Remarkable Newamplifier Design

MAROHI 1928

A REMARKABLE NEWAMPLIFIER DESIGN

PERCTAVHARR1S THE WIRELESS CONSTRUCTOR March, 1928

The master set that brings in station after station in daylight In One Hour without soldering, you can build the Mullard Master Three-the receiver that makes the most efficient use of three valves. Only 20 Wires to connect to terminals once you have mounted the few components by using the 20' Simplified Plan of Assembly sup- Only jrPs plied FREE. in Onenotres Easy to Handle. Only one dial for tuning,another for volume. As simple to operate as setting the hands of a clock. Wonderful Results are certain. You have a choice of six or more programmes at loud speaker strength. The Build the Mullard Master Three Editor, now !The cheapest and simplest 3 - Thre "Radio for the Million," valve receiver ever designed. 63, Lincoln's Inn Fields, London,W.C.2 Please send me FREE complete instructions and Simpli- fied Plan of Assembly for the MULLARD MASTER THREE & No. 5 Mullard " RADIO FOR THE MILLION " NAME (Block Letters) . MASTER RADIO Address W (ion. 2 March, 1928 THE WIRELESS CONSTRUCTOR

tc115-.40.721-4,+-11-ZTWAISIVLWRINKSZ-0114,111SIN +..iferNe2S".40:".WAila CONTENTS

Page Page The Editor's Chat 339 The " Sentry " Wave -meter In Action 365 Super Quality With Any Set 341 " The Cottager " 367 Using The 31 Tested Circuits 347 More About The " Business Man's Four "371 A Meeting of The Masters 349 Happenings At Savoy Hill 375 What Is a Mains Unit? 351 In Lighter Vein . . . 379 382 More About The " Short -WaveThree " 357 A Simple Plug And Jack rs Queer Queries 358 More Light On The H.T. Battery 385 A " Three " For Spare Parts 359 Within The Vacuum 392 What's New 394 The " Radian Three " . 363 Continental Broadcasts 364 Our News Bulletin 398

EDITED BY

IIIIIII H PERCY W. HARRIS, M.I.R.E. a' (t3

II 6c, ul 11 Dill ,..assliWi\iansmassum 1

THE PROPER ir'01c0;4-1 SELECTION OF ikfy A/fib/704:01/ VALVES iyA

For the convenience of experimen- ',)Se/'1;(1:///fi ters and listeners, the Marconiphone Company have tabulatedtheresults of numerous laboratory teats and design factors in theirbook " 500Marconi Valve Combinations." It is possible, withthisbook, toascertain thecorrect combination of valves for maximum results This book in any circuit.

For instance, a singleglanceshows you that thecorrect2 -volt valvestouse in a 5 -valve is 2 Anode -bend FREE circuit hooked up as H.F., Detector, 2 L.F.(one Resistance -Capacity, one Fill in the coupon below and we wi!l send you, free and Transformer) are-First,Marconi D.E.L.210, post free, a copy of " 50o Marconi Valve Combinations." Second, D.E.L.210,Third, D.E.H.210, This shows you, ata glance, the correct valves for of Fourth,D.E.L.210, Fifth 1,2,3,4, and 5 valve circuits using 2, 4 or 6 volts L.T. supply.It gives full details of impedance value, D.E.P.240. amplification factor and anode voltage ofthe valves themselvesaswellastheircharacteristiccurves. p`..;I:z;:44 . We shall be pleased to send you, too, a c0Vi 0.4,1?Pl1144c012,6, copy of that amusing little book," Back 6,.a Conroy Chat."Just unite "B.C." us the coupon. e 4tri 0,2s..,e/.pfr con 040, V:4epi?CONli Name el Address 4-IngthatVALVES W .C.12 valve should do 337 THE WIRELESS CONSTRUCTOR March, 1928 tOidtT T veiS°RE TOO

Read thisextract ii,,, from the "Wireless

I note . 1; ques t szont A,,am h aithi nee rom711 the. Bing eyktl, The de Certah, ;,:e are -"'reelc.vk n1 d sadb t-11:: Bahlto" fa "valr g o Thirtyt (a) (b) ficahe To fd mu)t of p, ia 171e, stat'ona is wne s. d Po4r, tta d atnot And L.3. IVit De a rested, d ' many :' .the E'S right. h. . build We are modest in our claims controh nd puck veyemzght oth for the Cossor " Melody Maker." We rwis. -0i.--'deterred a" b'ing Decomeiti:192; 6- Hdo not believe in over -statement.We &ad. St.Ans4Po know that we can say, truthfully, thatanyone 1 who builds the Cossor" Melody Maker " according to instructions will, without difficulty, obtain broadcasting concerts fromseven countries.That, in itself, is a remarkable statement.Yet Mr. Rowett, in a corner of England which is notoriously bad for Wire- less reception, gets results which surpass all our claims.Nor is he alone.From Land's End to John O'Groats comes a daily stream of thanks from satisfied users. Each one tells of new stations heard-stations in all parts of the continent ... even of American broadcasting. And every letter that comes isan- .... other link in the chain of evidence which 4 y ORA STS. proves the record -shattering efficiency of the wonderful Cossor "Melody Maker." " Cheap,easyto buildandrun,"says Mr. Rowett.Ask your Dealer for the free chart, " How to build the Cossor' Melody Maker' ", and see for yourself. IN OURCossor CLAIMS FORTHE 46MelodyMaker"

Advt. A.C. Cosset. ffighburY Grove. London.N.5.

ra\n1433 March. 1928 THE WIRELESS CONSTRUCTOR

WIRELESSCliNSTRUCTOR

Edited by PERCY W. HARRIS. M.I.R.E - Published by the Amalgamated Press, Fleetway House, Farringdon Street, E.C.4. THE EDITOR'S CHAT Percy W. Harris, M.I.R.E., the Editor of the " Wireless Constructor," hasan interesting chat on the question of purity of reproduction in wireless receivers.

AVERY interestingtestwas cast programmes isin most cases Prophecy inwirelessmattersis recentlyconductedforthe used as a kind of " background " in more than ordinarily dangerous. With purposeoffindingwhether thehome,concentratedattention the coming ofbroadcasting many the average listener prefers what may being given to the broadcast only people confidently predicted the death be termed a " pleasing " reproduction occasionally when some special item of the gramophone industry, which, or genuine fidelityofspeech and makes a particular appeal.Actual as readers know, is now in a far music.Twoloudspeakerswere fidelityofreproductionin many healthier position than ever before. used-one a most modern moving cases takes second place to a general Two years ago the Editor of this coiltypecapableofreproducing pleasing effect, and in this, as in so journal was told by a prominent with very great faithfulness all the many other affairs, " one man's meat manufacturer that within a couple tones normally broadcast, and the other a good modern cone type which. while considerably better than the average horn speaker, gave a reproduction rather deficient in the low tones. An Interesting Test The test was made before a number ofpeople andwithoutexception they exclaimed that the reproduction by the moving -coil instrument was " wonderful "-as, in fact, it was- theeffectbeingalmostweirdly natural.But the test did not stop there.After about half an hour's audition a number of listeners began to waver in their allegiance. Without disputing that the moving -coil instrument gave a much more natural reproductionseveralofferedthe opinion tha't for " general listening " the cone type seemed more " pleasing," although if they wanted to sit down and listen to, say, a Queen's AU that remained of the 210 -ft. mast and the wireless equipment of the Radio Hall concert or one of the excellent Research Board station at Ditton Park after a devastating fire which broke out in the laboratory. The mast, blazing furiously, crashed down on the main shed, forming classical programmes which the B.B.C. a terrible and majestic spectacle. occasionallybroadcast they would certainly prefer the moving coil type. isanother man's poison." Con- of years home construction would be sidering loud -speaker reproduction in dead.This particular prophet has Dangerous to Prophesy ! this light we can see why some people now turned practically all his business The result of this test rather con- prefer the horn type and others the over to the manufacture of com- firms the view we have formed that cone, and why there is no one loud ponents for the home constructor. loud -speaker reproduction of broad- speaker which pleases everybody. The advent of cone loud speakers 339 THE WIRELESS CONSTRUCTOR March, 1928 The Editor's Chat-continued led ninny people to predict that the ern type of moving coil loud speaker, deal of misconception exists regarding horn type would soon " pass out," and at the same time to be capable these useful accessories.A special yet there are a number of signs thatof giving a wonderfully good repro- article this month, to be followed by certain new horn loud speakers, giving ductionon any typeofspeaker. a further article in the next issue, a marvellously improved reproduction, deals with the whole subject of mains will shortly be available. The Quest for Quality units, the way they work, how they The fact is, that progress is rarely While to give its full output -a large, should be chosen, and the results of a made along straight or clearly defined demand is made upon one's high- numberoflaboratorytestsand lines.The qualityof reproduction tension supply, it can be used in a experiments.The subject is one of given by gramophones when broad- variety of ways-all giving excellent very great interest, and the home castilig started was very low com- reproduction-according to the high- constructing aspect is being carefully pared with that obtainable now, and tension current available. A particular considered in both articles.Every much of the improvement owes its feature which will make a wide appeal readerwillbeinterestedinthe origin tobroadcasting,forinthe is that the amplifier as a whole can article, whether or not he liras in mind recording studios, microphones and be joined up to any existingset, the home construction of a mains amplifiers almost identical with those home -constructedorfactory -built, unit, for it will help him to under- used in radio are taking the place of without altering a single wire in the stand why someof' the shoddy the old trumpet, while the technique receiver,it only being necessary to " eliminators " of foreignmanu- has developed along lines which have withdraw the detector valve from the facturegive thoroughly bad results shown themselves to be so successful receiver and to substitute forita when tried at home, although at a in broadcast transmission. And now plug connected by a flexible lead to demonstrationtheyappearquite with the use of electrical pick-ups it the amplifier.The detector valve is good. Fortunately, the British manu- is possible to play a record through then placed in the amplifier, where facturer is more conscientious than one's own loud speaker so that one provision is made for it, and the whole some ofhis foreignrivals, and a can have " fresh " or " preserved. " amplifierunitisthereuponauto- number of excellent mains units are music at will. matically substituted for any existing now available at reasonable prices. note -magnifiers in theset. Many Fidelity First receivers are giving excellent service High Tension The remarkable fidelity of repro- in every respect other than quality, The word " reasonable "isused duction obtainable with the moving and this amplifier will now enable deliberately,forawell-builtand coil type of loud speaker, such as that any user to get, the high quality which thoroughly reliable high-tension unit described in last month's issue, has led he has so long desired. cannot possibly be produced for the research workers and experimenters priceofanordinaryhigh-tension to pay much more attention to ampli- "The Cottager " battery.In the case of two different fiers, the defects of which a good So much forloud -speaker repro- makesofhigh-tensionunit,one moving -coil loud speaker will show duction.At the other end of the priced at, say, four pounds and the up very prominently.An amplifier scale,forthose whodesireonly other at ten pounds, both may be good enough to do justice to a moving - telephone reception, I can particularly excellentvalue,orneithercheap. coil loud speaker will, when turned commend " The Cottager " set, which The high-tension supply being such on to a cone or horn type, give a will come as a boon to many thousands a vital point in all wirele,ss experi- reproduction far better than one had of listeners who want a very simple ments, readers will be glad to find previously imagined possible with the setfor 'phone reproduction on the afurtherarticleonhigh-tension latter type of instrument, sothat local station only.I must leave it batteries and their performance. Both progress is being made along several to Mr. Wootton to tell you how the this and the article which appeared lines simultaneously. set has been designed. inlast month's issue have necessi- In this issue a design is given for a Many queries reachthis journal tated hundreds of tests on practically form of amplifier which has proved to relating to what are called " mains all the high-tension batteries on the be admirably suited to the most mod- units," and it is evident that a great market, and are thus unique.

Low Tension

310 March, 1928 TIlE WIRELESS CONSTRUCTOR LIFEROUALI TY WITH ANY SET A REMARKABLE NEW AMPLIFIER DESIGN 13Y "PERCY W. I-1 ARIUS M. I .R .E

A really modern L.F. amplifier, which can be plugged into any set-without disturbing the present L.F. side-to ensure good quality reproduction, and plenty of volume, when really first-class results on the " local " arc required.

THERE are threefactors which actually so.It is,nevertheless, so it. Thistype,ofcourse,isthe go to make up first-class quality nearly perfect that if the other two " moving coil," a description of which reproduction-the actual trans- factors are properly looked after the has already appeared in these pages. mission itself, the receiver used to reproduction possible can be far better Such speakers, when properly made, pick up the transmitted programme, than ninety-nine out of a hundred reproduce with remarkable fidelity, and the loud speaker which converts people would credit. giving a uniformity of reproduction the electrical energy into sound waves. which, while it is still some way below Two of these may be perfect, but if the Loud -Speaker Variations the ideal, is considerably better than third is faulty we cannot possibly get Receivers, as a whole, are unfor- that given by any other type.The that high-grade reproduction which tunately quite mediocre in their per- moving coil types, however, are by is the aim of every serious experi- formance.There are thousands, or no means so convenient or so sensitive menter. even hundreds of thousands, of sets as other kinds, and thus in their pre- Let us consider these three factors now in use which,insensitivity, sent form remain the less popular, separately.First of all, the broadcast selectivity, and tuning are up to all while their first cost is rather pro- transmission must be of the highest normal requirements, but in quality of hibitive unless home-made. quality,Here the British listener is reproduction are far below what they In the- next class come the many indeed fortunate, for the fidelity of might be. cone speakers, deservedly popular, as transmission from our stations is un- So far as the loud speakers are con- they reproduce many of the low tones ,rivalled in any other part of the world. cerned, there is only one type which which are quite absent from the re- For the purpose of this article theat present can do full justice to the productions given by the average transmission will ba considered as broadcast transmission even when a horn type of loud speaker. A careful perfect, although, of course, it is not first -grade receiver is used to "Iced " survey of the field has shown that the

No panel is required for this amplifier, as no controls of any sort are needed.This photograph is a valuable guide as to the layout and wiring of the components, and should be used in conjunction with the wiring diagram given on another page. 341 THE WIRELESS CONSTRUCTOR March, 1928

Super Quality withany Set --continued average modern cone type is capable operation, and if required it will pro- at least some is there. A good moving - ofreproductionwithremarkable vide sufficient modulated energy to coil loud speaker probably starts its faithfulness, and that very few sets actuatea first-classmoving -coil reproduction somewhere about sixty, are capable of doing justice to even speaker similar to that described in or eighty cycles, and specially con- this type. our last issue. structed ones can be made to go much lower.I recently had the op- *3 portunity of hearing one of these 142 which is capable of going down to 1.4)111 thirty cycles, but very special care ANODEhfr. has had to be taken in the design to enable this to be done.

COMPONENTS REQUIRED. 4 Anti -phonic valve sockets (Ashley, Benjamin,Bowyer -Lowe,B.T.H., Burndept, Burne-Jones, G.E.C., IgranicvLotus, W.B.,C.E.Pre- cision, etc.). I Fixedresistor(Any goodmake, to suit valves). 1 Terminal strip with ten terminals as shown (Eelex terminals have been used and suitthisamplifier very well). 1 Fixed condenser, .0001 mfd.(Lis- sen, Dubilier, Atlas, Mullard, Igranic, T.C.C., etc., etc.). 1 Fixed condenser, -0005 mfd.(Lis, The purpose of this article is to tell Before proceeding with construc- sen, Dubilier, Atlas, Mullard, readers of the WIRELESS CONSTRUC- tional details it is necessary to present Igranic, T.C.C., etc., etc.). TOR how they can build for themselves a number of facts, many of which will 1 Mica fixed condenser, -05 mfd. (Du- bilier, Mullard, T.C.C., etc.). a supplementary amplifier which can be new to most readers, in order that 2 Grid -leak holders (Dubilier Dumet- be plugged into any .set (home orwe can see why the apparatus is ohm holder). (Mullard, Lissen Coin- factory built) without altering any developed along the lines mentioned, binator, etc.) wires in the existing receiver, in such and how it is that the average set and IGridleak,z megohm(Mullard, Dubilier, Lissen, Igranic, etc.). a way that the present audio -fre- amplifier falls down so badly when 1 Gridleak, megohm(Mullard, quency side(everythingafterthe low notes have to be reproduced. Dubilier, Lissen, Igranic, etc.). detector)iscut out and the new 1 Anode -resistance in holder (Dubilier, modern amplifier,to be described, Those Low Notes Mullard, R.I.-Varley, C.E. Precision, etc.). substituted.This means that first- The stations of the British Broad- 1 On -and -off switch (Igranic, L. & P., class quality and volume, are obtain- castingCorporationreproduceall Benjamin, Lotus, etc.). able from even the cheapest valve frequencies above about thirty cycles 1 Radio -frequency choke (That shownisa Climax. R.I.-Varley, set, no matter how badly its audio - per second up to some 6,000 or 8,000, Magnum, Bowyer -Lowe,Cosmos, frequency side may be behaving at or even more.The proportionate Lissen, Marconiphonc, Ormond, the moment.Furthermore, the am- amount of energytransmitted on etc., can be used). plifierisextremelyflexibleinits thirty to fifty cveles is not large, but 3 Mansbridge - t ype condensers, 1 mfd. (Lissen,Dubilier, T.C.C., Millard, etc.). 1 Push-pull input transformer(R.I.- Varley). 1 Push-pull output transformer (R.I.- Varley). NOTE.-The R.I.-Varleystraight- line transformer is so arranged that it can be used either as the ordinary type of transformer or as the push- pull.

A very large number of horn loud speakers reproduce nothing whatever below about 150 cycles ;and the best type of cone speaker, while repro- The amplifier with valves in position. ducing tones lower than this, does not The first is of the reproduce them very efficiently.The R.C. type, for this has to act as dc - averagecone,however, reproduces lector if the amplifier is to be used on an ordinary set, the plug being the low tones to a far greater extent inserted in the detector valve socket of the receiver. than the ordinary horn type, although The next valve is of the power type, while if super- power valves are usid for the last stage the 95-meg- it is possible by building a very large elm I leak shown in the foreground has to be re,nored. horn of special shape to come down 342 March, 1928 THE WIRELESS CONSTRUCTOR Super Quality withany Set-continued possibly as low as any speaker thatvolume than we can possibly stand overloaded.It may come as a sur- can be made. Such instruments,in our room !What is more, every- prise to readers to learn that a hundred nevertheless, are totally unsuited forone says the reproduction of my times as much energy may be required - use in the ordinary living -room. loud speaker is practically perfect ! to give the same intensity of sound More Power Required If I run the set at all loudly it rattles on a low note as on a high, and while the loud speaker." quite a small grid swing may be The next point, and one which is " Rattling the loud speaker "is sufficient to reproduce all sounds with- both enormously important and barely quite a good description of the sound out distortion above, say, 200 cycles, realised by the average listener, is that that is heard, but in nine cases out of and with a volume quite enough for if one listens to two notes, one a high ten-I might even say in ninety-nine any room, as we go down the scale and the other a very low note, so thatcases out of a hundred-this rattle so the grid swing necessary becomes both seem to the ear to be of equalhas nothing whatever to do with the greater and greater. intensity but different in pitch, theloud speaker, but it is simply an indi- For low note reproduction we must amount of energy required to give thecation that the last valve is being have a valve which will stand a grid low note is greatly in excess of that needed to give the high note.This, indeed, is one of our biggest problems sa in radio reproduction, as the genera- tion ofthe deep tones requires a Special transformers have to be employed, with windings arranged for verygreatexpenditure of energy. push-pull amplification. Some realisation of this may have come to the reader who has had the opportunity of listening to a deep organ note quite close to the organ. Although the sound does not seem particularly intense, the movement of air required is so great that one can positively feel the air pressure on the skin. The variations of current required in our loud -speaker winding to produce the sounds we hear, come, of course, from variations in the plate current of the output valve.These variations are caused by changes of gridvoltage, and the greaterthe plate current change the greater the grid voltage change or " grid swing " necessary to produce it. Question of Grid Swing As variations of current in the plate circuit mean a variation of voltage in the grid circuit, we can soon arrive at a point where the question can be asked, what is the minimum variation of grid voltage required to give us satisfactory reproduction of the low notes (down to abeut eighty cycles)in an ordinary living -room ? The answer israther disconcerting for it can easily be shown if one has the apparatus(asin the case in my laboratory) that with a really efficient type of moving -coil speaker a grid swing of 25 volts either side of the working point is required !This is when using the push-pull type of amplifier to be described, and suitable output valves. " But," exclaims the reader, " this is nonsense !I am only using nine volts on apower valveand 120A general view taken from the detector socket end. Note the simple layout and easy volts on the plate, and I get far greater wiring employed in the design of this amplifier. 343 THE WIRELESS CONSTRUCTOR March, 1928 Super Quality with any Set-continued bias at least somewhere near the figure 1. How low are the tones which 3. The volume of sound you want mentioned above.How far down your loud speaker can reproduce. to produce. you need to go in your biassing will 2. What degree of perfection you depend upon: aim at in your amplifier. False Reproduction Many loud speakers seem to reproduce low tones, whereas actually they are only reproducing harmonicsof thelowtones.Thisisrathera complex matter requiringa much longer article than the present and much greater skill than I possess to make it clear, but briefly it may be stated that none of the sounds we hearisreally pureinthesense that it contains only one frequency. 0 The violin and the saxophone can play the same note, but they sound entirely different fromne another, owing to the fact that there exists inpracticallyallsoundsvarious overtones,allofwhich must be reproduced if we are to get faithful rendering. The violin, for instance, produces a very complex note in which the third harmonic is very prominent.If this third harmonic is reproduced by the loud speaker, and the fundamental note is missing, we may still get a fairly good resemblance to the violin tone, but if you were to hear the fundamental and all harmonics faithfully rendered, you soon notice the difference.Inmost caseswhat appears to be the low tones in a loud speaker are only some of the harmonics of the low tones, the funda- mentals often being entirely missing. The box, too,often " booms " on lowfrequencies,givinga kind of imitation low note reproduction. Easily Employed While on the subject, itis worth mentioning a few facts regarding the speechfrequencies. Goodspeech articulation can be obtained within a frequency range of 250 and 2,500 cycles, and if we do not reproduce any notes below 500 cycles it is still possible to understand what is being said.Readers who have compared loud speakers have often found that an announcer's voice on one loud speaker sounds entirely different from that on another speaker, although both seem perfectly naturalifone has not heard the particular speaker "in the flesh." So much, then, for theoretical con- sideration, which.I hope has not bored the reader, but it is essential that these points should be fairly grasped if we 344 March, 1928 THE WIRELESS CONSTRUCTOR

Super Quality withany Set -con tin ued are to obtain the high quality now detector valve and substitute others before.The alteration is simply to possiblewithmodernapparatus. for them. The existing grid leak disconnecttheleadwhich comes Knowing how poorly many sets repro- and condenser or anode -bend rectifica- from the reaction condenser and coil, duce the loci- tones, and how unfaithful tion is utilised, as are all the tuning and normally goes to the plate of the they aretothe' broadcasttrans- arrangement, high -frequency valves, detector valve, and to connect this mission, it occurred to me some time etc.,in the receiverto which thewire to the plate terminalofthe ago that it would be very useful to amplifier is attached. detector valve in the amplifier. design an amplifier which could be One point should be mentioned quickly attached to any set, so as to at once, before proceeding farther. Push -Pull Amplification provide a complete new audio -fre- If you are at present using reaction Spacedoesriotpermitafull quency unit which would take the in your set,thisamplifier cutsit description of push-pull amplification place of the existing audio -frequency out, on the principle that first-class in theory, butit may be briefly stages, for in ninety-nine cases out of reproduction can be only obtained explained as follows ;The primary a hundred (excluding reaction dis- from the -nearest station, and in such of the input transformer is used in tortion) the distortion which annoys circumstances itis advisable to "if the normal fashion, while the secon- us so much starts after the detector, out reaction.If, however, it is daryissplitinto two electrically andisnearly' always morepro- desired to use it, a slight alterationequal halves, each end going to a nounced in the set itself than in the in the wiring can be made in angrid of a separate valve, as shown loud speaker. existingset using Reinartz reaction, in the theoretical diagram ;grid bias so that this form can be used as Used with Existing Set being connected between the centre Few readers will wish to build an amplifierforonepurposealone, The instrument forms so pains have been taken to make a unitermil nrnplificr theinstrumentasadaptableas SUi fable far it w in all easeswhere loud- possible for a wide range of uses. speaker reeepUonis Furthermore, its use is not confined ;et -pared. to radio purposes, for it can be used as an amplifier with gramophone pick- ups for the electrical reproduction of gramophone records. A wide variety of valves can also be made use of, from ordinary general-purpose valves up tosuper -power valvesofthe latest types. The circuitisgiven inFig.1. Here will be seen a detector valve (without any detecting arrangement) resistance -coupled to the first note - magnifying valve, which is in turn coupled by a push-pull transformer to two output valves.The output of these two valves isre -combined in an output transformer which can be either of a 1-1 ratio for ordinary loud speakers, or a 25-1ratiofor the moving coil type, ifthisisof the low -resistance variety. No Alterations On the left of the circuit will be seen an extension terminating in a plug resembling an ordinary valve base with four pins. This . plug is used as follows :The existing detector valve is withdrawn from its socket and placed in the first socket of the amplifier, the plug just referred to being pushed into the detector -valve socket in the set. The effectofthis changeisto transfer the detector valve to the The L.F. frimsforiners can be mounted well out of the way as shown., leaving the rest new unit, and simultaneously to. cutof the board clear for the valve holders and other small components, and for the wiring, out theplateconnectionsofthe which is thus Made extremely simple to carry out. 345 THE WIRELESS CONSTRUCTOR March, 1928 Super Quality with any Set-continued pointofthesecondaryandthe set there is no needto provide a resistoris provided for' the second negative filament. terminal forithere. Incidentally, valve,and noresistorswhatever The two plates of these valves are such an arrangement makes it un-for the two push-pull valves. If joined to the two ends of the primary necessarytoinquirewhichlow- desired,the fixedresistorcan be winding of the output transformer, tensionterminalisconnectedto dispensed with for the first audio - the high-tension positive being con- high-tension negative. frequency valve. nected to the centre point..The The ping itself can be made from If you have a The Last Stage secondary then feeds the loud speaker. any old valve base. The plate connection of the first obtainagreat burnt -out valve, take hold of the base Itenablesusto audio -frequency valve goesto the increaseofvolume withoutover- firmly in the left hand and the bulb loading the valves, and, in fact, byin the right, and give it a sudden primary of the push-pull transformer, using two valvesin this way we twist. Youwillprobably break and the output side of this trans- can get with a moderate voltageaway the valve from the base, and former feeds the two grids of the last can then chip out the plasteror two valves. A .0005-mfd. fixed con- a distortionless amplification which denser is connected across the primary wouldotherwise mean twicethe other securing material.It is then a voltage, and different types of valves, simple matter to solder three leads winding of the transformer shown, as the capacity of this condenser is taken while owing tocertainelectrical to the two filament pins and the grid conditions we obtainother advan- pin. The plate pin is left unconnected. into account by the designers when working out their curve.To get the tages.I have asked Mr. W. James best reproduction with the particular to write an article describing push- Simple Arrangement detail, and I transformer shown (the R.I.-Varley) pull amplification in The two flexible leads which go this condenser should be included, must refer you to this when it appears. to the filament pins can be ordinary but if you use the Ferranti push-pull Constructional Details twisted flex, but the grid lead should transformer, thendo notuse this con- be kept separate and not twisted up denser, as a suitable condenser is built And now for constructional details. with the others. This lead should not into this make of transformer. The set, as you will observe, is built be made longer than isnecessary You will notice that the two plate up on a board, and no front panel is to extend to the present set. connections of the last two valves go used or needed. The amplifier can be Examining the setin detail we to the push-pull output transformer, used on a board as shown, or inserted see that on the left we hare the and that the output side of the latter in any suitable box such as thatsocket for the detector valve, the is connected to the output terminal illustrated on the front cover.This filamentandgridconnectionsof of the amplifier.Notice, too, that is merely an ordinary standard cabinet which go to the existing receiver. 1-mfd.Mansbridgecondensersare with a black wood or polished front. The plate connection goes to a small shunted across each high-tension posi- The on -and -off switch is carried on shunting condenserof.0001mfd. tive connection and are placed in con- the terminal strip, and ifyou look (joinedtothenegativefilament), venientpositionsinthe amplifier you will see that there is no high- and to a radio -frequency choke, the itself. The-1-megohmgridleak tension negative terminal. This is othersideofwhichisconnected which is connected between the grid due to the fact that the amplifier to the coupling resistance of 100,000 of the last valve and the centre tap of is designed to work with the same ohms, and to the coupling condenser, the secondary of the push-pull trans-

former is ohly used when one is using ordinary small -power or general-purpose valves.For super -power valves it should be removed from its clips. Suitable Output Transformers The push-pulloutputtransformer should be chosen with a 1 to 1 ratio if the amplifier is designed to use with an ordinary high -resistance type of loud speaker, such as one of the excellent cones or some moving coils. If a low -resistance moving -coil type loud speaker (such as that described in the lastissue ofthe WIRELESS CONSTRUCTOR)isused, then a25 A general view of the back of to 1 type should be chosen. the set, showing the disposition of flu; terminals and switch on the terminal strips. Excellent push-pull input and out- From left to right the terminals are:L.S., G.B.- 2, 6.11.- I,and then put transformers (the latter also in the H.T.+ 3, + 2; and -1- 1 in a group, followed by an on -off switch and G.B. L.T.-j- and 25 to 1, or 1 to 1, as desired) are also The input is made via the flex on the first valve holder. sold by Messrs. Ferranti, Ltd. batteryandaccumulatorasthe whichisofthe mica type. No It is not essential that the layout be receiver with which itisused, and filament resistance is provided for the very closely followed, but the general as the high-tension negative connec- firstvalve, as this is already con- layout and disposition of parts shown tion is already made in the existing tained in the existing set.A fixed (Continued on page 412.) 346 March, 1928 THE WIRELESS CONSTRUCTOR

Using the Thirty -One TestedCircuits In this article, the first of a new series, the Editor discusses practical points relating to the " Thirty,One Tested Circuits " Gift Book presented free with the "Wireless Constructor " for Ian February, 192.%

