ANTHONY ASQUITH on BROADCASTING FILMS E IRE Edited by NORMAN EDWARDS Vol

ANTHONY ASQUITH ON BROADCASTING FILMS E IRE Edited by NORMAN EDWARDS Vol. XI. No. 26. FEBRUARY, 1929.

My Programme - - By Rosita Forbes The" Neutro- Screen "Three The " Instanto " Two Radio and the Gramophone Supplement etc., etc., etc. MODERN WIRELESS February, 1929

In a recent Cape to Cairo and London car endurance test Mullard Valves were unhesitatingly chosenforthe radio installation in the car. A seven months' journey - over mountains, through rivers, across some of the roughest country in the world-andnotasinglevalve breakage or replacement during the whole journey. Mullard Valves were chosen because experience had proved their reliability; this severe test again con- firmedtheirsupremacy. Under the most adverse conditions the travellers were ableto maintain communication and to enjoy the B.B.C. programmes in their lonely camps. Use Mullard Valves in your receiver. Use them for reliability, for strength, for tone, volume and distance.

MullardTHE -MASTER-VALVE ADVT. THE MULLARD WIRELESS SERVICE CO., LTDMULLARD HOUSE, DENMARK STREET, LONDON, W.C.2. Arks February, 1929 MODERN WIRELESS CONTENT VOL. XI.No. 26. MODERN WIRELESS. FEBRUARY, 1929. Page Page 161 Editorial . . . 119 Kalundborg's Companion . .. 163 On the Short Waves . 120 Grid -Circuit Coupling Broadcasting Films - Will it Come to The New Pentodes .. ..165 That? .. How Time Flies in Radio .. 167 The " Neuiro-Screen "Three' 123 A Versatile Meter 169 An H.F. Fault -Finder 129 Short -Wave Schedules 172 Finding Foreigners .. . 131 Aerials Abroad .. 173 The " M.W." Tapped Crystal Set 133 Mixing Battery Acid . 176 " 6 L T " Crystal Amplifiers .. 177 B.B.C. Progress in 1923 139 Generating GiganticH.T. 179 Questions Answered .. 142 Sound Connections ..181 The " M.W." " Transportable " Four ..143 My Broadcasting Diary.. ..183 A Detector for Detectives .. ..149 In Our Test Room .. ..187 My Programme .. 151 In Passing ..190 Radio Abroad 154 Radio Notes and News ., ..21? The " Instant° " Two 155 " Safety -First " Radio ..224 Coils for the " World -Wide " Five .. 160 Short -Wave Condensers .. 22f SPECIAL SUPPLEMENT, " RADIO AND THE GRAMOPHONE, PAGES 195-210 As some of the arrangements and specialities described inthis Journal snap be the subject of Letters l'atevf the amateur and trader would be well advised to obtain permission ofthe patentee 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.

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117 MODERN WIRELESS February, 1929

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February, 1929. 11 Sets in this Issue-The B.B.C. Publications-" The Listener "-Cost of Programmes-The " Ideas Department." By The EDITOR. Four New Sets with the result that announcements were recently made THE four sets which we describe in this February concerning " The Listener." issue of MODERN WIRELESS have been selected The first issue was published on January 16th. Although froin over a dozen receivers which the Research it was stated by the B.B.C. that " The Listener " con- Department has been experimenting with for sow time cerned itself almost entirely with personalities, subjects past. The " M.W." "Transportable "Fourhasbeen and matter associated with the microphone, and that designed by the Research and Construction Deapartment it would not be inoompetition with other weekly journals, with a view to producing a completely self-contained and that, further, it would make broadcast talks more receiver which can, be moved from room to room with effective, inasmuch as it would tend to strengthen and the minimum of difficulty. widen the market of the printed word, a considerable The " M.W." `°Transportable " Four will bring in many amount of opposition has been created. programmes, and the home-made. loud speaker will be found tobe extremelyefficient.We shouldliketo " The Listener " point out that a striking feature of this set is that it ALTHOUGH it is quite true that under the terms of the has one -dial tuning, although there are no ganged con- B.B.C.'s charter there is nothing to restrictits publishing activities, it is undoubtedly unfair that densers or other complications.Itisaremarkably simple and inexpensive set and we feel sure that itis the B.B.C. should further supplement its activities by the undoubtedly one of the most practical portables ever production of this journal.It must be remembered that designed. the B.B.C. is a Government department and, on moral The " Neutro-Screen " Three is a powerful set specially grounds,itisunwise that such a journal should be designed for short-wave work.It employs a neutralised published, in view of its official " origin." screened -grid valve, giving maximum stability and ampli- Furthermore, it has been alleged that the B.B.C. pays fication.This receiver has been specially designed and no Income Tax, and its primary object in life should be provide. described by our well-known contributor,Mr.C.P. to broadcasting entertainment.Criticismhas Allinson, A.M.I.E.E. already been levelled at the B.B.C.'s efforts to take upon The " Instant° " Two incorporates two simple switches itself the task of educating the public, anditis not with which you may turn from any one to any other of surprising that all those vested interests connected with three stations without referring to the tuning controls publishing and printing should have condemned, in no ofthisefficientlittlealternative -programme receiver. uncertain words, a state of affairs which allows the B.B.C. It is an easy and cheap -to -build set, and the simplicity to produce these publications ad /ibilvm. of its operation needs no stressing.It has been designed As a result of the deputation which conferred with the and described by Mr. L. H. Thomas. Prime Minister, the B.B.C. has agreed not to publish any The " M.W." Tapped Crystal Set is another production morejournals,and,furthermore,torestrict" The of the Research Department.Its outstanding features Listener " in certain definite ways.The improvement of are high selectivity and a gain in volume instead of the actual 'broadcast programmes, rather than the production of more usual loss in sensitivity. journals which are outside their 'e 'itimate scope of activities, will now, it is hoped, occupy the B.B.C.'s attention.

The B.B.C. Publications " Daily Mail " has been taking a close interest As the result of a suggestion from Lord Crawfurd's Com- THEinB.B.C.finance,and although certain facts mittee in 1925, inquiries into the possibilities of which the public were not aware of before have broadcasting in relation to Adult Education were come to light, a good deal of thefullstoryhas not recently carried out under the joint auspices of the British yet been told-until our readers turn to the article in this Institution of Adult Education and the B.B.C.In the issueentitled" B.B.C.Finance,"which is based report of the deliberations and findings of the Committee, upon the statements of a most reliable authority. it was recommended that the B.B.C. should publish a The " Daily Mail," however, points out that the Chair- weekly journal, both supplementary and complementary man of the B.B.C., the Earl of Clarendon, receives a salary to its talks and educational broadcasts. This recommenda- of £3,000 a year ;Lord Gainford, as Vice -Chairman, tiou of the Committee has been acted on by the B.B.C., (Continued on page 223.) 119 MODERN WIRELESS February, 1929

K, U.S.A. (outlyingpossessions). H, Finland. 0 K, Czecho-Slovakia. Z, Denmark.P Y, Brazil.R Y, Lithuania. S M,Sweden. S P. Poland.S U, Egypt.T F, Iceland. U L, Luxemburg. U 0, Austria. V E, Canada.V 0, Newfoundland. W, U.S.A. Y I,Iraq. Y L,Latvia. Z L, New Zealand.Z S, Union of South Africa. In addition to the changes in the prefix letters, the form of call -sign has been altered also.Thus Danish stationshave been changed from E D-7 C G to 0 Z 4 C, while the old South African station F 0-A 3 Y now becomes Z S 6 D.In the Irish FreeState, G W-18 B has become E I 8 B, while G W-17 C has become Notes oInterest onShort -Wave Receivers and ReceptionE 17 C. Conditions. That Threshold Howl By W. L. S. I have recently been experimenting with all kinds of anti -motor -boating WE short-wave enthusiasts have would lose any amateur his licence devices,and have been delighted by now, I suppose, just had on the spot.Organised protests are tofindthat,with oneexception, sufficient time to form some to be made, and it is to be hoped, every caseofthreshold howl that opinion of what the " 1929 conditions " simply for the sake of fair play, that Ihavestruckhasbeencured are to be like, and how they will these will result in some benefit. simplybyananti -motor -boating affect us. The short-wave enthusiasts For the benefit of the DX listeners, scheme in series with the H.T. lead who simply listen to broadcast (and I am giving a list of the new prefixes to the detector. A 15,000- or 20,000 - these are probably in the majority) which are already inuse. These ohm resistanceinthe H.T.lead, will have noted that their lot appears become actually part of the call -sign, with a 4-mfd. condenser from the anode to have been altered in no way what- and must be sent every time the side ofitto earth, has proved a ever. The same stations come and go, call -signissent. Doubtless others practically certain cure, although it and-at the time of writing, at all will be in use by the time these notes seems that the more conventional events-no radical changes appear to appear, but these are at present either 2 mfd. is of very little in e ! have been made at all. actually in use or officially sanctioned : As you must know though, there With the " DX -hound, " who has are several different kinds of threshold todependchieflyupon amateur The New Prefixes - howl-the causes are various,but transmissionsforhisexcitement, C M, Cuba.C N, Morocco.C P, the effect the same-and there appears things are vastly different. Practically Bolivia. C R, Azores. C S, Portugal. to be one of them which does not all the amateur stations in the world C V, Roumania.C Z, Monaco.D, succumb to this treatment.I should have blossomed forth into new call - Germany. E A, Spain.E I,Irish have been a far happier man ifI signs, the A.R.R.L. system of " inter- Free State. E S, Esthonia. F, France. hadnotdiscoveredthis,butI mediates "havingbeenscrapped G, Great Britain. H A, Hungary. suppose I am wrong to expect so and the old " de " brought back into H B, Switzerland.I, Italy.J, Japan. inueli from such a simple remedy. use again. Fair Play Wanted One point is annoying me very much. As an amateur transmitter myself, I may be accused of speaking from selfish motives ;such, however, is not the case.I remember that when the new amateur bands were decided upon at Washington in 1927, certain gentlemen spoke half -apolo- getically to the effect that the bands were narrow, but they were to be exclusive. We were, therefore, looking forward to a reasonably clear field freefrom theattentionsofhigh- powered commercial stations. Have we got if ? No, by no means ! We have gotthenarrow bands, surely enough, but up to the present they areinfested with commercialClaimed to be one of the most complete school wireless installations in the world, this stationsturningoutsignalsthat amateur station is situated high in the Swiss mountains at Zuoz, Engadine 120 February, 1929 MODERN WIRELESS

The brilliant son of the Countess of Oxford, who produced " Shooting Stars" and " Underground," gives an intriguing survey of the future of wireless and the filmsin this exclusive interview with OSCAR M. SHERIDAN. ANTHONY AsQurru and I sat in fact stands out.It is the idea I have fection.For one thing, I am not of the comfortable stalls of the always cherished, that in the future- the opinion that owners of wireless New EmpireTheatre, once the near future, perhaps-there would television sets will stay for three hours the home of famous musical comedy, be a synchronisation of ideas in wire- watching an almost vague image that and to -day the shop window for the less and films that would mean a is confined to space even smaller than modern American film.The launch- revolution intheentertainment an ordinary cigarette card. ing of a ship, or the laying of a founda- world. " I see the possibility of television tion stone,familiar events in the " Let me paint the picture that I only when the necessary perfections modern film. entertainment, were the imagine.Of television, I know very have been made that will allow the inducement toconversation which little.I do know, though, both from wireless picture to be projected, or proved Mr. Asquith's versatility in what you tell me and what I haveshown on a space equal to the screen his knowledgeofthingsscientific. alreadyheard,thattelevisionat of a home cinema. It was not unnatural, then, that we present is the very reverse of per - spoke about wireless, television, and The Home Cinema the medium whereby the kinema "There are still to -day people who would be allied to broadcasting. complain that the cinema, even with its present lavish luxury, is tiring to An Entertainment Revolution the eyes, and sometimes a strain on " I think I was interested in wire- thenervoussystem,"wenton less before I became enamoured of Mr.Asquith." Therefore, it seems the possibilitiesof the film,"said doubtful that a whole entertainment Mr. Asquith." I realised, as every- viewed in the confines of an aperture one else must have done, that it would less than a postcard size will ever be be years and years before one could a genuine and popular family enter- even vaguely gauge the uses, advan- tainment." tages, and even the necessity of wire- Mr. Asquith went on to explain less. that if ever television, were exploited " As a science, and as a hobby, its to its eventual success, he would be novelty stimulated my interest, until one of the first to praise its utility and Iwas aware that wireless would necessity.The success of the cinema become, sooner than one imagined, a in the home, he told me, was that the predominant factor in the growth of realspirit of the silent stage was civilisation.And to -day, as I review presented,asthe same films can my interest in wireless, one important A recent portrait of Mr. Anthony Asquith. be purchased, and theonlyloss, 121 MODERN WIRELESS February, 1929

apparently, is the musical accompani- choice of a dozen British and Conti- cloudiness, however, and as a means ment as provided in the legitimate nental kinema or theatre programmes, ofprecautionagainstthetrouble cinema theatre. with a clarity of sound and strength occurring in the case of a clean or new " I suppose the day will eventuallyof picture that loses nothing by its hydrometer, one cannot advise any- arrive when, by means ofbroad- transposition to the wallofone's thing more suitable than having at casting andtelevision,theactual drawing -room, then thefutureof hand a small bottle of methylated cinema entertainment will be part of wireless televisionissomething to spirits. the equipment of every modern home, look forward to." After the hydrometer has been used just as the gramophone and the wire- And, in those few words, are ex- for taking the gravity of the accu- less set is to -day.4f, as I think, itpressed the sentiments of a young mulator acid, dip the nozzle of the may soon be possible to show a full- man who is well in the vanguard of instrument into the methylated spirits ize screen or stage, and hear thethe clever modern young men of bottle and allow the barreltofill same accompaniment that goes with to -day.Mr. Anthony Asquith has up with the spirits. Subsequently, the show in the theatre, then I thinkgiven the British film industry re- when the spirits are squirted back we shall have a revolutionary move newed hope ;when television comes againintothebottle,any slight intheartofentertainment,the to stay, I would not be surprised if cloudiness formerly present on the beneficial extent of which (or other- we do not hear more of him in that inner walls of the hydrometer will be wise) it is at present impossible to direction. found to have vanished. gather. The methylatedspiritscan,of " Its value in the provinces and in eiSct;IM,'=ZZ,2,c5PiGSSO'S9W;S'y,51:5, course, be used over and over again uncivilised countries will be tremen- TWO TECHNICAL g for the same purpose, and if the above ious.There will, of course, always TIPS procedure is adopted every time the be the difficulties that are at present -.`a A Hydrometer Hint-Drill Pointse)a hydrometer' is used, itwill remain encountered in the broadcasting of &T,OEPEE'at2;506302-0SI-CDE%.T5F,f, indefinitelyinaperfectlyclean ordinary wireless entertainments.If condition. in theperfection of television the A Hydrometer Hint theatres and musicalhallsare to NEARLY every reader will have Drill Points suffer, then every manager will be up had practical experienceof Itis not every amateur-especially in arms against having their particular thefactthatafter a hy- during busy constructional periods- entertainments televised. drometer has been in use for some time who takes the trouble of keeping the for the purpose of taking the gravity points of his drills ina perfectly Radio and Gramophones of the accumulator acid the inner sharp condition.An attempt, how- " The gramophone has only become wallsoftheinstrument tendto ever, should always be made to keep popular," he continued, " because it become cloudy, this cloudiness being drillpointssharp,forthepower has become a really perfected thing. due to the deposition of very fine required todriveadulldrillis The absence of' scratch ' on records, particles contained in the electrolyte. considerably greater than that which and the high quality of the actual willoperatea sharpone.Care- gramophone-made possible, it must Itfillti11111111111111111111111111111111111111111111fifillifififilltfifille THE RADIO -CINEMA. ful rubbing of the point. over the be admitted with the help of radio The interview with Mr. Anthony surface of a fine oilstone from time to valves and other wireless advantages E.-- Asquith was given before details of time will keep the drill point in a good -has almost totally done away with our Technical Editor's Radio -Cinema sharp condition. the idea that it provides mechanical invention were disclosed.It is, there- When working with small drills, music only. E fore, all the more interesting to note E.- thesignificanceofsomeofMr. do not use too great a degree of " With Kreisler, Paderewski, the Asquith's remarks :" It is the idea pressure. Even if they do not, actually Philadelphia Symphony Orchestra- E I have always cherished that . . . 1E- snap under excessive pressure, they 1;7 there would be a synchronisation of -1 to mention lust a few as contributors ideas in wireless and films that would E. will be liable to become distorted, and tothisentertainment-whatwas _ mean a revolution in the entertainment their rotation will be uneven. In using once a novelty has become a real world,"etc.He was alludingto F:- fine drills, therefore, make up for the thing, the loss of which would be a 74Television, but Mr. Dowding's con- lessened pressure by an increasein disastrous affair. =_binationofRadioandFilmsis=- eminently practical and is ready for E= speed. puttingintooperation, simply,in- Concrete Atmosphere expensively and without troublesome Hard Patches " Wireless, also, taken as a purely complications.Theresultwillbe a - If, during the course of drilling a high -class Film Talkies in your own scientificaffair (and not worrying g drawing -room.Mr. Dowding is con- piece of metal or other hard material, about thequalityofthethings E tributingaspecialarticleonhis you suddenly meet a spot which is broadcast), is perfect.The next step, F.:Radio -Talkie invention to next month's harder than the rest, do not force the ofcourse,is drill. and that, the most THE EDITOR. Rather withdraw it, and rub important step of all, is for the con- over it a little turpentine. Then crete atmosphere-by that I mean the u nutwlntuuuuuumuuuiuutlliulnwuuuunmiuuiti continue the drilling, decreasing the action, the players, the scenery, the In such circumstances it becomesspeed of the drill, and lessening its whole theatre, in fact-to be brought difficult to take an accurate reading pressure. In this way the hard patch into the home. with the hydrometer. Of course, the of material will be drilled cleanly and But it will have to be broughttrue remedy for the trouble lies in the effectively, and the drill itself will not lock,stock, and barrel, and nottaking of the hydrometer to pieces suffer any harm. devoid of any of the things that makeand washing it out with warm soap Finally, when putting your drills theatre and kinema-going a pleasure. and water, and, in fact,this pro- away for any length of time, do not " If one is able, in the near future,cedure should be carried out in bad forget to rub a little oil or grease over by means of an apparatus that costs cases. them. only a few pounds, to switch on the Inslightcasesofhydrometer J. F. C. 122 February, 1929 MODERN WIRELESS RO-SCREEN

A Very interesting receiver specially designed for short-wave work. It employs a screened -grid valve which is neutralised, in order to get maximum amplification. By C. P. ALLINSON, A.M.I.E.E.,F.Inst.P. Inc.

IN a recent article I expressed the tally their efficiency is reduced and the greatest precaution being taken to opinion that the real future of signal strength is lost. avoid coupling extraneous to the valve the screen -grid valve, especially itself. for short-wave work, was to use it in Siniple Screening The receiver I am going to describe a neutralised circuit. At the same time, it must be born has been developedespecially for As you know, the trouble with the in mind that the residual capacity of short-wave work, and so as to allow very high frequenciesis that coils the screen -grid valve is by no means of straightforward inductances being will couple together at unbelievable negligibleat these very highfre- used, and also to simplify the con distances,while mutualcapacities quencies, and 1 have found that a struction of the receiver as far as which are almost below measuring short-wave H.F. amplifierusinga possible by eliminating the necessity range will also give unwanted coup- screen -grid valve would oscillate when for extensive screening. It is an exact ling ; while if coils are wound astati- both circuits were in tune, even with copy of the set I use myself for short -

COMPONENTS REQUIRED

2 *0003 S.L.F. or square -law variable are the Bowyer -Lowe " Long 1 2-mfd. reservoir condenser (Dubilier, .. condensers(G.E.C. inset).(Any Range," Wright and Wearite, Burne- Lissen,Ferranti,Mullard,T.C.C., A* good make, either slow-motion or Jones, Lewcos, etc.) Hydra, etc.).

plain type with vernier dials.For 1 Six -pin coil base (Peto-Scott, Lewcos, 1 1-mfd. reservoir condenser (Dubilier, short-wave workitisadvisable Burne-Jones, Colvern, etc.). Lissen,Ferranti,Mullard,T.C.C., O

to choose a type with a particularly 1 Four -pinstraight-linecoil base Hydra, etc.). good connectiontothemoving (Colvern). 1 .25-mfd. reservoir condenser

vanes.) 1 Fixed resistor(Cyldon, Peto-Scott, (Dubilier, Lissen, Ferranti, Mullard,

1 '0002 reaction condenser (Bowyer - Dubilier, etc.). T.C.C., Hydra, etc.). Lowe, Cyldon, Burton, J.B., Igranie, 1 '004 fixed condenser (Dubilier, Mul- 1 On -off switch (Lissen, Lotus, Igranie, Peto-Scott, etc.). lard, Lissen, T.C.C., Clarke, Igranic, Benjamin, Burne-Jones, etc.). 1 Base -mountingneutralisingcon- etc.). 11 Indicating terminals (Belling -Lee, *0 denser(Gambrell,J.B.,Bowyer - 1 .01 fixed condenser (Dubilier, Mul- Igranie, Eelex, etc.). Lowe, Burne-Jones, Peto-Scott, etc.). lard, Lissen, T.C.C., Clarke, Igranie, 1 Set of Neutro-Screen short-wave coils 44. 1 L.F. transformer (Ferranti, Mullard, etc.). (Colvern). Igranic,Philips,Lissen, Marconi - 1 0003fixedcondenser(Dubilier, 1' Aluminium panel, 20 in. x 7 in. phone, ILL-Varley, Brown, etc.). Mullard,Lissen,T.C.C.,Clarke, (Burne-Jones). 1 1 H.F. choke suitable for shunt feed. Igranic, etc.). 1 Copper sheet, 91 in. x 61 in., for 1 H.F. chokeforreactioncontrol. 1 30 -ohm variable filament resistance inter -stage screen (Paroussi). (Both these chokes should be suit- (Igranic, Lissen, etc.). able for use on the shortwaves, and 1 5-megohm grid leak and clipor 1 5 -ply baseboard, 20 in. x 10 in. ese

shouldpreferablybe of different holder(Lissen,Dubilier,Igranic, Ebonite for terminal strip; and a coil Ediswan, Mullard, Pye, etc.). of o makes.A few suitable specimens Glazite for connecting up. soe

I I23 MODERN WIRELESS February, 1929 wave reception, except that I use two long leads to the L.F. valve, which Loose coupling with the aerial has L.F. stages instead of one, as I likeotherwise would have to be taken been used, the aerial coil being LI, tohave aset with an unusually right across the set. tuned grid coil is L2, and L3 is the high factor of safety. The arrangement employed does not neutralising winding, to which I have As itis intended for short-wave apply negative bias to the grid of the just- referred. work, I have considered it essential to H.F. valve as well as turning down The output circuit IA the H.F. use a metal panel for mounting the thefilament,asthemoreusual valve is,in .effect,ordinary tuned components. A photograph taken arrangement of inserting the filament anode, and here I have made use of from the front of thq,,receiver shows in the negative lead does, so that no an unusual expedientiff order -to that it presents an extremely dis-fear need be entertained that dis-simplify the question of nibunting tinctive appearance, while other views tortion owing to rectification will be the anode tuning condenser. taken from the back of the panel show the simplicity of the screening arrangements employed, an inter -stage 1 i ' screen merely being used between the H.F. and detector valves, and circuits.3 The theoretical circuit diagram of the receiver is shown in Fig. 1, and it 07.1\4 i tekt will be seen that the use of the metal t) No panel has introduced one or two slight eN,..... t . .))). 1 peculiarities into the circuit which I31 '4.------_C think I ought to explain in case they 20 should cause any confusion in the con- a m e G SD structor'smind whenconsidering K78o. "'G. 2. PANEL LA your building this set. introduced when the H.F. valve is With the conventional tuned -anode Varying Volume used to control volume. circuit it would be necessary to insu- In view of the fact that I wanted In order to allow any voltage valve late the tuning condenser entirely to be able to incorporate some formto be used in the H.F. position, I from the panel, since this condenser of volume control without having to have also included a fixed resistor would be connected straight across introduce extra complications in the R3, which merely requires the correct the anode coil and would therefore wayy making special ebonite bushes value of resistance to be clipped into have thehigh - tensionvoltageof and so on, it seemed to me that the it to ensure that the H.F. valve shall the battery on it. simplest way of achieving the desired be run at the correct potential when Now itisdesirable to eliminate result was to employ a filament re- the other resistance is at its minimum battery coupling if possible by isola- sistance to turn down the H.F. valve. setting. ting the tuned -anode circuit.ifI By connecting this in the negative had used ordinary shunt -feed this filament lead, the spindles of the con- Notes on Neutralising . would, of course, have made it a densers and the negative filament of The neutralising method employed simple matter to mount the anode the H.F. valve would all be at earth might almost be said to be a form of tuning condenser C4 on the panel, potential, for the spindle of the filar split -secondary, in that a continuation but in this case the damping of the H.F. choke would be across the tuned 5cREEN.0, circuit and would therefore introduce tz losses, so reducing the efficiency of CHOKE the amplifier. 10-00-0N-CHOKe #4 By using the scheme shown, how- Fl. 1 Lo 07,v000, CS ever, not only can we mount the con- 4;. denser directly on to the panel, but L5 also the H.F. choke L6, which is used to isolate the H.F. circuit, has both its ends at earth potential, so that V3 damping across the tuned circuit will in no way be introduced. Cs No " Noisiness " Further to ensure the elimination Cie of any possibility of a short-circuit T of H.T. occurring owing to the short- circuiting ofthetuning6 condenser 6 C4, a fixed condenser C3 has been

yC2C connected in series with C4 as shown. This also has the further advantage that should the tuning condenser x.vo. collect dust between the vanes, no ment rheostat, being in direct contact of the secondary winding is used to noisiness will result- as would other- with the bush which fixes this com- give the necessary phase reversal, the wise be the case. ponent to the panel, would complete voltage therefrom being applied to Since the receiver employs one theL.T.negativecircuit. This the plate of the H.F. valve throughstage of L.F. amplification only, I rrangement also avoids unnecessary the small neutralising capacity 02, haveusedleaky - grid - condenser 124 February, 1929 MODERN WIRELESS

rectificationfollowedbyatrans- come of considerable experience, and owing to the fact that the H.F. stage former, as this is the most sensitive introduces the results of much ex- isneutralisedsothatwiththe arrangement, and will give the greatest perimental work undertaken in order detectoroscillatingnoenergyis signal strength. that the maximum efficiency might radiated from the aerial, and some For the reaction circuit I have used be obtained. -nearby short -waver does not mistake throttle l'ontsrol, the reaction coilL5 A.704 your oscillating 4.eceiver for a trans- being conheAed directly in series in mitter, and in his efforts to find out the anode r circuitof the detector what you are dolig make it impossible live, ate; whichthe H.F. choke PIN N2/ for you to read the station to which 147,Isnciirtre reaction condenser07, you are listening. Z2 P/N .V1* epablecontrolofreactiontobe P/N 6 dbtained. L3 PiN4 High Amplification ! Not only does this method give the L mN95 It might be thought that the extra 144esinoothest and most satisfactory con- tuning control would somewhat com- trol of reaction on the very short plicate the operation of the receiver. wave -lengths, but in my experience This, however, is in no way the case, itwill frequently enable oscillation for the tuning of the H.F. circuit to be obtained where a straightforward (owing to the heavy aerial damping) /5-30 IWETR E44APROX / G.44 Reinartz circuit will not. is decidedly on the flat side. Sinee installing this receiver for This induced me to think that it Avoiding Hand -Capacity my own short-wave work, I may say, might be possible to do away with At the same time, the spindle of the incidentally, that I have only worn this tuning control, and instead of an reaction condenser is earthed,thus the headphones on two or three occa- ordinary aerial coil just connect an avoiding hand -capacity effects, and sions, and then only when extremely H.F. choke or high resistance between also simplifying the construction of weak signals had to be copied.For grid and filament of the H.F. valve. the receiver, especially in this case most communications the loud speaker I tried this out, and found that the where the metal panel is itself earthed. can be used on 99 stations out of 100, drop in amplification was so marked 1 may say here that this is not the and amateurs from all over the world that I determined to retain the extra first receiver that I have built on these comewanderinginatamazing control, for the extra amplification lines. Six months ago I built a similar strength. One of the great advantages obtained would be more than worth model for experimental purposes, and of this circuit will be found whenthe slight trouble involved in adjust- the present set is therefore the out- reading a Morse station. Thisis ing it.

Here is a view of the set which shows the exact spacing of the components and disposition of the wiring. 125 MODERN WIRELESS February, 1929

Another advantage of this circuit extra trouble in making insulating the coils, since there are many experi- (and this happens to be one of its bushes is required. menters who will no doubt want to greatest advantages) is owing to the The inter -stage screen is another make their own coils up. rather than factthatthedetectorcircuitis quite simple piece of work, since all purchase them ready-made. damped only by the output impedance thatisnecessaryisto bend over The aerial coils I have wound on of the H.F. valve. Tile result of this, in.along the long side ofitso 2/ in. diameter ribbed formers.The of course, is that no dead spots areas to mount it on the baseboard ; 15- to 30 -metre coil has one turn for ever found with this receiver except two screws, one at each end, sufficing the aerial coupling coil whiclis con- those which may posiibtly be intro- for this.The panel is fixed to the nected between terminals 4 .ancl duced by an HY. choke (a thing which front edge of the baseboard by means four turns for the grid coil connected should not occur with a good H.F. of fiveorsixsmall screws, andbetween pins 1 and 2, and a little. choke, incidentally). the only other constructional work less than one turn for the neutralising. involved is in making up the terminal winding connected between pins 2 No " Dead " Spots strips. and 6. Under these circumstances it doesn't it should be noted that the on -off matter whether the station you are switchisplacedonthebattery The Pin Connections receiving happens to come in tune terminal strip, where it is most con- The full details of the connections with the fundamental of your aerial veniently located. In this position it are given in Fig. 4 at A.For the or on one of its harmonics, whether considerablysimplifiesthewiring 30- to 80 -metre band Ihave used your aerial is a big or a small one, and also prevents meddlesome fingers auto -coupling, so the connections are highly damped or lightly damped, from switching the set on during your atrifledifferent.Thegridcoil whether your earthisefficientor absence, since the switch is concealedconsists of 10 turns with the aerial inefficient, etc. from view. tapped on one turn from the earth end. The neutralising winding in this case consists of 1turns connected between the same pins as before. The details for this coil are shown in Fig. 4 at B, which makes the matter quite clear.The turns of wire are well spaced, and I am of the opinion that this is a precaution well worth taking. Ample overlap is obtained on the two coils.If you want to go to the next higher range a suitable number of turns will lie between 20 and 30, according to the gauge of wire and method of winding employed.It is extremely difficultto getcoils to allow the condensers to match as regards their readings, for the aerial and detector loading are so different and the capacityin a short-wave circuitpreponderatesineffectso heavily as to make tuning condenser matching almost ;mpossible.If the condensers match at the top they won't at the bottom, and vice versa. The low -frequency wiring is shown in clear detail in this illustration of a portion of the For the H.F. coils the tuned -anode receiver.Note the connections to the "straight-line " coil -holder. coil L4, 3 in. in diameter, consists of three turns and the reaction coil L, Reaction demand will be found to I have taken particular care to seetwo or three turnsofthe same be consistent with the load on the that everything is well spaced out, diameter closely coupled toitfor circuitwithout dead orhalf-dead thus not only simplifying the actual the 20- to 40 -metre band.For the spotswherethe reaction demand wiring -up,but making the layout 40- to 80 -metre band the anode coil suddenly increases to the maximum considerably less critical than would has eight turns, the reaction coil five available. be the case if a more compact form turns, and the next biggest coil has Choose your components with care of construction had been employed. sixteen turns for the anode winding as regards their mechanical construc- andeightturnsforthereaction tion, in the case of any component Coil Construction winding. having moving parts, if you wish to Beyond the usual precautions of be able to operate the receiver with spacing out grid and anode leads as Rigid Reaction ease and certainty and unvarying.far as possible, there is no need for If you decide to make these coils satisfaction. me to deal with the wiring of the for yourself, care must be taken, of The constructional work involved receiver.It is not as if it were at all course, to see that a rigid and solid in making this receiver is extremely complicated and certain leads had to job is made of it, and that the coup - simple, since all the components which go into position before others. linobetweenreactionandanode are mounted on the panel have to be Before we come to the question of windings cannot vary while the coil in electrical contact with it, so that no operating the receiver, I will deal with is in use.At the same timeit is 126 February, 1929 MODERN WIRELESS preferable that it should not be able Now when the H.F. circuit is brought CoilNo. 1,i.e.the4 -turncoil, to vary when the coil is not in use, into tune it will be found that the 17.5 to 42.5 metres (rather a greater for if it does, then Ihe calibration of set begins to oscillate. wave -length range than one might your receiver will be upset. The resultis that with reaction at first expect) ;Coil No.. 2 (the 10 - The set can now be connected up, correctly set it is a simple matter to turn coil), 32%5 to 85 metres. after the usual tests have been made, Now, the smaller of the coils used A.703 toascertainthat L.T.and H.T. to couple the H.F. valve to the circuits are correctly wired, and the wNP/ detector consists of 3 turns 3 in. in first thing. to do is to get the H.F. 11111i1GIGI:11=MMVPIININI: diameter, and will not tune much valve stabilised. IIMIORMICIGIIMPS11101 below 20 metres.If you reduce the mobairds=sommum number of turns you willfindit iimaismasesselrown The Valves to Use noraminamememseumsPmNe5 difficult to get control of reaction, Essirromalm.orkiiimismerierion mono I don't intend to use the word N N92 so if you want to go down farther it neutralised at all as regards this set, is advisable to reduce the diameter of the coil.The coil I have just re- because, strictly speaking, it is not 111111.:1°M6..1111F necessary to neutralise the KY. valve ferred to is the smallest coil in the Collinson kit, and is all that is needed at all, but merely to stabilise it by 0 II for usual purposes, but if you are keen means of the small adjustable con- 30- aOMETRES denser 02. to get down farther you should make For the H.F. valve any good screen - keep the circuits tuned to each other up a 2 -turn coil having a diameter grid valve will do.I myself have within a couple of degrees on the dials of lf in., in every respect like the one actually tried the Cossor, Marconi, by keeping the reaction so adjusted I described for use in the three -valve Osram, Mullard and Ediswan, andthat the set will just oscillate when short -waver called " 3 S.W." described found them to give the most satis- they are both in tune. in MODERN WIRELESS last April. This factory results.For the detector a Now stations can be searched for article also gives you details as to high -muvalveofthe resistance - and tuned -in and it will be found that the wave -length range of the other capacitycoupling type should be the H.F. tuning condenser is by no coils, which are the same as those used in the " 3 S.W." used, while for the L.F. valve a means critical in its setting. . medium impedance valve suchas Now, most amateurs will have found the D.E.L. type should be employed, the foregoing information sufficient Operating Notes unless headphones are going to be to get .going with the set, but for the This coilwill,inthe"Nentro- used, in which case I prefer an H.F. benefit ofless -experiencedexperi- Screen " Three, go clown to about 12 valve having an impedance in the menters some further details will no metres, or perhaps alittlelower. neighbourhood of 20,000 to 30,000 doubt be useful. This is lower than the bottom limit of ohms. First of all,ifhe follows my in- the smaller of the two aerial coils of With reaction set to zero and the structions exactly in making up the,whichIhave given youdetails. correct voltages applied to the various coils he probably will like to know If, therefore, you want to get right valves, two coils covering approxi- more exactly what the wave -length down to 12 metres on that coil, too, mately the same wave -band range ranges are.Here are figures that I you will have to make up a third should be plugged into their respec- have checked up on a wave -meter : coil for the purpose. tive holders. Screwthestabilisingcondenser right out and rotate the two dials backwards and forwards to seeif the set oscillates at any position.It will probably he found that at certain positions on the two condensers the set will oscillate. All that is necessary to stabilise the set is to increase the stabilising condenser until the set has stopped oscillating.

H.F. Tuning It is quite possible, however, that no point will he found at which the set oscillates because the mere presence of the small condenser gives sufficient feed -back to prevent oscillation occurring, owing to the fact that the residual capacity within the valve is exceedingly small. When reaction is used it will be found that theset behaves ina perfectly normal manner.For instance, reaction is increased until the detector valve is just not oscillating,As in all short-wave. sets, the high -frequency wiring has to be caret ully and efficiently when the H.F. circuit is- out of tune arranged. 127 MODERN WIRELESS February, 1929

This should be wound on a small Now, in getting the best out of this You will probably find that the former, a 14 -in. former such as is set there are one or two points to bestresultsareobtainedwitha used in some binocular coils is suit- watch. For instance, the screen -grid lower voltage than that recommended. able.This should have two or three potential should be very accurately Next try out different valves as

. turns put on it with about half a adjusted in order to give the maximum detector. A short -waver is inclined to turn for neutralising, the aerial being amplification.This may differ from be rather fussy about detector valves. coupled to it by a single turn spaced the maker's figures by 10 or 12 volts It will refuse to oscillate with some, about 1in. away.The method of in some cases, owing to the fact that or with others itwill produce un- winding and connectingisexactly with astabilisedcircuit you can pleasant noises " off " that make the the same as coil No. 1,details of afford to work on a slightly different copying of a weak signal a difficult which are given in Fig. 4a, so no partofthevalvecharacteristic. matter.For the L.F. valve, too, be further illustrationisrequired, the Try the effect of varying it, therefore, sure to chobse one that gives a com- former being fixed to a standard six - in small steps up to 10 or 12 volts pletely silent background. pin base. above or below the maker's rating. (Continued on page 222.)

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LESSthan a year ago the world E11111111111111111111111111111111111111111111t11111111111iIIIIIIIIIIIIM cient to burn the copper and damage The use ofhigh -voltagehigh - was astonished by the news frequency as a method of testing the insulation. that a judge, sitting comfort- alternators and largeelectrical ably at his desk in New York City, plant current is a new idea which is Very High Voltages Used started the machinery of a great steel = proving very satisfactorylinAmerica " A high voltage, however, may be mill by merely passing his hand over By a Special Correspondent used,provided ahigh -frequency a small crystal ball placed on his desk. zt111111111111111111111110111111111111111111101111111011111111111111171 current is used. With a 60 -cycle cur- Incredible almost, but not more so rent of 10 amperes flowing through than talking half -way round the world, " The first test is relatively simple. the coil under test, the voltage drop or sitting in one's home and listening The second testis more difficult, across the coil may be 4 volts.If the to a concert hundreds or thousands of because impressing a high test voltage frequencyisincreasedto60,000 miles away. of ordinary frequency across the ter- cycles, 4,000 volts are required to Indeed, the radio wave is a quick minals of a coil will cause a heavy produce the same current. Hence, by and industrious little messenger, so current to flow.The current flowing increasing the frequency practically quick and industrious and reliable under these conditions may be suffi- any voltage may be applied across the that it becomes the busiest messenger of the world. It has gone on a variety of missions, but the most unusual service it has been called upon to perform is that of detective.Mr. J. L. Rylander, a Westinghouse engineer, is now emplOying the radio -frequency wave to detect insulation faults in the coils of motors, generators, induction regulators, and many other electrical machines.This has proved such an efficient and_ vigilant detective that since enlisting its services for commercial testingofcoils,insulation failures have been almost eliminated. Two Tests Necessary In describing this new method of testingcoils,Mr.Rylander says : To be sure that the insulation of a finished electrical machine will meet the demands of service, two insulation 'testsarenecessary ;first,atest proving that a reasonable overload will not cause a short-circuit between any part of the windings and the frame of the machine, and, second, a test proving that a reasonable overload will not cause a short-circuitMr. Rylander (left) believes that high -frequency testing of electric machinery will soon between turns of the coil winding. become universal practice.Part of the apparatus used can be seen above. 129 MODERN WIRELESS February, 1929

83:St90000Pf9t?resA50f3f3q3,673. 0230M the maximum reading, but if a faulty o.%aeao&0000agoamv0000 coil is put into the circuit of the trans- 61. H.F.6FAULTFINDER mitter the wave -length will be altered, BATTERY -continual the receiving set will be out of tune, and the milliammeter reading will @,Fgammaoocsa5Egig.{.o E.PEI55555oaEpoaEpepeo@w3)%w drop.What does this test mean in Never shake an L.T. battery un- terms of field failures ? necessarily, as if sediment from the terminals of the coil without causing bottom of the cell settles on any of the an excessive current in the winding. Invaluable Guide plates, " local action " sets in and the " For coil testing, the spark system " Theratiooffieldfailuresof battery may be ruined. of obtaining high -frequency current, machines per year since thehigh - familiar in radio circles, is employed. frequency methodoftestingwas If distilled water is absolutely un- " Power is supplied to the apparatus adopted by the Westinghouse Com- obtainable and it is essential to re- by a standard transformer. By adjust- pany to the number of field failures plenish theelectrolyte,as a tem- ing the length of the rotary spark gap per year beforethis method was porary measure it is better to use clean is oneto the point on the voltage curve at adopted approximately rain water, thoroughly strained, for this which a spark will occur is deter- twenty. High -frequency testing shows purpose, than ordinary tap water. mined. up poor workmanship, checks the * * * insulation design and the processes of After a battery is discharged,it Fault Immediately Found manufacture.It ensures that proper should never be stood aside for a and adequateinsulatingmaterials few days, as in this condition the " When this spark occurs the con- are in their proper places and not plates start to sulphate quickly, which denser discharges through thecoil missing or damaged, and that no isnot the caseifthe batteryis under test, resulting in a frequency of harmful foreign materials are present. promptly recharged. oscillation depending on the capacityOne of its chief merits is that it in- * * of the condenser and the character- variably shows the cause of the failure, Topping Up istics of the coil under test.This as the arc is of only such intensity as If the level of an L.T. battery falls, testing device, which provides high to burn out the weak insulation with - do not on any account add acid to make up for this, but use distilled water for the purpose (the acid would make the electrolyte too strong). * * * Be sure not to lose the little vent plugs on the top of an accumulator, as these play an important part in the maintenance of a cell in its correct condition. When connecting up an accumu- latortoacharger,itshouldbe remembered that positive should be connected to the positive side, and the negative to the negative part of the charging apparatus. * * * Althoughtheseparatorsinan accumulator may last longer than twelve months, it is often advisable to replenish them after they have been in use for about that period. * * * L.T. battery terminals should not only be kept clean, but they should be A corner of one of the large British radio works where all sorts of components are made covered occasionally with a good coat- (Benjamin Electric.) ing of petroleum jelly in order to protect them against the action of the acid. voltages with comparatively low cur- out burning the adjacent insulation * * * rent, is a simple type of radio trans- or the copper." Noisy Reception mitter. Irregular and noisy reception can " Any fault which may be present When crackling noises are troublesome, sometimes be caused by impurities in the insulation of the coil under test and itis uncertain whether these are due inside the accumulator, and ifthis detected to the set itself or to some outside cause, may be immediately by there is much to be said for the old-fashioned is suspected it is a good plan to con- means of a special radio receiving set plan of disconnecting the aerial and earth nect a pair of telephones across the having a sensitive milliammeter in the leads to see whether this stops the trouble. terminals.(Very little current will circuit. By adjusting its variable con- flow because of the high resistance of denser the receiving set is tuned to When crocodile clips are used for taps, etc., do not forget that if the springs of these the 'phones, but ifthereis an ir- the wave sent out by the transmitter. are allowed to get dirty there will be un- regularity in the supply this will be The milliammeter will then indicate necessary resistance at the point ofcontact. indicated by clicking noises.) 130 February, 1929 MODERN WIRELESS

