Questions and answers

Radio Record, Volume IV, Issue 15, 24 October 1930, Page 14

Questions and answers

W MACA (Heretaunga).-Can a six- * volt battery charged be used ag an "A" eliminator for four-volt valves? A.: Yes, you will need to incorporate a 80-ohm rheostat. AL BDlectrie (Auckland).-How many turns will be required on a stan‘dard six pin former tuned with a .00025 condenser to eover the broadcast band? You will require 72 turns of 24 gauge d.s.c.,, with 25 turns tickler, which should oscillate quite well on the broadeast band, AMATEUR (Wanganui).-How many : turns of 26 d.s.c, would be needed on a 1din. former with a .00035 condenser? A,: Secondary 75, primary 25. . How many turns of the same wire using a .00025 condenser? ’ A.: Secondary 120, primary 40. 8. Using 32 d.c.c. s.w.g. for the primary 26 d.s.c. for the secondary, and 36 enamelled for the tickler? Secondary on a 2in, former. A.: Taking it that you will be using a .00025 condenser, secondary 100, primary about 40, but it will vary according b the valve used, and the tickler about 4, My ‘set is not as sensitive as it was when I bought it, and the tone becomes harsh ang screechy. A.: It sounds as though the valves want renewing. A set of valves should last 1000 hours. 5. The earth wire is very long. A.: A long earth is sometimes more of a disadvantage than an advantage, Remove it, and see if the set goes better, otherwise try to shorten the lead. CONDENSER (Hamilton).-I am not having success with my shortwave set. 1 ean receive only amateurs and four or five stations. A.: Are the amateurs on telephony? Tf they are Morse, then you do not have the knack of tuning your set, which must not oscillate when telephony is required. 2. I am using a 201A valve, 45 volts on the plate. A.: Perhaps one of the special detectors in the A415 class would be better. Try removing the earth. A HLH. (Otakiri).-Can a listener cali- * prate his dials? A.: Yes, it can be done by a_hererodyne wavemeter or more simply by plotting a graph. Take a piece of squared paper, choose suitable units. for metres and dial settings, and plot points for the stations you receive. You must, of course, know their wavelength, and the dial setting. By connecting these points, the wavelength for any particular dial set- ting can be found by tracing the line representing that setting through to the curve, and from that point, down, to the wavelength. 2. From where can the diagram of the Ultimate Receiver be obtained?-Radio Limited, Anzac Avenue, Auckland. J S. (Wellington): I cannot receive ° e American stations. Why? A.: You are probably shielded by nearby hills, It hag been the writer’s experience that the city of Wellington varies remarkably as far as reception is concerned. American stations can be reéaiyed quite well in one point, while

in another a mile or so away they cannot be heard. 2. Is the enclosed sketch of aerial and earth correct? A.: Your sketch is very difficult to decipher, and it appears that you have a very long earth. Your best plan would be to-drive a pipe into the: garden as near as possible to the window. W S. (Dunedin): How many turns. _* are required’ on vale base coil using 24 gauge d.c.c. for primary. and secondary and 30 gauge for the tickler? The condenser .00025. A.: Primary 80,. secondary 180, tickler’ 75, but thé coil will’ be a bad shape: Use finer wire. SWITCHBOARD (Gisborne): I have. rigged .up..a switchboard to .use several speakers, When two of the three are shut off and the third one in operation I can still hear signals in those two faintly. A.: This is quite in order. If strong signals are available it will often be noticed that signals can be received faintly by connecting only one terminal. 2. What is. the most suitable length of wire to be stretched from pole to pole in my aerial, which is 30 feet high? A.: About 70 feet. ; R B. (Port Chalmers): Some time ago * I wrote you, but did’ not receive a reply. Do you know anything about the --- machine