The Crystal Receivers

ALTHouGH many crystalcircuits cannot be exactly specified to suit 25 coil will be used for the shortest have been published from time all conditions. A crystal receiver will English wave -length,suchasthe to time, the three given in at the best receive but three stations relays, or with a very largeaerial. " Thirty-one Tested Circuits " repre- at what may be termed " programme" sentthepickofallthe various strength "(Iam excluding weak Condenser Capacities methods which have been tried in the reception of distant stations on ex- The question is sometimes asked WIRELESS CONSTRUCTOR laboratory. tremelyfavourable occasions) ;the with regard to the condenser C1. is it One of these three will suit practically three being the local, 5 X X, and per- essential that it should be .0005 mfd. every need, and, of course, there are haps 5 G B.In all cases where the maximum ? A readersometimes sundrymodificationsinpractical aerialisconnected directly to the writes to say that he has a .0003 make-up which will give a still wider tuningcoil,asincircuit Al,the and will this do ?The answer is varie17,- of uses. larger the aerial the smaller the coil dependent upon the station you want Importance of Good Aerial I.,to tune toa particular wave- to receive, your aerial, and the size length. of coil you are using.If, for example, No wireless receiving circuit can For this reason, in the explanatory you are using a .0005 mfd. maximum be considered apart from the aerial text of circuit Al it issuggested a and only .0002 mfd. of it is used to and earth connections with which it is 25, 35, or 50 plug-in coil or a' single- tune your coil to the station you want used.Aerial connections and earth connectionsvaryenormously, the former more than the latter.Few Where the" Beam" Begins people are in the position to erect exactly the kind of aerial they would like to possess, and even those who are so fortunate may happen to live in a locality where a normally good aerialwill give poor results. Generallyspeaking,oneshould aim at having an aerial at which the top portion is suspended well above the receiving instrument, with the earth connection made as close as possible to the receiver itself.In a crystalreceiver, where we arede- pendent entirely upon the energy we pick up without further amplification, we must take more than usual pains, and it should be the aimofthe listenertogetthebestpossible aerial for the given conditions.A singleverticalwire,100 ft.long, would, ofcourse, give excellent reception, but the expense of erecting a suitable support for such an' aerial rules it out in practically all cases. A good practical compromise is to Britain leads the way in short-wave transmitting services high-speed communication have an aerial about 30 ft. high andbeing possible between this country and all the main points of our far-flung Empire. about 70 ft. long, the vertical andThis photo shows the Beam transmitter aerial system at Dorchester, whence messages horizontalportionsthustotalling are sent to Rio de Janeiro and Neu, York. 100 ft. layer coil of the same number of turns to receive, then any size of variable A Simple Circuit should be used. On an average aerial condenser which has enough capacity Now consider circuit Al. Here we the 50 coilwill only be used for to reach .0002 mfd. will give exactly have a coil connected directly to the stations at the top end of the lower the same resultsasa.0005 mfd. aerial, and shunted by a variable wave -length band,suchas 5 G B, tuned down to the .0002 mfd. you are condenser.. The sizeofthiscoil Aberdeen, and perhaps Glasgow. The using. The strength of signals will be 347 THE WIRELESS CONSTRUCTOR March, 191.!', Using the Thirty -One Tested Circuits continued exactly the same in all cases, pro- L2 so as to enable the 5 X X range to of the instrument may lose the good viding the condensers are of equal be included.Whichever circuit you spot, and require a good deal of search- efficiency. Practically all the variable use, Al, A2, or A3, be very carefuling to find it again.At the same condensers now sold are quite efficient:. in your choice of the crystal detector. time it must be remembered that a I have often been asked which is the good galena crystal has a very large A Popular Circuit better, the galena crystal with cat's - number of sensitive spots of quite a My own favourite circuit is A2, and whisker or the double crystal com- high order, and while extra sensitive while receivers had been brought out bination using a fairly firm contact spots can be found, it is usually not with arrangements to tap the aerial between the two crystals (generally worth the trouble to look for them. down the tuning coil, and also to called permanent and semi -permanent tap the crystal down separately, I detectors).It is difficult to give a Combination Crystals Certain think I was the first to show a circuit short answer as conditions vary so I am not particularly keen on the which combined both the aerial and much in different cases, but a fairly double crystal combinations which the crystal tap as shown. The circuit simple explanation can be given if are so arranged that one has to take A2 is far less dependent upon the we consider sensitivity and reliability. the contact made by the maker, with aerial, than is the circuit Al, and a So far as sensitivity is concerned no possibility of variation.Most of given variable condenser will cover the galena crystal and cat's -whisker the better double crystal types are a greater range of wave -length with isthe better combination provided now sold with a small plunger which a particular coil than will the arrange- (and thisisvery important)the can be liftedup,givingdifferent ment Al. galena crystal is veryearefully selected, points of contact between the two The circuit A2 is exceedingly sharp and most carefullysearched with crystals. For: generalusethese intuning=far sharper than most the utmost delicacy, using a suitable double crystal semi -permanent types readers would imagine who have not size of cat's -whisker expertly handled. are far more satisfactory than the tried it --and very careful measure- cat's -whisker types, for they maintain ments have shown that with many The "Sensitive Spot" Snag theiradjustmentsover very long aerials the signals received are even Wonderfully sensitive spots can be periods (my family set with a crystal stronger on A2 than on Al.In the foundonagoodgalenacrystal and two note -magnifiers following it, case of a few aerials the signals may be (by "galena " crystal I mean practi- operating a loud speaker, has some- slightly stronger with the circuit allof those sold under fancy times been left untouched months) and are, in general, thoroughly The Ether-and the Air reliable. The sensitivity of a good double crystal combination is at least as good as the average good spot on the galena cat's -whisker combination. In the circuit A3 a switch is shown, but those readers who have not a switch handy may care to use a flexible lead from the centre .contact,terminating in a Clix or Eelex plug, the two side contacts. (one connected to the coil L, and the other to the lower part of the condenser C) being Clix or Eelex sockets.The flexible lead can be brought -out through the:front of the panel, and the two sockets mounted on tlth front. so that: by plugging in to one side or the other one can receive on! the short or the long -wave band. Don't Forget the Earth If you want the best results with a crystal set, be sure you have a good earth connection.If your set is C: Radio constitutes. both the eyes and the ears of the Air Force, and this new station underin use near a ground -floor window construction at Mitcham for the air Ministry will play a great part in the futureit is comparatively simple to run a development of aviation. lead through the window frame and -to join it to one of the many excellent but the 'difference is scarcely appre- names ending in. " ite," looking like earth tubes now sold. ciable. littleblocksofcrystallisedsilver), By .theway,a very interesting Circuit A3 acts exactly as circuit but once these marvellously sensitive modification of the circuit A3 is that A2 on the shorter wave -band, and is spots have been found it is by no usedintile" Localong "receiver merely a modification to enable ameans easy to keep them, and a published in the October issueof change -over switch to add -thecoil slight -vibration in the.roora or a jerk the WIRELESS CONSTPXCTOR. 348 March, 1928 THE WIRELESS CONS fRUCTOlt

AMEETING OF THE MASTERS Al Fantasy. r-.1ruEnli was no doubt about it,I As Isat down a man with wild was lost.The street seemed By a Special CorreEpandent. storm -tossed hair and an ugly but to be a cul-de-sac ;and only powerful and intellectual face stood at the far end a single lamp cast a up and thumped heavily on the fitful glow over an open doorway "Broadcasting Conference-Masters table. Only." beneath the portals of which I noticed Now, I am fairly well known at " Ach ! "hesaid." Idonot a tall porter in uniform.I walked up agree.My works do not sound well to him intending to ask my where- Savoy Hill, and I thought perhaps I when broadcast.It is sacrilege.It abouts, but, to my surprise, he gave had stumbled on a meeting which I must and shall be stopped.To me me a cheerful greeting, took off his was expected to attend.So I turned these horrible loud speakers give but cap, and waved me into the openthe handle of the door and slipped a mutilated rendering of my sonatas doorway. quietly into the room. and symphonies.Why, theother I don't know why, but somehow I A single lamp stood in the middle evening they broadcast my Ninth found myself obeying the invitation of a big, round table, and provided Symphony.Ach !How horrible it andclimbing the only light ;the rest of the room sounded ! " some stairs, being almost indarkness.I took dimly realising advantage of this and slipped quietly Grumbles and Growls that the porter into a chair near the door.And only " Come, come, Ludwig,'said the was giving me then, as my eyes grew accustomedstout, jolly little man in the seven- instructions. tothe dimness, didInoticethe teenth -century coat and wig." Come, "Room 1, queercollectionofpeoplesitting come, liebe freund, you know you sir. First on the round the table. are very deaf ;you could not hear right." The Speakers thebroadcast " I suppose I ofyour Sym- shall be kicked Theremusthavebeennearly phony.Idid, out," I said to twenty of them, and all seemed to be and it was good. in fancy dress.There was one old The Abbe Liszt. myself, half Distinctly good; irritablyand man with silver hair and a clerical better,indeed, half in amusement, forI had no,collar-a very handsome old gentle-than I had ex- business there, and cannot analyse man indeed, except for a large wart pected. And the impulse which made me accept on hischeek.There was asliiii, they played my the porter's mistaken invitation, for foppish young man, with delicately Italian Concerto obviously he had mistaken me, per- palecheeksandlonghair,who quitewell. I haps for someone who was an expected constantly coughed intohishand- am inclined to visitor. kerchief.And there was astout, be friendly and Richard Wagner. sturdy, jolly looking little man dressed to help them." Masters Only ! ina costumeoftheseventeenth Theangry man called Ludwig I arrived at the top of the stairs century, with wig and all. grumbled and growled to himself. and found a door on my right which To my bewildered eyes, the others " Ah ! "hesneered." Iadmit was labelled " Room 1," and beneath all seemed dressed quite as incongru- there are, some who think their Rach it a small printed card which bore ously,and yet,curiously enough, is worse than their bite." this legend : somehow they all seemed familiar. There was a slight uproar at this, 349 E WIRELESS CONSTRUCTOR March, 1928 A Meeting of the Masters-continued

and it then dawned on me that I learntolovethem.Even street agree with Herr Bach that we should _was present at a very queer_ meeting. boys whistle my leit motifs.indeed, support the B.B.C." A very queer meeting indeed.Quite there ishope for Sir Thomas "-I still maintain," grumbled the suddenly I recognised nearly all the Beecharn's Opera scheme when such rugged Beethoven, " that my works people at the table, and very nearly an institution as the B.B.C. exists do not broadcast well.That Ninth fell off my chair in amazement. with the object of giving the public Symphony they played theother The angry gentleman I now recog- something a little better than it wants: evening, why it was--" nised as Ludwig van Beethoven ; the What do. von sag, Papa Liszt ? " " You must have listened to Bela jollylittle man in the wig as the Bartok by mistake," broke in Mozart great Bach ;the silver -haired benign - The Benign Liszt. witharathersillygiggle,and lookingold man sittingnextto ThebenignAbbesmiledvery Beethoven glared. at him so angrily Richard Wagner was the Abbe, Liszt ; sweetly at his friend-the man whom that I thought a row was inevitable. and beside him, in the pale -faced, he had championed so nobly when But theChairman,HerrBach, rather foppish young man I recog- alive -- and re- quickly moved the motion : That nised Frederic Chopin. plied :" My dear we Great Masters approve and pro- Richard, I agree. mise to support the broadcasting of Bach and the B.B.C. It woulcf be our works "-and it was easy to see Again I rubbed my eyes in amaze- strangeindeed by the show of hands that the motion ment, but listened with an increased if I did not, see- was carried almost unanimously. interest -to this meeting of the Shades ing how much of Just at this moment the porter of the Great Masters.Ihad not my time I once put his head round the door and realisedI was psychic before, but deyoted to help- addressed the Chairman tins meeting seemed to leave no doubt ingtheworld t o appreciate The New Master about itin my own mind !And, Frederic Chopin. curiously enough, what interested me genius-and " Excuse me, sir," he said, " but all the more was that the subject was yours in. particular.Broadcasting is, there'sagentleman down below obviously a 'debate on broadcasting. indeed, our ally, and perhaps it will'who says he's a New Master.Can he I could not help wishing I had teach the public one day to realise come up ? " brought my friend, Mr. Percy Scholes, that I wrote other thirigs besides my Herr Bach looked at his friends in with me ! Hungarian Rhapsodies and the rather surprise and some puzzlement. When the slight hubbub caused by hackneyed Liebestraume. Perhaps, "What's his name ? "he asked. Herr Beethoven's' rather rude remark indeed, one day my Sonata in B " Well, sir," the porter said." I had died down I noticed -with interest Minor will be more widely heard in- understands as 'is name is Mr. Jazz that Heri Wagner had risen to speak. stead of that little tour de force IArid---" " My, friends,"he began,ina named La Campanella." But he got no farther, for Beethoven, guttural but rather pleasant voice- with a mighty fist, knocked over the and then, pausing, he bowed in the table and roared with a hull's voice : direction of Herr Bach and. added : " ThroW hint out ! " " My master "-(at which Herr Bee- The lamp went over with a crash, thoven sniffed loudly)-`' as a com- See Next Month's the room was paratively modern master I would " WirelessConstructor " plunged in

like to support Herr Bach's motion F1111111111111111111111111111111111111111111111111111111111111111111111iF. darkness and I that we help broadcasting, and that felt myself we do all we can-and that is much- " And perhaps my sonatas, too," whirling round by wishing the B.B.C. well, and by broke in a 'little man with an Italian and round and inspiringt h e type of countenance, who I recognised round. artistes who as Scarlatti-and he cocked his eye perform our rather roguishly at Beethoven. Wakeup, .works forthe t.4eorge," said -greatlistening Broadcasting Beethoven an irritable public." " And perhaps people willlearn. voice in my ear, Herr Bach. There wasthat all my music is not the out-and I opened quite a ripple of pouringsofaneurasthenicsenti- an eye to see the accusing face of my applause alt mentalist,'' added.. Chopin in a voice wife." It's nearly two o'clock in the theseremarks. which, had it not been for a had bout morning and you've still left the wire- Herr -Wagner of coughing, would have been very Ludwig ton Beethoven less switched on. We shall want a new continued : melodious and pleasant to listen to. accumulator to -morrow." " Myself, I suffered many. years of " Consumption and Georges Sands I didn't say anything, but went neglect when on earth ;knew poverty have been the curse of my composi- meekly and switched Off.But I wish and the bitterness of dislike.Here, tions, but I think the B.B.C. artistesI bad dreamed a bit longer, forI in London, when I conducted my own will teach the public to realise thatwould have loved to have seen what works, few gave me encouragement. my workS should not be played withhappened when Mr. Beethoven laid To -day millions hear my works and morbid sentimentality. Indeed,1 his hands on Mr. Jazz ! 350 March, 1928 THE WIRELESS CONSTRUCTOR T ISA

For the first time a really comprehensive the cost of running will not be so surveyof modern" batteryelimi- economical.(See Mr. Hallows' article nators " and such devices is made in a nay that the ordinary amateur canin this issue.) understand.litre the Editor is at his best and. even if you have only a crystal "Wet" Batteries set, tee know you will thoroughly enjoy The second source of supply is the reading this ertiele. high-tension accumulator, whichif By PERCY W. HARRIS, you have facilities for charging, either at home or at areliable charging M.I.R.E. Y434t

TT is noteworthy that, while the reasonableperiod,withsufficient consumption of filament current intensity to feed the modern super- for valves has steadily diminished power valve.The first is the largest during the list few years, the demands size of high-tension dry battery, sold made upon the high-tension battery in 45 -volt units, each unit measuring have risen out of all proportion.Still about 82 in. long by about 41 in. more disconcerting are the signs that deep by 8 in.high.Typical good SET these demands will rise to still further examples of these are the Columbia, heights and, indeed, even now, if one the Siemens and the Burgess. wishes to get the very reproduction when using the moving - coil type of loud speaker, the high- A Question of Cost tension consumption of one's set is As they cost 25s. approximately each SMOOTHER AND greater than can be economically taken the cost of acquiring suitable high- VOLTAGE REGULATORDcRoss from any sizeof dry high-tension tension of this class for a super -power fia la battery. valve set is roughly £3 15s.This size of battery, however, will supply a set station, is a thoroughly satisfactory using a super -power valve in the last way of supplying your valves.The Where "Power" is Needed third method is by the wet teclancht It is true, of course, that only a stage for about nine months of average use. Cheaper and smaller batteries will type of cell,of which several good minority of listeners will care to avail also run these valves, but the life of examplesexist. Thesefallinter- themselves of such types of reproducer, the battery will be much shorter and mediate between the dry battery and but even with the more ordinary kinds the accumulator, for on the one hand of speaker the improvedquality their principle of working is practically given by a super -power valve in the identical with that of the dry battery, output stage is so marked that all who the main difference being that a liquid possibly can should use this type of valve.Any loud speaker which will reproduce the low tones can only do so adequately ifsufficient power is fed into it, and it is an easily demon- strable fact that far more energy is required to reproduce the low tones than the high.From this it follows that it is a needless extravagance to buy a first-class modern loud speaker if we cannot supply it with sufficient energy to reproduce the tones which make fornatural rendering. The valves to give such an output all requireavery considerablehigh- tension current. What, then, are we to do about our supply ?At the present time there An international group of L.F. chokes.The Croix,a French choke, is shown on the are only four practical ways of gettingleft ; in the centre is a British choke, made by Cliniax; and on the right is the Americas a steady flow of high-tension for a a Thordarson. 351 THE WIRELESS CONSTRUCTOR March, 1928 What isa MainsUnit ?-continued electrolyteis used in place of the negligible as is sometimes suggested, is indicate what the home constructor paste form of electrolyte in dry cells, still much cheaper than any of the can and cannot do in providing his while the parts which wear out (the zinc other forms of supply giving the same own mains supply and, incidentally, and the chemicals) are easily and amount of current. the risks he takes in experimenting cheaply replaced.You will thus see Thisarticleisanattemptto without adequate knowledge. that it is not so much a rechargeable battery as a battery which isin- expensively renewable initscon- fic. 2. sumable parts.

Onimom...10 HT Various Descriptions #10.16 ft2: ?if%71 A,C gwv,s The fourth source of supply is what 0 4 is generally termed a " mains unit," A C sometimes a high-tension elimina- SMOOTHER .No tor " (quite an incorrect description), 5er-24 VocrAoe. 19EC77 F/ER and in America a" socket power ReaucA TOR unit,"" Beliminators,"" power pack," etc.These forms ofhigh- explain in some detailjust what Let us start at the beginning With tension supply take the current from mains unitsare,how they work, a few diagrams which will help to the mains and supplies to the set as how some of them can be improved, explain the fundamental principles. a pure smooth direct current of the and some of their limitations which Take Fig. 1 for example.In Fig. la intensity we. require.The cost of are too frequently glossed over by we have diagrammatically shown a set running a mains unit,while not enthusiastic advocates.It will also ontheleftwithahigh-tension negative and two high-tension positive terminals, and on the right a high-tension battery with terminals for high-tension negative and high- tensionpositive 1 and2. We need not worry about the details, of the set ;we are simply taking a set which requires two high-tension posi- tives, and this is how we arrange our battery. D.C. Must Be Smoothed Now look at Fig. lb.On the left we have the set and on the extreme right the direct -current mains. Before we can apply the direct -current mains to the set we must pass the current obtained from this source through a unit which is a combined smoother and a voltage regulator. You might imagine that direct current requires nosmoothing,but what we call " direct current " (which is thoroughly satisfactory for lighting and heating purposes) is not really the pure direct current we require for wireless. The voltage regulator is merely a device which steps -down the voltage from the mains to what we require for the set.There is an important difference between the commercial direct current and the smooth direct current we require for our wireless set.This will be explained later. Look now at Fig. 2, which shows the kind of arrangement we have to

-* use when we have alternating current "Itthe back isthe American Thordarson unit, silk a transformer embodyingmains. On the extreme left, as before, filament windings and a high-tension winding, together with two ehohes. In front the Climax transformer (British) which has both filament and 11.T. windings.is the set, and on the extreme right The choke to go with this transformer is seen in the foreground the alternating current mains. Before 352 March, 1928 THE WIRELESS CONSTRUCTOR What isa Mains Unit ?-continued

battery maintains exactly the fame strength and uniformity all the time (until,ofcourse,itrunsdown). Fig.3b shows roughly what the direct current from the mains. is like. It is,as you will notice, only partially direct.That is to say, on top of the direct current we have a ripple -usuallya.steadyripple --caused by the commutator of the dynamo at the power station.Another way of looking at it is to consider that we have a tiny little alternating current placed on top of a perfectly smooth direct current.

The Climax H.T. unit for A.C. mains. we can apply the mains current to and voltage regulator is the same for our set we must first pass it through a both direct and alternating current rectifier, which changes it from alter- supply.The only difference between nating current to pulsatingdirect a mains unit designed for operating current ; next we must pass it through offdirect -currentmainsand one asmootherandvoltageregulator, designed to work from alternating At points A and B you will see which turn thepulsationsintoa current mains .isthat thelatter " bumps," differing from the regular smooth direct current and reduce the contains in addition to the smoothing ripple and occurring sometimes fre- and regulating device some - means quently and sometimes only occa- I for rectifying the. alternations. sionally,and alwaysatirregular intervals. Theselittlebumps or A " Strength Ripple sudden variations in current are due Now turn to Fig. 3.Fig. 3a shows to a variety of causes, such as the 2o(-) a simple little diagram in which the

space between the bottom line and Pam D.C. "No af.8.47-reRy /56.5.4. the upper line represents. the strength A 8 of the current and the bottom line 4 the time. From this 'you will follow that apure direct current froma

Iis7 ---3.- frz3a D-rFROMAliz ii/A/N5

A.C. FROM /1A/M.5 Fia.3c. Y436 voltagetothe figureswe want respectively. I have drawn the diagrams con- secutively because I want readers to realise that the set is the same in each case, whether we use a battery. D.C. mains, or A.C. mains.I alsoOn the 111 is liteRaytheon type B -A valve, the one standing vertically being a want to point out .that the smoother type B -H. 353 THE WIRELESS CONSTRUCTOR March, 1928

What is a Mains Unit ? con tinued sudden switching on or off of a powerful machine on the same mains, or, even closer at home, the switching on or off of lights in another room. Little surges and pulsations of current are occurring all the time on the D.C. mains, and while they do not make any material difference to the ordinary supplyoflight,power,etc.,they would make annoying sounds, such as clicks and bangs, in a wireless set. It is indeed such variations as these whichcauseanoldhigh-tension batterytogivethoseannoying crackles and bangs which are sometimes put down to atmospherics. Alternating Current Fig.3c shows, diagrammatically, thealternatingcurrentfromthe mains.From this you will see that the current starts at a given moment from zero, rises to its maximum, falls tozero,risesto maximum ina The Atlas A. C. " H.1'. Battery Eliminator " with variable voltagecontrols. negative .direction, falls to minimum again, and so on, making complete Firstly, we require a steady positive ing, place it " alongside " the positive, changes of direction and rising to voltage applied to our valve, whereas then we shall have, instead of a cur- maximum and fallingtozeroat this alternating voltage is alternately rent which periodically changes its perfectly. regular intervals of time. negative and positive, and, secondly, direction, a current which rises and The time takenforarisefrom the current is not steady but con- falls on the positive side only.This minimum to maximum, backto tinually rising and falling.What can is what is called " pulsating current." minimum again, to maximum in the we do ?Is it possible to use this in a The next step, as we shall see a little opposite direction, and again back to modified form ? Fortunately,the minimum, is called a " Cycle," and answeris" Yes,"and inFig.4 'the ordinary current supplied in this diagrammatic indications are given in country on the alternating current order to understand what can be mains has afifty -cyclefrequency. done. That is to say, there are fifty complete Look at Fig. 4a.Here we hate as Tisiz cyclic changes in a second. before an alternatingcurrent. If PARTLY SMOOTHED RECTIFIEDA.0 This current cannot be used directly by some means we can reverse the (6%.VE5 MA), 17 GSA in a wireless receiver for two reasons. negative current and, roughly speak -

1°.

)0_ Three British rectifiers. COMPLETELY SMOOTHED&RA-yr/F./ED heft)the Marconi U.5., a A.C. (FREE FROM Huns) t76. double -ware rectifier. (Centre) The B.T.H. (Hight) The Mallard D.U.10. later,isto smooth outor blew together all of these pulsations into one steady current. A Continuous "Hum " To digress for just one moment, many readers will have already used mains units, and some will have found that they get a hum in their receiver -a continuous hum, which perhaps is only just audible when the station to which you are tuned is not transmitting. Incidentally,I may say that 'practically. all mains units give a slight hum, although in nine cases out of ten the hum is not objectionable, 354 March, 1928 TIIE WIRELESS CONSTRUCTOR

What is a Mains Unit ?continued

the various ways in which this can be too, when the top end of L2 is nega- done. tive no current will flow, and it is thus Fig. 6a shows what iscalleda. simple to see how this single -wave half - wave rectifier, consisting of a rectifier operates. two -electrode valve, with plate and filament, and. a transformer. with an The "Full -Wave " Type iron core and three windings.-The winding L, is the primary and is Thehalf -waverectifierisquite connected directly to the mains..' The satisfactory provided we have an winding L2 is the high-tension Wind- adequate smoothing device for use ing, raising the mains .voltage to the with it, and when we have an alter- voltage we require for the valve,_ and nating currentoffifty .cycles the the winding L3, which. has .acentre output of such a half -wave rectifier is tap, is a low -voltage winding which fifty pulses of current per second. A will supply alternating current to the much betterscheme,butslightly valve filament. Fortunately,.our more expensive,isthat shown in amplifier will work quite satisfactorily Fig. 611, which shows afull -wave. with alternating current on the_ fila- rectifier.Here,again, we have a ment, for .all we require here is heat, similar transformer with a winding and if the filament will only maintain L, joined tothe mains, a winding its heat we shall get the emission of L2 for high voltage, and a winding electrons which we desire.If the fila- L, for the filament supply. ment were to become hot and cold In this case, however, we use two with each cycle, then- the working valves, the filaments of which are run would be unsatisfactory.But, for- in series and each end of the winding tunately, the filament loses its heatL2 is connected to theplate of a slowly and thus maintains a fairly rectifying valve. Obviously, each end of 1_12 will become alternately uniform temperature. ,,,ithve and iteative, and when the How it Works All three windings, L L2 and L3, are actually wound on the same iron core, but they are separated out in the diagram for clearness. The valve itself is very much like the ordinary type of receiving valve except that it has no grid and is generally larger and with a much Rectifying valves have large plates and generousfilaments. TheSateofamore substantial filament and plate typical anode willbe seen from thisthan in the ordinary receiving valve. interior view of the D.U.10 valve. The filament, when heated, gives off a copious stream of electrons, and andisnotnoticeablewhen the when the plate is made positive a transmission ison. Fig. 3a shows current flows across the intervening that if we have a current which isspace with great ease.When the only partially smoothed, there is still plate is negative the resistance of the a ripple left, and it is this ripple which valve is practically infinite and it acts gives the hum.Fig. 5b shows a as a pure " valve," using the word completelysmoothedor rectified in the old-fashioned sense as a device current having no variation.This is which allows the passage of some- free from hum, and therefore it is thing in one way and not in the other. practically -the same as the current Now examine the Fig. 6a carefully received from a pure D.C. source and you will see that when the top such as a high-tension battery or anof L2 connected to the plate of the accumulator. rectifyingvalvebecomespositive, currentwill flow across the inter- A "Half -Wave" Rectifier vening space in the valve to the fila- Thesepreliminaryconsiderations ment., through the centre tap of the are perhaps a little boring, but having transformertothewiremarked been through them we sall be in a " positive," which isjoined to the much better position to follow the smoothing device. The circuit,of practical side of the article.Dealing course, is then. completed through, the Tao gaseous rectifiers.Standing, the O.R.S.- 400 milliampere; onSide,the first of all with alternating current, wire marked " negative " back 'to theSethi Anotronrectifier,acon, inental which requires rectifying, let us see transformer secondary. Obviously, valve resembling the Raytheon. 355 THE WIRELESS CONSTRUCTOR March, 1928

What isa Mains Unit ?continued

. . top end is positive current, current will a second. It is twice as easy to smooth Y436 pass through the top valve to the the current with a hundred pulses a wire marked positive, and when the Second than one with fifty pulses a bottom end becomes ,pOsitive current second. will pass across the lower valve to the So far we -have dealt with valves which have a heated filament and a cold plate in a vacuum space, but there Ate: other formS of valve which ,can give quite satisfaCtory results as rectifiers:Fig. 7a shows a rectifier using the RaytheOn double rectifier. This is a filanientless valve working R4 Y 771EON OR ETI/0 TRON on quite a different principle froin- the DOUBLE RECT/F/ER fie7A. filament valve so far described: In the' ordinary types of rectifying valve we have, as previously explained, a filament which is heated and a cold plate in a vacuous space. In the Raytheon type of rectifier we have two electrodes which are made very small indeed and one electrode which is made very large. Gaseous Valves.

The two small electrodes are placed DOUBLE /'PAYEilaVT/E/CAT/ON/7678. extremely close to the large electrode and the whole bulb is filled with a small electrodes are made negative special gas, such as helium, at low and the plate positive, that only a pressure.The first surge of voltage few microamperes will flow, whereas from the transformer ionises the gas when the small electrodes are positive between the electrodes and. he current and the plate negative a very high starts across the vacuous space.The current will flow, that is, high when atoms of this gas in the tube are we consider what we require for high- wire marked positive.The advantage struck by the travelling electrons and. tension battery replacements. One of this scheme is that we utilise both caused to emit other electrons bytype of the Raytheon tube passes halves of the alternating current, and ionisation.The small electrodes are 60 milliampereswhenthesmall with fifty -cycle current and a double positive and the large ones negative, electrodes are made positive, another wave rectifier we get a hundred pulses and it is found on test that when the type passes 125, and another type 350 milliamperes. All three have been tested in my, laboratory. There are several makes of gaseous rectifying valves similar to the Raytheon. No Filament Current Fig. 7a shows the circuit and it will thus be seen that the two smaller electrodes take the place of the two separate plates of the double -wave rectifier shown in Fig. 6b, while the plate itself replaces the centre tap on the filament transformer. One advantage of these gaseous rectifying devices is that we require no current to heat the filament, and a very large numberofAmericanhigh-tension mains units are fitted with the Ray- theon type of tube. Fig. 7b shows a double -wave filament rectifier consisting of a valve with two plates as well as the filament. The circuit shown is practically the same as that of Fig. 6b, except that riln experimental rectifier using twothere is only one filament instead of B.11.10 valves mad full-evave rectification. two, and the two ends of the winding (Continued on page 410.) 353 March, 1928 THE WIRELESS CONSTRUCTOR MORE ABOUT ,7:6"SHORTNAVE THR PE R C Yw.

Full constructional details of the " Short -Wave Three" scare given in our January issue, but, in order to enable constructors to make their men coils, further directions are given in this article.

IN reply to a very large number of the original coils is to be obtained. very suitable, and the turns should of letters, asking for particulars The coils are numbered 1, 2, and 3, be spaced by about the thickness of of how to make the tuning coils, for the purposes of this description. the wire or more.As there are com- the following particulars are made Coil No. 1 has three turns grid wind- paratively few turns in these coils available.No exact dimensions for ingand twoturnsofreaction ; itis not too much trouble to file the base and pin spacing are given, as coil No. 2, eight turns of grid winding little niches in the fins so that the these -can be varied within reasonable and three of reaction ;and No. 3, turns lie snugly and properly spaced. limits to suit the convenience of the nineteen turns of grid winding and A triangular file will be found to do reader, and in any case a reference six of reaction. the job very quickly, and the finished to the original article on page 188 of The base has four sockets, three at coilwillthen be much easierto the January issue, where a full wiring one end and one at the other, and handle. diagram is given; will show a scale by each interchangeablecoilassembly which the exact dimensions of the The Reaction Winding original base can be quickly worked It will be observed that when the out. The coilisin the .base the three pins The aerial coil for all wave -lengths which are together come nearest to can consist of a coil of eight turns of "Radian Three" the aerial coil.. Considering the coil No. 24 D.C.C. wire wound.on a tem- is now available in from the aerial end, both grid and porary former 21 in. in diameter as a reaction windings are anti -clockwise. single -layercoil. Theapplication Envelope The first pin nearest the aerial coil of a little " dope," made of celluloid form, which contains full con- is connected to one end of the grid dissolved in amyl -acetate, on three or structional details and coil, the other end of which is con- four parts of the coil, will secure the nected to the pin at -the opposite turns together, and will enable the A end to' the aerial (that connected to coil to be slid off the former as soon Full -Size Blue Print. the grid condens6r): - asthecelluloidsolution hasset.. The second and third phis are the This aerial can be then gripped at On Sale Everywhere Price 1/6 beginning and' end of the reaction the base between two small strips of winding.This winding should be of ebonite or wood, and fitted on some must have four corresponding pins. fine wire; such as No. 28 D.C.C. wire, kind of hinge, so that the angle toThese may be valve pins,Cliff or and the winding should be made the main coil can be varied at will. Eelex plugs, or, in fact, any inter- with turns touching in a slot which changeable plugs and sockets which is cut deeper than the slot for the Only Three Coils may suggest themselves as convenient. grid coil, so that the coil when wound Three interchangeable coils,con- As a former, a Pirtoid. or Paxolin inplace comes at theaerial end, taining both the grid and reaction tube, 3 in. in diameter, may be used, concentric with the grid -coil, but of a windings, will cover practicallyall although it is better to use a finned diatheter slightlyless. In allthe the wave -lengths the reader is likely ebonite tube with' as much ebonite coils this reaction winding starts at to wish to receive on this set, and will -aspossible cut away.The Becol the aerialend, and a few touches give a similar service to the original people sell such formers. A fairly ofthecelluloidsolutionalready coilsdescribed. Thisdouble -coil heavy gauge of wire should be used mentioned will keep it in place.Both arrangement needs to be very care- for winding these short-wave coils. grid and reaction windings are anti- fully made if the same high efficiency No. 20 S.W.G. enamelled Copper is clockwise viewed from the aerial end. s57 THE WIRELESS CONSTRUCTOR March, 1928 Determined not to be done, he overhauled and carefully inspected every single wire in question-and, good man,hefoundthefault ! Can you guess .what it was ? If you have to " give it up "-and, quite frankly, I expect you will have to do so, for it was a fault in a thousand-you will be interested in the explanation below. His final inspection revealed nothing wrong with the earth, eliminator, condensers,indoorleads,nor the lead-in, but when he came to the aerial he noticed that his outdoor earthing -switch had a stray strand of aerial wire almost touching the earthedsideoftheswitch.And right opposite to this strand was a black mark on the earthed metal, Typical faults and remedies reviewed. where the full voltage of the mains By P. R. BIRD. had caused a spark to jump across to earth ! The Long and Short Of It! tors, he connected the lead-in to a The trickiness of the fault lay in flash lamp, the other sideof thethe fact that the gap between the IF you are fond of puzzles, try to strand of aerial wire and the earthed solve the one outlined below, flash lamp to a dry cell, and thepart of the switch was only just before reading the explanation. other side of this cell to earth.The lamp did not glow, as he expected, so largeenoughforthefullmains The set was a straight three-valver, voltage to spark across. Consequently which had been' giving perfect results, he took off the dry battery and put on a high-tension battery. itwasmuch toolargetopass and one day its owner decided to anything from smaller voltages, and utilise the mains for his high-tension Evidently the aerial insulation was good because there was still no sign his tests with a dry -cell and high- supply.It appeared to be a simple tension battery had shown up the job.He bought a D.C. eliminator of leakage.And just to cheek up the connections and lamp he tried putting aerial insulation as being apparently (the mains were D.C., 230 volts), and O.K., when actually it broke down at connected it up exactly as per in- about 230 volts ! structions.But no sooner did he Pulling away the offending strand plug-in the lamp -adapter than the THE TECHNICAL QUERIES of wire, he went indoors, plugged in main fuse went ! boldly, and was rewarded by full As luck would have it,it was a DEPARTMENT. volume on the loud speaker ! Sunday,andthehousewasin darkness for several hours until an Are you in trouble with your set P A Point To Watch Have you any knotty little radio Problems electrician could be obtained ! requiring solution'! " It's the little points that cause Resolved not to be " had " again, The WIRELESS CONSTRUCTORTechnical Queries Department has been thoroughly the most trouble "-as the man said the owner of the set waited till the. reorganised and is now in a position to give when he trod on some tin -tacks. following week before attempting to an unrivalled service.The airs of the department is to furnish really helpful advice And in radio the little points are not connect up again, and in the mean- in connectionwith any radioproblem, always too obvious ! time he had the eliminator tested. theoretical or practical. Full details, including the revised and, in Flexleads,forinstance.Who It proved to be quite O.K.' cases, considerably reduced scale of charges amongst us has not succumbed to can be obtained direct from the Technical He then joined it to the set in the Queries Department. WIRELESS CONSTRUC- the temptation of cutting up old flex correctmanner,andforsafety's TOR, Flectway House, Farriugdon Street, London, E.C.4. for further use as grid -bias, leads, sake put an extra large fixed con- A postcard will do : on receipt of this all the etc. ?Generally, it works all right ; denser in series with the earth lead. necessary literature will be sent to you free and post free, immediately.This applica- but an old flex lead can cause no end To make assurance doubly sure he tion will place you under no obligation what of trouble if its continuity or insula- removed the valves, and then, mak- ever.Every reader of the WIRELESS CON- STRUCTOR should have these details by him. tion is at fault. ing certain all was well, lie cautiously An application form Is included which will enable you to ask your questions, so that In one case which came to my notice plugged in the flex lead to the mains, we can deal with them expeditiously and recently, a two -valve amplifier (the and blew the fuse again ! with the minimum of delay.Having this form you will know exactly what informa- onedescribedin WIRELESS CON- tion we require to have before us in order Was it the -Aerial? eompletely,to solve your problems. STRUCTOR last December) had been almost completely re -wired inthe Being thoroughly on hismettle hope of improving results.But when now, he filled in the interval before completed for the second time there the fuse was put right by testing the 41 volts straight across the latter, was still a lack of the full, round tone leads used-all O.K.He then tested when the bulb lit brilliantly ! expected, until someone noticed that for a break in the insulation of the So he was faced with the fact that grid bias appeared to have no effect condensers used to isolate the setwith no path via the aerial, and no at all. from earth-all O.K. path via the earth, his mains persisted This led to the discovery that an . Thinking there must, therefore, be in shorting every time he plugged in old piece of flex (complete with red a leak to earth via the aerial insula- the eliminator ! (Continued on page 409.) 338 March, 1928 THE WIRELESS CONSTRUCTOR A '6 THREE" FOR SPARE PARTS

v°j-,.