How many times have you heard a station and have been unable to identify it?Here is a novel scheme to make the finding of foreign stations an easy matter. By A. G. ALLAN. ECENTLY I was able to read a The stations themselves have seen We have a score or so of metro- largenumberof different this need with the growing scope of nomestickingawayatdifferent people's opinions on the kind broadcasting over more than onespeeds, we have two cuckoos calling ofidentifyingsignalsbroadcasting country, and have attempted to solve us from Ljubljana and Wilna respec- stations should possess.Listeners to the problem in different ways.One tively, we have Morse signals from foreign stationswillallhave ex- thing must always be remembered : Hamburg,severalchimes,gongs, periencedi the trouble of not being the identification signal dare not be musical notes (Stuttgart), and about able to identify some station or other. so monotonous as to drive the local every kind of sound we can think of. As long as broadcasting stations listener to distraction. I had nearly forgotten the best inter- have not got a permanent wave- Thestations,especiallyonthe val signal as yet, the type employed length, not heterodyned by other Continent,haverendered,orare by Budapest-a pleasing melody, not stations, and with no new stations attempting to render, their intervaltiring to the local listener. cropping, up wanting a wave -length, signals so distinctive that they can and as long as every station has not serve as identification signals, for it is Ideal Interval Signal got one single distinctive wave -length quite clear than an internationally No doubt about it, the Budapest for itself alone-well, as long as these understood identification signal mustsignal seems to be the ideal. One andotherinnumerableconditions be some kind of sound, either musical usually is of different opinion about prevail, which will no doubt be for or otherwise. intervals : some stations(thank many years, every broadcasting station requires some characteristic signal or call, by means of which every civilised human being throughout the entire world will be able to identify the station. Definite Characteristics Wanted We all have names, we all have hundreds ofcharacteristic features which make us totally different from other people, but so has every broadcasting station, only that up to the present moment either you must be intimately acquainted with the station to recognise it, or you must understand the language, or one of the languages, used by the given station. What we require is a call or signal understood by everybody without the necessity of special knowledge, such as knowing Morse, Esperanto, etc. A musical -box interval signal is used by the Budapest broadcasting station. 131 MODERN WIRELESS February, 1929 goodness) .are slowly abolishing themtothelion'sroar and thefish's ality and knowledge, general or other- but the need for an identification signal silence. wise, can recognise a given station. remains. Let it be sounded before or Now a tune-simple, pleasing and after every item before the announcershort-meets all requirements, with acg@@EAFfficge@cgEgi@@@ W4cgig5 has his say.Local listeners will notone exception-how are we to register BELOW SIXTEEN 683 have to tear out their hair because of half a minute's ticking metronome, METRES but will like the simple little melody .0@@il)@@@@ @Wfe6P.S41'f03) typical to their own station. And the foreign listener in whatever country The Editor he may be, whether musical or un- MODERN WIRELESS. musical, will recognise the signal as SIR,-In your December issueof typical to this or that station, even the MODERN WIRELESS, W. L. S. if the wave -length is not that which wishes to know if any reader has heard was advertised. anytelephonybelow 16metres. Well, I should like to mention that Alternative Suggestions some fewweeksagoI heard an Surely there are sufficient simple Americanaccentcalling" Hallo, tunes to go round the stations.The Bridgewater " several times, following main station will have some funda- up with American news and gramo- mental tune, the relays will have some phonerecords ;andalsoI have slightvariation. Stationsinone lieard, wellblowthat - on,I countrywillhavedeepmelodies, should think, about 10 or 12 metres othercountrieswilladopthigh- -two Morse stations.(Being unable pitched tones. Thus we will always be to read Morse I cannot say who they able to tell what station, what relay, are, but I should very much like to and from which country the sounds A " cuckoo " signifies that you have tuned - know.) are coming. in Ljubljana or Wilna. Above isthe mechanism employed. I should also like to say I can get Morse is bad because it is monoton- almost any station with perfect ease ous and not understood by everybody. on the short waves, with very little ifaor publish it for those people who Esperanto would be allright reaction. mechanical signal were not far betterknow nothing of notes or pianos or, My set is called the " Handyman " and if really everybody could under -in fact, anything musical ? Once bland Esperanto as pronounced inevery station has its distinctive tune, Two, with an amplifier added, and differentcountries. Cuckoosare some enterprising firmwillsurely it's a gem, and I can assure you I monotonous to the local listener, and construct a kind of tiny, cheap, auto- have tried every short-wave circuit we really cannot have the wholematic gramophone which will per- that has been published (both in animalworldrepresented by themanently reproduce the tunes of all " M.W. "and" P.W."),but the different stations. Fancy one stationthe stations according to the alphabet " Handyman " Two is the master. using the " Bah -bah " of the sheep, or according to countries. Yours faithfully, or the " He -haw " of the donkey next Then another thing, why publish C. ANDREWS. the notes at all ? For the first year or so the change will go gradually, and Middlesex. wave -lengthsareprettyconstant nowadays, which means that distant listenerswillsoongetused and acquainted with every station's distinctive tune. A "Station Medley " ? Just imagine the pleasure to hear our friends in the morning train, or meeting them in the street, humming a tune and asking what station that could have been. Perhaps even somebody will compose a " Station Med- ley," and then we might dance to a mixture of Hamburg, Vienna, Prague, Berlin,Warsaw,Madrid,Rome, Munich, Cologne, with the London signal, perhaps, as a finishing flourish. Interval sighals are things of the past ;what we need are identification signals. And whether these are tunes or not, or if somebody else finds a better solution or not, every station needs some kind of earmark, or in this Milan's musical chimes form a well-known case some kind of " earsound," by Munich `avoLirs an electrical metronome interval signal. which everybody, regardless of nation - placed in a box with a microphone. 132 February, 1929 MODERN WIRELESS THE:MW: TAPPED CRYSTAL SST

In this remarkable little set it has been found possibletoobtain highselectivity, together with a distinct gain in volume, when compared with tapped circuits of the usual type. Designed by the " M.W.- RESEARCH DEPT. and described by A. JOHNSON RANDALL. ro design a crystalset which asthe tapped" aperiodic "aerial serted for the reception of Daventry gives loud signals as well as schemes,withatuned secondary (5 X X). sharp tuning is no easy mat- coil. ter.Many schemes have been tried, The " M.W." Research and Con- The Tappings but, in most cases, in order to get the struction Dept realising the need The method of tuning the set is required sharpness of tuning it has for selectivity without any lossof very simple.There are four aerial hitherto been necessary to sacrifice a volume, has for some time past been tappings, and the aerial lead should little signal strength. conducting aseriesof experiments be joined to all of them in turn in with variousarrangements in an order to find out which gives the effort to overcome the usual troubles bestresults.Alsotherearefour COMPONENTS REQUIRED. :: associated with crystal circuits. How- 1 Panel 7 in. x 8 in. x + in. or -ilf in.!! crystal tappings and the same pro- (Ebonart, " Kay Ray," Resiston, :: ever efficient the tuning coil, there cedureis adopted,i.e.the crystal Red Seal, Ripault, Trelleborgi Becol, :: is always one point to be considered, tap is tried on each of the tappings etc.). .. and that is, the effect of the crystal until the best combination of aerial 1 Cabinet, 7 in. x 8 in. x 7 In. deep.. :: approx. (Raymond, Bond, Arteraft, :: itself.Unfortunately a crystal is not and crystal tap is found for the par- Caxton, Raymond, Pickett, Cameo,:: like a valve. A valve exercises very ticular station being received Makerimport, Gilbert, Loek, etc.). :: little" damping "effectacrossa 1 Coil former, 3 in. diameter x 3+ in. :: tuned circuit.That is to say, it does long (Pirtoid, Radion, Paxolin, ete.). :: 1 Single coil holder (Lotus, Peto-Scott, :: not " flatten " the tuning very great- etc.). :: ly and thereby make it impossible to 1 0005 mfd. variable condenser with separate stations from one another. plaindial(J.B.,Lissen,Lotus, :: Cyldon, Utility, G.E.C., Raymond, :: Igranic,Formo, Colvern, Pye, tt Obtaining Selectivity Dubilier,Ormond,Marconiphone, ;; A crystal, on the other hand, does

Ripault, Bowyer -Lowe, etc.). " flatten " the tuning because of its

1 Crystal detector. low " resistance " and of the fact :: Wire for coil (see text).I lb. of each:: that it is joined directly across the size will be sufficient. :: 4 Terminals, markings according to:: tuning circuit. :: diagram (Belling -Lee,Igranic, :: Now in the " M.W." Tapped Crystal :: Eelex, etc.). ::1 Piece of ebonite for terminal strip,:: Setaspecialprinciplehasbeen

::51 in. x 1 in. x f in. adopted.Instead of connecting the :: 8 Panel -mounting sockets(Clixor:: crystalacrossthetuningcircuit

:: similar type). it is joined to a separate tapped coil :: 2 Plugs to fit sockets (see above). :: inductively and closely coupled to Quantity of No. 18 or 20 S.W.G. tinned ::

copper wire and Systoflex or, alter- :: the tuned circuit.This tuned circuit Now for the actual constructiona

:: natively, Glazite. is simply a semi-aperiodic arrange- part of the set.There is practically :: 1 Shorting bar for loading -coil holder.:: ment with tappings to which the nothing easier to build than a crystal aerial can be taken.There is also receiver.If you look at the photo- Ithas been the usual thing in a loading coil socket which is short- graphs you will see that the home - these sets to employ one of, the well- circuited on the medium waves and wound and loading coils are mounted knownmethodsoftuning,such in which a No. 150 coil can be in - on a wooden baseboard, while the 133 MODERN WIRELESS February, 1929 remainderofthe components are secured to the vertical panel.This procedure of using the vertical panel schemeisvery valuableincases where the listener desires to add an amplifying unit at some future date. The majority of modern amplifiers are built on this principle. Commence the construction by marking off and drilling the panel in readiness for the components. Making a Start The necessary dimensions are given in the panel drilling diagram.Take a straight -edge and a scriber, or a sharp -pointed nail, and mark off lines across the panel, measuring along these lines the various drilling points. Then take a centre -punch and give it a tap with a hammer at the centre points so that you will have a mark at each drilling centre deep enough to prevent the drill from wandering The.0005tuningcondenserwill probably require a 1 -in. bit and it is advisable to use this in conjunction with an ordinary carpenter's brace rather than one of the American hand - drills. tappings from the coil.On the right- Above the tuning condenser are the Then there are eight sockets-fourhand side (looking at the back) of the two holes for the crystal detector on each side of the panel-for the panel a small hole will be needed near mounting, and you will see that one

1.1 these sockets for the flexible from the of these screws has a flexible which aerial to the plug to pass through. terminates in a second plug for the L2 or crystal tap sockets. Here we see the four crystal tappings which Along the bottom edge of the panel, are taken at 20, 30, 4o, and 5o turns along about T-6- in. up, you will require three the winding L5.These taps are joined to holes to take the wood screws which sockets on the right-hand side of the panel secure the panel to the baseboard. (looking at the front) and are marked L2 in the panel layout diagram shown above. At the back of the baseboard is a strip of ebonite about 5k in. long and 1 in. or Ak in. in width for the four terminals.The terminal strip can be mounted horizontally on two wood blocks, but this is not very important, and if the constructor wishes it may be secured vertically directly to the edge of the baseboard. Winding the Coil After you have mounted the components on the panel and secured it firmly to the baseboard you will be ready to turn your attention to the construction of the broadcast band coil.This is made as follows : The basis for the coil is a former of any good material 3 in. diameter and 32 in. long.Upon this there are two Windings, one consisting of .60 turns of No. 24 gauge D.S.C. with four tappings, and another of 50 turns of No. 32 D.S.C. with four tappings, which has to be interwoven, turn by turn, with the thicker winding. This is how you proceed to wind the coil.Arrange your two bobbins on the table and take the two ends and. twist them together.Secure these by 131 - February, 1929 MODERN WIRELESS passing them through two small holes expect good volume if you have a really efficient circuit that will func- in the tube placed about three-quarters poor aerial. tion satisfactorily with the average of an inch from one end.Proceed to Many listeners frequently wish to crystal set, and in addition listeners wind on the two wires, side by side, increase the volume they are obtain- who have had no previous experience pushing them up close together with ing in order to work a loud speaker. of two -dial tuning would find such the thumbnail as you proceed. When The easiest way to do this is to add a unit rather beyond them. you have wound on 15 turns of the a separate low -frequency amplifying thicker wire, twist up a small loop, in unit to the set. Obtaining More Volume the thick wire only, to form a tapping To obtain decent loud speaking If you want louder signals, by all point.At the twentieth turn take a itis advisable to construct a two -means build an L.F. amplifier, but second tapping along the thick wire valve amplifier, because a single -valve do not try to add one of the H.F. winding and the first tapping alongamplifier is really only suitable for units intended for use with valve the thin wire winding. Take tappings use within a few miles (three or four) receivers.Itisa vastly different along the thick wire winding at 25 from the local station.A two -valve matter to design a high -frequency and 30 turns, and along the thin wire amplifier, on the other hand, will amplifier for a crystal set.It is not winding at 30, 40 and 50 turns, taking operate a sensitive speaker up to suggested that it is impossible to use care to keep the two sets of tappings distances of ten miles or so from a high -frequency amplification in con- well separated. main B.B.C. station. junction with a 'crystal.The use of Such a unit is quite easy to make, H.F. valves with a crystal set has, Wiring Up and its operation is simple and does however, dropped out, except in the When you have finished winding the coil, mountitverticallyonthe In this view may be seen the socket for the loading coil, and the four aerial tappings. When the set is baseboard with the aid of a strip of being used on the medium broadcast wave -band wood inserted in the coil former and the 5 X X coil socket is short-circuited, as shown. screwed down to the baseboard. When it is desired to go over the long waves, a No. The strip should have the ends z5o coil should be inserted in this socket, and the rounded so that it fits tightly inside aerial condenser readjusted. the former.Then place the loading coil socket in position. Now you are ready for wiring up. There is little to be said about this. The various leads-which can be Systoflex-covered16-or18 -gauge tinned copper wire-can be soldered to the tapping loops on the coil, but in many cases you will be able to use theterminalconnectionsonthe components, thereby obviatingsol- dering. When you have completed the wiring the set will then be ready for testing.Join the aerial and earth leads to the terminals so marked and a.pair of high -resistance (2,000 ohms) telephones to the 'phone terminals on the strip.Insert the L, tapping plug in the 30 -turn socket and the L2 wander plug in the 50 -turn socket. Short-circuit the loading coil socket with one of the plugs sold for the purpose and adjust the tuning con- denseruntil you hear your local station.Then try various positions for the L1 and L2 plugs to see which gives the best results. Receiving 5 X X To tune in 5 X X insert a No. 150 not add complications to the existing case of special circuits such as, for coil in the L3 socket and re -tune on set. instance, the reflex type. the tuning condenser. Thereisatwo -valveamplifier Constructors who are unable to This set should receive 5 X X up to blue print which is very suitable for erect a good outdoor aerial are very distances of 80-100 miles, and an use with crystal sets.Its number is badly handicapped when the question ordinary main B.B.C. station up to 38, and the price 7d. post free from of getting the best from a crystal 12 -15 miles.For a relay the range the publishers of this journal. receiver arises.A crystal possesses would be about 5 miles. Use,if Sometimes readers desire to increase no amplifying properties and in conse- possible,agoodoutdooraerial, the range of their crystal receivers. quence it relies solely upon the energy because the strength of signals depends This is not an easy matter, and the picked up by the aerial.Now, if the upon the efficiency of the aerial and'use of an H.F. unit is not to be aerial is poor and badly screened the earth systems, and itisuseless to advised.It is difficidt to design a total amount of energy picked up will 135 MODERN WIRELESS February, 1929

besmall and. signalstrengthwill tivity, the permanent type is to be Glmsgo2G0f3,0q3G1,c33 gig suffer.If you are situated very near recommended. your local station, say, within a mile Here is a final hint. Do not paraffin - 2 5SW IN INDIA qi3 or so, an indoor aerial may be quite wax or shellac the coil with the idea of mamt,oZt839SC300'83q3cM30 O.K., but otherwise it will pay you waterproofingormakingitmore to build a single -valve set,if you robust.This used to be the usual cannot erect a decent outdoor aerial. procedure with coils a year or two ago. SIR,-I am now going to give this informationregardingthetrans- mission of 5 S W (Chelmsford, England), of The British Broadcasting Corporation. Ireceivetheirtransmissionat good loud -speaker strength on using lb*" YS TA Z. one detector and two low -stage. Their DETECTOR transmission was very clear, like a IP local station (7 C A, Calcutta station, 12kw.) ;speech was asclearas 50 possible, very steady; the evening transmission from London comes here

as good as possible.It seems to me TUNING that 5 S W is one of the most powerful 40 CO IV D sR 25 0005,141- To stations in the short- wave telephony. ok PLUG I received their test transmission with the station 2 X A D (U.S.A.). 20 I am now regularly going to hear the following short-wave telephony stations :5 S W, 2 X A D (U.S.A.), 2 X A F(U.S.A.), 2 X G (U.S.A.) 20 /5 (the American stations come here on goodheadphonestrength),3 L 0 (Melbourne), 2 M E (Sydney), 6 A G (Perth, West Australia) (the Australian stations come here good loud -speaker strength).The Dutch stations, P C J J and P C L L, come here good headphone strength.The 7 L 0 station comes here like a local station.The Java short-wave stations, A N E and A N H, come here like a local station. I have heard sometimes the A N H station going to test with the station 2 M E (Sydney, Australia). This is the report of my short-wave work.I am now using the straight short-wave circuit.I hope that you @ VW will be glad to get this information. Yours faithfully, 50 M. MOZOOMTIER. Calcutta, India. 40 (30 OFScMQVM9C3SiG,X3f,'3(tZ TAPP/NGS THREE USEFUL TIPS ON TANN W/RE CO/L EA000EAEMES50)Z,PO&OSEP,c,,,

TOP E/Vd0 OP I , 7/1/CK WIRE CO/L A fact which is often overlooked is that (5)) er, wires running too close to one another in 1, (60 -72"TapivACD EA H ,4E a crystal set will often give rise to a serious loss of strength. W229 WIRING D/AGRA/14. Here is another tip.Never touch Modern development proved that Continuous scratchingnoisesinaset, accompaniedbyagreatlossinsignal a crystal with your fingers.If you it did not pay to cover the coil with strength,generallyindicateaburnt -out do, you will probably leave a coating a coating of varnish or wax, since the transformer winding. of grease on the surface and destroy " dope " increased the self -capacity of the sensitivity of the detector.If the winding and reduced its efficiency Although a little sag is advisable in the you require maximum signal strength, very considerably. aerial, it is important that it should not be allowed to swing too much, or one or more a good cat's -whisker crystal detector In the ordinary course of events of the strands may be broken, which will is best, but if you want reliability at there is very little danger of the wind- give rise to unpleasant crackling noises in the expense of a slight loss of sensi- ings getting damp. the set. 136 February, 1929 MODERN WIRELESS

Details of a " baby" short-wave transmitter which is being used for tests where a portable station is essential. By- L. H. THOMAS (6 Q B. 6L T "is the pet name of a portable transmitter which for the steady signal that it will put out when properly Owing, however, operated. " was built in the spring of 1927. to the almost entire absence of any summer during The valve in the socket is an L.S.5, which. was used that year, operations with the portable did not commence throughout the tests.The complete circuit is shown in in real earnest until this last summer, when the weather Fig. 1. was very much more in keeping with such pursuits. The receiver is a perfectly and one The transmitter was really made in the first place with stage of L.F.It is somewhat remarkable to note that as the object of touring round the neighbourhood in a small soon as one gets well out into the country this receiver will car, camping out at various points, and getting into touch often give far stronger short-wave signals on the smallest with the " home " station, 6 Q B, for the purpose of aerial, perhaps not more than 10 ft. high, than it will checking the directional effects of the " home " aerial, on the main aerial at home, although that is believed to and the screening effects of various large buildings and he in a fairly good location.

steep hills in the neighbourhood. 1st This year, however, the home station was moved to a better locality, where there is considerably less screening, and there was, consequently, rather less work to be done on these lines than was anticipated.6 L T, therefore, degenerated into a mere transmitter which was taken for a ride out into the country on occasions and used in conjunction with small aerials slung up convenient trees. A Complete Low -Power Station As yet no serious work has been done between the two stations, as there seems to be no real reason for carrying out such tests -unless over a fairly long distance. " 6 L T," of course, comprises a receiver as well as a transmitter, in compliance with the conditions of the licence. It must also carry with it a licensed operator who has satisfied the G.P.O. of his ability to send and receive Morse signals at a given speed. The interior of the transmitter, showing theL.S.5 valve and One of the photographs gives a good idea of the layout the, short-wave coils. of the transmitter, which is kept separate from the re- As will be seen from the photograph of the front of ceiver, although the two are mounted on the same frame the set, the two tuning controls of the receiver have been and baseboard.Although the very lowest powers were placed on a small panel mounted at the top of the frame to always used, the transmitter was constructed somewhat facilitate tuning.Only the rheostat is mounted on the solidly, and all wiring was carried out with No. 12 gauge front panel, which houses also all the transmitter controls, copper wire, for the sake of rigidity. the change -over switch, and the H.T. and L.T. terminals. The actual circuit used was the favourite Armstrong The frame has been made to fit snugly into the rear or " tuned -plate tuned -grid ':arrangement, chiefly be- seat of the car.The seat itself is fairly well sprung, and cause this lends itself to a compact layout and is noted for this reason it was not thought necessary to indulge in 137 MODERN WIRELESS February, 1929 the usual fancy mounting of rubber bands, inner tubes, Tins was very convenient for studying directional or anything of the kind, for the apparatus. No breakages effects also, since the car could be driven round the have yet been experienced, although some Very rough tree without disturbing the transmitter at allNaturally, roads have been traversed in the search for a good location. the amount of swing possible was usually limited by the From the L.T. terminals two thick leads are taken presence of other trees, not to mention ponds, fences, and other obstructions IThe spare two feet or so " beyond " the insulators at the lead-in end was simply taken to the aerial terminal on the transmitter ;thus it was possible to make the aerial quite reasonably tight without hauling the whole apparatus out of the car. The Most Startling Result The aerial was supposedly working as a " halt -wave voltage -fed Hertz," to give it the full title, being fed directly at the end.As will be seen from the circuit diagram, one side of the aerial coupling coil (that nearest Changing over from " transmit " to " receive " on 6 L T. the anode coil, in practice) was leftdead," the other straight down to the car battery, which is normally being taken to the aerial. housed under the near -side front seat ;these leads are, t herefore, quite short and do not interfere with the wiring of the car in the least. From the H.T. terminals, also on the front panel of the transmitter, two leads are taken to the H.T. supply. which is housed on the floor immediately beneath the transmitter, behind the front seats. TURNS The H.T. supply has been changed from time to time. An anode converter, delivering 550 volts, has been the standard supply for 10 -watt tests, but when much lower powers haVe been employed for various reasons, one or two 99 -volt H.T. batteries of a standard receiving type have been used, and stood up to their rough treatment quite well. A " Mobile " Aerial ! The meter at the left-hand end of the main panel is a Telefunken hot-wire meter with a shorting switch incorporated.Although the actual value of aerial current obtained with the transmitter means nothing at all, it is always useful to have a ready means of comparing aerial currents with one or more aerials and with different transmitter adjustments, and for this reason the meter was incorporated.The other meter is a Weston milli - ammeter in series with the H.T. supply. Two ofthe other photographs show the set in its natural surroundings, one in particular showing the method of erecting the aerial. For work on 45 metres, which was the wave -length used for most of the tests, an aerial exactly 221 metres (approximately 73 ft.) long was used. and

Probably the most startling result obtained. with the transmitter was on the very first test which was carried out.The location was between Chipstead and Reigate. An Immediate Reply The aerial was a makeshift affair slung to a dead tree lying in a field, the topmost parts of which were no more than 14 ft. high.Since the " home " end of the aerial, attached to the car, was but 3 ft. from the ground, the average height of the whole affair was just over 8 ft. With an input of exactly 1 watt (10 milliamperes at The transmitter is to the left of the change -over switch, the 100 volts) a short test call was transmitted, and a reply section to the right is the receiver. receivedimmediately from GW-11D, atNaas,Co. for the sake of convenience this was carried in the form Kildare, a distance qf about 250 miles. He reported the of a 73 -ft.lengthofrubber -coveredflex, with two C.W. signals as " RA very clear and dead steady." insulators permanently fixed at either end. At none of the locations tried since has it been possible The usual procedure was simply to fix one end of this to obtain another report as good as this with a similar to the top of a convenient tree, attaching the other_ end input. Strangely enough, this particular location was to the back of the car and driving the car slowly away apparently far from good from the receiving point of from the tree until it was fairly tight. view, since all the stations heard were extremely weak. 138 February, 1929 MODERN WIRELESS

A review of some of the outstanding broadcasting events of the year. By THE EDITOR. OSSOMMINIERMOSIWOMMIMS*

THE B.B.C. has circulated some wider area than the present 2 L 0. Our photo above shows Earl notes concerning the progress Furthermore, there will be less inter- Jellicoe before the microphone. oftheCorporationduring ruption, and eventually itis anti- 1928. These notes certainly make cipated that the station will give all remember that last January a new interesting reading, and the compiler South -East England aerial was erected at Daventry ex- of them is of the opinion that one of programme, first in an experimental perimental station with the result that the most outstanding events of the form and, later, when technical pro- the quality of reception of 5 G B's year 1928 was the start made in May gress has been made, on a permanent programmes in the North-East and on the new Regional Transmitter at basis. South of England showed a very great Brookman's Park. improvement. As every reader knows, this is the Further Regionals Some of the chief outside broadcasts new twin wave -lengthhigh -power Other sites in other parts of Great of the year included the relay of the station for London, and when it isBritain are also now being investi- nightingale's song from Pangbourne completed it will be the first of its gated by the B.B.C. engineers with a last May, when reception reports were kind to be erected in the world. It is view to the erection of other Regional sent in from as far away as New anticipated that this first Regional stations similar to the one now in Zealand. There was also the relay of station will be in operation some time course of construction at Brookman's a running commentary on the Univer- this summer, and that when com- Park. sity Boat Race last March, the relay pleted it will cover a much larger and Listeners who keep a diary will ofadescriptivenarrativeofthe

IIf ,- - . These illustrations recall two of the B.B.C.'s successful " outside " broadcasts, viz., the Oxford and Cambridge BDat Race and the debate between Mr. G. B. Shaw and Mr. G. K. Chesterton. 139 MODERN WIRELESS February, 1929

Derby on June 6th, and other well- nowontmuing, and is proving ex- Ronald,HamiltonHarty,Henry known races in June and September. tremely popular. Wood and Percy Pitt. Another important and successful Plays by Ibsen, Strindberg, Sheri- PromenadeConcertswerealso outside broadcast was the relay of the dan, Oscar Wilde, Temple Thurston, broadcast this year from the Queen's Armistice DayServicefromthe John Drinkwater, Maeterlinck, Yeats, Hall, and a series of B.B.C. Symphony Cenotaph, last November 11th, and Synge and Bernard Shaw were also Concerts began in October, the first listeners will also probably remember included in the dramatic programmes conductor being Sir Thomas Beecham. therelaylast March from Liege, for1928, and among the famous At a later concert, a special work which included a choral programme artistes who appearedbeforethe entitled " The Pilgrim'sProgress," given by the famous Liege Choir. On microphone may be mentioned Lady by Professor Granville Bantock, was March 12th, the B.B.C. gave the first Forbes -Robertson,PhyllisNeilson - . given,with the full newly constituted simultaneous broadcast from British Terry,MathesonLang,Granville - National Chorus. and German stations, the Second Act Barker, Fay Compton, Mabel Terry of the " Marriage of Figaro," per- Lewis, Wilkie Bard, Clarice Mayne, Operatic Broadcasts formed in the studio of the Cologne Arthur Prince, Muriel George and Some of the great musicians of station, being relayed to London. ErnestButcher,VioletLorraine, the day have broadcast during 1928, Harry Lauder and many others. and althoughthey cannotall be A Famous Relay 1928 also saw the inauguration of mentioned, they included such stars Then, in August, was the relay of variety turns relayed from the stage as Olczewska, Elizabeth Schumann, theservicewhichterminated the and broadcast to listeners. These Eugened'Albert,Suggia,Miriam British National Pilgrimage to therelays from the Palladium, London, Licette, Solomon, Medtner, Moisei- battlefields. This was broadcast from are still continuing,, and among other witsch,Gretchaninov, Myra Hess, the Merlin Gate to all stations of the stage relays of the year must be Albert Sammons, Pampanini. B.B.C. except 5 G B, and was also mentioned : Excerpts from " So this SomeoftheOperasbroadcast in1928included : " Maritana," " Pelleas and Melisande," " Samson The broadcasting of the and Delilah," " The Blue Forest," song of the nightingale " The Girlofthe Golden West," -one of the most popular of all the broadcast The Return of Ulysses," " Merry events-has been greatly Wives of Windsor," "Armida," " Cosi assisted by Miss Beatrice FanTutte,"" ManonLescaut," Harrison.She is here " Oedipus Rex ," and among the shown in the studio playing the 'cello that is used Light. Operas may be mentioned the to encourage the nightin- firstperformance of " Charming gales tosingforthe Chloe 'and " A Sea Change ;also microphone.Last year's must be mentioned the first broad- nightingale broadcast was from the woods near cast performance of" Merry Eng- Pangbo urne. land " and " Tom Jones' by Sir Edward German, and " The Rebel Maid," by Montague Phillips. Last February was formedthe' broadcast by the short-wave station, is. Love," from the Winter Garden NationalOrchestraofWales,in 5'B W. Theatre ; and " Virginia," from the co-operation with the B.B.C., when Other relays of the year included Palace Theatre, London.An out- the latter undertook to support the one of the first matches in the F.A. standing new feature commenced in scheme financially. Cup competition, the Cup Final at 1928 was the surprise item. The first Wembley,theWimbledonLawn surprise item wasgiven - inJuly Tennis Tournament, the final shoot andhasbeencontinuedweekly Well -Known Speakers for the King's Cup at Risley, etc., etc. ever since. In March, 1928, following a state- A. running commentary of the Tunney Probably the most interesting was ment made by ,the Prime Minister v. Heeney fight at the Yankee Stadium, on August 10th, when thebroadcast in the House of Commons, the B.B.C. New York, Was also relayed fromtook place from a Signal Box at announced that authority had been 2 L 0 and 5 X X in July, and from King's Cross, and also on September conceded to them to include contro- Lakehurst, in October, was given a 14th when Jack Hobbs and other versial matter in the programmes-a descriptivenarrative of the arrival members of the M.C.C. team broadcast satisfactory conclusion to a five years' of the Graf Zeppelin. a good-bye on -the eve of their depar- endeavour to secure thisprivilege. ture for Australia. Although it has been very difficult Outstanding Plays A musical relay of great importance sincetogetsuitablecontroversial Some oftheoutstandingradio occurred 'on January 5th, when the programmes, readers will remember plays of the year. included : " Pursuit " Royal Philharmonic Orchestra's pro- that some very interestingdiscus- (given lastJanuary)," Speed," gramme wasbroadcastfromthe sionshavebeengivenin1928, " Rampa," " Through the Looking Queen's Hall via 2 L 0.Symphony among which may be mentioned the Glass," " Caravan," " Montezuma." Concerts in London and the provinces 'debates between SirErnest Benn The B.B.C.'s new seriesofplays have been broadcast under the direc- and Mr. James Maxton,M.134, on selectedfromclassicsofBritish, tion of the world's most distinguished " Riches and Poverty " ;Mr. Pat Belgian,Norwegian,Spanishand conductors,including Dame Ethel Hendren and Colonel Philip Trevor other authors was started in Sep- Smyth, Eugene Goossens, Stravinsky, on " Cricket "-;the Rt. Hon. tember underthetitleof The Scherchen, Talisch, Schneevoigt, von J. H.Thomas, M.P.,andCol. World's Great Plays."This series is Hoesslin, Fried, Barbirolli, Sargent,J. C. T. Moore-Brabazon, and, later, 140 February, 1929 MODERN WIRELESS

Mr. Thomas's " gloves off ". debate the Memorial to the Merchant Navy, Fultograph system will be continued withtheEditorofthe" Daily the ceremony being relayed from for another twelve months. Express." Tower Hill. At the end of1928, the B.B.C. There was also the debate between His Majesty the King was heard announced that following the intro- MissEllenWilkinson,M.P.,. and in July, when he opened the new ductionoftheRegionalScheme, Mr. W. H. Thoday on the question of University Building in Nottingham, rather than withdraw. the relay stations " Should women be paid as much as and again in October lie performed an attempt was to be made to over- men ? "andMissMarjorieFry theopening ceremony of the new come interference and revive their and Captain Arthur Evans, M.P., on Tyne 'Bridge. usefulnesS by adopting the arrange- " Capital Punishment." The Prince of Wales' first broadcast ment of Single -wave working. in 1928 took place in March, when The Nottingham transmitter was Royalty Before the " Mike " he spoke at the Annual Banquet of taken out of action in November, and It would be impossible to give a the Master Mariners at the Mansion Nottingham listeners have since taken list of all the talks given in 1928, but House. their place among the Birmingham amongthedistinguished speakers In May the Prince was again heard listenersintheservicearea of may be mentioned :Sir Nigel Play - whenhisopeningspeechofthe the Daventry Experimental station, fair,SirBarry Jackson,MissV. Royal Tweed Bridge was broadcast 5 G B. Sackville-West, the Rt. Hon. Arthur from Newcastle, when the B.B.C. Ponsonby,Mr. GeorgeGrosnith, relayedtoLondon and broadcast Few Breakdowns Sir James Jeans, the Rt. Hon. L. S. from other stations. During the year the B.B.C. broad- Amery, Rt. Hon. W. Orrksby-Gore, The Princewas again heard in castprogrammesoccupied68,000 Rt. Hon. Philip Snowden, Sir Valen- June at the Unveiling of the Welsh hours,thisincludingall trans- tine Chirol, Lord Jellicoe, Lord Cavan, National War Memorial, and, lastly, missions ' from twenty-onestations Sir Sefton Brancker, Sir Alan Cob- on Christmas Day, when His Royal of the B.B.C. ham, Lady Heath, Major Malcolm Highness appealed from the studio The totalperiodofbreakdown Campbell, Emil Ludwig, Ian Hay, at 2 L 0 on behalf ofthe Miners' wasless than twenty hours; and, E. F. Benson, John Buchan, Lord Distress Fund. finally,as a proofof the steadily Dunsany, John Drinkwater, Compton growing popularity of broadcasting Mackenzie and many others. Fultograph Tests and thesuccess ofthe B.B.C.,it Among the Royal broadcasts of the Thefinaloutstandingeventof may be mentioned that the licences year was that of the Queen, when 1928 was the first transmission ofin force on November 30th,1928, Her Majesty was heard for the first still -pictures in October, the experi- numbered 2,580,342. Thisfigure time by listeners on December 12th mental broadcasts being so successful includes 13;826 free licences issued to on the occasion of the Unveiling ofthat itis now understood that the the blind.

ON Theleft-hand picture shows the equipment on the launch which followed the boat -race, and on the right is a viewof the Cenotaph service in Whitehall. 141 MODERN WIRELESS February, 1929

are as follow :One terminal of the transformer secondary is taken to one side of the potentiometer.The Questions other secondary terminal goes to the other end of the potentiometer resistance strip.The lead from the Answered secondary terminal to the grid of the valve 'is disconnected and taken to the moving arm of the potentiometer. An Efficient Two-Valver 0. A. K. (Glasgow).-" I am a com- parativenoviceinconstructional work, and I should like to make up a two -valve set for all-round work. I am rather keen on making up a set from a blue print, since I find these easy to follow, owing to the large Screening -Grid Voltage Yes, a volume control is beneficial scale to which they are drawn. with any set except perhaps two- " Can you tell me where I can G. K. (Sidcup) hasanH.T. valvers such as a' det. and L.P.In obtain a suitable blue print ? " eliminator and finds that he is un- the case of the pentode, one might Blue prints of a large number of able to adjust the. voltage on the say that a strength control of some receivers of standard type are ob- screeninggridofhisH.F.valve sort is almost essential. tainablefromtheRadioQueries (one of the vertical type) to his liking. The pentode has asteep curve, Dept., Fleetway House, Farringdon His mains unit has three tappings, since it has a very high amplification Street, London, E.C.4. none of which gives the required factor. In consequence, the per- The price is sixpence each, and all 80 volts. missible grid swing is about equal to applications should be accompanied Yourbestplan,G.K.,is to with a stamped addressed envelope. procure resistanceof a variable aill111111111ililM11111111111111111111111111111111111111111111111111111111 A list of blue prints in stock will be E the Centralab or Bradleyohm type, E forwarded uponrequest.. In your having a value not exceeding 250,000 ---. THE TECHNICAL QUERIES ..- .E.. - particular case we recommend blue ohms.Place this in series with the DEPARTMENT print No. 31, a " Standard " Two- H.T. lead to your screened -grid valve, Are you in trouble with your set P = Valver, which is a most efficient de- and adjust its value until you obtain Have you any knotty little Radio problems E. tector and one L.F., incorporating the desired results. E requiring solution ? The MODERN WIRELESS Technical Queries = plug-in coils and Reinartz reaction. You may have to use one of the E Departmenthasbeenthoroughlyre- = higher H.T. tappings on your elim- E organised and is now in a position to give E an unrivalled service.The aim of the de- E Selectivity and Crystal Sets inator, but the resistance will give partment is to furnish really helpful advice in connection with any radio problem, W. W. (London).-" I have a crystal you all the control needed. Do not E.theoretical or practical. E ettempt to measure the H.T. voltage E Full details, including the revised and, in E set which gives me all I desire in the cases, considerably reduced scale of charges, on the screening grid when the re- - can be obtained direct from the Technical = way. of volume from the London E Queries Department, MODERN WIRELESS, station. My trouble is to receive sistance is in circuit, because if you = Fleetway House, Farringdon Street, do you will find it practically im- = London, E.C.4. 5 X X and 5 G B withoutinterfer- E A postcard will do : on receipt of this all the possible to obtain an accurate read- E necessary literature will be sent to you free = ence from 2 L 0, from which station E and post free, immediately.This applica- I am only three miles distant.Can ing with a voltmeter of the ordinary E, tion will place you under no obligation type.Your adjustments should all EveryreaderofI1foDERN I improve the selectivity in a manner 17, whatever= WIRELESS should have these details by be carried out by experiment, and him. An application form is included which will enable me to do this ? " which will enable you to ask your questions, = You are situated in what one may when you get the best signal strength so that we can deal with them expeditiously E you will know that you have obtained and with the minimum of delay.Having = term the " swamp " area, and we are this form you will know exactly what E.= the optimum value of H.T. for the E information we require to have before us in E afraid that it will be very difficult particular valve you are using.One order to solve your problems. E- for you to cut out the powerful local of the advantages of this resistance 511111111111111111111111111111111111111111111111111111111111111111111110 transmission and receivethe two in the H.T. lead is that it helps to Daventry stations. Your best plan is prevent batterycoupling,because that of a small power valve, although, tobuild a two -valveset,with a in very nearly every set there is a of course, the actual volume obtained selective H.F. stage, and to use this fairly large by-pass condenser fromfor this small grid charge is much in conjunction ;with a wave -trap if the screening grid to L.T. -.This greater than that which one would necessary. in conjunction with the resistance getwith anordinary3 -electrode By doing this you will stand a' forms to some extent an" anti- valve.It is, therefore, essential to ad- much better chance of eliminating mobo " device, and is a help in pre- just the signal strength so that the this local interference.Such cases venting instability. pentodeis not overloaded, and to as yours are fairly common, and it is do this a volume controlis very always a troublesome matter to tune necessary. De -tuning is one method, out thenearby station' when en- Volume Control but perhaps the most convenient deavouring to receive another weaker D. T. A.(Chiswick)asks whether scheme is a potentiometer of about transmission. a volume controlis an advantage500,000 ohms (or more), connected With a valve set it is easier to when a stage of L.F. incorporating a across the secondary terminals of the obtainselectivity, and thereisa pentode valve is used. - L.F. transformer.The connections bigger reserve of signal strength. 142 February, 1929 MODERN WIRELESS

ivw" SPORTABLE FOUR This is a set that contains its own aerial, batteries, loud-speaker-in fact, everything. A set thatcan be picked up and carried from room to room as desired.A set that gives really good reproduction of your local station, with 5 GB and many foreigners as alternatives.In fact, just the set you have been looking for. Designed and described by the " M.W ." RESEARCH DEPT.

greatandstillgrowing The wholequestionisavery results,i.e.thenumber of valves popularity of the more power- interesting one, and its importance required.It seems that we must fultype of semi -portable hasbeenconsideredsuchasto assume that a built-in frame -aerial receiver has been quite a remarkable warrant the expenditure of a greatwinding must be used, since most feature of the current wireless season. deal of time in experimental work in people apparently object to a separate That such sets should be taken up sothe " M.W. " Research Dept. We one, however it may be arranged. widely during the Winter months may have investigated the whole problem This initselfisa handicap, since seem odd to anyone who has always with some' thoroughness, and in the such a frame cannot be as efficient as thought of them as holiday or picnic course of the practical work -under- a separate one, and this means that outfits, but the -factis that many taken we have arrived at some general greater sensitivity will be required. people- have been discovering that conclusions which may interest the they have really a far wider sphere of reader who is considering such a set The Enclosed Aerial

usefulness. . for his own purposes. Basing our exp )riments on such a Modern types of self-contained sets First of all; there is the questionmoderate sizeof frame as can be haveso improved in performance oftheamountof amplification fitted inside a normal type of " trans- that they now make very serious necessarytogetreallyadequate portable " cabinet, and allowing for claims upon the attention of everyone who wants the programmes in different parts of the house, does not want to erect an outside aerial, or objects to the untidiness of the ordinary set, with its exposed batteries and separate loud speaker. Growing Vogue of Portables They can now be produced in forms giving really good reproduction, and the larger versions can be depended on to receive the local, 5 G B, and quite a number of foreigners on the loud speaker without the use of an outside aerial.Taken all round, such a set is a very attractive proposition, bearing in mind its neatness and freedom from externalconnection, and it is evident that it will make an increasingly strong appeal to the home The containing case with loud speaker is shown to the left, whilst beside it is the frame constructor as time goes on. aerial assembly containing the set, which fitsinside the case. 143 MODERN WIRELiSS I February, 1929 the reduced 'efficiency resulting frem with. ordinary valves would be needed laid down. We nextproceeded, its being placed round the set, speaker to give the desired results, and it was therefore, to try out some aperiodic and batteries, we have found a single decided that the resulting increase in H.F. couplings for the S.G. -valve, normal three -electrode H.F. valve is the size and complication of the set and some very remarkableresults scarcely sufficient. was undesirable. were- obtained. Moreover, to get high amplification Accordingly,we turnedtothe We at first expected that there from such a valveitisgenerally screened -grid valve in hopes that it would be an inevitable heavy sacrifice necessary to use fully -tuned intervalve might be found that a single stage on of sensitivity on using an S.G. valve

H. T+/ .77-1- 2 r+ 3

FRAME 4ER/AZ.

C3 0003

I REACT/ON

w 247 circuits, and that means two tuning theselines would be adequate. A in this way, i.e. with an aperiodic dials.This, in turn, means a rathernormal fully -tuned stage was first H.F. coupling, and it was a very difficult set to operate, since tuning tried, and this, as might be expected, gratifying surprise to find that this is becomes exceedinglysharpand didactuallygivequitesufficient by no means the case.As a matter of critical on a frame aerial.Ganging amplificationforthestandardof fact, with the best of these aperiodic we do not find a satisfactory solution reception we had in mind (more as couplingstheamplificationunder of the problem under home con- to this later).. certain conditions is fully equal to struction conditions :it complicates A stage of H.F. on these lines, that obtained with one of the popular matters greatly and introduces risks however, was found to present a very fully -tuned S.G. circuits, i.e. the one of trouble, difficult problem from the stability known as " parallel feed." point of view, and in any case the That this should be so may seem One or Two Stages ? extra tuning dial was not inac- at first sight a little .hard to credit, To ensure simple handling and make cordance withtheplan originally butif we look at the elementary the set suitable for general domestic The loud speaker forms use it is evident that a single tuning a complete detachable dial is essential, and to this limitation unitwhichcanbe screwed in place behind we havetonformed. It was then found the grille in the front that two semi-aperiodic H.F. stages of the cabinet.

Here the se is turned upside down to show the arrangement of the output choke, etc., mythe underside of the baseboard. 144 February, 1929 MODERN WIRELESS theory of the "parallel feed " type of circuit we shall "soon see how it is. Remember that the essential factor. in getting good amplification with this valve is to provideahigh output impedance, that is, a high -impedance intervalve coupling.

COMPONENTS AND MATERIALS 1.1. .** 1 Cabinet, type known as " Birthday 11 Four "(Cameo). 11 1 Pane1,16 in. x 7 in x ik in. orin. 44 (Resiston,Trolite,Beeol," Kay 444 Ray," Trelleborg, Ripault, etc.). :: .. 1.0005-mfd. variable condenser (slow- :: 44.44, motion, or with vernier dial). *4 (Any :: .44. good make of a rather compact :: 44..type will suit.Very large or heavy :: 44 44 instruments are not desirable.A 11 ..44 few examples are the J.B., Dubilier, 11 s4+ Ormond,Lissen,Lotus,Utility, :: 44... etc.) 441 L.T.switch(Lotus,Benjamin, 44.. ,.Burne-Jones, Burton, Wearite, etc.). :: 4.i" Single -circuit " jack (Lotus No. 1 :: orsimilartypeintheAshley, ::

Bowyer -Lowe, Ormond, or Igranic

ranges). ** :: 1Panel -mounting neutrodynecon- .. denser (Used as reaction condenser. ii

.. See note in text re handle).(Any good make, but preferably with very .. .4, gradualadjustment,such as the ..

. Gambrell.) 11 Although so much is packed into a small space, it will be seen that the wiring is not

4.4 Sprung valve holders (W.B., Benja- iiunduly complicated, either on the panel or baseboard.All the battery leads terminate ..min, Lotus, Igranic, B.T.H., Wear- ::in plugs or sp de terminals (L.T.).Note how the output filter choke is m-iunted on the :I ite,Burton,Pye,Mareoniphone, :: under side o' the baseboard, immediately under the last L.F. stage. .4.:.Burndept, Ashley, Formo, Burne- ..Below is the complete set seen from the rear, with valves and batteries in place.Note

Jones, Bowyer -Lowe, etc.). that in spite of the necessary flexible leads the set is remarkably accessible, all leads :: 2 H.F.chokes(Bowyer -Loweand :: being easily reached if required. Igranicinoriginal. Anygood ::

makes of a small and compact type)... 4.4. 1R.C.C. unit,flat type with inter- ::

4.* changeable resistances,or similar :: compactform(Lissen,Dubilier, ::

. Carborundum, etc.). :: 1 L.F. transformer of low ratio (Must ::

..be one of the smaller types-e.g. :: Mareoniphone "Universal," Philips' .011 Igranic type " J," Mullard, R.I.- .. ...4 Varley " G.P.," etc.). O. 1 2-meg. and two .25-meg. grid leaks.. .. with holders (Dubilier, Lissen, Edi-::

swan, Pye, Mullard, Igranic, etc.). 3 Fixed condensers of .0003, mfd. and :: ...*::one of 001 mfd.(Lissen, Clarke, ::

T.C.C., Dubilier, Mullard, Goltone,

Burne-Jones, Igranic, etc.). **.. 1 Output filter dhoke of moderate size44 00 (Igranicc type"F,"Pye, Burne- .4.

