^4-4-4-Fn1 Help Us in Our Endeavour to Impress We Publish the Text the Authorities with the Need for Under Correspondence " in This CONTENTS Such a Station

i71r11K41. d 11W%r w,?9,P

No. 401. WEDNESDAY, MAY 4TH, 1927. VoL. XX. No. 18.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

Editorial Offices : 139 -4o, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone : City 4011 (3 lines). Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. Telephone: City 2847 (13 lines). Telegrams: "Ethaworld, Fleet, London." COVENTRY: Hertford Street. BIRMINGHAM: Guildhall Building3, Navigation Street MANCHESTER 199, Deansgate. Telegrams: "Autopres., Binnin than." Telegram.., "1 le, Manchester. Telephone: 0210 Coventry. Telephon::: 9970 and 2971 Midland. Tclep,,one- 8970 and 9971 City. Subscription Rates: Home, 17s. 4d.: Canada, 17s. 4d.; other countries abroad, lets. 6d. per annum. As many o,' the circuits and apparatus described in these par05 are 'covered by patents, readers are advesed, before making use of them, to sattsly themselves that they would not be in;ringi n; patents.

EMPIRE BROADCASTING. We lo not, perhaps, hear enough from our readers over - seas, and we take this opportunity of extending to all of N our issue of List week we put forward the them the invitation to write to us on this subject and give case for a central short-wave station for us their views on the establishment of a short -wave honte Empire broadcasting. By a coincidence, broadcasting station specially erected for the purpose of within a day or two we received a letter from overseas broadcasting. If our Colonial readers show their a reader in Western interest in sufficient numbers it will Australia, of which ^4-4-4-fN1 help us in our endeavour to impress we publish the text the authorities with the need for under Correspondence " in this CONTENTS such a station. issue. pAOE 0 0 0 0 Our reader deplores the fact that EDITOR I1L VIEws ...... 545 they have but one broadcasting sta- POWER AMPLIFICATION POWER AMPLIFIER FOR 40 -VOLTS H.T. tion in Western Australia, and goes WITH ... 546 on to ask ie When are the English- By A. P. Ca.stellaitl LOW VOLTAGE H.T. men going to broadcast on short PRACTICAL IIIN'rs AND 'l'IPS ... 552 waves ? " He reports reception of In the design of receivers where \VG1'''s programme relayed on B.B.C. QUALIrV FOUR" ... 554 considerable amplification is required at low frequency it has cus- 32.79 metres from 2XAF, and also CURREN "r TOPICS ... 559 reception of the concerts from Hol- tomarily been recognised that it is B R O A D C A S T IiEI.'FIVERS- THE land, the only telephony heard requisite that the plate voltage from England being from the ex- " DAVENSET " PORTABLE II 551 available should be of the order of 120 volts or more, since modern perimental station of Gerald ]\ lar- VALVES WE 1lAVE TESTED ... 563 cuse, G2NJI. power valves are not designed to This fetter no doubt expresses INVENTIONS OF WIRELESS INTEREST 565 function on voltages below that the feelings of almost every repre- BROADCAST BREVITIES ... 567 ligure. Considerable interest is sentative of the British Empire therefore likely to be aroused in NEW ArlADA-rus 569 abroad, who must feel very MANUFACTURERS' the power amplifier for 4o volts strongly that we in the mother I.EFIERS TO 'rilE EDITOR 570 H.T., which is described in this issue. By the employment of country are neglecting a wonderful HEADERS' PROBLEMS ... 572 opportunity which short -wave specially designed 4- electrode valves it has been found possible broadcasting offers for strengthen Ñi4r11-1,14- HrN1N1N+kr.++Ñ ing the, bonds of Empire unity, for, to obtain an output for the opera- quite apart from the fact that listeners wv-ouhl be hearing tion of loud- spcake s using approximately one -third of the concerts and other programme items emanating front this plate voltage requited with a three -electrode valve giving country, the station could also be employed as a means equivalent output. The four -electrode valve has hitherto of broadcasting events of national, and therefore Empire, been very much neglected, and this application is calcu- interest, and the usefulness of the station could well he lates] to stimulate new interest in its development in the extended, at some future date, to direct communication very' useful direction of reduction of high -tension voltage, to the assembled parliaments of the individual sections of which, from the point of view of compactness or the Empire. portability is so important

13 3

www.americanradiohistory.com WApigIlt00 D1.41' VII, 1927, Wad tl

An Efficient Four =electrode Arrangement Using Power Valves.

By A. P. CASTELLAIN, B.Sc., A.C,G.9., D.I.C.

rIL quite recently the idea of using only forty fully the advantages of push -pull amplification when low volts high -tension supply for a low- frequency H.T. valves are used. In Fig. r is shown the usual amplifier to give large volume output with good plate current -grid voltage characteristic curve for an quality reproduction would have been dismissed as absurd, amplifier valve for one particular value of plate voltage. and yet the amplifier illustrated in this article gives really This curve may be considered as consisting of a straight good strength and good quality on as little as 3o volts portion AB, followed at its lower end by a curved por- high- tension supply. tion, the straight part corresponding to a range of negative A short time ago' the writer described an amplifier grid voltage from D to C, and the curved part to grid using a four- electrode power valve embodying certain of voltages greater than that corresponding to C. his suggestions which gave sufficient loud- speaker results for the average room when operated from a crystal set Permissible Grid -swing. giving loud signals in telephones. The straight section AB is the only portion of the After the tests on this single -valve amplifier had been characteristic curve which is of use for distortionless completed, further experiments were carried out using amplifying purposes since it is only in this region that two stages of amplification with a view to obtaining suffi- the plate current varies exactly in accordance with the cient volume output for a very large room or small hall. variation of grid voltage, so that the maximum permissi- the high -tension supply having an absolute maximum of ble variation of grid voltage -or grid- swing, as it is 6o volts. usually called -is from C to D. In order to take full advantage of the low H.T. it was decided to ' make the last stage a push -pull one, since suitable push -pull transformers were already on the market. A push -pull amplifier may briefly be described as one in which the input voltage is divided equally between two valves, and in which the amplified voltages are combined in a special transformer to pass on to the loud- speaker or on to the next stage of amplification. In this way an input voltage which is too great for one valve to handle without distortion is split up between two similar valves, each dealing with half the- applied input voltage. Before proceeding with the design details of the amplifier it will be as well to discuss more

' The Wireless World, March View from back of instrument 9th, showing method of supporting 1927. grid bias battery. E 4

www.americanradiohistory.com Wfizamo :71:1 Y 4111, 7927. Woacl 547 Four -electrode Power Amplifier.- characteristics for actual valves on two different plate In Fig. I (also in Figs. 2 and 3) the curves showing voltages. It will be seen from these figures that increas- the relation between grid voltage and corresponding plate ing the plate voltage effectively increases the available current are only shown for negative values of grid volt- length of the straight portion AB of the characteristic age, for the reason that when the grid of the valve be- curve, and therefore increases the permissible grid -swing comes pósitive electrons will beattracted from the stream CD. At this stage it should be clear that, for any given going from filament to plate, amplifier valve, the maximum permissible grid -swing is thus causing grid current to fixed when the voltage on the plate of the valve is fixed. How -which will cause serious distortion... It is not here proposed to go into the ANELOY A.P. 425 'IMOMMOMMMEM reasons why grid current in OM% an amplifier produces distor- Ì has been MO AMMO tion as this subject ME III dealt with many times in the pages of this journal -so M I is sufficient to say that M that it /1 Ia! I it is only the straight por- omIIII tion of the characteristic r!IIMEI E curve corresponding to nega- EI'I.. I I, tive values of grid voltage IIIMMOMMOMMEMMAMMVMMOMME/.U Fig. 1.- Typical grid volt - which is permissible for dis- MMEII plate current characteristic. amplification. MA/a tortionless OMMIIMMIaI,a The next point to consider is the effect of varying the MOUr1 plate voltage on this straight part of the characteristic MMI.a//i/JIi curve. If this voltage is increased the relation between AMIIU w grid volts and plate current will he shown on the diagram EI H MMILI.a%/i J by a new curve lying to the left of the old curve a.nd of iAa a substantially the same shape, while reducing the plate old Mi/ the Ma to the right of MMMEW voltage gives a corresponding curve OM¡A one. In effect, then, increasing the plate voltage may EEEEEEEEMEE be regarded as moving the characteristic curve bodily -to 20 18 16 14 12 10 8 6 4 2 This point will be the left, and reducing, to the right. OUTER GRID VOLTS made clearer on reference to Figs. 2 and 3, which show Fig. 3. -Four electrode power valve. Amplification factor, 4.5; A.C. resistance, 8,000 ohms; inner grid volts, +30. 7 ANELOY if the input voltage required to be amplified is greater AP 412 II V/a grid -swing a given voltage, / than the permissible for plate then either the latter must be increased or, if this is not 0 6 . convenient, then the input voltage must be split up between two or more valves. IaI By the use of a special input transformer with a centre - E 5 EEEEEEd/ O E 1 tapped secondary, and a special output transformer with Ia I a centre -tapped primary, it is possible to divide the amplification evenly between two valves and then combine their /a 4 IIE 4 shows IaU outputs to operate a loud- speaker. Fig. the 11I complete circuit of the amplifier in which Tz is the special EiiiiiiiiEiiiiiiiiiïiii I input transformer to the push -pull stage, abc being the 3 11IIVaU centre tapped secondary, while T3 is the output trans- III1a/I former, with the centre- tapped primary xyz. :a., 2 _'I.I.,-. Increased Power Output. =EI,i It has nove been shown how bigger power outputs may EEE= E :EE:::EEEEEEEEE be obtained oh low H.T. voltages by the use of push -pull EEEEEiEeiiiiE¡EEiïEi amplification, so that the combination of this method of amplification with the use of power four- electrode valves, EE:EEEECEECE=EECEE:E:E which are essentially low H.T. valves, will give still fur- -20 18 16 14 12 1h 8 6 4 2 0 ther power output from such low H.T. voltages as thirty íOUTER GRID VOLTS to sixty. The four -electrode power valve is one in whit! an extra grid, connected to a tapping point on the H.T battery, is used to reduce the resistance of the valve by Fig. 2. -Four electrode L.F. amplifier. Amplification factor, 4.5; the space charge. A.C. resistance, 10,000 ohms; inner grid volts, -I- 20. the reduction of B 5

www.americanradiohistory.com WApagoo 18 NAY ¢t11, 1927. WorIl01 Foar- electrode Power Amplifier.-

The Valves. +G2 o The valves used in this +G, amplifier are the A.P.412 L.F. and the A.P.425 power, made by Messrs. 4.2 Aneloy Products, and two of their characteristic curves T2 b Y are given in Figs. 2 and 3. - 101111 II F In 2 T3 a Fig. the inner grid 411. o voltage is -+20, while in Fig. 3 this voltage is x-30, r which is a little high for 4o C2 volts on the plate, but about right for 6o volts. Both valves begin to show signs C of saturation at 6o volts H.T., which results in slight bending over of the H T +, characteristic curve at the top end. It is not notice- in 2, Fig. 4.- Circuit diagram of two-stage amplifier. The final stage comprises two valves operating able Fig. but in on the push -pull principle. point of fact it is quite noticeable with another six volts H.T., while in Fig. 3 is provided for switching on the valves, and a volume the 6o -volt curve begins bending just off the diagram at control is also fitted. This latter consists of a variable about 9 milliamperes plate current. high resistance K (Duvarileak) in series with a fixed re- However, as will be seen from Figs. 2 and 3, quite sistance of from half to one megohm. These two resist- large plate current variations are available with these ances are placed in series across the secondary of the valves with even 4o volts on the plate, so that they may transformer T as shown in Fig. 4, and the first valve truly be placed in the power class. (outer) grid and filament connected across the fixed resistance. The Circuit. In this way, when K is at a minimum value (practic- The circuit of the complete amplifier is given in Fig. 4, ally zero resistance), the full voltage across the secondary in which two grid batteries are shown for convenience in of '1', is delivered to the valve, while as K is increased drawing and explanation. In the actual set only one in value so the valve gets less and less of this voltage - grid battery is used, and a lead from the secondary of thus K acts as a volume control. The volume control is the first transformer T, taken to it. A filament rheostat not from zero output to full output, which is rather too much control for most requirements, but from about a quarter or so to full output, which is much more convenient. . ._.. Fixed condensers C C2, C3 and C4 of one -microfarad capacity are provided across H.T. and grid bias batteries, and separate H.T. and inner

A grid terminals used for each 7 stage as a refinement for experimental work, although it is not strictly an absolute essential. In the actual 312 amplifier all the transformer D D cores should be connected Ì -1- together and to -L.T. to L C lp jO prevent any trouble due to L.F. howling, which may Y/4 7 2' L3/4 -1^._2 -.. possibly occur otherwise 14f - this is a precaution which should be observed as a matter of course in building any Pi _g. 5.- Drilling details of panel. A, 3/8 in. dia.; B, 5/16 in. dia.; C, 1/8 in. dia., countersunk tor No. 4 wood screws; D, blind hole drilled and tapped No. 6 B.A. from rear of panel. kind of amplifier using iron - n 6

www.americanradiohistory.com 'Vfipamo MAY 4t11, 1927. MAO 549 Four -electrode Power Amplifier. - cored chokes or transformers. This connection is not shown in Fig. 4 nor in the wiring diagram, Fig. 7, as it might perhaps confuse the reader unused to this excellent practice. The input transformer TE actually used on the set_ is a Ferranti A.F.3, which has an earthing terminal for this purpose, while the connections to the cores of the other transformers are most conveniently made by threading soldering tags on two of the holding -down screws before fixing, making sure that the tags are in good contact with the frames by well scraping the latter. A general view of the amplifier in its case is shown in the title block, and a rear view with the case removed in the photograph on the first page. Plan view showing wiring and layout of components. \Vial the aid of The photographs, the layout of Fig. 6 and the wiring diagram of any convenient order. There is only one point which is Fig. 7, it should be quite a simple matter to follow the perhaps not directly obvious, and that is the was, the grid construction of this power amplifier -there are no snags bias battery is mounted. It will be found convenient to in the construction, as it is simply a matter of screwing mount this battery a short distance -say, about an inch down the components as indicated and then wiring up in or so -above the baseboard so as to allow short and direct wiring to some of the terminals on the back strip. ------The method of mounting T is by means of two IT shaped / TI clips made of l'. f';:I aluminium

www.americanradiohistory.com 550 Wfip@hoo dPAF ¢1It, 7927. ``Oo F1li . Four -electrode Power Amplifier. - been pointed out several times in this journal by the reasonable care should last a good many years and will writer and by others. probably require charging only four times per year with It is probable that many readers who want good normal use. The quality large 50 -volt dry battery should give reproduction with comparatively powerful output about 8 to 12 cannot months' good use, after which it will have afford the 120 to 16o volts of accumulators, to be renewed. or very large dry batteries necessary with three- electrode valves, but The ordinary small size H.T. dry batteries should not could afford 40 to 6o volts of this nature, so the set de- be used as they will be overloaded and will not last, be- scribed in this article will enable them to obtain sides giving what they bad quality results after a short time -as has want without the big expense in batteries. This power amplifier is quite suitable for adding after a crystal set which gives reasonable signals in o the telephones, while with a set which is quite close to the local broadcast station and gives loud signals in the tele- ,,, phones the output R from the ^`\ amplifier using 6o volts H.T. K should be much too I 0 loud for an ordinary room \ % with the _ ,/ o p. volume control adjusted for maximum results -in fact, it :; should be quite sufficient for 0 a small hall. Good Quality.

o o o The writer tested the amplifier illustrated in this article on a crystal set, with -. an efficient aerial, about three G , miles from 2L0, and ob- . e p an tained really good \ i volume, m/ e \ combined with good quality i P o of reproduction. r7 O O % It is quite o _A surprising to some how easy I 1 r2 9 ' it is ( x '® to get good quality re- Y. l! sults with these power four - electrode valves -and the real reason for these results is due to the ease with Ivhich they may be supplied with _v^= i I1!! l: relatively high plate voltages from large- ® capacity batteries. _ r From the point of view of CY .. . ' upkeep costs for good quality O Al--....r-T-( Q áwG.B. output in places where light- C4 Ti . ing mains are not available, -, ... O P 0`1 . .:O HT or it is not convenient to use i a L ® ® r _iQ them, the four- electrode / polder valve scores heavily. In a future article it will be shown how the overall efficiency of a four -electrode valve designed for low -frequency amplification corn- ÂoÂ pares with the efficiency of 0 0 0 0 typical three- electrode valves H T.2 . + designed for a similar pur- G2 H.T. G H T. Ìi INPUT pose. The method of comparison of these efficiencies is an ex- Fig. 7. -Go. npieie wiring diagram. tremely interesting problem, ii S

www.americanradiohistory.com WApigIl oz MAY ¢th, 1927. .' 551

Four-electrode Power Ampl.fier.-

LIST OF PARTS FOUR- ELECTRODE POWER AMPLIFIER (A.P.C.).

1 Push -pull L.F. Transformer, type 660 (Pye). 1 "Cameo" cabinet, 14in. X 7tn. X 9in. deep (Carrington 1 Push -pull Telephone Transformer, type 662 (Pye). Mfg. Co.). 1 Duvaril.ak (Dubilier). 1 Ebonite panel, 14in. x lin. x lin. (British Ebonite Co.). 3 Vaiveholders, "Lotus" (Garnett, Whiteley & Co., Ltd.). 1 Baseboard, 14in. x 94in. x shrouded (tsclling & Lee). 1 Transformer, A.F.3, 4 to 1 (Ferranti). 9 Ebonite terminal: & Lee). 4 Fixed condensers, 2 mfd. (T.C.C.). 2 Nickel -plated term! tali (Belling 1 Four- elcdrode L.F. valve, A.P. 412 (Aneloy Products, 1 Grid bias battery, 9 volt (Siemens). 36, Forest Hill Road, East Dulwich, London, 1 Grid Leak, Dumctohm 1 meg. and holder ( Dubilier). S.E. 22 ). - 1 Rheostat, 15 ohms (Burndept). 2 Four -elcctrode power valves, A.P. 425 ( Aneloy Products), 1 pair "Cameo" brackets (Carrington Mfg. Co.). Wire, screws, si:toflex, etc. Approximate cost (excluding valves) - £7 7 0

In the " List of Parts" included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer con: id :rs it necessary Mot particular components should be used in preference to otters, these components are mentioned in the crude itself. In all other ca ei the con- tructor can use his discretion as to the choice of components, provided they are of equal quality to those listed, and that he takes into con,idcration in the dimensions and layout of the set any variations in the size of alternative components he may use.

and one which is rather difficult to solve in a manner which proved worth the trouble involved and throws interesting gives a fair basis of comparison ; but the investigation has light on the probable development of the thermionic valve.

4C0 (ex FS) G. Blanequaert, 20, rue de Rome, lieneral notes. Lokeren. Mr. C. R. Pouting, 11, Woolcott Street, 40K (ex C1-12) M. Meunier, 105, Bd. des Etats- Redland, Bristol, sends us a somewhat Unis, Molle. TRANSMITTERS' NOTES 4CM Dr. M. Polain, 107, rue Louvres, lengthy extract from his log book which - Liège. we intend printing under " Calls Heard " SCO (K44) J. Dupree, 55, Vlostraat, Gisent. as he to compare notes with other 41;P (K:33) W. Geromez, 1, rue à Charrettes, wishes AND QUERIES. Flènu. readers interested in long- distance recep- ICU (Hd) P. Callebert, 211, Oostraat, Roulers. tion. We would warn them, however, 9DA (ex CBS) F. Jorsen, 15, rue de \Vitte, Ber - we do not encourage long lists of cham, Antwerp. that 4DF (ex E22) E. Van Gasse, 43, rue Dupont, this kind, for which there is seldom avail- 4AJ (ex CH) J. Hersleven, 50, rue du Bailly, Brussels. able space, nor any endeavour to create Brussels. 4FT (ex 08) G. Neelemans, 15, rue du Luxem- bourg, Brussels. a record for the number of DX stations 4AK (ex 01) P. Mattlet, 37, rue entre 2 Portes, Huy. 4FU (ex Z8) M. Ocreman, 8, Avenue b reed. Mc. Pouting states that last 9AL (ex L4) U. R. C. L. Cpt. Doudart, 28, rue Mabillon, Schaerbeek. month proved phenomenal for DX con- Louvres, Liège. 4FY (ex VO) E. Neiryncks, 2, rue de Pelichy, ditions on short waves, especially the 4AM (euLl) M. Laloux, 19, rue Bonne Fortune, Iseghent. 4QQ (ex A2) A. Bergneman, 17, rue Fontainas, roe =lit. of March 27th. when he logged ten Liège. 4AP (ex U5) M. Antoine, 48, Place de l'Eglise, St. railles. Australian stations in half an bout. Perronnes, Binche. 4SA (ex P2) R. Deloor, 26, Avenue Mont Kemmel, 0 0 0 0 9AR (ex F4) R. Boel, 25:3, rue Francois Gay, St. Gilles. Wolowe, Brussels. 9TM (ex I-4) M. Tricote, Vellereille- le-ttraveux. 4UA (ex U2) L. Humincks, 108, d'Auderlecht, Norwegian Amateurs. 4AT (ex GLl) I.. Charlier, 3.2, rue de 111erode, rue St. Gilles. Brussels. Through the courtesy of Mr. J. Diesen 4AU (ex H5) J. Male co, " La Manoir," Peruwelz. 4UC (ex M2) V. Lilsens, 23, ru _Ernotte, Namur. 4UU (ex U3) P. de Neck, 3:3, rue A. (LA 1A), we are able to give the follow- 4AX (ex X2) H. Boogaerts, '22, Avenue Mont - Renard, I selles. ing list of licensed Norwegian short- Kemmel, St. Gilles. 4AZ (ex 13) I'. Masson, 2.2, rue de Busquet, 4VU (ex S4) M. Diricq, :3:3, rue du Progrès, La wave transmitters :- Dison -Verviers. Croyère. 4WW (ex 1w1) G. Reguier, 17, Bd. Frère Orhan, LA IA j . mieses, Steen i Maalseiv, near Tromsii. 4BB (ex A22) M. Michelet, 59, rue E. Van G. H. Petersen, Inrlustrigaten 30, Oslo. Driessehe, Ixelles. Liège. LA 1D 4XX C22) Van Namvermeiren, 29, rue Ch. LA lE \O rvarslingen pas Vestlandet, Tiergen. 9BC (ex BD L. Era, 46, Avenue Van Put, Ant- (ex M. O. Bingen, Haste pr. Sandefjord. werp. Van Leerberghe, Brussels. LA 1F 4ZZ (ex Zl) E. Liane, Bd. Frère LA 1H Oslo sjörnannsskole, Oslo. 4BF (ex 14) R. Brachot, 141, rue des Grogeres, 44, Orhan, LA 1K Akademisk Radioklub, Trondhjem. Marcinelle. Liège. LA 1M Det Norske Meteorologiske Institutt, Oslo. 4BG (ex A1) G. Depauw, 73, rue des Ailes, o o o o LA 114 Ali G. Nielsen, Snaröen, Barum. Schaerbeek. New Call -signs Allotted and Stations LA 10 Ragnar Larssen, Tvholtveien 4:3, Trondhjem. 4BH (ex J44) T. Marchai, 222, Avenue Moliere, LA 1P N. J Soberg, [Miskolc Trondhjem. Ixelles. Identified.

LA lit Walter Riecl:, Vaagsalimenning 8, Bergen. 4BI - M. Much, 40, Rue Vinave d'He, 2BGU j . G. Ritchie, 15, Cloberhill Rd., Knightswoal LA 1X J. O. Berven, Uclandsgate 14, Stavanger. Liège. Glasgow. (Change of Address.) 4BK (ex TI) H. Servais, 6, rue Mali, Verviers. 2AN0 E. H. Walker,- W oodgrange, Overton Rd., 0 0 0 0 4BL (ex KS) H. de "Chier, 115, Avenue du Chèue, Sutton, Surrey. Heusy- Verviers, EU 08 (Ex UA). Gilarov, 19, Ulitca Mira, Lenin - Belgian Amateurs. 4BT (ex C2) J. Mussche, 63, Boulevard Poincaré, grad, Russia. (Transmits on :55.3, 42.3, 'through the courtesy of Mr. Louis Era, Anderlecht. and 50 metres.) 4B% u118) J. G. W. Stevens, rue Joseph I.ies, a (ex EI 1CR Vincenzo Quasimodo, Goriza, Italy. we are now able to give our readers Antwerp. ED 7HP Henrik Petersen, Hatsseminariet, Mönder, complete list of all Belgian amateur 9BY (ex D2) G. Pollart, 62, rue de Hollande, Denmark. stations licensed on April 10th :- St. Gilles. o 0 0 0 9CA - M. Commit, Wireless Inspector, 4AA (ex CH5) R. Verstrepen, 23, rue Van Shaelen, Antwerp -Radio O.S.A., Pilotage, Q R.%s Wanted. Antwerp. Antwerp. AC 8FJE (or SFJT), EB 4A13, 4RK, 4A0 (ex 18) l'. Duirgnan, 16, rue de l'Eglise, 4CB (ex P7) A. Depuydt, 6, rue d'Anvers, Antwerp. Ostende. N33, EK 4XY, 4MC, 4RL, 4XE, 4AE (ex D:33) P. Lamalle, 110, rue Franklin, 4CC (ex C5) R. Henri, 32, rue du Midi, Ctratelet. 4KRL, 4S AR. `B 2.\X, 111W, EC 2YD, Brussels. 4CD (ex A7) A. Reporter, 63, Digue de Mer, .1F 113, NU 8BFA, G 5BC, G 6WR', 4AI (ex A441 A. Romlout.s, 30, Place de Jamblime Middelkirke. de Meux, Brussels. 4CF - Radio Verviers, Verviers NO 13X. B 9

www.americanradiohistory.com 552 MAY 4th, 1927.

Aids to Better Theoretical Diagrams Reception. Simplified.

SOURCES OF DISTORTION. be obtained unless the amplifier is serted in the anode circuit of the Unless an elaî orate equipment of working at normal magnification. detector, with a by -pass condenser testing and measuring instruments is A good method of obtaining this (CO connected between plate and fila- available, it is fairly safe to say that condition is shown in Fig. r, which ment of the valve. C2 is, of course, it is a much more difficult matter to represents the connections of the last the usual coupling condenser. locate faults in a wireless receiver valve of a receiver. In place of the The second device consists of a than to repair them. The only loud- speaker, an L.F. choke is in- high ohmic resistance R, which is method possible to the average serted in series with the anode, and inserted directly in series with the amateur is to narrow down the field across it are connected a large stop- grid of the first L.F. valve. Its of search by eliminating possible ping condenser, a volume -reducing resistance may be from o. r to 0.25 sources of trouble. resistance, and the phones. The megohm, and in any case should be When the quality of reproduction best value for the resistance can only low in comparison with that of the is poor, it is advisable first to decide be found by trial and error ; it should grid leak. This is an extremely im- be sufficiently whether the fault lies in the amplifier large to reduce the portant point ; if we use, say, a or the loud- speaker; for example, audibility of signals to a sufficient any mechanical looseness in the parts extent, and several megohms will of the latter instrument may give often be necessary. rise to symptoms which are similar If a low -frequency choke is not available, the windings of the loud- speaker, with the diaphragm removed, will serve fairly well in this capacity. 0000 SEPARATING A.F. AND L.F. ' Poor reproduction or even instability is often attributable to the action of H.F. energy in the L.F. amplifier, and every effort should he made to prevent, or sat any rate to restrict, the development of high - frequency voltages across the grid circuit of the first low- frequency amplifier. In the case of a trans- Fig. 1. -A test for amplifier Fig. 2.- Keeping 11.F. currents out of the distortion. former- coupled instrument, this is a L.F. amplifier. simple matter, and provided that the to those produced by an overloaded usual practice of shunting the quarter- megohm grid resistance (R) in output valve. Although head tele- primary with a small condenser is conjunction with a half -megohm leak, phones are by no means perfect repro- followed, no special precautions need the available L.F. voltage applied to ducers, it is possible by their use to he observed. the grid will be reduced by one - obtain a very fair idea as to whether When the detector valve is fol- third, with a very considerable reduc- the amplifier is delivering undistorted lowed by a stage of resistance- tion in signal strength. signals to the output terminals, but capacity coupling, the problem be- An efficient H.F. choke may only when often volume is reduced to what comes a more difficult one, and the be substituted for the resistance, and, is generally referred to as " telephone methods shown in Fig. 2, indeed, it is strength." either certainly better when the This reduction, how- separately or in combination, are to receiver is primarily intended for ever, must take place after the out- be recommended. The first makes work on long wavelengths (over , put valve, as misleading results will use of an H.F. choke, which is in- 1,000 metres).

13 10

www.americanradiohistory.com ., tP" . s",vrjrt1,7:+" .-.._.. ... ---r - ..,- . .r, .

WIpishopS MAY ./111, 1927. Ull;'lSli 553 METAL PANELS. ary nowadays to bias negatively the panel, to the back of which a small In constructing receivers with metal grids of H.F. amplifying valves, and sheet of ebonite may be screwed: panels it is often overlooked that the also because a bias is required for A similar precaution should be ob- shaft of the variable tuning condenser " anode bend " detectors. In such served when fitting filament rheostats is often at a slightly different potential cases, when using a "one -hole fixing" to the panel, as a consideration of any from the negative side of the low - condenser, it is necessary to fit an in- of the circuit diagrams in these pages tension battery and " earth," to sulating bush. Where several fixing will show that there is a probability which the panel is generally con- screws are required it will be easier of introducing a L.T. short -circuit nected. This is because it is custom- to drill clearance holes through the unless this precaution is observed.

DISSECTED DIAGRAMS. The present series of diagrams is intended to show progressively, and in an easily under- :Muddle manner, the va,iaus points tb which special attention should be paid in the Practical Points in Design and design of typical wireless receivers, and al the same time to assi;t the beginner in mastering Construction. the art of reading circuit diagrams. If coraponents and values are carefully chosen, the No. 70. -A Single -valve and single -valve reflex receiver shown below is capable of operating a loud-speaker. The Crystal Reflex. dala given apply to the normal broadcast waveband, on which all reflex receivers work at their bast. (To be concluded in next week's :rsue.)

O O O O O CO /\ L Z % -,

- 1111 f--- 00 (-- 4 i CI CI O _

H T. ; - }QTCO ' f + + G.B- ¡ + L.T. T

(1) (2) (3)

The tuned secondary of a conventional The plate c:rcult is completed through the The tuned secondary is added. The " uutuned ? erial " coupler is connected primary of an H.F. trensfor.ner and /IT. secondary of an L.F. transformer, shunted between grid and filament of a valve ; the battery. The neutralising winding is con- by an H.r. by -pass condens r, is in erted filament circuit of which is completed in nected back to grid through a balancing in series with the grid circuit, with the the usual manner. condenser. addition of a bias battery.

irHE aerial -grid transformer may ingly have an adequate voltage - wire. A tuning condenser (C3) of he wound on a Sin. former, handling capacity, and one of the 0.0003 liifd. is assumed. with a secondary of 72 turns " power " type, with an impedance As the great majority of crystals of No. 22 D.C.C. wire. The of b,000 to S,000 ohms, is suitable. have a comparatively low resistance primary, wound on spacing strips The neutralised H.F. transformer under working conditions, it is over the " filament " and of the may he modelled on the general lines possible to obtain a considerable secondary, has about 15 spaced turns of that used in the " Everyman step -up of voltage in the L.F. trans- of line wire (No. 30 D. S.C. is suit- Four " receiver, although the use of former, so an instrument having a able). The tuning condenser C, " litz " multi-stranded wire is prob- ratio of 5: I or more should be should be of 0.0003 mfd., although ably not worth while in this case, due chosen. An 8 t ratio is not too a capacity of 0.0005 will serve. to the inevitable damping effect pro. high when a galena crystal is used. The production of grid currents doted by the crystal. When using a The best value for the H.F. by -pass (which result from overloading) is Sin. former, the secondary has 72 condenser C, is best ascertained by cben more serious in a reflex receiver turns of No. 22 D.C.C. wire. The trial ; the smallest possible capacity than in a straightforward L.F. primary and neutralising windings should be used here, and about amplifier. The Calve should accord- may have about 12 turns each of fine o.000r mfd. is often large enough. B ir

www.americanradiohistory.com WIpA®2.0 554 MAO MAY lib, 1927.

Design Suggested by B.B.C. for Good Quality Reception, with Liberal Output.

H1' it should be necessary to create -so many sharpen the tuning of the aerial circuit, a variable resist- and varied designs of broadcast receivers may ance to control the .input to the first valve, and self - be somewhat perplexing. Each, however, has oscillation in the H.F. stage, a choke H.T. feed to the its definite purpose, and, on asking for the particular H.F. valve with tuned grid coil, and reaction coupling application of the four -stage set exhibited by the B.B.C. at the detector. Anode bend detection takes the place at the Ideal Home Exhibition one would be told that of the customary leaky grid condenser, while compara- it is essentially a local station receiver, which, with a tively high values of anode and grid resistances are em- good loud -speaker requiring, perhaps, liberal input, would ployed in the L.F. couplings. 'fo prevent interaction give the most perfect reproduction that can be obtained between the successive L.F. stages, which might give under home conditions. rise to parasitic oscillation, a damping resistance is inter- Reference to the circuit diagram shows a direct- coupled posed in the grill leak to one of the L.F. valves. Parallel aerial, a tuned H.F. inter -stage coupling followed by connected power valves with a choke of liberal current - two resistance -coupled L.F. stages. Minor points of carrying capacity and condenser loud -speaker feed form interest are the provision of series aerial condensers to the output stage.

+ H.T.1 O + H.T.2 O +H.T.O 3

H.F. 250,000 CHOKE MIMS OHMS o 150,000 25 HENRIES OHMS TO CARRY 50mA

4mfc IL

FA, Olmfd 0.1Mn 0I I mfd

E ó e ó E J ó01 400 OHMS mfd SWITCH

G.8.4 0.6 a G.B.3 f.ip

gour stage setectivz receiving circuit. A resistance in the tuned aerial circuit serves as a control of volume ana self -oscillation. B I2

www.americanradiohistory.com .fth, 1927. Vffipaiwo sss MAY W0rcriol

1 ' ! I i _ 2I1¡'c D0I D®I C 1

. ® _.. _ _-. Ä 1 /2 - - 06 p (:.. -"110- t 2 3/

_(- a m i 3// ' w E E Et E E

Ì 3 "15e 4%s 6%a - 2 4 ' 45/9 I 1 26-

; in. for 4 B.A. The front panel showing drilling details. Size of holes : A, 3,8 in. ; B, 1,'4 in. ; C, 7/32 in. D, 5'32 and countersunk screw : E, 1; 8 in. and countersunk for No. 4 wood screws.

In the actual receiver, from which the set here de- Construction is commenced by fitting panel and base - scribed has been modelled, the tuning condensers were Loan] to the cabinet and then securing them together with spaced widely apart, but in order to provide simple the brackets. The cabinet was supplied with a five -ply wiring closely following the theoretical circuit in its ar- baseboard so as to obviate the fitting of cross battens, rangement, it was necessary to locate both the tuning though the longer side of the brackets when screwed to controls towards the deft -hand end of the panel. Only the hoard provide additional stiffening. The terminal standard components have been selected for making up supports arc macle up from lin. x tin. strip and elevated the set, all of which are attached to the baseboard or from the baschoarii Ity means of ebonite tube or wooden panel without experiencing difficulty or trouble arising spacers of sufficient length to give clearance to the ter- owing to positions for screws being found inarressid,le. minals on the underside. Long connecting tags cut front

If departure is made from the types of components shown, care must be taken in modifying the layout to provide for the movement of the reaction coil. Connection is made to the ter- minas either by means o& a multi w ire cable or through a row of 3.8 in. holes at the back of the cabinet. B 13

www.americanradiohistory.com WfirmIlcom MAI' g/h, 19 27. Wóric1

All leads are above the baseboard. This view shows the actual arrangement of the connecting wires. The H.T. and L.T. battery leads are covered by sleeving. - tin plate are secured to the terminals, as shorn in the down attachment to the baseboard. It measures tin. x diagram, so as to facilitate connecting up when the ter- 31in. The hole through the front panel is, of course, minal strips are in position. very slightly larger than the spindle which operates the The precise positions for some of the components is moving coil, so as not to serve as a bearing. not given, but from the location of the principal parts the smaller components can be set out among them falling Practical Points in Wiring. on the centre lines as positioned in the scale drawing show- Wiring up is carried out throughout with No. IS tinned ing the layout. Various round -headed screws are used wire straightened by stretching, and for slec ing is used on fixing the components, and blued screws give a good all the positive 1-1.T. and I,.T. battery leads, appearance. while short pieces are slipped over any other wires where, in cross- As terminal connectors will facilitate making the con- ing others, there might be a danger of contact. nectiuns It is to the flexible wires of the reaction coil holder, worth while carefully studying the photograph of the a small yin. ebonite base has been fitted, which, as well interior of this set in regard to the arrangement of the as carrying two small screw terminals, serves to elevate wiring, and it will be found that the grid and plate the control knob, so that it falls in line with the volume circuit leads, excepting in the case of the connections to control and on and off switch, and provides an easy screw_ the reaction coil, are little more than an inch in length.

_ __ 2 1/.; _- 2Y; -... 6l4 -___r___ L --' 7 7. -', '

Dmens,onai drawing showing the layout w me components on the baseboard. Care should be taken to arrange the parts so that they fall symmetrically about the dotted lines.

1314

www.americanradiohistory.com w ifEnhog MAY sah, 1927. MA& 557

COMPONENTS REQUIRED. 1 nlcg. Elec. Co., Ltd.). 1 Junior" two -way coil holder (Radio Communication 2 "Edtswan "grid leaks, (Edison S.ran "Pelar Ltd.). Co., Ltd.). 1 " Edi.wan" grid leak, 0.1 nieg. (Edi on Sean ELc...o., & Co., Ltd.). 1 One-way panel coil plug, (Edison Bell, Ltd.). 3 "Decorem" grid lerht holders (A. F. üulgin 5 "Lotus" valve holders Garnctt Whiteley & Co.). 12 Terminale (Igranic Electric Co.). Elec.. Co.). 1 "MB" H.F. choke (McMichael). 1 "On- and -off " switei (Igranic S. 2 Fixed condensers, No. 620 type, 0.0001 mfd. (Dubilier). 2 "Cyldon" lo; mid -line condensers, 00005 mfd. (Sydney 1 Filed condenser, No. 620 type, 0.0003 mfd (Dubiiier). L ird & Sons). & Co., 1 Fixed condenser, No. 620 type, 0.001 mfd. (Duiilicr). 1 pair " Magnum" panel bracket; (Eurne-Jones 1 Fixed condenser, No. 620 type, 0.01 mfd. (Dubelier). Ltd.). 1 Fixed condenser, 4 mfd. 300 v. type (T.C.C.). I Pctentiometer (Lissen, Limited). 2 Fixcd condensers, mica 0.1 mfd. 1 Ebonite pr.n'l, ?(Jin. X Sin. x in. 1 Anode resistance, 150,000 ohms (Varley Magnet Co.). I Lascboard, 2Gin. x 8in. Wood 1 Anode resi_ lance, 250,000 ohms (Varley Magnet Co.) 1 Cabina, 23in. X Sin. X 8in. deep, mahogany (Caxton 1 32 henry choke (Pye). Turnery Co.). 215 volt grid bias batteries (Siemens). Wire. SLtoflex, screws, 4 wander plugs and flex, etc.

Approximate cost - £11 0 0

As the connections are so near the surface of the board, critical, consistent with a smooth control of self- oscilla- a small piece of blotting paper should be inserted under tion, if it is hoped to make use of the reaction coil. For the joints to prevent flux or scorching marking the board reception at distances exceeding fifty miles, when a when soldering. All valve- holder tags should be scraped somewhat critical adjustment of reaction may be required, and tinned before mounting the holders, and when it will be found better to use a high -frequency valve making a connection the set should be tilted so that the with an amplification factor of about 20 as the solder flows away from the joint. Provided plenty of detector. solder is applied to the " T " joints, there will be no For local station reception, with a good aerial, a L.F. is need to make bends at the points of jo'.nting, as shown valve should be inserted in the third valve holder. It in the practical wiring diagram. Access to the connec- advisable, however, to test the results obtainable with a re- tions of the " on and off " switch is obtained by re- H.F. valve in this stage, and if one of the special moving the output condenser. Connecting tags are used sistance-capacity coupling valves is available then the as in every case for making contact under a screw. Where H.F. valve can be taken from the detector and used sleeving is used, it is, of course, slipped over the wire the first L.F. valve prior to bending, the exact length required being first To avoid the need of purchasing an additional to dis- measured off by laying it along the route to be taken by in this way, it can generally be taken that up average the lead. tances of four miles from a main station and an aerial that a H.F. valve should be used in the detector Selection of Suitable Valves. stage, and a L.F. in the first L.F. stage. Up to dis- he As the performance of any set is dependent upon the tances of perhaps, twelve miles the detector should careful selection of valves, the accompanying table has a special resistance coupling valve, and the first L.F. a should he been drawn up, showing the type of valve to employ in H.F. valve. At greater distances these valves each of the stages. interchanged to permit of smooth reaction control.

ER. 11.F. DETECTOR. 1s4 L.F. Pow

4 2v 4 y 6 v. 2 v. 4 V. v. 2 v. 4 v. 6 V. 2 v. v.

1-1.120 ' G.125 P.125 B.S..4. .... H.125 - - H.120 - - - - 8.11 B.T.H. .... B.511. B.4H. B.8 BSH. B.-IH. 0.8 0.0H. B.H.B. - - H.512 H.310 H.512 H.3I0 11.512 L.L.52j BDRNDEPT . - H.31e1 - - S.P.18R.R.- Cosmos.... S.P.1SG. S.P.ISG. S.1'.55B, S.P.ISG. - S.P.558. - - - 610R.C. 21011.C, 410R.C. 610R.C. 215P. . 410P. 6UtP. . 21011.F. 41011.I'. 610H.F. 21012.C. 41IR.C. CossoR G.P.l EDISWAN .. G.P.2 G.P.4 - R.C3 G.P.4 -- R.C.2 -- - D.F..H.11O D.E.OB. D.L".1'.21: D.E.P.IU) MARCONI .. D.E.2H.F. D.E.H.410 D.E.5B. D.E.211.F. D.E.H.110 D.E.013. D.E.aH.F. P.\1.013. P.1I.2 I'.11.231 P.M .2 ;r, :YIDt.LARD.. P.\1.IH.F. ßM.3 PM.O%. P.\I.lA. P.31.3 P.'4I.OB. P.01.1A. P.)I.î I D.Tf. D.E.LI.110 D.E..58. D.P..P.270 D.E.P.110 OSRAM .... D.E .2H.F. D.E.H.410 D.F..5B. D.E.214.F. D.E.H.410 D.E.bB. D.E.2H.F. S.T.61A. S.T.23 S.T.13 S.T S.T.21 S.T.41 S.T.61B. S.T.21A. S.T.41A. S.T.61A.. S.T.-'1A. S.T.4LA.

The first valve is of a type customarily styled a H.F. Power valves are used in the output stage. The H.F. valve with an amplification factor of about 20, and the valve should he operated with about 7o volts H.T. and he corresponding impedance value depending upon the type a grid bias of 1 to 3 volts; go to 120 volts can to the detector, the exact value being carefully of filament. - applied The anode bend detector valve may be one of the adjusted in conjunction with 3 volts grid bias. Although special resistance coupling valves with a very high am- quite good results can be obtained with 55o volts applied plification factor, though it is doubtful if in this circuit to the L.F. stages, a higher value is recommended in any greater signal strength will be obtained, while the order to maintain good quality with liberal signal grid potential adjustment will he found exceedingly strength. Grid bias cells up to 3o volts are secured to B 15

ï tx«:= :.éá.:.' www.americanradiohistory.com VflnIli@go WurIld MAY ¢tk, 1927. B B.C. " Quality Four." - creasing the value of the resistance in the tuned aerial the inside of the cabinet at the back by means of small circuit, or judiciously introducing a choke by way of the metal clips. primary of a L.F. transformer in series with one of Grid bias vak:es must be carefully adjusted, particu- the anode resistances. Parasitic oscillation should not be larly if any tendency towards the setting up of low - overcome by increasing the value of grid bias the frequency to self- oscillation is observed. When a battery point where a weakening of signal strength occurs. eliminator is used as a source of H.T., as is suggested linder normal conditions with an average aerial many by the B.B.C., special care must be taken to avoid low- distant stations can be tuned in at satisfactory loud- speaker

The wires are arranged near the surface of the board. Battery leads are covered with insulating sleeving. frequency oscillation, and many amateurs have recently strength, with a critical adjustment of reaction coupling. experienced difficulty when using an entirely resistance- Although the set is moderately sensitive as a long -range coupled set supplied with H.T. from an eliminator. receiver, the object of including the H.F. stage is not for Parasitic oscillation of a frequency as low as to cycles the purpose of distant reception. This set, which can, if is quite common, which, instead of producing audible necessary, be adjusted to be highly selective, is intended " pops," gives a periodic variation of signal strength. to provide good quality reception from the nearest station The effect arises from the detector stage oscillating or anywhere throughout the country. The control provided being on the verge of oscillation, and the heterodyne beat by the damping resistance was most helpful in finding note in turn beating with a normally suppressed, say roo- the best settings for the tuning dial. cycle, ripple from a 5o -cycle supply. Where a trans- There is a considerable demand for a not -too -costly local former is used in one of the L.F. stages, this effect does station set in which every endeavour has been made to not occur, and it is prevented in the case of an entirely give the very best quality of reprodutcion. It is doubtful resistance-coupled set, should it arise, by readjusting the if this straightforward set suggested by the B.B.C. can tuning condensers away from the oscillating point, "in- be bettered for fulfilling this purpose. s 16

.F: www.americanradiohistory.com Vbpe@oo 7927. 5 S WIuZc1c6 URPNT TOPICS

1 `flews of 1e VVec ~-gin Brief Review

TOO BAD. BRAVO, PCJJ already- budt up :in impressive chain of An Aberdeen listener is distressed be- The short -wave transit'issimis Loin transmitters, and the inauguration of cause his wireless set picks up conversa- PCJJ, the now famous Dutch experi- central offices in New York should mark tions from the flat below. Evidently the mental station, are being heard with the beginning of a new era in the talkers fail to give anything away. remarkable clarity by amateurs in India. hitherto trnnblous field of American 0000 0000 broadcasting. 0000 ROYAL VISIT RAISES WIRELESS SIR JOHN REITII TO VISIT U.S.. BROADCASTING FOR RHODESIA. SALES. We understand that Sir John Rcith The African Broadcasting Company is A mild boom in the Australian wireless has accepted an invitation from A1r. applying to the Southern Rhodesian industry is being created by the visit of Dler;in H. Aylesworth, president of the Government for permission to erect a new the Duke and Duchess of York, due to American National Broadcasting Coni- relay station for the benefit of lonely the broadcasting of some of the official settlers scattered over Rhodesia. ceremonies 0000 0000 TANGIER 'FO TELL THE WORLD. THE ARCTIC AUSTRALIA HEARS The Moroccan Government will include Mr. Phillips, a wireless experimenter, 120,000 francs in their next Budget for of Glenelg, Adelaide, has picked up iui the erection of a commercial wireless the first time in Australia a message from station in Tangier. Captain A`:'ilkins' expedition in Alaska. 0000 says a 7'i.:os correspondent-. The expedi tion station was transmitting on 42 B.B.C. PROGRAMMES IN BRAILLE. metres. As the result of the generous response 000 to a recent appeal for funds, the National POLICE WIRELESS PIONEER. Institute for the Blind has completed The late Sir Harry Lane, Chief Con- arrangements for the publication almost for Lancashire since 1913, who immediately of The Braille Radio stable Tintes. died last week, was ,t pioneer in the use of wireless for the detection of crime. U 0 0 0 As a result of his efforts, the Lancashire STRANGE. police were among the first in the country The experience of the Dorset farmer to have wireless patrol van. who was recently seized with an attack 0 0 0 0 of ' nerves " when confronting the microphone is a reminder that no similar BROADCASTING AND THE WASHINGTON CONFERENCE. malady appears ever to have overtaken a " pirate " when confronting the head- At its meeting on. April 25th at Savoy phones. Hill, the Wireless Ur_gauisations Advisory 0000 Committee expressed its concern ut the absence of a definite official pronounce- NO EXCUSE. ment mi the representation and status That the licence fee for his wireless of broadcasting at the forthcomiug TO VISIT AMERICA. A new portrait of set had been paid by the previous owner International Wireless Conference in Sir John Reith, Director -General of the was the unsuccessful defence put for- B.B.C., who. we learn, will shortly pro- Washington. ceed to New York to attend the inaugura- ward by a defendant at the Bromsgrove 0000 tion of the new offices of the National Police Court last week. Broadcasting Company. For the prosecution it was proved that LECTURES ON THE VALVE. the licence had expired. " The Theimionic Valve and its Use patty, to visit Now York and attend the 0000 in Wireless Circuits " is the title of a inauguration of the companys new build - THE PRESS. special course Of six lectures to be given ing 'and studios. WIRELESS AND by Capt. W. H. Date, B.Sc., A.M.I.E.E., The growth of the National Broadcast- Rates for the transmission by wireless at the Polytechnic, 307 -311, Regent ing l'-unpany- since its foundation in telegraphy of Press news are regarded as Street, London, W.1, on Wednesday November of last year has been watched too high by the Empire Press Union, evenings, commencing May 11th. with the greatest interest by broadcast- according to the annual report just The fee for the course is 7s. 6d. Full ing authorities in all countries. Aiming issued. It is stated that the newspapers particulars can be obtained on application at co-ordination among the principal are looking forward to wireless in the to the Electrical Engineering Dept., stati:ms in the United States, the hope that the competition will force the Polytechnic. National Broadcasting Company has the hands of the cable interests. B 19

www.americanradiohistory.com 56o Wt)cp,hoo 111-7 .It1i, I927. iOO lI'ilL

ARE YOU GETTING ONE ? It is reported that the latest Paris creation for the seaside resorts is the sun - bath costume with wireless set to match. o^oo

HAVE YOU HEARD POSEN ? The new Polish broadcasting station at Posen gave its inaugural transmission last week. The wavelength is 270.3 met res.

FORTHCOMING EVENTS. WEDNESDAY, MAY 4th.

!agitation of Electrical Engineers, {{'ire - less .Section. ,lt 6 p.m. (light refresh- ment.. at 5.30). 4t the Institution, Saroy Place I{'.C.2. Three Papers; (a) "The Holweck Demountable Type Valve," by Mr. C. F. Elrrr(l: (b) -',Silica { -ol ces in It' ire! eas Tel egret phy," by Dlr.ssrs. Ii. Norris- Airey, (',II,E., 11 Se., G. Shearing, and H. G. Ilughes, iII.Sc.: (rl "Cooled-Anode Valves, and Lires of Transmitting Valves,' toi Mr. W. J. I'irke n. ,il o.ererll Mat and District Radio Snrieta.- .1t 8 p.m. :It Tollington School, Tether- mn. Informal evening with, the Prod. dent (Capt. 11..1. Bowan! Tottenham Wireless Sorirty. -:l t 8 p.m. .il the Institute, 10, Bnree Grove. lini- nrss meeting, followed by a discussion. THURSDAY, MAY 5th. Institution of Electrical Engineers. -4t 6 jest. (Liait I re fresh menta nt 5.30). :I ro- Vaal General :Meeting (Corporate lleru- bers and .1 social es only). TELEVISION IN AMERICA. A form of television Golder. Green with receiver now being experimented and lie ndon Radio Swirly. in the Bell Telephone Laboratories, in New York, for reception from Washington -A t 8 p.m. At the Club ¡fosar, Willi- by wire and from Whippany by wireless. The scene is projected on field tray. D'.6.11. Beginners' Difficul- screen. Dr. Frank Gray, who is largely the frosted glass ties, %o. 2.-Components. responsible for the tests, is standing on the left. MONDAY, MAY 9th. thereabouts, represent the number of STRAIGHT FROM THE SHOULDER. Croydon ,Wireless and Physical Society. -,1t active listeners in the Free State." 8 p.ot. Al 128e, George Street. Informal Some rather frank evening for advice to the U.S, discussion and practical York. 0000 Federal Radio Commission, now strug- NO WIRELESS FOR BRITISH TRAINS? gling with the American broadcasting problem, is contained in the current issue In the lIuuse of Commons last week of Radio Broadcast, MORE LISTENERS IN NORTHERN Sir w, Mitchell -Thomson, Postmaster- New York: - - IRELAND. "r Gentlemen of the Radio Commission, General (Croydon, S,), replying to Mr. let but one voice rule you ! The number of receiving licences Day, said he was aware that broadcast " runs the current in Northern exhortation. 'The voice of the broad- Ireland on Feb- receiving sets had been installed in long - ruary 28th cast listener! Give him fair, efficient, was 28,455, while in the Free distante trains in sonie countries. Ex- and equitable State the figure on March periments service! Remember, not 31st was conducted some years ago in one of those 21,795. this tountry showed who seek to broadcast has that it was possible anything but a selfish purpose, r If the Free State Wireless Import to receive broadcast programmes however on disguised, in seeking a place in the Tax were removed," says The Irish trains in motion, but no application had ether. Radio Big and little, alike, have something to Review, "we have little doubt been received for a licence for the per- sell, whether that the present grand manent it be a cause depending upon total for all Ire- installation of wireless receiving contributions for revenue land would, within twelve apparatus in or a commodity months or trains. feeding its sales through goodwill."

IS TELEVISION IN SIGHT ? HERE is illuminated, When r a good deal of niisunder- pictures were trans- After demonstrating the transmission standing in the public mind as to nutted by telegraph or wireless a scan- of one small detail, he said that, so far the actual progress made in tele- wing cell and lamp passed over photo as vision," he knew, they had seen in this experi- said Mr. A. L. Rawlings, of the paper moving in synchronism with ment the most complete demonstration Admiralty Research Department, in an another recording of instrument which television that had ever been made in address before the members of the Wind- reproduced a picture. In ten or fifteen public. sor and Eton Scientific and Archaeological minutes a very good reproduction could As a serious Society. r' The solution to television sounds of a whole orches- be made. There were about 10,000 small nothing we had as yet tra can be reproduced by the vibration seemed of great of dots in an ordinary Press portrait. The promise. It could not be said to have a single telephone diaphragm, but there is scanning cell had to travel all over reached very much more the success even in the hands of involved in television. To picture to take up these elements. It experts, and would require transmit ali object, a person, or a scene, enormous was considered that a face could be trans - every separate bit must development before it could come into be faithfully mitted by 3,000 elements as a minimum. practical operation. Television reproduced by a single transmission." must be If they could transmit in this way a suc- classed as one of the problems, like the An experintenti was shown in which, cession of instantaneous photographs by means nature, and cure of cancer, which, after of two valves and two mechani- much more quickly, we should be getting cal relays, the current baffling mankind for a generation, still through selenium on to television. It was this rapidity of eluded us. At the could he amplified about a same time scientific million times. transmission that constituted the chief experts were accumulating useful to light a lamp, when the selenium facts, was difficulty. and television might yet be realised. B 20

www.americanradiohistory.com Mini lilt, 1927. Wapdszt 56 r WcwirIld roadcasf eeeivers DAvrNS_ET I onTNBLE a.

Dimensions,

12in. X 74ín. x 4in. Two frame aerials are wound round the inside of the Weight, 10 lb. case, each with a centre tapping in order that reaction may be introduced by the well -known Hartley method. A change -over switch is provided to select the wavelength Price, 10 Guineas. range required. An aerial and earth may be used, if desired, and terminal plugs and sockets have been provided for this purpose. A small fixed condenser in series OT many years ago the pocket wireless set enjoyed with the aerial terminal ensures that the wavelength range quite a vogue among journalists and writers of is not unduly raised by the addition of the aerial imaginative fiction. Topics of this nature go capacity. throt gh a period of intensive cultivation. They become a The valves are of the 2 -vólt type, and their filaments and when this stage is reached no journalist can fash'on, are connected in series. They are supplied with filament to ignore them. The subject of the moment is afford current from a 41 -volt dry battery of the type used in few papers go to press without a short Television, and hand inspection lamps. About 15 hours' service may he with an announcement of some paragraph commencing expected, and the cost of replacement is is. 9d. The and concluding with the usual newly discovered method H.T. voltage is rather low -22 volts -but the results But this sort of thing cannot be kept up prophecies. seem to be quite satisfactory, and the saying in space and and the topic frequently has to be dropped indefinitely, weight is considerable. before it is possible to publish news of actual achievement which would form a natural climax to what has gone British Components. before. When the thing is accomplished it is taken as a of course, for it has already become a common- The makers take pride in the use throughout of British matter with of the public. components, which include an Ormond condenser place in the imagination for Everyone will remember the portable wireless friction slow- motion control, Gambrell Neutrovernia valves, Tangent inter - prophecies -aerials in umbrellas, receivers in top hats, reaction control, Mullard P.M. Edison Bell plug etc. -but does anyone remember seeing a placard valve transformer, Siemens headphones, change -over switch, Ever -Ready bat- announcing the first portable set ? Vet to -day the manu- and jack, Utility wire. The components of portable sets is a most important branch of the teries, Cosmos choke, and Glazite facture round the out- wireless industry, and it is possible to purchase for ten are assembled in a rectangular framework, are wound. The frame- guineas an instrument packed in a small attaché case side of which the pick -up coils compart- which may be taken anywhere, and with which it is pos- work is sub -divided into battery and phone being with plush. With the sible to receive even while walking along the road. ments, the latter lined the whole of the interior Such a set is reviewed in this article, and should prove exception of this compartment a panel of Erinoid material of a of special interest to those lacking the transport facilities of the set is covered by gold. In this panel a necessary for the larger and more powerful portables. pleasing blue colour, lined with wavelength switch may he The design is based on a portable set described in these slot is cut, through which the pages last summer,' but a low -frequency amplifier has operated. been added to improve results. The tuning and reaction controls are ebonite rods knurled at the end, and just protrude through the side the I The Wireless World, July 21st, 1926. of the case. At the same end of the case below

B 25

www.americanradiohistory.com =M'láa--rfiP 562 Wfipg®E@ WoAZ MAY 4/h, 1927. Broadcast Receivers. - tuning controls will be seen the telephone jack. This is fitted with contacts by means of which the filament circuit is broken when the jack is removed, so that there is no possibility of the valves being left on when the set is packed up with the phones in their proper compartment. The construction and wiring throughout bear evidence of conscientious workmanship, and the appearance and finish are excellent. In testing the receiver it was decided to dispense entirely with external aerial and earth connections, as in our opinion the principal charm of the set is its essential portability. The absence of external wiring makes it possible to unpack, tune -in, and receive signals in 3o seconds -an important consideration when one is anxious to get the time signal and forgets all about interior view of the receiver with cover plate removed showing separate compartments for it until the last minute. components, batteries, and phones. In the London area signals from 2L0 are, of course, " phones on table " strength, but Daventry (68 miles) can be received only with difficulty. On one occasion, however, the 10.30 a.m. time- signal and weather report from Daventry were urgently required, and by critically adjusting reaction it was possible to follow every word in a quiet room. Incidentally, the reaction control on the " Local " wave range is as smooth as any that has come to our notice, but on the " Daventry " range a. certain amount of overlap or backlash causes instability when using critical reaction. Ideal for Motor Cycling. To test further the range and to demonstrate the portability of the set a. solo motor cycle journey down the London -Coventry road was undertaken. The set was packed in a rucksack, as it was thought that excessive vibration on the carrier might cause damage. The weight of the set (to lb.) was not noticed when carried in this way, and no fatigue was experienced, although the journey extended over ioo miles. The first stop was made five miles north of Barnet (2L0, 16 miles ; 5XX, 52 miles). Here the transmission from the London station could be enjoyed in the open at comfortable strength with a strong wind blowing, but only the carrier wave of 5XX could he picked up. Thereafter stops were made at intervals of five miles until Dunstable was reached, where a halt was made for tea. This afforded the interior appearance :s i- keeping with the neat exterior. an opportunity of testing the set _indoors, .and it was The range switch is operated through the slot in the pane, found both while the tuning is eftec ed by rotating the ebonite rods pro- that stations were of equal strength and just ie..ting from t e right -hand s'de of the case. sufficiently loud to be enjoyable. Outside, with a fairly B 26

www.americanradiohistory.com MAY ¢th, 1927. WAIMIlISOO 563 WopIlO1 Broadcast Receivers. - In passing, it should be mentioned that all tests were high wind blowing, a certain amount of concentration made in side turnings off the main road, several hundred was required to follow speech. The distances at this yards from the main -route telegraph wires. Abnormal point were : 2L0, 3o miles; 5XX, 33 miles. Pushing results are generally experienced on the main road itself farther north tests were continued at regular intervals on in the immediate vicinity of the wires. Daventry, 2L0 having been abandoned at Dunstable. Regarding the quality of reproduction, one must not At Stony Stratford (5XX, 20 miles) signals were suffi- expect too much With only 22 volts H.T., but there ciently strong to be heard above the noise of the wind. appears to be sufficient straight on the amplifier valve which by this time had risen' to half a gale. characteristic to deal with signals of telephone strength. Making due allowance for :Abnormal conditions,. we Curiously enough, better quality was obtained with strong would put the range of the set at 25 miles on 2L0 than with weak signals. 3o miles on. Daventry. The reader will at once notice Each set is sent out with working instructions, a test that the two ranges are not proportional to the powers certificate, and a twelve months' guarantee. The price used by the two stations, but the discrepancy is easily is £r0 ros., which includes the Marconi royalty of 25s., accounted for by the size of the frame aerial, which is and the set is made by Messrs. Partridge and Wilson, much smaller than the optimum size for 1,600 metres. 2r7a, Loughborough Road, Leicester.

VALVES WE -'AVE TE S1 ED. Six Valves of the B.T.H. Series.

L have tested six valves of the B.T.H. range, of the order of i20 volts, and may be used as the last manufactured by the British Thomson- Houston L.F. valve in the set. The measured valve constants Co., Ltd. Two of the valves tested are of for this valve are given below the curve. the 3 -volt class with low filament current consumption, The B4H valve has the same class of filament but so as to be suitable for use with dry battery L.T. a much higher amplification factor, which makes it suit- Taking the valves in order of their. number, the B4 able for H.F. amplification or for L.F. amplification valve is in the 6 -volt class, taking 0.25 ampere to heat with choke or resistance coupling. The filament current the filament. This type of valve is quite suitable for is rather on the high side for such a valve. giving good quality loud -speaker results with H.T. values The next two valves are in the 3 -volt class, the B51-1

I 3.5 B.T.H. 84 NNNEEN B.T.H. B4H NE.EEMIENN11 ENNEENNNE..MENENENNEiN ENN E EMME NNN'11G 3.0 ENINENINEE/ENall 11 IIIIIIIIIIIIIIIIIIIIII 13 a NN A E 2.5 E.ENEEINE. 12 NE.EMEE N N.INEEINE 11 EMINENNEINN1 EEINMEMENI.ENN ...I'IIIEE 10 .aNII 20 NNWI,I.NEMIaN EINIIN 9 I1f1I,NE11 ..MMM..: INMEINEEMEEINEIN.6a U. I 8 EE...EI, INNINEINMINMmMIN.INEEE . I1NEEEE=NN/I 1 1.5 . UE 7 ...... a. N. .E.E.. J.. . M .IN. 6 IIIIIIIIIIIIIIilIIiIIII MENE i1.a.I1. 10 NININEPIMPLMEUI 5 INEMC//N/4%E.. LIN//EVLI.eN 4 E11111'aEI.N. EAF%NEEI.MEN ENNIiaEM'a 3 EINI/IIM WANi EnMNE./LNN .N./aMNI 0-5 /LINEMInaINE iNmdmm/ENNNWM= 2 NENNNIEU0EIEEN U/... 11111M/MMI/INININININ .IL/ELAEEEIAIM/IINNFai/IE lMMEE 7 6 5 4 3 2 1 0+1 -11 10 9 8 7 6 5 4 3 2 1 0 +10 -8 GRID VOLTS GRID VOLTS

Amplification factor u 6.7. Amplification factor to = 16. A.C. resistance Ro 6,900 ohms. A.C. resistance Ro = 22,700 ohms. Mutual conductance = 0.96 mA ¡volt. Mutual conductance = 0.7 mA /volt. Filament 6 volts, 0.25 ampere. Filament = 6 volts, 0.25 ampere. 27

www.americanradiohistory.com 761 WAT@Noo n/U1t M Al AY ¢th, 1927.