An inexpensive, easily made three -valuer whichcan beconstructed from the various parts that litter the enthusiast's workshop.

IN spite of the undoubted advan- sists of a modification of a very old has been-from the ordinary stock of tages of the new screened -grid favourite circuit, but it can be justly wireless parts which most enthusiasts valves and screening boxes, and claimed for it that it has been brought possess. the enormous steps that have been upin accordancewithmodern The DX -hunter "generallyis made in radio reception since broad- practice, and will yield results that found to have some type of 3-valver- casting first commenced about fivecompare excellently with most sets unless he is one of those who wants every station on the loud speaker- and the combination of one H.F. stage,adetector, and onenote - magnifier is generally the most useful as well as the most popular for the average man.

A Simple Circuit The construction of the set is very simple indeed, since the circuit that has been used for the H.F. stage is simplyastraight" tuned -anode," and the detector and note -magnifier are, of course, also perfectly " straight." The H.F.stageisneutralisedby means of a split coil ;parallel feed years ago, we often hear of die- of the present day which do not in- isemployed,sinceitisgenerally hards " who are still using one of the corporate the newest components. acknowledged that _this arrangement ancient circuits, and usually obtain- Probably the greatest advantage of gives greater stability, and this was, ing very creditable results from it. The this set from the point of view of in practice, quite definitely found to receiver described in this article con - many readers is that it does not use be the case.Thus we have a centre - orneed any specialcomponents ; tapped coil as the tuned -anode coil, that is to say, it can in most cases be and. the H.F. valve is neutralised in COMPONENTS USED. built up-as indeed the set described the conventional way.This will be 1 Panel, 21 in. x 7 in. x in. Cabinet for same with baseboard, 7 in. deep, and pair of brackets. 2 .0005 slow-motion condensers. 3 Non-microphonic valve holders. 1 L.F. transformer. 1 H.F. choke. 1 Neutralisingcondenser, baseboard mounting. 015 fixed condenser, 1 .0003 fixed condenser, 1 OH fixed condenser. 1 2-megohm leak. 2 Baseboard -mounting coil sockets. 1 On -off switch. 1 Three -terminal stripand 1 seven - terminal strip. Centre -tapped coils, grid -bias battery, tinnedcopperwireorGlazite, Junit, etc., woodscrews, etc., etc. NOTE.-This is a set for those who The construction of the set is a simple matter, wish to use existing components. the circuit used being simply a straight tuned - Any good makes can be utilised, so anode neutralised H.F. stage followed by a detector and one note -magnifier. The that no special parts are mentioned. above photo gives an idea of the interior of the set, with valves and coils on board ready for.test. 333 THE WIRELESS CONSTRUCTOR March, 1928 A "Three" for Spare Parts continued

dealt with later in connection with the anode circuit used, and a fairly high been kept inside the set, but -there is general operation of the set. value of H.T.-about 80-100 volts- no reason why one of the panel - Fig. 1 shows the theoretical circuit. enables a very high degree of am- mounting type should riot be used if With reference to the " parallel plification to be obtained. it is preferred.As a matter of fact, feed " circuit, it is best described in The construction of the receiver, if a panel -mounting type of the same a few words as follows.Instead of as will be seen from the photographs, manufacture as that in the set were taking the H.T. to the anode of the should present nodifficulty. The employed, and placed low down on H.F. valve through the anode coil, components are well spaced out ;if the panel between the two variable it is taken to the same point through it is examined it will be seen that the condensers, hardly any alteration in a high -frequency choke.The anode coil is now connected. in series with a fixed condenser C3to theneu- 2/" ). tralising condenser in the usual way, the centre -tap also being taken to the 4011111"4%, , # Cl2 filament just as usual. The condenser C,, if made small, has a considerable mirq-- i lir9 stabilising effect upon the set, 'but it i i j ilL,_ 1 has been found. preferable to keep Anh------4* -- this at a fairly large value, and to z stabilise the set in the normal wav 44 6' 6, 42---i by neutralising the H.F. stage.The Y448 Pic. 2. PANEL LAYOUT value chosen for C, is accordingly .015 lad.It can be made bigger still if H.F. stage occupies nearly half the the wiring should be necessary, since desired. baseboard space, and the detector and the two terminals would come at note -magnifier share the other half. almost the same positions as do those Easy to Construct The aerial coil is Well away from the of the baseboard condenser. anode coil,and is placed at right - With carefuldesign and careful- The aerial terminals have been left operating there is not the least diffi- angles to it.This is very important, blank. Two were provided, but, there culty in making the set completely since, no screening being employed, are such a number of different methods stable over the whole of the range interaction between the coils is pos- of coupling the aerial to the set that which it covers, and a very pleasing sible, and very undesirable. With the it was thought advisable to leave the constancy of feed -back can be ob- actual.layoutused,however,no actual choice to the reader. ' The tained.For this reason no reaction troublewhatever wasexperienced writer is of the opinion that out of has been introduced on the detector, in this direction. about six alternative methods there and the set is thus deprived of one isgenerally one which gives very control, which is not lamented in the The Balancing Condenser definitely better results with a certain least. The condenserattheleft-hand. type of aerial. The most suitable valve for use in end of the panel is that Which tunes The reader, of course, knows his the H.F. stage is one of the fairly high - the aerial coil, and the other the anode - aerial, and may already have met the magnification factor valves intended circuit condenser.The only other type of coupling which suits it best, for resistance -capacity work, having component on the panel is our old in which case he will doubtless employ an impedance of about 60,000 ohms. friend the on -off switch. that method in this set.The alter- This, in conjunction with the tuned- Theneutralisingcondenserhas natives which may be used with little or no alteration are as follow. Auto -coupling " may be arranged by using an " X " coil in the aerial socket, and taking a lead from the aerial terminal to one of the tappings on the coil. Suitable Valves As a second test a centre -tapped coil may be inserted in the socket and the aerial taken by a flex lead to the centre tap.This will not give such good selectivity as the X "coil, but if a -0002 condenser is connected between the aerial and the centre tap results should be very satisfac- With rains and coils removed. The simplicity of the wiring and,tory. In the case of readers using very the lay out of the few components employedsmall or indoor aerials it may even be can clearly be seen.Most, if not all, of thefound possible to connect the aerial items used in the construction of this set are to be found here and there in the constructor's workshop, Thusthe direct to the grid of the H.F. valve, receiver becomes a very simple and economical one to build. but this method is not advised unless 860 March, 1928 THE WIRELESS CONSTRUCTOR A "Three" for Spare Parts-continued

itis definitely found to give good Now, if the two dials are rotated the stale the caliaeity of the neutra- results.The grid leak is shown asso that they keep fairly well " in lisingcondenser must be reduced connected to L.T. negative, this having step " the localstation shcruld be again, but only by the most frac- been found to give perfectly goodfound to be quite sharply tuned. tional amount. results without sacrificing stability. "Unlessa movement ofthe anode The correct position for it is that at Having completed the. wiring as in condenser of about 7 or 8 degrees, which the set is quite near the oscil- the diagrams the set should be con- and. about 10 or 15 degrees of the lation point without actually oscillat- nected up to the batteries, aerial, and aerial condenser, practically cuts theing at any point on the dials. earth, and. the valves inserted after local station right out there is some- the final check of the wiring. A high - thing wrong. Operating Details mu valve should, as previously stated, The writer tested the set out at a It is worth one's while to spend a be used in the H.F. stage, and, as de distanceofsixmiles from 2 L 0, little time and trouble in bringing tector,anH.F.valvewithan and these figures sufficed to cut out the set to this condition, for searching impedance of 20,000 to 30,000 ohms every trace of that station.For the is now an extremely simple matter. is suitable.For the note -magnifier a guidanceofreaders,thewriter's When the two dial' readings nearly small power valve should be used. aerial is 65 ft. long and 38 ft.. high, correspond a slight " hiss " or " mush " andgivesquitegoodselectivity will be heard, indicating that the two Neutralising when connected directly to the centre circuits are correctly in tune, arid the The first H.T. positive terminal is tap of the aerial coil.On the WIRE- dials should be rotated very slowly, common to the detector and. the H.F. LESS CONSTRUCTOR laboratory aerial, just keeping this hiss tuned in over valve,and. about 80 to 110 volts however, which is somewhat larger, it the whole of their travel. should be used.For the note -mag- was found necessary to use anX " It is rather difficult to explain on nifier the same voltage is quite suit- coil in the aerial circuit to give thepaper, but as soon as one has got able, although it will sometimes pay same degree of selectivity. hold of the set it will be understood. to go even higher.The grid -bias Analysing the movements of tuning - battery, which is fixed inside the set Increasing Sensitivity in, probably the aerial condenser will at the end, and. connected up by flex Having ascertained on the localhe advanced by about half a degree, leads, should be of about 9 volts, and station that the set is really working then the anode condenser by a similar 41- to 6 volts should be a sutiable value well, another slight adjustment mayamount, then another half degree on for normal working, although this is, be made before searching is begun. the aerial condenser, and. so on.As of course, one of the adjustments that It will probably be found that the soon as one circuit is out of tune the must be made individually. A No. 50 capacity of the neutralising conolenser familiar " hiss " will disappear. This coil should be inserted in the aerial may be increased. by a minute amount noise resembles the " background' socket, and about a No. 60 in the other. (i.e. the vanes may be turned fartherof the Continental stations. Without connecting the aerial the set should be switched on.It should be found, if the neutralising condenser is placed in a position approximately " half -in," that it will oscillate when the condenser readings are somewhere nearly equal.It will probably be found that itwill oscillate over a band of about 30 or 40 degrees on each.Now connect the aerial,remove the filament lead from the H.F. valve (the lead nearest the panel is conveniently taken off the terminal), and carefully search round for the local station.It will, naturally, not be strong, but it should be found. A bird's-eye view of the receiver taken before the wiring was completed.It frill Now adjust theneutralisingcon- be noted that exceptionally short grid and plate leads have been arranged, thereby greatly increasing the efficiency of the set. The components are so placed that the denser carefully so that no trace of maximum accessibility for wiring -up is obtained. thelocalstationremains,atthe same time making slight alterations.into mesh) without causing the set to If this test is being carried out in in the setting of the aerial condenser. oscillate. the evening, numerous stations should The adjustment should. be made now be heard at points round the Good Selectivity with the greatest care, advancing the dial.On headphones, with the origi- When the local station cannot be neutralising condenser by almost in- nal set, stations are heard at about found at all, connect up the filament finitesimal amounts, at the same time every 15 degrees.Langenberg, Ham- of the H.F. valve again, and the set slowly rotating thedialsto make burg, Stuttgart, Frankfurt, Toulouse, should be correctly neutralised and sure that the set still does not oscil- and others are excellent on the loud, ready for use. Do not remove the H.F. late at any point of the tuning range. speaker most nights, and. Langenberg valve instead ofswitching out its If it is found. that it suddenly starts is generally received quite well in the filament ! oscillating at the top or bottom of (Continued on page 362.) 361 THE WIRELESS CONSTRUCTOR March, 1928 .**.**********--****%.'* neutralising condenser, also Peerless time,asimperfectcontactsare >1* fixed resistors and T.C.C. condenser sometimes caused by the two halves 4* THE SIGNAL BOX IN insteadofthe McMichael forthe of the split pins being pinched too SOUTH AMERICA aerialtuning. Iuse an Amplion close together.Itisnot always >4* Some interesting experiences from 4 Junior loud speaker, which gives very realised that a faulty contact may an overseas reader. good results. bring about a considerable reduction ******************** Yours truly, of signal strength without indicating

A. NEILSON. its presence by a complete " dis." SIR,-I have just completed the Buenos Aires, Thisisparticularlythecasein Argentina. sockets connected to grid circuits. " Signal Box," described in the May To remedy matters remove the issue,It is without doubt one of the coil and open up the pins by inserting best sets yet described in your paper; a thin knife in the cut.If the coils theselectivityiswonderful,being F 5? are used in exposed places without able to tune in about a dozen stations See next month's a box or cabinet, the base should be by just tuning thefirst two con- kept well free from dust. densers,theotherstationsbeing " WirelessConstructor " H. P. W. completely eliminated. I ought to be able to hear Daventry 7A111111111111111111111111111111111111111111111111111111111111111111111117 with this set,I should think, as I have heard that on board ship here ***',-Y,**************** A "THREE" they can receive Daventry very well O A SIX -PIN COIL TIP0 FOR SPARE PARTS on a one -valve set. -contin,ed frow pafy; 361 4Poor contorts often cause no end 4- As to the volume of the set, it is >g of apparently tintraceable trouble. ,0 tremendous.I use the same valves asstated(P.M.5X, P.M.6,and 04,k*Ak*;AkAk**--********* middle of the morning. He can hardly P.M.256), withan accumulator of then be called " real loud speaker 6 volts, 100 amps.I also use an READERS who are in the habit of strength," but can certainly be heard eliminator for the H.T.I find that using six -pin coils and inter- 4 ft. or 5 ft. away from the speaker. the set works better with one grid changing them frequently so 5 G B is,of course, amply strong battery with 41volts throughout. as to tune in the lower and upper for loud -speakerwork,and on As tothecomponents,theonly wave -bands, should make a point of headphones some twenty-four other difference I have made is with the examining the pins from time to stations have been received.

z.r RANS 'LR

TAOTO CENTRE ON ;v.., TAR OA 4 p/N V2

TOP

!iTR !VD NII 1111111 W/R/NO D/ACRAM NIIIi T20 Z.S +2 1/7-1-/ H.T- + L.7:- A 302 March, 1928 THE WIRELESS CONSTRUCTOR

ygo 4x A X. : -W In-00,KOMM-ClaAC-F: ' wuot 0. :iteg MO Avg n l', structor, and the Radiano scheme, complete in all its details; ante -dated its imitators by many months. ViTHE " RADIANO THREE" It should be particularly emphasised As a result of widespread demand, full constructional details of this famous that the " Radiano Three " has been 'set have been published in Envelope Form together with a full-size Blue Print. carefully designed to work excellently :eraWKWAKSECVAATIM+8+80%481)1M1 *.: .4,1f10.41M*410;,,:aVr with all the leading makes of valves, with any good low -frequency transformers, and indeed with any sound READERS of the WIRELESS CON - wire to facilitate wiring -up and to componentsofgood make. The STRUCTOR willbe veryin- enable a wide range of first-class com- special and unique scheme of using terestedtohearthatthe ponents to be used. flexible rubber -covered wire for wiring famous " Radiano Three " is being re- The circuit, chosen after much ex- up completely obviates the difficulties published in the form of a complete periment, consisted of a detector with'which have to be faced in some sets ` how -to -make " envelope, containing Reinartz type of reaction and two using stiff wire, for with them unless fullconstructionaldetails,photo- stagesof note magnification. The the exact components illustrated and graphic reproductions of the set in choice of this circuit as most suitable named in the original design are used various stages, and a full-size blue for the average reader for general the wiring system falls to the ground. printofthe wiring(the Radiano loud -speaker work has been amply chart), together with other necessary justified by the remarkable results Standard Parts Suitable diagrams. obtained and published from time to Indeed, in designing the original Thousands of constructional enve- time in this journal.Testimonials of " Radiano Scheme it was the par- lopes from the pen of Mr. Percy W. . the success of this set, giving a long ticular aim of the Editor to evolve a Harris have already been soldin list of stations received, have poured systemwhichwouldenableany this country and abroad (the " Ail - intotheWIRELESS CONSTRUCTOR existing components of good makes Concert de Luxe " and the " Four -.offices since the first week of publica- to be used, as nothing is more irritating valve Family "receiversaretwo tion, and a careful analysis of these tothe home constructortofind, world-famous sets which appeared in lettershas shown that thesetis when he desires to build a set, that envelope form), and a further en- equally successful with a wide range he cannot get the particular trans- velope from his pen will, we are sure, of components. formerorcondenser required and be widely welcomed. It is interesting to note that within that otherequally good first-class the last few months other construc- makes cannot be substituted. A World -Famous Set tional schemes, claiming to be " new," Readersofthe WIRELESS CON- The present issue will be the first of have been brought out showing how STRUCTOR-and they are many thou- the WIRELESS CONSTRUCTOR series to build three -valve sets using a de- sands-who have already' built and of new constructional envelopes published at the highly attractive price 200 -ft. Pillar of Flame ofIs.6d.The " Radiano Three," rl which was first published at the early part of 1927, immediately roused universal interest, and thousands were successfully constructed and operated in every part of the country and abroad.Such was the demand for details that the issue containing the description went out of print at once, and as the result of thousands of inquiries from readers who are anxious to build this famous set the new envelope has been prepared. Much of the success of the " Radiano Three " was due to the greatly simplified method of construction first described in connection with that set. The " Radiano System " includes the following features : - 'a The result of a disastrous fire that broke out at the Dillon Park laboratories of the Some Special Features Radio Research Board.The station was completely gutted and the 210 -ft. mast crashed in a sheet of flame. 1.Full-size diagram Showing all components in place but without wiring. tectorwith Reinartz reaction and successfully operated the " Radiano 2. Choice of all components with two stagesofnotemagnification, Three " should tell their friends that terminals, so that the necessityof while the " abolition of soldering " complete constructionaldetailsare soldering is obviated. through the choice of all components now available in envelope form at the 3. The publication in chart form of with terminals has been featured as price of ls. 6d. from any newsagent or every wire shown full-size, the wires entirely new.The WIRELESS CON- bookstall.Be sure you ask for the beingletteredandnumberedto STRUCTOR is proud that it was the first " Radiano Three "EnVelope, by correspond with letters and numbers journal to describe this very simple Percy W. Harris, M.I.R.E.It is a on the terminals. method of overcoming one of the three-valver which works splendidly 4. Use of flexible rubber -covered difficulties which faces the new con - with any good valves and components. 363 THE WIRELESS CONSTRUCTOR March, 1928

ANfiIiil ..'+:MMAI-WW.M-0-AMMW-MM-MIKIWAM.-X.TC WAN- WAIAX-M-04-1 It will be remembered that when 5 G B first came on the air there was ' a lot of talk and a lot of controversy about interference with Langenberg, .. Continental Broadcasts . but as far as the writer is concerned- A review of the present-day conditions in DX reception. and he listens just on the outskirts of 44 By 2 D A.: V London-Langenberg's transmissions *4 may be received quite easily these ':748r4.41441.-M- N-Yla414.,i4Y+WifBie-graiWAWAIVIaalIV,:)f:'VKif.&;tAX 472j0 days without any interference.If any interference is noticed by. my readers, ISUPPOSE no two amateurs, even if strongly, and the station is quite easy I think it is of such a nature that an they live in the same street and to tune in.I was surprised to be ordinarystraightforward wave -trap operatealmostidenticalsets, able to pick up the Turkish station will meet the case quite satisfactorily. could ever quite -agree on the subject atConstantinopleatquitegood

of long-range reception, or even on strength, and, of course, Koenigswus- Farther Down the Dial - the subjectof logging Continental terhausen, on 1,250 metres, may be Another good station to listen for broadcaSting stations. relied on for a good transmission is Berne, while Frankfurt, of course, A few days ago, a friend of mine almost any evening in the week. has quite a reputation, despite spark who spends quite a lot of time listen- interference.Toulouse and Hamburg ing to various Continentalstations An Uninteresting Russian want separating a bit, but Stuttgart, delivered himself of a long and criti- I had a chance the other evening, which a few months ago gave me a lot cal surveyofpresentconditions, too, of receiving direct the programme of trouble, is now received with ease. and because he grumbled at the fact from Witzleben, which Koenigswus- Madrid was another station which that he found some of his favourite terhausen usually relays.As a rule, I used to receive quite well, but these stations difficult to receive these days, 5 G B interferes so much with Witzle- days, for some reason or another, whereas a few months ago he enjoyed ben, that it cannot be put down on the I find it difficult ;and the same their broadcasts with ease and regu- list as a station which can be received. applies to Rome.Another station, larity, and because he mentioned, in with average regularity.On 1,450 however, which comes inwell,is the course of his diatribe, stations metres itisquite easy to. pick up Barcelona, while the station at Milan, which he had not been hearing satis- Moscow, but the station's broadcast is now working on 7 kilowatts, is not factorily but which I had received enough to turn one's hair grey-it is difficult to pick up. quite well, I spent the next evening absolutely devoid of interest.Person - Other stations below 300 metres making a sort of investigatory tour ofthepossibilitiesofContinental reception to -day. The Two Sets Used I don't expect for a minute that any two readersof the WIRELESS CONSTRUCTOR will completely agree with my report, if it may be called such; but perhaps a good. number will admit that, after making allowances for geographical position, aerial efficiency and atmospheric conditions, etc., the report is fairly comprehensive and reasonably fair and accurate. I used two sets,one being the " Black Prince," a 4 -valve neutrodyne receiver designed by Mr. Percy W. Harris, which covers the ordinary broadcasting wave -band, and another set, also a 4 -valve neutrodyne, for the long waves over 1,000 metres. I might add that for several nights running I carriedoutthesetests,with the Mr. Gerald Mareuse adjusting his short-wave super -heterodyne which he uses for 'result that I came to the following. picking up Sydney and other ultra -DX transmissions. conclusions. ally, I plumped for Radio Paris as the which are quite easy to receive in- best of the Continental transmissions, clude Lyons, Dortmund andMuenster, Among the " Long -Wavers " although 5 X X again has a certain and, of course, higher up the scale, Over and above 1,000 metres there amount of " wipe-out " effect --as far Berlin is fairly easy. are quite a number of stations which as I am concerned. The great trouble on the 200 -600 - one can receive very well just now. By the way, I understand that a metre wave -length band is the lack Reception from Hilversum, on the new Dutch station at Huizen will ofco-ordination and lackofdis- whole,is good, although now and shortly be on the air just below 2,000 cipline among the stations.- When the againinterferenceisprettypro- metres.Tests which I have heard new systemofwave -lengthswas nounced.An interesting station isfrom this station are indicative of adopted in 1926, it was hoped that the new Danish one at Kalundborg. some very good broadcasts to come there would be a considerable falling These .signals come throughquite as regards quality of transmission. off in interference and jamming, etc. 361 March, 1928 THE WIRELESS CONSTRUCTOR THE "SENTRY" WAVE -METER IN ACTION

Some suggestions for calibrating and using this handy instrument, which teas described in the "'Wireless Constructor " last month. By A. V. D. HORT, B.A.

EFORE your new wave -meter can and listen with the receiver head- If you are unable to borrow a. tali_ 111) be of any service to you, you phones.Rotate the dial of your own brated wave -meter, you must pro must calibrate it, that is to say, wave -meter, whose knife -switch should ceed as follows.Have your blank you must establish the relationship beclosed,until thebeat noteis chart ready as before, and pick up which exists between the settings of heard, produced, of course, by thewith the receiver as many known its tuning dial and the wave -length combined oscillationsof the wave - stations as you can.As you find each range over which it will tune.There meters.Tune your own wave -meter station, switch on the wave -meter, are two simple ways of doing this ; exactly to the silent point and note and rotateitsdial until you heat whichever you adopt, you will need to its condenser reading.Now set the thebeat note produced with the draw up a calibrationchart.The calibrated wave -meter to asecond carrier -wave of the station.Adjust chart of my own " Sentry " wave - reading at the other end of its scale and to the silent point and note the con- meter is shown below, and ifyou check with your own wave -meter as denser reading on the wave -meter. have followed the instructions given before. Sufficiently Accurate inthe previousarticle,thechart 2981 which you make will be very similar. If you have any difficulty in finding 550 CA

MOMMOMMOMMOMELEMOOMMEBOL-32MOWLAWOOMMMclip -in type, with a capacity. of .9001 mfd., and a simple short-circuiting device is provided which can be slipped A TIP FOR THEAERIAL. on toit of removed -in an instant. This little device is very easily made. The foundation of it is a piece of SERIES CONDENSER finch ebonite, 21 inches in length By R. W. HALLOWS, M.A. and z inch in width.In one of the edges of this two 4 B.A. tapped holes MEMEMOGIEMOEMOSEOMMOOMMEMMOMEMEMEN are made, spaced. 71- inch from centre WIEN the so-called aperiodic aerial nolongerexists. Similarly,ifa to centre.The only other parts re tuning is used it is always a dead. patch " occurs with the con- sound practice to have a series denser inseries,oscillation can be condenser which can be used or not secured again by cutting out the con- at will.On very short waves itis denser. quite essential to have this condenser available, for one is bound to find Three Methods certain places at which the set will Fig.1 shows how the condenser might be placed in circuit or cut out by means of a short-circuiting switch placed on the panel of the receiving set.Though exceedingly handy, such 4 lAz a switch' is for two reasons not advisable on apparatus designed for reception of the very short waves. In the first place, one part of the quired are a pair of condenser clips switch must beconnected tothe and a brass strip 11 inches in length aerial, which means that body capa- and 1 inch wide, in which are drilled city effects are likely to be_ met with two 4 B.A. clearance holes 24- inch al. the hands are brought near the apart. The clipsare mounted as panel for tuning purposes.Secondly, shown in the drawing, with their to bring connections from both sets of tangsinwards,thescrewsbeing plates of the condenser to a switch passed through the holes in the clips on the panelmeans adding not a and those in the brass strip. little to the total length of the wiring, and in a short-wave set it is always Easily M4.de advisable to keep the wiring as short If you do not care about tapping, aspossible.Tho.secondmethod, make clearance holes in the ebonite, illustrated in Fig. 1B, shows how the countersinking them on what will be condenser may be thrown into or the upper edge.Use 4inch counter- out of circuit by using two aerial sunk screws, and clamp up the clips 463 terminals.This is quite a satisfac- and the strap by means ofnuts, not oscillate owing to its being tuned tory method, except that it entails afterwards trimming off the protrud- in resonance with the aerial's natural the bother of changing over the aerial ing ends of the screws with a file. wave -length or one of its harmonics. lead-in whenever a bad patchis Bringing in or cutting out the con- When such a spot is encountered with encountered. denser is now the easiest business in the condenser not in use one throws A method which the writer has the world.To throw it into circuit, it into circuit, and the set oscillates found most handy isillustrated in the device is removed ;to cut out readily once more, since resonance Fig. 2.The series condenser is of the the condenser it is slipped on.

any trouble in picking up the wave - will be of medium pitch.If you

. THE "SENTRY" WAVE - meter on the receiver, do not bring prefer to have a higher note, try, 'a METER IN ACTION the wave -metertooclosetothe lowering the value of the grid leak. e3 receiver itself, but place it somewhere If you give it too low a value, un- -colitinved from, page 365 ei.? near the aerial lead-in or the earth. interrupted oscillations will be produced.A variable grid -leak is useful time the receiver to the required point Altering the Note forexperimentingwith thenote, of the howl, and switch off the wave- - Avoid using the wave -meter in close though it should be noted that the -meter.You should then hear the proximity to the receiver or the leads calibrationof the wave -meter will station which you want, though A,for long spells during broadcasting be affected to a certain extent by the slight final adjustment of the receiver hOurs, since with a heterodyne wave- value ofthe fgrid-leak. You will may be necessary for -maximum signal meter used in this way energy can be probably have noticed already that strength. radiated from the aerial almost aswhen you change over from the You should find it quite easy to strongly as when the receiver itself is loudest point ofthe howl to the pick up the note of the wave -meter oscillating. heterodyne note when tuning in a when it is some feet away from the With the component and H.T. station the setting of the wave -meter receiver, though it is not then veryvalues given in the previous article, has to be altered slightly to find the convenient for use.If you experience the howl produced by the wave -meter silent point. 366 March, 1928 THE WIRELESS CONSTRUCTOR "THE COTTAGER" 46-k HARRY. P.WOOTTOH

A Long -Felt Want Supplied.

