so condenser loud -speaker by-pass sys- for treatment can be sent by ships on. tem, you can still employ the exten- needing medical advice through the With the instruments connected in sion leads as an aerial by adding the coastal wireless station at Antwerp series, if you disconnect one lead from two H.F. chokes and the fixed con- (O S A). any one loud speaker the whole denser. If there is room behind the system becomes inoperative. In order panel of your receiver you can place Amongst the great cities of the to cause one or more of the speakers them there, though it is probably world, Berlin claims to hold the to cease operating you will have to better to make them up in the form highest ratio of listeners to popula- short its terminals. That is to say, a of a small unit and have them outside tion, the figures for that city being simple on -off switch should be con- the set. 12 per cent, with London next (8 per nected across the two terminals of the I am including a small additional cent) and then New York (6 per loud speaker. When this switch is diagram showing exactly how this cent). closed the loud speaker ceases to work, and when this switch is open it be- comes active again. To cut the loud speaker out of circuit without using a switch you will have to disconnect both of its leads and join them together. Effect On Tuning When you are using this combined aerial and loud -speaker extension scheme an ordinary earth connection is still necessary. The earth terminal of the set should be taken to the usual buried metal object or water pipe. Naturally, if you change over from an outdoor aerial er from an ordinary indoor aerial you will find the tuning range slightly altered. You may also find, and I hope you do, that there will be little loss in signal strength from any of your usual stations, and that greater selectivity and more The layout is such that the connections from the input terminals to the output terminals freedom fróm mush and other sources of the unit adopt practically straight lines through the components concerned. The of interference will occur. terminal on the lower right of photo is an input terminal. This is joined to a terminal This last is joined as have already said, much of the choke, the lead continuing to a terminal of the fixed condenser. But, I to one terminal of one H.F. choke, the other terminal of this going to an output terminal. depends upo -,l the disposition of the The same series of connections is repeated on the other side of the unit, as you will see extension leads. Their length does by referring to the wiring diagram. 015 www.americanradiohistory.com MODERN WLRELESS June, 1928 possibilities of 10 metres as a work- able wave -length just yet. Of course, the trouble in getting down to these ultra -short waves is the inductances. At 10 metres they have been reduced to about one turn, 3 in. in diameter ; at 5 metres, half a turn for each circuit is about suffi- cient. To dive much lower we shall be using straight lengths of wire as inductances Rapid Progress The fascination. of short-wave work is, of course, the fact that however one seems to progress, someone is always ahead. When I thought I was very clever and listened on 80 metres, half the stations that were working receivers reception conditions. there seemed to transfer their atten- News of interest on short-wave and tions to 40 metres a day or so after. By W.L.S. So a nice 40 -metre receiver was installed, and by the time it was working really satisfactorily nearly Sl-MMER is a time of It is rather peculiar that there should undoubtedly everyone was down on 32 metres and far greater to the he such vast differences in the charac- interest 20 metres. To keep properly abreast than it teristics of the 23 -metre and 45 -metre short-wave enthusiast of progress one has to be really is to the listener who seldom dives bands of wave -lengths During a " nippy " nowadays ! wave recent I was listening below the ordinary broadcast thunderstorm I am wondering how long it will be on a short -waver, and although lengths The difference between before the vagaries of these shorter the atmospherics were almost over- summer and winter reception for the waves have been sufficiently smoothed 45 were latter is simply a matter of degree powering on metres, they out for regular broadcast services to he hears fewer barely loud enough to worry one on in summer generally be given in any numbers. I do not stations and those he does receive the shorter band. I also have some think it likely that the present 200- the has to put caused by are not so strong, and manufactured interference 600 -metre band will ever be completely with an electric railway a little over a mile up atmospherics dropped, but it is quite on the cards away, and this seems barely notice- that we shall find, say, 50 per cent of Different Stations able on the 23 -metre band> while it is the world's broadcasting stations however, very annoying indeed on the longer For the short-wave man, below 100 metres in a few years' time. the advent of the long days simply wave lengths means that lie will receive a different BERLIN'S RADIO TOWER set of stations, and that the old Straight " Coils" familiars will also be coming through, Fading also seems at certain times although at different times. In of the year entirely absent on 23 metres addition to this, those who listen and prominent on 45 metres, whereas on 25 metres and below very seldom at other times the reverse is the case. hear an atmospheric of any description. Incidentally, if the experimenter The early mornings on the 20 - wishes to do something more original, metre band are wonderful at this let him start listening on 10 metres. time of year for those who can read Quite a few American and Continental the Morse code. Amateur stations stations are now operating down from almost every part of the world there, and the chief bugbear r'p to the romp in at great strength, and our present seems to be extremely severe friends in the Antipodes are particu tadi ng. larly prominent The American sta- When the amateurs first moved tions right over on the Pacific coast down from 440. metres to 150 metres a] so come in with an amount of vim that they thought they had found a wave- they never equal during the winter. length free from fading ; 100 metres was even better, and 45 and 23 metres Fewer " X's " better still, but now the 10-metre For the short-wave broadcast man band seems worse than any of them. the summer is not quite so convenient, However, about six years back the for 2 X A D and 2 X A F, in addition writer was solemnly assured by a to the other short-wave broadcast. gentleman who is now a prominent stations, are not now received par- radio engineer that no wave-lengtl ticularly well until 11 p.m. and after, below 200 metres would ever be of Over 400 ft. in height, this radio tower not whereas four or five months back any practical use on account of the only supports the Berlin station's aerial, but its top platform affords a magnificent bird's- their " lunch-time programmes " were fading trouble, so that it is obviously eye view of the capital. The first platform received over here quite easily. useless to form opinions on the future is equipped as a restaurant. 616 www.americanradiohistory.com June, 1928 MODERN WIRELESS 11.A.RD1AI\IM COILS Standardisation in radio is of the utmost importance and could be carried further than it is at present with advantage. An important article by J. F. STANLEY, B.Sc., ROADLY speaking, the term of the ebonite panel, while the unwary, especially when technical " standard," in addition to ebonite manufacturer said it was no matters are freely discussed by non- l. being a measure of quality or use making certain sizes only, as the technical or semi -technical people. standard of comparison, denotes a customer would want a special size common unified practice, method or to fit his particular cabinet. Importance of " Tolerances dimension which it is to the interest This problem has recently been It is hardly necessary to point out of industry and the community to remedied to a very large extent by the desirability of securing inter- adopt. the issue of a British Standard changeability of parts by means of Specification for ebonite panels, in standardisation. Fortunately, there which is included a list of recom- is a certain degree of uniformity mended panel sizes which have been amongst manufacturers regarding agreed upon by the ebonite manu- interchangeability, but this has arisen facturers and representatives of in most cases through one manu- purchasers of ebonite panels. facturer copying the dimensions Consider also for a moment the adopted by a competitor rather than question of standardisation of tests. by the adoption by all of an agreed It would appear to be useful if a standard of dimensions together with standard method of testing telephones an agreed tolerance to allow for DIMENSIONS Or PLUG. FG.I. and loud speakers could be evolved. unavoidable variations of material Many wireless enthusiasts have been and workmanship. The limitation of known to describe the efficiency of these tolerances is, of course, just as " Standardisation " may embrace their pet receiver by declaring that simplification of types and sizes, " Sigs. could be heard with the standardisation of tests, nomencla- 'phones on the table downstairs." Of ture, interchangeability of parts, rules course, well -recognised methods of for performance and quality of testing the efficiency of telephones material, to name only a few of the are used by the Post Office and in aspects of a very wide subject. scientific laboratories, but there is still room for a single simple method Advantages of Standardisation which could be universally used and There is obviously room for stan- by means of which a definite figure dardisation of wireless apparatus, and of merit could be assigned to tele- no matter which of the aforemen- phones and loud speakers in general. tioned aspects of the question we consider, we find that advantage to the manufacturer and to the purchaser Full of Pitfalls would result. For instance, take the As regards standardisation of case of simplification of types and nomenclature, we are still hoping sizes. that valve manufacturers will one How many times have we wanted day adopt a uniform method of to change a grid leak, only to find designing the various types of valves. that our only spare will not fit into How many people could tell you the A simple and popular form of coil coup- the clips provided in the receiver ? technical distinction between inter- ling using standard apparatus. Again, in the case of cabinets and ference and jamming ? The British ebonite panels, how much simpler Standard Glossary of Ternis used in important, in certain cases, as agree- it would have been if everyone could Electrical Engineering has been drawn ment regarding the nominal dimer- have agreed, years ago, to use only up in order to settle these things, and sions. certain recognised sizes. The cabinet- also to tell us whether we should talk The advantages of a standard makers said they could not st4ndardise about the " impedance " of a valve method of testing loud speakers are sizes because it depended on the ideas or the " A.C. resistance." Verily, closely linked with the desirability of of the customer regarding the size nomenclature is full of pitfalls for the having standard rules of performance 617 Y www.americanradiohistory.com MODERN WIRELESS June, (928 of wireless receiving sets. To evolve This body sets up committees fully its solution on the technical ability any such standard rules would appear representative of all the interests of the members of our committee, to be a very difficult and complex involved in the particular subjects while the third and most vital question matter, as the conditions of operation being dealt with, and in the case of involves a point of policy which must in practice vary so considerably, wireless standardisation the com- receive our very careful consideration. depending on the size of aerial, mittees include in their membership geographical position, skill of the representatives of the radio societies, operator, etc. Nevertheless, an the radio manufacturers, valve manu- attempt at such standardisation has facturers, Government departments, been made in America, and the possi- National Physical Laboratory, and bilities of the idea should not be the Technical Press. Standard speci- ignored, as such standard rules would fications have been issued dealing at least afford some measure of com- with nomenclature, ebonite, con- parison between different receivers densers and coils, and it is with special under any given set of conditions, reference to the specification for although they may not give any coils that the rest of this article is guarantee of performance of a par- concerned. Other standard specifica. ticular receiver under other conditions. tions will, no doubt, be issued before We need say very little about the very long. standardisation of the quality of materials, as the advantages to be Important Considerations gained thereby are self-evident. The Imagine yourself to be a member most important aspect of this is of a committee the function of which probably the question of the quality is to draw up details of a standard of insulating materials, the electrical coil or series of coils. You would Standardisation is losses due to poor -quality material immediately be faced with the follow- intended to assist the industry, but if our efforts still being much greater than many ing questions : Are the coils at present are likely to result in people realise. on the market so different in perform- stagnation of design we shall not fail ance and design that it is too late to only to render this Unofficial Standardisation expect manufacturers to give up their assistance but we shall definitely produce the reverse It was for this reason that the first present pattern and adopt a new effect. Either the standard will not be worked to, and. British Standard Specification for pattern ? Or is the industry so young the specification will become in- wireless material was for ebonite, that we do not really know which is effective, or those manufacturers who which was drawn up at the request the best type of coil to standardise ? do adopt the standard will be of the Radio Society of Great Britain, Again, if we do standardise a certain put out of business by the keen competition in view of the poor quality of much of type or types of coil, shall we unduly of those have themselves what was sold as ebonite a few years hinder the progress of design and who kept abreast of the latest ago. The issue of this specification has remove all incentive to produce a improvements in design. undoubtedly improved the quality of better type -of coil ? the ebonite now generally sold. The last of these problems is per - "Coils AND Coils" METRES Y504. The committee of which you have 29350, 945A 3/40, /050, 350 constituted yourself a member will x50 probably decide that the design of I50. L5° 2430 e/00 B5U coils for wireless work is still in a; J yX40 state of flux, and that there appears O 0250 675 Q22T 5750 25, to be plenty of scope for further S40B40 V O h j A40!p,aX30 experiment before finality in design 1.16200 20C is reached. There a 53°B30 M3 are large number a of types of coil in use : long thin Z T804600 14 50. B 20.M20LáX 13.... /2/SO 14050 /350 ,1, 450 x/50 LO&X/O_ coils, short fat, coils, coils on paxolin ,,3 5/0.B/O.MO. formers, coils on skeleton formers, º ú ,; aioo (.,,roo;.. 900 0 30 coils without any mechanical support Q 0 ó/0c at all except the rigidity of the wire 444050 /35 kh450 /50 50 i' itself, solenoidal coils and torroidal coils, slab coils, and honeycomb coils, O O 1 0 O 00 Heath Robinson coils and litzendraht /00 200 300 400 500 COO 700 800 .900 /000 SHUNTED CAPAC/TY /NA/C0FARADS(/4/2f) coils ; in fact, coils and coils. Out of had CURES SHOW/NC WAVELENGTHS COVERED BY BR/T/SNSTAN7YARÛ PL1./6-/N CO/ZS. all this medley of coils, there is one - As has previously been said, a haps the most important ; the first fairly stereotyped variety which does certain amount of unofficial stan- question is a matter which depends for not seem to change much with the dardisation has already been achieved its solution on the far-sightedness and course of time, namely, what is usually by the wireless industry, but the most manufacturing resources of the pro- known as the plug-in type, so-called successful efforts in this direction have ducer of the coil, and a study of the because it eau be plugged into a obviously been those resulting from psychology of manufacturers as a socket. the issue of British Standard Speci- whole will probably help us to form This type of coil appears to have fications by the British' Engineering an opinion as to the ultimate success become more or less generally stan- Standards Association, commonly of the standardisation. The .second dardised among the various makers known as the B.E.S.A. question is a matter which depends for by a process of copying dimensions 618o www.americanradiohistory.com June, 1928 MODERN WIRELESS from rival makers, and provided we securing good contact in the coil moved, then, of course, a reversal of do not lay down exactly how the coil holder are standardised, these being the magnetic field would result. is to be constructed-thus limiting the diameter, spacing and length of In a receiver using plug-in coils, future design-it would appear that a the pin and socket. These dimensions it is usually essential that the direc- standard specification which would and the tolerances, or manufacturing tion of the field of a coil (i.e. the regularise the dimensions once and limits, are shown in Fig. 1. " coupling ") should be unaltered for all, would be of advantage to As the design of the pin itself is a when we change one coil for another. manufacturers and purchasers alike. matter of a controversial nature Otherwise, a receiver would have a (i.e. the pin may be solid, slotted, or positive coupling with one coil and a The Committee Gets Busy " sprung "), the specification confines negative coupling with the other coil ; were coupled to After a thorough investigation of itself to the requirement that when if the coils in question for purposes, the position, we should probably the pin is inserted into a socket of the aerial coil reaction capable of come to the conclusion that a compre- the diameter shown in Fig. 2, good the receiver would be case and hensive standard specification cover- mechanical and electrical contact is oscillation in the one in other. ing all types of coils would, at the obtained. For this reason the actual incapable the is not present time, be premature, if not diameter of the pin itself Direction of Winding impossible, but that the one type specified, it being obviously impossible which appears to have become to define the diameter of a " sprung " Hence it is necessary that all coils, stabilised, namely, the plug-in type, pin, for instance. of whatever size or make, should have their windings connected to the appears to lend itself admirably to An Erroneous Idea standardisation in certain respects. plugs in the same way, so that when * * The original design of the pin -and - once we know the direction of the That impressive -looking row of socket form of plug -mounting was coupling with one coil, we can rest dots indicates that, having decided no doubt evolved with a view to assured that it will be the same with to draw up a specification for plug- making the coil non -reversible, based any other coil. It does not matter in coils, our committee gets busy, on the erroneous idea that if the coil whether the inner end or the outer end consults representatives of the manu- were reversed, the direction of its of the windings is connected to the facturers and purchasers, and in due magnetic field would likewise be pin of the plug, so long as the pins course produces the British Standard reversed. The fallacy is apparent of all plugs are connected to the same Specification No. 289-1927. immediately we realise that when the end of the winding in all coils. The committee having done its coil is reversed the connections of its For the purpose of obtaining unifor- work, let us túrn our attention to the ends are also reversed, so that the mity, the specification has standardised specification itself. current still flows in the same direction the practice adopted by the majority In order that we may be quite relative to the remainder of the of the manufacturers, this being as clear as to the type of coil referred to circuit, and the direction of the follows : in the specification, a " plug-in coil " magnetic field is therefore unchanged. Looking at the coil in such a manner is defined as " an inductive winding Supposing, however, that the winding that the connections are at the and the pin on the left-hand secured to a plug : the winding may were reversed without its terminal bottom or may not be protected by total or connections being changed, or that side, the winding shall go in an anti- partial enclosure in a case or other the terminal connections were inter- clockwise direction from pin to socket covering." Thus it is seen that the changed without the winding being (see Fig. 2) and details of design and construction are left very largely to the initiative of the manufacturer. Plug Portion Dimensions It is further made clear that a plug- in coil is an interchangeable type of coil in which the two ends of the winding are connected to a pin and a socket respectively, the pin and the socket together being part of the i " plug portion " of the coil. The following features of the coils are standardised : (a) The dimensions of the plug portion and the tolerances thereon, in so far as interchange- ability is concerned. (b) The method of connecting the winding to the plug portion. (c) A range of " sizes " based on the inductance values. (d) A simple arbitrary system of nomenclature or designations. With regard to the dimensions of the plug portion, only those which are Three standard coils used as aerial, secondary and reaction inductances for which their essential from the point of view of tight coupling make them specially suitable. 619 www.americanradiohistory.com MODERN WIRELE$S June, 1928 (a) in, multi -layer coils the inner GRour X.-" Extra -long," intended ever, that at the higher wave -lengths lead shall be that which is to cover wave -lengths of 7,000-25,000 some of the coils may be dispensed connected to the pin, while metres. with, and for this reason the 25 coils (b) in single-layer coils the lead As will be seen from the schedule are divided into primary sizes and farthest away from the observer and the curves in Fig. 3, the actual secondary sizes, the primary sizes shall be that lead which is overlapping of the wave -length range being distinguished in the schedule connected to the pin. of each group is greater than indicated by being printed in bold type. The - above, this extra range being obtained secondary sizes are not considered Inductance Values by using the condenser at the extreme really necessary in practice, but have The most interesting part of the lower and upper limits of its range. been included in the schedule to make specification, at any rate from the Thus, Group S, instead of being con- the range complete, and users are academic point of view, is that which fined to the band from 20 to 175 recommended to restrict their require- deals with the inductance values of metres, which would be covered if ments to the primary sizes as far as the 'coils. These values relate to the used with a condenser having a mini- possible. mum capacity of 25k9,F. and a maxi- line inductance ; that is to say, the Designation Numbers apparent increase in inductance owing mum of something less than 500µµF. (0.0005µF.), would extend up to about The coils in each group are desig- to self -capacity is allowed for and by 10, 20, 350 metres if used with a condenser nated the numbers 30, 40, excluded. The standard series of and 50, this being more convenient coils is ingeniously designed to cover, of 0'001µF., and would also extend downwards considerably below 20 than 1, 2, 3, 4, and 5, as it enables with a minimum number of coils, the intermediate sizes to be interpolated whole range of wave -lengths from metres if the condenser were used at its absolute minimum setting. if required for any particular purpose. about 20 metres to 25,000 metres Also, if an experimenter had a coil when used in conjunction with a Wave -Length Ranges which did not exactly conform to any condenser in parallel having a value particular size, he could measure the of 0'001 mfd. or less. The range of In practice, however, it is not usual inductance (or the wave -length with coils is divided for convenience into to work right at the bottom of the a given condenser -setting) and per- five groups, as follows : condenser scale, nor is it usual to use a haps find that it was approximately GRour S.-" Short," intended to condenser greater than 0.0005µF. on half -way in size between the B.20 and cover wave-lengths of 20-175 metres. the short wave -lengths, and conse- B.30 coils. GROUP B.-" Broadcasting," in- quently the limits of 20-175 metres For his own convenience he would tended to cover wave-lengths of 150- may be taken as the extreme Iimits call this a B.25 coil, so that he could 750 metres, and therefore including for efficient use of the coils in Group S. immediately predict the wave -length the wave -lengths at present used most Incidentally, for those who prefer to range of this coil relative to a standard generally for broadcasting purposes. think in terms of kilocycles, the coil by reference to the schedule on SCHEDULE OF INDUCTANCE VALUES OF BRITISH STANDARD PLUG-IN COILS. this page. The following extract from the British Standard Approximate wave -length (metres) Approximate frequencies (kilocycles) Standard Inductance with shunted capacity (picofarads). covered by coil with shunted capacity. introduction to the specification is Designation (micro- of Coil. henries). 25 quoted in explanation of how the µµF. 125 µµF. 250 µµF. 500 µµF. 25 µµF. 125 µµF. 250 µ F. 500 µµF. sizes of the coils have been worked out* : S. 10 8 23 52 73 103 12,000 5,770 4,110 2,910 S. 20 9 28 62 89 125 10,700 4,840 3,370 2,400 " The inductance values, and there- S. 30 13.4 34 77 109 154 8.820 3,900 2,750 1,950 fore the wave -length range of the S. 40 20 42 94 133 189 7.140 3,190 2,260 1,590 S. 50 30 52 115 163 231 5,770 2,610 1,840 1,309 coils in a group, bear a simple mathe- 82'5µµF. 250 µµF. 500 µµF. 1000 s i F. 82.5.44F. 250 µµF. 500 µµF. 1000µµF. matical relation to the values of the corresponding coils in other groups, B. 10 58 109 218 309 435 2.750 1.380 970 690 B. 20 80 133 266 376 532 2.260 1,130 800 560 and a corresponding relation exists B. 30 120 163 326 461 652 1,840 920 650 460 B. 40 180 200 400 566 800 1,500 750 530 380 between the individual coils in any one B. 50 270 245 489 692 978 1,239 610 430 310 grou.p These relations are as follow : M.10 480 326 653 927 1,305 920 460 320 230 51.20 720 399 798 1,130 1,595 750 380 270 190 A " Geometrical Progression' M. 30 1,080 489 978 1,385 1,955 610 310 220 150 M. 40 1,620 600 1,200 1,700 2,400 500 250 180 130 " The inductance values of coils M. 50 2,430 734 1,470 2,075 2,935 410 200 150 100 8.10, B.10, M.10, L.10, and x.10, L. 10 4,320 980 1,960 2,780 3,915 310 150 110 77 form a series in geometrical progres- L. 20 6,480 1,200 2,395 3,385 4,790 250 130 89 63 L. 30 9,720 1,470 2,935 4,150 5,S70 200 100 72 51 sion, the common ratio being 9. L, 40 14,580 1,800 3,600 5,095 7,200 170 84 59 42 L. 50 21,870 2,200 4,400 6,230 8,800 110 68 48 34 " Similarly, coils S.20, B.20, etc., S.30, B.30, etc., form series in geo- R. 10 38,900 2,940 5,880 8,340 11,759 100 51 36 26 X. 20 58,300 3,590 7,180 10,150 .14,360 84 42 30 21 metrical progression with a common 5.30 87,500 4,400 8,800 12,450 17,600 68 34 24 17 X. 40 131,000 5,400 10.800 15,280 21,600 56 28 20 14 ratio of 9, and so on throughout the X. 50 197,000 6,600 13,200 18,680 26,400 46 ' 23 18 11 whole range. " The coils in each group also con- NOTE. -Those sizes printed in heavy type are primary sizes and will cover all normal req irements. Those sizes printed in light type are included in order to make the range complete, but users are recommended stitute a geometrical series in them- to restrict their requirements to the sizes in heavy type as far as possible. selves, with a common ratio of 1.5. GROUP M.-" Medium," intended corresponding values are also shown Thus the inductance values of coils to cover wave -lengths of 700-2,800 in the schedule. S.10, S.20, S.30, S.40, and S.50 form metres. There are five coils in each of the (Continued on. page 672.) GROUP L.-" Long," intended to above -mentioned groups, there thus Extracted by permission from British Stan- cover wave-leng*hs of 2,500-8,000 being 25 coils in all. The amount of dard Specification No. 289-1927. (B.E.S.A., 28; Victoria Street, London, S.w.1, price 2s. 2d. post metres. overlap in wave -length is such, how- free.) 020 www.americanradiohistory.com June, 1928 MODERN WIRELESS cmTïìÁIs" ) CRYSTAL SET There is a combination of capacity and inductance which, under certain conditions, will tune in a station with greater strength than any other. Here is a receiver which enables one to discover that ideal " L.C." ratio in practically any circumstance. By PERCY W. HARRIS, M.I.R.E. IN every practical application of one learns a number of highly inter- more we can cut out our losses in the electricity we first aim to obtain esting facts. Seeing that every wire- receiver itself the louder will be the definite results, and then, when less laboratory carries out its tests as signals, so that on the one hand these are certain, to obtain them with far as possible with instruments which the best designed crystal set would maximum efficiency. Looking back give quantitative indications rather give inferior results with a poor in radio we are bound to smile when than approximations and guesses crystal detector and, equally, the we think of the appalling reproduction dependent upon the sensitiveness of which at one time satisfied us in the ear of the observer, it is possible regard to quality, while, in the matter to obtain definite figures of efficiency, and these I have taken with crystal receivers for some time. :: LIST OF REQUIRED. e. . COMPONENTS Selectivity Required 221 Ebonite panel, l0 in. x 7 in. (Radion, e Whereas the valve receiver is in the Trelleborg, Beeol, Ebonart, etc.). t2 of 22 1 Cabinet for same with baseboard, nature apparatus which uses the 7 in. (Cameo, Caxton, Pickett, etc.). incoming signal to " trigger off " :: 1 0005-mfd. variable condenser (For- .. local energy from the high-tension mo, or any good variable condenser .. will suit). supply, the crystal receiver is depen- .. 21 Clix " parallel " sockets. .. dent entirely upon the incoming best crystal detector is wasted with - ::2 Terminals for aerial and earth signal, which we must take, convert out a properly designed set. . respectively (Eelex). .. of signal alone is not all Z21 Open -circuit jack (Igranic, Lotus). into unidirectional currents, and pass Strength .1 Plug for jack (Igranic, Lotus). through our telephone earpieces: The that is required in a crystal receiver, é 1 Socket for standard plug-in coil. .. 221 Crystal detector, complete on ebonite .. base, as shown (Any dealer). 22 221 Pair telephones. . :: No. 150 plug-in coil (Any standard e... make, Lissen, Lewcos, etc.). 22 Stiff wire for wiring up, such as º2 :: Glazite. .. 22 3 Short lengths of flexible rubber- 2+ :: covered wire. 40 221 Tube, 3 3', (Atlas e. .. x in. Pirtoid). .. ee4 ....4. e. of economy, I have in front of me as I write a seven -valve super-hetero- dyne receiver using a super -power valve in the output stage which, so far as filament consumption is con- cerned, uses for the whole seven valves less current than did my first one -valve set ! Increasing Efficiency Now the humble crystal set, which still serves as the key to broadcasting to many thousands of listeners, can be raised to a point of efficiency not generally realised. It so happens that my daily work includes the testing of all kinds of wireless components, The set is an easy and inexpensive one to build, and makes a neat, attractive outfit. It including crystal detectors, and in can be adjusted to tune in both medium and long -wave broadcasters with the maximum the process of examining such articles possible strength. 621 www.americanradiohistory.com MODERN WIRELESS June, 1928 we have also to consider selectivity. of the British stations and with the best way of using our crystal detector. With the Daventry experimental maximum to the longest wave- A measurement of the received current station 5 G B, crystal -set users in large length, excluding, for the moment, passing through the telephone head- areas of this country can listen to 5 X X ; yet if we do this the ratio of pieces soon shows that with a given either their local station or to 5 G B capacity to inductance will be un- crystal detector the best or loudest provided their sets are sufficiently favourable over a good portion of the signals are not generally obtained selective, whereas before this station opened there was no particular need for crystal sets to be selective (except in coastal districts where Morse in- terference was bad) as there was only one station to be received. Our ideal crystal receiver therefore should be selective and preferably with variable selectivity, so that on certain occasions there may be no need to sacrifice any strength to obtain the selectivity which is not at the moment required. This means that a variable aerial tapping is needed. For All Wave-Lengths The next point to remember is that we want to produce a crystal receiver which will be equally efficient when sed for listening to any of the British stations. True, it is possible to design a special set for each wave -length, but we want to provide a design which scale. It is better therefore to have when the detector is shunted across without structural alterations will suit an arrangement by which both in- the whole of the inductance, but when any station. It is easy to take a coil ductance and capacity are variable it is shunted across only a portion. and tune it with, say, a large variable so as to get the best L -C ratio for a The difference between signal strength condenser so that with a minimum given set of conditions. obtainable when the crystal is shunted of capacity across the coil the set will This does not yet end the matter, across the most favourable proportion just tune to the lowest wave -length for we have yet to consider the of inductance and when it is shunted across the whole of the inductance is very remarkable, and in carrying out experiments for this article I found that with a given crystal detector the current received when the crystal was shunted across approximately a third of the inductance was in the propor- tion of 140 to 80, or nearly twice as great. Greater Signal Strength Not only do we get better signal strength by shunting our crystal detector across only a portion of the inductance, but we also improve the selectivity, so that our properly de- signed crystal receiver will be definitely better in signal strength and selectivity than one in which the old method of shunting aerial and crystal across the whole coil is used. Experiments with a number of differ- ent crystal detectors show that the optimum ratio of crystal turns to total inductance is not constant, but varies very considerably with differ- ent detectors, which, indeed, is to be expected when we know how detec- tors vary in resistance. By this time the reader will have This close-up shows you exactly how the tappings are taken from the coil. In each case a turn of the wire has been gently prised up, a piece of match -stick slipped under it and fully realised that a tapped coil is the lead from the socket securely soldered to the subsequently bared wire. necessary in order to get best results, 622 www.americanradiohistory.com June, 1928 MODERN WIRELESS and that taps arc required for aerial, whisker type, as it is not easily it tight. When you have finished crystal and condenser if we are to deranged, and one can carry out all winding the coil and have secured the obtain all we desire. A multiplicity kinds of experiments with varying ends, count twelve turns from the of tappings, however, is not desirable L -C ratios, crystal taps, aerial taps, beginning, and then, with a sharp - from other points of view, and a series etc., without fear of the adjustment pointed instrument, prise up the of long leads connected to taps may being disturbed. twelfth turn, and slip under it a piece add considerably to the capacity of of matchstick. You will be surprised the coil and reduce its efficiency. The Tapped Coil at the elasticity of this gauge of The crystal receiver which I am about The coil itself is home -wound on copper wire. You will find that it to describe has been built for use in a 3 -in. former measuring 32 in. is not at all difficult to prise up the my laboratory, an& has proved very long. No. 24 D.C.C. wire is used, valuable in a number of investigations. and the procedure for winding the Although it can justifiably be coil is as follows : Pierce three ;; When Mr. Harris tested this crystal ¡¡ holes on the line of the diameter of ;; set in his laboratory at Wimbledon, it ¡¡ developed a record current of rectified ¡¡ /0" -i the former about a quarter of an ;¡ energy for a receiver of its simple ;¡ AfR/AL (TAP 2 - inch from one end, and wind on tightly j; 4 P r>";-'2'. nature. 