9 B.T.H. B5H BT H. B 6 EMME.. MAIM!!MMAE..M. 8 EEE1UE.7iM 1EE.E.M.! .-.ME 11111111111111111/1111M 7 11111111111111D:01M.:11 AMM..M...M.M.MM. 6 E.iMr,...... A E 20 .M.ME.AM íí,..1 5 1iliiiiiil/iiiiAiMiiiii MAMMAMIMMIAMM/...M..1i..IE..a.. 15 slIEI.'AEMME. 4 urA.N.MMMMI MIMIMMM.M 1.I..ÍI... 3 10 111C::11!..AMMO. 1M:11111111 1.%i" 1 _..M.MM..M.M...... I/..EEE..A.E1M 2 :=::1:::::C::::1:C: 0:11:11111111.111111111 a11110111111111111111111 -8 7 6 5 4 3 2 1 0 +7 -11 10 9 8 7 6 5 4 3 2 1 0 +10 GRID VOLTS GRID VOLTS

Amplification. tact or pt = 16.7. Amplification lector p - 8.4. A.C. resistance Ro 45,000 ohms. A.C. resista..cr Ro 13,300 ohms. Mutual conductance - 0.36 mA,1,o.t. Mutual == Filament conductance 0.03 mAivoft. - 2.8 volts, 0.06 ampere. Filament - - 2.8 volts, 0.12 ampere.

BT.H. 87 EMMA R B.T.H. 88 MMME .1.. A M. .. .MM 1..E..1.1..I.E.MMM ..1M..ME../A.MMMIM MM.M.1..A.U MMM..E...M.. 800 ...... 11111111111111: 1: .UE..iM 700 11EM....MM IM IIIIIIIIIIIIi!iiiIiuii . .1UMM.UE / .EANMIAAEMMVMNMMMIMEIMI,.M 1UUEIMM..EIMM ..EEAE 600 .. EI ...M..MFAMN/J. . ,. M..A :.CM 1U.EE1E.. 500 :1:1:11',G1:11',C11:::::1 11111111 1: 1111:m11 MMMM/AM'AM.r/IMMIM. u1 Am3 EM..U.E ..M. 11C11:111 400 Eir.iri MAMMAMMM. AIMDMM,.; A EIFAEANAEME.EU..UO...E. 1 M .A.ME=O.....EE.. 1:E::MÇ:=:::'A:::m::IC:11 300 iM.MEMI.I1EÌAEE /.....M iM/.AMM/.AMIMA..M 111111'111C.C1DA11°A=11I 200 .RA..I,MIMM.M.AE.E1EE :MZ:1'.:11'''MW:11: 1 1g11:sK11':=::1111111 :D:::1i11111::11111:11 M1.Ai::=.:ï 100 AM.=.E :::1111:1111 M..M.....EMME M.MUIM .IlíMi.M.0'11m./.MMMMMM -11 10 9 8 7 6 5 4 3 2 1 0 +1 -25 20 15 10 05 5 GRID VOLTS GRID VOLTS

Amplification factor µ = 7.4. Amplification factor p. 44.5. A.C. resistance Ro = 11,700 ohms A.0 resistance Ro 170,001 ohms. Mutual conductance = 0.63 mAwolt. Mutual conductance = 0 38 mA)volt. Filament = 6 volts, 0.06 ampere. Filament = 2 volts, 0.12 ampere. Beb

www.americanradiohistory.com 'Vfirff.f.Pcwo MAY .{ /h, 1927. 56 s 'vOOL'lt being suitable for H.F. or The resistance of the l-38 is detector positions, and the taken for 8o to too volts on B6 for L.F. work, althn igh. the pluk of the valve, so as shown by the curves. that if high values of plate much output must not he circuit resistance are used the expected from this valve, as H.T. voltage must be high the H.T. value should not if these ligures are to be ob- be too high. tained. The 137 is intended for When using about 120 volts L.F. power amplification. H.T. with plate circuit re- with the advantage of having sistances of 2 or 3 megohms the very low filament con- the A.C. resistance of the sumption of o.o6 ampere, va Ive itself will much exceed but, as will be seen from the figure of 170,000 ohms, the curves, it is more suit since the voltage on the plate able for fit st- stage I.. F. of the valve will be vcry lovy than for power output, since -this increase of resistance it shows signs of saturation under these conditions, of with plate potentials of over course, applying to all valves Tie B.T.H. 84 and 05H valves and cartona. loo volts. of this class. The last valve tested is of the now fashionable resist - However, the Iati compares very favourably with other ance-capacity type, intended for use with very high plate valves of similar filament voltage and amplification circuit resistances. factor.

- CLUB _- _ _-- 111 REPORTS Two Valves11" and a Fra nc. Te:evision. JU= Professor J. Menton, A.M.I.K.F., lec- At the . \piit meeting of the Kensington tured to the (solders Green and Hendon Radio i ! . Mr. H :udy, of the Radi- Radio Society on April 21st. his subject TOAPC S 1rc Elu trical Co., Ltd., gave a paper being " The Principles and Prospects of nn " \\'hat I Should Do with ' l'eco Television." After describing the possi- Valves." The speaker described a set bilities of television. l'rof. Denton ex- suitable for a frame aerial -a two -valve plained the spectrum and the relation of Secretaries of Local Clubs are invited to retlex --the special feature of which was the light octave to the other waves in send in for publication club news of general the H.F. transformer. This was wound the scale. and he showed how it had been interest. AU photographs published will be so that the capacity coupling between found possible to reduce the very bright paid for. primary and secondary was reduced to a light required by the television trans- minimum, and yet the magnetic coupling mitter so that it was now possible to Measuring Instruments Compared. was light enough to avoid undue losses. transmit in annarent darkness by utilising " Electrical Measuring Instruments " New members are cordially welcomed. the lower rays. was the of a lecture given by Mr. l'he hon. secretary of the Society is Mr. title t:. T. The polarisation of light and the pro- R. If. Laister at the last meeting of the lloes, 29, Upper Phillimore Place, perties of the selenium cell revealed fur- North Middlesex Wireless Club, held at W.8. ther steps towards the solution of the Shaftesbury Hall, Bowes i'ark, N. The 0000 television problem. and the lecturer pro- speaker dealt with the hot wire, chemical, duced some spectacular effects with photo- moving iron and moving coil types of Facts About Quartz. electric cells and Thompson tubes. instrument. Mr. Laister mentioned the Mr. A. Hinderlich gave a lecture on Lantern slides were shown of the appara- advantage of hot wire meters in that they "Quartz " at the last meeting of the tus of Hosing, Szczpanik, Belin, Holwick, can be used for direct or alternating Croydon Wireless and Physical Society. and other experimenters. Jenkin's pris- current. Moving iron voltmeters and The lecturer referred to the care neces- matic disc was illustrated, and the con- ammeters were cheap, but besides errors sary in selecting specimens of quartz and cluding slides dealt with the apparatus due to hysteresis and eddy currents in the difficulties experienced in cutting. An employed by Mr. Baird. the ire., they suffered from the disad- interesting demonstration followed of 0000 vantage that the deflection was not in crystal oscillation. Mr. Hinderlich ex- proportion to the current. In moving plained that it had been found that quartz Visitors. coil instruments, however, none of there of one millimetre in thickness oscillates At their last meeting members of the sources of error was present. Mr. Laister at a frequency which gives approximately Golders (been and Hendon Radio Society described how the permanent magnets 105 metres. and that various wavelengths were pleased to welcome representatives employed are artificially " aged " so that could he obtained by grinding the quartz from the Hendon Traders' Association the instruments do not alter after cali- to different thicknesses. One specimen and also a number of visitors from other bration. Many useful hints were given he had produced gave a wavelength of radio societies. as to the use of measuring instruments 33 metres. The hon. secretary of the Golders Green in wireless work, and Mr. Laister has Visitors are warmly welcomed at the and Hendon Radio Society is Lt. -Col. agreed to give a demonstration at an meetings of the Society. Full particulars H. A. Scarlett, D.S.O.. 357a. Finchley early dale. can he obtained from the hon. secretary, Road. N. \W.3, from whom particulars of Hon. secretary : Mr. H. :1. Green, 100, Mr. H. 'I'. P. (see, Staple House. 51 and membership can be obtained. Pellatt Grove, Wood Green, N.22. 52, Chancery Lane, London, W.C.2. e 29

www.americanradiohistory.com ;f41 Wtps Ilato WOfIl01 MAY 4/11, 1927.

011111111111.1

y munn11E2

ÍíiîlüïUlÌiuííñun111nnuuíumiuulunlunlfïíunnnlíiÌÌ 1111111 I 1111111

The following abstracts are prepared, with the permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Palen! Office, Southampton Buildings, London, W.C.2, price 1s. each.

Microphone Amplifier Circaits. tap is provided. It will be seen that which acts partly as a low- frequency am- (No. 266,029.) should the leads X, Y, and Z, that is, plifier, and also as a means of transferring the leads between the microphone any energy Application and the received from the aerial to a date: Nor. 9th, 1925. input of the amplifier be cut by any stray detector valve. Li one arrangement shown E. A. Graham and L. H. Paddle fields, any currents induced will be in the accompanying illustration an aerial describe in the above British Patent balanced out in so far as secondary A is connected to the grid of a valve V Specification some microphone amplifier potentials across the two' transformers T, the grid circuit of this valve containing circuits incorporating a centre point earth and T, are concerned. In other words, the secondary winding S of an intervalve system. The object of the invention, of no induced current will be amplified, and, transformer T. Potentials communicated course, is to prevent stray fields from therefore, the system will be stabilised, to the grid of this valve will cause high - affecting the amplifier, which may since the stray field from the output can- frequency currents to be produced in the emanate from the output circuit of the not cause any reaction effect with the anode circuit of this valve, which con- amplifier, or from current carrying con- input. Similarly, stray fields in conduc- tains an inductance L, coupled to a tuned ductors in the vicinity. The particular tors in the vicinity. of the leads X, Y, arrangement shown in the illustration and Z will not influence the amplifier. utilises two transformers in the input and Microphone potentials, however, will not output circuits, the two transformers balance out, and will produce potentials being arranged so that the fields are in across the secondaries of the input trans- the same sense. A magnetophone type formers. The specification also mentions of microphone is illustrated, and is pro- that with long microphone leads earthed vided with two windings W, and W_, sheathed wires connected to the centre the extremities of which are connected tu point should be used. the miters of the primaries of the two 0000 transformers T, and T,. The secondaries S, and S. are joined and are connected Preventing Radiation. between the grid and filament of the valve (No. 250,969.) V,. The centre point of the primaries Convention date (U.S.A.): April 18th, and the centre point of the microphone 1925. winding are joined by a lead Z, which A circuit which tends to prevent radia- is then earthed and connected to the fila- tion from a receiving aerial is described nient of the amplifier. The output circuit in the above British Patent by S. Y. of the valve contains transformers T,, White. The invention consists in con- and -T, connected in series, but no centre necting the aerial to the grid of a valve

Non -radiating receiving circuit. (No. 250,969.) circuit L. C connected to the detector valve V_. Reaction is obtained in this circuit from the anode circuit of the detector valve by means of a reaction coil L,,. The anode circuit of this valve also contains the primary winding P of the low- frequency transformer T, the primary winding, of course, being shunted by a condenser C_ to by -pass any high -frequency component. Potentials transferred by the valve V, to the circuit L. C, will be rectified by the detector valve and low - frequency currents will be passed on by the transformer to the valve V the anode circuit of which also contains the Microphone circuit independent of external electrical interference. (No. 266,029.) telephones T. B 30

www.americanradiohistory.com lib, 7927. wip@Il®§0 567 AMY wopIloi

NEWS FROM ALL QUARTERS.

By Our Special Correspondent. Making Us Laugh. -The Facts about "Daventry Junior." -The Great Event.- Birmingham's Summer Feature. -Koenigswusterhausen to Go. -The Music -hall Situation.

Community Laughing. mined not to hurry matters. Each com- waiting to plunge into the same congested ponent is being tested separately before channel. Not long ago I proffered a handshake the present month the Bureau in its inclusion in the plant, for it is realised During to the B.B.C. for their commonsense that any serious failures during the test Internationale de Radiophonie will meet rejecting a proposal for " Community in to discuss the position, but it is extremely as in period may engender doubts official Laughing." The practice fostered quarters feasibility of the unlikely that any new wavelength scheme of an ecstatic concerning the America consisted placing regional scheme as a whole. will be formulated before the great event negro before the microphone and asking to prove in September. The were If " Daventry Junior " were him to " laugh." audience a failure the regional scheme would un- 0000 supposed to respond until the whole doubtedly be consigned to the limbo of Washington. American continent rocked with amuse- things shelved. ment. 0000 The great event is, of course, the Happily this is not the B.B.G. idea of Washington International Radio Con. a proper stimulant for " Community A Tentative Talk. ference -an event which, to the keen Laughing," and I shall not withdraw my Meanwhile the long -wave experiments wireless man, has an importance exceed proffered handshake, despite the fact that conducted between the parent station at ing that of a solar eclipse. Savoy Hill has changed its mind and Daventry in collaboration with the long - There has been only one international intends to have " Community Laughing " wave transmitters on the Continent have radio conference in the history of the at an early date. provided some valuable data and some world, and we shall be considerably older 0000 indigestible food for thought. men and women before another is sum- The Stimuli. Nearly thirty European stations are moned. The first International Radio- stimuli will be using the 1,000- to 4,000 -metre wave- telegraphic Convention took place in Lon- Definite and tangible attended by present in the studio when this unusual band, and several new candidates are don in July, 1912, and was turn is attempted, and I understand that the equipment will include an exceptionally intelligent parrot and a number of irresistible gramophone records. The gramophone records have already been tried on certain picked individuals who have never been known to smile at anything less than a reduction in the income tax. The results were distinctly promising. 0000 A Little Grand Opera. " The Policeman's Serenade," a little grand opera from " Riverside Nights," will be broadcast on May 19th. The words are by A. P. Herbert. 0000 Stacy Aumonier Programme. Mr. Stacy Aumouier, the well -known man of letters, is arranging a programme in the " My Programme " series, and his effort will be heard by listeners on May 9th. 0000 Caution at Daventry. Although reports have appeared -not in The Wireless World -of test transmissions supposed to have been conducted already from " Daventry Junior," not a the aerial. single signal has escaped " WHITE MAGIC." Red Indians at the Fort Hall Reservation, Idaho, listening to The station is being built up slowly, the Mr. Coolidge, known as the " White Father," broadcasting from the big wigwam at chief engineer and his staff being deter- Washington. in Indian circles wireless is described as "the white magic." s 31 illikliiialti.i.ark, www.americanradiohistory.com w7,#i 1l9eN-'!Rs`1lPn!lvslts*ìeD?'A,;c,pg. .'.. . . -. . - _. :4':

.56,9 Wiipsh6o MAY 4th, 1927. W011iC1 plenipotentiaries of practically every and military hands from the Jephson A Famous Oratorio. government. Their deliberations covered Gardens. These should prove a most Mendelssohn's oratorio, " a wide field and yet, in comparison with attractive addition to the programmes. Elijah," will b3 broadcast from 2L0 and the work facing the Powers next autumn, The.first programme from the Gardens by other their task was a cheerful summer stations on May 15th. The Wireless the " Society Six Concert Party will be Chorus and diversion. heard on the Wireless Symphony May 25th. Orchestra (leader, I hear that the agenda for the Washing- O 0 O O S. Kneale Kelly) will ton Conference, issued from Berne, occu- 1)5 conducted by Stanford Robinson. ''l'us Koenigswusterhausen Superseded. - pies 800 typewritten pages! soloists are Dora Labbette (soprano), o00ó The German Posts and 'Telegraphs are Muriel Brnnskill (contralto), Spencer erecting a new station at Zeesen, near 1912- 1927. Thomas (tenor), and Rex Palmer (bari- Berlin, which will supersede the present tone). Every phase of wireless endeavour will be taken in hand, investigated, turned in- 0 0 O 0 side out, and, quite possibly, set upon FUTURE FEATURES. Story of the Military a new footing. Band. In 1912 the sole topic was wireless tele- Sunday, May 8th. The development of the military band graphy, and the chief problems related Locmow. -Light Symphony Concert. from the earliest times will be told by to the organisation of land and ship IIOUHNEat0UT}i. - Programme of Colonel J. C. Somerville in a broadcast stations, the collection of charges by Classical Music. en May 12th. Musical illustrations will different countries, time and meteorologi- CARDIFF. - Religious Service in be provided by the Wireless Military cal signals, hours of service, and other \Velsh. Band under the direction of Lieut. 13. matters of routine. Iu 1927 the new and Monday, May 9th. Walton O'Donnell, and some of the oldest uncharted realms of wireless telephony LONDON.- Chamber Music by Lou- forms of military band instruments will and broadcasting have to be explored. don Wince Quintet. be used, i.e., Serpent, Cornetto, Ophce- The countless ramifications of broad- NEWCASTLE.-" The Art of Pleas- leide, and Keyed Bugle. Colonel Somer- casting alone might be expected to tuna ing Nobody," by members of ville suas formerly commandant at the many a mans Lair grey, and I am not the Station Staff. Royal Military School of Music, Kucller surprised that certain countries are be- tLARGO W.- "'Tite \Monkey's Paw.- Hall. coming worried regarding the length of in three scenes, by \V. AV. 0000 time which the conference is likely to Jacobs. - The Music Halls. occupy. A conservative estimate puts it Tuesday, 10th. at two May months. LONmON. The Arcadians." Apropos the rumours and counter - 0000 -" rumours regarding M sNuntarsu. - Concert by the the music halls and A Conference with Power. " Celebrity " Orchestra relayed the B.B.C., I understand that the Enter- The Washington Conference will have from Hotel Majestic, St. tainments Protection Association, of an overwhelming advantage over every Amies -on -the -Sea. which Sir Oswald Stoll, Mr. Gulliver, and other music -hall proprietors are other form of wireless conference held in BELFAST. -" The House Agent," a recent years. It will have legal power. Sketch by Gerald Grace. members, has decided to place proposals Although its í°ecommendittions have before the B.B.C. for some form of work- Wednesday, May 11th. been laudably followed by .t large number ing agreement. The draft proposals will of countries,. the Bureau Internationale LONDON. -" Down Memory Lane." be discussed this week at a special de Radiophonie has no power in-the legal 131iSIINGAAM. -" The May Queen," meeting. Cantata by Sterudale Bennett. sense of the word ; indeed; unless I -am In the meantime it lias to be remem- very much mistaken, it bas never Thursday, May 12th. bered that the Entertainments Protection received full recógnitinn. from any LONi)ON. -\l il itary Band Concert. Association, Ltd., was one of the parties Gos=erument. \MAisenkSTEIi. --A Massenet Concert. to the agreement entered into by the - entertainment coon NEw'CASTLE. -" Five Birds in ;i industry and the B.B.C. in Cricket at the Microphone. Cage," in one act, by O. E. 1925. One of the clauses of that agreement Rev. F. H. Gillingham has agreed Jennings. was that aitists might be employed to for ordinary broadcasting when broadcast a running' commentary on the such Friday, May 13th. artists not by condi- cricket match between Essex and New LONDON.- Music. were precluded the Ballet tions of any contract existing at the time Zealand from the Essex County Club CARD] FF. -- " His Rest Day.- of the Iüoliosecl - ground at Lcyton on May broadcast. 14th. On the Comedy in one act played by The italics are mine. To the l:réaious Saturday, May 7th, Mr. P. F. ordivairy Cotswold Players. onlooker it would appear that the ternes Warner will give from the studio at 2L0 I it.Ascow.- Choral and Orchestral an eye of this agr ±eurent have . not beeii -witness account of that day's play Concert. adhered to, it the Surrey v. Hampshire match at the AscnnEEN.-Scottish Prograiutnc. Oval. 0000 0000 Saturday, May 14th. LoxmoN.- B.B.C. Concert Party. B.B.C. on Guard. A Happy Dissolution. BELFAST. -" The Half Door." ou As I mentioned in these columns last As a a last coact scion, uegro convicted act play by F. K. Fahy. week, the B.B.C. has not been directly of murder at Sing Sing was allowed to approached by the music -hall interests, listen to an entire programme broadcast all the controversy having been conducted from New York. After that the un- " Dentschlandscuder " of Kiienigssvuster- through the Press. fortnuate fellow was probably very glad hansen. The new station is the work of The position is being very carefully to die. - Wireless ocooWeekly, Australia. the well -known Telefunken Company of watched by the B.B.C., however, and Berlin, and German authorities claim that from the attitude wlilich is being pre- Birmingham Summer Feature. it will be the most powerful European served at Savoy Hill 1 gather that the One of the regular features of the Bir- broadcasting station. They believe that music -hall interests will receive no hasty mingham station during the summer it will surpass our Daventry, and also and -extravagant concessions. months will be the relays of concerts from the Rhineland station of Lamgenberg. " Quite 90 per cent. of music-hall the Pump Room and the Jephson Gardens, The station at Zeesen will transmit on toms," said a B.B.C. official, " are use- Leamington. It is hoped to take these a wavelength of 1,250 metres, which is the less for broadcasting purposes, and the every Saturday. In the afternoon the present wavelength of Köeuigswuster- B.B.C. is not prepared to pay large Pianoforte Trio, directed by Edna -Wil- hausen. British listeners will await with suns of listeners' money to secure an loughby, will be heard front the Pump interest the arrival of this new giant of occasional claim on the services of the Room, and iii the evening concert parties broadcasting. remaining 10 per cent."

B 32

www.americanradiohistory.com AIRY ¢th, 7927. WilTd.aM 509 WOIC11t1

D , 9 rus

A Review of the Latest Products of the Manufacturers.

THE LEION ELIMINATOR. continuously variable, by means of series - good value in view of the comparatively This arrangement low price at which it is offered. Of in connected resistances. A novel feature has been introduced is rather unusual as compared with the Jacobean style, it is not only pleasing in the design of the new Leion battery potential dividing resistance so com- design, and would not look out of place eliminator manufactured by Productive but the for supplying several volt - among high -grade furniture, Ltd., 10, Vyse Street, monly adopted British Grinders, age outputs. With this arrangement, in general dimensions have been carefully Birmingham. Not only is provision made considered to meet the requirements of the which the voltage is controlled by con- for obtaining H.T. potentials from tinuously adjustable high resistances, the set design. It is a two- section cabinet, D.C. supply mains, but a charging circuit of course, the upper half accommodating the set is incorporated for the filament battery. potentials delivered depend, of current passed in the with front doors hinged top and back. Although it is common practice,. where on the amount plate circuits of the valve, but, being while the lower compartment is provided D.C. supply is available, to derive H.T. the adjust- for the accumulators, high- tension and potentials from the public supply, there continuously variable, right The ment of D.T. potential can be readily grid batteries, or battery eliminator. are few instruments available which pro- smoothing circuit, which model shown is nearly 3ft. in height and vide for L.T. battery conveni- obtained. The 8in. charging iron core inductances and accommodates a panel approximately ently arranged so as to remove all trouble comprises bridging condensers, is liberal in the in regard to maintaining the L.T. battery and condensers em- in a working condition. As regards L.T. values of the chokes ployed. The. manufacturers test the the arrangement a - supply, consists of two severe conditions, position switch, connecting with a pair of eliminator under rather inasmuch as a 25 -cycle mercury arc rectified A.C. supply is taken as a source of D.C. This instrument, therefore. should he suitable for use on practically any D.C. supply mains. The front ebonite panel measures, roughly, 6in. x 6in., and the depth of the unit is Min. A lamp socket adaptor and a length of flexible cord is supplied, as well as a two - pin plug, so that in place of the charging lamp connection can he made to a lamp stand. 0000

A NEW CABINET. The time has come when even the enthusiast who normally constructs receiving sets of various types according to the many circuit systems must possess at least one really first -class set. One no longer hesitates when considering the hest circuit system to adopt, and several designs have been put forward which are likely to remain standard practice for some time to come. That well- finished sets are now being more generally built is indicated by the growing demand for attractive cabinets, and a wireless cabinet An inexpensive Jacobean cabinet with accommodation suitable for housing is of interest lias recently been produced by multi -valve set, together with batteries The Lelon battery eliminator, in which pro- Messrs. G. G. Ambatielo and Co., Ltd., or battery eliminator. vision Is made for L.T. battery charging. Ambatielo House, Farringdon Road, E.C.1, to house the home -constructed set x28in. The width of the top board is inside about 13in. batteries, and by means of a current - and render it an attractive piece of fur- 15in., and the depth limiting lamp connected to the supply niture. To offer an attractive cabinet at This size is ample for accommodating the mains one battery is on charge While the a moderate price lias been the aim, and most elaborate of receiving apparatus, other is connected through to the receiv- although, perhaps, some criticism can be and the lower compartment will easily ing set. On the H.T. side provision is made as regards lightness of construction accommodate H.T. batteries of the large - made for two H.T. voltage outputs, both in this instance, the cabinet represents capacity type. B 33

www.americanradiohistory.com t f Dr`,_ikh -kF°:' t1 "akvisv kP?+K:vs...:t1P5RaFi. t . ,.-,". . .. .,. .: 1 ,.:t -_r

WApighoo Weida MAY jih, 192'.

The Editor does not hold himself respgnsible for the opinions of his correspondents. Correspondence shoald be addressed to the Editor, "The Wireless W,rld," Dorset Haase, Thdar Street, E.C.4, and mast be accompanied by the writer's name and address.

CERTIFICATES OF MERIT FOR COMPONENTS AND No doubt the inauguration SETS. of such a joint service to public and manufacturers would entail expense, and we suggest tlsat- Sir, -In the advertisement columns of all British radio saure could be niet by a small fee for the preliminary laboratory periodicals are to be seen displayed advertisements of radio testing. We would certainly support such a scheme and are components which are, to say the least of it, somewhat ex- eager to see same introduced. travagantly written. Trusting you will find space in your valuable paper to insert We believe it would be highly advantageous, both to the this letter in your correspondence columns, together with your trade and the public generally, and particularly instrumental in comments, and that you will invite the opinion of manufacturers fostering that renewal of confidence on the part of the actual and the public, and also the trade generally., consumer of radio gear, which is so sadly needed by manu- Liverpool. CLAUDE LYONS. facturers to -day, if your paper, as the dominant journal of April 11th, 1927. its kind in this country, and the " doyen " of British radio publications, would establish some form of " Certificate of sr Merit " Service This has been done in the U.S.A., but, in that, country, these certificates are given in rather an indiscriminate manner, THE EVERYMAN FOUR." and we suggest that certificates might be issued over here in, say, three classes and only after the most thorough examination. Sir, -1 have noticed recently that several correspondents have Products could be given " Certificates of Merit," grouped, say, given readers their experience of the use of various 6 -volt ss : -" Star " Class, First Class, Second Class. valves in the wonderful set the " Everyman Four." As no It is suggested that the following might be the rough meaning doubt there are many who desire to use those of only 4 -volt type, of such grading: - perhaps my experience of the new 4 -volt Osram range may "Star " Class: -Products than which there is nothing superior be of interest. to be found : not necessarily the best. Claims made by the My set is to specification and I used the valves originally manufacturer as regards quality of materials and workman- mentioned until a couple of days before Easter, when I tried a ship, definite fulfilment of the exact purpose for which the DE1I410 as a detector. The result was excellent, so much so instrument has been designed, perfection of finish, etc., must that I completed the change over, with the result that I get a be beyond doubt. Merits judged irrespective of price. few more stations, much greater volume, purity better than ¡ "iii-st Class: -Price should enter into the question in this I have heard before, and, at the same time, I have reduced group and be considered along with the essential fulfilments my current consumption by nearly half, and that at four instead suggested in the " Star" Class. Articles in this class should of six volts. be.deemed to be the best obtainable at the price. A number of stations can be usually received during day- .Second C'tu.s..: -This should include all products which are as light, and after nightfall the volume of such stations as claimed by the manufacturer: which in the judge's opinion offer Birmingham, Langenherg, Hamburg, Stuttgart (to mention only excellent value for the cash demanded : products which have one or two) is such that I am considering installing some form a reasonable good all -round performance. of further control. One evening last week at about 11.20 p.m., Under no circumstances should certificates be granted where when all British stations were closed down except Daventrv, I claims made by manufacturers are not met by a reasonably counted 29 stations on the speaker, no 'phones being used. narrow permissible margin. For valves one and two F use DEH410 with a voltage of about We are very sanguine that the introduction of such a system 135 and 90. A higher voltage on valve one only appears to would considerably help to clear away confusion, and to dis- cause noise and bring in mush. Valve three is DEI410, and perse the present belief in the minds of a great percentage of four DEP410 with 150 on the plate, and O.B. of six and twelve purchasers of component parts and complete receivers that respectively. The 15 -olrm resister is left in, the other --shorted. advertisement propaganda may easily be halved. That this Aerial used 60ft. long, and 30ft. to 20ft. high (running impression is there and, moreover, is rapidly spreading, we have down), copper tube earth. convincing proof; we also consider that in many instances such A friend of mine who was not impressed by the performance disbelief is somewhat ,justified, occasionally fully justified. with the original valves is now constructing, especially as We are, further. equally sanguine that the introducf ion of h.' favours 4 -volt accumulators. such certificates would be highly beneficial to the establish- Before closing, I should again like to express my appreciation ment of a more healthy industry, and would ensure manu- of the many straightforward and inexpensive circuits that you facturers being painfully aware that mere weight of advertise- publish from time to time: circuits of the kind an amateur re- ment would not suffice if they could not " deliver the goods." quires, as they do not call for special and very often expensive Advertisers should be permitted to place a distinguishing mark ironponents that are useless afterwards. in theit announcement such as, we suggest, a star ( *) or the London, N.7. F. EGERTON PARKER. number 1 2 or encircled. April 25th, 1927. -

e 3-1

www.americanradiohistory.com MAI' 4th, 1927. 571 WCoiifilca1 FLUID SAC LECLANCHE° BATTERIES. place in India when I listened at 4 a.m. one morning. We like to hear the Westminster chimes, St. Paul's, etc., Sir, will be of interest to those contemplating the in- should -It when the B.B.C. or controlling officials find out that short stallation of a wet Leclanché battery to know that the use not results, due to waves will get to Australia. of earthenware jars will give 'satisfactory idea of 1,500 metres was on the of Good I consider myself that the the porosity of the material and leakage. electrolyte. wrong track for the broadcast of high -power telephony, but quality glass jars are essential for satisfactory results. of do not live in England and cannot even guess a number of course I Installation tests recently carried out on earthen- the conditions there. ware pots show that with a difference of 60 volts between a of from Best wishes to the gang over there. fluid inside and outside an earthenware jar, a current Subiaco. HENRY T. SIMMONS. 3 to 1,000 milliamps will pass accordingly to the quality of Western Australia. (Radio A6KX). the glazing. They are therefore obviously unsuitable. London, W.C.1. M. E. WATES. April 14th, 1927. THE WET H.T. BATTERY Co. INSUFFICIENT H.T. Sir, -I was rather pleased to read Mr. P. K. Turner's remarks in the valve issue of The Wireless orld (April 6th, evil of insufficient H.T. WIRELESS IN WESTERN AUSTRALIA. 1927) on the His estimate of the number of culprits is certainly very Sir, -I must congratulate you on the excellent articles which modest. The distortion brought about by this practice is very appear from time to time in your journal, of which I- am noticeable on cone loud- speakers, and in many cases is respon- a regular reader. sible for the belief that cone speakers cannot handle power. A few lines about broadcasting out here may be of interest At the same time, I admit that some cone speakers have this to your readers. fault. I have often heard it remarked that cone speakers have We have only one broadcast station in Western Australia a booming sound. While I cannot claim to have tested all at the present time and it operates on a wavelength of 1,250 makes of cone loud -speakers, I can say that in every case metres. This is somewhat unsatisfactory, as neither English of this kind I have 'investigated the fault has been incorrect nor American sets will work to the best advantage on the biassing of the grids or unsuitable H.T. local station. However, we manage fairly well on locally made The reason that distortion through these courses is more sets. Our nearest station, barring the local, is Adelaide, 1,500 noticeable on a good cone speaker than on a speaker of the miles away, so one has to go some distance for a change of short horn variety is, I suppose, fairly obvious. programme. I certainly think that to avoid the possibility of noticeable I saw a :.it of letters in your paper re amateur transmitters distortion by making a cone of very stiff material is a retrograde being so plentiful that they were interfering with broadcast recep- step, and in any case it only brings us back to reproduction tion-well, what about sending a few of them out this way? comparable to that of the short horn speakers. And say, when are the Englishmen going to broadcast on The above remark applies only to a stiff diaphragm clamped the short waves? We get some fine music from 2XAF on rigidly at its outer edge (such as a double cone), unless, of 32.79 metres, when they relay WGY's programme. The speech course, it is of abnormal size. and music are very good on two valves, and a loud- speaker Filially, if anyone doubts the amount of distortion possible can be used on a detector and 2 L.F. most times when they through a badly operated amplifier let him use a " coil drive are on I hive also heard some very nice music from PGJ,J free edge cone " and juggle about with the operating amplifier. in Holland. but the only telephony I have heard from England Ilford. R. CUSTERSON. was from G2NM, Gerald Marcuse, who was testing with some April 21st, 1927.

Belfast. Birmingham. Canada : --C lAC, lAM, 1AR, ICQ, Austria : -O OP. Czecho- Slovakia :- 1DQ, 2BC, 2BE, 2DO, 2HV, 2ZC, CS 2L N, 2YD, OK1. Tripoli : -DA Cm.. 3KP. 6DN, 1CW. Porto Rico : -PR 4SA. Färoe U.S.A.:- Il5AMT, 5FR, 7EK, 7VH, 7W U. Mexico :-M 1N, Islands : -D 7J0. Madeira : -P 3FZ. Extracts from Readers' 9A. Panama : -CZ 1LA, 68X. Cuba : -- Portugal : -P 1AE, 1AK, 1AF. Chile :- Q 8KP Porto Rico : 4JA, 4SA. CH 2AS. Argentine : -R BAL Panama. -PR Logs. Argentine : -11 AF1, C138, DB2, DX8, Canal Zone CZ1. Spain : -EAR 6. : DZ9, HB5, NA2. Chile : - 19, 24, 26, 41, EAC A5, Revista Radio HA2, - CH 2AB, 2AS, 2I3I., 2LD. Uruguay : Sport. Egypt : -SUC. Italy :-I 1AU. Y 1BP, 1BU, 1CD, 1CG, 2AK, 2AY. 1E11., 1BD, 1ITVZ. Germany : -K I2. EI 1A3, 10E, 1CN, ICY, 1DR, lAY. Brazil: -BZ 1AA. lAC, lAD, 1AF, W3, W9, 4ABG, 4UAI, 4VO, 4YA, 1GW, IUU. Belgium : -EB V33, N33, lAI. IAJ, lAK, lAM, IAN, 1AO, 4YAB, 4YAE. Poland : -TPAI, TPAV. Z33, 4QQ, -W1, 4CO3 4CB, 4WW, 6K, 1AP, lAQ, JAR, 1AU, lAV, lAW, Sweden : -SMT, SMXV, SMVG, SMWU. 4AI, 4ZZ, 4YZ. Holland : -- lAX, lAY, 1BD, 1BG, 1BH, 1131, Portable : -GX 6MU, XU 211V. Mis- EN, OPM, OFK, OST, PCMM, PCRR. 113K, 1BL, 1BR, 1IB, lIC, lIV, cellaneous :- -OCNG, OCNY, PCMM, Spain : -EE AR18, ÁR28, Aß42, AR44, 1QA, 2r113, 2AF, 2AG, 2A.J, 2AK, SPI, SGC, SQL, FL, BAR. ARA. Austria : -EA ,7Z, AK, GP. 2AL, 2AM, 2AR, 2AS, 2ID, 5AA, Leslie Marshall ((2BNR). Germany : -EK 4ABF, 4UA, 4GD. On 45 metres. U.S.A. :-NU 1BZO, 1DI0, 1ANQ, 5AB, 5AD, 6QA, 6013, SNF, SPAT, SQ1, 1RD, 1BHM, 1AUR, 2AGN, 2AGO, SQ4, SQIX, 11G. Australia : A 2BK, Bangor, Northern Ireland. 2CVJ, -2RS, 2PS, 2BAA, 2BGI, 2CNS, 21J, 2TM, 2YI, 7CW, 7HL. New (February 3rd to March 6th.) 2AFF, 2U0, 2AZK, 2UM, 2VM, 2BM, Zealand : -Z 2AC, 2AE, 2XA, 3AI, Great Britain :--G 2AG, 2AY, 20Y, 2BK, 2AGS, 2AKV, 3FD, 3BN, 3BH, 3AK, 3AR, 3XB, 4AA, 4AC', 4A1\1. 2VR, 2XY, 2WJ, 5AD, 5BY, 5DC *, 3TR, 4LA, 4OVU, 4TU, 7EB, 7BCQ, Philippine Islands : -PI 1AU, 1BD, 5NK, 5MQ, 5YM, 5QV, 5UP, 5UW *, 8BH, 8AFQ, WIZ, KDKA, 2ID, 1H11 Straits Settlements : -SS 2SE, 6DR *, 6UZ *, 6LR, 6UG, 6JS, 6IA, 2XAF. Miscellaneous : -D 7BJ, EP 8-MA X. South Africa : -0 A3B, A4L, 6JS, 2SR. Northern Ireland : -GI 2IT, IAE, IAW, EL IT1B, NM lAYS, SD A4Z, A5X, A6N. Miscellaneous : - -- 5W-D, 5110, 5NJ *, 5ZY*, 6JA, 6AT, 2AR, X 4GJL, FE IBM, ET 8B11, PAI, G XAN, M 1DH, KEL, DNSC', 6MU *, 6WG, 6YW. Irish Free State :- EJ 7WW, ES lUU, SMST, SMSH, IC AGI, KC Z4. TL 1Z, LIT 1B, GW 11B, 14B, 18B, 3NZ. France : -- IRCL, LA iR, O 1YD, NC lAD, FM CB F2, KTC, L:'. 1CW, TJ 011.1,

EF BJJ, 8BCi. BUD, 8KU, 8WI, 8GER, BAY. * Indicates telephony. J 3XP, . BXY, FI 1ACG, J:II 2PZ, 8KM, 8F0, 8KP, 8WD, 811G. 8XE, (0 -v -1 Reinartz.) WNP, VOQ. 8RLD, BCD, SXU, 8X UV. Italy :- C. B. Cleeland (2AX0). (0 -v -1) Lawrence L. Parry a 35

www.americanradiohistory.com wrPTS-"?Æ'rinT1tL,Mt.?°-, P° *!'N1!1xwfI;q&?§tt7Tk=$.k: ;w.77, t7rrarilfr

c72 WAPISIl®Mg, Wollá MAY ¢th, 1927.

- I PROBE

HIND.

" The Wireless World " Information Questions should be concisely worded, and Department Conducts a Free Service headed " Information Department." Each ANS°WERED separate question must be accompanied by a of Replies to Readers' Queries. , stamped addressed envelope for postal reply.

A Minor Trouble. method effects a cure, one may usually plate of third valve and grid of final I am building the " ¡f ireless World infer that the trouble was caused by valve is eliminated. You should not use Five," but find difficulty in obtaining earth currents. It is within our experi- a cheap transformer, but obtain one of the special "Can't-Cross " connectors ence that a particularly flagrant case of low ratio, which in the case of a reputable which you use for battery connection, tramway interference was completely firm will mean that the primary induct- my local dealer being unable to supply cured in this manner. ance is fairly high. them. Can you inform me where I 0000 0000 can obtain these? K. L. R. Receiving Long -distance Stations Series or Parallel? We advise you in the circumstances to apply direct to the manufacturers of Satisfactorily. I have recently purchased a loud -speaker I hare a 4 receiver of foreign manufacture, this device : Messrs, J. and W. Barton, -valve consisting of which I find 22a, Virginia Street, Southport, Lancs. an 1í.h'., detector, and two resist - is of 1,000 ohms resistance. I wish 0000 ance -coupled L.F. stages. I find to run this together with my exist- that this gives me excellent loud- ing loud -speaker which is of 2,000 Eliminating Interference from Tramways. speaker results on c ¿Pli quite distant 011105. , IOUld I connect the instru- e ments in I have lately moved to a slew stations. Some of the ;rceptioually parallel or .series? I wish, locality, to be able to and find that I nm greatly ilistant stations which I receive, how- control the volume of troubled ever, give each loud -speaker by noises caused by the electric me quite sstisfactory re- individually. tramway system, sults, but, presumably, owing to the L. D. W. which runs in fact that stages proximity to my house. Can you bout are resistance- Under the circumstances, you are ad- coupled, /(UnP is suggest any method of curing 'ra not quite adequate, vised to connect the two instruments in this and I should like: if possible, ace trouble? M. D. to series. You could then, of course, shunt G. a good transformer in the last L.F. Usually it will be found that the best each loud -speaker with a modern type of stage instead of a resistance -coupled volume control such as the " Pye method of all is to use an efficient coun- stage. " I enclose a rough sketch of obtainable from 3lessrs. W. G. Pye, Ltd., terpoise consisting of an arrangement of this portion of my receiver, which I wires carefully insulated and run Granta Works, Montague Road, Cam- a few wish to alter, and shall be glad if tiou bridge, or any other similar instrument feet from the ground parallel to the will explain the best method of ptro- aerial, and, if possible, slightly longer. by other makers. This would then enable cedure. S. Al. you to control the volume But each case most be judged on its of each loud- We reproduce in 1 speaker individually. merits, and many cases can be cured with- Fig. (a) the sketch We would point which you send out the we out such an arrangement, whilst at the us, whilst in Fig. 1 (b) that arrangement have given we show holds good irrespective of whether the same time we realise that it is compara- the alterations which you desire to make. You loud- tively seldom that space permits of such will notice that the trans- speakers are connected directly in a counterpoise being erected. former primary merely takes the place of the plate circuit of the last valve, or In general, the grid leak, one should avoid reflex circuits in whilst at the same time whether a choke filter output circuit is cases the small coupling condenser used. like this, and should earth the cores of between the L.F. transformers, or earth their shrouds if they are of the enclosed type. It is often recommended that a large fixed condenser be used in the earth lead, and also that the aerial should be stretched at right angles to (or at any rate at as great an angle as possible up to 90 °) the tramway lines, but this again is not always possible under the circumstances. One of the most successful methods of curing the trouble in cases of those readers who from one cause or another are not able to use a normal counterpoise, is to use a rough counterpoise consisting of 30ft. or so of rubber- covered wire attached to the earth terminal of the set i. and led away anywhere, such as round the C skirting board of the room, the far end of course being " free," and not connected to anything. Experiments should be made with regard to the length of wire, and its position ; it may be run under the carpet if desired. When this Fig. 1.- Circuit alterations for changing from resistance to transformer coupling, ii 36

www.americanradiohistory.com Wripa®00 MAY 411/, ¡927. 573 WoACI1 advice and make this Is a Separate H.T. Switch Necessary? course, be interpreted as meaning that you will follow our they be alteration you will then find that you - switch the signals received, whether I lucre a plain " On and Off" code signals or telephonic speech, have a very efficient long- distance head- one lead of my L.T. Morse ',chick breaks can be faintly heard in the headphones, phone receiver. to. switch off 0000 battery when desiring but too faintly for more than a letter or the receiver after a period of listen- to be distin- it is two or the Morse code A Sulphurous Question. ing. Can you tell me whether perhaps a word or two of use a similar guished, with I intend building a -multi-valve re- advisable for me to speech. R, indicates that ône can, in switch for .switching off the H.T. ceiver in a large cabinet, and wish the case of either Morse code signals or if any harts world be done battery? In other words, is the H.T. words, and to ¡now the telephony, receive several in includutq my H.T. and L.T. accu- battery wasting away during to indicate by the con- probably enough mulators in the, same cabinet as the periods when the 'valves are switched text meaning of the message. The off? R. L. S. the receiver. T. F. C. meaning of the other symbols is abso- not include these point You should definitely No, there is no need to incorporate this lutely straightforward. We would batteries in the same compartment as the extra switch, because when you turn off out that several interpretations of the trouble will appeared wiring of the receiver, or your valve filaments the valve emission various " R " symbols have very speedily arise. We presume front ceases, and the H.T. battery then is de- from time to time, but the one which we that you in- accepted your question, however, finitely on " open circuit," or, in other reproduce is the generally a very large type of be signal tend building words, it is " off," there being no com- scale. Possibly R, would the cabinet containing a separate compart- plete circuit joining any of the H.T.+ strength often referred to by amateurs ment for the batteries. This, of course, terminals to H.T. -. If, however, you as " phones on the table" strength. will he quite in order. It is advisable, have valve holders of very poor insulating 0000 however, to paint the inside of the com- qualities, then there will be a continuous anti -sulphuric paint and A -distance Headphone Receiver. partment with current flowing from the H.T. battery Long to provide vents for the escape of gas through the faulty valve holder, or, I have built a receiver for long -distance given off by the batteries. again, :f the insulation of your terminal headphone work consisting of the strip is poor, there will be a current " Everyman Four" set minus the 0000 flowing between H.T.+ and H.T.- - two L.F. stages, my phones being Volume Control. across the leaky ebonite. In any case, connected in the plate circuit of the be small, and I notice that in your -description of the however, the current would detector valve instead of the anode re- of these components were very " Neutraltsed Tuned Anode " if the insulation resistance, but results are poor in your October any leakage did take place. indeed. you tell me where 1 ceiver, published so bad that Can last year, you refer to the then you are not getting anywhere near hare gone wrong? P. R. O. 20th issue out of your receiver. fact that the volume control cased is the best results It is quite impossible for you to get of in the The remedy, therefore, would seem to similar to that made use switch, but good results front the arrangement you four -valve receiver published in your be not to purchase a separate mention for a number of reasons. In new valve holders, etc., of July 28th, 1926, issue under the title to purchase the first place, the valve is of much too you tell reliable insulating properties if necessary. of " Everyman- Four." Can high an impedance to utilise anything me what exactly was this method of You should not, however, switch off and its anode with the but a very high resistance in volume control? D. F. B. then proceed to " juggle" in any other manner scarcely set, as you must circuit, and vias valves or wiring in the any worth while results will be obtainable. The method of volume control used you might, in the course one, namely, the con- remember that It is of little use connecting an anode a perfectly simple of your experimenting, accidentally short - circuit the H.T. battery inside the set, or do some other damage. Even this does not, however, call for a switch, because on the comparatively rare occasions which you will wish to alter any of the wiring of the set you will naturally dis- connect the H.T. battery. 0000 "R8" or "Phones on the Table." When searching for distant stations often find that I receive a large number with varied strength. I understand that there is an official scale of signal strength by which one is able to record in a lorry book the strength of a signal received. If this is so I shall be glad if you will give me full particulars. W. H. M. The scale of signal strength measurement to which you are referring is probably the " R " scale, and we reproduce the scale herewith for your benefit. reception. R, =Signals unreadable. Fig 2. -The " Everyman Four " modified for headphone R,= Signals readable with difficulty. value in series with trolling of the H.F. filament temperature R, =Weak but readable. resistance of high the R,= Readable. the telephones, because then, apart from by means of a rheostat, dimming readable. the volts dropped across the filament causing, of course, a great in- R,= Easily other things, therefore; R, = Fairly strong. telephones would be a very small per- crease of valve impedance, and, the total voltage drop across a loss of volume. In no circum- R,.= Strong. centage of of R. =Very strong the whole impedance in the anode circuit. stances, however, should this method R,= Loud -speaker strength. The only way to solve the problem is to volume control be used in conjunction add another L.F. stage in accordance with with an L.F valve, or great distortion It will be noticed that R, indicates that result. signals are unreadable. This ,should, of the diagram which we give in Fig. 2. If will naturally e 37

www.americanradiohistory.com 5,* WbsIlsor Woh'!'ol MAY ¢tTt, 1927. Using Fdhr -vol;: Valves. In Fig. 3 (b), therefore, we are left l out building the " l: rerytnaa Your" re- with three capacities in parallel. The ceiver, and ant intending to use 4 -colt II solution is now easy. as we need only rat ceg throvhout. Are there any 0001 0 0005 mfd add these three capacities together, which alterations that it is necessary for vie gives us the solitary capacity in Fig. to make to the receiver for this? 3 (c). The capacity in Fig. 3 (c) is, W. L. S. therefore, equal to the resulting 0001 mfd capacity We would refer you to the reply given from the apparently complicated looking to A. L. C. on page 473 of our April 13th iI multiplicity of condensers in Fig. 3 (a). issue, in which Many people apt to confuse the full instructions are give.] 000005 mfd are for using 2 -volt valves throughout. method of working out. complicated series Exactly the same advice applies in the It parallel arrangements -of condensers with case of using 4 -volt valves. complicated series parallel arrangements of o o o o resistances. In the case of resistances II the opposite holds 00002 good, namely, the re- A lrathema!ical Miasma. mfd sultant resistance of several resistances 1 find it rather puzzling how to calculate in series is equal to the suns of the indi- the capacity vidual resistances, whilst the resultant given by connecting up 0025 fixed condensers in series, by connect- resistance of several resistances in parallel 00001 mfd mfd is ing them in parallel, or by conne t- equal to the reciprocal of the sum of Ing them in .'cries- parallel arran-e- II the reciprocals of each individual resist- nlent, and I shall be glad if you will (a) ance. It should be noted that in the case of assiet rfte in my di/iculties. Does the 0'W056 mfd capacities in parallel, the result saute rule hold good will always be greater than of any of the as in the case of II individual nerirs- parallel arrangements of capacities, whilst obviously in resist- the case of resistances ance's and inductances? P. R. 0'005 mfd in parallel the E. result will always be less than any of The problem is not at all difficult, as II the individual you suppose. resistances. A capacity of In the case of condensers 5 mfd. in series with one of 0.0001 mfd. connected in a parallel arrangement, the 000029 mfd resultant will, therefore, always be less than 0.0001 capacity is equal to the sum of II mfd., and the resultant resistance all the individual capacities. of a The calcu- (b) 10.000 ohm resistance and a 1 lation of the resultant ohm re- capacity of several 0-0009 mfd sistance in parallel will always be less condensers in series is no more difficult, although II than 1 ohnr. it might appear so. In brief, If desiring to calculate the inductance the resultant capacity yielded by con- (0) of various necting chokes, whether air or iron fixed condensers in series is equal cored, connected in series or parallel, to the reciprocal the of the Sum of the reci- same rule follows as in the case of re- procal of each individual capacity. Hg. 3.- Calcnlatiar of complicated sistances, except only Thus, capa- that it holds good take the case of three imaginary city combinations. if there is no mutual inductance between condensers of 0.0005 mfd., 0.001 mfd.; and the various chokes, is 0.0015 that to say, if mfd. connected in parallel. The capacity of 0.00005 mfd., and so without they are sufficiently separated from each answer will simply be 0.0005 +0.001+ more ado we know that this other to avoid any magnetic 0.0015=0.0Q75 will form interaction mfd. If, on the contrary, the same capacity in the second line from between any two or more chokes. we connect these same three condensers the top in Fig. 3 (b). The bottoni line 0000 in series, we must- -first proceed to of Fig. 3 (a) turn is worked out in exactly A Reac'ion Riddle. - them upside down, that is, taking the the sanie manner as was the top line, and 1 nisie to build a reeeicer coneistitig of ret''wocals of the which gives us we get the resultant capacity of this H.F., detector, and two L.P. icul' -i c, 1 1 1 bottoni line of Fig must add 3 (b) in the bottom using a stage of resistance coupling . We line 0.0005' 0.001' 0.0015' of Fig. 3 (b). in the first L.P. stage, a transformer these together, as it is the sum of these being used in the reciprocals second stage. I we, want, and the result is propose to use a 1 lnegoltnt anode 11000 -33-. This is the suns of the reciprocals, BOOKS FOR THE resistance, a 0.002 nlfd: coupling condenser, and a 3 niegohnt grid and we now take the reciprocal of it, WIRELESS EXPERIMENTER leak. ll'ill this be in order? I also, which is 0.00027 mfd., and this gives us of course, wish to react on to the the answer. In complicated banks of Issued in conjunelion with The Wireless lVorld." turfed anode, which forni of coupling condensers in series- parallel arrángenfeuts "THE AMATEUR'S 1300K OF WIRE- I hare foisted very successful. it is best first to work out the resultant LESS CIRCUITS," uy F. H. HAYNES. Price L. H. 316 net. By Post. 41 -. V. capacity of each little bank of paralleled Unfortunately if you are going to use capacities, which is a simple "TUNING COILS AND METHODS OF matter, as TUNING," by W. JAMes Price 2/6 net. By a 1 megohm anode resistance it will be it is merely the sum- of each individual Post, 2elo. quite impossible for you capacity to obtain normal composing the paralleled bank. " WIRELESS VALVE RECEIVERS AND reaction effects in the usual manner by Thus, in Fig. 3 (a), for instance, the CIRCUITS IN PRINCIPLE AND PRAC- connecting a reaction coil in series with first thing we TICE," by R. 1). BAxcav and N. ASHDRIDGE, do is to work out the B.Sc. your anode coil. You must, result Price 2/6 net. By Post, 2/ro. if you wish of the two paralleled capacities of "WIRELESS VALVE to use reaction, make 0.0005 TRANSMITTERS use instead of a mfd. and 0.001 mfd., which, it -THE DESIGN AND OPERATION OF comparatively low value of anode resist- will lie noticed, are in series with two SMALL POWER APPARATUS,' by ance, w. JAMBS. Price 9/- net. Post g!6. which should be wire wound. In fixed condensers of 0.001 mfd. and 0.01 By you idea. "DIRECTION AND POSITION FIND- brief, must make use of what some This leaves us with three series IN people are capacities ING WIRELESS," by R. KEEN, B.Eng. apt to terra the " old - in the top line, which, being Price gl- net. By Post 9/6. fashioned " method worked out by the rule of resistance given above, gives "THE RADIO EXPERIMENTER'S coupling. Wo would suggest a 150,090 us one single capacity in the top line, HANDBOOK," Parts r & 2, by P. R. Cousser, 11.Sc Price 3/6 net. By Post, ohm anode resistance used in conjunction which is shown in Fig. 3 (b) as 0.00056 3!ro. with mfd. The a valve like the Marconi D,E.51I top line of Fig. 3 (b) merely Obtainable by pox: irennttawe with order) from or the Mallard represents the resultant ILIFFE & P.M.5X. Indeed, such capacity of the SONS LIMITED, an arrangement was described with full top line of Fig'. 3 (a). Taking the second Dorset House, Tudor St., London, E,C.4, constructional - line ddtvn of Fig. or of booksellers and. Bookslalts, details in our issue of 3 (a), we have a solitary March 31st,. 1926.

13 38

www.americanradiohistory.com AN D RADIO REVIEW (151y Year (1 Publication)

No. 402. WEDNESDAY, MAY I I TH, 1927. VOL. XX. No. 19.

: H. HAYNES. Editor : HUGH S. POCOCK. Assistant Editor F.

Telephone : City 4011 (3 lines). Editorial Offices : 139 -40, FLEET STREET, LONDON, E.C.4 - - Editorial E.C.4. Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, Telephone: City 2847 03 lines). Telegrams: "Ethaworld, Fleet, London." MANCHESTER 199, De insgate COVENTRY: Hertford Street. BIRMINGHAM: Guildhall Building;, Navigation Street Telegrams: " Astopre... RIrndtyham.' Tekgranu: "Inne, Mancheeter. 2eGyrnnte "Cyclbt Coventry." Tekphun:' 8070 sul 8011 l'It,. Telephone: 5210 Coventry. Telephone: 2970 and 29971 MI.'Ie. eI. Subscription Rates: Home, 17s. 4d.: Canada, t7s. 4d.; other countries abroad, Cos. 6d. per annum. readers arc advised, before soaking use of them, to satisfy themselves that (het, As In toy of the circuits and apparatus d.scnbel in lacs. pages are covered by patents, would not be infringing patents. BROADCASTING VALVES AND VALVE PRICES. THE NATIONAL COMPANY. N this issue, under Correspondence, we pub- describes lish a letter from the British Radio Valve A\ interesting article published in this issue Manufacturers' Association which constitutes the work of the National Broadcasting Co. of %vice the object of obtain- n reply, written at our invitation, to letters America, which has been formed the princi- sent to us in criticism ing co- operation amongst and rais- of the Association's ...... pal broadcasting stations policy with regard to CONTENTS. ing the standard of the programmes. Fa':E In America there is a far large: s ,l 11 r prices. The Association has stations serving _dealt with the principal points ED)flllllAI VIEWS . 575 proportion of raised by our correspondents, the more thickly populated 'Ille \lt.inn Lrs' Poit'r.tet.E. in any other part whose communications have not districts than By F. H. ILaynes ... 576 many of been published in The Wireless of the world, but as stations are owned by com- World because spare would not l'ItecT :. r. HINTS AND 'PIPS ... 585 these pro - of so many paratively small concerns the permit of the inclusion t 'l'IHE \' UINA1, BROADCASTING not, on the whole, letters. grammes have PAN v. By A. Dinsdale ... 587 a high standard, al- No doubt our readers have been maintained excellent anxiously awaiting a further re- CI'I :PENI 'l'Orles ... 593 though from time to time performances have been put out ference to this important subject, HOME POItTARLE LOUD -SPEAKER when these have been externally and we regret the period of delay By A. P. Castellaiu 595 organised for purpose of either which has unavoidably occurred the or indirect before we obtained the letter BROADCAST BREVITIES 599 direct advertising. One aims of the National which we now publish. REVIEW OF APPARATI'S ... 601 of the We feel that this letter from the i Broadcasting Co. will be to ex- ... 602 Association gives an explanation RECENT INVENTIONS tend the advertising side so as to which, for the time being, should TRANSMITTERS' NOTES AND QUERIES 603 provide the necessary funds for really first -class programmes. satisfy our readers, and, in par- NESS'S l'ItOM THE CLUBS 603 2 ticular, we would draw attention Tn this country we have stead - THE EDITOR 604 to the statement that reduction in LETTERS To fastly set our faces against the prices should be made at the right HEADERS' PROBLF.AIS ... 606 introduction of advertising into time simultaneously by various ..+...... the broadcast programmes, and manufacturers, as otherwise the fortunately the annual licence fee prices of valves might vary almost from week to week and has provided ample, funds for broadcasting requirements. complications of distribution of valves amongst retailers Had broadcasting here been left to private enterprise in- under such conditions would be too great to contemplate. stead of being a Government- controlled system it is prob- We are satisfied that it is essential for the Association able that it would soon have been found necessary to to adopt this attitude, but at the same time we sincerely resort to advertising, hut we can congratulate ourselves trust that when the right time comes -and we hope it will that our system has made it unnecessary to depend upon be soon -the manufacturers will reward us adequately an expedient which, whilst it may he acceptable in for our patience. America, would find little favour with us. B 5

www.americanradiohistory.com 576 Wip@Il®00 MAY 11 M, 1927. WoTIlca1

Iour\'ilve loI)i!e Peceiver

By F. H. HAYNES.

no higher than the top of the car, and secured to the case in which the set is housed on the running board. Circuit Considerations. It has been observed, particularly during the past winter, that a well- constructed set embodying a high - frequency amplifying stage will, as a rule, without aerial or earth connections, give good reception on telephone re- THE owner -driver has probably devoted most of his ceivers up to distances of ten miles from a main station, spare time, recently, to an overhaul of his car, and and at much greater distances when connected to a short this wave of enthusiasm may have carried him piece of wire, as an earth, and a few feet of aerial wire. along to the consideration of fitting sonic new and useful The circuit system adopted, therefore, is a four -valve accessory. It is more than likely that if the car owner arrangement, consisting of a tuned input circuit to be is also an enthusiastic listener, being desirous of carry- excited, when used as a portable, by a short vertical con- ing his interest with him on the road, he will reflect on ductor, an efficient high -frequency amplifying stage, the design to adopt for building a portable set embody- neutralised and screened, and a valve detector followed ing the many points of progress which have been macle by two resistance -coupled valves with a choke feed output during the past winter. Comparatively few can afford to circuit to keep the H.T. battery voltage away from the construct duplicate sets for home and portable use, and telephones or loud -speaker. although the set on the car must be in every way a portable, specially designed for the conditions of the road, Non-microphonic Valve Mounts. it must be none the less suited to satisfying the require- The design of the components has been modified to ments of the enthusiast as a home receiver. meet the special requirements particularly in regard to the method of supporting the valves. A The Aerial Question. few preliminary tests at once revealed the need for entirely insulating the Although it has several times been demonstrated that 'valves from mechanical vibration. No form of spring reception is possible whilst travelling along the road, few valve holder was found to adequately guard against the sets have been specifically designed for this purpose.. setting up of microphonic noise in the valves, although Practically all commercial portables are fitted with frame providing some protection against damage by mechanical aerials, and although when placed aboard a car they give shock. The valve holders used were developed in another satisfactory reception, the directional properties of the connection, their purpose being to entirely screen the frame give rise to fluctuations in signal strength. A valves to prevent that form of distortion which occurs by frame aerial does not always point in the direction of the mechanical reaction between valves and loud- speaker when transmitting station when used on a mobile receiver, and the latter is used -in the same room as the receiving set. the strongest signals are obtained apparently from Various Everyone is well acquainted with that form of low -fre- directions as the car passes any vertical conductor capable quency howl which is set up when a loud- speaker is of acting as a collector, and therefore a radiator of the operated near a microphonic valve, but it must not be broadcast transmission. An exposed frame on a car is, overlooked that serious distortion occurs long before the moreover, conspicuous and unsightly, must be capable of mechanical reactioni between valves and loud -speaker being rotated in any direction, and will probably suffer arises, and it would appear desirable in the construction daniage owing to its considerable wind resistance. of future sets to adopt some form of non -rigid non- The form of aerial put forward here is a vertical rod, metallic mounting on the baseboard, at the same time B 6

d:.m-Sir. ,.. :r, 4-n70,www.americanradiohistory.com -s .,.;e>,.:;e9s.-.;.t.ai-.F-f,.-.a.w,>:v, ., -,daf;- . ::[1r'...74z.,,e.M».'._;wèi$'.ixìj`. Wñpg@M 577 MAY Ith, 1927. Would

for connecting the short aerial directly to the tuned input circuit. The IL.F. Fig. I.- Provision is made in the circuit arrangement -coupled L.F. stages. unit is in a screening box and is followed by an anode bend detector and two resistance should be supported covering the entire valve to prevent sound tvaves imping- 1'hc tuning coil within the screen almost centrally between the metal faces which lie at right ing upon it. neutralising mounts adopted serve other useful angles to its axis, whilst both sides of the The form of valve cannot be is first the entire elimination of stray condenser, being points of H.F. potential, purposes. There box. Both of introduced by the usual form of valve secured to the metal hase of the screening external capacities on to the walls connections are made by short flexibles these components are, therefore, mounted holders, for the and connected in arranged around the top of the thin walled " Sorbo of the container of the associated valve lined tube which supports and protects the valve. In circuit by short lead. the leads to the valve may he a tuned winding, a filament Constructional Details. an anode resistance, or a grid leak, and these resistance, actual process of construction, one interposed in the straight lead Hissing up from the Turning now to the being obtained all the necessary parts. very much simplifies the wiring, the actual should, after having baseboard several working drawings. The panel down screws connecting to the battery leads. carefully peruse the holding exactly cut to size. and can be ordered Leaks and resistances elevated in this way are protected may be purchased It is }in. in thickness, and its highly against stray capacity leakage, and in this connection with the cabinet. stage polished faces prevent the adhesion of dust. .1 metal advantage is gained in a screened high -frequency

f' 7

y www.americanradiohistory.com 578 Wibpa.®@ei MAY 11th, 1927. WOre Ilco1 The Motorists' Portable. - Adjustment to a true right panel cannot very well angle is essential, or difficulty be used in this instance owing to will be experienced when clamping the several bushings which the copper screening would be required. When box hard up against panel and baseboard. the panel has been made a loose fit in the cabinet, the positions for the holes may be set out with the point of a Making the Valve Containers. pair of dividers, centre punched and drilled. The large The preparation of the ebonite tubes should next be holes for the condenser bushes may be filed to size to a undertaken. The pieces are carefully sawn off to length, small circle scribed on the panel in the absence of a large working all the time to a line scribed right round the drill. Apart from the countersinking, which tube may be done and finished off by rubbing on a sheet of emery or carbor- H O` - O 7" OD Mq E

-O5Mf2 A\ °`_I

G. B- G.6- G.

\WOUND WITH 40 Sw.G. D.SC WIRE TO A DEPTH OF I'/8" 100,000 OHM:

80,000 OHMS Q LT.+A D OPPOSITE .EBONITE TUBES 2%a DIN 16 +16 TUR.N5 CLIP TO LT- LT+ AND X 4'LONG X 3/32 WALL OF 42 D.SC WIRE R Q OPPOSITE CLIP LT.+ AND TO LT- OPPOSITE CLIP T TO L.T. - =Y WINDING OF 70 TURNS OF 24 5WG D 5.0 12 EBONITE STRIPS I" LLONG X'/S" WIDE X ?/32' THICK

WINDING OF 12 TURNS OF 285vv.G DSC WIRE. WINDIN OF 70 TURNS - Z OF 24 5WG D.5.C. TO LTt WIRE

Fig. 2.- Constructionai details of the non -microphonic valve containers and connections are made. A, on the the H.F. transformers showing the points to which detector valve container, connects to the mica coupling condenser (C5 C4). battery terminal (+H.T.2 also Cr). C, to the lower end of also B, to the H.T. valve container, D the secondary of the H.F. transformer (T2 also C2). Next, on the output connects to the low- frequency choke (CHI also CO. E, to the mica coupling plug (G.B.4) shown on the opposite side of the cylinder. condenser (CO. F, to the grid bias connects to the grid Next on the left is the container associated with the fourth valve. H bias lead (G.B.5). J, to the high -frequency choke coil (CH1) and the mica valve grid lead and the H.F. choke (C114). L, coupling condenser (C -). K, to the to the coupling condenser (C5). M, to the H.T. terminal ( of the neutralising condenser. R, to tuning condenser (C2 and grid bias +H.T.2). ,, to the top of the detector valve). T, to the tuning battery G.B.2). S, to the tuning condenser (C, and the grid denser condenser (Cl also N.C.). U and V are the upper and lower terminals of the neutralising (N.C.). W, to the aerial terminal. X and Z, to the earth terminal. Y, con- of the components are given in the theoretical to the grid of the detector valve. The reference letters circuit diagram. Anode resistances and grid leaks are lightly soldered to the brackets. with a larger drill or rose bit, the sharp edges of all undum paper laid flat on the bench. There are live tubes, holes should be removed. each 4in. in length, for the aerial inductance, and The baseboard is of four }in. oak clamped and elevated by valve containers, and a fourth piece for the H.F. trans- fin. battens. This board, if not obtained with the former secondary winding, 2 ¡in. in length. The diameter cabinet, should be purchased already planed to thickness of the special thin - walled ebonite tube is in each case and adjusted to size with a small tennon saw and medium 2Iin. internal, and the thickness is less than 3132in. file. It is as well to attach the brackets at this stage, but 613.A. screws and nuts, .-rain. in length and countersunk, before fitting them they should be tested for squareness are used for securing the tags connecting to the flexible by placing the right angles side by side and examining wires as well as for holding the brackets which support the tl.e edges, which now fall in line, with a straight edge. resistances and are used for attaching to the baseboard. a8

www.americanradiohistory.com,.gir..t.a M-.E.r-HS.srv-6:w..eaSa,L'.i,ätlirid.'#r. \VAp IlToo 57) MAY 77th, 7927. OIlc The Motorists' Portable. sockets. No difficulty should be experienced in making the - and To screen the valves from mechanical vibration two rings coils and valve containers ; there are no tapped holes, of " Sorbo" rubber are attached to the inside walls of the it is merely a question of accurately setting up the positions cylinders, and a pad just slightly larger than the inside for the brackets. Completed valve containers as well as finished coils can,

diameter is pressed into the base. " Sorbo " indiarubber may be purchased in the form of a bath mat. The-inside ,valls of the tube should be cleaned with glass -paper and however, be obtained made up in accordance with the tubes should a little petrol. and indiarubber solution should be applied details given here. The outer surfaces of all or carbor- to both the " Sorbo" and the cylinder and allowed to be finished smooth by rubbing down with emery nearly dry before sticking the rings in place. The bottom undum cloth. A winding space of just over i ¡in. is occu- discs are held down by slightly protruding around the rim pied by the closed circuit inductance of the aerial circuit at the bottom. The valve legs are connected across to the transformer. Actual direction of winding is immaterial, tags by several strands of fine wire forming flexible leads though the overwound primary is in the same direction. and covered with insulating tubing. To avoid the danger The ends of the winding are soldered to home -made double - plate. tf the plate socket coming into contact with the others and ended tags cut from tinned copper foil or thin tin thus burning out the filaments of the valves, it may be The aerial winding, which, by the way, is only provided thought advisable to slip pieces of rubber tubing over all so that the set can be used for long -range reception on an

13%; r---2 14.--734.1-34--r- 1 74-.1-0 Yet-2 5/ti -~-r-

I é ® is

L A ®D Í44C

5' -- 5 5 5/e-i 24

for No. 48.A. screws. front panel. Sizes of holes : A, 3,Sin. B, 732in. C, 5,32in. countersunk FIg. 3.-Drilling details of the screws. The condenser holes are carefully set D, 1,81n. countersunk for No. 1 wood screws. E, 1 81n. countersunk for No. 6B.A. out with the aid of the template supplied.