AMONG the many designs of receiv- old ears. A single -valveset with use it during the day, and she is a ingsets which appear from reaction would, I know, give me quite little deaf." time totimecomparatively enough strength, but I do not want The result of these two conversa- few nowadays cater for the user of to have to bother with reaction Eet- tions suggested to the writer that headphones. The general cheapening tings, and I want my wife to be able there was much tobesaidfor of valves and component parts, and to use the set just as easily as I can. a combined crystal receiver with a in particular the very low demand now I want the quality to be as good as single note -magnifier.Of course, a made upon one's accumulator by the can be got, and the set must be very separatenote -magnifiercouldbe economical to run.What do youadded to any existing crystal set, suggest ? " but it is scarcely a neat arrangement, A few days later another friend, who and a built-in scheme is decidedly livesonlysevenmilesfrom the preferable. London- station, in a busy and thickly populated area, put another question : An Efficient Circuit " Our aerial is very low and badly " The Cottager " set, in its circuit, screened," he said, " can you suggest has nothing new-it is, in fact, the something which will give alittle very sharp tuning and efficient crystal more kick ' than our present crystal circuit originated by the Editor of receiver and would be just as easy to this journal, in which both crystal operate ? Iwant my mother to and aerial are tapped on the centre

Ion can see for yourselves what a really Simple set "The Cottager" is if you zssz. examine this photoof The eireuit, as this diagram shows, is athe completeset with very simple, straightforward one. valve and coil in position. The L.P. transformer is valve filaments, have done much tonot really mounted on its side as it appears popularise loud -speaker sets, but thereto be. This type still remain many people who prefer,isdesignedso for some reason or other, to " stickthatitcan be fixedin two .toheadphones," and,itmustbealternateways. admitted, headphone sets have several advantages. " The Cottager " grew up as a resultofaconversation with an elderly reader who spends much time alone in a small house well away from rural bustle.He put his case very much in this way : How the Idea Originated " I am living,"he said," some twenty miles from the nearest broadcasting station, and my garden aerial is quite a moderate one. The ordinary type of crystal set gives, my friends tell me; quite good signals, but my On the top and at the hearing is not what it was, and the left-handside of the back of the panel is the strength of an ordinary crystal set single telephone jack. is certainly not good enough for my 367 THE WIRELESS CONSTRUCTOR March, 1928

"TheCottager"continued point of the tuning coil, plus a high - ratio low -frequency transformer and note -magnifying valve.One or two practical points make for great ease of operation, one being the provision of an open -circuit jack so that the listener can leave the set at a moment's notice, without trouble of taking the headphones from the head-simply by withdrawing a plug-and a variable filament resistance instead of an on -and -off switch so that the filament of the valve need not be run brighter thanisnecessary,thustosome extent prolonging the life of the valve. At the same time, as 2 -volt valves are recommended thevalveitself cannot be injured by the filament resistance being turned. to the " full - on " position. Reliable Crystal The crystal detector is of the semi- permanent type which maintains its adjustment over very long periods, The set when tested proved surpris- crystaldetectorandsingle -valve and can be very simply reset without ingly sensitive-far more so than had magnifier,paiticularlyasmodern lifting the lid of the cabinet, as it is been expected from thecombina- transformers and modern valves are fixed. to the front of the panel, while tion. EXperimenters haverather vastly superior to those in use a few the change tothe 5 X X band is overlooked the undoubted efficiency years ago. made by changing a single coil. ofthisparticular arrangementof The particular circuit makes the receiver very selective, there being not the slightest difficulty in separating 5 G B from 2 L 0 at even four or five miles, and in the London area 5 G B and 5 X X come in at very good strength onquite a small indoor aerial.After dark, on a good outside aerial, Langenberg, Hamburg, Frank- furt and Madrid have all been heard clearly in the headphones. While it is not intended that such a set should be used for receiving these distant stations, the fact -that they have been received is a good index of the -sensitivity of the set and shows what a good reserve of power there is for those who wish to listen to the local station on quite a small aerial, or toreceivethatstationatbetter strength than an unaidedcrystal set would give. Simple Circuit The circuitis shown inFig.1. High-tensionnegative isjoined to low-tension negative, so that in the case of high-tension batteries such as the Lissen, which are tapped at one end for gridbias,this one high- tension battery can supply both the high-tension and the grid bias.It is, however, just as simple to use a You can sec practically every lead in this bach=of-panel photograph.The terminals from left to right are H.T. plus, H.T. minus, G.B. minus, G.B. plus, L.T. plus, separategrid -biasbattery, and so L.T. minus, earth and aerial. positiveand negativegrid - bias 36S M Irch, 1928 THE WIRELESS CONSTRUCTOR

" The Cottager "-continued

terminals are provided. A small two - are all of the one -hole fixing variety, as LIST OF COMPONENTS. voltaccumulator,ahigh-tension indeed are some of the crystal detectors 1 Panel, 10 in. x 7 in. (The mahogany finish looks well, such as Mahogany battery, and a valve are the only that can be used in this circuit. Ebonart, Radion Mahoganite, Becol accessories over and abovethose mahogany finish,or anyofthe required for an ordinary crystal set. H.T. and Grid Bias ordinary black polished panels will When constructional work has been be just as good electrically). The parts should be mounted on 1 Cabinet to take same, with base- the panel first ofall, then fit the completed, join the accumulator to board 7 in. deep (Artcraft,Bond, terminal strip, valve holder, trans- the two terminals marked and the Cameo, Caxton, Digby, Makerimport, former and coil base on the baseboard. high-tensionbatterytothetwo Pickett, Raymond, etc.). 1 Ebonite strip, 7 in. long x iin. Having done this, attach the front terminals on the extreme left (looking deep, carrying eight terminals as paneltothebaseboard, and wire from the back).If you are using the marked. up according to the drawings and Lissen H.T. battery with incorporated 1 Variablecondenser, 0005mfd. photographs.The holes for mounting grid bias, follow the instructions on (Any of the good makes advertised in this journal can be used.That thecrystalclipswillvarywith the label of the battery.In such a shown is the Formo). different makes, so be careful to follow case it will not be necessary to make 1 Open -circuit jack with plug (The the maker's instructions.The con- any connectiontothegrid -bias Lotus is shown.There are many positive terminal on the set.Notice otherexcellenttypes ofjacks denser, jack and filament resistance available,suchas *Bowyer -Lowe, A photograph that the lead going from the aerial Edison -Bell, Igranic, Lotus, Frost, which will help you terminal to the centretap of the withthewiring. - Raymond, etc.). Note the leads to coil is flexible, and do not forget to 1 Good crystal detector (That shown the jack, the short make this connection.Be sure, too, is the Brownie Permatector.There tag going tot he are numerous two -crystal permanent II.T. terminal and when wiring up the set that the or semi -permanent detectors avail- the longer one to moving plates of the variable con- able). the plate socket of denser are joined to L.T. negative and i Suitable dial, if this is not provided thevalveholder. withthe condenser (That shown to earth. is the Radion). If you are using a separate grid - 1 Anti -phonic valve socket (Benjamin, bias battery then you will need to Bowyer -Lowe, B.T.H.,Burndept, Burne-Jones, Igranic, Lotus, W.B., Ebonart, etc.). 1 Baseboard -mounting coil socket. 1 High -ratio low -frequency transformer. SPECIAL NOTE.-To get the best efficiency out of this arrangement it is essential that there should be abig step-upinthetransformer. That shown in the illustrationis the Pye, 6 to 1 ratio.Other makes of high - ratio transformer, not less than 6 to 1, can be used, but do not expect to get the same results if you use a transformer designed primarily for ordinary intervalve coupling. 1 Centre -tapped No. 60 coil for ordinary broadcast band, or one centre - tapped 200 coil for the 5 X X range, or both, as desired. Wire for wiring up. Inadditionyouwillneedthe following accessories : 1 Pair telephones. 1 2 -volt accumulator. 1 High-tension battery, 60 -volt. NOTE.-The LissenH.T.battery is tapped at one end for grid bias.If you do not use such a battery you will require an additional grid -bias battery of C. volts. 1 L.F. valve, 2 -volt (Any good make. Choose the L.F. type rather than the power type, as the L.F. valve will give louder signals than the power. The power valve is only for use when you have very strong signals operating a loud speaker.In such cases the power valvewillhandle the energy without distortion, but will not give quite so high a magnification.In this case we do not get strong signals for a loud speaker, and therefore itis much better touse an L.F. or general-purpose valve).

369 THE WIRELESS CONSTRUCTOR March, 1928

" The Cottager continued use both grid -bias positive and grid - itwillgo),and slowly turnthe instead of a 10 -ohm, and do not turn bias negative terminals.The choice condenser dial.You will soon pick it more than two-thirds of the way of H.T. should be the: maximum of up the local station and will find what on.In any case,only turn it far your battery, say, 60 volts, and the astonishing strength and purityis enough on to get good reception. grid bias should be arranged according obtainable from this set. The writer would be very pleased to to the instructions given by the valve hear from readers who build this set, maker in the leaflet sent out with the Two -volt Valves giving the distances over which they valve.When connecting your tele- It is quite possible to run the low- are able to receive the nearest sta- phones to the jack, he sure that the tension or filament supply from two tion, and also the strength of signals positive leadof the telephonesis dry cells connected in series, but in on small indoor aerials, and the like, joined to the terminal of the jack this case care must be taken not to since this information is very valuable which makes contact with the lead overrun the valve filament by burning to other readers. going to H.T. positive.In the case it too brightly.It must be remem- Queriesonthesetshould be of the Lotus jack you will see easilybered that two new dry cells will addressedtothe WIRELESSCON- which connection to make, as the give three volts, and the maximum STRUCTOR Query Department, accord- contacts are marked" ball "and that must be applied to the filament ing to the instructions given on another " stem," the stem going toH.T. of a 2 -volt valve is, of course, two page. positive. volts.When using two dry cells to heat the filament (this method is not *******************4 Remarkable Purity recommended when accumulators can When aerial and earth are joined, be charged) only turn the filament THE RADIANO THREE tit and the 'phones plugged in, turn the resistancejust on, or, betterstill, " 41 on the L.S." filament resistance full on (as far as use a30 -ohm filamentresistance ********************

WIR/NC D/A CRAm SIR,-It may interest you to know the results I have obtained with the SNORT LONG " Radian Three,"whichIcon- TONGUE TONGUE structed two months ago.With this set I have identified in all 41 stations on the loud speaker at good strength. These include Schenectady on 379.5 and East Pittsburg on 62.5 metres, and have received several others un- identified. 's From these results you f/XED will agree that it must be an excellent set. Quality is as good as can be desired. I use Ormond condensers and Igranic (1st stage) and Brandes (2nd stage) transformers. Stations Received r LongWaves-Norddeieh,Radio - Paris, 5 X X, Motala, Koenigswuster- hausen,Kalundborg, Warsaw and Hilversum. Mediunt Waves-Vienna, Brussels, 5 G B, Berlin (Witzleben), Langen- berg,Frankfurt,Glasgow,Cadiz, Cork, Hamburg, Toulouse, Manches- ® 01 ter, Stuttgart, Schenectady (W G Y),

Madrid (E A J Y), Leipzig, London, Cardiff,Barcelona(E A J I),San TO CENTRE Sebastian,Bournemouth,Almeria, T.4/2 Of co/A Breslau, Dublin, Newcastle, Belfast, Nurnberg,Hanover, Dor t m u n d, Bremen, Stettin. iui Short Waves-East Pittsburg D K A). Wishingthe WIRELESS CON- STRUCTOR continued success. Yours faithfully, At- CB.- CB+ z.r+ L.T.- E A V41. Middlesex. JOHN B. BARNARD. 370 March, 1928 'TIE WIRELESS CONSTRUCTOR

wrFo un PERCY W. HARRIS milts.

PrHE " Business Man's Four " made WI11111111111111111111111111M111111111111111111111111i111111111111P: The experience is already " in the its first public appearance on 'E. TheEditorinvited aB.B.C. instrument," and, therefore, the he - the evening of January 12th, = engineer to hear his latest and = gets just as good results as the when the Editor demonstrated the E bestset, and a special B.B.C. E more advanced student. complete receiver before the Kensing- message on the subject is one of 7..t E the featuresof this importantE. A B.B.C. Test ton Wireless Society.The meeting- article. place of this society is roughly two 7=1 The importance of a simple receiver miles from 2 L 0, and as an outside 7.1 111111111111111111111111111111111111111111111111111111111111111111111117: which can be used for general purposes, aerial was used, of a size comparable the fact that, once adjusted, a variety and which does not oscillate, cannot With that adopted by most listeners, ofstations can be picked up and be over -estimated, particularly at the an excellent opportunity was afforded general searching can be carried out present time, when several designs of demonstrating the good selectivity without any oscillation and, therefore, have been put out without the slight- of this instrument. without any radiation which would est warning to constructors that turn cause interference- with neighbouring ing one of the dials too far will cause a Without Interference receiver's. The preliminary adjust- great dealofinterference. Bearing The incorporation of a wave -trap ments of the set are made without this in mind, an invitation was issued accounts largely for this, and itis aerial and earth connections, so thatto the B.C.C. to send an engineer to interesting to observe that full loud- the listener, in making these prelimin- witness a demonstration. This invita- speaker strength from 5 G B with aryadjustments,will notradiate tion was accepted.The instrument excellent quality was possible with- squawks and screeches, which too was set out with batteries, valves, loud out any trace of 2 L 0.'When the wave -trap was cut out 2 L 0 came in " all over the dial," but with the trap in circuit 5 G B and Langenberg could be heard quite free from any interference from London. During the lecture the great simplicity of the reaction adjustment was demonstrated,and two valvesof different types were inserted in the receiver and the two reaction controls adjusted very rapidly.It was, of course, impossible in such a short space of time to show thesame experiment with all makes of valves, but, as explained in last month's issue, such tests have been conducted in the laboratory, which show that every A bac k-of-pcnel vkw of the " Busi- ness Man's Four," the set which embodies the make ofresistance -coupling.valve Editor's latest invention-a wonderful system of will give the constant -reaction effect. constant -reaction and sensitivity.

Many Stations Heard often occur when a reaction receiver is speaker, etc., on the table and the The remarkably good quality of tried for the first time.Half an hour B.C.C. engineer was invited to switch reproduction given on a cone loud in trying -out the circuit itself without it on and to turn the tuning knob. speakerbythe " BusinessMan's aerial and earth connections will be On doing so, he immediately picked Four " was widely remarked upon, amply sufficient to show any reader up,ontheloudspeaker,fifteen and a number of different stations what to do, and once he has found the different stations (not including, of were picked up at varying degreesadjustments all he has to do isto course, those on the 5 X X range), of strength-all, of course, on the loud connect aerial and earth and turn the and remarked upontheamazing speaker.After the meeting members single tuning dial, whereupon he will simplicity of handling, and the general had an opportunity of trying out the pick up several stations, the number sensitivity of the circuit.The next Set for themselves. depending upon his aerial, his local step was tocompletely upsetall One of the most important features -conditions, and whether it is daytime adjustments and to invite the visiting about the " Business Man's Four " is or night. engineertoname any makeof 371 THE WIRELESS CONSTRUCTOR March, 1928 More about the "Business Man's Four"-continued

resistance -capacity -coupling valve now a small wooden baseboard measuring In the case of the Litz wire, how- on the market. A certain make was 21 in. by 21 in. and about in. ever,a somewhat more elaborate named at random ;the valve handed thick, the intention being that this method must be adopted sinceit to him, whereupon he himself made baseboard shall bescrewed down must be remembered that in making the adjustmentsdescribed inthe directly upon the wooden base of connections to a Litzcoil at any article, and in a few minutes put the the receiver.The coil is mounted pointitisessentialthat a good receiver inthestateofconstant onthisinahorizontalposition, soldered joint should be made to reaction. with its centre 2 in. above the lower every strand of the wire.In this The B.B.C. engineer was obviously edge. of its baseboard.The coilis case, then, the simplest way isto impressed by the evidence of the rare wound uponapieceofebonite, regard each tapping as a finishing combination of sensitivity and Paxolin,Pirtoid,orsimilargood point of the coil, cutting the wire and stability. Anything that can be done material, 2 in. in diameter and 3 in. passing the end through two small to reduce the risk of radiation when long, and this can be mounted in any holes as before.- Then drill -two 'mire searching fordistant stationsisa convenient fashion which does not small holes farther round the tube, matter of intimate concern toall entail the use of large pieces of metal. and secure the end of the wire from listeners and consequentlytothe In the trap illustrated the method thereelasbefore,and carry on B.B.C. itself. is to fix an ebonite end disc into the winding until the next tapping point tube and attach this by means of a is reached, where the process should The Daventry Range screw to an upright strip of three-ply be repeated.At each tapping point, Withregardtothelong -wave wood,whose loWeT extremityis therefore, the coil will be broken and side,it must not be forgotten that similarly secured by means of screws two ends will be left sticking out. when one reaches the 1,000- to 2,000 - to the edge of the little baseboard. metre range the efficiency of resistance - The coil consists of sixty-four turns Careful Soldering Required capacity amplification has risen very in a single -layer of either No. 28 D.C.C. The ends of the strands should then considerably, and therefore a different wireor,-alternatively,thesame be bared at these points, and all care- adjustment Must be made.It will fully soldered together, the two ends probably be fbund that the amplifica- next being soldered to each other tion is so high'in the first stage that and to. the connecting wire. a dimming of the ELF. valve filament This point brings us to the question by means of the baseboard rheostat of whether Litz or solid wire should will be necessary in order to obtain be used.The answer isthat Litz stability.The best way of arriving should by all means be used by the at this setting is to adjust both the constructor who feels that he has bad Reinattz-comfenser and the feed -back enough experience of soldering and conden4r from the plate of the de- handling fine wire to be certain of tector valve toa minimum value, making a really perfect joint at each and then to set the tuning condenser point.At one time it was believed with the plates " all in."With the that Litz wire was notof much - wet finger touch the fixed plates to see Y330 - value our the broadcast band of wave- The wiring connections can be seen Whether yofi get the double " plock " above. lengths, but more recently research characteristicofoscillation. Itis has shown us that even on these waves assumed that when you do this thenumber of turns of 9/38 Litz wire. there is a very definite advantage to volume control is at thefull on " As the coil is wound, tappings are be gained by the use of this material. position (as far as it will go to the made in the sixteenth and twenty- Itis,therefore, desirable that -it right) and that the baseboard resistor fourth turns, these being the alterna- should he used in this case provided is also set with its slider at the " full tive positions for the aerial tap, the that the constructor is quite certain on " position.If you find that the set ends of the windings being secured thathecan guaranteeaperfect oscillates (as it probably will do) in by the simple procedure of passing joint.This is absolutely vital, and this position, dim the high -frequency them through two small holes drilled if you feel the least doubt about it filament by means of the baseboard in the tube at the correct points, by all means use the solid wire and resistor until it just does not oscillate. while the two tappings may be made be sure of a coil which is at least in a variety of ways.For example, reasonably good. The Wave -Trap in the case of the solid wire the whole It is best to dim it just a little coil can be wound without making The Main Difficulty beyond this point so as to have in any tappings whatever, and then the At this point it may be as well to hand a little reserve from the feed- sixteenth and twenty-fourthturns mention that the real difficulty of back condenser from the plate to the can be prised up slightly with the using Litz is simply that of properly first grid.You can then make the blade ofa pocket knife, and two baring, cleaning, and soldering each adjustmentsasdescribedinlast short pieces of match stick about strand, and this will be found a very month's article for the shorter waves. half an inch long slipped under them. much easier process if the type of Turning now to the practical details The wires thus lifted up can be Litz chosenisthat which issilk- of the construction of the standard scraped bare of cotton covering by eovered only without enamel' insu- wave -trap,itwill be seen in the means of a knife, and the appropriate lationofeach strand.With this diagram that itis assembled upon leads soldered on to them. (Continued on page 404.) 372 March, 1928 THE WIRELESS CONSTRUCTOR

N ,11.i.74X47.Atitt,DISTANCE

From the void comes the tiny ith strength weak voice. . Hamburg per-

haps-or Rome..Tantalising, isn't it, that signals are not strong enough to be understood ? 21 It is when you are trying for distant stations that you will appreciate the service Lissen transformers give you. Space - weakened signals are coaxed from minuteness to magni- tude. Yet if you judged them from their purity and clarity you mightimagineyour foreign station inthe next town.

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Lissen transformers fully amplify every note, every tone, every over -tone, and

every harmonic against a background of dead silence. Test one for seven days against the most expensive transformer you can buy. If you do notdefinitely .preferthe Lissen transformerineveryrespect, returnitandyour money will be refunded. Turns ratio 3: iResistance ratio q: r Guaranteed is months. LISSEN LIMITED, 26-30, Friars Lane, Richmond. Surrey. LISSEN(1,6Ingina Director: Thomas N. Cole.) TRANSFORMER8b you can use three LissenTi ansfornters in (ascade THE WIRELESS CONSTRUCTOR March, 1928

11.TFROM YOUR MAINS 44,COSSOR 0r0.001MAKER " Fresh as the Daly,' IF you have electric light you eve-ry morning. are wasting money every time you buy H.T. bat- tcries.Start saving money- A PERMANENT SOURCE OF H.T. build an H.T. Eliminator and SUPPLY THAT RE -CHARGES IT- get current from your mains. SELF WHILE YOU SLEEP. Send the coupon for a book which shows you how to do No matter how much you use it-night after night, it." How tobuildyour week in and week out --the Standard self -generating own H.T.Eliminatorfor Leclanche battery will provide your set with abundant A.C. or D.C." is writt2n by H.T. supply. an authority for the makers Enthusiasts everywhere are loud in its praise,, and they of T.C.C. Condensers. If you have good cause to be. follow its concise instructions, Itbrings constant, permanent, unfailing H.T. current clear photographs and simple at a price within the reach of all.The secret . . . . diagrams you will have no IT RE -CHARGES difficulty in building an Elimi- nator which will give you constantH.T. fromyour electric light mains-for neg. 0;64.0000 ligible cost. And, if you use et T.C.C. 600 volt Condensers, you will build an EliminatOr Stocked by Take the first step that is utterly safe and reliable. Ilalford's Cycle bysending for Sendthecouponto -day. Stores. FREE Booklet State number and describing every Itwillcostyounothing. typeofvalve detailforinstall. usE when ordering. ing and maintain- ing'this super- Single units of11 efficient and volts from 41d. money- saving each. battery. For 2 Valve Sets,A.4,90 Write NOW to Forvolts, 3-5 25 Valve 1. Sets, D.6, 108 volts,37 3. Dept. G, ForSuperSets, F.6, 126 volts, WETH.T. tD E N 69.6. BATTERY CO. co N GOODS VALUE 0., 10- OR OVER 12, Brownlow 1.7 CARRIAGE PAID. Deferred Terms Street, London IG'c'3 t2P's'" NO DEPOSIT W.C.1 CA&Z \D.V. k,0,42'(03, G. Cfi "CPkt,$ stoi \14 vri vomAto Aft 6{'(' 161).'1 ree!

pa t. I. dielh " sals 11'1 .1 me 1111 on. 1.611 la" 1111.11 me mi ti AMi 411.0 l ISMS, 11111, 110,11, 4 "MO' 11 40' 40' 49" stviPIY NP' 40' qr. '0" 11' () 7heVilial _Power la Radio! M.B. 50 iiiffMn 374 March, 1928 THE WIRELESS CONSTRUCTOR HAPPENING S AT SAVOY HILL

By OUR SPECIAL COMMISSIONER

THE Board Room of the B.B.C. Since 5 G B's new masts have been Hill is not. satisfactorily committed. might appropriately vary the changed, and the power again in- I -refer to the permanence of 5 G B. classic inscription over its door creased, much of the trouble in the The policy announced last year, toread :" Abandon publicityall North and Nerth-West has been met. and repeated frequently, was that ye who enter here."Anyway, this Yorkshire has now been brought for 5 G B was only a temporary experi- has always been the rule at Savoy Hill the first time into a service area of ment, and that it would probably since the early days of the old Com- the Daventry Junior station.But close down in August or September of pany. The recent brawling in public listeners in Birmingham who fondly 1928, when the new London Regional is decisive proof of the wisdom of expected that therecent changes station might be ready.This will the Company in these matters. would help them have been disap- never do, and I hope Savoy Hill do pointed, On the other hand, it would not base any budget plans on such Troubled Times be difficult to show that the service an unsound foundation.5 G B has they are now getting is really inferior been a tremendous success, both ex- During all the troubled times of perimentally and actually.It has the original B.B.C., when there were in any way to what they were getting acute differences between both the before the masts were changed. taken its place as the Midland Regional interests and the opinions of indi- transmitter,anditmust not be The Permanence of 5GB tampered with.However difficult it vidual members of the Board, not a may be to solve the problem of dis- murmur of these differences reached The argument of the B.B.C. is that tributing wave -lengths, some means the outside world.However acute Birmingham,theWest,andthe must be found to leave 5 G B alone. may have been the argument, it was South are getting just as good a The washing -outof 5 G B would behind closed doors. To the public the service, Northand befollowed by a Storm the like B.B.C. preserved unbroken. unity ; to North-West arebroughtintothe of whicheventhe B.B.C:has the public it was engaged only in pro- 5 G B scheme of things for the first never encountered, and one which gramme making, its proper function. This sound tradition,established by Lord Gainford, Sir William Bull, and their able colleagues, was carried on for a period under the Corporation, but it was obvious from the beginning that there were elements in the new Board which neither understood nor agreed with thisattitudeofself- effacement. No one outsidethe B.B.C. knows what has been happening during the past year ;'but it is fairlyobvious now thatconstant conflict has been in progress, and that at last the trouble has been exploited in public. Now with". ultimata " flyingabout,with acute personal differences freely canvassed; the position of the B.B.C.is weakened. A Blow to Prestige The alleged subject of the trouble is of far less consequence than the The German people always have been very keen on physical training, and now that blow to. the prestige of the B.B.C. broadcasting services have been established a fresh outlet for their gymnastic If these incidents are continued, then energies is available.Health lessons are broadcast regularly and this photo shows two youngsters carrying out the instructions given from the loud speaker.So far my original contention of the folly nosuch ideas have been exploited by the B.B.C.-Why? of the change in constitution will be fully, if sadly, proved.The limited time.The B.B.C. declares that thec 1inl ythe B.B.C. could not oppose. liability form of organisation, with a experimentwith5 G B has been businessboard, was immeasurably successful, and that they are learning Who Wants Controversy? superior to this elaborate compro-a lot that will be of help in develop- The controversy, about " contro- misebetweenStatecontroland ing the new system of distribution. versy " has become curiously unreal. devitalised private enterprise. But there is a point on which Savoy Eminentwritersandleaders,of 375 THE WIRELESS CONSTRUCTOR March, 1928 Happenings at Savoy Hill-continued thought have debated the various broadcasting is attention to light accountsappearinginCanadian aspects of the problem ad nauseam. entertainment, variety, and middle- newspapers. This incident appears to And the one point that really matters brow music. Every penny available ha-N4e had an unpleasant effect, which hasnot beenmentioned. What should be spent on these things. The subsequent apologies and explana- are the wishes of the two million B.B.C. would do well to reduce its tionshave notquitedissipated. people who pay the receiving licence talks by a good 50 per cent, and cut Then Australia, New Zealand, and fee ? out " yapping " of all kinds. South Africa were upset about the The demand for" more contro-- alleged lack of graciousness on the vexsy " means more talk if it means B.B.C. Unpopular in the part of the B.B.C. in failing to send anything at all.No doubt some of Dominions a Christmas or New Year greeting the present talks will be made less The B.B.C. seems to fare better over 5 S W. dull and therefore more palatable, withits European relations than The newspapers " down under " hut those whose business it is to look with its Empire ,relations.The part are openly charging the B.B.C. with after the so-called " serious " side of taken by Savoy Hill in the Geneva anti -Empire sympathies.At least broadcasting will be quick to take Union's work is praiseworthy.The one of the Dominion Commissioners advantage of the situation.It is appointment of a specialist officer to in London is reported as having really a golden opportunity for the look after the foreign side is justified made complaintstotheBritish " uplift " school.Mark my words, and the B.B.C. stands well in the Government.I do not believe there ifthereispresently aconcession opinion of the broadcasters of the is anti -Empire bias in the policy of from the P.M.G. about controversy Continent. theorganisationofwhich Lord in the programmes, this will be made So far so good.But the position Clarendon is the titular head, but the excuse for an all-round increase is entirely different within the Em- I think there is some very stupid oftheproportionofprogramme pire. Canada was the first to be managementofthe Dominion affairs " end of the B.B.C. business. The probability is that it is no one's business in particular, and therefore goes by default. Obviously it cannot be handled by officials engaged in the European end of the business.If the Gover- nors are looking for odd jobs, here isonebadlyneedingattention. Lord Clarendon and Dr.Rendall should beabletotidy up the Empire mess in about half an hour ofconcentration. Butsomeone must tidy it up soon. Progress of Radio Drama Mr. R. E.Jeffrey; the B.B.C. dramatic producer, keeps on slogging away, constantly bringing more grist to the mill.It is no exaggeration to say that Mr. Jeffrey has done more for B.B.C. programmes than any other specialist. He discovered early on that a new technique had to be evolved and that sound effects were the first part of the problem to be tackled. Every now and then some " idea Elaborate radio gear is now fitted to the up-to-date air liners. Though compactnessmerchant "or bright star of the is - a necessary- quality a remarkable amount of gear can be stowed away in antheatre production world is put over extremely small -space. Above can be seen some of the radio gear employed in a modern aeroplane. On top is a small transmitter, which has underneath it theMr. Jeffrey ;but this leaves his receiver.. Farther down is a large transmitter and below this the reel used forimperturbability quite unruffled. He letting out the aerial wire.On the left is the motor generator which supplies the H.T. and which is swung outwards when the plane is in flight. carries on the main job, and the programmes offer a faithful reflection allotted to talks and education.No aggrieved.An invitation was ex- of his accelerating success.Thanks sensible person in actual touch- with tended to the B.B.C. to be repre- entirely to R. E. Jeffrey, the B.B.C. public opinion would approve such a sented at a conference in Canada is now easily pre-eminent among the course, that is,if his object were to thisspring. Theinvitationwas world's broadcasters in the vivid satisfy public opinion. -ignoredfora longtimeand reproduction of sound and dramatic . The crying need of the moment in then curtly declined, according to " atmosphere." 376 - March, 1928 THE WIRELESS CONSTRUCTOR

I THREE WINNING LINES

THE LISSEN COILHOLDER Pro iflcrce of control to permit of extremely selectivetuning.Gear ratio selected as the best for all practical purposes.Big knob for comfortable finger grip and wide range of movement with one turn: No slip or backlash, coils will not move as the result of -their own weight.Noflexibleconnections to break.Moving block on the right-hand side, but may easily be changed over to left-hand side by followingthe simpleinstructions enclosedwitheachcoilholder; Model A,With 2in. spindle (2 way).. 4,6

Model B.With 5 in. spindle (2 way) .. 5f6

LISSEN LISSEN RESISTANCE CAPACITY HEADPHONES Never before was it thought possible commer- COUPLING cially to make headphones so light and at the ,,ame time so sensitive.These headphones are 'rovides a complete Resist- so light they may be worn throughout an evening without the wearer realis- ance Capacity Coupling Unit: ing they are on the head.Cords will Includes two LISSEN Fixed cot twist or tangle but will always Resistances and one LISSEN

hang straight down no Mica Condenser. - Values matter how the head incorporated have - been may be turned, moved selected ' as themost, suit- ortwisted. The two earpieces are extremely ableforgeneral use,but sensitive and both are theresistancesareeasily exactly matched in im- interchangeable. pedance. They settle May bemounted at once into comfortable upright or flat positions and may be securedthere by the singlemovement of a special joint ..ba.11! 8/6

LISSEN LIMITED 26-30, Friars Lane, RLehmond, Surrey

Managing Director :Thos. N. Cole

LISSEN LEADS IN RADIOPARTS

377 March, 1928 THE WIRELESS CONSTRUCTOR

IF, to -night, at a friend's house, you a great little were to hear the krowit Mascot Loud Speaker without knowing you were condenser/ listening to a loud speaker, you would be almost sure to ask who was his singing friend. Then when he replied that it was Dubilier fixed condenser a loud speaker you heard, you would THEwith its di -electric of best laugh and offer himthe otherleg. India Ruby Mica isher- At that his eyes would sparkle, as he metically sealed into its bakelite disillusioned you, and you would be quite case to render it absolutely im- astonished that a mere instrument could mune from the effects of damp or be so human. After that you would want -dust. a Vt0W11 Mascot Loud Speaker for your- Before being sealed, however, the self, and when you had bought one you condenser element is subjected to would say that in all the world there was no better place than your own fireside, in your old chair, enormous pressure, immersed in with this almost -living loud speaker to thrill boiling wax, and kept so rigidly the evening hours. clamped when assembled that the excludedair can never regain The Wireless shop round entry. the corner has the 16t0wil Finallytheexcellentbakelite Mascot Loud Speaker Orly 90/.isitsprice. Dubilier Mica moulding acts as an extremely Condensers. high resistance and prevents losses Types 6to and 620 through current " creeping " (vertical) across between the terminals. 0.00005 to 00009 mfd. 2/6 Years of experience and specialised croot to 0'006 mfd. 3/- craftsmanship go to the making 0.007 to 0.009 mfd. 3/6 of this great little condenser ;see 0.01 mfd. ..4/- thatitfigures prominently in 0.015 mfd. ..4 6 every set you build.

