Questions and Answers

Radio Record, Volume VI, Issue 7, 26 August 1932, Page 10

Questions and Answers

A W.L. (Hamilton): Thanks, the cor- * rection was made last week. NICORN (Christchurch): What is fa ihe capacity of a condenser with 13 Pp A.: It depends on thé size of the plates. Probably .0001 or .00015, 2. I wish to use the condenser with a 00015 differential for a shortwave adaptor. What are the coil specifications ee the 80-metre band, using valve base coils. A.: Use 30 ds.c. wire. Primary 12, secondary 45, tickler 30, Dx. (Hamilton) : I can hardly hear 1YA, although 2YA ean be heard ‘ well, All stations above 4QG come in at. great strength, but below that they are very weak. -I have recently replaced the by-pass in the plate supply with a 1mfd. A.: In all probability the condensers are not ganged properly, and need retrimming. 2. Could an a.c, sereen-grid valve be used in a d.e. set? A.: Not successfully. 3. What is the lowest screen voltage with which the 224 would operate satisfactorily? A.: No less than 135 volts on the plate and 65 on the screen. The writer adds: "Could any reader supply me with the cireuit of a booster using a coil and formodenser to be used with a set with an aperiodic coil." N L.A. (New Lynn): Would a short- * wave adaptor which obtains its power from the wiring of the mains set be a satisfactory proposition? A.: It depends upon the design of your set, but it should be. 3, Would results be as good or better than a straight out two or three valve s.w. battery set? . A.: Usually the best results are ed on such a battery set. Whe results on a eonvertor are usually quite good, 8. Conditions being favourable, would it bring in the main world stations on a good aerial?-Yes, ») ACKO (Otahuhu).-With my "Sparrow Hawk’ one I am using two chokes, one for shortwave and the other for long. Would I get better results if I purchased a commercial choke? A.: Providing you are getting good results and smooth oscillation, no. The choke designed in the "Radio Record" is a perfectly good one. . . IL wish to make an output filter so that I can use phones and a better set with "B" eliminator, Will you give me the specifications of the choke A.: You will find standard ‘Radio Record" choke "O" (vide 1982 "Radio Guide’) quite satisfactory. 8. I ean still hear music when the headphones are disconnected. . ‘A.: This is due to a loose lamination in the transformer. It is doing no harm. [E2 (Waiuku).-The vents of one of the 8 mfd. electrolytic condensers in my set becomes coated with a sticky substance which dries hard if left, On being wiped , away, more forms. Should I replace it~ with a new one? | A,: Yes, electrolyte may ooze out or harden and in time cause a short cir | euit. _ 2. When the volume is increased a buzz- | ing crackling noise is heard. This is not | eaused by a worn volume control, A.: Such trouble is hard to diagnose | without instruments. Possibly you are | overloading the detector valve ;there may | be a defective valve or speaker, the | moving cone of which may be rubbing | against the pole pieces, | 3.: My aerial is 30 feet high at the dis- | tant end, and 18 feet at the near end. | Would it be improved if it were 30 feet at | both ends?-Xes, ‘

(CATHODE SUPHR (Clyde): I have a power switch and volume control incorporated in the one article, Is this permissible? A.: Only if you connect the set to the mains by a non-reyersible plug and make certain the switch is in the phase wire. 2, Can I have a tuning indicator fitted? A.: Yes, if you can obtain one. M L.B. (Rangiora): Where has a bat- * tery charger to run from the 230. volt a.c. mains been described? A.: One appeared in the 1929 "Radio Guide." J G. (Auckland): My eight-valve com- * mercial set has developed a metallic singing, which is more pronounced on high thin notes, A.: Possibly the moving coil of the speaker is rubbing against the ¢ pole pieces and needs recentring. >. \ ECONOMIC (Oamaru) : Should the top pole of my aerial, which is erected on sloping ground, be higher than the one nearer the house? A.: It is the height above the ground which counts, so raise the top pole and make it at least as high as the one nearer the house, A.: Does the grounded aerial improve reception? A,: Several dxers have found that by grounding the distant aerial of their set they can get better results, It is worth trying, 38. What is meant by a directional aerial? A.: If an serial is of certain proportions, ¢.g., with a very long top and short lead-in, it is directional, that is, it has directional properties, i.e., when pointing toward a station it will receive that one stronger than all others. The lead-in should be at the end more distant from the station. Your aerial would not be directional even if erected to point in certain direction, PUZZLED (Otago): I cannot log stations below 600 ke.? A.: Very few people can with any degree of satisfaction. 600kc. represents a fairly long wave, and most sets are more or less insensitive at this part of the dial. However, your condensers may be short= ing, or Some such thing happening to pre vent reception at that end. D*NAMo ((Waitomo): Why does my set whistle when I touch one of the speaker terminals? A.: Because you are introducing a certain amount of high frequency current. It is nothing to worry about, 2. Is 150-180 volts too much for two P215’s in push-pull?-No,