4, and with turns touching seventy-five .. .. /f vurrlr turns of No. 24 D.C.C. The choice ¡ ,. ,. ,.,ctoc, of this gauge of wire enables us to wire sufficiently to insert the match- obtain a coil which has very efficient stick, which will remain in position proportions for the inductance we without slipping. Now count on E want. Put in another way, we obtain another twelve turns and lift the 'l CONO ii Y1 I a coil which contains a very high twenty-fourth turn in the same way, TAP CR stat //2\% 1 TAP PHONE JACK inductance for the amount of wire repeating the process at the thirty- Y577 PANEL LA Your used. At the other extreme, if we were sixth, forty-eighth and sixtieth turns. to wind a single -layer coil of thick It is advisable to " stagger " the ca led a " de luxe " instrument, its wire on a narrow former, the pro- tappings as showing in the photo- 'cost is remarkably low, and as it portion of length to diameter will be graphs. contains a few novel constructional very large and the coil inefficient. features, and as it will enable readers Do not bother about snaking the Soldering the Leads of MODERN WIRELESS to carry out tappings as you go along. Wind the The next step is to take a sharp some very interesting experiments, no coil tightly, and with turns touching, knife and serape away the cotton apology is made for describing it in until you reach the number of turns insulation immediately above each detail. mentioned ; pierce three more holes matchstick so as to expose the bare An examination of the photographs and thread the wire through, pulling copper. A hot soldering iron should and drawings will show that the front panel carries aerial and earth t. terminals, a jack for telephones, a variable condenser and twenty-one sockets in three separate rows of seven. At first glance this suggests that twenty-one taps are taken, but a closer examination shows that on the coil itself there are only five tappings, and that the leads from these are quite short and well spaced. Each socket in the top row is connected to the two sockets immediately beneath it, so that we have seven rows of three sockets in parallel. The extreme right-hand sockets are only used when it is desired to receive 5 X X. " Permanent" Detector The crystal detector itself is mounted on the baseboard of the cabinet, access to it being easily obtained by lifting the lid. It is just as well to obtain one of the kinds designed to take the cat -whisker - galena detector, as this will probably be needed among others in the experiments. The small glass barrel and its fittings can be removed in a moment, and one of the permanent types substituted when desired. For general reception work there is no You will note that each tapping from the coil is joined to its own row of three sockets. These sockets can accommodate any one or all of the three plugs provided for aerial, crystal doubt that the permanent type is and condenser taps. Dozens of circuits thus become available and the ideal one for your generally superior to the cat's - particular local conditions is readily found. 623 www.americanradiohistory.com MODERN WIRELESS fune, 1928 now be obtained, and the tapping about three -eighths of an inch in reveal this quite clearly. It is now points tinned. At the saine time thickness, and measuring 2 in. by 1 in., quite a simple matter to cut short cut off the ends of the wire at the cut a V-shaped slot in one end of leads and to solder them between the beginning and end of the former, your tube, as shown, and drill a hole in tappings and the sockets, as shown. leaving about half an inch projection, the tube immediately beneath this Notice particularly that a lead goes and tin these two ends ready for slot. The purpose of the slot is to from the end sockets right round to further soldering. enable you to insert a screwdriver the holder for the plug-in coil. conveniently. Now drill a hole in Component Assembly the small strip of wood in the correct Final Preparations The first step is to drill the panel position (which you will find by You will notice that three plain and to insert the Clix parallel sockets. experiment), and when this is done holes are drilled in the panel, two Before mounting other components place it beneath the tube and pass beneath the bottom row of sockets on the panel lay it face downwards a j --in. round -headed wood screw and one immediately above the top and carefully tighten all the nuts on through the tube and the piece of row. After you have wired up all the sockets, tin them, and solder in wood into the baseboard, screwing the components needing stiff wire to position the seven short lengths of it up tightly. The effect of this will join them, take three flexible rubber- ccrvered leads and fit to them the three plugs. Plug in the first plug o into any socket in the top row, and i;l f thread its flexible lead through the SCALE /N //CNES 7.17 AER/AL PLUG top hole, and soldering it to the aerial A terminal. Plug in the second socket into the second row and pass its flexible lead through the bottom left- hand hole (looking at the panel from 000000 the front) and from there to one 0 0 ( ) 0 0 ().() terminal of the crystal detector. TO CO/O SR Now insert the third plug in any socket PL UG !U_UUUUUU in the bottom row, and pass its flexible lead through the bottom PANEL right-hand hole, taking it inside the F/XEO R7 CRYSTAL set to the fixed plates of the variable MOY/NC PL UG condenser. PHONE 11,, 1 JACK Selecting Your Circuit You are now all ready to begin work with the set. The top plug varies the aerial tapping, the second plug the crystal tapping, and the bottom plug 75 the condenser tapping. As a start, IIIJ9 try plugging the condenser plug into the third socket from the left, and the aerial plug in the third from the left, with the crystal tapping in the second to the left. Plug in your telephones, and tune with the variable condenser, when your local station should be heard quite well. Notice the amount of condenser you have across the coil, 7STURNS N2240.C.0 and if it is large, say, 100 or 120 ® degrees on a 180 -degree dial, bring CRYSTAL l!U .- hr!q your condenser plug one socket towards the right and retune, where- upon you will find that the station will tune in with less capacity than W/77 W/R/NG O /AGRA /19 before. After you have experi- mented a little with the aerial and wire shown. Be sure that you solder be that the coil will be securely fas- condenser taps, try varying the crys- each wire firmly in position, and after tened to the baseboard without any tal tap and you will probably find all the joints have cooled, carefully of the turns touching the baseboard that the best signal strength is tighten all nuts again, as the heating itself. obtainable either in the first or in the of the sockets will probably loosen a second socket. The diagrams in Fig. number of them. Arranging the Coil 2 show a number of various arrange- Next mount aerial and earth ter- In arranging the position of the ments which can be tried with this minals, condenser and jack, and lay coil on the baseboard, see that it comes set. the panel aside for the time being. in correct relation to the sockets for For 5 X X insert a No. 150 coil in It will now be necessary to mount the leads, which will have to join the socket at the back, and place all the coil on the baseboard. In order to the tappings to the sockets. An plugs in the extreme right-hand do this take a small piece of thin wood inspection of the photographs will sockets. 624 www.americanradiohistory.com June, 1928 MODERN WIP.ELESS `ffliffliílafflemi3egesmemezzem :; egie egc mememeneffl ;: .á°iF 5!%egt"geeffleMellgii 9t Mä egg This exceptionally interesting article was written exclusively for "Modern Wireless" by Mr. F. Dearlove, the man selected to link up Labrador by wireless. How that Titanic task, carried through in the face of difficulties and dangers, constituted a real romance of radio and a triumph for short waves, is thrillingly told below. THE very name " Labrador " calls to mind a vast The dog* trail is dotted with " tilts or crude hats tract of snow and ice -covered territory, inhos- every thirty or forty miles, but men have died, simply pitable both to man and beast, and while this is frozen to death, within a few hundred yards of this only too true in the long winter months from November shelter. Doctor Wilfred T. Grenfell, the man who has to May or June, in the summer, short though it be, done more for Labrador than any other living man, things are very different and the Newfoundland and building hospitals and caring for its people when they Labrador fishermen reap a rich harvest cod -fishing in fall sick of the dreaded T.B., conceived the idea of con- their schooners from June to October, sailing along its necting up his hospitals by short-wave radio, so that rocky coast where not a tree is seen for hundreds of the Labrador base at Northwest River, and the main miles. base at St. Anthony, northern Newfoundland, could be in touch with each other and with the office in New York, and thence to England, and it is due to the generosity of an American gentleman and wireless enthusiast, Mr. Eldon McLeod, of Massachusetts. in providing funds and apparatus, that the scheme is now a reality. The First Station Completed Doctor Grenfell. or Sir Wilfred Grenfell. as we must now callhim, for he was kniAted at the dedication of his new hospital in St. Anthony, last July. gave me the task of installing the stations and training operators to work them, and the Marconi Co. very kindly released me from their staff until such time as the task was completed. and "accordingly I sailed from England on the 25th May. 1927, for St. Anthony, Newfoundland. The operating table at N E 8 A E. The short-wave apparatus Towards_the end of July the first station at St. Anthony is to the right and the receiver in the centre. To the left is was nearing completion, though the transmitting equip-. the set for working on 600 metres. ment had not yet arrived. I was enabled to carry on, In the months of March and April thousands of seals however, with equipment I had brought out with me. are caught on- the ice and shipped to St. John's, N.F., and very soon we were " on the air." for export. Unfortunately, the country is absolutely undeveloped, no roads exist of any kind, and whilst communication is maintained along the coast during the short summer months by a series of small wireless stations comprising induction coils and crystal receivers; these stations are not open in the winter, and the only means of travel or communication even is by dog -team and " komotik," as the sled is called. Life -Saving Links Due to the fishermen's habit of living for the most part on tea and bread and fish alone, in badly ventilated huts, super -heated by wood stoves-when they can get wood-tuberculosis is the great white scourge in this rocky, barren land, and it is a frequent occurrence for a man to set out in search of medical aid, with a team of " huskies " and a kornotik on a journey of two or three hundred miles to the nearest doctor or nursing station, Above is shown the " Smoky " wireless station, from which with but a slim chance of getting through in safety the world first learned the news of Peary's dash to the North Pole. The mast is a one -hundred -and -twenty -footer, on the top should an arctic blizzard, invariably followed by a tem- of a mountain, the transmitter is a Io -in. spark coil, and the perature of far below zero, catch him abroad. receiver a crystal. www.americanradiohistory.com MODERN WIRELESS June, 1928 In addition to the short-wave equipment a 500 -watt The long aerial has harmonics at 84, 42 and 21 metres, spark transmitter was installed, together with a long - which proved very useful when one day the normal wave receiver, and one for 600 -metre work. The call - transmitting aerial, a current -fed Hertz, was blown down sign of this set is V 0 L. in a terrific gale which unroofed a couple of houses at The short-wave set consisted at this time of an " 3I.L." the same time. The current -fed Hertz aerial has a fun- converter, tyke E," running from a 12 -volt accumu- damental of 21 metres, and for 40 -metre transmission the lator, and supplying 500 volts D.C. to the plate of :i complete Hertz was worked against an extra quarter - Mallard S.W.50 valve. The inductances were made wave counterpoise, the Hertz acting as a T. from copper ribbon stripped from an old Ford spark e coil. The condensers were just plain receiving condensers, whilst the aerial ammeter was a flash -lamp bulb. Gale Blows Aerial Down The set was built of well -dried oak, right on the spot, and worked beautifully on 20 and 47 metres ; later, 42 and 45 metres were added. The circuit employed was a split Colpitts, and as will be noticed from the circuit the grid -leak and plate supply are at points of relatively little or no difference in high -frequency potential, making for extreme efficiency. The receiver used on the short waves at St. Anthony is a three -valve Reinartz, of standard construction, the ' Fishing Head," the uncompromising entrance to St. Anthony Harbour. only alteration macle being the addition of certain re- sistances to make the set more stable in operation, as Almost my first Q S 0 was my old friend, E G 2 X Y, described elsewhere. The receiving aerial is quite large whom I liad visited before leaving England, and who and very high, though a very short one having a funda- promised to Q R X for us. It was 5 a.m. G.M.T. when mental of 30 metres was found to be unsurpassed for we made contact, so he was certainly " on the job." short distances. Stations in Rome, Paris, Germany, Sweden and Austria very quickly followed, but the very greatest thrill of all was one quiet evening when hardly a station was work- ing I sent out a tentative but pessimistic C Q on 20 metres, and the only station heard was S A D A 8 calling me, and saying Q S A R 4: He gave his Q R A as Bernal, Buenos Aires. I often look at his card now to convince myself we really did work him with so little a power input, less than 20 watts. Since that time many stations have reported hearing N E 8 A E, as we are called, on days when we could not hear a signal because of the aurora borealis putting a blanket on the ether. Stations Patrolled By Yacht Towards the end of August preparations were under way for the second station at Northwest River, Labrador, and great anxiety was being felt by the `people there lest winter should arrive before the apparatus which had been furnished by Mr. Eldon MacLeod and John L. Reinartz;- the well-known pioneer on the short waves, came to hand. The arrival of the mail boat was awaited with great excitement, and telegrams were arriving from the nearest coastal wireless'station on the Labrador from Dr. Paddon, expressing great apprehension as to whether or no he was to have a set before winter. Dr. Paddou's stations on the Labrador are at Indian Harbour ; Gordon, on the south side of the Hamilton Inlet ; and at Northwest River, the winter station, one hundred and forty miles from the sea, standing on the shores of a vast inland salt -water lake, wider in parts than the English Channel, called Lake Melville. It is on the way to the famous Grand Falls, in quest of which Hubbard lost his life not long ago, being frozen to death within a few miles of Northwest River. Dr. Paddon has to patrol his stations in his yacht, the " Yale," simply at the mercy of the wind, during the summer. The boat is only The long -wave receivers at N E 8 A E. These are used in con- one of fifteen tons, and though junction with the 600 -metre spark transmitter, the inductances it is soon to have an engine, it is without one at present, for which are shown attached to the wall. and November approaches and terrible gales lash 626 www.americanradiohistory.com June, 1928 MODERN WIRELESS Lake Melville into a fury. The salt spray freezes as it a Delco lighting plant. was put at my disposal, and ì comes aboard and the whole surface of the water is decided to take the M.L. converter to Labrador and build covered with a thick slushy ice called " slob," which the more powerful station for St. Anthony. precedes the annual freeye-up ; his position is serious As time was running very short before the Labrador indeed. But that does not deter him from going out to winter set in, the St. Anthony station was hurriedly anyone calling for his assistance. completed, using the 500 -watt generator supplying power to two 50 -watt tubes in a Hartley loose -coupled AEaiAc ANO Cowvreavo,se, as before. AaailNGCOFoa 4Oderaes circuit on exactly the same wave -lengths G A Standby Generator One photograph shows the present layout of the apparatus, the starter for the M.G. being placed con- veniently to the right of the operator, on an upright L2 of the In addition to the M.G. an AZ/7/A.1 ARRANGED FOQ built at the edge table. 20/WErae5 Evershed hand -generator has enabled N E 8 A E to com- mrmicate with England when, due to a failure of the supply, we should otherwise have been unable to carry on. Taking with me the apparatus which had served so well at St. Anthony station, I set out to install N E 8 W G, C [T- as the Northwest River station was to be known " over NT - the air," on the steamer " Meigle," which during the takes supplies north. Alter a sixteen -day +IL short summer voyage, during which very severe weather was encountered. we arrived at Rigolet, forty miles or so up the Hamilton Y561 Inlet, with another ninety miles tò go, and apparently Above is shown the Colpitts transmitting circuit used the only way to get there was in an open motor boat. at St. Anthony, and finally at N E 8 W G (Labrador). After spending a couple of days here in considering The constants are as follow : ways and means, a young American doctor also bound L5.-7 turns each, spaced 4 in. ; No. 14 bare cu. ; 3 in. diameter. L2.-3 turns, spaced in. ; No. 14 bare cu. ; 22 in. diameter. Ci.-00025 variable. C2.-0005 variable. C3.-001 fixed. Ri. -5,000 w., grid leak. R.F.C.-45 T. No. 28, Lorenz wound. M.A.-Hot-wire ammeter, 5 amp. A.-Antenna Hertz fcir 20 m., T. for 40 m., each arm 18 ft., down lead 24 ft. C.-Counterpoise for 40 m., 18 ft. M.L.-M.L. Converter, E type, machine 12-500 volts. V.-Mullard S:W.50, later replaced by R.C.A. U.X.210. A.L.-Artificial Ioad used when key is up, to prevent rise in voltage on M.L. converter (carbon resistance). Accumulator supply and filament connections omitted for sake of simplicity. 1Z.-DZilliammeter. A.L. is adjusted so that thereading on M. is the same with the key up or down. Weeks passed by and August gave place to September, and still there was no sign of the apparatus. One boat did arrive, and I spent a good two hours carefully carrying two heavy boxes which looked as if they might contain radio gear down to the station at 4 a.m. one day. On being opened they contained tins of paint, and as one of my American friends remarked, " the joke was on nre." The "Component Boat" Arrives At last in came the " Kyle"-the same boat, by the way, which later picked up the wing of the " Old Glory " of transatlantic flight fame-bringing with her a 500 -watt generator, tubes, condensers, etc. What a collection for the short-wave enthusiast. The like was never seen in the amateur's wildest dream became apparent, however, when the pardonable It installed at excitement began tc cool, that there would not be sufficient The 2,000 -volt, -kilowatt Esco " generator N E 8 A E. The accumulators used to supply this machine have power available at Northwest River to supply this to be charged very frequently-twice a day sometimes l ---for generator, so as facilities were better at St. Anthony, the machine takes 3o amperes. 1327 www.americanradiohistory.com MODERN WIRELESS June, 1928 for Northwest River and myself managed, with the At St. Anthony an automatic transmitter had been permission of the Hudson Bay factor, to get aboard the left in operation which; when switched on, would transmit " Fort Rigolet," a motor schooner, and set off to brave A.B.C. de N E 8 A E. A schedule was arranged before- Lake Melville. We were soon at St. John's Island, where hand, and the very first evening at N E 8 W G I was we anchored for the night, it not being considered safe delighted to hear these signals at a strength of at least to proceed farther in the darkness owing to the sudden R.8. Q.S.S. was very apparent, however, though it storms which are likely to spring up on this dread.''l proved we should be able to work fairly consistently, inland sea. especially as they were heard between 11.3 to R.6 for over -Next morning we were well out of sight of land and, a week. beyond the fact that the rest of the voyage took us four We were then Q.S.O., though with difficulty, as Mr. days, during which time we neither had the chance to E. MacNeill-or Ted, as we call him-who will work wash nor sleep, we were fairly comfortable. Minor NE 8 A E after my departure, is only just learning set -backs, like sudden gales, which necessitated our anchor- the code. He did splendidly, however, in picking us up ing behind some island, were of frequent occurrence and at all with this handicap. seemed to be expected. We did eventually arrive, however, and all deficiencies in the way of sleep, etc., were soon In Touch With The World remedied, and the next day I was ready for business. All this time N U 2 H V, operated by Mr. Edward Blodgett, of St. Albans, N.Y., was in touch with both stations, NE 8 A E and N E 8 W G, and handled traffic from me in great style often at the. rate of 35 words per minute with no repeats. He used also to send us Press consistently every day, and so we were in touch with everyday affairs. I have to thank this station for keeping his schedules so consistently and contributing in a large measure to the success of the whole venture. - About this time we were puzzled as to where we should obtain an operator for this station at Northwest River, as I was scheduled to return to St. Anthony to operate there during the winter. We suddenly remembered that the coastal stations were closed during the winter, and forthwith approached Mr. J. Watts, the operator at Smoky station, and found that he was willing to go up to Northwest River and operate the station there during the winter. I am informed that Smoky was the first contact with civilisation made by Peary after his dash to the North Pole, and from which station the news of his success reached the outside world. It was now necessary for us to get hold of Mr. Watts after his station closed for the winter, so five of us left for Smoky, a distance of over a hundred and fifty miles away, in the " Yale," under sail and entirely dependent on the vagaries of the wind. We were only six hours out on the " Bay," as the natives call Lake Melville, when the wind began to rise This interior view of a transmitting " panel " at the Auckland, N.Z., broadcasting station affords an interesting contrast to the "Those Sinister 'Dry Islands" simple short-wave apparatus used in Labrador. Very soon we were being swept fore and aft, and it There had been a radio broadcast receiver in use the was all we could do to get our tiny craft to an anchorage previous winter, and two fifty -foot masts stood in position behind a small group of islands called " Dry Islands "- in front of the hospital, so there was no need to erect very appropriate, but not very reassuring, for we had any other than those. In about two days, the aerial only one small water-butt aboard. Day, followed day, having been made to the same measurements as that at and the weather continued to be atrocious. We could St. Anthony, the set was in operation exactly as it had not get away ; moreover, we were nearly fifty miles been at NESAE. from the nearest fresh -water supply. Remarkable Low -Power Performances Five days passed slowly by, during which time we were heaved and tossed about like a cork ; then, on the The very first call was made on twenty metres and morning of the sixth, all was quiet, and at dawn we elicited a reply from New York, and before the week was crept out and, with the wind on the quarter, we put out stations had been worked in Sweden, Germany, seventy miles between us and those sinister Dry Islands. Austria, France, Italy, Belgium, and Porto Rico, whilst We replenished our water supply and made ail fast for several stations in England and Scotland will remember the night, and anchored at St. John's Island, with nearly working us also, both in daylight and at night. One of half of our journey outwards over. the strongest stations worked in England was 6 Q B'F, The next morning we hauled up our anchor in the who reported he was using an 3I.L. converter also. This freezing cold, half -blinded by snow, and reached the shows what can be done with low power, and the very (Continued on page 686.) same evening this communication was eclipsed by the fact * It i8 inlcreslind to .note that " 6 Q B" is tlic member of the that F Q O C D L, at Duala, in Cameroons, the French MODERN WIRELESS Technical Staff who contributes the " Equatorial Africa. reported our signals a steady R.5 1 monthly article On The Short Waves." 628 www.americanradiohistory.com June, 1928 MODERN WIRELESS The first scientifically designed receiver with an H.F. stage which is efficient on both long and short broadcast wave -length bands and which is provided with simple switching arrangements to enable an instantaneous change in wave -length to be made. It employs the new "M.W." standardised loading coil. Designed, constructed and described by the " Modern Wireless" Research Dept. a vJIE idea of having a long-range on the H.F. side to an absolute some small adjustment upon inserting receiver able to cover all minimum, and also the great danger a second set of coils to cover á differ- broadcast wave -lengths with- of hopeless uncontrollability occur= ent range of wave -lengths. out the necessity for changing the coils ring should the slightest interaction With these thoughts in mind the is very attractive. Its achievement, take place, or if the circuit is not of a difficulties of trying -to- eliminate the however, has been one of the most properly " balanced " type. necessity of having to change the coils difficult problems in radio -set design. at' once begin to manifest themselves. A long-range receiver requires an Early Difficulties The MODERN WIRELESS Research e ff cient stage of high -frequency am- These factors apply to any normal Department- has for many months plification, and it is chiefly this factor H.F. circuit arrangement intended realised the need for such a set, and which complicates the design of an to cover only a limited wave -band has been conducting a considerable all -wave set. with a single set of coils. Even with amount of experimental work with Readers already know how very such a straightforward design it is the object of evolving a really soutld important it is to reduce all wiring only too often necessary to perform and simple design. IS!T.+/! -10-1 7:+21 250,000 R.C.0 ONMS UN/T REACT/ON N.F.C. tf. T.- AFC.C. 000/ 00/ /.P. 0 2MFz, 25 L.S. EG. Z--0 - .f...+L.7: W179 The theoretical arrangement of the receiver. L. and L are " M.W." standardised loading coils, which are brought into circuit when it is desired to change over from short to long waves, by means of a very simple switching device. 029 www.americanradiohistory.com MODERN WIRELESS June, 1928 The ideal, no doubt, is to employ slightly fromthe published layout. feed H.F. stage, stabilised with the a single push-pull or throw -over The circuit finally decided upon aid of the neutralising condenser switch which will change over from was that shown in the theoretical (N.C.). This neutralisation is neces- one wave -band to another with but a diagram given on the previous page. sary because when the loading -coil is " flick of the finger." The arrangement has proved to be switched into circuit for the longer In practice, unfortunately, the use highly efficient, with no signs of losses. waves the feed tap includes a very of only one switch tends to produce large proportion of the total, winding serious troubles, resulting from the Two Switches in circuit, and in consequence there is fact that certain vital leads from Two switches are used, the slight enough feed-back to produce self - each grid circuit are brought exceed- inconvenience of the extra switch oscillation. ingly close together at the switch being more than counterbalanced by By arranging a filament tap on the contacts. Even supposing the actual the resulting gain in simplicity and loading coil it is possible to include losses could be reduced to a negligible efficiency. in circuit a sufficient proportion of the turns in the correct phase rela- tionship to enable neutralisation to be carried out. In addition, these turns supplement the existing reaction coil, thereby giving a Hartley reaction effect on the 5 X X band. The reader will at once say : But why not employ some form of neutralising on both wave -bands ? " The answer is that neutralised circuits with switching are too com- plicated. Tests have shown that in ninety-nine cases in a hundred re - neutralisation is desirable when the change -over to another wave -band is made. H.F. Chokes The parallel -feed method enables simple shielding to be adopted, which makes for ease of construction. The Fig. s. The simplified conventional short-wave H.F. circuit. A "parallel feed " scheme is aerial circuit is conventional, employed, the neutralising condenser N.C. having no effect upon the functioning of the circuit. but tappings are provided on the primary quantity, there still remains the ever- The complete theoretical circuit winding so that the best ratio of present danger of instability. looks rather complicated. at first signal strength to selectivity may be Thy Circuit Chosen glance, but it is really very simple. obtained on aerials of different types Fig. 1 shows the short-wave portion and on different wave -lengths. Simi- After exhaustive tests, the MODERN only. It will be seen that the arrange- larly the detector grid coil is also WIRELESS Technical Staff came to the ment is that of a perfectly straight- provided with tappings, thus making conclusion that although it was forward " parallel-feed " circuit, the it an easy matter to obtain the correct possible to construct a receiver on neutralising condenser (N.C.) having proportion of the coil to ensure these lines, such a design would not no effect whatever upon the function- stability with H.F. valves of various at present be of a type suitable for ing of the short-wave side. types. the home constructor, who often On the long -wave side (Fig. 2), the The changeover from short to prefers to use alternative components, circuit arrangement becomes an auto - long waves is arranged for by bringing or who may inadvertently deviate coupled aerial circuit, with a parallel - two loading coils into circuit, these .4.. COMPONENTS REQUIRED ... 1 Panel 21 in. x 7 in. (Radion Maho- square law, S.L.F., " log mid - i R.C.C. unit (Dubilier in set. Any ganite used for original. Any good line," etc., according to preference). good make, Lissen, Mareoniphone, branded material, Ebonart, Red 2 Vernier dials (Igranie in set. Any Mullard, etc.). 04. 1111 Seal, Trelleborg, Trolite, etc.). good make). 1 L.F. transformer, low ratio (Mar- Cabinet for above panel, panel brackets, 1 '0001 miniature type reaction con- coniphone in set. Any good make). 1111 and baseboard 12 in. deep (Art - denser (Bowyer -Lowe, Cyldon, Or- 1 L.F. output choke, 20 henries craft, Bond, Cameo, Caxton, Maker - mond, Peto-Scott, etc.). (" British General " in set. Any . import, Pickett, Raymond, etc.). 3 On-off type switches (One of these good make, R.I. & Varley, etc.). 4 Anti -microphone valve holders, is simply the battery switch, and can 2 Mansbridge condensers, 2 mfd. each baseboard -mounting type (Benja- be any standard make. See text). (Dubiller, Ferranti, Lissen, Mullard, min, Bowyer-Lowe, Burndept, Fixed condensers, capacities 001, 0003, T.C.C., etc.). Burne-Jones, B.T.H., Igranc, Mar- 001 (Clarke, Dubilier, Igranie, 1 Terminal strip with 8 terminals and coniphone, Pye, Redfern, W.B.). Lissen, Mullard, T.C.C., etc.). one with 2 (A good appearance can :4 2 Standard " M.W." loading (coils 2 Grid leaks, 25 and 2 meg., and be obtained with indicating ter- (Burne-Jones in original. Any holders (Dubilier, IgranIc, Lissen, minals such as Belling & Lee, Eelex, 04, standard make). Mullard, etc.). Igranie, etc.). 1 Neutralising condenser, baseboard- 2 H.F. chokes (Bowyer -Lowe, Burne- Copper screen 12 in. x 6 in., wire, 1111 mounting type (Any standard make). Jones, Collinson, Cosmos, Igranie, flex, material for coils, etc. (Copper ..4 2 0005 variable condensers (Igranc Lissen, Ormond, R.I. & Varley, screen can be obtained ready for 04/ Lokvane In set. Any good make, Sovereign, Wearite, etc.). use from Messrs. E. Paroussi). 630 www.americanradiohistory.com June, 1928 MODERN WIRELESS coils incidentally being those recently which incidentally should consist of These have to perform a very produced by Research Staff under the a stout piece of 5- or 8 -ply wood, important function, viz., that of MODERN WIRELESS standardisation since it has to support quite a con- changing fromone wave -band to the scheme. (See May issue of MODERN siderable weight. other. When the knobs are pulled WIRELESS.) In a circuit of this type, or, in fact, in any " parallel -feed " arrangement. it is essential to employ radio chokes of proved efficiency. This applies in particular to the choke in series with the H.T. feed to the H.F. valve, and a poor choke will have a very serious effect upon signal strength on both wave -bands. The losses will be especially marked on long waves. The two wave change switches are the two little knobs seen here, one between the two the tuning dials, and the other to the right of the second tuning dial. The L.F. side of the set is quite standard, and it is scarcely necessary Next mount the Various components, out, the loading coils are short- to make any comments on the various taking care, to make a secure job of circuited and the receiver is ready to components except in the case of the the slow-motion dials, otherwise there operate on the normal broadcast anode resistance. The value of this will he a tendency for them to rotate hand of 250-500 .metres. >-H,T.