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 com- plete 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 diffi- culty, 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.

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