7 4144) r`---t.. . www.americanradiohistory.com 580 Wñp@Il@oo Wadi MAY rrth, 1927. The Motorists' Portable. - clamped hard against the bact of the panel by means of elevated aerial, is carried on twelve plain or grooved two " H.A.H." battery clips, one side of each clip having spacers of wood or ebonite. A rubber band round the been broken off. The screening box is next secured in spacers holds posi- them in position while winding, and the ends tion by being clamped down under the fixing screws of are the terminated on two iin. 8B.A. screws with recessed variable and fine adjustment variable condenser. The heads nutted in position at the end of one of the spacers. holes for attaching the metal strap which grips the 3 -volt The terminating points may be at the back of the coil or biassing battery should be marked off so that this part on the of side remote from the H.F. stage. Alternatively, the box can be removed and completely drilled. Eight a piece of " Paxolin " tube similar to that used in the holes are drilled in the base for screwing intervalve down to the H.F. transformer may be secured by three board, the hole in one of the corners being slightly dis- 6B.A. screws and nuts at the lower end of the closed cir- placed to hold the H.T. bridging condenser. Another hole cuit winding to give support to the turns forming the is required for screwing down the bridging condenser, as aerial circuit. If this is done the winding should consist well as another pair of holes adjoining the bridging con- of 12 turns of No. 26 D.S.C. wire, turns touching. denser terminals through which sleeving- covered No. iS The H.F. Transformer. leads can freely pass. Four holes are necessary for clamping down the valve container with sin. cheese-headed The sketch should be carefully referred to when con- 6B.A. screws, as well as two more holes for the sleeving- structing the H.F. intervalve transformer with regard to covered leads to the filament.

31%s , 3is - 3% 6% ++ p n o . . . f. ® ® ® - ® ® o o o ®+ __`-`G -421-r, a v' _ [7 C '+ + ` O i i 2 /2 $ C n$ <, , .1.,.._...1_,L_-{ v a yg +p .iv--17- i' , L (PI 6 o ' !1 ' < ` \O- 4ÈU'ì /`° U1 4 ii ; a ^ ` - y IJ-'!» ` -o 11 ® + -,3;,_-- i71 Y 24

g. -DImensional drawing showing the layout of the components on the baseboard. the positions of the screws upon which the windings are Make suie that the two sides of copper terminated. box bed The secondary winding is wound on the well down against the panel and baseboard, and see ebonite that tube, and then the " Paxolin " tube is placed in they do not become distorted when screwed in position. position. It is secured at three points, in one place by The moving plates of the tuning condenser must swing well the terminating screw of the secondary, with a small nut clear of the neutralising condensers and the grid battery. as a spacer, by the screw which holds the coils to the valve Two rin. x ein. diameter ebonite spacers are required for container, using shaped ebonite spacers, and by another attaching the panel mounted fine control neutralising con- screw and ebonite spacer. denser. These should be drilled for gin. at each end so Having first set the " Paxolin " tube in position it is that q. B.A. x tin. countersunk headed screws can he forced removed and wound with 32 turns of No. 42 D.S.C. wire into the holes. The positions for holes required in the with a tapping point at the centre turn made by twisting up ebonite plate of the condenser are obtained by marking the wire and tinning it. In removing the insulation care through, using the front panel as a template. Before must be taken to avoid damaging the wire, and in using attaching the 3 -volt grid battery, the two cells should be " Fluxite " as an aid to soldering any excess must he re- pushed out of their wrapper and a short flexible wire sol- moved before continuing to wind. The ends are wound dered across between the centre cap of the lower round cell and the terminating screws and then soldered. the zinc container of the one above. Mind that the metal Little need be said as regards the making up of the strap does not cut through the wrapper of this battery. or remaining valve containers, all constructional information one of the cells will become short- circuited. A piece of being gleaned from the drawings. The clips holding the wire is also soldered to the underside of the lower anode resistances cell and leaks should be tinned where they joining to the copper box, or alternatively a thin strip of engage, and subsequently soldered to the ends of the leaks springy brass can be attached to the base by the holding - and anode resistances. down screw in the corner near by. Assembling the Components. A connecting wire is clamped under the nut of the panel With all components to hand the process of assembly mounted neutralising condenser and brought round to a can now be commenced. First the r5 -volt grid battery is convenient position near the top of the Gambrel] condenser B IO

x . . : ,.Aì:,ta.rm soi, www.americanradiohistory.com__ _ w htir.7ivae.k--.::a.r iraGtï ra irrAx, , - - MAY 11th, 1927. Wp®Ilcft 581 Wa.-11& The Motorists' Portable. - condenser terminal to provide ready connection to the before placing the coils in position, also, a connecting tag tuning inductance. is secured to the frame connection of the tuning condenser With this done and the valve unit previously wired up as well as a long double -ended tag or wire to the lower as much as possible, the assembly of the H.F. stage can be completed. To prevent breaking the fine wire primary winding the lead which connects to the terminal of the H.T. condenser should be curved and of about No. 28 gauge. Every care must be taken in finding the correct location for the hole in the box through which the handle of the neutralising condenser protrudes. The position should be determined by measurement from several edges, and at this stage a hole can also be drilled through the top of the containing cabinet. The aerial tuning equipment should next be fitted up, and the connection between the lower end of the winding and the frame of the condenser is made by a long, narrow tag clamped down under the corner holt prior to fixing the coil in position. The lead which connects on the lower side of the fixed plates to the grid and neutralising condenser of the H.F. unit should also be run before' securing the coil. As the L.F. equipment is somewhat cramped the 15 -volt grid battery should be left in position while marking out the positions for the holes. Wiring Details. Before the wiring up can be done a seven -tag terminal strip must be made up from a piece of lain. ebonite, 51in. x ¡in., and attached a short way in on the underside of the base. The filament wiring is' carried out entirely Beneath the baseboard by joining together the tags and the holding -down screws of the valve containers. The H:T. wires also run on sleeving directly to the bridging condensers. Interstage wiring is effected by short bare leads, using the practical wiring diagram as a guide. Three battery plugs connected to short flexibles are required for connecting the L.F. valves to the grid battery. With the wiring completed and checked the leads should be connected up to the filament battery and next to the high- tension battery, and the set tested on the usual aerial. Testing Out. The H.F. valve is a P.M.5X, detec- ö3ve3e50OU tor P.MI.5B, first L.F. P.M.5, and second L.F. P.M. 2 56. With both neutralising condensers at zero setting self -oscillation should occur when thè

www.americanradiohistory.com 582 Wfipg@go WopIld MAY rrth, 1927

k o g " I II ® ®O ®

I Ii wMC Oo° 4 t 4 V n V t , 1I L i'l © O O id U '1 f r--.h a , I a .3 /¡ so ó ó oeó o t- .- iii i-L.T. IH.T.I +H.T. 3t4 LT] +H.T.ü2

6. -The arrangement of the battery leads under the baseboard. Reference letters have been added to show the continuat:cn the leads above the board. of two tuning circuits are adjusted to approximately the should be taken to the point where self -oscillation same wavelength. just The potential applied to the H.F. maintains when the tuning condensers are set valve during to positions test should be about So, to the detector roo, near in the middle of the scales, fine adjustment being a somewhat critical valve being required for maximum obtained from the neutralising condenser on the front signal strength, and 15o to the two. L.F. valves with panel. bias of 6 15 and volts. For obtaining uniform stability over the entire tuning Tune in to the local station and screw down the range the primary and neutralising windings neutralising must be condenser just to the point where heterodyn- identical in their inductance and capacity values, and as ing ceases, and this position should approximately corre- these values change with the setting of the tuning con- spond to that obtained when adjusting for the elimination denser across the secondary it follows that they should of the local signal with one of the filament pins of the be equally influenced. In the modern Hazeltine neutro- H.F. valve disconnected. The Gambrell condenser dyne arrangement a two -start winding is employed, though constructional difficulties are encountered in adopting this arrangement for amateur use. In this instance the windings being of fine wire occupy limited space and are very tightly coupled. The aims in H.F. transformer design which have been fulfilled in this instance are that resistance losses in primary and tuned circuit have been kept as low as possible by the use of a good secôndary coil and tuning condenser. The primary is of fine wire to produce a conipact low- capacity winding, its actual high frequency resistance being of small account corn-. pared with the resistance of the valve with which it is series connected. Next, that the tuned winding is as large as possible, consistent with covering the required ttining range. Thirdly, that the primary to secondary turns ratio has been adjusted to suit the impedance of the valve, limiting, as far as possible, stray capacities which might serve as a leak to Fig. 7.- Calibration of the H.F. tuning condenser. The scale can be copied or cut out and slipped behind the dial. As the condenser follows a the radio- frequency holds logarithmic law, this calibration potentials, keep- good irrespective of the size of the coil. It is only necessary to correctly set it as to ing the primary winding wavelength when tuning to the local station when the other markings will be found to near the fila- be correct ment connected end of the secondary. B I2

www.americanradiohistory.com Wp®ll@2,2, MAY zzth, 1927. Wo01111d

LIST OF FARTS Magnet Co., Ltd.). 1 Anode resistance, 50,000 ohms (Varley tube, 2Ain. internal dia., 3132in. wall (Britannia 2 ft. Ebonite Anode resistance, 100,000 ohms (Varley Magnet Co., Ltd.). Rubber and Kaniptulicon Co., Ltd.). I Cyldon condensers, 0.0003 mfd. Iog mid line (Sydney screening box (Wright & Weaire 740, High Road, 2 I Copper S. Bird & Sons). Tottenham, N.17). 2 Ethovernia dials (Burndept). I 7x24; 8tlin., with fittings (W. E. Man Ltd., Cabinet, 16 Valve pins. Windus Works, Windus Road, Stamford Hill). 1 pair Brackets, .5 1, ' S i in. (A. J. Dew). 1 panel, 7 x 24x Elec. Ebonite &in. 1._, V -type ` O " cell (Portable 24in. I Ever -Ready 1 Baseboard, 61x Light Co.). Labe, 3in. dia. X lin. long. 1 Paxclin I Ever- Ready, 3 V -type, No. 1839 cell. 5 -ohm fixed resistors (Bedford Electrical Co.). 4 Peerless I Ever -Ready, 15 V. G.B. battery. 1 (Gambrell). Neutrovernia 5 Terminals (Igranic Elec. Co., Ltd.). 1 micro -condenser (Ormond Engineering Co.). Neuirodyne lb. 24 D.S.C. green wire. 4 condensers, 2 mfd. (T.C.C.). l Fixed 3 doz. small stiff vertical grid leak clips. 1 Fixed condenser, 0.2 mfd. (T.C.C.). (T.C.C.). Battery leads. 2 Fixed condensers, 0.1 mica brass rod. mfd. No. 620 (Dubilier). Screws, nuts, I Fixed condenser, 0.0001 sponge. - 0.5 meg. Sorbo rubber 2 Grid leaks, Dumetohm, Wander plugs, etc. 132 -hen;y choke (Pye). Approximate cost of complete equip:nen.' .. t14 . 1'Je. Od.

was set up by obtaining of the set by local recep- The actual aerial on the car Having proved the connections exactly fitting one in the other be tuned in by carefully rotating two pieces of brass tube tion, distant stations can When stationary the aerial may finally controlling any tendency to Oft. and aft. in length. the dials together, giving improved signal strength. 'self -oscillate by the critical neutralising adjustment at be extended, the front of the panel. Ignition Noise. - it As the tuning condensers follow a logarithmic law Earth connection is actually picked up by deriving the dial in is possible to give the tuning scale of the second filament current from the car accumulator, making sure irrespective of the actual size of the tuning coil. The scale shown can be fitted behind the H.F. tuning condenser and adjusted to read correctly on signals from

on the case of a twelve-volt system that the three cells the earth -connected end of the battery are used.. On a leads directly to the This calibration will be found to be six -volt system it is better to run the the local station. up connection at the switch for other settings. The calibration is battery rather than to pick closely correct ripple and induction effects. practically unaffected by adjustments of the neutralising box, so as to avoid -volt H.T. batteries can be probably condenser, which does, of course, slightly alter the tuning The three 5o near the car accumulator, a five -wire cable, position of the aerial condenser. accommodated with insulating tape and passing through Test cary next be made for local station reception, using well wrapped edge of the back of the cabinet, being an earth wire and a short indoor lead connected to A2. a hole at the lower s 13

iWYLS3 - ...:.-- _ - ...... w,:rr.ï.a;..-...:.s;w.,á,A-.www.americanradiohistory.com s-y..nrvn.s:-4 ',,,rao...s.^.w,..wri'»r,ur;,>ti,:,w:Y'.iwsr...... :m.-.. _.,i.... 'Madam WOpIld. MAY 11th, 1927. The Motorists' Portable. - Tests on the Road. used for the purpose. Connection to the aerial rod is Th4 containing cabinet is built from ein. mahogany made by a thin lead passing across the top of the cabinet. with a completely removable cover and .finished The magneto, a polished sparking plugs and ignition leads may be black, as is usual in the case of car fittings. Holding found to give rise to considerable noise when attempting down clamps are made from ¡in. brass rod hooked orie to obtain at reception with the car in motion. end and threaded to take tin. Whitworth This interference wing nuts at is not due to sparking at the other. Recesses in the top the points of the cabinet locate the of the contact breaker on the mag- hooked ends. These should he nickel -plated neto, and are neither does it arise from the sparking quite inexpensive to buy. at the plugs, for with the engine running at Many interesting observations 1,5oo r.p.m. will be made journeying 5o sparks occur a second, pro- through a suburban area and listening to the local station , ducing a constant low- pitched buzz. Inter- with telephone receivers. Signal strength will be found ference, if experienced at all, will be found to to vary considerably, and from tests made it is obvious that reception is greatly improved when passing near to an aerial to which an oscillating valve set is connected and tuned to the local station. As the set is not used in an oscillating condition, a heterodyne beat note will not be set up, evidencing that it is essentially the oscillating set which is interfered with by other oscillators. When, however, a receiving set was adjusted to create a heterodyne note, that same note was picked up quite strongly by the car receiver. Vibration may cause the dials to slip away from the correct tuning position unless clamped up to give a somewhat stiff movement. There is little point in going to the trouble and experis. Fig. S.- Constructional details of the An ebonite cabinet and the aerial fixing. of building any set that is not in some way better than bracket, as shown in the photograph at the beginning of this article, should be fitted to hold the aerial previous In holding only loosely steady, though sets. this instance the writer takes the re- to allow for differences in the vibration of the body of the car and the running board. sults given by the Special Demonstration Receiver' as to its ability to bring in distant transmissions as a standard be intermittent and is principally caused by brushing and for comparison. In building this set each of the parts feeble sparking taking place through weak points in were interchanged with the equipment of the Demonstra- insulation the of the leads to the plugs. Rather than wrap- tion Receiver and tested for comparative performance ping the leads with lead foil or braiding it is better to before adopting them. renew them to ensure perfect insulation. ' Described in the issue of February 16th, 1927. Hackbridge, Surrey...... March 4IF, 4IT. 4IZ, 4JR, 4JS, 4LL, 40C, 18th to 24th. 40M, 4RW, 4RY, 4ST, 4TE, 4TI, Brazil : -SB 1AD. 1AL, lAR, 1 AV. lAD, CaIlIle, 414%I, 5AAF, 5AKY, 5Eli, 5JY, 50A, lAW, lAY, 1AJ, 1BR, 1}3Q, lis TZ. 9AFX, 9AKK, 9CAJ, 9CPM, 9DHI, 1BI, 1BL, lIC, 1ID, 2AB, 2A0, 2AR. 9DOL, 9SV, 9VZ, 9XI. Various : 2AV, 2AK, 2AX, -AQE, 7AA. Chile : -SC Extracts from ARDI, KEM, KDO, KTC, KUMT, 2AB, ZAS, Readers' 2BL, 31J. Argentine :-SA NE8JC, NE8AF. The following heard on \F1, CB8, DE3, DW4, EN8, 0A2. Logs. 20 metres Brazil : II :- -SB 5AB. Canada :- A2. HA3, 111)4, HEl. Uruguay NC lAR, 1CO, 1DJ. U.S.A.: -NII t. 10A, 1CD, 2AH, 2AK. 3AKG, 3BWT, 3CCH, 3PS, 4BI,, H. E. Smith 4DV, 4JR, 4QY. 4SIy 7EK, 9AFÌ1, (2BZW). 2AR, 2AS, 2BL, 3A0. Costa Rica e- 9AWB, 9AXB, 9BAS, 9BPM, 9CCA, (0 -v -1 Schnell) NR on 30 -36 metres. CTO. Cuba : -NQ 5BY, 8KP. 9CP, Dutch 9C_xX, 9DPM, 9ES. 9KV, 9ML. Bristol. West Indies : NL li'. Egypt :- (0 -v -1). C. R. Ponting. 1HF. French Africa. (March 20th to April 20th.) -FQ P.M. French Indo -China e -AF HVA, 1B. Haiti e- Acock's Green, Birmingham. Argentina : -SA BA1, BR7, DB2, NT DCZ. India : -AI 2KW, (February 4th DE3, D115, DR4, DW4, EN8, 2KX. to April 4th.) FC6, Italian Libya :-FI 1CW. Jamaica U.S.A.: 3AHL, 313W, HA2, HA3; Hß1, IIEi, HD4, H01. :- -NU 3AFW, NJ 2PZ.'' Mexico : -NM, 1J, 513. 9AX, 9CN, 95.1, 9BZ. Brazil: Australia : -OA 2AY, -SB 20W, 2MS, Nicaragua :-NN M3Y. New Zealand 2SA, 2SH, 2TM, 2WB. :- AAA, lAB, 1AK, lAO, lAW, lIB, 2YI, 3AM. OZ 2AE. 2B0, 2BR, 2BX, 2GA, 1BR, 2AG, 2AR, 2AX. 3ßQ, 3DC, 3ES, 3X0, 4BD, South Africa: - 5AX, 3AI, 4A A, 4AE. 4AC. South Africa :- F0 A3W, A3B, A6N, Morrocco:- 5B0, 511G, 5KN, SLF, 5WH, 6MU, FO A3B, A3W, 7CW, 7HL. A4X, ASZ, A3X. FM 8MB, ERGS, 8PMR, 8VX, OCRB. Belgian Congo : -CBF2. A6N, 3SR. Syria 8LHA. Brazil: -SB 1AF, :-AR Uru- Argentina : -SA CW4, HD4. Russia :- lAJ, LAN, 1AO, : guay -SU -1AM, 1BU, 1CD, 1CG, EU 05RA, 0811A, 09RA, 1VZ, 1UK. lAR, JAW. IBA, 1BR, 1BK, 1BL, 1CX, 1NA, 10A, 2AK, 2BC. U.S.A.: Canada : -NC 1BR, lAD, 3JM. India 1BO, 1BU, 1ßW, 1BY, 1CA, 1CB, NU 3ABL 3ACM, - :- 3ADL, 3AHP, AI DCR. Uruguay : -SU 2AK. Syria 1CK, 1Iß, 11C, lID, 2AA, 2AG, 2AJ, 3AJH, 3AKS, 3AUV, :- 3BCD, 3BQZ, AR 8LHA. : 2AL, 2AR, 2AU, 2AV, 2AX, 2EG, Australia -OA 31)C, 5WH. 3CBV, 3CDS, 3CE, 3CJN, 3CP, 3DQ, New Zealand: -OZ 2AC, 2BX, 3AC, 2IB, 2IG, 3AC, 5AA, 7AA, 7AB, 3EF, 3FZ, 3GP, 3IU, 3LD, 3LQ, 4AM. Jamaica : -NJ 2PZ. Abyssinia AUX. Canada : -NC lAD, 1BR. :- 3LU, 30W, 3QF, 3QL, 3QW, 311E, FA FAA, FA2. Tripoli:-FI 1CW, 2AX, 2BE, 2DO, 2FG, 3BT, 3FC, 3SK, 3S.H, 3SJ, 3TI, 3VF, 4BK, 1TA. Iraq : -AQ 1DH. 3NJ, 31VAB, 3X9. Chile : -SC 2AH, 4BN, 4CB, 4CK, 4DB, 4EF, 4HZ, (0 -v -1 Reinartz.) L. Davis, Jun. B r4

. . . . - ,L.:sR:.u:ietc.-v.aF..:il`.:;..ttr'riia,.v:-3shìa.lti4..,afiuii:.e--'lavi'd3lQ.:.i:P.2a1G+-.bF.--www.americanradiohistory.com - -- Vlimlls@o 565 MAY 1itTi, 1927. WOpIldI

imnnnnumml muunnluunnnnnnnlllníltmumMMmamMmnnMUmuMMmMmnnmmIhumiilïülimimEnnnMmimmnwñuniuïn

A Section Mainly for the New Reader. in NEUTRALISING. .' All- Wave Four " receiver.` 'file that perfect contacts are essential an H.F. transformer, so both pins The mistaken idea that the balanc- method of construction shown in the in and sockets should be very carefully ing or neutralising of a receiver hav- accompanying diagram results transformers as effective as the ori- chosen; the so- called " banana " ing a single H.F. amplifying valve may be still ginals. 1Vhile they are easier to wind plugs, with spring sides, is a difficult matter seems to be better than the more precautions by mechanical means, no other ad- found to be prevalent. \Vhile special split pins. taken when setting up a vantages are suggested. common have to be In the illustration the lettering amplifier, the balancing of A Paxolin cylinder, 31-in. long and twO -stage each pin indicates the ulti- stage calls for no elaborate Sin. in diameter, is fitted with an against a single dia- mate connections of the correspond- procedure. ebonite ring having an external into one ing sockets. To carry out the operation, the meter suitable for insertion 0000 condenser is set at mini- end, and an internal diameter of neutralising tags MECHANICAL VIBRATION. mum capacity, and the tuning con - rain. Six pins, Avith soldering equally is experienced with densers are rotated until the circuits (one is " dead "), are spaced When trouble An ebonite the cause may some- come into resonance. If everything on a diameter of 2ÿin. L.F. instability as a conve- to the transmission of is in order, the H.F. valve Avill now cross -bar, which serves times he traced coils, from the loud- oscillate violently, as will be indi- nient handle when changing mechanical vibrations other end. receiver. This is par - cated by the production of a rushing should he fitted to the speaker to the to be the case when in the telephones, or a hetero- ticularly likely noise are on the same dyne whistle if the set happens to be both instruments of course, the remedy is tuned to a station. The balancing table, and, The effect is comparable to condenser should now be rotated until obvious. of howling which is pro- this oscillation ceases. The next step that form by the action of sound waves to readjust both tuning capacities duced is loud- speaker on the valves. and then to re- balance if necessary. from the 0 0 0 C The above procedure may he repeated again if the set is not per- THE SELECTIVITY OF AN H.F. fectly stable. It is, of course, easiest AMPLIFIER. signals, to adjust when listening to One of the most certain and easiest as under these conditions the presence methods of improving the selectivity detected. of oscillation is more easily of a receiver with the modern type of to carry out the opera- It is as well high - frequency transformer with of balancing a receiver with the and air- spaced tion ` Litz " secondary H.F. condenser set at approxi- primary and neutralising windings is capacity ; mately half its maximum to use an H.F. amplifier, a valve this way an adjustment made in having a higher impedance than that whole should hold good over the for which the transformer is de- set is tuning range provided the signed. Generally speaking, an im- correctly designed. pedance greatly in excess of 50,000 0 0 0 o An interchangeable H.F. transformer. or 6o,000 ohms is not recommended, it should be pointed out that the "ALL-WAVE FOUR " ebonite base, carrying but A suitable published ligures of 70,000 or 8o,oca- TRANSFORMERS. sockets, must, of course, be six plug ohms relating to a number of valve: has access to It should be remembered The amateur who provided. at present on the market may he a lathe may prefer to make his by in- April 27th, 1927. '.iron ht down considerably own formers for the coils used in the ' The Wireless 'World,

TS l .5

www.americanradiohistory.comyc.strw.i pe@OR, 586 MAY Was lid zztth, 2927. creasing the H.T. voltage applied to their makers' instructions to the effect obtain the working life per charge, it slightly more than the usual 120 that no grid bias is required should is merely necessary to divide volts. the The valve should have a high be observed. ampere -hour capacity of magnification 0000 the battery factor, of some 3o or by the total current consumed. The ço ; a number of suitable patterns, ACCUMULATOR CHARGE result will be in hours. which are usually DURATION. sold for resistance Certain batteries are rated in " ig- coupling, are on the market. It is an easy matter to ascertain nition ampere -hours "; in this case ' Great care must be taken not to the length of time which a given accu- the result as given by the above cal- apply an excessive grid -bias to these mulator should last .on a single culation must be divided by two. high ; impedance valves certain types charge, provided the current con- Fortunately, this misleading method have a special electrode construction sumed by the valve filaments and the of rating (as far as wireless purposes giving a "delayed" grid current, and capacity of the battery is known. To are concerned) is now almost obsolete.

DISSECTED DIAGRAMS. The present series of diagrams is intended to show progressively, and in an easily under- standable titanner, the various Practical Points in Design and points to which special attention should be paid in the design of typical wireless receivers, and at the sanie time to assist the beginner in mastering Construction. the art of reading circuit diagrams. If components and values are carefully chosen, the No. 70 (a). -A Single -valve and single -valve reflex receiver shown below is capable of operating a loud- speaker. The Crystal Reflex. data given apply to the normal broadcast waveband, on which all reflex receivers work (Concluded from last week's issue.) at their best.

^77 '0, O O Op p CC> -r b b _ , O b ó O C3 o - C3 = ' ó C3 z ó ó U o O i o 0 0ó ° T i z. rJ . . ' É Îr pO .rC á e oC t Oa d J C4 J. :+'- .---. , 1 = i 1 r-i' + + g IO H.T. H.T. + T 2 TC2 H.T. 0 1 1O q`O ,_._o G B i - G B. _ + G.B. L T. L.T. L_T. 1 T - { = (4) (5) (0/ L. r. negative is earthed ana the crystal is --the L.1'. negative lead is common to --may be improved by the addition connected across a part of the H.N. trans- part of this circuit, and is at the low- poten- of former secondary. an H.F. choke and a by-pass condenser C; The rectified output is tial end. The insertion of telephones, with as shown above. Willie not essential, this passed through the primary of the L.F. an H.F. by -pass condenser, completes the modification generally makes for easier transformer. Note that -- receiver, which, however- and more stable operation. PIHEL connection of the crystal to a perikon combination is often tapped A capacity of o.00r mfd. is suit- the transformer secondary is a to the centre point. In practice, a able for the by -pass condenser C4. matter of great importance in a re- numlLr ) of temporary tappings should The H.F. stroke may be of a com- ceiver of this description ; unfortu- be made and the final connection de- mercial pattern, with an inductance nately, however, it is impossible to cided upon as the result of an actual of some 40,000 or 50,000 micro - lay down hard -arid -fast rules, as trial. henries ; it must be kept clear of the everything depends on the effective re- It will be noticed that the lower other H.F. coils, and should be of sistance of the crystal. The lower end of the H.F. transformer second- small diameter. The condenser C5, this resistance the fewer should be ary is joined to L.T. negative; this which is, in effect, across the L.F. ti.e number of turns across which it means that the low -potential part of transformer primary, should be is connected. A low- resistance speci- the H.F. circuit is definitely " tied chosen in accordance with the recom- men of galena may be joined to per- down " to earth potential, with a mendation made by the makers of the haps the twentieth turn above the considerable improvement in the latter component; a capacity of from eat the I end of the secondary, while stability of the receiver. 0.0003 to o.00r is generally suitable. s 16

ìt-,www.americanradiohistory.com .._.ro_ú: ,:,sa .èaa..as.:.ans.s«9áw-.:n»:ae uu,inii 1p®Il@gg l/AY Iltlt, 1927. WóIlc The COMPANY NA' IONAL 1 111) ROADCASTING Amen I1eJo Quality of American Broadcasting. How Unified Control is Rapidly Raising the By A. DI NSDALE. these stations with programmes of - object is to pro\ ide N November 15th, i926, tige National Broadcast to such other broad- national scope and to distribute them ing Company made its formal bow over the air them. We shall, casting stations as may wish to take to the great radio audience of the United States. of programmes in however, endeavour to avoid duplication The formation of the company marks a logical step in the same territory." of broadcasting in the country of origin or Mr. Aylesworth re- the evolution The writer was privileged to meet we know it to -day. and was fortu- the art as while travelling on the same boat, of the company are to provide a truly cently at first hand and in The objects nate in being able to discuss matters national broadcasting service which will bring within easy wherever securing the special message range of every inhabitant of the United States, readers printedl iiclesron the situated, the very best page. programmes it is possible Mr. Aylesworth further MERLIN H. AYLESWORTH, to A Special Message from the National produce. Company, to British described Owen D. Young, a President of the National Broadcasting Broadcasting Company's member of the National Broadcast Listeners. position by explaining our Broadcasting Company's listeners are already very familiar with that, from a broadcasting re- British broadcast WEAF, Advisory Council, said American broadcasting, as broadcast through Stations point of view, the N.B.C. These are the four high-powered cently : " It is quite ap- WJZ, 1VGY, and KDKA. is to the local broadcast- National Broadcasting Company parent that to a large stations in the networks of the ing station what the Asso- often heard by British listeners. broadcasting muse that are the most is to the local degree accepted our invitation to come over to ciated Press in Sir John Reith has and news he national in scope the inauguration of our new building newspaper, from a New York to attend with order to give listeners the I hope then to have an opportunity to discuss distribution point of view. studios, and Broadcasting kind of service they Sir John ways and means whereby the National The company has also Corporation may proceed should have. If the Company and the British Broadcasting made arrangements with to an interchange of programmes. National Broadcasting institutions the leading electrical firms this can be arranged, and the engineers of both Company can provide the If we hope to make still further can overcome the technical difficulties involved, to prosecute highest quality of pro- Broadcasting as familiar to American listeners throughout their researches into radio British American broadcasting grammes which exists in the country, by means of our networks, as problems so that they may no is to British listeners. of the the United States, of great he able to make use would seem to be no reason why some message matter where the point of There Britain, which latest technical develop- importance, either from America or from Great origin may be, and can countries, should not would be of interest to the people of both ments. of the facilities offered disseminate it completely be freely exchanged through the medium throughout the country so by both broadcasting organisations. Radio Advertising -the that everyone can hear it, American Attitude. no matter where he may And how is this he, and if it can do this ideal system to be paid - without charge upon the for? Who will provide listener and without un- the super -excellent pro- fair discrimination be- grammes, since there is to tween those fairly entitled he no tax or other Obliga- to use the facilities, it tion upon the listener? will, in my judgment, lies in indirect advertising. In America, service to the American people.' The answer have rendered a great advertising has become an exact science Hall Aylesworth, President of the National as is well known, Merlin an art. Commercial and business interests will Broadcasting Company, put it in another way in his open- -almost He eagerly seize upon every possible medium which can be ing remarks at the company's inaugural programme. name and line owns only used to make known to the public their : " The National Broadcasting Company said of business. The American public is used to this, and one station, and that is WEAF in New York City. It still not mind the inclusion of 1- Broadcasting as will manage stations WJZ in New York and WRC in does medium, especially when it gets something in Washington. Using stations WEAF and WJZ as centres another fine programme. we are able to provide at least two net - return -a of distribution, on their side, have discovered that associated stations throughout the United States The advertisers, works of offers an unrivalled medium for reaching, and so ensure a wide diversification of programmes. Our broadcasting B 17

www.americanradiohistory.com """wwK 588 WAp@Il200 MAY 11th, 1927. The National Broadcasting Company. - Before the formation of the N.B.C., Station in America, some six million WEAF, homes, in a manner that New York, was owned and operated by the no other medium could possibly American do. For this reason Telephone and Telegraph Co., and WJZ was owned and Frank A. Arnold, Director of Development operated National of the by the Radio Corporation of America. Both Broadcasting Co., says that " commercial broadcasting these stations were linked up with a limited number of is the fourth dimension of advertising," the other stations in other three dimensions States, and these networks were known being the newspapers, magazines and as the Red and Blue chains. posters, signs, etc. To In taking over the two New York stations the N.B.C. -day, therefore, an American advertiser who wishes retained to use the Red and Blue chains, and these have formed the broadcasting medium engages artists and a suit- the nucleus able broadcasting from which has grown a nation -wide network station and broadcasts what is known of " S.B. " on a gigantic as the " sponsored programme." scale, with alternative pro- His name (and some- grammes available almost throughout. By that is meant times that of his goods) will be mentioned as being re- that an alternative programme of the highest quality, but

Fig. 1. -Land -lines used for the transmission of President Coolidge s address, Washington's Birthday, February 22nd, 1927, broadcast by the National Broadcasting Company through its 42 associated stations. sponsible for giving the radio audience an opportunity to of different character, is available. There hear so- and -so. are also available to most listeners, of course, the lesser When this plan was low- powered first tried out there was consider- stations, providing more or less inferior programmes. able outcry against it, for the obviousness and sometimes The N.B.E. do not in any way desire to the blatancy of the announcement usurp a was unpalatable to the monopoly of broadcasting. They do not desire.to elimi- listeners. To -day such announcements are made with nate the small broadcaster. much greater On the contrary they invite unobtrusiveness and create no offence. As competition. The small broadcaster has Mr. Arnold puts it, his place. He " No one thinks less of Grand Opera cannot afford to supply a high -grade programme, but because it has its guarantors." there are thousands of listeners who desire to listen to the class of matter he has to purvey. The N.B.C. do not wish Extending the Networks. to broadcast such matter, so that the two interests cannot clash, and both may Over $2,000,000 live without there being any question will be expended for broadcasting of a monopoly. talent alone in 1927 by commercial and business interests It would scarcely sponsoring programmes be possible for one organisation to over the National Broadcasting hold a monopoly of Company's networks. broadcasting in a country so vast as America, which has twice the area of Europe. The B r8

- ._* -.a s www.americanradiohistory.com;dc '---iCi;lnaiiCti+ld'diYi - Nw'1,paoo 5899 .ilAl' /ilk, 1927. Wolflic1

The National Broadcasting Corn- pany. - distance from New York to San Francisco is about equal to that between the west coast of Ireland and Moscow. It was at first anticipated that the task of widely extending the Red and Blue chains would take many months, but the country -wide demand for the opportunity to hear the very best artists in every sphere speeded up the process considerably. To date, over too stations have applied for the network service, which, starting from 3 New York, extends north to MiCito NICHES 7 the Canadian border, south IN FOOTLIGHT to Florida and Texas, and 02CH E5T StA MICROPHONES vest to the Pacific coast from PIT Seattle in the north to Los Angeles in the south. How the Chains are Operated. To explain the operation f the chains, let us consider " from tam Fig. 2.- Arrangemint of microphones for broadcastinit a performance of Faust the Red chain. which uses Chicago Civic Opera House. Station WEAF as the key suit. " special circuits " which are user I station. 'l'he complete network is shown in Fig. i, and 'Prue, these for linking up the broadcasting stations are telephone cir- covers a total line distance of some Jo,000 miles. The been cleared of all other traffic and stations are, of course. linked up by telephone lines, and cuits, but they have to carry the. wide range of frequencies when the entire chain is in operation 400 engineers are specially prepared it. Half of -this number are tele- involved in broadcasting. required to operate telephone circuit and half radio engineers. The ordinary American long -distance phone engineers or five telephone mes- up the special circuits, testing them and may carry at the same time four Connecting messages. Each of sure they are kept free from noise and in sages, besides numerous telegraph making that so that it can- constant connection with each other occupies the attention these is transmitted on a special frequency not interfere with any of the others, but a special circuit f the telephone engineers. The term ' ` special circuit " stations can carry only the broad - .hould not be confused with the ordinary telephone eir- between broadcasting cast transmissions. It must he equipped with special repeáters or valve .amplifiers, since the ordinary repeaters used in telephone conin unication are not designed to cover at one time such a wide range of frequencies. The cut-off of the ordinary long -distance telephone line and its associated repeaters is at about 2,50o or 3,000 cycles. whereas a circuit for broadcasting must carry frequencies up to about 8,000 cycles. Starting from the studio of \VEAF, programmes are first carried by special telephone circuits to the Bell System Building. at 24, Walker Street, New York, where ;he central exchange is situated. At the same time they are also sent by wire to the Bell Telephone Laboratory, at .t63, \Vest Street, on top of which building \VEAF's aerial is suspended. From Walker Street a huge network of lines radiates, covering the entire country, and the outgoing programmes are put on to the special lines of the Red chain. The ramifications of these lines can best be followed by refer- Announcer's control panel at the National Broadcasting Com- pany's Station, WEAF. This instrument is situated In the studio ence to the map in Fig. i. reel(.

B 19

www.americanradiohistory.com 590 Wfipamo WodIld MAY Illii, 1927. The National Broadcasting Company. - On New Year's At junction points Day listeners in the north -eastern sec- ii here two or more circuits join, tion of the and at other positions country, in the grip of the intense cold of along the line, valve amplifiers are midwinter, were treated used to amplify the to a detailed report of a foot- signals travelling over the circuits, in ball match being played order to make sure that practically in California, where the the same signal announcer sat in the open in his shirt sleeves. strength is delivered to each of the stations which are broadcasting the p; ogramrne. Grand Opera. In addition to the special telephone circuits on which The first nation -wide transmission of Grand the programme is carried, another circuit paralleling the Opera from the stage was accomplished by the first is used to keep all stations in the chain in constant N.B.C. on January 2zst of this year in a manner which attracted communication with each other by telegraph. In this the manner, the condition attention of the whole country, not only as an artistic of the various circuits is checked at achievement regular intervals to make but as a technical achievement as well. On sure that every word and every this occasion note of the programme which there came to millions of homes, for the is originating at WEAF is first reaching all of the stations time, not only the arias of a great opera, bht the in the chain with good volume actual feel and without extraneous noise. and atmosphere of the Civic Auditorium in Chicago, where a distinguished audience Programme Material. sat enraptured at a performance of " Faust." Of this, more anon. Turning now to the programme side of the National On February 22nd forty -two stations, as shown on -Broadcasting Company's activities, the a review of the pro- map, broadcast President Coolidge's address on the occa- gramme's presented during the few short months of the sion of Washington's company's birthday. It is estimated that in existence reveals a surprisingly large number the United States alone of outstanding twenty -five million people heard features. this address, which was Commencing also picked up on the short wave with the company's inaugural programme, and rebroadcast by the B.B.C. we find such internationally known features as the New Besides this list of leading features, there is York Symphony Orchestra; Harold a list made Bauer, the distin- up of 14 famous operatic stars, 15 great concert stars, guished concert pianist ; Mary Garden, the opera star ; four leading orchestras, nine stage stars, and many others and the inimitable Will Rogers. A remarkable feature who have broadcast. of this broadcast is that Mary Garden's voice was Amongst the material broadcast are rq. recitals " picked up " from Chicago, and and Will Rogers spoke from tabloid operatic performances, seven light operas, Independence, Kansas, and anal yet the entire programme four dramatic performances. 'Three of _America's lead- went through without a hitch, perfectly timed. ing bands and six of her leading religious lights have ileo appeared before the micro phones of the Red and Blue chains. Other matter includes labour discussions, addresses on governmental and political education, general education, discussions on current events, outstanding sporting events, agricultural courses and information and popular orchestral music, all broadcast by persons who are acknowledged leaders in their particular sphere.

How " Faust " was Broad- cast. The broadcasting of " Faust " from Chicago Civic Opera House was an

outstanding t e c h n i c a 1 achievement in itself, for as many as fifteen microphones in parallel had to be used. Such a large number had never been handled before, and some clever work had to be done to arrive at the correct positions and 1ni u: control be: rd at Ftation EAF, 195, Brcadway, also in connection with foreground is New York. The telegraph sounder in the the for maintaining communication with other stations in the N.B.C. chain. controls, or " mixing

Ei 20

www.americanradiohistory.com ritfi, 1927. Wpigha 591 MAY WCAIlt The National Broadcasting Company. - panels ' as they are galled. For a week before the performance engineers were busily engaged installing their apparatus and making trials during the rehearsals. To pick up the sounds from the stage two microphones were placed in the flies, and seven along the footlights. Three microphones in the orchestra pit picked up the orchestra, whilst two more, hung high up over the audience, served to pick up the incidental noises amongst the audience which go to make up the " feel " and atmosphere of a great auditorium. These sanie two microphones also served to provide an echo effect by picking up sounds from the a fraction of a second stage Reception room at one of the N.B.C. Stations. later than the footlights microphones. Vork's latest picture house, the Roxy Theatre. This is shown diagrammaticall3 in Fig. z. The arrangement the largest in the world, and superlative in trials to find the best positions for theatre is During the initial in everything appertaining to it. trained musicians joined the engineers every degree the microphones, building of it a large space was left empty for means of a monitoring system, to the In the in listening, by broadcasting purposes, and the N.B.C. engineers were and they offered expert advice on the musical results, given a free hand to fill it. side of the effects. moving picture entertainment, the the problem of linking Besides giving a Musicians also helped with variety turns, and every Monday and in their proper control at Roxy Theatre provides microphones into groups entertainment from the theatre is broad- This panel served as the central night a variety the " mixing panel." cast through WJr.. point for all the groups of microphones, and it control For this purpose the studio was constructed on the fifth was here that all the microphone outputs were added floor of the building, far enough above street level to sent out over the line as the complete together and ensure that no interference should be experienced from broadcast. street noises. A unique feature is the visitors' gallery. 01niously, careful handling was necessary, or certain It is sound- proof, and shut off from the studio by a glass in the orchestra, or parts of the perform - instruments window through which visitors can watch the perform- easily have been over -accentuated. That a atice, could ance in the studio below whilst listening to it as repro- was obtained throughout, to the complete perfect balance by a loud- speaker. even amazement, of musical critics duced satisfaction, and Having been given an entirely free hated the engineers, over the country, speaks well for the careful listening all working in conjunction with the architects, were able to expert work of the controlling engineers and and design a studio with as nearly perfect acoustical proper- musicians. ties as modern experimentation in the study of sound the occasion of this broadcast, only twenty -six On echoes can at the present time produce, and a system been linked up in the N.B.C.'s network. It and stations had of control apparatus for relaying the programme to the not until the occasion of President Coolidge's address was broadcasting station which is a model of convenience and the chain was extended to forty -two stations, as shown that efficiency. in Fig. r. The studio is constructed) without pillars or breaks The Latest in Studio Design. in the wall surfaces which might destroy its acoustical corner of the room, including those The N.B.C.'s engineers recently had an opportunity properties, and every the side walls and the ceiling, is exactly a 90- to make use of all their accumulated knowledge of studio between design when they were called in to design one for New degree angle. B 2I

www.americanradiohistory.com Wilpd2AT 592 Weal MAY zith, ¡927. The National Broadcasting Company. - of lengths in the decoration and lighting effects of their Through the middle of the ceiling a square shaft runs new studios. to the organ loft, which contains a specially designed Thy gaudily decorated and brilliantly, even garishly, organ used for broadcasting only. Above the surface of lighted studio may be expected to suit some artists; the ceiling, in others the loft, the four valls of this shaft may prefer a quiet drawing -room effect; whilst consist of shutters, any still of which can be opened to any another type of artist may prefer a sombrely decorated, degree, controlling the volume of the organ music which dimly lit library. can enter the studio and reach the microphone, as well These, it is understood, are the general lines as allowing emphasis upon to be placed upon any desired por- which the N.B.C. are working, and the fruition of their tion of the music. The organ is played from a manual plans, and the results of their execution, will be awaited in the studio directly below the loft. with interest. When further particulars become avail- At regular intervals round the walls of the studio are able, the writer hopes to give a detailed description of microphone outlets connected to the control board. Since these studios, and the results obtained by their use. many different kinds of music are to be broadcast from the studio, including the work of a large chorus, many Educational Features. more microphone outlets have been provided than in most Another plan under consideration has to do with adult remote -control studios. education. Just as now, under the present system of Special lighting arrangements have been made, with a broadcast entertainment in America, that entertainment is view to illuminating every portion of the studio without virtually endowed, so the N.B.C. hope soon to establish producing any objectionable glare. Special attention has an endowed " University of the Air." also been bestowed upon the question of ventilation, a This plan is based on the idea that it should be just point overlooked in a great many studios. as easy for philanthropically inclined individuals or in- From his place at the control panel the control en- stitutions to endow a University of the Air " as it is to gineer can see the whole of the studio through a glass endow an ordinary university or other institution of panel, and a complete system of signal lights enables learning. him to communicate with the artists. Also seated in Many people may be somewhat dubious as to the out- the control room with the engineer will be one of the come of such an experiment, but at least the results will assistant conductors of the theatre, who will assist the be awaited with considerable interest by both " high - engineer in his control work so as to ensure a correct brows " and " lon brows." musical balance.

Future Plans of the N.B.C. Amongst the future plans of the National Broadcasting Company, perhaps one of the most important is the building of a new WEAF. This decision was made when the station was sold by the American 'Telephone and Tele- graph Company to the N.B.C., the reason given being that the station, as at present located, interferes with research work being carried on at the Bell Telephone Laboratories, on top of which WEAF is situated. The new station is to be built outside the city limits, on Long Island, and it will have a power of so kW. It is expected to be ready some time this autumn, and it will incorporate all the latest principles of construction and equipment. Some of America's foremost engineers are engaged upon the work. By placing the station out in the country the screening effect of tall steel -framed buildings will he eliminated, and this, coupled with the great increase in power over that at present employed, will give the station a vastly increased range. About June ist next the N.B.C. expect to move into their new office building, which is at present under construction at 711, Fifth Avenue, New York. This building, besides housing the executive and engineering staffs, will also contain all the studios. In connection with these new studios an interesting experiment is to be tried. It has been argued by many that a temperamental artist cannot be expected to give of his or her best under conditions which are not har- monious to the AUSTRALIAN BEAM SERVICE. Telegraphic instruments artist's particular temperament. Bearing at the Central Radio Office, London, through which messages this in mind, therefore, the N.B.C. are going to anheard- are sent to the beam transmitter at Grimsby and received from the corresponding station at Skegness. B 2 2

_. -. nlr'-*-X'www.americanradiohistory.com aa:. .4w-.Ñr S WApSll@girg MAY rrth, 1927. W`MIlCI 593

--_ , UIiIÌIi 41N0 News of the Week in Brief Review.

BOOMING WIRELESS IN ITALY. MORE RECEIVING LICENCES. TOC H WIRELESS SET. To " popularise " wireless reception, The receiving- licences issued at the A wireless installation subscribed for the Italian Government proposes to end of March numbered 2,253,845, as by the public through the Wood Green exact a small radio tax from all house- compared will]. 2,235,000 at the end of Group of Toc H has been handed over to holders, whether they listen or not. February. A year ago the licence figure the North Middlesex Hospital, Edmon- Signor Mussolini is reported to have had just passed the two million mark. ton, by Sir Arthur Stanley. planned su Italian " Daventry." 0000 0 0 0 0 0000 AERIALS IN THE FATHERLAND. ACADEMY PORTRAIT OF LIFEBOAT INSTITUTION'S WIRELESS In Germany, according to a Court DR. FLEMING. EXPERIMENT. ruling, a tenant is not necessarily entitled A portrait of Dr. J. A. Fleming, The uew motor lifeboat provided for to erect a wireless aerial against his by Sir William Orpen, R.A., is Rosslare Harbour, County Wexford, by landlord's wishes. The question must exhibited at the Royal Academy. in the Royal National Lifeboat Institution. depend upon the terms of the lease. Room XI. This portrait was commis- is the first of the Institution's boats to 0000 sioner) by friends and the old students be provided with a wireless transmitter MARCONI'S AS BOLIVIAN C.P.O. of Dr. Fleming for presentation to Uni- and receiver. London, a memorial 0000 Under a contract with the Bolivian versity College, as Government, Marconi's Wireless Tele- of his 42 years' tenure of the Chair of RADIOTELEPHONY AT R.A.F. Electric-al Engineering in the College. It DISPLAY. graph Co., Ltd., has taken over the control and operation of the entire postal, is considered to be an excellent likeness. At the eighth Royal Air Force Dis- telegraph and wireless services of Bolivia 0000 to play, be held at Hendon on Saturday. for a period of 20 years. P.M.G. ON TRAMCAR INTERFERENCE. 2nd, air drill by radiotelephony will July The Marconi Company entered into a Sound technical advice regarding the again occupy a prominent place on Ilk' similar arrangement with the Permian elimination of interference from tram- programme. It is understood that the Government in 1921 with highly satisfac- cars is contained in a letter sent by Sir wireless nranceuvres will be conducted by tory results. W. Mitchell- Thomson, 11.P., the 'Post- No. 41 fighter squadron in place of Nu. 25 squadron, which has performed the task for the last two years. 0000 1,000 -METRE FOG BEACON. 'The wireless beacon fog signal at Round Island Lighthouse, iu the Isles of Scilly, will be brought into operation on May 20th. In foggy weather it will transmit the call sign " GGG " re- peatedly for 48 seconds with intervals of three minutes, using a wavelength of 1,000 metres. 0000 " RED RUFUS." Unpleasantness arising out of' an " oscillation " problem had a sequel at the Bradford Police Court last week, when Mr. W. Marsden was summoned by his neighbour, Mr. S. Brown, for threats. Mr. Brown complained that on Easter Monday the defendant had banged at his door shouting : " I will ram this knife in your back, you oscillating . I will swing for you." The defendant's wife admitted banging on the wall and de- manding that " Red Rufus " (as she had nicknamed the complainant) should " give over oscillating." Marsden was bound over for six HOW TO MEET A HEAT WAVE. -A suitably equipped motor -boat, with wireless months and ordered to pay 4s. costs. receiver and cage aerial, photographed last week on the Thames near Kingston. B 25

www.americanradiohistory.com 594 NAY Iltk, 1927. WolTTic1 master -General, to Mr. W. J. Baker, LISTEN FOR KHABAROVSK. The Osram Bulletin.

M.P. for East Bristol, in response to an The Russian wireless - station at The April number of the Osram G.E.C. appeal by -Bristol listeners who are Khabarovsk. which is one of a chain of Bulletin, just received, contains an in- troubled by this form of annoyance. about a dozen stations in Eastern Siberia, teresting article on the three new Osram The P.M.G. recommends the modification is being completely modernised by the\ 4 -volt " steep slope " valves besides of sets to improve their selectivity and, Westinghouse Electric and Manufactur- pages devoted to the K.L.1 valve and the alternatively, the fitting of suitable ing Company of America, which is sup- Gecophone power transformer specially chokes and condensers in connection with plying new valve equipment in place of designed for feeding current at the correct a counterpoise earth instead of the usual the existing spark apparatus. voltage from the mains to the heater direct earth. The Wireless World understands that element. With regard to suggestions that the Mr. Carl J. Madsen, the company's engi- interference should be combated by sub- neer, who is installing the plant, is a short -wave enthusiast, and has taken with him his short -wave transmitter. On FORTHCOMING EVENTS. or about July 19th Mr. Madsen will WEDNESDAY, MAY 11th. attempt to communicate with KDKA. Tottenham Wireless Society. -At 8 p.m. transmitting on 63 metres. At 10, Bruce Grove. Demonstration of ' Neutrosonic- Seven " Receiver, by Messrs. The Igranic Electric Co., Ltd. Muswell ¡till awd District Radio Society. - At 8 p.m.. At Tollin.gton School, Tether- down, N.10. Demonstration: " The NEWS FROM THE Uses of the Waremeter," by Mr. C. Jordan (G6JD). North Middlesex Wireless Club. -At 8 TRADE. p.m. At Shaftesbury Hall,'Bomea Park. Lecture: "High Frequency Amplifico- tion," by Mr. W. Gartland. The SUNDAY, MAY 18th. Hart "Purse." Tottenham Wireless Society.-Field Daft A useful novelty has on the River Lea at Broxbourne, with advertisement transmission between various expert. been issued by the Hart Accumulator mental stations. Co., Ltd., Stratford, London, E.15, in MONDAY, MAY 16th. the form of a colourable imitation of an Croydon Wireless and Physical Society. - At 8 p.m. At 128a, George Street. imitation crocodile leather purse contain- Talk on "Methods of Amplification and ing a folder giving details of Hart bat- Reproduction," by Mr. W. E. Ansel ¡. teries for all wireless circuits. WEDNESDAY, MAY 18th. Institution of Electrical Engineers, Wire- 0 0 0 0 less Section. -At 6 p.m. At the Institu- tion, Savoy Place, W.C.2. Lecture: " A A Battery Deal. Wireless Works Laboratory," by Mr. P. K. Turner. The General Radio Company, Ltd., 235, Regent Street, W.1, has purchased Radiobats, Ltd , securing control of that stituting carbon rollers for the metal company's high- tension factory, which has rollers in the trolley arms and by fitting an output of 7,500 cells per week. 0000 condensers of 30 microfarads capacity LOUD- SPEAKERS ON THE FRONT. across the overhead and earth contacts, Wireless in Southend Charity Effort. In connection with an appeal for the local Sir William states that considerable ex- hospital, a Southend wireless firm in- In connection with an endeavour to stalled its own broadcast and public perimental work would be necessary raise £10.000 for the addition of a address system on the promenade. before these remedies could be adopted. children's' wing to the Southend New 0000 General Hospital, an enterprising effort to Supplying Fifty Loud -speakers. gaits publicity for the scheme was recently One of the largat hospital receiving AIRCRAFT WIRELESS. made by .the local wireless firm of S. H. sets in existence is on view at Messrs. At the opening session of the Inter- Davis and Son. A public address system Iloldron's, Ltd., of Rye Lane, Peckham, national Commission of Air Navigation, was installed on the front by the firm's S.E. Built for installation in St. held in London last week, it was recom- engineers and a mayoral speech was Giles' Hospital, Camberwell, under 7'he mended that all passenger airplanes broadcast in addition to numerous Doily .Vt,y scheme, the set contains 12 should carry a wireless operator com- musical items from Daventry. A sum of valves, and will feed 1,100 pairs of head - petent to transmit by wireless telegraphy. £200 tea, (.ole-led. phones and fifty loud -speakers.

EMPIRE BROADCASTING. The need for the establishment of a short -wave broadcasting service to the Dominions has been frequently emphasised in THE WIRELESS WORLD, and formed the topic of discussion in our Editorials of April 27th and May 4th. Readers may be interested in the following extract from a London evening paper, in which our proposals are strongly supported. r g HE topic of Empire broadcasting, the possibility of such a development. High power stations are the fashion at that is, transmitting direct from the Perhaps one of the best performances, the moment, but, so we are assured, will Mother Country to the Dominions which gives much weight to the argu- work on the broadcast wave band of about and the Colonies, has again been made the ments of the advocates of an Empire 400 metres, if and when erected. subject of discussion, and the B.B.C. are service, was that recently accomplished by Would it be too much to expect a little being urged to make some effort in this a. Dutch station, which had its programme experimenting on the lower bánd, so direction. received at Sydney and rebroadcast to that Britisbers all over the world could So far the best achievements have been Australian listeners. listen? made on the ultra -short waves round If a foreign station can successfnilly If Australia will relay a transmission about 20 -30 metres, and the majority of transmit to the Antipodes on a wave- from a Dutch station, writes our wireless the successful communications have been length of 30 metres, there seems to be correspondent, what would she give for carried out by amateurs. There is no no logical reason why our own Corpora- the opportunity of dealing with a pro- doubt, however, that listeners, both here tion should not begin to delve a little gramme from England ?- Er'erting Stuod- and overseas, are intensely keen about deeper into the possibilities. nod, May 5th. 1927. B 26

; rR-, ä:.eás>àrwww.americanradiohistory.com iirr..p,ttsar.a,rt43 MAY Illlt, 1927. Warioll.go WodIl 595

Using Four = electrode Valves with 40 Volts H.T.

By A. P. CASTELLAIN, B.Sc., A,C.G.1., D.I.C.

