QUESTIONS AND ANSWERS

Radio Record, Volume IX, Issue 14, 11 October 1935, Page 47

QUESTIONS AND ANSWERS

"\V AGNBTIC" (Dunedin):.It is quite possible to re-magnetise headphone aud speaker magnets by the method you outlined: As the current taken by the magnetising coil is very heavy, a high capacity accumulator such as a car battery’ should be‘used for the job. . The accumulator should not be left connected too long, and also, as the wire will get yery hot, be careful not to burn yourself. R. (Palmerston North): You could y * * use a single winding from a i75 k.c. | LI. transformer as the 175 k.c. coil for ‘ your oscillator. "GO T*" (Cambridge) : As your superbet has an r.f. stage, the repeat peints should not be objectionable, From your description of the set’s behaviour it seems apparent that all that is reyuired is accurate realignment with a calibrat: l oscillator. : "(CG(OMET" (Petone); The shortwave converter described in the "Radio Guide" should work quite successfully with your receiver. However, you would get far better results by building up one of the a.c. operated converters described in the May issue of the "Radio Times." "NJONPLUSSED" (Oamaru): After my set has been operating for about 15 minutes, reception begins to fade out, but switching the current off and on quickly brings it back to normal until the next fade occurs. This happens on cvery _{station. I have had the valves tested, have fitted a new volume control, and nave also checked over the lightning arrester and aerial. A. It is almost impossible to diagnose the cause of a fault such as this without an examination of the set, though the trouble is most likely due to a thermostatic joint or a defective by-pass condenser. The trouble may lie in one of the valves, even though you have had them tested, because in many cases faults of this type do not show up in a tester. There are’so many possible causes of intermittent fading that it would be out of the question to cover them all here. However, the location of faults of this type was outlined in -de-

tail jn au article entitled "Iutermittent ‘Fading of Radio Signals-Causes and™ Cures," published in the August issue of the "Néw Zealand Radio ™imes," and ‘we suggest that if you ‘want to locate’ the fault ‘yourself you, procure.a copy .of this magazine and study the ar ticle mentioned. UO-DYNE ONE" (Wellington): I have built up the "Duo-Dyne One," described in the "Radio Timés," gnd it has given quite good results. I have logged W9XF, WSXKE (49m.), as well as VK’s, 3ME, 2Mn, 3LR and FYA, Paris. GSB’ comes in very well every evening. My aerial is only 50ft. long, and I am using a "B" eliminator which I think is causing a very high-pitched squeal. This is so strong with the 80 to 200-metre coil that I have been unable to log any stations at all on this band. How can I cure this squeal? A: It sounds as though the trouble is due not. to instability, but to the fact that the voltage on, the plate of the detector section of the 19 is too high, and super-

regeneration is taking place. Try b-eaking the connection between one side of the reaction control potentiometer and "B -" and taking it to the "B + 22}v." or "B + 45y." tapping on the eliminator. This should cure the trouble. 2. Could you give me details of a suitable coil to cover the broadcast band? A. Two coils will be required to give complete coverage of this band. The following are the. details:-220 to 350 metres, grid winding, 165 turns, reaction, 14 turns; 350 to 520 wietres, grid winding, 210 turns; reaction, 16 turns. Nothing heavier than 82 gauge enamelled wire or 34 d.s.c. should be used for these coils. The reaction windings should be wound over the bottom ends 0. the secondaries, the windings to be separated by a layer of insulating tape or Empire cloth. H J.C. (Carterton): I have been inter*ested in radio for some time, but know very little about it. I would like to build an a.c. dual-wave superhet, but am doubtful as to whether I would be successful. Do-you think I could,.and if so, what type of set should I build? ; A. Normally one needs a fair amount of experience before tackling the construction of the average dual-wave superhet, but there is a new kit of this type which

has just appeared on the market.that anyone could build, even ‘without. previous experience. The receiver is the Radiokes "Simplified) Dual-wave . Superhet, Type 12/85S,". and ‘it is fully. described in the October issue of the "New. ‘Zealand Radio Times." The placing of every component and the way to make every connection is given ‘in: the minutest detail in a book "How to Build a Dual-wave Superhet." obtainable from Radiokes agents throughout New Zealand, or direct from Radiokes Ltd., Box 10, Redfern, Sydney, New South Wales. EGINNER" (Christchurch) ; Could you recommend a circuit for .a onevalve amplifier, to be used in conjunction with a crystal set? A: A: one-valve amplifier: would give good headphone strength from the locals, . but ‘two stages would be needed to give good loud-speaker strength. If you will send in the information. coupon, : together with the necessary fee for a postal reply, we will send you'full details of two simple amplifiers. 2. Which is the better set, the "Selectra" crystal set or the- "1982 Radcord?" A. The former is more selective, though the latter ig easier to build and operate. In your location’ the. "19382 Radecord" set should: be quite selective enough to prevent interference from the loéals.

Information Coupon (To be used with all requests for information.) Name of set ePeonccoesoseoaeeeesser® Model] severe eeee OO Desee DESO eCesere Name on eceesecedterrovevecveesoceyes Address SOCCR SOOT Sseeenreeesessenees ee se ee SOSSSSSSBSelseterenceguncesseseeace SORSSESHTSSSHOOSSH SOS EHTS SESESSOSESEOSEE COSA P SSE SHS SHETES SES SESE THSSSESSSESOSESE Nom de plume ..ccccccevvcceccesese To be kept in subsequent inqhiries. Please Note:(1) Be specific and brief, tabu: lating if possible. * (2). Write legibly’ and on one side _'.. ,of the paper, (3) ‘We do not design circuits. (4) Limit three’ questions unless 1/- is enclosed, ; (5) Postal queries limit 4. questions. Enclose . stamped ,-and addressed envelope and: Ve fee.

Would ‘correspondents to’ this section please address their letters to: The Technical Editor, "Radio Record," P.O. Box 1680, Wellington, .C.1.