-F/ A Point to Note To R.c.C. If the contact between the spindle R.F.C. t UN/T and the two tongues of the second 000/ 00/ @R. F. C. switch is imperfect there is a danger N. C. of instability arising, since the exist- ing reaction control will be supple- mented by the long -wave reaction turns. To obviate this it is a good scheme to solder a piece of flexible wire between the centre contact knob (i.e. the spindle) and the stiff busbar connection which goes to the spindle L.T.- from L.T. - ). > Before mounting the components > L.T. on the baseboard the two short-wave `W` aerial Y584 coils should be wound. The are wound Fig. z. How the H.F. circuit is arranged for reception on the long waves. The aeria primary and grid windings circuit, it will be noted, becomes auto -coupled and the H.F. valve is neutralised. upon a former 3 in. diameter by 3 in.. long. This former can be made of any resistance should not exceed 250,000 with the condenser vanes. Now just good insulating material with low ohms, otherwise it may be difficult a few words about the change -over dielectric losses, such as Paxolin, to obtain smooth reaction control. switches. Pirtoid, Radion. etc. The L.F. transformer can, of course, be of any reputable make, and the ratio should not exceed 4-1 if maximum quality is desired. So much for the theoretical con- siderations, and now we shall come to the actual construction and opera- tion of the set. Simple Construction To start with, I should like to impress upon the reader that the set really is easy to construct-much easier, in fact, than many of the popular `' straight " neutralised re- ceivers which are so common at the present time. This ease of con- struction is largely due to the use of only one small shield separating the aerial and H.F. circuits. Take the panel and mark it off on the back to the dimensions shown in the drilling diagram. Drill it and From this back -of -panel photograph it will be seen that the metal screen is supported screw it to the edge of the baseboard, by a strip of wood which is screwed to the baseboard. 631 www.americanradiohistory.com MODERN WIRELESS June, 1928 The grid winding consists of 60 turns of No. 24 D.C.C., unspaced, with coil and the other end to the grid turns of No. 24 D.C.C., unspaced. On tappings at 10, 15, 20, 25, and 30 condenser. top of this and at the earth end of the turns. The first tapping, viz., the The first tapping at 10 turns is at winding is the primary or " aperiodic " 10 -turn tap, is taken at the end of the loading coil end of the winding. aerial coil, consisting of 25 turns of the same gauge wire. Tappings are taken at 10, 15, and 20 turns, and connection is made to these points with the aid of a small spring clip, which is joined to the aerial terminal by means of a short length of flexible wire. The Coils The aerial or primary coil is separated from the grid winding by X 329 PANEL LAYOUT short lengths of wood, such as those supplied with packets of Glazite. the coil nearest tjie reaction winding, The reaction coil is wound in the These strips have a diameter of hence the coil should be commenced same direction as the H.F. coil. about in., and the number actually from this end: The reaction coil If you arrange your .tapping used is immaterial, since they only consists of 30 turns of No. 34 D.S.C. wrongly you. will get uncontrollable serve to separate the two windings. You must be careful in connecting oscillation. Six is a convenient number. the H.F. coil in circuit. Remember The method of mounting the coils The H.F. coil is wound upon a that the end of the coil nearest the can .be seen from the photographs. similar former, and consists of 60 reaction winding goes to the loading Two 1 kin. lengths of wood are EARTN/NO PLATE 'Z TERM/NAL 0M/T TN/S L EAO /F f f NQENSER NAS I /N 7 NO E TERM/NAL /NCHES REA p M ' CONDENSE/7C7/0,vSCALE 000/ WAVE g CHANG E irQ SW/TCN WAVE 0005 CHANCE SW/TC// Oc :. h.* 0005 Oo .0.'! =Q. i O O I i L ToN-OFF SW/TCH ZMEGS F L.F.TAANSFR 45 inifflil cm lizi .00/ 0 0 0 a.r 1 pG 0 0003 0/ Oo N. . II 0v OV O S o'''' O , '' o' G. B-2 ^0 0 / o e óEvó _' O L3ó 1_ 0 60C) 1.». C4 '.CC UN/T m l I 00/ O J ` a o o \ ' 0°` 0 0 oPÍ o ° 2/ u, 25MEG -li V4 ,. t . . o eie e `ó° oo ' B o HF. o CHOKE\. O r=0_ _ % Nh LC' º'' e 2SMEG K i !-, Ó WXV SECO/GAFY 20h! L.F. 2F0 UO 2Mfo f ? lTAPP/N6S 20 CHOKE 't E 0.- 1a. % COILOS Wh n C.B.+ L.+ B o . , J--= L4 ^ s 530W/R/NCqC_LLS. H.T.+3 H.T.+2 H.T.+/ HT-11 iEARTH D/ACRAM. AER/AL 032 : www.americanradiohistory.com WIRELESS June, 1928 MODERN used for each coil-z-in. diameter however, it is probable that all Detector : A similar valve or alter- of R.C. type. curtain rod is suitable, but square - cabinets will be standardised and that natively one the an section strips will do equally well. a 2 -in. slot will be cut right along the First L.F.: A valve having Now commence the baseboard lay- back to take the ordinary vertical impedance of 12-20,000 ohms, such out. Screw down the components type of strip. as one of the L.F. or " H.F." type and mount the copper screen in The type of terminal strip employed (not power). position. This is attached to a strip is immaterial, either serving equally Secqud L.F.: A valve having an of wood, which is secured to the well. impedance of 6-8,000 ohms if signals baseboard with three or four wood It will also be noticed that a very of moderate -strength are being ohms for screws. large power choke of low D.C. re- handled, or one of 3-4,000 sistance is incorporated., in the set. large volume. Wiring -Up A big choke is desirable in cases where In the preliminary tests apply Wire -up as many of the com- it is intended that 'a " super=power " H.T.- voltages as follows : H.T.+1, a 60 volts ; 60-100 volts ; ponents as :possible, but neglect . for valve is to be used, or where heavy bias the time being those leads which anode current is flowing, such as H.T.+3, 120 volts. The grid be pass through the screen. Then work might be the case on high H.T. on the first L.F. valve should last out the position for these leads with vòltages supplied by a mains unit. about 3 volts, and upon the according to the the aid of the wiring diagram and For ordinary small -power valves, or valve 9 or 18 volts, drill the necessary holes for the wires for super -power valves operating on type of valve used. to pass through. These points can a moderate voltage, a smaller choke Working the Set be marked in pencil on the metal could be employed. be shield, which can then be removed The operation of the receiver is The grid bias; in any case, must of from the baseboard and drilled. Cut quite straightforward once- the pre- adjusted to suit the requirements valves employed, and the holes clearly so that the edges liminary adjustments have been the particular details will be found will not chafe the insulation covering carried out. the necessary carton or on the wires. Connect up the aerial and earth on the valve -maker's Use good stiff 16 or 18 gauge wire and insert valves of the following pamphlet supplied. Place the'two wave -change switches throughout, preferably No.. 16 for types : the loading longer leads. The form of insula- H.F. socket : A valve of the in a position in which the and connect tion covering employed is immaterial " H.F." type, impedance 30,000 ohms coils are short=circuited, spring clip on, say, the so long as it is of good quality. Systo- or thereabouts, amplification factor the aerial on the 'aerial winding. flex tubing is very convenient. about 20. middle tapping The terminal strips Used, as will be seen, are of the horizontal type and will suit any cabinet. In future, 1 ä ; (3) and (5) the z-mfd.=H.T. shunting and Here is a complete plan view of the receiver : (i) and (2) are the aerial and H.F. coils be of the low -ratio type ; (7) is the reaction output condensers ; (4) is the filter choke, and (6) the L.F. transformer, which should while (rz) is the aerial grid condenser; and (8) and (i4) the two H.F. chokes ; the condenser marked (9) tunes the H.F. circuit, circuit tuning control.; (ro) and (z3) are the loading coils for the long waves. 633 www.americanradiohistory.com MODERN WIRELESS June, 1928 Join the spring clip for the H.F. the loading- coils, but -you must re- In the type of wave -change switch ," feed " tap* (viz., thé H.F. coil) on 'member that a high tapping point required one `cóntact is joined to two the 10 -turn tapping. Keep. the re- on the H.F loading coil will increase others in the " on " position," and action condenser at its .minimum and the reaction effect and may make is separated in the " off " position." 2djust the two tuning controls until the detector valve oscillate very freely, In the " off " position these latter you hear your local. station. Then thus giving the impression that the two contacts must also be separated adjust the aerial tap for. Maximum H.F. valve is oscillating. from each other.- Suitable types are results. You will . soon _ find the For maximum selectivity on .the thé Lissen and Lotus " on and off " position which gives you the best long -waves try taking the feed tap switches, to mention- two examples. signal strength combined with selec- (the spring clip joined to the 001 If you examine the wiring diagram _tivity. Try various -positions for tie fixed condenser) to the 80, and the and the photos carefully you will spring clip o the H.F. coil. Choose filament tap to the 60 tappings On have little difficulty here. the taliping which gives you *good the loading coil.` 'stability, over thé whplé wave -band. Remember that selectivity oil the .. long waves is also controlled liy the .; POINT-TO-POINT CONNECTIONS. Join moving vanes o! C, to terminal 0 Final Adjustments ' adjüstmerit Of ii the spring dip on the on L3, to one filament contact of V1, to ' Then adjust the reaction condenser aerial `loading _cbii, whereas the clip earth terminal and to screen. Join L.T. -. terminal. to $.T.- ter- ¡¡ and vary the H T.'voltage on the on thé H. -F. loadM coil controls ;; mina!, to screen, to one side of first 2 mid. H.F. `valves condenser, to one filament oontact of V2, ¡¡ and detector for the the reaction effect ánc) neutralisa- :: V.,, and V2. Join remaining filament inaxnnnln results.. contacts of V,, V_, Vs, and Va together, and to. . one side of L.T. on -off switch. Join G. of V, to one side of neutralising t, condenser, to fixed vanes of C, and to top of secondary winding L2. Join bottom of secondary L. to top contact of first wave -change switch, and to ¡: terminal on L, marked 216. Join middle ¡¡ contact of first wave -change switch to ¡¡ bottom of primary coil L,, and to a flex ¡t lead terminating in a clip for L. ¡¡- Join bottom contact of first wave -change ¡¡ switch to terminal on screen marked B. .Connect plate of V, to one side of -001 ' fixed condenser, and to one side of first ¡¡ H.F. choke. Join remaining side of first H.F. choke to H.T.+1 terminal. ¡¡ , Join a flex lead terminating in a tapping clip for tappings on L., to remaining side of .001 fixed condenser. Join remaining side o! neutralising con- tj denser to terminal marked 0 on Ls, to ¡¡ moving vanes o! G_, to top contact on second t¡ wave -change switch. and to the side of ¡¡ reaction coil L5 nearest to L.,. ¡¡ Join fixed vanes of G_, to one side of ¡¡ 0003 fixed condenser and to top end of L.,. ¡¡ Join remaining end of L4 to terminal . marked 216 on L,;, and to bottom contact on second wave -change switch. Join middle contact of second wave- ii change switch to earthing plate terminal ¡¡ on reaction condenser and to filament contact on V. which goes to L.T.-. ¡¡ Join remaining side of -0003 fixed con- denser to G of V2 and to one side of 2 meg. :: leak. Join remaining side o! 2 meg. leak to ¡: filament contact on V2 which goes to ¡j filament switch. Join P. of V2 to one side of second H.F. 11 choke and to one side of second '001 fixed .. \`r ii condenser. Join remaining side of second -001 fixed The connections to the aerial circuit can be clearly seen in this photograph. (I) Is the i condenser to fixed vanes of reaction con- .. tapping clip for the " aperiodic " aerial winding; (2) is the H.F. choke in the plate circuit denser. i Join remaining side of second H.F. choke ii of the first valve; (3) is the neutralising condenser ; (4) is the aerial circuit tuning con- to terminal on R.C.C. unit marked A. denser ; (5) the aerial loading coil, and (6) the aerial tapaing clip for long waves. Join terminal marked H.T. on R.C.C. unit to H.T.+2. Now place Join terminal on R.C.C. unit marked G both the switches in There is no need to touch the clips ¡¡ to one side of 25-meg. leak. the position for long -wave reception, on the short-wave coils when operat- Join remaining side of 25-meg. leak to ii G of Vs. i.e. with the tongues insulated from ing the set on the long waves. Take a flex lead from terminal on R.C.C. unit marked - G.B. to G.B.-1. P. the centre knob. Connect the spring Join of Vs to O.P. of L.F. transformer. clip on the aerial loading coil to the Test Report a Join I.P. of L.F. transformer to one side of L.F. choke, to remaining side of first 60 or 80 tapping, and that on the These stations were received on a a 2 mid. condenser and to H.T.+3. H.F. loading coil to the 80 tapping. loud speaker, using a t Join 0.S. of L.F. transformer to G. of . poor aerial ap- V.,. Take a flex lead from I.S. to G.B.-2. With the reaction control its proximately 100 in ¡¡ Join P. o! V4 to one side of second 2 mid. at ft. length, and condenser and to remaining terminal on minimum tune in 5 X X. It is prob- having an average height of only 15 ft. ¡¡ L.F. choke. Join remaining side of second 2 mfd. able that the H.F. valve will Nürnberg Rome 13 condenser to one L.S. terminal. oscillate, so rotate the " neutralis- Muenster Langenberg Join remaining L.B. terminal to filament ¡¡ contact on V., which goes to L.T.-. ing " condenser very slowly until Munich 5GB Join remaining side of L.T. on-o[ switch ¡¡ to L.T.+ terminal. oscillation ,ceases. Then try to tune Toulouse Brussels Take a flex lead from the filament con- in other stations on the long waves Dublin Vienna :: tact of V2 which goes to L.T.- to a tapping .e 88 clip for Ls. and adjust the `' neutralising " con- San Sebastian Hilversum Join a flex lead terminating in a tapping ¡¡ clip for L, to the aerial terminal. denser slightly, so that the set is Hamburg Berlin Join remaining side of reaction con- perfectly stable even lower ¡¡ denser (moving vanes) to remaining side 8 at the Ecole Superieure Motala of reaction coil. end of the tuning scale. You can, Bournemouth 5XX V," Take a flex lead from L.T.- to G.B.+. if you wish, try various tappings on -Milan Radio -Paris 634 www.americanradiohistory.com June, 1928 MODERN WIRELESS A section for the Music Lover. Conducted by KEITH D. ROGERS. is As we are discussing gramophone M:\ N\- readers have written and speaker; and the bass reproduction asked me for a circuit of a exceedingly good because the set reproduction we are more concerned receiver which will operate has been designed give good ampli- with the low -frequency side of the equally well as a radio or gramophone fication at frequencies well below receiver than with the high -fre- record reproducer, and I do not think twenty-five cycles per second. quency -detector section, although in I can do better by way of a reply Of course, one cannot get a loud discussing the circuit it will be neces- than to give a circuit which I speaker that will operate anywhere sary to refer to the first two valves, have often used. near that depth of tone, but if you even though we may be more con- It is true that it errs rather on have the deep bass delivered from cerned with the last four. It will be the side of luxury from the point your set then it will give your speaker noticed that two valves are used in' of view of the number of valves, the best chance it can pissibly have parallel in the last stage, while when because on very many records one may of reproducing those notes in a full the pick-up is in use we have four have to tone the reproduction by a and round fashion. L.F. stages. That is, as you will large amount by means of the volume imagine, a luxury. a factor .. control. But the set has large With the rapid development. taking :: of safety and can be relied upon to place in the design of L.F. amplifiers and Factor of Safety give good results not only on the local :: loud speakers, and also in the pro- :: There are very few records that ;¡ duction of gramophone records, it is ¡¡ broadcasting but on several D.Y. ;j natural that these two sections of the ¡¡ really need four low-fregttencystage.s,. stations and also on any gramophone radio and gramophone industries should It even though they may be resistance - .. be combined for the benefit of the coupled, but the valves and resist- records worthy of that name. :: music -loving public. ¡¡ The electrical "pick-up " has enabled ;¡ ances used in this set are chosen so ¡¡ this combination to take place, with ¡¡ that small amplification per stage is Those Bass Notes the result that anyone with a reasonably of the Because the circuit is rather on efficient valve set can, for a very small . obtained, and the whole idea :: outlay, enjoy all the benefits that radio receiver has been to provide the set the elaborate side readers must not offer. ¡¡ and the gramophone have to ¡¡ a of as imagine that it is necessary to have = In this section of MODERN ¡¡ with as large factor safety an elaborate set in order to get good WIRELESS each month will be dis- possible, both from the point of view cu- sed both technical and other data of amplification and from that of reproduction from a gramophone of interest to the set owner who is also i: record. But if you want the best, both interested in gramophones, whether ¡¡ being able to carry large volume. then ¡j from a technical or purely utilitarian ¡¡ High -mu valves and high -magnifica- from radio and the gramophone, point of view. you must go a little bit farther than In addition to articles on the operating tion L.F. stages have been" avoided the average three- or four -valve set, side of amplifier and pick-up combina- .. altogether, and the result of this set ¡¡ tions, and various hints and tips of 2: a receiver having about and build something more on the ¡¡ value to the constructor and set owner, ¡¡ is that of style of the one indicated in these a brief survey and critique of the latest ¡ II- valves less than the maximum gramophone records is included, possible if high-magnification stages pages. .. making the section of vital interest to Such. a -circuit is quite suitable for :: all music -lovers were used, but the quality is far and use with the moving -coil type of loud ...... away beyond that possible were very 635 www.americanradiohistory.com MODERN WIRELESS June, 1928 high -magnification stages to be em- grid circuit of the detector valve one coupled to the anode coil Actually, ployed. is enabled to switch over from when used for the local station or The output choke is marked as gramophone to radio and vice versa 5 G B, as the set usually is, this re- having twenty henries inductance, but without any other alteration. action condenser is disconnected so in actual practice I use two chokes of The rheostat in the filament circuit that no feedback through that coil that value, or approximately so, of the H.F. valve enables that to be occurs. Another 0001 dotted con- connected in parallel. This is done to turned out when gramophone repro- denser between the H.F. choke and cut down the D.C. resistance so that duction is to be enjoyed, and, as a the filament of the detector valve is the H.T. voltage drop acrosa the choke matter of fact, a double -pole double - used as a precautionary measure in is made' as low as possible. switch could have been arranged case any H.F. gets through that choke. instead of single -pole switch in order -The same may be said of the 1-meg. The Coupling Condensers to automatically cut out the filament leaks used as H.F. stoppers in the The 1 coupling condensers in the of that valve. It was, however, grid circuits of the first two L.F. L.F. stages are used so as to provide decided to use a filament resistance in 'valves. plenty of bass amplification, and the the circuit of the high -frequency anode resistances and the grid leaks valve, to act as a volume control on Bias Batteries are chosen to suit those factors. It radio, and it was therefore decided These stoppers, of course, have will be noticed that each plate circuit, that it would be simpler to employ no significance when the gramophone or, rather, I should say each H.T. this for turning out the H.F. valve is employed, as practically pure L.F. circuit, on the L.F. side, is by-passed when the gramophone was to be is supplied to the set from the by a 1-mfd. condenser, and this is to employed rather than complicate pick-up, but when radio is being ensure that trouble due to L.F. feed- matters by using a double -pole switch. received, especially on the long waves, back and anode coupling shall be The aerial circuit is of the ordinary a certain amount of H.F. is likely to eliminated. tapped variety and is not particularly pass through into the L.F. side and In practice those by-pass condensers selective, as the receiver is used this will cause no end of trouble. tsoV t/10V -tlZ0V +/soV I /50,000 OHMS fAhy/6oV SI-REENING Box i Q 15p0o- S".'113"-+/60/250 Y -A 1k 000i p 100,000 SO000 2011 V RF`p¡ OHMS OHMS .1c/ L'S' 4 %I MFD' 2Mf0 T 000a f9CH i Eacw SCaEENEO ( r'i Gale VALVE.---\i, I r -- __J E o o 31 c> Sa ó sa -1""g 0005 500000 w 1 I OHMS p VOL . 0N r4++L s HT_ M .QI zt P/cK UP WAg Though of an apparently elaborate nature this circuit is not an expensive one to build, while, if desired, the H.F. stage can be omitted and grid -leak rectification employed on the detector valve. are connected close up to the resist- mainly for the local, 5 G B, and one especially. as the set is resistance - ances and taken to the nearest filament or two of the more powerful stations. coupled. points. They are not placed by the A screened valve is employed and Screening is employed for both H.F. H.T. terminals or near the H.T. gives ample H.F. amplification, so that circuits-that is, the aerial coil and battery, which, by the way, consists on the local, 5 G B, 5 X X, and those the anode circuit-while volume con- of accumulators in this case, but they other few stations, reaction is not trol can be obtained either by the are placed as close to the resistances really necessary. variable resistance in the filament as possible so as to provide a direct circuit of the H.F. valve or else by path for the L.F. impulses. Stopping H.F. detuning. The first valve has its own Incidentally, this receiver allows Provision for reaction, however, is grid -bias battery, while the detector rapid tests to be made between broad- made, and is shown by the connections grid bias is supplied by the same cast reception and gramophone re- in the dotted line from the plate of the battery when the set is used as a radio production, for by just moving a detector, through the variable 0001- receiver. When used, however, as a single -pole double -throw switch in the mfd. condenser to the reaction coil pick-up amplifier, the grid bias, which 636 www.americanradiohistory.com June, 1928 MODERN WIRELESS is connected to the pick-up, is taken factor than the P.M. 5X , works very British market, and have made it to the main grid -bias battery, as will well in the detector position, while the lighter-an action that is to lie be seen in the diagram. D.E.P.610, 7,000 ohms, and a magni- highly commended. The pick-up, as More sensitivity could he obtained fication of 7, works quite well in the is shown by the photograph, is well - on radio reproduction if the grid leak first L.F. stage. 'those mentioned are made, and is adaptable for any type of the detector valve were 2 megohms, only typical valves and it should be or tone -arm. On test it gives very but with the l rnegohm I found quality remembered that no attempt is made satisfactory results and can be ob- is better, although the selectivity is to specify any particular make. tained with or without a volume slightly less. control and plug adaptor. However, one sloes not expect great Two- or Six-Volters f.. when using a screened -grid The approximate H.T. voltages are selectivity tjj valve, and it will be observed that the marked on the diagram, while the fila- detector is worked as an anode -bend ment voltage, of course, is fixed by GRAMOPHONICS rectifier, the grid leak being taken the valve. I have tried 2 -volt valves t'g to grid -bias negative. As a matter of and, while excellent results were fact, this is one of the main objects in obtained, I cannot get quite the sanie It is better to control volume at using a screened -grid valve-to pro- volume and even roundness from the input of your receiver or amplifier vide a good input for the detector them as I find can be obtained from than at the last stage. valve. the 6 -volt type. One is more inclined to overload, Blasting or less noticeable dis- "Boominess" especially in the last ,stage, because tortion is not always caused by the as It might be remarked here that, 2 -volt super -power valves have not pick-up or a fault in recording,. it this set is designed to give good ampli- yet reached the sanie efficiency as the may be due to overloading in one or fication of the very low frequencies, 6 -volt valve. They will, however, other stages of the amplifier, or even repro- and it is inclined to make give excellent results for medium due to the loud speaker. duction sound rather " boomy " if volume. used on a loud speaker which has receiver is to be used with a If this A gramophone, in common with plenty of bass colouration, I have -resistance loud speakerwhich has a low all mechanical devices, needs careful noticed that on some cone types of of course, use winding, then one.must, attention and the motor should be loud speakers which are rather con- a suitable output transformer oiled occasionally with the specia inclined to manufacture their own nected to the loud speaker ; but, in lass, so to speak, the reproduction is oil sold for that purpose. ally case, I prefer to employ the filter * * certainly on the boomy side, but this circuit shown in the diagram, whether can be removed by increasing the a loud -speaker transformer is used or Records should be kept in cool resistance of the grid leaks on the not. This filter circuit has no ap- places and kept level or vertical ; L.F. side, and lowering the values of preciable bearing upon the results if stored in a warm place and allowed the coupling condensers to something obtained on any type of loud speaker, to rest in a slanting position they are to the order of 006 mfd. so that the set is, one might say, liable to warp-with disastrous results. Slightly higher anode resistances isolated as a set or amplifier from the can also be employed here, but these loud speaker, so that any kind is quite Fhould not be raised too much or a. suitable for use with it. rather serious cutting -off of the higher frequencies may occur. With regard to the valves used in G this set; at the present moment I am Uj PICK-UPS TESTED using the ordinary 6 -volt screened - E' grid valve, followed by a P.M.5X. (', , _. . . ,. 2_;3231;: J s'ii sii u7 vJ ßj tiì':7 detector, an S.-S.610P. as the first THE number of pick-ups on the L.F., followed by a D.E.5A., and then market are steadily increasing, two L.L.525's in parallel. Actually in and it is becoming more and this last stage two P.M.256 valves in more difficult to differentiate between parallel, or a couple of D.E.5A.'s, them. One which, however, is well work quite well, while those who have worthy of the attention of all gramo- plenty of H.T. voltage and plenty of phone -radio enthusiasts is that mar- filament current might care to try a keted by the Loewe Radio Co., Ltd., The Gecophone pick-up described in couple of 4.S.5A.'s or D.F.A.7's. In of Tottenham. this page. this latter case, however, they will Exceptionally small, this little pick- or require anything from 250 volts up- up is exceedingly well -designed and Don't forget that a fall in H.T. wards for H.T. reproduces the whole range of the L.T. voltage may completely upset musical frequencies dealt with by the the quality of your reproduction, if - capacity Other Types best of records in a manner that one especially resistance These particular valves mentioned, might expect to get only from an coupling is employed. however, must not be taken as being instrument of several times the price. the only ones which work properly in This latter is of the modest order of Keep an eye on the grid battery the set. Any valves of good type and 18s. 6d. as well as on the L.T. and H.T. supply the correct impedances will work if you want to ensure good results- equally well. For instance, the Another Model and invest in a plate -circuit milli - D.E.L.610, which has a lower im- The G.E.C. have improved their ammeter, it is an excellent aid to pedance and lower magnification pick-up, one of the earliest on the distortionless amplification. 637 www.americanradiohistory.com MODERN WIRELESS June, 1928 can be employed. In the case of the L.F. valve, the grid circuit can be broken at either points D or G, and preferably the latter, since the grid -bias arrangements for this valve are not then altered by the insertion of the plug. As the grid is already biased, the sheath of' the jack (con- tact l) in this case should be connected direct to L.T-. Contacts 2 and 3 will be joined to one side of the H.F. choke (and anode resistance) and grid condenser Easy methods of changing over from Radio to Gramophone. respectively. With regard to the fila meut switching, there are in this case By G. T. KELSEY. two valves to be extinguished, and filament circuits should be broken at the points 7r HE jack and plug method of The sheath of the jack (contact 1) marked A and H. switching, with which most should be joined direct to the L.T.-, The side of the break at A which people are familiar to some or, if it is desired to bias the valve, goes to the rheostat requires to be extent. is one that lends itself very to G.B.-. The grid circuit of the connected to the same side of the detector valve should be broken at break at H, and also to contact 4. the point marked B, and contact Contact 5 can then be joined direct 3 requires to be joined to the grid to L.T.+. of the valve, whereas the other lead caused by the break (that going to The Output Circuit 7/ the condenser and leak) is joined to The insertion of a plug into a jack o,. r7. contact 2. of the single open filament type Next conies the filament switching, joined in the anode circuit of the and the two leads caused by breaking last valve can perform the dual the circuit at A should be taken function of joining up the loud to contacts 4 and 5. speaker and switching on the L.T. 3 It will not be difficult 2 to see exactly Referring to C in Fig. 2, which what happens with this arrangement. shows the type of jack required for / .. , ,/ o4. The insertion of the plug, which, to this purpose, contacts 1 and 2 should of course, the pick-up is connected, be joined to the plate of the last will place this latter across the desired valve and H.T.+ respectively, while points and will also break the circuit the two leads caused by breaking at points A and B. the filament circuit at F are joined An to contacts 3 and 4. Alternative Position A pair of 'phones can, if desired, Provision can also be made for be placed in the anode circuit of the using the pick-up across the first L.F. third valve by means of a plug and stage thereby cutting both the H.F. a single closed jack such as is shown and detector valves out of circuit. at B in Fig. 2. In this case 1 and 2 ulruirably to use in conjunction For this purpose, a similar jack- are joined together and to the anode with a gramophone pick-up. namely, the five -spring automatic-. resistance, while 3 goes to H.T.+. Taking a perfectly straightforward circuit arrangement such as that shown in Fig. 1, which, it will be seen, consists of a neutralised H.F. stage, detector and two resistance -coupled L.F. stages, supposing it is desired to use the pick-up across the grid and filament of the second valve. How can this be done with a jack ? Filament -Grid Switching First, it is desirable to break the grid lead at the point marked B, and, second,it is necessary to makeprovision for the H.F. filament to be broken. Both of these functions can be done by the use of a five -spring automatic jack, a side view of which is shown in Fig. 2A, and the following con- nections are necessary. www.americanradiohistory.com !une, 1928 MODERN WIRELESS Angels Ever Bright and Fair and Come, Holy Ghost, our RECENT RECORD Souls Inspire. Sung by Kenneth Purves (Boy Soloist). (1s. 3d. 224.) ELFABES Very well sung and well recorded. Old Barty and Learnin' (Bass Solos). By Harry Dearth. (1s. 3d. 234.) Two more popular items sung by one of the most popular of British bassos. Every word is clear-cut, and the good diction is a feature many others would do well to copy. Pathé Actuelle. Did You Mean It ? and Is She my Girl Friend? By Jay C. Flippen. (10 in. 11541.) Two further items from an American jazz vocalist. We are not struck with these from an entertainment point of view. The latter is un- Orchestral and Band Two lively pieces of syncopated doubtedly the better of the two. " Did You Mean It ? " being horribly Dolly's Dancing piano -playing. Brunswick. from rendered and, in our opinion, utterly and Estudiantina. The Paul Minuet (Organ Solo " Berenice and Chimes spoiled by the way it is " sung." Godwin Orchestra. (12 in. 4s. 6d. "-Handel) and Hymn Tunes (Bells of St. Who-oo, You-oo, That's Who 60004.) 3d. 225.) and Are You Happy? Annette An excellent record, full of good Martin's). (1s. first side of Hanshaw. (10 in. 11540.) quality and tone that are expressed A novelty record the which is an organ solo on the St. Another light musical record by very well by pick-up reproduction. .Martin's in the Field Organ. a well-known artiste. Londonderry Air and Drink to Pathé Popular. I Heard You Me Only With Thine Eyes. Listening and The Islander (Bell by Billie Whitlock). Sing (Solloway) and The Hours Solloway and his Orchestra. (10 in. Solos (1s. 3d. 246.) I Spent With You(Baritone Solos). 