A.: We are sorry about your reply: you are recorded as having been replied _to, but we cannot trace this in the paper, We do not know anything about the machine and advise you to consider, if you are buying, one of the more widelyknown makes, '* 2, Is an aerial 100 feet long, 50 feet high, too long? .: Yes. Your selectivity would be poor. Try the effect of a series con.denser .00025. .. 3. Is an lead-in resting on the window still detrimental?-No. 4, Is there a list of distant stations published? ‘Av: Yes, the 1930 "Guide," but if you do not have one you will have difficulty in obtaining one. Lists of Australian and New Zealand stations have been published in the "Radio Record." 5. Would it cost very much to alter the machine to screen grid? A.: It would not be worth while, J. H. (Auckland): What would be the gauge of wire, number of turns, and the size of core required for a 1 to 1 output transformer? A,: Your better plan would be to make a choke capacity output such as described in the 19380 "Guide." 2. Could an "A" eliminator be successfully built by an amateur? Is one likely to be deseribed in the ‘Record’? A.:; The essentials were given in the 1930 "Guide, " but because this has been sold out the "A" eliminator will be re-

described in the "Record" within the course of a week or s0, 3. I am using a home-built eliminatyr which hums badly on the local stati n. There is. a silent background on "all other stations, and the hum disappears when the station closes down. A.: That is the carrier wave and not a defective "B" battery eliminator. The station hum from local is always: more pronounced than from distant stations. _ 4 What is the remedy for a microphonie ring? A.: Change the detector valve with another of the same kind, otherwise use a lead cap on the detector and shift the speaker to a greater distance, (CCARBORUNDUM (Wellington): I am contemplating making a battery of 90 Daniell cells to drive three valves for seven hours a week. What is your opinion of the suitability, approximate size of the containers, and the electrolyte? A.: See the article by "Hard-up" which appeared in the "Radio Record’ dated. June 6. The most suitable "B" battery » you can make is a Leclanche type us« ing the centre portion of torch cells, as described in the article. Daniells cells would not be an economical proposition, The electrolyte should be saturated. M.E: (New Plymouth): I wish to at- * tach a short-wave adoptor to my set. Can you recommend an expert?

LSTENERS must attach this coupon to all queries sent to the Technical Editor (Box 1032, Wellington), Questions arriving without it are likely to go astray or be delayed, Name of set ....ccccacccccccccceces Number of Valves ....scccscssccsce Name ; Address See nmerseseceseseseseceseeeses COO r eed eso eeeeeeereseaase i TA OTOE HORSE OURO OSE G ees eceeneEmeereeaeds SPHOHOHTH TOE HO OTHE ESSE SESE eEEEEEEEEEEeEEs Nom de Dlume . To be kept in subsequent inquiries. Date SOT HTHTETE SH eeE TE EESEDeSeeTEeeE Please Note:-~ (1) Be speciffe and brief, tabulating, if possible, (2) Write legibly, and on one side of the paper, (3) We do not design circuits, but accept suggestions for feature articles, ; Solving trouble, as different from advice, is difficult by correspondence and while letters are given every consideration, answers are not necessarily correct-they are only our opinion based on the matter supplied, which may: be quite inadequate. Intricate and involved specifications cannot be . supplied without a specialist’s fee,

A,: The only shert-wave adaptor we have tested is the "Addaphone" (Mack’s Radio, Wellingtop), You can obtain more particulars by writing to the proprietors, EF, A.E, (Yapier) --My "T" aerial is 100 feet long, with a lead-in of 50 feet. What size condenser will I need to. help clear things up? A.: The effective length of your aerial is only 100 feet, and is consequently the right size. Mee {Nelson) Who. are the agents for my set?. : A.W.A., Nimmo’s Buildings, Wel2. Length of aerial to use? A.: 100 to 125 feet, including lead in. 3. Cana shortwave adaptor be used with my set?-yYes, 4, Where can I purchase extra coils? -A.: If you. want shortwaves coils you will have to make them yourself, but try A. W. A.. first. AISY BELLE (Invercargill).-How ean I add an extra stage to my two"valve set? : It is almost identical with "R, the a See the description of "R. the W3," published on March 7. UNK BOX (Christchurch).-What are the number of turns for secondary and tickler on valve’ base coils, using .00082 tuning condensers? A.: 200 turns of 30 d.s.c. secondary, tickler 50 turns. Qve VADIS (Wellington).-What is the best combination. of valves for my American set? A.: 5-221’s, and a 171A type power

