Editorial Comment Hugh S
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THE PRACTICAL RADIO JOURNAL 27th Year of Publication No. 931. FRIDAY, JULY 2ND, 1937. VOL. XLI. No. 1. Proprietors : ILIFFE & SONS LTD. Editor : EDITORIAL COMMENT HUGH S. POCOCK. Editorial, Even for those who may not con- Advertising and Publishing Offices : Television template building a television receiver DORSET HOUSE, STAMFORD STREET, Our Receiver Design themselves, the articles will neverthe- LONDON, S.E.I. less be found a source of complete Telephone : Waterloo 3333 (so lines). information of a practical nature such Telegrams : "Ethaworld, Sedist, London." N this week's issue we begin a series of articles describing the as it has not hitherto been possible to COVENTRY : Hertford Street. obtain from any other source. These Telegrams: Telephone: practical design and construction "Autocar, Coventry." saxo Coventry. of a complete sound and vision practical articles, studied in conjunc- receiver for the B.B.C. television trans- tion with general articles on television BIRMINGHAM : Guildhall Buildings, Navigation Street, 2. missions. We make no excuse for the which have been appearing for some Telegrams : Telephone apparent complexity of the apparatus time in The Wireless World, may be "Autopress, Birmingham." 2971 Midland (4 lines). -this is inevitable at present, and is, regarded as a complete course of MANCHESTER : 260, Deansgate, 3. of course, common to all television re- instruction in the subject. Telegrams : Telephone : "Riffe, Manchester." Blackfriars 4452 (4 lines). ceivers, but the complexity can be The design is one which is particu- said to resolve itself into only a larly suited to the requirements of the GLASGOW : 26s, Renfield Street, C.2. question of quantity when the equip- student and experimenter, because of Telegrams : "Iliffe, Glasgow." Telephone: Central 4857. ment is dissected into its component the accessibility of every párt, whilst PUBLISHED WEEKLY. ENTERED AS SECOND - taken as for instruction and demonstration re- CLASS MATTER AT NEW YORK, N.Y. units. The construction, units stage by stage, offers no greater quirements this feature is invaluable. Subscription Rates : difficulty than an ordinary receiver and, Home, Ls Is. 8d. ; Canada, £i is. 8d. ; other countries, ¡I 3s. sod. per annum. in fact, may be considered to be less exacting in many respects. Radio Propaganda As many of eke circuits and apparatus described in these Very special attention has been given pages are covered by patents, readers are advised, before Probable Official making use of them, to satisfy themselves that they would adjustment Attitude not be infringing patents. in the design to make initial simple and to render the operation of WHILST we know that the controls as little critical as possible, so Government deplores the that, when constructed, no technical policy of some foreign CONTENTS knowledge or special skill will be governments of broadcasting, particu- in order to work it. Page necessary larly on short waves, anti-British propaganda, yet we believe that there Editorial Comment .. 1 High Quality Throughout is no evidence at present to justify the The Wireless World Television Re- The different units have been made rumours that action is to be taken to ceiver -1. The Vision Receiver easily . accessible by the particular compete in this sphere. It can be and Power Unit .. 2 design adopted for the cabinet frame- regarded as certain that any move Delayed Switching 7 work. No attempt has been made to which it is decided to make will not be cheapen construction by the use of com- in the nature of reprisals, but will take Current Topics .. 9 ponents with a bare margin of safety, the form of seeing fhat, wherever Periodic Variations of the Iono- but every component is chosen to anti -British propaganda reaches, there sphere .. .. .. .. 10 have ample voltage and power rating also would the influence of accurate Listeners' Guide for the Week .. 12 to guard against risk of breakdowns. British news be extended with at least All high voltage sections are pro- equal radio power. Principal Broadcasting Stations of vided with proper protection so that the On the question of language, any Europe . .. .. .. 14 constructor who undertakes building broadcast to counteract the effect of Random Radiations .. .. 16 the equipment should be involved in no propaganda would, no doubt, be put Broadcast Brevities . 18 risks, provided the ordinary pre- out in the same languages as were cautions, such as his experience in being used by the of#ending foreign Practical Hints and Tips.. 19 .. building other mains -operated appa- stations. This use of languages was Letters to the Editor . 