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KX 1140 AdoL DI the Didilier Condenser Co.(1925) Ltd.,Dncon Works, Victoria Rd., North Acton,W.3 378 March, 1928 THE WIRELESS CONSTRUCTOR'

V 14 &te. wilt.E.LEC'SNAYVAPER

Soclampand clammy -- Let joying her evening out, the kitchen garments behind HoWever, by us start again.So damp and meat -chopper is borrowed.An old Contriving a kind of ballet skirt out clammy is the weather at the batteryisthen placed upon the of a pair of dusters and' two clothes moment ofwritingthat mossis kitchen table, and a few shrewd blows pegs, he soon made himself perfectly sprouting between the vanes of my with the back of the chopper serve presentable.Myself, I refused. to do variable condensers, and mushroom to splinter the bitumen sealing which any heaving, and insisted upon the things are growing upon the high- covers the cells beneath.Bitumen is Professor fetching a saw from his tensionbattery.Thatbatteryis awfully jolly stuff. workshop, with which he cut off the providing me with one of the most If you give it a really good whack legs and. 'the back of the chair.I difficult problems that I have yetit flies about the place in the most was then able to assume an upright encountered.The instructions issued satisfactory way..It treads splen- position without further ado. by its makers state that the batterydidly into carpets, heartlrugs and - On my way- home. I encountered must be kept in a cool, dry place. things, and if anybody, stands on it Sir. K. N. PePper, who tackled me in Now the only places that I possess whenithas got warm _heeither a nasty kind Of.way about a ridiculous are either cool and damp, or dry and remains fixed in position or takes the littleMatter of a couple of geared warm. carpet with him when he essays to variable condensers that I had bor- When I consulted Professor Goop move. rowed from him only a couple of about the difficulty he was not really yearsbefore.To show my utter Very helpful.The only suggestions We Commence Investigations disgust at the violent language that that he had to make were that either A quaintlittleexperiencetook he was using, I simply shrugged. my placeon thefirstoccasion when shoulders and turned my back upon I Professor Goop and I, in the absence him.Thinking that his opportunity of both Mrs. Goop and thecook, had corne;Sir K. N. launched a mule - exploredtheinnardsofahigh- like kick.The ambulance removed tension battery in the kitchen of hiM to hospital with two broken toes. " The Megohms."I was armed with the chopper whilst Professor Goop. The Various Ingredients " Bitumen is awfully jolly iduff." wielded a coke hammer. Between us, But toreturn tothe drycell we fairly made things fly. battery.Having removed acell, I should install a meat safe thingmejig Wearied at length by our labours, the next part of the business is to in the drawing -room and keep the we sank into chairs and proceeded cut it in two in order that we may battery in that or, alternatively, that to examine the cells that we had inspect its little inside.There are, I should forswear fires for the rest of laidbare.Havingrecoveredour of course, heaps of ways of doing the winter, and apply blotting paper`wind, we decided. to take the remains this, but by far the most sporting is to the battery every four hours. down to the potting-shed-I should to place the thing upon the chopping - say, the laboratory-for further in- block and to have shots at it with The "Dry " Cell vestigation, since, as the Professor sabre,cutlass, orbattle-axe taken I do not suppose for a moment that pointed out, Mrs. Goop was about from thewallsofyour ancestral the intelligent reader really under- due to return.The Professor and I halls. The unsporting who don't like stands how the dry cell functions, and. rose simultaneously to our feet.The I have found that every writer upon chairs upon which we had been sit- wireless, whenever he gets on to bat- ting rose with us.The bitumen had teries, skates neatly over this part of done its deadly work. the subject and passes hastily on to something else. For this reason I Sir K.N. is Annoyed feel that a little explanation in my own We thought of climbing out of our lucid style will be widely appreciated. trousers and leaving them behind, " The chairs upon which we had been The dry battery is called dry because but the dictates of modesty prevented sitting rose with us." it is really wet.If the battery be- the carrying of this scheme into effect. comes really, dry it ceases to bat, or, After some discussion we decided that to use such manly weapons can obtain in other words, dries up. the only thing was to use violent a longitudinal section by fixing the Every enthusiast should seize the measures.I placed. my foot firmly cell in the vice and. working away at earliest opportunity of becoming ac- upon the Professor's chair,whilst it with emery cloth. quainted with the inside of a dry cell. he heaved.With a sound likea Whichever method is employed it To do so is perfectly easy.- Having "superatmospherichecamefree, will be fOund that when the cell has chosen a time when the cook is en- leaving the entire seat of his nether been cut in twain akiiag its long axis 379 f HE WIRELESS CONSTRUCTOR March, 1928

In Lighter Vein-continued there isdisclosed. to view a rather filled with water. When you turn the thingmetite, which is positive, plus beastly mess.Just inside the zinc tap on water flows from the tank down oneor morethingmejigs,which pot is a nasty sticky compound which toearth,doesn'tit ?Well,just are negative.Water, though froth - loOks and feels rather like bird -lime, imaginetheprocessreversed andblowers may find it hard to believe but is really sal -ammoniac mixed with water flowing from the ground into thisstatement,isan exceedingly whatyoumaycallit and thingmetite. a tap in a high tank and you will not active liquid.It has the effect of Immediately surrounding the carbon have the slightest difficulty in seeing ionizing solids dissolved in it, which 'positive element (or anode, said he how the battery really functions. means in plain language making them with a condescending smirk)isa go all niuzzy. horrible black - mince compbsed of A "Practical". Illustration They go on, in fact, just anyhow. manganesedioxide(quitediStinct When Ifirstlearntaboutthis Some of then" chuck electrons away from ordinary oxhide such as is used reversal of the so-called facts that one and become positive, whilst others for the manufacture of boot soles and learnt in one's younger days I was pick up any "stray electronS that may restaurant steaks) and powdered car- fearfully bucked.Since positive is beknockingaboutand become bon. Should you happen tobe represented byaplussignand negative.Thus the bird -lime stuff in going to a fancy dress ball you will negative by a minus sign it became a dry cell plays all sorts Of funny find that a little of this rubbed on the perfectly clear to me that the over- games, part ofit becoming, so to face and hands will turn you into a draft about which my hank manager speak, overdrawn, whilst another part nigger far more quickly and more was doing so much silly talking was permanently than burnt cork. really a credit balance. Full of the new knowledge, I went Why. Positive is Negative round to see him at- once.Itis curioustofind how obtuse some Having followed. my directions so people drawing big salaries can be at far you are now thoroughly familiar times. When I demonstrated to him with the interior of the dry cell.The quite clearly that it was now known " Now ivater was long ago discovered next process is to use Monkey Brand 'that negative was really positiVe and by brewers and dairymen." and hot water.If Monkey Brand fails vice versa, and therefore his blessed. try glass paper.If glass paper fails I bank owed me quite a lot of money, I is heavily in credit.Anyhow, it goes would advise you to consult a beauty completelyfailedtoconvince thefor the zinc just as you and I go specialist, who for a trifling considera- fellow.After all, what can you expect for the fellow who digs his foot into tion will remove, the worn-out surface of people like accountants and othersthe front -door, and tries to sell you skin and make you look ten years of that kidney who when you makethe works of Dullbore in thirty-five younger.If the reader is under ten£100 shove it on to the Dr. side, and. volumes, with indexes and appendices. years of age he should stick to the when you spend the same amount The Zinc Succumbs glass paper. push it on to the Cr. side ?They Now that you have examined thesimply do not understand the funda- The poor old zinc, though, is much inside of the dry cell let us proceed to mental meaning of plus and minus and. less hardy than you and I.It suc- see how it works. You know, of course, you can't argue with them. cumbs to the attack, and it does so that current travels from the positive with certain reservations, just as you pole of a cell through a circuit to the and I, if we do sign the order form, negative.You really do know that. How the Battery Works date it February 31st, 1958. It is one of the things learnt at school But about these funny old dry The electrolyte-a neat little word, cells.The electrolyte consists of sal - this, derived from the Greek elektron, ammoniac and water. Now water, as meaning amber and luo, meaning I was long ago diseovered by brewers untie (if anybody can untie amber and dairymen, has an extraordinary I will award him, here and now, with effect upon the solution of which it the Most Noble Order of the Biscuit)- formspart. Ifused insufficient the electrolyte attacks the zinc just quantities it enormously increases the as we attack a steak when we are dividends. In the dry cell it serves an " Sir launched a mule -like kick! " entirely different purpose. You prob- feeling peckish. ably know, or if you did not you do Chunks of metal, which itdoes that you have not forgotten.I am now, that the chemical symbol for not seem to find tough, are torn out rather sorry about this, because the water is 1120.In the words of the andmasticatedby , thebird -lime first thing that you have to do now stuff.But just as the steak always that you have placed yourself for poet : looks rather better than it really is, instruction in the hands of the ultra- Young Wilkins was a thirsty lad so the zinc is able to place-meta- modern Wayfarer is to forget it as And now he is no more, phorically, of course-its fingers to its rapidly as you possibly can, or even For what he took for H2O nose as the electrolyte gets to work.. more quickly than that. Was 112804. It may part with chunks, but, they Really, the whole thing is abso- The symbol 1120 merely means that are not complete chunks. Each one, lutely simple. Just regard the positive water consists of two thingmebobs of asitisengulfed, leaves behind a pole as a kind of tank raised some hydrogen and one of oxygen.Each proportion of its electrons. feet above the surface of the earth and thingmebobis made ofacentral (Continued on page 402 ) 380 March, 1928 THE WIRELESS CONSTRUCTOR

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381 THE WIRELESS CONSTRUCTOR March, 1928

over. the end of the plug. These bends prevent the plug from being pushed too far in. A Simple Plug and Jack Mount the jack contacts on the Details of a tilde gadget that can easily be made by the home constructor. panel as close as possible to the edges of the hole and bend them in slightly. By A. V. D. HORT, B.A. The holes for the bolts which secure 33 MMMMMM 012 MMMMMMMMM 3 MMMMMMMM MMMMMMMMMM 0 MMMMMM 02 MMMM MMMMM elam.smecas,33 them should be on the line previously scribed on the panel. When you put in the plug, the ?THOSE pins which are fitted to -the Between the knob, which is held by ends of your 'phone cords were a short length of 4 B.A. threaded rod, never designed to stay under and the body of the plug is a strip of theheadsofordinaryterminals. 1, -in. ebonite. This has two holes at the You can, of course, provide them with ends and is meant to keep the leads special 'phone terminals, but there is in position. The ends of the leads are a great attraction in being able to soldered to tagsander the round - headed

Making the Jack 19R/L4. 3491"/OLE COT AWAY When you have finished the plug, SHA.0E0 PORT/ON. mark on the panel with a .punch the centre .of the hole behind which the round -headed bolts willslide along jack is to be mounted.Scribe a line the contacts and drop into the holes through the punch mark parallel toat the ends, making a firm contact, Two strips of brass form the jack the top edge of the panel, and drill while no difficulty will be experienced portion of the gadget. the hole ,with a Fin; drill. Round this in pulling it out again. circle scribe a rectangle with sides You must fix the 'phones securely plug the 'phones, or the loud speaker, in. and,in. long, and file out up to to the plug, but that is no disadvan- straight into the set which you are your lines with a small flat -file,till tage. When you put away the 'phones going to use. the end of the plug will just fit into Made from "Scrap" the hole (Fig,. 2). .Next take a " rat-tail -file, and The plug and jack shown- in thecut away the recesses at the sides photographs can be made of materials till the round -headed bolts on the taken from your box of scrap.The plug will pass through.Finally cut body of the plug is a piece of Fin. away a piece at the top of the hole to ebonite, and the jack contacts are clear the cheese -headed bolt. The plug two strips of stiff, springy brass. The can then be pushed through the hole remainderoftheassembly-bolts, one way up only. soldering tags, the knob, and so on- you can adapt .to suit the materials The Jack Contacts which you have by you. The dimensions of the brass strips Inserting the plug in the hole in the for the jack contacts are given in panel. 1'347 Fig.3. Before bending their tips, place each one on the side of the jack with the plug attached, you can be in its correct position, with the round- certainthatno" unauthorised " headed bolt resting in the hole in the member of your household willbe strip.Then bend the tip of the strip able to use the receiver.

T 4=8,4CL EA RANCE,:

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746 Drill the four holes in the plug first / of alli and tap them all 4 B.A.The contacts at the sides are round -headed iN bolts.This shape is chosen so that the plug will slide easily in and out of / the jack.The cheese -headed bolt on ,/ //ERE the top, of the plug is a refinement, / designed to ensure that the plug is always put in the same way round. The H.T. positive cannot then fail to STRIPSOF1/3; SRASS .fiCICCONTAcTs be connected to the correct side of (ALL./DOLES OF 4.8A. CLEARANCE.) the 'phones (Fig. 1). Z792 382 March, 1928 THE WIRELESS CONSTRUCTOR There isnosubstitute forSIX -SIXTY

If you want to get positively the best results from your Receiver you must use Six -Sixty. Nothing else will do. Take a Six -Sixty valve- here is scientific perfection. A valve which will cause your Receiver to yield maximum results at a minimum cost.Six -Sixty is a valve which will last much longer than most other valves you buy. The filament of a Six - Sixty valve operates at rated voltage without the slightest sign ofglow, and itcannot possibly sag. Do you know that eight of the range of Six - Sixtyvalvesconsumeonly-075 Ampere FilamentCurrent ? Isthereanything parallel to this in Radio to -day ?You know there isn't. Then considerthatmasterpiecetheSix - Sixty Cone Speaker. Imagine a Speaker which is mellow in tone, beautiful in appearance, a Speaker which emits every sound, whether of the human voice or of musical instrument, with a distinctness which has never before been achieved, and above all things, a Speaker which is economical to buy, and you have Six -Sixty. Six -Sixtyvalves,Six -SixtySpeakers-the most perfect combination in Radio to -day. PRICES OF SIX -SIXTY SPEAKERS PEDESTAL TYPE £2 5 0 CABINET TYPE £4 4 0 SIX -SIXTY Ask your dealer for attractive brochure describing the full range of Six -Sixty Glowless Valves,

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383 THE WIRELESS CONSTRUCTOR March, 1923 Haveyoutried this newLewcos Coil The range of LEWCOS Centre Tapped Coils-already popular among. experienced constructors for their high efficiency -has now been completed. Wound withLitz wire,they give greatest selectivity at a moderate price.All coils are identical inexternal measurement.Obtainable fromradio dealers everywhere. LEWCOS LEWCOS CENTRE TAPPED COILS (Protected Type) D::461:iFl

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* # # 384 March, 1928 THE WIRELESS CONSTRUCTOR

Another highly important article specially prepared for the " Wire- less Constructor,"which By R. W. HALLOWS, M.A. should. bestudiedby every set user.

user can work out its probable life Very Short Life by reference to the curves, and, last In the previous article it was shown but not least,the current passing that, no matter how good it may be, at any point in the curve, is alwaysthe standard capacity battery made IN a preceding article the results exactly one -tenth of the voltage. up of cells. of the same size as those were given of actual tests made Suppose, for example, that you use generally used for fiashlamprefills uponstandard capacity" high- a nominal 150 volts of high-tension is too small to be able to deal econoriii- tension batteries of different makes and wish to see how your batteries, cally with a load of more than about with a nominal 10 -milliampere load. whatever their capacity, are likely to 5 milliamperes. Claims are sometimes I say " nominal " because since the behave, you have only to redraw made that these small batteries will resistance used for the tests is fixed theappropriatecurves, adding 50 stand up to much larger drains, but the current naturallyfallsas the per cent to each of the readings.Or, actual tests show that they cannot be substantiated. Fig.1 shows the life chart of a Thisisatypical battery upon the case of which_ it highqualitydry battery such as is was stated that the normal discharge used by thousands rate was 10 milliamperes. Run for . ofsetowners all over the country. three hours a day upon weer. --days only, and kept at a constant temperature of 62 degrees Fahrenheit, this battery proved to have a useful life of just voltage declines. Actually, resistances again, should you rely upon a single under eleven days, or thirty-two and of 150 ohms per cell were employed, 66 -voltbattery,itsprobablelife which means that when the battery history under a 10 -milliampere load a half service hours !The chart itself was up to its full E.M.F. of 1.5 volt may be plotted out from the appro- well repays attention, for it shows per cell the discharge was at the rate priate curve by taking 66 per 'cent how distortion may gradually spoil of 10 milliamperes, falling off gradu- of the voltages shown at the various reception if the battery is not up to ally to rather under 7 milliamperes points. its work. as the potential declined to the neigh- bourhood of 1 volt per cell. DAYS A Convenient Scale 12" N 1F Y Xi' Yd YE Zr X 22 As in the precedingarticle, the is 9/29%K 9 /29/2 9 /2 9 /2 9 /2 9 a 9 tia 9 a 9 a 9/2 " life history " curves are reduced to Thus, a percentage basis in this. 14 irrespective of the number of cells 41 in a battery under test,aninitial ;voltage of 1.5 per cell is shown as 100 per cent, and the " cut off " in all cases is taken at 70 per cent, A 4.1 which is a little more than 1 volt si ct 0 c per cell.The percentage method is 00 WO oc exceedingly convenientforseveral reasons. Itenablesbatteriesof 11Yillgi r different E.M.F.'s to be compared III evN 40 q) as regards their performances ;100 (9 s volts is a commonly used potential I. L/PE CHART OF A POOR tSTANDARD CAPAC/TY" for wireless receiving sets ; whatever R0N..9NOORS PER DAY ON WEENDAVS TNROOGN the initial E.M.F. of his battery, the RES/STA/VCE OF /50 OHMS PER CELL. 2.974., 385 THE WIRELESS CONSTRUCTOR March, 1928 More Light on the ELT. Battery-continued

The average potential drop of this to be expected during the first hour, readings taken after a rest period, battery during its daily three hours' a smaller one during the second, and and before the battery is placed under run was nearly 12 volts.Reference a still smaller one during the third. load, may be entirely misleading. On to a family of valve .curves will show When, therefore, small batteries arethe eleventh day,for example, a reading taken prior to the working 872WA 9t1'DAY // a'OAv period would have shown a voltage of 84.2 ;one might, in fact, have thought that the battery was by no means in 'bad conditio'n.

z , co0 ...... %,, Batteries of Larger Typo ...... K"...... "...... At the end df the first hour, how- 0 ever, the voltage was 72.8 and at . 3.5.1MR.2NRS3#6es. /NA.2alea3mm /NR.P afrAt the end ofthe second, 70.4. A I I I iI I I I II I I 0T4o ,roo 'so o so ioo/so o SO 100 ASO 24 reading should never be taken until MMN/71S Al/NOTES A4/NOTES

40.4/LY DISCHARGE CURVES OF SMALL BATTERY, they have been for at least an hour Z.97S under their normal working load. that unless the grid bias is reduced used under a fairly heavy load, a In addition to the standard capa- tocorrespond,the workingpoint reduction of the grid bias may be city battery two other sizes are upon will sink before the end of the evening desirable at the end of the first and the market.These are the " large far too low down, with the result that second hours of each run.It should, capacity," made up of cells 11 in. bottom bending islikely to occur. howevef, be remembered that any indiameter by 21in.inheight, The actual rate at which the voltage such reduction will mean an increase andthe" super capacity,"whose drop occurs during a three hours' run in the current and, therefore, a still cells measure on the average 13 in. is also a matter of considerable im- more rapid fall in the voltage. indiameter byratherlessthan portance.It might. be thought that it would take place quite regularly, WEEKS if . but this is not the case.During its r zr zr Y zr '17 .n zrB dI 2727 ZIP Zr ZW zarzsr period of rest the battery recuperates, .sz4R7.4 po47-44- the potential rising to a reading much above that obtained at the end of the previous working period. o 144. A "SUPER BATTERY Win,' A NOMINAL /0/WA DISCHARGE

Grid -Bias Adjustment 7.977. _ _ _ As soon as the battery is placed Another point worth attention is 31- in.inheight.What perform- under load again a rapid falling off the amount of recuperation shown ances are to be expected from these is.seen owing to rising internal resist- by the battery. On some days, in the under a load of 10. milliamperes ?In ance.The current declines in pro-caseofthe one whose historyis Fig. 3 is plotted the life history of a portion, and when a point is reached plotted in Fig. 1, this was as much as good quality large -capacity battery at which the discharge rate is such 12 volts, or rather more. Now, rapid (by no means the best of those tested) that the battery can cope withit recuperation, especially if it means a over a period of eighteen weeks, the fairly well the reduction of potential -quick fall in the voltage at the be- conditions of the test being the same becomes much more gradual.Fig. 2 ginning of the next working period, as those previously described, that shows discharge curves for a small is not altogether a virtue ; in fact, one is, discharge through a resistance of battery on the eighth,ninth and would much prefer a battery which 150 ohms per cell for three hours eleventh days of its service ; the volt- showed a smaller temporary recovery, daily on week -days. age readings having been taken every and a subsequent voltage drop of less fifteen minutes during the three hours' amount. Heavy Initial Drop run. Another point which emerges from This curve is most instructive.It It will be seen that a heavy fall is a study of Fig.1is that voltage shows that, as might be expected, 2.976. a fairly heavy fall takes place during WEKE S Iz M I" 17 171liZq Zr Z7227 2Z7 Zit Z7 ZU Ziff 21Z1the first week, after which the battery settles down and maintains a comparatively steady E.M.F., with a very gradual falling off. The point at which it begins to steady down is. approximately 93 volts, thus showing that about 9 milliamperes is a load with which it is well able to deal. At the time of writing, none of the many large -capacity batteries under A6.3. A *LARGE CAPACITY* BATTERY AV/ TH NOAWNAL /0/11.4 DiSCAWAPCE. testis anywherenearthe cut-off 38i March, 1928 THE WIRELESS CONSTRUCTOR FERRANTI If you have direct current Supply in your home DISPENSE WITH H.T. BATTERIES and build an Eliminator with Ferranti Components

BZ DIAGRAM TO &NO L.F. (NZ 1,0WER VisEVZ

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An Eliminator built to this specification is free from hum and motor-boating, and when used on a 230 volt supply will give an output of 200 volts100 milliamps.If further information is required, such as the values of the resistances,this will be furnished on application, stating the valves used and the mainsvoltage.

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387 THE WIRELESS CONSTRUCTOR March, 1928

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388 March, 1928 THE WIRELESS CONSTRUCTOR More Light on the KT. Battery-continued voltage after eighteen weeks of ser- and mine come in for a very great deal. One of their great virtues is that vice.On a conservative basis their of heavy work.When experiments they very seldom become noisy even average useful life may be estimated are in progress the loads imposed when their voltage has fallen to some- as at least six months.This means upon them,authemilliammeter thing very low indeed.Recently I made an interesting test with a num- I N 8 Prtmit 5 5, a' z U 227 Z27 %DT Zr zit Jahustrz ber of old batteries of this kind which WEEKS had been discarded eithe-r by myself sT or by friends some time previously, G. and had been standing idle ever since. 1111 They were given an hour's preliminary 41.0/406. run to steady down -the E.M.F. after their long rest, and were then con- NEM nected to a -receiving set. 90.6: A S/M/MR BATTERY TO F/0.4 wirm A NOAVNAZ /SMA LOAD Average Cases that two renewals will be required in shows, are often of the order of 25 the course of a year at a cost of or 30 milliamperes for long periods Theaveragevoltageforeach roughly fourpence pervolt. The onend,anditnotinfrequently 45 -volt unit was something under 10, annual cost thus works out for 100 or rather less than .3 volt per cell. Z980 There was some noisiness on first volts at £3 6s. 8d., or .8 penny per suALW. hour for 1,000 working hours. 'LAMM }AT 5414 switching on, but this was tracked SMALL down to one half of a particular unit, An Important Point SUPER which showed 3 volts instead of its LARGE AT /ONLA original 221.When this had been cut A very important point to notice ..ThLACL out of circuit it was found that the re- about the life curves of the large - SUPER mainder gave perfectly quiet working. A7/5A1,1 capacity battery is the small fall in LARGE The average life of a battery of tkis E.M.F. which takes place during a kind under nominal 10- and 15 -milli- SUALR AFPOMA working period.On the last day of L ROE ampere loads is seen in the graph the first week, for example, the average .4 ie. COMPA RA 1,,,E L? LINN / / G COSTS. which appears in Figs. 4 and 5.It fall during the three hours' run was wilt be noticed that even under the just over 3 volts out of the 100, andhappens that the battery is in uselarger load the temporary fallin matters were very little worse after for six hours or more out of the voltageisquitesmall,whilst the eighteen weeks. twenty-four with aload.offrom permanent fall is even and gradual. It follows that no noticeable dis- 8 to 15 milliamperes. In such circumstances it is a simple tortion is likely to occur during an evening's receptionifthe low -frequency valves are properly biassed at the beginning ;it will be seen that there is very little need to bother about the grid bias, provided that it is correctly adjusted at the end of the first ten days or so.The life of the average small grid -biasbatteryis about nine months, and its own fall in E.M.F. will be almost sufficient to allow for that which takes place in the high-tension battery. The "Super" Class We come next to the super battery, usually made up in nominal 45- or 50 -volt units weighing from eleven -to twenty pounds apiece.The actual weightdependslargelyuponthe nature and amount of solid insulating material used.These batteries entail rather a large initial outlay, but my experience is that whenever the average load is 10 milliamperes or more they are well worth the extra money. During the last eighteen months, using these large units, I have only An H.T. battery consisting of a group of wet Leclanehe cells.This type of anode had to buy two lots of batteries, battery is becoming eery popular. 389 THE WIRELESS CONSTRUCTOR March, 1928 More Light on the H.T. Battery-continued matter to avoid distertiOn due' to 2979 . rA ,.., bottom bending; for the grid battery IC.19.6.N.TDATTERY Z/FECURVES la needs scarcely any attention. 0)1, FORalleothesPERIPE,EK) The provision of super batteriesI represents an initial cost of about sixpence per volt.Under a 10 -milli- Z. . ampere load at least a year's working on an average of three hours a day is.2 . ..r to be expected. The annual cost 'VI c.,tee. for 100 volts, therefore, works out k ia ,t .T..j>. at £2.10s., or .6 -pence an hour for a .ft* thousand hours of work. V. It will he realised that the life of any .,..1 - .4... sizeofbattery depends (provided --,..,,..,, that it is of reasonably good quality .9-0-,4.,;,,... and is kept in a suitable place) mainly SMgfL upon the number of hours per week (4., 4.4,,,,.,.? that itis run and the average load wz,,,,, imposed upon it:In Fig. 6 are seen 0 5 /0 /52025 30 .9540 45 SO.5560 65707S 80 85 90 curves from which the life normally possibly stand up to a greater load battery of larger capacity.Should to be expected from any kind of for more than a very short time. the fall be very great -10 per cent, battery under various loads can be The reader may wonder how he forexample,or more-the wisest found. can best determine, if he does not course will probably be to purchase a possess a milliammeter, whether bat- super battery on the next occasion. Cost Comparisons teries of the size that he is in the Another method of economising in If the average amount ofH.T. habit of ming are suitable for his own high-tensioncostsistousetwo current taken by theset can be receiving set.A method that I can batteries instead of one.It might measured by means of a milliammeter recommend is this.Ten days or so seem atfirstsight that any such it is easy to work out from these which after a new battery has been installed course would be most uneconomical,. type of battery will be the most take a voltage reading at the begin- but this is not so.In the average economical in the long run. A com- ning of the evening's run and others at set containing high -frequency, recti- parison of the running costs under half-hourly intervals. fying and note-mainilying valves and loads of 5, 10, 15 and 20 milliamperes, If the fall in E.M.F. exceeds 3 volts provided with a common high-tension using batteries of differentsizes, is per cent at the end of the first hour, battery the heaviest load is borne by seen in Fig. 7. Beyond 10 milliamperes or5 volts after the threehours' the portion of the battery lying be- only the two larger sizes are con- working, then it will pay to install, tweenthe negative end and,say, sidered, since small batteries cannot when the next renewal is made, a 45 volts, for this has to supply current to all three kinds of valves. Unequal Loads The next hardest -worked portion is that between about 45-60 volts, which provides current for the H.F. valve or valves and the note -magnifiers.The lightest load is thrown upon the remainder of the battery, which has only the last valve or valves to look after.A glance at the life curves in Fig. 6 will show at once that even a slightincrease in the drain upon any portion of a battery means a big reduction in the useful life of that portion. High -frequency valves, especially if given a small negative grid bias, pass very little plate current, whilst the requirements of the rectifier seldom exceed 2 or 3 milliamperes ;if it is resistance -coupled to a following valve it will need very much less than this. If, therefore, a small -capacity battery An II.T. battery of the secondary type which functions on the Edison princip!e. An is used for the high -frequency valve alkaline electrolyte is employed. One set of plates is formed of nickel and the other or valves and the rectifier only, it may of iron. (Continued on pdge 406.) 390 March, 1928 THE WIRELESS CON:. CRUCTOR

nvaluable toeveryAmateur and Constructor The "POPULAR WIRELESS" BLUE PRINTS OF TESTED CIRCUITS The following is a list of the " P.W," 6d. Blue Prints for Constructors in stock showing the different circuits available. P.W. BLUE PRINT P.W. BLUE PRINT Number Number 1. DETECTOR VALVE WITH REACTION, 16.H.F. (Tuned Anode), CRYSTAL DETECTOR AND L.P. 2 UNIDYNE DETECTOR VALVE WITH REACTION. (With Switch for Last Valve). 3. 1 -VALVE L.F. AMPLIFIER. 17.CRYSTAL DETECTOR WITH TWO L.F. AMPLIFIERS 4 CRYSTAL DETECTOR WITH L.F. AMPLIFIER. (With Switching). 5. H.F. (Tuned Anode) AND CRYSTAL WITH REACTION. 18.1 -VALVE REFLEX AND CRYSTAL DETECTOR, with 6.H.F. AND CRYSTAL (Transformer Coupled, without 1 -VALVE L.F. AMPLIFIER, Controlled by Switch. Reaction). 19,H.F. DETECTOR AND L.F. (With Switch to Cut Out 7,1 -VALVE REFLEX WITH CRYSTAL DETECTOR the Last Valve). (Tuned Anode). 21.THE 2 -VALVE LODGE " N." 8.1 -VALVE REFLEX AND CRYSTAL DETECTOR 22." THE GUARANTEED REFLEX." (Employing H.F. Transformer, without Reaction). 23.THE 1 -VALVE " CHITOS." 9.H.F. AND DETECTOR (Tuned Anode Coupling, with 24.THE " SPANSPACE THREE."Three -Valve Receiver Reaction on Anode). employing 1Neutralised H.F. Valve, Detector with 10.H.F. AND DETECTOR (TransformerCoupled,with Non -Radiating ReactionControl,and 1 L.F. Valve. Reaction). 26.A " STRAIGHT " 4-VALVER (H.F., Det., and 2 L.F. 11.DETECTOR AND L.F. (With Switch to Cut Out L.F, with Switching). Valve), 28.A " MODERN WIRELESS - 5-VALVER (H.F., Det., 13.2 -VALVE REFLEX (Employing Valve Detector) and 3 L.F.). 14.2 -VALVE L.F.AMPLIFIER (TransformerCoupled, 29.AN H.T. UNIT FOR DIRECT -CURRENT MAINS. with Switch to Cut Out Last Valve). 30.A REINARTZ ONE-VALVER. 15,2 -VALVE L.F. AMPLIFIER (Transformer -Resistance 31.A STANDARD TWO-VALVER (Detector and L.F.). Coupled, with Switch for Cutting Out Last Valve), 33,The " CUBE SCREEN " THREE (H.F., Det and L.F.). ALL "POPULAR WIRELESS" BLUE PRINTS 6d. EACH

All orders forthese Blue Printsshouldbe sentdirecttothe" PopularWireless " Queries Department, Fleetway House, Far, ingdon Street,London,E.C.4,enclosing a stamped addressedenvelope and apostal order for 6d. for each Blue Print ordered.

391 THE WIRELESS CONSTRUCTOR March, 1928 WITHIN THE VACUUM Do you ever test your own valves?Itis quite an easy_ procedure, and besides being interesting will provide ea/noble information of the " characters " of the particular specimens you have in your possession. A suspected " dud " can easily be checked up in this way.

By KEITH D. ROGERS.