.r 'I HE idea of making a complete, self -contained, port- running on one charge is made possible by the use of four - able receiver, with aerial, batteries and loud- speaker electrode valves. all in the one case, is by no means a new one, The writer has recently described I two receivers using but in iìì, t cases portable sets are designed from the point four -electrode valves for L. F. amplification, where H.T. of view of obtaining a very low weight, even at the ex- voltages of the order of only 4o volts were used and really pense of efficiency. good loud- speaker volume and reproduction obtained. The average portable set for loud -speaker work, using 'l'he advantages 6f the use of large capacity H.T. batteries ultra- lightweight batteries, will not give distortionless have several times been discussed in this journal, but in results for very many hours, owing to the load on the small - view of the fact that accumulator H.T. is provided for capacity H.T. battery, and also will not run for very in the Home Portable Set, these advantages will now long on one charge of its I. T. supply, even though valves briefly he shoe n again. having a very low consumption may be fitted. An ideal valve ampliler should be supplied with con-

The set to be described in this article, as its name stant H.T. voltage -which implies a source of high - implies, is not intended to be taken on a walking tour or tension of negligible resistance-as otherwise the output carried to picnics, except in a car, but is intended prim- current in the plate circuit of the valves twill hot vary arily for use at home or in the garden. Its batteries are exactly in accordance with the input voltage to the grids, sufficient to give a month's average use with one charge i.e., distortionless amplification will not be obtained. Now of the L.T., and good quality is ensured by the use of when a dry battery gets old and exhausted its resistance H.T. accumulators, while the loud- speaker reception is increases enormously -the resistance of an average 6o -volt restricted to the local station. This set is eminently suit- battery, for example, may become many thousands of ohms able for those people who wish to receive the local station -and in a two- stage L.F . amplifier this resistance, in the but who do not want to be bothered with " wires all over absence of a shunting condenser, is usually quite enough the place," and who object to an outside aerial as being to couple the low- frequency valves together and make either unsightly or inconvenient to erect, or both -and them " howl," giving a high pitched note in the loud- quite a large number of listeners come into this category. speaker. A condenser of one microfarad (or more) capacity used in parallel with the battery will have the effect The Question of Weight. of stopping the howl, since its impedance (or effective re- It might be objected that a self -contained receiver using sistance) is only a hundred ohms or so at a frequency accumulators for high- tension as \yell as low- tension sup- corresponding to the howling note, and thus the total plies is not going to be very light in weight, and thus effective resistance of the battery supply trill be reduced could hardly be called a portable set. However, this to the order of a hundred ohms, which \sill not give suffi- trouble is not nearly so bad as would be expected, since cient coupling for the valves to oscillate, but -and this the H.T. accumulators complete actually weigh less than is a point which cannot be too strongly emphasised, as it the L.T. accumulators, and the weight of the whole set is often forgotten -the actual resistance of the H.T. is only 381b., of which the batteries contribute r i lb. This comparatively light weight for the long time of 7'hc Wireless World, 11arch 9th, 1927, and MCC 6th, 1927. B 27

.... .i,. .. . .,,.._ . . . . - :eac..:Y.kAi.ár9í)ifiiinLlr..'«f{iiAwï'Filll`'d_www.americanradiohistory.com i`eiYL17.rnw:e l 3" aïSiíll"i'RIiNYNI.rYrre WApISÌ1®045 596 Mptill MAY zitb, 1927. Home Portable Loud- speaker Set. - where it is limited it is of the utmost importance to reduce battery has not been reduced by using a condenser across this loss as far as possible. 1 he choke Y actually used the H.T. in this way. Owing to the large current required is a Pye 32 henry choke, which has the comparatively low by the average L.F. valve -the mean current being 5 milli- D.C. resistance of about 700 ohms -giving a D.C. voltage amperes or more per valve -the small type of high- tension drop of about 3? volts only at 5 milliamperes plate current, battery using the smallest type of cells will be hopelessly overrun, giving a very short life, also distortion will be introduced, since the actual H.T. voltage supplied by such a battery at any mown.' depends on the current taken from it. It follows, therefore, that from the point of view of obtaining good reproduction it i., essential that the H.T. supply shall not he overloaded -i.c., if dry batteries must be used on the score of convenience, the large size type cell is essential, even from the point of view of cost, if good quality is to be maintained. :auall cell battery which is overloaded will only keep a sufficiently low internal resistance for a very few weeks, after which it must be discarded, while the very large cell battery, costing about two or three times as much in first cost, will last nine or ten times as long before being discarded for high resistance, while H.T. ahcumulator:. of good make keep their low resistance for several years it kept charged, say, from two to four times per year, depending upon the capacity of the cells. A view showing the detector valve This compartment. Note the method of question of H.T. sup. mounting the H.F. choke on the valve ply lias been gone into at some platform. length because so many people think the small cell H.T. is all right for loud - speaker wort: which is not a serious item even with low H.T. ioltages. if an H.T. condenser is used, and to show that the more The use of a choke feed output, as it is called, has expensive large size dry cells or accumulators are really another advantage in that no direct current flows through worth while from the quality point of view and also from the loud- speaker ivindings which would tend to saturate the the cost point of view when the cost of correctly running soft iron pole -pieces of the latter, thus producing distor- the set for, say, a year is taken into account. tion, and in the case of most small loud- speakers 5 milliamperes ivuuld go some way towards doing this. The Circuit. The inner grids of the two L.F. valves are connected To return to the Home Portable Set, the circuit is given together and tapped on to about to to 12 volts positive on in Fig. r. The low- frequency side will he dealt with first, the H.T. supply, and thus are used as space charge re- as it is with L.F. four -electrode valves that the writer has ducers. So much for the L.F. valves. The next thing to already dealt in previous sets, and which will therefore be consider is the detector, or first valve. more familiar to readers: The first L.F. valve is coupled On examining the circuit it will be seen that the input in the usual way to the second valve by means of a 4: i to the valve goes between inner grid and filament and that transformer X, and a choke feed output to the loud -speaker the output is taken from the plate in the usual way, the is used from the latter. valve being used as an anode bend rectifier. Neglecting This choke (Y in Fig. r) is used in order to make full for the moment the order grid, it will be seen that the use of the tow H.T. of 4o volts, although it introduce:, frame and first valve constitute a normal Hattley circuit, more weight into the set. The average loud- speaker resist- with C; as the feed back, or reaction condenser, and R, ance (D. C.) is between 2,000 and 4,000 ohms, and the mean and C; a resistance -capacity coupling to pass on the recti- current in the last valve is somewhere about 5 milliamperes. fied voltages to the next valve. so that the D.C. voltage drop across the loud- speaker, if In the case of an ordinary three- electrode valve of high the latter is connected straight in the plate circuit of the amplification factor, the value of capacity C2 required for last valve, would be from ro to 20 volts. This voltage the valve to oscillate is very srall -only a few micro - drop is not serious when plenty of H.T. is available, but microfarads -and it quite often happens that this amount B 28

www.americanradiohistory.com rp,"lire

MAY 111/1, 1927. Wilpa®0g WOliM 597 Home Portable Loud -speaker Set. - of capacity, or most of it, +40 V is provided between grid w and plate of the valve it- cc R1 self so that the detector valve oscillates very readily indeed -often so readily o ó H.F. X that it cannot be controlled. w CHCKE For the reception of tele- á 02 cc phony it is distinctly desir- u. able not to oscillate, but - é6 LS. fór the reception of distant Cl stations it is necessary to +10-12 V. be able to go nearly up to z the point of oscillation in w order to get sufficient sensi- cc U tivity. co The Hartley circuit is quite suitable for reception provided valves with low or medium amplification are used, but when it is desired to increase the +12-16V. amplification of the valve, then the trouble begins, as Fig. 1.- Showing the circuit diagram. The first valve is operating as a screened grid anode bend tile reaction becomes diffi- detector and the last two valves as L.F. amplifiers with space charge reducers. cult to control owing to the extremely small capacity required for C2. If it were control. By the use of a 4- electrode valve, as shown possible to cut out the capacity between grid and plate in the circuit of Fig. r, where the eitler grid is connected of the valve, while still kèeping high amplification, then to some suitable point on the H.T. battery, it is possible it will be possible to increase the value of reaction to eliminate effectively most of this Capacity, since the capacity and thus once more bring the set under efficient outer grid forms on electrostatic screen between the iirne, rid (which is the operating grid in this ease) and the plate, just in the same way that an earthed metal plate between two tuned circuits eliminates most of the capacity coupling between them. When the four- electrode valve is used in this way, the amplification factor is very high -over 5o in the case of the usual type -and the reaction condenser required for the circuit shown in Fig. r will he comparatively large-the reaction effect depending partly on the voltage applied to the outer grid -i.e., the greater this voltage, the less capacity will he required to make the valve oscillate. Values of Components. The frame aerial is wound on a wooden former about 15 inches square, as 1Yill be described later, and is tuned by the condenser C, of 0.0003 mfd. capacity, which should preferably be of the slow- motion type. Two -thirds of the turns are used between inner grid and filament and the remainder for reaction through C., to the plate. The small condenser C, of o.000r to A view showing the two L.F. valves 0.0002 mfd. is used to fix the H.F. in the foreground. Note the method potential of the end of the H.F. choke of mounting components on the loud- speaker frame. and should not much exceed the value B 29

www.americanradiohistory.com Ninpd®OZ 598 Wogla MAY rrtla, 1927.

LIST OF PARTS. 1 Musicalpha loud- speaker (Joublin & Kingsley, 317, High 1 Grid leak, Du,netohtn, 0.5 meg. ( Dubilier). Holborn, London, W.C.1). 1 Grid leak, Dumetohm, 2 meg. ( Dabilier). 1 "Cameo" portable cabinet, oak, type O.P.T. (Carrington Mfg. 2 Dumetohm holders (Dubilier). Co., Ltd.). 1 Fixed condenser, 2 mfd. (T.C.C.). 2 " Exide " 2 -volt S.P.7 (20 amp. -hr. actual) accumulators (Chloride I Filament rheostat, 30 ohms (Burndept). Elec. Storage Co., Ltd.). 1 Variable condenser, 0.00025 mfd. (Ormond) R/122. 2 "Ever- Ready" H.T. accumulators, No. 2110 (1,800 mA. -hrs.) I Variable condenser, 0.0003 mfd., slow motion. (Portable Electric Light Co., Ltd.). 3 "W.B." valve holders (Whiteley, Boneham & Co.). 100ft. "Lewcos" frame aerial wire (London Elec. Wire Co.). 1 Baseboard, 5x 16. 1 " Ever -Ready " 0 -volt G.B. battery (Portable Elec. Light Co., 1 " Cameo " panel, 16 x 11 x -iein. (Carrington Mfg. Co., Ltd.). Ltd.). 3 Plugs and sockets (Lisenin Wireless Co.). 1 32-henry choke (Pye). 1 A.P.406 four -electrode valve (Aneloy Products', 36, Forest Hill 1 Transformer (Pyc) 4 -1. Road, East Dulwich, London, S.E.22). 1 " Cosmos " H.F. choke (Metro -Vick Supplies, Ltd.). 1 A.P.412S four-electrode valve (Aneloy Products). 1 Fixed condenser, 0.002, No. 620 type (Dubilier). 1 A.P.412L four -electrode valve (Aneloy Products). I Fixed condenser, 0,005, No. 620 type (Dubilier). Sistoflex, screws, aluminium, brass, W. plugs, etc. 1 Fixed condenser, 0.0001, No. 610 type ( Dubilier). Approximate cost complete with all valves, batteries, etc., £16. In the "List of Parts" included in the descriptions of THE WIRELESS WORLD receivers are detailed the components actually used by the designer and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should be used in preference to others, these components are mentioned in the article itself. In all other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed, and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use. given, or else the quality of reproduction, especially in variable condensers, and the latter are kept away from the higher notes, may be affected. the screen by 1-r6th inch ebonite spacing washers. The resistance R1 is o.5 megohm in the set described, 'The choice of a loud- speaker for a portable set is rather and R2, 2 megohms, with a coupling condenser, C5, of limited as the space occupied by most of the better -known 0.005 mfd. types is so large as to prevent their use for this reason The condeser C which is across the grid bias supply alone, while some of the small speakers available are to the first valve, is used to keep the path of H.F. cur- rather inefficient. The " Musicalpha " loud -speaker used rents as small as possible and is not critical in value, is a cone type, with a doped silk cone, and mounted in a anything of 0.0005 mfd. and upwards being suitable. wooden frame approximately 8in. x 8in x 4in., so that being rectangular Capacity Screening. it will be seen that the space occupied, in section, is reasonably small. The frame of this In order to eliminate hand effects in tuning, which may speaker is also very convenient for mounting some of the he rather had on a frame aerial set, an aluminium screen components and also for serving as a rigid support for is us'ed behind the part of the panel covering the two the panel. Although the efficiency of this loud - speaker is not so good as, for example, the big " Amplion " or the

Standard ' ` Bone," yet for its size it is quite good and the output is pleasant to listen to, while the price is very reasonable. There would seem to be quite a field for small or compact loud- speakers for portable sets -and it is to he hoped that British manufacturers will produce several types in the very near future. The constructional details of this set, including alternative arrangements of the frame for 3oo -6100 metres and for the Daventry wave - 'engths, will be dealt The set opened and ready for use. The cover of the battery compartment has been removed to show with in next week's the batteries. The H.T. consists of two 20 -volt blocks of Ever -Ready accumulator cells and the L.T. of two 2 -volt Exide portable accumulators. 1SSue. Et 30

www.americanradiohistory.com MAY nth, 1927. VAp®iligoo War)Il01 599

NEWS FROM ALL QUARTERS. By Our Special Correspondent.

S.R. Innovation. -The Silence of " Daventry Junior. " -F.B.C. Staff Qualms. -Radio Etiquette in U.S.A. -The Studio Audience. -If Summer Comes.

S.B. in Britain and France. plus B.B.C. staff in view of the closing The arrival of the French President, M. FUTURE FEATURES. down of many of the present stations? Doumergue, at Victoria Station on Mon- Sunday, May 15th. Will there be more candidates for the day next, May 16th, will be the subject LONDON. - " Elijah " (Mendels- dole? " of a running commentary by Mr. L. Hore- sohn). No; it is unlikely that any of the staff Belisha, M.P. Gr.Asoow.- Glasgow Musical Festi- will suffer. The impression I gather is An important feature of this event will val relayed from St. Andrew's that, although fewer in number, the be the relaying of the President's reply Hall. regional stations will entail more work by landliae to Paris for rebroadcasting. Monday, May 16th. than the stations of to -day, and that the This will be the first time. I believe, that LONDON. -Variety Programme. contemplated arrangements will provide a speech in England has been simultane- ABERDEEN. - " Mains's Wooin'," for the absorption of the whole of the ously broadcast by stations in Britain and presented by Aberdeen Radio present staff. France Players. 0000 M. Doumergue's speech will be made BELFAST. -" Faust " (Gonnod), In- More Work for London. between 2.15 and 2.30 p.m. troduction and Acts I, II, and On the other hand, there will undoubt- 0000 Bart of III. edly be greater concentration of work in Have You Heard " Daventry Junior "P Tuesday, May 17th. the London area, which will probably LONDON.-Symphony Concert from have to provide the bulk of the pro- At the time of writing, evidence is still Manchester. lacking, either on the grammes for the stations in, the provinces, ether or in B.B.C. BIRMINGHAM. -Band Programme. engineering circles, to show that anything so that the London staff will grow still even faintly CARDIFF.-A Welsh Miners' Night more and the necessity of finding larger resembling a signal has sped arranged by Hywel Precelly. upon its flight from the aerial of offices, as I hinted in last week's Wireless " Daventry Junior." Wednesday, May 18th. World, will grow more pressing. LONDON. An English Rose," As a youngster the station may be very -" ilk More than 50 per cent. of the B,B.C. promising, Light Opera by Harold Daw- staff are already to be foúnd behihd the but its natal cry, if it has son. gone forth, has been very effectually classic portals of 2, Savoy Hill. MANCHESTER. of smothered. I imagine that the full realisa- -Songs the He- 0000 of the significance brides, by Hugh Mackay tion of the forthcoming (tenor). All Programmes from LondonP tests is afflicting the engineers with some- An opinion which seems to be gaining thing akin to the " microphone fright Thursday, May 19th. " BIRMINGHAM.- Symphony adherents is that the ideal broadcasting of which we read so much and hear so Concert. CARDIFF. -A Bristol Programme. dispensation in these islands would in- little. volve the distribution of nearly all pro- No doubt the engineers appreciate MANCHESTER. -Vaudeville. how Friday, May 20th. grammes from London, with occasional fatal it would be to encounter failure at interludes of purely local interest from the present juncture, BOURNEMOUTH.- Operatic Concert. when the regional stations in the provinces. - scheme, which produces such anticipatory G-IASGOW.- Belfast Radio Players in " Between Ourselves." But what have the provinces to say to delight at Savoy Hill, has yet to satisfy such a suggestion ? the people who count. Saturday, May 21st. 0000 0000 Loçrow. -The Wireless M i 1 ita ry Russian and Swiss. A Doleful Query. Band. BIRMINGHAM. - " The Carrier Variety on May 13th is to be provided "Assuming that the regional scheme Pigeon," a Play by Eden Phill- by Julia Bar, in Swiss yodelling songs, actually comes into being," writes a corre- potts. Virginia Faire, Walter Todd, and the spondent, " what will happen to the sur- Russian Corps de Balalaika. B 31

www.americanradiohistory.com VTAp®IlIMg 3l-9Y rrtla, OOn pIld. Radio Etiquette. The American nation is suffering, according to Mr. Arthur R. Freed, secretary of the Freed-Eisemann Radio Cor- poration of New York, from the lack of " radio etiquette." To prove that there is some justifies tion for such au alarming pronouncement, Mr. Freed cites a particular case. " The man who killed his wife," he says, " because she wanted to listen to classical music when he wanted to hear sports shows to what extent bad radio manners can go." Could anybody put it more clearly than that 0000 A Note of Hope. " This k an isolated case," adds Mr. Freed, ";rid I hope -it trill urrrr order (main." 0000

No Alternative ! Mr. Freed need not worry himself over the possibility of such a tragedy in this country for many a long year. We don't quarrel about alternative programmes in England for an obvious reason!

B.B.C. Criticised. The coveted honour of being Champion The broadcasting authorities in Grouser for 1927 surely friend RUNNING COMMENTARIES IN GERMANY. belongs to a Germany have been quick to recognise the value of the running commentary " as of mine who grumbles at the humorous exploited in this country. This photograph, taken recently on the Cologne race -course, sportsman, Herr H. Muller, giving his account of the spring meeting. turns because they make him laugh, shows a popular and Dortmund. When he laughs, the headphones rub The description was broadcast from Langenburg, Muenster his cheek -bones and cause inflammation. only the stories which he had alt eady Matheson Lang at 2L0. 0000 tried with success on the stage. At the The B.B.C. have made a coup in arrang- conclusion of the turn the deadly silence ing for the broadcasting of "The B.B.C. Again Criticised. of the studio and the professional restraint Wandering Jew " on June 7th with Another friend chews the rag because of the announcer conspired to engender Matheson Lang in the part of Matatliias. the London Radio Dance Band plays too doubts as to how the jokes had " got Sorne days prior to this broadcast. viz., quickly between 6 and 7 p.m. over." He consulted a listening friend, on May 23rd, there will be a Royal com- have my tea he writes, " I then," who said : " The turn was quite good, mand performance of the play at Drury " and, hieing musically inclined, I have to but you didn't give us time to laugh." Lane, and many of the artists taking part masticate in time with the music. I'rn This is a case when the presence of a will also lie present in the studio on getting indigestion." studio audience would have given a clue ,tune 7th. This will be the first occasion O 0 0 to the " time value " of each joke. The on which Mr. 1Vlatheson Lang has ad- to pause to enable dressed the microphone Pity the Studio Audience. artist had forgotten his audience to recover itself. o000 People are always ready to pity the lot 0000 If Summer Comes. of the poor broadcast çomedian, and will summer burst upon us means Last year, when countenance any of amelioration, A Mozart Opera. with its accustomed severity, the B.B.C. it be in the shape of whether spotlights of Mozart's opera, amtounced a special summer -time schedule a " studio audience." But what about A studio performance or Flute," will be broadcast in which, among other things, the news a little sympathy for the 'studio audience? " The Magic from 2L() and other stations on May 26th. bulletins occurred at an earlier hour. The studio audience suffers the incon- Nelis, Miriam little change is necessary, as all for The artists include Sylvia This year venience attending things required Suddaby, Alice Moxon, the present order of programme is con- a purpose other than the ostensible pur- Licette, Elsie Gladys Palmer, Heddle Nash, Frederick sidered eminently suitable for summer pose. It is in rather the sane case as the Russell, with the conditions; in fact, we have had a poor relation whose presence at the family Ranalow. and Sydney Wireless Chorus ;directed by Stanford " summer " schedule since January. feast is not unrelated to his willingness to Wireless Symphony 0000 up or occupy Robinson and the wash to the fourteenth conducted by Percy Pitt. Cult of the Running Commentary. chair. Orchestra audience and re- 0000 The " Seaside Nights " which gave so Let us pity the studio are to be member that the poor thing is in constant much satisfaction last summer fear lest it laugh too loud and offend the Robots on the Radio. repeated. Among the resorts which will laugh too softly Life on a remote island in the decade provide the fare are Brighton. Blackpool, ears of the blasé, or and and East- incur the wrath of the comedian. 1950 to 1960 provides the plot for Margate, Yarmouth, Southend, Karel Kapel, which is to bourne. 0 0 c 0 " B.U.R.," by last be broadcast on May 27th. The play has A feature which was absent from What He Forgot. been translated front the Czech by P. year's activities is the running coin- the empty Selver, and arranged for broadcasting by mentary, which promises to fill an import- Some entertainers prefer Im- souls run a risk. Cecil Lewis, who will be- the producer. ant able during the " dog days." studio, but these hardy at will The recent experience of a well -known The cryptic letters composing the title portant tennis matches Wimbledon stand for " Rossunt's Universal Robots," be described, and tinte may also he de- artist is interesting several important swimming He preferred to broadcast in an empty and the characters consist, of course, of voted to studio, but took the precaution of telling Robots and Robotesses. events. B 32

www.americanradiohistory.com MAY 11th, WAnilsasi 1927. %wIld hoz

: s \1 : ,_, t _, _ r _ _ - \ Latest Products of the Manufacturers.

DUBILIER RESISTANCE COUPLING ample number of turns to produce the re- the speech currents passed to the loud- CONDENSER. quired value of inductance, the winding speaker Now that the use of mica condensers possessing a minimum of self- capacity. The " P.D." volume control manufac- has become standard practice in the con- For the construction of a short -wave tured by Automobile Accessories (Bristol), struction of resistance -coupled low - receiver special care must be taken to Ltd., 93 -95. Victoria Street, Bristol; is a frequency amplifiers, amateurs will be ensure that the winding possesses an ex- compact wire -wound variable resistance interested to learn that the Dubilier Con- ceedingly small value of self -capacity, and provided with a 17-stud switch. It is in- denser Co. have recently produced a tended for connecting in parallel with special mica condenser for use in resist- the loud- speaker, and the resistance ance- coupled circuits. change varies from the off position when Although, no doubt, this condenser can the loud- speaker is unshunted to the be obtained in a range of capacity values maximum position when the volume con- to -suit various requirements, the stock trol acts as a short circuit. This com- size condenser has a capacity of 0.1 mfd. ponent can lie conveniently added to any It is suitable for use with anode resist- existing set, and is secured to the panel ances having values between 50,000 and by the usual one -hole -fixing nut, and its two terminals are linked across to the output terminals of the set. The maxi-

The air-spaced fine wire Eddystone choke coil for use in the construction of receiving sets operating over a wave range of about 20 to 100 metres.

Stratton and Co., Ltd., Balmoral Works, Bromsgrove Street, Birmingham, have included in their range of components a single -layer coil consisting of a practically air supported space winding. For building a receiving set for use on wavelengths between 20 and 100 metres this coil can be recommended. A mounting base with pin connector is supplied with this component, so that it can be changed for a coil of higher inductance value if the An easily fitted volume control for connecting in parallel across the output same receiver is to be used for reception terminals of a receiving set on broadcast and other wavelengths. A new Dubilier resistance capacity coupling condenser. 0000 mum resistance is about 6,000 ohms, and being wire wound it was found to be 150,000 ohms, the corresponding value of P.D. VOLUME CONTROL. constant in its resist: - ce value at any setting. grid leak being probably 0.5 to There are many sets' in which no pro- 0000 1 megohm. In the accompanying illustra- vision is made for critically' controlling tion a condenser is shown slightly smaller volume. Volume control is, of course, NEW POLAR NEUTRALISING than the actual size. The moulded case essential, partly to regulate the sound in- CONDENSER. the terminals, and extension carriles tensity to suit the listener's requirements There are very few neutralising con- are at the base so that it pieces provided and also critically to regulate the input densers available in which the design can be secured to a baseboard with wo to the loud- speaker in order to reduce The introduction provides for baseboard mounting and round- headed screws. distortion to a minimum. The tuning which are capable of providing new condenser completes the the of this controls are invariably used for reducing critical degree of capacity adjustment Dubilier range, so as to meet all re- as well as increasing ' volume when a required. quirements. 0000 multi -valve set is used for local reception, Modifications have been macle to the but much better quality can be obtained neutralising condenser manufactured by EDDYSTONE H.F. CHOKE. and volume control more conveniently the Radio Communication Co., Ltd., The aim in designing a choke coil for carried out if a variable resistance is 34 -35, Norfolk Street, Strand, London, use in a R.einartz or similar circuit arranged either to regulate the input to W.C.2, so that, as well at being suitable arrangement is to provide a coil with an the low- frequency amplifier or to control for securing to the panel by one -hole B 33

ed :s...í-_...,bi..:-,wcm-,,..::.iieC.au.i.,, www.americanradiohistory.com WhP@Il@ez MAY t r tb, 1927. 602 WoyIld fixing, a flange has been fitted to provide for screwing down to the baseboard. Ir -J Instead of the plates consisting of two cylinders sliding one into the other, only RECENT _N VENEN OHS. half cylinders are employed, so that a very of capacity can be critical control the permission of the Controller pbtained, not only by advancing one The following abstracts are prepared, with of H.M. Stationery Office, from Specifications obtainable al the Patent Office, 25, Southampton Buildings, London, W.C.2, price is. each.

Spiral Earth Tube. ment T provided with an adjusting screw S. This type of movement has been (No. 265,389.) previously described in these columns. Application date: Feb. 17th, 1926. The diaphragm is enclosed between two An earth tube is described in the above metal cones, the back one being fixed to British patent by T. Nicholls. The the housing H, which contains the tele- illustration shows the form of the tube, phone mechanism, and the whole is fixed which consists of a rod portion R pro- to a support stand E. The back cone is vided with a spiral thread T having an actually provided with perforations, al- appreciable area. The upper end of the though this is not shown. The two cones tube or rod R is flattened, and is pro- A and B are attached at their peripheries, and the two are held together by bolts passing through flanged edges F. This junction is also used to hold in position a ring W of wood, which in turn supports the edge of the diaphragm D by means of very thin tissue paper or similar material as shown at X. The front cone is trun- cated, and is provided with a perforated

The modified form of Polar neutralising condenser suitable for baseboard as well sa one -hole fixing. plate towards the other, but also by rotating. A locking screw is provided to hold the spindle of the moving plate secure. The condenser is quite durable, possesses good insulating properties, and is of a suitable capacity for use In a stabilised circuit where the number of neutralising turns is equal to- the primary turns of the H.F. intervalve coupling.

BOOKS RECEIVED. Sp rai earth tube. (No. 265,389.)

vided with a hole H, and terminals B. " Modern Scientific Ideas, Especially tube into the Oliver Instead of hammering the the Idea of Discontinuity," by Sir ground it can be screwed in simply by Lodge, being the expanded substance of placing a tommy bar through the hole H six talks on " Atoms and Worlds," broad- and screwing the tube right into the cast in October and November, 1926, 79 the Lon- ground. An additional feature of pp., published by Ernest Benn, Ltd., invention, of course, lies in the fact that don, E.C. Price 6d. the area of contact is considerably in- " Effect of EL.; Currents in a Core creased by the use of the spiral thread Consisting of Circular Wires," by Chester T. Snow. 24 pp., with 4 diagrams (curves). Published by the Bureau of Standards, 0000 Washington, D.C. (Scientific Paper No. 544). Price 10 cents. An Enclosed Cone Speaker. ' " Radio Formulario," compiled by Ugo (No. 266,271.) Guerra. A wireless pocket -book of tables. pplication date : Nor. 28th, '!925. Section of enclosed cone loud -speaker. data, circuits and useful notes. With (No. 266,271.) detachable diary. Published by Casa S. G. Brown describes in the above Editrice, " Elphis," Naples. British patent a form of fairly freely sup- " Funkbastlers Radio Bucherei (Part I) ported cone which is protected on either circular disc P through which the sound -Selektive Hochleistungs Schaltungen," side by two metal cones. The main f ea- from the diaphragm can pass. The chief by Joachim Winckelmann. A handbook tures of the invention will be obvious object of this form of construction is to for listeners giving notes and diagrams of from examination of the illustration. The secure a fairly light and free method of circuits and instructions for winding coils. diaphragm D is a cone of paper or other supporting the diaphragm, and at the 30 pp., with 19 diagrams. Published by light rigid material, and is connected at same time make the loud -speaker fairly Leo Kajet, Leipzig. Price 1 mark. the base to a reed type of telephone move -_ robust. B 34

www.americanradiohistory.com WIpdisom MAY 11th, 1927. Wald 603 European " E " occasionally proves a cathode, such as is obtained in the Osram stumbling block when given out by radio- K.L.1 valve, while the advantages of telephony with its Continental pronuncia- having a large cathode diameter wore TRANSMITTERS' NOTES tion. We have heard of an enthuiastic also explained. amateur who believed he was picking up Passing on to the control of anode AND QUERIES. clear telephony from Nepal (AN) and current, the lecturer showed how in a was bitterly disappointed on discovering two - electrode valve the anode current that the station he had beard was in could be controlled by the magnetic field Holland (EN). produced by a solenoid placed round the Amateurs Rome. The prefix ET is, under the American valve co- axially with the filament and in scheme, The Royal Frederico Cesi School, Via divided between Poland, Es- anode, the magnetic field deflecting the thonia, Latvia electrons is Cernaia 4, Rome, of which Prof. Ruggero and Lithuania, and we from the filament. This understand known as magnetic as Vicaro is Director, is now that amateurs in these coun- control, distinct transmitting tries will distinguish from the electrostatic in on 33 and 43 metres, using the call -sign their respective control obtained EI IFC. normal working this nationalities by the initial letter or figure the usual way by means of the grid. For of their call -signs, thus station uses a Hartley direct circuit with :- 0 0 0 0 Radiotecnique or Philips Transmitting ET P - - -- will indicate Poland. The Past Year in Manchester. valves, the supply being 2,000 volts A.C. ET 1 - - Lithuania. ET 2 -- Latvia. The reports of the secretary and or R.A.C.. and for low -power work the - treasurer, read at the annual general same circuit with Philips or Weston 10- ET 3 If Esthonia. 0000 meeting of the Radio Experimental So- watt valves and 300 volts D.C. or R.A.C. ciety of Manchester on April 29th, were EI IFC will be glad to get into touch highly satisfactory. The attendance with British amateurs New Call -Signs Allotted and Stations willing to carry Identified. during the past year has been gqod at out experiments on low -power and high - all meetings, and has justified the power work, and, in return, the Director GbB@ S. J. Styles, 15, Pickwick Rd., Dulwich, S.E.21. Transmits on 8, 2:3, and 45 metres arrangements made for providing lectures will put his laboratory and technical staff and welcomes reports. and demonstrations. It is hoped shortly at the disposal of British amateurs G 5H \V. H. Martin, Lynwood, Myrtlefield Park, to publish a syllabus of next season's desiring precision measurements. IFC Balmoral, Belfast. acti vities. is on the every night for G 5ML (ex 2BVL) F. W. Miles, 286, Earls.len Ave., air European N., Coventry. Transmits on 23, 45 and 1)0 The individual research scheme. and DX work. metres and will welcome co- operation and launched with such success last year, is 0 0 0 0 reports. G 5ZC F. J. Clark, 2, Acre Rd., Colliers Wood, being carried on, and new members have

Swiss Experimental Station. ' Merton, S.W.19. been urged to take up subjects for re- A small 60 G 6WT Capt. G. C. Si ihuot, 20, Parkfield Rd., Sefton search. -matt short -wave experi- Park, Liverpool. (Late KM1 and FN2C, mental transmitting station is now Nigeria). Transmits on 28 and 44-46 Dr. St. John has been elected Presi- operated by the Telegraph and Radio metres. dent, while a new Vice- President has 2BIX J. Butterworth, 1088, Manchester Rd., .been appointed in the person of Mr. E. Service, with the call -sign EH 90C. Pro- Castleton, Lancs. grammes from the Berne Broadcasting 2BNB J. N. Fenly, Hughenden, 546, Chester Rd.. Butterworth, M.Sc., A.Inst.P., who has station are relayed from 20.30 to 21.45 Erdington, Birmingham. also been elected an honorary life mem- 2BNII J. W. Knight, 203, Yorkshire St., Rochdale, ber for services rendered. B.S.T., on 32 metres every Monday. Lancs. Hon. Secretary : Mr. Levy. 19, Thursday and Saturday, after which ex- 2BPII (ex 6GR) J. Scotson, Entwistle Rd., Roch - J. Lans- perimental CQs are sent for half an dale, Lanes. downe Road. West Didsbury, Manchester. hour. Reports will be welcomed and EAS 2 Leonardo Picallo, Palms, Mallorca, Spain. o00o should be addressed to Case No. 63. 0000 Transmissions from 2FZ. Poste Transit, Berne. QRA's Wanted. 0 0 0 0 G 5BC, G 5F0, G 6LP, G 6WW. Regarding future transmissions from Radio Jargon, the experimental station 2FZ, the Radio Society of has We have never concealed our dislike of Experimental Manchester the misuse of " Radiese " in ordinary decided to continue these on Tuesdays correspondence from 7.30 to 10 p.m., operating on 200 written and have some- metres. times commented on the curious mixture NEWS FROM of languages in the columns of some of 0 0 0 0 our French contemporaries. We are Wireless in Dublin. therefore HE CLUBS.So entirely in agreement with a The new Marconi " straight " 3 -valve correspondent in the Jcnr,'nol des S" who type follows receiver employing the K.L.1 of writes as on the absurd misuse of Internal Action of the Valve. valve was demonstrated by Mr. F. G. the code " 73 " as a suitable finish to In a very interesting lecture given be- Clarke, of Marconi's (Ireland), Ltd., at correspondence : " The employment of the April meeting of the Wireless Society " after the formula of fore the Radio Society of Great Britain "'s courtesy " 73" of Ireland, held at 12, Trinity Street, is superfluous, for " 73 " stands for " best on April 27th, Mr. A. C. Bartlett, of the Osram valve research department at Dublin. The lecturer gave a clear de- regards " ; why then add a possessive Wembley, dealt with the laws governing scription of the manner in which the " s " ? Perhaps to give it a more Ameri- motion of electrons in the vacuous K.L.1 valve functions, and he showed can air; but is it not a redundance? the of and showed that good and clear loud- speaker recep- Again, why put a superfluous space the thermionic valve, " best " rested on simple tion could be obtained from the Dublin before the " 73 "? " 73 " itself means that their behaviour physical laws, and could be calculated to and Daventry stations with complete regards " ; " best would you write in absence of A.C. " hum." French " meilleurs meilleurs souvenirs "? a reasonable degree of accuracy. onoo Mr. Bartlett gave some fascinating de- The Society's short -wave transmitter tails concerning the problems of design- has recently carried out some interesting Nationality Prefixes. ing the electrodes. It was shown, for tests on a wavelength of 45 metres with The nationality prefixes suggested by instance, that long filaments are over- local experimenters and with amateurs the A.R.R.L. of IIartford, Conn., appear heated by the " space current," and that in Great Britain, Sweden, Spain, and to be generally adopted by most foreign the magnetic field in long filaments is Latvia. It is hoped shortly to turn countries. and, despite their obvious im- sufficiently strong to deflect the electrons attention to short -wave telephony 'trans- perfections, are to be welcomed as evolv- front the anode. This effect (known as missions. ing some sort of order from the old state the magnetic effect) was clearly illus- The Society's club room is now open of chaos. It is still somewhat difficult to trated by lantern slides. every Monday night for experimental associate a Brazilian station with SB, or A method of overcoming the magnetron work and informal discussions. a Chilean amateur with SC, and the effect is the use of the indirectly heated The Hon. Secretary is Mr. H. Jlodgens. a 35

,-3x.;.sR-,o.11.r.:ád::m-átc:'e"",.c.L'.:.ta..ic.wv9ra.werwl.:.,kwww.americanradiohistory.com ,._. ..oslaaa'i...af 604 WI gang MAY rrth, 1927. Wo Ilol

The Editor does not hold himself responsible for the opinions of his correspondents. Correspondence should be addressed to the Editor, " The Wireless World," Dorset House, Tudor Street, E.C.4, and must be =computed by the writer's name and address. VALVE PRICES. certain instances, but it must be realised that the British foreign Sir, -After the publication of my letter in your issue of manufacturer, if he desires to get his valves on to the kindly sent and Colonial markets, must. be prepared to sell them there at February 16th on the subject of valve prices, you type he me copies of a selection of the letters which you received from the current prices in those countries for valves of the manufactures; this sometimes means that he must sell at a your readers in reply, and, after consultation with the members he pf this Association, I am now replying tb the principal points very low price, but unless he were prepared to do this raised by your correspondents. would have to keep out of the foreign and Colonial markets (1) of your readers suggest of this altogether. Several that the purpose prices are Association is to maintain prices at a high level. This is (5) There are valves sold in this country where of these certainly not the case. The primary aim of the Association in competition with those of this Association. Some valves are manufactured here, but the majority aie imported is to attain and maintain the highest possible standard in any rate, the manufacture of valves and to ensure that the most suitable from abroad. In the case of the latter valves, at of valve for every made the the purchaser is at a disadvantage, in that he has no certainty type requirement is available to be public. This necessitates the control of prices, not only to of redress if a valve purchased by him should prove to of the prevent a price war between members of the Association, which, faulty, and certainly he lias no service at the back valves manufactured in this country apart from other objections, would inevitably lead to cheese - valve. Non -Association paring in research and manufacture, and the of poor are, we believe, mostly copies of Association types, but without production to a quality or unsuitable valves, but also to provide so that when infringement of patents we doubt if valves would be up reductions in prices are made they should be made at the satisfactory standard, and if they are, then sooner or later right time and simultaneously by various manufacturers, as those firms manufacturing these valves will find that they are otherwise the prices of valves might vary almost from week to selling at an uneconomic rate, as has been shown by the closing week, and the complications of distribution of valves amongst down of several valve factories during the past twelve months. retailers under such conditions would be ton great to London, W.C.1. H. HOWITT, contemplate. April 30th, 1927. Secretary, Association. (2) It is suggested in some of the letters which you havé British Radio Valve Manufacturers' sent me that the selling price of a valve should be based on the actual manufacturing cost, plus a reasonable additidn for EMPIRE BROADCASTING. profit. It is true that the actual manufacturing cost plays an important part in deciding the selling price of a valve, but Sir, -I was much interested in your Editorial in the issue - many other points have to be taken into consideration, and of April 27th on Empire broadcasting. Your remarks with amongst these should be included the cost of research work, regard to the Dutch being the first nation to broadcast to her the cost of new machinery, and machinery which becomes obso- dominions bring home the fact once again that we are, as lete with developments, also the cost of patent rights, which a nation, far too conservative, and never do anything before have to be acquired often at considerable cost. If British manu- the paco has been set by someone else. The value of such facturers are to continue to lead the way in valve development, a service would possibly extend above that of just a broad- it is essential that they should be prepared to incur considerable casting organisation, and might prove beneficial to a very high expenditure on research work. extent in times of disturbance. We are constantly having the (3) It is suggested that the valve should be produced on the word " Empire " put before us, and it is a recognised fact " Ford " car principle of mass production. If this were possible that any measure which is going to bring our dominions in the price of valves would undoubtedly be brought down, but closer touch with the Mother Country is of foremost importance. the development of the valve is at present in far too great a Like most useful suggestions, however, one imagines that any really state of flux to permit of manufacturer adopting the bodies or organisations whom this particular case might mass production methods. One has only to look back over concern will say : " " Yes, very nice and so forth," and there the past year to observe how frequently new types of valves will suggest, therefore, that measures should have been meet and so long the matter rest. I produced to special requirements, by the right persons, with a view to as this kind of thing continues it is not possible to employ be taken immediately wave Empire " broadcasting really mass production 'methods. The development of the valve establishing a high -power short is so rapid to -day that, to keep up to date, expensive apparatus station in this country. It appears that some difficulty is likely to arise as to who has to be relentlessly scrapped at quite frequent intervals to in hand. But it make place for new equipment, and many processes in valve are the right persons to take such a scheme manufacture which have been developed at great cost during seems that we have here an admirable opportunity of bringing the past two or three years have, in the course of time, been back some of the prosperity to the present time badly de- abandoned as obsolete and have given way to other and more pressed British wireless industry. British manufacturers have recent methods. The valve manufacturer has to face this con- never done radio export trade of any magnitude, possibly due tinually changing situation, which, although present to some to the difficulties of obtaining licences from the Marconi Co., extent in most modern industries, is quite exceptional in the to do so, but if they could show that a large amount of rase of valve manufacture. One direction in which added costs business could be done with the colonies that difficulty would may be reduced is by limiting the number of types of valves, possibly disappear. and this matter is at present receiving the close attention of At present the radio manufacturer in this country does little the Association. or no business abroad, comparative to what he does at home, (4) As regards the prices at which valves of British manu- because there is not the demand. Supposing, however, the facture are sold in the Colonies and elsewhere, on the face Government licensed an organisation of British manufacturers of it it may seem unfair that the purchaser at home may, in to erect a station such as that suggested, the trade would some cases, be paying a higher price for a valve than his friends not only greatly benefit, but also the entire community of the abroad; it is unfortunate that this situation should exist in British Empire B 36

www.americanradiohistory.com MAY ritti, 1927. WApagoo 605 WolfIld. Britishers abroad are sufficiently patriotic to buy British roundings. In this respect I think Dr. McLachlan, who also goods (not only due to patriotism, but because we happen to is, I believe, a musician, sums up the situation in the case produce the finest goods in the world in so far as radio for the moving coil- driven cone speaker : " . . . it would be apparatus is concerned) when they realise that the service car- idle to deny it offers advantages. . " ried on for them at home is supported by the British industry. My own experience of modern reception is somewhat limited, With the number of quite wealthy radio concerns in this but also confirms one of your correspondent's statements that country at the present time one sees no reason why a number greater efficiency appears to aggravate the contrast between the of them should not form a company for the purpose of Empire good and the moderate in transmission. In passing, the effi- broadcasting in exactly the same way as the B.B.C. was cient reception of the good in transmission amply repays any formed. A very necessary measure, of course, before such a trouble involved, from a musical standpoint, and is an eloquent scheme was gone into in detail, would be the definite assertion tribute to the high standard of present -day transmission. that the Government would allow such a service to operate. Incidentally, there is no excuse for not being up to date Such a scheme as the one outlined would not require very having regard to the excellent articles which have appeared large capital; quite a small private company with money put in The IVireless IV odd on faithful reception. up by the various members of the industry interested, the My impressions are that pianoforte transmission, while im- return on their money being a large export trade. Difficulties proving, has not reached the " perfect " stage yet. In coupling of a minor nature might arise, but one sees no reason why the " human element " in regulating transmission as further the basic scheme should not be a success. To put an Empire criticism, I offer it in all kindliness for the betterment of a broadcasting station under the control of the B.B.C. is rather system unique in its rapid development and efficiency, a system a tall order, as one imagines that the B.B.C. have quite that must have brought immeasurable happiness to the majority enough to do in supplying the British Isles with broadcasting of " ordinary listeners " and, I trust, to the many blessed on their not over -abundant income, let alone providing the with a musical ear. H. C. WALKER. whole Empire. I put forward my little idea above because Roby, I think Empire broadcasting would be an excellent institution, May 1st, 1927 benefiting the colonies and Great Britain in more ways than one. And as a previous radio manufacturer and wireless engineer of some years' standing, I believe that an Empire broad- B.B.C. HIGH -POWER STATIONS. casting station run by the trade would help to bring in much Sir, -May I once again be allowed the courtesy of your more business and so relieve the depressing period that the columns to reply to Capt. Eckersley's letter in your issue of radio industry is now passing through. DALLAS BOWER. April 27th, in which he states that I am labouring under a Brighton. misapprehension ? I fear that Capt. Eckersley himself is April 29th, 1927. labouring under two misapprehensions as regards my own letter in your issue of April 13th. If he will read my letter more Sir, -I notice that in your Editorial of April 27th and carefully he will find no mention of a central six -transmitter May 4th you refer to a new wireless station PCJJ erected in station ; in fact, I think such an idea too absurd to be taken Holland and now working on 30 metres, and that you suggest seriously by any radio engineer. I must perhaps labour the that this country should follow its example. There seems to point that the six single transmitter stations of my scheme me to be no reason why this should not be done by utilising the are intended to be spread out in suitable places all over Great present beam stations, as I understand successful telephony Britain ; to quote the words of my letter, " located in suitable transmissions have taken place at these stations while they were, spots midway between populated areas." at the same time, handling ordinary traffic on a.utomatic C.W. Capt. Eckersley's second misapprehension is that I did not Your readers who have listened to PCJJ have no doubt even mention foreign stations and was only concerned in re- noticed that the station is being largely used for propaganda ceiving the further British ones of the chain. I think that purposes on behalf of the company which runs it. This seems most people who have listened to the B.B.C. so- called alterna- to me to be a matter which should occupy the attention of tive programmes will agree that only two will not give much British manufacturers who are prohibited from using wireless relief. Technically, I still venture to disagree with Capt. for this purpose. OTHO W. NICHOLSON. Eckersley and maintain that, using sets having the selectivity 06 MP. of those recently designed by the B.B.C., one double -wave London, May 5th, 1927. 50kW. station, with a field strength of the order of 30 milli- volts per metre at 20 miles, is likely to interfere seriously with B.B.C. TRANSMISSION OF PIANOFORTE MUSIC. the reception of further British alternative stations. will show who is correct, but my own scheme Sir, this correspondence is Time alone -If not already too prolonged, does disability to same may I reply to Mr. Gough's letter in your recent issue undoubtedly not suffer from that the as was a serious attempt to solve the programme one who also enjoys in some measure the qualifications he speaks extent. It problem as far as it is possible with modern technical progress, of, including a trained musical ear ? My experience has been that pianoforte music a matter which, as far as I can see, the B.B.C. do not seem transmission has not been of the same very seriously. consistent standard as, say, the bigger orchestral works. to take would almost Finally, the six single transmitter stations of my scheme, It seem that at the period criticised a certain whilst providing two alternative, daily changing, programmes amount of experiment was in hand on this. Moreover, a at crystal set from the nearest two stations in a superior recent lecture one of the B.B.C. specialists frankly admitted to the the manner, give the, at present so much needed, encouragement problem of pianoforte transmission was difficult owing to the receiver the better the service. liercussion effects. Also, in one of your correspondent's that the better letters Nottingham, W. J. RANDALL. is quoted an admission at a similar lecture that the lower April 27th, 1927. frequencies in this transmission were at that time deeper modulated, presumably for the benefit of the average receiver. In judging reception of this nature no one doubts but that THE BEST FILAMENT VOLTAGE? the majority of receivers are capable of producing pleasing Sir, Your correspondent, Mr. C. E. Chester, will receive musical sound, but it is a vastly different affair to reproduce plenty of support for his contention that the filament voltage with full justice to modern transmission at its best, and it of valves should be standardised at 2 volts, and not 4. The is probable the receivers and speakers that are capable of this 4 -volt standard is a useful compromise between the efficiency of are none too numerous. As an engineer, I have a feeling the 6 -volt and the convenience of the 2 -volt, but it is clearly that the receivers described by the previous correspondents not the ideal standard. on this subject and used at reasonable range are more likely The slight loss of efficiency -we shall probably never go to offer a true basis for judgment than a superheterodyne used back to high amperage for compensation -would soon be over- at the distance Mr. Gough is placed. taken. Who dreamt two years ago of a valve with an amplifi- Judgment of reception is also dependent upon the type of cation factor of 35 and an A.C. resistance of 60,000 ohms? speaker and its position with reference to its acoustic sur- Manchéster, W. M. WHITEMAN. B 37

www.americanradiohistory.com .,i; -=..: .4.M1 6n6 WRp®Il®00 MAY 11th, 1927.

The Wireless World Information Department Conducts a Free Service ónnuuumumuuununuuuummnuuuwunuuuunuumununmunnnnuununumumnmmuun of Replies k Readers Queries. Questions should be concisely worded, and headed " Information Department." Each separate question must be accompanied by a stainped addressed envelope for postal reply.

Does Resistance Cause Losses? since magnification does not depend upon practice, from this point of view alone, I understand that if a resistance is intro- amplification factor alone. It has often and ignoring other considerations, you duced into a tuned circuit serious been pointed out in this journal that to would get less amplification by substi- lasses will be caused in the circuit get the approximate maximum of the tuting this particular valve. with the concomiteni effects of flat amplification factor of any valve used tuning, loss of sensitivity, etc. I in a resistance- coupled stage, it is neces- prc.cunae that the higher the resistance sary that the external resistance be at An Efficient Hartley Receiver. the greater are the evil effects pro- least five times the valve impedance. In 1 was interested in the portable receiver ducwl. h this so? A. T. R. your case your external resistance of using a single -calve Hartley circuit, 150,000 which, 01 You do not state in your letter whether ohms is roughly five times the was vutaished in trour issue impedance of July 21st last (rear. am desirous of you mean a parallel resistance the D.E.5B, which is 30,000 I shunted ohms, adding shall across the tuned circuit, for if this is the and so you are getting as near as an L.F. stage to it, and case your deductions are wrong, and the possible the full amplification factor -of be glad if you will gire me the neces- higher the resistance the less will be the the valve; about 90 per cent. probably. sary diagram. G. L. S. We will assume, evil effects produced. brief, if a however, for the sake We publish in Fig. 1 the diagram which In of resistance io shunted in parallel with a simplicity, that you are getting the you require. A good neutralising con- tuned circuit, then the lower the resist- full amplification factor (in practice this denser will serve as the reaction con- is ance the greater the losses. If on the not possible). If you now substitute denser, whilst the H.F. choke may con- contrary, the resistance is connected in your proposed - valve, we find that at once sist of any of the commercial ones which series with the tuned circuit such as in its impedance is exactly five times that are upon the market, or may be home- the lead running from one side of the of your previous valve, therefore in made, in accordance with the instructions tuning coil to the tuning condenser, then order to get 90 per cent. of its ampli- in the " Readers' Problems " section of the converse in true, and the higher the fication factor of 50, your anode resist - January 12th, 1927. You should not for- resistance the greater the losses. One ance would have to be raised to at least get to use a good type of L.F. trans - practical instance of the foregoing is the 0.75 megohm, and you would trot, as you £ordier. By careful adjustment of the ease of a variable condenser shunted suppose, be getting the full 50 amplifica- detector valve H.T. voltage you will find across a coil for the purpose of tuning it. tion factor of the valve, but would only that the reaction control- of this receiver The condenser is obviously in parallel he getting a percentage of it. In actual is very smooth. with the inductance, and, therefore, the iuenlation resistance between the fixed and moving plates of the conden =er should be as high as possible to avoid ]osse, in this manner. Obviously, if this insulation resistance is lower, the name effect will be produced as if an actual resistance had beer '-hunted across the condenser or coil. 7 mfd= C O C O A Dangerous Pitfall. I have a receiver consisting of an H,1'. valve, detector, and L.F. valve. The detector is a D.E.5B, and the I.P.O 00003 rnfd O 0 coupling to the L.F. -valve is by a means of a 150,000 aloe anode 0 -r 0 resistance. I see that there are now several valves on the market having O.P. 1.5. a magnification factor greatly in 9 G.B. excess of the 20 giren by this valve. + Should 1 get 'greater amplification, -0 therefore, by substituting one of 0-oo0c5 mk, these high. magnification factor -valves? 'l'he. t-alre 1 hare in mind has an impedance of 150,000 ohms LT and an am plification factor of 30. + G. L. G. AirN o The answer is definitely No. In any you would get less amplification,c_asr Fig. 1. -Frame aerial Hartley receiver with a stage of L.F. amplification. B 38

www.americanradiohistory.com Wilp@Ilwg 6o8 MAY zzth, 1927. WOTIlol Soon Remedied. method of connecting telephones and latter case, of course, the part of Fig. 3 I hare on hand a number of cylindrical loud -speaker which we give in Fig. 3. which we have labelled output terminals inductance coila made by myself, and The volume control across the telephones of set will be the output terminals of the wound for various wavelengths. I will, if it is a good one, enable you to choke filter device, or the secondary of flow wish to experiment with centre - control the volume of your telephones the transformer as the case may be. from inaudibility tapped coil circuits, and should be up to full strength. If 0000 glad if you would tell me the num- possible, use a good wire wound instru- ber of turns for the various wave- ment such as the " P.D. Volume Con- Getting It Both Ways. lengths. T. L. S. trol," manufactured by Messrs. Automo- / hare built a single -v'lrc set employing bile Accessories, Ltd., 93-95, The number of turns for specific bands Victoria the " 11'eagant " circuit. I find that of wavelengths Street, Bristol, or any similar instru- this receiver gives perfectly satisfac- is, of course, no different ment by other makers. There from the number of are, of tory results on the normal broadcasting turns which would be course, a large number of inferior volume required in a coil having no centre tap. liant!, but reaction is extremely erra- tic on the the not Thus if one has made a grid coil for use long wave band, set in a straight detector and two L.F. only increasing the reaction effect and finally oscillating when the receiver, and one decides to change over I increase capacity of the reaction condenser, as to the Hartley circuit, which requires a it do normally, but also exhi- centre- tapped coil, the same coil will should biting the same phenomena when I cover the same band of wavelengths. You are advised, therefore, merely attempt to cut out reaction altogether to put by setting the reaction condenser to a centre tapping on each of your coils. 0000 its minimum position. Can you tell me where 1 have gone wrong! A Simple Conversion. T. N. I have at present a Three -valve broad- mention is prob- cast The trouble which you receiver consisting of a "Hart- ably due to the fact that your H.F. choke ley" regenerative detector, followed Fig. 3.- Simultaneous use of headphones is resonating on the long -wave side of the by two transformer- coupled L.F. and loud- speaker. receiver, and if it does this. of course, you stages. I shall be glad if you it'd! will naturally get these effects, because inform me in what way I can convert controls, many of foreign design, upon you will get the normal type of " We- this into the " Schnell " circuit. the market. 'i'his will control the volume agant " reaction when increasing fhe con- T. R. G. D. in your telephones without in any way denser capacity, and owing to the reson- It is quite a simple matter for you to affecting the loud -speaker volume. ant choke you will simply get a tuned convert your receiver from the " Hart- Naturally you could, if you so desired, plate circuit when setting the condenser ley " to the " Schnell " circuit. All you have another volume control across the to minimum value. The result is that the have to do is first to remove your exist- loud- speaker which would enable you to valve will oscillate if the grid circuit ing " Hartley " reaction condenser, and control loud- speaker volume without damping is not too heavy owing to the substitute in its place a 0.00005 mfd. altering the volume in the telephones, fact that both grid and plate circuits fixed condenser; such instruments are although usually, in most receivers, there are in tune with each other. This method sold by Messrs. Peto Scott, Ltd., 77, is some device for controlling the total of tuned -plate regeneration used to City Road, London, E.C.1, but if unob- output which could be set so as to give be a great favourite in America for broad- tainable two 0.0001 mfd. fixed condensers adequate volume in the loud -speaker, and cast receivers before the coming of modern may be used in series. Having done this, then the telephones volume control ad- H.F. amplification. The remedy is to you must connect a 0.0005 ntfd. variable justed afterwards. Needless to say, if alter the value of the choke so that it is condenser (preferably fitted with a slow - you connect your volume control directly no longer resonant, and we would advise motion device) from the plate of the across the output terminals of the set, it you to remove turns from the choke until valve down to L.T. -. It should be re- will affect both the volume control of this trouble is eliminated, although you membered that if the plates of this con- the telephones and loudspeaker. This can cure it by putting another H.F. choke denser touch, the H.T. battery would method is quite sound, as it can be used in series. In the former case you would be short -circuited, and we should advise either in the case when the loud -speaker be moving this resonant point below, and a large fixed condenser in series with it and headphones are connected directly in in the latter case you would be raising the in order to avoid the possibility of this the plate circuit of the final valve, when resonant point above the wavelength band mishap, or, of course, you could get over a choke filter circuit is used, or after a on which you desire to work. the trouble by connecting from plate of 1 : 1 ratio telephone transformer. In the 0000 valve to II.T.+ instead of to L.T. -. This new variable condenser will then A Rule of Thumb. control reaction. You. gate very recently a rough -`end- ready 0000 BOOKS FOR THE formula for ascertaining the correct any valve. have un- A Useful Device. WIRELESS EXPERIMENTER grid bias for I fortunately mislaid the copy contai-r- I have a detector and two L.F. set, which Issued in conjunction with The Wireless World." tag the necessary information, and gives adequate -volume on the loud- should be obliged if you would repeat speaker. "TUNING COILS AND METHODS OF Owing to ear trouble I find TUNING," by W. JAMES Price 2/6 net. By it. N. V. that I myself can hear much better Post, 2110. A rough idea of the correct grid bias on he(ulphrnee. If I arrange to con- WIRELESS VALVE RECEIVERS AND required may be obtained by dividing the nect IL,. telephones after the first CIRCUITS IN PRINCIPLE AND PRAC- H.T. voltage applied by twice the ampli- L.F. rodee, then TICE," by R. D. BANGAY and N. ASMBRIDGE. not only is it not B.Sc. Price 2/6 net. By Post, 2 /lo. fication factor of the valve. As an quite loud enough for me, but the ` WIRELESS VALVE TRANSMITTERS example, we may take a D.E.5 valve. loud-speakerer does not function as -THE DESIGN AND OPERATION OF which has a voltage factor of 7, with 140 cell. Briefly, then, I desire to use SMALL POWER APPARATUS," by gives us 140+ W. JAMES. Price 9/- net. By Post 9/6 volts on the anode. This telephones at the same time as the 14 which equals 10; in practice, this grid loud- speaker is in operation, and I THE RADIO EXPERIMENTER'S bias or perhaps even a slightly HANDBOOK," Parts I & 2, by P. R. Coossey, voltage, require some method, therefore, of B.Sc. Price 3/6 net. By Post, 3; to. higher one, would work well. It should controlling the volume in the tele- he clearly stated that this formula must Obtainable by pos: (remittance frith order) iront phones independent of that in the only be taken as a rough indication ; it is. loud- speaker. W. G. ILIFFE & SONS LIMITED, nevertheless, very useful, and applies a Dorset House, Tudor St., London, E.C.4, Your problem is perfectly simple one, or o/ Booksellers and Bookstalls. particularly to the more efficient types of and all you have to do is to adopt the valves. B 40

www.americanradiohistory.com Th rele AN D RADIO REVIEW (151P }ear of Publication)

WEDNESDAY, MAY I8TH, 1927. VOL. XX. No. 20.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES. , (3 lines). Editorial Offices : 139 -40, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone.: City 4orr Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. Telephone : City 2847 (13 lines). Telegrams : " Ethaworld, Fleet, London." COVENTRY: Hertford Street. BIRMINGHAM: Guildhall Buildings, Navigation Street MANCHESTER 199, Deansgate Coventry.' Telegrams: " Autopreev. Birmingham." Telegrams: " Ililfe. Manchester: Telegrams! "Cyellot 8970 8971 City. Telephone: 0210 Coventry. Telephone 2970 and 2971 Midland. Telephone' and Subscription Rates: Home, 17s. 4d.: Canada, 17s. 4d.; other countries abroad, nos. 6d. per annum. of these, to satisfy themselves (hat they ,4 s many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before leaking use would not be infringing patents.

and it seems BROADCASTING AND THE PATENT monopoly in manufacture of receivers, likely that the licence from the Post Office for the British POSITION. Broadcasting Company to operate was granted on the N this country, broadcasting and the design understanding that boita fide British manufacturers of broad( ast receivers is so closely linked up would he able to come into the industry and be licensed with the general licence to manufacture under Marconi patents on terms which had the approval under Marconi patents N41".+. of the Post Office. which is issued by A Mixed Blessing. that company that it CONTENTS We have in the past pointed would seem out of PAGE out that, whilst the granting of place to omit to make reference to EDITORIAL VIEWS ...... these general licences by the Mar - an important modification in the FOR 7IIE NUCLEUS LONG -WAVE UNIT coni Company no doubt opened terms of this licence which the 611 RECEIVER ...... of this new industry to Marconi Company is at present the door By H. F. Smith. who other - requiring of its licensees. many manufacturers NEWS FROM THE CLUBS ...... 616 wise would have found it difficult 617 Early History. SAC LECLANCHÉ CELLS ... to compete with those who had Blakey and J. F. the use of existing It will be remembered that about By F. access to on the other hand, it the time that the Broadcasting Samuels. patents, yet, 619 has had one very unfortunate Company was formed by repre- PRACTICAL HINTS AND TIPS .. CONDENSER 621 effect. in that, because for a cer- , sentatives of the wireless industry THE LOGARITHMIC tain sum all manufacturers have with the sanction of the Post By Fi! H. Haynes. 627 been able to utilise circuit arrange- Office, the question of manufacture CURRENT TOPICS ... . - i use circuit ments necessary for the operation of sets involving the of HOME PORTABLE LOUD - SPEAKER SET Com- of satisfactory receivers, they principles which the Marconi (Contd.) 629 were covered by have sadly neglected to undertake pany claimed By A. P. Castellani. held was the research work on their own account patents which they ... 633 subject of much discussion, and BROADCAST BREVITIES and acquire for themselves patents ... 635 eventually the Marconi Company LETTERS TO THE EDITOR of importance, the value of which undertook to license all bona fide NEW APPARATUS ...... 636 would, perhaps, only become fully British manufacturers who agreed PE.Aputs' PROBLEMS ... 637 apparent as certain fundamental to pay to them a royalty calculated 4-11-4-4*s patents held by the Marconi Com- on the basis of Its. 6d. per valve pany ran out. holder. This general licence, it was considered, would 'l'he modification to the general licence which the Mar- avoid the very difficult task of collecting royalties in coni Company is now requiring of its licensees is in respect of individual patents which might be made use respect of the basis on which the royalties have been of by the manufacturers. At the time that the establish- calculated, viz., 125. 6d. per valve holder. It is now re- ment of broadcasting stations in this country was under quired that, to avoid any misunderstanding or dispute in consideration by the Post Office, a state of affairs existed connection with the meaning which the Màrconi Corn- Where the Marconi Company might, in virtue of the pany attached to that original wording, another clause patents which they controlled, have held a position of should be inserted in the agreement to define I valve

A 5

www.americanradiohistory.com ózo Wilpdsoo MAY 18th, 1927. WorIld holder as applying only to a valve containing the usual arrivals in the market. We may, in point of fact, find three elements of filament, grid, and plate, and placing that the industry has returned to its former state when outside the terms of this general licence the employment the Marconi Company held a monopoly control over the of any valves containing anything other or in addition to supply of broadcast receivers, and, unless there existed the usual three elements. any understanding on the subject of a general licence between the Marconi Company and the Post Office when The Marconi Explanation. the Broadcasting Company was constituted, then the issue On making enquiries at Marconi House an official of of licences to permit the manufacture of sets employing the Marconi Company explained that the action taken the new valves may he restricted to certain manufac- was solely with the object of elucidating the present turers instead of being generally available, and it may situation. When broadcast- be that the royalty charges ing began and licences for which the Marconi Company the manufacture of broadcast %vill feel it necessary for receiving apparatus under them to impose will have a Marconi patents were first very serious influence on the issued, the only type of valve future prosperity of the likely to be used was that broadcasting industry as a containing the three usual whole. electrodes. With the rapid 0000 development in the design EMPIRE and manufacture of valves, however, many fresh types BROADCASTING. of valve with multiple elec- I'l'H pardonable trodes and multiple perform - pride thè Dutch ance have come into use in nation is rejoicing connection with broadcast over the prowess of PCJJ, reception. the Philips experimental The intention of the origi- short -wave station at Eind- nal licence was that a charge hoven which awoke one recent of 125. 6d. should be made morning to find itselt for the service performed by famous. each three -electrode valve, The spirit animating the but with certain of the new enterprise of Holland is sym- types of valve there is a bolised in vigorous style in possibility of misunderstand- a cartoon, by the celebrated ing in regard to the intention artist Louis Raemaekers, of the licence. The Marconi Nvltich appeared a few days Company, therefore, has ago in the well -known Am- communicated with its sterdam " Telegraaf," and licensees with the object of Dore the following legend :- clearing up the situation and " 'Phis evening the trans- enabling the business of mission of the 9th Symphony manufacturing under licence of Beethoven will be broad - to be carried on without mis- cast to all listeners in the understanding on the basis world by the short -wave that was originally intended. station of Philips Radio Works. At the same time, Effect of the New Clause. s ` mar ;e s this thought -wave of peace The above explanation and charity will find an echo makes it clear to us that the terms of the general licence in the hearts of all who enjoy. the reception." so modified will not authorise manufacturers, unless a " Broadcast to al i listeners in the world " is an separate licence is negotiated for, to use four -electrode optimistic phrase, but the success already secured by the valves, multiple valves such as the new German Dutch station justifies a sanguine outlook. " Loewe " valve, nor the new Hull screened valve recently British colonists can at last hear programmes from developed in America, the importance of which, for high - Europe, but the thought is hardly calculated to bring a frequency amplification, can scarcely be over- estimated. glow of pride to British cheeks. Until Britain follows It is possible that, within a comparatively short period, the lead already set and establishes a short -wave broad- sets which employ three -electrode valves only may come casting station for maintaining touch with the Dominions, to be regarded as obsolete. By this it is not meant to we can only hope that the delight with which our kith and convey the impression that they will be unsatisfactory in kin overseas pick up the Dutch programmes may blind their performance, but that the new valves will be so them to the lethargy at home. popular that it will he difficult for sets employing only Under Correspondence we publish further interesting the three -electrode valves .to compete with the new letters on the subject of Empire Broadcasting. A 6

www.americanradiohistory.com w.:.y,... 11:1 Y 18t1a, r927. Wbpight6 brr WoreRo1 NUCLEUS ECEIVUP

By H. F. SMITH.

An H.F. Amplifier for Wavelengths from 800.3,000 Metres.