.0 Jones, etc.). .. 1 2-mfd. condenser(Hydra, Mullard, .... T.C.C.,Lissen,Ferranti,Dubilier, . ... Marconiphone, etc.). .... Setofcopper-foilsheetsfor screening textfordimensions). (Ready _.(See.Radio, etc.) .. :: Set of parts for loud speaker (Type

*4 knownas" TheConnoisseur's .0 Cone ").(F.Squire,Raymond, ii

::Pearl, etc.) Materials for frame aerial and reaction ::windings (see text). .04

::Flex, wire, H.T. and G.B. plugs, etc. .4. iIn the parallel -feed circuit we have in the anode circuit of the valve an Ii.F. choke, and from the anode end of this a feed lead goes off through a .blocking condenser to the tuned -grid circuit of the valve which follows. Now, the output impedance of this 145 MODERN WIRELESS February, 192 arrangement is simply that of thecircuit we shallaffect the output theH.F.chokealoneforint e tuned -gridcircuit, shunted by the impedanceveryslightlyindeed. valve coupling we shall not, upon the 11.F. choke, which is to all intents and Actually, under some conditions we average, lose sensitivity at allseri- purports in parallel therewith.Ob- may even increase it ! ously, provided that the choke is really viously,ifwe omit the tuned -grid Evidently, then, if we depend upon good. All that we shall lose will be the

S'.9N/ON/A1 /V0/10 V 21 ON/ON/44 7 V/ cY .7 V 7 V/6'791-V V6ed dO 3V-1/teee dO NOkt/kV0.9 Ol ONY 70/.9.1170 0.1 IONS

O0 )

I I I

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711/b'e'.2'0 .70/S NO 2Y7c1c/0.2 aZ February,1929 MODERN WIRELESS

LEAD SOLDERED TO itwill worksatisfactorilywithout SCREW HOLD/NG &ONOsA' theholding -downeffectof the earth connection provided on the FROM LONG normal receiver. SPRING ON The possibilitiesofthe pentode L.S../AcK valve were explored in the course of COPPER SHEET this work, and it was found that there were several serious objections to its use for this particular purpose.In TAG SOLOERED the first place, there is the question TO SCREW HOLO/NG of H.T. consumption, and this is a coNDENS serious one, for in such a setthe TO THE NEGATIVE amount of battery space which it is CONNECT/ON ON 2VOL7- ACCUMULATOR practicabletoprovideislimited, TO 0.PON L.F and the pentode necessarily takes a TRANSFORMER considerable current. For and Against the Pentode Again, we did not find a single pentode stage any simpler from the stabilitypointofview than two ordinary stages, so that there was no apparent gain here. The final decidingpointwasthatof am- WIRING DIAGRAM OF THE CHOKE A'/ZTER plification, since,in our experience,. C/RCUIT ANO SURROUNO/NG CONNECT/ONS. X.425. thepentodedoes notgivequite extraselectivityprovidedbyan isneeded,yetthecircuitmust asmuchmagnification as two additional tuned circuit, and this is a be of such rock -like stability that normal stages of L.F. matter oflittleor no importance ,III111111101MINMENIMMEM" when working on a frame aerial. This arrangement is the one finally adopted for the set, and in the particular details of the reaction arrangement, etc., it is due to Mr. Percy W. Harris, who first pointed out its poten- tialities. Getting reaction, by the way, is rather a difficult matter with this method ofcoupling,sinceit obviously cannot be applied to the grid circuit of the detector valve in the usual way. Special Reaction Circuit In the final version of the circuit it is done by providing a form of the so-calledReinartzcircuitforthe H.F. valve, with a special reaction winding on the frame aerial and a very smallreaction condenser from the plate of the S.G. valve. So much for the circuits affecting general sensitivity.That they are extremely effective you may gather from the fact that the sensitivity of the set is such that it is capable of tuning -in quite a creditable string of foreignstationsat pleasantloud- speaker ,strength, and the easeof handling is all that can be desired. The detector valve works on the leaky -grid principle, since the greatest possible sensitivity is obviously necessary for frame -aerial work. Following uponthis comes a low -frequency amplifyingcircuit,upon which a great deal of work has been expended. The L.F. side of such a set is obviously ofvery great importance,since a Thisis the detachable framework inside which the set is placed.The frame aerial is considerable amount of amplification wound outsideit.Note the ledges on which the baseboard of the receiver proper rests. 147 MODERN WIRELESS February, 1929

The final choice, then, was for two normal fairly high -magnification L.F. stages using ordinary valves. The first stage is resistance coupled,. with a medium valueanoderesistance ( meg.).The next stage is transformer coupled, and it is important that a component of fairly low ratio be used here. Important Stabilisers The various provisions made to ensure stability and correct working on the L.F. side are absolutely vital, and no changes whatever should be made here.First, there is the question of excluding H.F. currents. This kinegohm resistance is connected (in deed.First, to suppress tendencies is attended to` at two points.First, series in the lead to the grid ofthe toL.F. oscillation,i.e.howling, a a fixed condenserof .0003 mfd. is first L.F. valve) as an " H.F. stopper." resistance (grid -leaktype) of connected from plate to filament of On the last stage precautions are megohm is shunted directly across the detector valve, and, secondly, a taken on a very thorough scale in - the secondary terminals of the L.F. transformer. Next, to reduce risks of trouble from battery coupling an output filter is -used for the loud speaker, which also helps to prevent trouble due -to the loud speaker being right inside the frame aerial.This last is a most vital point, and has received far too little attention in the past. Unwanted reaction may operate at either L.F. or H.F. (or both !) and gave us lots of trouble with the first model of thisset.It was finally cnred by introducingastopping and by-passing system of H.F. choke and .001 mfd. fixed condenser.This alone, however, was not sufficient, sincetherewasstillinteraction between the L.F. circuits themselves and the frame winding. To stop this we found it necessary tointroduce a limited amount of copper foil, partly to provide actual screening and partly to provide a floor of metal at filament potential to act as an " anchor " for the 'set in the absence of an earth connection. Full constructional and operating details we must leave for a further article in next month's issue (we have already over -run our space allowance), but a few brief summarised points will enable you to make a start.The copper foil for screening consists of one piece 14 by 5i in. (screwed to underside ofbaseboard), one piece 5i by 5 in., and one 54- by 13 in. (the usesofthesewillbe given next month.) The aerial is wound round the mail frame and consistsof 14 turns of No. 22 D.C.C,spaced about A. in. apart with the ends taken to Clix sockets mounted directly through the Hereisthe completewood.The reaction winding has foue receiver, open to showturns (same wire, in same directioh, the controls.The smaller dial, to the left, is forunspaced)againstthe" filament" reaction, tuning being carried out by means of the central dial.To the right is the on -off switch, and below it a socket by means of whichend of the main winding, and ter- an extra loud speaker can be plugged in. minates in another socket. 148 February, 1929 MODERN WIRELESS

In this interesting article the valve is depicted in a new role-that of Sherlock Holmes ! Thevariouswaysinwhichitwatchesagainst wrongdoers make absorbing reading. From a Special Correspondent. BACK -COUPLED valve when on A similar effect can, of course, be inductance sets the valve oscillating the threshold of oscillation is secured by inductive action. For and so gives warning of any un- - known to be extraordinarily instance, a small wire solenoid sur- authorisedattempttoenterthe sensitive to outside influences. A rounding the keyhole of a door, and premises at night or during forbidden valve so adjusted is commonly said forming part of a tuned circuit, will hours.Normally the guard circuit to be " triggered "-a word which have its inductive value reduced by would be rendered inoperative by well describes its tendency to " spill the insertion of a key. The principle means of a switch. over " suddenly into sustained oscilla- is the same as that used in so-called In these cases the valve acts as a tion. spade or " shadow " tuning, where " watchdog " owing to the capaci- The slightest impulse applied to the a metal plate is moved over the face of tativeorinductiveeffectofthe grid circuitis sufficient to start self - an inductance coil to alter the latter's intruding body, as a whole, upon the oscillation. This causes a sudden wave -length. tuning of one of the valve circuits. change in the value of the current Here, again, the alteration of the The action does not depend upon the flowing through the valve, which in particular composition of the body, turn can be used to energise a local except that it distinguishes between relay, and so ring a bell or operate conductors and non-conductors. some other form of indicator. A Radio Doctor Burglar Alarm Ithasrecentlybeenasserted, A triggered valve can be made however, by two American inventors, to serve as a burglar -alarm. The Dr. Simon and A. O'Connor, both capacity effect of the burglar's hand of California, that the sensitivity of on a hidden coil of wire as he fumbles a triggered valve oscillator 'can be with a safe, or of his body as he passes usedtodistinguishbetweensub- through a door, is sufficient to throw stancesofdifferent chemical com- the valve over into definite oscillation. position, and even between different Here the effect is due to an increase biological organisms, such as bacteria. of capacity in the grid circuit.This They claim that their apparatus brings the latter into tune with the will not only discover the presence platecircuit,andsostartsthe of certain germs, but will also identify system oscillating.Once oscillation the type of bacillus and so permit a has commenced a local hold-down radiological, or high -frequency, diag- Further, relay is energised and continues to French sleuths listening -in to headquarters nosis, of particular diseases. ring the alarm, even after the original whilst rushing after criminals in a police the oscillator distinguishesbetween stimulus has been removed. van. germs that are alive and those that 149 MODERN WIRELESS February, 1929 are dead,. so that the progress of the forms a sunlit to earththrougha Itthe telephone note is identical patient can be duly recorded day by second variometer N2. with that previously obtained, then day. The valve is first set on the threshold strychnine is present in the suspected Amongstothersubstancesthe of oscillation by adjusting the coupling solution.Otherwise it is absent. oscillator will give a definite response between the coilsL, L1,L2,the A similarprocedureisadopted to such poisons as arsenic, strychnine, variable grid condenser C, the resis- when testingforthe presenceof etc.By making a comparative test,tance R, and the tapping point P. disease germs. A solution is first made the suspected presence of these sub- The vial is then inserted in position, from the blood of the patient and is stances in -the human body can therefore be tested for and the particular poison identified. The circuitarrangement ofthe apparatdsusedisshowninthe figure. It consists essentially ofa back -coupled valve V, with means for adjusting the degree of reaction so as to set it on the threshold of self - oscillation. This is termed the response circuit. The Circuits Employed Tapped off from the plate of the valve is a second circuit to which the substance to be tested is applied. This is called the control circuit. The plate circuit of the valve contains an untuned. coil L, to which a coil L, forming part of the tuned - grid circuit is coupled.The plate circuit is completed through apair of 'phones and the usual H.T. battery to an adjustable tapping on a potentiometer P shunted across the filament The circuit employed for detecting the presence of poison. battery. One side of the tuned -gridcircuit containing, say, a solution of a definite then compared by the " detective " C, is connected through a variable poison, such as strychnine. valve with a standard culture of the high -resistance R to the plate circuit, When this has been done, the vario- particular bacillus suspected. whilst the other side is coupled to the meters N, N2 are adjusted until a grid electrode through a variable con- characteristic note is heard in the Action Not Understood - denser C. A separate flywheel circuit 'phones, indicating that the system The inventors admit that the under- L2, C2 is coupled both to the grid and is barely oscillating. The apparatus is lying causes of the, reaction ofthe plate circuits as shown. then ready for test. oscillatortospecificelementsor chemical compositionsisnot fully understood.It may lie in the particular atomic or molecular formation, or possibly in electronic emanations or radiations thrown out by the body under test.They do, howeve'r, claim to have detected in this way the presence of matter not discoverable by means of a microscope. Whether these claims can be sub- stantiated or not, the device certainly offers an interesting field for further speculation and research. 0&:M6-PT,%6P0E3) 00000006PqN81 THEORY AND PRACTICE 43 This receiving set of the Berlin police is installed on the outskirts of the city, and controlled from police headquarters. 6 6o666666e66 66 Although there is no absolute dividing The control circuitis tapped off If the vial T is now replaced by a line between high or radio frequency and low from the plate winding L, and com- similar vial containing the suspected or audio frequency,itis usual tocalla current a high -frequency currentifthe prises a variometer N, a free -ended substance, the inventors claim that the alternationsareoftheorderof15,000 transformer winding W, and a second characteristic telephone note will not cycles or more. open-ended winding W2, which sur- be heard unless the substance for rounds a casing containing a vial in which the apparatus has been set (in Telephones which are in constant use are often rendered insensitive by the forming of which the substance undertestis this case strychnine) is present in the rust inside the diaphragms.(This can be placed.The secondary winding .W1 substituted vial. removed by a soft oiled cloth.) 150 February, 1929 MODERN WIRELESS

We all have, our own ideas about the ideal Wireless Programme.Rosita Forbes, who is known ,to millions as an explorer of courage and resource, has written this exclusive article for " Modern Wirelesson a theme which will always be interesting-for the simple reason that we shall seldom, if ever, agree as to what constitutes an " idealprogramme.But other people's views are interesting, and certainly Rosita Forbes has some ideas on the subject which the B.B.C. might adopt with considerable advantage.-THE EDITOR.

UJUNG the General Strike-why should these two A lecturer can appeal to every quality of intelligence words, which represented a stinging -nettle rather in his necessarily mixed audience, though he has only one than the Sword of Damocles, always be written subject at his disposal.A broadcasting programme, with with capital letters ?Well, then, during the general every topic to choose from, ought to be able to do the same. strike, a voice of velvet stroked with gold announced from The fare must be as varied in quality as in quantity. Savoy Hill that a certain East End district was quiet It is an age of labels and I'm sure most broadcasting " with the exception of sporadic ebulli- officials try to docket their different tions." Next day a gardener remarked audiences - " thiswillappealto to me that " it was bad luck some sort women, this to clerks, this to football of infectious disease-he didn't rightly fans," and so on.But in 1929 it's know what-had broken out in East impossible to do this.There isn't London on top of the strike an' all." onegeneral mentality for flappers, So the first thing about my pro- forcharteredaccountants,orfor gramme would be its expression in the husbands! simplest possible English that no one could misunderstand. Ensuring General Appeal /1= This country is possibly the least The only way you can possibly be musical in the world, so I would keep certain of a general appeal is to gauge a wary eye on the length and quality theamountofcommonsense dis- .of concert programmes. I confess that tributed through what is a particularly I should have to leave the selection to practical race, and play up to that. others, because my own tastes would There are a few common denomin- run to undiluted grand opera, when, I ators.The love of travel and adven- felt lazy and the latest jazz when the ture is deep embedded in the kinsmen day hadn't provided me with enough of Drake, Sir Richard Burton, and exercise. Cecil Rhodes. We are a discontented Rosita Forbes-the famous won -fan race, suffering from lack of industrial Talks Are Enjoyed explorer. and agriculturalopportunity, from In every country -house I've ever under -employment and all the ills of known the wireless is always turned over -population.Broadcasting might off when the news bulletinis finished, unless, of course, be a panacea for all these sores, if it were fully conscious some ingenuousexperimentertriestopick up the of its possibilities. Antipodes or U.S.A., or a political speech is expected. The main object of my programme would be to familiarise Yet country -house mentality is not particularly highbrow. England with the colonies and the opportunities they 151 MODERN WIRELESS February, 1929 represent;to interpret one country to another.Savoy C3 men, who from the time they leave school have no Hill could people the fallow lands of the Empire, and ease chance of getting work.I don't know where to send my the burden on the rates of every British manufacturing sons, or what to do with them." Why shouldn't the town if it would teach its thousand thousands of listeners - wireless help with information and advice ? in what the world really is ! My programme would include a practical travel talk A few years ago I broadcast an appeal for the housing showing what sort of holidays can be taken on what sort of refugees. A farmer's wife wrote to me that she would be delighted to take in a Greek family, but would they be black or white ? My programme would be the greatest factor for prevent- ing wars, because when governments disagreed, the ether, which belongs to no political party, should inform the people of any potential enemy land what the English public was thinking and feeling.If the peoples of the world could get together and understand each other, there would obviously be fewer opportunities for those tragedies of political ambition which end in war. Information and Advice Wanted Every normal human beingisan egotist.He is naturally most interested in things which have or may have some relation to himself-hence the popularity of politics, sport (which is an opportunity for gambling). and romance !I would appeal to that personal egotism in my programme. A broadcast bridge party in progress.On the right is Lady We are a serious people. We want to know about Oxford and Asquith, who was one of the party. things.We have inflated the standard of living beyond the average man's earning power.Obstinately, doggedly, of means.I would familiarise the most adventurous and, we want to improve our conditions.I should say the I believe, the pluckiest race in the world with the pos- main object of every boy and girl to -day is " to better sibilities of travel. themselves " in one way or another. My programme There are worlds still uncultivated, if not unexplored. would show them how they could do it.I would have The unemployed of England might be the makers of a weekly talks on " opportunity, " showing what the actual new Africa, a new Australia, or a new Brazil.Every practical openings were for youth when it left school. week I receive an average of a hundred letters, from adventurous youth wanting to work or to holiday abroad. My wireless programme would tell them how to do it. - We are too insular in England.Everything across the Channel is " foreign."A century of wireless ought so to connect the world's workers, their interests and their objects, that there would be no " foreigners " at all. My programme would deal with that horrible domestic problem that confronts us all at the moment-how to

make a great deal out of very little! I would have a house and home expert whose descriptions would rouse the imagination of householders and housekeepers and whose explanations would enable them to put their ideas into practical form. Solving Domestic Problems In our houses, our clothes, and our pursuits, we lack imagination.We're not as comfortable, as interested, or interesting, as pretty or as happy as we might be, if we employed a little more brains in the disposal of our ordinary means. My house and home expert would tell women what they really want to know, not all the short skirt and lipstick stuff they learned years ago and now consider as much part of their natural equipment as a tooth brush and Broadcasting the ceremony of the opening of the New South artificial silk hose ! Wales Parliament, which was carried out by 2 F C, the Sydney station.The arrow points to the microphone in the top left Modern women-and women have always been the corner of the picture. modern element in whatever century they were born, because it was they who had to adapt primeval needs to Parents would thus be taught what trades would be most changingstandards-modern women,Irepeat,are profitable to their children, and the young people would interested in just the same things as men, their comfort, know the difficulties and possibilities of the careers they their work, their " rights " and their wrongs. contemplate. Beauty in all forms appeals to them, of course, so 1 A Welsh miner wrote to me a few months ago :" Instead would have practical dress talks.Women fathous for of the old-time sturdy Welsh, we are breeding a race of their knowledge of clothes should analyse the possibilities 152 February, 1929 MODERN WIRELESS of the dress allowance, showing how to obtain the best & E56450Et00tiDEPOE3)&&&06c)(60,0&&00& tb qi results fOr the least expenditure. Q. Every new wife and most old ones want to make the WHO WAS CHATTERTON ?0 most of their houses and themselves, but they don't know j 0 how to do it.My house and home expert would tell them. fb From a Correspondent Ca Most women are obliged to work in order to run the home 0 according to the elastic standard of 1928. &E3)%&06g&e,46)0&E,PEgW&00&@@0(4 The pin -money girl works for experience, latitude and opportunity, but she looks forward to a home at the end. -,ao exactly is (or was) this Mr. Chatterton in My programme would appeal toall women wha are whose honour the well-known adhesive com- trying to combine domestic and office life. poundofrubber and tarrymaterials has been named ?That, indeed, is an interesting question A Real Problem which has often beenasked. Hadthiscelebrated This is the real problem that besets the youth of 1929. Mr. Chatterton anything to do with radio in its earlier Every girl wants to make a success of marriage and of her days ?Was he the inventor of any remarkable com- job.I would get the famous women who have succeeded ponent or pieceofapparatus, or did he effect some in both spheres to broadcast their ideas on subjects of great advancementinthetechniqueofthe early vital, not superficial, interest to women. science ? At any rate, how didhisinsulating and adhesive composition originate ? Well, after many moons, I have at last succeeded in tracking the elusive Mr. Chatterton to earth.The fact of the matter is that this renowned gentleman, whose nameis,among radioamateurs, of greater fame than that of many a greater man, had nothing to do with radio ;living, as he did, before the science of wireless communication was thought of. Curiously enough, however, Chatterton was an early pioneerofthetelegraph,particularly ofthesub- marine telegraph.He was associated with the firm of Messrs. Glass,Elliot and Co., cable manufacturers, of London. Thisfirm made aspeciality of supplying heavily insulated long - distance cable about the middle of the last century, and Chatterton,being employed in the capacityofchemist,founditnecessary to devise special insulative and damp-proof compositions in order

to render these early cables efficient. , Here, therefore,liesthe originatingsource of the A programme should be as " varied in quality as in quantity." This picture shows how a recent broadcast of reptile noises was famous " Chatterton's Compound."Itis noteworthy carried out by an American station. that the compound was employed in the insulation ofthefirstAtlantic cable laid in the years 1857-8.

It is odd that though the average woman nowadays Since that time, the rubber compound has been em- lives the same sort of life as a man, the majority of those ployed extensively for all types of electrical work, its who cater for her amusement and interest imagine her radio -constructional uses constituting, of course, merely outlook limited to fashion, make-up, and make-believe ! additional applications of the well-known commodity. The modern woman has got two problems to man's one. She has not only to supplement her husband's earnings with her own, but has to dispose of those earnings for the benefit of the family in a manner as elastic as possible. My wireless programme would interest her because it would give her new ideas and the ideas of people she's read about for the solution of such familiar puzzles ! " The World in Pictures " Wireless, on the whole, is better adapted to interest than to amuse.In any literate country, where lending libraries abound, it is much easier to read a book or a paper than to listen -in, if sheer amusement is all that is required. Itis up to my wireless programme, therefore, to provide what is not to be found on a bookshelf or in a newspaper.I would try to do it by combining music, sport and news with up-to-date topical lectures in tabloid form. In fact, instead of presenting " the world in pictures," I would put the whole world on the wireless and show every " My programme would deal with that horrible domestic problem listener -in what it is and what it might contain for him that confronts us all . how to make a great deal out of very or her 1 little," says Rosita Forbes, in the article concluding on this page. 153 ODERN WIRELESS February, 1929

stration,which was made inthe --r presence of David Sarnoff, the Vice - President of the' Radio Corporation of . \ A \ America, was conducted between the ADK) AB stations at Bridgwater, England (receiving), and Montreal, Canada (trans- 441 I. mitting). HIV(1101thii mit It is claimed that this apparatus, which has been produced by Senatore Marconi and Mr.G.A.Mathieu, Eindhoven One well-known expert, after relat- diminishes fading to a great extent ANEW station (which is intended ing in some detail his experience with and thus gives a constant volume of only for communicating with various frequencies and expressing the speech and signals. amateur receivers throughout hope that " the reliability of short- the world, and not forthe broad- wave channels may be made such The Growth of Listeners castingofmusical programmes) is as some day to eliminate altogether According to figures given by Mr. the k indhoven short-wave transmitter thenecessityforthelong -wave Thomas F.Logan whenrecently erected recently, and working on 41.3 channel with its much more expensive addressing the International Adver- metres. The call-sign'is P B F 5. plant," goes on tosaythatthe tising Association in Detroit, Michigan, information available regarding short radio receiving sets are now to be Unique Event waves does not suggest that they will found in 35 per cent of the homes in An American business man, Mr. evergiveareliabilityofservice the United States, these sets serving Firestone, of Akron, Ohio, U.S.A., had comparable with that over similar a total audience of some 40,000,000 distances by land -line circuits. the unique experiencerecentlyof people. listening by wireless to the speeches In discussing the advertising phase made at the opening of a factory Anglo-American Channels of radio, the lecturer said that first - belonging to one of his subsidiary It is expected, therefore, according night audiences of popular musical companies in England. The occasion to the present views, that suitable programmes by national advertisers was the opening of the Firestone Tyre service between America and Europe numbered from10to 15million factory at Heston, when a speech was will require the continuation of the listeners. made by the Home Secretary,Sir long -wave channels, notwithstanding William Joynson-Hicks. Mr. Firestone the fact that much more extensive and Taking No Chances sat in his office in Ohio and heard the complicated plant is required than for Commander Byrdistakingno whole proceedings. short waves. chances on the radio side of his ex - The Australian Way In Australia, radio set owners pay licences which are used to support * " Class A " stations ;while " Class B " stations, owned in most cases by The technical, con- organisations which desire a mouth- trol, administration piecefortheir views,are not so and advertising office of the W H 0 favoured. broadcasting station Since the Commonwealth's postal of U.S.A. An article authorities have undertaken aco- fully describing this broadcaster ap- ordination of the programmes and peared last month activities of the " Class A " stations, in " M.W." a request has been presented on behalf of the " B " stations for either a share of the licence revenue or the exclusive right to accept paid advertising. In the latter case, the virtue of the sponsored programmes might be fairly tried out-were it not that the Austra- Although short-wave transmitters pedition, for in addition to the special lian listener must pay the bills of the perform with extraordinary efficiency precautions taken with batteries (al- preferred stations, whether or not he underidealconditions,thetotalready mentioned) he is having 25' prefers other programmes ! percentage of the twenty-four hours operators who are being given an during which any short-wave channel intensive preliminary training. Short or Long Waves ? serves between two given points is In view of the great expectations at present distinctly limited. Whose Island ? ofshort-wavetransmission,itis Antarctic meteorological informa- interesting to note that international An Important Demonstration tion is to be distributed from a new discussionsarenow takingplace The simultaneous transmission of Norwegian radio station at the remote as to the limitations of short-wavetwo high-speed telegraphic services islandof Bouvetinthe Southern transmission andtheintroduction and one telephone service over the Ocean. It is uncertain whether this of long -wave ditto for the periods same wave -length was recently .de- island belongs toGreat Britain or when short waves are not properly monstratedattheEnglishbeam to Norway and both_ countries have. effective. station 'at Bridgwater.This demon - claimed ownership. 154 February, 1929 MODERN WIRELESS

THERE is still, in this age of com- tunein2 L 0. Pullingoutthe 44 right-hand switch,we V tunethe plicated receivers with prac- An efficient " alternative " three- . tically unlimited range, a class .4,*4 programme receiver for the :: " Formo-densor behindituntil :: listener -constructor.The opera- of listeners who consider that all the Hon of two simple switches changes.. 5 X X is heard.Then, pushing it in extra " bother " introduced into a Y. the set from one station to another, 14, again and pulling out the left-hand ::4.* no tuningadjustmentsbeing .: set to give it a long-distance per- 4 *4o switch we adjust the other " Formo- 44 necessary. *4. * 4* densor " until 5 G B is received. We formance is not worth while.They ** 44* *41. 44 prefer a set which will receive the 44 By L. H. THOMAS. 44 then need not know the first thing local station, 5 X X, and perhaps one 44444444444444444. +4,4444.... about radio or electricity to " tune otherstation,suchas 5 G B,on in" these three stations for ever after. occasions, and they want a set which the trouble.On the other hand, we (A " local expert " may, if desired, be will do this for them with the absolute have those who simply want to move engaged to tune the set in the first minimum of trouble and expense. themselves from one station to another place, and afterwards nothing but without even having to think, and the switches need be touched.) " Three -Station " Set thisreceiveris designed fortheir Just as there have always been, express benefit. The Circuit Employed and will always be, motorists whose It is essentially a " three -station " Fig.I shows the full theoretical chief joy in driving is the use of the receiver, the change -over being ar- diagram, and it will be seen that the gearbox in such a way as to extract ranged entirely by means of two circuit employed is perfectly straight the last ounce of performance from switches. With the set in use as it is fundamentally. We have three coils their car, so there are radio enthu-at my own home, an instantaneous with fixed coupling, one in the aerial siasts who are enthusiastic enough change -over from 2 L 0 to 5 G B and circuit, one for the secondary and a to build themselves sets which are 5 X X may be made by the use of the reaction coil.Across the secondary, real hard work to handle, and the two left-hand switches on the panel. in series with a switch, is a " Forrno- wonderful results that are sonzetiines With the right-hand switch pulled denser " which can be brought into obtained with such sets often justify out and the left-hand pushed in, we circuit when desired.

******44444444444444:1 ****** 444444444444444444444441 44444444 ****** *44444444 #44.411,4r4r41 4* 4,M = 44 44 44 44 44 44 44.. COMPONENTS AND MATERIAL REQUIRED 44 44 44 44 1 Ebonite panel, 18 in. x 7 in. (Trelle, 2Non-microphonie valveholders Burne-.Tones, Igranie, Marconi - 44 44 4* 44 borg, " Kay -Ray," Red Seal, Resis- (Benjamin,Lotus, Pye, Marconi - phone, etc.). 44 44 ton, Beeol, Trolite, Ebonart, etc.). phone,W.B., Burndept, Wearite, (Ediswan, 4444 44 1 2-megohmgridleak 44 Cabinet for above with loose baseboard Ashley, Burne-Jones, Redfern, 44 ti Lissen, Mullard, Dubilier, Igranie, 44 44 10in.deep (Raymond, Pickett, B.T.H., Bowyer -Lowe, Burton, etc.). 44 44 Pye, etc.). 44 44 Cameo, Arteratt, Makerimport, 44 44 1 L.F. transformer (Ediswan, Brown, 1 H.F. choke (Burns -Jones, Lissen, 44 44 Caxton, Lock, Gilbert, etc.). Lissen,Igranie, Colvern, Leweos, R.I.-VarIey, Climax, 44 44.. Ferranti,R.I.- 44 44 I '0005 variable condenser (Cyldon, Varley, Philips, Mareoniphone, Igranic, Cosmos, Bowyer -Lowe, Peto- 44 44 44 44 Lotus, J.13:, Igranie, Dubilier, Mullard, etc.). Scott, etc.). 4* 44 Lissen,Bowyer -Lowe,Raymond, 4444 44 3 Baseboard -mountingcoilsockets 1 Volumecontrol (high -resistance 44 Colvern, Ormond, Ripault, Geco- 44 (Burne-Jones,Peto-Soott,Lotus, potentiometer type) (Burne-.Tones, 44 44 phoneUtility, Burton, Brandes, etc.). 44 etc.). R.L-Varley, Igranie, Gambrell, etc.). 44 1 Miniature type reaction condenser 44 (Bowyer -Lowe, Igranic, Peto-Scott, 1 Standard loafling coil (Burne-Jones, 1 Formo-densor, type F, and 1 type 4444 Ready Radio,Wearite,Paroussi, G (Arthur Preen & Co., Ltd.). 44 Lissen, J.B., Dubilier, Ormond, etc.). .. 3 On -off switches, one of suitable type etc.). 1 Seven -terminalstrip and1 two - U 44 for S3 (see text) (Lotus, Lissen, Ben- 10003 fixed condenser (T.C.C., Lissen, terminal strip. 44 Burne-Jones, etc.). !Miller, Clarke, Goltone, Mullard, Tinned copper wire, screws, flex, etc. 44 44*4 4 4444 ::::::4444444444444444::444444444444*44444444 *** * 44::::$ 155 MODERN WIRELESS February, 1929

Then we also have a loading coil, for that express purpose, which is aFor one thing,therearepresent wired in the usual manner, for long - high -resistance potentiometer. very few awkward corners in the wave reception, and across part of The reader should have no trouble wiring, and most of the leads are of this is another Formo-denser, enabling atallinfollowing the baseboard the minimum length possible.It is us to tune the new value of induct- layout from the photographs and the preferable to drill the panel first of ance to the wave -length of 5 X X or, back -of -panel diagram.Of the three all,after which itis fixed to the for that matter, any other long -wave station that we particularly want to 0+1 listen to.Apart from this, there is c2000/ 2MEG VOLUME nothing peculiar about the set. CONTROL The whole receiver is,it will be noticed, rather on the large size for a two-valver, but it was thought more advisable to " spread " the components slightly, and be reasonably certain of good results, than to take the usual risks attendant on cramping the layout, simply for the purpose of producing a small, neat -looking ieceiver. Volume Control One other point is the use of a volume control, arranged potentiometer -fashion across the secondary THEORET/ CAL CIRCUIT of the L.F. transformer. It was LOAD/NG Fig. 1. thought that in several cases this set CO/ L X 4/2 might be made up for the benefit of someone with absolutely no radio coilsontheright(lookingfrom baseboard by five or six screws along knowledge at all, and left to theirthe rear), that nearest to the aerial the bottom edge. mercy. terminal strip is the aerialcoil No brackets are necessaryifa reasonablythickpanelis used. Then mount the components in their correct positions on the panel, following them up with the baseboard components, and wire up the whole set as it stands. With many receivers it is preferable to wire up the baseboard components firstofall,but with this there seems to be so little " interference " between panel and baseboard that the whole thing may be done at one sitting, so to speak. Wave -Change Switches A word as to the sizes of the Forma- densers.That connected across the loadingcoilmust,ofcourse,be fairly large, while it is essential that the other one, connected across the small portion of the secondary, should not be too large.If your local station is one whose wave -lengthisvery close to 514 B, the " short-wave " Formo-denser must haveavery Could anything be more simple than the wiring of this receiver, which can be constructedsmall minimum capacity, or switching in a few hours. it into circuit will make the set jump In this case, if the volume were at the centre coil the secondary, and the right over the wave -length. any time too great for them and they third the reaction coil L3. The value I used for this condenser were to attempt to reduce it by the C1, with a capacity of .0005, is, of -(C3) was .00002.-00015.The value usual process (for receivers, of this course, the main tuning control, while of the larger condenser C4 was -0001- type) of detuning, all the adjustments a -small -condenser with a maximum .0005.More will be said about these for the three stations to be received of sbOut .0001serve's for reaction and their use under the operating would: promptly beupset, and it control.The volume control, on -.off notes, at a later stage. would` probably result in an S.O.S. switch, and the twu wave-change With regard to, the wave -change for the maker of the_ set. There is_swifehes complete the listof com- switches, it must be toted that the now no excuse for this,since the ponents- mounted -on the front panel. centre switch S3, which arranges the volume should be controlled only by The baseboard layout shown should change -over from short to long waves, means of the component provided be adhered to as closely as possible. must have three separate contacts 156 February, 1929 MODERN WIRELESS all insulated from each other.The Regarding values of H.T., about 60 region of 7volts, generally speaking type used, an " L. & P," has anto 70 volts on thedetector and with plate voltages of the order of insulated centre -piece which makes 105 to 120 on the note-mag.will that mentioned. Plug-in Coil Values Connect the aerial and earth to 9" their terminals, and insert coils as follows :Aerial coil L, (nearest back 2: of baseboard), No. 30 or 35. Secondary, in centre, L2, No. 50 or 60.ReaCtion, L, No. 30 or 35.In general, these sizes will always be found quite satis- VOLUME factory, although for extremely long GI CONTROL 3/2' aerials a smaller size for L, may be 32 s;2 advantageous.The tap on the load- /8 - ing coil will always be connected to a) ci) the " 60 " terminal. Y783 PANEL LAYOUT. Now., with the centre switch pulled out(i.e.shortingout the loading contact with both theoutside probably be about the most suitable coil) and the left-hand switch in (the " brushes " together.Thus we have voltages for average use, and the grid - Formo-denser thus being out of cir- three contacts which are all indepen- bias on the last valve will be in the cuit), switch on the L.T. and listen. dent when the switchisin and allconnectedtogether whenthe switch is out. In the diagram of the circuitit will be seen that the two " brushes " of the switch are connected to the extremities of the loading coil, while the centre -piece is connected to the " 60 " point on the coil and to earth. Actually a flex lead is soldered to the centre (moving) part of the switch, and Wm can be seen in the back -of - panel diagram. Parallel H.T. Feed It will be noticed that " parallel feed " has been employed for the H.T. supply, to make possible the scheme forusing the loadingcoil both for the aerial . circuit and for reaction.This being the case, itis essential that the H.F. choke in the H.T. positive lead should be a really good one. This is mentioned because it is the fashion nowadaystouse" series feed " and some form ofthrottle control for the reaction, in which case a choke is often not necessary at all, and when one is used there is no need to be particular about its efficiency. This case, however, is quite different. There is really nothing, more to be said about the layout and construction of the set.The wiring is not complicated, and should be completed within an hour or so. Suitable Anode Voltages Having finished the set, the wiring should as usual be carefully checked over with the diagrams, and then the first tests may be proceeded with. For the detector almost any general- purpose or H.F. type valve will be An end view of the set, showing the valves in position.Of the three coil holders in the suitable, and for the note -magnifier foreground the left is the aerial coil, the centre is the medium -wave coil, and the right- any small power valve may be used. hand for reaction.Behind these the standard loading coil can be seen. 157 MODERN WIRELESS February, 1929

Ifallisin order the setwillbe 5 G B is heard at maximum strength. greater than that ofb G B, orof behaving just as a straight detector- There should be no difficulty aboutyour otherfavouritestation,this and-note-mag. should. this unless you are in one of the station must be tuned -in first, and the The local station should be found regions where 5 G B is never audible higher -wave station found afterwards at very great strength somewhere on at good strength, in which case you with the Formo-denser. the main condenser,and reaction shouldsubstituteyourfavourite The lowest station that you wish to control by the small condenser0, foreignstation,oranythingyou receive with the set must be the first should be smooth and. even.For the plea se. one tuned in, and the others follow. sake of simplicity I am henceforth Now, having found and settled the going to refer to the local station as Completing the Tuning positions of two stations, push in 2 L 0 "andprovinciallisteners Remember that the entire processthe knob of the centre switch, thus must substitute their own call -sign. of tuning -inthis stationmust be changing overtothe long wave- Tune -in 2 L 0 now, and leave the performed on the Formo-denser and length range.Still the setting of the condenser settingat the optimumthat the main control CI must be main condenser must not be altered. point.If the volume is too great for left absolutely alone. By means of the second Formo- comfort, alterit by means of the Now there is another point to be denser, immediately behind the centre volume control and not by de -tuning. mentioned.ForLondon listeners switch, 5 X X may now be tuned in. Now pull ont the switch on the left, 2 L 0 is naturally the station to be If 5 X X is not wanted, there is no thus bringing the small Formo-denser tuned in first, as 5 G B's wave -length reason why the set should not be into circuit, and by means of a screw- isconsiderably above his.If your pre -adjusted " to Radio Paris or drivercarefullyadjustthisuntil beststationhasawave -length any other station that is heard on the

7 0 1 2 3 alp C2 III,! I I I I Oo01 0 0 CI 0005 CEMTRE

L5# - - L. T. V90 1)s February, 1929 MODERN WIRELESS long -wave range.In London, Radio by merely setting the centre -switch @@E84156g6POW8tEg@%%gii@O Pariswasreceivedat sufficient at the long -wave position and using REPRODUCTION WRINKLES ea strengthtobequitecomfortably the main dial as tuning control quite fl 03 understood on the loud speaker, anda wide wave -range is covered, and 423cE9q3479109E300'60G4SCY3C3C3OCF9/3 would have made quite a good sub- when themaximumpositionis In order to reproduce the lower musical stitute for 5 X X. reached there is the Formo-denser in frequencies the horn of the loud speaker should be as long as possible. One point must now be mentioned. addition. * * It may possibly be found that if the Idonotrecommend tuning Instead of connecting the loud speaker set is originally tuned to 2 L 0 with indistantstations with a screw- directly in the plate circuit of the last valve, itis a great advantage to use an output just the right degree of reaction, itdriver, butitcan be done when filter which excludes all the ordinary plate begins to oscillate when switched over necessary ! currentandutilisesonlythecurrents to the long wave -length. As a final word of advice, let me representing music, speech, etc. say this : Do not look on the receiver * Setting the Reaction One advantage of an output circuit as as a freak circuit,or you will be compared with the connection of the loud Now the whole purpose of the set pretty certain to manufacture difficul- speaker direct to theplate circuit is that is done away with if we have to alter ties that are really non-existent.If with the former the loud speaker overloads the reaction control when the station less easily than when the direct current is you regard it as a perfectly straight flowing through the winding. we listen to is changed, so that the set and treat it as such you will have * * * remedy in this case is to reduce the no trouble with it, and will find the Although in many cases distortion troubles reaction on the short-wave side to switching scheme a great convenience are due to the H.T. battery, it should not be just such a point that the set does not forgotten thata faulty grid -biasbattery even if you are bitten by the " DX " can cause distortion, and the voltage of this oscillatewhenswitchedoverto craze. should be checked occasionally. long waves.In general, hardly any reaction at allwill be needed for 2 L 0 and 5 G B, so that the difficulty will not often arise, but it is possible that some cases will be more stubborn than others, and it is on this account that the matter is mentioned here. At my home it is difficult to believe that a movement of the switch has really changed theset over from 2 L 0 to 5 X X, when they are transmitting the same programme, since the two stations come in on this set with absolutely identical volume and quality.Both are received well on the loud speaker, as is 5 G B, with no trouble whatever. The set has been left for over a week without being touched at all, and after this time the settings were found to be perfectly correct for the three stations, showing that changes in temperature and humidity do not have a very great effect upon the constants of the receiver. As a " DX " Receiver When operated in this way it makes an admirable receiver, as I suggested, for " non -radio " folk, but it may also be used for long-distance reception by anyone fairly skilled in the art, sinceif we ignore the switchesit becomes aperfectlystraight and normal receiver.On the short-wave sideitissufficientlyselectiveto receive a C.W. station working in between Langenberg and 5 G B without the slightest interference from either,a testwhichallreceivers should pass before they are certified " O.K." Quite a large number of German stations were logged on the first night, 40KrarMsgMiPtgm:M5, many of them on the loud speaker, The two leads coming right out of the picture in the foreground in this photo are the and on the long -wave side innumerable end G.B. = leads, the G.B. battery having been removed from its usual position in the C.W. stations were logged. Of course, foreground near the panel. 139 MODERN WIRELESS February, 1929

+11C774=01 41 11=4.1011414)1 AD,4r**4 4 The abovefiguresforprimary ski windings are given for the average 4 H.F. valve of 25,000 to 30,000 ohms Coils for the `World -Wide' Five impedance. With a lower impedance Constructional details of the long -wave coils for the five-valver described in valve it will be desirable to remove a p. last month's " 111.IV.", together with further operating notes. few turns equally from primary and Ey C. P. ALLINSON, A.M.I.E.E., A.M.I.R.E., F.Inst.P.Inc. neutralising windings, though this is not really necessary unless stabilisa- Z*1;:IZI.,`:411103'.<'..:tiV10:1140.10.TV>Z1 1(e : v.;" MCA vr, 1010:011M7IM tion becomes difficult owing.to having too big a primary winding. A(.THOUGH wireless is becoming and 4th slots.If a very high degree In some cases it may be found moreand moreaprecise of selectivity is required, an additional with thisset, whether on long or science, there are still many tap might be taken at the beginning broadcast waves, that easier stabilisa- things that puzzle us in the behaviour ef the 2nd slot. tion may be obtained by reversing of a wireless set. For instance, as you For the H.F. transformer windings, the connections to the primary wind- have probably found out yourself, the secondaries L4 and Le will have ings, i.e. to pins 3 and 4.In any it is often found that two wireless setsthe same windings exactly as L2, case, it will be found that only the built exactly alike will notalways while the primaries will be wound one neutralising condenser C2 is at all behave the same. over the L.T. end of the secondary critical in its adjustment, C4 will only Why this is so one can very seldom on top of ebonite spacers. These be found to have any very definite say.Even assuming that the com- spacersare made of fin. ebonite influence either at the top or bottom ponents are exactly the same they tubing, each piece being a little less of the condenser scale. may not behave the same in differentthanahalf -sectionofthetube. sets. Eight of these spacers will be needed Uniform Stability for each primary winding.(They can I would like to repeat here the For Long Wave -Lengths beobtainedfrommostwireless importance of having the right size Ionce built a short -waver that dealers.) primary winding for the valves you would insist in giving a threshold The primary consists of 50 turns of are using.On medium wave -lengths, " growl " ;I tried substituting every 38 D.S.C. wound withtheturns with the 20 -turn primaries (which are component in it with others which touching, after which the neutralising intended for use with valves of 30,000 were working in another short-wave ohms impedance), using valves of the receiver that gave no trouble of this P.M.5X type, which have an imped- description without curing the trouble. ance of only 20,000 ohms or there- To thil day I don't know what the abouts, I found that it was a little cause of the trouble really was. more difficult to stabiliseover the Itispossible,therefore,that whole scale than if I used the correct when you have built the " World - primary winding for this type of valve, Wide " Five it may not behave exactly or alternatively the H.T. had to be like mine does in some respects. There cut down. are one or two points, therefore, I It is also important- to have the should like to deal with so as to values of the two variable resistances assist you in any difficulties that may R, and It, correctly set, otherwise arise. you may find difficulty in getting the First ofall, though, I Nust give settostabiliseproperly over the you the details of the long -wave coils whole band of wave -lengths covered for this set.These are practically by the tuned circuits. identicalwitha well-known type With these resistances correctly set and are to all intents and purposes you will find you can use a much higher standard. A fair amount of work is value of H.T. than would otherwise be involved in making them, so if you the case, with stability at all points. prefer to buy them ready-made you Bias for the Detector will have no difficulty in obtaining Now there is a little question about them (I understand that Wright and the detector valve.You will have Weaire are making them.) noticed that I have connected the grid leak to a separate terminal, so as Aerial Tappings to allow of either positive or negative However,forthekeen home The aerial input end of the " World -Wide " Five, showing the aerial coil in position. bias being applied.This is obviously constructor here are the details : The a compromise, though a useful one, aerial is tapped on to the long -wave winding is put on top of the primary but I prefer to use about 14 volts grid coil L2 ;this winding consists of windingwiththe same ebonite positive, as this gives greater signal 280 turns of 38 D.S.C. wound in 10 spacers as used before. strength on weak stations, and easier slots 3/32 in. wide andin. apart on The connectionsare asforthe control of reaction, than the use of a 3 -in. ebonite former ; the slots may broadcast coils.The 2nd H.F. trans- negative bias.Zero bias is, to my be about 3/32 in. deep, and 28 turns former has a continuation of the mind, utterly useless, for it is neither are put in per slot. secondary winding which forms the one thing nor the other. And as The aerialis tapped on in two reaction winding (L7), consisting of a regards quality, frankly I can detect placessoas to provide alternate further 56 turns, i.e. two more slots no difference between 14 volts positive tappings at the beginning of the 3rd with 28 turns in each. and 14 volts or 3 volts negative. 160 February, 1929 MODERN WIRELESS

SomeinterestingdetailsoftheDanish Broadcasting Company'sislandstation at Sorel'. From a Special Correspondent.

transmittingpowerisnotin keeping with its high wave -length,theaerialpower ofthestation being 2 kilowatts. Still, however, the Sorel station is of interest to the yERY few " station getters " in this country are keen amateur, because, unlike the more popular European unaware of the existence of the Danish radio stations, itis not " overworked " in the respect of its station at Kalundborg.Itisa station which being received here at any old time, so to speak. comes in frequently with good strength, and, asits musical programmes are of interest, it has- been received Where is Sorel? very often in this country. But where is this Sorel, you may ask ?Get down But few seem to have heard of Kalundborg's com- yofr atlas, and glance at the map of Denmark.Among panion station at Sorel, a station which is almost of equal the almost innumerable small islands to the south of importance in Denmark.Like the transmitting station Copenhagen you will come to an " Isle of Sjaelland," upon at Kalundborg, the Sorb radio station is owned and - which will probably be marked the nameSorel."Here, operated by the Danish Broadcasting Company, and it is then, lies the radio station which we have under descrip- equipped with the most up-to-date apparatus. tion at the present moment.Itliesin adirection Probably, however, the reason why the Sorel station south-west of Copenhagen, the Danish capital, and approxi- has not been picked up very often in England lies in the mately 80 miles from that city. fact that its wave -length is an undoubtedly high one, Sorel constitutes one of the several Danish relay stations, being ofthe orderof1,153.8metres, and thatits and, perhaps, it is the most up-to-date equipped of them

`"'-' Figs. i and 2.These two pictures show different parts of the transmitting apparatus at the Sorel station.To ihe left are the rectifier and modulator panels, with an air condenser and inductance in the background.In the right-hand .picture are the tuned circuits Note the large tuning condensers mounted on stands. 161 MODERN WIRELESS February, 1929

all.True, there is some type of studio at Soro, but most every possible control is mounted in a convenient position of the programmes come from Copenhagen, to which latter in order that rapid adjustments may be made. station the Soro transmitter is permanently connected The oscillating circuit of the transmitter, which exists by land- and sea -line. between the rectifier and the oscillator -modulator valves, The heading photo will enable the reader to form some idea is seen on the right of the photograph, Fig. 2. This of the exterior appearance of the station and of its aerial. The comprises two vertical coils of copper strip, and a large latter comprises a cage aerial having an electrical length air -spaced condenser which is placed immediately behind of approximately 150 ft.It is suspended between two it. 180 -ft. masts, the latter being of interest on account of Turning now to the illustration, Fig. 2, the reader will the fact that they are not of the steel tubular type ordin- be able to obtain a good view of the aerial tuning induct- arily employed, but consist of nothing more or less than ance of the transmitter, this portion of the apparatus tall telegraph poles which have been impregnated with special preservative material. Into this aerial, as we have said, the station's transmitter sends up a power of 2 kilowatts. The Generating Plant The Island of Sjcelland being in a somewhat isolated position, the Soro station has to rely on the generation of its own electrical power.It does this by means of the single motor generator shown in Fig. 3.This supplies an alternating current of 500 cycles which, by means of a transformer, is subsequently -stepped -up to a voltage ,of 10,000.This voltage is then rectified by the usual series of rectifying valves, and then conveyed to the anodes of the oscillating and modulating valves. The three smaller generators seen in the background of the illustration, Fig. 3, supply the filament current to each of the valves.