Now increase the plate voltage to a higher value, P2, and note that the platecurrenthasincreased.Next alter the grid voltage, making it more negative untilvalue -is reached when the milliammeter in the plate circuit reads the same as it did before (C1). Take the grid voltage now being HAVE just finished carrying out a The H.T. voltage is fixed and a applied and call it G2. Ilarge number of tests with valves, seriesofgridvoltagesaretried, noting the various irregularities the corresponding readingsofthe Amplification Factor intheircharacteristic - curves, and milliammeter being noted.This gives Now subtract G, from 0, and call where they differ from those readingsforthecurve.Different the answer G3.Subtract P1 from " average curvesgivenbythe H.T. voltages give different curves, P2 and call the answer P,.Now aker)i. and so with voltages ofabout 50, divide P, by 03 and the answer is the It occurred to me therefore that 75, 100, 120, or so, a series of curves amplification factor of the valve.In some ofmy Constructorreaders truly indicating the static properties other words, we have the amplification might like to do some tests for them- of the valve under test are obtained. factor representing the relative effect selves, and so I propose briefly to Now, if the amplification factor is ofgrid voltage changes and plate give descriptions of the various tests required we proceed as follows :Set voltage changes in their control of tho that can be carried out with just athe grid. voltage at some negative current. couple of voltmeters (L.T. and H.T.) value (G1), and then fix the plate Thus, if Gi = 4, and 02 = 6, andamilliammeter. A potentio- voltage at some convenient voltage and if P1 = 60, and P2 = 80, meter is also useful to give accurate (P1).Then there will be a certain then we have grid -bias voltages. plate current flowing (C1). G2 - = 2, - P1=-7.20; The filament voltage is measured 20 by connecting a voltmeter across the and thus, - 10. filament terminals of the valve holder G-, in which the valve to be tested is The impedance of the valve can, placed. be simply calculated" by noting the Simple Calculations change of plate current for a given changeofplate voltage-thegrid. The platevoltageistested by volts being kept at zero as a rule. connecting the H.T. voltmeter across Thus, if have a plate voltage of the plate and. L.T. negative filament 40 giving a current of 2 milliamps, terminals.It is best to connect the and a voltage of 60 giving 4 milliamps, H.T.-- to L.T.- in this case, so that we have a change of voltage of 20 we have L.T.+ to filament; L.T.- to giving a current change of 2. H.T.-, KT.+ toplate,gridto Thus we have sliderofpotentiometerconnected Plate voltage change 20 across a grid -bias battery, the positive 10 Current change 2 ofwhichistakentoL.T.-. A voltineter between grid and L.T.- will give the grid -bias. voltage. The Plate Impedance The circuit now requires a milli - But the 20 are volts, and to corre- ammeter between 1-1.T.-4-and the spond with thosevolts we -must An unusual photograph taken of one of change the milliamps into amps, for plate of the valve, when the arrange- the masts of the most poweiful broad- ment is ready for most purposes. castingstation inthe world-Zeesen we are dealing, with Ohm's law, pure (near Berlin).With stations of this des- and simple.In other words, we can With this hook-up it is possible to cription on the air small inefficiencies in take the usual characteristic curve valves do notappear in theirright either divide the milliamps by 1,000 proportions. Weak signals are far better or multiply the volts by 1,000. (grid -voltage -platecurrent)of any for testing suspected valves, or for com- valve, and this is done as follows ; paring efficiencies. (Continued on page 408.) 392 March, 1928 THE WIRELESS CONSTRUCTOR

Showing the Relay for the Remote Con- trolfor set using eL.T. Accumulator and H.T. Bat. WAVE tery. CONTROL TOD/MY SET0

Showing the Relay of the Remote Control BECAUSELotus Remote Control for an"ALL MAINS" has proved itself such a great con- Receiving Set. venience to thousands of users of the ordinary H.T. and L.T. wireless set, we are now making it to suit any type of receiving set. No matter what sort of set you are using, you can have simultaneous reception and control.No more going from one room to another to switch on and off-no more crowdinginto one room to hear the wireless.Never mind where the set is ;listen -in in every room by installinga Lotus Remote Control. FREE Blueprints and instructions showing how you can fitit up easily and quickly will be sent by return on request. Showing the Relay of the RemoteControl for set using L.T. Accumulator and H.T. Eliminator.

iitr.0 set '4s rrr 2

a .t rt lac? Cos : to:C nYS PoloncoN110" 0:10 t and u :du

or fC0.3021,jete 45-1. for 411.4:1rliektetfssrteZ7oillis In each Made by the makers of the Lotus Buoyancy Valve Holder, 17/6 / Lotus Vernier Coil Holder, LotusJacks,Switches and Plugs. extran Garnett, Whiteley & Co. Ltd.,Broadgreen Rd., Liverpool

393 THE WIRELESS CONSTRUCTOR March, 1928

IMINININIIII71A11111111111111111W 110111111111111177A1111111W1 i tiVeasstestanriz

A Good Rheostat :11uulnlnuuuminluu11i IIIuulnnuulululnlnlunuln1.-: expected. The holder is thus of sound design and can be thoroughly recom- it4 Rom the General Electric Co. we ;7 A MONTHLY REVIEW OF have received a new type of TESTED APPARATUS mended. (NOTE :All apparatus reviewed E filament resistance,two pat- E in this section each month has E An Excellent Trickle Charger ternsbeingmade, oneforpanel been tested in the Editor's private E- Readers of the-WIRELESS CON. mounting and the other for baseboard 77- laboratory, under his' wn personal STRLTCTOR will remember that in the mounting.Both patterns are pro- = supervision.) g. November issuewepublishedan vided with a well -finished moulded Uniteninnanunninunimannwilmuniniiininnae, knob with an indicating arrow, con- all of the anti -phonic sockets now sold, tact between the moving arm and wire but in most of them the effect is ob- being made by means of a spring plun- tained by some sort of spring. In the ger which bears against the resistance Ebonart socket the springiness is due wire wound on a former inside theto the rubber, and the connections between the soldering, lugs and the valve sockets themselves play no part in this, being of flexible stranded wire solderedtothesocketsandter- minals. Submitted to high -frequency tests the socket proved to be particularly good,showinglowerlossesthan several of the well-known makes of anti -phonicsocketsnowonthe market. Thisnovelcalve holder is made of Terminals of the size usually fitted soft rubber, thus ensuring aperfect In this ingenious rheostat a spring con- to valve sockets and a good size of cushioning " of the filament. tact presses against the inside of the soldering lug are provided. The colour resistance winding. articledealingwith dryrectifiers, chosen for the rubberisofdark brown, and appears to .be of excellent in which a description was given of circular moulding. The accompanying someofthelatestdiscoveriesin illustration shows the construction of quality, so that a good life can be rectifying units.Messrs. Ferranti are the baseboard mounting type which now marketing an excellent British - was very successfully used in the madetrickle charger incorporating " Business Man's Four."The current -carrying capacity proved to be This trickle charger is capable of giving half an ampere chavging eurrent to either a 2-, 4-, or adequate and the movement is parti- aecumulafor. cularly smooth and positive.It is a very well -made component and is up *to.thehigh standardset by the company for their other components. An Interesting Valve Socket FromMessrs. -RedfernsRubber Co., makers of the Ebonart panels, etc., we have received a new Ebonart valve socket which atfirstglance appears like the old-fashioned rigid ebonite holder, but on closer examin- ation is found to be made ofsoft rubber with an air -cushion effect, so that when the valve is inserted the usual anti -phonic effects are obtained, the valve swinging from side to side at quite a. low period when inserted. This feature, of course, is common to 394 March, 1923 THE WIRELESS CONSTRUCTOR

-1

1-. .1

*...vIll ( (.1 ...... --t col vas.cxolo f/ --... . / iit-111 Il'(-z;) 1 gutter sideup You met disappointment early.Bread and butter you dropped, for instance, alwaysfellbutterside down. Re- member ? The Peto & Radford Indicating Accu- mulator obviates one disappointment for you, though.It doesn't let you lose a programme because you thought there 1,,, as plenty of juice.This P. & R. Lc/is you whetherit'sfully charged, half charged, or dead. You merely look Regulation at the indicating floats,And that's an extra advantage. This P. & R. is like every P. & R. Built of voltage for service. Solidly.Carefully.Like a BATTERY. bymeans of The Peto & Radford Indicating Accu- mulatorkeepsyour wirelessbutter side up. And yet it costs but little more WESTON than the ordinary accumulator. Write for our leaflet to Peto & Radford,50. Instruments Grosvenor Gardens, London, S.W.I. gives improved AN DR, reception PETO & ADFORD To obtain maximum results from your receiver you must he sure that the H.T., L.T. and ACCUMULATORS G. B. voltages are regulated correctly. For an The beginning and the end in exact measurement of these variable voltages use a Weston Pin -Jack Voltmeter with high - PO VII.' 1E. R range stand.Only the Weston standard of Telephone :Victoria 3667 (5 lines). accuracy and reliability is sufficiently fine to Works : DAGENHAM DOCK, ESSEX. be of any use for such measurements. London Sales & Repair Depot, 107a, PIMLICO ROAD, S.W.I. Tel. Sloane 6114/5. The Weston free booklet "Radio Control" explains the necessity for accurate electricalcorftrol of yourradio ._.,_. receiver and gives much helpful advice.Let us have I II d kat 1117 ---.....LA:__sw,_ Glasgow your name and address. Accumu- -. _. --' Distribut- lators from ...---*-- mg Depot: MODEL 506 Pin Jack Voltmeter complete with 136Ren- 20to 60 ..ts F field St, high range stand and testing cables £2 :10 : 0 (::] : ,___H=1::310 amp. hours i Glasgow, capacitymi Vagbpilliii C.2. Telephone a c t u a I. :141QC1M Douala; PCF7, 30 141, :7111C:il: 242. WESTON amp.hourst Ill'll ri STANDARD THE WORLD OVER actual, 2 1-"Illr...t:ii

volts. Price . 4 '5 '...... --111 .. dvia.rtsIng Pioneers since 1888 15,'6 l''''. --,4 WestonElectricalInstrumentCo.Ltd. 15,cIt.SaffronHill, London, E.C. 1

393 THE WIRELESS CONSTRUCTOR March, 1928 What's New-continued one of these " dry rectifiers " capable positive and negative terminals of the Two American Components of giving half an ampere charging accumulator to positive and negative current to a 2-, 4- or 6 -volt accumu- terminals of the charger and to plug From the Rothermel Radio Cor- 'poration wehave lator, according to the terminals used. theflexiblelead into the nearest receivedtwo The unit, which is quite compact, as convenient electric lamp socket. The " Pilot " components, one a tumbler will be seen from the illustration, is device must, of course, be used with switch and the other a " Micrograd " variablecondenser perfectly silent in working, and on alternating currentmains. When The tumbler test over a considerable period was ordering, the voltage of the mains switchisa 'verywell -made com- found to be thoroughly reliable and should be specified. ponent, capable of carrying far more to give the rated charging current Double -Range Coil Holder The L. & P. coil holder, which is illustrated intheacc,ompanying photograph, is designed for the convenient useofplug-incoilsina receiver designed for both the ordinary 250-550 band and the 5 X X range. In most plug-in coil sets it is necessary to remove both the reaction and tuningcoiland tosubstitutefor them other coils when changing froth This coil holder is fitted with a switch one range to the other, but in this in- A contpactroriablecondenser,the so that there is no necessity to alter the genious coilholder both long and Micrograd." coils when changing over for 5 short-wave tuning and reaction coils current than the wireless experimenter without variation.This little acces- are kept permanently in position, the will ever put through it for filament sory should commend itself to a wide change -over being made by means of a switch which can be fixed to any switching ; a clear indicator shows on circle of users, for it is perfectly silent andoff,whilethemovementis in working, there are no liquids to convenient part of the set. positive and " clean cut," leaving no spill, no bulbs toreplace, and no A good vernier movement is pro- doubt as to whether the contact is appreciable heat is generated during vided and fine adjustment is facilitated properly made or not. the charging process. At 55s.it by the very convenient dial clearly The Micrograd condenser, illustrated represents excellent value and can marked in degrees from 0 to 90. Even the largest make of plug-in coil can be above, has a very smooth movement be thoroughly recommended toall by means of an adjusting knob.A readers: Operation is simplicity itself, taken in this holder, the movement of range of these condensersis made it being merely 'necessary to join the which is very smooth without any and the particular specimen submitted backlash. The moulded. material used for the to us for test shows a maximum of socket is of a high grade, and high - .00053mfd.andaminimumof frequency tests show that it is of good -00018 mid., the limit ofvariation quality and quite suitable for the pur- thus beim,.00035mfd.,whichis pose for which it is used.A particu- larlywell -made component, which can be thoroughly recommended. The Ediswan "One -Der " Loud Speaker Fromthe on -Swan e Co., Ltd., we have received for test and report a sample of their:` One - Der " loud speaker,ahornlype. which is selling for the very loV figure of 50s. The horn, as will be seen from the accompanying photograph, has a particularly, large flare.Tested on a An efficient tumbler switch of unusual number of sets the tone was surpris- design. ingly good forahorn -typeloud speaker, and it is quite evident that about the average for this type of particular pains have been taken in adjustable condenser. - the design to get rid of the irritating It should be noted that the speci- resonance effects which too often mar men submitted to us was marked the reproductionofthistypeof " .002 mfd.," afigure which obvi- instrument.It is a very good horn - ouslybears not the slightest relation Me new One-iler " loud speaker type of loud speaker, and represents to either the maximum or the mini- (m distran). exceptionally good value. mum. March, 1923 THE WIRELESS CONSTRUCTOR

!was? UPotki SPECIFIE COM I YOU WANT You'd be up to your eyes in MAXIMUM trouble if you ignored that EFFICIENCY warning, wouldn't you ? THERE would be a zip, a crack, a splash, IF you are about to construct the and you would disappear from view. Mullard Master Three Receiver But then you would not be so foolish you should remember that there is as to ignore such a warning. We all endeavour to avoid obvious danger, every reason why you should adhere and especially in Radio, where the slightest to the author's specification. departure from the right track leads to all SELECTIVITY to the desired degree is sorts of endless trouble.Especially in the case of components is this true.When a easily obtained with Colvern Coils. A person designs a Receiver and specifies the few turns to requirement should be re- components by the manufacturers' names, moved from the aerial winding and the he knows that those components are going to yield the best possible results.If you take end of the wire reconnected to Pin home one or two alternative components, No.4. andconstructtheReceiver,you cannot Prices :- RANGE depends to an extremely grumble ifitfailsto yield the results you Broadcast Wave. high degreeupon efficientcoils expected. Accurate Space - In that famous Receiver " The Mullard woundtogive and it is very important that these Master Three," for example, two J.B., S.L.F. maximum effici-7/6should have a very low. high -fre- Condenser are specified.Now it would be ency. quency resistance.To obtain this disastrous to depart from that selection when Long Wave. you are constructing the Receiver. The Sectional wound Colvern Coils are accurate space - excellent and unparalleled results yielded by togivelowest wound.Experience proves that the use of " The Master Three " are due- in no small high - frequency Colvern Coils, increases the range of a measure to the sharp and accurate tuning of resistance. 8/6 radio receiver. In the case of the Master ColvernAluminium the J.B. Condensers. Three Colvern Coils give maximum range. So remember, when yourdealersays, Panel.. VOLUME is similarly dependant -upon the " These are quite as good," you reply, " No, is also specified for the Mallard efficiency of coils.Logically, the signal thank you.I must have J.B." Master Thri e Re- strength of distant stations is greatly in- Then there will be no need of a Danger Signal. ceiver 18' x r ; tt creased by Colvern Accurate Space-W.011ml gauge;sprayed instrument black; Coils. drilled forvari- Therefore be advised-adhere strictly to the able condensers switch and panel author's specification, you will be most 8- POLAND ST -OXFORD ST UeJipfione:- brackets. 7/6 satisfied. LONDON - W. GERRARD 7414 COLVERN ACCURATE SPACE WOUND COILS Colvern Ltd., Mawney's Road, Romford.

J.ILS.L.r.

3.17 THI. WiRELESS COAMRUCTOR March, 1928 ****************************************** At the timeof writing,however, Zeesen is- only broadcasting in the 0 evenings.As a rule, the programmes 0-- * OUR NEWS BULLETIN consistofrelays of other German stations, e.g. Voxhaus, between 7 or Some of the More Interesting Happenings 7.30 p.m. and 11 p.m. G.M.T.It 0 looksas though some interesting in the Radio World this Month developmentsbetweentheB.B.C. and the. German broadcasting people ****************************************** may shortly take place, for recently a deputation of German radio experts THE Radio news from Americayears and. his " home sets ".are a visited this country and were in close during the last few weeks has comparatively recent development. touch with Captain Eckersley. Exactly Chiefly been in connection with The experiment seems to have been what will transpire it is. hard to say, theG.E.Co.'stelevisionexperi- quite successful-up to a point.The but arrangements for" swapping " ments-experiments,bytheway, demonstrator was seen, by wireless, programmes are hinted at. which the Baird Co. should take stock to move, gesticulate and to smoke ; the Too Many Talik of ; for at any rate they do indicate smokefromhiscigarettebeing writing thefactthatrealanddefinite " clearly seen." Mr. Otho Nicholson, attempts are being made in the U.S.A. If we are not careful, America will recently in the" Daily Mail " on to formulate a good practical scheme be the first country to start a regular " The Public and the B.B.C.," points for a public television service.So far television service, despite the fact that out how the programme policy of the we have had only promises from the we have lOng been promised one inB.B.C. is definitely contrary to the

Baird Co.The G.E.C. experiment -- this country. wishes of the majority of listeners. news of which was first received in It is up to the Baird Co. Comparison with the " Daily Mail " London on January 15th-has been programme ballot, for example, shows . The Zeesen Station described as the first public .experi- that " whereas the expressed desire of The " Daily Telegraphs " recently the ballot placed talksofvarious home television." . ment published some useful data about kinds. 5th and 11th on the list, with The teleVision method employed was Zeesen, the new German high-powered an allowance of 11 per cent in all one, developed by Dr. Alexanderson broadcasting station.A power of of the total (programme time), the -consulting engineer to the Radio 40 kw.is used and the station is analysisshowsthattalksstand Corporation of America, and to the eventuallytoreplace Koenigswus- easilyfirstinthe pointof time G.E. Co.He hasbeenstudying terhaustn (an 8 -kw. station) - on the occupied, with 23 per cent.' television problems for the last eight samewave -length -1,250 metres. (Continve4 on page 4C0.1

MAGNUM CONSTRUCT MAGNUM STANDARD H.F. CHOKE WAVETRAP Embodies the following The Super -quality essential features: High Inductance - i6o,000 ,ttf. Low Self Cap- AMPLIFIER acity - (as described in this issue) 8 µW. Ample Wave- x Baseboard 16 in. x 8 in. 1 9 lengthrange 4 Magnum Valve Holders :: : : 8 0 50'3000 a Magnum FixedResistor and Base, 4 0100s 2 6 metres I R.I. Straight Line Transformer .. 1 5 0 Dimensions : a R.I. Push -Pull Output Transformer.. 1 2 6 Overall height, 2 in. Base, 21 x II in. x Climax H.F. Choke .. 8 6 Small External field- Dubilier Mica Condenser, 0-05 5 6 Protected windings (no celluloid or other infiam- x Dubilier Resistance and Base, roo,oeu ohm. 6 6 x Dumetohm Base with 0.25 Leak .. 3 6 able covering). Price7/6 3 Lissen Mansbridge Condensers, a mid. .. 7 6 When buying an H.F. Choke, specify Magnum and x Lissen Leak, o.5 meg... 1 0 ensure magnificent results. a Watmel Fixed Condenser, 0.0002 1 3 This little Unit is suitable for any make or type I Terminal Strip, g fn. x xl in., fitted with so of set, and enables you to eliminate that unwanted Eelex Terminals and I Push -Pull Switch 6 0 station. Razor. 14 -pin Adapter with Flex. 1 6 As used by Mr. P. W. Harris in " The Business Glazite Man's Four," also in the original " 192S Solodyne." Sharp .; 1 6 Wave. £5 2 6 Price15/.complete A suitable Mahogany Cabinet for the above can be Copper Screening Box can be supplied forthe meter supplied.Price£1 4 0 above,Price R. P. Envelope No. 14 RADIAN()3 Containing BI u e Print, Calibration quarts andfull ENVELOPE Constructionalde- RNEJONES containing Blue Print and Constructional details tails. .0 . LT D . %:'4::> of this wonderfully popular set is now available. Price1/6 MAGNUM HOUSE Price1/6 This instrument can be supplied ready wired and TELEPHONE : HOP 6257 Lists dealing with The Radiano Three, Business tested and calibrated. Man's Four, Straight Line Four, AThree for the New Price Valves, 1928 Solodyne, Master Three, etc., includ- Or, as a complete set of parts for Home Construc- 288980ROUGH HIGH ST. ing 36 -page catalogue containing full constructional tion, including coils r8o/z000 metres. details of Magnum Screened Receivers, will be sent Price E44 0 LONDON. S.E.I on receipt of rid. stamps.

398 March, 1928 THE WIRELESS CONSTRUCTOR

C,,1,, -,r Plain Valve Holder

Indigraph Vernier Dial L.P. Transformer, Type "G" Lokvane Variable Condenser Not the cheapest but the. best The best results can only be obtained by the use of the best components.Any circuit or receiving set can be improved by the use of Igranic Components throughout. 1111 Take as instances such popular sets as :- 1111 1V1 ULLARD MASTER THREE. MULLARD MIKADO. Pre-set Resistor MULLARD TOREADOR. MULLARD . RALEIGH. .Springinore " Plug COSSOR MELODY MAKER. SOLODYNE. Any of these give their best performance if Igranic Components are used in their cans:ruction. Only the best can give the best results. You pay more, but you get better value. May we send ycu the illustrated Igranic catalogue, List No. J445, which gives full particulars of these components.

149, Queen gi14PAN Bratty:ten: Victoria Strut, nins- ba CI .v, Lees, LONDON, E.C.4. Newcastle.Bristol, Wcrks : Cardiff. BEDFORD. Radio Switch. H.F. Choke. WAAAAAAAikAAAIAAAAAAAAAAAA/AAAAAAAAAAAAAAA

-----,:\111111111111111111111MMIIIMMIZI BUILD THIS "IDEAL" CONE The " Ideal " Cone Loud Speaker Constructor'sKit contains complete components and instructions for building this attractive and efficient cone, 16 inches in diame:er. Gives full volume, clear tone, and can cope with the highest energies. Price 2 GNS. EE.EX WANDER PLUGS MODEL EELEX SPADE ENDS No. 44 Incorporating the wonderful WIRELESS ACCESSORIES "IDEAL"4 -POLE PATENT arechosenand recommendedforthe Mullard " Master Three" the Cossor winnwr " Melody Maker," and the " 1928 Solodyne," also Eelex Treble -Duty Terminals. They are 7117 BALANCED ARMATURE UNIT also used and specified for all the best sets This Unit, included in the constructor's kit, is the perfect driving to -day. This alone is G=4=0" sufficient testimony that unit for the Cone -type Loud Speaker.It eliminates distortion and EelexAccessoriesare false resonance and makes an assured success ofyour home - the bestobtainable. constructed cone.It canalso be bought separately at 25: - Write for catalogue V25, which gives details of all from all Radio Dealers or the EELEX accessories. Te'rminal Complete set of EELEX Price 41d. each. F. A. HUGHES & COMPANY, LIMITED Terminals,Plugsand Terminal T2LN , la'11,14C)i) Spades as required for: with Plain Top, 204-206,GreatPortlandStreet,' London, W.1 " Master Three,"2 10 Price3d.each. Telephone : Museum 8630 (3 lines). Telegrams : " Distancing, Wesdo, London." Colouren spades,(Plugs& Spades only, 1, 4.)J. J. EASTICK & SONS, 185, Princess Street . . . . - Manchester plugs, pins and eyes,"MelodyMaker,"3/4 2d.each,coloured"1928Solodyne,"6,3Eelex House, 118, Bunhill Row, Telephone: City 3329. flex r id. yd. (Fuse -holder 4d. extra) Chiswell St., London, E.C.1

39 THE WIRELESS CONSTRUCTOR March, 1928 more likely to be true in view of the Cheaper Valves? improved continental trunk telephone OUR NEWS BULLETIN A scientific discovery which, itis -continued from page 398 lines.Captain Eckersley has already told a pressman that it is hoped, by claimed,willgreatly: cheapen the means of a combination of land lines productionofelectriclightbulbs, and Sea cables, that listeners will be wireless valves, and X-rays apparatus " The public may call for what it I. wants," concludes the author of the able to hear programmes from Euro- has been made by Professor G. pean capitals; Finch, professor of electro-chemistry article, " it must take what it gets. at the Imperial College ofScience The Corporationsitsremote and New Lines and Technology i- South Kensington, beyond appeal." This is made possible because of S.W. That is true enough-but publicthe new telephone lines-of a type agitation can make it very uncom- ProfessorFinch explainedtoa specially suitable for wireless relays- pressman that his invention served fortable for the B.B.C. chiefs if they which are now being laid in Central will persist in ignoring the definite as an extremely delicate pressure - Europe.It is considered likely that gauge of gases.He added : wishes oflisteners. As itis,the these new continentalrelayswill public is just waking up to the fact start from Brussels-possibly Berlin My apparatus is simply an im- that its broadcasting serviceisin -before the year is out. proved mercury vapour trap.The wrong hands-and that the present liquid which you see in the tube there Board of Governors, without one single More Licences is an alloy of potassium and sodium. exception, should be scrapped, and a Thesteadyincreaseinlicence I discovered that this alloy thoroughly new boardcreated,consistingof figures, month by month, is one of absorbs the mercury vapour which people who are suited for the difficult the B.B.C.'s best answers to adverse hitherto has given so much trouble taskofcateringforalarge and critics.Certainlythesefiguresdo during the process of vacuation. diversepublic. What the B.B.C. not indicate any waning of the popu- It is because vacuation is such a wants is a C. B. Cochran in charge. larity of broadcasting, and there can be no talk of " saturation point " yettroublesome and costly business that Then things would be vastly better wirelessvalves,forinstance,and than they are now. being reached. X-rays tubes are so dear.With my In December,1927,therewere European Broadcasts device it is a simple matter to secure a 2,383,726paidlicences issued-an vacuum more perfect than has ever The reference I made in a previous increase of 30,000 on the figures for In short,in before been attained and far more paragraphtotherecentvisitof theprevious month. cheaply than hitherto." German radio experts to this country, 1927, 216,915 new licensed listeners and the possibility of " swopping " were added to the B.B.C.'s unique Well, let's hope this will lead to programmes with Germany is all the audience. cheaper valves-and soon, too !

The Home For Your Wireless Set This HANDSOME PIECE OF FURNI- TURE will keep your wireless set free from dust and locked up to prevent meddlement. Think of the comfort to have no more wires acrossthe room, no batteries on tablesorcarpets; you just unlock and tune in I ECTRO-DYNAMIC Our Standard WIRELESS CABINETS HAGNAVOX are made in three sizes, on mass production lines, hence the low prices, and can POWER SPEAKER UNIT accommodate any receiver or panel up to Manufactured tinder Magnavox British Patent No. 197,836 of May 24th, 1923, 30" X 18".SOLID OAK or MAHOG- ANY throughout (no plywood used) and perfect workmanship guaranteed. From 4 . 15 . O. Write to -day for free descriptive pamphlet and suggestions for adapting your receiver or panel in our Standard Cabinets.

DELIVERY from stock ON APPROVAL R4 UNIT , R4 UNIT Two thousand Cabinets already supplied to the utmost satisfaction of our clients. MAKERIMPORTCO. (Dept. 20), 50a, Lord Street, Liverpool. 9.10.0 £9.10.0

FOR THE

1928 SOLODYNE The World's Finest Speakers by the oldest speaker manufacturers. Write for particulars of the wonderful " Cyldon " 3 Condenser A revelation in reproduction with results equal to moving coil Assembly for this popular Receiver. It,s chassis -mounted with speakers selling at five times the price. thumb -control. Simpler tuning. No extra Drum tobuy. The fieldof the Magnavox Type R4 Unitis operated from a Easier adjustment.Greater selectivity.Comalete with screens 6 -volt accumulator or any standard trickle charger.Consumes and drums, £4 10 - 0.Bebe Condenser (0001), 7 6. ampere. Resistance 12 ohms.This field currentiseasily available from the L.7'. battery of your receiving set. The unit is supp'ied complete with attachment cords and built- in input transformer. Permanent Magnet Type No. M7, 60: - Write for full list Our new 1928 Catalogue and circuit supplement is now ready.Send 9d. 'in. stamps to cover cost of postage.It's the most instructive and The designer cf the MULLARD RALEIGH RECEIVER specifies interestinglistavailaldc. Cyldon " Condensers.It requires three " Cyldon Log Mid.. THE ROTHERMEL CORPORATION LTD. Line (0005), price 15:6 each, and one S.L.F. (00035), price 15'-. 24.26,MADDOXSTREET,LONDON, W.1. SYDNEY S. BIRD & SONS, LTD.,Cyldon Works, Sarnesfield Road, Telephone: Mayfair 0578, 0579. Enfield Town, Middx. I 'Phone : Enfield 2071-2 'Grams'' Capacity, Enfield." 400 March, 1928 THE WIRELESS CONSTRUCTOR What About Actualsizeof Condenser Your Future? ARE you content with the position you occupy now-with the money youare In two earning-or do you wish forsomething better capacities : and something more? '00035. Ask yourself these questions; then consider for a moment what you "1928" .000.1 ought to do. Don't for a moment imagine that integrity, punctuality; and length of service will of themselves carry you far.The one thing more than any other that enables a man to rise above his OG Also fellows and win a way into the better -paid jobs is a sound and DUAL and practical technical training.He cannot possibly get such a training TRIPLE GANG in the course of his everyday work. Absolutely the - The I.C.S. originated spare -time technical training by post 36 years ago, and is by far the largest institution of its kind in the woild.It has teaching centres in eleven 2'Behind Panel. countries and students in fifty. 3V Span Fully Open. Write to -day for full information as to how the I.C.S. can help you SMALLEST - in your chosen vocation.There are 36o Standard Courses, of which 4'. ounces, the following are the most important groups:- LIGHTEST- Wireless Telegraphy (Elementary and Advanced) Accountancy Draughtsmanship Salesmanship and most Advertising Engineering (all Scientific Management Perfect to Architecture branches) Showcard Writing Building trench and Spanish Textiles EFFICIENT- Logarithmic Law. Commercial Art General Education Window Dress n: yet produced. Commercial Training Professional Exams. Woodworking There isa special booklet for each group, which will be Write for Literature containing full details. sent free on request.Tell us the one you would like to see. CROWN WORKS, 22, CRICKLEWOOD LANE, N.W. 2. Telephone:Hampstead 1787. International Correspondence Schools, Ltd. 172, International Buildings,Kingsway, LondonW.C.2.

WIRELESS CABINETS IN SOUND QUALITY OF WOOD HighlyPolishedFirst -ClassCabinet Work Makers of all designs for old and new Wireless Sets as periodicallyannounced inthisjournal Special line of closed cabinets totally enclosing Batteries and Accessories Thousandsof satisfiedusers. Send forIllustratedPrice List Morn), returned if quality and workmanship not equal to our guarantee

CAXTON WOOD TURNERY CO., MARKET HARBOROUGH THE LATEST O in the Wireless line are the famous LOEWE High Vacuum Resistances and Block Condensers. As an expert you should know them. KON ACT Please ask for free literature by mailing the Coupon below. LEADS THE WAY IN ECONOMY, LOEWE RADIO COMPANY, LTD., 4, Fountayne Road, POST Tottenham, London, N.15. Telephone .Tottenham2076. TO -DAY 'UTILITY AND EFFICIENCY KONIACTcoloured connecting wire LOEWE NIDIO is supremely easy to use, and gives a finish to any receiver. To the LOEWE RADIO COMPANY, LTD.. PRICE per carton of I Colours : 4, FOUNTAYNE ROAD, TOTTENHAM, N.I5. four 5 ft. coils-f IL/ Red, Blue, Green, Yallow. Please send me your literature concerning Loewe High Vacuum Resistances ...111 all good dealers and Loewe High Vacuum Block Condensers, \BRISTOL WIRELESS CO.,LTD. Name. QUEEN'S ROAD, BRISTOL W.C.:3 Address THE WIRELESS CONSTRUCTOR March, 1923 perfectly simple if we take a straight-. them,justastheverbosetalker IN LIGHTER VEIN forward analogy.Just imagine that flings words. The Wretched hydrogen -coptinued from page 380 in the unlikely event of your paying atoms cannot help theMselves. Under in a cheque forfifty pounds, your the influence of the oxygen they turn bank promptly debits you with that towater,preciselyas you and I The result is that the zinc, whilstamount, and you willsee precisely give way and hand out ourhalf- being eaten away,isleftwith what happens. crowns when we realise that the eyes surplus of negative electrOns, exactly Electrons dash through the circuitof the meeting are not only upon as yon and I,when writing our from the negative to the positive pole. ourselves, but also on the muffin cheques for the gas bill end the rates plate in which we place our offerings. and the butcher and the grocer, are Depolarising If you are still old-fashioned enough left with a surplus on the wrong side. E111111111111111111111111111111111111111111111111111111111111111111111':, As we become charged with a balance toinsistupon remembering your on the Dr. (or is it the Cr. ?I never schooldays' lessons, you have only F5 -? can remember which)side,so the to think of them as travelling back-' zincpilesupanegativecharge. wards. But what happens at the. See Next Month's Very well, then, positive pole ? Well, the H's get " WirelessConstructor."

dropped. The hydrogen thingmetites :-.1111111111111111111111111111111111111111111111111111111111111111111111[7:. The Electron Flow sit down round the positive element, What happens when we connect just as ladies at a. tea -fight' sit down positive to negative by means of a round the bun -table.The latter-by The positive element is thus freed wire ?You will answer at once that which, of course, I mean the ladies fromtheembarrassing swarmof the batteryis done in. You areand not the buns-can be dispersed hydrogen atoms.They are, in fact, perfectly right, except that you are only when a professional bore rises neutralised or placated, even as the entirely Wrong.Remembering your to his feet to appeal for the formation flapperis placated by the Govern- school lessons, you will say at once of a fund for the provision of braces ment's offering of a vote. A flow of that a heavy flow of - current takes for the Hottentots. current thus takes place which you placefrompositivetonegative. The part of the bore is played bywill realise as being from negative Remembering, however, on second the nasty black mess, which is known topositive,orfrompositiveto thoughts that these must be forgotten as the depolarizer.No sooner have negative, according. to your degree even if they are remembered, which the hydrogen bubbles got comfortably of senility. is doubtful, you will See that the flow settled down round the carbon rod You find everything now as clear of current takes place from negative than along comes themanganese as mud ? topositive. The whole thingis dioxide and simply flings oxygen at I thank you.