20 ratus will already have taught him, foreshadowed in the Broadcasting Recent Inventions.. .. .. 22 are observed. Report. www.americanradiohistory.com Wireless World, July 2;id, 19S7 The wireless World Television I. FULL DETAILS OF THE VISIOZ FOLLOWING upon the theoretical articles which have been appearing in " The Wireless World," complete constructional details of a television receiver are being given in a new series of whiéh this is the first: The vision receiver and its power unit, which also supplies LT for tube and time -base, 'is described here in detail. A front view of the complete equipment. The time -base will be seen that three RF stages for the first, second and third stages. controls can be seen on the are used with a diode detector Single tuned circuits are used for the left of the tube. and one VF stage ; the remaining intervalve couplings and are suitably two valves are a diode for restor- damped so that the requisite band -width ing the DC component to the out- can be secured. No artificial damping is put signal and an RF pentode for employed in the case of the first three cir- sync separation. cuits, for the low input impedance of the ASTRAIGHT set has been selected' For the RF stages pentodes of high pentodes at ultra -high frequencies is as the most sùitable type of mutual conductance have been selected, chiefly relied upon for damping. In the vision receiver fér reasons which and they operate with the screens at the case of the first circuit L2 Ci, damping is have been given In recent articles' same steady potentials as the anodes. It also imposed by the aerial circuit. in The Wireless World.' These reasons ire is consequently possible to use common The second and third couplings are of briefly that it requires fewer valves, is decoupling for screen and anode and so the tuned anode type, the tuning coils simpler to construct and adjust, and, most effect a saving in the number of com- being L3 and L4 tuned by the condensers important, is free from The serious inter- ponents required. This decoupling is C5 and Cg. Because the input imped- ference problems of the superheterodyne. effected by the resistances and condensers ance of the diode detector is much higher The circuit diagram of the receiver, R3 and C3, R5 and C7, and R8 and CI' than that of an RF pentode at very high which has been based upon many months of theoretical and practical research with Fig. i. -The 'complete circuit diagram of the vision receiver and amplitude filter is shown here. many types of set, is shown in Fig. 1. It Three RF stages are used with a diode detector and one VF stage ; the remaining valves are the DC restorer and the sync separator. JO/ 5000 soo n 200 n R3 R5 RS EL3 BL4 6 1.000s mrd C; 4 C12 0 0005 IJ 0.000085 mid TSP4 TSP4 3. TSP eL2 .--o-. ?L1 (o° ,c1 all o R7 C5='( 0.1Mn b0-- ooC3rdT 0.01 mtd C11 R10 10,0000 R11ó R4 21i S.m mid R9 C10 1000 T 000i 000 0.01 mid K ) ) ò R2 10,00011 C R TUBE MODULATION OUTPUT SOCKET www.americanradiohistory.com Wireless World. hu!y 2nd, 1937 3 DESIGNED BY W. T. COCKING Receiver RECEIVER AND ITS CONSTRUCTION frequencies the fourth and last tuned cir- cuit must be artificially damped by the resistance Rio. This last RF coupling differs from the others in being of the tuned grid type ; this is necessary because the detector must have an external path of low DC resistance apart from its load resistance Rir. A choke feed with Chu and Cie is adopted for this circuit, therefore, and this last RF valve is operated with fixed bias provided by Rq. The two early valves have initial bias provided by RI and R4, but can be further biased for gain control by the variable resistance R2. The Vision -Frequency Stage The detector is a low impedance diode with a 5,00o-ohm load resistance RI', and a ioµµF by-pass condenser Cr4. The A rear view of the output is applied directly to the grid equipment wi.h the of the VF amplifier, which is another RF back removed. pentode. Bias is obtained from the roo- ohm resistance Ria which is shunted by the 500 -,uF condenser Cry. The full HT voltage is applied to the screen, no de- coupling either of this or the anode cir- A view of the upper cuit being necessary. The output shelf showing the coupling vision receiver and consists of the resistance Rie time -base to the left and right o: the tube . z .le and the coil L6, and enables a response are also applied through R15 to the grid Iaa v 14 characteristic to be obtained which is fiat of the RF pentode, which functions as a within some 3 db. up to the extremely sync separator. This valve is operated high frequency of 2.o Mc /s, and this with with some 40 volts screen, 140 volts a stage gain of about 20 times. anode, and -4 volts grid potentials.