Fig. 4.This photograph shows the control panel of the Soro transmitter, and also the relay panel connecting the Copenhagen station, 75 miles away.Transmissions from Copenhagen are frequently relayed from Soro.

being seen on the right of the photograph, and consisting of two horizontal copper stripcoils mounted with a smaller condenser at their base.All the tuning circuits are, of course, provided with the usual fine controls, these latter being seen mounted upon small wooden trestles in the foreground of the picture. The heavy porcelain insulation of the various circuits should be noticed, this high efficiency in insulation seemingly being a special consideration of all Danish stations. Relaying Copenhagen's Programmes The speech currents received at Soro over the lines from the Danish Broadcasting Company's main studio, some 80 miles away at.Copenhagen, are amplified before being applied to the grids of the modulating valves.The

Copenhagen relay board of the station to which is con- Fig. 3.In the foreground are the motor generators from which nected the speech amplifier will be seen at Fig. 4.On the io,000 volts H.T. is obtained.The generators supplying the left of the photograph, also, will be seen the control filament current are shown in the background. panel by means of which the quantity and quality of the current sent up- into the aerial is governed. Coming now to the transmitter proper, which is of A small control panel leading to the miniature studio some interest in that it shows the type of transmitter which the station maintains is also included amongst the employed at most of the Danish stations associated with control apparatus seen in the photograph, Fig. 4. popular broadcasting activitiesin that country, two However, the studio broadcasts of- the Soro station are general aspects of the transmitting gear will be seen at seldom heard, for not only is the entire station somewhat Figs. 1 and 2. difficult to get at by would-be broadcasters, but there is In. Fig. 1 we have on the left the rectifier panel of the hardly more room in Sorii's little studio for more than a station.This contains six valves, and its function is, of few individuals at a time. course, to rectify and smooth out the H.T. currents derived The station, however, functions excellently as a relay from the motor -generator of the station.On the right station, transmitting the admirable programmes from of the rectifier panel is seen the oscillator and modulator Copenhagen to the islands around that of Sjwlland, many portion of the transmitter.This panel containsfour of which, for the use of simple types of receivers, are quite oscillating and four modulating valves.On both panels out of reach of Sora's companion station at Kalundborg. 16Z February, 1929 MODERN WIRELESS GRID -CIRCUIT COUPLING

In this article the author follows up his remarks on L.T. switching contained in " Switch Off I " which was published in" M. R'." last month.He shows that this apparently very simple business deserves greater consideration than is usually given it and brings forward some practical and novel view- points for the guidance of amateurs.

By G. V. DOWDING, Grad.I.E.E. IN an article published in MODERN battery for providing the G.B. in my things will no doubt be as much a WIRELESS last monthIdis- home set at this very moment ! source of wonder to MODERN cussedthesubjectofL.T. WIRELESS readers as it is to myself. switching. Passing from one problem More Care Needed However,' I am ratherstraying to another in connection with this There is no doubt about it that away from the subject I set out to apparently simple subject I eventu- some of our sets are becoming high - deal with.Referring to the accom- allyoutlinedascheme whichis powerelectricalinstallationsand panying diagram(itis reproduced shown theoretically in the accom-need to be treated as such.It isfrom my articleintheJanuary panying diagram. quite all right so long as the outfit MODERN WIRELESS), you may re- This diagram shows a three-point is handled only by a skilled amateur, member I said :" There is one snag, switch and a fuse used in such a way but when it is a household affair, then and I am wondering how many of you as to provide what Iconsider to precautions must be taken. are going to spot it." be maximumsafety. Whenthe I have always deprecated the light- At the time of writing I have not switch is in the " off" position both hearted way many manufacturers received a single letter from a " suc- the H.T. negative and L.T. negative case up mains units, as though they cessful solutionist," but probably this leads are broken, and there is then is due more to the fact that most of. no dangerofH.T.short-circuits you spotted the snag right away, and occurring inside the set and burning consideritalmost too obvious to out the valves, or ruining the battery, need pointing out. providing the switch itself is properly and correctly wired. An Interesting Letter The valves arealsofairlywell I have had one letter of interest protected against the grid -bias battery, concerning the diagram from a reader which, as I have shown, can provide who signs himselfSherlock." He quite enough currenttoburn -out wrote primarily in connection with valves if it is of the 18 or more volts my Radio Cinema Scheme (I have order.The " pealamp " fuse is there had enough letters and to spare about to guard against any otherH.T. that !), which is being dealt with in shorts that are liable to occur. " Popular Wireless."But he adds a were low-tension devices, and I have P.S.inreference to my " Switch High Voltage G.B. said so a number of times in various Off ! " article in which he says : Personally, I feel rather inclined articles.But there is now a tendency " The snag is that ifthe,bypass to advocate four -point on -off switches to make such devices conform to condensers are good ones they will so that the G.B. battery can be as standardpowerpractice, and we retain their charges for long periods cleanly cut off as the H.T. and L.T. have to thank the I.E.E. for laying of time. when the set is switched off, more down regulations for the guidance of " The poorlistenerwilloperate especially in view of the high G.B. designers.Evenso,peculiarand your oh -so -perfect L.T. switch and voltages modern sets demand. The dangerousmistakesare made by thenthinkhecando whathe grid -biasbatteryusedinsome some of theless prominent firms, likes with the inside of the set. A receivers is as large as that requiredsuch as connecting protecting cases bypass condenser discharging through for the H.T.in more modest sets.I of A.C. units to one of the input hisfingerswillswiftly make him am myself usinga108 -voltH.T. leads.Why these people do such realise that static electricity can be 163 MODERN WIRELESS February, 1929 dynamic in causing galvanic action ! " mains unit by post and got a shock least 4 microfarads would be needed Rather clever that ! from one of its condensers which had to eliminate all risks of such. But I said in my article, referring held its charge only too well.How Should my circuit be incorporated to the bypass condensers:" For a long it had held it, I never found out ; in a set and coupling effects actually time they will retain their charges if but it must have been a good con- are troublesome, I would say do away they are in good condition, but they denser. Anyway, it was a good shock ! with the fuse.With such carefully - will not be under strain for twenty- planned switching its value is not four hours in every day." The Circuit " Snag" very great unless pentodes or S.G. And even if the condensers were But reverting once more to the valvesbeused,when the whole connected in the usual way directlysubject in hand, the " snag " in my subject of protective fuses needs to be across the H.T. battery terminals, diagram does not concern the storing completely revised. The closeness no switching bar external battery capacities, ofcondensers ;atleast, of the electrodes in these new valves switching could affect them. -The not directly.The " snag " is this : makes valve short-circuits a danger, alternative would be to leave them Everygridcircuitwhichderives instead of, as in the case of ordinary connected as shown in my diagram grid bias from the grid -bias battery valves, a very rare event deserving of and deliberately make them inefficient shown will be coupled by the common chronicling as a " curious incident." regarding their charge -holding capa- resistancerepresented by the fuse By the way, in view of some of the cities by joining grid leaksacross lamp. above remarks, it occurs to me that thesubjectof" gridcoupling " FILMING THE FIRST RADIO -TALKIE through common sourcesofG.B. supply has failed to receive as much attention as it may deserve. I wonder how much apparently very obscure distortion effects which have puzzled amateurs have been due to this ? Useful Information But if your G.B. supply is in the form of a dry battery, you can safeguard yourself against such trouble by seeing that the battery is discarded the moment it shows signs of deteriora- tion. To keep the G.B. as well - maintained as the H.T. and L.T. is yet another good rule to observe. I had intended to deal with other points in switching, but find that I now have not the space to do so, and must reserve my other ideas regarding switching for some future occasion.Nevertheless, I do not feel that I have wasted space on irrele- vancies, '` Shooting " a " close-up " scene in " A Dash for Liberty," a play written by the Editor because re -readingthis especially for the, Radio -Cinema.This film was the first complete drama to be produced article and the article in the January for this purpose,Mr. G. V. Dowding, inventor of the system, can be seen (second from " M.W." Inote that some really left) watching the Kodak camera -man at work.The object of the Radio -Cinema is to useful information has beenforth- combine a broadcast play with a home -projector film and to produce a perfect "talkie " while leaving the broadcast as a normal programme item for those listeners not having coming as a result of my research projectors. into one of the most humble, but most important, of radio components theirterminals. Not an expedient Youmightconsiderthatthis -the " on -off " switch.At least, light-heartedly to be practised, owing could hardly do any harm, because, that is my belief, and I trust my to its possible effects on the operation anyway, they are already coupled by readers will endorse it. of some circuits. the resistance of the G.B. battery A further scheme would beto itself ;and, in any case, they are employ a multi -contact switch which merely grid circuits.Dealing with **o9megoo4oso*eoss automatically short-circuited all thethe last question first, don't forget6§ ABOUT AERIALS g H.T. by-pass condensers as well asthat every grid circuit, except that performing the other duties assigned of the first valve, may be virtually e%@@E3,000000006)0S)50: to the " on -off " switch. a plate circuit ; there will be couplings It is possible for a crystal set to receive a -some very tight, indeed-between programme from a foreign station through An Efficient Condenser ! the medium of a nearby aerial attached to these and the anodes of the preceding a powerful valve set, which is not only pick- Actually, I do not think any of these valves. ing up the distant station's programme, but schemes are worth while. Nevertheless, But whereas the resistance of a is re -radiating this with sufficient strength my correspondent rubs home a good grid -bias battery in good condition for the neighbouring aerial to pick up the point, and that is, always beware ofshould be but a few' ohms, that of impulses. thebypass. Particularly in A.C. the " flash -lamp " fuse may be forty. The maximum amount ofinterference mains units,condensers are to be Even so, it is not certain that serious between neighbours'aerials occurs when encountered which can holdtruly coupling effects would occur ; but a by- they are parallel to one another, and at stunning charges.I once received a pass condenser of the order of at about the same height. 164 February, 1929 MODERN WIRELESS

THE NEW PENTODES Some details of a few of the 5 -electrode calves recently placed on the market. By KEITH D. ROGERS.

As I write these notes the newit is not necessary to feed the valve As regards the other pentodes, the five -electrode or pentode valve with as much signal strength as would Mullard P.M.22 and the P.M.24 are is gradually making itself more be the case with the ordinary valve, both excellent valves, for 2- or 4 -volt widely known on the British market, for a given output strength. accumulators respectively, and having and the valves are now not nearly so The long and short of it is that the very high magnification factors.In difficult to obtain as they were some pentode valve can be placed in the exchange for a somewhat high plate weeks ago, when the supply appeared last stage of a small receiver and can current they will stand a useful input, to he very limited indeed. be expected to fulfil the magnification and so considerable punch can be got powers usuallyassociatedwith a out of the valve in' the way of signal couple of low -frequency stages.Care strength. do has to be taken, of course, to see that Plate Current Required The Cossor the valveis not overloaded, and, furthermore, care must be taken with The P.M.22 takes about 12 to 14 Pentodevalve. milliampsplatecurrentfor150 Note the ter- the circuit in which it is used. This does not mean that the circuit volts with properbias,andthe minal on the P.M.24 a little more. It should there- base,thister- must be tricky or that any particular type of circuit has to be employed, fore be remembered by all who are minal being for desirous of using pentodes that they t h econnection but merely that the output circuit impedance should be of such a value will have to get H.T. batteriesor tothepriming mains units capable of supplying the grid. as to suit the impedance of the pentode valve itself.This, of course, milliamps required at the voltages holds good with all the pentodes, and it required if the best results are to be is essential for really good results that obtained.These pentodes are priced an output transformer suited to the at 25s. each. Up to the present I have had op- pentode, which is now on the market I must also mentiona French portunities of testing four types of in several makes, shouldbe used. pentode which has come into my pentodes, the 2-volter and 4-volter possession, marketed by theDario made by the Mullard Valve Company, The Output Circuit Company, and which issold for a the Ediswan 2-volter and the Dario . The method oftaking the loud guinea.This is quite a good little Bi-volt.Most have come up to my speaker direct to the plate of the valve valve, and although I have not had expectations as regards amplification isto be deprecated,andifpure time fully to test it, it seems by just and general behaviour. results are to be obtained, with a fair a rough try -out that it is quite a pro- Let us take as example the Ediswan amount of bass and not too much mising proposition. pentode, the 5E.225, first. This valve preponderance of the high notes, it is has a filament voltage of 2, and takes essentialthat aproperly designed quarter of an amp., while the anode output transformer should be used. volts are 150 maximum and the The Ediswan 5E.225 works best on priming grid volts 100 to 150 maxi- 150 volts H.T., and a grid bias of mum. The amplification factor is 6-7k volts.The H.T. consumption, given as 80, while the impedance is of course, is not a low figure, but it only 66,000, thus giving a slope of must be remembered that the pentode

1.2 milliamp per volt. is taking the place of two valves and, 1.M. moreover, is taking the place of one ar; Grid -Swing Problem power orsuper -power valve. IM7',/ It MMMMMI FAIPAIM Thus it will be seen that the valve should. also be remembered that when 01,/ /.4 : has a fairly steep curve, and it will usingapentode with thehigh- .... PRIMNCCRID pg Ng j PRIMINGGRID RommTPT T 20Y ,P' r.'i AT100 V. not, unfortunately, carry any very pitched type of loud speaker, that is, stem. MMMM Illrvl great grid swing.But thisdisad- one which will give a preponderance vantage is off -set by the fact that of high notes, one is liable to increase IIIP:gr; tremendous magnification is obtained, the prominence of the high notes, and W -GRID VOLTS compared with that of the ordinary thus get arising characteristic when This is the static characteristic curve of valve, for any given input, and so using this type of loud speaker. the Ediswan Pentode valve. 165 MODERN WIRELESS February, 1929

The construction can be seen from supply be above suspicion, motor - f3GG '-'30Z0cF30 the photograph, and it will be noticed boating is likely to occur. that in this specimen the connection Especially is trouble likely to be THE "INVINCIBLE" 0 of the outer grid to the filament does encountered if the anode current is FIVE not go to the centre of this latter, but being provided by a mainsunit, a little to one side, and thus the more especially if separate tappings 000&005&03cmg,E8,00,59, characteristics of the valve are in- for the various stages are not avail- clined to vary according to whether ableorifthetappings are not SIR,-Having just completed the any one filament pin is made positive`properly arranged. " Invincible " Five, as described in - or negative. the November issue of " M.W.," I In the case of the Dario valve the thought you might be interested to 41. know how it behaved. plateisof the horizontal variety, and is not to any really great extent I must congratulate you on such a successful design as theInvincible " hidden by the gettering, and so one The Mullard Five, and I have handled quite a few, can see quite clearly how the valve is 2 -volt Pen - tone. Note including your" Solodyne."Your constructed and how the various the centreclaims are not in the least exaggerated, electrodes are spaced. insulator which is used and the set behaves exactly as you Keep H.T. Down as a support describe it to all its controls, and it is This valve is also of the2 -volt and connec- thefinest" five-valver "Ihave tor for theyet met.Using two -volt valves, and variety with the usual high -imped- various elec- ance and high -magnification factors trodes.The only a mile from the local broadcasting associated withallpentodes, and connectionstation,Ipicked up about fifteen capable of carrying quite an average to the centre stationsallatfullloud -speaker of thefila- pentode grid swing.Care should be ment cannot strength. taken to run it at the specified H.T. be seen. voltage, or a little under, as increasing Further Details the H.T. above the maker's figures I did not make a log as I have not causes serious loss of emission. got the set properly neutralised yet. Incidentally, I have also been try- You stated in your November issue ing the Dario Bi-volt power valve of " M.W " that further notes would (7s. 6d.), which has an impedance of follow next month, and I was dis- 4,500 ohms, and magnification factor When a potential divider is used, appointed when I went for my usual of 9-very good characteristics. and tappings for various voltages are copy to find it made no reference to it. In practice is certainly taken, between the If you could give me any further good value for money, and makes a various tappings isliable to cause wrinkles on the neutralising, etc., of useful 2 -volt output valve. coupling between the various stages this set I would be greatly obliged. in the set and so cause motor -boating. Again thanking you for placing such In such cases an anti -motor -boating a fine set through " M.W." at my The interior deviceshouldbeplacedinthe disposal and wishing your valued of the Dario detector plate circuit, but if this does paper every success. Pentode not stop the trouble it may be found I remain, valve show- Yours faithfully, ing the con- to be due to coupling between the struction anode an 1priming grid circuits of A. O'LEARY. and assem- the pentode valve. Ballyhooly Road, Cork. bly of the Therefore an output circuit of the [Ed. Note.-The further details re- electrodes. The disc at correct impedance should be used ferred.tobyMr.O'Learywere theside for the pentode, and the grid connec- published in MODERN WIRELESS for carriesthe tion taken to the H.T. terminal via January.] " gettering " compound a choke and condenser, the latter which is being of the 2-4 mfd. variety. 0&00@0@&0000@0%-00E8 volatilised onheating CONCERNING LICENCES the valve The Output Circuit after the The output choke or transformer is 0060E6)0000E1.0 bulbhas an important feature owing to the beenex- high impedance of the pentode itself. Your receivingreceiving set and your licence are hausted. open to inspection at all reasonable times by It is obviously bad practice to run duly authorised persons from the Post Office, the valve so that the loud speaker who will produce cards of identity upon if? comes into the plate circuit. request. The problem of using pentodes to Finally,it must be remembered It is a condition of your receiving licence thebest advantage is not such a thatifH.T. mains units are not that when an aerialis crossing above, or difficult one as is sometimes thought, employed when pentodes are used, liable to fall upon, any overhead power wires provided that care is taken in thethe H.T. battery must beof the (including electric light and tramway wires) it must be guarded to the reasonable satis- H.T. supply. large capacity type. faction of the owner of the power wires. Where a pentode is taking the place As amplifiers following short-wave of an ordinary L.F. valve -followingdetectors pentodes are excellent, and Any permanent change of address on the especially when they are inserted in part of a B.B.C. licence holder should imme- a plain detector, no trouble is likely diately be communicated to the postmaster to occur, but when it is preceded by place of L.F. valves in sets consisting of of the district in which the station is now an L F. stage then, unless the H.T. two valves --detector and 1 L.F. stage. situated. 166 February, 029 MODERN WIRELESS

This article, written for the listener who is interested in the working of hisreceiver, deals with the time taken by the programmes to travel through spacefrom lecturer to listener. By P. R.BIRD. Amoisnotreallyinstantaneous. Whenthe Applying this to your own case you can soon find out announcer says: "Here is the second news bulletin," how much delay there is upon the time -signal or other it might be thought that every working loud transmission between the transmitting aerial and your speaker in the British Isles utters those words, at the same awn.If you divide the number of miles separating the instant.- Actually this is not so.There is a time lag-in two aerials into 186,000, your answer will give the fraction fact, there are several-and as they are not generally con- of a second it takes to travel that distance.In the case sidered it will be interesting to see when and how they occur. of a listener living, for instance, at twenty miles from his Lookingfirstat the purely wirelesspart ofthe nearest station, the local programme always arrives about transmission, we will imagine a wave leaving the local 1/9,300th of a second late. broadcasting station's aerial, being flung, out intoall Even if you are listening to a foreign station and the directions, and arriving practically simultaneously upon distance between the aerials runs into hundreds of miles. your own aerial.Although the transfer of energy from you will soon see that the time lost is so infinitely small that distant aerial to your own was practically simul- as to be inconsiderable, and consequently we can regal'. I taneous, there is a certain amount of time lost between wireless. communication, even between stations thousand, aerial and aerial. of miles apart, as being practically instantaneous But, This does not mean to say, of course, that the B.B.C.'s before we leave this part of the subject it will be interest- time -signal is wrong by the time it reaches your aerial ing to notice how time flies in radio over the Atlantic. From a practical point of view the time -signal can be regarded as arriving at the very instant of its dispatch. The Transatlantic Time Lag From a scientific point of view, however, there is a pause- If you have managed to pick up a programme from one an almost infinitesimal fraction of time lost in travelling. of the American stations direct, such as K. D K A,-2 X A I) You can easily calculate how much time is lost, for the or 2 X A F, the distance between aerials would be a electro-magnetic waves of wireless travel at the same speed matter of just under 3,000 miles, and over such a tremen- as light itself.Long before wireless was invented the dous distance the time lag is really worth noticing. By speed of light had been ascertained pretty accurately by dividing 3,000 into 186,000 we see that the signals coming independent investigators and found to be about 186,000 the shortest distance between these points would be about miles per second. 1/62nd of a second late !This means that if the world were wide enough to hold sixty-two Atlantics, placed side Nature's Own Quick -Step by side, a wireless signal could cover the distance from There is something fascinating about this .speed and one end right across to the other and still arrive within something fundamental.For those things which man one second of dispatch !No wonder then that signals commonly regards as instantaneous, i.e. light itself, the from the local station (generally only a few miles away) electric telegraph, and wireless, are all tuned up to this appear to be absolutely instantaneous. particular pitch, and no other.Whatever the reason for As this universal speed of 186,000 miles per second it, this speed of 186,000 miles per second is Nature's own applies to electric currents running along wires as well as quick -step, and is used by her for wireless, for light, and to wireless, the simultaneous broadcasting of programmes for certain other phenomena. is, to all intents and purposes, really simultaneous. Because 167 MODERN WIRELESS February, 1929 if any station taking the London programme is situated Then after the necessary voyage by wire and wireless, even 300 miles away from London, we find on dividing they were sound waves again, travelling this time from our 300 into the universal speed that the journey only the diaphragm of the loud speaker to the ear of the takes 1/620th of a second.The extra mile or two to a listener.In any wireless programme it is chiefly in these listener's aerial makes a negligible difference to the time sound waves that the time lag lies.For compared with taken, so that the wire and wireless part of the programme wire or wireless, sound is sluggish and slow. pays very little toll to Father Time. Sound waves move in the air not at thousands of miles But that wily old gentleman sets another trap for the a second, but only at the rate of about 377 yards per transmission.Either by wire or wireless one second of second.Although it has to cross only two small rooms, time represents many thousands of miles, but we must the sound impulses take more time to do that than the remember the programme exists before it reaches the wire and wireless take to link up the transmitter and the microphone, and after it leaves the loud speaker, and this distant receiver. is where Father Time gets his chance ! Let us take, for instance, the case of a speaker in the The Slowness of Sound studio who is just going to give a talk.Mr. What's -His - The comparative slowness of sound cannot be appre- Name starts by drawing a breath, moistening his lips, and ciated from figures, but it will be apparent if we try to saying to the unsmiling mike, " Hello, Everybody." A followoutthisjourneyoftheparticular"Hello, fraction of a split-second later, people all over the British Everybody" uttered by Mr. What's -His -Name, giving Isles have heard their loud speakers say to them, in life- average distances to show the comparativetimesof like imitation, " Hello, Everybody." transit. Coining from the speaker's mouth, these sound waves Suppose, for instance, in the case to which we have ,travel outwards, across the studio, and reach that super - reverted, Mr. What's -His -Name stands six feet from the electric -ear, the microphone.Here a sensitive diaphragm microphone.By this latter the "Hello, Everybody" is is shaken by the sound wave, and that movement is translated into electric currents, and after an adventurous translated into electricity.From that point the words journey of, say, 100 miles by wireless, currents representing exist not as words, but as corresponding electric currents. those two word's arrive at the diaphragm of John Listener's

Despite the great distances covered, and the complexity of wiring in the modern transmitter and receiver, no time is lost in the really radio part of the transmission.What lag there is between the original sound and the duplicate of it heard by the listener occurs before the sound reaches the microphone or after it leaves the loud speaker.

They are hurried along to the aerial, flung out into loud speaker.This perhaps is in a corner of a room, so the ether in the form of electro-magnetic disturbances and that John Listener himself is ten feet away from it. eventually reach the listener's aerial, where they are The total journey through the airin the form ofair transformed back into high -frequency electric currents. waves in such a case would be six feet from the speaker After operating the various valves, they are fed, now in to the microphone plus ten feet from the loud speaker to the form of low -frequency electric currents, through the the listener, a total of sixteen feet through the air.The windings of 'phones or a loud speaker. electricaldistanceis100 miles (thatistosay,the Here their magnetic effects are utilised to move the electro-magnetic impulses have to travel 100 miles between receiving diaphragm backwards and forwards in the air; the diaphragm that receives the speech and the other thus transforming electro-magnetic energy into sound diaphragm [loud speaker] which will give it out).The energy.As they were originally controlled by the distant electrical journey of 100 miles took these two words only speaker's voice, so they now control the diaphragm of the 1/1,860th of a second to do.The air journey, although loud speaker, giving it the necessary pulls in order to make only sixteen feet, took about 1/70th of a second ! it set up a similar air commotion. In other words, the time taken by sound to get across the two _orslinary rooms is about 27 times as great as the Where the Time -Lag Lies time occupied in " wirelessing " that sound over a distance It is these waves, travelling across the room through the of 100 miles !The whole transaction is so rapid that it air, that reach the ear of the listener and reproduce the appears to be instantaneous, but if we investigate the " Hello, Everybody." delay we find, as shown, that practically none of this Notice particularly that those words have existed twice delay can be laid at the door of radio.Nearly all the in the form of sound waves.Once they were sound waves time lost is lost by sound, either before radio began the travelling from the speaker's lips to the microphone. transmission, or after it had finished. 168 February, 1929 MODERN WIRELESS

METER

THE milliammeter is the handiest j111111111111111111111111111111111111111111111111111111111111111111:: of all wireless instruments.As An easily constructed and com- Er.." paratirelyine.rpensiveinstru- = we shall see. it can be made to =meat, with which practically all .7=. read not only the milliamperes of the electrical measurements the plate current, but also the voltages = amateurradioexperimenter = current.In the central -zero instru- = desires to make can be carried out. E ment the coil can move either clock- of filathent, plate, and grid batteries, By a simple system a very high -5 and the amperes consumed by the degree of accuracy is achieved. wiseoranti -clockwiseandthus indicate the direction of thecurrent. valve filaments. Firstofall we Designed and Described by 11- had perhaps better see just what the For the purpose to be indicated the E R. W. HALLOWS, M.A. best form of moving -coil milliammeter milliammeter is.It was discovered munuuuuuuuuumuunuuumnuurunuununn many years ago that if a magnetised is that which has a left-hand zero needle is suspended in a coil of wire and reads from 0 to 25 milliamperes. magnetic flux.In the_ small space This wireless milliammeter is, then. a deflection occurs when current is between the poles and the cylinder passed through the wireThe degree nothing more nor less than a cali isa rectangularcoil,so mounted brated moving -coil galvanometer, so 06-045 that it is free to move. SO, 01- -11 Itis wound generally upon an E = 25 V aluminium frame mounted in jewelled bearings. The coil carries the pointer, 4o0o aims C=25/1-9. A which is made as thin and as light as possible. Two spiral springs, one at either end of the coil, return the pointer 190.2.Y OHM ..1" LA 11/ EM. E to the zero position when current OP 25 VOLTS DRIVES 25 MIL L /A Al AER ES THAD UGH A is not passing.These springs also SHOW/NG Non' CURRENT RES/STANCE OF 4000 0/1/1f..7. form the contacts between the ter- D/WDES WHEN THERE ARE minals of the instrument and the TWO AVSS/ElLE PATHS. of the deflection depends upon the windings of the coil.When current amount of the curfpnt flowing, whilst adjusted that a current of 25 milli- is flowing through the coilit tries amperes , suffices to make the coil itsdirectionisgoverned by the to set itself so that its flux is parallel direction of the current flow. carry out its maximum movement ; to that of the magnets. if this current is flowing the needle Moving -Coil Meters The coil thus moves when current passes from zero to the top end of This principle forms the basis of is passing, the amount of the move- thescale.To convert the instru- the majority of current and voltage ment depending upon the flow ofment into a voltmeter. isquite a measuring instruments, and it is still PS09 simple business, bearing in mind the used initsoriginal forminthe facts already stated. moving -iron voltmeter and ammeter. The moving -coilprinciple isa de- Milliamps to Volts velopment of the same idea.Here Let us take a milliammeter read- we have a fixed permanent magnet ing from 0 to 25 milliamps. Suppose and a coil, carrying a pointer, which that we desire to read from 0 to 25 is free to rotate within certain limits MAGNET volts,the problem issimplythis. MOVING between its poles. Moving -coil in- COIL We must so arrange the instrument struments are preferable for radio that an E.M.F. of 25 volts will drive a work, since they are more sensitive current of 25 milliamperes through and enable dead -beat readingsto it.Ohm's law shows us that if we ss"' be obtained. ROLE connect in series with a source of The principle ofthe moving -coil PIECES /AON CYLINDER direct current supplying an E.M.F. galvanometerisseeninFig. 1. of 25 volts a resistanceof1,000 Between the pole pieces of a perma- TERM/iVALS MOUNTED ON CASE FsI ILLUSTRATING THE ohms, the current flowing in the nent magnet is fixed a cylinder of iron WORKING PRINCIPLE OF ALL circuit will be 25 milliamperes.This whose purpose isto intensify the MOVING COIL INSTRUMENTS. is made plain in Fig. 2. 169 MODERN WIRELESS February, 1929

All that we have to do then in order the flow along each branch of the R508 to make the 0 to 25 milliammeter circuitbeingproportionaltothe read accurately from 0 to 25 volts resistance in that branch.Look at isto arrangeinseries withita Fig. 3, which shows such a condition resistance whose value plus that of ofaffairsdiagrammatically. Be- the windings of the instrumentis tween the points A and B there are exactly one thousand ohms. Voltages two paths for current, the one con- less than 25 will then give propor- taining a resistanceof 900 ohms,, tionately lower 'readings, and each and the other a resistanceof100 division of the scale will represent ohms. Nine -tenths of the current 1volt. will flow through the smaller resistance and one -tenth through the larger. In making the milliammeter read " Constructors who wish to get a little :: :: more accuracy can obtain resistances from 0 to 2.5 amperes the problem is :: accurate to within 1 per cent.With :: to bypass 99 per cent of the current :: these the greatest possible errors are :: and to allow only 1 per cent of the :: so small that they are negligible." :: .. current to pass, through the' windings FIG.5./%1E7,100 OF CAL/BRAT//VG of the instrument. THE Slle//V7: Similarly, itis easy to make the Fig. 4 shows diagrammatically how milliammeter read from 0 to 250 this is accomplished by means of a ante of the milliammeter as much as volts.In this case a simple calcu- shunt.The resistance of the shunt 25 ohms. lationwillshowthatthetotal is so arranged that when a current of, We now have a total of 1,075 ohms, resistance required is 10,000 ohms. say, 1 ampere isbeing measured, and a simple calculation shows that This range is exceedingly useful for 990 milliamps pass through the shunt 25 volts will drive 28.25 milliamperes keeping a check on the H.T. battery. RESISTANCE OPSNI/NT %.9g7NAT through this.The instrument, there- For the filament and grid batteries OF /eVSTAY/MENT il/M7D/AWS. fore, under -reads by 115 volt on 25 the 0 to 25 -volt range may be used. volts, and by .7volt on 10 volts. Slit/NT Afos So much for the moment for the This is the greatest possible error that milliammeter as a voltmeter.Now can occur, and it is not serious, since let us see how it can he made to read the finished instrument can afterwards amperes as well as milliamperes. be compared with an accurate one AGANOW THE AfiLL/AMMETER belonging to a friend and a note Useful Ammeter /S MA OE 70 READ AMPERES. made of the amount by which it over - A very useful range for the wireless and only 10 through the milliammeter. reads or under -reads. receiving set is from 0 to 2.5 amperes. Any other range within reasonis If the resistance is actually 5 per We have already seen that a full- equally possible. cent low, that is 950 ohms instead of scale deflection of the instrument is It goes without saying that if a 1,000 ohms, the milliammeter whose secured when a current of 25 milli- multi -range instrument of reasonable windings have a resistance of 25 ohms amperes is passing.Now 2.5 amperes accuracyisdesired there are two will show only 2.5 per cent over the represent 2,500 milliamperes. essentials. In the firstplace the true voltage at all readings up to Ohm's lawofresistances shows milliammeteritselfmustbea 25 volts. us thatifthere are two possible thoroughly good instrument. The pathsfor,currentitwilldivide, more accurate it is the more precise Negligible Errors will be the readings obtained on all Actually the errors are likely to be ranges, and vice versa. much less, since% the resistanceof Secondly, the resistances and shunts the instrument may be well under 25 must be made with every possible ohms, whilst the degree of inaccuracy care.It is by no means a difficult in the resistance is seldom so great as business to make them dead accurate, 5 per cent.For the 250 -volt range a but for general wireless work, where RES/STA /VCE 44/./RE R1'0¢ laboratory precision is not required, a 'WILED great deal of trouble can be saved by SOLDER NUT using ready-made resistances for the voltage scales. Standard Resistances The standard resistances made by TER;ti/A14 LS ToD.PC.0 . the R.I. & Varley Company have a SW/TCH maximum error of + or -- 5 per cent. THE piRsr PROCESS The actual resistance of the whitings hfAA7/VG THE SHUNT. ofthe-averagemoving -coilmilli - 10,000-ohmresistanceisrequired, ammeter of reasonably good quality, and here the error is smaller, even if reading from 0 to 25 milliamperes, the actual value is as much as 5 per does not usually exceed 25 ohms, and cent out. it is often a great deal less. Constructors who wish to get a Let us see what is the maximum little more accuracy still can obtain error in voltage readings that will resistances from the same firm guar- The various ranges are always immediately i.vailable and can be read directly from occur if a " 1,000 -ohm " resistance is anteed accurate to 1 per cent.With the one scale. actually 1,050 ohms, and the resist - these the greatest possible errors are 170 February, 1929 MODERN WIRELESS so small that they are negligible ; in circuit and the rheostat is adjusted fact,if the milliammeter is a good until the current flow is just 1 ampere. one the accuracy of the instrument The shunt is made to begin with on on either range will be quite equal to the lines indicated in Fig. 6.In a thatobtainableinamoving -coil small strip of ebonite two terminals MASCREW4 SCREW voltmeter costing twenty-five shillings are mounted one inch apart. To the ea or more. tip of one of these is soldered the end

*4144 of a piece of No. 22 Eureka or other NI NUal 41, resistance wire.On to the shank of " The instrument is most convenient :: SNUNT :: to use since direct readings are always :: the other is turned a nut, preferably 11 :: obtainable from the existing scale." . of the milled -headed type, so as to *1' 414a) \r, make it into a double terminal. ,,c/c. 8. The wire is drawn under this nut NOW THE.SHUNTOPERATES. The components required for mak- and clamped down so that to begin ing the multi -range instrument under full ampereispassing. Wait with there is only a very short length minute. We have not quite finished description are :Sloping -front cabinet between the two terminals. This with panel 71 by 5 in. (Peto-Scott, yet. We shall come presently to the from whom the panel can be obtained final process of calibration. ready drilled and engraved) ;1,000 - We are now ready to proceed with ohm resistance with holder (R.I. & the simple drilling required for the Farley) ;10,000 -ohm resistance with panel. The layout is shown in Fig. 7. holder (R.I. & Farley) ;0-25 milli - This is for a panel -mounting milli - ammeter (any good make) ; 5 sockets ammeter ; if a flush -mounting instru- (Eastick, or similar type) ; small piece ment is used the resistances may be of springy metal ;short length of placed a half an inch nearer the top No. 22 Eureka resistance wire (or a of the panel and the position of the piece taken from an old 4- or 5 -ohm milliammeter will be a little lower rheostat} ;. Glazite for wiring. than that shown by the dotted circle, so as to give ample clearance. Easily. Made Shunt It is a fairly simple business to Completing Construction make the shunt which will enable Mount theresistancesand the the instrument to read from 0 to 25 sockets and insert the countersunk amperes. To enable one to do so an 4 B.A. screw marked B in Fig. 7. Now ammeter must be borrowed. The cut out a small piece of sheet metal othercomponentsneededarea so as to make the springy second D.P.C.O. switch and a rheostat, by contact for the ammeter shunt which means of which we can regulate the is seen over the middle socket in the flowofcurrentto,say,exactly photographs which show the upper ampere.Fig. 5 shows the circuit This is a photo of the original instrument, side of the panel. and you can compare it with the wiring Fig. 8 will explain the way in which used.The battery used for calibra- diagram which also appears on this page. tion is preferably an accumulator wth the shunt contacts operate.As the an E.M.F. of 6 volts. having been done, connect the shunt plugisinsertedinto the ampere The switch is turned over so that to the milliammeter as shown in Fig. 5, socket it makes contact first of all the borrowed ammeter is thrown into and the milliammeter to the switch. with the. springy strip, which is con- Turn the switch over and note the nected to the -top end of the shunt. N° ' MORSE FOR L /SE N /N (Cont i n ned on page 230.1 SOCKETS : FOR EELE reading. Very possibly the needle will hardly move at all ; at any rate, the reading will be very low. This is 1 ++ ± + 250Y2Y 2:5A25mA- just what we want. Place the switch - 25mA2.5.4 25V 250P LF ,// in the open position, slacken off the 0 C 30 C 2 A 2 nut of the terminal in the shunt and 4_I44 ... '11"/ 4 / pull a little more wire through so as 49..4.CZ EA 48.A.CS* to obtain a rathergreaterlength A. &S.A.ca -x. , 68.A. between the two screws. . ii SPA CEO TOSU/T./?/.&.c's W. VARLEY RES.NOLDER Testing the Resistance

111 E. ,- VIII"l' , Close the switch and try again. /2 ,x `'i ii sscs' /"Dosir/ON O. Continue until the milliamperes read- Mr / Ai/LL/AMMETER \ ing is about 10 per cent low, i.e. the ks....4 : PANEL /WOUN7TYPEI 'If. . 0 needleis recording9. milliamperes .. ' . 7 111 i when 1 ampere is passing. Then cut 6 a..i.,FOR the wire, remove it from the screws 7V Ai/Z L/AA,tbiETER ' L EA DS,TO .., I " / MIL L /A /KMETERL.--1/ and make it into a spiral, taking care, though, that the turns do not touch. What is the use of a stunt like 111/R/A/G .. 0/A CRAM. 5 that ?The milliammeter is reading F/C.9. If only about.9ampere, whilst the F.0.7,PANEL LAYOUT y699 ammeter shows that a current of a Y698 17] MODERN WIRELESS February, 1929

SHORT-WAVE SCHEDULES A list showing the more important of the tri

world's short-wave stations, together with notes on reception and the usual times of transmission.

PRINCIPAL STATIONS WORKING ON WAVE -LENGTHS BELOW 31 METRES. Wave-Frequency wave-Frequency length in length In in Kilo- Name of Station. Remarks. in Kilo- Name of Station. Remarks. Metres. cycles. Metres. cycles. 15.74 19,059 Bandoeng (Java) ..Call -sign, A N E. Weds.,2116 13,661 SCHENECTADY, NEWCall -sign, 2 X A D. 12.40 p.m. to 2.40 p.m. YORK Sun., 10.30 p.m. to 3.30 a.m. Mon., 7 p.m. to 9 p.m.Wed., 11p.m. Call -sign, 2 X G.Mon. 16-02 18,726 Rocky Point (Long to4. Fri., Island), New York and Fri. from 7 p.m. p.m03. a.m 11 . to 4 a.m. On onwards. Wed. and Fri. 2 X A D relays the programmes 16.88 17,772 HUIZEN, Holland..New station, wave- from W G Y. length subject to alter- 22'99 13,049 Houlton Maine ....Call -sign, 2 X- A A. ation. Transmits after 11 p.m. 24.5 12,244St. Assize, France..Call -sign, F W. 251 11,750 CHELMSFORD .. ..5S W. Maximum power 17 17,647 BANDOENG, JAVACall -sign, A N H. Weds. 15 kw. Mon. toFri., (Radio Malabar) 12.40 p.m. to 2.40 p.m. 12.30 p.m to 1.30 p.m. Power of 30 kilowatts. and 7 p.m. to midnight. 28.5 10,526SYDNEY, AUSTRA- 2 F C. 18 16,666 KOOTWIJK, HOL- P C L L. Weds. 2 p.m. LIA . LAND to 4 p.m. 30 10,000 Bergen, Norway ..L G N. NOTES.-To cover this wave -band a 2 -turn coil is generally used for aerial, a 4 -turn for the grid circuit, and a 5 -turnin the reaction coil holder.Where there is no separate aerial coil the aerial lead is usually clipped on to the grid coil at a point about one or twoturns from theearth " end of this. The new station at Huizen, Holland, will doubtless be watched with great interest, and it is probable that there will be regular transmissions with full orchestra on Wednesdays from this station.This section is the most prolific part of the short wave -bands, special favourites in this country being Radio Malabar (17 metres), 2 X A D (2196 metres), Chelmsford, and Sydney 2 F C (28.5 metres).

PRINCIPAL SHORT-WAVE STATIONS WORKING ON WAVE -LENGTHS ABOVE 31 METRES.

W ave- Frequency Wave- Frequency length in length in in Kilo- Name of Station. Remarks. in Kilo- Name of Station. Remarks. Metres. cycles. Metres. cycles.

31'4 9,554SCHENECTADY, NEWCall -sign,2 X A F. 33.5 8,955 NAIROBI (KENYA Call -sign, 7 L O.Daily YORK Aerial power of 10 kw. COLONY) 4 to 7 p.m.Sunday, Mon., 11 p.m. to 5 a.m. 7 to 8 p.m. Tues., 11 p.m. to 4.3037 8,108 PARIS, RADIO VITUSWed.,Fri., and Sun., a.m.Thurs., 11 p.m. 9 to 10 p.m. to 5.30 a.m.Sat., 1137.65 7,968 DOBERITZ ....Call -sign, A F K Mon., p.m. to 5 a.m.Silent Wed., and Fri., 6 to onSun.,Wed., and 7 p.m. - Fri. 4375 6,896 Rome ...... Call -sign, I M A.Sun., 31.4 9,554HILVERSUM, HOL-Call -sign, P C J. Tues., 4 to 6.30 p.m. LAND 4 p.m. to 8 p.m. and58.5 5,128 NEW YORK CITY ..Call -sign, 2 X E. Relays 11 p.m.to 2a.m. W A BC's programme. Thurs.,4p.m. to 8 Weekdays, 11 p.m. to p.m. and 11 p.m. to 5a.m. Sun.,3.50 3 a.m.Fri., 4 a.m. to p.m. to 5.30 p.m 7 a.m. 59.96 5,003 Boundbrook, N.J. ..Call -sign, 3 X L. Power 32 - 9,375Melbourne, AustraliaCall -sign,3 L O.Sun., of 30 kw. 7 to 8 p.m. 62.5 4,800PITTSBURG, EAST ..Call -sign, . W 8 X K. 32.5 0,231 Copenhagen ....Call -sign,7 M K. Tues. Power of40 kw. and Thurs. Daily, from 10 p.m. NOTES.-For stations on this wave -band the usual coil sizes are: aerial 2 turns, grid coil 4 or 6 turns, reaction 4 or 6 turns. The most consistent foreign station is Hilversum (P C J, formerly P C J J), and of the distant stations that firm favourite 2 XA F (314 metres).For a long-distance station using comparatively low power, Nairobi (Kenya Colony, East Africa) has been remarkably -well received in this country, whilst the Paris stations and Doberitz are worthy of special mention. 172 February, 1929 MODERN WIRELESS

Some observations of intereston th e different types of wireless masts and towers employed in other lands. From a Special Correspondent. has been said with.a certain amount of truth that power, and of a means of friendly communication between ITwireless is a science connected with the placing of nations.And in another respect a wireless mast con- landmarks up and down a country.Certainly it is stitutes a landmark in the progress of mankind. tr at the oncoming of radio has resulted in the erection of aerial masts and towers which possess all the character- Not Very Beautiful ! istics of landmarks. There are,of course, aerials and aerials.Thereis After all has been said and done, there is something obviously nothing very beautiful in the slinging up of a ennobling in the sight of an aerial mast or tower which wire or a series of wires between two adjacent buildings. has been properly erected.It is symbolical of a new Yet that type of aerial construction is one which our own B.B.C. seems to be rather fond of.Take, for example, the aerialof the Manchester station,2 Z Y, slung between chimneys.

