Questions and answers

Radio Record, Volume IV, Issue 17, 7 November 1930, Page 14

Questions and answers

GPARKS (Christchurch) : Can a transformer which reduces 230 volts to 12 be used for charging a 6-volt battery or otherwise supply a power pack for 6-volt valves? A,: If enough current at 12 volts could be supplied it could be rectified and smoothed to supply the power for sixvolt valves. You would need a resistance of 6 ohms to regulate the voltage. The smoothing apparatus would consist of a choke such as that described in this week’s "Record," and a 2000 mfd. electrolytic condenser. 2. Which is the better for a shortwave adapter-the one in the 1929 "Guide" or the detector stage of "R. the W 2"? A.: There is very little difference. The one from the "Guide" would be possibly easier to construct, but omit the 1Imfd. by-pass condenser between the plate and earth. 8. How can hand and body capacity be stopped? ‘ A.: The best way to ensure that there will be no body capacity is to have all moving parts of the condensers earthed to a metal panel. This means that a separate coil must be used for reaction. MAc4A (Heretaunga) : I have incorporated a 30 ohm rheostat between my battery charger and set as you recommended, but get a noise loud enough to spoil reception. A.: We took it for granted that you would be using smoothing devices betweeen your charger and your set. Evidently you did not do this. Try a 2000 mfad. electrolytic condenser across the charger, and if hum still persists use a choke such as described in the "Record" this week, This

v will be followed by the resistance, and it would be advisable to have a voltmeter permanently installed across the smooth output to check up on the voltage. FRANK (Mercer): On two occasions my set of valves has blown out when the set has not been turned on. A.: As yours is a commercial set you should contact with those who sold it to you, for undoubtedly there is something wrong. A fuse between the "A" and "B" battery would prevent this re-occurring. 2. Would the H.R. or B.D. set give better results than a 5-valve neutrodyne? A.: Yes, either of these should be better than a neutrodyne. 8. Can you recommend anything better than either of these sets for selectivity distance getting and tone? A.: Yes, we propose to describe the two stage screen grid B.D. very shortly, and this should be an improvement on either of these two models. . Do you recommend four or six-yolt valves? A.: Six volt are more sensitive, but if you have a set of four yolts it would not be wise to change them until they are done, 5. Where can T obtain detailed deseriptions of the two sets in question? .: The B.D. was. described in the 1929 "Guide" and the H.R. in the 1980 edition. . 6. I have an earth of tinned copper wire, 80 feet long. Is this all right? A.: If at least 70 feet are coiled and buried in the earth-yes, The coil should be kept damp. M.K. (Waitanguru): Where ean I * obtain advice concerning the Daniel cell charger? A.: It is being described very fully this week. 2. Where can I obtain serap zine? A.: A foundry should be able to supply it to you. You could write to one of the big city newspapers who may have some old blocks they would be only too pleased to dispose of. Ke RAND (Khandallah).-Will you sup- ™ ply details of valve base coils for use a .0003 moving condenser? A.: Reduce the capacity to .00015 by a 0008 fixed condenser in series with the. tuning condenser, and wind. the coils described in the Questions and Answers page recently. REVAL (Morrinsville).-The lower frequencies on my set are received very weakly, Can they be improved? A.: Some sets bring in the low frequency stations not as well as the high, an this evidently is what is happening in your ease. You cannot do anything to overcome it providing everything is in order. It might be worth mentioning to your dealer. KARI (Whangarei) -I cannot get Japan on my set. Can you suggest a better combination of valves? A.: No, but your valves may need renewing; other than that we are at a loss to make a reasonable suggestion. If you are not satisfied with the resulis you are getting you should write A.W.A., Nimmo’s Building, Wellington. Y4 (Palmerston North): I have recently purchased a short-wave adapter for my set, but cannot hear the sta-