3s. 159.) Another very interesting novelty By Gilbert Austin. (10 in. Is. Gd. Once more we have that Irish P367.) favourite played with a depth of record. Parlophone. Dainty Miss and Two average songs that are neither feeling and clarity that make this Solos). Raie da striking nor particularly attractive. record one that should be bought Polly (Piano Costa. (10 in. 3s. R3534.) Henry's Made a Lady Out of by all'_music lovers. The reverse side An exhilarating jazz piano record Lizzie and I Scream, itYou is also well played, but is not, in our is a marvel of mastery and Scream. By Jack Kaufman. -opinion, as good as the " Londonderry that technique. All radio -gramophone and (10 in. ls. 6d. P366.) Air." should hear Two excellent comedy songs. The Broadcast. Martial Moments gramophone enthusiasts this record. former has a peculiarly topical appeal 1 and 2). The Band of H.M. (Pts. of and Girl of and should be heard by all. Life Guards. (1s. 3d. 244.) Roses Picardy (Organ Solon. Zonophone. Vocal Gems from A lively record that should be My Dreams Sigmund Krumgold. (10 in. 3s. " Patience " (Pts. 1 and 2). The very popular among military band Zonophone Light Opera Co. (12 in. enthusiasts. R3538.) Two excellent pieces of cinema 4s. A336.) Pathé Actuelle. Carmen (Entracte organ recording, the latter piece A perfect record, wonderfully sung Act 4) and Peer Gynt (Morning). having a vocal interlude which. pro- and doing full justice to that pecu- The Pathé Symphony Orchestra. vides a pleasing novelty. liarly beautiful music associated (12 in. 15255.) Zonophone. Janette and Can't with all Gilbert and Sullivan operas. Well played and very enjoyable Love You? An excellent record for pick-up except for a peculiar harshness that You Hear Me Say I (Organ Solos). Charles W. Saxby, purposes. we have noticed on several of the F.R.C.O. (10 in. 2s. 6d. 5094.) Abide With Me and The Lost " Actuelle " recordings. This harsh- A superb piece of recording that Chord (Contralto Solos). Esther ness is not present on the Pathé better subjects. The former Coleman. (12 in. 4s. A337.) Perfect records, and seems peculiar deserves piece is rather monotonous, though Well sung and well recorded. to the former types. the latter is worth hearing. There Perhaps Miss Coleman is a little is nothing the matter with the harsh on some of the higher notes, Instrumental recording or playing, and the effects but the whole forms a delightful Brunswick. Baltimore and are good. record. Brandy and Soda. Piano Solos Constantinople and She's Gone by Fred Elizalde. (10 in. 3s. 161.) Vocal Crazy (Comedy Songs). Clarkson Two excellent pieces of recording Broadcast. Macushla and Rose. (10 in. 2s. 6d. 5091.) ¿played by that master of syncopated Because (Tenor Solos). By Victor Excellent recordings and amusing pianoforte work. His harmonies are Karne. (1s. 3d. 243.) items. The former is going to be works of art. Two exceedingly well sung and extremely popular. Clarkson Roso Broadcast. Sometimes I'm recorded examples of two famous is a little harsh, and could be further Happy and Possibly. Piano Duet. and popular songs. We should like from the microphone with advantage. (1s. 3d. 232.) more from the same vocalist. (Continued on page 678.) c.39 www.americanradiohistory.com IODERN WIRELESS June, 1928 was not sufficient variation in the resistance between a bright copper wire and the same wire after it had 'acquired a . . heavy coating of oxide to be o recorded with certainty. " If the '\ IL' acquisition of oxide by copper wire I` causes any change in high -frequency z ;. vu1JUt. ¡ Ili) NMI, .o.., resistance," says W. M. Roberds, " it is very small." The foregoing is taken Lamp " Aerials " A Radio Delusion from " Popular Radio," U.S.A., and a full account will be found in the AN interestirp system for testing. Another familiar radio delusion has " Physical Review " (Minneapolis), out a broadcasting station, so been exploded. For years it has volume 29, pages 165 to 173, under the as to make sure everything is been imagined that the coating of heading of " The Resistance of in proper working order before starting oxide and other corrosion produarts Copper Wires at Very High Frequencies." a session, is in use at WE AF and which forms on wires of copper or W J Z. About half an hour before the brass when they are, exposed to the Short -Wave High -Power broadcasting period the transmitters air has a considerable effect in in- A French military radio engineer, are placed on test on a dummy aerial creasing the resistance of such tar- Mons. Descarsins, has developed a consisting of large banks of electric nished wire to high -frequency electric circuit into which he can put as much lamps lighted by the radio-frequency currents. According to the theory of as 20 kilowatts at a wave -length of energy and providing the equivalent the " skin effect," it has been assumed 45 metres. His transmissions have of the actual radiation system. Fre- that the electric current would tend been heard throughout various parts quency measurements are then made to the outside layers of the metal in of Europe and the East, as well as in throughout the entire transmitter, such wires. South America. Mons. Descarsins uses ensuring that the apparatus is func- All this is a plausible theory. The valves of the Holweck demountable tioning correctly. only detail the matter with it is that type, which he has found greatly When a broadcast programme is it turns out to be untrue, as has been facilitate his work owing to the fact ready to " go on the air," a signal is proved by the best test in the world -- that they can be readily taken apart, received at the transmitter from the someone has tried it ! repaired and reassembled. studio. Immediately the carrier -wave WE is fed into the aerial and this effect Not Measurable AF is Station W E A F, at Bellmore, Long. in turn signalled back to the W. M. Roberds, of the University of Island, which is now on the air, studio. In the case of W E A F this Kansas, is of has found that at 10,000 the finest of modern broadcast appara- signal is automatic, since the carrier - kilocycles (30 metres), at 8,600 kilo- tus and cost over £150,000. The wave energises a coil which operates cycles, and at 15,000 kilocycles there a relay in the control room, illumin- (Continued nu j)(rjr (79.1 ating a green light on the announcer's YOUNG BRAVE BRAVES RA1.)l(_) control box in the studio. "Grid -Glow " It is no longer necessary to press a button to start a 170,000 horse power electric plant. Radio does this by a wave of the hand ! This was demonstrated recently when the Chairman of the United States Steel Corporation set in motion the power station at Homestead (Penn.) by a motion of his hand over a " grid - glow " relay tube in New York. The hand -capacity effect set Off telegraphic relay which transmitted an impulse to a short-wave set in Newark. Its wave, 4295 metres, actuated a receiver at Pittsburg, the relay of which in turn closed a switch at the power station and started 6,000 -kilowatt generator. A New System A very elaborate broadcast system is planned by the Italian Government, and it is proposed, presumably in order to avoid any possible difficul- ties with the listening licences, to placo a small radio tax on all house - holders, whether they have radio sets Speaking at Buffalo, N.Y., in the Seneca tongue, throwing in a war -whoop or two for effect, at present or not. this Indian brave delivered the first -recorded radio lecture to the red man. 640 www.americanradiohistory.com June, 1928 MODERN WIRELESS 74,106, Under this heading month by month our Broadcasting Correspondent will record the news of the progress of the British Broadcasting Corporation, and will comment on the policies in force at B.B.C. headquarters. An O.B. From Bethlehem? As for changes in programme material, apparently the big symphony concerts have been " washed-out " for the APROMINENT American weekly journal is promoting summer. There is to be dance music regularly from a proposal to do a special Christmas " Outside B Tuesdays, Thursdays, and Saturdays at 10.15 Broadcast '' from the actual Manger in Bethlehem. 5 G on p.m. Curiously enough, there are no changes in the The spokesmen of this message are to be Dr. Cadman and evening talks arrangements. Mr. J. B. Kennedy, two well-known American preachers. This, I believe, is the first year in which the B.B.C. The National Broadcasting Company of the United States been bold enough to attempt to carry its full talks has agreed to participate. has programme straight through the summer. Most people The plan is to carry the signals over landline to Cairo, doubt the advisability of such a plan, but Savoy relay thence by Marconi beam to England, radiate through would Hill is more convinced than ever of the growing popularity the B.B.C. system, and relay again across the Atlantic by the talks, irrespective of weather conditions. Marconi beam. This seemed all very nice until the B.B.C. of was invited to accept its part in the enterprise. Then The Carnegie Trust Affair a snag was encountered. The B.B.C. sailed close to the wind in its arrangements The B.B.C. will have nothing to do with it, and its with the Carnegie Trust for the subsidising of the per- attitude is undoubtedly right. British listeners do not formance of some of the prize new works being pushed want their broadcasting system turned to such stunts. by that body. Savoy Hill has been to some pains to To " exploit " the Manger at Bethlehem for the circula- explain that the sole object of the effort is to encourage tion of a weekly journal is against the British idea of good British composers who might not otherwise get a chance taste. It is not known whether the scheme will be under- of recognition. taken independently of the B.B.C. Savoy Hill will say It is added that the performance of these new works nothing at all about it ; but the American Press are requires a great deal more rehearsal than is possible or making up for this reticence ! that can be afforded for the normal broadcast programme. The Communists and Political Broadcasting THE FIRST OF THE REGIONALS British Communists applied to the B.B.C. for the same facilities as Conservatives, Labour, and Liberals under the " controversial broadcast " scheme. They were told that they could not expect to rank with the main parties owing to their numerical inferiority. It was added, however, that their views might not be excluded from discussions or symposiums. This seems to be an admirable solution of an admittedly difficult situation. Quite apart from considerations of political doctrine, there are not enough members of the Communist Party to entitle them to the same broadcast opportunities as are given to Conservatives, Liberals, and Labour. Never- theless, now and then they will be given a chance to put their views. Summer Broadcasting There is some contraction of broadcasting hours this summer For instance, the afternoon programmes of 2 L 0, 5 X X, and 5 G B will not start until 4 o'clock except on Thursday, when the time will be at 3, in order and This photograph of the 2 -kw. mobile transmitter was taken a to include the service from the Abbey. Saturday few miles north of London, where the B.B.C. is busy choosing Sunday afternoon programmes will remain as at present, a site and carrying out tests in connection with the new that is, they will start up at 3.30. London station-the first of the twin -wave broadcasters. 641 www.americanradiohistory.com MODERN WIRELESS June, 1928 It 13ss, been represented in quarters unfriendly to broad- One station director is quoted as saying that it took casting that this arrangement, is virtually a breach of the Governors three months to decide to knock £5 a year the condition of the licence which debars the B.B.C. off his already meagre reward. It is to be hoped that the from the right to take money for broadcasting. Then Chairman of the B.B.C. will take an early public oppor- there is the further suggestion that such an arrangement tunity to reassure listeners that there is no solid foundation involves the inclusion in programmes of items which would for these disquieting rumours. No one grudges the not be selected by the programme builders in the ordinary Governors their generous allowances from licence way. revenue ; but they are expected to be at least as generous This means that the B.B.C. is lending itself to the to those who actually do the work. propagation of the uplift ideas of the Carnegie United Kingdom Trust. The objections are mostly far-fetched The Regional Scheme but there is a trace of rationality in them. Uplift is Now that " single wave -length " working has been always a temptation for Savoy Hill ! accepted by the B.B.C. engineers as a practicable and efficient device, the prospects of the Regional Scheme are distinctly brighter. True, the Post Office have not yet given permission to the B.B.C. to go ahead with the four stations apart from London, but I understand that the conditions of the permission for the new high -power London station contain a clue to a formula which may make possible the simultaneous construction of the other stations. The Post Office have made it clear in connection wills their sanction of the London station that it is to be worked at first as a one-wave station, and that the intro- duction of the second -wave service is to be gradual and experimental. A similar formula might be applied in the case of the other stations of the scheme. If this is so, and there is some reason for believing that it is, then the Pennines, the West Country, and Scotland may have their own high -power transmitters fairly soon after the London one is complete, perhaps all of them about the end of next year. The Danger of the Dead Level I have been disturbed lately by the unanimity of the opinion of several discerning listeners who complain that the B.B.C. is suffering from a dead level of mechanical efficiency. This is appropriate in the engineering end of the business ; but it leads to bad results in the pro- gramme end. There is no longer an occasional " stunt," such as formerly distinguished programmes and stimulated licence revenue. One suggestion is that the programme staff is stale. Colour is lent to this view by the fact that the B.B.C. complains it has tried all possible stunts and peaks, and that there are none left now. 'This, of course, is nonsense. The alert, imaginative programme builder is never at a loss for novelty or originality. Is it that there should be drastic changes in personnel ? Last year one of the B.B.C. Governors declared at a semi-public dinner that the new board had agreed on periodical changes in the executive and artistic staff, and that they thought two years was quite long enough for the ordinary broadcasting official to exhaust his usefulness. The special aerials erected at Daventry by the B.B.C. for This policy Daventry Junior "-5 G B. would be distressing to a good many officials ; but it might be modified by some switching about. For instance, it is well Discontent at the B.B.C. known that Captain Eckersley would be quite willing to take over the programmes from The coincidence his of two separate but similar " public brother. Captain Eckersley is as strong au adherent indiscretions " by B.B.C. station directors calls attention and practiser of " peaks " as his brother is of the to an alleged change in the working conditions of that average standard of efficiency. Incidentally, Mr. R. H. organisation. The suggestion is that the only effort made Eckersley is an engineer of recognised competence. by the new Board of Governors has been to cut down Why not change them about ? salaries and stop increases. It is impossible to confirm A change of position would be refreshing to the official or disprove the allegation ; but a strong impression and possibly provide him with stimulating food for persists that the Governors are much meaner to their thought. And it would add to the strength of the staff staff than were the Company Directors. as au entity if it were elastically constituted. 642 www.americanradiohistory.com June, 1928 MODERN WIRELESS OPERATNC T "EASY-TUNE FOUR inima\ Akin& In this article are given details of the coils for both long and short waves, together with further data concerning this remarkable receiver. By C.P. ALLINSON, A.M.I.R.E. IN the last issue of MODERN former and the end of the winding of the fact, however, that I have WIRELESS I described the con- taken to pin No. 1. definitely recommended the use of an struction of a four -valve receiver The primary winding, which is ordinary H.F. valve having an which I called the " Easy -Tune " wound on an interchangeable former, impedance in the neighbourhood of Four, on account of its extraordinary is connected" so that if the winding 20,000 to 30,000 ohms, the correct ease of handling. begins at that end of the former which number of turns will be 15 for the I propose here to deal with the is nearest to the pins-that is, the short broadcast wave -band. question of the construction of the coils bottom of the former-the beginning Here, again, where greater selec- for both the long and short waves, of the winding is connected to pin No. tivity is desired, the number of turns and also give some information as to 4 and the end of the winding-that may be cut down. If 8 turns are used, the correct adjustment of the receiver is, the top-to pin No. 5. it will be found that a greatly in order to obtain the maximum increased degree of selectivity is efficiency on all wave -lengths. Increasing Selectivity obtained with only a very slight loss With regard to the coils, we will Where the question of selectivity is in signal strength. take the short broadcast waves first. not an important one I would suggest The winding L4 consists of one-half The aerial coupler, which consists of two formers in order to obtain the only of the whole inductance which two coils, L1 and Lr, is wound on a maximum efficiency, namely, 10 turns is in the grid circuit of the detector featherweight former, the primary for the lower half of the broadcast valve and 35 turns should be wound being wound on an interchangeable on in this position. The beginning former which fits within the secondary of the winding, as before, is taken to so that the degree of coupling can be pin No. 2 and the end to pin No. 1. adjusted according to the aerial and The same gauge of wire and spacing earth system in use, and also to vary are employed as in the aerial coupler. the selectivity in cases where this is an important point. The Reaction Winding We now come to the question of The Grid Coil the coils L; and L3, that is, the other The grid winding L, consists of half of the grid coil and reaction wind- 55 turns of 28 D.S.C. copper wire, ing respectively. spaced one diameter, a tap being taken These are wound on a 3 -in. paxolin in at 14 turns from the bottom end. former on a 4 -pin base, as shown Where the constructor has no means Fig. 2. On examining this mount it for space winding I suggest that he will be found that the distance uses 22 D.C.C. wire and winds the between two pins, as shown at A in turns side by side. This will give wave -band and 20 turns for the upper the figure, is greater than that a coil differing very little in its half. In cases, however, where a very between the other pins, namely, B characteristics from the one recom- great degree of selectivity is required, and C. mended. the primary winding can be reduced The winding L; is connected 1 2 The sketch in Fig. 1 shows the' to about 5 turns, though this will, of between pins No. and and consists method of connecting the coil. If course, result in a drop in signal of 35 turns of 22 D.S.C. wound side we commence at the bottom of the strength on distant stations. by side, or else the same number of former the beginning of the winding The windings L3 and L4 are wound turns of 28 gauge D.S.C. spaced is connected to pin No. 2. We wind on on another featherweight former. The one diameter. The beginning of the No. 1, 14 turns and then take a tap which primary winding will, of course, winding is connected to pin is connected to pin No. 3. The remain- depend to a certain extent on the and the end of the winding to pin der of the winding is then put on the H.F. valve that is to be used. In view No. 2. A space of 1, in. is then left, and 643 www.americanradiohistory.com MODERN WIRELESS June, 1928 the reaction winding put, on, the wound full, while the secondary portion of the circuit when the vari- beginning going to pin No. 3, and the winding consists of 125 turns of able resistance across one half of the end, if a fixed winding is used, going gauge 32 D.S.C. wound on side by grid coil is as high a value as possible to pin No. 4. side, the beginning being connected consistent with a satisfactory degree I ham' found it, however, a slight to pin No. 2 and the end to pin No. 1. of reaction being present. advantage to take a number of It may be thought that the primary tappings on this winding and connect is decidedly on the small side, but if o 2 43 ruRNs you desire to obtain absolute stability TAPP//VG PER SLOT under all circumstances on the long - 86ruRNs 3 SEW/ND/CONONCARY " FROM Ph V2 :: A curious point with this circuit is :: wave side, complete freedom from ¢ 3 that the H.T. voltage on the detector tt parasitics or other forms of oscilla- 2 L2 tt valve has practically no influence on tt tions, and absolute interchangeability sLOTs tAR4 i/ yt the reaction control." tt PLs W/DEx .. .. between long and short-wave coils e without having to re -set the neutralis- Pi PEEP pRLMARY t< 4 ing A a spring clip at the end of a piece of condenser, then the number of 25ruq/s turns PER flex to pin No. 4, so that the correct given above is correct. SLOT size of the reaction coil may be found F/G.3 to suit all requirements. The largest Interchangeable Primary SECT/ON Tf/ROf1Cf/ CO/L FORMER. number of turns required will be Greater amplification may be ob- The first thing to do is to see that 35 turns and tappings may be taken tained by increasing the number the H.F. valve is correctly stabilised, 20 25 30 at and and turns from the of primary turns to 37, but it will then and the procedure for carrying this beginning. be found that it is necessary to out has been described last month. We will now turn to the question readjust the neutralising condenser In view of the fact, however, that the of the coils for the long -wave band. when changing over from the short particular circuit I have employed The aerial coupler for the long waves to the long waves, while if the primary is one that gives a slight amount of can be obtained from Messrs. Collinson is increased still further instability under -neutralisation at the higher Precision Screw Co., but should you may result which can be uncontrol- wave -lengths, it will sometimes be wish to construct it yourself you will lable in some cases. found an advantage slightly to in- need a slotted former in order to The circuit used in the " Easy - crease the value of the neutralising accommodate the number of turns Tune " Four is somewhat more liable condenser above that required to give required. Fig. 3 shows the necessary to give instability on the long waves, neutralisation at, say, 250 metres. dimensions and gives the number of owing to the division of the detector This will give a somewhat more turns of wire required in each slot. coil into two portions, than a straight- constant -reaction demand with the Long -Wave Aerial forward circuit, and this has therefore circuit used in this receiver. -Coupler enabled me more easily to determine With regard to the long -wave aerial the cause of instability on the long Tuning Adjustments coupler, it should be noted that the waves when using any form of split - Having correctly adjusted the beginning of the winding, that is, secondary circuit. neutralising condenser, increase the that at the bottom of the former, is A further advantage is obtained by value of the resistance R until connected to pin No. 4, and the end the use of an interchangeable primary the detector just oscillates when the of the winding to pin No. 5, the winding for the long -wave coupling, two tuned circuits are brought into beginning of the secondary winding in that it enables selectivity again step. L, is connected to pin No. 1, three- to be controlled, especially in cases This, incidentally, provides a simple quarters of the winding being put in where severe interference from test of determining whether the two position, and a tap taken to pin Daventry is experienced on Radio circuits come into tune at the same No. 3, and the end of the winding Paris. reading on the dial, 4nd, should they taken to pin No. 2. not do so, then it is a simple matter Obtaining Maximum Efficiency to adjust one of the windings until FOR L3 13.0//sFOR 5XX The coils L5 and Ls consist of they come into tune at exactly the TAPP/NCS 125 turns for L5 of 32 D.S.C., L6 same reading. It should be noted consisting of 35 turns of the same that whichever dial reading gives the CL /A lowest TO gauge wire, spaced in. away from reading belongs to the con- TAPS the grid portion of the coil. denser tuning the inductance which It is necessary- for the reaction has too many turns on winding to be quite small for the long .t /r/C. waves, and this is no doubt due to the 2 ¡¡ "Over 4.5 stations on the lower increased efficiency of the detector tt broadcast band have been received at valve as an H.F. amplifier on the loud -speaker strength on the Easy- t tt tt longer waves, so a larger Tune Four." .3:94444 that H.F. PAXOL/N component is present in the plate A FORMER circuit. A smaller reaction winding Should it be found that the resist- is therefore rsao required. ance has to be decreased to a fairly We now come to the question of low value before the detector stops For the two windings L3 and L,4 a obtaining the maximum efficiency oscillating, then the number of turns featherweight former is again used. from receiver. the One point that on the reaction winding Ls should be The primary winding should consist should be emphasised without further reduced. This test should, of of 25 turns on course, an interchangeable delay is that the greatest signal be former, carried out on one of the longer that is, the former should be strength is obtained from the detector (Continued on page 673.) 644 www.americanradiohistory.com June, 1928 MODERN WIRELESS Great Britain was the first country to place broadcasting in the hands of a single authority. How our radio programme services have developed is told below. By Dr. J. H. T. ROBERTS, F.Inst.P. WING to the fact that broad- more of a technical hobby than an very great value in building up the casting was an entirely new artistic pleasure. service, and it has been shown that art not more than five or six The eight main stations brought an annual revenue varying from years ago, the engineer called upon to approximately 50 per cent of the £5 to £10 was received to the expendi- design and lay out a series of broad- population of the British Isles within ture of every £1 of capital outlay cast stations so as to give the best areas where the programme was not upon the relay stations. possible service throughout the country interfered with by extraneous dis- The relay stations involved only was evidently faced with a formidable turbances. Iri order to increase the small capital risk, whereas a high - task, and one in which there was little effectiveness and scope of the service, power 'scheme, had it failed, would or no previous experience to guide him. it was evident that more stations had have ruined the Company. High - to be erected or else the power of the power stations are wasteful, giving Birth of Broadcasting existing ones had to be increased. too great a signal strength nearby This was the difficult and onerous and too weak a signal at a distance. position in which Captain P. P. Additions Add to this the fact that the relay Valuable created great local enthu- Eckersley found himself upon the careful consideration it was stations After siasm, and it will be possible to appre- inauguration of the B.B.C., and in a 11 stations, having a decided to erect ciate their great value to a growing paper recently contributed to the of 100 watts (this has since power service. Institution of Electrical Engineers been increased to 200 watts), in many he describes in considerable detail towns and cities not included within how he went to work to solve the the service area of a main station. Use of Landlines many problems of broadcasting and The erection of this series of The programmes for relay stations how, during the succeeding years, " relay " stations has many times have mostly been provided from experience has shown the way to been criticised, but it should be London via landlines, since it various important improvements. pointed out that the stations were of has been found unwise to dilute Captain Eckersley's paper is a com- pendium of information relating to general broadcast engineering and should serve as a valuable guide iii other countries where a broadcast system is being introduced or may be introduced in the future. The British Broadcasting Company started with a contract with the Postmaster -General for the erection of eight stations of 1 -kilowatt power. Relays Required It soon became clear, however, that the stations of this power, situated as they were in the hearts of large cities, did little more than serve adequately areas between a radius of 20 to 30 miles around them. Out- areas the weakness of the side such A corner of the control room at the Leeds -Bradford relay station. The future of such signal strength (compared with ex- stations is still undecided, and is dependent upon the success or otherwise of the Regional traneous disturbances) made listening Scheme. 645 www.americanradiohistory.com MODERN WIRELESS June, 1928 programme revenue beyond a certain engineers of the B.B.C., and the service, because it is hoped that in point. The addition of " relay_" to definitions have been accepted by clue course some of the interference " main " stations brought 70 per cent the Technical Committee of the Union mentioned in the above categories of the population within reach of Internationale de Radiophonie. The will be eliminated at the source. uninterrupted service. It is, however, " service area " is defined in four As fading may set in outside a uneconomical fill to the whole area categories as follows : radius of 80 to 100 miles the obvious of .the country with relay stations, ideal is to make the " B " service as they are only effective in densely Four Divisions area have a radius of 100 miles. populated parts, and there is a limit, 1. The " Wipe-out " area, in which Various factors, such as wave- which was apparent even in the a service from the local station can be length, type pf ground covered., early days, to the number of available absolutely guaranteed whatever the transmitting aerial and mast design, " channels." It may be said that the sources of extraneous interference ; a and so on, have their influence upon main and relay stations were effective listener within such area will, however, the question of " service areas " so in bringing the British urban popula- require a receiver of very special that it is always difficult to give an tion within reach of a proper service, design if he is to hear relatively dis- exact prediction as to what type of and it remained to fill in the gaps tant or weak stations. service may be expected at any par- and serve those lonelier country 2. The " A " service area. A ticular point. As an average of obser- districts where broadcast has perhaps listener within sauh area can be vations taken from the London and an even more real function to perform guaranteed service, even if he lives Daventry medium -wave stations, how- than in the towns. near to the usual sources of electrical ever, using frequencies between 800 interference, such as - First High trains, electro and 600 kilocycles, it is possible to -Power Station medical apparatus, electric signs and so give some rough idea as to the extent This was the reason why the on, and he will have a good chance of of A, B, and C service areas for B.B.C. sought, and received, Govern- distant listening with properly de- different powers. ment permission to erect, first experi- signed receiving apparatus. mentally at Chelmsford and after- 3. The " B " service area in which Question of Wave -Length wards permanently at a a listener can be guaranteed Daventry, crystal The question of available wave- relatively' high -power station reception with a good outdoor aerial, using lengths is also an important one for a much longer wave -length than had but in which he will he at the mercy the broadcast engineer. In some been formerly employed for broad- of severe types of interference which recent tests undertaken by night in casting. The Daventry equipment occur in perhaps 5 per cent of cases winter -time, it was found that two comprised at the time of its instal- normally met with. 1 -kilowatt stations, 500 miles apart, lation the world's first high -power their carrier -waves separated by 1,000 long -wave broadcast station, and 100 -Mile Radius cycles, produced an audible beat out- it has since fully justified its 4. The C " service area, which side a radius of 2 miles from either existence. With the advent of the will be subject to interference from station. Other tests showed that Daventry station the percentage total spark sets, electric trains, atmo- stations separated by about 100 of the population living within the spherics and so on, but which in time cycles in fundamental frequency, and service area of a station was brought should be assured of an 80 per cent separated geographically by 1,500 up to 85 per cent. The use of so-called " long waves " for broadcasting has also been criti- cised, but it is economical in certain important respects and, thanks to the less rapid attenuation with long waves, the service area for a given power is greater. The " fading characteristics " are better, and service without fading up to 300 miles is common, in addi- tion to which interference by spark transmitting apparatus and from other causes is much less. It is estimated that 50 per cent of listeners rely upon the long -wave Daventry station and that no Other station is listened to in 90 per cent of the rural areas of the country. "Service Area" Recently what is known as the " Regional Scheme " has been started, experimentally at first, by introducing a second high -power medium -wave station at Daventry, giving pro- grammes contrasted with those of the older long -wave station. It is rather interesting to notice that the term " service area " has One of the numerous earth leads which run under the building at Daventry. 5 X X is probably the most popular of all ourstations, and has earned a world-wide reputation for been defined in a special way by the excellence of transmission and reliable service. 