Left, the lattice masts erected upon the roof of the broadcasting station in the Magdeburger Platz, Berlin.The down -lead is in the background on the right.On the right is the "umbrella " type of aerial used at the U.S. Air Corps' Beacon station at Wright Field, Ohio, 173 MODERN WIRELESS February, 1929

Naturally, this type of aerial construction may serve its own purpose quite efficiently, but for high -power broadcasting and transmitting stations some better type of aerial support is necessary, and is,indeed, in the majority of cases forthcoming. In general, all aerial supports may be classed under two heads, viz.,aerial masts and aerial towers.The term "mast "isproperly appliedto an aerial -supporting structure which must of necessity, be itself supported by a series of ropes or wires.On the other hand, a " tower is the term applied to an aerial erection which is of itself self-supporting and for which no stay -wires or ropes are necessary. Difference Between " Masts " and " Towers " The terms -" mast " and " tower " are often confused in meaning by the amateur, and therefore it would be well to bear the above facts in mind. What we may term a classic example of a simple type of wireless mast is that by the aerial system ofthe Prague broadcasting station. Here, it will be observed, the masts are stayed by means ofsteel guy ropes, and that the masts themselves are of the steel tubular type, a type which combines reasonable lightness with stability. Some stations, however, rely upon the lattice type of mast, as witness the Melbourne station, Australia, whose aerial we see below.In such instances, also, some system of stay -wires must be employed in order to protect the mast against the force of the wind.

A recent example of a " tower aerial support.The new 350 -ft. aerial towers at the recently erected J OAK station (Tokyo) of the Japanese Central Broadcasting Company

The Melbourne masts are noteworthy it only in view of the remarkable means of raising them bodily which has been adopted by the station engineers.One of the photos opposite shows a " close-up " of the base of one of the 200 -ft. masts used by the Melbourne station. This base converges to an apex which rests upon a series of glass insulators, the latter being let into a concrete bed.When occasion demands, the entire mast can be jacked up and the insulators renewed, the mast itself not being directly embedded in the ground. Dealing, now, with the second class of aerial -supporting f structures, we come to the towers, of which there are many well-known examples all over the world.One of the most recent examples of this class of aerial structure is to be seen in the aerial towers of station J 0 A the Japanese broadcasting station in Tokyo, which were erected during the summer of 1928. Resisting Enormous Wind Pressures These towers are nearly 350 ft.high, and they rest upon widespread concrete bases. 'ley are constructed to resist an enormous wind pressure, and it is estimated that they will remain in good condition without requiring any attention whatever, except, of course, in the way of painting. It will be more or less obvious, of course, that the main source of strain or " load " to which a wireless tower or mast is subjected is that of the pressure of the wind upon itssurface.This pressureisproportional to a certain constant (K), the latter depending upon the pro- portions of the surface of the mast or tower which is exposed.The wind pressure of the mast is also pro- . A typical example of lattice type of mast is to be seen at the 3 L 0 portional to the square of the velocity of the wind, and to station in Melbourne, Australia. the area of the mast or tower exposed to the wind. 174 February, 1929 MODERN WIRELESS

Mathematically expressed, therefore, we have : P (Wind Pressure) = KV2A. For these reasons, therefore, a wireless tower must be erected upon outstretched feet, and a mast must be well stayed with stout wires or ropes, otherwise the entire structure would quickly blow over. Germans Fond of Roofs Provided the foundations are firm enough, a radio mast or tower may be erected upon the roof of an already existing building, and, indeed, in many countries this type of construction is popular.The German broadcasters, for instance, are fond of erecting lattice masts upon the roofs of their buildings, as witness the aerial at the Magdeburger Platz station, Berlin.On the other band, some stations erect squat towers upon the roofs of buildings ;the aerial towers of the Madrid station being a typical example of this type of construction.

A classic example of an aerial mast of steel; the tubular type a Prague The aerial is of the three -wire flat -top variety. type of aerial is, indeed, a very peculiar one, but it serves its purpose, being in certain respects specially directional. Let us not imagine, therefore, that aerial -supporting structures are put up by station engineers more or less as fancy takes them.There is a vast science inher3nt in the construction of such erections, and much observation is necessary before their construction can be undertaken.

The base of a modern aerial mast, showing the glass insulators

and the concrete pillars for jacking -up the mast. Then, of course, there exist a certain number of freak aerials in different parts of the world.Perhaps ohe of the most interesting of this miscellaneous class is the aerial shown opposite. This is the aerial support of station W L B W, of Oil City, Pennsylvania, U.S.A. It comprises a light wooden tower which is, in reality, the framework of an old oil well, and the stay " ropes' seen in the picture are, in actual fact, long wooden poles which have 'long been impregnated with oil and which are thus permanently rot -proof.Two of these wooden towers support W L B W's aerial,sufficientstability being afforded by the wooden supporting rods. A Very Peculiar Aerial As a final illustration of a peculiar type of aerial which is sometimes seen abroad I give as an example the peculiar " umbrella " aerial employed by the United States Air Corps' Beacon station, situated at Wright Field, Ohio. This aerial erection comprises nothing more than a stayed steel pole, some 90 ft. high. The actual aerial wires spread out from the top of the A curious aerial support comprising the tower of an old oil well. The supporting " ropes " are wooden masts, impregnated with pole, alternating in this respect with the stay wires ; thus oil.Appropriately enough, the tower is to be seen at Oil City, forming a sort of gigantic umbrella framework.Such a Pennsylvania. 175 MODERN WIRELESS February, 1929 Make sure, however, that you take your readings after the acid has been allowed to cool down, for just after mixing, when the electrolyte is still MIXING BATTERY ACID very hot, the density reading you obtain will be much lower than it Some valuable hints on a subject of interestto all practical amateurs. should be. An approximate correction By C. P. A. is given by reckoning a decrease of -001 in density for every 3 degrees WZ4P+5-41 -W4MP"M- -WWW, -WIWF.WWW, " ***** 6, ,+ -W45-1154541W -W14-

The Valve amplifier has so much to recommend itthat other means of strengthening the pro- grammeareoftenoverlooked. Here isa practicaltalk onthesubjectof microphone amplifiers for crystalsetuse.

IN past years, quite a number of By J. FRANCIS. varying typesofmicrophone amplifiers for use with crystaloperation, and I propose mainly to flowing from the latter is varied in receivers have been marketed.Most confine my remarks to amplifiers of accordance with, the vibrations. Con- of them were more or less efficient in this type more than to the older and sequently a pulsating current flows action, although, perhaps, some of now almost obsolete types. across the microphone.This passes them may have proved rather trouble- Ofcourse,Iknow that many down into a suitable transformer, and some in use. amateurs regard the use of an ampli- from thence is led to a pair of 'phones However, at the present time I think fier to boost up the signals from aor to a loud speaker which is con- we may safely divide up the crystal - crystal set as a rather childish pro- nected to the instrument. set microphone amplifiers which are ceeding." Why not,"those good now in use into three varieties, to " fans " remark," get a valve set, Don't Expect Too Much wit, the so-called " box type " ampli- and have done with it ? " Used with reasonablecare, any fier,inwhich avibratingreed You have got to remember, how- typeofmicrophoneamplifierfor actuated by headphone magnets im- ever, that there are still a lot of elderly crystal set use will give satisfactory, pinges upon a sensitive microphone ; and infirm people to whom even the although, of course, limited, results. amplifiers which are contained in the simplest valveset,withitsusual Isay " limited "becauseIhave base of a loud speaker, and which accompaniment of batteries and accu- known some keen radio amateurs to operate on a similar principle ;and mulators, appears to be an awfully have appeared to expect amplifiers finally the "-bar " type of amplifier, complicated device, and it is in the of this type to give results something an illustration of which will be seen main, I think, for such people that equal to that of a three-valver !The at Fig. 1. the microphone amplifier caters. truth of the matter is, however, that After all, the microphone amplifier a crystal -set amplifier of aty of the Easily Operated of any type is a very simple piece of above types is intended solely to boost Probably, at the present day, this apparatus, despite the fact that its latter type of crystal -set amplifier has best use requires a certain amount of retained the greatest amount of popu- skill in affecting its most sensitive arity on account of its simplicity of adjustment.Consider, however, the principle of the apparatus. What It Is In the latesttypes you have a carbon granule microphone fitted into a rectangular metal casing, as shown at Fig. 2. The microphone is made to slide into what is nothing more or less than a single headphone, suitably mounted in an upright position.A detail of this latter, with the microphone casing removed, will be apparent from a glance at Fig. 3.Here the magnets are clearly seen. Current from the crystal set is led to the headphone magnets.These cause the diaphragm of the microphone to vibrate, and, the microphone Fig. A crystal -set microphone amplifier being connectedinserieswith a Fig. 2.A close-up of the amplifier, show- of the adjustable bar type. battery, the strength of the current ing the microphone and diaphragm. 177 MODERN WIRELESS February, 1929

up the signals which have alreadythese will naturally get the listener .q9ZeeQ423(cfPg'83c594Fa cfScW3S'. been obtained by means of a crystal into a most exasperated frame of set. mind. SIMPLE TESTS FOR a If,therefore,acrystalreceiver -D FIXED CONDENSERS refuses to give you a required station, Current Consumption you may be pretty sure that the em- The easiest method of adjusting an O@Pe1513,5P0 gEE- ployment of a microphone amplifier amplifier of this nature satisfactorily will not be likely to bring about much is to screw down the microphone knob ANY present-day fixed condenser betterresults.If,however,your untilscrapings and cracklingsare of the receiving set type will crystal set receives your local station heard, and then to unscrew it very hardly ever give trouble, pro- clearly and distinctly, although the slightly so as to make the latter just vided that excessive voltages are not signals received may be uncomfort disappear.The instrument will then applied across it, but, nevertheless, it ably weak, well, then, an amplifier of be working atitsmost sensitive is sometimes the case that a radio the microphone type will give you adjustment for practical use. worker may suspect one or more older the results you want.That is to say, And as regards the current con- condensers of the small " fixed " type it will bring in the signals loud enough sumption of these amplifiers.This to be the cause of bad and noisy for any headphone reception, and naturally depends to some extent upon reception. probably it may allow some loud- the size of the microphone and the Naturallyenough,thesimplest speaker reception to be carried on areaof carbon -granule surface ex- method of" testing " a suspected as well. posed to the action of the current.In fixed condenser is by taking it out of average cases, however,- a crystal -set the circuit and by substituting a new Adjusting the " Mike" microphone amplifier, used two hours condenser ofthe same type and The vital portion of any microphone or so nightly, will exhaust a flashlamp capacity value for it. amplifier is, of course, the microphone battery in a month. It will, however, However, it is not everybody who adjustment, and it is in the operation worksatisfactorilyoff twolarge possesses a varied assortment of new of this adjustment that many people bell -batteries (in series) for nine orcondensers at his disposal. In nearly gowrong.If,forinstance,the tenmonths, and sometimes even everycase,therefore,asuspected adjusting knob is nat screwed down more. fixed condenser is best tested accord- far enough, the signals will be weaker Everything,therefore,istobe ing to the following scheme even than they would appear with gained by the use of large batteries in the crystal receiver alone, and, in conjunction with microphone ampli- Test for Direct Electrical Con- fact, in such an instance they may fiers. Their current -giving capacity is tact Within the Condenser even be conspicuous by their com- far greater than that of any flashlamp Connect up in series with the con- plete absence. battery. Furthermore, the current denser a flashlamp battery and a suit- Attheotherextreme,ifone deriVed from a new flashlamp battery able bulb.If, on making the contact attempts to attain too sensitive an is rather too strong for use with the to the lamp, the latter does not light average amplifier. Such batteries tend up, the condenser is more or less O.K., toproducedistortion,andthey in the respect that it does not permit certainly create a good deal of noise at direct electrical leakage. times, owing to the erratic nature of their current flow. Test for Dielectric Quality Two large batteries, on the other The dielectric, that is to say, the hand, give a rather lower voltage insulating medium of the condenser, than does a flashlamp battery,a will hold a charge for some time, pro- voltage,however, whichisamply vided that the material is of good sufficientfor the operation of any quality. A good way to test out the amplifier of this type.The current capabilities of a condenser in this flow from these batteries is more even. directionismomentarily tobring Thus their use brings about .freedomleads from it into contact with the from distortion in the signals, ease of poles of a 2 -volt accumulator. Imme- adjustmentofthe microphone,a diately after this, connect the con- freedom from extraneous noise in the denser in series with a pair 'of head- headphones, as wellas,of course, phones. On completing the circuit to a far greater working life. the condenser, a distinct click should Fig. 3.A close-up of a bar -microphone be heard in the 'phones, this repre- amplifier,showingthemagnetsand Need for Battery Switch senting the giving up of the electrical windings. One word more.Should you be charge acquired by the condenser fitting up any type ofcrystal -set from the battery. adjustment, matters willbe made amplifier for the use of an invalid or almost asbad. For under thesean old person, don't forget to include Further Test for Dielectric circumstanceseverylittlemove- a small switch somewhere in the Quality ment of the leads to and from the battery .circuit. Thiswillhelp Touch the condenser with the poles amplifier; every little inequality in enormously in economising batteries ; of a small battery, as before ;but the flow of current from the battery, and also, as under these conditions this time allow about an hour to a.nd any maladjustment CA the crystal the current can be switched off with- elapse before conducting the 'phone contact on the receiving set, will give out handling the amplifier itself, the test.If the click is heard this time it rise to a series of scrapings, clickings, chance of the instrument getting out will prove the condenser to have a and hissings in the headphones, and of adjustment will be lessened. good charge -retaining quality. 178 February, 1929 MODERN WIRED; ENERATI NC GIGANTIC 1-1 .T.

An interesting description of the methods and apparatus used to produce electrical pressures of Some of the apparatus used for the developing of hundreds of the order of millions of volts. thousands of volts. By W. K. CASTLETON. THE news of the employment of marvelled at the sparks up to one electrical transformers, and the ends stupendouselectricalpres- foot long which hisinstructor in- ofthe coilarefitted with metal sures like that of over 5,200,000 formed him represented pressures of caps 8in.indiameter,whose volts, described in a recent issue of 100,000 volts and which might be rounded surfaces prevent spark -dis- " M.W.," for the purpose of a more taken into the body without danger, charges out into the oil when the complete and thorough investigation because of the high -frequency of the caps are raised to such high voltages of the internal structure of atoms, alternating current from the coil. - by the action of the coil. has been received with enthusiasm The coil is excited to the high volt- byatomicphysicistseverywhere. A Familiar Principle age by -means of a primary circuit To them it opens up a new vista ; The principle employed is the same consisting of a large glass -plate con- the possibility of coming very closeas that operating inthe familiar denser, a spark -gap, and a primary to the fundamental laws of matter. acoustical example of a violin string coil of two turns of copper tubing They foresee not only the exquisite vibrating" sympathetically "when wound about the middle of the high - beauty of atomic structures revealed the string, tuned to the same note, is voltage coils and spaced some distance on an incredibly minute scale, butstruck on an adjacent piano.The from it in the oil. The condenser and they cangetimpressionsofthe same principle of" resonance " or primarycoilareadjustedtobe universe reached even to the farthest " tuning " is also familiar to all radio electrically " in tune " with the high- star.That is their poetry.On the enthusiasts. voltage coil. practical side there yet remains to be The high -voltage coil itself consists told something of the methods which of 8,000 turns of silk -insulated copper When the Condenser Discharges are employed in order to provide them wire, wound on a single layer on a The condenser is charged to 50,000 with these instruments requisite for Pyrex glass tube 3 in. in diameter and or 100,000 volts by means of an their researches and investigations. 36 in. long. This coil is immersed in an ordinary high -voltage X-ray machine, insulating oil, such as is used in all and when it discharges through the Spectacular Demonstrations A laboratory source of high elec- tricalpressureslikethatofthe Carnegie Institution, which, as we showed, developed 5,200,000 volts, is usually based on an adaptation of high -frequency resonance coils. That was the case here.There is nothing new in this, of course, for it will be remembered that coils operating on the same principle were con- structed38or 40 yearsago by Nikola Tesla and Elihu Thompson, whilstcertainlyforthirtyyears similar things have been used as spectacular demonstration toys for amateurs and schoolboys. That is the marvel-that in these littlecoilsshould have been the genesis of such enormous far-reaching results. Every student in an elementary or high school has seen a coil of the nature in operation.He has A Tesla coil sparking in air at about 300,000 volts. 179 MODERN WIRELESS February, 1929 spark -gap the surges of current in this. OgEa'ZEO,0E0C&&ZOS3 of the rim in order to facilitate the primary circuit by " resonance " set O 0 dripping of water away from the lid. O A BLACK ENAMEL 0 In rainy weather this article ,(a the high -voltage coil into oscillation Q3 0 and build up the very high voltages O FOR METALWORK g " close-up " of which is seen in the (of the order of millions of volts) photograph)isslippedoverthe between the two balls on its ends. qL'Z'.ZOOZGO.- OGO(C3f3t,:'.',C3 aerial down -lead 'at some convenient position,suchas,forinstance, Surrounding the high -voltage coil THE many varietiesofquick - by oil is an important feature of the drying black enamels which the one depicted in the diagram. method. An ordinaryTeslacoil are sold in bottles or tins are The lid will then act as a sort of operating in air will not go to voltages Water -trap. It will not only allow not usually inexpensive commodities, the water running down the lead-in higher than 300,000 to 400,000, be- and for some trifling local enamelling cause of the large sparks and streamers of a loud -speaker horn, a transformer and " corona discharges " which occur case, or some similar component which from all parts of the coil, but when this has acquireda somewhat shabby spectacular display is prevented by appearance, the expense incurred in immersing the coil in 'oil, the energy purchasing an entire tin or bottle of which would ordinarily be, used up enamel is quite out of proportion with by sparks goes into raising the coil its usefulness. to a very much higher voltage. Many constructional amateurs, however, have by them a quantity of Five Million Volts! ordinary clear varnish, and, in such In the case of the Carnegie Institu- instances, a black enamel suitable for tion's equipment, it was found that the above -mentioned uses can very voltages up to about 3,000,000 were easily be made. readily obtainable by using a coil Dissolve two parts by weight of of this type in an ordinary open tank, finely -powdered ivory black in twenty A photo of the actual device in use. but above this voltage, sparks from parts by weight of the clear varnish, the caps on the ends of the coil would and stir the mixture very thoroughly. wire to drip off harmlessly, but it will flash out into the oil. This compositionwillmake an also,to a certain extent, keep a By placing the high -voltage coil excellent black varnish.. It is slow portionofthelead-inwiredry, inside a large steel tank fitted with drying, but it possesses a good " body" owing to the sheltering effect of the oil under a pressure of 500 pounds to and, next to a stove enamel, it is very rim of the lid. the square inch, we were able to obtain resistant to rough handling. More- In fine weather, of course, the lid is over 5,000.000 volts. over, the black varnish can be made easily removed, and it can be slipped up in very small quantities at a time, on again at a moment's notice. thus eliminating any possible waste. Works " Most Satisfactorily" @00000060E7,E3)0000 Of course, a more artistic -looking O 6 gadget of this nature could be con- g AN AERIAL LEAKAGE a structed out of a piece of plain sheet Et PREVENTER Et metal or wood, but not being blessed ® (or cursed) with the artistic tempera- cli9 543f3*83643Sf9G100. Ot4C30q9W ment, the writer pins his faith to the IN summer and in autumn, as well yellow lid of the celebrated Messrs. as in -winter, the aerial system Gold and Flake for the above radio of a house is, at times, apt to undergo electrical leakage in inclement weather owing to rain -water trickling' down the aeriallead-in, and thus /ER/AL providingalow -resistancecircuit to earth for the feeble aerial currents. The writer has seen many schemes LEAD /A, for avoiding thisoften very considerable trouble, but to his mind there is nothing simpler or more effec- A-C/11C Uz. AR tive in providing a cure for the trouble Disc than the use of the little home-made gadget described below. 76,5E7

All That Is Needed ZERD/N6 //Y The " raw material " for this little 4/SULAProR. aerial -leakage preventer consists of nothing more complicated than a of/3 circular tin lid which may be obtained either from a cigarette tin or from one purpose, and he has still to experience ofthe innumerablecontainersof an occasion upon which the article domestic commodities. refusestocarryoutitsrequired A typical Tesla coil such as is used in Make a radial slit to the centre of functiontoamostsatisfactory developing high voltages. the tin lid, and cut away a small piece degree. 180 February, 1929 MODERN WIRELESS

mommommummainIImnimmimeimmom mulunisumesmia, anummiummg CJ .."=::=2======::11SOUND CONNECTION ! Faulty contacts and connections areone of the most frequentcausesof troublesin modern radio sets.Here is a practical article which tells you how you can take precautions against them when building your set. By C. A. OLDROYD.

04 solder or not to solder," Comparative tests of the contact At first sight, the joint illustrated isa question home con- resistance, of soldered and clamped in Fig. 1 looks excellent ;the end of structors must face sooner joints have been made by American the winding has been clamped under or later. Do you remember some ex- radio engineers and they maintain a washer insidethe formershell. perimental sets hurriedly thrown to- that " ten unsoldered joints increase gether on the hook-up board ?Any the resistance in the conductors four old bits of wire were used for the times inless than three months." ENO or )z,Nrsiz &aka {ORE LOOPED ROUND The connections, components were placed A well -solderedjoint, on the other anyhow. leads straggled all over the hand, " will lower the resistance in 610 OF 10RE--). baseboard.And yet the set worked the joints to approximately sixty per splendidly, and when rebuilt in a cent of the resistance offered by the 3000 SOLDERING more, permanent form as a finished conductor itself." gaCO/LW/NO/NG/ TAG

Good and Bad Joints 00118LE ENDED SMALL A soldered joint cannot deteriorate 5040ERINGLue4 ScRew since the airis excluded from the SOLDER HERE. / .411" / contact surfaces.For a similar rea- POI son, a flat soldering lug appears to be 30 FORMER) WASHER SOLDER betterthanaroundwirewhen LEADS TO /11 Nur clamped under a terminal nut.The SECIION FREE END OFLUG ///////////////////%7, nut bears evenly on practically the "76.3. whole contact surface of the lug and keeps the air from the bright contact The soldering lug is fixed under a nut surfaces for a considerable time. on the outside of the former.Now A connection cannot be too direct ; let us regard this joint from the point often two joints are made where one of view of a feeble radio impulse receiver it appeared to be no better would be better. A typical example passing through it. asfaras performance goes.Why may be a home-made solenoid coil First of all, the current must pass solder then ? wound on a cardboard or Paxolin from the bared wire end through the On the surface, it looks as if the former (Fig. 1). washer into the screw stem,after soldering iron would speedily become obsolete and end its days in a dim corner of the workroom.There is another side toit, however. The rough-and-ready experimental set was used a short time only ;if it had been in use for months insteads of days some of the connections might have workedlooseandcausedthose mysteriouscracklingnoiseswhich are most difficult to trace. Must be " Airtight " A clamped joint cannot be perfectly air -tight over the entire surface. and when the contact surfaces become oxidised the resistance of the joint may rise appreciably. One poor joint might not greatly affect the efficiency of a set, but a number of The use of screens gives the added advantage that " earth " leads can be shortened and them will ultimately make a differ-reduced in number.But connections to screens should be soundly soldered and not ence in both volume and range. haphazardly bolted. 181 MODERN WIRELESS February, 1929 ravelling down the latter it reaches end of the stem, but a tar better And, finally, don't forget to wipe t he underside of the nut, and from method would be the one shown in the soldering flux from the soldered here it finally reaches the soldering Fig. 4. The end of the terminal stem tug. Unless all contact surfaces have is drilled out to take round tinned wire COON TER SUM< been very carefully cleaned the re- for a depth of about k in. or so. HOLE FORZEAD 11111111111, sistance of this joint may be con- Automatically thehole registers SMOULDER OF Poinvo10.0E siderable ;a better way is shown in the lead at the exact centre of the 7A-RNI/ NAL ZERO Flo. 2. stem and the solder has a large surface to " bite " on (see Fig. 5).If the terminal strip is tilted to bring the WASHER Tiawrim. terminals into a vertical position flux I ..577/P H&c FOR 71RitovvAL Srkxt and solder will nottend to ran off the Nur A_Lasr,oNcE joint and the resulting connection Assam Sraw I3ECES will be both neat and efficient.At the end a shoulder of solder will form which adds to the strength of the joint. Fia6,'BASEBOARD of Sir no - ?,SMALL licuEs FOR LOCATING LEADS nag A joint while the latter is warm.Sur- ifsz Question of Terminals plus flux will eventually causecor- Some constructors prefer to mount rosion and its subsequent troubles. Here the bared end of the winding their terminals upright on a narrow is taken several times around the strip of ebonite held clear of the base- 6). szeow3ocmfscfm343t3ctwsc tongueofthesolderinglug and board by distance pieces(Fig. fi9 e, soldered toit.The small hole in In this case the method suggested the extreme tip of the tongue is left above failssince the tipsof the f8' RADIO ODDS AND ENDS terminal stems are no longer accessible free for outside connections. Such riS200&Z-Z-ZicM3 ci3ZZ8C3c33(89ZS a joint is easily made and a perfect with the soldering iron. connection is guaranteed even if the Listeners who are also amateur screw holding the lug should be slack. gardeners should remember that this DR/Z ZED Our 501 -DER is the best time of the year to inspect An Ideal Method or re -arrange a buried earth system. Ideal would be soldering lugs with (If left till later -in the season there is two small holes in them, as illustrated likely to be interference with gar. in Fig: 2A ; one for the end of the wind- dening.) ing and the other for the outside lead. The writer has not succeededin Grid resistances inserted to keep tracing a commercial lug of this type, CONNECTING LEAD H.F. out of the L.F. side of the receiver are lesseffective for that perhaps some manufacturer will oblige ENLARGED WEW OFEND °FA-PM/NZ us with an improved design in the near purpose on the long waves than on future. fia S. A64I the shorter ones. On the other hand, a double -ended * * * tug could be used (see Fig. 3), un- Still, the former method can be A Useful Tip fortunately the inner joint is some- adapted even to this case.A small times hard to get at with the soldering A rubber band placed round the hole might be provided in the shoulder top of a grid -bias battery will steady iron. of the terminal, just above the ebonite Speaking of manufacturers brings the flexible leads to the plugs and strip (see Fig.6), to allow the end prevent them from coming loose. me to another bone I have to pick of the lead being inserted. with them.I wonder if they ever * * The month of the recess could The standard split -secondary trans- beslightly countersunk to prevent former was designed for use with a ESOlvIre TixtauvRt Snzu, spreadingofflux and solder;the completed joint will look neat and fairly small tuning condenser,say, WRSNEP .00025mfd., and consequentlyit hysERrLEAro the connection is bound to be above A-Nur may not tune downproperlyif ; 100 Irvin Hasp reproach. shunted by a tuning condenser of -i-4716 /86,tuGE 77fte.69 WIRE .0005 mfd. Final Advice * * * (LEDI./RAOur TO 7-AKE *RE Gradually, personal experience has 7E-VMINAL A good indicatorfor condenser BASEBOARD converted the writer from clamped to dials can be made from an ordinary soldered joints, and my parting ad- tapping stud, filed down to a point.. vice can be summed up in a few words. Make a friend of your soldering iron, * * * fic Rattling on loud speakers or 'phones RiS3 keep it clean and treat it well, and you will find soldering a pleasure. can often be cured by tightening up find time to build a set themselves l Carefully follow the numerous hints loose screws on the base. If they do, how do they connect the that have been published from time * * * leads to the stems of the terminals to time in these pages, and with some A decided softening of the loud- mounted on a terminal strip ? experience and alittlecare your speaker reproduction can sometimes Assuming that the joint is to be soldering efforts will not have to fear be obtained by standing the instru- soldered, we may spot the lead to the comparison with professional work ! ment near a heavy curtain. 182 February, 1929 MODERN WIRELESS

41111111111111111111\1111111111111111116A 11111111111.11W.

1441121 FRA11111111111111M91.1

Under this heading month by monthour 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.

A Muddle and a Blessing Those Publications' Announcements LMENEM are still mercifully saved from the threat- No doubt many other listeners share my vexation at ened flood of political oratory which menaced the the weary and seemingly endless repetition of advertise- programmes last autumn.But the professional ments of B.B.C. publications on the microphone.More politicians do not like being excluded from the micro- recently I thought I noted a contraction both in the phone. number of such announcements and in their length. I heard the other day from a member of the Abingdon On enquiry at Savoy Hill, I am told that this is the Street staff that the Liberals had sent a special committee case, and that the policy is to reduce still further the of inquiry to examine and report upon the use of broad- use of the microphone for this purpose.Apparently it casting inpolitics in the United States.The report bas been realised at long last that even on elementary speaks in the most enthusiastic terms of the splendid commercial considerations it is not good selling policy opportunity given the American politician to educate his to irritate your market. public over the microphone. The Liberals are so impressed that they make no secret B.B.C. Publishing of their intention to attack the monopoly of the B.B.C. The recent press campaign against the B.B.C.'s new at the General Election if, meanwhile, they fail to obtain publication would come as no surprise to readers of this satisfaction in their demand for microphone time.They page, where I anticipated developments over a year ago. would -like about an hour a night, between 8 and 10 p.m. Fortunately for the entertainment of listeners, there is SCOTLAND'S RADIO BEACON no sign as yet that any agreed scheme of political broadcasting will come into force this side of the General Election. There may be discussions of one or two exceptionally important matters,inadditionto the electionpro- nouncements ofthe Partyleaders, but beyond this listeners are unlikely to be disturbed.Nor need the B.B.C. fear any attack on its monopoly on this account. Realism in Drama There is a revival of criticism of the B.B.C. for allowing" objectionable " passages to be included inits dramatic broadcasts.A case in point is " Montezuma," the history play by Cecil Lewis, which was given early in the year, and which the dramatic critics praised. But some correspondents to newspapers developed a real white -heat of fury over some of the things said in this play.Taking into account the advance descriptions, I found nothing wrong with the play at all. There is much more ground for criticising the B.B.C. for silly censorship than for passing " immoral or objectionable "broadcasts." Montezuma " was a play set in the fifteenth century in Mexico.It was a reason- This wireless beacon station, built at Fraserburgh, was the first to be built on the mainland of Scotland.Note the fog siren in the ably faithful representation of those rugged times.The foreground. only thing 1 had to find fault with was the introduction of modern slang such as " rumpus."So far as re- The B.B.C. probably wishes it had never set up that laxing censorship of impropriety in literature, I say to " Hadow Committee ' on education. Savoy Hill," go to it," and leave Shakespeare alone Everything that has happened as a result of the activi- when you broadcast him. ties of that Committee has got the B.B.C. into trouble. 183 MODERN WIRELESS February, 1929

The suggested extension of educational talks before the restricted way, and that, after a decent interval, the Regional Scheme had been finished was met with strong B.B.C. will quietly draw in its horns in publishing. opposition.And now the publication of an educational Anyway, there will be no new series of educational " follow-up "._paper has united the whole of the newspaper publications such as Mr. Stobart was supposed to have and publication industry against the B.B.C. announced.It is curious to note that once again Mr. But the campaign does not seem to have been very Stobart, the most peaceful and amicable of men, finds well managed.Apparently no protests or representa- himself in the centre of a tumultuous campaign.He tions were made to the B.B.C. itself.The idea was to has had to bear the brunt of several attacks on talks and tackle the P.M.G. direct, and get him to order the B.B.C. broadcast education. to desist.Even if he had been willing to do this, he has no status in the matter unless it could have been proved Smaller Provincial Orchestras that the B.B.C. had declined to receive a deputation I am told that plans are now complete for the reduction first. of all B.B.C. provincial orchestras, except those' of Bir- Another thing, too, was that the paper was announced mingham and Belfast, by fifty per cent, in about six months last summer, when the Hadow Committee's report was time.This sweeping change is supposed to be rendered published by the B.B.C., in a book entitled " New Ven- necessary by the financial requirements of the new permanent orchestra under Sir Thomas Beecham. THE MADRID BROADCASTER It is purely a matter of money ;but nevertheless it -will bring in its trail a lot of trouble for the B.B.C. at a time when it can illafford unnecessary difficulties.Savoy Hill would have been much better advised to carry its existing orchestras a little longer.As things stand it will probably be forced by fierce local campaign to make some compromises which will satisfy no one. No sooner has the B.B.C.establisheda National Orchestra of Wales, and .a Northern Wireless Orchestra, thanitwashes them out.Incidentally, why spend money on studio accommodation in Manchester, Glasgow and Cardiff if there is to be no programme work done there ?This is a matter which needs investigation. Broadcast Opera Decline I hear that there has been a big decline in the number of copies of opera libretti which the B.B.C. has disposed of this season in connection with its monthly opera scheme.The reason for this is that the selection of the operas is not above criticism.There has been a growing tendency at Savoy Hill to neglect the " popular classics " in favour of obscure works with an exotic flavour. Broadcast Drama at Last I believe the appointment 'of Val Gielgud to take over all the B.B.C. dramatic work means a great improvement in that part of the programme organisation.Mr. Gielgud has a sound journalistic background, is not handicapped by stage or music -hall prejudices, and has a mind at once receptive and resilient and original.

A B.B.C. BIack-List The aerial of the Madrid broadcasting station is erected on the It was mentioned the other day at a dinner party roof of the building.The call -sign of this station, which is often heard in this country, is E A J 7. where I was a guest, that the B.B.C. kept a black -list of people who had offended it.It was suggested that the tures in Broa.dcasting."There the recommendation is last name to be added to this list was that of Lord Melchett. much more objectionable from the press standpoint than The same night in the news from 5 G B was given a what the B.B.C. actually contemplated. glowing account of the progressof Lord Melchett's From what I am able to gather, the result of the cam- rationalisation scheme.So the black -listing, if it exists, paign will be that " The Listener " will go on in a chastened does not extend to the news bulletins.

"M.W.'s " Exclusive Broadcasting News Now that Broadcasting is a powerful force in the life of the nation, a well-informed survey of its developments and possibilities is becoming increasingly necessary. tjlIn " My Broadcasting Diary," MODERN WIRELESS presents to its readers month by month a thoughtful, exclusive, and authentic review of British Broadcasting.Compare this with any similar feature in any other periodical and you will realise at once the superiority of Modern Wireless.

184 February, 1929 MODERN WIRELESS

TO SECURE SILENCE IN THE BACKGROUND and the way a Lissen Transformer amplifies, keeps that background just as silent asit was inthe Studio. The acoustic experts of the broadcast studios use every effort to obtain a background of absolute silence for each item of the pro -gramme.To obtain the same effect from your receiver, use Lissen Transformers for each stage of amplification.Then you get a silence upon which the broadcast instrument or voice can paint a living picture, building up the melody without a trace of extraneous sound to interfere with it, every word and every note standing out in stereoscopic. relief. Lissen Transformers can be used in every receiver and in every published circuit-use them whatever receiver you are building and you will always get the true effect of every broadcast item.

The famous 816 Lissen Transformer has won for itself the reputation of "The Transformer that will never break down."Suitable for all ordinary purposes. Turns ratio 3 to 1.Resistance ratio 4 to f . . 8/6 THE LISSEN SUPER TRANSFORMER This Super LISSEN Transformer is made in two ratios, 31 to i and also 2.f to f.The 3f toiis suitable for use in either the first or the second stage of an L.F. amplifier, or can be used in cascade for both stages, and with practically any valve.The 2.1 to i transformer is suitable for use after a high impedance rectifier valve without fearof distortion orlossof high notes and overtones.The price is the same for both ratios ISSBN

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185 MODERN WIRELESS February, 1929

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186 MODERN WIRELESS

A Philips Amplifier-British General Components-Loewe Receiver-Ferranti Safety Box- Brown Cubist Loud Speaker-Lewcos Loading Coil. A Philips Amplifier is the same, i.e. 18s. 6d. The one is an Loewe Receiver THE power -compactness ratio of aerial tuning unit designed for cover- We recently had the opportunity the Philips gramophone am- ing the range of 250 to 2,000 metres oftestingaLoewetriple -valve plifiermustsurelyreach simply by operating a switch control. receiver.This remarkable little set record heights.The accompanying The device fixes to a panel (two has the appearance of a one-valver, photographs will give a good idea of holes only are needed), and of the two although, in effect, it is a det.-2 L.F. the small sizeofthis instrument, front knobs the one is the above - set. more particularly when it is mentioned mentioned wave -length switch con- Referringtotheaccompanying that the valves shown are of quite trol,and theotherthereaction_photograph, it will be seen that the normal dimensions. instrument comprises a smallflat panel on the side of which is fixed a ManufacturersandTradersare coil holder.The panel also carries invitedto submit for test purposes radio sets, components and accessories the tuning condenser dial and an to the " Modern Wireless " Test Room on -offswitch.Theflexiblecable at Talus House, Tallis Street, London, E.C.4. Under thepersonalsuper- which can beseen embodies the vision of the Technical Editor all tests battery connection. and examinations are carried out with the strictest of impartiality. Readers can accept the Test Room reports published monthly under the above heading as reliable guides as to the merits and demerits of the various modernproductionsoftheradio industry.

Note the compactness of the Philips ******** amplifier. control.It is a robustly and soundly The amplifier is provided with a constructed component and operates rpmovable metal cover, and so is, in well. fact,practically a totally enclosed The other British General item is an device.Ithas a multi -flexcable L.F. transformer, the particular one for the batteries, the robust terminals sent us having a ratio of 5 to 1.It is on the end of this being very clearly styled. a Super Shrouded. Transformer, marked.There is an efficient poten- and it is worth noting that it carries a tiometer type of volume control at twelve months' guarantee.This, too, the input end, and a Philips L.F. isa component that can hold its transformer,notedbothforits own. efficiency and small size,isincor- Thisis the Loewe triple -valveset,a porated in the amplifier.. A pentode feature of which is its extraordinary small valve is used in the last stage. size in comparison with the results given. With a high amplification type of valveinthefirstposition,great When itis stated that the valve amplification can be obtained. is not much larger than an ordinary Altogether, this Philips gramophone valve and smaller than some power amplifier is a notable achievement. valves, the compactness of the arrangement will be apparent.The valve is British General Components a most complex assembly of elements. The British General Manufacturing It incorporates in the one bulb the Co., Ltd., recently sent us two of their elements and coupling devices of three components, the price of each of which Internal view of the Philips amplifier. valves. 187 MODERN W1RELES$ February, 1929 The -set is quite a simple one to units which can be enclosed in the handle.While the reaction effects do Safety Box.Box. Any one of the five not seem to be quite normal, the set, appropriate charts, which are fully in general, operates like an ordinary explanatory from aconstructional one.The makers claim little more point of view, are available to anyone for this receiver than loud -speaker free of charge on request.The price reception of the local station, but we of the Safety Box is 13s. 6d., and we found no difficulty in getting some of consider it as good value for money as the more powerful continental stations anything we have seen. during our tests.Bearing in mind the price of the little outfit, we can Brown Cubist Loud Speaker only consider ita most successful Thedesignof moving -coil loud application of a unique principle. speakers seems in general to have settled down to very hard and fast Ferranti Safety Box lines.But there is one very notable " The safety problem in connection exception.This is the Brown Cubist with the use of supply mains for radio loud speaker.One of these (it is of purposes has not in our opinion pre- the permanent magnet variety) was viouslybeengiventheattention recently sent us for test. A view of the Brown "Cubist " after the which it merits," say Messrs. Ferranti, The most outstanding feature of back of the cabinet had been removed. Ltd., in a covering letter when sending this most interesting speaker is that we could, we had to admit that we a sample of their new Ferranti Safety liked the reproduction as much as Box. And undoubtedly, to a certain anything we had heard.This Brown extent, this is the case, although we Cubist decidedly lines up with the think that we can claim that we have best,andallthoseinterestedin done our share to impress upon users moving -coilresults should make an of mains the desirability for observing early opportunity of hearing one in certain precautions. action. But this Ferranti Safety Box is going to make things somewhat easier. Lewcos Loading Coil It is made of steel and is fireproof, and The " M.W." standard loading coil, is provided with a three -core flexible which has figured in so many well- cable, one arm of which is for earthing known receivers during the past year purposes and should normallybe or so, has no doubt become a familiar connected to the earthing pin of the objecttomost" M.W."readers. power plug in order to comply with The Lewcos versionofthiscoil, regulations. therefore, will probably cause con- If there is no power plug available siderable surprise. this lead needs no connection. Although it follows the electrical The object of the Safety Box is, of specification of the standard model, course, completely to enclose an H.T. itsphysical dimensions are totally unit, but the novel feature is that a differentIn fact,itvery closely double -pole switch and fuse are pro- resembles an ordinary Lewcos plug- vided and arranged so that on the lid in coil, except that instead of having being lifted all the apparatus inside is the usual plug-in socket it is mounted disconnected from the mains. The Lewcos loading coil. directly on a flat base suitable for Messrs. Ferranti have also produced instead of the usual straightforward baseboard mounting. rivedesignsofsatisfactory supply cabinet or baffie, it has fixed to it a Three of the terminals are disposed large metal " flare " mounted in a around the periphery of the coil, the, handsome cabinet.Setting the dia- (Continued on page 220.) phragm back behind this structure seems to have the effect of brightening the response. There is another novel feature in this Cubist, and thatisthat the moving coil is of octagonal or eight - sided shape, instead of being round, and the eight magnet bars are bent round and lined up closely in the same form, providing a very strong field. The assembly and the finish of all the parts concerned are up to the highest of the Brown standard.The handsome mahogany case is a first- class piece of work. The impressions that we received whilst the instrument was undergoing itstest were distinctly -favourable. Front viewof the Brown " Cubist " The Ferranti safety box Keyed up to criticise everything that loud speaker. 188 February, 1929

MODERN WIRELESS

MR. WEDGWOOD D ID NOT MAKE K NIVES

tstFORKS!

