QUESTIONS AND ANSWERS

Radio Record, Volume VII, Issue 12, 29 September 1933, Page 27

QUESTIONS AND ANSWERS

A J.M. (North Auckland) : I have add4+* G49 valve to the "All Wave One" deseribed.in the 1933 "Guide," but the set is not working satisfactorily. Should the fuse light up while the set is working? A.: No. Probably the vanes of either C8 or C5 are shorted, Have you wired the set according to the circuit diagram given on page 59? 464 (Auckland) : My cone speaker has developed a rattle, particularly on the lower notes, . A.: This may be due to the power valve losing its emission or to a run-down "C" battery, though it may be due to the speaker, Have you tried the effect of changing the setting of the adjusting svrew ?° 2 Are dc. type valves included in the new Philip’s "Golden Series"? A.: No. 8 Can the class "B" system of amplificntzon be operated satisfactorily from a "B" eliminator? A.: Not from an ordinary type. An eliminator of special design, capable ot good voltage regulation, should be employed. _ F.l, (Wellington): I intend bury- * ing 100ft. of copper wire beneath the lawn, directly under the aerial. Will this give the effect of a counterpoise in addition to making a good earth? A.: No, because a counterpoise shoul be as well insulated from earth as the aerial itself. However, your idea of burying the earth wire under your aerial is theoretically correct, but’ whether results would be better than those from 4 well-installed earth of the ordinaty type is doubtful. 2. Would 150ft. of wire be better than 100£t. ? A.: We think not. However, this again is purely a matter of experiment.

R J. (Feilding): I have a 7-valve com*mereial superhet. which gave very good results for two months, when a detector by-pass condenser and resistor broke down. ‘These were replaced, but the tone of the set was changed from very clear and pleasing to dull, flat and muffled. The set was then sent to the aakers, who replaced the pentode valve and.several resistors, but no improvement in tone resulted, and the set failed again after two hours’ use. Would it be advisable to proceed further or discard the set and obtain a higher-priced one? I do not require distant stations, but regard tone as the first importance. A.: We certainly do not advise you to discard your set. Dither return it to the makers again or call in a qualified serviceman. "READER" (Napier) and LH.F, (Oamaru): Your requests for constructional details of a portable set have been noted, and we hope to be able to describe one in the "Radio Times" very shortly. , " i\ UT" (Dunedin): At frequent intervals the programmes from both local and distant stations are considerably marred by a hissing noise, which. increases in volume till it almost drowns the music, It then ceases suddenly, only te commence again after a short interval of clear entertainment,

A.: This may be due to power interference coming through the aerial or to some defect in the set. ‘Try detaching the aerial, and if the noise ceases the trouble is due to power interferencepossibly from a vacuum cleaner or some other domestic electrical appliance. If it does not, then the fault lies with the set, and is prebably due to a defective by-pass condenser or valve. B. (Pukerua Bay): Replace your * valves with the types you are at present employing. 2, 2YA covers the dial from 4YA to 1YA. Where can I obtain details of an efficient wave-trap? A.: In the July "Radio Times."

"FIVYRO" (Napier): During the past few months daytime reception from 2yA«has varied considerably. For ten months I could tune in this station during the day and be wure of getting practically perfect reception. Suddenly in May, daytime reception weakened-so much so that I could scarcely pick up the station. This continued for about five weeks, when just as suddenly the old strength returned aud eontinued until three or four weeks ago, when it went off again. Curiously enough, reception during the evening hus been perfect all through. My neighbours say that they have noticed no difference in 2YA’s daytime reception. 1 have noticed that the sudden changes have coincided with occasions on which I have lifted the set to dust the table. Could this have anything to do with it? A.: Yes. There is obviously a loose or poor connection somewhere. The aerial may be shorting to the chassis, or one of the valves may be loosened in its socket. The only suggestion we can make is that you have the set completely overhauled,

AIL" (Dunedin): My aerial is 40ft. high and 60ft. between the masts, making a total length of about 100ft. 1 intend covering the vertical portion of the aerial to a height, of 20ft. with 3-Sin. rubber tubing, and then winding 20-gauge copper wire round the tubing right down to the lead-in tube, where it will be earthed. Would this help to eliminate interference? A.: It certainly would, though we think the rubber tubing is scarcely of wide enough diameter to prevent loss of signal strength through the capacity effect formed between the shield and the aerial. However, it certainly would be well worth trying. 2. My set uses three 27’s, two 35's, two 47’s, one 24 and one 80. Which of the new type valves should I use to replace them? A.: Replace the 27’s with 56’s, and the 24 with a 224A, [Note: The valves you mention would not be suitable for your set. ] "LISTENER" (Wellington): We cannot make comparisons between commereial products. "GPARK" (Rangataua): What are the coil specifications required to tune from 20 to 100 metres, using 00025 mfd. tuning condenser and .00035 reaction con-

denser, all coils to be wound on valve bases? ‘ , A.: You will find the following specifications suitable :--

Use 24 or 26 d.s.e, Note: Evidently you intend using -80 turns for the broadcast coil; 90 turns would be better. " HIZBANG" (Frankton Junction) : What type of valves are used in the Mullard Screen-grid Four? 1 have a spare PM12 and PM2., A.: PM12 r.f., PM2DX detector and: first audio, PM2 power valve.

"PADIO BUG" (Rotherham): I have a new four-valve all-wave commercial battery set. When I plug in the broadeast and 35 to 90 short-wave coils, the set motor-boats badly. A.: This may be due to one of many causes-a faulty grid leak, too high a voltage on the detector, a run-down "B" battery, etc. We would not advise you to interfere with the set in any way, but to return it to the dealers for adjustment. "A&A URUM" (Westland): A 100-volt 24 amp. dynamo used for lighting purposes creates bad interference. I tried earthing the frame of the machine, but the noise became twice as bad. I then connected two 1 mfd. condensers, one to each main, and earthed the centre terminal. This improved matters a little, but it is still very noisy. A.: Try increasing the capacity of each condenser to 4 mfd. Also there may be excessive sparking in the commutator, which may need re-facing. "(AINGE" (Frankton Junction): I am compelled to run my aerial over the house. Would reception be improved if L-used insulated wire for the portion running over the roof? A.: No, this would make no difference at all, If you are compelled to run your aerial over the house, the only thing to do is to make it as high as possible. —

Information Coupon (To be used with all requests for information.) Name of set ....... se ceawcccwasoes Mode) PPrrrrrrrriti tri tt ii i Name PrrvrTiviirrt iti ACGLESS sevcvecccccccccsccovccrer® _enee Oe c eS OOS SEES HOHOSEEOHOHSOOREOD Beh Ree eee He Oe ee SESS OSHOSSE SSO SUOE Nom de Plume ,..ccccoececessece: To be kept in cuhsequent inquiries Please Note:- . 41) Be specific and oriet, tabutating, if possible. #2) Write legibly, and on one side of the paper (8) We do not design circuits, (4) Limit three questions unless \/- is enclosed. (5) ‘Postal queries limit 3 questions. BEnelose’ stamped ang addressed enyelope and 1/- fee, ~

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