646 www.americanradiohistory.com June, 1928 MODERN WIRELESS miles, produced audible beats at 10 check, the B.B.C. offered invitations to satisfy a larger number of persons an miles from either station. to representatives of other countries because there will always be Added to these specific tests there to meet in London for a discussion alternative choice, and, secondly, each is the accumulated evidence of private of this important question. This programme is able to achieve artistic listeners who have from time to time resulted iu_the formation of the Union unity and need not consider com- complained of interference inside the Internationale de Radiophonie, with promise. " B " service area, due to the hetero- headquarters in Geneva. The organi- dyne produced between the station sation is framed to allow discussions - . . Many receiving sets are in use ;; to which they are listening and some between different nations on all ¡¡ which, to all intents and purposes, do are matters relative to broadcasting in ¡¡ not tune' at all. This is particularly other station. These effects found in 'wipe-out' areas." chiefly noticeable at night and, of its international aspect. .. Z course, programmes are listened to The wave -length problem which by a maximum number of persons at confronted the Technical Committee For such a service to be practical, night. of the Union was easy to state, it is obvious that the two transmission although very difficult to solve : strengths should be equal. If, for The Heterodyne Problem There was room for roughly 100 instance, a listener lives within the In order to obtain a solution of the stations; there existed more than 150 " C " service area of one programme, problem of the heterodyne inter- stations ; more stations were being he should also live within the " C " ference we cannot seriously rely upon built; what, then, was to be done service area of the alternative pro- any principle other than adequate about interference ? gramme. separation of fundamental frequencies British listening has so far been between stations which are within The Geneva Plan conducted upon a technique in which 3,000 miles of one another. Various On the suggestion of Captain the average listener has been content suggestions have been made from Eckersley (who is a member of the to listen to one programme. In con- time to time to overcome this type of Technical Committee) a compromise sequence; many receiving sets are in interference, but taking into considera- was arranged. Of the 100 available use which, to all intents and purposes, tion the rapid growth of small -power wave -lengths, 84 were to be allotted, do not " tune " at all. This is parti- stations in many parts of the Con- according to an agreed formula, for cularly found in " wipe out " and tinent, the desire of many countries the exclusive use of the more impor- " A " service areas, where the listener to have a service at small capital tant European stations, while the has taken the greatest liberties, but, cost, the expense involved in ex- remaining 16 were to he shared by the thanks to the overwhelmingly loud tremely high -power stations and the surplus stations. The " Plan de signals, has to some extent been growing need for alternative pro- Geneve," as it is called, was based satisfied. grammes, it is obvious that even a 10 - upon these principles and was put Any scheme of broadcasting must kilocycle separation of fundamental into practice on November 14th, rely to some extent upon the possi- frequencies is really insufficient, whilst 1926. Under this plan, Britain has bility of linking any studio or micro- anything less than that degree of nine exclusive wave-lengths. Counting phone point to a distant transmitting suppression is in practice, impossible. Daventry long -wave station there station. This is most conveniently The separation of 10 kilocycles are ten channels in all available 'for done by the use of telephone lines. makes room for 101 stations within a British broadcast. It has been found by experience frequency span of 1,500 and 500 kilo- Now we come to a question which is that it is quite practical to rely upon cycles. of very particular interest to the the use of such a form of connection. Realising so long ago as 1924 that broadcast listener, namely, the No serious loss of quality in the if stations were to go on being erected question of alternative programmes. transmission need be feared if proper at a rapid rate, if the frequency It is true to say that the provision of precautions are taken. span allocated were not further ex- alternative programmes more than tended, or if some international agree- doubles the value of a broadcast Inter -Linking ment were not arrived at, broadcast service. An alternative programme It is interesting to consider how possible to link national development would suffer a severe has two advantages : First, it tends it may be systems. (already linked by landline between themselves) so that a world system of broadcasting may be estab- lished. No engineer would think of using anything but landlines for this purpose, but the landline method of connection has its limitations ; it can- not be used, for example, where it has to pass under considerable sea areas. The success of the London to New York radio -telephone service has brought up the question as to whether a similar system might not be used for linking up different national broad- cast systems. An ideal scheme might seem to base : itself upon the erection of a giant When the London station 2 L O was moved from the Strand to Oxford Street many central station radiating from one alterations were made, and the transmitter was brought right up-to-date. This photo- point as many programmes as there graph shows part of the main transmitter, satiated just beneath the aerial on the roof of Selfridges. (Continued on page 674) 647 www.americanradiohistory.com MODERN WIRELESS June, 1928 small stiff spiral brush, each of which is useful after soldering operations, and they are capable of getting into all sorts of odd corners to remove offending material. The small one can be inserted into valve holder, coil holder and dry battery sockets, and twisted round to clear dirt, the stiff bristles ensuring that the work is properly carried out. Other Items A camel -hair paintbrush, such as - the one shown-with a long whité w` handle, is very useful for cleaning up panels, tops of accumulators (after being rubbed with a rag), dry bat- teries, the loud -speaker Peculiar and apparently untraceable crackling noises, fading, poor signals, and many horn and the baseboard generally, and is capable other " faults" can often be attributed to the evil effects of dust. The remedy ¿s of getting into very obvious, keep your sets and batteries clean by the means indicated in this article. out-of-the-way places, but the favourite one is By H. J. BARTON CHAPPLE. undoubtedly the wireless brush, also depicted in the photograph. The Aaccumulation of dust on a cases, been wholly upset as the hair is particularly soft, and is held wireless receiver will sooner result of this. in a close wire spiral passing through or later bring trouble in its When a set is first constructed, the centre. This is bent round at the train. With the older types of sets, particular attention should be paid top, and although normally the which were constructed so that they to ensure that the soldering flux is brush diameter is 12 in. it will had a fairly large horizontal panel, used sparingly, and, after joints are close up to a very narrow thick- serving to accommodate a large made, superfluous material must be ness, and this proves a most effective proportion of the components exposed wiped away so that the work is dust remover in all circumstances. to the air, the effects of dust were more quite clean, otherwise this material If one's set has been standing idle marked, but even with the present- will soon collect dust and cause for some time in a spare room, the day designs favouring a vertical panel deleterious effects by reducing insula- dust is liable to be so thick in parts carrying the fewest of controls, the tion resistance to very low values. as to necessitate the use of the components in this case being mounted " blower;' attached to the " do- on a horizontal baseboard and all Necessary Equipment mestic " vacuum cleaner, but a housed in a cabinet, the problem is It does not take long to do the periodic clean-up of any wireless set, .:till one that requires careful atten- " spring cleaning " provided one has whether in use constantly or not, tion. the necessary simple equipment, and is really essential, for as far as wireless Although apparently totally en- the accompanying illustration shows is concerned it can be said quite closed, particles of dust have a the four brushes which I always keep truthfully that " cleanliness is next knack of getting inside the cabinet, by me for work of this character, to good reception," and a little time and it behoves the possessors of sets and the combination proves equal to spent in that direction is duly periodically to overhaul their re- any occasion. There is a large and rewarded by improved results. ceivers and remove all traces of dust from the interiors as well as KEEP YOUR SET CLEAN from the front ,panel. It is fairly well-known how the spaces between the fixed and moving vanes of variable condensers are favourite parking places " for dust particles, and unpleasant crackling noises can frequently be traced to this source. Cleaning " Variables" Probably the best plan to adopt in these cases is carefully to insert a feather or pipe cleaner between the vanes and remove any ' offending particles, but there are other spots which serve as " danger zones " as far as dust is concerned. Bad leakage effects on what was previously good insulating material can be caused by any undue dirt accumulating - a The between terminals or contacts, and four types of brushes used by the author. The largest one is a special soft " wireless ' brush, the next in size is an ordinary soft paintbrush, while the two spiral cleaners are receiver performances have, in many useful for dealing with valve sockets, coil sockets, and similar awkward items. 648 www.americanradiohistory.com June, 1928 MODERN WIRELESS "E'<ïii;.:": VALVES FOR PORTABLES sx..mE 'choosing a circuit for a portable JIIII IIIlIII11111111111111111111111111111111111111iI II1I111111111111111e H.T. one has to keep down the receiver there are two main The sensitivity of a portable number of valves, and possibly the be con- E receiver is largely dependent upon number of stations to be received, and things which have to the valves employed.as is explained sidered. One is the question of = in this article. _ to watch very carefully the consump- of current for the whole w eight and bulk, and the other is the By KEITH D. ROGERS. tion anode question of reception and receptive set-which means a careful watch on powers. The former will, of course, I=iiiiIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIl hill IIIUIIIIIIiIIlII11IIIilt the anode current of the last have to be answered with special valve. have 'phone or loud -speaker reception, regard as to the uses to which the A Typical Example set will be placed. and in the latter one may have recep- tion of good quality, or of just Let us take a typical form of The of Weight mediocre quality, while together with receiver; employing four valves, an Question ordinary H.F. stage, followed by a if you want the the point concerning reception goes For instance, detector working on the grid -leak for use picnics and the question concerning sensitivity. or receiver at principle, and then followed by a out-of-door recreation, and have no range of reception. resistance and a transformer or of other than in If a loud speaker is desired, several means carrying it another resistance -coupled amplifier. your own hands, so to speak, then the valves will have to he used, and you weight certainly must be cut down. will have carefully to consider the It is no good having a multi -valve set types of valves you would employ. with a heavy, stout case and loud Whatever kind of reception, whether speaker and plenty of H.T., and all 'phone or loud -speaker, is desired. the luxuries which might go with such one will naturally employ valves a set, unless you have some means of which will give the maximum signal transporting it. strength under the circumstances, I know of several sets on the and while in a telephone receiver market which are really fine jobs from one cannot go very far wrong from the radio point of view, but when the point of view of quality, when one looked upon from the point of view is dealing with a set which is to be of portability are quite outside the used to work a loud speaker, the pale, which, of course, is because they quality will largely depend upon the are designed not to be used for pòrta- circuit and especially upon the bility from the point of view of one valves used in that circuit. being able to carry them about from place to place out of doors, but so The H.T. Problem Four -electrode valves make ideal valves that they can be used in any room in So in a portable set, as in others, the for small portable sets, and enable good be dis- of sensitivity and quality results to be obtained with very small the house without having to question anode voltages. connected. In other words, they have to be considered together, one are transportable self-contained re- against the other, and a compromise ceivers. made which will best suit the needs of Now it is obvious that in an H.F. the owner of the set. stage one can use either an ordinary Quality and Sensitivity It stands to reason that in a port- H.F. valve or a screened -grid valve, When one has decided upon the able receiver one does not want to while whereas the latter may be very matter of bulk and weight, one has to carry about any more H.T. than is efficient in its operation, it requires decide upon what type of reception is absolutely necessary, and in order not far more screening and careful design to be obtained. For instance, one may to need a tremendous amount of (Continued on page 674.) 649 www.americanradiohistory.com MODERN WIRELESS June, 1928 " Readers of ` Radio News ' are e again assured that, whenever there is a really -worth -while development in American Views On Home Television television available to the constructor * Some trenchant transatlantic comments concerning the "Simple and to the public, this magazine will í Televisor" and the present position of Television in general. s be the first in giving them full details. Until the laboratory apparatus, which ***#***#*****e*****e******e**e#*****##eve* has made possible the remarkable demonstrations we have in previous THE fact that television sets and they had never seen anything better, issues described, is released for public parts have appeared on the with what could they make a com- sale, the amateur can make nothing English market seems to have parison ? Therefore, the store's in his workshop except interesting caused a good deal of interest in advertising carried only the impres- toys-such as that which might be American amateur radio circles, and sions of laymen desirous of being first built up out of the components in the June issue of " Radio News," in a great and profitable field ; not offered by Messrs. Selfridge. the London .correspondent of that that of trained radio men who have paper has a " message," which he seen the most successful demonstra- Television Not Yet Here cabled over at the request of his tions in television, and can judge of " As related in the April issue of editor. the comparative merits of the per- ' Radio News ' (on page 1163), we have In the course of this message he formance. talked with engineers of the General says : Electric Company and of the Bell " The ` Televisor ' described is a Only a Toy Telephone Laboratories, and they very crude piece of work ; it serves as " Such advertising, therefore, is put the time for the amateur to come both transmitter and receiver ; to hound to cause a reaction -in readers' into the field at five years hence. avoid synchronising, the two discs sit sentiments, and scepticism, to even They are, of course, conservative on the same spindle.* an undeserved extent. The backers gentlemen, and the time may be only of a promising invention who have three years from now, or less-but, Many Difficulties but limited capital, and wish to retain anyhow, it is not bow." " In practical construction, this control by financing the device The above extracts from the 'Radio ` Televisor ' model appears to offer through popular sales of stock, face News " need no coniment ; but many difficulties to the fan ; he is the problem of attracting investors readers who have perhaps considered asked to invest also in a four- or five - through striking and skilfully - the MODERN WIRELESS television stage audio amplifier to boost up the arranged publicity. In so doing, policy rather pessimistic will no received impulse so that the impulses there is a great danger that exagger- doubt realise that, even in America, can flash a neon lamp ! The B ' ated or over-optimistic propaganda, our policy is supported and sub- voltage required for this purpose is even though it is permitted but stantiated. . volts ; given as four to 'six hundred passively by the promoters, will cast *Editorial Note:-The "Radio News" corre- as the power tube specified is a most doubt on their proposition in the spondent makes a slip at this point. The expensive transmitting tube. minds of the well-informed, and for machine actually incorporates two discs I am afraid that the Baird system a short time appeal to the mounted on separate spindles and driven by only separate motors, both discs being required for is hopeless, after all. It cannot give credulity or inexperience of the public transmission. One of these same discs is also sufficient detail and, if you glance and the unwary experimenter. used to re -build the received image. through recent copies of English radio magazines, you will find quite un- ANOTHER ELECTRICAL MUSIC MAKER biased opinions of leading physicists which point to. only one conclusion --something radically different and novel is wanted if television is to be sister science to radio." A Matter of Perspective The " Radio News " editorial com- ment continues as follows : " From the contents of this letter, it might seem as though someone had been trying to foist on the public something which operates-yes, in- deed !-BCT HOW ? Of course, a store with such a high reputation as Selfridge's enjoy cannot afford to sponsor anything that smacks of -crookedness ; but it is true that the managers of the store are not scientists or engineers, but only enterprising merchants. " These business men might be Rene Bertrand, a French electrical engineer, with the device he has invented for pro- on which appeared a ducing musical sounds electrically. He claims that his " instrument " is easier to shown a screen play and has more possibilities of range and power than other devices of the kind, such as silhouette of a man's face, and be the Theremin apparatus which has recently been heard in most of the large cities of the told that " here is Television.' If world. 650 www.americanradiohistory.com June, 1928 MODERN WIRELESS New Mullard L.F. Transformer-A Celestion Loud Speaker-A Short-wave H.F. Choke- The " Time -Saver "-The New " Lotus" Plugs and Jacks and Jack Switches, etc., etc. New Mullard L.F. Transformer tage of amplification down to 50 cation such as percentage figures, but, considera- HAD it been our practice to judge cycles. Messrs. Mullards say that unfortunately, there are by appearances, we should the windings of their transformer tions such as that of price which have put aside the sample have been so selected that no reso- make this impracticable. >Vlullard Permacore L.F. transformer, nance peak occurs at about 8,000 For instance, not all of our readers which recently arrived, as being an in- to 1.0,000 cycles, as in most other would be able to afford £7 5s. for an efficient component. It has the size makes. oak version, or £7 10s. for a mahogany Celes- of of the so- ee version, of the model C.12 " and weight the smallest ....ee.e.e e. called cheap transformers, but we tion " loud speaker, but we do not must say right away that its per- Manufacturers and traders are think that anyone could quarrel invited to submit for test purposes is one of the formance ' is that of a high-grade radio sets, components and accessories with such a purchase. It product. to the "Modern Wireless" Test Room very best instruments we have heard. at Tallis House. Under the per- In our opinion this C.12 runs the ex- Its compactness and lightness has sonal supervision of the Technical been achieyed by the incorporation Editor all tests and examinations are pensive moving -coil variety very close. carried out with the strictest of It has practically no colour and its of a new design. Incidentally, the impartiality. silver wire used for the primary Readers can accept the Test Room projection is crisp and clear. It pro- winding in order to provide a high reports published monthly under the vides ample bass, and speech is almost above heading as reliable guides as to conductivity also has the advantage the merits and demerits of the various uncannily natural. that it stoutly resists deterioration. modern productions of the radio It is of the cabinet cone type, and industry. Nickel is used in the secondary its dimensions are 14 in. by 14 in. by winding, and the core is of a special 6 in. We thoroughly endorse the iron known as " Permacore." In this makers' claims that its outstanding It is, in fact, a very excellent trans- way effi- features are " its sensitivity, its the component obtains an former, and can take its place in the ciency out of all proportion to its ability to . handle great power, and highest grade of this kind of com- its even response." Its construction dimensions. ponent, with the added advantage There is an unusually high degree is tastefully and beautifully carried that it is ideal for portable receivers of transference of energy, and the out. The woodwork displays a owing to its small size. high degree of craftsmanship and, Price Reductions Messrs.. Ripaults, Ltd., inform us that their well-known lateral -action condensers have- recently been greatly improved.' Furthermore, they have found it possible to reduce the prices, either the 0005 mfd. or 00025 mfd. now being available at 10s. 6d. each, without dial. The price of the slow- motion dial is 4s. 6d. This is the "Permacore" L.F. transformer, which, although it has a high degree of A "Celestion " Loud Speaker is remarkably small. efficiency, Good loud speakers are of com- primary will handle large D.C. cur- parative excellence-there are good rents without saturation. Its curve loud speakers which we cannot en- is very straight from 200 cycles thuse about because we have heard upwards, and the falling off below much better ones. Wewish we could The `' Celestion " C. r2. A high-class loud that figure still gives a large percen- adopt some sort of scheme of classifi- speaker. 651 www.americanradiohistory.com MODERN WIRELESS June, 1928 altogether, the speaker has a most and its exceptional compactness. and plugs or jack switches. But, handsome appearance. We consider One was included in a special short- hitherto, many constructors have it an excellent proposition and very wave receiver built by the " M.W." been debarred from using them owing good value for money. Research Department and found to to the fact that they necessitated be completely satisfactory. Con- soldering. It will be, therefore, good The Stewart -Warner structors need have no hesitation in news to many of our readers when Reproducer embodying this component in their they learn that Messrs. Garnett, looking for Amateurs a variation next short -waver.. It retails at Whiteley & Co., Ltd., of Liverpool, in the usual design of loud speakers 7s. 6d. have placed a most comprehensive should be interested in the- Stewart - range of jacks and jack switches on Warner Reproducer due to the Stewart The " Time -Saver " the market, all of which are provided Engineering Co., Ltd., of Long Acre, with terminals instead of with the London, W.C. It is a heavy instru- Something quite new in the way of radio station logs has recently been more usual and irritatingly closely ment, finished in antique bronze, and placed soldering tags. it bears graceful figure mouldings placed on the market by Messrs. Adsigns, of 265, Strand, W.C.2. The The " Lotus " jack switches will be in a sort of Grecian style. It is a of exceptional interest to radio set totally enclosed model, and has no neat little -article can be screwed to the lid or to the front of a set without builders. They are push-pull switches adjustments. Although it is sensitive which are just as easy to mount on a it will also carry fair inputs. It has detracting from its appearance. In principle is to panel as the familiar and simple on- not the projection of the open cone it similar a small roller blind. By pulling a nickel ring at the off filament switch. Indeed, this type, but the reproduction is clear. comprehensive Lotus range includes It is moderately good on speech, and bottom some 10 in. or so of white linen can be pulled out. a battery switch at Is. 6d. has a fair bass. Its price, complete Only one hole has to be drilled in with a length of silk flex, is £6 15s. This has printed on it all the well-known broadcast stations, to- the panel to mount even the double - Trix R.C.C. Unit gether with wave -length details, throw double -pole jack switch, and and so on. Three columns are pro- the six terminals on it are widely Messrs. Eric J. Lever (Trix), Ltd., spaced and most accessible. Neverthe- of London, E.C.1, vided for the insertion of dial readings. Clerkenwell Green, less the switch is compact and neat have two units. When the ring is released the log produced .R.C.C. in appearance. Similarly to all other are known as the A and B types springs back into the case. The They " Lotus " components, it is well respectively. The former is for use " Time -Saver " should, in our opinion, achieve popularity both on account made and nicely finished. The action immediately following a detector is positive and the contacts firm and stage, or after a medium -impedance of its novelty and its genuine useful- ness. good. The price of this D.T.D.P. valve. The B type is for use after It appears to be quite reason- ably priced at 2s. 6d. jack switch is 4s. The other jack high -impedance special resistance - switches are similar in design and coupling valves, and employs high similarly attractively priced. of anode and New Lotus Components values resistance grid There are five jacks available, ranó leak. The units are compactly built There is no neater and, in many ing from the single -circuit type at 2s. into moulded bakelite cases with cases, no more efficient method of to a double filament -control jack at nickel -plated terminals. They retail switching than by the use of jacks 3s. The Lotus jack plug costs 2s. at 5s. 6d. each. On test we found Messrs. Garnett, Whiteley & Co., Ltd., them quite satisfactory and the re- are to be congratulated on their new sistances embodied were found to productions which will undoubtedly carry the moderate currents handled open a new field of interest to many recordable variations. constructors. A Short -Wave H.F; Choke An Amplion Extension An H.F. choke as normally used Owing to rapidly increasing busi- in a receiver employed for the recep- ness, Messrs. Graham Amplion, Ltd., tion of the ordinary broadcast stations and its subsidiary company, Messrs. does not need to be ultra efficient, Alfred Graham, Ltd., have found it but on the short waves the reaction necessary to acquire new and exten- choke becomes of paramount impor- sive premises comprising 165,000 sq. tance. As a matter of fact, practi- ft. floor space at Slough, Bucks. cally any det.-L.F. or det.-2 L.F. receiver will successfully bring in the A Useful Book short-wave stations providing it has Messrs. Longmans, Green & Co., a moderately efficient capacity re- Ltd., recently sent us a copy of action control and providing, the " Intermediate Electricity and Mag- necessary coils are used and the netism," by R. A. Houstoun, M.A., H.F. choke replaced. D.Sc., It is a book the serious ama- Copstructors will no doubt note teur should have on his bookshelf in with interest that Messrs. Burne- order that he can from time to time Jones & Co., Ltd., have produced a A section of the Marconiphone Public refresh himself in what are the basic version or their very well-known Address gear with which the historically elements of his. hobby. A chapter on H.F. choke, which is suitable for sets famous York Minster has been equipped. electrical oscillations and waves is tuning from below 10 metres up to This amplifier can, if necessary, operate included. There are well -drawn seven loud speakers, including one placed and 100 metres. The choke retains its outside the building for the benefit of informative illustrations in practically familiar tapered cylindrical form "overflow" visitors. every page. 652 www.americanradiohistory.com June, 1928 MODERN WIRELESS The TRANSFORMER that NEVER BREAKS DOWN Nearly two years ago every one of Lissen's expensive transformers was withdrawn in favour of the present Lissen transformer. For not only does this one amplify fully every note, every tone, every harmonic, every overtone, but it never breaks down. Many tens of thousands of these Lissen transformers have been sent out. They are being used in all kinds of circuits in all parts of the world, including India. India has a notoriously had climate for transformers. There is a humidity in the atmosphere which has played havoc with expensive transformers of all makes and countries of origin, but the Lissen transformer has withstood the Indian climate without the slightest trouble. It has earned there, as it has at home, a reputation for never breaking down. You can use it in every circuit, no matter what other transformer may be specified. It will suit every valve, and it will give you full satisfaction all the time. You can test it for 7 days ! We challenge comparison of it against the most expensive transformers or chokes you can buy on money -back terms. You can return it to any dealerwithin 7 days of purchase and he will willingly refund your money if you fail to prefer the Lissen to any other transformer you have tested against it, no matter how expensive those transformers may be. PRICE Guaranteed for 8,6 12 months Turns ratio 3 to 1; resistance ratio 4 to 1. Use the Lissen transformer instead of any other transformer that may be specified in any published circuit, LISSEN LIMITED, 20-24, FRIARS LANE, RICHMOND, SURREY (Managing Director: Thomas N. Cole.) 653 www.americanradiohistory.com MODERN WIRELESS June, 1928 changes, and my set now consists of detector, one transformer -coupled L.F. and one choke -coupled L.F., with series -controlled reaction, and careful by-passing of all stray H.F. currents. 5 5 W is now- on the loud speaker at fair strength every night from 10 p.m. to midnight, and is much en- joyed. Unfortunately 8 p.m. here is midnight at home, and at the end of this month the introduction of Summer Time both here and in The Plain Detector -5 S W in England will increase the time dif- Chile-Regarding 5 G B, etc. ference to six hours. As there is no transmission as yet during the week- The Plain Detector light, but fades a good deal after dark, end we shall not be able to hear much while 5 G B is weak in daylight and of the Old Country during our winter. SIRSI am glad to see that MODERN varies from very strong indeed to We are anxiously looking forward WIRELESS has of late been devoting very weak night. to hearing some definite news as to more space to plain detector sets at Spanish stations are easier here than in the S.E. area, the promised extension of the times (some [and why not all ? ] for short- and often great of transmission, and if you could see wave work).. Given a fairly good at strength. French, Italian, Polish and German ,your way to publish an authoritative aerial (my own is 60 ft. long and stations are nearly as easy here as in Suffolk, statement you would be doing a great 40 ft. high), it seems that a good while practically service to a large number of Britishers detector will bring in any signal which everything N. or N.E. of is abroad. rises sufficiently above the general us very badly screened. Yours faithfully, level of X's, mush and muddle to be of Stations K D K A, W G Y, and any use on any set. It's a pity F. C. JAMES. 2 X A F are well received here later St. Mawes, stages don't refuse to amplify in the evening, but credit must be H.F. Cornwall. this background, but, alas, they seem undoubtedly given to our own home to delight in exalting it, and the station for the manner in which it 5 S W in Chile noisiest set I know is the 8 -valve comes through the ether. The latter super -het. SIR,-Your March number contains is " one low-frequency valve " better than If a detector set is made to work a comment to the effect that reports the Americans, and can be regu- larly depended upon, well down to 15 metres, will get good, of the reception of 5 S W, the new whereas the U.S. clear signals from 3 L 0 (Melbourne), short-wave station of the B.B.C., will stations vary in strength from night night. and very loud signals from 2 X A D, it be welcomed. to will work well enough on the ordinary On February 21st of this year I The broadcasting in this country broadcasting bands, and there is no completed a two -valve receiver on and the Argentine on ordinary wave- difficulty in designing a quick change- the lines of the two articles in your lengths is poor in the extreme, and over by shifting coils. Such a set, with 1927 Christmas Number. Within the atmospherics around 200-500 two good L.F. stages, is very satis- five minutes of testing out I was metres have to be heard to be be- *factory for any sort of loud-speaker listening to music from London, very lieved. Components are costly and work. clear in the 'phones, but subject to difficult to obtain, but short-wave Our " local '' station here is considerable fading. transmissions are opening up the Daventry, 250 miles distant, and we Since that date I have added possibilities of good reception here are quite 200 miles farther from the another valve and made various little by little. majority of European stations than London is, but the station -getting powers of such a simple 3 -valve set here compares quite favourably with your published reports of, say, the 5 -valve " Solodyne." The selectivity is, of course, lower, which doesn't matter here. The quality is equally good. My own 5 -valve " Solodyne " has been a " quarry for parts " for some time, and the general tendency here is to alter H.F. sets to plain detectors, in spite of our very unfavourable position. Cardiff, only 100 miles away, is usually inaudible on anything. Ply- mouth Relay (45 miles) is very strong, but heterodyned six deep. Bourne- mouth, at 170 miles, is moderate strength, but usually useless from interference. Of the two Daventrys. 5 X X is strong and reliable in day - \ Grk;nen erecting one of the giant masts at the new station at Teheran. 654 www.americanradiohistory.com June, 1928 MODERN WIRELESS ß rilTHIS special enlarged number of "Radio for e Million" is waiting for you ... send the coupon to -day. In it there are over 20,000 words of intense interest to every radio owner and a special message to those contemplating the pos- session of a first radio receiver embodying every modern refinement. e America on the The ta. Master Three Mikado P.M. The tens of thousands -a wonderful two `o of owners of this valve version of the It ^ amazing three valve Master Three, giving v' z pleasing, powerful so receiver are given in 00 -e.. this new issue the and certain results in 7Or magic key to the re- return for a minimum fb.°i ?oo ception of American, outlay of time and Continental and Aus- money. Anyone can P áo ''Ór tralian stations on construct the Mikado the fascinating short P.M. regardless of ex- c, Ó0 Com- r waves. Many letters perience or skill. 7d '.,._ Ì4ot rL, plete instructions and t0e from owners of Mul- d ,o s, simplified Blue Print ^`'0 lard P.M. Sets are are supplied free with . published describing every copy of this ; J' `,. ó .fi eP'. r \ remarkable trans - issue. Make sure of world results. your copy. \ \} \ \\ \ \', rs e +d 9d e %.??"o, \\ ' : Mulland \..:'.\.