T.C.C. Electrolytic Condense?. Capaci y 2,000 mfds. Ina case JOSIAH WEDGWOOD was aspecialist. He devoted his 5 inches high.Price 15!-. whole life to one thing- the making of pottery.Again and again he failed, but, undaunted, he p rsev..red until ult mite y his pottery became the fashion of the period and is still to -day in great demand. Like the Burslem potter,we are special sts.For nearly a qusrter of a century we have made nothing but condensers. And because we have never deviate.' from our task -never expended our energy in the making of other components-t e name T.C.C. on a condenser is accepted throughout the world as the undisputed hall -mark of accuracy an I dependability.For this reason the A miralty, the G.P.O., and the Cable Companies of the World consistently use T.C.C. Condensers. For this same reason, too, it will pay you to use T.C.C. Condensers in your next Set. FOR OVER 22 YEARS WE T.C.C. Flat Type Mica Con - dens r. Capacities from 001 m fd., 1/10 to .01 mfd., 3/6. HAVE MADE THIS COUPON NOTHING BUT BRINGS FREE

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M7067 189 MODERN WIRELESS February, 1929 in the shape of young Bill, who piped out that it was a sound notion and that he would help me. This made me thoughtful. Bill likes to help me clear out drawers and cupboards ;in fact, he frequently proposes some such

IJ operation. He is like the jackal ;for when the tiger has finished, the jackal finds plenty of bits and pieces.On the day after I tidy my desk Bill's pockets bulge with chunks of brass, small coils of wire, screws, etc.And then his ma blames me ! AccouniNGto mycalendar_ me that I must clear out my wireless presented by the grocerat den.It runs : Demon Drink Christmas as a delicatere- Make ready thy house against the However, on this occasion I felt the minder that his bacon is not so tough coming of the Dark Angel.Lo, he need of support, be it ever so self - as the Co-op's-we are now entering stealeth upon thee with a wallop in both interested, and I took Bill over un- upon the month of February.This mitts !Bo, you are sure for it.-(Fra month is devoted to tossing pancakes, Pongelico). filling dykes and generally preparing I tell you that this Ethelred the for the Ides of March. Unready business was fairly preying About this calendar ! Its main on my mind.Only the week before, feature is a coloured picture-a sailor Chiggles, the stockbroker at No. 17 with a plum -coloured face, sky-blue our road, had died, two ' days after trousers and a green parrot enters the renewing his dog -licence.His widow garden gate of a cottage covered with saidthat Edwardalways lacked green roses. The cottage chimney foresight. emits smoke of crimson lake. I had no wish for my executors to go fooling about with my layouts, " Drat It ! " short-circuitingbatteries,buckling - The lads who travel to town with me At the door stands a nut -brown up condensers, and what not, and so daily. maid. She is buxom. She has weak I suggested at breakfast on January eyes,too, because although sheis 17th that I had better clear up the conditionally,withtherankof looking away from the sun, which is wireless room, a gesture which brought sergeant-maj or. either setting or rising in the north- my better three-quarters'batteries This move so rattled -the enemy judging by the weather -cock thing on of sarcasm into action on the instant. that she promptly told Bill to look at the church in the distance-she is " Shall you-do you think ? " she hiS hands. I'm sure they've not been forced to shade them with her hand. cooed. washed to -day, leave the table and Underneath the picture is the legend, Now how's that for rotten grammar, don't wipe the dirt off on the towel. " Jack's Return, printed in Germany, I ask you ? Bill had to execute that evolution un- with the compliments of A. J. Bulk - " Iremember,"shecontinued, supported and " at the double." horn, Grocer." " that you were supposed to have Well, they say that strange news is tidied the place up four years ago, like a prairie fire.It spreads and then before grandma came to stay.And some. When I reached the platform for months afterwards everybody in on the following morning a faint cheer, the house was being accused of steal- redolent of irony, greeted my ears. ing wire and things." This emanated from Glapp and Co., the lads who travel to town with me The Perfect Pickle daily.I suppose that there had been A flagrant exaggeration. As a some intensive Communication work matter of fact, young Bill-that's my amongst the wives.Anyhow, Glapp son-did sneak a pet bit of rubber - and Co. were very witty ; Glapp offer- covered ;and the maid had the long - ing to lend me a baize apron and a Young Bill piped out that it was a sound handled screwdriver to open a tin of notion and that he would help me. feather broom, and old Pa Tippins sardines with. promising to give me a free boost in It is a " tear off " calendar, and each " I should let sleeping dogs lie, if I the miserable rag he edits.Colby's day's sheet beers a beautiful text, were you," added my wife. theory was that I had joined the sacred or profane. To -day's is : That made me feelvery bitter, Salvation Army, while Dingham, a No good ever came of saying " Drat because I was always being told that low brute who has no interests be- it."-(Mrs. Aphra Twobley). the room was in " a perfect pickle." yond bowls and Halma, asserted his Last Sunday's was : And then when a man suggested belief that all I was going to do was to I do not subscrthe to the doctrine of But there, they are all alike ! As search for a lost ha'penny. ruining the vessel for lack of a guinea's - Tennyson sings, " Women and wal- Driven to bay, I ticked them off-I worth of bituminous caulking material, nuts and little green peases, arelike to wish you could have heard my shafts demmit.-(Lord Drage of Chesterfield). like as a row of Dutch cheeses." ofsatire-and ended by invit'ng Now, then !It was the text for At this stage of the campaign I Glapp to assist me.He accepted. January 16th which finally convinced received an unexpected reinforcement Papa Tippins wantedtosend a 190 February, 1929 MODERN WIRELESS

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191 MODERN WIRELESS February, 1929

reporter, but I shut him up by asking when you crammed Ethel's oldbicycle healthy -looking lot but not my idea him why he had the gall to read a into the dustbin." of Art.That remindi me-did you

paper before the local literary society, We took off _our coats and looked hear " entitled " The Demon Drink," and around, young Bill's eyes bright with " So I said to Jinkins,Of course, accept the ads. of four wine and spirit the fever of the hunt. if you insist on that clause I'll do my merchants. " First of, all we'll de -wire every- best to persuade the Board, but I'm thing and make a wire dump. Then afraid they'll buck at sixty per cent. Crump Crumples Bill can sort the wire into kinds and However '-mm-mm--" Mention of the demon " drink " lengths."In fifteen minutes it was That - lastspeech represents me reminds me of poor old Crump. Now, done and Bill began to sort the heap, guarding the position till I heard my Crump decided to have a thorough whilst Glapp and I undertook, next'wife's footfalls receding. clearance of his wireless den. On the tocollectloosebitsof brass -and great night he ascended to the sacred ebonite, terminals, small tools and so room and by dint of herculean labour forth.Presently Glapp said, " Was- got all his gear shifted from one sido of sis ?Something come adrift ? " He the room to the other.Then he was shaking a one -stage " note mag." thought he deserved a drink. Which (or L.F. amplifier) and the sound done, he said to himself, " All thisindicated that a large heavy object clutter had better be carefully shifted was loose inside. We opened the case. to the other side of the room and " So that's where the key of the sorted out."So he did it and had a garage was," I exclaimed, in amaze- drink to keep himself going: ment." And I nearly sacked Barton, After that he thought he ought to too, for lying." move -to the other side of the room Bill turned greenish. The poor chap had been winding sticky all the stuff that was any good, leaving insulating tape round himself. the rubbish where it was.So he Ma's Vase " Oh," I said, " do you know how Well, next we started in to re -wire moved the whole lot over, including the sets.Whether Bill had snipped a No. 6 Meccano set of his son's, and the key managed to get inside and parts of the mangle and of his wife's screw itself down ? " bits off the wires or what he had done sewing machine, which somehow or " Yes,dad,"exclaimedyoung I cannot imagine, but I do know that other had got there.This labour Washington." Y -you see, - me and allthe lengths seemed eitherin- obviously called for a little refresh- Fatty Bowyer were playing hidingadequate or redundant.We pawed ment. things, and I hid that there and then around the floor and got as black as we broke Ma's blue vase and hopped sweeps.Glapp upset a box of two it, and when I came home I forgot all million terminals, which spread them- about the key and-" selves in an even layer, and I had the " Wassis ? "saidGlapp, with misfortune to knock over Bill's white middeninterestinhisvoice. mice, -two of which dived into an open I turned.." Tha-that's only an old tin of soldering flux. bottle," I replied. Presently Glapp, who was deter- He inverted it." Nothing in it," minedly trying to make six inches of he said, pensively." Wassitdoing " flex " stretch a foot, remarked that behind_ this,seven-valver, Jones ? " his limbs felt sluggish. Just then my wife popped her head in the room. - Glapp, with a ready wit, Touch of Trench Fever 'exclaimed. "Shall I get you some " It's a touch of trench fever, I Glapp and I entered upon our labours. more varnish, old man ?I see you've believe," he added. In a few minutes run out."And that deep womanhe said that he was afraid he had ' After sluicing down the inner man, answered forme," Don't bother, creeping paralysis and that the skin Crump manfully tackled the job. Mr. Glapp !It's gone up-since the of his legs felt tight. " All this junk must be sorted out," war, and is very weak as well ! " " Great heavens ! " he muttered. he said.So he carried over to the What did she mean ? " It's magnetic.I'm being sorter oppositesideallhe wanted.- He Presently we had separated all the pulled. Lemme get a light." wanted it all, apparently. sets from their accessories, and the My wireless garret boasts but an By' this time the fourth bottle was accessories from the dust, fag -ends anaemic oil -lamp, sowestruck half empty, but he carried on tilland burnt matches.Bill had been matches and peered at his legs.The cock -crow. -Result --a hole in the very silent and hard-working, and the poor chap had been winding sticky lino and four empty bottles.Next room looked like a ruined rope -walk. insulating tape round himself from a evening he found everything wrong, Just then Glapp said : huge roll of the stuff which had been and on interrogating his wife, she said, " Hullo, Jones !Isthis a' Vie set aside by Bill and had finally got " Well, you always had that rubbish Parisienne ' ? " wedged between the table and the on that side of the room-so I've put " Yes, I believe it is," I retorted. wall.I cut him off from the main it there." " I must speak to the housemaid. spool and unravelled his cocoon, but Now behold Glapp,Bill and I Leaving her fashion books all over the the crease in his trousers will never be entering upon our labours. place.Bedtime, Bill."Bill went off, the same again.After that he retired " Mind you leave yourself a few with pockets bulging, and we sat and Maisie and the housemaid hacked bits to play with," called out ray wife down for a pipe and a rest. their way in and cleared up.After as we went upstairs." And don't " Yes," remarked Glapp, after a all, it's a woman's job, this clearing -up forget,how the dustman growled few minutes with his latest find,." very business 1 192 February, 1929 MODERN WIRELESS

M111111111 lllllllllll 1111 lllll

CHARTS Let THESE guide you to trua radio reproduction.They make set construction plain sailing to anyone who can drive a screw or drill a hole. Every home constructor who isac- quainted with the Ferranti reputation will be well satisfied with the Ferranti claims for these receivers.Superlatives will come later ;they will come from delighted constructors. Performance :the Two -valve receiver will give good reproduction from the local station and 5 X X, and the Three - valve receiver will bring in local, 5X X, and certain Continental stations.Other programmes may be received at various strengths, according to the position of the listener.Also, a chart of a screened - grid 3 of exceptional quality is available. Get your free, full-size instruction chart and enjoy an easy, happy evening at set building.Ask your dealer, or write to Ferranti direct. Remember :- NO COIL CHANGING NO SOLDERING RANTI FERRANTI LTD. HOLLIN WOOD LANCASHIRE

193 MODERN WIRELESS February, 1929

41CCO MILES WNW 14 AERIAL The Ducon was suc- cessfully used by Mr. F. Dearlove for communication radorbetween andLab- VALVE Pittsburg. set. Oiratria

hasgreaterpossibilities with LEWCOS Coils

`,..":0....iriv-, ,,,,..... 2003.).sibcoic-cin.:st;,,,,c:s..,,a.-0 , 1.t,v.t.ts ut.adaptor stclo.tt'.10c0.e. Ducot.1' ... . COSItesvols,e,of a.

nth OV to-ea.usdtc.til.tl. .e.sia.l. "Waettv-4tliteV1311./aCT plueavyligrus iu -- .W. totine asc.c1e 1918'01 a.p. isoca OpetatottoVIt-IV,. V5..tsactofDececubes,1,0,101.2,a0L, of Vgise\essGtenfell.uact.s SIX -PIN COILS. less Cbie4 by SUPER COIL. N&CiCiltlITCSSic.1.1i1Vtaco.outposts Pat. No. 285 723.) iDeaslove,by B.B.C. Coils 10;6 poiutedVabtadot Daventry Coils 12;6 ttytheayeNIfis.e1ess SbostIs THE LEWCOS STANDARD LOADING COIL can be purchased through all radio dealers.Suit- No Aerialtroubles are ever able for use in all circuits If unofain- in" ModernWireless," able encountered when usinga where standard loading your dealer, Ducon.Simply plugged into an coil is specified. write direct to us, men- electriclampholder and con - Price 716 Retail. tioning his BINOCULAR COILS. name and nectedtoaset,the Ducon address. replaces an aerial.It consumes no current and is perfectly safe. "TOREADOR Price 5/ - SCREEN -GRID REGD. FOUR " This set incorporates the latest RADIO PRODUCTS developments in Receiver design ILIER THE LONDON ELECTRIC WIRE -full construc- RADIO PRODUCTS tional de tails DUB COMPANY AND SMITHS, LIMITED, free on request CHURCH ROAD, LEYTON, LONDON, E.10. Mvt. of Dubilier Condenser Co.(1925)Ltd., Due -on Telephone : Telegrams s Walthamstow 2531. " Lewcos, Phone, London,' ©21.5 Works, Victoria Road, North Acton, London, W.3. LEWCOS RADIO PRODUCTS FOR Trade Counter and Cable Sales BETTER RECEPTION.7, PLAYHOUSE YARD, GOLDEN LANE, E.C.Y. 1111101111Ralisus 'WM 194 February, 1929 MODERN WIRELESS EEM'IM'EE.T.C_STIM'ETEEMEMEgETEEETEEEEK.'\EgEEMETEEEM'I'EcM'ESEEEI'M'EEEED1

H[r; Padi0 dndthe Gramophone U tea. In this section of MODERN WIRELESS each month will be discussed both technical and other data of interest to the set owner who is also interested in gramophones. Besides articles of a practical nature,abrief survey and critique of the latest gramophone records is included, making the section of vital interest to all music -lovers. Conducted By KEITH D. ROGERS CONTENT S Page Page .. 2 A Super -Amplifier.. 7 Some New Carriers.. Details of a demonstration radio -gram outfit Details of three new pick-upcarriersthat ^ have recently been placed on the market. capable of providing enormous amplification. A Simple Tone Control .. 8 IQ Balancing the Pick-up .. 3 How to remove the harshness so common in the [5,7 Does your pick-up wear the record badly ? If reproduction of many loud speakers. UJ it does because itis too heavy, the scheme discussed in this article will help you. Round the Turntable .. The question of tracking is discussed by a reader Ifs]nisi 4 of " M.W." Pick-up Points How to make sure that your choice and method This Month's Pick-up Programme 9 El ofusing anelectricalsound -boxisthe A representative collection of numbers espe- Ia " best." cially chosen for pick-up reproduction.

. . DI .. 6 Recent Record Releases.. 10 Using the Pentode The popularity of the Pentode valve as a gramo- Our regular review of some of the records pub- phone amplifier is rapidly increasing, and the lished during the month, written from the notes given here will be of value to many point of view of their suitability or otherwise readers. for electrical reproduction.

,C g. E EEEESE 5MT. 1"1' Mc.f Dr] That Tracking Trouble THE problemof correcting needle tracking degrees out of track over that which is caused by when pick-ups are being used is still vexing a needle that is perfectly aligned.As regards tonal a great many, both listeners and traders. quality, this does not seem to suffer even when the [c.)] U] Uff Many firms are beginning to realise the advantages tracking is badly out-though there are limits to U ofoffsetcarriers,whileothersaredesigning the error possible before roughness of reproduction " straighttracking "devices which allow the and increased wear are made noticeable. COI needle to run straight across the record, remaining tangential to the grooves over the whole of its A Valuable Article path. The ideal should always be our goal, but experi- DI In addition to descriptionsofnew pick-up carriers based on these two methods of obtaining ments have shown that there need be no heart - burning if the tracking of any particular pick-up tracking we publish an interesting letter from a Uisl radiogram enthusiast which expresses what must is not exact. be the thoughts of large numbers of listeners. Readers about to purchase pick-ups will find the Ecil article, " Pick-up Points," by E. H. Turle, M.I.E.E., No Noticeable Difference ofvalue, while operating notes on the pentode valve, and details of a super -amplifier for demon- Uisi Lc Is there any noticeable difference in the tone of the reproduction or in the life of a record when it stration purposes, are given in other pages. Uis used with a perfectly" tracked needle and when Finally,listeners'experiences with pick-ups

used with a needle that is approximately tracked ? of various types and with different methods of LeA There certainly does not seem to -be any visible carrierconstruction wouldbewelcomedand increase in wear when a pick-up rieedle is several would he of value to many readers

Ifs [.Q a'&5T-I'M 1' 'MEZE,%'&21',TIE EEEEEETEEM 1-7.%%' 5'..% ,C.1 .E ,CaT. -ST 1 =3 EZEM 195 MODERN WIRELESS Radio -Gram Supplement (page 2) February, 1929

pillar and an adjustable swivel and a

long, straight arm so constructed that

a little carrier having two wheels on

. it rims along a single rail, which is of if SOMENEW CARRIERS .. aluminium rod, and on this carrier is

.. .. placed the pick-up holder.

Detailsof three new pick-up carriers thathaverecentlybeen

The pick-up, therefore, is enabled placed on the market.

. to run straight across the record and

.. can be so arranged that it runs dead in line all the way across.The construction of the carrier is such that the WE have just had an opportunity the whole of the track of the needle. pick-up may be swung clear of the of testing the new Geco- The movement is easy, and the radius record at any time, -and though there phone pick-up and the pick- of swing is extremely large. is no weight adjustment or counter- up carrier (illustrated elsewhere). The Theonlydrawbackthat can balance on the present model to take former is an improved model of thereasonably be taken to be a draw- up the weight of the pick-up should an old Gecophone pick-up which was back, in the case of this arm, is that on exceptionally heavy one be used, we placed ,on the market some time ago; completing the record no provision is understand thisis to be fitted in and it can be obtained in severalmade for the pick-up to be swung future. types to fit various tone -arms and in back, as is the case with many pick-up In action the carrier is quite satis- a special type to fit the Gecophone carriers and with tone -arms. factory as regards the tracking.It pick-up carrier. Good Value runs freely and enables the .pick-up This latter has a slotted holder so to go straight across the record, but it that the pick-up itself fits on to the The pick-up and carrier arm have to be lifted, swung clear of the record, is apt to he noisy in operation itself, carrier in much the same way as it while the question of the disposition does on to a gramophone tone -arm, and then either rested on the side of the gramophone or on some suitable of the pick-up leads in a satisfactory the adaptor ofthe pick-up being manner is a tricky one.The carrier providedwithalittlepin which support, or else held in the hand while the new needle is placed in, and a running along the single rail is not slides up the slot on the arm.This too well designed, the wheels and the automatically gives you some idea of fresh record placed on the turntable. If the makers could have seen their general movement being rather loose, the correct angle at which the pick-up and so upon heavy organ passages or should be used, and provides a locking way to provide a little swivel joint at the end whereby the pick-up itself particularly loud notes the whole in- device which makes the pick-up quite strument is inclined to rattle. secure. could be lifted and swung back, with A very commendable feature of the Vibration and Chatter pick-up is the provision of leads of The extent of the chatter can be amplelengthforusewithany well judged from the fact that it is reasonable apparatus.In fact, we extremely violent on some passages, do not know of any pick-up with and in intensity quite twice as loud which such long leads are provided. as the ordinary chatter produced by the average pick-up, which, as readers Ingenious Component will know, is by no means negligible. In operation the pick-up acts quite The pick-up carrier is made by the well, being extremely brilliant on the Robinson & Hands Electric Co., Ltd., high notes, though not lacking in, the of Birmingham, and is being placed bass.It is,however, rather heavy on the market for 35s., rather a large and really requires to he used with an sum when one considers that only if adjustable carrier such as the one correct off -setting in an arm is ob- provided by the makers themselves, tained one would seem to be able to or one of similar type.It is quite get perfect tracking without the need sensitiveandrequiresavolume The cheapest model " Beamu " drive and for elaborate design. control in order that the best shall be offset carrier is covered with " Rexine ' And reverting to swivelling arm got out of it. cloth. carriers,itisinterestingtonote In regard to the pick-up carrier, the needle faced upwards, it wouldthatMessrs.Beagley and Musto, thisis a very ingenious little con- have greatly increased the facility of whose" Beaniu "carrierwasre- trivance, and is extremely well made. needlechanging and provided an viewed in a recent issue of " M. W.," Constructed of aluminium it is well automatic rest for the pick-up. are now altering, the design to give over eight inches in length, and is But one cannot expect every refine- correct tracking all the way across by provided with a spring adjustment at ment in a carrier which is placed on means ofoffsetting.This,inad- the pillar end, while the long arm is the market at thesmall sum of dition to the weight adjustment, small slotted to take the wires from the 12s. 6d., and at this price the Geco- size,swivelledend -piece,and in- pick-up, and at the pick-up end thephone pick-up is certainly very good visible leads will make the " Beamu " holder is off -set at an angle which can value for money. carrier one of the most popular on the be varied to suit the particular pick-up market.The old price of 10s. 6d. is in use. Straight Tracking being retained, and the -firm is re- It is extremely easy to centre a Another carrier which has come to placing all the old models free with pick-up with this arm, and with a our noticerecentlyisthe" Ray-.new offset models free of charge-a little care itis possible to get the trak "carrier based on the mono- trulycommendableandgenerous alignmentpracticallycorrectover rail principle.It consists of a stout action.

196 February, 1929 MODERN WIRELESS

FOR EVERY GOOD CIRCUIT YOU NEED AO,- tot% set .16 6,Ai .61Q1, 21/ Wave . . . . t%Coll, 9; .45; 4ttls kep,iter:- to Priria61e .t/ 9; Vol% fiikir 4% mous SolgteP1118,9 aiteks; COMPONENTS .1?eli?oteCoil'Coi/SepiteheSI c.? tO Cot?tp0/ iri eoery If you are building the Mullard "Master any /or4% Three Star," Cossor "Melody Maker," or typeroot)? any other popular set, ask your dealer for all tryset./par)? Lotus Components. Paclio efectlers.

Garnett,Whiteley & Co.,Ltd.,BroadgreenRoad,Liverpool .iimmiammainimmimimmansu

197 MODERN WIRELESS Radio -Gram Supplement (page 3) February, 1929

Eff0E7)00EPP300,g,E?)&32%63)050E3R@@e9)E3,@E3)E3,@0E5EP,W340 point C is in motion in the arc of a circle, with X as centre, itis impossible for A, X, and C to remain Balancing the Pick -Up exactly in a straight line. &5§, g) Dort your pick-up come under the " heavy " class, weighing more than For this reason a slight allowance 5 ozs. ?If so, try the simple scheme outlined below. must be made for a variation in tension.In other words, the adjust- By a Correspondent. .q,g3 0. ment ofthecrocodilecliptoa ec,SW3C9G'30c93cf3q3f300000:f3 00(e30f3fADQT9f3f900f3 position beyond which any further increase in tension causes a falling off IN view of the widespread popu- coveredvariety, in.inwidth, in the tonal quality should be carried larity of the electrical pick-up, perfectly satisfactory for any sound - out with the tone -arm in that position the method detailed below ofbox or pick-up, even the heaviest whichcausesthetensioninthe balancing the tone -arm should prove available. elastic to be a maximum. of interest to many. Should any pick-up come to hand At all other positions the pressure This arrangement has been found so light that it is found that theexerted by the needle on the record by the writer to minimise greatly 1 -in.elastic is too wide to give the will, of course, be just a very little wear of records due to the weight of required degree of elasticity, it would more than it would be required to the pick-up or sound -box. Wear indicate simply that this pick-up does exert ifit were possiblefor A to dueisdamping,etc.,isnot,of not need to be balanced. move in an arc about the same centre course, considered here. The tension of the elastic should be as C. adjusted by altering the position of the crocodile clip until the pick-up Slight Pressure Variation bears on the record with a weight However, the writer has found that ofabout three ounces orso. If this small variation in pressureis thepick-upispermitted tobear insufficienttowarrant theslight on the record with less weight than extra trouble of attaching the end this the tone will become distinctly of the elastic to the top of a column "fuzzy."Thus the procedure to be mountedonthetone -arm(thus followed in adjusting the clip becomes allowing A to move, and thereby obvious. remain in exact alignment with X One morepointofgreatim- and C), instead of to a drawing -pin portance : When fixing the drawing - on the inside of the lid, as shown. pin at A, care should be. exercised In the case of the gramophone to see that the latter, the pivot (X) used by the writer, the needle -point of the tone -arm and the point C N travels in an arc of 9 in. radius. remain in approximately a straight Using the Fin. elastic,it has been line (when looked at in plan) through- found inadvisabletoincreasethe out the travel of the pick-up, in order distance A X (again when looked at that the tension in the elastic may in plan) beyond about 2 in.;1 in. remain practically constant. gives every satisfaction and a large Isay " practically " because as margin of safety. Y800 the point A is not at the pivot In conclusion, the total cost of the How the counter -balancing scheme (nor does it coincide with X when materials required is about twopence- operates. looked at in plan), and since the halfpenny. In the accompanying diagram -the device is shown in use on a portable gramophone ; however, modifications of the principle will, no doubt, occur to the reader to enable him to apply it to any particular type of machine. The pressure which is exerted on the record by the needle is reduced by means of a narrow piece of elastic, one end of which is fixed to the lid of the gramophone case at A, the other end, after passing round the tone -arm immediatelybehindthe pick-up, being clamped at some point, B, of the elastic by means of a small " crocodile " clip, as shown. An Important Point It is important that the supporting system should possess just the right degree of elasticity.After trialof several different kinds of elastic, the The new Igranic-Pacent pick-up and arm. The fibre needle model of the Phonovox was writer has found the ordinary cotton - reviewed last month. 198 February, 1929 Radio -Gram Supplement (page 4) MODERN WIRELESS PICK-UP"POINTS

THEadvantages to be gained by MI1111111111111111111111111111111111111111111111111111111111111111111111111 it will jump the deeper passages, and, utilising an electrical pick-up, = How to make sure that your choice iftoo heavy, tone will deteriorate and method of using a pick-up wireless amplifier and cone E is the " best." What to look out and wear of records be excessive, loud speaker in place of the gramo- for, and what to avoid. while the needle may break through phone amplifier and horn are now so By E. H. TURLE, M.I.E.E., 174. the walls of the grooves on the record. great that to the owners of reasonably M.I.R.E., M.I.W.T. good wireless receivers this method QuestionofWeight ofreproductionfrom gramophone The weight of an efficient sound -box records is now the only one that can on a gramophone is usually of the satisfy them, and any appreciative To obtain these advantages to the order of 5f ozs., as in the case of and discriminating hearers. fullest practicable extent, however, the H.M.V. No. 4, but as a weight of The steadily growing demand for requires not only discrimination in four ounces is sufficient to maintain gramophoneelectricalpick-upsis the choiceof pick-up, but correct contact with the normal undulations being met by the considerable number application in using it, and as very on a record, and the resultant loss in of makes of differing design now avail- many people will be adopting the volume can be readily compensated able, and for the most part all capable above method once they have heard in the valve amplifier, the pick-up of good, or at least very fair, results, for themselves the vastly improved should weigh, say, 41 ounces, thus so that a wise choice between them reproduction obtahed, the following markedly reducing wear of the records, is not a simple matter to the inex-important pointsofnote may be while at the same time needle -scratch perienced. opportune. noise is reduced in volume, and this Many Advantages / As compared with a mechanical 02 gramophone, and providing that it is 3 used under suitable conditions, an #11.77 efficient pick-up can effect the following advantages: (1) Needle scratch noise so much reduced as to be unnoticed and barely audible. (2) Volume under smooth control from a whisper to the fullest loud -speaker strength. (3) Reproduction clearer,particularly in lighter passages, while the loudest remain rich and full, that is to say, undamped. (4) Record wear reduced very con- GRID Bias siderably. (5) The broadcast voicecan be The first consideration should be is rather more than are the impulses given a pleasing background of given to the weight of the electrical from the sound waves recorded on soft music. pick-up, because if this is too light the wax. 199 MODERN WIRELESS Radio -Gram Supplement (page 5) February, 1929

Needle -scratchnoiseislargely transformer -coupled, then those trans, To meet the case of records that caused and is accentuated by un- formers can be satisfactorily utilised, give rise to an unusually high ratio necessary play of the needle, and it is and this need involvelittleor no of needle scratch noise, such as the therefore important to choose a pick- alteration to the setif the pick-up older records (acoustically recorded), up in which the needle is properly be of the .high -resistance type, which the ratio can be usefully reduced by mounted. is preferable.The diagram, Fig.1, The _electricalpick-upiseither shows the detector and two low -fre- exchanged for the mechanical sound- quency transformer -coupled stages of box on the tone -arm of a gramophone, awirelessreceiver,where sockets either already are, or can be, provided at " A " and " B " for the ready connection of headphones for tuning purposes.

Plug-in Connections The sockets serve admirably for the ready connectionofthepick-up. " A " being used where the record employed for reproduction is moder- A light and efficient instrument-the ately loud and the room is not large, R.I.-Varley pick-up is well -designed. where it must be a really good tightfor in these circumstances one valve will usually suffice.When greater fit,oritcan with advantage be connecting a condenser of the order fitted on an entirely separate arm volume isrequired the pick-upis of .5 to 1 mfd. across the terminals free to give the same range of travel, connected to sockets " B " ; and in of the pick-up and, if necessary, in- but in either case the needle must be exceptional cases, and for still greater creasing the volume by the control at an angle of 65 degrees with the volume,connectioncan be made provided for this purpose. between the grid of the detector valve recordforthemostsatisfactory Electrical reproduction from gramo- and a negative terminal of a grid - phonerecordscanprovidemost results, while the flexible connections bias battery. must be so supported as not to impede excellentmusicaleffectsforlocal the pick-up in its travel across the The positive terminal ofthisis dances, socials, whist drives and din- record or to give increased weight connected to the negative end of the ner or card parties, where someone to it detector -valvefilament,whenthe can be deputed to put on the records volume is still further increased by in a predeterminedorder from a Attaching the Amplifier raising the value of the positive H.T. position unseen and even remote from to the anode of this valve by 40-60 the places occupied by the audience. The pick-up mw't be connected to volts and adjusting the value of the the valve receive] in such a manner that the tiny electrical impulses setgrid bias to avoid distortion, thus Increasing the Effect up by the armature (to which the utilising the amplification properties The effect can be heightened by of the detector valve also. oral announcementsoftheitems, needleisattaelied) vibrating in a In either of the above cases the magnetic fieldare impressed upon also through the loud speaker; by the grid of .she detector or a low - volumeiscontrolled by a poten- utilising an ordinary domestic tele- tiometer of about 30,000 ohms of the phone type of hand combination trans- frequency valve. graphite track type, which it is im- This is best done through a step-up mitter mouthpiece connected with a portant should be connected exactly R.e46 transformer, the ratio of which can To as shown in Fig. 2, and which gives MN/MUM/PA no such complete control that with the pick-up connected to sockets " A " (Fig. 1) while.the set is reproducing wireless transmission at comfortable loud -speaker strength (the somewhat dull news bulletin, for example) can be brightened by super -imposing music as a subdued background by the aid I--1 Sommer 72. of a suitable record such as a violin 9.v. RHODE or 'cello solo, or perhaps the more 7:* TeRiesmarA-ROPA'.cwo comalitgrion WITHl/St091.SNITCH IN /4/ANEKEDEPRESSED dreamy Hawaiian music may be WHILESPERKIMS. considered a match. 9 -volt grid battery through a 3i to The Needle Problem 1 ratio low -frequency transformer to The choice of needle has consider- sockets " B " as Fig. 3. able bearing upon the results.The The adoption of the above proce- best practice is therefore to use adure adds so large a measure to the The Burndept " Electrical Soundbox." "half -tone" (moderatelystout) enjoyment of gramophone music that needleforallstring instrumental it has only to be put into effect to be be as high as 70-1 if a low -resistance music and the like, and " tungstyle " so much appreciated by its hearers pick-up and separate transformer be (ordinary loud)needle for singing, that they will never willingly go back usedbut where the low -frequency brass bands, organ and similar loud to the mechanicalsound -boxand valves of the wireless receiver are music having heavy crescendos. gramophone amplifying horn, 200 February, 1929 MODERN WIRELESS

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201 MODERN WIRELESS Radio -Gram Supplement (page 6) February, 1929

ic7.7:nnr, v.riArr,= USING THE PENTODE The popularity of the Pentode valve as a gramophone amplifier israpidly increasing, and the following notes will be found useful to many constructors. By G. W. EVANS

1r4:3101e&:7XE

FOR those who want a neat little valve set and do not want togotothetrouble of building a big set, but who yet can supply an adequate amount of H.T. current, and want gramophone reproduction as well as broadcasting, the ordinary two -valve wave -change set, cally impossible to obtain with the The circuit shown on this page using a detector and a pentode valve, ordinary super -power output valve. gives some idea of an average pentode forms perhaps an ideal combination. After all, the high-tension current receiver which can be used with great requiredisnot greater than thatsuccess, and which incorporates a The H.T. Supply needed by an ordinary det.-2 L.F. wave -change switch if it is wished to From 'the point of view of repro- set with a super -power in thelast use the set for the long and short duction, using the average cone loud stage, whereas the space occupied by waves without the trouble of chang- speaker, it can be strongly recom-the set itself is less than that in the ing coils. mended, but itis essential that it case of the three-valver. On the other hand, if ordinary plug- be designed properly, and that suffi- For the man who wants to build in coils are used and care is taken in cient H.T. voltage as well as H.T. his set in a compact cabinet, perhaps the construction of the set, then it current should be available to operate together with the gramophone,a would be quite suitableforshort- the pentode in an efficient manner. detector-L.F. pentode combination is wavereception down amongthe Unfortunately, together with the very suitable, if he is within reason- twenty- and thirty -metre bands, as advantages of increased magnifica- able range of any local station. well as for the ordinary and long - tion-for the pentode takes the place It is essential in such a receiver to wave programmes forming an ideal of two ordinary low -frequency stages employ a volunie control for pick- receiver. -we have the disadvantage that itup work, as overloading of the first requires a heavy plate current and stage would cause horrible distortion Volume Control also a special output transformer if by the time the pentode has ampli- With the usual types of pick-up best results are to be obtained. fied it, and, of course, one has to be a detector and pentode is quite suffi- The platecurrentoftheusual careful not to overload the pentode cient for all household work on the two -volt pentode varies between 12valve, which israthercriticalas averageloudspeaker,whilethe and16milliamps, and thefour- regards the maximum grid swing it volume control allows one to have volter requires somewhat more, so will carry. complete control over the strength that it is obvious that one requires Unfortunately thisgrid swing isobtained from the gramophone, so the largest size of dry batteries, ornot very great, but the valve makes that it can be brought up from a else one must use an accumulator or up for that by amplifying everything whisper to full strength in a perfectly H.T. mains unit for high-tension, if to a tremendous extent. smooth and regular manner. successful operation is to be obtained WrODE OLITPUT-y. Improved Refroduction 7A9/15PORMER Offsetting these disadvantages, the PFC. Anrimoso man who can supply the high-tension CteokE without any trouble has an added ONO ) advantage that often better reproduction can be obtained from a detector and pentode than from the popular detector and two L.F. stages. Especially is this the case with loud speakers which tend to emphasise the bass rather too freely at the expense of the higher notes. With such speakers as the average cones, which are usually rather on the deep side in tone, the use of a pentode will rectify this fault and give a wonderfully clear and straight- line reproduction, which it is practi- A Useful two-valver capable of being used for broadcasting or for gramophone work. 202 February, 1929 MODERN WIRELESS

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marvellous performance onthelower tones L.V. Trans- Cossor the new theroll of With theyoull hear bass -the Made and guaranteed by former thedouble violins the makers of the famous drums - piccolos instrument of theeveryinstrumentFit this COSSOR VALVES Pi bear rns- -you'll reproduced.Cossor faithfully new and geta new wonderfulto yourset Thesuperb formerof realism.thefamous standard Makerof islargely reproduction Pt CossorMelodyrTransformer.give -your due totransformer willit hasever Cossor tonethanone atyour set abetter See ossor before. bad Dealer's. Advt. A. C. Como?Ltd.. tiothbury C,ove. London. N.5 ILIF.Transformg

203 MODERN WIRELESS Radio -Grain Supplement (page 7) February, 1929

" straight curve " characteristics had to be employed.For this purpose 480 volts had to be used. A SUPER -AMPLIFIER The voltage (from the mains) is cut down to about 410-420 volts, and it will be seen from the photographs that special Mullard valves of the D.F.A.8, D.F.A.6 and D.F.A.7 types were chosen so as to stand up -to the high plate potential supply.Current is drawn through four L.F. chokes, two on a separate D.C. unit and two on theamplifier,while condenser by-passestotal about 30 mfd., 16 mfd. of which is also included on the amplifier. Smooth H.T. Supply In consequence of the large smooth- ing system the output is remarkably ademonstrationradio -gramoutfit free from hum, although it must be of providing enormous amplification. admitted the D.C. mains are in the first place very silent-a tribute to By G. V. COLLE. the efficiency of the electricity service. Since the 480 -volt supply is on a IvHEN one speaks of a public large hall from a gramophone pick-up, three -wire system, it will be appre- radio demonstration therewas commenced. ciated that even with a choke filter immediatelyleapsto the Special amplifiers requirespecial output, which the amplifier includes, listener's mind a picture of bellowingattention, and in this respect itis the earth is 240 volts below earth loudspeakers,givingforthlarge very interesting to see what has been potential, so that a 4-mfd. 1,000 -volt volumes of sound without a semblance done in the one under discussion.In condenser is place each side of the of quality, or memories of the raucous the firstplace,ithas to give an loud speaker, toisolateit and to tones of a speaker whose voice hasoutput suitable for operating. three or prevent shocks. been amplified out of all recognition. four moving -coil loud speakers at a Even so, the writer must record This, therefore, represents a fairvolume equivalent to the original that during adjustments at one of the view of how most people regard a transmission. meetings he nearly had the misfortune demonstration of this sort, and in to electrocute himself in front of the many cases adverse criticisms are not Tremendous Volume audience through coming into acci- wholly unjustified. Thusif,say,thePhiladelphia dental contact with the anode of one Like in every new science, how-Symphony Orchestra record of the of the power valves.One cannot be ever, rapid strides have been made inHungarian Rhapsody No. 2 is played, too careful with high voltages. perfecting the radio amplifier, while equal attention has been given to the Z8,4 28//4/1 tHr loud speaker.In addition, with the POWER 0.4CA 450 reurs introduction of the gramophone pick- .L CONOEN.FEA AAR.OX up we now possessameansof TAT/ amplifying " canned " music without /50 000 the attendant ' disadvantage of what 0005 OEMs are usually termed ".gramophone " 2011 H.C. 5:° 'SigscF; noises. 0003 4 60X IVA? Perfect Reproduction 2 1.$ Naturallyenough,thecostof making an amplifier and maintaining PICA'OP it so as to give the desired results is an expensive business, but it is gratify- I-0.137;1'SOY. ing to balance against this the fact 2coma that it takes a person with a keen G.B. a - TO CARRY, ""-3v -3-41vT4,g aym, musical ear to differentiate between WOE the output from a good gramophone The theoretical circuit of the super -amplifier in its final form. amplifier and a good radio set. A number of experiments have beenthe output from the bank of loud An interesting part of this amplifier conducted on the writer's large six - speakersshouldapproximatein isthe involved system of scratch valve set, as described in a past issue volume somewhat to that when the filters and frequency corrector incor- of " M.W.," and it was in consequence discwasrecorded-notaneasy porated.After much experiment the of the results obtained with some of job. writer would add a few words on his thelatest types of pick-ups that Secondly, to enable the last power results-on the whole they are not the construction of a super -amplifier, valves to handle the grid swing given worth it.The filters always appear suitable for giving an output for athem,valveshavingverylong to do their work too effectively and 204 February, 1929 MODERN WIRELESS 14©,, Leadership ellIAVOX The Originators of the Moving Coil Speaker Andnowread what otherssay : The " Wireless Constructor." The Magnavox Speaker gave arenderingof programmes which was a sheerdelighttothe discriminating ear. The " Broadcaster." Our tests convinced us that the Magnavox is the best moving -coil speaker sold. The reproduction was as realistic as could be. Mr. IV. James in the " Morning Post." Regardless of price the very best I have ever heard: Radio Editor of a well-known Northern Newspaper. D.80. No other speakers compare in the slightest degree with the Magnavox. To endeavour to publish allthe testimonials which we have received from the leading Radio Engineers and amateurs in the country would mean our booking all the advertising space in this journal. REALISM- You can hear the bowing of the strings of the double bass and the beats of the drums in their true tone colour.There are no jarring sounds and the harp does not sound like a flute with Magnavox Speaker Units.There are models for A.C. or D.C. TYPE R.4 £8 00 5 0

D.80/1 £1100 D.80/2 00 26 Belvedere Fire Screen Baffle for all Lyric. Magnavox Units.... £400 The Lyric, with M.7.K unit .. £4 26 Lyric Baffle only.. £1 00 REMEMBER THAT ALL MAGNAVOX SPEAKER UNITS ARE EQUIPPED WITH Belvedere. INPUT TRANSFORMERS,10 -FT. INPUT AND FIELD CORDS AND FIELD SWITCH THE GREAT VOICE The Second Edition of the Great Voice Booklet is now ready.This booklet tells you all about Moving -Coil Speakers, Pick-ups, Volume Controls and Amplifiers for A.C. and D.C.There are 36 pages full of illustrations and diagrams. Sen 1 for your copy of this new booklet to -day, price 3d., post free.

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205 MODERN WIRELESS Radio -Grain Supplement (pale 8) February, 1929 cut off the higher frequencies, a state construction of this amplifier unless ******************** which is to be expected if one under- ample H.T., from either A.C. or D.C. *A SIMPLE TONE stands over what band of frequencies mains, is forthcoming ;and the des- discs are recorded. cription and circuit are reproduced CONTROL Good records are recorded up to hereforthe benefitofthe more ******************** about 10,000 cycles, but owing to advanced radio -gram enthusiast.All AN importantfactorinthe the values are given in the diagram, tone quality of a gramophone RSA which shows thatthesetisnot outfitisthequestion of difficult to build, but requires a certain " tuning " the loud speaker by filter- / POTENT= amount of knowledge to operate and ing .the output from the set.In the maintain in its 'maximum efficiency. first place,itis taken for granted Referring to the theoretical circuit, that a power valve is being employed it will be seen that no provision has at this late stage, so as to have the been madeforanti -motor -boating necessary volume available for repro- L.T. devices, although it will be appreciated ducing a wide range of signals. GB- how four L.P. stages tend to oscillate The output from the power valve CAP7:ROUND'S METHOD OF under the best conditions: should be transferred to the loud FREQUENCY CORRECT/ON ONTNE AlACNET/C LEAKAGE AR/NC/RLE speaker by means of a suitable output Inter -Circuit Coupling filter, such as an output transformer channel wear and the wax affecting Actually,thereneverwasthe or a condenser -choke combination. the needle, the effective frequency is slightest sign of unwanted coupling The next stepistofilterout as about 6,000 cycles, while scratch can between the valves in the original much of the higher frequencies, in - he heard down to 5,000 cycles, using, amplifier,duenodoubttothe of course, a good pick-up.It will, efficiency of the H.T. supply, which therefore, be seen that a filter circuit appeared equivalentto a low - would cut off these frequencies and so resistance H.T. accumulator. Whether defeatourobject. However,for- the amplifier behaves normally on a tunately the problem is not an acute rectifiedA.C.supplyisa matter one, so the writer's advice to those for test ; but, in any case, the remedy interested is " leave well alone " where is obvious. filters are concerned. Operating an outfitofthisde- scription often brings to light things Scratch Filters of interest.For instance, the writer METHOD OF F/L7ER/NO NEEDLE SCRATCN 1164'/Che WAS TRIED Correction filters appear to offer well remembers installing the amplifier AND SUBSEQUENTLY ABANDONED. possibilities for experiment, the writer inbig demonstrationshowrooms having tried various types and values and,havingarrangedeverything, eluding scratch, as seems necessary on the magnetic leakage principle, astheoutfitoperatingasexpected, to obtain the necessary mellowness. advocated' byCapt.Round, with it was switched off for the night. It is a fact that in some instances various degrees of success. On switching on the following day, thecrisp,' sharp,penetrating tone Up to the present, however, no a violent howl was produced which resulting from the higher frequencies filterhas been tried that has notno amountofjugglingwiththe ismostdesirable.Thiscrispness reduced to some extent the brilliance controls stopped, until it was realised may not always berequired, and of the rendering, and this is a very that the gramophone had been moved may even be undesirable ;it depends important point when one is repro - someinchesnearertheamplifier, on the speaker used. Removing Shrillness There islittle we can do to add the higher frequencies to our gramophone reproduction, but most good L.F. amplifiers and most loud speakers have the necessary higher frequencies to begin with. The problem is therefore one of controlling those higher frequencies, and this can be accomplished through the use of by-pass condensers. A .01 mfd. mica condenser will take off the sharp edge or disagreeable shriek in any loud -speaker rendition whenshuntedacross the loudspeaker terminals. A good idea is to have a variable tone control. For the purpose,a combination of a .25 mfd. condenser The whole outfit is laid out on a large baseboard, much of the wiring being taken below and a volume controlisshunted the board.The scratch and frequency filters shown were afterwards omitted. acrosstheloud -speakerterminals. hieing orchestral and other string bringingthepick-upleadsnearer It now becomes possible to obtain instrument items. theloud -speaker output, and pro- any degree of mellowness in keeping The writer does not advise the ducing feedback effects. with the selection and the taste. 206 February, 1929 MODERN WIRELESS 171 I : [411 1 What a difference It's just as simple as switching on the light. Batteries are entirely dispensed with ;recharges and renewals become unnecessary. The only requirement is a lighting socket and the Marconiphone Power Unit. The result-a generous, smooth flowing stream of power that is readily controlled, always available, and meets every demand with minimum cost. All -Power Units for supplying H.T. and L.T. Model A.C.4, All -Power Unit for A.C. Mains.With power supply costs only 2d. per week.Model B.1153 for 100-125 volts, and 200-25o volts, 4o cycles and over.Price, including valve and royalty, L.4 15s. od. Model D.C.4, All -Power Unit for D.C. Mains.Entails little or no alteration to existing circuits. Model B.1154 for 200-250 volts, 5s. od. H.T. Supply Units. Model A.C:2 for A.C. Mains.Supplies H.T. to receivers of almost any type.Output 40 milliamperes at 120 volts.Two models available for 100-125 and 200-25o volts.Price, including U.5 valve, cos. od. Mode! D.C.2 for D.C. Mains.Output 5o milliamperes at 120 volts.Tap- pings at 42 and 84 volts. Suitable for use on 100-250 volt mains, Z4 25. 6d. For One- or Two -valve Receivers, Models A.C.3 and D.C.3.Model A.C.3 for A.C. Mains.For 100-125 or 200-250 volts.Complete with valve and royalty,70/-.Model D.C.3 for D.C. Mains.For 100-125 or 200-250 volts.Price 35/-. Model A.C.4. Write for Catalogue No. 453, mentioning MODERN WIRELESS.

THE MARCONIPHONE CO., LTD., Dept. P, 210-212, Tottenham Court Road, London,W.1. Showrooms .210-212, Tottenham Court Road, W.1., and Marconi House,Strand, W.C.2. 1111 ;11.171 1 .1k IN

The Heart of the Set Regular transmission of current, steady, smooth response to the extra demand, no " murmurs," these are the qualities which make these AERIAL TUNING batteries with the sturdy, extra -thick plates the Premier Batteries for wireless sets. Ask your dealer;or write for detailed UNIT and be sure list to of every wave -length Alterations do not affect the set which has a British General Tuning Unit, which covers Accumulator Co. (1921) Ltd. ALL Wave-lengths between 250-2000 metres. Northampton Plug-in coils are designedfora very small Estd. 1898 range and with the new B.B.C. and Foreign Z -TypeHigh - The Low - Tea wave -lengths you may find reception difficult. TensionPre- Premier. mier. Plates are 5o% Fit a British General Tuning Unit thicker . than In handsome average. teakcase, as This and make certain. Easy fixing, illustrated, rites longer life. simple tuning. Price1816 From all good dealers, or direct from BRITISHGENERAL' MANUFACTURING CO., LTD., LONDON: GLASGOW : BROOKLe.Y WO KS LONDON, S.E.4. 53, Victoria St.,S.W. 149. St Vincent St. MIIIIMENIMMEMEMilab..alliENEMEME 207 MODERN WIRELESS Radio -Gram Supplement (page 9) February, 1929 ROUN NTABLE

A page of odds and ends of interest and value to all radio or gramophone enthusiasts.