IT was reported in the daily Press a few days ago missions. It is, then, both for the benefit of those who that a South Coast listener, charged with maintain- have to depend on Daventry, and also for the not in- ing an unlicensed receiving set, made the excuse considerable number who like to be able to tune in the that during the last eighteen months he had heard foreign high -power stations with some certainty, that t: nothing worth while listening to." Now the B.B.C. the instrument to be described in this article was has to put up with some harsh criticism, but it is hardly designed. conceivable that over this considerable period of time The unit - comprises a single stage Of transformer - anyone could have failed to find a single item which coupled high -frequency amplification, and, while pri- appealed, so the only possible conclusion is that the marily intended for use with the " Nucleus " receiver,' alleged unlicensed receiver was itself at fault. The it is possible, as a rule, to. add it to any conventional majority of those living on the coast at some distance detector -L.F. set without any great difficulty. The cir- from a station have learnt by hard experience that trans- cuit diagram given in Fig. r shows that the aerial is missions on the normal broadcast waveband are spoilt loosely coupled and separately tuned ; the writer is con- by spark interference, and that Daventry is the only vinced that, in spite of the extra control necessary, it is station which can he relied upon to provide good signals worth while reverting to this well -tried arrangement, which with any degree of reliability. Moreover, many have has considerable advantages on the longer waves. An found out that even on the long waves something rather alternative series condenser is provided, in order that a better than the average in the matter of selectivity is wide hand of wavelengths may he covered without the necessary to overcome interference from the growing necessity for frequent changing of coils. number of broadcasting stations working between r,000 H.F. Transformer Design. and 2,000 metres, and also from commercial Morse trans- A conventional neutralising system is included, as this is absolutely essential when aerial damping is reduced by loose coupling. The secondary of the transformer is joined to output sockets marked A and B in the diagram. These are for connection respectively to grid and filament of the detector valve contained in the `.` Nucleus " set, the transformer being tuned by the 0.0003 mfd. variable condenser contained in that unit. The wavelength band cóvered with that capacity is from about 800 to 2,200 metres ; to receive the Eiffel Tower transmissions it is necessary to connect in parallel a fixed condenser of 0.0002 or o.00ó3 mfd. The heart of an H.F. amplifier is the transformer, and it is worth while taking pains to produce a coupling which will give good amplification combined with sufficient selectivity. The design chosen is based on one described. by W. James in Experimental Wireless for January, 1927 ; its secondary consists of a No. 300 Fig. 1. -The circuit diagram of the unit. C1, 0.0003 mfd.; C_, C,, 0.0005 mfd. ' l'he Wircless World, Dec. 1st, 1926. A7

www.americanradiohistory.com 612 VA. pislissco Walló MAY 18th, 1927. Long -wave Unit for the Nucleus Receiver. -- " Lewcos " coil, with plug and pro - tective band removed. Over this is wound the primary winding, separated from it by ten spacers cut from ebonite,' and measuring loin. x -kin. x hin. thick. A shallow depression, yin. in length, is filed on each of these strips, one of which is fitted with a roB.A. screw at each end, while two others carry a single screw. The disposition of these strips, together with the connections of windings to the screws, will be clear from a consideration of Figs. 1, 3, and 7, in each of which the same lettering (G, F, P, N.C., and H.T. +) has been adopted. The primary winding has a total of fifty turns No. of 4o D.S.C. wire. Fig. 2.- Dimensioned sketch of ebonite stand for the H.F. transformer. spaced to occupy the full length of the .inch -long depression on the strips already mentioned. ness, should be placed over each of the originals, and These strips are not grooved, so the spacing between turns held in position with either a rubber band (which is after - must be estimated, and need not be perfectly regular. wards removed) or else a trace of molten Chatterton's When the primary winding is completed, another spacer compound at each end. These are for the support of measuring gin. in length, resin. wide, and -1-16-in. in thick- the neutralising winding, also with fifty turns of No. 40 D.S.C. wire, which is spaced to occupy nearly the full length of the strips. EBONITE SPACER, STRAPS BETWEEN PRIMARY The completed transformer is slipped on an ebonite ANO SECONDARY support cut from a piece of scrap ebonite to the dimen-

>3'' ` sions given in Fig. 2, a single screw being inserted into e PRIMARY its upper surface to hold a double -ended soldering tag for 4:\ WIND NG anchoring the. inner end of the secondary winding, the outer of which is NEUT. end led straight to a short length of stiff WINDING wire soldered to the appropriate socket. While winding II SPACEC the transformer every care should be taken to avoid ORIGINAL COIL STRAPS BETWEEN FORMER. PRIMARY AND breaking these leading -out wires of the original^ coil, NEOT. WININN05 which are of stranded cable; they may be protected by 5 LAYER SECONDARY SJANDARD N °30O attaching them temporarily to the inner surface of the 'LCWCO5' COIL WITN WINDNG CONNECTION TO H,T.t BAND ANO PLUG coil former with Chatterton's compound. It should also REMOVED be remembered that secondary, primary, and neutralising SECONDARY windings should all run in the same direction. Layout. The general arrangement of the unit corresponds closely with that of others in the same series which have already been described, and it may be accommodated in a cabinet of similar dimensions. The baseboard is raised on wooden strips rjin. in depth in order that the bias cells may be mounted underneath it. Some apology may appear to Flg. 3.-" Cut- away" sketch and section through the H.F. trans- he necessary for the apparent crudity of the coil mount- former, showing method of construction and connections of the ends of the windings. ing, hut, in practice, this simple arrangement proves

LIST OF PARTS.

1 Ebonite panel, 12in. x Bin. x tin. 1 Valve holder (Triumph). Variable condensers, 0.000.5 mfd. (Utility). 1 Rheostat, 20 ohms (Jennens). 1 Fixed condenser, 0.0003 ntfd. (Dnbilier). 1 Coil, No. 300 (Lewcos). 1 Neutralising condenser (Gambrell). 2 Dry cells, "0" size (Ever Ready). 2 Single coil holders (Athol). Sockets, ebonite, screws, aluminium sheet, wood, etc. Total cost, without coils or cabinet, approximately £9 8 0 in the "List of Parts" included in the description of THE WIRELESS WORLD receivers are detailed the components actually used by t';e designer, and illustrated in the photographs of the instrument. Where the designer considers it necessary that particular components should he used in preference to others, these components are mentioned in the article itself. In all other cases the constructor can use his discretion as to the choice of components, provided they are of equal quality to those listed and that he takes into consideration in the dimensions and layout of the set any variations in the size of alternative components he may use. A8

www.americanradiohistory.com"qt.t t a.i' ,.r >M MAY 18th, 1927. Wilpshoo 613 W®pDd Long -wave Unit for the Nucleus Receiver. - quite satisfactory, as when the best coupling is once found it is seldom necessary to alter it; by adopting this plan it is possible to make the dimensions of the instrument uniform with that of the others. A consideration of the photograph on page 614 will show that the aerial coil socket is secured to the baseboard by a single screw, so that it may be moved in relation to the secondary, which is fixed. The wiring was carried out with No. 18 bare tinned wire, no insulation being considered necessary where leads are taken through the baseboard, as they are all at low potential. It should be noted that the connections to the moving coil holder are Fig. 4.- Drilling details of the panel. A, 518in. ; B, 3 /8in.; C, 3/16in., tapped IB.A. ; D, 1/81n., 4 screws. made of flexible wires, which countersunk for 6B.A. and No. wood are anchored to screws inserted in a small ebonite Mullard P.M.5X, and S.T.61. Most of these have their block. This is clearly shown in the practical wiring plan. counterparts in the 2- and 4 -volt ranges. The use of The H.F. transformer as described is intended for use an unsuitable valve may result in a .very considerable with a valve of, very roughly, 20,000 ohms impedance, reduction in amplification. which ' will have an amplification factor of about 20 Before connecting the amplifier to the " Nucleus " re- (a little less in the case of 2 -volt filaments). Representa- ceiver, it should be realised that-the difficulties, of separat- tive valves having suitable characteristics are the Cossor ing H.F. and L.F. currents in the anode circuit of the 610 H.F., Marconi and Osram D.E.5B and D.E.H.6io, detector valve become more pronounced as the wavelength is increased, so it will be almost essential to connect a damping resistance of from 0.25 to o.5 megohm directly in the grid circuit of the first L.F. amplifier. This arrangement was discussed in connection with the " All Nave Four " described in The TVireless World for April, 27th, 1927. a Tuning and Neutralising Adjustments. The operation of a two- circuit tuner is at first rather strange to those who have been used to direct- coupled receivers with not more than two dials, although it is an art which is easily acquired with practice. Before attempting to master it the H.F. valve should be balanced. The amplifier is connected to the detector - HOLE DIAMETER L.F. unit by joining adjacent sockets with short lengths

of . wire terminating in plugs, and Nos. 150 and 25o coils are inserted in aerial (L1) and secondary (L2) holders, Y" their axes being set at an angle of about 45 degrees. All three dials should be rotated until their circuits come into r© tune, the resulting oscillation tieing checked by manipu- lation of the balancing condenser, as described a number of times in this journal. When the set appears to be perfectly stable, even with the aerial coil removed, the search for actual signals may be commenced, remembering that the golden rule for operating any receiver of this description is to make comparatively small changes in the dial readings of each condenser in turn, thus keeping the Fig. 5. -The screen, made of No. 20 gauge aluminium sheet. circuits more or less in tune. The table on page 615- A g

www.americanradiohistory.com WAY®Il®05 Wald MAY ¡Rtb, rgz7. Long -wave Unit for the Nucleus Receiver. - which shows the actual adjustments for several of the more popular long -wave stations on the receiver actually described, should be of assistance, although it must he pointed out that the data for the aerial circuit (L1 and CO will vary -often very con - siderably-as the condenser setting depends on the characteristics of the aerial system. That on which these tests were made has a somewhat lower capacity than the average, and it is for this reason that a No. zoo coil was used for L in place of a No. rso, as recommended above. As soon as a station is tuned in, a record should be made, both in order to facilitate future reception of the same station and also as an aid to finding others on near- Rear view of the unit, with aerial and secondary colis in the by wavelengths. Provided " loose -coupled " position. that the coupling remains fixed, the set may be calibrated with considerable secondary circuits at an angle of about 8o degrees. accuracy. It is a good plan to find a satisfactory aver- It is never an easy matter to convey to the age prospective coupling position, and then to keep to it except under constructor information as to the results unusual which should conditions, where maximum selectivity becomes be obtained with any particular instrument. I.ocal necessary. Incidentally, condi- the data given in the table was tions, and the efficiency of the aerial -earth system, will obtained with the axes of the coils in the aerial and al ways be the deciding factors, but, as reception on the long waves is always more certain than on the Soo -soo- metre band, it is considered that a description of results obtained will not be likely to mislead the reader whose conditions are up to the average. Tested near London, with an aerial about ,34ft. in height and an overall length of about 8oft. in conjunction

with the " Nucleus " - receiver and an extra resistance - coupled L. F. stage, it- was found that all the principal European high -power stations were receivable at loud - speaker strength in daylight. With the second L.F. valve omitted, Daventry signals were still strong enough to overload an ordinary power valve, as were those from Hilversum. Radio Paris and Eiffel Tower, under these Fig. 6.- Layout of components on the baseboard, which is cut away to clear the moving vanes conditions, were a little too of the secondary tuning condenser. weak for really good loud- A 10

www.americanradiohistory.com 'WhpISIl®E0 MAY r8th, 1927. 6z5 Woalltd, Long -wave Unit for the Nucleus Receive*. - TABLE OF ADJUSTMENTS. speaker reproduction, although ample volume was obtained with the addition Aerial Aerial Coil Sec. Coil Condenser Readings. STATION. Socket. (L1). (L1). of the second amplifier. Cr C',. H.F.C. It was found necessary to use a No. 25o coil as Ll for the reception of the Hilversum A, Lewcos 200 Leweos 250 13 29 26 last- mentioned station, although a No. Koenigswusterhausen. A, ,. , 26 36 39 Motala A, ,. .. 30 47 44 zoo would be large enough with many Daventry A, .. 40 57 62 aerials. With a secondary coil of 25o Radio Paris A., ., ., 60 66 71 turns the condenser C3 was at almost maximum capacity, so it would be pre- ferable to use a No. 300; indeed, it is probably best to «-ill be slightly less than if a higher ratio of capi city to retain this coil for all wavelengths, although selectivity inductance is employed. The aeroplane and aero- drome telephony transmissions on 90o metres may he well received by the help of this unit. An aerial coil of from ioo to 15o turns will HT+ N.C. be required for this wavelength, and if the latter is used the aerial should be 01 connected to the A terminal. Reaction Control. 'file neutralising condenser Of is mounted in an accessible position on the panel, and thus may be considered as a control of reaction; when its capacity is changed slightly on either side of that giving a perfect balance, a certain amount of regeneration is . produced, and the whole receiver becomes more sensitive. However, it has been found that this control is hardly necessary, and the amateur is recommended to operate his set in a neutralised condition. By doing so, risk of causing interference with others is entirely ob- viated, and in any case the advantage gained by using reaction in this particular set is very slight. When the amplifier socket marked H.T. + is joined to its corresponding socket on the " Nucleus " receiver, as it is intended to be, the high - tension voltage applied to the H.F. valve Nvili, of course, be the same as that supplied

to the others -as a - rule about 120 volts. This pressure is quite suitable for the type of valve recommended G.B. above, but if necessary the socket may be connected directly to a tapping on the Fig. 7. -The practical wiring plan. The grid bias cells are actually mounted under the baseboard, below the moving coil holder. H.T. battery. A 11

www.americanradiohistory.com,:..qp¡s -sal -, - r .-'..Ie-atr'.saasa,4fàitiC 616 wflpa@go MAY 18ti1, 1927. wopfl4 NEWS FROM THE CLU so Secretaries of Local Clubs are invited to send in for publication club news of general interest. All photographs published will be paid for...... Loud -speakers Tested and Demonstrated. were necessary to give a full scale de- Before an audience of about 100 persons FORTHCOMING EVENTS. flection. Turning to current measuring in- at a meeting of the Muswell Hill and Dis- struments the lecturer took as his example trict Radio Society on April 27th, Mr. WEDNESDAY, MAY 18th. the Kelvin Electric Balance. In this case J. E. Roe, A.JLLE.E., of the B.R.C. gave Institution of E!,,,ricul Engineers, Wire- two coils are balanced on a very ingeni- less Section. --At 6 p.m . At the Institu- a demonstration of the R.K. type loud- tion Savoy Place, 11-1`.2. Lecture: ".1 ously suspended bar, and placed in the speaker, which gave very impressive re- A'ir&less {Corks Laboratory," by Mr. field of four fixed coils. The coils are so P. K. Turner. sults. 'l'he lecturer tested a number of Hassell Hill and District Radio Society. connected up that when current is passed cone loud -speakers, owned by members, At e p.m. At Tolling? on School, Tether. through the whole six coils, a torsional down. A'.10. Demonstration of Screened effect is is counter- giving fairly good results, and he affirmed Coils, by Captain Tiny,y, (of Alessrs. produced, which that it was impossible with a born loud- Pets Scott, Ltd.). balanced, and the pointer brought back to speaker to reproduce the low notes Tottenham IJ irele.v,c ,Society. -At 8 p.e. zero, by the movement of a rider on a AI I 0, Renee Gerce. Leviure: L.F. properly unless the horn is some 16in. long. A hnptification," by Mr. l,. Tracy. graduated bar. The graduation of this 0000 bar, and the displacement of the rider H.F. Neutralising. THURSDAY, MAY 19th. necessary to bring the pointer back to zero, Golders Creel, and Hendon. Radio Sin,' a. Capt. H. J. Round. M.C., M.I.E.E., was Ae, 8 p.m. At the Chub House, Willi- can be arranged to give a direct reading field IVay. N.W.11. Elementary Wire- of the current flowing. present at an informal meeting of the Mus- less Transmission, with den, o net rat is n, well llill and District Radio Society on by Mr. Harrier Child. o o o 0 May 4th, and he gave members particulars FRIDAY, MAY 20th. of a highly efficient Tricks with a Voltmeter. H.F. neutralising Radio Sods! a of Great Britain. - I hfe r mal method which he had evolved. The sys- meeting. Al 6 p.m. (tea at 5.30). At The lecturer concluded with a series of Orr laici i ti, fion 61 Electrical Engineers. a tem embodied an ordinary Ii.F. and de- ,Saco& ?'bare, 11'4',2. Discussion: "F;Irr- carefully explained instruments with tector stage, the aerial coil being tapped tri,,-! .tIe,r,curen, et, ts," ta be opened ha valve circuit designed to demonstrate that at about one -third of its length and the Sir. F. M. Colebrook. the readings on a voltmeter applied to tuned anode at about one -quarter. A such a circuit could not be accepted at tightly coupled coil their face value. This was strikingly was wound round the mer members earth end and H.T. end of the and intending are asked to illustrated by placing the voltmeter first aerial and communicate with Hun. Secretary, Mr. anode coils respectively with about 14 the across the H.'l'. battery, then in turn turns on an ordinary solenoid. The G. S. Sessions, 20, Grasmere Road, Mus- plate and filament of the end well Hill, N.10. across the turn of the aerial neutralising coil was valve and across the phones. It was joined to the first turn of the anode o o 0 0 found that when the drop of potential Measuring neutralising coil and the first turn of the About Instruments. across the ' phones was added to the aerial neutralising coil was coupled Mr. E. H. Laister continued his lecture voltage of the plate, the sum of these through a small variable condenser to the on " Electrical Measuring Instruments " voltages did not make up the voltage of end turn of the anode neutralising coil. at the meeting of the North Middlesex the H.T. battery. The discrepancy Reaction could be introduced by joining Wireless Club held on April 27th. The lec- amounting in some cases to 8 or 10 volts a variable condenser to the detector plate turer, dealing first with the Kelvin Quad- was due to the resistance of the volt- from the condenser to a reaction coil and rant Voltmeter, said that the great advan- meter. thence to earth. tage of this instrument was that no current Hon. Secretary. Mr. H. A. Green, 100, The Society is planning an active sum-um- flowed through it though some 40 volts Pellatt Grove. Wood Green. N.22.

SOCIETIES VISIT OSRAM VALVE WORKS. Members of the Western Metropolitan Group of Radio Societies photographed on the occasion of a recent visit to the works of the M.O. Valve Co., Ltd., at Hammersmith. The societies represented were Golders Green & Hendon, Hounslow, Inland Revenue, Lyons, Muswell Hill, Tottenham, and Wembley.

A 1 2

www.americanradiohistory.com wtpgego 617 MAY z8th, 1927. wopIle,

SAC 71 AECLd j]A V Cli 111LJ CELLS. Discharge Tests on Small, Cells Designed for H.T. Supply. By F. BLAKEY and 1. F. SAMUELS. r i HE question of the supply of high- tension current of zinc chloride, it Was necessary to renew the for wireless receivers has met with considerable solution after the equivalent of two months' use. attention in some of its aspects, and it is not pro- Originally, it was decided to subject the cells to a posed to re -cover any of this ground. Rectified A.C. discharge of io milliamps. with fixed intervals for re- supply, smoothed D.C. supply, acéumulators and dry cuperation and so to obtain a comparison of their re- batteries, have been dealt with fairly exhaustively, but spective lives as well as general information on the shorten the on a subject which appears to be evoking considerable in- subject. Afterwards, however, in order to terest at the present time, length of time necessary for running the cells down, a viz., that of small bat- higher discharge was decided on. Since it was assumed teries of the sac Leclanché that 8 milliamps. would he the average amount of current type, very little appears to to be supplied, double this output was arranged for, this size of the be known. not being considered unreasonable for the in In view, therefore, of the cell. An 88 -ohm coil of Eureka wire was connected scarcity of information series with a sensitive milliammeter. No voltage read- available, other than that ings were taken, since from a consideration of Ohm's cal- of a general nature, sup- Law, the potential existing across this coil could be plied by the various makers Fig. 1.- Simple circuit used in discharge tests. Neglect- of this type of cell, it was ing the resistance of the meter, the E.M.F. of the cell 20 decided to conduct some (on load) is 88 x current reading in amperes. tests of a quantitative na- 18 ture on a recognised make. Two types of cell were under consideration, one containing a large sac approximately rin. in diameter, and one using the smaller type of sac. The zincs in each case were weighed, and the loss in weight determined at intervals. A solution of ammonium chloride of zo per cent. strength was used in both cells. In the case of the larger cell using the same volume of liquid as the small cell it was found that, due to an accumulation

20 40 60 80 100 120 140 160 180 200 HOURS

Fig. 3.- Discharge curves for the small type cell (2). culated accurately for any reading of the current. two cells were tested separately. At the commencement of the test the discharge was 16.0 milliamps. in each case, giving a potential drop of 1.41 volt across the coil. This is the closed circuit voltage, and is comparable with that obtained ordinarily across the H.T. terminals of the set while working. The graphs show the readings taken during discharge. The discontinuities in the curve show the recuperation intervals. It was not found possible to keep the time periods of the tests of cells r and 2 altogether comparable, but the results are so conclusive as to make this a secondary consideration. Fig. 2.- Discharge graph of large type cell (1). Recuperation In the case of the larger cell the amount of zinc sup- periods are indicated by discontinuity of the curve, only discharge for a theoretical life of approxi- time being indicated on the graph. plied (8.4 grams) allows A 13

www.americanradiohistory.com ()/.S' VaTe®§0 NAY r8th, WolfRA 1927 Sac Leclanché Cells. - mately 7 ampere -hours, and on the basis of 8 milliamps. for three hours per day, this should be sufficient for 290 days or 9. months. In the smaller cell the zinc was larger (12 grams), and allowed for a theoretical life of thirteen months' service on the same basis. It was found from the weighings that in practice, due to disintegration, it would be impossible to count on more than six months from either of the zincs. From the curves the influence of the size of the sac is readily observable. _The very steep slope of the lines in Fig. 3 indicates rapid polarisation, and the ultimate E.M.F. is as low as o.13 volt. The more gentle slopes in Fig. 2 are indicative of slower polarisation. Fig. 4- Appearance of cells The photograph (Fig. 4) shows the cells at conclusion of tests showing disintegration of zincs. with zincs and sacs after use. The disintegration of the these cells are not to he recommended, both on account zinc is quite marked. of their hulk and for the ease with which the electrolyte The tables below give the principal details of the cells is spilled. and also the measurements taken during discharge :- There is, however, one field in which they are likely to prove extremely useful. Stocks of zinc, sal TAf1LF. I. ammonia, and sacs can easily be maintained without deterioration. Large Cell. Small Cell. and for places where it is impossible to use the other types of cell, this type of cell is a veritable ]won in Size of Zinc . 3.75 x 5 ems. î x 3.75 ems. Thickness of Zinc 0.5 mm. 0.5 mm. that a new battery can be made up quite easily at any Weight of Zinc 8.4 grams 12 grams time. Volume of Solution . 25 c.c. 25 c.c. Further, it is quite ap easy matter to remove a Size of sac .. 2.5 cros, dia. 1.5.cros. dia. faulty cell and recharge it.

Ch'.Ll. 1. CRYSTAL DETECTORS. No,.ot Total No. Starting Finishing Hours. Hours. Current (mA.). Current (mA.). Average (mA.). Recent Research with Galena Crystals. 16 16 16.0 14.0 15.0 04 40 14.0 13.0 14.0 rectifying action of crystal detectors has been the 23 13 13.5 11.5 12.55 .1`HE 24 87 13.0 10.6 11.8 subject of many theories and much speculation. At 244 114 12.6 10.6 11.6 one time it was thought that the rectification was due to 174 129 12.2 10.5 11.35 16 145 11.4 9.8 10.6 a thermal effect, and more recently an electronic theory 16 161 11.0 9.2 10,1 has been 6 167 10.9 9.1 10.0 put forward which accounts for many of the 22 189 12.0 6.5 9.8 observed phenomena. The distribution of sensitive and insensitive spots over Total : 189 hours. Average discharge : 11.7 mA. Total discharge: 2,220 milliampere hours. Test discontinued. the surface of a crystal, however, does not seem to obey any fixed law, and no theories have so far been advanced CELL 2. which satisfactorily account for the fact that good and bad spots are often found close No. of Total No. Starting Finishing in proxirhity. Hours. of Hours. Current (mA.). Current (mA.). Average (mA.). Some light is thrown on this problem, however, by the 24 24 16.0 11.0 13.5 results of investigations by Messrs. A. Schleede and H. 16 40 13.1 9.8 1l.11 Buggisch of the chemical composition of galena. They 24 64 12.0 2.0 7.0 24 88 10.0 2.0 Qn have shown that small crystals of galena, chemically 16 11)1 9.8 1.5 5.6 24 128 8.0 1.5 4.7 formed from lead and sulphur, are not of uniform chemical composition and that certain crystals contain more Total: 128 hours. Average discharge: 8.7 mA. Total discharge: 1,180 sulphur than is indicated by the chemical formula. It milliampere- hours. was found that crystals with the highest sensitivity as Conclusions. detectors contained an excess of sulphur. In drawing any conclusions from these tests many The logical conclusion is that minute crystals rich in factors have to be considered. Generally speaking, space sulphur constitute the sensitive spots in a galena crystal occupied is not of primary importance, and so the extra detector, and in this discovery also is to he found an bulkiness of this type of battery is not serious. There explanation of the wide difference in quality between are occasions, however, which would on this account specimens of natural galena mined in different parts of render their use undesirable; for portability, for instance, the world. H. R.

A '[

www.americanradiohistory.com Wflp®Il@go r8iIi, 1927. 619 MAY WópTi0

Aids to Better Theoretical Diagrams Reception. Simplified.

H.F TRANSFORMER CONNECTIONS. ing dials. Constructors of sets in- is no doubt, however, that there are Experience shows that the great cluding these transformers who are some points in favour of this arrange- majority of failures to obtain good dissatisfied with the performance of ment as applied to the leaky grid results with several of the receivers their receivers should check the wir- including the modern type of H.F. ing carefully, being guided by Fig. transformer are directly traceable to r, in which the connections of both faults in this component itself. aerial -grid and H.F. intervalve trans- Attention lias already been called in formers, as well as the relative posi- these columns to the need for good tions of the various windings, are insulation and correct spacing between clearly shown. The letter indicates primary, neutralising, and secondary the points to which the ends of each windings, but emphasis may also be section are connected : G corresponds laid on the absolute necessity for to grid, F (or G.B.) to filament proper connection of the various (generally through the grid bias bat- terminal points. In particular, it tery, as stated above), P to plate, should he remembered that the prim- N.C. to neutralising condenser, A to ary and neutralising coils are wound aerial, and E to earth. over the low -potential end of the In the sketch showing the H.F. secondary -that which connects, transformer, the section of the generally through a grid bias battery neutralising winding is indicated by or potentiometer, to the filament of full dots, while the primary, with the succeeding valve, and not over which it is inte.rwound, is shown by circles. Fig. 2.- Controlling grid voltage of a that end which is joined to the grid. 0000 reactor valve. Results, of a sort, may be obtained if this connection of the secondary is THE REACTOR VALVE. rectifier, which usually has to perform a re- incorrect, but the amplification will The advantage of separate the operations of ' oth detection and. - be poor in comparison with that which acting valve is most pronounced when regeneration. Its adjustment can should be expected, and the set is cer- it is used in conjunction with one of hardly be absolutely correct for both tain to be unstable; it will generally the recently introduced high-magnifi- functions, and in practice one has to he found that a separate adjustment cation valves functioning as a bottom - effect a compromise between those high ohmic of the neutralising condenser becomes bend detector, with a giving best detection and smoothest - necessary for each setting of the tun- resistance in its anode circuit. There control of reaction. When a separate reactor is used with an anode detector, where there is no grid circuit condenser (which would act as an insulator), the grids of both valves automatically assume the same potential, and thus types having different characteristics must obviously be fitted, as the rectifier should be working on the bend of its curve and the reactor on the straight portion. With the grid circuit detector, however, conditions are different, and provided that the leak is connected between grid and filament, and Fig. 1.-Sectional sketches of aerial -grid and H.F. transformers, showing ultimate of connections of the terminal points. not across the condenser, the grid A 15

www.americanradiohistory.com Ó 2n Wip@Il@@0 WoACl MAY ,8th, 1927. the reacting valve will normally be at tive of the bias voltage applied to the greatest care; they cannot in - zero voltage. them lh order to economise the reactor. selves add amplification, but in H.T. 0000 make battery current and to pre- possible the use of vent additional lightly damped damping, it is advis- efficient circuits, and in particular of able to insert a small bias battery of THE REASON FOR NEUTRALISING. a loosely coupled and selective aerial - one or two cells, as shown in Fig. 2, It must not be thought that the grid coupling. Were it not for the in- in such a way that a negative voltage addition of a balancing or neutralis- troduction of the principle of neutrali- is applied to the grid of V1, which ing device adds anything to the effec- sation, the application of such devices is reactor. the The detector. V, is tiveness of a high- frequency inter - to a receiver including H.F. effectively insulated amplifi- from this battery valve coupling. Indeed, it would not cation would be impossible; or, by the condenser, more and its grid poten- be far short of the mark to say that accurately, valueless, as tial is determined artificial by the point of con- such arrangements are rather more damping would be required nection of in order the lower end of the leak likely to introduce a reduction in to prevent uncontrollable self- oscilla- to the filament circuit, irrespec- signal strength, unless designed with tion.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 71.-A Neutralised Tuned Anode Receiver. (To he concluded in next week's issue.) The present series of diagrams is intended to show progressively, and in an easily under¿tandable manner, the various points to which special attention should be paid in the design of typical wireless receivers, and at the same time to assist the beginner in mastering the art of reading circuit diagrams. While giving less H.F. amplification than a well- designed transformer, the neutralised tuned anode coupling shown below has some advantages from the point of view of simplicity and easy interchange of wavelengths.

o HT.}

. H C I LT. -----0 = t YvvvlL+ J\--1 o (1) (2) The filaments are connected in parallel across the L.T battery, with -- the aerial Is connected to the centre point through one of separate controlling rheostats. A tuned coil is connected the alternative series condensers. The plate between grid and filament of the II.F. valve. A bias of this valve is cell Is connected to one side of n tuned anode coil, the centre point of interposed, while- which is joined to It.T.

AL'I'H0 l ;H . separate rheostats wire on a sin. former. For the long should he regarded rather as a con- are shown for each valve, this waves, a section -wound coil of 25o trol of aerial coupling than a tuning elaboration is hardly necessary, par- turns of No. 28 D.C.C., with a mean device. The anode coil and its tun- ticularly in a circuit of this descrip- diameter of gin., is recommended. ing condenser C. may be similar to tion, if valves of similar filament The series condensers C, and ('_ are those suggested for the grid circuit. characteristics are used. inserted in order to reduce aerial The choice of the H.F. valve is a A capacity of about o.0005 mfd. damping ; they should have capacities matter of some importance. If good is suitable for C although one of of about o.000r and o.000,; mfd. amplification, combined with o.000g selec- mfd. may be substituted. The respectively, the larger being used tivity, is to he obtained, one with an coil may be of the commercial centre - for long waves. Alternatively, a vari- impedance of about 70,000 ohms and tapped pattern, or can be home -made, able condenser of 0.0005 mfd. may an amplification factor of about ;5 with about 7o turns of No. 24 D.C.C. replace these two fixed capacities; it should be used.

A 16

411411:.... sy,r,:rria.1.0tß1rawww.americanradiohistory.com ,r.ta .c-4r9r -,,- ---4ritrsS3i 'IV ' Hove the New Condenser Serves as an Aid to Tuning. By F. H. HAYNES. l' is interesting to reflect that less than three years ago their relative frequencies= instead of by uniform all variable wrodensers used for tuning purposes were numerical difference of wavelength it is obvious that the fitted with semicircular shaped plates in which the scale of the tuning condenser should be so devised that change of capacity advanced uniformly as the dial moved " frequencies " rather than " wavelengths " should be from o to tiio degrees. 'l'hus if the rapacity at to deg. equally spaced around the scale of the tuning condenser. condenser was 20 1,. ¡4 12,1 then at 20 deg. the capacity would he This is the aim of the straight line frequency 4o /Ltd.', and at 90 deg. ido'4µF. At that time it was in general use to -day. As frequency varies inversely with customary to allocate bands of wavelengths for certain wavelength, their product being a constant. it follows that classes of communicatit tn. and the wavelengths adopted the plates of the S.L.F. condenser must he shaped so that I.y the various stations within a hand were evenly spaced. the capacity change is inversely proportional to the square contour of plates designed to I f wavelengths of 200 to .100 metres were to he used for of the scale divisions. The broadcasting then station A might operate on 200 metres. produce a capacity change varying inversely as the square It on 25o metres, C on Soo, and so on. of the wavelength (S.L. F.) follows an hyperbolic spiral, the actual part of the spiral employed depending upon the Square Law and S.L.F. Scales. simple ratio between the highest and lowest frequencies As the wavelength to which a circuit tunes varies as the to which the condenser is required to tune. . square root of the capacity of the tuning condenser, it was It may be said that comparatively few of the S.L. con soon observed that stations near the lower end of the densers available on the market are mathematically per- tuning scale of the condenser were separated by only small fect, yet the particular plate shape adopted may add to intervals, while it was necessary to rotate the dial through the convenience of tuning so that any errors in plate shape a much greater distance to produce the same wavelength which may exist are not readily revealed to the user. change when using the condenser near its maximum capa- Condenser plate design is now to undergo another modi- city. This led to the straight line capacity condenser fication. the need for which haying primarily arisen from being completely superseded by the " square law," or the practice of linking together several tuning condensers straight line wavelength condenser having plates shaped so to a common control though bringing with it other advan that the capacity change was proportional to the square tapes. Recently tuning condensers have appeared on the of the degree setting of the dial. With the scale of the market in which the capacity change varies loga- dial increasing according to the square of the capacity rithmically. value of the condenser, and the wavelength depending Slide Rules and Abacs. upon the square root of the capacity, it is obvious that the condenser scale of a square law condenser is directly pro - "ro more easily appreciate the merits and particular portional to the wavelength, a given increase in the degree application of the logarithmic condenser, one might con- setting of the dial representing a definite hand of wave- skier the method by which the relationship between induct- lengths. ance, capacity, and wavelength (or frequency) is deter- Now that station wavelengths are allocated according to mined. Wavelength is proportional to the square root of

' µpF=mieromicrofnrads. 20 µ;,F=0.00002 infd. 2 Frequency x wavelength = 300,000.000 approximately. A r9

.-.11*. .+e>..111y..; 7Rq7-r.+... 4 , www.americanradiohistory.com WAp®hoo Wortcl MAY z8tlr, The Logarithmic Condenser. - In setting out the scales it is only necessary to determine the inductance- capacity product or expressed in practical one point on the wavelength line, marking off the logar- units, ithms of the wavelengths above and below this point. A=1885 ,./LC. . (I) It will readily be seen that for a given increase or de- 1l being the wavelength in metres, L the inductance in crease on the scale (c) representing the logarithms of the microhenries (p.H), and C the capacity in microfarads capacity, and with the straight edge at a fixed point on the inductance scale (a) that the point of intersection on the wavelength scale is moved by half the amount of the a b c logarithm of the capacity. Similarly changes on the in ductance scale,(a) produce a change on the logarithmic

www.americanradiohistory.com Mp@Il@Eg MAY /Rh, r927. 623 Woiflkol Calibrated Wavelength The Logarithmic Condenser. - Supplying Condensers with capacity pointer is rotated the Dials. fixed position, and as the can resulting wavelengths can be read off or vice versa. It Just as a square law or S.L.F. variable condenser so can will be noticed that the logarithniic capacity scale (and be supplied with a calibrated scale of capacity, be hence the inductance scale which is similar) occupies a tuning condenser fitted with logarithmic plates nearly r8o degrees, and can therefore be marked off with supplied with a wavelength scale which is correct irrespec- is the corresponding scale degrees of a particular condenser. tive of the size of the tuning inductance with which it rota- It will, however, be necessary to measure the capacity to be associated. It will be seen that the extent of of the condenser, say, at every to degrees, and mark in tion of the condensar spindle required to change from the dial settings to coincide with the measured values of one given wavelength setting to another is the same irre- be capacity. If, however, the tuning condenser is fitted with spective of the size of the coil, and it will therefore plates shaped to follow a appreciated that " gang r' logarithmic law between the condensers, if required to minimum and maximum tune several circuits simul- settings, then a uniformly taneously in which small spaced scale of degrees on differences in the inductance the calculator can take the values of the coils may exist, place of the logarithmic that the plates óf the con- to s ^ale of capacity. densers must be designed follow the logarithmic law. Relationship Between The much sought after ideal Circular Calculator and of building a long -range Logarithmic Condenser. receiver with several stages The utility of the arrange- of tuned high- frequency ment will be appreciated by amplification and operated setting the wavelength and with a single dial is only capacity scales to the wave- possible provided that the length and tuning dial read- condensers which are linked ing in degrees when listen- together on the common ing to a local station of shaft are logarithmic, and known wavelength, so that assuming, as one must, irre- the apparent inductance of spective .of the " law " of the tuning coil will be re- the condensers that the dis- vealed on the inductance tributed capacities in coils scale. That the inductance and valves are nearly simi- value of a coil can be readily lar in each case and that the determined in this way is value of such stray parallel perhaps in itself of little im- cip'tcity is comparable with but feature that decided upon . by the portance, the Fig. 3.- CIRCULAR WAVELENGTH CALCULATOR. The aimed at is to be able to logarithmic scale of wavelength on the centre dial is marked off manufacturer when deter- on twice the scale of the semicircles representing inductance mining the shape of the predetermine the condenser and capacity. it is from a consideration of the operation of required to tune to this form of calculator that the action of the logarithmic condenser plates. settings as an aid to tuning can be more readily understood. any given wavelength. With Nothing has been said up the inductance pointer retained in the position which is to this moment concerning the capacity of the tuned cir- given by combining the dial setting in degrees with a cuit at the zero setting of the condenser, and in determin- known wavelength it is only necessary to rotate the wave- ing the shape of a condenser plate which is to follow a length indicator to the setting of a station to which it is straight line in respect of the tuning of a circuit all stray desired to tune when the actual condenser setting in capacities which are added to the capacity of the tuning degrees will be revealed. If the tuning coil is changed condenser must be taken into account. The plate shape the inductance pointer must be reset by again tuning to (Fig. 6) is obtained by taking a sheet of graph paper in the local station. which the lines along the vertical axis are set out logarith- Progressing, it must now be apparent that the adjust- mically, or, alternatively, ordinary squared paper may be able scale of wavelengths can be accommodated on the used as in the accompanying calibration charts, the anti- tuning dial itself when used in association with a tuning logarithms of the numbers subsequently being taken from condenser following a logarithmic law (Fig. 4). A a table. A straight line is drawn joining the estimated logarithmic scale of wavelength is engraved around the capacity of the condenser at zero plus an average value rim of the dial, the scale being twice that of the capacity of coil, valve, and other stray capacities with the required change of the condenser. This scale is adjustable and maximum capacity to which again the external stray provided with a simple means for locking it in position capacities have been added.5 (Figs. 7 and 8.) on the centre disc, which is rigidly attached to the Experience shows that an average value of stray spindle of the condenser (Fig. 5). Wavelengths in 5 Refer to "Condenser Plate Design," by W. H. F. common use are engraved right round the dial, and if Griffiths, The ll'irelees troth?, June 23rd, 1926. Also Experi- necessary the markings may be extended in spiral form. mental Wireless, January, 1926. A 2I

www.americanradiohistory.com The Logarithmic Condenser. - The " Ormond " wavelength calibration (Fig. 9) parallel capacity can I, taken as. some 26 1tµF, in addi- plotted with logarithms of wavelength closely approaches tion to- the zero capacity of the condenser. This value a straight line, though here, again, the minimum capacity has been determined using a single layer inductance of differs slightly from the figure used by -the designer. 15o nlicronhenries bridged across with the grid and fila- It would seem a mistake to build a condenser with a ment of a Milliard type 256 valve with the normal voltage very low minimum, as the stray capacity which has to be applied to its filament together with the associated valve - taken into account is large corn- pared with the holder and wiring. minimum capacity of the con -''. denser. In Tests on Logarithmic Condensers. r .. ; At present there are on the market the " Cyldon," jA U Ormond," and " Formo " logarithmic, condensers, and curves showing capacity and wavelength calibrations are given on the adjoining page. That these curves very slightly deviate from the straight line is due to the fact that somewhat different values of estimated external capacity were adopted by their designers. When 'plotting the capacity curve (Fig. 8) of the

Fig. 5.- ADJUSTABLE LOGARITHMIC DIAL. The centre dial A is locked on to the shaft of the condenser. By means of the locking plate C the outer dial B is secured to A but can be independently rotated and carries a wavelength scale which holds good in respect of the condenser and is independent of the size of the tuning coil. It is set in position by tuning to a station of known wavelength when the wavelengths produced at other settings of the condenser are then revealed. Scales of inductance Fig. 4. -The new Cyldon logarithmic condenser. and capacity may be arranged as shown on the centre dial, one reading against an index on the wavelength dial and the other against an extension of the pointer which is used with the wave- " Cyldon " condenser, however, before extracting the length scale. logarithms of capacity obtained at every to degrees an order that a reasonable latitude may be allowed for amount of only 20 µµF. was added, this value in being the value of the stray capacity, it would specified by the manufacturer. The curve slightly be advisable bows to adopt a higher zero capacity in the condenser itself. away from a straight line between zero and 8o degrees the Incidentally, a low zero value invariably increases the maximuni error occurring at about 5o degrees. From 90 18o degrees the logarithms of the capacity fall on a perfectly straight line. In the case of the " Ormond " condenser the capacity curve (Fig. 7) is practically a straight line, and in the absence of any stated value of circuit capacity 26 µµF was added as representing the stray external capacity to the capacity values obtained before taking the logarithms. A wavelength calibration of the " Cyldon " condenser (Fig. to) shows an almost uniform bowing away from the straight line joining the maximum and minimum capacities the bottom of the bend occurring at about 45 degrees. This arises, however, from the fact that the plate shape was determined with a stray of 20 µµF which, it may be pointed out, is a value appreciably lower than that which normally exists in practice. Fig. 6. -The plate shape of the logarithmic condenser. A 22

www.americanradiohistory.com MpsIlmo 625 MAY 18th, 1927. Wohilcl

2'8 ...... E.M....M..M.....MMM.=MM 2.8 E.M..M.M. .UM...... M.E.M.. CYLDON ORMOND ...... '.... 00005mfd ....i...... °...... 0.0005mfd ...UUUOE.ME.MUM..U..../AE.... 27E== \.M.....U.UU.U..U.... 2.7 ...... ii..... :::'..:'=::::C:::::::' ::::::'::::: .....: ...... T:...... '.:...... E..E\EMEEEE..EME.EM.iEEEE.E.' 26 ':: : 2.6 ...... \...... ri...... EEEE.EE..EEU.MEM.U.EE.UE.EMEU rí'...=.....=i .....°Ei...... ii...ï ...... UMUU...E.M.M.EE.M.E..E.MEE. M.EU..M..U..UMMN.. .E.MM.EUE.y.ME....MM ...... UMM.UUM.M..EEE...Vi.ME..E..E 2'5 \\\\\\\\\\E.EM.E....MEEEEEMaMEEEEE.M.E 2.5 ...... E..\E.EM...\NEE.MEEM.EE=.EEE. \\mE.M.EEE.EMEEE.EMMEMEE..r.E.E.EE.E. ...U.EE.E.EEEE.M...... U..U.EM.E .EMME. .E EU....EE..EEEM.ME..MM/....EE.....E .E....E.E..E..E..ME...M.fSU.E MMM.U.EE. \\\\\\\\\MEE..EM...E.E.EVAEEMEEEEEUEEME 2.4 .....UE..MM....M..M....E.M....M...... 2 4 \rrU...M..EEM.M...ME.M..W....E.E.M.E.M. ...Ei....i ...... ii...... mÌi...... MUUMUUU..UEEE.000U.E..EEMEM ...... i...... EEMEEEMMMEE=EEEEUMEUUEEEEEEEE.EEEEEEU.E 2'3 \EEEEEEEEEE....ME.Er...M..M.UM...\\\ 2.3 ...M.M. ..E MEM....ßMEMMME.ME...... M ..E\EE\\M..E....EaEE..MM..EE...M...... EEMEMUEEUEE.ENE..EEMMEEE\ME.E.MM. \\\.MEEEEEUEEMEUMMEEU.U.E...E\..UMM.. MEM...EEE.MEMEM.EPAEMEEMME.E.MMEEM.EE.. ..MMEEEUEEM..E.E.EMMMM.E..ME.EE\..MM.E. U 22 ...... iï...... i... U 2.2 EE.EEEEEMEEE.ME..UME\E.EM.M.M.M..EE.ME. \\\\\\..M.M..EA.U.M.E\M.U..MU.N.U..E ME.M.UM\EU.MM.M.\..E.E.MM.MM.MEM.MMM.M \ME.E.EEEEEEVEE...U.U\EEEEMM\\E 0 \EM.MEEME\EEMEEI..U.M.M..MU.EU..MUUM.EEU. ó 2,1 ..UM..E.EM.E....\\EEEEE...... E..... M.M..MUM...MUMEW.E.....MEM.M.UMM.UMEEEM \\\\\E\EE\.EI.NM..UMMEM.\E.EEE. JO 21 .EEEEE..EEEE.'IEMEEEEEM.EM.EMME.E\MEE.. \\\E\\\...EE.EEE..\EEE..MEEM EEMEEMEMEEU.IiE.EEM\E.EM.EMEM.iEM.M..M. \E\E\E.EEEEEE\IIE\\EEE\E\E\EE\EE\EEEEEEE =UE.EE..EEEE.EMUE.MEEO.EMU.EU.EEUE.EEEE .M..EMEE.. r,\EEE..\EE.EMM\E...... M .MU.EEM.EiNE..E..MM.MMEMMUEEE.EEE. 20 .E.EE.U...%A.E...UEM..MUEUM..E...MU 2.0 .MM\.EMEE.tAM.....M.M.E..MMM.MM..MMMMM. \\\\\\\\.M.E....EEEEMUMOEE..UE..E...U. ..MMM..U.E.EMM...ME.U.E.MU.NU..EUM.. \..E.E\\EUEE\\\EEEE\\E\EE\\\\\E\\\\\\\ EM....EUEU.E.UE000.U....UMEEEUUM.E.EE.. \EEEEEEEENEEEE\E\E\EEE\EE\\\EEE\EE\EE EMEE.E.oEE.MMEEM.EM.EMEM.\.EEMEEME.MEEE \M.ME\EMN.\EE\\\EEE\EEEEE\\E\\EEE\E 1.9 .MEEUEE/..MEE.UE\MUEUE000..M.EM.EMUE.UUE. \EEE\E\t1\E\\EE\E\EE\E\EE\E\EEEE\\E\ .E....EAM..M....M...... M..M\..MMMMM.M.M. EE\EE\\IE\EE\E\E\\E\\E\E\\\\\EE\\EE.ME. M.OUEEE.M.E.E.M.\.UMEMMEU.U\MEMME\E.UUME U...... UU.EU..UEM.ME\EEE\EEEEE\\EEEEE\E .....UE.EE.EEEEEEE..U.E....UU.U..UUM.U. \\\\i\...\\\\.\\\\\.\\\\\\\\\ Ern \\\\ 1.8 .EEEI..M.M...UMMU..M...UU...E.MM.EM..E...... ß ...... EU..U... M..EEEU.U..U..EMM..U.M.OU..UE.UUEMN ..\....\..UNM..UMEM.....E....E.E..MEM M..I.MU.M.OMM.....EUMUMM..E..EM....UE. ...I.N.U.M..MM..UE.\.E...U\.....\...... M.I.M..M.E.M...ME.....MM.UMEU.M.U.000MEM .\E M...M.M....M 1.7 E MME.EEE.....M..M....M.M.MUMM.M.MM ..E.M.EE.E.EEE.EEM..EE..U...ME\.EMU.. .EUE.MEEEEMEEMUUEEEE.EUEE.\E..E.EEEEEEEE .EU..E.E\E\USEN.NMU.M..EMU...MU.M.MEUM E.MU.NE.EMMM.M.M =MTh M.U..MME.....UM.M IE.U...... M....E ...... U..E.E...EME..UU...UM...MEU.EM.U.E..M ...U...... M...... M..U...... 18 ..M.M.M.E..EE..ME..E.E.M.EMME.EEMEE..M.M ..\...\\.MEUMUOE.M...M.U.MMU..UUMM.M...E .....:...... EUUU.MUUE...MEUE.NE.\.\.\\.\\...ME.E..EM.M...MM.E=EEU.EUUU.E.E. M..M.MM.E.. 1.50EEM..EU..E\UMM..O.EMUMM.MU.M...000.U.M 20 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180 CONDENSER SCALE CONDENSER SCALE

2.76 .UM..\.U..MM.EEEUM.UU.\..EEE. 2.76 CYLDON MUM U..MMME..EMMEMMi ORMOND .M.O.UEE.M...... M.MU...M.M..MEMM. 00005mfd ...MU.EUM..ME..EE.EEMr...ME. EE.E...M.EE\.MEE.E.EE..EEEE. ..MUM...E.M...E.NUEUME 0.0005mfd MEMO ...... MU.MMMMU.EMUM.MM. E..ME..EEE..M.EME.EEU.....MriM.MEM MEE MEE.MMUMEEEEEUM.U.MM.U.MU 2.70 ...UU...... UEMUM.MUM..E.EUM...EEMEE.EMEMMU.EM..EME.M.M.V.E.MMMEE 2 70E.EEEMEEME.E...... M.EMMEEME.\.A..EEMEE.M..E..E....ME.M....E.MMa.MMMMMM. ME..E..EEE.E.EE..EEEEE.EEEEEri..EE.M..E ..EM.E.ME.M.E.MUEEUEMM.E..EME9.EE..E.M.MEE.E EE.íM..EE.E.. M.M.ME....EMU.M.MMEEE..E.ME...E...... EEM...... mom MUM_.UEU...E.E....EE.UMM....\.E. .U.M.E.MMEMM.M.EUWEE.E..EEE.E. \UU.EUE...M.E...U.I,N.E.E.MU\..\EEE.E.E..\....MEri.E..E..MM.M M..ME..ME.E.E...U..M.....A.MU..UUMM..nUU..EU..\ MUME.M...ME.M.M.M.:E....EUEMUM ..M...UMMM...M.\M.MMMMMM M..E..EEUEEUEM..EEEUEEEEru.UE.ME.EEEE.. 2.60 H...... %..i M..M.M..MM.M.E.M.E.MMMMU 2 60 ä....ï...... '.'i...... °i...... MUM E..M.M.EMME.E.EU.EEMEMMEU.MNUE...M.EU .\....EM...E.ErW.EEE.EMUUE..MM.E..UM.E.EU..ME.M.E.M..r..EE..EM.ME.EMM \E....EEE.E.ME..EME\oMEU.EU.EU.E.EEEE \.UU.EM.E.EE.EEn.UEEU.EU.MEEEEEU U.EU..E.E.EEEEM.E\M.IMEEE.UM..EEMEE.M M...... E.M.M.ME.M.E NM..MMM.M.E..EM. .MM...EMMME..E..E.E.EM.EEEU.UE...... M. ..EUMEE.E.Eri.EM..E..E.....M EEEEEEEEEE.EEEEM.EUr.\.E..MUE..M.M...M. M.E...MUE...U...ME..EM.MMM...E M...MM.EEEEEEEE.EEEWEEEEEEEEEEEEEEMEEEE M...M..EM.EU.U..E..M.U.EE...... M .E.EEUEEEEU.E.ErW.EE.EEE.EMEME.MEME e< ü ...... irEi...... C.....i.... E..M..E.U.E..r,EMMM.MEME...M.UM...M EEE..E.MEU..EE..wE.E..ME.M. .U.E..E. o 250 E.ME.E.E...AE.MME.=.EEEE..E.M.0 c7 2'50MM.M..M....EM.E.MUN..E.EEE.EE.EU.U.E.E M.M.U.ME.EE.EEE..a.EEEM. ..UMEU.M...M p U....EE.EE....E..EE..M.MM..EEE..EMM...E O ...... I...M...... EEEEEEEE.N.ME..NEUUMMUME.UEM.UEEM.E.E. J ...... A .EEEEE\EEUE.EEEEE.EEE..EE.E'.EU.EOEEM...... UUM.E....E\...\ UE...EMEM.Em.U.E.EU.EEE.E MM.UU.EE E...... r...... EEEEEEEEEEEE.VN.EE.E.E.EMEEUEEUMEEEUEEE...... U...U/UM.....EU.UNM...M.M.EWE .EEEEUUEEEEEEE\EEEEEEEEEEEE\EEEEEEEEEE \...... E.Ei....EEE...E.E...... EE.\E.E..oEEEE.\.EM.MEEM.EE.EEMEEEE ...... E...E.ME.E..EEEEE.E.M..M M ...E.ME.EEW.nEEE.EEEEEEEEEEEEEEEEEEE ...'...... /,....N.EEU...... EM... .EEEEEEEEE.iEEEEEEEEEEEMEEEEEEEEEEEEEE 2.40 ..E .....n...... E...... 2 40.EE.E.EEEEUEEEE\EEEEEEEEEEEEEEEEEEEEO ...U..EUfUEE.EU.EUMEE..EME.E.EE.EE .E..E..E.MEEEEEEE.EEEEEEEEEEEEEEEEEEE ...... i..\ ....EEE.IE.EEE....E.EEEEEEEE.EEEE.EEEE ....E..,I.NE....E...EEEEE.E.EE\E.EE...... w/E.M.ME...EM..EE..U.EE..sM ...... i.....° ...... ü C.....E.EEEEME..ME..EUMEUEM.EEE.E.M E ..EUUaEM..EEEEEE.EU..E.\E.M..E.EE.E.EE ...... E N.EE.r.MMMEMEE.U...M.E.EMU.E..UMMN..EE ...... 0 \....E...EM.EEM.EEEEEEEEEEEEEMEEEMEEE.. ...I..N.UE..E..ME...M.E...MM..M...MM..I.UU.EE.M.E.EEM.E.EEEEE..EEEEEE.EEEE EMU M....U.ENE..MU.EMEN.MM.E.M.ME= EE1..U\MEEEE.EEEUEE\.E..E.E...... U\U 2-30 .iuN..E..N..E...E...M..M.M...MEE 2 30..iiMï ...... MEEEMEM..E.EU..EE.E..EEEE.EEMEEME.. ..EE.E.EUU.E.EEE.EE.EEEEE.EEEEEEEEEEEEEE E.M.EE.EEE..EEEEE E.E..EEEEMEEEEEEE.... .UME..EEEEMEME.EME.EEE..MME.EEU.E.E.E.EE .EE...i=UEEEEEEM...E.EE.E.E..E.EME.EE.E...... Mï. M.M. EEEM.EE.MEEEOEMEM.... E..EE..E ..ï..i...ï...... i.....i .. 2.24 2.24...E....EEEEE.M.EEEE.\E..M.M.E..EM 20 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180 CONDENSER SCALE CONDENSER SCALE

the scale settings in the case of the Ormond and Cyldon logarithmic Figs. '7 and 8.- Logarithms of the capacity plotted against the stray capacity Before taking the logarithms of the capacity values a small value has been added representing condensers. in the condenser circuit. of wavelength plotted against scale degrees. The departure from a Figs. 9 and 10.- Curves showing the logarithms the being different from the value straight line in the case of the Cyldon condenser is partly due to the zero capacity of the circuit used when designing the plates. A23

www.americanradiohistory.com 626 Wlinfl@g30 MAY WoyIld 18th, 1927. The Logarithmic Condenser. - scales will be found to be reasonably accurate for tuning resistance of the condenser near the zero end of its even the aerial circuit of a receiver, assuming the use scale. of an aerial transfOrmer An accuracy equivalent to one It will be realised in the case of the square law and or two degrees of a i8o- degree scale will he obtained S.L.F. condensers that the aim is merely to provide a when tuning on intervalve H.F. coupling. It is, of convenience in tuning, and any error which may exist course, first necessary to correctly set the dials by tuning in their design will not be readily apparent. The to a station of known wavelength. Assembled ro form a logarithmic condenser, however, serves the definite pur- gang condenser a sufficient closeness of tuning between pose of permitting the manufacturer to supply a wave- the several tuned stages can be obtained providing that length scale irrespective of the size of the coil within the the sections are individually adjusted to correspond at limits with which the condenser is to be used, and errors one setting. Incidentally, the contour of the logarithmic in the plate shape will be readily observed when using plate shape is midway between square -law and S.L.F., the logarithmic condenser for predetermining the wave- giving a tuning scale which in general use is. to be length settings for tuning to particular stations. Well - preferred while " sharpness of tuning " is uniform designed logarithmic condensers supplied with wavelength throughout the scale.

MERITS OF THE LOGARITHMIC CONDENSER. 1. Convenient tuning scale midway between square -law and S.L.F. 2. Sharpness of tuning is constant throughout the scale. 3. Can be supplied with a calibrated wavelength dial. 4. As a gang " condenser it correctly compensates for differences in the inductance values of the several tuning coils.

VOLUME CONTROL. A Useful Circuit for Resistance =coupled Amplifiers. NOW that dull -emitter valves are in almost universal merely amounts to shutting the stable door after the use, and high- tension accumulators and mains horse has escaped. units are coming into favour, it is becoming more Tapped anode resistances, tapped chokes, and tapped and more usual to dispense with switches for cutting out transformers all provide simple and satisfactory means of amplification stages. Generally speaking, this tends control and can be strongly recommended. Unfortunately, towards simplicity and freedom from stray however, it is often undesirable to use couplings, and is therefore a step in the transformer coupling for the first L. F. right direction ; but, although we may no stage, and there does not seem to be a longer need to switch out a valve in the suitable tapped choke on the market. interests of economy, we are still faced Tapped anode resistances are obtainable, with the problem of adjusting the total but are fairly expensive compared with the amplification of our sets. fixed type. Where a high -frequency stage is used A circuit which has given every satis- the volume may usually be sufficiently re- faction in practice is shown in the diagram. duced by dimming the H.F. valve when This volume control is really a potentio- receiving powerful signals, but when no meter with one fixed and one variable arm, high -frequency amplification is employed the latter being an ordinary variable grid - filament dimming is a most unsatisfactory leak. method of control, and almost invariably As may bo seen from the diagram, the leads to distortion. Reaction reduction or potential variations E on the plate of V, reversal An effective volume control is fairly satisfactory in the hands `lrcuit. V,, detector valve; are applied across R_, C. R3, and. of enthusiasts, but is not recommended V'2. 1st L.F. valve; R,, anode neglecting the effect of the impedance resistance 150,000 ohms; of with sets of the " family " type. One R2, variable grid leak 0 -5 C, which is comparatively small, the input drawback to reaction reversal megohms; R3, fixed grid is, of course, leak 0.5 megohm; C, grid to the grid of V, will be :- that it considerably broadens tuning, and condenser 0.01 mfd R3 (Total available potential, E) X this is particularly undesirable on long R,+ R, wavelengths where interference and " mush " are at all This means that if components of the values shown are times fairly had. used,. approximately any degree of loudness between full Perhaps the worst method is one sometimes advised by and one -tenth of full volume may be obtained. The con- manufacturers of components, namely, the inclusion of a trol is smooth and continuous, and does not in any way variable resistance across the loud -speaker. It is cer- cause distortion. Care should be taken to select a vari- tainly very effective for controlling the amount of noise able grid -leak which shorts out in its minimum position produced, but cannot possibly prevent distortion due to or full volume will not be obtainable. valve overloading. In fact, as far as this is concerned it R. J. S. A 24

www.americanradiohistory.com MAY 18711, 1927. Wt@Il@m WopIll 027

nnza . : u,; 01p . K' I : IIlnll lg f11 l@NI0III1 Fy I Ill l; i III Tl - IInñ 7 cUFTN' L TOPICur News of the Week in Brief Review.

AN IMPORTANT WEEK. LOOKING AHEAD IN SOUTH WALES. PORTUGUESE WIRELESS NETWORK. The 1927 National Radio Exhibition It is hoped to hold a wireless ex- The Portuguese network of wireless is to be held in the New Hall, Olympia, hibition in Swansea during the autumn communication to her colonies has been from September 24th to October 1st. under the auspices of the Wireless completed by the inauguration of iIar 0000 Retailers' Association. coni services between Lisbon and the ANOTHER STEP FORWARD ? 0000 colonies of Cape Verde, Angola and According to the daily Press, Pro- Mozambique. AUTO ALARM ON SHIPS. 0000 fessor Quirino Majorana, of the Univer- At the annual meeting of the Marconi sity of Bologna, announces that he has International Marine Communication THE WIRELESS CHESS MATCH. invented a secret wireless telephone em- Co. at the Connaught Rooms, Mr. F. G. General disappointment was caused by ploying ultra- violet rays. Kellaw ay said it was hoped that mer- the abandonment of the wireless chess 0000 chant ships would soon be permitted to match begun last week between Members ON THE CARPET. use the Auto Alarm, which has been the of the Flouse of Commons and of the Thomas Brown, of Eastbourne, subject of experiment for several years. State Legislatures of Australia. described as a carpet planner, was fined The Auto Alarm gives audible warn- The tourney was opened by the Prime 40s. last week for operating a set with- ing when an S.O.S. is received, and thus Minister in this country and by the out a licence. He contended that he dispenses with the need for constant Duke of York at Canberra, and during had not received anything " worth talk- watch. the early moves all went well. Later, ing about.,' 0000 however, trouble developed on the land - line between Canberra and the beam c0oo AIR MINISTRY AND 900-METRE WAVELENGTH. station at Melbourne, with the result LINKING UP THE COLONIES. that the intervals between moves became At a. conference held at the Colonial Morse interference on 900 metres has too long to be endured! Office last week attended by senior led the Air Ministry to undertake Finally the contending parties agreed officials representing twenty -four self - further experiments towards its elimina- to a draw. governing Colonies and Protectorates, tion. A 20- seater Vickers Rolls -Royce 0000 the queetion was discussed of linking up Vanguard aeroplane equipped as a wire- NOT A DULL EMITTER. the various territories by wireless with less laboratory is making a series of the general scheme of Imperial radio flights to carry out exhaustive tests of The day of the dull emitter is gone, communication. It was generally agreed short -wave wireless telephone communi- judging from the fallowing cryptic para- that much had still to be done in this cation between aircraft in flight and graph which appeared in the " Daily direction. ground stations. Express " of May 11th :- Among the territories involved are If the tests prove successful there is " DOUBLE PURPOSE VALVE. Nigeria, Northern Rhodesia, Gold a possibility that the present working " A wireless valve which will revolu Coast, Kenya, Tanganyika. Seychelles, wavelength of 900 metres may be aban- tionise the design of receiving sets Barbados and Trinidad. doned. throughout the world is shortly to be

EXTENDING THE WAVE RANGE OF THE WIRELESS WORLD FIVE." In this set, built by a reader, Mr. A. Ryall, carefully designed interchangeable I nductances wound on Colvern formers have been introduced to give reception on wavelengths up to 2,000 metres. A 25

www.americanradiohistory.com 628 'Wilpdszg MAY 78M, 1927. WoTDcl placed on the market. The new device, and component parts may henceforth be been overcome in Vienna, Budapest and it is claimed, will not only provide all imported without special permission by other Continental cities by the use of power required for the set, but also anyone having a licence for the produc- the " Fischer " roller, an .adjustable iron illuminate the room in which it is tion, sale maintenance and use of a plate which runs easily and smoothly placed." receiving set. Transmitting apparatus is along the overhead wires. A rash correspondent states that he still subject to severe restrictions. We understand that the Tyrol Radio distinctly remembers a valve which per- Club has offered to bear the expense of formed the same dual function many equipping the Innsbruck tramways with years ago. " It was known," lie a similar device. writes, " as a bright. emitter." 0000 c000 RADIO SOCIETY OF GREAT BRITAIN. WIRELESS PICTURES IN GERMANY. At an informal meeting of the Radio The " Carlogram " is the name Society of Great Britain to be held at officially given to a photo transmitted by 6 p.m. on Friday next, May 20th, at the the Telefunken -Carolus- Siemens system, Institution of Electrical Engineers, Savoy which is now the subject of further ex- Place, W.C.2, Mr. F. M. Colebrook will periments by the German and Austrian open a discussion on " Electrical Measure- Post Offices. It is hoped that in the ment." near future there will be a " Carlo - On Wednesday next, May 25th, the graph," as the transmitting instrument Society will hold an ordinary meeting at is called, in each of the leading post the Institution of Electrical Engineers. offices. The lecturer will be Mr. G. G. Blake, The system is strongly supported by M.I.E.E., who will take as his subject : Dr. Hans Bredow, Wireless Commis- " The Hot Wire Microphone and Audio sioner in the German Ministry of Posts. Resonant Selection." A number of 00oo original experiments will be performed. " CRYSTALLISATION OF THE WHOLE 0000 COUNTRY." 2XAF RELAYED IN AUSTRALIA. The above rather alarming headline Members of the Australian Industrial appears in a Tokio newspaper. Actually Delegation, now visiting the United States, it refers to nothing more drastic than were enabled to talk to the folks at the decision of the Japanese Broadcast- home recently, when 2XAF, the short- ing Association to increase the power of wave experimental station of the General existing stations and extend their crystal Electric Company at Schenectady, N.Y., range. broadcast speeches by four members of the Three Marconi 10kW. transmitters delegation. have been ordered for installation at The signals from 2XAF were received Tokio, Osaka and Kumamoto, while an so strongly in Australia that several order has been placed with the Western stations were able to rebroadcast them, Electric Co. of America for three trans- and listeners in many parts of the con- mitters to be installed at Sapporo, tinent heard the .programme originating Hiroshima respectively. 11,000 miles away. Sendai and o00o 0000 IMPORTANT AMALGAMATION. IMPORTANT CANADIAN PATENT Many readers will be interested to JUDGMENT. learn that Messrs. R.I., Ltd., and the The Exchequer Court of Canada has re- wireless section of Messrs. The Varley cently handed down a judgment of the Magnet Company have joined forces, AN ALPINE STATION.-A picturesque utmost importance to the Canadian Radio and will in future be known as R.I. and view of the new broadcasting station near Trade; and one that may not be without Innsbruck, in the Austrian Tyrol. The effect Varley, Ltd. Mr. J. Joseph, the station relays the programmes from an important repercussive in the managing director of R.I.", Ltd., and Vienna, 400 miles distant, transmitting States, writes our New York corre- Mr. J. M. G. Rees, of the Varley on 294.1 metres. spondent. The judgment is the result of Magnet Co:, are the directors of the new a suit brought by the Canadian General company. A MOUNTAIN RELAY. Electric Company against the Fada Cor- Both these companies have made an Few relay broadcasting stations are poration of Canada for the alleged in- intensive study of L.F. amplification - situated as far as 400 miles away from fringement of Canadian patent No. R.I. in transformer- coupled circuits, the parent transmitter, yet such is the 208,583 (British 147,147), which relates Varley in resistance capacity-with the case at Innsbruck, in the Austrian Tyrol, to tuned radio frequency amplification, result that the public will benefit from where the new relay station derives its or, more correctly, geometric selec- the pooled experience of the two firms. programmes from Vienna. tivity incorporating the use of valves. 0000 Not all that distance is covered by Its effect will be that practically THE DANGERS OF WIRELESS. land -line, however, "and Innsbruck has every Canadian receiver of recent A Polish landowner named Wyre- perforce to rely on wired -wireless over manufacture will have to pay ,tribute to zemski nearly lost his life a few days certain sections of the route. the owners of the Alexanderson patent. ago, says a Warsaw message, when vil- From Vienna to Linz the transmissions Of course, the judgment may be appealed lagers attributed a violent thunderstorm are carried by ordinary low- frequency against, but no information on that point to the evil agency of M. Wyrezemski's telephony over laudlines. Thence they has yet been published. It is only a few wireless set. As soon as the storm was travel by high frequency over lines to weeks since the same court upheld the over the villagers broke into the house, Wörgl, a little town some 45 miles from validity of Canadian patent 244,847 but M. Wyrezemski and his family Innsbruck. At Wörgl a receiving station (British 147,148) to Langmuir, relating to escaped by pretending to have been connects to Innsbruck by cable. The the grid leak. 0000 struck by lightning. Their prostrate new station is using a wavelength of 294.1 PHOTO SYSTEM ? forms scared the villagers, who ran away metres with a 51)0 -watt transmitter. ' NEW WIRELESS panic- stricken. 0000 According to the Jewish Graphic, Herr 0000 TRAMWAY INTERFERENCE. Louis Weissglas, a Jewish engineer in HUNGARY OPENS THE DOORS. One of the peculiar local conditions Vienna, has invented a new system of The Royal Hungarian Minister of Com- with which the Innsbruck station lias to wireless photography " based on the use merce has issued an ordinance pointing contend is interference - from electric of a magneto." The device is described out that wireless receiving apparatus tramways. This difficulty has already as " a cheap commercial proposition." A 26

laid,» :I ., w ..'4. www.americanradiohistory.comdt. é:410k!;>0414iiriytt WAT@Ilws MAY 1811r, 1927. W0iti 629

Directions for Construction and Operation.