Information Coupon (Lo be used with all requests for information.) Name of set SPST eS SCESSSOZSEBOESS Model SOO eCerseeseveresesceseoness Name seewoecsesesvesesesegeeseosAddress PePReCoeeesresooseeuseves: COC OORSCOSETAOODSSERSCOEMOS SE HEAEES bia tata aaatIraitititiitititiitiy Nom de plume ......sccceccacces To be kept In subsequent inquiries , Please Nate:- ; (1) Be specitic and brief, tabulating, 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 . three | questions, Enclpse stamped envelope and 1/- ‘fee.

— ~ tetas t: 3. I have all the "B" leads on.to the 120 volts tapping. Is this right for the "Super Six" A.: B -- 1 might be lower, -*83Mc (Christchurch) : When. volume is full on, with the aerial disconnetted and the set on the local switch, I get jumps and thuds which is not static, as I tune the dial-from 200-250 metres. A.: Without further information as to the behaviour of the set with an aerial, on the distant switch, and at full volume, we cannot help you. In any case, service instruments would probably be needed ta diagnose the trouble. A.W: (Wellington) : Would a Beverage Ae serial improve my reception, and what ig it? . : _A,: A Beverage aerial is one about 400 yards long, and is erected about 10ft. high. . It must point toward the station to be received, and the distant end is grounded through a_750 ohms resistance, It wouid probably improve results ¢onsiderably. Can you suggest anything to improve my reception? . _A.: You are in a bad place." The bush nearby is likely to absorb a large portien,of the signal strength, while the hills actyas an excellent shield. . -3,.Would a pre-set condenser improve the number of stations received?-No, A P.. (Otau).: The more I increase the * volume the greater the selectivity of the aérial tuning condenser -decreases, Is that in order ?-Yes. 2. Qn short-wave the condensers will resonate only very wéakly with the oscillator condenser. : " wo .: It is important that the mixer valve be either HL610, 630 or one with an impedance yarying between 25. an 50,000 ohms.. Other types:.are ‘unsatisfactory. Are the 8.g, valves o.k.? Take B tot to 110 or 115V, even to max.

Mes (Palmerston N.):- -With | the aerial disconnected I find that turning on the electric hot water element yolume decreases, but with the aerial there is no difference. A.: Without the aerial you are operat: ing the set at maximum, and by turning on the heater the volume is decreased slightly, and the loss is apparent. When the aerial is on you are not working your set at peak, and the slight drop in voltage is not noticed. (CURIOS (Pukekohe E.): The last we heard of these sets was that they were handled by the Natela. Radio Company, Wellington. X60A. (Hamilton) : Would the en- ~ elosed circuit be suitable for a short: wave adaptor to plug . into the detector socket of my a.c. set? A.: Yes, if you. take the. lead from the tickler coil to the plate terminal of an old valve socket, and -connect the earth to the

chassis of your set as well as the chassis. of the adaptor. The grid condenser ‘should be about .0001, grid-leak from 7-9 megohms. Use a .0001 tuning condenser if the coils are specified for the "Night Hawk" Two DurFry (Lincoln) : The power pack should be approximately 450 volts, A humbucking device in this circuit is not: considered necessary, 3 5A, (Auckland) : What is "band-pass Aw? * ne em employing two tuned secondary coils to one primary eoil in’ the aerial circuit, ‘The idea is to get greater selectivity. 2. What stations are between 100 and 200 metres? A.: In N.Z, there are practically none to be heard. American police stations | operate generally on this band, 3. Would a Beverage aerial give good | results on shortwave? : We have not heard of it being used on and think it would be unsuccessful, H IW. (Auckland) : Yes. we shall * publish the circuit of an all-wave receiver, with a gramophone switch in a. forthcoming issue of the "Radio Times," probably the October issue. The circuit, like the "Radiogram Tive," could use plug in coils, 2, Could -I use my ordinary trans | former in place of the pushpull ones illustrated? A.: They ean be used by shunting both | primary and secondary with but usually such practice is not satisfactory. puss (Taitville):: You want a copy. of, the "Night Hawk" Two-and ¢laboration of the "Sparrow Hawk" One. Unfortunately copies of this have been sold out. Possibly we may alter it. slightly and redescribe it. It was very. popular.