(1) The disadvantages are : Chatter, The Tracking Problem .. A Reader's Views :: THIS MONTH'S PICK-UP PROGRAMME. itt. thick needles essential, wear much

SIR,-I thinkrathertoo much ORCHESTRAL. greater, and blasting and resonance :: Ballet Egyptien -Luigini .. Col. 9566/7 :: stress has been made of late on the Orchestra Symphonique de Paris. in the record much more apparent. it: Overture-Light Cavalry-H.M.V. B2856 .. To my mind, the advantages of the subject of correct tracking of_ pick- .4, Suppe ups and carriers. New Light Symphony Orchestra. second method are many with practic- 11, Le Rouet d'Omphale- Parlo. E10789/90 .4.1 ally no disadvantages.

In the first place, it is rare to find Saint Suns arecord whichisperfectlyflat ; Opsra Comique Orchestra. It would be interesting to know

INSTRUMENTAL itisfar commoner to find them Nocturne in E Minor- .. H.M.V. DB1106 the method used by theB.B.C.,

:: Chopin though even this would not form a considerably warped, even when pur- Vladimir de Pachmann. chased new.In the second place, :: Organ Fantasie in G Minor-Bach Col. 9552 :: complete guide, owing to the fact :: Eduard CommetteonLyon'sCathedral :I; that they play mostly new and un- itisstill rarer to find a perfectly Organ.

true turntable. Both these factors LIGHT ORCHESTRAL. worn records. 1,1 Friend o' Mine-Sanderson H.M.V. B2857 :,1; will account for quite a large error De Groot andthePiccadillyOrchestra. in a correctly -tracked arm and pick- I': The Londonderry Air.... Ccl. 5158 :: Scratch Eliminators J. H. Squire Celeste Octet. up. r: Leslie Stuart Melodies .... Parlo. R241 :: Scratch eliminators have several Orchestra of the London Coliseum. The method I have myself adopted .. The Carmen Selection....Regal G1050 :: times been mentioned, but I have Classic Symphony Orchestra. is to use quite a heavy pick-up in sofarseen no details concerning VOCAL conjunction with a spring counter- :: Abide With Me-Liddle ..Bruns. 20073 :: these. I should imagine, from my *is Master Frederick Firth. balance, giving an effective weight :: Solveig's Song-Greig .... Col. 9577 :: own experiments, that the volume of only two ounces. Dora Labbette. iie would be reduced in proportion to the on the record :: Sea Shanties...... H.M.V. B2831 8 Thereedisheavilydampedto ::, John Goss and Cathedral Male Voice Quartet. :: scratch, in which case the advantage o SYNCOPATED VOCAL. preventchatter,andtheneedles would be nil. Crazy Rhythm ...... Col. 5146 i9: thin variety of Layton and Johnstone. The ideal, to my mind, is to take used are the soft, You're In My Heart.... Zonophone .. about a in.length, and alleged on Maurice Elwin. as little energy as possible from the 4.4i all sides- (quite wrongly, in my judg- :: When I Set Eyes on You.. Parlo.R239 record,and then make up with

Red Anders. ment) to be " record destroyers " on 4.4. amplification to the desired volume, DANCE. 13 Dakota...... Parlo. R237 thus dispensing with volume controls account of their " whippiness."

Roof Garden Orchestra. :,Little Dream Nest .. H.M.V. B5560 and getting the greatest amount of

Played 200 Times as. Ambrose and his Orchestra. : life from the record.Otherwise why

HUMOROUS. The amplifierisadequate,and Ee, by Gum ! .... H.M.V. B2880 :: go to the trouble of electrifying the 9 consists of four valves with push-pull Gracie Fields. :: McGinty on Marriage .. Parlo. R248 :: reproduction at all ? output ;and the volume is such as A. C. Astor (Ventriloquist). Yours faithfully, to be unbearable in a room without 2e Gardening ...... Winner 4869 :: Tommy Handley. 4. FRANK B. THOMAS. the least distortion or chatter from E.15. the pick-up.The lid of the cabinet being mostly left open while playing. A certain record (12 in.) has been played two hundred times with the above arrangement, and there is no visible sign of wear.This, I think, would satisfy most people. It seems to me that there are two sides to the matter, and they may be summed up as follow : (1) Pick-up weight on record in region of 4 oz. ;(21 about 2-24 oz. (1) Pick-uplightly damped;(2) heavily damped. Note the adjustable off -setting (1) Stylus or reed very free ;(2) angle -piece close to the fairly rigid. pick-up itself. (1) Tracking very important owing to weight(21 not so important. (1) Little needed in the way of amplification ; (2) a good amplifier reed. The Gecophone pick-up and new balanced carrier reviewed in another page in this section. :203 11. p es Crni rY ;es67 o Z

trc'c-,:, '-etr-v )....,3 ,>. ,,r43-..z.3 8 i cri s c4,' ...... ::ko ... 8 " ,,1.,.1 a z ir, a' 0-' S ?-14 -2- 7.6 8 (A cm'-'+' 2 C - " ' (3%< ..- a, cn '' '''' -.7,,...] z-,r -t0 a)P., .0 ",0

4004% -1015, 6t11.13

!BLUE 1130T 59 PENTOVOX 3 Speaker-£4. 4. 0 Never before has a set of such outstanding perform- anc2 been avai:able at the price of the Pentovox To listen to the Blue Spot 59 model is a Three. A typical Bowyer -Lowe p oduction,itis revelation in loudspeaker reproduction. de igned to the must advanced _standardsnd bu It from testedcomponents oftheh.g eatquality. The secret lies in Blue Spot 66K, the Smooth and evenreproductionoverthe hole adjustable 4 -pole armature unit.It is musical range-ample volame for loud -speaker reception --een selectivity over a wide range of stations. the finest unit obtainable, and can be Wave -length ranges are 250/ 00 metres and 1,000/2, 00 supplied separately with full directions metres.There are no coils to change, no complica [ion, of any kind.Hear this wonderful set at the for the home constructor, price 25/-, t rst opportunity. from any leading wireless retailer.It PRICE Includirig Royalties and 3 special valves, tested and will give results that will astound you. COMPLETE matched to set £11 Askyourwireless dealer about the won- F. A. HUGHES & CO., LIMITED, derful range of Bow- yer -LoweSetsand 204-6,Great PortlandStreet,London, W.1 Components, or write DISTRIBUTORS FOR NORTHFRN ENGLAND, SCOT- to -day for illustrated LAND AND NORTH WALES:H. C. Rawson (Sheffield and London) Ltd., too, London Road, Sheffield;185,Princess literature. Street, Manchester.

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vov0,0:re s of es Lektophone Corporations.' 65* 6 .e°tcPtI'l° r,eaQ Ott 617eWNIstt.,,,it`U. ,006 o oe'l'e,(4) kol'G62'-',"eno sew', olvcseet.15,i4, oos,e, c\coV

' t 44'sv0 0 V,<° R

.v.° a ' Go '5 k,e' 1,W4' e.06 &tO°. Vac \ We BLUE BOWyerro SPOT .4-fetticktpsekir-S-S. 66K Unit 25/- BOWYER-LOWE CO.,LTD.,IcknieldWay, LETCHWORTH 211 MODERN WIREFFSS February, 1929

.q3fet;.24ft),-s&39.&T,46-,elocy34e,-tgssescis.;T:7.2cir?-7.-'?.1-&,57 7 -`,0T4 ments, and Viscount Byng of Vimy, gl 66 the new Commissioner, who has seen ., ,z3 03 RADIO NOTES AND NEWS OF V the results, has expressed his approval. c3 q3. It is forecast that in the near future THE MONTH there will be a string of Police wireless Q3A feature in which our Contributor brings to your notice some of the stations in England, and that wire- 6a more interesting and important Radio news items. less will be used more and more for

C3 (%3 the prevention of crime. D Conducted by "G.B." D C3 C3..&8'.:gfc3OSOGiC3Z' S'Z'85.C3433Cr83SaS'tiSZ:e&tiGOV;3<83'83(83 Party Palavers The B.B.C. has invited the three Straight Talks RegionalScheme,givinglisteners political parties to take part in a RECENT experiments conducted by choice of programmes. debate on theGovernment's De - Marconi hold out the proSpect 3. Commencement of work on the Rating Scheme and the Local Govern- that in the near future the lead- new .Broadcasting House at Portland rnent Bill.It is probable by the time ing Dominions of the Empire will all be Place. this issue of MODERN WIRELESS is on linked together by wireless telephony. 4. Establishment of a permanentsale the broadcast debate will have The next step is, likely to be the ex- B.B.C. Symphony Orchestra in con- taken place, but as the matter is perimentofestablishingtwo-way junction with Sir Thomas I3eecham. under consideration it is not by any communication so that London - can 5. Progress with educational broad- means yet certain. speakto Canada and Canadato casting. The B.B.C. has suggested that a representativeoftheConservative London. -Later Oh, -it is', held that all1111111111111111111111111111H11111111111111M1111111111111111111111i= communisation hetween SouthAfrica, Party should speak for about twenty India and Australiawill be made READ . minutes, followed by spokesmen of possible. "POPULAR WIRELESS" E: the. Labour and Liberal parties, who -= Fualunamununnumananwamiumim annaanurm would speak for the same length of The Year's Forecasts time, and that then the Conservative 1929 seems to give promise of con- Radio Finger -Prints representative should be allowed a siderableadvanceinbroadcasting Experiments are being carried out final ten minutes in which to reply technique, and some of the develop- at New Scotland Yard in connection to his critics. ments forecast are : with the -transmission by wireless of The Liberals have announced that 1 Bigadvancesinshort-wave photographsandfinger -prints of they will accept the invitation, and transmission technique. criminals.It. is said that great suc- it is understood that the Conservative 2. Definite progress with the cess has already attended these experi- (Continued on page 214.)

BUILD THE MAGNUM "UNIVERSAL" THREE M.W." TRANSPORTABLE' FOUR MAGNUM As described in this issue. £ S. L.F. Oak Cabinet with frame and. baseboard .2 12 a Ebonite Panel 16 ins. by 7 ins., ready 7 CHOKE 2 Magnum H.F. Chokes 15 A. Magnum \lino Valveholders withcentre 3 Magnum Fixed Condensers, 0003 infd. 4 x Magnum. Fixed Condenser, mot 1 tap, 20:40 Magnum L.T. Switch .. 1 x Set of Parts for Cone Speaker, as described 1 14 henries x Variable Condenser, -0005 mfd., with small 6 The most perfect receiver yet designed x Neutralising Condenser (panel mounting) for the ultra -short waves from 13 metres 15 /. with knob 5 I Lotus No. a Jack 2 up to 2,000 metres. x Lissen R.C.C. Unit 4 Price a Mullard L.F. Transformer .. 1 5 18 Igranic Choke, Type F 15 including coils,3 valves and Royalty. a Hydra Condenser, 2 mfd. 3 a Grid Leak, 2 nteg., and holder .. 1 Free demonstration in your own home 2 Grid Leaks, meg., and holders .. 3 within 5o miles of London. MAGNUM lb. No. 22 D.C.C. Wire on reel.. Glazite Connecting Wire . . I STANDARD SCREENS Spade Tags and 'Plugs and Sockets as described .. 2 £9 15 MAGNUM The above Transportable Receiver wired, tested VOLUME and ready for use, including valves, KT.. L.T. and Royalty £16 0 CONTROL 2 meg. or I meg. BURMLIONES 7/6 As specified forseveralsets described "gtriP C 0 LT' D "

212 February, 1929 MODERN WIRELESS

RADIO DEVICES Use Igranic Radio Devices and give your home -constructed receiver the accuracy and efficiency of one built in the Igranic laboratories.

1GRANIC " LOKVANE " CONDENSER The vanes are positively spaced and rigidly braced by an ingenious locking bar method. DARIO Stations always come in atthe same settingifthe rest of the circuit remains constant. Special bearings ensure smooth movement. Prices : 000rs mfd.86 -coo3mfd.9,60005 mid. 10;6

-AND THE CHEAPEST WAY, TOO, guaranteeing utmostsatisfaction. Just look at the prices below-made IGRANIC possible by reason of the biggest valve MICRO CONDENSER output in the world.Radio without An accurately made IGRANIC INDIGRAPH ' smooth -working miniature Dario can never be radio atits best. VERNIER KNOB & DIALcondenser for neutralisM; SUPERLATIVE FINISH - LOWEST CONSUMPTION Enjoy velvetsmoothness reaction or vernier control. and dead accuracy of con-Also made as a Balancing TWO VOLTS. trol on all your tuning andCondenserforequalising FOUR VOLTS. reactioncondensers two tuned circuits Genera. Purpose, General Purpose, by . fittingthis uniqueslow Baseboard type, '05 amp. 5;6 '05 amp . . 5;6 4/. R.C.C. '06 amp. 516 R.C.C. '07 amp.5/6 motion dial. Panel type with knob and Super -Power, Super -Power, dial, '18 amp. . . 7/6 '1 amp. . 7/6 Price 6/- Super H.F. & R.C.C., Super H.F. & R.C.C.. '18 amp. . . 1/6 'I amp. . . 7/6 147 Pe ntodion Pentodion, QueenVici;;SN '15 amp. . . 21 - '15 amp. . 21- IGRIVHC IMPEX ELECTRICAL, LTD. ELECTRIC Co.ltd. -Wept H '."°1\1W 538, Works BEDFORD High Road, Leytonstone, Have you read " Radio-How it works and how- to get thebest from it ? "Price 6d.Send this coupon with your E.11. name and address and get YOUR copy FREE. NAME ADDRESS J786. 213 MODERN WIRELESS February, 1929

Eg 0000Egawg5Ego@000cgEn findfreshtalent and brain -waves ested in the Dramatic Control Panel ota RADIO NOTES AND -9 generally. which enablestheproducerofa ,q,.. radio play to control effects without c3NEWS OF THE MONTH 6 Ballan Beam Burnt seeing theartistes,and to merge 6a -continued from page 212 43 The expensive Beam stationatvoices, music or any other sounds e.43 z.M3f3c5;9f3C90,f3Q930,i73(83600130 Ballan, about fifty miles from Mel- from as many as twelve different bourne, Australia, narrowly escaped studios.It appears that members Party aredisposed to considerit complete destruction on the 28th of the Commission were unanimous in favourably.As we go to press, the December last owing to an outbreak theiropinionthatthisdramatic Labour Party has not yet come to a offire.It destroyed the roof and control -panel arrangement is an ad- decision. damaged thegenerator, anditis vance on any other device known to understood that the transmitting gear broadcasting in other countries. Royalty and Radio was also damaged by fire and water. Eiffel Tower and 5 X X Owingtoill -health,theKing's 1111111111111111111111111H111111111111111111111111111111111111111111111IE uncle-the DukeofConnaught- Owing tothe new wave -length spent Christmas abroad, and heard Were You Disappointed ? changes, the Eiffel Tower may now be heard on a wave -length of 1,485 news of the King's progress by wire- 2Ifyoucouldn'tgetthe" Radiano E. less. His chauffeur erected a wireless Three " Blueprint when you tried, you-2 metres, which should bring it within set at the Duke's villa, and it is under- will be glad to know that this has now the scope of any ordinary wireless set. stood tke Duke listens -in regularly been reprinted. Radio Paris (Radiola) remains un- toallthebulletins. The Duke is - Obtainable at all Booksellers, price 1/6, changed at 1;750 metres. The power of the Eiffel Tower station is 5 kilowatts seventy-eight. or direct from " 'Wireless Constritctor " E. Envelopes, The Amalgamated Press,7. There have been complaints, how- Bright Ideas Ez Bear Alley, Farringdon Street, E.C.4. ever, that the Eiffel Tower station As repOrted exclusively in our con- By post, 1/9. now interferes with. Daventry. We temporary, " Popular Wireless," the should be glad to hear from any readers B.B.C. has 'founded a " Bright Ideas who find their reception is being spoilt Department."Itisofficially called B.B.C. Best.Best by the Eiffel Tower. the Programme ResearchDepart- It is stated that foreign members A Long. Way Round ment, and Mr. R. E. Jeffrey, late of the Commission of the Interna- The radio operator in the " New Directorof Dramatic Productions, tional Radiophone Bureau have been York Times " wanted to send a mes- will be the head.Mr. Jeffrey's new very much struck by the way in which sage to a colleague living in a suburb department's duties will be to put the' B.B.C. transmits plays from its of New York.Failing to reach him sparkle into the programmes and to studios.Especially were they inter - (Continued on page 216.)

1-(1111n1 SEE 11111[ so/ ,dr-T11Pri

111111 At its introduction, the." Ideal " Transformer achieved an immense advance in wireless reproduction. To -day all amill1111.1111101111ftwis40, transformers are judged by that high standard.Not only is every " Ideal " guaranteed against mechanical trouble, but each one has a guaranteed amplification curve within 5% of the standard.From the- top of the scale, right down to the lowest register, every frequency is perfectly interpreted and amplified ; every note is given its own true value, undistorted, uninterrupted.

"IDEAL " TRANSFORMER This famous Marconiphone Transformer combines particularly high inductance with an unusually low self capacity, whilst the large iron core precludes any possibility of saturation under normal working conditions.The " Ideal" is, to all intents and purposes, distortionless throughout the musical scale, and guaranteed against mechanical and electrical defects for twelve months.In four ratios: Marconi phone " Ideal" Transformer. 2.7 to r, 4 to 1, 6 to r, and 8 to r. Price 25'. each.

UNIVERSAL POPULAR THE MARCONIPHONE COMPANY, LTD. (Dept. P),210,'212, Tottenham Court Road,London, W.1 TRANSFORMERS TRANSFORMER Showrooms: These have a higher inductance than An inexpensivebutefficient little any .other at a similar price, and offer 210,'212, extraordinary value.Two ratios are instrument suitable for small receiver; Tottenham Court Road, W.1, and 'garcon,House, available: 2'7 to I and 4 to I.Price 16/. or portable sets. Price 1216 Strand, W.C.2. 214 February, 1929 MODERN WIRELES:

a a a a 11 a III a to ' STILL FURTHER,' GcARKE-

TESTIMONY

to the wonderful PIRTOID TUBING WEILO By reason of its wonderful insulating properties Pirtoid Tubing is the ideal former.It is

TRANSFORMER. especially suitable for the making of High 1111 This unsolicited testimonial from one of the many satisfied WEILO Frequency Transformers, AerialCoils, or users indicates the remarkable results achieved with thisultra- any of the specified solenoid coils for special value Transformer.Experts and listeners alike join in acclaiming WEILO as the new Standard of transformer value-the equivalent receivers.

of many ofthehighest instruments on the market. priced

Read Mi. Fleet's letter : - Oldham, Dec. l8tn,192a. Pirtoid Tubing can be had in any Diameter, Gentlemen,-I anidelightedwith the Wall or Length ;it " Weilo Transformer. I was using is easy to drill, unbreak- twotransformersofaweft -known able, and is highly insulative. make; onebroke downinworking and Ireplaceditwith a " Weito Inoticed improvement inthe ton, and I then decided to replace the re There is no substitute for gen- niaining transformer with a " Weito," and the improvement was remarkable.r. uine The volume was increased, and the Pirtoid Tubing-nothing tone was rounder and crisper.Ican else that will give as good results. 111111111

honestly recommend them. rrtt (Signed)II. Plea. POWER type Heavy type IIIIQIIJI a Write for details and prices to Model 10 Model 3

Price 1116Price 8/6 a H.CLARKE & CO. (Manchester) GUARANTEED TWO YEARS.

WeitoTransformers have been specified LTD., for the Pitman " All Europe 3 "and the Manchester Erg. Chronicle " Las " ATLAS " WORKS, lance2.'Send for fullyillustrated catalogue describing the quality Wells OLD TRAFFORD, and N.S.P. components, free and postgo MANCHESTER. free on request.Stocked by Harrods Storesandmost Good -class Radio dealers. S. W LEWIS & Co., Ltd

Indian Agents:BombayEadto Co., (Dept. M. W. I Bombay and Calcutta 39Victoria Street. London, S.W.1U 114 lag al IN aei ON NO IIIn MI Ing 111 111 RI No

EXTRACT FROM LETTER RECEIVED. "I have recently been experimenting and demonstrating with yourScreenedGrid Three' and I must say thatalthough 1 have been able to build many sets of good @SW4r design, of four and fivevalves, and have just dismantled a good five -valve set with two H.F. stages, Detector and two L.F. BUILD and OPERATE in screenedcoils,etc.,Ifind your Receiver beats them all, and I am more than pleased - ONEEVENING-- with its performance." The above is one of many UNSOLICITED TESTIMONIALS. Ootain a Broadsheet from your Send post card for FREE FULL-SIZE dealer and read why you should- LAYOUT PLAN and wiring instructions THE FORMO CO., Completely Screen the Grid Crown Works, CRICKLF.W000 LANE, N.W 2

FOR ALL POPULAR asuperk_044900d CIRCUITS, MOVING COIL valve-holder for AND CONE SPEAKERS A widely used and recommended pro- CABINETS NEW LIST duct has come down in price.The W.B. Anti -phonic Valve -holder now FREE costs !r3 -an unusually reasonable Write to :- price for a first-class Valve -holder. Carrington Mfg. Co., Ltd., WHITELEY BONEHAM & 00. LTD. Cameo Works, Sandersteal Road, Manufacturers of the famous WhiteleyBoneliamLoud Speakers. .Prices f eon,47/6. South Croydon. NOTTINGHAM ROAD, MANSFIELD, NOTTS. Telephone )Croydon 062342nnes) 1,1

215 MODERN WIRELESS February, 1929

'z%EgeaEgs830@%06gvg00Egg00. alongside the ice packs, sits at a type- denied, in no uncertain terms, by. writer and describes how Byrd " re- the' B. RC. RADIO NOTES AND 4 disCovered " Scott Island, withits 04.f3 NEWS OF THE MONTH q;3 two peculiar -looking peaks rising 300 An Official Statement -continued from page 214 feet above thesea,the home of The B.B.C. has sent round another thousands of sea birds. memorandum concerning television, As the expedition continues the asking for it to be repeated, as there on the city telephone, and knowing wirelesswillbring news dailyto still seems to be some misapprehen- that his colleague was at home lis- sionaboutbroadcasting,sohere tening to a message from the Byrd IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIL it is : Antarcticexpedition10,000miles " On October 17th we stated that a away, he wirelessed Byrd's operator THE "TITAN" THREE demonstrationoftheBairdTele- on board the " Eleanor Bolling," the A free ofthis visionDevelopment Company on blueprint October 9th had failed to fulfil the vessel in the Antarctic which does g_- wonderful receiver is E_ conditions which would justify trial Byrd'sradiobroadcasting. The 3 Eleanor Bolling's " operator relayed GIVEN AWAY =-.-- through a B.B.C. station, but that L: E any claim of improvement would be the message to the " City of New E- ..f. with the Feb. 2nd issue of examined." York," the converted sealing vessel .. - which is Commander Byrd's advanced "POPULAR WIRELESS" 2 post, and carried the aeroplanes with "No Improvement" Now onSale Everywhere, 3d. ET-- whichhis Antarctic flight is to be The statement continues as follows : attempted. Here the operator inserted 71111111111111111i1111111111111111110111011111111111M1111111111111111fr: " The Baird Television Company has it into a Press despatch he was sending not yet intimated to the B.B.C. any to New York, and it was promptly America from the ship, from the ice claim to improvement.Any such delivered after its Polar adventures. packs, and even from the exploring improvement would be examined by aeroplanes. the B.B.C. with a view to deter- Byrd Broadcasts mining whether the above decision should be modified." So far there has been no break in The B.B.C. Contradicts the wireless communication linking In the middle of January reports New York with Commander Byrd's were current that the B.B.C. was Why Not ? expedition, and apparently none is willing to grant broadcasting facilities The Managing Director of the Baird expected.A reporter on hoard the to the Baird Television Company. Television Company statedinan " City of New York," which is now Very promptly thesereports were (Continued on page 218.) Pr More Sound Waves FromDay's PORTABLE SETS THAT SPECIAL LINES YOU CAN RELY ON SOLDOMETA Pocket SELECTOR 3 Comprising 1 Soldering outfit for 2/6 S.G. Valve, Det., and Pen- MogenH.T.Generator, tode Valve. (Oak). 20 Gns. 400 v.200 m.a. output SELECTOR 5 In Blue leather From £22. carrying case, 12 stations PORTABLE GRAMOPHONES charted. 30 Gus. Allthebest makesin M.H. 5In Brown leather stock.Prices from £2 15 carryingcase. A really to £10. handsome unit. £27 10 0 SMALL TABLE GRANDS SPECIALLY DESIGNED Alltheleadingmakes FOR USE on A.C. with always available for im- Oicgaist% Cossor, Igranikit, G.E.C. mediate delivery. or Mullard Master 3, THE Pricesfrom £6 10to The TELSEN REGENTONE W.I.B. £8 10, andother larger "RADIOGRAND" Unit, delivery 120 v., 18 models. Transformer at12/6, M.A. £4 196 RECORDS andthe " ACE "(a ALL EKCO A.C. and D.C. H.M.V. 3/- to 10/ - compact, light and Units in stock from Columbia 3/- to 12/6. efficient instrument 29/6 each. Zonophone 2/6t34/-. specially designed for ALL AMPLION, B.T.H., MUL- Brunswick 3/- to 8/-. LARD, PHILLIPS, CELES- Parlophone 2/6 to 4/6. Portables) at 8/6, are TION AND MAGNAVOX . Radio 1/3. two models which have SPEAKERS IN STOCK. Duophone 1/6. achieved overwhelming Don't fail to visit our Gramophone Saloon when you next call. popularity with Radio Radio or Gramophone Booklets free on request. enthusiasts.Install a TELSEN and note the ' extraordinary amplification and purity, \or, iitlitilidiO Entirely British, guar- , ,/ ...- anteed 12 months, and ,, obtainable everywhere. Ratios5-1and 3-1, shroudedand with detachable feet. Illustration shows the RADIOGR A ND.' tISLECTSTIEEET,13tfl/CETSTINEVSQTUHAREE, E0?4fD/OINT,V.C.2, TELSEN ELECTRIC Co., Ltd., efrphone tatfirOkiiergh 0921uad 09?2 O'filrants le3,1YeAdird. Leaden 207, Aston Road, Birmingham. 216 February, 1929 MODERN WIRELESS GaMXngq9C3cM43,830f3,fq \\I SPADES, PINS I @ 0 1 AND EYES I EQUAL TO THREE for use with 1 MAINLY ABOUT o I EELEX a AERIALS ORDINARY BATTERIES ITREBLE -DUTYI ,q111 I TERMINALS I i EACH 2d. j Q.MGf3C3C3GT3tkW3C3C3T3, The great disadvantage of a frame -aerial is Mille that it is capable of picking up only a fraction of the energy which is receivable upon a good 2.2277"4'6!"11.1.4( outdoor aerial. Generally speaking, a frame aerial is more suitable for short wave -lengths than for long. * * * Amongst the advantagesofframe aerial EELEX TREBLE -DUTY reception are the greater selectivity due to its directional properties, and its portability. TERMINALS * have multiple uses and cost from 2d. to Where interference from neighbouring power 4d. each, according to size and finish. stations or electricalplant is extremely bad, a No. 4780. frame aerial is sometimes the only satisfactory 60volts. New Reduced 41D. TERMINAL T2 LC, as illustrated, method of tapping the ether for broadcasting Prfce, £1. nickel -plated, withchoice of 90 programmes. indicating tops. * 3D. TERMINAL T2 LN, as T2 LC with- Although a great many experiments have Columbia outindicatingtops,withslightly been made and many variations tried, the smaller head. favourite grid leak and condenser arrangement RADIO BATTERIES 21D. TERMINAL T2 SN, as T2 LN except is a capacity of '0002 mfd. and a resistance of The Columbia No. 4780 Triple smaller in size. 2 megohms, the latter being connected to the Capacity H.T. Battery possesses positive lead to the filament battery. the emission, the lasting power, Write for Booklet S65. and learn all * * * aboutthe EELEX System and the quality of three ordinary of stan- Although 100 ft.of wireis the maximum batteries. dardisation. length allowed for a listener's aerial itis not For the man with the good necessarily the best length, especially for an Receiver, this Columbia battery J. J. EASTICK & SONS, indoor aerial. is indispensable. It's as * * * Eelex essential as the good valves he House,BunhillRow, Generally speaking, whilst indoor aerials are uses. Chiswell Street, London, E.C.1. satisfactory for the reception of the local station J.R. MORRIS, when this is situated only four or live miles Imperial House, 15, Kingsway, LONDON, W.C.2. 'Phone: Clerkenwell 9282-3-4. away, they are not suitablefor long-distance reception. SCOTLAND-J. T. Cartwright, 3, Cadogan St., Glasgow S 01. BUILD THE PEERLESS " PESONIC 2 "

Anyone can build this set in 60 minutes.No drilling. No soldering. All Wires cut and bent.JUST ASSEMBLE, and then immediately enjoy the radio entertainment which is of splendid tone and comes in at good loudspeaker volume. KEEP YOUR VALVES YOUNG Circuit allows use of standard valves (1 H.F. & I Power). The valve'slifedepends on Blue Print and easily followed the valveholder-use Vibrol- IT COSTS ONLY DiagramofConnectionsin- ders and keep your valves cluded with every set.Cabinet young. Vibrolders give perfect and full Kit supplied in Carton. contact, are absolutely shock- proof and follow air spaced 13/15/0 Obtainable from low -loss design. They are the alldealers or valveholders witha name andefficiency THE BEDFORD ELECTRICAL & RADIO CO. LTD., entirely their own. Price116 22, CAMPBELL ROAD, BEDFORD. Scottish Office :113, St. Vincent Street, GLASGOW, C.2. 131

Benjamin ElectricLimited, Brentwood Works, Tottenham,London. N.I7 217 MODERN WIRELESS February, 1929

CE*M5683a$35 WgEtEMEPEV4 Radio Drama READY RADIO SRADIO NOTES AND g Mr. Val Gielgud, who has succeeded 163 Mr. R. E. Jeffrey as Play Producer SUPPLY COMPANY, 0 NEWS OF THE MONTH a of the B.B.C., has some pretty concise 159, BOROUGH HIGH ST., -continued from page 216 E2? views as to the direction of radio 413 LONDON BRIDGE, S.E.1. ecsiyscgq3o,m3sosoocan3c3f3t3s drama. He has made it clear that he 3 Minutes from London Bridge Southern Rig. and is not going to attempt to produce Tub.Stations. plays pleaseeverybody.His Telephone: HOP 5555 (Private Exchange> interviewinconnection with this to Telegrams: READY HOP 5555, LONDON communication from the B.B.C. that policy will be to cater for all tastes it was hardly borne out by the facts. in turn.He seems to want it em- Price List of ALL the CORRECT Herecalledthatapplicationfor phasised that he is not highbrow, PARTS for the broadcast was made by Mr. Bairdbut all the same he would like to inSeptemberlast. PostOffice improve the standard of the plays TRANSPORTABLE engineers witnessed experiments with produced. FOUR the system some time later, and the Managing Director claims that the Microphone Plays A HIGH-CLASS PORTABLE G.P.O. sent him a written statement Mr. Gielgud said, in a recent inter- AT A MODERATE PRICE in which he said that the engineers view : " I want to induce dramatists s. 1 "Birthday Four " polished oak were delighted with the system and to write plays specially for us, but 7 considered it commercially practicable. there is the difficulty of oui not being 2 6 cabinet .. 1 Resiston panel, 14" x 7' .. 16 2 If this is so, why doesn't Captain able to offer them very substantial 1 J.B. .0005 slow-motion cond. and dial .. 66 Hutchinson, the Managing Director, inducements, because our plays run 1 Lotus L.T. switch .. 1 6 issue a copy of this letter for publica- for one night only.We may over- 1 Lotus No. 1 jack 20 tion in the Press ? come this difficulty by running plays 1 Lotus jack plug....' .. 20 1 Gambrel! P/M neut. condenser.. 56 4 Sprung valve holders .. 7 alimiiiiiiiiimminummulimilininiumummumumummiiiiimuutullimumminimmiummmimmiummiuly 2 Igranic H.F. chokes 10 1 Lissen R.C.C. unit.. 4 1 Marconi universal transformer 16 1 Dubilier 2-meg. leak & holder.. 3 " There's always something new in Radio." 2 Dubilier 25-meg. leaks & holders 7 3 Lissen -0003 fixed condensers .. 3 1 Lissen .001 fixed condenser.. 1 1 Igranic type "F " output choke 15 E-E Keep yourself in constant touch by reading 1 Hydra 2-mfd. condenser .. 3 1Ready Radio set of copper foil sheets.. 2 "POPULAR WIRELESS" 1 Kit for Connoisseur's Cone, with 25/- " Blue Spot " unit .. 119 1Ready Radio turntable.... 8 1 Lissen 100 -volt battery.... 1211 Every week contains something to interest every listener. 1 C.A.V. jellied acid non -spillable accumulator (2NS13) .. 146 1 Screened -grid valve .. 1 26 How -to -make articles Dependable Sets 3 Valves (Det., L.F., Power) .. 1136 Frame aerial and reaction wind- Broadcasting News ing materials .. .. 26 Flex, Glazite, H.T. & G.B. plugs, -all phases of radio are covered. 30 Inclusive Price .. £1497 On Sale every Thursday - - Price3d. PLACE YOUR REGULAR ORDER NOW. READY RADIO PARTS used In the "Transportable " Four. TURNTABLE .. 8/6 COPPER SCREENS .. 2/ - A Jazz Studio_ for three consecutive nights. Mr. The B.B.C. is introducing a Jazz Ashley Dukes, who wrote ' The Man Studio-its latest novelty for mak- with a Load of Mischief,' is writing a STANDARD COPPER SCREENS ing brighter broadcasting.It appears radio play for us now." 10" X 6" 2/6 7" X 6" 1 /9 Any type of screen made to specification. that artistes have complained of the drab atmosphere of the old 2 L 0 The Indian B.C. IMMEDIATE DISPATCH studio, so Number Three Studio has Mr.Eric Dunstan,thepopular OF ANY OF THE ABOVE SPECIFIED PARTS. now been converted into a jazz one. announcer who left Savoy Hill early In other words, it is decorated with in 1927 to take up the post of General. WE HAVE SATISFIED CUSTOMERS much of the night-club touch, and it Manager of the Indian Broadcasting ALL OVER THE WORLD. has a night-club atmosphere.The Company, has now returned to the CALL IL.bR 'PHONE ceiling is silver-grey, the Carpet has B.B.C. headquarters.Mr. Dunstan WRITE OR WIRE. a cheerful pattern, and the lighting is spent, twenty months in India, but subdued but radiates in a cheerful many difficulties arose, and it was COME TO US FIRST- way. more than once suggested that broad- AND SAVE TIME. This studio will he used in future casting would have to cease.Piracy for chamber music (and it is sincerely Send for our 144 -page General Catalogue. Price _and the small number oflicences One Shilling.Free with all Orders frequested. hoped the new decoration will make that were issued combined adversely INLAND. Allorders post tree.OVER- chamber music a little more cheerful l), to affect the Company's finances, and SEASConsignments carefully packed and militarybands, dancemusic, and insured, charges forward. in October oflast year the whole light broadcasts of other kinds. staff resigned. 218 February, 1929 MODERN WIRELESS ALUMINIUM CRADLE FRAMES (Prov. Patent No. 32559) Sq AND CONE KITS, FOR VARIOUS BALANCED ARMATURE SPEAKER UNITS SOUI RE N9 97. No. 97 CRADLE- - 12/6 91" CONE KIT - - 2/6

Ready to receive Blue -Spot, Triotron, Bull- Phone Units, etc., for securing DIRECT to Aluminium CRADLE. This Larger and Distinctive Model is fully described on our yellow leaflet.

No. 60 CRADLE 8/6 6" CONE KIT - 2/ - Designed forPortability,leaving ample provisionforValveSet. Overall measurements, 8" x 8" x 6" deep. Frame weighs io ozs. For Blue -Spot Unit only. The Aluminium Cradles are not influenced by either magnetism, or variations in climatic conditions. The Plywood Clamping Washer is included in each complete Kit.Everything is accurately cut-out. Send for Yellow Leaflet dealing with our No. 97 KIT, and illustrated instructions for Cone mounting, which applies to either above Kits. We can supply framework as shown on page 147 and used in " Transportable " Four, or improved type as illustrated above. 24,LESWIN ROAD, STOKE JFIRJETVII. SQUIRE, NEWINGTON, LONDON,N.16

NOW ON SALE WIRELESS CONSTRUCTOR ENVELOPES

RECD EnvelopeNo. 1.-THE "RADIANO" THREE. OCSIGN (Recently reprinted).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. Envelope No. 2.-THE " CONCERT " FOUR. Made MP FLOATING of standard parts, all easily obtainable, this is a highly -sensitive long-distance set, giving powerful POINTS NO reproduction of wonderful quality on 3 or 4 valves. RIGIDITY In these envelopes you will find every detail of the set simply EVERY VALVE explained, photographic reproductions and diagrams are included as well as a full-size Blue Print. SOCKET GIVES FLOATING ACTION AT ALL BOOKSTALLS Price 1/6 By post, 119, from Wireless Constructor Envelopes, the Amalgamated Press, Ltd., Bear Alley, Farringdon Street, London, E.C.4. .F. E 11. B u rToN PROGRESS WKS. WALSALL itIJPSILo ULLI,S SERVICE 211 MODERN WIRELESS February, 1929

..685EgE1456gEgV0,560@EA0000Egat E3,@E@@EE,EMEgi%EMPE(icc,!',',,, te? O IN OUR TEST ROOM 0 A VERSATILE METER

-continued from page 188 -continued from page 171 t5; -;:t9(M941.9,SQT9f2qP0d300t:i0f9g,'30 e eft! r Of5f3f3q3f3gfP4NM3&Mir3q3&nc3 216 -turn terminal being in the centre The other end of the shunt is con- and " zero " on the base. nected directly to the negative ter- May Facilitate Wiring minalof the milliammeter. The Although, of course, it is in some ampere socket is connected to the respects an advantage for standard positive terminal of the instrument. objects to remain standardised in every As,therefore, the plugispushed respect, it must be pOinted out that home it connects the shunt between this Lewcos loading coilfulfils the the positive and negative terminals ArapuniThe Great " M:W." technical requirements.- We of the instrument.The strip should dam,part of New lea asked for a certain total inductance be shaped so that itlies normally taMrs mze hydra..elee - and certain tappings. Providing these about I, in. clear of the top of the tric scheme. are all in order, that is all that matters ampere socket. so far as the operation of the set in The Final Process which the coil is to be used is concerned. And on test we find the Lewcos The hole initover the socket should be a close fit for the plug (A versionofthe" M.W. "standard in the diagram).The strip is fixed in loading coil to be -quite satisfactory place by means of a round -head or andfullyup tostandard.Con- structors need have no hesitation cheese -head fin. screw. To the tip of in including them in sets in which such this screw, and to that of the counter- a device is specified, and, indeed, in sunk screw 1 in. below it, the ends The somecases the Lewcos form may of the shunt are now soldered. facilitate wiring. wiringofthe instrumentisthen carried out in accordance with Fig. 9. Useful Books ENGINEERING Two useful books have been pro- :1010101111111111111111110111111111111111111111111111111111111111Se PRECISION.° duced by the Standard Wet Battery -.17- THE BEST SETS Co. The one is a handbook of in- are described in the Imagine the genius, the inspiration, the structions for assembling and using the tireless labour expended on this vast dam-a standard Sac Leclanche wet H.T. `P.W."White Prints supreme achievement of modern engineer- = which are included in ing. One flaw indesign,one slipin batteries, while the other also deals = workmanship, might cause untold disaster. interestingly with the products of Every Copy === With wireless instruments such inaccu- thefirm. Anyone interested can of racies would lead to a defective set-surely damage enough-damage, however, that obtain free copies of these booklets. 1.-E--- " Popular Wireless " can be prevented by using J.B. precision .. on sale instruments. A Pocket Soldering Outfit - The J.B. New Type Slow Motion Condenser Elmesan (London), Ltd.; arethe Every Week (Ratio 40-1) is really a wonderful job.The height of the Vernier Knob and Dial is less sole distributors in Great Britain of than that of last year's model, but the new that well-known solid fuel " Meta." Price 3d. :: Every Thursday arrangement provides remarkably convenient Place a regular order. control, and is vastly improved in appearance. They have now produced the " Soldo- Completely enclosed in dustproof mechanism- meta," a pocket soldering outfit which a real protectionfrom accidental damage. retails at 2s. 6d.In a handy size tin Tension offriction mechanism adjustable. Absolutelysilentonshortleaves. Every are " a small soldering iron, a tin of The only remaining process is the possible precaution has been taken to prevent " Fluxite," a tin of " Soldo " (this final calibration of the ampere shunt. wear. is a soldering compound in powder Use is again made of the borrowed PRICES: S.L.F. PRICES: LOG. form which dispenses with the need ammeter and of the D.P.C.O. switch. '0005 14'8 '0005 14,8 for flux or resin, etc., possessing in One lead from the ammeter is plugged '00035 13 8 '0003 13,8 '00025 13 - itself all, the solder needed for tinning into the negative socket of the multi - *00015 13 - '00015 13/ - and soldering). range instrument and the other end There is also, of course, a smallinto the 3.5 -ampere socket. We left packet of Meta and a stick of solder. the shunt with rather too high a Finally, there is a small holder for resistance in order to allow for con-. the fuel. tingencies. It will probably be found With all these excellent things onethat owing to soldering its ends the could hardly fail to make a goodresistance is not now very much too soldering joint. Despite its small size high. the outfit is quite a practical one, and small jobs suchaswiring a A Resistance Adjustment radio receiver can be carried out with The final adjustment is made by it.'"Meta " is a clean and a safe taking a very little solder on the point PRECISION fuel, and it gives out a hot flame. of a small iron and applying it care- INSTRUMENTS The small iron soon loses its heat, fully to one of the turns of the shunt. and a little skill is needed to avoid The resistance of the solder is much clvt. of Jackson Bros., 72, St. Thor.as' St., London, S.E.1.Telephone: Hop 1837. " dry " joints. (Continuedon, page 221.) 220 February, 1929 MODERN WIRELESS