By A. P. CASTELLAIN, B.Sc., A.C.G.I., D.I.C. (Concluded from page 598 of previous issue.)

THE first part of the set to be constructed should for the ball -legs of the latter should be cut in the base- be the panel and baseboard. The latter is of good, board and the various other holes, as shown in Fig. 2, well- seasoned wood about i-inch thick, and the drilled in the panel. panel from hin. to tin. If desired, a panel already cut The piece of ebonite cut out of the centre of the panel to size can be obtained from the makers of the case. is sufficient to make the two valve platforms illustrated The panel should be very carefully cut with a hacksaw in the photographs and shown with detailed dimensions to fit round the actual loud -speaker purchased -the in Fig. 3 These two valve platforms are supported at dimensions given for this in Fig. 2 being only a guide. the panel end by two brass angle brackets, and at the rear Having cut the panel to fit the loud -speaker, slots end by tin ebonite rods, as will be seen from the photographs showing the rear views of the set. Before the loud -speaker is finally fixed into position a pair of flex leads about 8 inches long should be fixed' to its terminals, which latter then fit into slots in the baseboard. It will be seen from the two rear view photographs in

the previous issue that most - of the wiring is short and that there is not much visible except leads to the grid bias battery. As will be seen, the detector valve with tuning and reàction condensers and the H.F. choke are all mounted on one side of the loud -speaker and the two L.F. valves on the other. By adopting this scheme it is possible ,to make the wires carrying H. P. currents short, The complete receiver ready for use. Noie that the leads to the frame aerial are deliberately lengthened to prevent fracture through repeated opening and closing of lid. with consequent efficiency. A 27

www.americanradiohistory.comai:: w:oiWNr{ivw.nrilGi siair.:rMiY/r-a.e+.ir uiais WApA®oo MAY 18th,, r927. 630 WOli'!l Rome Portable Loud -speaker Set. - The only visible lead joining the two compartments is that which goes from the junction of R1 and the H.F. choke to the condenser C5 (see Fig. i), and the other leads -L. T. and -H.T. are fitted into slots under the baseboard, as shown in Fig. 4. These slots are quite simple to cut by making two parallel cuts about ¡in. apart with a small tenon saw and then chipping out the wood between with a stout pen- knife-with a little care they may be made with the knife alone. -The only components not mounted on the baseboard or valve panels are the L.F. transformer X and the 9 -volt grid bias battery, both of which are mounted on the top of the loud -speaker. The transformer is screwed down direct, and the battery is held in position by means of a strap union, which is conveniently made of aluminium. When finally assem- Fig. 3.- Dimensions and layout of components on the valve bling before wiring, do not forget to put in the aluminium platforms. screen and the tin. spacing washers behind the variable condensers. This screen should be drilled with good which to wind the frame aerial. The case is \veil and clearance holes for the spindles and the leads to the strongly made of oak and is fairly light, weighing only frame, and should be made of very thin aluminium, Dr ro lb There are three things only to be done to the case there will not be enough thread showing on the condenser in 'order to fit the set-first, two large clearance holes, spindles for the clamping nut to hold. about One inch in diameter, should be drilled through the shelf dividing off the battery compartment for.the battery The Cabinet. leads; secondly, bin. square wooden battens should be The case used to contain the set and batteries is of a fixed round the upper compartment for the panel standard type made by Messrs. Carringtons, and is to fit tip against; and, - thirdly, two small angle marketed complete with battery compartment with drop- brackets should be made to hold the frame aerial out front, and a wooden former about 15in. square, on in position in the lid. The Frame Aerial. For the lower broadcast hand (300 -60o metres) this frame consists of 18 turns spaced 12 turns per inch and tapped at the 12th turn. The wire used may he ordinary No. 26 D.C.C., but the Lewcos stranded frame aerial wire is not expensive and gives a frame of lower H.F.. resistance, and therefore of better efficiency. Before winding the aerial it is necessary to_ slot the wooden frame at the corners to hold the wire. in position and to make up a little ebonite bracket with three plug sockets which is mounted on the inside of the frame, as shown in the photograph of the complete set opened out for use. Note that this bracket is mounted near the bottom of the frame, and not directly in line with the holes in the panel through which the leads from the set come. Fig. 2.- Dimensions of the main panel. A- 7 /16in. dia.; B= 118in. dia., countersunk for No. 4 wood screws; C= 118in. dia.; D = 332in. dia., countersunk for No. 8B.A. screws. This is done intentionally so A 28

www.americanradiohistory.com 4

Wilf@ilsoo .1/1Y ¡Ph, z.927. 631

Portable Loud-speaker Set. - as to save these leads from being lladlv kinked and eventually breaking with repeated Opening and closing of the lid of the rase-a little point, but .a very practical one. 45/4 fr,-?:-- Y If the wire is tight wound on the frame, the slots at thc l!orners will be found quite '1: I g. sufficient to hold the wire - firmly in place. Three or four turns of fine wire wound 16. over the frame and brought out to two terminals will be found useful for using an L outside aerial at any time. The Daventry frame consists of 55 torus of No. 26 D.C.('. wire close wound and tapped at the 38th turn. The larger portion is used between grid and filament of the first valve, just as with the other frame. It may he objected that Fig. 4.-Layout of the components on the efficiency of this longer the baseboard and the wiring underneath it. wave frame will not he so high as in the short-wave case, tuning almost constant, as expected, and a further point owing to the tight winding, but the frame in any case is was noticed that it was desirable not to put the set straight on the small side for DaVentry reception, and the extra on the ground, as this damps the frame aerial rather much difficulties and work involved in making a two-layered in many- cases, but to set it up on a hook or a cushion or spaced o i nd ing do not result in appreciably better anything else handy so as to raise the bottom of the signals. frame a few inches. The Valves. After tryino. in Richmond Park, the set was mounted The lye is of the 6o milliamp. class-the on the car ande' carried further out to see how far loud- A. P .4o6--the second an speaker receptioncould be obtained. The first stop was A.P.4r2S, and the last an Oxshott Woods, where reception was good, but, of course, L. F. power valve-the not so loud as on Wimbledon Common-however, it was A.P.412L. The two I..1'. quite loud enough to enjoy. At Esher reception was valves are of a new and about the same as at Oxshott. so the set was taken out highly efficient type de- farther still, to Dorking, where reception was, if any- veloped by the writer, and thing, better than at Esher. are very suitable for portable However, all these tests were made out in the open, sets, since they only take o. and it is not to be expected that the range of the set to 0.12 ampere filament cur- would he as much as 25 miles when used inside the house, rent at 4 volts and are small owing to the screening effects of the latter, but an in size, besides being capable " internal " range of about 15 miles from 2L0 and of handling considerable corresponding ranges from other short-wave stations loud-speaker volume on even should he easily obtained. _to volts H . T. The reception of Daventry is, of course, possible up to much greater ranges, of the order of 4o-5o miles or more Results. front Daventry. The set has been tried at As an experiment, the set was tested in London, in the varying distances from 21.0 region of Fleet Street, and it was found possible to tune with very satisfactory results in Daventry so that speech and music could just be dis- indeed. It was first tried on tinguished on the loud-speaker. Although London is Wiml)ledon Common and decidedly outside the 50-mile radius from Daventry, the then in Richmond Park, and result of this test shows that the set is quite sensitive on in both places good loud- the longer wavelengths, in spite of the comparative ineffi speaker strength was ob- ciency of the long-wave frame. The two frame aerials tained. It was found to be One thing that is most marked in using the set is the wound for long and short wavelengths. quite directional, and the absence of microphonic noise from the valves, in spite A 29

www.americanradiohistory.com 1Wá'cAc MAY r8t1a, 1927. 6,;2 -JopIlcól

ó 0 ó r

GRID BIAS BATTERY

L.T. +

LOUDSPEAKER

1 r t

+10 -12 VOLTS

Fig. 5. -The wiring diagram of the set. C1, C2 and C3 are the inner grid leads of the valves. of the fact that the loud -speaker is mounted right up ing type valves when they are mounted very close to the against them and that they are of the extremely close - loud -speaker. spacing type. The very smooth control of reaction obtainable on both Of course, if the panel is knocked with the valves on, long and short waves is no doubt the main thing which the usual " ringing " will he heard in the speaker, but makes the range of the set comparatively wide for an it very soon dies down, and ofi no occasion has a " howl " o -v -2 working on a small frame with a not too efficient built up, as it quite commonly does with other close -spac- loud -speaker.

G 2NQ J. W. Pallister, 20, Woodlands Rd., Middles Beam Stations. brough. (Change of address.) In response to enquiries from several G 2YQ W. P. Wilson, 54, Princes Ave., London, N.3. correspondents we give below the wave- (Change of address.) TRANSMITTERS' NOTES G 5VY T. Vickery, 274, Mount Pleasant Rd., London, lengths of the Marconi beam stations : -- N.17. Grimsby (GBH).- 29.906 metres. G 6BB (Ex 2AJC.) H. Brabrook, 31, Court Lane, 26.086 metres (sub- Dulwich, S.E.21, transmits on 23,45 anti Bodmin (GBK).- AND QUERIES. 150 -200 metres. (This call -sign was ject to alteration shortly to two wave- formerly owned by Mr. J. Bolt, War- lengths). rington.) Melbourne (VIZ).-25.728 metres. G 6HW L. A. Lafone, Harrow School. Montreal (CG).-26.269 metres- (subject G 6VV ¡. A. McKinnon, 22, Medway St., Chatham. to shortly to two wavelengths). G 6WN (Ex 2BAO.) H. and L. Wilkins, 81, Studlanrl alteration CG, are very constant. The receiver Rd., Elthorne, W.7. One of our readers, writing from Bath, used has a modified Hartley circuit, with 2AAM N. A. Champness, 6, Hale Gdns., London, W.3. he can easily pick up the states that a Mullard PM2 valve for detector. 2ABA E. P. Allen, "Meadowcourt," Radcliffe -on- .Australian station on two valves with no 0000 Trent, Notts. aerial or earth, but that it fades out 2AFA E. Thomas, 7, Turdon Rd., Morriston, regularly at 10.30 G.J.T. and reappears New Call Signs Allotted and Stations Swansea. Identified. 2AVR E. Cook, Crooked Billet St., Morton, Gains- at 13.00. Maximum strength is about borough, Lincs. 18.15 G.M.T., when signals are easily G 2FV W. Scott -Hay, 24, India St., Glasgow. 2BJC E. H. Ptdcock, 31, King Edward Ave., with (Change of address.) Worthing. readable on a loud -speaker three G 2LW W. E. Benham, 88, The Ridgeway, London, 2BOD A. Hargreaves, 5, Ridge St., Barnoldswick, valves. Other beam stations, especially N.W.1l. via Collie, Lancs. A 30

www.americanradiohistory.com 18th, 7927. `11 p®11@oo. MAY Wald 6.7.7

--,?,QliLFPQEGQRRfÌQQgFL12C(.ek 1Od c/Ca S .,BrevÍ Íe blr!mYéreeudnnndse.T``

News from All Quarters : By Our Special Correspondent. An Elusive Wavelength. -The Talks Programme. -Radio and U.S. Politics.- Cutting Out the Soprano. -The Military Tournament.- Sundays in Cork.

Australia's Mystery Station. Summertime Talks. will he enticed from summertime delights The inter history of the " broadcasting Approximately once a quarter the in order to hear these talks might be of the Duke of York's speech from Can- B.B.C. issues in a carefully arranged rather rash, but the B.B.C. have spare(' berra last week is not without a flavour booklet its programme of talks and lec- no pains to secure the hest material. of humour. tures for the ensuing three months. The 0000 A London newspaper received late in- new programme embracing the period The Old Brigade. formation from an unknown source to May to July shows that a wider field of .\ programme by Veterans of Variety the effect that a special station would interests is being aimed at. is in preparation for May 25th. transmit the speech from Melbourne on In the adult section the subjects 0 0 0 0 a wavelength of 33.4 metres. Although covered range from Astronomy, Physio- Microphone Politics in U.S.A. the B.B.C. had not conducted tests in logy, Botany and Biology to Psychology In view of the severely non- political short -wave reception from Australia, it and Literature. The lecturers number 52, nature of British broadcasting, it is was arranged that Keston should remain and the list includes such naines as James interesting to note the enthusiasm on the look -out during the early morning Agate, Sir H. Walford Davies, Percy already growing in America over the use hours, Davenfry keeping in readiness to Scholes, Stacy Aumonier, Dante Hen- of radio in the Presidential election of broadcast anything that could be " got rietta Barnett and the Rt. Hon. W. next yeah'. over." B uncintan. The broadcasting concerns, as inter So Keston waited, but no signal was To hope. that the majority of listeners ested parties in the question -political heard on 33.4 metres, which wavelength, by the way. does not figure on any Australi,uc lists. o000 Significant Testimony. There was no question as to the ability of Keston to pick up Australia, for earlier in the evening the well -known amateur 3BQ was heard on 32 metres. Mr. Bell, the New Zealand experimenter, who was in morse communication with the B.B.C. engineers, stated that no short -wave broadcast from Australia had been picked up in New Zealand and that, so Mr as he knew, the Melbourne station did not possess a short -wave transmitter. There is something elusive about that 33.4 -metre wavelength! 0 0 0 0 Ventriloquist at the Microphone A. C. Astor, the humorous ventriloquist, who arrives in this country on June 4, will broadcast from 2L0 on the saine evening. 0000 Duke of Connaught to Broadcast. Following the luncheon of the 'Hinted Associations of Great Britain and France, the speeches will be relayed from the Hotel Victoria to 2T.0 on May 20th. The Duke of Connaught, the Earl of Derby, the Marquess of Crewe, and the AN EFFECTIVE TEACHER. Now that the novelty has worn oft, broadcast lessons are taken more seriously by pupils In London schools. This photograph was taken Marquis de Vogue will be heard by recently at the Acland Central School, Fortess Road. N.W., where wireless lessons listeners. are becoming a regular item in the curriculum. A 31

a'iéAlYOili www.americanradiohistory.com 634 Wipamo NAY 7Sth, ;927. 'W(DpIld candidates have to pay for time on the Yelping Sopranos. air -are booming the value of the radio FUTURE FEATURES. We all know the type of soprano voice speech as a means of reaching the largest London. which, issuing from the mouth of a loud- body of the electorate. speaker, will penetrate to every room in M v 22ND.- Instrumental and Vocal Listen to Mr. Merlin Hall Aylesworth, Programme relayed from the house and half -way down the street. president of the National Broadcasting Hall. Mr. Robert Hurd, programme director Company, giving his opinion on radio and Rudolf Steiner of the KFI broadcasting station at Los MAY 23RD. Programme relayed the - 01 :served the sanie woman's vote. fron Brighton. Angeles has evidently 0000 phenomenon; for he is now making things 1\ Ivy 24TH. Day Pro- - Empire unpleasant for " yelping sopranos." Appealing to the Kitchen. - gramme. no offence to musicians, he of Variety. He intends " Whatever may be the degree of eman- MAY 25TH.- Veterans says, but in the interests of the KFI Los MAY 2brs. The Magic Flute " cipation which the modern woman has -" Angeles audience i o has issued a strict reached," said Mr. Aylesworth, address- .(Mozart). (Karel edict that nomore than one soprano may ing the National League of Women MAY 27TH. - " R.U.R." appear during the course of an evening's Voters, " the fact remains that the back- Kapek). prop mime. bone of the women's vote is the woman MAY 28TH. - Oxford Sumner ccoo in the home. Radio broadcasting, with Eights, running commentary. Royal Military Tournament Broadcast. its illimitable ways of communication, Birmingham. Descriptive commentaries on the Royal can reach out from the broadcasting 22Nn. Orchestral Con- be at the fireside, in \IAY -Light Military Tournament at Olympia will station to the woman cert. broadcast on May 21. The features of the parlour, and in the kitchen itself ! " MAY 23RD. -" The Perfect Mar- the programme to be dealt with are as 0000 riage," a comedy by Leonard follows :-Musical ride by the Royal Horse Listener Psychology. White. Guards; the trick riding display by the A word from Mr. Aylesworth on Bournemouth. 16/5th Lancers; the physical training dis - play by the Royal Air Force; the Scot- another aspect of the subject MAY 23nn.- A Mixed Grill. " A rude awakening is in store for the tish Pageant. Band music may possibly MAY 28TH. - Vocal and Instru- be included. orator of the old school who would mental Programme. 0000 attempt to spellbind his audience by radio. Mass psychology plays little or no Cardiff. Belfast Empire Week. part in radio reception. No greater mis- MAY 23n-rm.-Opening Night of the For the first time Belfast is celebrating take could be made than to visualise the Parks Concert Season, relayed this year a British Empire Week, and broadcasting audience as a mass. The from Llandaff Fields Pavilion. the B.B.C. is co- operating to make the speaker on a radio is really talking to a Speech by Lord Mayor of event one of outstanding importance million or thirty million individuals, not Cardiff. - . throughout Northern Ireland. The in- to a mass audience of thirty million MAY 24TH. -Our Tudor Heritage augural speeches on May 23 will be broad- people. The flowers of his speech, there- (an English -Welsh Programme cast from the Belfast station, followed by fore, are likely to die by the wayside. for Empire Day). a choir of one thousand voices and massed You cannot stampede the radio audience Manchester. bands. Other broadcasts through the en- as you might in an auditorium." suing week will include speeches by Mr. MAY 24TH. -Empire Day Concert. 0000 Stanley Baldwin, M.P., the Duke of Aber - the King ! " " Gentlemen, -a corn, Mr. L. S. Amery, M.P., the Lord Verb. Sap. play by Campbell Todd. Mayor of Belfast, the High Commissioners Ignoring the political side of the ques- MAY 25TH. -" A Change of Spirit." New Zealand, Sir E. A. of Australia and and tion, there is much in the last paragraph a new radio comedy by Lawrence Weaver; a running commentary Bryan. which might be borne in mind by broad - on a parade of the Army, Navy, Air cast entertainers and lecturers. Newcastle. Force and O.T.C., of Queen's University, of A few entertainers and a sprinkling MA Y 22ND.- Popular Wagner Pro- Belfast; and concerts and instrumental lecturers can still " spell -bind " a wire- gramme. solos. less audience; but no one can "stam- MAY 25TH. -Northumberland and 0 0 0 0 .pede " it. 0000 Cumberland Concert. On Sunday Only from Cork. A Cricket Talk, Glasgow. For the next three months the new Cork station will confine its programmes " Warwickshire Cricket," with a general MAY 22ND.- Sacred Scottish Pro- gramme. to Sunday evenings, beginning either at review of the outlook for 1927, will be 8 or 8.30. Gaelic music, especially the subject of a talk by Mr. R. V. Ryder, \[1Y 23nn. -Scottish Songs and Dances. singing in the traditional method, is to secretary of the Warwickshire Cricket be a special feature. Indeed one of the Club, from the Birmingham station on MAY 27TH. - Wagner and Tchai- kovsky Programme. main objects of the Cork station is to June 2. 0000 cater for the Gaelic -speaking population Aberdeen. of Southern Ireland, so that the music The Old Order Changeth. MAY 25TH. -Light Musical Humour will be principally that of the Celtic Bremen's " Old Weigh House," an and Variety Programme. countries, viz., Ireland. Scotland, Wales, ancient renaissance building famous MAY 28TH. -Solo, vocal and instru- and Brittany. throughout Northern Germany, is being mental concert. 0000 converted into a broadcasting station by Belfast. The Derby Broadcast. Aktienge- the " Nordeutsche Rundfunk MAY Speeches at the open- of the Derby on June sellschaft." 23nn.- The broadcasting 0000 ing- of the Empire Exhibition; 1 is to be carried out by Mr. Geoffrey relayed from Ulster Hall, Bel- Gilbey, who will undertake the running A New Grouse. fast. commentary on the race, and Mr. George A friend of mine blames the B.B.C. for MAY. 24TH.- Running- commentary F. Atlison, who will be responsible for putting out such good programmes on on the Imperial Parade as it the introductory matter and local colour. Tuesday. passes the City Hall. Four microphones will be used : two in a "Tuesday is the only day on which I MAY 27TH.- Running commentary portable but on the roof of the grand- get a chance to test nay set, as the family on the Parade of British In- stand, in line with the winning post, a happen to be out," he says, "but the pro - dustry and Commerce as it third in front of the stand to pick up

gramme is generally so good that I forget passes the City Hall, Belfast. - incidental sounds, and the fourth in the the testing and listen all the evening." s unsaddling enclosure. A 32

www.americanradiohistory.com MAY iSth, 1927. Wfipshoo 635 Wor IlcI

The Editor does not hold himself. responsible for the °opinions of his correspondents. Correspondence should be addressed to the Editor, " The Wireless World," Dorset House. Tudor Street, E.C.4, and must be accompanied by the writer's name and address.

EMPIRE BROADCASTING. control ; (2) because the revenue would be more steady than Sir, -You are rendering a public service in calling attention in the latter case. for some effort to be made in Britain to provide a It is extremely interesting to note that section B (5) of the to the need agenda short -wave station which could be heard in some of our of the Colonial Conference being held in London at the present time deals with " wireless communications, external Dominions or Colonies. and internal, If the British Broadcasting Corporation are approached with and broadcasting." Lt view of the fact that Empire broadcasting is a a request that they should provide such a station they will matter which might interest the Conference, perhaps it would be pos- probably say that they require all their funds for the develop- sible and an Empire for Mr. Nicholson to give notice of a question in the House ment of their tnited Kingdom Service, that to the Colonial is would be so variable Secretary as to whether the matter might be Service, with technique as it at present, discussed when the time worth I do not arrives for Section B (5) of the agenda and intermittent as to be scarcely starting. to come under discussion. though there I know-, The 1.'cening Standard hating entirely agree with this point of view, are, brought the question still further to light, powerful arguments which can be brought forward to defend it. one awaits with interest the B.B.C. opinion on the matter. It seems, as I men- Lt particular, of course, the B.B.C. are aware that a new station tioned in my letter, that the B.B.C. have quite enough of this sort would have to be paid for out of their funds, and to do and are probably fully occupied at the present time with that they would probably gain no increased revenue as a result the regional high -power station scheme to give much attentioíi of such a venture. to the establishment of a short -wave station. Although ultimate - Would not the Imperial interest be best served if the Post Government control would he desirable in an Empire broadcast- Office were to license a private firm which has a market in the ing service,. the B.B.C. should not, I think, be the actual Dominions, particularly South Africa, whose time is synchronous controlling body. May I take this opportunity of congratulating with ours, to erect and manage such a station? The firm need The ll "ireles.s World on the excellent and progressive way it not advertise obtrusively, but might be allowed to call its name has placed this important question before its readers? at the beginning and end of each programme. This, coupled DALLAS BOWER. with the interest aroused by such an effort in the Dominions, Brighton, May llth, 1927. would probably be more than enough inducement to any big British fi rm to erect the station, and thus a further link in B.B.C. TRANSMISSION OF PIANOFORTE MUSIC. forged Imperial communication would be without difficulty, and Sir. -Apropos of the recent correspondence about distortion a useful experiment would be conducted. in piano music from London, this seems to have resolved licence for or be itself A two three years might granted, and after largely into a controversy between highly technical gentlemen, that time, if the need were demonstrated and the service had half of whom insist that the distortion is was fairly reliable, in the transmission, developed until it the B.B.C. could take it. and the other half that the trouble is at he receiving over and enter into some financial arrangement for hiring end. the Perhaps the experience of a provincial listener may be in- service to Dominion broadcasting companies. teresting. I, and many others to whom I have spoken, find it The principle of unified control of broadcasting in Britain, impossible to tune in the London transmission without in which I would distortion. thoroughly believe, not be prejudiced by the This applies not only to piano items, but to the speaking voice issue of a separate temporary licence fit' this purpose, but it as well. " Alta ! receiver again," says our gentleman from will be prejudiced if through lack of initiative and enterprise the higher regions of mathematics and acoustics. I'nm afraid Britain falls behind other countries which allow greater freedom. I cannot meet him On his own ground, but I can say that, after House of Commons, TAN FRASER. making every possible adjustment in the attempt to May 1927. secure 7th, decent quality from London, I can change to Manchester and at any time tune in pure, undistorted music and speech. And the quality of my reception has been remarked upon bx one Sir, -Further to my letter of April 29th on Empire well -known violinist, as well as by my " wireless " friends. broadcasting, which I note you were good enough to publish. My own theory is that the trouble is due to slight but per- It is gratifying to see that the matter is interesting a Member sistent heterodyning. It did not exist six months ago, for at of Parliament in the person of Mr. Otho W. Nicholson, and that time I have enjoyed a whole Sunday afternoon's programme his mention of how the matter concerns manufacturers is, I from London on the load-speaker without noticeable distortion. think, very closely allied to my suggested scheme. The other possibility is, of course, local' oscillation. London On closer consideration, however, it appears that the formation is the station most easily reached by the local one -valve merchant, of a company composed of British manufacturers to run the and, apart from actual howling, there may be enough radiation service relying on large export trade as return on capital out - to upset things from the greatly increased number of valve laid is too large a gamble. Some more definite arrangement sets in the neighbourhood. I think, however, that the hetero- would have to be arrived at in order to provide .a regular and dyning theory fits the case better. It would probably be more comparatively steady revenue. apparent to a distant listener, but enough to cause slight dis- It seems, therefore, that this might be obtained in two ways : tortion to London listeners on particular notes such as those to put the control of the service in the hands of the Radio of the piano. Manufacturers' Association or a newly formed body of manu- This evening I have been listening to a delightful loud -speaker facturers and let the Government subsidise it for a given number conceit from Manchester, including piano solos. An attempt to of years, after which time it would become self -supporting on get the London chamber music was productive of an announcer's a percentage of the licence fee for reception collected by the voice with the characteristic " quack " in it as though the set various colonial governments; to form an organisation whereby were oscillating (which it definitely was not), and music which revenue is obtained by indirect advertising, as Mr. Nicholson no one with a musical ear could endure. suggests in his letter. One imagines the former scheme is the Birmingham, FRANK SMYTH. better of the two : (1) because it is partly under Government May 9th, 1927. A 33

aa,v-_.. =',s4<.."ra.'ö(.,iy6ír;,' www.americanradiohistory.comAc: .:á -,.4.e TM alea oM :;BF:t::i wgpoisog warm MAY t8th, 1927. NEW APPARATUS. A Review of the Latest Products of the Manufacturers.

HINDERLICH CRYSTAL DETECTOR. The lower crystal is mounted in a cup A NEW B.T.H. LOUD -SPEAKER. a holding - A. Hinderlich, 1, Lechmere Road, and is removed by unscrewing It must not be thought that the horn London, N.W.2, has long specialised in down ring. Two holes are required for type loud -speaker is obsolete in view of of mounting the detector on the panel. the popularity recently attained by the the supply crystals for use as detectors, cleanly The. extensive use of crystals for detection The ebonite parts are turned and cone type. Comparatively few listeners nickel - to -day has created may sources of supply, knurled,' and all metal parts are wish to use receiving sets incorporating though Mr. Hinderlich has built up the plated. the necessary amplifying stages which are reputation for himself by his several 0000 essential if good results are to be obtained articles and instructive pamphlets of with a less sensitive loud- speaker. Horn being well acquainted with the properties, A NEW " EVERYMAN FOUR " type loud -speakers are invariably sensi- selection and operation of crystals used in CABINET. tive and can be operated with small input. A new design of cabinet specially produced for building the " Everyman Four " receiver has been recently placed on the market by W. E. Marson, Ltd., Windus Works, Windus Road, Stamford Hill, London, N.16. The quality of cabinets supplied for amateur use varies considerably, and this new cabinet can be employed where it is the intention to 'build a really high -class instrument. no accompanying illustration shows the general details of construction, and it might be pointed out that the ends of the drop front are clamped to prevent warping. The panel, which is of figured aluminium and lacquered, fits into a frame, and is an improvement on the more general method of fitting the panel close up against the walls of the cabinet. A baseboard is also supplied, together Hinderlich detector dismantled to show the vertical aluminium screen which the method of securing the crystal with containers. separates the aerial and H.F. tuning equipment and with the simple design " a detectors. Now that a detector is being adopted in the " Everyman Four set marketed by him, one can be sure that it good receiver can easily be constructed, fulfils all the necessary requirements for it being necessary only to assemble the giving a reliable performance. components on panel and baseboard. The several pieces which comprise the Special ebonite bushes are supplied with detector are shown on a slightly reduced which to insulate the condensers and scale in the accompanying drawing. The other components on the metal panel. spring blade is adjusted as to height and Unless the condensers are insulated in position, and the crystal cup is attached this way, the grid cell for the first valve by means of a small bushed ebonite knob. would be short -circuited.

The B.T.H. horn type loud- speaker, giving good signal strength with small Input. The British Thomson-Houston Co., Ltd., Crown House, Aldwych, London, W.C.2, have recently introduced an inexpensive model suitable for giving good volume with small input. For the reception of distant signals this new loud -speaker gives excellent results without the need for an additional amplifying stage to that used for local station reception. One need not hesitate even if the aim is to obtain best possible quality of reproduction to adopt this loud -speaker, particularly when price is a consideration. The curved upright of the horn is of polished aluminium, and the flare as well as the base is enamelled brown. A perforated grille covered with gauze is mounted in the neck and prevents dust or other foreign matter from falling on +, to the diaphragm. is acces- A new departure in wireless cabinets. A framed aluminium panel is supplied fitted An adjusting screw provided, with baseboard and aluminium screen. sible from under the base. A 34

- - - -- ,.a.,-.641,-.::ë:t..sx..._::::d - - www.americanradiohistory.com ,,, 1i1.4I" tSlh, 7927. WIp®Il®00 WopIld 6.77

" The Wireless World " Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply.

" Screens " or " Screened " Coils. inch added on to both the length and aerial results in the frame wires being I have constructed a neutralised type of breadth. This is done by merely extend- kept at a distance of half an inch from receiver employing one L.F. stage, ing the wooden framework in the manner either the wooden framework or the but find that the neutralising coti- of certain old - fashioned picture frames. leather case, the wires making contact denser requires resetting frequently, We show this clearly in Fig. 1(a), the with the woodwork only at the four and one setting does not by any extension pieces being the reason for the corners of the frame. The result of doing means hold good over the whole slight enlargement of the suitcase. We this is to ensure mutin less damping in wavelength band covered by the re- then cut two large slots in each of these the frame than when wound tightly in ceiver. I have been told that it is extension pieces as in the manner of Fig. a groove as in the case of the original due to the absence of screened coils. 1(b), small " nicks " being niade in these receiver, and not only is reaction control Can you tell me if this is so? slots to hold the wires at a certain spac- considerably smoother, but the range of T. S. J. ing apart. Another suggestion would he the set is considerably enhanced. It i' to extend the framework as in Fig. 1(a), advised that the low wavelength frame It is* by no means improbable that the and instead of cutting the two big slots be wound, as in Fig. 1(b), with spaced. cause of your trouble is due to a certain as in Fig. 1(b) to bore a number of holes winding. One cannot similarly space the amount of magnetic reaction between the in a line half -way down the extension winding of tiie long -wave frame aerial aerial -grid H.F. transformer and the piece (in the position occupied by the unless a very much deeper case is used, intervalve H.F. transformer, and the bottom of the in Fig í(b)), these hut, fortunately, a spaced frame for the would slots adoption of proper screening small holes being for the purpose of long waves need not be used, and on the probably clear up the trouble of mag- threading through the frame aerial wires. tong waves the frame may be wound netic reaction. You should, however, Of course, the holes should be spaced straight into its groove without spacing. arrange that the screening used is as regularly at the distance at which it is It should be observed that even in the as no more simple possible, and that desired to space the frame aerial wires. case of the long -wave frame wiring, how - screening than is absolutely necessary ever, contact is made only at the four is used. You should not place the corners of the wooden framework. Do H.F. transformers too close to the not forget that Figs. 1(a) and 1(h) are metallic screen, but should follow the not drawn to the same scale as the draw- design of some such receiver as the " Alb ings in the original article, and are only wave Four " in this matter. This re- explanatory diagrams necessary for the ceiver was published in our April 27th purpose of illustrating our meaning. issue. Do not attempt to place a screen oono fitting closely over each coil, because In this way, owing to the proximity of coil Cutting Out Complications. md screen, you will introduce severe 1 understand that some time ago you pub- losses into the circuit. lished a single -valve broadcast re- 0 0 0 0 ceiver capable of bringing in distant Improving the " Everyman Portable." stations on the telephones which employed merely one coil, no extra re- Last summer I built the " Everyman Port- action coil or other device being used, able," de.=cribed in your issue of Judy although, I nie told the receiver used 21st, and obtained great success with reaction, and at the same time used a it, but now contemplate rebuilding magnetically coupled aerial circuit. this receiver, and I was .wondering Fig. 1.-Constructing a frame aerial for a portable set. Can you tell me in which issue this whether you have any improvements appeared' D. M. to suggest. I might say that I my- In Fig. 1(h) actually, of course, two This receiver was fully described on self have tried to add an extra L.F. large slots are shown, the idea being page 799 of our Junè 16th, 1926, issue, stage, but found that it was not worth merely to indicate the two frame aerials, and, as you state, being only a single - the extra .Weight entailed. the one for the local station and one valve receiver, of course received distant P. M. P. for Daventry, as in the case of the original stations only on the telephones, al- There is one very definite improvement receiver. The. Daventry frame aerial may though the addition of an efficient L.F. which you can make, without adding he wound with narrow -gauge wire, as amplifier would enable you to receive dis- more than an ounce or two to the weight, was done in the case of the original re- tant stations on the loud- speaker with ex- although a slightly larger case is called ceiver. It will be noticed that this im- cellent quality. Tine June 16th issue may for, having the saine depth, but an proved method of winding the frame be obtained a- t a cost of 7d. post free A 35

www.americanradiohistory.com WAp&R@ZO 6,38 a1:4Y rb'th, 1927. WelFDc1 H.T. Accumulators of Inadequate position of the switch S1, and should have every weekday except Saturday), which stand- Capacity. the capacity recommended by the makers is in any caso always a reliable of your transformer. Another pole may by station, then, naturally, the receiver I have an II.7'. battery consisting of be the switch S, and wired in for you to build is the " Everyman in added to sixty small accumulator cells such a way that the filament of the Four." Should it happen, however, that series, but I find that their ampere - second L.F. valve may be extinguished you are desirous of receiving Radio hour capacity is really not large automatically when it is not in use. Paris, Moscow, Komintern, Warsaw, Hil- enough for their work, and -I propose ö 0 0 0 versum, Konigswusterhausen, etc., with adding another accumulator battery no interference from other long -wave of sixty cells in parallel with them, Which ? stations, or should it happen that you or, alternatively, sixty Leclanché I am desirous of const,,tctinq a really desire Daventry reception at a greater dis- cells. il-hieh do you advise? efficient and up -to -dole receiver for tance than 100 miles or so, then this re- R.A.S. reception of British and European ceiver must be placed into the same cate- It will be quite in order for you to broadcasting stations, and I am gory as the others we have mentioned. add sixty accumulator cells to your exist- definitely intending to build either of With regard to the " All -Wave Four, ing sixty -cell battery, and such cells need the following four receivers: the this receiver will receive not only a very not necessarily be of the same ampere - " Everyman Three," the " Ererytman large number of distant stations working hour capacity as those you have already. Four," the " Wireless World Five," on the 200 to 600 metre band on the Sixty accumulator cells give an E.M.F. or the "All-were four." 1 shall be loud- speaker, but will do likewise on the of 2 volts, and since sixty Leclanché glad if you will assist me to choose long -wave band from 900 to 2,000 metres, -cells give an E.M.F. of only 11 volts, it the ;Host suitable receiver. covering the long -wave stations we have is obvious that sixty Leclanché cells, no W. B. J. mentioned. The reason for the ability to matter of size, would give only what The question which you ask is rather a receive distant long -wave stations at loud - 90 volts instead of 120, and, conse- difficult one, since it depends entirely speaker strength is that it makes use of quently, the accumulator cell would dis- upon what, duties you intend the receiver its H.F. valve not only on the 200 to charge through the Leclanché battery. to perform. If, for instance, you require 600 metre band, but also on the 900 to You would have to have ninety Leclanché loud -speaker volume only on the medium 2,000 metre band. Since you know your cells to give you 120 volts, but we on distance broadcasting stations, head- requirements best, it will be necessary no with account advise that you use the phone reception of a large number of dis- for you to finally decide upon the re- accumulator battery in parallel with a tant stations operating on the 200 to 600 ceiver which you will build after care- Leclanché battery. We think your best metre band, then undoubtedly the fully considering the particulars we hate plan would be to dispose of your present " Everyman Three " would be the re- given. H.T. accumulators to someone who uses ceiver for you to build. If, however, 0000 a set taking a smaller output, and to pur- you desire to receive either on telephones Two Volts for Efficiency. chase for yourself a complete new battery or loud- speaker any long -wave stations at of adequate ampere-hour capacity. all, then naturally this receiver would I notice that in several receivers described 0000 be ruled out. If you desire to receive by you, you use 6-volt 'eaves in every a huge number of eery distant stations position except the detector position, Crystal or Valves. operating on the 200 to 600 metre band where a 2 -volt valve is used. Can you .1 wish to add a two -stage transformer- on the loud -speaker, then undoubtedly the tell me the reason for this? coupled L.F. amplifier to my existing "Wireless World Five " is the receiver T. A. W. crystal set, rebuilding the whole into for you to build ; but, of course, in the In the receivers to which you refer it a single instrument. Please give me a matter of long -wave stations this receiver will be noticed that the detector valve is circuit diagram of the simplest pos- falls into the same category as the used as an anode bend rectifier, that is sible arrangement, including switch- " Everyman Three." Should you desire to say, it rectifies by reason of the fact ing, whereby the one or both valves to build a receiver which will give you that its working point is adjusted to the may be used with the loud- speaker or a large number of distant stations on the bottom bend of the grid- volts' anode -cur- crystal only on head telephones, loud- speaker on the 200 to 600 metre rent curve. Indeed, the sharper this bend A. P. L. band, and desire also not to be deprived the more efficient the rectification, or, it We give herewith the circuit diagram of the pleasure of listening to the morning might be said in one way, the more sensi- of a suitable receiver (Fig. 2). The con- concert from Daventry (since, of course, tive the valve to weak signals, provided denser C will be across either phones or it must not be forgotten that Daventry the working point was adjusted properly transformer primary, depending on the invariably gives a morning concert on to the bottom bend. A 2 -volt valve has, of course, a much shorter filament than a 6 -volt valve, and since it so happens that a short -filamented valve usually has a more sharply defined bottom bend than a long -filamented valve, the reason for using a 2 -volt valve as detector will be clearly seen. o0oo Multi -stage H.F. Amplification. I propose to construct a set with two H.F. stages, following closely the circuit diagram of the " Wireless World fire," described in your issues of Jan. 5th and 12th. I should like, however, to avoid the complete enclosure of the coils, valve, and tuning condenser in screening cases, and to use simple vertical screens. Is this idea practicable? H. S. S. If your coupling transformers are to be of an efficiency and physical size equal to those used in the receiver mentioned, we are afraid that complete inter -stage be necessary, as two H.F. Fig. 2.- Crystal and two -valve amplifier with switches for cutting out one or both screening will valves. amplifiers areproposed. A 36

i[ta " -Y ,xeMr ., ?.'+F.-..IH,,. Acv www.americanradiohistory.com JheìH AN D RADIO REVIEW I (151h Year of Publication) No. 404. WEDNESDAY, MAY 25TH, 1927. VOL. XX. No. 21.

Editor : HUGH S. POCOCK. Assistant Editor : F. H. HAYNES.

: City 401I (3 lines). Editorial Offices : 134 -40, FLEET STREET, LONDON, E.C.4 - - Editorial Telephone Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.C.4.

Telephone : City 2547 (z3 lines). Telegrams : " Ethaworld, Fleet, London."

MANCHESTER : 199, Deansgate. COVENTRY : Hertford Street. BIRMINGHAM : Guildhall Buildings, Navigation Street. : " Ilifte, Manchester." Telegrams : "(- ycliet Coventry." Telegrams: " Autopres , Birmingliam." T,l grams Midland. Tdnphone: 8970 and 8971 City. 1rlrphnne : 5210 1. oventry. 7'elephone: 2970 and 2971 Subscription Rates: Home, 27s. 4d.; Canada, 17s. 4d.; other countries abroad, 19s. 6d. per annum. themselves that Mc. As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy would not be infringing patents.

of distinct classes ßROADCASTING. detail with sets which are representative EMPIRE should provide a -useful guide to those who are in doubt HE efforts of Tltc tireless World to stir up as to what type of set will meet their own requirements. interest in the subject of Empire Broadcast- In the past year or two there has been an enormous ing already show definite promise of bearing increase in this country in the extent to which the public fruit in the near future. The daily Press s1 icnd their leisure time in the summer out of doors, for not only has there been a pheno- has taken up the sub- ...+..+-.+ ject with interest, And i menal increase in the number of the B.B.C. has issued cars on the road used for pleasure, and other means a statement giving its view of the CONTENTS. but the railways PAGE of the position. The matter is also to conveyance can all testify to EDITORIAL VIEWS ...... 639 of the open -air habit, come before the Colonial Confer - development sets ence, which is at present holding SUMMER. WIRELESS. and it is natural that portable share in this popularity. sittings in London: By N. P. Voicer- Minter 640 should The statement of the B.B.C. is The portable set will undoubt- NOVELTIES FROM OUR READERS 644 into its own to an even to the effect that it is ready to co- edly come A NEW TALKING FILM SYSTEM. high operate in any practical enterprise greater extent as soon as the giving for ,providing broadcasting for By A. Dinsdale ... 645 power regional scheme alternative programmes is in different parts of the l' nipire, but PRACTICAr. HINTS AND TIPS ... 648 of course it is recognised that at operation. PORTABLE RECEIVER TYPES ... 651 the present stage guaranteed results 655 Post Office Regulations. in all parts of the Empire are not NEWS FROM THE (I.UBS An issue largely devoted to possible. even with a twenty -fotn - t .URRENT TOPICS ... 657 is an opportune hour service, and naturally the Summer Wireless BUYERS' GUIDE, PORTABLE Ii ECEIVERS 659 readers of the B.B.C. does not feel justified to occasion to remind OF 'WIRELESS INTEREST 669 towards the use expend what, in fat't, amounts to INVENTIONS Post Office attitude receivers. Under or- public money on such an enterprise BROADCAST BREVITIES ...... 671 of portable dinary circumstances a licence for without full authority. It is to be NOTES AND QUERIES 673 TRANS:tIITTTERS' receiver is expected, however, that the neces- the use of a portable LETTERS TO THE EDITOR ... 674 who are sary authority will not be long granted only to persons of a for a withheld if the colonies and over- READERS' PROBLEMS 676 already holders .licence Where a person has seas dominions express a desire for fixed station. address an exception the establishment of such a station. no permanent 0 0 0 0 is usually malle, but application must then be macle to SUMMER WIRELESS. the G.P.O. for the special licence. A fixed station U\I \iER time is with us again, and each year we find licence only covers the occasional temporary use of 01 an increasing interest in wireless receivers for use out apparatus at another address. If, therefore, regular of doors. The number of commercial portable receivers use of portable apparatus is desired, an additional port- has increased very largely this season, and in this issue we able licence will he necessary. Receiving apparatus have endeavoured to give a description of all the types may not be used simultaneously at more than one place which are now available, whilst an article dealing in more under a single licence.

A 1 ,3

www.americanradiohistory.com NiTpisll@oo Wer1id MAY 25th, 1927.

Portable Sets : Their Applications arid Limitations. By N. P. VINCER=M1NTER.

THE spiritual future of those portable set designers the meaning of " to carry away with strong emotion," a %vho have the temerity to calla receiver weighing as thing which the writer has many bitter recollections of much as a hund--edweight of coal (which does not, doing with certain portable receivers; the dictionary gives in these days, mean anywhere near as much as 112 lb.) yet another meaning, which is also astonishingly applic- by the name of " portable " was always a subject of able to the circumstances under discussion (applicable in considerable conjecture by the writer until he happened to this case, perhaps, both to the designer and to the set),. look up the word " portable " in a dictionary, when namely, " to carry away into banishment." The adoption he found that " portable " meant anything " that may of such a suggestion would instantly banish about ninety- be carried." With regard to the method in which the nine per cent. of " portable " receivers to the new carrying is to be done the dictionary emulates the example classification of " transportable." of many home constructed sets, and is silent. The writer, therefore, desires to offer his sincere apologies to the Contradiction Invited. designers and others unwittingly wronged through his So far as the writer is aware, there has been only one literary ignorance, but at the same time thinks that it receiver described in any British radio journal which should be compulsory for all journalistic designers of comes under the heading of " portable," and that one portable receivers to if/dude some suitable method of was described by himself ' (cries of " Shame ! " and transport in their " list of parts " and to indicate whether " No, no ! "). This is, of course, exclusive of portable the estimated cost does or does not include this all - crystal receivers designed for use " in a certain Oxford important item,- whilst manufacturers should be com- Street store," the exact whereabouts of which no journal pelled tc do likewise in the list of accessories required. or member of the public seems to be aware. The receiver designed by the writer had a very conservatively esti- Portables and Transportables. mated " R7 " range of fifteen miles from any main Surely, although the word " portable " is, gram- station, the Daventry range being, of course, greater. matically speaking, equally applicable to the 6o lb. and Needless to say, this instrument was for telephones only 12 lb. receiver, it would be far less misleading if the word and used only one valve. Its weight was under to lb. " transportable " were used in conjunction with the complete with all accessories, including licence and former. This plea is strongly reinforced by the dic- " Every-man's Portable," /'he Wireless World, .' ly 21st, tionary, which inter alia ascribes to the verb " transport " 1926.

A 14

www.americanradiohistory.com mme pcIlSOM MAY 25th, 1927. 641 WoOTIl 0..1 Summer Wireless.- word that has made the so- called portable wireless set station- logging chart pasted inside the lid. The dimen- an object of derision, and has given birth to such foolish sions were only rzin. x Sin. x :}in., and it could be used journalistic clichés such as " the first essential of a port- with the lid closed. Such an instrument could really be able set is that it should be portable." The primary carried by a pedestrian without either fatigue or risk of essentials of a portable receiver are good volume coupled dislocating his arm. with good quality of reproduction, reasonable compact- It may he said that limiting the weight of " port- ness, and ample battery power; but, of course, of an ables " to 12 lb. is rather taking the line that they unspillahle and not of an ztn;eccessarily heavy type. Above are intended for invalids only. This is by no means the all, the instrument should operate from its own frame case, as anyone who pauses to reflect will readily see, and built -in loud- speaker, and should not need that port- and, indeed, the writer has doubts whether he has not able set users run the risk of being apprehended by the been unduly generous in the matter, as even 12 lb. is Commissioners for lunacy by throwing stones over trees quite enough for even the " strong, silent man " to and driving stair -rods into the ground. The writer well carry r. ith comfort for any distance. Since it is obviously remembers the same derision greeting the " portable " impossible even for an experienced wireless engineer to gramophone when it first made its appearance, due to a construct a loud- speaker receiver which, inclusive of loud- popular misconception of the true meaning of the word speaker, batteries, etc., could give good loud- speaker portable. The portable gramophone appears to have out - results at fifteen miles (the range of the " Everyman's lived this derision, and to have still retained the title of Portable ") from a main station, even though " small portable, chiefly owing to the fact that it is possible to cell " batteries and " Antiron " transformers he used, it make a truly portable headphone wireless receiver, which will at once be perceived that a portable loud -speaker is and will always be impossible in the case of a gramo- receiver can never exist until some revolutionary invention phone until some revolutionary recording process is in- comes about. vented, and partly because the portable wireless receiver has not yet, like the gramophone, lived clown the word From Derision to Triumph. portable." The writer suggests the use of " trans- It is absolutely necessary, then, that portable receivers portable," or some more suitable word for all those in- Le capable of loud -speaker operation? The answer is struments unable to " weigh in " at 12 lb. emphatically, yes. The portable wireless receiver has to compete with the portable gramophone, which one constantly hears, on the river, at tennis parties, at picnics, etc., bellowing forth its tempestuous tintinnabulations. A good transportable loud- speaker receiver will put the average totablc gramophone out of business any day, such instruments being only comparable to an inferior receiver designed and operated by the local plumber. It would be ridiculous, however, for a " headphones only " receiver to attempt to justify its existence in places where a portable gramophone is habitually used. A real portable receiver, which, as we have seen, means headphones only, has a certain very definite field of usage as we shall see later, but it will never be able to compete with an instrument, be it gramophone or wireless receiver which is capable of being used without headphones. We have decided, then, that a really portable loud- speaker receiver is out of the question until some revolutionary invention enables us to bring the weight of a Who wouldn't own a portable set ? good loud- speaker receiver to a figure not exceeding 12 lb. at present But is it necessary that a receiver be really " portable " The sooner the public realises the fact that is a technical im- before it can attempt to compete with the " portable " a truly portable loud -speaker receiver gramophone? Most decidedly not. Who ever heard of possibility, and learns to appreciate the wide and mani- the better it will a really portable gramophone? One must not fall into fold uses of the transportable receiver, the error of weighing the actual gramophone alone in be for all concerned. and order to make it come into the " portable " category. Now let us dismiss this aspect of the question, see This would be no better than weighing the wireless set if we cannot investigate the truc possibilities of both the from or estimating its cost without taking into consideration " portable " and the " transportable " receiver apart 'buses, batteries or other accessories. No, the gramophone must such freak suggestions as using it on the tops of in positions be weighed with its records, and the fact that records are at football matches, in the bath, and other heavy enough to necessitate taking a few only is amply so beloved of the daily Press. Apparently from what one indis- exemplified by the monotonous repetition of the same old reads a wireless receiver of the portable type is round of negro noises that pollute the air on the river pensable in all walks of life, which is obviously non- more harm than good or elsewhere during summer days and evenings. sense ; such inane suggestions do It is this mistake of imagining that a portable receiver to the cause of wireless. C)ne cannot imagine Thomas must necessarily be portable in the popular sense of the Gray sitting in Stoke Poges churchyard committing to A 15

www.americanradiohistory.com - i, m. . .. OPPIFTRIP - - m . .._i r (512 o01cíl MAY 25112, 1927. Summer Wireless. - annoyances mentioned earlier in this article ; sand among paper his immortal words to the accompaniment of " Yes, the eatables can, however, be very indigestible and sir, that's my Baby," bawled from the loud- speaker of unpleasant. Messrs. So- and -So's " Portdeluxe " receiver, price 6o Leaving the sea coast we now pass inland again, where guineas, grid bias 2s. 6d. extra. We will take the case a fleet of passing char -a -bancs or chars -a -banc (proof the transportable receiver first, as it is mentioned last, nunciation, Oxford or Cambridge as desired) covers us for no other reason than to be contrary. with dust and reminds us that here again is admirable scope for a portable A Sure Cure for Pneumonia. receiver of the largest and heaviest type it is possible to obtain. Hurtling swiftly and The first horrible thought which occurs to us is noisily through the country roads on this mechanical " Picnics." Ugh ! What scenes of martyrdom does not monstrosity, we presently spy through the trees, amid this word conjure up; what mental nightmares of sitting the deepening shadows of twilight, a caravan drawn on damp grass with a plate balanced on one knee, con- up in some neighbouring grassland, with a cheerful taining bread, butter, jam and wasps, and on the other camp fire glowing, while music emanates from a portable a teacup containing lukewarm tea with an admixture of set, and hastily we descend to -pay onr respects to the grasshoppers, a strong nor' -easter meanwhile finding the occupants. vulnerable parts in one's summer clothing. Think what a long way a good wireless receiver will go towards miti- Where my Caravan has Rested. gating these horrors until one can return once more to Here surely we have stumbled upon the ideal situa- civilisation and sanity. In such circumstances a wireless tion for a portable receiver. We are not unduly receiver would be worth its weight in gold, would it not? restricted as to weight, as we have such admirable means even though it weighed sixty pounds, and was found to of transport, whilst what better way of spending an be all covered in jam afterwards. The necessity for wash- evening than with a caravan far from the madding ing the jam off the receiver after the picnic naturally crowd and with congenial entertainment supplied direct turns one's thoughts to water, and one thinks of long, from the metropolis even though it be a talk on " The lazy summer afternoons spent in a punt in a shady back- Habits of Insects " with which our caravanning eperi- water with a good loud -speaker set and enjoyable ence has made us perfectly familiar, more familiar music. probably than the man who is addressing us. Here, too, Passing on down the river to the sea, we find the we learn from our host that during the day -time when portable receiver in evidence on the beach, valiantly keep- on the road, passing through sleepy old world Villages, ing its end up amid the raucous cries of the rock sellers, where old and young folk alike gape at the wonder of the screaming of children. the hoarse cries of the char- the present century, and children follow awhile, anxious to learn where the music is coming from, a constant and enjoyable programme is available all clay from I I a.m. onwards with no interference from the " magneto " of the caravan. But come, while we have dallied awhile in this back- water of the main road both time and our char -a -banc have passed, and we must take leave of -our host and hostess and return to the main road, where we speedily pick up a motor 'bus and, climbing to the top, find our old friend the freak, struggling with a crystal set, using the framework of his umbrella for an aerial and the framework of the motor 'bus as " earth," surely bringing home to us how summer wireless should not be attempted. Summer wireless we say aloud (" and some are not " rejoins the freak, giving a vicious jab at the crystal with a spearpoint Selections on the seashore. catwhisker). Wireless Awheel. a-banc touts, the clangour of the local band, and all We are now entering the outskirts of town, and here the myriad noises which go to make up the local colour and there we meet a cyclist with a suspicious looking of the beaches of popular seaside resorts. Along the object covered with a waterproof cover strapped on to quieter sections of the beach we find it well in evidence his carrier. Can it be a portable receiver of the head- among bathing parties, where the well modulated phone type? Yes, surely, for farther on we meet tones of the 5XX announcer in the dressing tent has another resting by the roadside and intently listening to frequently nipped pneumonia in the bud by bringing a the first news bulletin. A few miles farther and a warm blush to the skin of members of the less radio- raucous roaring informs us that the evening programme active sex. A picnic on a lonely part of the coast with, is being used for demonstration purposes by some wire- of course, a car for transport purposes, is another sug- less engineer- cum -plumber, who points out proudly to gested venue for the portable set. These functions are his prospective customer how merrily the plate- circuit usually more tolerable than their countryside counter- milliammeter dances and pirouettes in the glare of the part, owing to the absence of some of the concomitant electric light, unlike that of his rival which remains A 16

'w.a;411,';;.,-1',[ www.americanradiohistory.com ,....M,4'..-.,CT'4.!faT"a.7P_..+ßi,t?PF!'.Y):$7 _'!l071i . . ._.«, .. ,

" ñp@Ilem 643 .i/ I Y 251h, 1927. WodCl if they could don a pair Summer Wireless. of those camp -stool martyrs - while away some of the tiring hours by .t, ,idy except on Thursday evenings following the second of phones and local programme. \\-e cannot help think- ic.ws bulletin. Finally, we reach home, and, thankfully listening to the we at the theatre queues of the unique oppor- >inking into the comfort of an armchair, switch on our ing as gaze is presented for the enterprising seller of permanently- installed quality receiver, and drawing at tunity that pounders " to take his place in the our pipes, reflect lazily on the potentialities of the wire- these small " twelve- queue himself. How his immediate neighbours would less set and in particular those of the transportable would they not. to his kindly invitation to listen type. respond, how the faine of the receiver would spread But stay, what of the real lightweight portable? Has awhile, and far end of the queue with many eager queries as that no further use than that of prop iding extra weight to the a boon could lie obtained? for cyclists. which we have already noticed. Most to where such Mr. Pickwick's Portable. Presently, as we still sit meditating over these things, after our clay investigating the possibilities of a port - table, the. voice of Sir Ernest \ \'ild, emanating from our to big moving coil loud- speaker, ceases, and gives place the noisy and pompous meeting of the Pickwick Club, and we see once more in our drowsy imaginings the ghostly figure of the benevolent old gentleman driving on the top of the coach in great haste towards Bury St. Edmund's on his world -famed mission to deliver certain young ladies of that town from the awful wiles of that rascal Jingle. But with him on the coach top the is the latest transportable receiver which, since children's hour is now on, is giving much scope for the comments of the redoubtable \ir. Weller.

An enjoyable nicuic.

assuredly it has. \ \Tat of the invalid in his bath - chair spending monotonous summer days in a sunny part of the public park or being slowly propelled along by a lugubrious attendant. What better use can one think of for a portable of this type, for, needless to say, in an invalid chair of any description, a big, heavy receiver is totally out of the question. It is, of course, necessary in the case of such a receiver that the riser he at a not greater distance than 25 miles at the very outside from some broadcasting station, and preferably within the 15 -mile limit. Whiling the Weary Hours Away. Within tlipse approximate limits a receiver of this description is also invaluable to commercial travellers and other people compelled to spend a great part of their lives in hotels. In such cases the range can be A riverside rhapsody. increased to well over ;o miles, since this extra range should be mentioned that the golden can always be obtained in the seclusion of the hotel In conclusion it in mind when building or purchasing a room by the attachment of a small temporary indoor rule to bear is first to make up one's mind aerial consisting of a length of ordinary electric light " portable " receiver require a portable or a transportable receiver, flex. Various other uses for such a receiver can be whether we to bear in mind that it can never he, imagined, although even in the centre of London one and if the latter, words of Gilbert, ' ` light and airy, like can scarcely credit that any enjoyable results could be to quote the to use a heavy transportable from the top of a 'bus. a fairy," and any attempt obtained leads sooner or later to the appear- Surely, however, -if a holiday caravan is the ideal receiver as a portable a insertion in the Miscellaneous columns place for a transportable receiver, the theatre queue is ance of brief World, " For sale, large portable set; the ideal place for the true portable. One can imagine of The Wireless how much less wearisome would be the waiting hours owner having harp.

A 17

www.americanradiohistory.com 614 Vilp®Il,sog MAY WopIlcal 25th, 1927.

A Section Devoted to New Ideas and Practical Devices. PHONE CONNECTIONS. coats should be given and the panel WIRING HINT. As a substitute for the conventional polished, when dry, with a little type of connector consisting Mansion polish followed Although wiring can frequently he of a by dry rag. simplified metal sleeve with set screws at each A really fine, even polish by leaving out certain is thus ob- components end, it would be difficult to find any- tained. Needless to say, the enamel until wiring is completed in obscure corners of thing better than a piece of thick - tends to improve the insulating pro- the baseboard, this is a risky walled rubber tubing. Ordinary gas perty of the panel. F. H. L. procedure since it is tubing is quite satisfactory, and rub- very easy to forget the missing parts 0000 and ber tubing of suitable diameter and run wires through the space they thickness is obtainable from dealers L.S. DIAPHRAGM. should occupy. in chemical apparatus. A really light and rigid free -edge loud- speaker diaphragm may be readily adapted from a child's toy Japanese paper sunshade, which should be glued If and doped in the ¡ííiíyÍ<ïMtur open position after cutting away the handle and all unnecessary wood from the hub. 0000 TRANSFORMER SPACERS. Connecting phone tags in series. When constructing tht H.F. transformers for the " All Wave Four," The method has two outstanding advantages. difficulty may be experienced in filing First, the constant the Wiring awkward connections. pressure V- shaped groove on the under- exerted by the rubber en- side sures of the spacing strips. a noiseless contact, and, To A better plan is to screw down all secondly, obviate this, the strips can be the rubber itself insulates made from components and then make awkward the tags ebonite tubing cut in from possible contact with halves lengthwise connections by the method shown in other parts with a fine hack- of the circuit. L. C. H. saw. the diagram. The end of a fairly long piece of wire 0000 Tubing about lain. diameter with is bent to the shape required and then a 5-32in. bore is a suitable stock nicked so that it ENAMELLED PANELS. may be broken off when size, and before cutting it will be the soldered joints have been made. The In a large number of sets now- found convenient to screw -cut the extra length serves as a handle when adays all the components mounted on outside of the tubing with 32 threads manipulating the wire in position. the panel touch it at places which are per inch. G. C. W. E at zero H. F. potential, and hence, A. C. as has been mentioned in this journal, 0000 three -ply wood can be used. PROTECTING CABINET POLISH. The disadvantage Valves for Readers. is that the In some types of recd\ er cabinet colour of the wood does not generally there is a polished fillet running match the cabinet. This may be along the front parallel with the avoided by bot- enamelling the panel, and For every practical idea sub- tom edge of the front panel. Fre- the colour need not be restricted to mitted by a reader and quent withdrawal of the set from the usual black. Royal accepted the blue, for in- cabinet will scratch the polish. To stance, is most effective. for publication in this section the prevent this the underside of the The enamelling Editor will forward by post a base- should be done board should he covered with thin after the panel is receiving drilled and before valve of British make. felt or baize which should be fixed mounting the components. Two with glue. R.-N. B. A Ió

www.americanradiohistory.com MAY 25th, 1927.

N,LI,W TALKING F I SYSTEM. Cinematograph and Sound Records on the Sanie Film.