\ \ \ MASTER RADIO ss www.americanradiohistory.com MODERN WIRELESS June, 1928 I manage to get your valuable paper local station, and Birmingham had " My Broadcasting Diary" month :by month, and it is much nothing at all ? the article My appreciated. Sin,-In " Broadcast- With regard to his remarks about ing Diary," in a recent number of Yours faithfully, the new transmitter being fifty miles your always very interesting paper, G. R. JOHNSON. from London, if this is to be the case, MODERN WIRELESS, there is the Casilla 1874, is and it to serve both the South and sentence : " The only point Valparaiso, that the Midlands, I see no reason why concerns the public is that the Chile, S. America. those in the South should not have programme service should be the best to reach out as far as the thousands available, and that every possible Regarding 5 G B who live in the Midlands. It is the penny should be devoted to the fairest way-in fact, the only fair way. programmes." was very surprised indeed SIR,-I As a matter of fact, I believe the With this, to read the selfish and insulting every listener will whole- first Regional station is to be about heartedly agree. letter from Mr. C. P. Brown in your ten miles north of London ; if that is During the March issue. past twelve months not near enough for Mr. Brown, for a there has been a I am afraid that in his anger he great improvement 30 -kw. transmitter, I should like to in the programmes, and much of the has let himself go a little too far. know what he does want. Incident- In his remarks about 5 G B, he ally, the lot of the distant listener, says that it was made directional with this high-power station right because Birmingham " screamed," as on top of him, will not be very he calls it, when their local station enviable. was closed down. I should think At any rate, when the scheme is that one of the most important of the . ///N///// completed, Mr. Brown will have // provincial cities has a right to com- the / //%/ satisfaction of knowing that Midland plain when its local station is replaced listeners will have to reach about by one at some distance, which, as out 100 miles for programmes, if Mr. Brown himself admits, cannot be their one may go by the scheme outlined received at all well in Birmingham, ti4RTH in while almost every other large city the B.B.C. Handbook. It appears from while PLATE still has its " local." this that the Regional will all other In these circumstances it *as up stations be outside the shall be to the B.B.C. give Birmingham the principal cities, we totally to ignored. very best service possible from 5 G B. Mr. Brown speaks as though 5 G B As a matter of fact, although the position is pretty hoepless here with The earth -plate modification referred to in regard to crystal sets, and not too Mr. Barrow's letter on this page. good with valves, H.F. valves are certainly unnecessary to receive 5 G B present grumbling is unjustified. Still, efficiently, and 1 see no reason why there is much room left for improve- conditions should be different with a ment. But I much doubt if outside similar station the same distance from grumbling from listeners is going to London. effect much more without inside help at Savoy Hill. It seems to me that The fact is, I am afraid, that what is really needed is someone in Londoners have got a very inflated authority there who is really keenly idea of their own importance, and want absolutely perfect service at interested in the question-as a whole, and not just keen on one or two of the the expense of everyone else. Why, many types of programme which when there are only five stations must be broadcast to suit different available, should one be devoted tastes. At present, as of course almost entirely to London, leaving you know, there is no individual, or Board, only four to serve the rest of Great as supreme or central moving force Britain ? in connection this very Yours faithfully, with important branch of the work. The members of BARRY J. DAVIS. Corporation will have nothing Birmingham. the to do with it-and a very good thing, too ! Loud speakers are now being used exten- But surely there is one official who sively at railway termini for announcing An Earth -Plate Tip not only might, but who ought to platform arrangements. This illustration his shows the " announcer " at Liverpool SIIt,-I enclose sketch of a little make it the chief part of work-the Street. tip re earth plates, which may be Director -General. helpful to some of your readers. The Rumour is again afloat that Sir was quite efficient, but was made sketch explains itself. John Reith is retiring from that post. directional deliberately. I thought it By this means one can be certain This may or may not be actually a was well known that, owing to that nothing has gone wrong under- fact, but its persistence seems to screening from the 5 X X masts, ground, as the soldered connection is indicate that he is at least thinking reception was poor in one direction. always visible. of retiring. Would it have been fair to make that Yours faithfully, Cannot something be done to secure direction that in which Birmingham A. E. BARROW, someone as his successor who is known lay, when London already had its Bexley; Kent, :Continued on page 677. ) e5h www.americanradiohistory.com MODERN WIRELESS June, 1928 Equip your valveholders with SIX-S[ : TY VALVES The reception of -your receiver will improve out 4 -of all recognition Full Particulars, post free -Write today Advt. of The Electron Co, Ltd., 122-124, Charing Cross Road, L012.107Z, W .C.2. Tel.: Regent 4365 657 www.americanradiohistory.com MODERN WIRELESS June, 1928 TELEVISION NOTES OF THE MONTH Tins month television has for- ray oscillograph at the"receiver. Each Ideas " Stolen " saken startling technical pro- Month he makes an increase in the Baird says the American Telephone gress for business development. number of units into which he can and Telegraph Company have come When the whisper that Baird Tele- split his object, and each month M. out with several bright ideas he had vision Development Company, Ltd., Holweck is able to report an increase years before. Jenkins, too, says that had sold American rights " for a in the sensitivity of his screen or a some of his rights were stolen for the large sum " reached the Stock Ex- reduction in the potential necessary famous Washington -New York de- change, one pound shares which not between the filament and the grid. monstration by the A.T. & T. long ago were fourteen shillings leapt For 30 years M. Bélin has been experi- The telephone company turn round in a few days to £2 17s., and one menting in television. and accuse Jenkins of infringing their shilling shares rose to twenty-one patents in demonstrations he has given shillings. I know a man who sold his Patents First before members of the Government. shares and pocketed £135 profit. A man who has a television idea A case in the courts is threatened, and not the £10,000 needed More Boom to try it but it is the opinion in America that out, asked me the other day to offer both sides will wait to see who is the Sir Charles Higham has been en- the idea for him to a large electrical first to make money out of sets con- listed in the booming forces of tele- firm. The company are interested, taiM,ng the supposedly stolen ideas, vision. Going aboard the Leviathan but there can be no negotiations until and then the other side will act I on his way to visit New York and the inventor has received patents. Chicago he was full of his new subject. " We have seen so much trouble with Charlatans ! If present plans fructified, said he, inventors alleging that their ideas have Rivalry is a mild word for the feel- the Leviathan would he the first been stolen," said the head of the ing between some television investi- liner to be fitted with a floating company to me, " that now we will gators. Two I know call each other television receiving station. The American rights, he carefully ex- plained, had- been sold to groups of radio dealers, " instead of leaving it to big companies." The Other "T." ` I am going from tea to television.'' said Sir Charles. Sir Charles Higham, as you should know, is the publicity expert who went to America on behalf of tea producers and started the 4 o'clock tea habit over there. Looking Ahead One idea behind the amalgamation of the Radio Corporation of America (who joined forces with the G.E.C. for the recent television broadcast* to homes) and the powerful Victor Talking Machine Company is that all gramophones sold will be fitted so that they can be used to turn a tele- vision disc. News From Bélin This photograph shows so:ne of the apparatus used in Mr. Baird's London laboratory. M. Edouard Bélin, the famous French television experimenter, has not look at any proposition unless the charlatans. But I have been able to been seriously ill. He is well again inventor has himself fully covered by carry greetings between others over now, he tells me, and back at his work. patents." In television, when one thousands of miles, and several have He has not yet reached the limit move forward has been made, it is helped each other along in their of achievement with his oscillating surprisingly easy for several un- early days with the loan of light- mirrors at the transmitter and M. connected investigators to take the sensitive cells and similar pieces of Holweck-'s specially designed cathode - next step simultaneously. apparatus. 658 www.americanradiohistory.com June, 1928 MODERN WIRELESS continue to describe Mafeking night as though it occurred only the week before. It seems only yesterday, that time; when to be a wireless man was to be wellnigh as good as a wizard. Respectable householders looked at me as they would Iook at Dr. Nikola or Svengali, and warned their children " not to go too near." Why, I remember that when I demon- strated a wireless spark transmitter to an Indian prince in 1910 he was plainly in doubt as to whether he should clap me in prison or fall down MY radio career, as the attentive and re -imbibe all the radio theory I reader of these pages may had forgotten during twenty years' and pray to the spark. And now have remarked, has been a grappling with the facts, plus a lot skinny school -kids in England talk to Australia by radio. The bloom is off series of bumps and depressions ; but more invented by college professors of all the phenomena of that kind who never get nearer to the funda- the peach. with which it has enriched my ego. mental wickedness of radio than A Week-end " Holiday" is (and a lot more alphabet commend me to that one which x-y=e I was snugly ensconced in the 4.39 now a for to the same effect) I should not now to be described-like circle, " down " from Victoria en roule to have found myself wishing my name instance, round a point. I am the Pugglebury, where I was to spend the point. were Johnson, or Smiggins, and that week-end watching Tackham-vul- del A point, like a Scotch trader's dis- I lived in Tierra Fuego. garly called Tack-hammer-try to count, has no and no magnitude. There is no authenticated instance parts pick up 3 L 0 (Melbourne) on half a feel hide on record of a man who tried to teach I like a point. You could valve, no aerial, three volts on the me his how to put a safety - behind -an undergrown electron. grandmother anode, and plenty of imagination on My size in hats has- diminished so pin in a baby's plus -fours and lived greatly that I have not as much it down. Plato tells the tragedy of superiority complex as a window - young Epimondas, who asked Socrates cleaner's apprentice viewing the Wool- whether Xantippe married him or worth Building in New York. I wish whether he married Xantippe. Old I were the Invisible Man. Or anail Soc. cleared his throat and asked, by with a nice shell, double -convoluted. way of an answer, whether his Or a millionaire-when all of. me to (Epimondas') mother bore a fool for be seen would be four secretaries and a son or whether a fool claimed her my wife's diamonds. for a mother. He then spoke for a day and a Walk Warily night on the answer, holding Epi- Let me say now, because I shall be mondas; as the Ancient Mariner held "It was a ` smoker.' I am fond of feminine incapable of moderate expression by the Wedding Guest, " with his,glitter- society." the time I have finished, that (1) a ing eye." .And when old Sop: bad the tympanum of the ear. Tackham's lot of knowledge is a dangerous thing done with him, Epimondas crawled first wife divorced him in Reno, -especially knowledge of radio ; (2) off on all -fours and entered the olive- Nevada, for technical desertion. That at good deed xnay- be a bad egg ; (3) oil- trade forthwith, I believe I must would be about the time he swore he don't judge by appearances-a man be descended from Epimondas, des- got Writtle, when he was living at i.s often a bigger fool than he looks pite the fact that olive oil and. I have Portland, Oregon. On a bit of home- nothing in common. made galena, too ! Some men have no sense of shame or proportion. Times Have Changed - Only an artist can lie convincingly. Oh, I forgot ! - (No. 5). Beware It was a " smoker." I am fond o the inquiring stranger with whiskers. feminine society. He is bound to be a deceiver. Say Just as the guard piped all hands unto him " Baa ! " and let him go. aboard, some cretinous porter stuffed If lie has those half-and-half spec- the bloke and his baggy umbrella in, taeles, one half for reading and one followed him up with an unspeakably half for looking innocent, drop him disreputable suit -ease, rooked him as yon would a live coal. For a live for a " bob," slammed the door as coal from off the altar cannot bite as only an N.U.R. Communist can. and keenly as he. In fact, if you are wise, shouted " Br -way Goin' on, there' " I have not as much superiority complex as a window -cleaner's apprentice viewing you will either strangle him or change -a shibboleth which, I gather, is the Woolworth Building in New York." carriages. sacred to those attendant. on trains. The root of the matter is that 1 Then, I presume,' the fellow went (4) don't forget the smile on the failed to realise the passing of the home to Lambeth, devoured liver whale's face when he said of Jonah, years. It becomes increasingly diffi- and -bacon and beer, and took his " Lo ! he was a stranger, and I took cult to realise that as they mount wife to the " movies " to see " Blood him in." over one's head, and I expect that and Passion," featuring Helms. de hi If I had not been ass enough to go when I am a great-grandfather I shall Ghetto, née Bates. 659 www.americanradiohistory.com MODERN `lVIREI.ESS June, 1928 The intruder turned his back and blew his nose like blazes-he could the pride of a V.C., and then wept, whiskers on me, and began to stow his see I was passing through a crisis and whilst old G. coughed and choked suit case, umbrella, hat, muffler, three he showed sympathy l from pure jealousy. paper -covered packages, two books We had a great old time. I was and a rug on the luggage -rack, puffing The Lecture Continued at the top of my form and took the meanwhile like the Blue Train at rest. He ivas tickled to death and invited opportunity of inveighing against the This job being done, he flopped on to nie to his house. As I could not dine pretensions of college professors who, the seat, ran his fingers comb -wise at two places at the same time, I I said, " obtruded their absurd, through his chin crop and sized nie agreed to beg off from Tackliam's and academic conceptions into a realm of up with a pair of eyes which, seen from spend Sunday evening with him, so my side through his spectacles, might that I could explain amperes and have belonged to a bull. I took dielectrics at length. MODERN WIRELESS from my pocket Thus, behold me knocking at the and got behind it. . Lindens - old Whiskers' place - at After the lapse of half an hour I 6.45 p.m. on the Sunday. Quite a crept from my hiding-place and lit passable ménage. Quiet and respectful my pipe, laying the magazine open servants, bath, and clothes laid out and cover upwards on the seat. The ready. Grub ? Well, the old boy old boy focussed his lenses upon the knew the difference between eating picture. and the mere mangling of garbage. There was a- wife, I believe, but she I Commence to Explain " They clung together and cried like was almost as respectful as the house- children." " he " I observe Hem," clucked, maid. Very sad ! Probably a third that you are a devotee of wireless. cousin. knowledge opened up, explored and My son amuses himself with one of After dinner he and I toddled off made fruitful by the blood and sweat those-hem-broadcasting receivers, tó a room at the top of the house, of the practical pioneers.' Hot stuff, I believe they are called, and derives where he produced coffee, brandy, eh ? the most extraordinary effects." and cheroots, and bade lire continue At this they both dissolved into That word " effects " should have the lecture on radio. general ruin ; they clung together warned nie. I see it now, alas ! I took an immense amount of and cried like children-and filled To cut a tedious conversation short, trouble over hint because, as I told my liqueur glass again and I may as well confess that bit by him, lie was a clean slate for inc to again. bit I led him to believe that I am write upon ; because he was. not absolutely the B.B.C.'s text -book puffed up and arrogant with the awful I Meet Disaster on radio science. I now regret that superiority of the half -instructed, " This young man," said Chalps, I hinted that to the lay mind, his and because I could see that lie tried ' is a veritable tonic. I am enor included, the theory of radio is still hard to understand what must he itiously indebted to you, my dear as incomprehensible as is the Egyptian a very difficult subject. Yes. I told Gundlestuck, for bringing him to " Book of the Dead " to a Solomon hint all that. Every word of it. my notice. I am rejuvenated and Islander. shall not now require my usual " Well, well, well, well," lie said, Another " Pupil " summer vacation." with the suspicion of a chuckle, as lie He asked me to repeat my visit on I had arranged to sleep at Tack - the following Sunday, an invitation ham's, and when I got to his place I accepted, and told me his name I gave him a résumé of the whole was Octavius Gundlestuck. triumphant business. - When I arrived the second time I " Gundlestuck ? Chalps ? " he found that the party liad been aug- exclaimed in a tone of mixed joy, mented by another comical old daddy. horror, and incredulity. " Oh, my Name of Chalps. Old G. half apolo- dear, poor lunatic fellow, do you gised for foisting Chalps on me, but know who they are ? " said that lie did so much wish to " Oh, a couple of decayed City share his pleasure with his oldest directors, or export agents," I re- friend. And they nodded and winked plied lightly. at each other like a blessed pair of " May Heaven help you ! " he said. idiots. " It's a put-up job. Gundlestuck is " His eyes positively glistened with joy." Side by side they sat, all ears, a Senior Wrangler, a Nobel prize- spectacles and beards, as I held winner in Physics, Head of the Re- settled himself down like a chicken forth on the subject of radio for search Department of the National about to caress its favourite egg, or beginners. I pointed_ out all the Physical Laboratory, owner of in- !ike a fellow who is about to hear the pitfalls and snags which beset the numerable patents in radio, and Con- Will of his rich auntie. " Tell nie some- path of the unscientific learner. I sulting Radio Engineer to at least thing of these wonders." waxed almost inspired as I taught six Governments. As for Chalps, So I began by sketching lightly the them about oscillations, high -fre- he is the mathematical and physical electro -magnetic theory of light. It quency, and how the little electrons genius ` behind the throne' of the was all wrong, but I could see by his nip up and down. I was very profound new cable -wireless merger. Go home eyes that he thought it was top -hole. on " skin effect," and playful about and pray." By the way, lie was awfully consider- wireless waves. - I sketched a sine Beware of whiskers, pride, and ate ; when I got into the. stickiest curve on old Chalp's shirt -front. and old brandy, my brothers. I've had part of the theory he coughed and he pointed it out to Gundlestuck with some. cuu www.americanradiohistory.com June, 1928 MODERN WIRELESS Philips Transformer because special gives even amplifica- new materials are tion over the whole used for both core and range of music and speech windings to give the frequencies, because be- right results while keep- tween 200 and 10,000 ing the size within the cycles amplification is absolutely smallest limits. Consequently constant and at even as low as Philips Transformer ensures 50 cycles it is well over half of very rich tone and faithful re- the maximum. Intermediate production, prevents distortion and high frequency oscillations and maintains purity, takes are not amplified, because little space on the mounting beyond 10,000 cycles amplific- board and is easily fitted, even to ation rapidly diminishes Dexisting sets. The ratio to zero. The size is con- is 3-1. Dimensions: PHILIPSvenient and compact Base 32" x 1:; ". Height 2". R.3 Advert. Philips Lamps Ltd. Radio Dept., Philips Hcuse I 4$ Chu, C Roud, \l'.C.'. www.americanradiohistory.com MODERN WIRELESS June, 1928 VAM PI RE VALVES HAVE, during the past month, great care as to the layout and screen- been carrying. out a number of The results of some interesting ing, etc., so that no external errors H.F. measurements of different tests Ulrike the author ask, should be introduced, or where these are lose descriptions. ' -toss ratées needed ? " were unavoidable that they should be During these experiments I had By C. P. ALLINSON, A,M,I,R.R. occasion to remove the valve from the holder and much to my amaze- ment the H.F. voltage across the course, the most lightly damped grid circuit in the receiver. It is evident that in the case of the first H.F. valve considerable damping is intro- duced into the grid circuit owing to the aerial, while in the case of the detector circuit, of course, we have the rectifier damping, which can be of quite a considerable order. Marked Increase fiat The actual H1+. voltage between v!M grid and filament at V2 was 7 volts. This tuned circuit went up by an extremely was with the II.F. valve in large percentage. position, but with the filament turned The receiver that I was investiga- out. ting at -the time used the circuit On removing the valve, however, the voltage went up 9.5 which is shown in skeleton form in to volts, representing an increase of 36 per cent. Fig. 1 on the H.F. side. I was so staggered by this marked I have been carrying out some increase signal further investigations with this cir- in strength that I determined investigate whole cuit, and the result is a receiver to my stock of valves a view to deter- incorporating two stages of H.F. with which has given me every satisfaction mining the losses introduced by the in operation. various makes and types into a tuned circuit. compensated for in all cases, and The H.F. Voltage For this purpose special apparatus therefore not introduce any actual I was carrying out measurements was got together and assembled with errors as to the results obtained. on the experimental set, in which two stages of H.F. were employed, by coupling a local oscillator into the aerial so as to inject a signal of adjust- able strength. Readings of the H.F. voltage be- tween grid and filament at V1 and were being taken, and it was while some adjustments were being made that one of the H.F. valves was removed and the increase in voltage noted. The actual voltage being measured Apparatus used in the " Modern Wireless " research 'aboratory to determine the degree was that shown at V2, which is, of of efficiency of a tuning coil or unit, or an H.F. transformer. 662 www.americanradiohistory.com June, 1928 MODERN WIRELESS THE In DARK BLUE CONTAINERS COST St RVICE 60 VOLTS 7/ these Batteries provide 66 VOLTS 7/6 THE FINEST 99 VOLTS II'6 H.T. VALUE vo,TsGB v3 OBTAINABLE EVER READY BRITAIN'S BEST BATTERIES 9heir pure tone makes listening worth zneile www.americanradiohistory.com MJDERN WIRELESS June, 1928 Great care had to be taken, of , H.F. G-F - P -F course, to see that all the components Type Volts g No Load 1 2 3 4 5 1 2 3 4 5 used were really low -loss components, 3 Á 23 2-05 2.07 - - - 196 2-18 - - - since otherwise small additional losses B 23 - 2.05 21 1.85 - - 2-05 212. 1.8 which might be introduced by the á C 2-3 1D 2.12 1-95 1.55 - - 2.15 1.6 valve Ñ D 23 - 202 - 2-0 - - 2-03 - 205 or other component which I E 23 might be testing would be swamped ------ A 23 21 1-9 2-05 ' owing to a very high initial resistance á - - - 185 - - - B 2.3 2.04 2.0 2.0 2.1 being present in the measuring circuit. ê> ------e -C 2.3 -- 2-05 -- - - - 2.03 - - - The Testing Outfit a.' D_ 2.3 2.1 = - - 212 - - ' - E 2-3 2-1 - - - 1-8 215 - - - 1.75 Fig. 2 shows the theoretical circuit A 2-3 2.1 2-05 - - - 22 2-12 - - - of the completed arrangement. A * s s > B 23 215 21 21 21 21 21 2-15 2.15 215 215 low -loss coil L1, having an induct- a - - , - - ance of approximately "200 micro - C 2.3 2.15 This is a scree ned-grid valve. ó - - -. - - henries and an H.F. resistance of T.. c3 -D 2-3 --- 215 1.9 -- - - 2.2 195 - - 5 ohms, tuned' by a low -loss Variable E 2.3 1-95 - - 2.15 2.05 1.9 - - 215 2.05 condenser Cl; is coupled to an oscillator by a link circuit having a Fig. 3. The results obtained by the author, tabulated in a manner which make them convenient for reference. variable condenser C2 in series with it. By means of this condenser an be read. Actually this meter was D. A small -power valve. easy adjustment is obtained of the backed off so that a small change in E. A super -power valve. current could be noted with ease. The next column marked H.F. The chief purpose of this experi- volts is a reading of .the voltage ment was, of course, to get a compara - rive idea of the losses introduced into the circuit by the valves owing to dielectric leakage and the like. Two sets of measurements were taken, one between grid and filament and one between plate and filament. Interesting Results In order that the results may be clearly examined by every one I have amount of energy transferred from tabulated them in a comprehensive the oscillator to the tuned circuit. manner ill Fig. 3. In the first column Across the tuned circuit a valve we have the type of valve, 2-, -1-, or voltmeter is connected as shown, 6 -volt, while types A, B, C, D, and E while the components to be tested represent the `following types of across the timed circuit L1 Cl when are Connected across the terminals A valves. unloaded. It will be seen from this and B. A. High -mu high -impedance valve. that this value was checked up con- A milliámmet.er is also included in B. Medium -mu medium -impedance stantly so as to avoid am errors the plate ciri.mit of 'the oscillator valve valve of the H.F. type. arising owing to variations in output iii order tltil yhange in current might C. A general-purpose valve. f rom the oscillator. Column 1, which is subdivided into five columns, is the H.F. voltage obtained when the grid and filament of the valve were connected .across the tuned circuit ; 1, 2, 3, 4, and 5 represent five different well-known makes of valves. - Comparative Tests Column 2 represents the reading obtained when the plate and filament of the valve were connected, the same figures applying to the same make of valve. I would like to state here that I have not used any but the valves which -have the best reputation, and these give the results which are tabulated in this figure. Farther on I give some compari- sons between the best of the British valves and some odd Continental This is some of the apparatus used by Mr. Allinson in order to gain the interesting data on valves which I had by me, and the losses " embodied in the accompanying article. ;Continued on me 678.) 664 www.americanradiohistory.com June, 1928 IIOU1dN WIRELESS ` Ideal ' speaker reproduction for 37/6 «°\\%. British yteß fct°piiy ° a lßävlb$ teói ßc$11 so aße eD9` eg.é e i4ßaeß6 eseG. c°ßatvsy. ea a ca c iß e s Gof a baa e 10i 1 e,° es ßatteßsetse4eßaíe sZstt °f q a Qet 5ß c04°eßset t° Go°i( óc° 9c°at a e e oß' el % sc°st'- ben'a t oßSac The popular ` Ideal 44 ' Cone e°4a' áeets b`i t° ea G°ß cher tbe Speaker at a reduced price vyo e',aéa°ye a b °taeZ G ° Right from its introduction the popularity of the ' Ideal' cdst s Cone Speaker has been indicated by continually climbing a te a sales. This increasing demand has enabled us to revise production costs and we are now able to offer our 44 model e at a reduced price. Everyone who has heard the ' Ideal 44' is eloquent of the purity of its reproduction, its range of interpretation, its exceptional quality at either extreme of the scale. You would not believe that such a speaker was obtainable Specified for the at such a price, yet you can prove it to your satisfaction in COSSOR your own home to-day-your dealer is selling the ' Ideal' " MELODY MAKER" Cone Speaker at the new reduced price, 37;'6.1 l This price reduction applies also to the ' Ideal' Loud Speaker Kit, from which you can build up the ' Ideal .. 44' in your own home. For the home coustruet the Ideal' Four -Pole Balanced :Ir"rature supplied as n separate unit exactly as embodied in the Ideal 44.' Supplied complete with two padded washers on threaded spindle, 25/- AtOn. FaK yo,Y ql4DEAL K l>u eK of . to Co^`ens a coo C etiegYa4}ti seta ,.. _ ,,,," . please Ot ' .... ,..--'.. la. citd4'G`fLetilie El,t" ° Tension ''RddTtss.. .W. 44CONE lish, SPEAKER F. A. HUGHES & CO., Ltd., Dept.W31, 204; 6,Gt. Portland St., BLUE IF OT LONDON, W.I. www.americanradiohistory.com MODERN WIRELESS June, 1928 ez;%36gEgaeiageegeetepeeg?e,36Peeeegaeeeeegre year. When the subject was raised last year the Home Secretary said that, v RADIO NOTES AND NEWS OF while he declined to remove the ban, o THE MONTH he would be happy to consider the question as sympathetically as pos- eA feature in which our Contributor brings to your notice some of the - sible in light of such indications of D more interesting and important Radio news items. popular feeling as might be available. Conducted by " G.13." As a result, repeated applications by e the B.B.C. fon permission to broad- 2Jeeeeeteeeee,23 'jeezo ti-,, war 1- :r< 315 L - " 4 cast the Cenotaph ceremony have been refused hitherto by the Cabinet, but Radio Drama for the invisible " actor " cannot the Home Secretary has now reversed H1RR F1'ECHTWANOER, the become theatrical. his decision, and it would be inter- fainons German playwright, Indian Broadcasting esting to note what evidence has been recently wrote an article in available recently to make him change According to Mr. Eric Dunstan, the which he gave it as his view his policy in this direction. that General Manager of the Indian Broad- radio drama was a failure, and Mr. casting Company, a vast new field The Third " Eck " Qeorge Bernard Shaw seems to agree for British industry is lying fallow in According to " London Calling," with him. Drama, according to Mr. India. Mr. Dunstan, who is visiting a third member of the Eckersley Shaw, really depends as much upon England on business, said recently : family is to join the B.B.0 This is visna acting as upon words, and is " There lies in India a great èountry Stephen, well known for his scientific therefore beyond the reach of both with a population of over three research work with the Marconi microphone and cinematograph. We hundred million, where a service of Company. The other two Eckersleys are coming more and more to recog- broadcasting is the only thing which at the B.B.C. are, of course, well nise that invisible drama can only be can fill a vital need in the lives of the known. There is Peter, the chief presented by the human voice. Every- inhabitants. If we only reached engineer, and his elder brother Roger, thing depends upon the tone and half per cent of them we should be responsible for programmes A trio quality of the voice and of individu- able to sell one and a half million of Eckersleys at Savoy Hill should ality. The microphone magnifies and wireless sets " prove a strong combination. also suppresses. The difficulty is to get distinct variety ' in tone in the. Another Ban Lifted Not " Blithering Idiots " expression without -exaggeration, and The ban imposed on the broadcast- Captain Eckersley. at a recent to get it home it is personal quality ing of the service at the Cenotaph on lecture before the Manchester Radio of voice that unquestionably counts, Armistice Day is to be lifted this (Continued on page 668.) Modernise your Rel. No. DSP9 One SP Aerial Coil and' two Split 1926 " SOLODYNE "! Primary H.T. This LEWCOS Dual Screen Coil improves reception and makes tuning easier. Transformers, the You have 250-550 and 1,000-2,000 wave -length range in one unit. Panel last with Reinariz controlled, the set fits exactly into the space occupied by the old type of Reaction. Per unit three separate coils and bases. Perfectly balanced. Obtainable from stock through all wireless dealers. THE LONDON ELECTRIC WIRE CO. AND SMITHS LTD., £5 Playhouse Yard, Golden Lane, London, E.C.I. S DUAL SCREENED COILS sas www.americanradiohistory.com June, 1928 MODERN WIRELESS Take the Speaker on the lawn You will want to listen outdoors these coining summer days, but make sure that the long leads from the set will not impair quality or short the H.T. batteries. Connect the Igranic " C.C. " Output Units between the set and the loud speaker and the long leads will not have the slightest effect. The lgranic t ` C. C." Output Unit is a self-contained filter which may either be built into the set or connected externally to the loud- speaker terminals as desired. You will be surprised at the improvement in quality which it makes with even ordinary length leads. Price 21, 6 List No. J.563 gives full particulars. 149 Queen Branches: Victoria Street, Manchester, Bir- LONDON, E.C.4 mingham, Cardiff, Leeds, Newcastle, Works: Bedford Bristol, Glasgow. VALVE SCREENS HOLDERS "PAREX" NOW ON SALE THE "SYDNEY TWO" DE LUXE Highly polished and mottled copper screens, as specified 2, 6 Coil for same .. .. 7,6 Choke .. .. 4,6 WIRELESS THE "QUICK -CHANGE" FOUR Partition screen, highly polished and mottled .. 3,6 CONSTRUCTOR Coils as specified, 8, 6 each. "M W." Loading Coils, 7, 6 each. 1928 " SOLODYNE" Coils Short- or Long -wave, 15:- each. Wave -trap, 15;-. ENVELOPES 10, FeatherC.1.stone Buildings, High Holborn, E. PAROUSSIf Lond on, W. Phone; Chanccry1010 Envelope No. 1.-THE " RADIANO " THREE. A famous loud -speaker set which you can build in an hour or two-no soldering and a wide range of components to choose from. Building the 1928 Solodynes ? Envelope No. 2.-THE " CONCERT " FOUR. Made of 5 -VALVE MODEL' 3 -VALVE MODEL standard parts, all easily obtainable, this is a We claim outstanding advantages for This circuit specifies the " Cyldon " the special ' Cyldon" 3 Condenser highly -sensitive long-distance set, giving powerful Assembly. Greater selectivity, easier Twin Thumb Control Condenser. liming, better control, finer adjust- Price, complete with drums (00051 reproduction of wonderful quality on 3 or 4 valves. ment, and no extra drum to buy. Built as one unit on aluminium £2 7 u chassis. PRICE £3 12 6, or com- plete with screens, £4 10 0. for the 1928 Solo - Drilled Aluminium Bose. 7,6. Bébé Condenser Drilled Copper Base, 12;6. dynes. Price (-000r) 7,6 In these envelopes you will find every detail of the set simply Write for FREE explained, photographic reproductions and diagrams are I Booklet " Concern - IMMEDIATE big Variable included, as well as a full-size Blue Print. dealers" and Book- DELIVERY let of 6 Selected [3, ©RI Circuits, enclosing AVAILABLE 3d. in stamps fo;. AT ALL BOOKSTALLS Price 1/6 postoge. By post, 1/9, from Wireless Constructor Envelopes, the SYDNEY S. BIRD & SONS, LTD., Cyldon Works, Sarnesfield Road, Amalgamated Press, Ltd., Bear Alley, Farringdon Street, Enfield Town, Middlesex. London, E.C.4. . 