C9cct7: 3073 0q960g150 66 LEADING HOUSE FOR 0 A VERSATILE METER2. K. RAYMOND g-continued from page 220. g 27 & 28a, LISLE ST., LONDON, W.C.2 KITS of Parts --,T,:,f3,T3ggegq3t3eq33,,yscT3oc383f3 Come to LEICESTER SQUARE TUBE. See weekly Advts. This address isat the back of Daly'sAny list of components over 25/- quoted Theatre. 'Phones : Gerrard 4637 and 2821 for at a special price, where possible. lower than that of the wire, and by WE ARE OPEN its use small portions of the latter ALL DAY EVERY DAY Hours 9 a.m. to 8 p.m. WHY BUY EXPENSIVE can be short-circuited until the total ALL DAY SATURDAY Sat. 9 a.m. to 9 p.m. resistance is exactly right. ALL DAY THURSDAY Sunday morning 11-1 MOVING COIL SPEAKER The instrument is most convenient .DSEND ORDER.PAY MAKE YOUR OWN. POSTMAN.(U.K. Only). tousesincedirectreadingsare .Must be over 5 -value. HANDSOME OAK POLISHED always obtainable from the existing 0.0 SPEAKER CABINETS 13x13x6 scale. On the 25 -volt and 25 -milli- ALL WAVE WESTINGHOUSE CABINET ampere ranges each full division equals H.F. UNIT.METAL RECTIFIER 1 -volt or milliampere, as the case " P.W.," Jan. 19, '29.TYPE H.T.1 84,1- 0005 Variable, with S.M. 12111 may be. On the 250 -volt range each Dial,8/11; L.T.Switch, REGENTONE POST 1/3 division is 10 volts, and on the 2.5 - 1/3;Valve Holder,1/3; CoilStand,1/3;0003,Mains Transformer ampere range it is .1 ampere. 1/-;1 mfd, 2/6; Neutro- Blue Spot dyne Condenser. 2/-; Leweos for above 30/. H.F. Choke, 8/8 (20/2,000 Please State Voltage. 66 K (101) metres).Price,Including ii1111111111111111111111111111111111111111111811111illidill1111111111112i Screen 7 a 6, Strip 8 a 2,OSRAM MUSIC MAGNET 8 marked Terminals Kit of Parts & Valves Clips, Wire, Flex £8 : 12 : 6. 25/- Going to Build a Set ? Post 9d. 30/- BOOKLET FREE. BUCKRAM CONE The 1929 TRINADYNE Similarto above butcannot 12 in. FREE Why not get one of the P.W. 19 Jan. 'at. guarantee exact pattern of front '0005 Formo or similar, 6/-; o,'o Switch, 1,3;'0001 panel but all good designs. carriage paid. Reaction 4/- ; Semipermanent Detector, 2/6; Sprung Wireless Constructor Valve Holder 1/3; Lissen Choke, 5/6; Watmel, 5/-; SQUIRE C. O. B.B. Neutralizing, 5/-;R.I. Varley, 15/-' Lissen SEND ORDER and L.F., 8/6; '002 and '001 Lissen, 2/6 ; 2 Coil Sockets 2/6. CONE KITPAY POSTMAN ENVELOPES POST=9/a 2- comprising KRAFT FREE WIP X.EXTRA Diaphragm, CARDWe despatch within For 2/- extrawithpartsIwillincludeHigh-grade 24 hours where pos- Ebonite Panel,12 a 7, Baseboard, Strip 10 a2,8 Ring and Seg- oig No. 1.The " Radiano Three." Engraved Terminals, Wire, Flex, G.B., Clips, Plugs, etc. sible.C.O.D. U.K. mentstby post only. 71 No. 2. The " Concert Four." Aluminium Cradle DO YOU WANT COILS? Frame ; ready /..L. COILS WE HAVE THEM ! to use (post free) (Short Wave). Price1/6each at any Booksellers. Wound 3in.diameter;fit All by approved makers for ' A.W." " P.W.." Complete Lot 15/- standardcoilholders. 3 111.W." and " W.W." Sets. (Plywooa Clamping Washer 57, 9, 7/6 set.Send for E Or1/9by Post from The Amalgamated Everyman 3 pr. 3300,1: A.C. Valve Receiver, Free) list of Q and other eAls. Everyman 4 pr, pr.25/ - Press, Ltd. (Wireless Constructor New E.4 (8.13.)pr.30!-Pentode 2 Coils, Envelopes), Bear Alley, Farringclon St., All -W. 4, B.B.C. and B.B.C. or 5XX, 3/8 SIX -SIXTY MYSTERY RECEIVER pr.20/- ea.; B.B.C. in Lit:6/ London, E.C.4. LongB Wave, no Base. Europa IIICoils(with Kit of Specified Components: loading coil) Magnum Brackets,2/6.2 Lokvane .0005 at10/6: .17 or lab- set 22/ ;0063 ditto.916.2 I'graphDialsat 6/ .2.Plain Regional Receiver, James Special Three, Dial, 1/6 50 -ohm Rheostat, 2/6. Neut. Con..41-- Standard 4, B.B.C., set 25/ - S. Fil. Jack, 3/9. 4 Vibro V.13at 1/6.Kit of Coils :.--(1111111111111111111111111111111111111111111111111111111111111111111111115 ea.,16/3; Long W.M.Tonehstonepr.30/ - 32/6. Sovereign H.F. Choke,5/-. Climax " Wave, 20/-; Bases... 2/-M.M.3, B.B.0 416 S.L.L.F., 2 H.F. Everyman 4, ,. 5X X 8/6 Transformer. 25/, R.I.Six -terminal B.B.C. Coils, 35/-; Dual 5.3 Star...... 7/8 3 Anti-mobo at 8/6.2 mfd. Dubilier. 3/6; Do, -0003 By making up, the multi -range in- 5XX 22/.M.W. 1928 Solodyne, and 2 meg., 5/, " W. World" Five, B.B.C. or5XX, Carriage Paid. strument one obtains what amounts Coils 45/. set 45/- Total £9. 10. 9. Selection Four Coils, Standard Loading Add 1 /-and Exceptional offer of Cabinet. practically to four high-class moving - B.B.C. 24/6; 5XX Coils(as specified) 7/6 I will include 1 Best 21' a21' a 7' a10' deep,for 16/-; Bases 2/-D.C.MainsThree...set 72/ - 7.Panel, Baseboard 21. aabove, Mahogany or Oak, coil instruments.The resistance of New All -Wave Four, Mexavox, B.B.O. 10',Strip10 2. 8American Type, Hinged B.B.O.16/3; 5XE 16/.; 5XX 10/6; Marked Terminals.. x, WanderLid,grandquality,15/, the voltage ranges is of the high order 20/-; Bases 2/. Base 1/6 Plugs,Wire,9.volt Grid Bias. (With Parts only.) desirable and no damage can be done LEWCOS PRODUCTS WATES' 3 - in - One C.T Coils, 40, 50, 60. 75, 3/6 each; 100. 150, 200, tobatteries,since forafull-scale 5/3 each. Glazite, 10d 10ft.; Frame Aerial DARIO Vela TEST METER Wire, 3/6 100ft.Batters, Leads, 5 -way, 5/6; READINGS deflection the maximum current taken 6 -way,7/6,7 -way,8/6. Binocular 6 -pin Coils, VALVES 0-150 B.A.0.5,16/-'B.A.0.20. 12/-'B.S.P.5, 15/-' 20, volts 6 from them is but 25 milliamperes, B.A.R.5,10/-B.A.R.20,12/-.QCoils, C.P. R.C.C. 5/6ea. 0-30 milliamps Aerial, 15/, H.P.Transformers, 21/, Touch- 0-6 volts and, of course, at the voltages coM.- stone, 30/. pr. For Pentode 3, Super -Six -pin Coils, SUPER POWER 7/6 Res.5000 ohms etc., stooked. Post Extra. monly measured it is very much less Ebonite cut while you wait at CYLDON CONDENSERS SIF,PL.fml Ad. square inch, also t in. at (1 milliampere at 120 volts). Triyle Gang and Shields, £4!1716;Auctethill,'Ltfoorr.,," F4u4.1: 25/6;Syncratunefor H.R. VOLTMETERId. Only the test supplied. LISTS FREE. 7 6 Drilled Panels 'or all Circuits COUPON. M.W. FEB. " TRANSPORTABLE " FOUR ONLY ONE COUPON ON ANYONE ORDER KIT OF COMPONENTS 5/ 9 ;L.T.Switch; 1/6;Single Circuit IN/P CLAROSTAT If you spend 25/- or more you can buy for Jack,0005 Lotus,2/8; P.M. Gambrel] Neut., 5/6; 4 Sprung V. 3d. extra any one (only) of the following: Holders, 5/-; 2 H.F. Chokes (Diwyer-Lowe & Igraine), S.M.Dial100ft7122 Copper Aerie!,12yds. 12/- Lissen R.C.C.Unit,4/.;Igranic Type" J IN Lead-inFuse andHolder,12NickelTerminals. L.F.; 17113; 2-meg. and 2.25 Leaks, 7/6; Holders, 60X Coil. H.F. Choke, Permanent Detector, Battery 3.0003Fixed,41.;Igranic VARIABLE Switch, 0003 and 2-meg. Leak, 9 -volt Grid Bias, 1/6; .001Fixed and 3/6. Panel Brackets, 6 -pin Coil Base. 100 ft.Insulated F" Output Filter Choke, 15/-; Hydra 2 mt. RESISTANCES Aerial, Loud Speaker Silk Cord 30 ft. Covered Con- necting Wire, Ebonite Panel, d x 6, 12 yds. Twin Total 85/3 FOR VOLUME ,TONE, Flex100 ft.Indoor Aerial, Cycle Rear Reflector. For 2/6 extra you can buy with above set of Copper Foil Sheets to specification. material for Frame Aerial DISTANT CONTROL, and Reaction Winding, Flea Wire, H.T. and G.B. Plugs, ELIMINATORS ETC.. SPECIAL. COUPON. best quality Ebonite Panel, 14 a 7and handsome S.M. (Only available at R. Raymond's). Dial.Carriage Paid C.O.D ,1/ As frequently specified by -The Experts: POST or CALL with this coupon, and if See top ofcolumns set of parts for Loud your order is £3 or over FOR 6d. EXTRA t you can buywhne o of thefollowing (state Speakr. HIGH QUALITY LOW PR ICEd. which required): New 20 Page Brocure free on request-, mfd. Mansbridge Condenser; 0005 B.L.F.Vari- ORMONA able Condenser 4In.Slow Motion Dial,100 ft. 140 p.CATALOGUF 3.MDrum Dial, 5/.; Rheo- Many unique circuits. Silk Frame Aerial Wire; 0001 Reaction Condenser; stats, 6, 15, 30 ohm. 4/-;-1 16 -volt Gee Biastapped 11; 12 yds. Extra Heavy ILLUSTRATED Midget0001 max Double Rubber Lead-in;5 -wayBattery Cordfor D Log -0005 and4'Dial, H.T. and L.T.; 10 Engraved Terminals (take plug Eit Log 0003and4. CLAUDE LYONS LTD. or spade), state names requIred. ALLLATEST Dial 5/9.S L.F No.3 DON'T FORGET THE COUPON. M.W. same price. We always stock 76,OLDHALL ST.,LIVERPOOL. COMPONENTS all ORMOND PARTS 221 MODERN WIRELESS February, 1929

`PeY'S5a?C)@ Otgi E,`00c.0f8lEA@OO$D a 7- or 10 -turn coil .placed inside the 03 THE "NEUTRO-SCREEN"s, secondary, while L3 will be 6 or 7 k3 THREE turns wound on as a continuation of the secondary with a fairly fine gauge BIZWd -continued from page 128 of wire, say, 28 D.S.C. As the actual TO PERFECT RADIO Goez-eGrnozzeoezget3onumber of turns for L,may be slightly influenced by the layout, if Next remember that gridleaks In addition to their own extensive you have departed much from the range, PETO SCOTT offer YOU also give rise to noises very often, and layout I have used, it will be advisable Every KnownRadioReceiveror try out a good selection before you to put on about 10 turns and then Component-all on decide which you are going to use. strip them off, a turn at a time, till See that all valve pins are clean and you find the correct number.This EASY TERMS ! making good contact in the holder. The Pets Scott Easy Way atlastsolves your winding will be found to be critical Radio difficulties.Every article known in Radio This also applies to coil -mount pins. to -day may be obtained on Easy Terms from Peto within 1 turn, arid as you take the Scott,andallleading makes arestocked.In See that all connections 'are tight, addition the Easy Way also is available for all turns off you should explore the full kits of parts for Home Construction of sets adver- especially if you have just begun to use tised by leading valve makers,publications, and range of the stabilising condenser. " Modern Wireless " sets. a soldering iron. As a matter of fact, L2 should be 65 to70turns of 27/42 COSSOR MELODY MAKER. Send only 10'-. I know some amateurs who have balance in 11 monthly instalments of 14/7. Litzendraht wound on a 3 -in. former, HULLARD MASTER THREE STAR. soldered their joints for years, and Send only10/-,balance in11 monthly Pay- the aerial coil being coupled to the ments of 15/3. LEADING MAKES OF H.T. ELIMINA- even then a careful examination of end of the secondary that is connected TORS from 4/7 down, balance in 11 monthly payments of 4/7. one of their sets will often reveal a to L.T. ULTRA DOUBLE ACTION AIR COLUMN LOUD SPEAKER. Send only 8/3,balance couple of " dud " joints. in 11 monthly payments of 8/3. BRANDESET THREE. Sendonly 13/4, You will find that the setting of the Matched Tuning balance in 11 monthly payments of 13'4. PHILIPS' TWO -VALVE A.C.MAINS stabilising condenser C2 is not at all For L4 the same winding will be RECEIVER. Send only 12/3, balance in 11 monthly payments of 12/3. critical with the small coils.It will AMPLION LION LOUD SPEAKER. Send correct, so that the two tuning con- only11/-,balancein11 monthly payments only actually need adjusting with the L5 of 11/-. densers keep pretty well in step. Moil Coupon in unsealed envelope under W. stamp. larger coils.This is preferably done will be 10 to 15 turns of 24 D.S.C. with a long ebonite rod filed to a chisel wound in the same direction as L4, To edge at one end, and cutting a slot in the outer ends of the two windings PETO SCOTT Pk the top of the ebonite adjusting handle 77, City Road, London, E.C.1 being connected to grid and anode Please send me your big Illustrated Lists. of 02. respectively.This gives the correct Try the effect of reversing primary NAME connections for reaction to be ob- and secondary windings of your L.F. tained. ADDRESS transformer if you get any signs of M.W. 112. latiinannaanammumannallainnaananamaamE MMMMMMM MOM MI NMI threshold growl.A reversal of con- Freedemonstrationsandadvicebyqualified nections will often cure it. engineers at anyofour shops. THE "TITAN" THREE 77, CITY ROAD, LONDON. E.0.1. On the wave -lengthsbelow20 62, HIGH HOLBORN, LONDON. metres you may find it an advantage E Have you heard about this great 4, MANCHESTER STREET, LIVERPOOL. new 3-valver ? Full construc- 33,WHITELOW ROAD, CHORLTON- to use a small series condenser in the tional details are appearing in CIIN-HARDY. MANCHESTER. aerial lead, or else to use a special small aerial.On several occasions I POPULAR WIRELESS On Sale January 3 zst.In every SOLVE ALL H.T. TROUBLES have triedchanging overinthis = issue will be found a magnificent manner with a marked improvement WET.) in results. 2. FREE BLUE PRINT BATTERIES Make sure of your copy now. On Sale Everywhere, LONG On Broadcast Wave -lengths IrAyilrAir SILENT = Price 3d.. as usual. LIFE LE ECONOMICAL I now want to touch on a very tlllllllllllllllllllllllllllllilllllllllllllllllllllllilllllllllllllllllr interesting application of this set, and SELF that is to broadcast reception.By On plugging these two coils in you CENERATINC using suitable coils this set can be will find that the H.F. amplification JARS ,waxed x W sq. 1/3 doz. 2INCS, new type lid. doz. SACS 1/2 dos. used for broadcast work, and, it will given, after the H.F. stage has been Sample doz.(18 volts), complete with bands andelectrolyte, 4/3, post 9d. be found, will give a degree of ampli- correctly neutralised, is simply enor- Illus. bookletfree. Sample Bargainunit, 6d. list free. fication that I think will be a revela- mous.I have a set built on these AMPLIFI'RS 30/- 3 -VALVE SET £5 H. TAYLOR, 57. Studley Road. tion to you. lines only with another L. stage, STOCKWELL, LONDON. There is one point you want to first built about a year ago, that SOMETHING NEIN!!! watch, and that is the H.F. choke L7. bringsinstationsfromallover "Uncle Tom's" EXPONENTIAL HORN If this is a special short-wave choke Europe at terrific strength.Even in Tried againsttheBEST ontheMarketand it will not be suitable for broadcast daylight itwill bring transmissions provedVastlySUPERIOR tothem ALL. Moviiri Coil and Cone Speakers beaten every time. work ;it will result in the detector like Minster, Frankfurt, Langenberg, Prices from £2 12. 6. to £6, valve going into continuous oscilla- etc. including Unit. Particulars Free. at far too great strength for " 'uncle Tom," PAYNE & HORNSBY, Ltd.. tion. But if you are using a universal Gallowgate, Newcastle -on -Tyne. con;.fort, whileon the long waves it And at Dublin, Sunderland, North Shields. choke you have no alteration what- is equally efficient. ever to make to the set so as to make At night thereare few ofthe it suitable for broadcast work. stations that one usuallyreceives For the coils you will want induct- free of interference that can be borne DARIO Super H.F. ances wound with Litz for secondary fully tuned in, and drastic use of the means Super Radio and anode coilsif you are to get volume control has to be made. thefullbenefits that this setwill If you try out this set on broadcast See page 213. bring you in the way of H.F. am- waves it will be a revelation what plification. The aerial coil L1 may be can be done with three valves. 223 February, 1929 MODERN WIRELESS

tg.a.eooTaeo@ootii5o63,%@@Eg EDITORIAL The only --continued from page 119 EZ1 Universally OgeCAD .11e ova9c3DQZ1?,vgDqk receives £1,000 ;Sir Gordon Nairne, Standardised Dr.MontagueRendallandMrs. Philip Snowden each receiving £700 Component a year.The salary of the Director - General,SirJohn Reith,isnot in Radio definitely known.

Other interesting resultsofthe " Daily Mail " inquiry show that, in 1927, £487,728 8s. 6d. was expended MAKE upon programmes ; there were 68,296 hours of broadcasting ; which means, 4 according to the above figure, that THESEand ii programmes were sent out at an ek el A IN ti 4111k PonvA average cost of £7 2s. 8fd. an hour. MAINt MUNCT! 4 But, as the " Daily Mail " rightly Type B, 4 points out, that is an illusory figure, 6d. for there are many hundreds of hours At Home! Some components are frequently mentioned when one programme served many for use in new circuits-others less fro quently-Belling-Lee inevitably. This con 4 stations, while much of the £487,000 stant recommendation of Belling -Lee ter At Once!! Mualsisno mereaccident.Itfea 4 was spent on persons and things MEN !Here is the chance of a lifetime A GOLDEN tribute to the ingenuity of design and tc Opportunity in every sense of the word.Itis an swervingly high standard of workmanship 4 having no relation to the microphone. opportunityforyoutoparticipateinthe BIG Always associatedwiththeseexcellen ittle products. 4 However, perhaps someofthe PROFITS now being made inthe Electrical and Type B.6d. Type 31,41d. Type It,3d. Wireless Industry-a business which has enlarged 4 mystery of the B.B.C. will be cleared enormously of late years, but which has not yet reached a tenth of the size to which it will eventually up when our readers have read the attain.My new and improvedPatentsarein 4 article on that subject in this issue. increasing demand everywhere because theyare rBETYRET,S!IPEr such an improvement upon all others.This I can 4 prove to you by Certified Tests. AL AAA:. LA A AA/L AAA/ The Ideas Department Baling & Lee, Ltd., Queensway Works, Ponders End. Middlesex. THE formation of the B.B.C. Ideas -:.3 ervt1.1.1%42 Department has long been forecast.As a matter of fact, five Spare Trme years ago Mr. Cecil Lewis put this suggestion before the B.B.C. chiefs, B-usilvess! and at variousotherperiods we The work is so easy that the whole lamily-including lie the children-can help.Even though you have no understand that he has made such knowledge of Wireless or Electricity you can commence at once to turn your spare time into CASH proposals.However, slow but sure and earn anything up to seems to be the B.B.C.'s motto in this respect, and we are glad to note that at last the formation of this 500a Year! essential department has been decided No expensive " plant " or machinery, and no ,special skillis required. Iwill supply you with all details upon, and that Mr. R. E. Jeffrey, Entirely Free of charge.Your Kitchen or any small ey Outbuilding can be your workroom.Nobody can thepopularChiefoftheB.B.C. encroach upon your business; it is protected under DramaticDepartment,hastaken RoyalLetters Patent. over his duties with a full knowledge all of their significance and importance. II GUARANTEE: Your Profits. --Only a limitel number are allowedtoManufacture,so your PAR Market can never be overcrowded. If SCREENS II COILS necessaryIarrangetopurchaseall "THE INSTANTO 2 " your stocks. Thus you are positively STANDARD LOADING COIL.. 7/6 certain of profit ! ticci H.F. CHOKE .. each316 This is not a dying Industry but a rapidly growing TimmoLA "THE NEUTRO-SCREEN 3" one whichiscompetingsuccessfullyagainstbig Alum. Panel, 20 X 7, polished and mottled5/6 Combines. It has been established a decade and is the meal Wireless Cabinet you have offersa tremendous opportunity now. always wanted ,o put th, finishina tou^h Copper Screen, 91 x 61, with flange.. 3/6 to your set.It Is a Writing Bureau, H.F. Choke.. 3/6.Binocular Choke ..6/6 Send at once for Full Free Particulars.Don't hesi- Wire...es Cabinet, Gramophone Storave Copper Foil for" TRANSPORTABLE 4 "1/6 tate-thisisaStraightforward, Genuine, Honest Cabinet, and a beautiful article of furni- Proposition.Commence to eaen casy EXTRA W's ture, too IThink of the delight .it will From your dealer or direct from NOW and becomeanindependent Master man. give you and your friends IThep is 10 Featherstone Bldgs., member that you can have it on seven E.PAROUSSIe HIGH HOLBORN, W.0.1. days' free trial, carr. paid to your borne. 'Phone: Chancery 7010. SENO THIS FORM NO W. In polished oak or mahogany, sold at MM. MEM .11 MIMS =NM 1112 makers'pricebecausewearethe makers. Write for illustra. I "MODERN WIRELESS" COUP ,N ted lists of all models from A / To Mr. V. ENGLAND-RICHARDS, I The England -Richards Co., Ltd., 108, King's Lynn, Norfolk. Keep on Saying Sir,-Please send me at once, and 1.KEL, PICKFTIN Ifulldetails as to how 1 can Make Money Wireless - Cabinets at Home in my spare time. Ienclose 2d. DARIO for Radio stamp for postage. MODERN WORKS, BE XLEY- See page 213 I Print your name and address boldly in capital letters HEATH, Nr. LONDON on a plain sheet of paper and pin this Coupon to it. " Modern Wireless," Febiozo =23 MODERN W IRFLESS February, 1929

o cg,00s5000000000s5o:e.g By throwing the switch over to the e02 right the accumulator is connected in "SAFETY FIRST" -. series with it, so that it is on charge. tE vki: a RADIO V- Care must, of course, be taken to see 2' II31C P ALLINSON,A.M.I.R.E., F.Inst.Pf81 that the polarity is correct, so as not

OGGO&Oec9t9C3C9OcT9f3c.VBC9,830 to run the accumulator down instead 91AVVI of charging it.The usual salt -water INEARLY had an accident the other test will tell you which lead is positive day which would have resulted and which negative. in the loss of one of my favourite It is also advisable when installing accumulators,,much spilled sulphuric a switch of this description, especially acid, and probably much ruined ap- if it is an unprotected switch not of paratus, to say nothing of my suit. the " quick -break" kind, to have it As my lighting supply is D.C. and mounted well away from the battery I have a separate power point off which on charge. Irunanelectricheater,taking Explosive Gases approximately 4 amperes, I usually This is owing to the fact that a bat- charge my L.T.accumulators bytery which is being charged, when it putting theminserieswiththis begins to gas freely in the last stages, t I ftI ASO flf SSW heater. The accumulators are of largegives off oxygen and hydrogen. The capacity, so that this current givesmixture of these two gases, as 'you justaboutthecorrectcharging know, is highly inflammable, and if CELESTION, the Loud -Speaker used by rate. - all the leading national set manufac- Up till now I have had a couple of wilimmumnimininimmunimiummilmmimm: turers,is" Better than you ever heavy flexleads permanently con- dreamt of."Celestion has been acclaimed nected so that I can put the battery " First On Merit-On Demonstration " Are You Collecting -because of its realistic powers of re- on charge. When no battery is being production,its symmetrical beauty charged the ends of the leads are THE NEW and finished craftsmanship, which twisted together. together create an atmosphere of A few days ago I had put a big " P.W." White Prints rare distinction in the most dis- accumulator on charge, and when it cerning home. Hear Celestion provided with every number of for yourself at our show. had come well up and was gassing rooms, one minute from freely I went to take it off. The heater Popular Wireless? E=Ez_ Victoria Station,where was on, and I just loosened off one 7, - you can also hear the finest radioset,. terminal and pulled the lead away. Make sure of your copy BRITISH THROUGHOUT. Fire Just Avoided Unfortunately, the lead was frayed EVERY THURSDAY and one strand was left behind, and as the circuit was broken a 4 -amp. arc was started that burnt up this strand. Price 3d. On Sale Everywhere. The resulting flame ignited the cellu- =E BRITAIN'S BEST RADIO WEEKLY.=2-:- loid case of the accumulator, and had it not been that the top was wet from sprayed acid I am afraid the accumu- present in sufficient quantities may lator, and many other things too, even be explosive. The arc from the switch, if mounted close to the battery, may ignite the mixture,andwithcelluloid -cased //EA TER accumulators the results would be Model C.14. unpleasant. It isalso inadvisable Made under. Licence.Models from L5 to o. therefore to bring a naked light close to a charging accumulator when this SHOWROOMS: is gassing freely, and a case was re- 106, VICTORIA STREET. ported in the papers where a serious fire occurred at an electrician's owing LONDON, S.W.1. to the gases from the batteries being Write for Illustrated Booklet "H." ignited. Where you have electricity in the /47.11 F/G.i workshop it is usually found that one point is not sufficient to supply all would have been a complete " write- your needs, and a flex lead isfre- CELESTION off." quently taken from the ceiling rose, Now I have installed a heavy copper or from a double lamp holder, to give TheVerySoul of5fusic double -pole double -throw switch con- you a handy point on the work bench. nected as shown in the sketch. With It is advisable, however, to take a CELESTION. KINGSTON -9N - THAMES. the switch on theleft the heaterlittle care over the provision of an When a better Loudspeaker is circuit is closed and the, accumulatorextra point. When experimenting, made-Celestionwill makeit. is " dead," i.e. it is not connected to short-circuits occur from time to time, the mains on either side. ._(Continued on _Rage 221) 224 February, 1929 MODERN WIRELESS

ValgUINVq',A0W65WWWWWYTAMT,RM9115 Q"SAFETY FIRST " RADIO g -continued from page 224 (23 6-6RARFYIMIMIM2A2AGLFUZA2Mg2a03%.9;? Doyouknow and if ordihary lighting flex is used it may gradually cause the insulation to the break down at some point. This may result in a partial short, not enough to blow a fuse, but enough to give rise BASEBOARD to a fairly heavy arc. If the wire is strung along a wooden back to the bench, or along a piece of UNIT? batten, or under a wooden shelf used for storing wireless components, a fire may easily be started. wires from a condenserI To be on the safe side, therefore, and a coil,to these 4 you should carry out such wiring with terminals-COMP/ET, lead -covered cable, or else run it in a 3-VA1VE RECEIVER j iron conduit tubing, if you have the skill for it.The former method is, of course, far the easier to handle. The lead covering should be earthed, and this is of especial importance when the mains supply is A.C., for troublesome interference may result with reception from a length of unshielded flex carrying alternating current. Safeguarding the Leads HERE is the Lamplugh Base- When a set is run entirely from boardUnit,thecom- mains, or even where the H.T. supply ponent that makes radio Tracere:difq is provided from mains, especially in setconstructionsimple,and the case of D.C., and the loud speaker guarantees the efficiency of the is installed in a living -room, both loud- finished receiver. witha speaker leads should be condensered The Baseboard Unit consists ofa specially moulded Panel upon which are mounted Valve sl FAN Sockets, Condensers, Trans- RADIO METER formers, in fact all components SCREECH.... WHRH EEOOWEE usually fixed to the Baseboard The Soprano's voice takes on an uncanny resemblance to a vociferous roar. of a Receiver, each in the correct The distortion fiend is at it again, and all position,andproperlywired, enjoyment is gone.Why be put off with this when with a Sifam Radio Meter you thus obviatingtheuncertain can obtain truly perfect reception. Sifam Radio Meters trace and rectify distortion, work of Baseboard Layout. avoid burnt -out valves and run-down bat- The whole unit is surrounded teries, and correctly regulate plate and filament supply. Nearly half -a -million by a metal case (acting as a listeners use them.Ask your dealer or write for leaflet" What Simple Meters screen) and attractively finished Can Show You." Free from Dept. M.W. in crystalline enamel.All ter- SIFAM ELECTRICAL INSTRUM.:N CCO., LTDBush Rouse, AldseYeh, minals are clearly indicated by rArqpsrirqr,wwqr,nrwhvqwwwwwsirmswq raised lettering. h411111111h4ELAUshilltiShAISALAEOlhlIELIIIi4h.111%Att4h4h11its 114 11s4 RA P BASEBOARD UNIT PRICES as'114 PLEASE be sure to mention 118 and a filter circuit should be used as ttld 2 ValveTrans. Couimi 37 6 RA "MODERN WIRELESS" RA shown in Fig. 2.There is always the 50 - X7,1 3 whencommunicating with possibility that someone may catch 3 Resist. 2 3, haPA RA hold of a loud -speaker -terminal and Advertisers. THANKS! Lal RAFrp 12741 place the other hand on something ot ARARARARARARARA connected to earth, and get a nasty Send Wiring F,111:1727241:11a1R,71211F.,1 for full Diagrams, shockif this precaution is not taken. particulars, etc. The Pict ;re Paper with the MOST News Even where the negative main of a :: SUNDAY GRAPHIC :: D.C. supply is earthed there is nevertheless a difference of potential be- LAWN...UGH' tween this main and a direct earth in All Lamplugh Radio Products the house, owing to the voltage drop are gua-anteed for 12 months. Write for the New across the main lead.This may in DARIO some cases amount to as much as 40 S. A. LAMPLUGH Ltd. Folder volts ;enough to give one of your King's Road, See page 213 kiddies, and they are the meddlers, an TYSELEY, BIRMINGHAM exceedingly unpleasant shock. 225 MODFRN WIRELESS . February, 1929

#aaAaa Another cause offaint noisesis dust on the condenser vanes. This may even cause partial short-circuits SHORT-WAVE CONDENSERS between the fixed and moving vanes, which makes thecondenservery By J. ENGLISH. noisy in operation. Even in a totally - enclosed receiver the condensers accu- # mulate dust in a surprisingly short right accurate tuning that any small elec- period, and itis about time some CHOOSING and using the enterprisingmanufacturerbrought type of tuning condenser in a trical or mechanical defects are mag- out a totally -enclosed variable con- short-wave receiver is a matter nified into quite serious faults. A most desirable feature in a receiver denser for short-wave work. of more importance than some ama- Meanwhile, itis a good plan to intendedforshort-wavereception teurs realise.Often mediocre results remove the dust periodicallywith isaperfectlysilentbackground. can be traced to the use of variable oneofthosefluffypipe -cleaners, condenserswhich,althoughgood You do not want loud signals so much enough for tuning on medium and as clear, readable signals, which are which are justtherightsizefor difficult to obtain if the set is at all insertingbetweenthevanes. A better way of cleaning them isto noisy. pass a bunsen flame between the Ensuring Quietness If the receiver isperfectly quiet in operation, then even a weak carrier - wave can be resolved into readable signals, so that the range of reception is dependent to a very large extent on the amount of background noise. Often breathing and scratching noises are traceable to the tuning condenser, if this is of the type where the contact to the moving vanes isa rubbing contact of small area.I have often noticed that the substitution of a variable condenser with a " pigtail " connectiontothemovingvanes /(o). A7/7 produced a very definite improvement in reducing background noise.The F/G /lb) long wave -lengths, are quite unsuitable friction contact type of condenser, 47/8 for a short-wave receiver, by which however, appears to be quite satis- vanes, but not every amateur posses- I mean a receiver tuning below 50 factoryasareactioncontrol on ses a bunsen burner, while the opera- metres or so. short waves, and it is only in the grid tion requires care. The shorterthe wave -length the circuitthatavariablecondenser When making up ashort-wave greater the need for a really good con- with a sound electrical connection set you may be tempted to use a spare denser, because such small variations to both sets of vanes is really neces- variable condenser to save the cost ofcapacityare then required for sary. (Continued on page 227. ) Insiston Condensers

ON! END PLATE ONLY $ALL BEARINGS PIG TAIL ONE HOU MOM CONNECTION You can obtain " Utility " Condensers in Square SMOOTH Law, S.L.F., or Logarithmic pattern illustrated. SURFACE. EASILY The unique mechanical features of these instru- (LEANED HOLLOW ments are emphasised in the illustration ;you TERMINALS INSULATOR can mount them for Thumb -control or Base- AND SOLDERING board operation.IfVernieradjustmentis TAGS BALL naming required we fit the " Utility " 4 -in. slow-motion Dial for the purpose.Ask to see " Utility " GuaranteedComponentsatyourdealers. Write for the " Utility" Catalogue. PRICES R 0 M LTD 7'6 SPACED ',ARES WILKINS LWRIGHT HOLYHEAD RD BIRMINGHAM 47.1 February, 1929 MOURN WIRELESS gegA7iNMOOEM7CEE)000-1 SHORT-WAVE QUALITY CONDENSERS , ---ai c'A--- Eg, -continued from page 226 ET? :.. COUNTS ! "-- COGZS132&1,9t01300&.5:3t9 The persistent high quality, in every way, of Gam-brell Products keeps them ever to the :-.4-- fore.The two described here, the Voluvernia of a new one.This may be of too and the Neutrovernia, have both proved their large a capacity, for even with a worth to those in radio. slow-motion dial a capacity exceeding GAM-BRELL NEUTROVERNIA -0005 mfd. is too big. There are other The fact that this is chosen for inclusion in so reasons why you should use a tuning many commercial sets and receivers described condenser of small capacity. Not in technical papers is proof that itis a real SILENT only is tuning easier but the ratio quality component and one which does its duty as Reaction Control, Balancing Con- PRICE between coil inductance and tuning denser or Neutralising Condenser with ELIMINATORS capacity is higher, which gives you perfect efficiency. 5,6 The secret of obtaining powerful, silent, and enduring results better signal strength. GAM-BRELL from the H.T. or L.T. Elimina- It is now generally accepted that VOLUVERNIA tor you are about to build de- atuningcondenser pends entirely upon the right of-0003,or, A small, neat, compact betterstill,-00025 mfd.capacity, and efficient Volume selection of its component parts. Control. The move- Success with SUPRECISION istherightsizeforshort-wave ment is smooth and Power transformers and chokes tuning, while for reception below 20 velvety andgivesa is a guaranteed certainty. Specify continuous and evenly them and you follow the lead of metres I prefer a variable condenser variable controlof thousands of satisfied Customers. of .00015 mfd. capacity.If you want volume from full How to build your own Elimina- yourset strengthrightdown to tune over the most to nothing.Its yes:st- tor inexpensively is explained in interestingwave -bandof, the new list 935. Any output say, 15 ance value makesit obtainable from 2 voltsto 500 to 50 metres, then a compromise also suitable foruse volts. with Gramophone must be made, using a condenser The pick-ups. Write, 'phone or call. of -0002 mfd. capacity. Voluvernie PRICE 6/9 Please write for the Gans-brell Components Booklet C) F. C. HEAYBERD & CO., A Useful Scheme 8/9, Talbot Court, Easteheap, E.C.3. Some receiversaredesignedto GAMBRELL RADIO, LTD. (One minute from Nonument tinderground4t a.) receive on both medium and short 6, Buckingham St., Strand, London, W.C.2. waves, in which case the ideal variable condenser for the short-wave range r DON'T COVET':is too small for the medium -wave Your Neighbour's Wireless Set range.A condenser of -0005 mfd. A BUILD YOUR OWN RECEIVER- II capacityisabout right for wave- BUT BE SURE to Buy on the Best Better Terms from THE P.D.P. CO., LTD. lengths between 250 and 550 metres,

and a recognised expedient for re- Terminal EVERYTHING WIRELESSII ducing its capacity for short-wave i work is to arrange for a small fixed aEASYTERMS;condenser to be switched in series . New Cossor Melody Maker. Master Three with it when changing over to the a Star, etc. a BEST MONTHLYTERMS: short waves. CLIIC IN quoted by return for all Receivers I This is quite a good way of getting PANEL I and Components. I over the difficulty, because, although TERMINAL e 111 the tuning condenser has a nominal CASH ORDERS promptly ev ed COILS for ALL Receivers supplied. value of -0005 mfd., the fixed con- Goods sent C.O.D. by return. ii 4° Call at showrooms or post your Ascot requirements. Ill denser in series makes its effective IThe P.D.P. Co., Ltd. ! maximum capacity smaller, according Better in many ways.It takes Seale, Pin or (Dept. M), 121, CHEAPSIDE, London, E.C.2. to the size of the fixed condenser. bare wire connection quickly and gives perfect [WM 'Phone: City 9E46.0RPRIII contact. Has polished insulated knob with If this is -0005 mfd.. then the variable metal inserts.The non -soldering wiring device gives excellent contact and makes assembly 4111MIMINIEr condenser becomes one of -00025 mfd. easier.Is highly nickel -plated and improves WIOIFING COILS capacity,whichisjustrightfor the appearance and performance of any receiver. Send for our FREE new rozo edition short-wave work.A good idea is C 7.4 I X 36 -pagebooklet TO -DAY. Ittells to arrange for a second fixed con- SPADE TERMINALS all about moving -coil loudspeakers, " Clix "Spade Terminals are far and how togetperfectreception. denser to be inserted in series for ahead of all other makes because BAKER'SSELHURST RADIO, wave -lengths or the patented Bridge Wiring Chan- 89, Selhurst Road, South Norwood, S.E.25. below 20 metres nels and Shank Slot present the Also manufacturers of Wzreless so,its capacity being.0004 mfd., mosteffectiveandconvenient Receiver components. means of wire attachment ever which will bring the main tuning devised.Made of best brass, and condenser down to a fraction over obtainable either nickel -plated or lead -plated for accumulators. Red .00015 mid., the capacity mentioned or Black Insulators.Obtainable in two sizes suited to all types of above forthis wave -band. These Screw Terminals. DAR1O fixed condensers should be connected as shown in Fig. 1(a), which illus- PRICE 2d, EACH This week's best bargain Ask your dealer of write for the Clix Catalogue See page 213. trates severalotherpointsabout IAECTEtC) LINX LTD. short-wave condensers. 254, Vauxhall Bridge Road, S.W.I (Continued on page 228.) 227 Aft MODERN WIRELESS rebruary, 1929 ti00@0%%RrgR64.7,0,%EM0005,`, " straight-line "typeforreactionThis is used as shown in Fig. 2(a), SHORT-WAVE 66 control. The capacity of the reactionone-half being the series feed con- condenser depends upon the circuitdenser and the other half the throttle CONDENSERS of the receiver, and in the diagram control.As the moving vanes are -continued from page 227 66 of Fig. 1 you will find recommendedrotated the capacity ofone con- 46 Ofdcri')G134;9cMC3c834M8f90f3f9ee'46" denser is increased as the capacity of the other is decreased. When choosing a condenser for Thisprovidesaveryefficient short-wave work preference should reaction control and, at the same time, be given to the condenser in which the capacity across the transformer the vanes are specially- shaped for primary is always the same, which is better for quality than the usual straight-line tuning, either straight- - line frequency or straight-line wave- throttle -control arrangement. A con- length. Low -lossconstruction is stant shunt caiacity of this nature highly desirable and a small, compact also has less effect on tuning when condenser isuseful, asitssmaller making reaction adjustments. The external field ,gives less trouble due circuit of Fig. 2(a) can be somewhat to stray -capacity couplings. troublesome as regards hand -capacity effects; but the modification in Fig. The Reaction Control 2(b) is free from such troubles. For your reaction control condenser A Curious Feature you can use any of the standard capacities for the various well-known types, and, as mentioned before, there An interesting feature arising out of circuits. isno need , for a .special low -loss connecting a fixed condenser in series component, although one with a pig- In each case you will see that a withavariableoneisthat the small fiXed condenser is inserted in characteristicsof thevariableare series with the reaction condenser considerablyaltered. TheS.L.F. chiefly as a safeguard against shorting and S.L.W. 'type, for example, be- the H.T. supply.This fixed series comes very much like condensers with condenser should always be used, but do not insert any condenser regardless of its capacity. Double Condensers In the by-pass control system of Fig.1(c),for example, theseries condenser C4 is virtually connected across the transformer or 'phones so that if it exceeds .0005 mfd. capacity the total capacity, with C2 C, in parallel, will be too much for good quality. This is a point to be watched when making up a set to receive on both short and medium wave -lengths. tail connection is to be preferred ; A particularlyusefulcondenser evenacondenserwiththeold- forthrottlecontrolin short-wave circularvanes,andthischanged fashioned circular vanes can be pressed sets is the double condenser, such as capacity -characteristicproducesa into service, as there is no advantage the Pye differential condenser andcrowding of wave -lengths over the inusing an S.L.F.or any other the Igranic screened double condenser. lower readings of the condenser.

PAGE PAGE Gambrell Radio, Ltd... 227 Premier Accumulator Co. (1921), Ltd. .. 207 INDEX TO ADVERTISERS Garnett, Whiteley & Co., Ltd. 197 P.D.P. Co., Ltd... Graham Amplion, Ltd. .. 117 Popular Wireless " 217

PAGE Heayberd, F. C., & Co...... , 227 Raymond, K. .. 221 211 Baker's Selhurst Radio .. 227 Hughes, F. A., & Co., Ltd... Ready Radio Supply Co. .. . 218 Bedford Electrical it: Radio Co., Ltd. 217 R.I. & Farley, Ltd. .. : :Cover iv Belling & Lee, Ltd. .. 223 Igranic Electric Co., Ltd. ..213 Rothermel Corporation, Ltd. ..205 Benjamin Electric, Ltd. 217 lumex Electrical, Ltd. ..213, 2.2.2, 223,225, 227 Bowyer -Lowe Co. Ltd. 211 Six -Sixty Radio Company.. 191 British General Mfg. Co., Ltd... 207 Jackson Bros. 220 Sifam Electrical Inst. Co., Ltd. .. 225 Brown, S. G., Ltd. 209 Squire, F. 219 Burne-Jones & Co., Ltd. 212 Burton, C F. & H. 219 Laujplugh, S. A., Ltd..... 225 Lectro-Lhix, Ltd...... 227 Taylor, M...... 222 Lewis, S. W., & Co., Ltd...... 215 Telegraph Condenser Co., Ltd... 189 Carrington Mfg. Co., Ltd. 215 Lissen, Limited ...... 185 Telsen Electric Co., Ltd. .... 216 Celestion Radio Co. .. 224 London Elec. Wire Co. & Smiths Ltd. ' .. 194 Town & Country Homes .... 201 Clarke H., & Co. (M/cr.), Ltd... 215 Lyons, Claude, Ltd. .: ...... 221 !I Cossor, A. C., Ltd... 1.111, 203 Whiteley, Bonham & Co. Ltd. .. 215 Marconiphone Co., Ltd. .. ..207, 214 Wilkins & Wright, Ltd. .. 220 Day. Will, Ltd. .. . 216 Net-Yick Supplies, Ltd. .. , ..Cover iii Wireless Constructor " Envelopes'. 219 Dubilier Condenser Co. (1925), Ltd... 194 . .." 217 Millard Wireless Service Co., Ltd..Cover it Eastick, J. J., & Sons.. 217 AU communications concerning advertising

England -Richards Co. Ltd. 223 Paroussi, E. (PAREX) 223 in "Modern Wireless " must be made to Payne & Hornsby 222 John H. Lile, Ltd., 4, Ludgate Circus, London, Ferranti, Limited ... 193 Peto-Scott Co., Ltd... 222 E.C.4. Telephone :City 7261. Form° Company.. 215 Pickett's Cabinet Works .. 223 228 Din February, 1929 MODERN WIRELESS

% bt 44 bt 44 % % 44 % 44 Ns, 49 4/ bt WHY WORRY WITH BATTERIES? 44 bt 49 bt 44 bt 4451. 44 b, 44 bt 4N St % 4N St 441' 44 bt 44 bt 44 bt 49 bt IN I, 44 bt 49 bt 49 bt 46 bt 44 bt 44 bt 49 bt 44 4 44 bt 46 St 49 % Model "B" 49 bt 46 bt 44 bt 49 bt 49 % Eliminator. 46 bt 49 St 44 5' bt 49 bt 44 bt 44 bt 49 % 49 bt 44 4, 43bt 491. By substituting Met -Vick all -electric Valves foryour 44 44 St 44 bt existing valves the new Met -Vick Model ' B' Eliminator 441. 49 % enables you to dispense with batteries altogether, and IN4 % operate straight off your Electric Supply. 4i 4 444bt 4.61 441 44 % 49%St Connected to a wall plug or lamp socket, the model 4N% bt 4bt " B " will provide you with heater current for your 4 bt sob 44 bt valvefilaments, 5tappings for the hightension 44 St 49 bt IN 4 441' supply to your valves, and automatically regulated -49 bt 446, grid bias taps for your last stage. 49 St 46 1. 44bt 44bt 4451. 44 bt Model " B " Eliminators can also be obtained for 491' 44 bt 44 bt 44 St supplying H.T. and G.B. only. 44 5' 44 bt 49 bt 49 % IN % 49 % Prices of' Met -Vick' Model 49 St 4i* L.T., H.T. & G.B. B' Eliminators for providing H.T.& G . B. 49 St bt 180 Volts on the last valve. 49% % Complete with S.P. 41 U recti- 49 St 44* £8 0 0 fying valves.100-110 volts or £7 7 0 bt 44 St A specialmodelfor 200-250 volts, 40-100 periods. A special modelfor 46 bt 25 periods issupplied 25 periods is supplied 44bt at 510 0 0 at 5950 44 St 44 bt List M.S. 4745 List M.S. 4746. 44 bt % Ask for leaflets shown. 46 bt 44bt 46 bt bt 44 bt 44 bt These eliminators are eminently suitablefor the operation of the Met -Vick A.N.P. 44 bt 441 receivers described in leaflets S.P. 711712 and S.P. 711714 and for 3 and 4 valve 44 St 441 receivers listed in leaflet M.S. 4742. 44 4 49 bt 44 bt bt 49 bt % 49 4 44 St 44% 44. 49 5* MET-VICK 49 6, % 44 b, 44 bt 4% 4 44 bt ELIMINATORS 44 bt % 49 bt 44 bt Other types of Met -Vick Eliminators for A.C. and D.C. circuits are briefly referred to 44 bt 49 % below and the corresponding leaflet numbers given. 44 bt 44 % 4i 6, 44 St Ask your own dealer for copies or write direct to 44 bt 44 bt 44 bt bt Metro -Vick Supplies Ltd., 155, Charing Cross Rd., London, W.C.2. 49 % 4ibt 441 44%1. 44 % 44 bt bt 4i bt % 496, % 44 bt 44bt Stous,4541. 44 bt % 141. 49 so We are exhibiting at the British Industries Fair, Birmingham, February 18th to March 1st. Stand 20M 16 Ss iii MODERN WIRELESS February,119 6ratnoplion ,(10evr trgirw,:'eirw 0

thanksk)this WONDERFUL l+ PICKUP Old-ish records sound new, s. and new-ish records sound "brand new" when you're using the R.I. & Varley Com- pound Mass Suspension Pick- up.High notes are brought out in all their brilliance, low notes in all their depth, and the richness of reproduction over the whole musical scale is something to be wondered at. " Chatter " and " Distortion " are abolished-the wear on the record isreduced to a minimum. By its exclusive principle of Compound Mass Suspension of the Moving Parts the R.I. & Varley Pick-up abolishes these evils without recourse to excessive "damping,"whichisalways harmful to the records. The R.I. & Varley Pick-up has set a new standard for gramophone reproduction. Buy one and note the difference in your instrument. PRICE £3:3:0

THE MARK OF BETTER RADIO

Kingsway House, 503, Kingsway, London, W.C.2.Telephone: Holborn 5303. Prnted and published by the Amalgamated Press, Ltd., Fleetway House, Farringdon St., London, E.C.4, 'on the let of each month.Address for advertisements on y : John EL Lile, Ltd., 4, Ludgate Circus, E.C.4.Telephone : City 7281.Registered for transmission by Canadian Magazine Post.Subscription rates :Inland and Abroad, 17/- per annum ;8/6 for six months.Sole Agents-Australasia :Gordon & Gotch (Australasia), Ltd. ; South Africa : Central News Agency, Ltd. -February, 1929. T) It

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