By A. DINSDALIE..

camera. Somewhere out of range N the issue of this journal for September r5th, 1926, ordinary cinematograph form of microphone, the writer described a very successful talking moving of the camera is mounted a suitable amplified by means picture system which had just then been demonstrated the output current of which is suitably amplifiers. in New York. In the following article it is proposed of ordin.u-y L.F. is caused to actuate a tiny vibrat- to describe another system of talking " movies " which The amplified current spot of light through a developed by a different group of engineers ing mirror, which reflects a tiny has just been The result is, General Electric Company. lens and on to the margin of the film. belonging to the sounds. ('inematograph performances, or " movies," as they therefore, an oscillograph record of the sound record can be macle in different ways. Roth are called in America, have been developed until they This and the accompanying sounds can Ice simul- have now reached a very high pitch of perfection. The the picture recorded on the same film by mounting the two same applies to sound reproduction, whether through the taneoulv as a unit, with the sound recorder medium of the gramophone or by means of electrical ap- recording elements in the latter uppermost. The two recorders can also he mounted paratus ; and the present -day perfection and the sound and picture film negatives made direction owes much to broadcasting, for many of the separately, units, such an arrangement Icing prefer - methods used in broadcast transmission and reception as ini bvidual the pictures are being made in studios and have been adapted to mechanical and electrical sound able when when the camera is being shifted constantly. In this reproduction. making the two records must be driven to be solved in the development of a case the cameras The problem motors to ensure, synchronism between the talking moving picture system, therefore. is by syn,-hronous successful two records. simply one of accurate synchronisation . \gain, as in the case of music to record (the cinematograph of a visible a accompany an important feature film, with a record of the accompany- filet) film can be entirely finished Efforts to do this date the picture ing sounds. and titled, the record of the music about twenty years. hack a separate film and referred to above, the then being mole on In the article on the finished the Vitaphone produc- the two combined writer described positive. tions, in which simultaneous records of scenes and sounds are made on P The Projector and Reproducer. a gramophone record W a film and front standard During this and the The only modification respectively. in the projector is the attachment which process of reproduction, subsequent can be seen just below the upper drum is obtained by electro- synchronism Ilhich holds the films. Mechanical means. This attachment consists simply of a The New System. small electric lamp and a photoelectric cell. The former, together with a suit - In the General Electric Company's able lens, is placed in front of the film, system both records are made on the width cine- while the latter is placed behind it. As same - medium -a standard the Ellin is run through the projector a matograph film. A standard motion small spot of light is caused to shine picture camera is used for making the the margin of the film. and the picture, and a standard projector, upon intensity of light which ultimately with an attachment for the sound re -. reaches the photoelectric cell depends producer, is used for the presentation upon the density of the oscillograph of the two effects. record on the edge of the film. The sound record is made along the The result of this action is that a margin of the film, where there is a very minute and varying current, an strip a small fraction of an inch wide exact replica of the sound wave, is pro- upon which can be seen a series of in the output circuit of the cell. horizontal light and dark bands and duced This tiny current is then amplified by lines, of varying widths and intensi- means of ordinary L.F. amplifiers and ties. It is this series of bands and speaker which reproduces which produces the sound. feci to a loud- lines volume to fill In making the new films the scene is the sound in sufficient A specimen film showing scored record auditorium. " shot " in the usual manner with an on left -kand side of visua. images. the

A 19 i ñÀc,' . . www.americanradiohistory.com 646 WiiTa®00 Wald MAY 25th, 1927. A New Talking Film System. - Although the picture does not suffer to any noticeable Any suitable loud -speaker can be used. The one for extent when a few feet of film are cut out, it might be large auditoriums which has been used in the demon - thought that the sound reproduction would suffer. Ex- trations is a Hewlett loud -speaker, chosen because of its perience has proved that such is not the case, however, ability to give the necessary volume, and because of the for as a rule only a letter or two of a word is lost. quality of tone reproduction of which the device is Another point in favour of the system is that if the capable. film should happen to break during exhibition -not an in- Synchronism Assured. frequent occurrence -it is impossible for the sound repro- Cinematograph films are extremely fragile things. duction to continue. It must stop simultaneously with the Before they have been exhibited very many times they reproduction of the scene. commence to tear at the edges and even break. Such The System Demonstrated. dalnage makes it necessary to cut out as much as six The new apparatus was demonstrated in New York or eight feet of film before a satisfactory repair can be recently before an audience of radio engineers and moving made. picture theatre owners. While the demonstration was confined to orchestration, singing and a few introductory remarks by an announcer who appeared in the films, the results obtained were exceptionally good. The films were very good and very well presented, and the quality of the sound reproduction left little to be desired. Those who are accustomed to attend the presentation of big feature films in the largest cities know that a suitable orchestral accompaniment is of vital importance if the film is to be followed and appreciated to the fullest extent. One has only to witness a presentation of the same film in a small town, where the picture - house " orchestra " consists merely of a decrepit piano, indifferently played, to appreciate this point. By means of a talking movie system the necessary orchestral accompaniment, Combined sound and picture projector. A standard projector is used, played by a first -class or- being mounted the sound reproducing element directly below the upper film drum. chestra, can be recorded on the Ordinarily the amputation of such small film, circulated round the sections of provincial theatres, and properly presented film in this manner is unnoticeable when the picture there, so that is the small town picture goer can enjoy next exhibited, unless the film is very old and has the benefit of a performance equal to that possible to suffered many breakages. Any system of talking films the city dweller. which employs two separate records Tor the scenes and Fields of Application. accompanying sounds immediately comes up against a A feature of the General Electric system is the serious problem of synchronisation extreme when the film breaks. rapidity with which the photographic records of sound Obviously, if a portion of the film is cut out without a and action ran now be made. A demonstration of similar portion of the this sound record being eliminated, the was given when the orchestra of the Capitol Theatre, New delicate timing of the entire system is bound to he thrown York, commenced at midnight to play music to accompany out of gear. " The Flesh and the Devil." In the system under review, however, the timing cannot Synchronism in this case was obtained by making be thrown out, both for the sound record is on the edge of the records simultaneously on the same film, and the film. Consequently entire if the film breaks the appropriate film was complete and ready for presentation by noon part of the sound record comes out along with the picture the next day. record. Another field of application is in connection with news

A 20

M[ S4 , Rrr[:LLA,!F.l.kLyí<'-'_"i'www.americanradiohistory.com 43[ tfF_;+mt_

M Wfi&'Cilsep 6 17 MAY 2511/, 1927.

A New Talking Film System. - reels. Not only will it be possible to show important personages when they attend public functions; they will also be able to address a few words to the audience, and visiting notables will be able to extend their greetings. It is not usually possible for famous musicians and orchestras to appear in small communities. Talking motion pictures will permit them to be both seen and heard in the twist remote corners of the country. F r o m an educational standpoint there are also many ways' in which the new development will be of service. Many schools and colleges are now equipped with cinematograph apparatus as an aid to class -room work, and the new films will be recording of voice A scene in the G.E.C. experimental laboratory studio during the simultaneous found of even greater assist- and gesture. ance. to benefit students In America broadcasting has been. called in to aid class -rooms and thus enabled them have hoped to hear such education, and by this means it has beem found possible who could not possibly in any other way. for eminent lecturers in certain subjects to reach remote masters of their subject Where demonstrations are necessary concomitants to a lecture, however, broadcasting cannot be employed, and this is where the talking film can step in and supply the want. In the case of pro- fessors from abroad, it will be .possible to record their lectures and demonstrations simultaneously, and thus render their lectures of the greatest possible value by the circulation of the film to colleges and universities throughout the country. These are but a few of the possible fields in which the new talking motion pictures will find applications. The list can and will be extended. Thus we have one more development to add to the rapidly growing list of inventions which depend for their successful operation upon apparatus which was originally developed for use in con- ' nection with radio communication, the foundation stone being that modern Aladdin's thermionic valve Hewlett loud- speaker used for reproducing the sound film in large auditoriums. lamp, the

A 2i

u 11 N 11

_ _ e .... , v- , :,na , a ``o-.`E+,_- _ %j6 iI 't.... Illllllllllllllllllll ouuummmummmmuuuuumuumuuuumumuuuuumumlmiumm mmit.,tilmmnmimiùïlimuumnunnmuuñmiiiu

A Section Mainly for the New Reader.

SIMPLIFYING THE D.C. ELIMINATOR. H.T. values, it is advisable to through the mains, and reduces the There is a tendency include to introduce resistance -coupled low -fre- possibility of the introduction of unnecessary complications into quency a amplification, and the resist- " hum " due to the existence of a short-range receiver designed ances to be should be large. If this prac- probable difference of potential be- fed, as far as the H.T. supply is tice is followed, the anode current tween the " set earth " and the concerned, from the D.C. will supply. It be reduced, and the remarks " mains earth." Where reception on may be pointed out that if the cir- made above regarding valve life -as the normal broadcast band only is cuit is suitably chosen it is possible far as those actually having resistors desired, the set may be simplified to supply all by the valves with a com- in their anode circuits are concerned the substitution of an " untuned mon voltage, which, moreover, may -will no longer apply. aerial " coupler. be that of the mains- possibly over The circuit diagram of a suitable Modern " high magnification zoo volts. is It admitted that the arrangement for operating direct from valves may be used as detector life of the and valves will be reduced by zoo -240 -volt D.C. mains is given in first -stage L.F. amplifier, although the application of high voltages, but Fig. r; suggested values for the in the immediate vicinity of a only very slightly station if ample negative coupling components are indicated, almost any valve will give sufficient bias is applied to their grids; in any while the tuning circuits may follow amplification in the latter position. A case, the improved power -handling conventional practice. The receiver, power or super -power valve wili capacity and better quality of repro- which includes neither H.F. ampli- naturally be required in the last duction will, in the opinion of many fication nor reaction, is intended stage, depending on the sensitivity of listeners, be ample compensation for purely for local station work, up to the loud- speaker and the volume re- small increase in upkeep cost. distances of about thirty miles, with quired. At the same time the initial expense perhaps alternative reception of the The output choke L, (which is involved in the construction of the high -power station under favourable not absolutely necessary) may have an amplifier will be reduced, as no circumstances. inductance of from r5 to 3o henries, potential -dividing or voltage- reduc- It will be noticed that a coupled while the smoothing choke, L;, should ing devices will be necessary. direct circuit has been included ; this be of from 3o to 5o henries. When using exceptionally large allows the filaments to be earthed only 0 0 0 0 A CURE FOR NOISY CONTACTS. Rubbing contacts in receiving circuits, such as switches, plug -in coils, friction contacts to moving vanes of variable condensers, etc., are often imperfect, and give rise to scraping sounds. An excellent remedy for this is to apply a spot of lubricant such as vaseline or oil to the rubbing surfaces of the contacts. Not only does this improve the smoothness of the mechanical action of the contact, but greatly improves the certainty of electrical contact-a rather extraordinary fact when it is remembered that most lubricants are in themselves excellent insulators. Only á bare minimum of lubricant should be used, as an Fig. 1. -A simple local -station receiver drawing H.T. current direct from D C. mains. excess tends to collect dust. A 22

www.americanradiohistory.com " t'. cstP Wpilseo 649 71.9Y 25t1a, 1927. Woreild mfd. maxi- SOME "REFLEX" CONSIDERATIONS. tirely by the use of a choke 1, able condenser of o.00r coupling at C2. The The beginner is apt to lose sight having a large value of inductance mum is used for about 2 meg- fact that the reflex or dual but a low resistance. By placing the grid leak R. should be of the the capacity of amplification principle, by means of choke L in series with the loud- ohms. The smaller larger will he the pro- which a valve is made to amplify at C. is made the portion of bass frequencies cut out. lc ith high and low frequency, was de- to reduce the higher purely as an economy measure. If it is wished vised frequencies with respect to the lower 'l'he most fervent advocate of this ones, C_ is replaced by a larger capa- system could hardly affirm that city fixed condenser of anything be- reflex receiver is better than a 0.01 and o. r nifd. , while a circuit, in which the same tween " straight " CI is shunted across the operations are carried out by separate condenser anode resistance R,. According to valves. Indeed, most of them would the degree of suppression required on he ready to admit that it is not ,ßìn /, the higher frequencies, C, will need as good. to have a capacity somewhere be- this fact in mind, it will be Bearing 0.001 rirfd. and o.or mfd. the introduction of tween realised that must naturally sacrifice a cer- and, above all, more One better, cheaper, tain amount of signal strength with economical valves (upkeep is even parallel connections almost any form of tone control, more important than initial cost) tends 2.-Series and . of choke for tone control. since the correction is made by previous advantages of to discount the weakening the unwanted frequencies and to account for speaker, as in Fig. 2(a), the higher - the reflex receiver, and not by strengthening the required in popularity. It pitched sounds are suppressed, while its present decrease ones must be admitted, however, that these by connecting the choke in parallel 0000 circuits are interesting, and for this with the loud- speaker, as in Fig. reason will probably have a follow- 2 (b), the higher- pitche I sounds are SAFEGUARDING THE VALVES. ing for some time to come. Further- favoured and the low frequencies It has been noticed that the aver - of more, it cannot be denied that a reflex suppressed. The actual number age amateur, before making internal receiver can give amplification, from turns, etc., required on the choke 1. adjustments to his receiver (with the in the point of view of quality, indis- depends upon the loud -speaker batteries connected) almost invariably tinguishable from that obtainable use and the amount of correction re- switches off the filament current. Of from a " straight " set under average quired. ' Some interesting experiments course, the correct practice is to dis- working conditions. Such results, in this connection can be performed connect all batteries, but it is realised -cycle however, will only be obtained when using various small -power 5o that there is a natural tendency to The impor- the " dual " receiver is really well transformers as chokes. save time by ignoring this precaution. of the designed, well constructed, and, tant thing is that the resistance It should be pointed out, however, with generally speaking, operated by some- choke should be small compared that it is much safer to leave the one ivith considerable theoretical its inductance. valves " on," as the voltage de- coupled knowledge of the subject. Where a resistance- capacity veloped across their filaments by an 0000 amplifier is used, a better and more accidental application of the H.T. may be OF LOUD- SPEAKERS convenient form of control battery pressure will be automatic- TONE CONTROL itself, as AND SETS. effected in the amplifier ally limited by the presence of the If broadcast transmissions, receiv- L.T. accumulator, and in the will ing sets, and loud- speakers were all majority of cases no serious harm perfect tone control dgvices would not he done to the valves. be permissible. As things are, we 0000 often find circumstances, both at CORRODED ACCUMULATOR transmitter and receiver, which tend TERMINALS. unduly either the upper to exaggerate The incrustation which forms on extremities of the audible or lower the positive terminal of badly de- the only method of range. Somehow, ned accumulators should be re- tone control which has si loud -speaker as soon as it begins to make so far is the moved gained much prominence or the terminal will condenser across the its appearance, simple use of a ruined. The cleaning is This is really a very be quickly loud -speaker. easily effected by pouring hot method of control, and should be very poor water from a kettle over the terminal as possible, since by resistance -coupled circuit in used as little Fig. 3. -A when the incrustation capacity across a highly which tone control is effected by varying to be cleaned, shunting a condensers C1 and C2. rapidly washed off. There is inductive instrument like a loud- becomes no need to remove the acid from the speaker we are likely to defeat our shown schematically in Fig. 3. To accumulator, but the operation should own ends by introducing electrical suppress the low frequencies and be conducted over a sink or drain of resonance. In Fig. 2 (a) and (b) we favour the high frequencies the con- some sort. show a method of controlling tone en- denser at C, is left out, and a vari-

A 23

www.americanradiohistory.com WIpAisom Wor lïd MAY 25th, 7927. WINDING FRAME AERIALS. 25oft. of wire will give approxi- the lamp a preliminary Although test on a 200 - the calculation of suit- mately the right inductance value. volt supply of known polarity. If able windings for the type 0000 of frame this cannot be done the alternative is aerial usually included THE NEON LAMP AS A POLARITY in a portable to remove the brass base from the receiver is a INDICATOR. matter of some difficulty, lamp and get at the wires, which it is a fairly easy matter A glow- to get a discharge lamp, such as the can be followed to the electrodes. A good idea of the number of turns familiar " Osglim," is very handy word of warning required. is necessary here, for determining which are the posi- however, as the little series safety re- To cover the normal broadcasting tive and negative wires of a D.C. sistance incorporated in the cap is waveband it will be found, if a supply of 200 volts or more. The fragile. A neon lamp should fairly conventional never method of wind- only thing to remember is that the he connected straight across the ing is used, that a total length of pink glow covers the negative elec- mains without a series safety resist- about 8oft. of wire will be required. trode. Of course, it is essential in ance, so if the original cafety resist- Thus, if the frame has eft. sides, the first instance to find which lamp ance is scrapped a 40 -watt ten complete lamp or turns should be used. contact goes to which 'electrode. The similar resistance should placed For the long be in -wave stations, about simplest way of doing this is to give series with the neon lamp.

DISSECTED DIAGRAMS. Practical Points in Design and Construction. No. 71 (a). -A Neutralised Tuned Anode Receiver. (Concluded from last week's Issue.)

o H.T.-}

wr C4 N.C.='

-0 O H. T7 0 e po

'VVV.".-1 L.T. + o (3) (4)

Amplified H.F. voltages developed across the anode coil are The anode applied to the grid of the detector circuit of the detector is completed through the primary through a small condenser. A of an L.F. transformer, the secondary of which leak is inserted between grid and the positive side of the filament, grid and filament is joined between in order that rectification effects of the output valve, with bias battery interposed. may be obtained. Phones or loud- speaker are inserted in the anode circuit. r HE grid condenser (C5) and the mended that the detector valve should cation ; failing any instructions on leak may have the conventional have an impedance not greatly in ex- this matter, one of from 0.0003 to values of 0.0003 2 mfd. and meg- cess of 20,000 ohms; this, if of 0.0003 mfd. should be tried. ohms respectively. There will, as a modern design, will have an amplifi- With only a single stage of low - rule, be some slight gain if the lower cation factor of about zo, or rather frequency amplification, an ordinary- end of the grid leak is connected to less if the filament is rated at only z power valve should be able to handle the slider of a potentiometer, the volts. the signal voltages to be dealt with windings of which are joined across The above recommendations rein the .L. F. amplifier. A grid bias the L.T. leads. This refinement is garding the detector valve presup- voltage of 712 or q volts is generally generally recommended for grid de- pose that the L.F. transformer will suitable for this type of valve, with tector circuits, but its advantages are have a high primary inductance, and 120 volts of high tension. As a high - less pronounced in receivers like that consequently a low ratio of from 2 : I magnification, high-impedance under discussion, valve as reaction between to 3i : I. The capacity of the shunt- is recommended for the H.F. ampli- anode and grid circuits is not used. ing condenser across its primary fier, it is permissible to apply If good quality the reproduction is an winding should he chosen in accord- same voltage to both first and last important consideration, it is recom- ance with the manufacturers' specifi- valves.

A 24

üahri9l. ,- - .. www.americanradiohistory.com 7nreg®0g 651 11.4Y 25111, 1927. Won:' lica

Current Practice in Portable Set Design.

friends. He may even be genuinely possessed Of such catholicity of taste that he is really dissatisfied with the programmes of one station or even one country, and TrNT glancing through the pages of the Buyers' Guide of the intricacies of any Portable Receivers in this issue, the first impression will go to the trouble of mastering 1 in order that he may be able to draw is one of wonder at the variety of circuits and methods number of controls his amusement and instruction. of construction. The student of design will, no doubt, on foreign countries for by this class of listener is supplied hold very definite opinions as to what constitutes the ideal The demand created who believe that the secret of portable receiver, and will marvel that manufacturers by those manufacturers is to produce a universal should waste time and money on the production of re- success in the wireless business wavelengths, and for use under any set of ceivers so manifestly inferior to his own favourite type. receiver for all But let him reflect that other experts may hold with equal conditions. sincerity diametrically opposite views, and, further, that Limitations of Space and Weight. whatever form the final product may take it will fulfil these two extremes will be found the majority the ideal of a section of the public however small. Between of sets on the market, but for whatever object they may Supply and Demand. have been designed all are subject to the limitations of instance, z -volt valves are almost For instance, there are still some strong silent people space and weight. For 2 -volt accumulator has one -third of who are not afraid to run counter to prevailing fashion by universal because a one -third of the space of a 6 -volt proclaiming (by the purchase of a set for Daventry only) the weight and occupies same ampere -hour capacity. At one is nothing seriously amiss with the B.B.C. pro- accumulator of the that there while to incur the extra grammes. They are met on equal terms by those de- time it might have been worth of the superior performance of 6 -volt signers who argue that whereas the genius is not yet horn weight for the sake 2 -volt valve has reached such a high produce a set to cover all wavelengths with maxi- valves, hut to -day the who can this measure is unnecessary. efficiency, the present state of high- frequency state of efficiency that mum accumulator in order of weight comes technique does enable a qualified engineer to design a Next to the L.T. and here we are limited to the small really fine set for one -particular a az clengtla. When that the H.T. battery, type dry cell battery. This is unfortunate because, for wavelength happens to be used by a station of exceptional port- and to a given volume of sound from the loud -speaker, a power served by programmes from the capital, battery than what possible argu- able set makes greater demands on the H.T. be particularly free from interference, aerial. Large creative instinct from setting a receiver working off a standard outdoor ment would deter a man with batteries are out of the work? type dry cells and accumulator to four -electrode valves are used,' so that At the other extreme there is the inveterate " knob - question unless of the H.T. battery must he regarded twiddler " who is oppressed by a sense of social in- frequent renewal feriority unless he can demonstrate alternative reception as a matter of course. 11th, 1927, page 595. from at least a dozen stations to a circle of admiring See The Wireless World, May A 25

www.americanradiohistory.com Wflp@IlC@EZ 652 MAY 25th, 1927. WOVA. Portable Receiver Types. - formers tuned and balanced on a wavelength of The method of mounting valves must receive special 1,6oa metres. The frame aerial is wound on a former consideration. Not only will the set be subject to jolts fitting in the hinged door at the back of the cabinet. and jars during transport, but trouble from microphonic The receiver is perfectly stable and works equally well noise must be guarded against, since loud -speakers are generally mounted inside the cabinet itself and will trans- fer acoustic vibrations to the set as a whole. Sponge rubber is freely used in valve mountings, and if in sonie cases H.F. and L.F. valves are rigidly supported, spring mounts for detector valves are almost universal.

Interi r of ie Pye rcelver. simplicity and sound construction ara :he ke- sot'' of this in- strcmeat. -s with the door open or closed, but due to such masses of metal as the loud -speaker horn in. the interior of the set the tuning of the frame aerial depends on the relative position of frame, and must be allowed for by some suitable control. This taques the form of a compensating condenser, which is the right hand of the three controls

The Pye 5-valve portable for Daventry only There remains one other factor peculiar to portable sets which must be taken into account by the designer. This is connected with the frame aerial which is wound round the outside of the set or in the hinged back of the cabinet. The field associated with this coil permeates the whole of the set, and it is difficult to avoid stray couplings with .other tuned circuits in the receiver. When the direction of the field is variable, as in the case of the hinged frame, the difficulty of dealing with stray couplings is greatly increased. - So much for generalities - let us now "consider one or two representative types in

further detail. - The Pye S -valve portable receiver is an excellent example of a single- station receiver. There are two stages of high -frequency Balancing condenser used in amplification, the Pye portable. Note the coupled with split The gees Mace "All-in ' receiver for use with or without an bush and locking nut. neutralised H.F. trans- external aerial. 26

www.americanradiohistory.com s r: i"- T"!StR`ff1 1+ ,ti tw .x1"s: ; . - -rrv;

MAY 25th, 1927. WIpdszo 653

Portable Receiver Types. - gether with the plug -in coils and variable coil holder, are seen in one of the photographs. The left-hand control housed in a sepa rate ccmpartment in the top left -hand is a combined on -and -off and change -over switch, by corner. The sides of this compartment are covered with means of which one of the L.F. amplifying valves may he cut out of circuit. The central knob operates a continuously variable volume control -a feature which should he regarded as essential in any receiver, but which is all T h e Celestion the amplification 4 -valve portable too rarely seen at the present time. If incorporates the is made sufficiently high for reception in any part of well -known Celestion loud- the country, it stands to reason that at close ranges over - speaker. loading will occur without some forni of volume control.

thin sheet metal, presumably tor selecning purposes. On the right -hand side of the set will he seen the L.F. valves and their associated transformers. In the centre is the djusting screw for the loud- speaker, and a little to the feature Interior of the Rees Mace set. H.P. components are assembled left a flash -lamp bulb H.T. fuse. An interesting in a screened compartment in the top left -hand corner. of the set is the key switch for the filaments, which effectively prevents unauthorised persc-'s from using the set. The workmanship throughout is excellent, and the re- The makers give a year's free servi' c Avith each set, exclud- ceiver as a whole is a thoroughly sound and reliable taken ing valve and battery failure. proposition. Although the appearance of the Rees Mace " All -in " it as a portable, the makers receiver immediately classes Resistance coupling emphasise that it is a general -purpose receiver, suitable is used in the Celes- lion portable and the for use in the home as well as out of doors. It may be instrument panel incorporated in the set or may be raised for used with the frame aerial inspecttoa. with external aerials of varying lengths, four aerial sockets being provided to suit aerials of any given capacity. With interchangeable plug -in coils the wavelength range of the receiver is 25o to Goo and r,ioo to 2,600 metres. There are two push -pull switches associated with the frame aerial, one to alter the wavelength range, and the other to vary the degree of reaction in the circuit. continuously variable reaction control is also provided and is the centre control :x marked " Volume." Inci- dentally, the reaction is negative, that is to say, the set oscillates when the coils are apart and ceases to oscillate when they are brought to- The arrangement of T- vaLv // gether. components is interesting, and is shown in the back view of the instrument. The Key switch used in the Rees Mace portable. H.F. and detector valves, to- A 27

www.americanradiohistory.com Mpdisto 654 WoyPI MAY 25th, 1927. Portable Receiver Types. - ('unsiderable ingenuity is shown in the construction of In the l-'elestion portable receivers resistance- coupling components. The valves are guided into their sockets is used .for the low -frequency stage -a very shrewd idea by funnel -shaped mouldings, the grid and anode sockets since it materially reduces weight. and also gives excellent being marked on the front of the panel. Provision is quality of reproduction, especially when combined with made for the use of an external collapsible frame, or the the Celestion loud -speaker, which is incorporated in the range may he increased by using an elevated aerial in conjunction with a special coupling coil, which is placed near the back of the receiver. Not the least noteworthy feature of the B.T.H. equipment is the excellent instruction book issued with each set.

B.T.H. portable 3 -valve superheterodyne. lid. A single stage of H.F. amplification is used, coupled with interchangeable neutralised transformers for long and short waves. Separate neutralising condensers are incorporated in each transformer, and these can be adjusted once for all, so that the wavelength range may be changed with the minimum of delay. All components are mounted on a hinged panel, which may be- raised for inspection and for chancing the H.F. transformer. which Battery clamp used in the B.T.H. portable amplifier. Finally, we come to the aristocrat of portables, namely, the multi -valve superheterodyne. In this class may be placed such sets as the " \ eutrosonic Seven,' which was reviewed in some detail in the April 13th issue of this journal. Sets of this type are necessarily heavier and more bulky than their humbler relatives, but are quite suitable for motoring expeditions or other occasions when adequate transport facilities are available. An interesting receiver in this class is the " Liberty " eight -valve portable superheterodyne . Although a continuously variable wavelength range of 200 -2,000 metres is available, the tuning controls are extremely simple, the change -over from short to long waves being effected by a A stop S on the door of the B.T.H. portable automaticallS single switch. There are no interchangeable units, and switches off L.T. current when the set is packed up. is the barrel -shaped component at the left -hand end of the panel. The B.T.H. portable receiver (Type V 1{, ;) is a three -valve receiver employing the superheterodyne principle, and as such is probably unique, at least as far as commercially produced sets are concerned. The first valve acts as oscillator -detector, the second as intermediate- frequency amplifier, and the third as second detector. Needless to say the receiver as it stands is intended for telephone reception, but a portable combined amplifier -loud -speaker, unit is available for those who desire loud- speaker reception. The number of controls looks rather forbidding, but only two of these are used while searching for stations, the others being of subsidiary importance -such as volume Portable power amplifier and loud- speaker designed for use with controls, wavelength range switches, etc. the B.T.H. 3 -valve superheterodyne. A 28

www.americanradiohistory.com B7.417 25t1,, /927. Wfipa,ß@@ W011'Il0 Portable Receiver Types.- the switch alters the range of the oscillator as \yell as the detector circuits. In addition to the usual tuning controls there is also a volume control and an on-and-off switch. The volume control is really a potentiometer controlling the grid potential of the intermediate frequency valves, which oscillate when the grids are made sufficiently negative. By operating just off the oscillation point a high degree of sensitivity is obtainable, while the application of a more positive bias results in a diminution of volume. 'l'hat the simplification of controls results in no reduc-

in laying out the interior of the Liberty Superheterodyne accessibility has re- ceited special attention.

tion of efficiency is evident from the number of stations logged on the calibration chart supplied with each set. In conclusion it may he said that the trend of design of portable sets seems to be towards two extreme types : on the one hand, the simple robust single or two- station set, and on the other the superheterodyne. Frame aerials are now almost universal, as the addition of external aerials introduces an extremely variable and incalculable factor into design. By concentrating on a frame aerial, however, it is possible to produce a single -station set of high sensitivity for use in any part of the country, or a The Liberty 8 -valve Super- superheterodyne with almost unlimited range, both types heterodyne being unequalled for stability and ease of control.

41,

CLUB -1111r- REPORTS The Super- heterodyne. ND The Hon. Secretary of the Society, Mr. heterodyne receiver formed E. C. Wilson, "Lingmell," hirklees The super- will be pleased the subject of an absorbing lecture given Road, Birkdale, Lanes, TOAPIC S to of membership to by Mr. II. S. Walker at the last meet- forward particulars in the district. ing of the Hounslow Wireless Society. experimenters After dealing with the difficulties of 0 0 0 0 amplification at, extremely high fre- Institute of Wireless Technology. quencies and how they are overcome or Secretaries of Local Clubs are invited to 'l'he annual general meeting of the partly overcome by the nentrodyne send in for publication club news of general Institute will take place this evening system, the lecturer explained low, in interest. All photographs published will be (Wednesday) at 7 p.m. at 71, Kiugsway, the super -heterodyne system, the fre- paid for. London, W. C.2 (members and associate quency of the incoming signal is reduced mend Pers only). to a lower and more manageable fre- 5KL Demonstrates. Iuformation respecting the activities of quency, when amplification becomes a The difficulties encountered by the the Institute may be obtained front the comparatively easy matter. After an novice who tackles short waves were de- hon. secretary at the above address. interesting discussion, Alt'. Walker scribed by Mr. O. B. Kellett (h 5KL), in 0000 demonstrated a superheterodyne receiver the and Dis- a lecture before Southport the " Osram " Valve Works. of his own design which worked exceed- trict Radio Society on May 2nd. Besides At ingly well, bringing in many (listant elucidating many of the common troubles tembcrs of the Western Metropolitan stations on the loud -speaker with good met with, the lecturer described the re- Radio Societies spent a profitable morn- strength and quality. lative merits of a number of short wave ing recently when they visited the M.O. works at Hammersmith, Hon. Secretary : Mr. W. R. Collis, 7, circuits and demonstrated his own trans- Valve Co.'s Algal Road, Isleworth. mitter which was on view. where they were enabled to see

A 29

...}a..`T..M1 . www.americanradiohistory.com 656 Mpohoo WofIldl MAY 25th, ¡927. " Osram " valves in process of manufac ber, ture. Over stamped, and put into its box and fifty members Were present. sealed. These representing the following processes are all done by societies :- Imand so that the possibility of any Guiders Green and Hendon. damage after test is reduced to a mini- Hounslow. mum. Inland Revenue. 0000 Lyons. Loewe Valve Set Demonstrated. Muswell Hill. At a meeting of the Golders Green and Tottenham. Hendon Radio Wembley. Society held on May 5th, Mr. D. 1'. Scanlan, B.A., demonstrated Very capable guides escorted the party one of the Loewe multiple valves. This over the works. The cleanliness, airi- contained three complete valve systems, ness, and lighting of the factory im- viz., detector and two resistance -coupled pressed everyone, as did the ingenuity amplifier stages. The filament voltage displayed in the design of the various was 4, and the total filament current 0.3 labour- saving machines. amps., while the anode current was Space forbids a full description of all 2 -3 milliamps. The valve was used on a that was seen, but several features set of Mr. Scanlan's own construction. deserve special mention. As practically all the connections are in- Great interest was aroused by the side the valve the set was very simple spectacle of the tungsten powder being and compact, consisting of a coil holder and leads for L.T. and H.T. No reaction was employed, and the aerial system was semi -aperiodic. The valve gave ample loud- speaker volume with excellent quality. At the same meeting Mr. W. J. T. Crew exhibited an interesting five -valve Henderson portable set with two stages of H.F. The frame aerial, wound round a small " Celestion " loud- speakeir, was THREE MEN IN very efficient. A BOAT. The Tot- Hon. Secretary : Lt. -Col. II. A. Scar - tcnham Wireless lett, 357a, Fiuchley Road, Society spent a N.W.3. highly successful 0000 field day on Sunday, L.F. May 15th, when Transformers. wireless telephonic At the last meeting of the Wireless communication Society of Ireland held at 12, Trinity was maint .lned be- Street, Dublin, Mr. tween a car station, R. Garside, of a boat station and Messrs. Ferranti, Ltd., gave an instruc- a fixed station near tive lecture and demonstration of the Hoddesdon. T h e amplification 1 photographe show of speech and musical the boat station sounds, utilising transformer coupling. 5TT. The lecturer dealt with his subject in a practical manner and carried out a num- pressed into ber of interesting tests with specia4 sets blocks and finally being pointed out, howeve -, that drawn out into new and im- of transformers in the reception of 2RN. lengths of various proved types of valve were so frequently Hon. Secretary : Mr. H. Hodgens. diameters. The highly important pro- designed that it was found cess of exhaustion to be an 0000 was carried out in pro - uneconomical proposition to erect pressive stages special by means of a mercury machinery for certain classes of work. The Winning Lecture. pump and gas oven. The stage of Every individual valve The last meeting of the Tottenham exhaustion obtained, is carefully however, was not tested ; it was then given a serial num.- Wireless Society was mainly devoted to sufficient, su a piece of magnesium which a discussion of the field days which the had previously been attached to an society will hold this summer. electrode wits volatilised by means of a It was announced that the cup pre- coil carrying a high frequency current FORTHCOMING EVENTS. sented by the president, Prof. A. M. placed round the valve. This produced WEDNESDAY, MAY 25th. Low, for the best lecture given by a eddy currents in the metal electrodes, Radio Sneicty of Great Britain. -Ordinary member during the past winter session raising them to a very high temperature. mutiny. At 6 P.m. Teti at 5.30. :it the had been won for Instita tiara of Electrical Engineers, Sacoy the second time by The vapour produced removed any gas Place, W.C.2. Lecture: The Hot Wirr Mr. R. F. G. Holness. The result was Microphone still left and condensed on the glass wall and ,i udio Resonant Selec- arrived at by means a ballot tion" (accompanied by original experi- of taken at of the valve, producing the silvery effect mental, by Mr. G. G. Blake, ,1LLE.E. each meeting. noticeable Tottenham Wireless Society. in dull -emitter valves. -At 8 p.m. Hon. Secretary : Mr. A. G. Tucker, 42, .4 t 10, Bruce (,'rove. Lecture: " Wireless 0000 and the Eclipse." by air. E. S. Usher. Drayton Road, Tottenham, N.17. 7 net it ale- of Wireless Technology .-.4 no ceci 0000 False Economy. general 'meeting. At 7 p.m -. A1 71, Maass -nu, 11'.1'.2. (Mr m bers and Aseo- Radio Society of Great Britain. An exceedingly interesting demonstra- riot e )leur les rs only.) tion was afforded to one of NaswlI Hill and I)istrirt Radio .Sorirlv.- The Incorporated Radio Society of the parties, 41 8 p.m. At Tollington consisting of the " sealing -in " School. l'ether- Great Britain will hold an ordinary meet- of one of dov'n, 717.10. Demonstration by Mr. Y. A. ing this evening (Wednesday) the largest rectifying valves, viz., the Turner (Chief of Itostarrh Departs. rat, at 6 p.m. Tesare. Bnrndept, Ltd.) on "Modern (tea at 5.30) at the Institution of Flea CAR.4, an enormous cooled )Mode salve Broadcast Rrrcirers." of exceptional power. trical Engineers. The lecturer will be THURSDAY, JUNE 2nd. Mr. G. G. Blake, Amongst so many labour -saving devices M.I.E.E., who will take C'olders Green and Hendon Radio Society. - as his subject: " The Hot Wire Micro- it appeared that much of the work it 8 p.n +. At the Club House, li-i7Rfield now Way, phone and Audio done by hand could be more N.JI-.11. Exhibition of Members' Resonant Selection." A economically Apparat as. number of original experiments will be accomplished by machinery. It was performed.

A 30

www.americanradiohistory.com WIpA@go f5; 11121Y 1927. 211/, G`'Icok].

TELEPHONY TIME TRANSMISSIONS FOR BRITISH MIRACULOUS WIRELESS. 'IRA\SA'I'LANTIC L.S. EXTENSION. AMATEURS. is the doctor who is curing '- Wireless The Transatlantic Telephone Service In order to enable British amateurs to us of our halait of incessant chattering." Shtr, Women's is now available from 12.30 p.m. to 11 hear American short -wave transmissions --glary Glynn e, Thr including Sundays. early in evening the General Electric p.m. (B.S.T.) daily, the Page.ge. of tite hours of service of has arranged a special 0000 This extension Schenectady of particular interest tu schedule of regular transmissions on 22 shuulti be WIRELESS AT SOUTH KENSINGTON. -American visitors tu titi: country. metres from 2X Al) every Tuesday front 0000 4 to 5 p.m. E.S.T.. i.e.. 10 to 11 p.m. The wireless sect inn of the Science BSA'. Museum at South Kensington now in- KILL OR CURE BY CODE. of u C Co cludes among its 200 exhibits the models 'rite practice among ships at sea of a control room AN ILLICIT AERIAL. a broadcasting studio and asking for medical aid from other View at the Ideal Home Residents in the Irish Free State are which were on yt.csels carrying doctors is l acoming su confronted with an unpleasant restric- I :sbibitinn. coiuutou that an American concern is 0 0 O 0 tion. ,judging tr.int the e- lerieuce of compiling n special cumule book for the t loutart'. who Bridgetridget, G;u ry. of ESPERANTO BROADCASTING. purpose.u it is reported was lined [s. and 2s. costs 0 0 0 upon its nteetittg at Lau- at the Dublin District Court list week for Following MUSIC WHEREVER SHE GOES. erected without a licence. sanne from May 11th to 13th, the Union having eu aerial Al;uroei band repeater bas been in- is rather like fining a man for Internationale de Radiophouie has de- A This tut the well -known liner Otranto. a car licence when he cided to recommend that all broadcasting stalled not possessing This equipment reproduces the music of owns a starting handle. stations endeavour to arrange regular transmissions in Esperanto of from 10 to the ship's orchestra through loud - 0 0 0 G of Vessel. 15 minutes once a week. spea1;ers in various parts the TRACKING THE CANADIAN Stations are to be asked to announce .A small mot 'n .;eneratur set, run from OSCILLATOR. their identity iu Esperanto at least once Uhe ship's i' -'.)er supply, renders bat - Canada appears tu he emulating the every evening. ) cries :Hid ai unnlatur.s unnecessary. example of the British Post Office in instituting ;anti- oscillation patrol vans. Government, depots for the l;nrpnse ore situate I in t)ttawa, Toronto. AV-innipeg, Vancouver, Montreal and Halifax. ;id residents troubled with oscillating neighbours merely report the trouble tu the oeare t depot. The tiuteminent does the rest. 0000 AMATEURS IN COMMAND. According to it report from the Ameri- can Consul- Ueneral at Algiers, ;t local society of amateurs, the " Amicale of Radio Station P.'p.T.,'' has been awarded the Government contract for the construction of a large broadcasting station. C O C O AMERICAN TELEVISION WAVEBAND. The l'.N. Federal Radio Commission has definitely assigned tlu' wavelengths lying between 150 and 200 metres for television experiments, writes a New York correspondent.. These sitvcleugtlts have been practically abandoned by American amateurs. Another announcement of some interest is the decision of the Commission to reeoguisc the right. of local authorities to regulate stations, THE OPEN -AIR " NEWSPAPER." Broadcast news bulletins have largely sup- hours, and prohibit the use of Soviet Russia. This photograph, taken in a Moscow square, prescribe planted newspapers in affairs. eveessive power in r trio. teil districts. shows the crowd eager for the latest intelligence concerning the world's

www.americanradiohistory.com = 653 nlpCl1@ ñ1AY 25th, 1927. WOpIlCI ECONOMICAL BROADCASTING. NEW DUTCH BROADCASTING At Po:.iiette, Wisconsin, the local STATION. broadcasting station derives its power Within three or four mouths Holland TRADE from two windmills, which charge the will own NOTES. accumulators a new long -wave broadcasting operating the transmitter. station which will work on 1870 metres. 0 0 0 0 The station will be owned by a limited R. L and TELEPHONY TO CANADA? liability company formed by the Nether- Varley, Ltd. In the near future the province of lands Christain Society and the Catholic Last week we referred to the important Manitoba may be linked up with the Radio Broadcasting Company. The amalgamation of Messrs. R.I., Ltd., and transatlantic telephony system, accord- station will be known as the " Neder- the wireless section of Messrs. The Var. ing to the commissioner of the tele- landsche Draadlooze Omroep." It is in- ley Magnet Company. In this connection phone system in Winnipeg. teresting to note that the station will readers will be interested to note that 0000 be installed under the direction of an R.I. and Varley, Ltd., as the new com- is BOMBAY CALLING IN AUGUST. Englishman, Mr. G. W. White, who pany called, combines the resources of has been associated with Dutch broad- the two firms in the manufacture of all The Indian Broadcasting Company classes hopes to provide casting for many years. of components hitherto produced the Bombay district 0000 separately. These include, with regular programmes early among others, in LOCAL NEWS BULLETINS. anode resistances and H.F. chokes, H.T. August. Transmission will be for a eliminators, besides Mr. Scrymgeour asked the Postmaster - L.F. amplifiers -both minimum period of three hours daily. transformer 0000 General in the House of Commons last and resistance capacity week whether he was aware coupled. MOST NORTHERLY STATION? that the 0000 broadcasting of the regular supply of What is stated to be the most north- American Radio Gear. erly wireless station has been erected at Bearing the alluring Cape Desire, title " A Buried west of Archangel, by the Billion at Your Doorstep," the new 1927 Soviet Government. The station is in- catalogue and circuit supplement tended issued for communication with aircraft. by the Rothermel Radio Corporation of 0000 Great Britain, Ltd. (24 -26, Maddox AIRSHIPS AND THUNDERSTORMS. Street, Regent Street, London, W.1) con- A radio weather map receiver of the tains a mine of useful information for Jenkins type, similar to that experi- those who seek to keep in touch with the mented with by the U.S. Navy last year progress made in American component de- on two of its ships, has been fitted sign. The catalogue, which is well illus- aboard the American dirigible Los trated, covers a number of the principal Angeles. It is expected that this pro- American lines and deals with construc- vision will be effective in preventing a tional kits, transformers, condensers and repetition of the disaster which de- other indispensable components. An in- stroyed the Shenandoah, which was teresting article is included on " How wrecked in a thunderstorm. and Why the Infradyne Works." The 0000 catalogue is supplied to dealers free of TRANSATLANTIC TELEPHONY charge, but a nominal charge of 9d. is made to amateurs. RECEIVER. 0000 The newly erected Post Office receiv- New ing station at Kemback, Fife, is now Address. ill frequent use as the receiver for trans- We learn that the Walter R. Bottomley atlantic telephony. On enquiry at the SHORT WAVES FROM A CAR. An Private Telephone Co., which undertakes General amateur transmitter and receiver in use all classes Post Office The Wireless World on a car in the northern suburbs of of radio work, is now installed was informed that the Wroughton sta- London. at the Providence Electrical Works, Luck tion is still in fairly regular use, Lane, Marsh, Huddersfield. but it local news in the respective is hoped that in the near future all districts of 0000 the country had been discontinued, to traffic will pass through Kemback. General Radio Co.'s New Showrooms. Owing to its northerly the disappointment of listeners; position the and On May 10th the General Radio Co. Fifeshire station gives superior whether he would in such circum- reception stances make representations to opened their new Radio Display and De- over the Atlantic, especially when atmo- the spheric Broadcasting Corporation in support of monstration Rooms at 105, Regent Street, conditions are bad. London, W.1. An interesting 0000 the appeals that were being made for feature of the renewal of the localised news the new headquarters is the " Dome BROADCASTING FROM CANBERRA. service. Room," where school and public hall We regret that a paragraph entitled Sir William Mitchell- Thomson said radio reception conditions are demon- " Australia's Mystery Station," appear- that this was a matter within the re- strated. In addition luxurious private ing on p. 633 of last week's issue, was sponsibility of the British Broadcasting demonstration rooms are provided. likely to give a mistaken impression re- Corporation, which, he had no doubt, An entirely separate section is devoted garding the arrangements made by The would consider any representations on to supplying the needs of the amateur Daily Netts in collaboration with the the subject. and the man ivho makes his own set. Broadcasting Company of Australia, for 0000 Specially designed testing equipment pro- the short -wave reception in this country TECHNOLOGY RESEARCH vides a visual or oral indication of the of the Duke of York's speech from Can- SCHOLARSHIP. quality of any components in which the berra on ' visitor May 9th. A limited number of Research Scholar- is interested.0000 The Daily News received cabled infor- ships in Technology are being offered by mation from Major Conder, of the the governing body of the Manchester The Brown Budget. Broadcasting Co. of Australia, that a Municipal College of Technology (Univer- A special " Overseas Number " of the transmission would be made on 33.4 sity of Manchester). The scholarships, Brown Budget has just been issued by metres; on this information the B.B.C. which will not exceed £1C0 each in value, Messrs. S. G. Brown, Ltd., North Acton. was approached and arrangements were will be tenable during the session 1927 -28 Special articles are included dealing with made to attempt reception. That the in the College. Among the departments the radio markets in different countries transmission was a special one accounts in which research may he undertaken are throughout the world, and they serve to for the fact that the 33.4 metre wavelength Electrical Engineering, Mechanical Engi- show that the " Brown " loud- speaker has does not figure on official Australian lists neering, Applied Chemistry and Textile made its influence felt over a large por- at the present time. Industries tion of the globe. A 32

www.americanradiohistory.com MAY 25th, 4)27. 7fiill® Woplrld 659

IIIIIIp1II1pIIliIII111111II1111IIIg11111111U111111JIIIllIlI1(IjJI11JI1111111111I l ( ç1

11111111111111111111111111111111111111 1i,linuIII 011111111 111111111 111 III 1 11111 III

Nui.

Brief Specifications of this Season's Portables.

Big -Ben. portable receiver, this loud- speaker amplifier is useful ASIX -VALVE superheterodyne incorporating three with other sets which are normally intended to give re- intermediate H.F. amplifiers and a single L.F. ception on head telephones only. It is a two -valve trans- stage. The first valve is a combined detector and former-coupled amplifier, the loud- speaker opening being oscillator, the associated tuning circuit covering the wave- immediately above the control panel. The outfit weighs bands 30 to 600 and i,000 to 2,000 metres by means of 27 lb. and measures T5in. by 14in. by Bin. Price LTO. interchangeable units. The frame aerial is enclosed in British Thomson -Houston Co., Ltd., Crown House, the lid of the case, together with a Celestion loud- speaker, Aldwvch. London. W. 1'. 2. and a break jack is provided to permit of the use of head telephones. The batteries are contained in a separate case and connected by a multi -lead cable fitted with a plug -in connector. Price £35.* Stockall, Marples and Co. (1912), Ltd., 6 -1o, Clerken- well Road, London, E.C.T. Brunswick. Five 2 -volt valves are used to give two stages of H.F. amplification, valve detection, and two L.F. stages. The self -contained loud- speaker is an Amplion Radiolux. Filament heating is provided from a 2 -volt 3o ampere hour accumulator, and the H.T. battery is a io8-volt Ever Ready. A frame aerial is enclosed in the cabinet, which is of mahogany. Price £28 2S. 6d. M. Foster and Co., 64, Brunswick Street West, Hove, Sussex. B.T.H. Superheterodyne. The circuit arrangement consists of three valves arranged as a superheterodyne. Reception is intended on head telephones. The manufacturers state that the range of reception is 3o to 4o miles from a main broadcasting station and approximately Too from Daventry. A self- contained frame aerial is provided, though by means of a coupling coil connections can be made to an ordinary aerial and earth system. A compass is mounted on the top of the case to facilitate the determination of the best directional position for reception from any particular station. The standard receiver is finished in leather nurndept Portable Five. rain. by i6in. by bin. is cloth and measures The weight Burndept. 23 lb. Price, including one set of head telephones, £20. A five -valve set, including two high - frequency stages B.T.H. Portable Amplifier and Loud -speaker. tunable over the wave ranges 25o to 55o metres and i,000 Although designed as a companion for the B.'I'.H. to 2,600 metres, change of wavelength being effected by

* Prices; unless otherwise stated, include loud- speaker (or head telephones), valves, batteries and patent royalties.

A 33

www.americanradiohistory.com v.., ' 1.ewo1Ní41F.fi-tir...H ^:1ílÁ ;:..414t F ÿ PA%**15- 40' f*Pe.,YF-ii 10-11.±av .

66o WIpK®,44,g MAY 25tli, 1927. Wo1d& Buyers' Guide : Portable Receivers. - immediately over the loud -speaker. Dimensions, r8in a three -position switch which in the central position by i6 in. by 8in Weight, 4o lb. Price £3o. switches off the set. The coiled horn of the loud- Burndept Wireless, Ltd., Eastnor House, Blackheath, speaker is of panier mache and mcasnres no less than London, S.E.3. Cantophone. The four -valve portable which is fitted with a frame aerial is built in an attache case measuring i6in. by 6in. by Itin. A high- frequency amplifying stage is provided, and the tuning dials are marked with actual station call signs. A self- contained loud- speaker is fitted, and within the case also is a roz -volt high- tension battery and a 2 -volt zo ampere hour unspillable accumulator. Weight, 20 lb. Price £26 5s. The Cantophone Wireless Co., Remo House, 3ro -312, Regent Street, London. W.r.

C.A.V. Three-valve Portable. aft. in length. Separate output terminals are provided so that an external loud -speaker can.bc fitted if required. 'l'erminals also provided for the use of a mains unit or batteries. The tank-1g panel is under a hinged cover and

The Davendyne Flvc -valve set by Peter Curtis, Ltd.

C.A.V. Three valves are used, one of the stages being reflexed. The receiver, together with H.'F. and L.T. batteries, is housed in the lower part of the case, the batteries being

covered by a removable panel. The lid carries the frame - aerial and loud -speaker. The valves are set up in special holders to guard against microphonic effects and mechanical shock. The cabinet is finished in maroon or black morocco. Dimensions, r6:} in. by I rin. by sin. Weight, 26 lb. Price £21 175. 6d. C. A. Vandervell and Co., Ltd., Acton Vale, London, W .3. Celestaphone. The five -valve model is fitted with a single high - frequency amplifying stage and three resistance- coupled easy the Davenset for'Daventry reception with telephones L.F. stages. Theme are two tuning controls, and an A 34

www.americanradiohistory.com z

MAY 25th, 1927. VAp@Il@OO 66r WoFIlCo1 Buyer's' Guide : Portable Receivers. - Celestion. change -ovr is provided front' the local station wave- This four -valve set includes a high- frequency amplifier length to Daventry. Three aerial terminals are arranged and makes use of 2 -volt valves working from a non - so that the set can be used with an improvised elevated spillable accumulator of 25 ampere hours capacity and a ro8 -volt H. T. battery. The H.F. stage is neutralised, and no intentional reaction is introduced. The L.F. stages are resistance- coupled, and a Celestion loud- speaker, as well as frame aerial, are included in the cabinet. Two tuning ranges are provided for local station and Daventry. The control panel carries the tuning dials of the two condensers, master rheostat, and on -and- off switch. Price X39. .Celestion. Radio Co., 29, High Street, Hampton Wick, Kingston -on- Thames.

The Gecopkone Seven-valve Superheterodyne. aerial. Supplied in an oiled mahogany or rexine -covered cabinet, as well as in an aluminium container. The loud- speaker, which is included among the accessories, is external to the set. Price £45 mos. Denison Bros., Stonecliffe Works, Wakefield Gate, Halifax, Yorks.

Halèyon Five -valve Portable. Chakophone Super. A superheterodyne circuit is employed with eight valves. Three intermediate H.F. amplifying stages are provided, together with a two -valve L.F. amplifier. Wave ranges covered are 28o to 540 metres and 1,400 to 1,800 metres. The set is calibrated on actual station settings, and the readings recorded on a chart. Plug -in oscillator and tuning units are used for covering the two wave ranges. The tuning controls are carried on a recessed panel at one end of the cabinet and covered by a lid. The frame is hinged to the cabinet, and when swung open reveals the diaphragm of a hornless loud- speaker. Hart Collins Five -valve two -range set,. One charge of the accumulator gives twenty hours' Cora- A ;5

www.americanradiohistory.com 662 WAYdszo MAY zSih, 1927. Wo1sIlLd Buy ers' Guide : Portable Receivers. - walnut cabinet with canvas cover. Price, including all tinuous use, and tile 9c-volt H.T. battery has an esti- necessary equipment, mated life of two to three months. A 9 -volt grid bias The Eagle Engineering Co., Ltd., Eagle \forks, battery is fitted. The manufacturers state that practically Warwick. all European stations can be tuned in on the loud- Five. speaker. A smell voltmeter is enclosed in the cabinet Claremont for testing the batteries. Dimensions, 22in. by 56in. by A live- valve set with two H.F. amplifying stages work- Slin. Weight, .}o lb. Price Z56. ing from a 2 -volt accumulator and 520 -volt H.T. battery. The controls, which are illuminated, are mounted on a metal panel. Self -contained loud- speaker is supplied with portable aerial. Shock absorbers are fitted so that the set can be accommodated on the running board of a car. The Claremont range also includes three - and four - valve sets. Price ,35. P. Sherman, 52, River Street, Clerkenwell, London, F.C.

Henderson Five -valve Portable.

Chakophone Five -valve. The circuit arrangement incorporates two H.F. stages, valve detector, and two I.. F. stages. Essentially a local station loud- speaker set, or if Daventry reception is required frame and H.F. transformers can be changed, M.P.A. Five -valve Portable with cone loud- speaker and elevated being fitted with pin mounts. ('omtain in a dull polished frame aerial. Claude Lyons Portable. This compact long -range receiver measures 24in. by 5;in. by l in. and weigfis only 12 lb. It is built as a complete receiver, and for use as a portable it is housed in a separate carrying case with a collapsible aerial having 24in. sides. Space is provided for one pair of telephones, and a small loud -speaker is fitted. The tuning range is 5o to 2,500 metres. Claude Lyons, 76, Old Hall Street, Liverpool. C.W.C. Three L.F. stages are provided in this set, in addition to H.F. and detector valves. Both frame aerial and loud -speaker are included in the oak case, together with a Columbia super H.T. battery and 2 -volt 3o ampere hour accumulator. A jack is provided for using an external loud- speaker, as well as a terminal for making connection to an elevated aerial. Plug_ -in H.F. transformers cover the wave bands Soo to boo metres and r,roo to 2,r00 metres. Price ,-2S ros. Cook's Wireless Co., Ltd., t'.Af.C. Works, 23, St. Helen's Street, Ipswich, Suffolk. Davendyne. A five -valve receiver making use of two high- frequency The Levis Four-valve Portable. stages tuned for the reception of Daventry. No tuning A 36

www.americanradiohistory.com MAY 25th, 1927. WAp@Il,som 663 WorIlc1

Buyers' Guide : Portable Receivera.- as the filament- heating accumulator, H.T. and grid- dials appear on the operating biasing batteries. Price £35. panel, which accommodates a The Portable Utilities Co., Ltd., 8, Fisher Street, volume control. The frame, which Holborn, I.ondon, W C.1. is tuned by a variable condenser, Galloway. is enclosed in the hinged back of the cabinet. Supplied with a 2- A lightweight superheterodyne, batteries and loud- polt dry charged battery. The speaker being a separate unit. The circuit arrangement controls are revealed under a hinged cover at the top of the cabinet, beneath which is the loud -speaker. The cabinet is of polished oak. Price £31 ros. Peter Curtis, Ltd., II, Red Lion Square, London, W.C. r.

Ediswan Toovee. Two valves are used in a reflex circuit with valve detection. An aerial wire is supplied for suspending The Neutrosonic Seven of the Igranic Electric Co., Ltd. from a tree or other convenient point, and the equipment includes H.T. and L.T. batteries and two pairs of and general design are unique, inasmuch as that tuning is headphones. The case is of hard wood and covered carried out on a single dial. Three intermediate H.F. valves with black leatherette. Price £r r 5s., excluding valves. amplifying valves are used, as well as two L.F. Edison Swan Electric Co., Ltd., 122 -125, Queen after the second detector, eight valves in all being fitted. Victoria Street, London, E.C.4. The frame aerial is enclosed in what is normally the lid of the set, and is arranged to stand up vertically and Eureka Orthodyne. swing about on its hinges. Dimensions, rgin. by rein. Two stages of high- frequency amplification are pro- by 8in. Price £39, exclusive of accessories and loud- vided, with valve detector and two L.F. stages. The speaker. frame aerial and loud -speaker are self -contained, as well J. and L. Galloway, Ltd., 38, Mair Street, Planta- tion, Glasgow, Scotland. Gecophone. A seven -valve superheterodyne, including batteries and loud -speaker and contained in a cabinet measuring 2tin. by 91in. by r Sin. Wave ranges of 25o to 65o metres and 800 to 2,800 metres are provided by means of a change -over switch which also serves as a " battery -off " key. The two tuning dials are recessed behind a double - door opening. The frame aerial is contained in a hinged door forming the rear part of the set, and with the self - contained loud- speaker arranged behind a grating no external connections of any kind are required. The cabinet is polished a medium dark oak. 6 -volt Osram valves are employed, working from a 3o ampere hour accumulator and two 66 -vclt high- tension batteries. Prig,+ Z50. The General Electric Co., Ltd., Magnet House, Kingsway, London, W. C.2. Gillen. The apparatus is enclosed in a solid hide suit, case and consists of a four -valve set incorporating one high - frequency stage. The equipment includes unspillable accumulator, internal frame with provision for external aerial connections, built -in loud- speaker with connecting points for external telephones or loud- speaker. Tunes to both local station and Daventry. Weight about 21 1b. Price Z25. Gillan Radio -Electric, Ltd., 63 -64, High Holborn, Nul!i- Secundus Five -valve set. A cone loud -speaker is at the back. London, W.C.T. A 3 i

www.americanradiohistory.com A°"r. :;.2e1t7:1;s_F_ s!+pt ti,/ktkr:

p@Ilsto 66.E MAO d1.4f' 251h, 1927. Buyers' Guide : Portable Receivers.- Levis. Halcyon. A four -valve receiver incorporating a tuned high- A five -valve arrangement is adopted, comprising two frequency amplifier. The set is mounted in a leather H. F. stages, one of which is untuned, followed by a valve attache case with a separate compartment for batteries. detector and two transformer -coupled L.F. stages. The Plug -in coils are used for tuning to cover all wave- operating panel is behind a hinged cover immediately over lengths. Dimensions, 'Fin. by loin. by 5?in. Intended the loud- speaker opening. Filament current is supplied by a z -volt 40 ampere hour non -spillable accumulator. A 99- volt high- tension and 9 -volt grid battery are provided. Dimensions, i8in. by '.}in. by 8in. When the receiver is in operation a red pilot lamp glows on the panel. Price Halcyon Wireless Supply Co., Ltd., r'o, Knights- bridge, London, S.W.1. Hart .Collins. A five -valve set complete with loud -speaker is housed in a carrying case measuring 16in. by 16in- by 6in., weighing about 3o lb. when fitted with batteries. The change -over switch gives the wave ranges of 300- to coo metres and goo to ,3,000 metres. As well as the self -contained frame, provision is made for the use of

The P.D. Five of Automobile Accessories (Bristol), Ltd. for use Nvith a small temporary elevated aerial. Price £2 1 1os., exclusive of valves and batteries. Butterfìelds, Ltd., Albert Road, Stechford, Birming- The Four-valve Osman. ham.

a conventional aerial ; z -volt valves are employed. The Langharn. set is operated with a single tuning dial and is provided A four -valve set incorporating two high - frequency with a volume control. Price Z31 sos. amplifying stages. Filament current is obtained from a Hart Collins, Ltd., 38A, Bessborough Street, London, z -volt non -spillable 25 ampere hour accumulator. and the S.W.'. high -tension battery is an Ever Ready giving 84 volts. Henderson. The frame aerial is enclosed in the lid. and the entire equipment, which includes loud -speaker, is housed in a Two high -frequency amplifying stages, followed by a leather attache case. Price ros. valve detector and two 1..F. stages, are used. The set £31 Langham Radio, 9 -i1, Albion House, New Oxford is completely self- contained, including frame aerial and Street, London, W. C. 1. loud- speaker. The cabinet is of oak- or mahogany. Price £30. Liberty. W. J. Henderson and Co., Ltd., 351, Fulham Road, London, S.W.ro. The circuit arrangement is a superheterodyne employing eight valves The aerial is self- contained. together J. and P. (Mark II). with a cone loud -speaker and H.T. and rechargeable Four valves are used, giving one stage of high - L.T. batteries. The wave range is from 200 to 2,000 frequency amplification operating from a z -volt accumu- metres, the necessary circuit changes being effected by lator and rob -volt Ever Ready high- tension battery. a two- position change -wave switch. Dimensions, zoin: 'Plie cabinet is of walnut or oak, and fitted with a built - by zoin. by lin. A compass is fitted to assist in cor- in frame aerial. Tuning range, 25o to S5o metres. rectly setting the frame aerial, and the receiver is cali- Price £20. brated. Price J. and P. Manufacturing Co., 5o -54, King Street, Radi -Arc Electrical' Co., Ltd:, Bennett Street, Cambridge. Chiswick, London, \V".4. A 38

www.americanradiohistory.com MAY 25th, r07. WATAC@oo WalIld 665 Buyers' Guide : Portable Receivers. - Merritone. Neutrosonic Seven. The four -valve model consists of a valve detector, fol- A superheterodyne receiver consisting of a high- lowed by three low- frequency stages. A polished case frequency amplifier, oscillator valve, first detector, two encloses a built -in frame aerial, loud -speaker, 2 -volt accu- intermediate H. F. mulator, and rob -volt H.T. battery. Price £16 15s. stages, second detec- Merritone Radio Supplies, 35, Bownes Road, Catford, tor valve, and one London, S.E.6. low- frequency ampli- M.P.A. fier. The two wave - The circuit arrangement consists of two H.F. stages, one hands are covered by of which is tuned, a detector valve with magnetic reaction means of interchange- on the tuned H.F. intervalve coupling and followed by able plug -in tuning two transformer -coupled L.F. stages. A potentiometer is units. A frame aerial fitted, together with a volume control and push -pull change. is incorporated with over switch for long or short wave reception. The frame the receiver or sup- is loaded by means of a plug -in coil. Provision is made plied as a separate for an external aerial and earth. The H.T. battery is a unit. The operating 72 -volt unit and the 2 -volt L.T. accumulator has a capacity of zo ampere hours. The grid bias is a 4t -volt battery. The hinged lid carries an M.P.A. sprung diaphragm loud -speaker behind a grill and an extending frame aerial supported ,on rods. Dimensions, r4tin. by rotin. by Irin. Weight, 32 lb. Price £33 12S. M.P.A. Wireless, 62, Conduit Street, London, W.I. Neophone. Two valves are used in combination with a crystal detector in a reflex circuit. A frame aerial is contained in the lid of the set. The equipment includes loud- and horn. Dimensions, r5in. by speaker unit wooden The Qualitone Four -valve 15in. by gin. Price, in birchwood case, £6, exclusive two -range Portable. of valves and batteries. panel carries the three tuning condensers, a balancing con- Neophone Radio Manufacturing Co., 9 and to, Little denser for the H.F. stage, volume control, filament Saint Andrew Street, St. Martin's Lane, London, W.C.z. switch, filament rheostat, and output jack. The receiver, which is finished in black leatherette, measures r6i-in. by ruin. by rotin. and weighs approximately 24 1h. Batteries are in a separate box measuring r44in. by r3tin. by gin. Price x,66 175. 6d. Igranic Electric Co., I.td., 147, Queen Victoria Street, London, E.C.4. Nulli-Secundus. The set is contained in an oak cabinet measuring r5lin. by r8in. by rotin., and weighs approximately 40 lb. Two H.F. stages are provided, though only one is tuned, so that two tuning dials are needed, one of which tunes the frame aerial. The small knob in the centre of the operating panel is a fine -tuning control and the main controls have no slow- motion adjustment. Reception on long and short wavelengths is obtained by means of a change -over switch, while a master rheostat serves as an on- and -off switch. A valve detector is employed, followed by two L. F. stages. The batteries consist of a 99-volt H.T. unit, grid bias battery, and a 2 -volt non -spillable accumulator. The enclosed loud- speaker is of the cone type. Price £33 2S. 6d. C. Creswick Atkinson, 48, Kimbolton Road, Bedford. Osman IV. Local and Daventry reception is obtained by means of a change -over switch. Four valves are used with one dial tuning. A Celestion loud -speaker and frame aerial are enclosed in the hinged lid. A volume control is fitted. Pegasus Nine -valve Superheterodyne. The 2 -volt valves derive filament current from a 30 A 30

www.americanradiohistory.com Oh6 WIT@llMM Al AY 25111, 1927. WopIld Buyers' Guide : Portable Receivers. - Portadyne Five. ampere hour accumulator. and the H.T. battery is a 99- A five -valve set with self- contained frame. batteries volt Hellesen used with a ..0 -volt grid battery. Dimen- and loud -speaker. Two tuning ranges for local and sions, r6in. by i6in. by gin. Price X35 Daventry reception. The operating panel and loud- Osman Radio Co., 27 -28, Harcourt Street, Maryle- speaker opening are covered by a pair of doors on bone, London, \V. r. the front of the cabinet. Tuning is effected by a Oxford. Five valves are arranged either as one high- frequency stage, valve detector, and three low- frequency stages, or, in an alternative model, as a two -stage high - frequency amplifier, valve. detector, and two low - frequency stages. The frame aerial is enclosed in the door of the set, and the Amplion type A.R.6r loud- speaker is built into the cabinet. Provision is made for the use of an external loud -speaker or telephones, and connecting points are available so that the set can be used with an elevated aerial. Filament current is obtained from a z -volt unspillable accumulator in celluloid case, and the H.T. battery is a 99 -volt Hellesen. The frame aerial is wound in three sections, which, by means of a switch, is suitably connected for either long- or short -wave reception. Dimensions, r5in. by r7in. by gin. Price £37 Jos. Oxford Wireless Telephony Co., Ltd., Titmouse Lane, Oxford. The P.D. Five (Mark 18). Designed to receive Daventry anywhere in the United Kingdom. Although fitted with H.T., L.T., and grid - biasing batteries, provision is made for connecting up external batteries when used as a borne portable, connection being marie by means of a ten -way cable and connector. Provision is also made for using an elevated aerial. Five valves are used. An unusual feature is the absence of a tuning panel. The cabinet is protected Selector Five -valve by a waterproof covering, a flap being provided to Portable. expose, the grille of an Amplion loud- speaker. Size of cabinet, r7in. by 'Min. by lin. Price £30 125. 6d. single dial. The range of Portadyne receivers includes Automobile Accessories (Bristol), Ltd., 93, Victoria three- and four -valve sets, also a five -valve set for Street, Bristol. Daventry reception only. Price £35. Pegasus. \Vhittingham Smith and Co., r ro, Kew Green, Kew, A superheterodyne circuit is employed, incorporating London. four intermediate high -frequency amplifying stages and Pye. three resistance -coupled amplifiers following the second A five -valve receiver with two tuned high - frequency detector valve, so that there are nine valves in all. The stages stabilised by neutralising. There are no actual total filament current is about r ampere, and is supplied tuning controls, one of the operating knobs serving as from a z -volt zo ampere hour accumulator. The H.T. a fine -tuning adjustment. Designed to tune to Daventry battery potential is 16o volts, and the maximum grid only. A three -position switch serves as a battery key, biasing potential 18 volts. A push -pull switch is used as well as for taking one of the L.F. stages nut of circuit. to change over from short to long waves. The loud- Volume control is provided. The set, which is enclosed speaker is contained within the cabinet. Dimensions, in a polished walnut case, is entirely self- contained as rg ¡in. by r6lin. by lin. Price Z63. regards all necessary batteries, frame aerial, and loud- A. G. Franklyn, 95, Woodhouse Lane, Leeds. speaker. Dimensions, i8in. by 164in. by Tin. Weight, Pelican Five. 32 lb. Price £3o 125. 6d. hive -valve portable, including two high- frequency W. G. Pve and Co., " Granta " Works, Montague stages with one dial tuning. The operating panel is behind Road, Cambridge. double doors at one end of the cabinet, the flare of the Qualitone. loud- speal:er being immediately below the panel. Price Four -valve receiver, comprising a tuned high - Z:}o. One, two, and four -valve portable sets are in- frequency stage, valve detector, followed by two trans - cluded in the Pelican series, the four -valve set being pro- former- coupled L.F. stages, using Mollard valves vided with an A.C. mains battery eliminator supplying throughout. The H.F. stage is stabilised by the H.T., I..T., and grid biasing potentials. use of a neutralising condenser, and detection is by Cahill and Co., I,td., 63, Newman Street, \V.x. leaky grid condenser. Tunes to both the local station A 40

www.americanradiohistory.com MAY 251h, 1927. 667

Buyers' Cui le : Portable Receivers. - out on two dials, and the Change -over switch provides and Daventry, the wavelength change being effected by for local and Daventry reception. The frame aerial a strip of plug -in connectors. The H.T. battery is a which is fitted around the lid is arranged on a pivot so Hellesen 99 -volt, and grid bias is obtained from a 9 -volt that it can be rotated apart from the remainder of the battery. A 2 -volt Exide unspillable accumulator is used receiving equipment. The loud- speaker, which is of the for filament heating. Can be used with an elevated cone type, folds down flat against the tuning panel when aerial if desired, additicrial terminals being provided for the set is closed, and a. hinged arm provides for readily this purpose. The last I.. F. stage is optional and is bringing it into use when the lid is open. Terminals are provided for external loud -speaker, head telephones, and, when required, external aerial and earth. z -volt valves are used operating from a non -spillable accumulator, and 8z.5 -volt H.T. battery. The case is covered with real hide. Price £32 ros. Engineering Works (Electrical and General), Ltd., 7 and 8, Great Winchester Street, London, E.C.2. Real. The four valves are arranged as high- frequency amplifier, valve detector, and two low- frequency amplifiers. The set is complete with self -contained horn type loud- speaker, 2 -volt valves, frame aerial, and batteries. The frame aerial is enclosed in the hinged lid, and a two - position switch provides for either local station or Daventry reception. The high -tension battery is 6o volts and is used with a grid bias battery of 4- volts. Dimen- sions, r¢in. by rain. by 61in. The single tuning control and change -over switch, together with the loud- speaker opening, are covered by a hinged door at one end of the case, which is of polished mahogany, leather, or " camera finish." Price £26 cos. Read Radio, Ltd., 67, Newman Street, Oxford Street, I.ondon. W.r.