'Phone : Enfield 2071-2 'Grams : " Capacity Enfield." www.americanradiohistory.com MODERN WIRELESS June, 1928 -o eecoormez000000000 " My audience, 1 am sure," he said, neers, whether they could suggest a RADIO NOTES AND " did not represent the average wave -length by which he could experi- g listener. NEWS OF THE MONTH D While knowing something ment so as to get in direct communi- about wireless, you know, they were, cation with him. A group of people, 2, -continued front page 666 e after all, amateurs. I fail to under- regarding whom suspicions were oßeoeeeezeezoGooGesß stand this sort of criticism. It is aroused by their persistent oscillating, incredible. What is 5 G B to do with wrote to the station emphatically Society., was rather badly heckled, Manchester ? 5 G B was only in- denying the innuendo, and adding and more than one speaker openly tended as an experiment. It was not that they had a private earth. charged the chief engineer with` part of the Regional Scheme, though And, finally, a lady wrote to Mr. insincerity when he gave answers to it will be crystallised into such. I Appleton the following : " Enclosed the questions in connection with the hope to get a twin wave -length is a copy of my aerial. Can I get attitude of the B B.C. to the satis- station close to Manchester to do for Cardiff ? " faction of reception from 5 G B in Manchester what 5 G B is doing for First Controversial Manchester. Captain Eckersley said the Midlands. As for the compls ints Broadcast The first he was at a. !oss to understand the of bad quality, I may say that for broadcast item under the new B.B.C. scheme which permits the attitude of his audience.. " Why do every letter of unfavourable criticism discussion you always :assume,'.' he retorted, the station receives here we get eight of controversial subjects was " that we are blithering idiots and appreciative ones.' decidedly interesting, and it was a good stroke in inviting Sir Ernest you are the wisest people on earth ? " Amusing Benn and Mr. He was asked why the quality of Anecdote James Maxton, M.P. (two very old reception in Manchester was poorer Mr. E. R. Appleton, the director of antagonists), to debate the question of than that in London; and he replied 5 W A, told some entertaining stories the problem of poverty. We hope that the Manchester engineers had about wireless at the Third Annual that more broad- been working on the matter, and that Dinner and Dance of the Barry Island cast debates like this will figure. in the programmes. a marked improvement might be Radio Club. The best story was, expected shortly perhaps, the one about the Scotsman Loud -Speaker Ban who wrote to the studio ,stating that Twin Manchester Station The York Watch Committee are lie was deaf in one ear, and asking if asking the City Council to adopt a Interviewed after his lecture, Cap- he`could have a 50 per cent rebate on by-law forbidding the use of a tain Eckersiey loud said, that he liked his licence. speaker " in such a Manchester mannes as to and Manchester people, One man wrote to the station say- cause annoyance to, or disturbance but as for being terrified of the criti- ing that he had a brother in Australia, of, residents or passengers." cisiñs in Manchester, he wasn't a bit. and asked Mr. Appleton, or his engi- (Continued on page 670.) For all that is A. Popular Condenser The Gambrell Neutrovernia is popular among constructors and designers alike for many reasons. Portable First, its remarkable efficiency. For really efficient working it has no equal. The control is delightfully smooth and in Wireless Apparatus you uniform over a wide range. (2/38 m.mfds.) Next, its construction. It is perfectly designed and constructed, cannot do better is dust and damp proof, and cannot short. It occupies minimum space and can be conveniently mounted on either than go panel or baseboard, and is ideal for portable sets. to- Then, its usefulness. The Gambrell Neutrovernia can be used either as a Capacity Reaction Control, a Balancing Condenser, or a Neutralising Condenser and will answer either purpose WILL DAY, LTD. perfectly. (The Best in the West) Price 5/6 each who always have a large GAMBRELL CENTRE -TAPPED COILS selection Because of their high general efficiency and of Portable Wireless the greatly improved results which their design ensures, Gambrell Coils are used and: Cabinets and Components recommended by experts for selectivity and in cases where the utmost results are to be obtained. The coils are completely enclosed ; OUR INTERNATIONAL RADIO CATALOGUE are fully insulated and absolutely dust (3rd edition) will be sent to all enthusiasts and sending 6d. to cover cost of postage and damp proof. Their use is not limited to packing. centre -tapped circuits. In any circuit requiring plug-in coils, " Gambrells " will ensure the finest possible results. Size 19, Lisle Street, Leicester Square, a? a A B1 R ' D El E P G Price - - 4;10 4 10 5,- 5,3 5'6 5;9 6,3 6/9 7,'9 8'6 10 Approx. No, of turns 18 25 20 40 50 75 100 .150 200 ist `,00 London, W.C.2. Centre -Tapped 6d. extra. Gambrel! products 1 eieplrone (2 Imes): Telegrams: are obtainable from all dealers. Regent 0921 and o922. "Titles, Westrand, London.' GAMBRELL BROS., LTD., 76 Victoria Street, London, S.W.1 C68 www.americanradiohistory.com June, 1928 MODERN WIRELESS IEKCO'S LATEST AND GREATEST- BRAND NEW PERMANENT TRICKLE CHARGER 52'6 RETAIL 411 accumulators safely, CHARGESsilently and soundly from A.C. Mains. Voltages of too to I zo or 200 to 25o with frequencies of 40 to too cycles in each case. Self-contained with a sturdy step- down transformer constructed of highly- insulated windings which supply required voltage and current to a Westinghouse Patent Metal Rectifier, that completely dispenses with the bugbear of valves and their expensive renewal. NO REPLACEMENTS OR MAINTENANCE COSTS ARE NECESSARY. Will last many years without attention. Size 6I inches by 4 inches by 4 inches. Efficiency guaranteed second to none. In metal case with extremely neat bronze-oxydised finish. Charging rate is amp. continuously to 2, 4 or 6v. cells. Charging rate when electricity is 6d. per unit is approximately 8o hours for 6d. hßq ,13?.GW TiiLfR Two models are supplied: 40-100 cycles. ( T.500a for 100-120v. 40-100 cycles. T.500 for 200-250v. ?ka7e&tit Oppeo'ia#we . K COLE J- LONDONROD, LEIGH ON - EA THIS SIGN INA I GOOD CIRCUIT EELEX 1 LIGHTNING SWITCH Safety First - protect your ,INDICATES DUBI LIER set during the summer months against heavy elec- trical discharges by fitting Dubilier Components embodied in a set an Eele: Lightning Switch. It's a combined switch, and make all the difference between moderate lead-in tube, waterproof results and results as good as the set is li'ith 6 -in. tube, 5,6 capable of producing. Though the circuit Postage 6d. to be built with efficient EELEX .EARTH BOWL is good it requires Improve your reception by using an components if its best is to be obtained. Felex Moisture Retaining Earth es it collects and holds all the available And Dubilier Components are not only moisture and is far better than a spike, good to start with, but their efficiency is or tube. steadfast. Write for List 548 to The Type 620 Mica Condenser J. J. EASTICK & SONS, illustrated is made in 21 different Eelex House, 'Dunhill Row, Chiswell Street, Price 4/ - standard capacities between London, E.C.1. With Oft. copper wire 0100005 and 0'015 at prices connector. ranging from 2,6 to 4.'6. They will take either the Parallel or Series Dumetohm Clips. Type 610 is the flat type Rest design, best materials, 1 of the same condenser. I \ lest workmanship. Answers esery requirement. Specified by leading set designers. Write for full details. "IDEAL" MODEL h ailt to accommodate any gone unit, complete with inner frame, baseboard, lock, nickel - THE CABINE,r plated fittings, etc. a ES Oak - 52/6 FOR PORT AWL Mahogany - 581- tidewatt' CARRINGTON MANUFACTURING Co., Ltd.. Cameo Works, Sanderstea9 D!.'!J..ER'i ©151 Road, South Croydon. .e: l: rogdna 4623 {2 line..?. Advt. of the Dubiliu Condenser Co. (1925), Ltd. North Acton, London, W.3 1u0 www.americanradiohistory.com MODERN WIRELESS June, 1928 that are bound up with animal tance away. I should add that since RADIO NOTES AND experimentation. Apparently the ad- the set was purchased none of the mission of controversial matter is NEWS OF THE to vital parts has been either renewed or MONTH have no meaning so far as concerns in any way repaired, this including -continued front page 668 those matters in which we are inter- the valves. ested." e o 3 !t e4`114` ß'Gcsoee3Go£ " Yours very truly, ` G. F. WALE America on L.S. Y." But if the 'fork Watch Committee Ealing, W.13. are going to gain their day on this One of the principal charms of wireless point, it is only logical to assume is its unexpectedness. PCJJ that the same ban must apply to Whether one is a skilled transmitter Until further notice P C J J, the gramophones, street organs, and little or merely a simple listener one is Dutch short-wave station, will trans- girls and boys practising on the certain, sooner or later, to encounter mit as follows': Tuesdays and Thurs- the unusual. Mr. G. F. of piano. Waley, days, 16.00-20.00 G.M.T. ; Fridays, Ealing, has just done so, as is ex- 23.00- 2.00 G.M.T. ; Saturdays, 15.00 Lecture "Turned Down" plained in the letter printed below. -18.00 G.M.T. The - Anti -Vivisection Society re- There can be no doubt about this cently asked the B.B.C. for permission being a fine achievement, with which I I I I I I I I I I I I I I I I I 1 to broadcast a lecture on the move- the skill of the operator has no doubt iJ I I I 1 11111111111111111111111111111111111111111111111111L` ment in its relation to public health. had much to do. All the leading authorities The B.B.C. carne to the conclusion Mr. Waley in his letter says : on that the subject was " I should like to unsuitable for inform you that , radio matter write for broadcast discussion. on Friday night, April 13th, utilising The " Anti -Vivisection Journal," a two -valve ` Gecophone ' set pur- POPULAR WIRELESS commenting. 'on the B.B.C.'s refusal, chased in January, 1927, I was suc- says " Why is one aspect, and one cessful in picking up Schenectady, the paper that made of vast importance on the subject. of America, which came through at public health, to be ruled out ? Even loud -speaker strength, at about WIRELESS POPULAR before the Prime Minister's declara- 11.45 p.m. Greenwich time, for over tion of the admissibility of contro- three-quarters of an hour with prac- E. versial matter for broadcasting pur- tically no distortions of any kind. CET A COPY NOW. poses, those who voiced the orthodox The voices were perfectly audible and medical views have been permitted understandable through the loud Every Thursday - Price 3d. to make reference to medical theories speaker, even at a considerable dis- IIlIIIIulunllnnInnuInunuIlnnlnnn1nllIIJnnInn11111r leAnd now FORMO- DENS OR A high-grade Variable Con- denser costing no more than a fixed condenser. For use as : U AVOX Neutralising Condenser The Originators of the Moving Coi/Speaker Aerial Condenser Grid Condenser FOR A.C. or D.C. Reaction Condenser Phasing Condenser Tone Control Condenser Type D80. Incor- Two Types. Baseboard porates line trans- and Panel (Baseboard former and dry illustrated) and a range rectifier giving a of 5 varying capacities. constant and un- failing D.C. supply for field of speaker. TRANSFORMER Equipped with field switch and input The transformer. Con- sumption 20 watts. Popular 0801. 100-120v., 50 -cycle, A.C. £11 11 0 D80 2. 200-240v., 50 £11 11 0 Type R5 for D.C. Mains, 100-240v. £10 10 0 Shrouded Model Type R4 for 8 -volt accumulator -4 amp. £9 10 0 All Magnavox M.C. IIr., to are equipped with input transformer and field switch. Ratios THE GREAT VOICE 1 3 fi err is the booklet you have beu waiting for- Il irty-two pages full of information, circuits and and illustrations. Tells cou all about Moving Coil Speakers, Pick-ups, 8/6 Power Amplifiers and Phono- 1-5 graph Amplifiers. Post free, 6d. Send for your copy to -day. The Rothermel Corporation, Ltd. Full details of all Formo Components including the " 1928 " 24-26, Maddox St., Regent St., London, W.1. LOG CONDENSER 'Phone: 'Crams: at 5,-. The Smallest, Lightest and Mayfair 0578 & 0579. Rothermel, \Verde, London most Efficient obtainable. Ask your dealer or send p.c. to Crown Works, Cricklewood Lane, x. W.2 THE FORMO CO , 7elephone: Hampstead 1757. 670 www.americanradiohistory.com June, 1928 MODERN WIRELESS Something new 9 1 1111-11 in Condensers Il._ LI I;/1`III-,._. Irl.11fú4.. n'fili I 11 PRICES : I I _ illl i Li ly , ít Supplied with pointer lit _ knob and drilling template. f,:ll I I1 11 '00015 mfd. 111 ._ List No. 312. II - _ Ip Also supplied in three Iñro'III; I'IÌ other sizes. List No. .la IIT II`J '0001 mfd. 311 319 II/ vl rhI. IIY 0002 mid. 313 613 I '00025 mfd 314.. 6;6 1 lisp Illustration shows the "Elfin" compared with vv the Bowycr-Lome Popu- OOv lar," itself a compact instrument. The I ULTRA -SHORT The smallest and Master lightest condenser WAVE COILS Three model made-the 'ELFIN` 00015 mfd. weighs A precision instrument of quality, ARE NOW AVAILABLE only 21 ozs.,and with a miniature logarithmic condenser. fully extended vanes Specially designed for reaction FOR THIS RECEIVER occupies only 21 x control or for tuning -in sets where ii" x2"behind panel. space is at a premium. Joe Bowyer -Lowe catalogues et Components and Receivers. Ask IF you are about to construct the BOWYER-LOWE Co., Ltd., Spring Road, Letchworth, Herts. Mullard Master Three Receiver you should remember that there is every reason why you should I I _ 1 I 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111V. Two Short Wave adhere to the author's specification. COIL -DRIVEN Coils : Space- ivound-2o to 45 SELECTIVITY to the highest degree metres, and 45 7/6 LOUD SPEAKER to 90 metres. Each. is easily obtained with Colvern Coils. Parts for Easy and Accurate Assembly. Broadcast Wave. RANGE depends to an extremely Accurate Space- high degree upon efficient coils, and it Improved Model " D," wound7/6to give is very important that these should pct of Parts for Mains, Ina simu nl rIh- ciency. Each. have a very low high - frequency £4:18:6 resistance. 'fo obtain this Colvern Long Wave. Coils are accurate space - wound. DE LUXE MODEL " E," Sectional wound Experience proves that the use of Set bi Parts for Mains, to give lowest Colvern Coils increases the range of a Consumes 60 Milliampa. high - frequency 8lJ ,.6 radio receiver. 6, 6 extra. resistance. Each. In the case of the Mas- I'or .lr,unmtlator, ter Three COIN -ern Coils give maximum Consumes 1 amp. Colvern Aluminium range on each of the three wavebands. Panel is also specified VOLUME is similarlydcpendent upon F. SQUIRE, for the Mullard the efficiency of coils. Logically, the 24, Leswin Road, Stoke _E \fasterThree Re- signal strength of distant stations is 'Phone: Cliueold 0334. Newington, London, N.16 ceiver 18" x 7"; greatly 14 increased by Colvcrn Accurate 1111111111111111111111111111111111111111111111111111111111111111111{1111111111111111111111111111111111111111111111111i gauge; 11 sprayed instru- Space -Wound Coifs. ment black ; drilled for vari- Therefore be advised-adhere strictly able condensers, switch and pane 7 6 to the author's specification, you will IT IS IT! brackets. Each. be most satisfied. THE LATEST 4 and 6 Finless Contact Foolproof Beco! Formers. Complete, ready for winding. NO PINS-NO WRONG CONTACTS. Can be fixed in the dark. i FORMER 6/-. BASE 4;6. LQOK Inland Postage and Packing, 9d. extra. N Inside formers for above HATEa 11 x ii" x 2t" 6d. each. Packing and postage, 3d. extra. ACCURATE SPACE WOUND As described and illustrated in Modern \\'Tireless, " January, 1928, issue. Write for Handbook on Circuits and Windings, fully illustrated-Price td. free. COILS post Sole Malter, : Colvern Ltd., Mawney's Road, Romfotí d, THE BRITISH EBONITE CO LTD., HANWELL, LONDON, W.I. 71 www.americanradiohistory.com MODERN WIRELESS June, 1928 amplifier of magnification factor 20 " It should be noted that the wave- impedance 20,000 length ç3 A THREE -VALVE PORTABLE and to 30;000 values shown in the schedule ohms, and, for the second a in 4 -continued from page 604 stage, and Fig. are given for the in- small power valve of magnification formation of the user, and are not factor 5 to 7 and impedance 40,000 intended to form part of the specifica- If the set refuses to oscillate, to 80,000 ohms. tion. The values of the shunted cheek the connections to the reaction You should have no difficulty in capacity comprise the self -capacity winding. Better still,. change over the selecting from the multitude of valves of the winding and its mounting, the leads, as this is easier than puzzling available two having approximately capacity of the condenser connected out the various direction of windings these characteristics. Of course, in parallel with the coil, and any and connections. Also, make sure with three -electrode valves the two inherent capacity in the circuit in that the valve is suitable for the Fila - inner grid leads are omitted, and if which the coil and condenser are dyne detector, although any general- 2 -volt valves are used, working from included." purpose valve should give results. a 2 -volt accumulator, the common In case the term " picofarad " is resistor will have a value of 12 ohms. new to any reader, it should be ex- Final Assembly plained that this is the term generally If the set works satisfactorily, as Mlv recognised by scientific bodies as it should do if there has been no fault 4 -, STANDARD COILS e denoting a micro-microfarad. -in construction, you can place it -continued froºn page 620. finally in position in the case, in A Simple Principle .which it should fit snugly, but not It will be noted that the standard a series in geometrical progression, as too tightly. The middle rail carrying designations of the coils are not based do also the values of the coils B.10, the doors, when screwed in position, on the number of turns of wire in the B.20, B.30, B.40, and B.50, and simi- will retain the skeleton rigidly in winding. - The number -of -turns sys- larly for the remaining groups. place without any fear of it shifting. tem of nomenclature is excellent so " These ratios of F5 between coils This middle rail is easily removed, long as all coils having the same in a group, and 9 between correspond- so that the set can be taken out number of turns have approximately ing coils in successive groups, have again without much trouble. the same inductance, but unfortu- been used in calculating the values Having connected up the loud nately owing to differences in design shown in the schedule. The values speaker (+ terminals to H.T. this is not the case, and, as a matter there given, however, have been you can try the set in its completed of fact, in some instances the number rounded off for the sake of conveni- form, and it should work as well as of the coil does not correspond even ence. Should it be desired to calcu- it did on its trial run. This time, to the number of turns ; a No. 50 of late the values to a greater degree of however, you can walk about the one make being called a No. 50 coil accuracy than as shown in the room with the loud speaker working merely because it is more or less schedule, such calculation should be at full volume ! equivalent in wave -length range to based on the exact values of the coils There is no consumption of current, a 50 -turn coil of another make. in Group B as shown below, either L.T. ór H.T., when the switch this group When once the simple principle having been as the basis for all is in the "off " position. If yóu taken underlying this system is understood. calculation. require to use 'the 'phones,' remove it is claimed that the standard desig- the pieces' of wire shorting the Winding Self -Capacities nations will prove to be more useful terminals B and C, and connect " The figures for other groups are and comprehensible than the number - the 'phone tags to A and C. obtained by successively multiplying of -terms system or any other system The valves required are : For the or dividing the inductance values by having a physical relation to the first L.F. stage an ordinary L.F. 9 and the wave -length values by 3. properties of the coils. "Utility " "Utility" LOGARITHMIC MICRO - CONDENSERS DIAL By using light thimble insulators with walls An aluminium dial and only 31 inch thick we hair -line cursor has have minimised loss in simplified the reading these switches. Ball of this dial to a very bearing spindle and pig marked degree. Read- tail connection are other COMPONENTX ings may be taken desirable features. clockwise or anti -clock- Capacities from '000z wise (a necessity when to at prices used with S.L.F. Con- '000s Never -varying quality densers). From 7/6 7/6 You should definitely refuse substitutes for " Utility " products- NOTE: We still list our there are none other that can show such a standard of unvarying very popular plain model at 7/6. high quality. Most high-class Wireless Dealers have "Utility " Components in stock, but, if you wish, we will send you a List including No -Capacity Change -Over Switches; Low -Loss and Neutrodyne Condensers, Micro Dials, etc., by return of post. Every "Utility" line is guaranteed. WILKINS & WRIGHT, LTD., "Utility" Works, Holyhead Road, Birmingham 672 www.americanradiohistory.com June, 1928 MODERN WIRELESS should now be decreased somewhat in value until the set is just stable, :3 THOSE CLASSICAL and after this it will be found a BROADCASTS perfectly simple matter to tune in Crystallised in -continued front page 606 ' E any station within reach of the receiver either. on the upper or lower "CELESTION" wave -lengths. Take the great B Minor Sonata by For the best possible results as are the 6 essentials Liszt ; in this work Liszt gave a musical regards long-distance work you will, of Ideal representation of the good and evil course, probably like to use the of the in himself-good and evil at war with variable resistance as a regular Loudspeaker each other ; and the tranquil ending reaction control, and in view of the suggests that the old Abbé Liszt at characteristics of the circuit this will least came out of the fight fairly at EVEN RESPONSE. be found to be delightfully smooth Not only on the low, but on the peace with himself ! One wonders, middle and the high frequencies, assuring and constant. natural reproduction from both speech after reading his life story, whether and music. he did ! A Curious Point EXTREME SENSITIVITY. Chopin's music is, of course, so, ( A curious point which will be found Sensitive to the output from the poetical and so full of melody that weakest set. with this circuit is that the H.T. few listeners who have even the voltage on the detector valve has Ç ADJUSTMENT. slightest " taste " for music can say Ability to produce weak as well as practically nee influence whatever on very heavy signais without readjustment. that Chopin is dull or highbrow in the the reaction control. I carried out . condenunatory sense. But Bach is IÇ UNAFFECTED BY CLIMATE. an experiment with this receiver in Impervious to humidity and changes difficult to appreciate unless one is of temperature. which I put 120 volts on the detector prepared to concentrate, although not and then reduced it to nothing at all, ei IMPROVES WITH AGE. so difficult to appreciate as some of Improves and does not deteriorate rather, to 6 volts to be exact, by who, like or, with the passing of the years. the ultra modern composers taking the high-tension positive lead Bela Bartok, seem to delight in a ig DISTINCTIVE APPEARANCE. to the positive terminal on the low- loudspeaker breathes cacophony of sound apparently An excellent that tension battery. craftsmanship in appearance, so careful means nothing and sounds like a and capable is the workmanship wrought It was found, however, that the upon it. a Froth- thousand tom -cats having went into oscillation at Blowers' detector Reunion. almost exactly the same setting on AND, TOO, IT IS BRITISH Appreciating Technique the variable resistance which controls it, while the use of a different valve, As for chamber music, I will say from a very high -mu valve down to a nothing. One must forbear to suggest power valve, hardly affected the listener can learn to how the average oscillation control either. because it is enjoy chamber music, The only point which does affect really a matter of individual taste. it is the use of different voltage valves. But even chamber music which is Thus a 2 -volt valve and .a 4 -volt not " can be enjoyed if you " tuneful valve will have a different reaction can learn to appreciate the technique demand from each other and also which goes to the planning and com- from a 6 -volt valve. position of some of, say, Mozart's chamber music. Chess probably means On the Long Waves nothing to a man who only plays golf a man who plays Bridge could The number of turns I have given =but therefore, easily learn to appreciate chess. for the reaction winding, The analogy may seem obscure, but is the maximum number of turns MODEL C.12. which will be required, and with the it is there all the same ! particular voltage valves which you Models range in Oak and Mahogany may be using you may find it an from £5 10s. to £25. -3e4; ez-:g4..2veezez:rz,?e 3*? advantage to cut it down a trifle. Write for illustrated folder and OPERATING THE For the long waves the operation also for new Gramophone Pick-up "EASY -TUNE" FOUR will be found exactly the same as on leaflet.. -continued from page 644 the short, and the only difference that e may be noticed when the long -wave coils are plugged in instead of the wave -lengths (about 480 metres), and short-wave is that the setting of the the adjustment should be made so reaction resistance has to be altered that the receiver can just nicely be a trifle. By following the details ELESTION made to oscillate with about three- given as to the coils, however, there quarters of a turn to spare on the will be no need to readjust the neu- The Very Soul of dfusït variable high -resistance. tralising condenser. If, however, you Write to Dept. FI Having made this adjustment it wish to experiment with the long - THE CELESTION RADIO CO. will be found that when the dials wave coils, then it should be remem- Hampton Wick, Kingston-on-Tham's of various are adjusted to tune the circuits in bered that readjustments Showrooms: French Agents & CO. the neighbourhood of 280 metres, descriptions may be necessary when 33/33 VI`LLI ERSST;. I CONS PARIE that the receiver will probably oscil- changing over from one type of coil 'ate a little The variable resistance to another, :;s www.americanradiohistory.com MODERN WIRELESS June, 1928 c[ !?' f'^G'=f:h((^^ Mi[±.L:`h ^' 4t4'KJ-u'nJ'.ii',iJ54J'4r'V'YGr-U'ìrwc"in W'w"4Yi)- upon densely -populated, parts. The majority of stations existing to -day 4` HO?J4'YOUR BROADCAST ---_3 4.;' D0 produce a " wipe-out " area over large IS PROVIDED cities. A reduction in field strength -coali,,rd fro,,, , ,,,7, G1- under the new scheme may be right Wireless oll scientifically while wwWwwtJ`ú .__rmr z.f,yti. wrong psycho- ov r the house logically. from your are available channels. Thus, if Two Receiving there are ten available channels, one Problems wave -length might be allotted per- It is better, therefore, to arrange manently to the lighter type of enter- for the least possible reduction in tainment, another to news, another actual signal strength in any area, to symphony music, another to and, even if this results in interference modern music, another to opera, and between two programmes, this is so on. From a programme service better than that the ordinary listener INCREASE the should hear nothing. There are two en joyment point of view such an arrangement might be considered ideal, but techni- receiving problems to face when and comfort of changing the distribution system to good reception. cally it is unsound. Firstly, the power of the station would have to be of the dual -programme type, viz., sensi- Don't have a tivity and selectivity. It is important good set and hundreds of kilowatts, and even then the service area " might not extend that the general level of signal strength restrict it to one on change -over be as high as pos- room. Recep- more than 100 miles owing to fading. There would be an enormous " wipe- sible. The listener will soon equip tion from your himself with the necessary wave -trap. Cossor Melody out " zone in which the use of highly Maker can take selective sets would be necessary if place in every any other foreign station were re- room in the quired to be listened to. Dense centres VALVES FOR house indepen- of population are apt to be found 300 fl PORTABLES - and 400 miles apart. and it is almost dent l y-simul- 2 -continued from page 64,8 taneously-a n d essential to give an " A " service area £a without interference, if you fit a over large towns and cities owing Lotus Remote Control. to the prevalence of electrical dis- of the set than the ordinary H.F. turbances of all sorts in such localities valve, which may or may not be You can wire two rooms yourself and because " A " service areas have neutralised. in half an hour at a cost of a few previously existed there. As in a portable receiver both shillings. Ask your retailer space and weight are considerations, for a Always an Alternative free blue print or send a postcard I would not advise you to use screened - to the makers. On a single -programme service grid valves which need careful and there must be as many centres of heavy metal screening, and inciden- For your " Melody Maker" you distribution as there are available tally would need more H.T. on their need :- channels. The provision of alternative anodes than the normal H.F. valves. programmes makes it necessary to So in a portable set which is to employ t Lotus L.T. & H.T. Relay, divide the number of wave -lengths an H.F. stage we would usually 2 Filament Control Wall available by two in order to obtain decide upon an ordinary H.F. valve, Jacks, 2 Jack Plugs, 21 yds. the number of centres of distribu- which, of course, can either be 4 -strand wire .. 30,/ - tion. resistance- or transformer -coupled and Similar outfit, but for set The above reasoning underlies the neutralised. using H.T. Eliminator, 45!-. proposed so-called "Regional Scheme" This wires two rooms. Each for broadcasting in Britain, in High -Mag. Detector additional room 7'6 extra. which existing stations will be done In this case a valve having a away with and replaced by high - moderately high -magnification factor power twin -wave -length stations out- should be employed, so that as much side cities previously possessing single magnification as possible can be ir 27C1UrS transmitters. The scheme assures to obtained from this H.F. stage. REDE every listener an alternative pro- The detector valve, if resistance - cornet' gramme, gives to the selective valve - coupled to the next, as it often will be set user a choice of as many pro- in order to keep down the weight, Recommended by the designers o)' grammes as may be occurring simul- may use anode -bend or grid -leak the Cossor Melody Maker. taneously-although some will fade rectification, the latter giving a little Made by the Makers of the famous and be interrupted-and makes the more sensitivity, but in any case a Lotus Buoyancy Valve Holder, field strength over the country as fairly and Lotus Vernier Coil Holder. high -mag. valve should be uniform as possible. employed. It is assumed, of course, GARNETT, WHITELEY & CO., Ltd., It is' important in choosing sites that the portable receiver owner is Broadgreen Road - LIVERPOOL for these stations to take account of not aiming at the quality of recep- the dislocation that will inevitably tion that can be obtained by a occur. Scientifically it would be right very up-to-date receiver which may to site the station so that the " wipe- contain any number of valves, out " area fell upon sparsely -popu- and have high anode voltages. One lated, and the " A " service area (Continued on page 675.) 674 www.americanradiohistory.com June, 1928 MODERN WIRELESS e Convincing Proof!!! VALVES FOR The claims which we have consistentlyng madH.T. for Self-Regenerative PORTABLES brings DRY BATTERIES arS e upheld 1716 by the leading " Wireless " publications. -continued front page 674 g y Read these interesting extracts from BaTc Ae test" reports. R.K. From ' Modern Wireless," April, 1928. " We have just exhausted a 60 -volt ILT dry Loud Speaker battery submitted to as for test by Messrs Ripaults Moving Coil Ltd. . . Model C.M. Standard typo which retails 17;'6.) at 10/6. We found that the capacity would cannot expect in the space at one's (Balance in 11 monthly payments of give the battery a life of about 6 months if it were disposal, and with the small loud Above payment fer R.K. Loud Speaker Unit only. operated at 4 hours a day regularly during this - period.'' From " Popular Wireless," March 3rd, 1928. speaker that one must use, to be able " The actual battery we have had under test is the Triple-capacity type, Model H.M , a 90-colter which to obtain the quality from a portable sells at 29/6. On the test we gave it wo exceeded the maximum discharge advised and after delivering receiver that it is possible to get from a current of 21 miliiarnps for well over 300 hours the battery is still capable of doing somewhat a well -designed household broadcast lighter work for some time. It will be seen that Messrs. Ripanits have not overrated their battery set. and have, in fact, given a conservative estimate of its life. We have also tested one of the smaller So a certain amount of quality is types and find this similarly satisfactory. They quickly depolarise and give consistent and long service." bound to be sacrificed, and one must From '' Wireless World,'' May 2nd, 1928. " We hope that other dry battery makers will make up as far as possible on the Messrs. Ripaults' lead and come out into the open with details of the average life which may be sensitivity side by. using fairly high - expected from their cella. In preparing this comprehensive table the makers magnification valves. For instance, must have realised that they were panting into the hands of the purchaser a means of checking the in the detector stage in an ordinary performance of his battery, and flits in itself ins - plies unusual confidence in the consistent quality of broadcast set one might use a valve their products." Copies of complete test " reports, including the of 13,000 to 20,000 ohms, but in the " [Fireless World" discharge curve, will be sent Free to all who write us and mention Modern case of the portable set, especially Wireless." Ask for " Tests " and Chart 31W, 90. RIPAULTS SELF -REGENERATIVE if it is resistance -coupled, one can do H.T. DRY BATTERIES very well by having a valve with a Give 50 % Longer Life magnification factor of 35. (As used for the " Roadside Four " and many other excellent sets). Handsome Polished Console Cabinet in Mahogany, The L.F. Stages Dark Oak or Golden Oak. As illustrated. This may cut off a little of the high Cash Price £4 : 4 : O notes, but that will not be noticed in Or 12 monthly payments of 7/9. a portable set like it would in a R.K. Loud Speaker and Cabinet. As illustrated. Cash Price £ 13 : 14 : O really up-to-date indoor receiver, Or 12 monthly payments of 25/3. 1, KINGS RD., ST. PANCRAS, N.W.1 while will give a far R.K: Loud Speaker and 6 volt 40,`80 uncharged Accu- it certainly greater mulator. magnification, and a high -mag. valve Cash Price £11 : 18 : 0 is worthy of its position in this stage. Or 12 monthly payments of 21/9. Or with Trickle Charger instead of Accumulator, Cash Coming to the first L.F. stage, we Price 112 4 0, or 12 monthly payments of 22/6. 