QUESTIONS AND ANSWERS

Radio Record, Volume VIII, Issue 36, 15 March 1935, Page 47

QUESTIONS AND ANSWERS

"A THOS" (Hikurangi): Sorry, but aa. stated ‘on our information coupon, which you enclose, we do not design circuits for individual requirements. "859" (Kopaki) : Could I: fit a shortwave converter’ to my battery-. operated portable receiver, and if 960, where could I obtain details? A.: A battery version of the singlevalve short-wave superhet converter to be described in the 1985 "Radio. Constructor’s Guide" should be satisfactory. The "Guide" will be published at the end of thig month. C, L. (Dunedin) : Could you. supply me with coil details of the "Tiny Tim," using two .00005 mfd. midget condensers for tuning and reaction? A. A condenser of.so small a capacity would definitely not be satisfactory for reaction control, though you could try the effect of connecting a .0001 to .0002 mfd. condenser in series with it... :-Even then the number of turne on the reaction: winding would be extremely critical, if effective control of feed-back was to be obtained over every tuning band, Suitable coil details. using a .00025 to .0003 mfd. reaction condenser and a .00005 mfd. tuning condenser, are as follows :-

It would not be practicable to make a set of coils to cover the broadcast band with such a smail tuning condenser. "A LLUWAVER"™ (Duntroon): Whenever there is a fog in my locality a loud crackling and buzzing appears in my set. How could I cure it? A. This phenomenon is due to one .of two causes. Wither the moisture is providing g conductive path to earth somewhere in the aerial system, or the particles of the fog are clectrified and on coming in contact with the aerial wire are charging it. These tiny charges flowing eT tT NTT ETT TTT ETT ELT ETT ELE STE PTT TTT TTT TTT OLLT ttT Sit TTT tT TTT TTT TTT TTT Ti? ttt ted

to earth ‘may be causing the crackling of which you complain. If the first ‘explanation is correct, then the é¢ure jg’ to completely overhaul the aerial system, not forgetting the lightning arrestor, and to improve the insulation wherever possible ; if the second, then an insulated aerial might cure the trouble. Alternatively. you could’ use an indoor aeria] during fogs. . "RF (Whangarei) : Suitable coil * details for your set are ‘as follows:

It ‘is assumed that you are using a .0002 mfd. differential condenser for reaction. If you are using a .00015 mfd., then increase the number of turns on tbe reaction winding for the 20, 40 and-80 metre bands'by 1, 2 and 3 turns respectively. Decoupling the’ detector plate supply as you-suggest. would assist. in cutting out threshold howl. but a simpler way would be to: connect a resistor of from 50,000 ohms to .6 megohms in value across, the secondary of the audio transformer. Use the highest value possible, consistent with curing the trouble. The B406 would be all right as the detector valve and the 201A ag the first audio valve, R A. (Timaru): With my new 8-valve * all-wave commercial superhet, when the volume is turned down there is a distinct hum. Is this a. characteristic of the set, and can you suggest a remedy? A. The. hum should not. be noticeable more than three or four feet away from the speaker. If it is objectionable, then the set should be returned to the agents for adjustment. "COX DENSER" (Wellington) : How can the minimum capacity of a variable condenser be calculated when the maximum capacity is known? A. It cannot. The minimum ¢apacity of any condenser depends on a number of things, the most important being the quality ‘of the insulation used, type of mounting and the distance the two sets of plates are apart when the moving plates are "full out." "Kkiwe (Ohura): I am operating a 7valve battery kit-set. When one of the push-pull valves is removed from the socket marked "X" in the sketch, the get continues to play. but if the valve in "X" is left in, and the other removed, silence results. Both valves are sound. Why is this? "A. It could be due to a number of reasons, a defective valve socket being the most. likely. Check over the continuity of the -centre-tapped secondary and primary of the push-pull input and> output transformers respectively. If these windings aré intact, then the defective socket should be dismantled and overhauled. When the volume contro] is turned back there is no difference in the sound level until it is nearly off. Then it makes a scratchy. noise while being turned, A.: The potentiometer is evidently defective and wants replacing.

J S. (Auckland): I ‘would like to oper- * ate the "Tramper’s' One" between 20 and 50 metres. Could you give me the coil details? : A.: Aerial primary, 5 turns, secondary. 12 turns, reaction 4 turns. However, as the "Tramper’s One" uses a .00085 mfd. tuning condenser, you will find that the tuning will be so sharp on this band that it will be Very difficult to find any stations at all. 2.: If two radio sets are used in the one home, should separate licenses be obtained ? bs A.: Not if both sets belong’ to the’ one person. J K.D. (New Plymouth) : My set is the * "Kiwi Four," described: in. the "Radio Times" some time ago; For the past two years, it has given the utmost satisfaction, but recently it stopped playing. All the valves still light'up. What is wrong? , .*: vs A.: You have given us little or’nothing to go by, but the chances -are that a valve has gone. The fact that they all light up is absolutely’ no -indication. as, to their condition; otherwise the fault might he anywhere. . ,

Information Coupon ) (To be nsed with all requests for information.) Name Of SCt ...sesccccececcccecececs Mode} OTTO TETTTTITTTTTTTTrTriy TTT et Name eeeee ee eerseaeseeeeseeenseereeese Address SO eee er eseeeaveseseneseseees COCO SSSESESESESEHHEEEHESSEEEEEEEEESE COCO HHHSEE ESSE SESESESESESESESESESESEE Nom de Plume ..y eee ecccceeece’s To be kept in iaguiries . Please Note:(1) Be specific and briert, tabulating if possible, . Write legibly and on one side of the paper. (8) We do not design circuits. (4) Limit three questions unless 1/- is enclosed Postal queries timit' 3 ques: tions. Bneclose stamped and addressed envelope and 1/- fee. (2 -~ ~~ (5 —

p erox. | Band. Primary. See’dry. Reac’tn. 18 to 28 m. -f 9 26 to 40 m © 5 18 5 38 to 60 m. 9° 22. 8 60 to'S5 m. 12 36 10

Band. Primary. Secondar y. Reaction. 20 metre 3 9 5 40 metre 8 18 . 9 SO metre 10 30 14