Trix Four -valve Portable.

taken out of circuit by means of a switch. The self - contained loud- speaker operates through an aperture on the side. Approximate weight, 28 lb. Diniensions. r5in. by r5in. by 7-¡in. Price £25. B. and J. Wireless Co., 2, Athelstane Mews, Stroud Green Road, London, N.4. Radiocraft Ideal. A five -valve receiver consisting of two high- frequency stages,. valve detector, and two L.F. stages using 2 -volt P.M. valves. Filament current is supplied from a non - spillable accumulator, and the high -tension supply is a 6o -volt Hellesen battery. The loud- speaker, which is detachable and can be used separately if desired, is a Crossley Musicone. A change -over switch gives reception either from the local station or Daventry. Price £25. Radiocraft Supplies, Ltd., 9, The Arcade, Walsall. Rayol Four. A high- frequency amplifier is provided, followed by detector valve and two L.F. stages. Tuning is carried Truphonic Five -valve Portable.

A 4 .

www.americanradiohistory.com yt

66f Wflp4@oo MAY 25th, 7927. WOIYtki

Buyers' Guide : Portable Receivers. - Stratton. Rees Mace. Three valves are used, the circuit arrangement con- The Super Four model comprises one high - frequency sisting of a R.einartz tuned frame, detector valve, amplifying stage, valve detector, and two L.F stages. resistance- coupled L.F. stage followed by a transformer - Transformer coupling is used in the L.F. amplifier. coupled stage. The double -wound frame, whicli is Self- contained frame aerial and cone type loud- speaker. rotatable apart from the set, tunes to wavelengths of 250 Tunes to both local station and Daventry. Filament cur- to 600 metres. A grid bias up to ro volts is provided, rent is supplied by a 2 -volt non -spillable accumulator. with an H.T. battery of 90 volts. The loud -speaker Dimensions, '8in by 'yin. by 8in. Price £36 15s. horn has a fiare measuring yin. by 5lin. Tuning controls Rees, Mace Manufacturing Co., Ltd., 39A, Welbeck are on the end panel, so that the receiver can be operated Street, London, W.I. when closed. The wooden cabinet is covered with Rexine cloth and measures 16in. by y ¡in. Rolls. 16in. by Stratton and Co., Ltd., Balmoral Works, Bromsgrove This set differs from the usual form of cabinet con- Street, Birmingham. housed in an struction, the receiver and batteries being Symphony Dual Range. attache case the lid of which accommodates both frame The with self - and Celestion loud -speaker. Five valves are used, in- circuit is a five -valve superheterodyne frame aerial. A cone type corporating two H.F. stages, filament current being sup- contained interchangeable loud -speaker is enclosed within the set. Dimensions, plied from a non- spillable accumulator giving approxi- r ¡kin. by 19in by 81in. mately fifty hours' working on each charge. 'Tunes to valves to provide two stages of H.F. both Daventry and local station. Two controls are pro- Five arranged amplification for Daventry reception is another type of vided for tuning and reaction. A switch removes two of portable included in the Symphony range. Fitted with the valves from circuit. Dimensions, r}in. by 1r7,in. by self -contained frame, cone loud- speaker, and batteries. Tin. Weight, 23 lb. Price 1os. £3' Dimensions, r4ÿin. by by and Jagels, 28 -29, Great Sutton Street, r6in. 8in. Hoare Walsall Street, London, E.C.r. A. j Stevens and Co. (1914), Ltd., Clerkenwell, Wolverhampton. Runnymede. Trix. A five -valve self- contained set fitted with two high - The circuit consists of a detector valve with capacity frequency amplifying stages. Filament current from the reaction followed by three resistance- coupled L.F. 2 -volt valves is supplied by a Certax non -spillable stages, a power valve being used in the last stage. The accumulator. The high -tension battery potential is 120 batteries consist of a 2 -volt 20 ampere hour accumulator volts obtained from two 6o -volt H.T. units. Liberal and two 6o -volt H.T. units with a 9 -volt grid bias bat- grid biasing is provided by an Ever Ready battery. The tery. The single tuning dial is carried on a small panel frame aerial is self- contained, together with the loud - sunk into one end of the cabinet and covered by a hinged speaker The cabinet is either polished mahogany or door which operates the on- and -off switch. The loud- can be supplied with a waterproof finish. Price £34 13s. speaker is an Edison -Bell cone mounted behind a grill on Runnymede Engineering and Electrical Co., Dacre one side of the case, and on the opposite side is hinged House, Victoria Street, London, S. \V.r. the centre -tapped frame aerial. For long wave reception Salient. it is necessary to change the frame. A jack is provided head telephones or external loud -speaker. A three -valve set making use of S.P. type valves. for connecting The circuit arrangement makes use of valve detection Dimensions, 18in. by '8in. by 9in. Price £20 7s. Lever, 33, Green, London, E.C.r. followed by two L.F. stages. A portable frame is used Eric J. Clerkenwell which,. as well as the loud- speaker, is external to the set. Truphonic. H.T. and I,.T. batteries, together with the receiver, are The tuning controls are mounted on a metal plate contained in a despatch case. Price, exclusive of loud- carrying edgewise- operated dials with loud- speaker open- speaker, £r8. ing immediately below. The receiver is a five -valve S. A. Cutters, Ltd., Clutha House, 1o, Princes Street, arrangement with frame aerial, plug and jack connectors Westminster, London, being provided for making connection to an elevated Selector. aerial. The carrying handle can be removed to modify the set for home use. Dimensions, 1rlin. by 13ín. by 8-}in. employing five The circuit is a supersonic heterodyne The Truphonic Wireless Co., Triumph House, 189, two tuning controls are under a pair of valves. The Regent Street, London, W. r. small doors which carry a calibration chart. There is a. volume control and a switch for long and short wave W.L.L. reception with a central off position. By means of a This receiver, in which four valves are used, is de- break jack the L.T. accumulator can be charged without signed for reception on the lower B.B.C. wave range. removal from the set, while another jack provides for the The equipment includes a self -contained aerial in the lid,, use of head telephones in place of the loud- speaker, grid bias and high- tension batteries, 2 -volt accumulator, which is an Amplion unit with a short horn opening and loud- speaker. The containing case is of cowhide behind a grill at one end of the cabinet. Dimensions, mounted on fibre. Dimensions, 14in. by 15in. by Sin. r6in. by r2in. by 6in. Weight, 28 lb. Price Weight, about 24 lb. Price £27. £38 Western Laboratories, Ltd., ' 1, Hanbury Road, Selectors, Ltd., r, Dover Street, London, W.I. Acton, London. W.3. A 42

n96ü; a se... .. www.americanradiohistory.com MAY 25th, 1927. WIEMIl®@0 hho Wopfld

IL+i1111111111i1 IullllllllllluO

.=NTERIE43T.,/.

1Ì11999tU111111itüiüiiluüi1111üüllili111ü111111i111i11111111i11`II í11Ì1ÏÌÌ I I1i11111

The following abstracts are prepared, with the permission of the Controller of H.M. Stationery Office, from Specifications obtainable at the Patent Office, Southampton Buildings, London, W.C.2, price is. each.

Short -wave Oscillator. the aluminium and sulphide contact washer W which prevents the gas which (No. 261,350.) variety. The invention will te best under- is liberated by the vaporisation of the stood by referring to the sectional drawing' liquid from escaping from the rectifier. Confirmation date (Gcrmany): Nor. of one form 10th, 1925. of construction. The rectifier The specification shows several familiar consists of a copper or aluminium cup C circuits in which the rectifier is included A very interesting forni of short -wave provided with a screwed copper plug P. for supplying high - and low- tension cur- oscillator is described by Dr. A. Esau rent to a receiver. It states that high in the above British patent. The accom- voltages are preferably obtained, not by panying diagram, which illustrates the connecting a number of cells in series, invention, shows a pair of valves V, and but by providing each cell with a separate vi with their anodes connected together transformer winding. Another use of and joined through a source of positive the device is as an oscillator, since it ex- potential B to the filament. The two hibits a negative resistance characteristic. grids are also joined together and con- The diagram shows a suitable circuit, nected to the filament through a resist- and is similar to an arc generator. Here ance R. The specification mentions that a rectifier B is connected in shunt with a the wavelength of the oscillations can be tuned circuit L1 C and is provided still further shortened by connecting a from a source of potential E through an condenser C between the two anodes and impedance Z. In another modification the two grids. The system functions by the device can be used as an ordinary virtue of the provision of two similar crystal detector in a wireless receiver, Oscillatory circuits constituted by the when a fine aluminium wire is used as grid -anode capacity, the variable capa- one of the elements. city, and the leads connecting the anode 000a Contact rect fier and circuit used in generating oscillations. (No. 265,652.) A Thermoelectric Generator. (No. 265,519.) Inside the cup there is an insulating disc Application date : Aug. 11th, 1926. D of bakelite and attached to the disc D is an aluminium A thermoelectric generator is described disc A by H. A. located by means a stud in the above British patent of S and the diagram nuts N for the purpose of making Roberts, and accompanying connection. A similar connecting means is attached to the plug P and is shown at X. The space R between the two portions is filled with the rectifying compound,

which is made in the following manner : Copper sulphide is first Circuit diagram of short-wave oscillator. made by heating (No. 261,350.) finely divided copper with sulphur, and the resulting sulphide is then ground in and grid to the condenser C. It is stated a mortar until the powdered grains have that an aerial system may be either diameters of the order 0.2 mm. Any traces directly or inductively coupled to of metal are removed by sieving the the Thermoelectric generator for H.T. and valves. grains. The granular powder is then L.T. supply to receiving sets. 0000 made into a paste by mixing it with a (No. 265,519.) An Interesting Rectifier. liquid such as ammonium hydrosulphide. Before the rectifier is assembled the should illustrate clearly the arrangement (No. 265,652.) aluminium disc A has to be made per- of the device. The elements consist of Application slate : Oct. 9th, 1925. fectly clean and free from oxide, and alternate plates of positive and negative A very interesting form of rectifier and this is accomplished by carefully polish- thermoelectric active metals P. The device which can be used for other pur- ing the disc. It is also very important plates have wires W cast into the ends of poses is described in the above British to keep the device gastight. This is ac- them for the purpose of making connec- patent by L. Levy. The rectifier is of complished by including an annular tion. These wires are twisted together. so

A 43

www.americanradiohistory.com 670 Wilps11@ez 111.417 25tlr, 1927. WoHVI as to connect a number of elements either Another Reisz Microphone. example, very fine dust is mixed with in series or parallel, according to the rela- (No. 258,542.) granules of two different types. One mix- tive voltages or currents which may be ture, which is stated to be satisfactory, required. The plates are separated from Application date : Aug. 11th, 1926. consists of a mixture of 22 per cent. of each other by means of washers E, which E. Reisz describes in the above British dust not exceeding 0.0015 mm. diameter, are of heat -resisting material such as as- patent a modification of a microphone and 47 per cent. of grains of 0.07 inni. bestos paper. The illustration shows one which he lias described previously and is diameter, the remainder consisting of assembly of plates clamped together by no doubt familiar to readers. It is :neu- grains of intermediate sizes. The accom- means of a framework F. The edges of tioned that the response is very materi- panying diagram shows a cross- section of the plates are insulated from the frame- ally affected by the size of the granules. a microphone using a layer of the carbon work by means of strips of insulating mixture. The microphone itself is com- material I. The portion H represents a posed of a block of marble M or other heater which may be an electric element, very solid material, and a portion of the or, alternatively, this may be dispensed front is removed at X and provided at with and substituted by a series of gas the sides with two recessed portions. flames. These portions shown at Y contain elec- 0000 trodes E of carbon or non -oxidisable metal connected by rods to terminals 'f Multiple Plug -in Coil. located at the back of the microphone. The (No. 285,801.) portion X is filled with the carbon Application date: Nov. 6th, 1925. mixture, and the carbon is held in posi- A multiple plug -in coil is described in tion by means of a thin sheet of rubber S stretched sr, that the natural period is the above British patent by G. W. Mel - land, the arrangement being shown in below 50 cycles per second. The front of the rubber is then protected by a thin the accompanying diagram. It will be seen to consist of four inductances L gauze shield G fixed to a frame F. The is such having different values, fixed as shown, dimension of the frame that it lies in front of the carbon or other electrodes to a centre support S. Each inductance Cross -section of the Relsz microphone. so impinge is connected to brushes B fixed in insulat- (No 258,542.) that sound waves cannot directly upon them. This prevents any ing supports I. The centre portion S resonance of the rods occurring. is mounted on a rod R fixed to a circu- If the granules are large there is a con- lar insulating plato P, provided with the siderable space between them which usual plug and socket members N. The allows the sound waves at higher frequen- plug and socket are respectively connected cies to be absorbed, thereby materially to two contacts X. Thus it will be seen lowering the efficiency at such frequencies. BOOKS AND ti at by rotating the centre portion S the The thickness of the layer of carbon also er ds of one of the inductances L may be has a marked effect upon the frequency connected with the plug and socket by characteristic. These difficulties are over- CATALOGUES v'rtue of the brushes B co- operating with come in the present invention by using a the contacts. mixture of granules of various sizes. For RECEIVED.

" La T.S.F. des Usagers," by P. Hémardinquer, with preface by L. Lumière. A simple description of various types of receiving apparatus, with instructions for their installation and upkeep. Written for the benefit of the non- technical listener. Pp. 136, with 80 illustrations. Published by Masson et Cie, Paris. Price 10 francs. W. H. Agar, 19, Whitecross l'lacc, London, E.('.2. Leaflet describing high - class cabinets designed for the Mallard P.M. Master Receivers. W. and T. lock, St. Peter's Works, BAIL and 96, Victoria Street, London, s. \v.1. Supplementary List, April, 1927, relating to ' Cabinolu," pedestal and other cabinets for wireless receivers. A. F. Bulgin and Co., 9 -11. Cursitor Street, Chancery Lane, London, E.C.4. Folder containing complete set of revised price lists of Der /.preen, Compeler and other radio products. Philip's Lamps, Ltd., 145, Charing Cross Road, London, 11í.C.2. Leaflet Ito. 81, giving particulars of the new Philips D.C. High -Tension Supply Unit. Burne -Jones and Co., Ltd., 288, Borough High Street, London, S.E.1. Leaflet dealing with the " Cube " 3 -valve self -contained receiver. Pamphlets relating to " Magnum " wireless products in eluding calibrated rheostat, screened coils, Mtultipte plug -in coil. (No. 265,301.) valve holders, etc., etc. A 44

www.americanradiohistory.com \\\:- "'` BROADCA-k, ;

NEWS FROM ALL QUARTERS.

5GB Awakes. What's Yours ? " Daventry Junior," or, to give the All that listeners are being asked to new station its correct title, 5GB, has do is to let the B.B.C. know to which burst into spasmodic life. of its stations they listened wholly or The first transmission occurred on mainly during last winter. Listeners May 7th, and a Wireless World reader, need only address their postcards Mr. Richard C. Le Mare, of Heaton " B.B.C., London," " B.B.C., Daventry," Chapel, Stockport, tuned it in forthwith. " B.B.C., Manchester," etc. It is, how- In his report Mr. Le Mare writes : " The ever, essential that postcards should be signal strength on a set using 1 -v -2 was sent to the particular station with which a little weaker than 5XX. The signaL By Our Special Correspondent. the listener is more intimately concerned, would offer an excellent alternative pro- Tests and not to London, unless that is the gramme. Crystal reception was pos- from " Daventry station to which the information on the sible, but only very faint. The quality Junior." -The B.B.C. reverse side of the card refers. On the of modulation was very good indeed." Referendum. - Portable top left -hand corner on the address side The transmission was received between Platitudes. the letter " R " should be written 11.0 and 12.0 (noon) and consisted of plainly. pianoforte music and reading. is made one of the twenty -one The special request that 0000 stations of the listeners to Leeds or Bradford should be B.B.C. ? How ninny of the twenty -three postcards either "Stronger than 2L0." to twenty -five millions careful to address their of the population to or to the Bradford station, 5GB was within 100 miles' radius of Daventry are the Leeds also testing last Wednesday whichever they support, and not to morning (May 18th) between 9.30 and broadcast listeners, and how many listen regularly " Leeds -Bradford," although the two 11.0 a.m. The wavelength is between to their local station, or to a uy same address. 300 "t.her B.B.C. transmitters have the and 400 metres, and there is no law station" The only information required on the to prevent listeners from calibrating the distance signals with postcards is (a) the approximate a wavemeter. I understand of the receiver from the station, and that the new station has already been re- (G) whether a valve or a crystal set is ported as " stronger than 2L0 a " by used. The facts can be given thus : listener at Dover. 15/ V. Postcards should reach the B.B.C. 0000 stations by May 30th. Why Not July 27th? 0000 Now that the first regional station has been coaxed into activity, it seems rather Questions Which Will be Answered. a long time to wait for regular trans- This referendum is the first of its kind missions until November, the month to be conducted in this country, and will which has frequently been mentioned in probably reveal some interesting figures. connection with the inauguration of the How many people listen to Bourne- first regional programmes. mouth as compared with Birmingham ? Provided that the tests are successful Does Dundee speak to thousands, or tens -and there is no indication of failure - of thousands ? Is Swansea wasting its there should be no insuperable obstacle fragrance on the desert air? in the way of a much earlier start. These are some of the questions to The second anniversary of " Daventry which the referendum may find an answer. Senior " occurs on July 27th. Why not And I should not be surprised if its celebrate this auspicious occasion by the revelations form the basis of calculation initiation of alternative programmes on when the Corporation tackles the prob- that date ? What about it, B.B.C.? lem of regional distribution. 0000 0000 The B.B.C. Referendum. A Musical Event. The B.B.C. are at present busy receiv- The accession of Sir Henry Wood to ing postcards in connection with the re- the ranks of broadcast conductors as ferendum which they have instituted in from June 1st represents an important an endeavour to obtain information re- step in the musical history of the gard lug the effectiveness (or non- effective- B.B.C. ness) of the different stations. I understand that, for a few months From four to five persons in each at all events, Sir Henry will be mainly OUTDOOR BROADCASTING. A banjo household probably listen at some time solo from 5VY, an amateur station which associated with " outside " concerts, or other to items in the broadcasting pro- took part in a recent field day of the and in this connection it is interesting grammes. IIow is this vast concourse Tottenham Wireless Society. The trans- to note that the B.B.C. contemplate in the missions on 45 and 90 metres were picked divided matter of time spent in up by many amateurs in the neighbour- making a further offer to Mr. Boosey in listening to the programmes from any hood regard to the lease of the Queen's Hall. A 45

www.americanradiohistory.com 072 Wkdsog MAY 2511?, 7927. Wosiicda Portable Platitudes. A novel sound experiment will be con- stations have followed the principle of :Many writers on wireless topics (not in ducted on Friday next, May 27th, at the picking out the mote from anybody's eye T1ie Wireless World) appear to experi- broadcast performance of " R.U.R .," in but their own. ence at this period of the -year a price- which the noise of the Robot factory will The. official listening station will at in- least be unprejudiced in less and peculiar urge. Fortunately, its be produced by means of orchestral 0000 its findings. manifestation is confined to cold print, struments. That anything approaching otherwise We might all go mad and gnaw realism can he achieved by this method Service from the Ceno`aph. batteries. The point is, the urge must seems rather unlikely, but, fortunately, An impressive broadcast will take manifest itself, or assuredly the writers a Robot factory is itself unreal. place on Whit Sunday, June 5th, viz., would die. the British Legion Memorial Service at the Cenotaph at 5 p.m., to be conducted Bubbling forth pretty much like sul- FUTURE FEATURES. phate on an old accumulator, it sounds by the Dean of Westminster. Familiar London. like this : " Now that summer is here, hymns will be sung, and listeners will dear reader, let us direct our attention MAY 29í-11.- Orchestral and Vocal also hear the sounding of the " Last to portable receivers and all the delights Programme. Post." which they hold in store. In the first MAY 30Tä. -Act. III. of " The The microphone will be slung from place, a portable receiver must be really " Huguenots," relayed from one of the adjacent buildings. portable. . . . Covent Garden. coon ,Ii'NE 1sT.-Running Commentary And so on. And the amusing point Who is "Harold " ? is amidst a welter of facts and on the Derby, relayed from that A new party of mirth -makers will fancies the chances are 1,000 to 1 against Epsom. JUNE 2ND. -Elgar Birthday Concert broadcast from 2L0 on May 28th. The the writer observing the real reason why nucleus of this respect, conducted by tSir Edward Elgar. party consists of Geoffrey the poorest portable has, in one Gwyther, Donald Calthrop, Rex Evans, a erushing superiority over every other JUNE 3RD.-Trooping the Colours. Printers' Pension Fund Ethel Baird, and Carmen Hill. Donald vpe of broadcast receiver. JUNE 4ra.- Calthrop, 0000 Concert, from the Royal Albert acting as compiire, will treat Hall. the microphone as a telephone to call the Those Endearing Young Charms. Birmingham. World and his Wife to a wireless entertainment. He will tell you that the charm of a JUNE 4TH.-Military Band Concert, The feature of the broadcast portable receiver is its portability, suita- relayed from Royal Leamington will be the introduction of a new char- bility, respectability. Ile will impart the Spa. acter in broadcasting, who will be known information that it can be disguised as as "Harold." There never has been a Bournemouth. wireless a suitcase. And when it is time to go Max 31sT.-Speeches at Banquet mascot. If " Harold " fulfils home (and he has still half a column to given by the Mayor of Ports- the expectations of the broadcasting fill) he will rhapsodise on the fact that to Officers and Men of officials, it is not improbable that those mouth who favour a baby portable is more musical and less the French Naval Squadron, mascots will adopt him as irksome than a portable baby. relayed from the Guildhall, their own, for it will be made clear after And still he will have missed the main Portsmouth. the broadcast that " Harold " is physic- ally suited to the part. point. Cardiff. 0000 0000 JUNE 31-tn.- Harpers and Chanters The Blissful Illusion. -a Celtic Salute from Wales A Useful Voice. The main point is that a portable re- to the West of Scotland. Miss Ruby Helder, the lady tenor, will ceiver, operated in the open air, Manchester. broadcast on May 31 in songs by Am- nourishes far more effectively than does MAr 29.0L-Hymn Singing Festi- broise Thomas, Coleridge -Taylor. Hatton, the best parlour set that blessed, if ni- val, relayed from the Pavilion, and Graham Peel. When Miss Helder accurate, reflection that you are. getting Buxton Gardens, conducted by was touring in America, burglars at- something for nothing. Sir Ivor Atkins. tempted to break into a friend's house

The most awe -inspiring, receiver, en- JUNE 3RD. -- Municipal Orchestral where she was staying. No member of - sconced in its niche in the dining -room, Concert, relayed from the Royal the male sex was sleeping in the house, with connections to batteries or elimin- Hall, Harrogate. and it was surmised that the burglars ator, gives a subconscious impression of Newcastle. had knowledge of the fact, but Miss contact with the transmitter. In appear- MAY 31sT.- Lnfauriliar Works by Helder shouted out in her best masculine ance it is no more independent than the Great Composers. voice : " What do you want ? Wait until ordinary telephone. IrNE Ora. -North of England Musi- I come down." The burglars were But hike out the portable and pull in cal Tournament : Community scared away. the music from 5NO in the silence of a Songs relayed from the Town 0000 o lonely moorland, and . . . weel, ye ken Hall. The Old Brigade." it's grand, mon ! Glasgow. A series of reminiscences inspired by It's very easy to believe that the music M- y 31st. -" Twopence all the Chelsea Hospital will constitute a broad- is really free for the asking -until the Way," a programme by The cast entitled "Boys of the Old Brigade," batteries run out, or a Post Office official Corporation Tramways Depart- by Amyas Young, to be given on May 31. taps you on the shoulder and asks to see ment. 0000 the jolly old licence. Belfast. For the Blind Listener. JUNE 1sT. Too Many Cooks 0000 -" "- Equipped with a copy of the Braille a Revue by Numerous A Noise. the blind Peculiar Authors. Radio Times, listener can he The departure from 2L0 of Mr. Alfred said to start from scratch in the matter Whitman, the " noise expert," is a re- of broadcast reception, enjoying precisely minder of the progress made in the last A Central Listening Station. the sanie facilities as those who possess few years in the manufacture of what To establish a permanent central lis- their sight. - may Le termed " artificial noise." tening station to check the wavelength The first number of this weekly It was :flr. Whitman who was largely of European broadcasting stations was periodical has just been published by -the : responsible for the introduction of those an interesting decision of . the Union National institute of the Blind, and con- - weird and wonderful creations capable of Internationale de Radiophonie at its re tains a summary of programmes from the producing anything from the whisper of cent sitting at Lausanne. Something of English- and Welsh E.B.C. stations. - The sad sea waves to the sound of riveting the sort has been badly wanted ever since price of the paper is ld., or by post 1d. in a Tyneside shipyard. Mr. Whitman the Geneva scheme came into being. Up The first issue is one of 1,250 copies, but has returned to his first love, the films, till now, in the absence of such an it is expected that this number will be but the good work will go on. official and minatory eye, the various increased with subsequent issues. A 46

' www.americanradiohistory.com Á, x r".TR°u,,..,Ry.Ay4-r.y,!..1?:.nT,+f4aÿ

. .

MAY 251h, 1927.

TRANSMITTERS _ NOTES AND From the Arctic Circle. May 4th. The QRAs marked with a A correspondent in Cheshire tells us differ from those in the previous list, that on April 17th he received signals in QURIEiS and are, presumably, later corrections. the early hours of the morning from NC 5FS, 4AD G. Harvengt, 27, rue Gust -Biot, La Louvare- which is believed to be a station 9AF H. Stienaers, 7, rue du Tram, Hasselt. at Aklavik on the delta of the Mac- 4AG A. Wust, 66, ay. Elisabeth, Berchenq Antwerp. kenzie River, in North -West Canada. capacities which form a feature of the 9AH R. Destrée, rue de Rivieren, Ganshooren. '4AJ A. Redemans, 150, chaus. de Charleroi, The signal strength was about R4 and down leads in this system. Mr. Era St. Gilles, Brussels. the wavelength 33 metres. He will be adopted the Lévy aerial on the advice of 4AN A. Damnseau, C, rue de Block, Machelen. interested to know if other Mr. Franco 4A0 P. Tollenaere. 115, ay. des Hortensias, readers heard Marietti (EI 1N0), of Turin, Schaerbeek. this station and if they can give the and is enthusiastic over the increased 4AQ G. Mareska, 66, avenue de l'Armée, Etterbeek. exact QRA. range of his station. He states that be 4Av O. Laroche, 617, boulevard de Smet de Naeyer, is in regular telephonic communication Brussels (2). 0 00 *4A% Fouassin, 64, rue de Serbie, Liége. Among the Belgian A0mateurs. with stations in New Zealand and the 4BE I'. Cardon, de Lichtbuer, 30, avenue d'Ameri- M. P. Duvignan (EB 4AC), 16, rue Philippine Islands, and has worked in que, Antwerp. de l'Eglise, Antwerp, transmits daily Morse with stations in America, J. Mussehe, 63, boulevard Poincaré, Brussels. South 4BM E. Quitton, 17, rue de la Bravoure, 17, Jette. from 5 to 6.30 G.M.T. on 31.50 metres India, French Indo China, and many 4BN B. Van Engelen, 73, rue du Moulin, Borsheek and has been in two -way communication others parts of the world, including the (Antwerp). with OZ 4AA, the well -known in 4B0 F. Lodewijck, 18, rue de Lille, Menin. station 5th and 8th Districts of 4BP H. Obreen, 40, Krijgslaan, Gand. New Zealand operated by Miss Bell, and 0000 9BQ S. Keups, 156, rue de Jumet, Marchienne- OZ 4AC; also with NR CTO in Costa A Roman Amateur. Docherie. Rica, whose signals are 4BS J. Puttemans, 14, rue de la Limite, St-Josse- stated to be fairly Signor Alfonso Martillo (EI 1CU) Via ten- Ncode. strong until 7.45 G.M.T., and various XX Settembre 89, Rome, is now conduct- *9BT Raillez, Manhay. other stations in Australia, New Zealand, ing low -power telephony tests on a wave- 4BU F. Vauhay, 1, 2, r. Braemt, Brussels. and South America. He uses an input of 33 metres, using a Western 4BV A. Ressort, ri ute de Bovenistier, Remicourt. length 4BW L. Menne, 68, t ue de Joie, Liége. of 100 watts to a Hartley circuit with a microphone and modulating by absorp- 4BZ G. Janssen, ChHteau d'Emptimm (Ciney). single wire aerial 40ft. long and a 20ft. tion. He is generally carrying out these 4CE E. Lucas, 3, place Albert ler, Chatelineau. counterpoise. 19.30 4CH L. Mestag, 76, ay. Clays, Brussels tests from 13.00 to 14.00 and from 4CI L. De Pauw, 87, Gastbuisstraat, 87, Aren- 0000 to 21.30 G.M.T. He is also " on the air " donck. Mr. Louis Era (EB 4BC) tells us that every evening for D.X. work, using an in- F. Barils, 123, rue de Dison, Verviers. he has lately any 9CÑ M. Elbert, 13, rue des Croix, Flénu. been experimenting with put of 30 watts, and will welcome 4CR R. Cauwerts, 18, rue Gratés, Waterntael- the Lévy type of aerial in which the reports of his transmission. Boitsfort. down lead is in the form of a closed cir- 0000 9CS A. Charles, 28, avenue de Séville, 28, Grivegnée to 9CT R. Mitteau, 36, rue de Saxe-Cobourg, Brussels. cuit tunable half the wavelength and Belgian Amateurs. 40% A. Rousseau, 3, place de Bayemont, Jumet- inductively coupled to the tuning coil of We are now able to supplement the list Gohyssart. the transmitter; it is similar to the Alex - of licenced Belgian amateur transmitters 4CZ L. Dierckxsens, 36, rue Quellin, 36, Antwerp. of 4DB X. Deparadis, 21, rue de la Brasserie, Vaulx anderson aerial but without the variable published on page 551 of our issue (Tournai). 4DC G. Demey, 22, Galeries Ensor, 22, Ostend. 4DE M. Dieudonné, 220, rue Fidevoye, 220, Yvoir. 4DM M. Delsemme. Ill), rue Verte, It'), Brussels, 4GA F. Ryckx, 118, chaos. de Charleroi, Brussels 4G0 G. Vanden Eynde, 22, rue du Remorqueurs, Brussels. 4GS M. Ruth, 321, nue de la Croix Rouge, Wegnez. 4LL I -. Lelarge, 37, rue Oscar Lelarge, 37, Wanze. 4LS A. Staimer, 85, chaos. dc Tirlemont, Corbeek- Loo. aSiV M. Navaux, 37, nie de France, Verviers. 40A L. Houben, 173, rue de Verviers, 173, Amid- mon t. 9PC E. Parmentier, 118, rue de Bison, Verviers. 4Q5 L. lienrotav, 26, rue des Carmes, 26, Verviers. 4RS R. Pirotte, 10, rue du Parc, Verviers. 4SF J. Mallinger, 17, rue Jos. Stevens, Brussels. 4%S R. Parent, 183, chaus. de Heusv, Verviers. '4xx M. Van Hauwermeiren, 28, rue Ch. van Lerberghe, Schaerbeek. 4YU G. Bianchi, 31, rue de la Chaussée, Mons. 4YZ A. Courtois, 50, rue du Punt Iiopold, Hodi- mont.

O 0 O O New Call-Signs Allotted and Stations Identified. G 2TP Lient. C. W. Andrews, 4, White Horse Drive, Epsom. (Change of address.) G SPH (ex 211W F). B. F. Phillips, 21, Byng St., Landore, Swansea. (Transmits on 23, 45, and 90 metres.) G 5YD (ex 2BZD). H. C. Daynes, 15, Elton St., Stretford, Manchester. (This call -sign was formerly owned by Mr. E. R. Bridg- water, at Longton.) G 6BY W. R. Bottomley, Glynwood, Brighouse, Yorks. (Transmits on 8, 23, and 45 metres.) OD PKO (ex N OR W' and EI DANE 2'. C. J. Gouwem NU 9CPM owned and operated by Mr. W. J. Mashek at 5032, Lyndale Avenue South, tak, Medan, Sumatra, Dutch East Indies. Minneapolis, Minn., U.S.A. Mr. Mashek, who transmits on 20 to 45 metres and is (Transmits on 27 to 33 metres, usually Justly proud of his installation, would like to exchange photographs of stations with between 1200 and 0600 G.M.T., and will British amateurs welcome reports.) A 47

www.americanradiohistory.com 674 Wfipe@00 MAY 25111, 1927. WOrr lico1

The Editor does not hold himself responsible for the opinions of his correspondents. Correspondence should be addressed to the Editor, "The Wireless World," Dorset House, Tudor Street, E.C.4, and must be accompanied by the writer's name and address. EMPIRE BROADCASTING. plant for a 24 -hour service, there should be no financial obstacle to making a start forthwith. An average of two hours' recep- Sir, -Following my contribution to The Wireless World prac- tion in the twenty -four would be ample, and on the short wave year of home tically a ago', emphasising the inestimable value there should be a negligible amount of interference from atmo- broadcasting to colonial residents, this progressive periodical spherics, even during bad local conditions. One must not has consistently brought -the subject to the fore. The result lose sight of the fact that theorising beyond fundamentals will is that contemporaries have seen fit to fall into line, which get us nowhere, and it is only by trial and error that we should spur the authorities to consider the erection of a rela- shall eventually make progress until such time as the science tively high- power, snort -wave broadcasting station in one of becomes more exact. the London counties in the very near future. Looking ahead a little, it would seem that some organisation It is a particularly opportune moment for the preliminaries should represent the views and requirements of the exiles in to be discussed, observing that colonial representatives are now the various Dominions and Colonies, from both the technical in conference in London, and it is to be hoped that every and programme sides; in a great number of instances, the advantage will be taken with a view to gleaning the possibilities individual would even require representation, and I have no of the revenue to be obtained from local receiving licences, in hesitation in suggesting that my Association would gladly and order to provide funds for the maintenance of a 24 -hour trans- efficiently undertake to act on their behalf in the event of in i ssion. sufficient Colonial subscribers coming forward to warrant the Such transmissions need not consist so largely of entertain- overhead expenditure involved. I have received many letters ment as -provided for local consumption at home, at any rate confirming this need, and hope in the very near future that for some time to come. The essential factor to be considered we shall see the consummation of the scheme outlined above. would be the " Home Contact," and it is conceivable that H. ANTHONY HANKEY, " News " and topical events would be of the most practical Secretary The Wireless Association of Great Britain. and psychological value. In this connection, it would be a fairly May 16th, 1927. simple natter to record special sporting events, which could be retransmitted over a period of several hours in order to ensure that the widespread Dominions and Colonies would re- CERTIFICATES OF MERIT. ceive either the original or record. Mr. This gives rise to the important question of technicalities. Sir, -With more than passing interest I have read Claude World with Tt is taken for granted that there is a layer of ionised gas Lyons' letter in the May 4th issue of l'he Wireless surrounding the earth for an average distance of perhaps 100 regard to the granting, by some disinterested and unassailable miles above the earth's surface, and that this layer is subject authority, of certificates of merit for radio components and sets. to complex physical and electrical changes. We have also to Mr. Lyons has promulgated, at an opportune moment, a sug- consider that there is a definite relationship connecting the gestion to which I feel sure both radio trade and public will mean position and effect of the sun with the wavelength em- give favourable notice. While concurring in basic principle ployed, and its reflection distance. The variables involved, I would beg to differ in detail from Mr. Lyons' scheme. therefore, are considerable in the light of our present knowledge, To bestow three classes of certificates would, to my mind, and the difficulties of obtaining continuous reception as far as present a fallacious perspective to such a proposition and tend broadcasting is concerned are pronounced. In consequence to create an ambiguity which could too easily become a " bone of these somewhat conflicting factors one's thoughts naturally of contention." turn to " Beans," and were it not for the expense involved Surely it is as meritorious to produce a reliable, utilitarian for the erection of a multiple beam station, the efficiency arising article at a low figure as to create some masterpiece of work- from concentration would doubtless be of a high order. In manship, irrespective of initial or productive costs. this connection the terns " efficiency " can he very misleading, Providing. an article fulfils efficiently and straightforwardly as the requirements of a useful broadcasting system are totally its correctly imposed duties, and duly justifies whatever claims distinct from a commercial wireless telegraph or telephone may be made for it by its manufacturer, and furthermore sells system. In any case there is no reason why a commercial beam at a reasonable price, I fail to appreciate why its prospective station should not superimpose a very special broadcast occa- purchaser, whose pecuniary ability may not permit of some more sionally, in the event of a political speech concerning a parti- extravagant outlay, should be debarred the satisfaction of feel- cular Dominion. As the outcome of the original Colonial ing that he is obtaining something which has achieved recog- Station, one may visualise a beam broadcasting transmitter as nition as " fully meritorious " under expert examination. Any concentrating the energy directly upwards to the highest stratum intelligent buyer will realise that an article selling at two-thirds of the Heaviside layer, and finis conserving energy by making the price of another similar will not, in the ordinary way, attain a ":getaway " with the minimum of absorption losses. the same level of general perfection, and that further decreases These are matters which will have to be investigated at some in price will indicate usually proportionate decline. To grade future date, but the fact remains that with a station of from definitely as suggested appears to me outside the legitimate and 20 to 50 kilowatts of high- frequency energy working on two useful scope of such a scheme, and, while quite comprehending wavelengths between 20 and 40 metres, and with duplicate Mr. Lyons' reasons for such action, wherein he intends each class to be designated as meritorious in degree, I would beg to ' The Wireless World, April 14th, 1926. suggest that it should also provide a category into which any A 48

www.americanradiohistory.com Vflbp®II@o0 MAY 25th, 1927. 675 WopIlc1 article may be fitted without undue elasticity, thereby allowing heard as an unintelligible jumble of -sounds on an ordinary for the well- advertised, well- produced, but practically useless, receiver it contains the essentials of good speech and can be " brilliant idea " from which we have suffered so long, to rank received as such only with a very accurately adjusted " horno- with its " honest to goodness ". but unpretentious fellows. dyne " -that is to say a separate heterodyne oscillator adjusted Whereas my ideal would be to remove such encumbrances from to exactly zero beat frequency With respect to what would be the one class " meritorious " by the process of entire elimina- my carrier -wave if it were there. it is quite hopeless for any- tion. HETHERINGTON APPLEBY. one to try to pick nie up properly with a self -oscillating receiver, London, S.W.19, and any such attempt is only likely to interfere with the recep- May 4th, 1927. tion of the stations which are properly equipped to observe my tests. Sir,-The letter advocating the establishment of " Certifi- *l'or the benefit of your more technical readers I should like cates of Merit for Components and Sets " in The Wireless World to state that I am transmitting both side -hands minus carrier prompts one to say that anything which helps the public to component and not one side -band only as Rugby does. know exactly what it is buying is worthy of support. The system is not intended as an attempt at secrecy. It is On this score, however, the disclosure of electrical valves, of simply a rather advanced method of economising power. impedances, resistances, capacities, inductances, in fact all de- E. HOWARD ROBINSON (2VW). tails and qualities in given components which the many excel- Loudon. N.W.3, May I7th. 1927. lent technical articles in The Wireless World have educated us to look for in experimental work aucl set building-all these, I. say, are the data the public need to protect it from much disappointment with its sequels of wasted money and eventual abandonment of the hobby. At present it is useless to go into a wireless dealer's and ask for a proprietary coil of a particular inductance with a specified minimum resistance, or a transformer with a needed minimum primary impedance and enquire about self- capacity values, etc.. etc. Yet your excellent journal urges us, and rightly, to follow certain rules and laws in these matters in our long quest for perfect results. From my observation, unsatisfactory wireless reception is due, not so much to ill -made components, as to excellent components unsuitably used. There is, of course, much more to be said on these subjects, and I look forward to reading my fellow -readers' views. Hove, W. M. CARR. May 4th, 1927. EXPERIMENTAL SIDE -BAND TRANSMISSIONS. Sir, -In the course of the next few weeks listeners in the Lou- don area who listen in during the week -end below 200 metres may hear rather weird sounds emanating from my station between 6 p.m. and 8 p.m B.S.T. on a wavelength of 194 metres. In order to allay any misconception which may arise I should like THE FIELD DAY SEASON. Members of the Tottenham Wire- to point out that I am carrying out perfectly responsible experi- less Society picking up signals from mobile transmitters on a ments on a system of " side -band " telephony. Although it is recent field day.

SHORT -WAVE TESTS FROM WGY. r " WO important short-wave transmission tests are to be It is highly import ant that those who participate in the carried out from the General Electric Company's station tests should make every effort to secure a complete twenty -four- WGY, Schenectady, on May 28th and June 4th next. The station's hour record. Records which cover only a portion of a twenty- technical department is anxious to secure accurate data as to four-hour period are useful, but in general the data they con- the wavelengths which are most effective in daylight and dark- tain is too meagre to permit the drawing of accurate conclusions. ness for long- distance transmissions. It has been found hitherto In reference to this, the station directors point out that at that the wavelength of 32.77 metres has been most effective in certain periods of the day the signals will in all probability reaching great distances, but it is thought that possibly the be inaudible, therefore reports stating that the station was 26 or 22- metres wavelength may be more suitable for daylight listened for, but not heard, may be just as valuable as those transmissions, or where one -half of the area covered is in the which give the characteristics of a received signal. daylight zone. We give below the schedules of these trans- As one of the primary objectives of the test is to determine missions from WGY, which will be of considerable interest to the utility of given wavelengths for international broadcasting, British wireless amateurs. it is essential that a record should be kept of the times, if any. For the tests on Saturday, May 28th, the transmission of when, in the observer's opinion, the signals are suitable for music and speech will be made from Station 2XAF on rebroadcast purposes. 32.77 metres, and from Station 2XAD on 26.8 metres. The From the quantity of data which it is hoped will result transmission will commence at 12 (noon), Eastern Standard from these tests, the WGY engineers hope to increase con- Time, and last until noon on Sunday, May 29th. The two siderably their present knowledge in relation to (1) the com- wavelengths of 26.8 and 32.77 metres will be used simul- parative merits of 22.02, 26.8, and 32.77 metres for the carrying taneously, both being modulated from the same source with out of an international broadcasting service ; (2) the periods voice and music. The times given are in American Time, and of the day that are most favourable to foreign reception of correspond to 6 p.m. in our own time. these wavelengths ; and (3) the co- ordination of time and wave- In the second test, on Saturday, June 4th, the wavelengths length, so as to give maximum service to foreign listeners. of 22.02 and 32.77 metres will be used simultaneously, both Our readers will understand from the foregoing remarks being modulated from the same source with voice and music. how important are the above tests which are being organised It is possible that both transmitters will not be heard at the by WGY. We would like to urge British listeners who are same time. In this case, also the transmission will begin -at successful in picking up these tests to communicate their 6 p.m. B.S.T. and last for twenty -four hours. observations to the Station Director of WGY, Schenectady. A 49

j{f'+_+i.. .- . . - www.americanradiohistory.com ., 44,4PPFle*,+

V v h; 6 fipigCag fIAY 2511r, 1927. Wail di

"The Wireless World" Information Department Conducts a Free Service of Replies to Readers' Queries. Questions should be concisely worded, and headed "Information Department." Each separate question must be accompanied by a stamped addressed envelope for postal reply.

Charging from D.C. Mains. figure only I,ciug a rough approximation. A Reaction Problem. I propose to chortle my 120 -volt X.T. It will usually be found, however, that I was so pleased with vty " Everyman accumulators, as oven as a 6 -volt L.T. a 2 -volt valve makes a much better anode four" recover that I used a similar battery, direct from the 240-ro/( 1).C. bend rectifier than either a 4- or 6 -volt circuit for a portable receiver with- mains. Is the enclosed circuit dia- valve, because it has a shorter filament, out the long- iearr attachment. As gram ca)vect, and what lamp .should and therefore a more sharply defined it -wa.s possible to Use only 60 volts be used? A. H. S. bottom bend. The 4 -volt valve rather two L.F. taans /,,rrncrs acere In the first place, we would strongly falls between two stools. and it neither rased with leahy grid condenser dissuade you from attempting to charge gives the full efficiency of the 6 -volt a'ectifieatinn Results are fair, but an L.T. battery- from the D.C. mains. valve nor the utmost, economy of the 2- selectivity is disappointing when flue This is an extremely wasteful procedure, volt valve. From the point of view of set is Used. with a short improvised as the greater part of the current con- efficiency, of course, it lies between the aerial. Would reaction improve its 2- and 6 hour could sumed is wasted in heating lamp or other -volt valve. Usually in a modern sensitivity, and, if so, it be, is resistances. At the usual rates, a charge receiver, especially using modern types applied? Space limited. may well cost four or five shillings. of cone and moving coil load- speakers, A. C. N. Regarding the H.T. battery, however, it is essential that a 6 -volt valve be used It is certainly possible to add reaction, in the case is quite different, due to the the last stage, and it is advised then and we think you will find the caplcity- smaller difference between the voltages of that, if utmost economy- be desired, 2- control method to be the simplest. The the mains and that of the cells. Your volt valves be used in every position skeleton circuit diagram given in Fig. 1 a in series with except the last, stage, where a. 6 -volt will show you how the necessary altera- circuit (showing lamp valve the is quite in order. should be used. This does not tions may be effected. The reaction coil, mains and battery) necessitate You do not state the makers' recom- running your 2 -volt valves off wound close to the grid end of the H.F. it 6 -volt, accumulator, but mended charging rate, hut as a rule a entails merely transformer secondary, should have about having 4 240 -volt, 60 -watt lamp will pass a suit- an auxiliary -volt accumulator 40 turns of very fine wire-say No. 38 or able current, as the " back- voltage " of working in conjunction with a 2 -volt one, 40 D.S.C. -while the reaction condenser the battery must be taken into considera- as shown recently in a diagram given in R.C. may conveniently be small, with a tion. these columns (page 544, April 27th maximum capacity of 40 or 50 micro - 0 o 0 o issue). farads.

Two, Four, or Six ? O,ue Imp( nit!' comes orro.çe the .etale- unevt that 6 -runt valves are adrisrd to be used in any given receiver if H.T. maximum efficiency it desire(1. Can tell you vue if this is true, and what yQQQOQr- percentage of loss there is tchen using o 2 -roft valves in comparison aria 6- o volt calves? S. L. Q o In a 6 -volt valve we have naturally a o greater wattage available, and so they o°) are, generally speaking, more efficient than valves of lesser voltage. 'Thus, a, N.C.T C. 2 -volt, 0.1- ampere valve gives its 0.2 watt ,Hi a l- and 6 -volt, 0.1- ampere valve gives ns 0.6 watt. A 6 -volt power valve consuming 0.1 ampere. therefore, will always be 6 more efficient than a similar 2 -volt power H.F. ODET. valve consuming the same current. It is usually taken that on an average a 2 -volt calve gives 70 per cent. of the efficiency of a 6 -volt valve of a similar type, this Fig. 1.- Method of adding reaction to the " Everyman Four " circa ?t. A 50

www.americanradiohistory.com MAY 251h, ¡927. WIpaISM 677 W0T11Ld Moans or Music. wound anode resistances having total was recommended in the article to'which long - constructed a receiver consisting values of megohm, and even 1 megohm, you refer as highly desirable where I -have is of a detector without reaction and already on the market, but so far as we distance reception the first considera- three stages, to give very great are aware there is no tapped instrument tion. L.F. in anode volume on the local station. Imme- having this high value. It would be im- The use of a transformer the diately upon switching on, however, possible to tap a -megohm resistance of circuit of a bottom bend rectifier is hardly advisable, because the type of valve the set gives vent to a moaning sound. the " grid leak " type. However, the usually recommended for this function has This is. not (lue to a mechanical feed problem is by no means insoluble because it is now possible to purchase 100,000 normally a fairly high impedance, which back /rune the loud -speaker, as I applied have proved conclusively by operat- ohm resistances in " grid leak " form and is increased, by the negative bias ing the -speaker in another room to make it work on the bottom bend. loud be em- entirely, and resting the receiver on beyond the point where it can " these circumstances ployed in conjunction with an average Sorbo.'' Under good the howl, which is a steady one and transformer. unaltered by moving the tuning dial, still continues as before. Will you Transformer By-pass Condensers. please give nie the cause and the remedy? S. T. B. Z notice that in some circuit diagrams showing receivers with capacity -con- You do not give us full particulars controlled reaction the usual by -pass concerning your receiver, but undoubtedly denser across the transformer primary is to it due your attempting to use three is omitted while in others it is re- L.F. stages running off the same H.T. tained. As there is already an H.P. battery. This is extremely liable to cause choke in series with the primary, and a howl of the same type you mention, the reaction condenser acts as a by- due to coupling in the H.T. battery, and often pass, surely this condenser is un- occurs even when only two L.I'. necessary? R. T. stages are used if the receiver is badly laid out, so that there is already a ten- From the " H.F." point of view there dency to instability in the L.F. stages is. as you suggest, very little reason for due to various causes, such as magnetic this shunting condenser, but it should be coupling between two transformers. You remembered that some of the better L.F. must increase the size of the condensers transformers are designed to operate with shunting from each H.T.+ tapping to Fig 2.- Volume control with tapped a certain value of capacity across their H.T. -, and this should cure the trouble. anode resistance. primaries, and in this matter the recom- Another excellent method is to use an mendations of the manufacturers should one may thus connect 5 of these in series be observed. entirely different source of H.T. supply be- for the final stage. and take a tapping at the junction 0000 L.F. By this we mean " grid leak " resistance, and not merely a separate tapping on the tween each so have a very compact volume control. A Case of Mistuning. same H.T. battery, but an entirely sepa- to be rate battery. We presume you There is one great precaution I have been using for a long time a re- that have and is special made certain that your valves are being observed, however, that ceiver designed for Dacentry only operated under their proper care mast be taken to avoid introducing having a short aerial of only 40/t. working con- effects due to the wiring ditions, and none of them is overloading. stray capacity Results have been quite good, al- to the stud switch. It is permissible, of though there was not quite so much 0000 course, to shunt the total anode resist- volume as I would like. I recently ance with a 0.0001 mfd. fixed condenser, had the opportunity of erecting a Tapped Anode Resistances. and, indeed, such a condenser is neces- much longer aerial to my hitherto I built th, tno -valve amplifier described sary to obtain rectification efficiency, and 40ít., and now find that Daventry is in your issue provided' that reasonable care is taken distinctly weaker instead of stronger of March 31st, 1926, in result from which a home -constructed 150,000 rein wiring up no harm should as I anticipated. Why is this? sistance was used in the anode circuit the little extra capacity introduced, as R. H. de K. of the detector valve. This there will already be this 0.0001 con- resistance there are fixed In the first place, the additional length had tappings on it for volume control. denser there. Or course, have the effect condensers of smaller capacity than of aerial would, of course, Sinsthen the high -impedance, high - in parallel on the market, namely, such of adding additional capacity ma1ni fication factor valves have made 0.0001 mfd. with your tuned aerial circuit, and sig- their appearance, and I ant using one values as 0.00005 mfd., and if it is the this stray capacity was nals would be weaker owing to with u -megohin anode resistance of thought that out of tune with then we would suggest receiver being thrown the "(pill leak " type and am ob- slightly excessive This could be compensated merely reducing the value of the normal Daventry. taining every satisfaction on the local for by turning your condenser to a station and Daventry. Control of shunting condenser from 0.0001 mfd, to until We by refer- slightly smaller capacity value ?Warne by dimming the H.F. valve 0.00005 mfd. think that were heard. Even then, ring to the diagram which we give you loudest signals filament is denied to me because I you might find signals weaker in 2 the necessary connection however, have Ito H.P. stage, and 1 earnestly Fig. because of the increased would be made quite plain to you. than originally desire to revert to the tapped anode 0000 aerial damping, but if you have reaction resistance method, but cannot see how incorporated in your set you could com- it is to be done when a -'z- megohm An "All-Wave Four " Modification. pensate for this by increasing the reac- anode resistance of the " grid leak" I am about to build the " .Ill-Wave tion coupling slightly, but if you have type is used. Your advice on this Four" described in your +ssue of no reaction yoù must try the effect, of matter is therefore desired. I it pos- April 27th, but u-ish to use two L.F. not directly coupling the aerial to the top sible to construct a wire -wound in- transformers already in my possession end of the tuning coil. You can use a strument having this high resistance? in place of the resistance as specified. two -coil holder with a separate aerial R. G. J. K. Do you advise this -course? coil, but possibly the best method is tc From a mechanical point of view there H. S. A. insert a condenser of 0.0003 capacity in would be no difficulty in constructing a We can hardly recommend you to sub- series with the aerial lead -in. Please tapped instrument having a total resist- stitute a transformer for the first resist- note that this will necessitate turning a greater capa- ance of 2 megohm or even more. The ance coupling, but there would be no your tuning condenser to point is that the self- capacity might be harm in using it between the first and city value; in fact, probably a greater excessive. There is, as you know, wire- second L.F. valves; indeed, this course value than originally. A 57

www.americanradiohistory.com 67S Wflmhoo M AY 25th, 1927. WOrilcl Cutting Out Local Interference. Thus, by putting the switch over to the is if it were desired to make the set 1 have built a receiver consisting of a left we first adjust the 0.0005 mfd. con- give either Daventry or Radio Paris by detector followed by two H.P. stages, denser until the local station is brought the movement of the switch, but even the purpose of which is not to rein, and then we put the switch over to then only the Radio Paris circuit need . ceive distant stations, but merely to the right and do not touch the main have reaction applied, first for the pur- give me the local station or Daventry 0.0005 mfd. tuning condenser, but adjust pose of rendering the set sensitive enough by moving a double -pole switch. the compensating 0.0001 mfd. condenser to bring in this station, and, secondly, Whilst ereryth.in'g is all right when until Daventry comes in at full strength. for the purpose of making sure that receiving the local station, which is The left -hand coil, that is, the local Daventry was eliminated. The best about eight miles distant, I find that station coil, will, of course, be no longer scheme to adopt in this case is to use on switching over to Daventry, the tuned to the local station, the 0.0005 Fig. 3 (c) with a four -pole switch, thus local station gires an unpleasant mfd. condenser being removed from it making provision for reaction if neces- background. Can you help me to and at the same time, when putting the sary, but having short- circuiting pings improve matters? M. K. D. switch back to the left, the right -hand in each of the two reaction coil holders We notice that yod use separate tuning circuit shunted by the 0.0001 mfd. con- when desiring to use the set for its nor- condensers for the local station and denser will no longer be tuned to Daven- mal purpose on the local station or Daventry. Fig 3 (a) is your circuit, try, but will resonate to a wavelength Daventry. The two coil holders and two with the addition of a 0.0003 mfd. fixed considerably below Daventry. We can, pairs of plug -in coils which it will be condenser in series with the aerial, which if we like, put a compensating condenser necessary to use to effect this may make

0 0003 00003 mfd

(a) (b) (c)

Fíg. 3.- Methods of eliminating interference from a near -by station. will effect some improvement in selec- across the local station coil instead of the receiver look rather clumsy, and small tivity. The probable reason why you across the Daventry coil, and exactly the turfing units such as the " Polar " unit receive the local station when the switch ,same thing happens, namely, that when can be used instead if it is desired. is we is over to Daventry that you have in switch over to Daventry the local o o 0 0 the receiver a complete tuned circuit station circuit resonates to a wavelength adjusted to the local station, and this far below that of the local station, and Plug -in Coils in H.F. Couplings. picks up direct from the local station, so causes no trouble. Here again the I should be glad if you can give me a which is arid, since 0.0003 mfd. is not far away, the series condenser optional, circuit of a live-valve receiver em- two tuned circuits are in fairly close but in any case it is advisable to include ploying two 11.P. stages detector will be seen and proximity in your set, it it, as it will lessen aerial damping and two T.I'. stages in which plug -in coils is probable that the local probably improve in that it highly. signal strength this are used, in. order that till wave- when re- station will forni a background manner, apart from sharpening up the lengths may be covered. N. M. ceiving Daventry. tuning. We advise, therefore, Fig. that We a circuit to 3 (el cannot conscientiously recommend Fig. 3 (b) is much better should be used. you use, since, in this case, when changing over Of course, you doubtless know that by that build a receiver of the type you mention, as it would in- from the local to Daventry, there is no using a ,four -pole switch instead of a probably be very efficient indeed, and we go as longer a circuit left in the receiver tuned two -pole one it would be a would so far simple matter to say that it would probably be less station. Fig. 3 (b) may be to use also a separate reaction to the local coil for efficient than a properly designed re- used with or v: ithout this series 0.0003 both the local and the Daventry stations, ceiver employing only 1 stage. mfd. condenser. This condenser will thus sharpening H.F. If tuning considerably, but, you are specially desirous of using 2 H.F. help to improve selectivity. and you will in our opinion, Fig. 3 (e) is ample for stages, we can only advise you to build find that 0.0003 mfd. is just about the your purpose, and Fig. 3 (b) should only the " Wireless World Five " described rig,,t size, being small enough to sharpen be advised in those cases where it is in our issues of January 5th and 12th. the tuning on the short wave stations. desired that the set also be capable of We would point out, however, that this yet large enough to prevent unduly sharp tuning in, say, Radio Paris, Moscow, or receiver only covers the 200 to 600 metre tuning on the long wave stations. some other long wave long -distant stations band, and if therefore you are intent The disadvantage of Fig. 3 Ib) is that on the right -hand coil, when, of course, on covering four wavelengths, it would be one cannot just change over the double - reaction would he necessary. Similarly, necessary for you to turn your attention pole switch, but must readjust the 0.0005 reaction would be necessary in the case to the " All -Wave Four," described in nrfd. tuning condenser each time a change of the left -hand coil for bringing in a our April 27th issue. Although the " is made. This defect may be overcome long- distant station on the normal broad- Wave Four " possesses but 1 H.F. stage, by placing a compensating variable con- casting band. we have no hesitation in saying that it denser of 0.0001 mfd. capacity across Another occasion when it night be would be considerably more efficient than the crib. illustrate this :_ ? (c). necessary to add Fig. 3 (el) to rig. 3 (c) the receiver you propose. A 52

,tit. www.americanradiohistory.com -rß'1'!