7heNVj foryour> find that here resistance -coupling or R.K. Loud Speaker, in Console Cabinet, and 6 -volt E 40,80 uncharged accumulator. transformer can be employed. Here ( j- jWIRELESS SET Cash Price £16 : 2 : O a little more care is necessary, and Or 12 monthly payments of 29/6. Owing to expiration of lease and ultimate re- grid bias must, of course, be em- Or with Trickle Charger instead of Accumulator, Cash moval, we have decided Price £16 8 0, or 12 monthly payments of 30/3. to reduce our large stock of ployed, but a valve with a magni- STANDARD WIRELESS fication factor of 20-35 can be used 3 -Valve Amplifier, for use with R.K. Loud Spea4er. CABINETS and we are To work from A.C. Mains Complete with H.T. Elimina- making in this stage if resistance -coupling tor and valves. No Batteries required. Cash Price £21 : 10 : O GREAT REDUCTIONS is employed, for with the majority Or 12 monthly payments of 39/6. DURING JUNE of portable receivers there is no fear Complete Outfit, comprising R.K. Loud Speaker in Seize this opportunity at of badly overloading at this stage, Console Cabinet, Amplifier and Valves, Eliminator and once. Prom £3 15 O. Trickle Charger. No Batteries required. To work off Write to -day for descrip- especially if a frame aerial is employed A.C. Mains. Co. tive pamphlet and sug- MAKERIMPORT gestions for adapting your as the pick-up. Cash Price : O : O Dept. 2, £38 receiver or panel in our Or 12 ;aonthly payments of £3 9 6. 50a, LIVERPOOL Standard Cabinets. If this stage is transformer -coupled, Lord Street, Immediate Deliver a transformer having a fairly high - Prices quoted apply only when .Amplifier is used with a gramophone. if used with Radio Set, add £2 10s. to impedance primary should be em- cash price, or 4/6 to each instalment, to coter Marconi ployed and a valve of about 12,000 Royalties. The World's Finest H.F. Choke ohms to 20,000 ohms impedance can QPECIALLY r e c o be used. This will enable a reasonable / mended for all receivers with 2 or more stages of magnification to be obtained, and lip. because the Climax v binocular method of wind- will enable the owner of the set to ee ing gives no field effects. O Y The only effective A.P get as much range out of the receiver Choke for both long and as he can. Y el'see' short wave work. ti4.2 High self inductance. Low self capacity. One -bole fixing. The Last Valve Ideal as anode or re. °17ie. ' action choke in any The last valve is always a probleni circuit. The Climax when one is designing a portable set, H.F. Choke 8e for here one has to watch the question i Prom all dealers. " Insist on the name 'CLIMAil.' ' of overloading even more carefully PETO -SCOTT CO., LTD. than one has to in an ordinary Climax Radio 77, City Road :: London, E,C.1- Eleetrie,Ltd., broadcast receiver, because the H.T. Quill Works, Branches: ' voltage is limited, in fact, I may say, CLI Putney, LONDON -62, High Holborn, W:C.1 rsrm'lllltits S.W.15. it is very limited indeed, because if A YEAR AHEAD LIVERPOOL --4, Manchester Street. (Continued on page 676.) 2781 675 www.americanradiohistory.com MODERN WIRELESS June, 1928 merely wish to point out that in the VALVES FOR majority of designs of home-made sets e a certain amount of quality has to be PORTABLES sacrificed in order that sensitivity r;, -continued f,-.,;, ,,,, r;. of a fairly high degree can be obtained. r.s. Care Must Be Taken one uses a super -power valve in the This is inclined rather to militate STANDARD WET last stage of a portable set, this valve against the quality-not seriously, H.T. will probably take anything from In "Unibloc" container as shown. - perhaps, but it is bound to suffer Assembled with detachable terminals. 15 milliamps upwards, so that one slightly. So in designing your port- 43 volts, 15x 8x 41, No. 1 cells, ; No. 2, 1. 18/- 22 would have to use more , bulky 48 volts, 15x 8x 51, No. 3, 31/9. able set, and in choosing the valves All containers fit in one another to make up to H.T. batteries in order to last for for it. you will have to choose between any voltage. (Lid for top tray, 116.) Also complete batteries without containers any reasonable length of time. sensitivity and quality, or a mixture thing, For 2 - Valve Sets 3 to 5 -Valve Sets Sup e r Sets Now, the best as a rule, to of the two. If you go all out for A.4. 90 volts 0.6. 108 volts F.6. 126 volts do in a portable set is either to use an 24/10 3816 69/3 sensitivity and do not worry about All Spare Parts at Raymond's. List free, ordinary power valve having an quality, then use fairly high -magnifi- Ebonite cut while you impedance of somewhere about 5,000 cation valves as far as possible. If STAR TUNERS wait at Id, square inch, also 5 in. at id. ohms and grid bias it very carefully, you want quality and not much New Reactive Model. Only the best supplied. W. L. 150/2000 metres. No cheap rubbish. putting as much H.T. on it as is pos- sensitivity-that is, you do not want Complete with Dial' Keystone (Peto-Seott) sible, or to use the super -power to use the a Post Free. 2/6 Midget -0001 Conden- set far from broad- ser, 5/6; Neutralising with average batteries and not expect casting station-then use valves with COSSOR, B.T.H. 5/-; Six -pin Base. 2/9; MIILLARD, EDISWAN, Standard Wave Trap, them to last too long. fairly low -magnification factor, grid SIX -SIXTY, MARCONI 15/-. VALVES. Burne-Jones (Magnum) bias carefully, use plenty of H.T. 11.F., L.F., R.O., 10/6. 000025 Neutralising Don't Expect Too Much f-¡ Power, 12/6. Super Power. 5/- Coil Plug on Base, 4 and design your circuit accordingly. 20/-. 2-v., 4-v., 6-v. all in Terminals, 1/9. ALL The quality will not be quite the stock. PARTS STOCKED. same in the former case as ob- that _Illlllllllllllllllllllllllllllllllllllllllll11llilllll COSSOR MELODY MAKER tainable from more carefully chosen lllilllllllllllllli_ GENUINE COMPONENTS FREE 2 Ormond 0005; 2 Do. apparatus, but it can be reasonably S.M. Dials; 6 T.C.O. Con- WITH PARTS densers, .001, 002 two good, and as the signal strength from BUY BRITAIN'S -0003, -0001, 2 m{d.; 2 Drilled High-grade Grid Leak Clips, B.B.; 1 a portable set is never expected to be 21x7 Polished Panel Var. B.B. Rheostat; 3 Grid Leaks, 25, 3, 4 Meg,; 3 that obtained from the larger broad- Leading Radio Weekly and Strip, 5 - ply Lotus V.H.; 1 Ferrante A.F,3; 2 Panel Switches; cast receiver of a more bulky type, Baseboard 21 x 9, I Cossor Melody Wound Wood Screws, Pair Coil; Terminals, Name Tabs, the power valve will usually handle Glasite, 9-v. Grid Bias. quite sufficient for ordinary use. "POPULAR WIRELESS" Panel Brackets. : ABOVE FREE WITH KIT £4 10:0 kit. After all, a portable set should not Carriage 21- the paper that made be expected to give enough volume WE ARE OPEN New 100 -page cata- ALL DAY SATURDAY to fill a dance hall or anything of that ALL DAY THURSDAY logue. Profusely and you should WIRELESS POPULAR ALL DAY EVERY DAY description, find that Hours 8.30 a.m. to 8 p.m. illustrated. Post an ordinary power valve suitably Sat. 8.30 a.m. to 9 p.m. FREE Sunday morning 11-1 for postcard. biased in the last stage will operate CALLERS OR POST ORDERS the loud speaker u.suallyincorporated Every Thursday Price 3d. We stock all available lines in Wire- in such a set with every satisfaction. less. LET US QUOTE YOU PLEASE. Make out list with names and makers. It is largely a matter of choice, of On Sale Everywhere READ THIS. course, whether one has range or PLEASE I I 11111111 III III III 11111 II I quality in such a set, but it should be lilI liii liii 11111111/I I ill WITH ORDER OF remembered that ultra good quality should not be expected from any But if you want a mixture, then you should follow the lines that I have 301 (or more) portable set, because the loud speaker whole laid out. Use valves of fairly high ONE ARTICLE ONLY ON ANY ONE and the design of the set rather militates against super quality impedance, but do not go too high, ORDER being obtained. especially in the last stages, and YOU CAN BUY FOR always employ as much H.T. as is 3da The True "Portable" practicable. Do not forget the grid Any one of the following Articles. When talking about a " portable " BRAND NEW. bias, and remember that in the Retail value 2/- to 5/- each. receiver, I mean that type of set that majority of sets resistance -coupling Kindly Select and enclose 3d. extra. can be carried about with 'ease. I is almost as sensitive as transformer SOLD ONLY AS AN ADVERTISEMENT am not referring to a receiver that is with a good valve, and it is much Vernier Dials -2 volt Detector Valves trcu,cportable, and can with difficulty cheaper from the point of view of -60 "X" Coils-Set of 3 "Sutra" Anti - Micro Valve Holders -2 mfd.Mansbridge, be carried from room to room, and H.T. consumption, and is usually ' Sutra" or `Forward" L.F.-Jewel Indoor Aerial-H.F. Chokcs-Set of which is norlhally used as an ordin- lighter. eight 6d. Engraved Terminals -100 ft. ary broadcast set. This article is So that an H.F. stage and grid -leak 7/22 Coppet'-`0005 or '0003 S.L.F. Variable Condenser. devoted solely to the question of the detector, followed by two resistance, SEE FULL PAGE " W. CONSTRUCTOR," JUNE outdoor portable, so that I do not or one resistance and one trans- want the reader to get the idea that former, if the transformer is not all portable sets, or, rather, all sets bulky, forms an ideal four -valve K. RAYMOND that are called portah,.l:., must neces- portable receiver, provided the design sarily give mediocre quality. 27 & 28a LISLE ST., LOIYDO i, w .C.2 and choice of valves and components Come to Leicester Square Tube. There are " portable " sets on the are given due consideration and IMPORTAN , -This address is at the back of Da iy's Theatre. Be sure it is RAYMOND'S 'Phone Gerrard 4637 market that give excellent quality. I careful thought.. 676 www.americanradiohistory.com June, 192b MODERN WIRELESS teecegegegeeeeemeegeo ti WHAT READERS THINK FOR EVERY e -continued from page 656 TYPE OF VALVE to be really keen on " this Programme there is a " Peerless " Junior Rheostat. No rheostat will give you easier or finer control. Business ? " An outsider would not A definite OFF position makes short circuiting do-it requires someone who thor- an impossibility. The current of two valves can be safely carried. Silvered dial, one -hole oughly understands studio and micro- mounting, size Ir diam., }" high. Resistances 3, 6, Io, 15 or 6o ohms. phone work and requirements, in a practical way, from practical ex- Froto all good dealers or direct : - perience, therefore it ought to he some The BEDFORD ELECTRIC & RADIO Co., Ltd., 22, Campbell Road, Bedford. one already on the Staff at Savoy Hill, London: Glasgow: and it is probable there is no one so 21. Bartlett's Bidgs.. 113. St. Vincent St., Holborn Circus, E.C.4. C.2. capable of managing this important work as Mr. Rex Palmer. He has been on the Staff from the beginning, PEERLESS' and has worked not only behind the JUNIOR RHEOSTAT scenes, but also at the microphone-a very important point-and that as an announcer in charge of various programmes, and also as a pro- fessional vocalist. The Suggestion That he is very deeply interested in the programmes I know, for a few months ago T visited Savoy Hill several times in the course of three weeks for the purpose of being present in the various studios for transmissions of every class of pro- gramme-except Military Band-and, at his request, I then met Mr. Palmer, AT LAST. A DIXIRON. and we had several conversations on A really reliable Electric Soldering Iron. broadcasting in general and pro- grammes and transmissions in particu- lar, and I found him very keen indeed. I have no idea if he would care for the Light and well balanced in weight, beautifully Sniahed. Complete with flex cord and adaptor. Effectively post of Director -General; I am con- handles the large as well as the small lobe. Load- ing 75 watts, and supplied for voltages of 100- sidering the question from the 110, 200. 220-250. You know them. They just want Guaranteed for One Year. State voltage when ordering listeners' point of view only. PRICE 12,6 and 15/- Post Free, from to try something in your set. Ping ! Can you not make a move in the ELECTRADIX RADIOS, An awkward hand has hit your matter in your papers, which are so 218, UPPER THAMES STREET, E.C.4. valve. popular and read by such large num- bers of listeners ? There is no doubt A Benjamin Valve Holder would that Mr. Palmer's appointment would have saved you the cost of a new Bright ! be very popular-particularly if valve. For this valve holder is Witty !! pressure were brought to bear on the sprung on 4 one-piece springs. " powers that be " to make him Strong springs but delicate. Gay !!! ex -officio Head of the General Pro- Springs that absorb the slightest vibration or the greatest shock. This new weekly . . LONDON gramme Department. CALLING . . . you've heard it Fit Benjamin Valve Holders in talked about . . . seen it on " A Highly -Trained Musician " every stage of your receiver. But the bookstalls . . . . wondered If any move be made in the matter what it is like . . . nearly be sure the valve holders are I beg that my name may be kept out bought a copy . . . met people Benjamin, because no others will who like it. . Seems to have of it altogether, please. If you wish so efficiently absorb shock and some good features . latest to publish this letter in part, or the disperse microphonic noises. and most intimate theatre gossip whole, do so brilliant book reviews by all means, but with- humorous drawings by the best out my name. artists. . . . Why not get a copy I am a highly -trained musician with to -day and judge for yourself ? a large concert experience, and, on EN...:77&41 N my mother's side, a member of an Att-' old well-known theatrical family. I VALVE HOLDE RS -r- i f received most of my singing training ^G HsE F P from the late Alberto Randegger and Every Friday. Manuel Garcia-from which you will gather that I am no longer young. THE BENJAMIN ELECTRIC LTD., Yours faithfully, --- Brentwood Wks., Tariff Rd., TOTTENHAM, NIT 677 www.americanradiohistory.com MODERN WIRELESS fune, 1928 6 -pin coil former plugged in position. Why buy VAMPIRE VALVES The valve holder I used was an anti- microphonic one of a popular type, -conlinxrd from page 664 e the other components. also being of waste space? standard make. The readings ob- tained were as follow figures obtained prove somewhat 1. Signal voltage; -2.9. 2. With an interesting to compare. average valve inserted in valve ° To return to the table, it will be holder connected across the tuned 1 found that of the valves tested, which circuit, 2.1. 3. With valve, holder, are more or less a representative 6 -pin coil base and 6 -pin coil, 1.9. when the Columbia stock, four give a drop in signal strength in the neighbourhood of Effect of "Lighted" -Filament "Layerbilt'is filled to 25 per cent, four give a drop of 20 I also tried the -effect of lighting capacity with layers of per cent, and the balance give a drop the filament of the valve, and as electricit of 15 per cent to S per cent. The soon as this was done the H.F. majority of readings show a drop in voltage dropped to 0.95. On H.T. the neighbourhood of S per cent. being applied to the valve, however, the value actually used being 60 i Why Figures Vary volts, the signal voltage rose to 1.45, These readings, however, only refer and on applying grid bias the voltage to the losses occasioned by connecting rose one pair of electrodes across the tuned +vwxe-c2-' circuit ; the two main divisions repre- 42'; senting the losses between grid and RECENT RECORD filament and plate and filament. r4sk your Daalerfor :- .RELEASES Readings were taken between grid -continued from page 639 Columbia naklyedt1Lt " and plate, and these were found to THE 1007. nATTEIW: be of the same order as those occa- sioned by the connection of the other Dance Records J. R. MORRIS two pairs of electrodes. Brunswick. The Sunrise (F.T.) 15, KINGSWAY, LONDON, W.C.2 Now, in actual practice, neglecting and The Man I Love (F.T.). Scotland: J. T. CARTWRIGHT, 3, CADOGAN ST., GLASGOW. the H.T. battery-, the circuits asso- Ben Bernie and his Hotel Roosevelt ciated with any one valve are ap- Orchestra. (10 in. 3s. 3735.) proximately as shown in Fig. 4 at A. Two very good pieces, played well The "RADIO/ A Ìf we redraw this as at B, showing and excellently recorded. They are grid -filament, grid -plate and plate - both very tuneful. filament elements as resistances, it Broadcast. Can't You Hear Me will be seen that we have not got one Say I Love You ? (W.) and 1, set of losses only across the tuned Music and Moonlight (F.T.). For A circuit. This the fact (1s. 3d. 239.1 your '; STATELY accounts for rA Set ay HOME ! that in the practical circuit on Worryin' (W.) and The Trail of which I first took measurements the the Tamarind Tree (F.T.). Harry losses obtained were greater than any Bidgood and his Broadcasters. Batteries,'`4r From of those shown in the table. (ls. 3d. -238.) etc. 0. . £5.5.0 .1A,';'r r It will be noted in the table of the Sunshine (F.T.) and Singapore readings which I took that certain Sorrows (Slow F.T.). Ciro's Club In many items have been marked with a cross. Dance Band. (Is. 3d. 236.) sizes. In view of the fact that I had not.got What'll You Do? (F.T.) and Fully 2-, 4-. and 6 -volt valves of all makes I Let a Smile Be Your Umbrella " RADIOLA" De Luxe Guaranteed. have not been able to use the saine (F.T.). Riverside Dance Band. WINS HIGHEST APPROVAL of Radio Press, leading experts and over 3,000 make for the tests in each column. (1s. 3d. 241.) delighted clients. 3 ft. high. Rich solid oak or mahogany-a The valves marked with a cross, All such good records that is magnificent finish-at loud -speaker coat only. it LET HS HELP YOU.-Suggestions and FULL therefore, do belong to the type difficult to differentiate between them. LIST of exclusive designs FREE. Send now. not Lilo amable auto from ;- indicated by the column heading. PatU Perfect. There Must Be 0. Somebody Else (F.T.) and Dream e 5 Foreign Valves Kisses (F.T.). Meyer's Dance Or- Three different types of valves of chestra. (10 in. is. 6d. P358.) M.W. Works, BEXLEYHEATH, Kent. continental make were also tested, An excellent record. The latter these gave quite reasonable Make but figures item is particularly tuneful. and were in no way as bad as one Parlophone. Enchantment (Tango ' The DAILY SKETCH might have expected from their Blues) and Jalousie (Tango Blues). YOUR Picture Paper appearance and price. One of the The Pavilion Lescaut Tango Orches- RARARAfcARRRTARAfrARARARARARARARARARARARA worst indeed (10 tide 4b.necnKnnnts4K4SasntcnKnecntinliMt entcaKaks1 valves that I measured tra. in. 3s. R3529.) was an old bright -emitter, and this Two of the prettiest and best - PLEASE be sure to h ñ mention was not as bad as the reading given by played tangos we have heard for a RA "MODERN WIRELESS" á valve C, type No. 1, in the 2 -volt class. long time. Lovers of this .kind of Érl when communicating with RA INRA As a matter of interest, I took some music should certainly get this record. Advertisers. THANKS! La áÁ readings with a valve in a holder Superbly played and equally well RARARARARARARARARARARARARARA RARARSCAAPÁR 1,0444 intcnönKnKaeineiaeinriaecntcneintentimintinLana connected across a 6 -pin base with a recorded. 678 www.americanradiohistory.com MODERN WIRELESS June, 1928 H.T. Working off the mains & L.T. 623 RADIO ABROAD from 'j -continued from page 640 r > .??r,,, ,. A.C. Mains :,r+,.v.a zw.av.w'c.::. e. w .,7t:, .:; This latest SCP- RECISION Unit is a com- power output is 50 kilowatts, which, bined H.T. Eliminat o r according to Dr. Alfred Goldsmith, and L.T. engineer, can be OVER - the chief broadcast NIGHT depended upon to give a reliable Batter y Charger service within a radius of 100 miles type A.2. It gives 7 under all conditions. positive The 250 -ft. aerial is supported H.T. tap- CLIMAX AUTO-BAT MAINS LuMPONENTS pings, and upon two lattice steel towers 300 ft. The first home constructors' charges in height. The towers will be illum- CLIMAX Unit was built L.T. accu- AUTO-BAT H.T. Supply mulators 2 to 6 volts at 1.4 amps. inated by flood -lights at night, to TRANS- with Climax Auto -Bat Com- COMPLETE UNITS from £6.5.0 serve as a guide for aviators, and also FORMER. ponents-the first mains from 35, - receiver was possible only COMPONENT PARTS £4.9.0 as a warning in case the aeroplanes :'end for details of SUPRECISION Indestructible with Climax products. Power Transformers, OVERNIGHT Battery Chargers, might strike the masts or the wires. CLIMAX The Climax Special Choke kind, and Eliminator components of every The power supplied to the installa- HEAVY is specially constructed to CHOKE. low frequency ir- F. C. HEAYBERD & CO. tion is sufficient to light 10,000 homes. For Manus Re- eliminate 8 9 Talbot Court, Eastcheap, E.C.3. ceivers .. 21/ - regularities in H.T. supply T of ,one Minn!, Itor.nmmit i t rgr,arid Station.) The current for the filaments the derived from electric light- big transmitting tubes would operate ing mains A.C. or D.C. CLIMAX mag- ACCUMULATOR HIRE 200,000 of the low -consumption POTEN- The core is a complete H.T. OR L.T. TIAL netic circuit of the highest SERVICE. receiving valves, or about 50,000 DIVIDER. grade stalloy iron. Far used 20,000 ohms average receivers. The energy or t o,000 ohms superior to the or- I n/6 We lend you one of our fine wireless accumu- in the plate supply of the trans- with ten tap- dinary choke. Price j lators while we recharge yours. Or keep you pings .. 5/ - continually supplied with our own fully - mitter would provide sufficient charged accumulators. Collection, maim tenance and delivery free, anywhere within H.T. supply for about half a million 12 miles of Charing Cross. Any voltage or Complete lists ordinary receiving valves. upon applica- r capacity. Skilled service. The famous Ax C.A.V. accumulators supplied for H.T. tion from any .I Write for loll particulars to -dart: o. RADIO SERVICE (London) LTD., Trouble in Sweden firdirect to A YEAR AHEAD 105F, Torriano Avenue, Kentish Town,N.W ELECTRIC L'ID. Telephone; North 0623-4-5. curious and rather amusing CLIMAX RADIO A Quill Works, Putney, London, S.W.15 problem is troubling wireless en- When replying to advertisers please be thusiasts in Sweden, owing to the sure to mention "Modern Wireless." prevalence of large apartment houses to and to the fact that on the roofs of Come many of these houses there is a FOR GOOD RECEIVERS tangled mass of aerials, whilst the ELECI RADIX hot-water installation of the building i i is made use of as a common earth return. It is not difficult to imagine HOUSE the readiness with which " diplomatic 4 218, Upper Thames St., London, E.C.4 t relations " may break down between two otherwise perfectly friendly neigh! FOR EVERYTHING hours in the event of their respective aerials crossing, or even being sus- ELECTRADIX RADIOS Telephone: City 0191. pected of interfering ! A house in Gothenburg has adopted a very simple contrivance for getting When replying to advertisers please be to mention " Modern Wireless." ... -.-. .: Parent out of the difficulty by which everyone sure The Belling -Lee Terminal will give real shares alike. A small iron ring is finish and distinction to your receiver. It is beautifully finished and Bakelite insulated. supported at the centre of the avail- We',A, Quality Cabinet" Belling - your Set Made with 30 different engravings, able roof space a few feet above the rail illustratedfor particulars from the Actual Mana -,40 Lee terminals possess the following unique facturera, V.C. Bond & Sons, 61, ftackney Grove, advantages: roof, and from this the various aerial era, St., London. E.S. 'Phone- Clissold OSSI The top does not rotate. The head does not come of . wires radiate more or less at regular Smooth stem ensures that strands of wire intervals. The net result will not bind up with thread. angular Transverse slot with clamping nut elimin- by the time about fifty aerials are ates soldering. Prices: erected is a kind of gigantic spider's (Standard Model) 9d. each. Type "B" web ; but, at any rate, there can be Type "M" (Popular Model) 6d. each. Type "R" (Cheap competitive no actual crossing of aerials, and no insulated model wills rotating name) - - 3'd. each. individual can allege that anyone All types guaranteed. is receiving preferential treat- Illustrated catalogue free oit request. else ment. Every tenant is required to pay a fee of 15 kroner (about 16s. 3d.) RADIO BETLLINGLEE' for his aerial. In Stockholm, in some of the METERS , aAct TERMINALS hospitals, a system is now being sI adopted similar to that in use in FREE leaflet SIFAM, Ltd.. BELLING & LEE, LTD Distortion.' from 10a, Page St.,West- of hospitals in this country. M.W I. minster, Queensway Works, Ponders End, Middlesex some the IDept. 679 www.americanradiohistory.com MODERN WIRELESS June, 1928 miles from Smoky radio station, with a sense of great relief, donned our sealskin boots, and started off across RADIO WITH GRENFELL IN LABRADOR 2 the land, covered feet deep in snow, towards the wireless -continued front page 628 station. The photograph shows the barren spot it occupies vez?- but cannot convey the bleakness of the place, standing -el gee áe9eesee ` etá G3 9 zee G2,ee, as it does at the top of a small mountain lashed by the end of Lake Melville where it joins a very narrow waterway fierce winter winds and blizzards. and so reaches the sea twenty miles farther on. Here We found Mr. Watts dismantling his apparatus, and a 10 -knot current is running. and it behoved us to be news of the outside world was received next day as the very careful. last mail steamer left the Labrador coast for many long There was a very strong, blustery wind blowing, and months. at times our lee rail was entirely under the water as we We listened in silence to the news of many disasters simply flew down that narrow waterway. Then just to vessels less fortunate than ourselves, for we still had` ahead we saw the water was lashed tto fury 'as -a squall to brave the terrible Hamilton Inlet and Lake Melville was coming from a half -hidden cove. on our return trip One hundred and fifty miles does After a short consultation we decided to reef our not seem far when one thinks of a fast railway express, sails, and made in under the land to do so. Our lucky but with an. Arctic blizzard and contrary winds we star was not .in the ascendant, however, for before we might have been ten thousand miles away. could. do a thing the squall was upon us, and we were driven ignominiously ashore: Communication With England A kedge anchor was immediately thrown over, and I am writing this at Indian Harbour at anchor. It has there we lay quite quietly, apparently none the worse, been snowing all day, and we are comforted by the though very hard and fast. Fortunately the tide was thought of raising that anchor with twenty-five fathoms of rising, and a few hours later, when the weather had chain by hand, partly covered by ice as it is, to be hacked moderated, we hauled on the kedge and, to our satis- away at dawn to -morrow when, if weather conditions faction, floated easily, none the worse for our stranding. permit, we will venture out on our return trip. Two days later, after but one more incident worthy On arrival at Northwest River, Mr. Watts will be of note, we arrived at Indian Harbour in a very severe initiated into the mysteries of short-wave apparatus, as snowstorm. The incident should not have happened, compared with the " rock -crusher " variety, and then but, remembering how very nearly we liad run out of endeavour to return by some means or other to St. water, we replenished at a creek not far from the scene Anthony, Newfoundland. Should the " Bay" freeze up of our stranding. We were over two hours out when, -as is more than likely-it --will be necessary to do the sitting down to lunch, we found milk, tea; soup, and journey by dog -team and komotik, a very pleasant everything as salt as if made with brine. prospect indeed. The Smoky Island Station As it may interest some, I give a list of the British There was nothing for it but to go in again for water, stations worked from Northwest River since its opening as we might very easily have encountered bad weather some three weeks ago : E G 2 A 0, 2 D N, 2 N H, 5 B Y, which would hold us up for days. We made inshore 5MA,5ML,61Y,6WL,6NX. and anchored off the mouth of a fair-sized stream. 6 W L tells me that his transmitter consists of a B.T.H. Over went the dinghy, and we rowed very carefully B.5 valve supplied with H.T. by dry cells ! His signals in a very big swell over immense rocks just showing tinder were R.5 at times. Another tribute to low -power work. the surface. A little farther along we saw the water In addition to the above E G stations, over sixty N U tumbling over a fall composed of huge boulders, and with stations were worked, as well as Holingren Radio in great difficulty we manoeuvred the tinycraft as near as Malmo, Sweden, and many stations in different parts possible in order to ensure the water being fresh this time. of Europe. It was so cold the barrel was covered with ice by the Both NE SAE and N E 8 W G will be operating in the time it was full, but for all that it tasted better than the 20- and 40 -metre bands this Arctic winter, and every finest wine on earth. We returned to the yacht, and the station communicated with will receive a Q.S.L. card, rest of the outward trip was without particular incident. though, owing to the length of time it takes by dog - It was a bitterly cold morning in the first days of team for the mails to be carried to the outside, cards November when we anchored at Indian Harbour, three may not be received for many months. Page Page Dubilier Condenser Co. (1925), Ltd. .. 669 Mullard Wireless Service Co., Ltd. Cover ii, 655 INDEX TO ADVERTISERS Eastick, J. J., & Sons 669 Electradix Radios .. 677, 679 Peto -Scott Co., Ltd. .. 675 Electron Co., Ltd. .. .. 657 Philips Lamps, Ltd. 661 Page Ever -Ready Batteries .. .. 663 Pickett's Cabinet Works 678 Bedford Electrical & Rad. Cc.. Ltd. 677 Paroussi, E. .. 667 Belling & Lee, Ltd. .. .. 679 Formo Company, The .. 670 Benjamin Raymond, K. . .. 676 'Electric; Ltd. .. 677 Radio Service (London), Ltd. 679 Bird, Sydney S., & Sons. Ltd. 667 Garnett, Whiteley & Co. Ltd. 674 .. Gambrel] R.I. & Varley, Ltd. Cover iv Bond, V.C., & Sons .. .. 679 Bros., Ltd. .. 668 Bowyer-Lowë Rothermel Corpn., Ltd. .. 670 Co.. Ltd. 671 Heayberd. F. C., & Co. 679 Ripaults, Ltd. .. .. 675 Brown, S. G.. Ltd. .. 578 Hughes, F. A., & Co., Ltd. 665 Sifam, Ltd. .. .. 679 Burne-Jones & Co., Ltd. .. .. 577 Squire, F. .. 671 British Ebonite Co., Ltd. 671 Igranic Electric Co., Ltd. 667 ...... Telegraph Condenser Co., Ltd. .. 665 Manfg. Co. 669 Jackson Bros. .. 667 Carrington .. .. Wilkins & Wright, Ltd. Radio Co.. .. 672 Celestion The .. 673 Lis.sen, Limited 653 Wireless Constructor Envelopes 66 - Climax Radio Electric, Ltd. 675, 679 London Elec. Wire Co., & Smiths, Ltd. 666 Cole, E. K.. Ltd...... 669 " London Calling " 677 Cossor, A. C., Ltd. .. .. 578 All communications concerning advertising Makerimport Co. 675 in "Modern Wireless" must be made to Colvern, 14 '.. , .. .. , . 671 John H. Lilo, Ltd., 4, Ludgate Circus, London, Dietro -Vick Supplies, Ltd. Cover iii E.C.4. Telephone: City 7261. Day. Will, Ltd .. 668 Morris, J. R. .. .. 678 680 www.americanradiohistory.com June, 1928 MODERN WIRELESS jpLVEg MUTISH rR,4COLOUR THE `STANDARD' OF COMPARISON " Cosmos " Valves have also set the standard for the six -volt user, as well as for those who prefer ta use two volts. The S.P.5o/B Blue Spot for H.F., The S.P.5o/R Red Spot is acknow- Resistance Coupling, and possibly ledged to be the super -power valve. Detector stages. This valve has an Used in the last stage it has an amplifi- amplification factor of 35 and an im- cation factor of 6.5 and an impedance pedance of 50,000 ohms. of 4,500 ohms. tor This valve is particularly suitable The S.P.5o/R is the ideal valve tor use with the Cosmos Resistance Coup- operating a cone -type loud -speaker. ling Unit. Price 10/6 Price 12/6 No other valves in the same class give such astonishingly good results, because no other valves can have the advaitage of being built on the SHORT PATH principle. Every Wireless paper and Technical correspondent recommend them, but no one more so than present users. Ask your dealer for Booklet 4.117 3, which a'so gives details of the S.P. 2 -volt valves and the remarkable' Cosmos" A.C. Mains Valves. A line to the makers will bring it to you free by return post. MET-VICK VALVES, SETS & COMPONENTS RV METRO-VICK SUPPLIES LTD., 155, CHARING CROSS ROAD, LONDON, W.C.2. 'II www.americanradiohistory.com MODERN WIRELESS June, 1928 SPECIALISTS N çØqUE4CYAMPLIçc of thousands-are satisfied only with real YOU-oneQUALITY in wireless reproduction. In the past, tens of thousands were content with very poor reception provided they could tune in a few stations at audible loud- speaker strength. But the time is coming when the public as a whole will insist on really good reproduction, and, what's more, many already know they can get it by using R.I. & Varley components. We have made a special study of all forms of L.F. Intervalve Coupling, because we realise the necessity for QUALITY if radio is to be really worth while. The famous Bi -duplex winding, developed and perfected after years of research, has been incorporated in our Resistance Capacity Couplers, and has resulted in a degree of real tonal purity undreamt of hitherto. The National Physical Laboratory Curves of our R.C. Couplers and Straight Line Transformer show that a wonderful degree of amplification has been attained, together with remark- able uniformity at all audible frequencies. That explains ono AM WO MO ZW, 9 why you can hear the deepest bass notes and yet lose none of the high frequencies when using the R.I. & Varley Transformers or R.C. Couplers. In this connection it must be remembered that no matter mr how good an L.F. Transformer or R.C. Coupler may be, ,.I C distortion is bound to result if the H_F. Choke fails to choke t rI back the H.F. currents efficiently. Here again our Bi -duplex winding has enabled us to pro- Comparative curves showing duce a component which for negligible self -capacity, relative choking efficiencies. field, It minimum external extremely small dielectric will be seen that the R.I. & This diagrammatic sketch illus- hysteresis, and maximum choking efficiency over a very Varley H.F. Choke-distributed trates the effective way in which wide range, has no equal on the market to -day. capacity 25 microfarads-cliokes the R.I. & Varley Bi -duplex efficiently over a range of from wire -wound H.F. Choke (9/8) 30-4,000 metres ([0,000 to deals with H.F. currents. 75 kilocycles). RESISTANCE General Purpose Transformer CAPACITY 15 COUPLER " Popular Wireless " writes-" It must have been very skilfully designed for it gave results far superior to those its price would lead one to anticipate. We must admit it falls very little short of transformers in the one pound class." BI -duplex Wire.wound Resrst- alice Capacity Coupler. Straight Line Super Type Transformer Type B 22 6. 25 - THE MARK OF BETTER RADIO A'ngswa ' Houst , 103, ley Kin; sway, London, W.C.2. Telephone . Holborn 5303. Printed and published by the Amalgamated Press, Ltd., 1'leetway flouse, 1?arringdon St., London, E.U.4, on the 1st of each mouth. Address for advertisements only : John H. Lile, Ltd., 4, Ludgate Circus, E.C.4. Telephone : City 7261. Registered for transmission by Canadian Inland and Magazine Post. Subscription rates Abroad 17/- per annum ; 8/6 for six months. Sole Allents-Australasia : Gordon ltz Gotch (Australasia). Ltd. ; South Africa : Central Canada: Imperial i News Agency Ltd. 'News Co. (Canada), Ltd.-June. 1928. D,R www.americanradiohistory.com