PENTODE (Papakura): Is it in order to take the high tension lead from one of the filament legs of the rectifier. socket instead of from "the eentre tap?ry Where can I fit phones to the "DX Four’? A.: Instead of a speaker, but you would necessarily have to incorporate an output choke, 8. Where could I put in pickup terminals on the "DX Four’? : A.: The pickup would need to be connected between the grid of the detector and earth, 4,: Can the filaments of all three valves be taken from the same filament winding? : Yes, if it will carry the current. BZ YOU" (Waimate): When tuned below 8ZC, Christchurch, the ‘set distorts badly," but the distortion disappears when the volume control is on full. A.: Sueh trouble is hard to diagnose without instruments. In all probability the condensers are out of alignment or the volume control is faulty. FrARad (Tauranga): The flexible lead to the grid of the screen-grid valve fell against "the metal cabinet. A 00d spark was thrown, and the set has been dead ever since, i : It could not have -been the grid which caused the spark unless there was some mistake in the wiring of the set. If you are using batteries you have probably ruined the battery. Further details of your set would have enabled us to-help you. . H A.J. (Hamilton): Which would im- * prove the tone most, two 245’s: in pushpull or a pentode? ‘A.: The tone of the. pentode is more brilliant, though most people prefer ‘the — less brilliant tone of the 245, so that tone controls ‘are used with the pentode. 2. Where is the correct place to use & pickup to a set with a sereen-grid valve as detector? :

_A.: Break the grid return and put the pick-up in there. Tp=880¢. (Otago) : What is a Beverage aerial? A.: See reply to A.N. (Wellington). tt is fully described in. the 1931 "Radio uide.’ RGUMENT (Waitepeka) : My » Daniells cell charger operates at the rate of amp. Would it keep a wet "B" battery discharging at the rate of 4 amp fully charged? ' . A.: No, not unless you constructed 90 to 100 Daniells cells. By the ‘way, there is something wrong with your set if you are discharging a "B" battery at the rate of 4 amp. Lee (Wanganui): Does a J/2 branded "8000 ohms in pushpull" match the power output in the last stage (245’s in pushpull) ?-Yes. ’ 2, Could a Magnavox dynamic No. 416 be matcbed to the last stage in the set? A.: You could find this out as easily as we could by writing to the N.Z. agentsMessrs. Spedding, Ltd., Auckland. 8. The matching transformer for two 245’s in pushpull of the average dynamic speaker is 25-1 ratio. A W. (Timaru): How ean I attach a **convertor to a superheterodyne set? A.: Try it by. connecting it between the antenna and the ground. If you cannot get results like that, connect it across. the first intermediate transformer, i.e., the one following the mixer valve, One side should go on the plate terminal of this valve and the other to earth. PpAdvdy (Wellington): One of my valves does not light, although the set goes well. Does this indicate a fault? A.: Not necessarily. Some valves have a very dull filament, and the inside of the glass is coated. 2, Will perspiration affect phones ?- No. It should, however, be cleaned off. to prevent rusting. 8. In a month I have logged 118 stations. Is this satisfactory ?-Yes. N R.D. (Roslyn): The coil particulars * you require will be in the "Link Three" in this month’s "Radio Times." (CorLs (Auckland): Your condensers appear to be satisfactory. 2. I cannot bring in stations under 332 metres with any volume, even: locals.

A.: Have you tried re-neutralising the set at a frequency of about’ 300 metres? This: should step up reception of the lower wavelength stations, 3. I have not had luck with the "Sparrow Hawk’ adaptor. A.: Take the grid return to a potentiometer across the "A’’ battery. -This alteration should smooth regeneration. Have you a good r.f. choke, and is the shorting switch and condenser in series with the main tuning condenser? Unfortunately some of the earlier diagrams showed this in parallel, and had the grid condenser and lead wrong. Otherwise the diagram was all right. 7. L.107 (Huntly): Could I use other valves equal to #442, 488 and 404? A.: Not unless you alter the filament voltage to your set. If it is designed for those valves, it is better to keep to them. 2. Can the plate and filament supply be switched on simultaneously in a powerpack without detriment to the valve, or is it better to switch the filament circuit in first? A.: It is better to switch in the filament cireuit first, although no serious result will occur in. the average set if this is not done. 7" WIRELESS (Oamaru): Would jthe shortwave adaptor published in’ the 1931 "Guide" go satisfactorily connected to my battery set?-Yes, How would the "Sparrow Hawk’ differential adaptor suit? A.: It would be excellent. R4+ REC. (Wellington): What resistance is needed to break down 180 volts to 185 to use with the power stage of a Browning Drake? A.: It depends upon the valve you are using, but providing it takes about 10 milliamps you would need a resistance of approximately 5000 ohms.