UN,

SAA11.: 5; 7; dad C.)0

402 March, 1928 THE WIHLLESS CONSTRUCTOR

A IIIIIMIMMI11111111111111111111111111: IRE [ME VERNIER C DRUM CONTROL MAKE THIS VALUE A remarkable combination of skill and manufacturing UNP LED design. THIS Drum Control provides fast- and slow- motion wheels for regulation of condensers. The double model, accommodating two variable NEW condensers, consists of two main wheels and two separate vernier wheels.The. single model (as REDUCED illustrated) accommodates one condenser, and also PRICES has its independent vernier wheel. It may be used forright-or left-hand mounting. Detachable 0005 ivorine scales included with both models, also drilling template and beautifully etched panel face plate. No, 1280.Single Drum Control Price 17:6 each

No. 1281.Double Drum Control 32, 6 ,, (PYiCCS

.000s 716 (WITH 3' DIAL) With " Two Speed " dial Telephone: Telegrams: and Station Recorder. Regent 3160 200'2, REGENT STREET. " Pleasingly 0003 151- (6 lilies) LONDON, W.I. -0005...1516 Last year we concentrated our resources and experience to the production of a first-classprecisioncondenser at a OARIBRELL CENTRE - TAPPED COILS popular price. Approx."To. Size, Price. of Turns. Few wireless constructors have not heard of the won- Universal Coils- a2 4/10 18 usenotbeing a 4/10 25 derful success that followeditsintroduction. The limited to centre - A 51- 30 experts describeditas a condenser worth at -least fittapped any standardcircuits, 51 5;3 40 socket, easily B 516 50 double its price. Constructors from all parts of the interchangeable, C 5/9 75 country have expressed their astonishment at finding and 1) 6/3 100 occupybase- El. 6/9 150 such efficiency at so low a price. minimum 5, 7'9 200 board space. F 1.16 300 Now this value is to be even greater.Our new factory, CT 10/- 500 equipped for a far greater output, is able to produce Prices quoted, Standard Coils. Centre-tonped, 65. extra. these " Popular " Condensers still more inexpensively. THE GAMBRELL NEUTROVERNIA Condenser hasdefinitelyestablisheditselfas the We pass these economies in full to the public. very best Neutrodyne Condenser obtainable.It can beused asabalancingcondenser,forcapacity Every good dealer stocks Bowyer -Lowe quality com- reaction control or as a vernier condenser if desired. Capacity rangeof approx. 2/38 lo/mfds.Allen- ponents. closed, dust and damp-proof, will not phort, gives a proportional capacity increase or-dcerebSe We shall be happy to send you our catalogues on byeachturnoftheknob. Can be request and to 'ell you where you can obtain our com- three ways :on baseboard,on ponents in your district. Panel, or through panel. PRICE5/6 Obtainable from all Dealers. End plates are aluminium press-Straight-line wave -length curve. GAMBRELL EROS., 76, Victoria Street,London, S.W.1 . ings.Rotor mounted on ballGirder con struc t i o nfor bearings.No " sloppy " bear-strength.Perfect balance and ings, springs or spring washers.dead accurate adjustment. &silkIETs tiellAlico.(*.wiry-GIVE YOUR o*ferrotowe SET THE PROFESSIONAL LOOK Illustrated catalogue, showing a complete range of Cameo Cabinets. The best of sets looks amateurish in a make- Panels, and Brackets, shift cabinet.Install your set in a Cameo freeOn ITO11,1,1". cabinet and make it look as attractive as the dearest sets you can buy in the shop. SEND A P.C.TO-DAY PopularCondenser CARRINGTON MANUFACTURING CO. LTD., Cameo Works, Sanderstead Rd., South Croydon BOWYER-LOWE CO., LTD., LETCHWORTH "oydon 0623 (2 line,). c,k 77, :t.- 403 THE WIRELESS CONSTRUCTOR March, 1928

The question of a reallyefficient MORE ABOUT THE wave -trap for the 5 X X range is now "BUSINESS MAN'S FOUR" beingstudiedintheWIRELESS -continued from page 372 CONSTRUCTOR laboratory,andas soon as a thoroughly reliable design type of Litz it is fairly easy to get has been produced it will be published, the silk off by lightly singeing with a whereupon theselectivity on the matchand.thenalittlecareful longer range will be just as good as scraping of each strand will make it on the shorter. quite bright and fit for *soldering. Mounted upon the baseboard im- ********************

mediately beneath the end of the FAULTS WITH coil is a small variable condenser of the compression type which is now .1** "ONE -HOLE FIXING" * becoming so popular for work of this sort.Thecapacityofthiscom- onot assume that because a ponentdependsupon thewave- component is of the one -hole - length of the station it is desired to fixing type one side of it is eliminate.Ifthewaveofyour necessarily connected to the fixing local station is below 400 metres, a bush.For instance, some " on and .00025 mfd. or .0003 mfd. will be off " switches have two soldering tags required, while if it is 400 metres orat the back, neither of which is con-. over, one of .0005 mfd. should be netted to the metal knob which con- 60131111 011 chosen.(The alternative capacities trols the switch. Failure to notice such of .00025 or .0003 mfd. have justpoints may lead to mysterious faults. been given because in some makes PEERLESS onlya-00025mfd.isavailable, *******************014* whereas in others a .0003 mfd. is pro- DUAL RHEOSTAT duced, either will serve.) A NOTE ON THE 4t

AFFonat Using the Wave -Trap it"NEW FAMILY FOUR" It PERFECT These components have a screw - CONTROL down adjustment whiCh can be per- ANUMBER ofreaders who have formed by means of a screwdriver, built, or are building the " New The Peerless Dual Rheostat is and, of course, the condenser can be FamilyFour,"described in specially made to meet the demand for a Rheostat covering left permanently set to the correct the August issue of THE WIRELESS needs of both bright and dull capacity once this has been found. CONSTRUCTOR have written to ask emitter valves.Has two wind- Screwed to the edge of the base- where the four1 mfd. condensers ings, a resistance of 6 ohms, with mentioned are used outside the set. a continuation on to a 30 -ohm bbard of the trap is a small piece of strip winding.Resistance wire in. thick ebonite, 2i in. by 12 in., The useoftheMansbridgetype wound on hard fibre strip under carrying a terminal and two sockets condensers of 1 mfd. capacity, or more, great tension and immune from such as the Clix or Eelex types, asshuntsacrossthehigh-tension damage. One -hole fixing,ter- battery is often a distinct advantage minals conveniently placed. Con- these being for the external connec- tact arm has smooth, silky action. tions to the trap.In use, the lead particularly with batteries which are All metalparts nickel -plated. from the set to the trap will be con- not " intheirfirst youth." The Complete with ebonite combined nected to the. terminal, while the connectionsare very easily made, knob and dial. aerial lead will terminate in a plug as one simply places the four mans - PRICE 3 /- which willbe inserted in one or bridge type condensers side by side other of the sockets, according tolthe (screwed on a board for convenience), number of turns on the coil which it andjoinsoneterminalof each is desired to use for coupling purposes. condenser to a common lead, which is taken to the L.T. negative.A For the Long Waves separate lead from each of the other The selectivity of this set on the terminals is then taken to its particu- Daventry 5 X X range is not good, larhigh-tensionpositiveterminal. and in many casesitwill not be Thus one leadistekentoH.T. passible to cut out 5 X X and get positive 1, the second to H.T..positive Radio -Paris,free from the former 2, the third to H.T. positive 3, and station, but the sensitivity is so great the fourth to H.T. positive 4.When that one can reduce the size of aerial connected up in this way there is a on this range and use a small indoor condenser of 1 mfd. capacity joined aerialverysuccessfully.Such an between each high-tension positive aerial will give much higher selec- tapping and the valve filaments. tivity, and the reception results will Sometimes, with almost any set THE BEDFORD ELECTRICAL be excellent. using H.F. and an old high-tension AND RADIO CO., LTD., battery,instabilitymay beex- A CORRECTION. 22 Campbell Rd., Bedford. In the December issue of the "Wireless perienced due to battery resistance, LONDON : GLASGOW : Constructor," the price of the Eureka Baby and the shunting of such condensers 21. Bartlett's Buildings, 113, St. Vincent Street, Grand No. 2 Transformer was given as HolbornCircus. E C.4. 0.2. across the various tappings will be 13/,This should have been 13/6. found to remove this fault at once. 404 March, 1923 THE WIRELESS CONSTRUCTOR

IMPORTANTTHIS COLUMN IS FOR We stockIgranic, Climax,Ever -Ready, RAYMOND'SHellesen, Siemens', Formo, Ferranti, Wearite, Ormond,I.B.,Benjamin,Lotus,Mullard, Dubilier,Lissen,Lewcos,Utility, Magnum, Peto-Scott, Peerless, Burndept, Pye, Marconi,CALLERS ONLY Cosmos, Carborundum. R.I.- STOCK Varley,McMichael, Gambrell, Brown's, Sterling, Amplions NO POST ORDERS ON SAME. -in fact, everything itis possible to stock.TERMINALS. Nickel W.O.. Pillar, 'Phone, 1/. doz. OUR NEW (3 for 4d. with N. and W.); )rasa do., 10d. doz.(1c1. each with N. and W),allhighquality.Valve -Pins, BULLPHONE UNITS 100 -page CATALOGUE with outs, 2 a id. Ormond Screws, 6 or 4 B.A.6d. Okid firstowed dozen, with nuts; washers 12 a id. Red and Black Gramophone Profusely Illustrated, valve data, 10 - Spades, screw at side, 31d. pr.Plug and Socket, Red Cone Unit Very handy for reference, order. orBlack, 3d.Wander Plugs,Red orBlack,3d. Attachment etc. pr.(large good).'Phone Connectors, ld. Flush panel sockets and nuts, 4 for 4d., 10d. dozen. Brass Spade Tags, 6 a Id. Large ditto, 3 a 13.Nickel Soldering 151 - 15'- IT IS IMPOSSIBLE TO ADVERTISETags, 4 a 13.Valve Pins and Nuts, 2 for 114. Full ALL THE WIRELESS PARTS NOW ONset of Circular Discs for Panel, 6d. SOLDER. with Resin, 2d. toot.1/16 eq, Bus Bar, SALE, BUT IF YOU WANT THEM2 ft. 13. Tinned Copper, 16 and 18 gauge, round, 9d. per 1lb.D.0.0., 5lb20 gauge, 8d.; 22 gauge, 9d.: RADIANO "THREE" TRY RAYMOND'S FIRST 24 gauge, 1034 26 gauge, 11d.; 28 gauge, 1/; 30 RADIANO " THREE " (March, '27, Wireless Con-BE SURE YOU VISIT THE Bargain Window.gauge, 1/2.D.S.0 and LITZ stocked. structor).All parts as specified with Terminals. New 100 -page Catalogue.Profusely illustrated.GRAND VALUE IN GRID BIAS. 41-v.,tapped 2 ORMOND S.L.VARIABLES, WITH FRICTION 1013.. & 11.; 9-v., tapped 15-v., 1/3, 1/6, 1/9, 2/-. GEAR; 3 COIL SOCKETS; T.C.C. 0003 AND CLIPSPrice 1/- Post FREE, allowed off first 10/- orderAERIALS. -100 ft7/22EBONITE, GRADE A. AND 2-MEG. LEAK; 3 BENJAMIN VALVE HOLDERS; Hard drawn. 1/11.ExtraStocksizes, 6x6and 3 FIXED RESISTORS. AND BASES; ON AND OFF heavy, 212.Phosphor 49 7z5, 1/3; 8 x 6, 1/6; strands, 1/6. Electron9 z 61/9; 10z8. 2/9; SWITCH; GECOPHONE 1ST STAGEL.F. B.T.H. stocked SpecialINDOOR12 x 6. 2/9; 12 x 8, 3/6; 2ND STAGE L.F.; ENGRAVED STRIP, WITH TER- Aerials. phosphor, with12 x 9, 4)-: 14 x 7. 4/6. MINALS AND NUTS; 2 B.L. TERMINALS FOR FRONT ebonite separators and rub-ALSO CUT TO SIZE while PANEL:, 5 GROSS PINCH -ON SPADES; RUBBER berrings(12ft. x 8you wait attd.perSq. strands), total 100 ft, 416.inch_ 3/16th. and Id.sq. FLEX. £411010 LOT, POST FREE U.K. CigsoTiviTETIDI7ECKZi0.V.. 216. Rubber Lead-ininch for 1 in.Special cheep highestquality,10ydspanels for Crystal Sets. COMPONENTS FOR SAME1/- 10 yds. 1/3; 10 yds NEW ENVELOPE ISSUED BY MR. PERCY 1/6.Extra heavy, 2d. andH.T. BATTERIES. No KARRIS FOR RADIAN() 3 NOW ON SALE 3d.yd.R.& B Twincheap and nasty batteries SERE,1/6, ALLOWED ON ORDER FORP°st £4.10.0 Kit ExtraFlex (best), 6 yds.10a.;soldhere;onlyhighest 2 Ormond -0005; 2 Do, S.M. Dials; 6 T.C.C.12 yds., 1/6; 36 yds , 41.;quality. atlowestprices. PARTS. ALTERNATIVESET OF COM-Condensers,-001,.002, two .0003,.0001. 2 Ins. Hooks, 2 for 193. EggAdico(Tradetestaward PONENTS (SPECIFIED BY THE AUTHOR)mid.; 2 Grid Lk. Clips, B.B.;1 Var. B.B.Insulators, 2 for 11d. Ins bestgiven)60-v.,6/11; FOR £3 NETT. ALL GOOD MAKES. Rheostat; 3 Dubilier Leaks, 25, 3, 4 meg.; 3Staples. 4ald.Earth100-v., 12/6.Dr. Nesper, LotusV.H. ; 1 FerrantiA.F.3 ;2PanelTubes. Copper, extra value,60-v.' 6/11; 100-v., 11/6. Switches; 1 Cossor Melody Wound Coil; Ter-1/11and2/3. Climax.These are extra value. Also 111E NEW No. 3 minals, Name Tabs, Glazite, 9-v. Grid Bias5/-(also at 2/6). good make,60-v. 5/11; 7-4ISSMIST(ac as specified). HEADPHONE CORDS.100-y..10/11. 1.5 L.T. a FEIVIOPTEDValve -Holders, 1 /-' Fixed DrilledHigh-grade 21 x 7 Goodquality.113;1/6 -Hellesen' s , 2/6. Adico, 1/8, S.L.F.CONDENSERCon., 1/-, 1/6; Leaks, 1 /-; Polished Panel, with RadionLoud Speaker Cords. '1/9. B.T.H., 2/-. Flag, 2/-. Switches, 1;6, 2/6; LatestNOTEStrip, FREE with above kit. 4 -way Battery Leads2/-;COIL PLUGS.Ebonite 00025, 5/6. -00035, 5,9 7 -way, 3/6. on Base, 74d. 0005, 6/.. With 4 -in. Dial.2 -way Cam Vernier, 4/6; Handsome American Cabinets, GEARED 00D, STANDS 653., WithFriction55-14 -in. hingedlid,baseboard.List: 2.way, 2/3, 216, 2/11 upLotus,8d. Burns -Jones, Dial, 6/- each extra. Rheostats, 2;6; B.B1/13;NOTE Oak, 25/-, for18/11; Mahogany, 1/9. Low Loss, 81d. and ORMOND, Square LawLissenola, 13/6; L.F. polished, list32/., for 22;6, it 3 -way, grand value, 5/11.1/..Various stocked. aboveurchased kit. ALL Back of panel from 3)11. Low -Loss. -0005, 9/6;Transformers, 8/6; 100 v. ALL it All ebonite ' and bestCRYSTALS. Superzite, 0003, 8/6 (1/6 each lessH.T., 12/11; 60 v. H.T., VALVES CARRIAGE AND PACKINGquality. Only needs seeing.1/6; Shaw's sealed genuine no vernier); Friction7/11; STOCKED. EXTRA. Newey, G.E.C. Lotus,Hertzite 8d., 11-; WyraY, Geared, -0005, 15/, Coils, 60 X, 6,4 ; Polar stocked 1/6; Neutron. 1/.. .0003, 14/6; -00025, 13/6.250 X, 9/9. Straight Line VALVE HOLDERS. Ant -Microphonio, 1/2, 1/3, 116 quency Fre- EDISWAN NEW THREESOMEW.B., Lotus, Benjamin, Burndept and all good makes Geared, Friotio,20/.;J.B. CONDENSERS stocked. Cheap B.B. V,H., 63. 00035, 19/6. S.L.F.0005, T.T. Friction Ver. LIST OF COMPONENTS. SWITCHES on Porcelain, PERMANENT DETEC- Three Coupling Units, Tubular Fixed Con- , 121.; 00035, 11/-. Plug,-0003 . ., TORS.Red Dianiond FILAMENT RHEO-'0005, 16/6 '00035, 15/9denser,Multi -RexCableand 813. and 101d. Soundtopper),2/'.LionMicro STATS, Dual, 2/6; '00015, 16/- Variable with S.M. Dial, 2 -way Geared Coilquality.Panelswitches, (latest, cannot be equalled), ohmsor30ohms.21-. S.L.F. Holder, Connecting Wire, Red & Black Flex.with Ebonite handle. worth2/6.Brownie,2/6. En. Potentiometer, 400 double. S.P.D.T., 1)-;closed Detectors,1/-, ohms, 2/6.0001, Reac-'0005, 11/6 '00035,10/6The lot post free 42'- nett.D.P.D.T.,1/6.Insulating113. Micrometer, 2/.; tion,41.;Air Dielec-'00025, 10/- '00015, 10/-EBONITE PANEL The two withTape, 41d. Copperfoil, 4d.Service do., 2/6 (both with tric. 2i.; Neutralising, Sq. Law above kit only.toot(6in.wide) Gridcrystal). Cat's -whiskers, 4/-;Neutrodyne,2/,001 5 Ply Baseboard2/6 BiasClips,6d. Panel2d., 3d.Set of 6, 4d. Twin Gang, .0005, .. 9,6 '0005 .. EdiswanValves,10/6each;Power12/6.Brackets, 913.'1/-pair BASEBOARDS stocked 32/-; Triple, 40/, H.F. '0003 7/ - 2 60 -volt Batteries (if purchased same time)Shorting Plug. 3d in standard sizes. Choke, 7/6, GearedNeutralising .. 3/6 the 2 for 12/6 nett. Very good make. Dial. 51-, 2 volt Accumulators (with parts), 7/11 nett.COSSOR MELODY COILS, -wound to specification BE SURE IT IS All other accessories stocked. with D.S.C. wire, very special price. 4/11 (on an extra COSSOR, MULLARD, Please add sufficient for carriage. specialtube withSystotlex,5/6.AlsoD.S.C.wire B.T.H., EDISWAN, stocked, 20 and 32 gauge. COSMOS VALVES. RAYMONDS IP DOUBLE - READING"MULLARD MASTER THREE Push -Pull Switches,1/-.Flashlam`pBatteries, DR. NESPER GRAMO- Cat's-eye Bulbs, 3d. ea..4.5, Adieu, 413..Dr. Nes- VOLTMETERS,For NO SOLDER-ONLY 20 WIRES TO CONNECT.BatteryTesters,3d.per, 41d.. 4/3 doz.Ever. PHONE or LOUD SPEAK-and LT. A real necessity Safety Fuse and Bulb,ready. 6d. Battery Clips, ER UNIT. Adjustableand these arefirst-class SET OF COMPONENTS 5(1.,11-, 1)6.Grid LeakRd. doz. magnets, wonder- value,usually 7 /11 The components specified : Clips for baseboard, 6d.,Glasite, all colours.Also ful tone. Try one, 10/6 now VI 2 Terminal strips, 25 in. x1 Broadcast wave Master9d.ea. Brownie De-fine connecting wire, various Post 9d. Three coil (Colvern). tector parts stocked. colours, Sd. for 5 feet. Post 6d. 2 . Voltmeters, 0-12, for 1 Coil base. 1 On and off switch (Bul-MountedInductanceL.T..3/6.3/11. Also EIVOLT 2-v.05, ,7,6; 1 S.L.F. variable condenser, gin). Coils, 30, 40, 50, 60, 75,double reading for L.T. and 1 R.C.C.unit,type A 100,150,200,250,inH.T., extremely good DARIOVALVESLoud Speaker Valve, 10(9; 0005 mid.(J.B.) (R.I-Varley). variousmakes from1/-. 1 S.L.F. variable condenser,1 L.F.transformer,O.P. quality, 6/11, 7)11. each. (Genuine Radio Mem) 7-1; 00035 mfd. J3.3.1 (R.I.-Varley). Clix Plugs & Sockets.2mfd.filansbridge,2/11. Best in the World. 1 H.P. choke (Climax). 1 Combinedgridleak.2 1;76v.e'PogIA; UhR(Y.ae7),.3 Anti - vibratory valve megohms, and condenser, Headphones, all 4,000 ohms.Dr. Nesper de Luxe, holders with terminals. 0003 mfd. 1927 model, reduced from 10/6 to 7/11. Dr. Nesper 1 Pairpanel brackets. Adjustable,latestmodel,.11/6.Dr.NesperLoud 8 Wander plugs -4 red,4 Speakers, horn type, 17111 to 101-_- 4 Terminals-A., E.,L.S.-, black. DON'T FORGET OUR' BARGAIN WINDOW! NOTE WONDERFUL OFFER BELOW ! L8+ . Suitable length of red and 1Set of ABC. connecting black flex. If purchasing your regular wireless supplies here, you links (Junit). 1 Ebonite bosh, 1 in. diam., can at the same time select from these wonderful 1 in. bargains, SOLD AS AN ADVT. ONLY. 2 Spade terminals - 1 red, in.hole,3/16th AMAZING VALUE CA LLERS 1 black (Eelex). thick. BROWNIE CRYSTALPlease make out your 1/11 and 2/3 each. Brand H.F. CHOKES, 2/6 each, And 3 Mullard P.M. Valves. SET (200/1.700 metres) new Var. Condensers, 0003 absolutely guaranteed, brand Latest Model No. 3, 12'6list for orders over 20/ - and .0005 Sq. Law, Log new. (Usual price,51-) Pair4,000 ohm Head-if requiring component Mid -Line, S.L.F. 100 -volt H.T. BATTERIES, ABOVE KIT (Usual price, 4/11 & 5/11.)Tapped, very good make, £617 6 phones,7/6. Aerialandparts for any set and 3/11each. Brand newall brand new and fresh. GRID BIA S,T 9 VOLTS Lead-in2 we will give you a D'bleR'd'gdeadbeatUsual price 12/11; now 7/11.FREE 100 VOLTH.T. Theabove/11.lot fixedinclusiveprice. VOLTMETERS. (Usual ALUMINIUM PANEL, 18 x 7 -- NO POST. price,7/6.) BritishmadeVERNIERwith above. 3/. each. SPLIT PRIMARYDIALS, with log, really ex-OR, alternatively, YOU CAN BUY CABINET H.F. Transformers, Brandtraordinary value. List price, for 15111(List25)-). Panel free. OPEN new, 6 -pin, London or Day. 7/6; allat 2/11 each. PLEASE ADD CARRIAGE. WE ARE PERSONAL (Usual price, 101-) LOUD SPEAKER Cords, ALL DAY SITU,' DAY 3/- each. SPLIT SEC. dittovTeezthhighe, stt qupiailcitey, SHOPPERS London, 3/9 Day.(Usual A LLBAY II RSDAY price 10/- and 14/-.) all at 10d. each. ALL DAY EVERYDAY 83. each. No. 50 mountedLOUD SPEAKERS. various, Hours 9 a.m. to 8pm. coils. All brand new,3/11, 5111, 6,11(usual Sat. 9 a.m. to 9 p.m. usually 1/6 each. price treble). Sunday morning 11-1 HUNDREDS OF. OTHER BARGAINS .RAYMOND ALL ABOVE BRAND NEW. 27 & 28a LISLE ST., LONDON, W.C.2 BE SURE IT'S RAYMOND'S! Come to LEICESTER SQUARE TUBE SURE IT'S RAYMOND'S IN ORDER TO REAP THE BENEFIT OP ABOVE, YOU CAN ONLY BUY THESE AT RAYMOND'S WHENThis address isat the back of Daly's Theatre. BUYING OTHER GOODS.NOT SOLD AT ABOVE PRICES ALONE, OR BY POST. 'Phone: Gerrard 4637. WE HAVE THE GOODS

405 THE WIRELESS CONSTRUCTOR March, 1928

When Valves get out of hand..., 11111111111THISUEzigzolum MORE LIGHT ON THE H.T. BATTERY ARTISTIC -continued from page 390

EFFICIENCY! be expected to last well even in a large receiving set. Shouldthefirstlow -frequency valve, either of the " first stage L.F." or of the " R.C." type, be resistance - iritir,"En coupled, it may also be served by the small battery, for the total load for THE RADIO PANEL DE LUXE the whole of this portion of the set is in this case not likely to exceed 3 or 4 milliamperes.The valve in the The distinctive Trolite panels last stage may then be provided with can be bought in five beautiful a battery of its own of the medium finishes-Black polish e d, capacity type ifitisof the small Mahogany polished, .Walnut power kind, or of the largest type if *AN polished, Wavy design, Cube it is a Super -power valve. incommand design.In each, high insula- Besidesleadingtoeconomyin tion and low surface leakage working, the use of a separate battery 46 GEEING is believing."is an age - is guaranteed.Drilling, saw- )7old adage that has found a new for the last low -frequency valve has truth in the control of modern radio ing and machining is easy and other advantages, which cannot be receivers.What with filaments that do not acknowledge the current with even permanent joints can be made dealt with here.Let us take a con- a suspicion of a glow and plate consumption in thousandths of an ampere, with acetone. - crete example of the saving produced valves cannot perform attheir best byusingseparate batteries. On without the aid of Sifam Radio Meters. Your set needs discipline-put Sifam in measuring the total current taken by command-tune with your eyes on the Trolite does not fade,dis dial and regain that perfection of tone colour or warp.Use Trolite a three -valve set we find that the and fidelity that your set was designed amount is, say, 10 milliamperes. On to give. But don't pay extravagant panels for your set. prices for ordinary measuring instru switching off the last valve, however, ments.Get the popular -priced Sifam Meters specially constructed for every the currentfallsto3.The high - Radio requirement. Your dealer will PRICES per sq. inch : frequency and rectifying valves are show you the complete range.Leaflet " How to detect distortion " FREE. Polished MahoganyCube thus passing 3 milliamperes and the Black. Walnut. Wavy. Advt. of The Slim?) Electrical Instrument Co., Ltd.(Dept. power valve in the last stage 7. -C), 10a, Pape Street,We.,t- " in.- -A, in. -id. tailiSter, S. WI. in.-id. .1 in. -1d. NEW MODEL. Annual Costs Pocket Voltmeter. HighResistance, Referencetothelifecurves in 4,000ohms. Heavy Fig. 6 shows that under a 3 -milli- Nickel -plated Case, ampereload abouthalfayear's working may be expected from the smallbattery, whilstat 7 milliamperes oneof medium capacity should last for some thirty-five weeks. The small battery will thus have to he replaced twice a year, the annual cost being thus about £1.for H.F. andrectifierH.T.supply. The Its safe' r with Sifami also medium -capacity battery willneed renewal about once every nine months. -11Gr1STTS ViriLDTTI:)-- ask for spare time or otherwise, for the sale of Wirele-sa If, therefore, 100 volts are used, the Sets and Accessories only.Excellent Commission basis now inoperation. Write,firstinstance, J.E.Ellis & Co.. annual cost will be about £2. Peterborough.62, Burmer Road, We thus get a total outlay of £3 per 100 volts, which for a thousand hours works out at .72 pence per hour. Now, if a common battery To All DIALS, MOULDINGS, of the medium capacity size were used to supply the 10 milliamperes Advertisers COIL - FORMERS,etc. PLEASE note thatcommunica- needed for the set, its useful life, as tionsconcerning advertisingin Of all Radio Dealers,or the curves show, would be about half WIRELESS CONSTRUCTOR ayear.Theannualexpenditure MODERN WIRELESS F. A. HUGHES & Co., Ltd., would thus be roughly £4,or .96 POPULAR WIRELESS must be made to 204-206, GREAT PORTLAND STREET, W.1. pence per hour for a thousand hours. JOHN H. LILE, LTD., 'Phone :Museum 8630 (3 lines). Thereisthusaverydistinct 4, Ludgate Circus, London, E.C.4 'Grams:Distancing, Wesdo, London. economy in such a case in using two (Phone: City7261) Manchester Office:185, Princess St. batteries.With a super -heterodyne and NOT totheEditorialor Publishing Telephone : City 3329. Officers. (Continued on page 407.) 406 March, 1928 TidE WIRELESS CONSTRUCTOR THE WORLD'S BEST VALVEZ3/6 MORE LIGHT ON THE H.T. BATTERY 111111111111111111111111111111111 GIGANTIC SUCCESS OF N11111.11111111111111!!!111111111i1 REDUCEDPRICE -CCM it cued front page 406 BRITISHSKILLTRIUMPHS P.R. SUPER DULL EMITTER VALVES challenge comparison receiver fitted with a super -power with ANY OTHER VALVE ON THE MARKET. valve ill the last holder an even more Don'timagineforone marked economy would result from. momentthatthey are ' tripe '-such as bank- -the use of a medium -capacity battery rupt stocks or rubbishy foreign valves. It was for the I.F. and rectifying valves and onlyby the lucky a super -capacity battery for the last. discoveryofnew elements and new methods of manufacture that the Do not be Misled P.R. VALVE at NO 3,6 became an BETTER One cannot too strongly emphasise established CAN BE oftaking voltage fact. BOUGHT thedesirability Hitherto, ANYWHERE readings every now and then at the it had Io Icl C.io. been NOW ONLY end of the evening's run, and of not sold at relying upon readings taken when 86 316 the battery is under no load and has BRITISH Post S Packing 4d. been rested for some little time.An instance of how misleading the latter FRO M EVERY 2 Valves for6;9 'Phone Post S Packing 6d. kind ofvoltage readings may be ANGLE orderyour3 Valves for 101. occurred only a day or two before City 3112.Post, & Packing 6d. the present article was written. Do not be put off with a foreign Pay thePost- 4 Valves for 13/. man C O.D. Post & Packing 9d. A friend complained that .2 L 0's loudspeal(er. Fit. Fit lisp. Amp. transmissions became very bad in TY Pe Vts.Amp. (Hulls. Fae. ...,, quality towards the end of the even- For .our protection insist on PR 1 2 -06 33,000 15 4 H.F. ing.Itwassuggestedthatthe PR 2 2 .06 25,000 12 43Det. "Celestion." PR 3 2 .Ott 18,000 8 .44 L.F. source of the trouble was probably to PR 4 2 416 120,000 40 .33 11.0 . PR 5 2 .15 40,000 20 .5 H.F. be found in his receiving set and not The January,1928,issueof PR 6 2 .15 30,000 15 .5 Det. in the transmitting plant, and in- PR 7 2 .15 12,000 6 5 L.F. the" Broadcater " says of PR 8 4 .06 23,000 15 65H.F. quiries were made about the condition PR 9 4 .06 19,000 9.5 .5 Det. "Celestion " :" The Celestion' C.12 PR 10 4 -06 11.000 6 .55 I.F. of his high-tension battery.It had is exceptionally pleasing bothin PR 11 4 .06 120.000 40 .3:3 R.C. been in use, it appeared, for about appearance and results.As yet we P.R.POWER VALVES are superb and challenge com- five months, but he assured me that have to find a finer loudspeaker at parison with any other, no matter the make or price. it was " well up."He had, in fact, Power 2V /0 j 6,000 I 5 .82 I P. the price." Valves I 4V I '15 I 4,400 I 4 I 1'O P. taken it round only that morning to 7;6 Each.Post and Packing 4d. the shop from which it was purchased 43 There is character in " Celestion" All valves despatched under guarantee of Money Bark -11 -correctdesign,carefuland inFtillif not satisfied.All valves are carefully in order to have it tested and the packed and breakages replaced. voltage readingworkedoutat capable workmanShip, perfect finish, 92 per cent of the original E.M.F. all allied to the patented "Celestion" P. R. VALVESROW,.PPI LONDON,E.C.4sRENtW reinforced diaphragm. A Typical Instance c " Celestion " is the loudspeaker Disgusted by the quality of the so often imitated but never yet Does reproduction, he had not used his set duplicated.It is "On demonstra- for some little time, and in answer to tion-First on Merit." H.T/BA4 TT/ERY a question it was learnt that the battery had lainidlefor a week Write for illustrated folder. Models 11..1 onths: beforethereading was taken.I -in oakor mahogany from j,:5.10.0 went round that evening, taking an to125. accuratehigh -resistancevoltmeter with me.The open -circuit reading A careful study of the article " A Searchlight on the H.T. Battery," by R. \V. Hallows, M.A., in turned out to be not 92 but 84 per last month's issue, reveals that his advice is centoftheoriginalE.M.F.The USE HIGH -CAPACITY BATTERIES grid bias was adjusted accordingly, wherever a Loudspeaker is employed. Standard capacity batteries are recommended for and for a short time reproduction use with sets that employ headphones only. was as good as could be expected. ELESTION RIPAULT'S SELF -REGENERATIVE H.T. At the end of two hours, however, verysoul of music. DRY BATTERIES rhe are suppliedinStandard,Double,Treble,and only the smallest volume of sound Quadruple Capacities. could be obtained without obvious THE CELESTION RADIO CO., Giving 5o per cent. longer life overloading, no matter how the grid Hampton Wick, Kingston -on -Thames. than the normal type of battery, Ripault's Quad- ruple Capacity Battery, for example, has six times bias was adjusted.The reading then Showrooms : 33:35 VILLIERS STREET, STRAND, W.C.2. the value of an ordinary standard capacity battery. obtained was63percent,thus Obtainable from all dealers. showing that the battery was actually French Agents : Write for free "Life Chart" and " Right Choice" CONSTABLE & CO., PARIS. Folder C '50. at the end of its useful life instead of