2. W. .t type of speaker would you suggest for the above combination? A.: You could use a mains operated dynamie cone speaker, HAMISH (Ch.ch,).-The © short-wave set described in the 1980 "Guide" is working indifferently. I cannot: control oscillation except by the use of’ wander plugs in the "B" battery. Can I make alterations suggested by my diagram? A.: No. If you wish to alter thé. cireuit ‘the one given herewith is’what you are aiming at. If you are using a variable high resistance across the "A" battery and grid leak, place a resistance of 100,000 ohms in the detector "B4-" lead and shunt it with a 1 m.f.d. condenser. Use the 500,000 ohms resistance across the secondary of the firstaudio transformer. Place your .001 condenser between the sliding arm of the | potentiometer and A-; do not use a reaction condenser greater than .00025.

RA210 (Christchureh): I am more » than pleased with the results obon "R, the W. 3." I.wish to substitute a variable resistance for the condenser control regeneration. "Would you give me a suitable diagram? A.:. Yes, the idea can be seen in the sketch on this page. The moving condenser becomes: a fixed one. 2. Would the resisto-grad be suitable for-a resistance? ave vee ; A.: We have not tried it, but would imagine it to be satisfactory. 3. To what lead is, the grid.return connected for a 615?-The positive. 4, Which do you consider to be the best combination for "R. the W. 3," using Philips 6-volt valve? A.: 615 detector, 609 first audio, and for quality B609, second audio. 5. I have constructed the lead accumulator described in the R.R. Some of the plates are being eaten away. Is this due to impurities in the lead? A.: It may be due to that or to the strength of the solution not being correct. J L.S. (Waipukurau).-As I sent you a * stamped and addressed envelope it is only by a "fluke" that I saw your reply in the "Record." I was expecting one by post, as.I have never previously read that page. I intend installing a lighting plant, with 80 amp. hour storage batteries. Can my five-valve set -be operated from one of the lighting plugs using am "A? battery eliminator? A.: If all our correspondents were like you we would be all the week dealing with queries. We eannot undertake to reply personally, even. though a stamped and addressed envelope is_ enclosed. Thanks for the compliment about not

reading the page. You may operate your wireless set from your lighting plant by breaking down the voltage with resistances, Another plan would be to lead directly from: the accumulator, taking off the six volts required for the set. This would need neither resistances nor smoothing. If there was any noise a choké such as that to. be described in. the: "Record" or an electrolytic condenser would cure the trouble. ° D*XNAMIC. (Dunedin): What is the ~ Correct gauge of wire for a high-re-dynamic speaker, and the approximate number of turns for a B405 output valye? . ’ A.: About 2000 turns of 40 gauge wire, and you must use a 1-1 output filter as well. Why not make a low-resistance speaker coil and operate with a 25-1 stepdown transformer? J E. (Wellington) : Can I receive Auck- ° land. and -Chirstchurch on silent nights on my local station ‘receiver? . .: No. "The particular set you mention will only receive the local station. ICK-UP (Gore): My pick-up reproduces too much base. How can I remedy this? A.: Try the effect of a -series condenser of about .00025 mfds: in series with the leads from the pick-up. 2. What is the best combination of valves for my American machine? A.: Use four 221’s and B605, or its equivalent. .°

LIMINATOR (Dunedin): I have made spools for the eliminator described in the "Record" in December, 1929. I now am unable to build up to the full 400 volts. Can the spool be used for a 200-volt winding? 3 A: Yes; when it-is finished, lift all the spool-ends.and cut your stalloid accordingly. The wire will not fall down if it is kept back: an. eighth of an inch from the ends. ges 2. What should be the size of the primary and where the tap for surging mains? oe A.: The primary would remain the same, but another 200 turns should be wound on for surging mains. 8. What would be the average voltage for gc. valve with 180 to 200 on the as . A.: 120 to 150 with 12 volts grid bias. 4, Which is the most economical rectifier, filament or filamentless? A.: There is little difference, but you stand less chance of burning out the filamentless. _ _5. Would one stalloy choke as described in the "Record" do for say 200 volts? A.: No, you need two.