I'Ktiz1.41115NS,tiql.1Ciera9' being in a " well up" condition as RIPAULTS LTD its owner had believed. 1111111111111111111111111111111111111T11111111111111111111111111111111111111 407 THE WIRELESS CONSTRUCTOR March, 1928

WITHIN THE VACUUM 0,1°SC011for -continued front page 392

GUARANTEED RADIO In these cases we get the following : 20 (volts) Copex = 10,000 ohms, or .002 (amp.) Screening Boxes 20 x 1,000 WELL -MADEfrom high - grade copper. =10,000 ohms. Highly polished and lacquered.Standard 2 (milliamps) unit assembled ready for useSize 6i- in. sq. x Thusfortheconditionsunder 6 in. high, 25/-.Copper Box with lid onl-as which thevalvewastestedthe used in the" Straight Line Four "-12/6.Other impedance = 10,000 ohms. standard sizes :81 in. x 71 in, X 7k in.-as used in the " New Everyman Four "-16/6 ; Now, assuming the valve was the 13 in. X 81 in. X 61 in., two compartments and same one whose amplification factor lid-as used in theWireless World "Selection we have just taken, we can calculate Four," 30/-. the mutual conductance, orefficiency Keystone Midget factor, from the figures arrived at. Palest We have Amp. factor = 10 One of the many outstanding advantages o' the Reaction Condenser Felling -Lee terminal is that no Soldering is re- Impedance = 10,000 quired. The terminal Is fitted with a transverse Then the mutual conductance is the slot with clamping nut, which eliminates this Extensively used tiresome task. amp, factor divided by the impedance, Make your set distinctive by fitting Belling -Les byMr. Percy terminals.Made with 30 different engravings. and W. Harris the answer being in mhos (the 'unit Prices :Type " B "-Standard large insulated other leading of conductivity, and the reciprocal of model. Polished black bakelite.9d. each. technicians. resistance). Type " 111 "-As type " B," but smaller Capacity.0001 and with only the engraved top insulated. Thus we have Rest nickel -plated brass -8d. each. mfd. Both types Guaranteed. 10 Price .001 mhos, or 10,000 5/6 multiplying by1,000,000 = 1,000 BELLING -LEE micro -mhos. TERMINALS Often we do not mention the actual -and now unit (micro -mhos), but simply give the Belling 6 Lee, Ltd., Queensway Works, the scientifically - mutual conductance as a fraction of Ponders End, Middlesex. unity, so that the above becomes 7Ae WHITELINEVALVEHOLDER. designed Keystone 10 .001, or to give it a more Mechanically and Logarithmic Condenser 10,000 = Electrically Perfect. convenientfigure we multiply by ii" 1,000 = 1. r or Thus a valve with an M of 15 and uowycr-Lowc 3 an impedance of 30,000 ohms has an 111141i1:117101:1i il:101: I al Z4 111113111 15 - (mutual conductance) of X I . 30000 of Quality 1,000 = .5, and so on. for every Set. Full illustratedparticulars Irons Cablethe Actual Manufacturers.S V. C. Bond & Mealuring Mutual Conductance Sons, 61, Hackney (trove, Marc S t .London. The mutual conductance can be "RED DIAMOND" 2 -WAY., obtained practically by. taking the valve and givingita fixed plate COIL voltage.Then vary the grid voltage HOLDER Easily between A and B (both negative ganged values) and take readings of the plate together currentatthetwogrid voltage No. Floating steelspindle. Cone bearings and readings.Call them X and Y. Then Parallel working. Fine ad- H.D. 32, micrometer balancing adjustment. Easily ganged we subtract A from. B and Y from X justment. Worm driven. Coilscannotfall. Easy together. Savescostof buying special ganged and we get two readings, C and Z. movement.Perfect finish.4 EACH condensers. Rotors insulated from end -plates. Now divideZ by C,Z being Ofallhighclassradio Without dials :'0003 mfd., 12/6 ;'0005, 136. dealers or by insured post, Twin ganged (ready assembled). '0003, 25 6 ; expressed in amps and not milliamps, 4/6, fromSole Makers : (ready assembled), and the result will be in mhos, which co., '0005, 27i6.Triple ranged JEWEL PENLTD '0003, 38, 6 ;'0005, 42:-. (Radio Dept. 411 multiplied by 1,000,000gives the 21/2, Gt. Sutton St., London, E.C.1. mutual conductance in micro -mhos. REGP_ All good dealersstockPeto-ScottCorn; ponents. If yod cannot obtain, send us your For example, if A = - 2, B = - 4 COMPLETE SETS, LOUD SPEAKERS. order and your dearer'. name and address. volts, X = 10 milliamps and Y = 5 COMPONENTS. Etc. suppliedforallcircuits,including theMilliard Master 3,Cosner milliamps, we have B -A = 2 volts, Melody Maker,alsothe new circuits featured PETO-SCOTT Co., Ltd., X -- Y = 5 milliamps, or .005 amp. in this tone 77, City Road, E.C.Z. Then the mutualconductance-- Senalist of requirements, and Branches: -62, High Holborn, London, W.C.1, .005 .005 x 1,000,000 best monthly terms will 4, Manchester St ,Liverpool. - mhos micro - be quoted by return. 2 2 THE P.D.P. COMPAN1 (Dept. C). 1$09 (Continued -on page 409.) 41, GREAT TOWER STREET, LONDOI4

408 March, 1928 THE WIRELESS CONSTRUCTOR

WITHIN THE VACUUM _echtin tted from ptir

mhos = 500 micro -mhos.A corresponding unityexpression for tins valve's mutual conductance being .5. Therefore you see that with a few meters and a little patience you can Columbia find out a considerable amount about any valVe you may have in your possession,, and once you have com- Every inch a battery menced delving into the secrets of valves and their characteristics, and Buy the new Columbia Layaibilt and know that every cubic inch ofyour comparing then" with their practical battery ispacked with electricity -pro. ducing material; that its efficiency is behaviour in a set, you will not only increased, and ail danger of loose or learn. a lot hut will find ita, most broken connections avoided by contact of full area of carbon against zinc plate ; fascinating study.

that itis by far the cheapest battery in the long run though its initial cost may Plantations be higher; that itis the H.T. Battery used by all discriminating radio enthusiasts because, of its pert and and Panels. economy. QUEER QUERIES Price 25/... .-continued front page 37,8 5. The lastlap in the long No increase in price over old type. journey. Layer building is a process perfected at immense cost by the world's largest battery .plug) was broken inside itsrubber manufacturers, and the "Layerbilt" is sold under National Carbon Co.'s full guarantee. covering, and consequently there was NOW comes the last lap in no bias on the last valve.This is a the journey of the rubber J. R. MORRIS, good instanceof thelittlepoints whichistobecomea 15, Kingsway, London, W.C.2. that need watching when hunting Resiston Panel.The long, thin Scotland: J. T. CARTWRIGHT, 3, Cadogan Street, Glasgow. for a fault.Itisoften the very sheetsof purerubberare now simplicity of the fault that makes it ready for ever to leave the land mystifying. oftheir birth.The native tree Lit "Better Without an Earth " tapper would see little resemblance " London is good either way, but in one of these sheets to the milky I find that Bournemouth is better fluid he knew, but he would be without an earth," writes a puzzled more amazed to see what strength Hampshire reader. and what beauty is given to this ONLY Amperite can give This difficulty is one that is likely self -same latex when, finally,it utmost life and perform- to trouble any country listener whose ance from your valves.Con- becomes a Resiston trols valve filament current local station uses a fairly low wave- automatically, Eliminates hand rheo- length. stats. Safeguards against valve damage Only the pick of the rubber ever and premature burnouts. Simplifies wir- The trouble usually arises from an findsitswaytotheResiston ing. Accept no substitute.Types for over -anxiety to get a good aerial.It all valves.Sold everywhere. factory. That is why Resiston Price 5/..with mounting. isnotgenerallyrealisedthat an Distributed by aerial may be too long, as easily as has such sheerstrength. Such ROTHERMEL RADIO CORP. OF CT. BRITAIN, LTD. too short,soif an elastic view is lustrousbeauty. Suchperfect 24, Maddox Street,London, W.I. taken of the 100 ft. allowed by the insulation Why its colouris Postmaster -General,theminimum permanent. Why itsdielectric wave -length to which the setwill constant is so low.If you want tune may not be low enough. your Set to have the finest panel The remedy,ofcourse, isto shorten the aerial by a reasonable that ever was made, you will fit G AT. GF,TE degree, making it,say, 70 ft. long a Resiston Panel. `7he'SELF-ADJUSTING"Ttheartai including thelead-in ;orelseto Res'ston Panels c me in 13 insert a small fixed condenser(of "01,stock sizes in black and Ma- PLEASE besure to mention IZ hogany -grained. From 6 in. x 9 in. " WIRELESS CONSTRUCTOR "rt .0001 or .0002 mfd.) in series between in black, 3/5, to 8 in. x 30 in. when communicatingwith Ll the aerial and the aerial terminal, Mahogany -grained 19/-. Advertisers. THANKS! Ci thus giving the electrical equivalent of a reduction in length. If this is not done, the aerial coil C RA iFT whichwasrecommendedforan p c4BINE average aerial may be too big, and EST1YALU consequentlytheremovalofthe"24 hours Cut Panel Service" 92eee eazzioriae 7 -fee earth lead may improve the tuning- Advt. Ames seen Hard Rather Co.,Lt 3a, Fore St..,E. C. THE ARTCRAFI COMPANY an effect that never occurs with a Go ills 156,CHERRY ORCHARD ratOYDON k.... normal aerial system. 409 THE WIRELESS CONSTRUCTOR March, 1928

For YOUR Wireless! WHAT IS A MAINS UNIT? The -ronti lined from page Wi -A RADIOLik, HYDRA:) L DU R 'V Fully described in " POPULAR WIRE- L5 go to the two plates in the one LESS," page 416, Oct. 22nd, 1927:-. valve instead of to two separate plates . " . is amagnificent production dignified and graceful style . .appeals strongly indifferent valves. tous . . worthyofiheterm deIone Otherwise the . . . a good return for one's money." functioning of the device is the same. PROTECTS your Set from DUST or It is also possible to use certain INTERFERENCE ensuringBETTER FIXED FOR LIFE REPRODUCTION. chemical' rectifiers, but generally these are messy and are rarely used nowa- Hydra Condensers are unmoved by 3ft.high, Solid Oak, days.Practically all rectification for atmospheric conditions.They are orMahogany, beautifully Ilnithed.In many mains units is done with one of the guaranteed accurate to within 5 to slam. twotypesoffilamentrectifying io per cent. of their rated capacities From valves (half- or full -wave), or one of that remain constant through all £5 5 0 to £15 the gaseous rectifying valves of the variations of temperature. Sent on Approval Direct Raytheon type. You can buy Hydra Condensers from Factory. withthe'assurancethattheir No need to rebuild.In sizes for every set and Practical Considerations capacities are fixed tor life ! heaviest batteries. Full Lists FREE. We have now reached the point PRICES where we understand how an alter- Tested on 500 volts D.C. mfd., 2, 6 ; 2 mfd., 3/6 ; 4 mfd., 5,3.Tested ] I..I.g current is turned into a pulsat- on 75o volts D.C., equal to 50o volts A.C. PACKET -141 ing .electriccurrent, and the next I mfd., 3r-; 2 mfd., 4/-; 4 mfd., 6/9.Inquire for prices of condensers tested at1,000, CABINETS thing to consider is a few practical 2,000, 4,00c, and 6,000 volts D.C. Albion Rd., BEXLEYHEATH, Kent. points in relation to the transformers and the valves themselves.Before proceeding farther we must consider D P A FOR MOUNTING ON From all good dealers, or direct EBONITE METAL OR WOOD exactly what we want at the output PERFECT end of our mains units, and how far LOUIS HOLZMAN BUSHES INSULATION Orders under 1/- Two required we can compromise.Questions we 34 KINGSWAY, LONDON, W.C.2 send lid. postage. 1 , for each hole. Tei,phone: Holborn 6209 NUMBER 0 1 2 3 4 5 6 must ask ourselves are : What voltage SBA, 4BA, 2BA, 1", 5/16", r, 7/16' PriceHole in each:Bush Id.ld.1d. ltd. 2d. 2d. 2d. we will require at the input terminals ? (Complete List of sizes free on application.) DAREX RADIO CO., What maximum voltage do we re- Waldram Rd.. Forest Hill, London, S.E. THE DIX-ONEMETER TRADE SUPPLIED. quire at the output terminals of our device ?What voltage is required is a precision instrument of --- LOUDSPEAKERS -- universal use, with an inge- to be impressed upon the plate or nious system of Multipliers, 1 GRAND 24 100 MODELS AT HALF-PRICE. Yours for 5/. Deposit and 14 fortnightly pay- platesofthe ments of 3,6, or £2 50 cash.Lists free. rectifiyingvalves ? whichenablefullscale WORLD'S WIRELESS, WALLINGTON. And what loss of voltage is there in readings of any value to be the valve and in the devices attached made over a wide range. 1 Millivolt to 2,000 volts, WET H.T. BATTERIES" - to it ? 50 ohms to 50 megohms. Solve all H.T. troubles. Mirror Scale, Jewelledknife- SELF-OHARGING,BILENT,ECONOMICAL Generally speaking, unless we are edge, a £10 de Luxe =51. JARS (waxed) 21" x sq.,1 3 doz. Zinc. New type, 11d. doz. BADS 1 2 doz. going in for what may be termed Model- - PRICE Sample dos. (18 volts), complete will, " super -power amplification " for Multipliers, 6/6 each. bands and electrolyte. 4(3. post 9c1 Get our New 72 -page Catalogue. Sampleunit.6d. 16 -pagebooklet moving -coil loud speakers, the maxi- ther a thousand bargains arelisted, and free.Bargain list free. hundreds illustrated.Bend td. in Stamps. AMPLIFIERS. 1 -Valve 195.2 -Valve 30s. mu.m output voltage of 180 will be 2 -Valve All -Station Set £4. ELECTRADIX RADIOS, Ur8vDohma,mEentreet. C. TAYLOR, 57, Studley Rd., ample, and in nearly all cases 120 Stockwell, London willserveourpurpose.Quitea number of high-tension units on the REPAIRS market give a maximum voltage at Any make of L.F. Transformer, Loudspeaker or Headphones repaired and despatched within the output end of 120.Some give 48 HOURS-THREE MONTHS' GUARANTEE Ifyour accumulatorsareserviceableletus 150, and some go as high as 200, while, with each repair.4/. Post Free. correctly recharge them.If not, hire ours --- ofcourse,there are various lower Terms to Trade. High and Low Tension and both perfect, TRANSFORMER REPAIR CO., trouble -free services. voltage tappings.At the moment we Dept. " C," Weekly, fortnightly or monthly deliveries any- 214. High Street, Colliers Wood, London, S.W.19. where within 12 miles of Charing Cross. are considering. the maximum volt- Particulars free on application. age. RADIO SERVICE (London) LTD., 105, Torriano Avenue, ADVERTISEMENTS Camden Road, N.W.S. 014 Voltage Drop Phone : North 0623, 0624, 0625. As far as possible all advertisements The rectifying valve itself has, of appearing in " Wireless Constructor" course, resktance, and as a voltage are subject to careful scrutiny before EVERYTHING RADIO is required to send a current through publication, but should any reader experiencedelay ordifficultyin resistance the presence of this resist- getting orders fulfilled,or should ance in circuit means a drop involtage. the goods supplied not be as adver- We must remember, too, that if we tised, information should besent EllASWOOLL:IDGEIt totheAdvertisementManager, RADIO CO LTD. areusingadouble -waverectifier " Wireless Constructor," 4, Ludgate l7S.22LIELE' STIIE with a centre tap on the high -voltage Circus, London, E.C.4. ..:44EICLItggit;'1-0 DO N. W C .U.. (Continued on, page 411.) 410 March, 1928 THE WIRELESS CONSTRUCTOR

WHAT IS A MAINS UNIT? -continued from page 410 winding; then each half of the transformer must be capable of giving the full voltage we require to apply to the valve.A typical gas -filled rectifying valve in a unit giving a nominal 180 volts output maximum requires 230 volts applied between the centre tap and each extremity of the winding, so that the actual voltage across the whole secondary of this transformer is 460 volts, which leads me to the first warning ! Note this Warning The voltagesinside a mains unit are very high and extremely dangerous. For this reason the maker's enclose all high. voltagetypesinsidea sound casing.Do not open up any high- tensionmainsunitwithoutcom- pletely disconnectingthe mains and removingtheplug from thesocket before you attempt it.If you do not bearthisprecautioninmindthe WIRELESS CONSTRUCTOR may lose a valued ,reader ! Each particular type of valve has its own characteristics and maximum current which itwillsafely carry. The, filament types of rectifying valve can be destroyed in two different ways.The first way isby over- running the filament, causing a " burn In Radio, Benjamin have the honour ofsettingthe out," and the second is by passing standard for five types of components.They represent too strong a current between plate the culmination of many years' experimental work and and filament, causing the plate to the attainment of the highest degree of efficiency.They become red-hot, and either to melt are classics. (in extreme cases) or tocause the 1.-The BenjaminAnti-3.-The Benjamin Battery valve to become soft. mieropisonie Valve -holder Switch. No otheranti-microphonic valve - Sheersimplicity-sturdypositive The Maker Knows holder so efficiently disperses micro - action for high or low tension. phonic noises and absorbs shock so It's OFF when it's IN. Price AI"' The gaseous rectifying types of non - thoroughly as the Benjamin. Nearly filament valves if made to pass too 1,000,000 manufactured and on / sold to date. Price Al a' 4.-The Benjamin Earthing much current will overheat internally, Device. and will lose their, rectifying proper- 2.-The Benjamin Self- contained Rheostat. An earth designed on scientific lines ties.The makers of rectifying valves The winding is inside the dial. Only at last !280 square inches of sur- usually explain quite clearly just what a locknut and soldering tags go behind face area. The special design gives their valves will do and their instruc- the panel.Three windings Ai definiteconstantcontact je. tions should be obeyed if a reasonable -6, 15 and 30 ohms.Price APT with the earth. Price 31/rk lifeis expected from the valve. Re- 5.-The Benjamin Battery Eintinaton The Majestic-for member that no maker wants to alternating current 200-240 v. 5) cycles. Delivers current for loads up to thecapabilitiesofhis 12 valves, 180 volts for power valve.Two variable voltage controls ensure under -rate fine tone quality. A really dry eliminator unit-no .07 valve, and if he says that it should acid or liquids, and no hum. Priceday ..11.31 o not be run above a certain figure you may be perfectlycertain that he knows what he is talking about !

1:1 IMPORTANT NOTICE. 711_ The Editor will continue this inter- estingdiscussionon the subjectof THE BENJAMIN ELECTRIC LTD. "Mains Units" in the April issue of the " Wireless Constructor." Brantwood Works, Tottenham;, ORDER YOUR COPY NOW. London, N.17. 1:( 411 THE WIRELESS CONSTRUCTOR March, 1928

consumption of two such valves in a that you have connected the correct SUPER QUALITY WITH push-pull stage is very large and will'grid bias for the first power valve and be greater than can be economically for the push-pull valves (the terminals ANY SET taken from dry batteries. Each valve are clearly marked) and connect hp -continued from page 340 will take about 18 milliamperes of cur- high-tension positive 1, 2, and 3 to rent, so that the total consumption of the same high-tension supply as your the set using 150 volts will be in the existing set.High-tension positive 1 will be found very convenient fOr neighbourhoodof40 milliamperes. shouldbeabout120' volts, H.T. wiring, and much time was spent in This should be taken either from high- positive2 can be 100, and H.T. getting a really convenient arrange- tension accumulators or from a mains positive 3, 120 or150,ifthis is ment. u nit. available. The low-tension negative The detector valve can be your and low - tensionpositiveare,of existing detector valve, or if this is The Final Tests course, connected to the same accu- not an B.C. type thenI would re- mulator as the set. commend you toobtain an R.C. It must not be thought, however, valve for the purpose.The second that really wonderful reproduction valve should be any good ordinary cannot be obtained from a moving - Loud Speaker is Protected small -power valve, and. the two push- coil speaker without allthis.The Note that as one uses a push-pull pull valves must both be of the same valves recommended for this purpose output transformer there is no need type and make.Which valves you and the figures given are for giving to use any filter following the ampli- use here will be determined by the really first-class reproduction without fier, as no direct current flows through high-tension supply you have avail- overloading the valves, thus doing the loud -speaker windings, which are able and the type of speaker to be fulljusticeto the wonderful loud fully protected by the output trans- operated.For general purposes with speakers now available. former. oneofthe modern types of cone Final tests on thisamplifier to The set can be run quite well tem- speaker, two small -power valves with prove its suitability with a high-grade porarily with only one valve in the 120 volts on H.T. positive 3 and about moving -coil speaker were carried out push-pull stage,the second pair being 7!, - volts grid bias will suit excel- with a of Mullard P.M.256's, withdrawn for the time being.You lently.A hundred volts will with 150 volts high-tension and 222- will not get so great an undistorted generally be sufficient for the first volts grid bias.Used in this way the reproduction, but for general use with low -frequency valve (H.T. positive 2), lowest notes of which the loud speaker.medium strength of signals this ar- while on H.T. positive 1 with the R.C. was capableofreproducing came rangement will prove quite satisfac- valve you should use the full voltagethrough without any overloading of tory, and, of course, will affect a very of your battery (say, 120 volts). Grid thevalve. Other veryexcellent considerable economy in high-tension bias is used for the push-pull valves valves for use in push-pull with the current. in exactly the same way as in ordi- maximum outputaretheCossor When this amplifier is used with a nary valves and the makers' recom- Stentor 6 and the Marconi and Osram gramophone pick-up for the repro- mendation should. be followed here. D.E.5A., while splendid. results were duction of gramophone records, one also obtained with the Cosmos S.P.50 side of the pick-up should be con- Red Spot and the Six -Sixty six -volt Using -Super-Power Valves nected tothecoupling condenser super -power valve. terminal which is joined to the radio - If you wish to drive a moving -coil frequency choke and the other to speaker and to get the best repro- Operating Notes negative L.T.High-tension positive duction from -it then .the first two There is very little to be -Said about 1 is disconnected and no valve is used valves should be as already described, the operation of this set as it is sim- in the first socket, the existing grid and the two .plish-p-ull valves should plicity itself.As pfeviously described, bias on the first note -magnifying valve beofthesuper -power type with- remove the detector valve from your being used as before.This arrange- about 150 volts on the plate- and a existing set and plug itin the first ment will be found to give wonder- grid bias recommended by the makers socket, substituting the plug on the fully good reproduction on the loud for these valves.It should he pointed end of the flexible lead for the detector speaker from the modern electrically out, hciwever, that the high-tension valve in the original set.Make sure recorded gramophone records.

PAGE PAGE Electradix Radios.. ..410 P.D.P. Company .. Ellis, J. E...... 408 11 INDEX TO ADVERTISERS I ..406 Pickett Bros. (Cabinets)...... 410 Ferranti, Ltd... ..387 P.R'. Valves -...... 407 Formo Co., The . . .. 401 " Popular Wireless 7 Blue Prints .... 391 Garnett, Whitelec &'Co., 'Ltd. ..` .. 393 Popular Gardening Annual.. :. .. ..402 PAGE Gambrel] Bros.; Ltd.--.. 403 American Hard Rubber Co., Ltd... ..409 Haiuley Brothers, Ltd... Raymond,K. - .... 405 Amperite Rheostat ..409 Holzman. Louis .. 410 Radio Service (London), Ltd...... 410 Arteraft Company, The .. ...409 Hughes, F. A., & Co., Ltd. (Trolite) 406 R.I.& Varley, Ltd...... CoVer iv Bedford Electrical & Radio Co., Ltd... 404 Ripaults, Ltd...... 407 .. .(Blue .Sp.ot) 399 Rothermel Corporation, Ltd., The Belling & Lee, Ltd. -.- . ..408 Igrnmc Electric Co., Ltd. .. 309 .. 400 Benjamin Electric, Ltd... ..411 International Corr. Schools, Ltd... 401 Sifam Electrical Inst. Co., Ltd. ..406 Bird, Sydney.S.; & Sons.. ..400 JaeksonDros. - ..397 Taylor, C. - ...... 410 Bond, V. C., & Sons 403 &408 Jewel Pen Co., Ltd. .. .. 408 Telegraph Condenser Co., Ltd. .. 374 Bowyer -Lowe Co., Ltd. .. 408 Lissen, Ltd. ' .. 373.6:377 Transformer Repair Co...... 410 Brown, S. G., Ltd. 378 Loewe Radio Co., Ltd... '. 401 Bristol Wireless Co., Ltd. 401 London Electric Wire Co.. & Smith's. Ltd... .384 Wet H.T. Battery Co...... 374 Borne -Jones & Co., Ltd. 398 London Radid Mfg. Co., Ltd. .. 102 Weston Elect. Instrument Co., Ltd. ..395 Carrington Mfg. Co., Ltd. .. 403 Makerimport Co. .. ..400 Woolldridge Radio Co., Ltd. ..- .. 410 Caxton Wood Turnery Co... 401 World's Wireless ...... 410 Marconiphone Co. Ltd. .. 337 ' Wireless Constructor " Envelopes .. 388 Celestion Radio Co., The .. 407 Metro -Vick Supplies, Ltd. - .. Cover lii

Colvern, Ltd... 397 Morris, T. R. 499 Cossor, A. C., Ltd. .. 338 Mullard Wireless Service Co., Ltd. ..Cover ii Alt communications concerning advertising in Darex Radio Co. .. 410 " Modem Wireless" ..384 "WirelessConstructor" mustbe made to Duhilier Condenser Co. (1925), Ltd... 378 Ormond Engineering Co., Ltd. .. 381 John H. Lite, Ltd., 4, Ludgate Circus, London, Eastick, J. J., & Sons 399 Peto & Radford .. 395 E.C.4.Telephone: City 7261. Electron Co., Ltdt, The 383 Peto-Scott Co., Ltd. .. .. 408 412 srrrR March, 1929 THE WHILL.-1. ONS RUCTOR t/14 talail44

ONE H.F. STAGE ThereV°1111 is a large Public who are content with reception from the local Station and Daventry, whose requirements can be met by the ordinary 3 Valve re -acted Detector Set of which there are so many varieties advertised with fanciful names. To get more than this inevitably means "oscillation" with consequent howling and annoyance to your neighbours. The B.B.C. definitely state that one H.F. stage is essential at the following ranges, if loud speaker reproduction is to be anything but "indifferent": - 100 -150 miles from Daventry. 5XX.4 Valves.1 H.F. stage.

50-100 f t 5GB. 1 H.F. stage.

Over 15 Main Station >9 1 H.F. stage. These figures obviously allow for that factor of safety which is so necessary if consistently pleasing reception is to be obtained under all conditions. One neutrodyned stage of H.F. will give that additional sensitivity necessary for more distant reception, with radiation reduced to a minimum. The Met.Viclt 4 Valve A.N.P. Constructor's Set is the ideal solution. With the additional H.F. stage, there is no need to force the set.Using A.N.P. coils the set is stabilised, screening is unnecessary and high voltage factor Valves can be used.Additional selectivity is provided by a Tuned loose coupled aerial circuit, brought into action when required.Delightful to operate and cheap to build, the parts with two sets of coils costing only a. The Met -Vick A.N.P. 4 is pre-eminently the 4 Valve Set of the Day. If unable to obtain instruction book from your dealer, write for Pub. lication No. 7117/5 or 7117/4 ( the A.C. Valve Model) free on request. MET -NICK

RP 104

'PLIES LTD I55,CHARING CROSS RD.LONDON.W.C.2./A THE WIRELESS CONSTRUCTOR March, 1928 itmusthave beenverys skilfully designed " Fide Popular Wireless,' Jan. 7th, 1928."

15/ Ho 4 to 1. " It must have been very skilfully designed, for it gave results far superior to those its price would lead one to anticipate.In fact, we must admit that we consider its performance falls very little short of transformers in the one -pound class." This is an extract from a test report by Popular Wireless,- under the heading Art Efficient L.FTransformer intheirissue of the 7th of lanuary1928 The results obtained withthiswonderfullittletrans- former have been truly remarkable.Take the case of the Mullard Master Three. If you substitute a cheaper Transformer the signals from a large number of stations are so faint as to be hardly audible even on earphones, and the quality of reception from the very few that can be heard is distinctly poor. Now, r use the R.I. & Varley General Purpose Transformer (that specified by the designers of this efficient Receiver), and at once the number of stations which can be heard at good loud -speaker strength are more than trebled, and the quality of reception is improved out of all proportion. Actually,26stations have been logged at Loud- speaker strength 2 miles from2L 0 on the Master Three, using our G.P. Transformer. Of course, if you want still better results build the Master Three with the R.I. & Varley Straight Line Super Transformer.You will be able to listen in to still more stations on the loud speaker, and the increased amplification of the very low frequencies will add still further to the " roundness " of the reception.The patented system of winding, which, owing to the small self - capacity, takes care of the high notes as well as the low, adds remarkable realism to the reception of both music and speech.

16 -page illustrated leafletC.rj-free on application-gtveN lull particulars of all typesofR.I. & Varier Transformers. THE MARK OF RI BETTER RADIO Kingsway House, 103, Kingsway, London, W .C.2. Vai ley Telephone : Holborn 5303.

Printed and published on the 15th of each month by the Proprietors, The Amalgamated Press, Ltd., The Fleetway House, Farringdon Street, London, E.0.4. Advertisement Offices only : Messrs. J. H. Llle, Ltd., 4, Ludgate Circus, London, E.C.4. Registered for transmission by Canadian Magazine Post. Subscription Rates : Inland and Abroad, 8/6 per annum.Canada only, 7/6 per annum.Sole agents for South Africa : Ceptral News Agency, Ltd. Sole agents for Austtalia and New Zealand :Messrs. Gordon & Gotch, Ltd., and for Canada :The Imperial News Company (Canada), Ltd. N/R