tions strongly enough when the set goes out of oscillation. Can a stage of radio be added? A.: A stage of radio is not a practicable proposition. Try altering the grid leak-it should be as high as 10 megohms for short-wave-and increase the detector voltage. Froxy (Hokitika)-Can I make a ’ shortmove adapter for my set, and would would be the price? A.: A super heterodyne adapter was described in last week’s issue, and an ordinary adapter has been described in the 1930 "Guide.’’ In neither case should the cost. exceed £5, and it is probable that it would not be as much. We do not publish blue prints. J.C. (Auckland).-What _ stations * other than the New Zealand and Australian should I be able to receive on my six-valve set? Can I receive stations after midnight? A.: As so much depends upon locality it is difficult to say whether or not your results are good. Your valve combination appears to be a good one, though perhaps if you replace the PM.6 in the last stage with a PM.256 you would ‘do better. See the DX club notes for hours of reception of different stations, 2. A month after I purchased the set one of the valves burnt out. A.: Without investigating the set we cannot tell you why this happened unless the valves were at fault. Would a burnt-out transformer cause a howl when the set is turned on to six valves. A.: Quite probably the transformer is at fault. GIGNAL (Dunedin): Can ,I add another valve to my Midget set? A.: No, the set is designed for the number of valves now operating. and an increase would not be economical. ‘iD F.B. (South Dunedin): I have a de- * tector and two audio stages, using g.p. valves. Could I obtain better results by using different valves? A.: If you wish to continue using Philips use 215 ag detector, 209 as first audio, and B205 in the last stage. The B.G.E., 31-37 Taranaki Street, Wellington. were the New Zealand agents. 2. I wish to receive 2FC, 2BL, or 4QG with sufficient volume for dancing. How ean I do this? A.: By using your detector to feed a power amplifier, but even then you are ambitious. You really need.a set with high frequency amplification. 3. Why can I not receive 3AR or 7ZL? A.: These are on low frequency, and evidently your set will not go down to those frequencies. 4, What is the correct C voltage? A.: For B205 with 90 yolts, about 9. ‘5. My set is variometer tuned. Is this efficient? A. :Yes, but not as efficient as condenser tuned. 6. Could I receive Morse on extra coils? ' A.: Yes, but it would be difficult to design the coils, and then you would only get commercial stations. D X.. (Dunedin): On a four-valve set * should I be able to get 2YA without interference from 4YA, and 38YA without interference from 4ZM or 4ZL?

A.: It is most unlikely that you .will receive these ‘stations without interference, as one stage of screen grid is not selective, 2. The tuning is very broad. How can I make it sharper? x A.: By using a wave-trap, by incor porating loose coupling in the aerial citcuit, or by using.a shorter serial. 8.-The set will not oscillate below 315 meters. I am using 18 volts on the detector. A.: Your detector is not high enough. Try 45, or if that causes instability, 224. 4. Would .0003 reaction condenser be too big or too small for the job? A,: It would be the right size.

c ISTENERS 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 Number of Valves eeeesccecccccecce Name Addresg fee oewooeoreoecoae se ooeeooos ees atrecaeecorta00s0eeo00000 SSPSHOOACHHTOOLOCESOEEHE De resroerereersoesOD Nom de plume .....sccccceeccccccuse To be kept in subsequent inquiries. Date .c.eccecevecsecces Please Note :- (1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side of the paper. ; (8) We do not design 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.

G M. (Dunedin): Can a 20 ohm. rheos- * tat be used instead of the amperite in o the W. Two’ ?-Yes, a Can one of the windings of the earbe used as an r.f.c.2-No. Can you, send me a diagram of how ‘to i valve base coils for the Cossor Melody Maker? : The making of valve base coils has been in the 1930 "Guide." You will have to reduce the capacity of your eondenser by a suitable tuning condenser and following svecifications given for a .00015. Probably you will need a .0002 fixed condenser. A. B.S. (Timaru): Where does the extra terminal go when connecting a pentode to a set? A: To the highest B plus tapping on your battery. Note. you for your offer. It should prove very interesting. 4%. (Taupiri) : I made the short-wave described in the 1930 "Guide." With several adaptations, I receive Morse and static but no broadcast. Apparently you are not used to short-wave tuning, as when you are receiving morse you are oscillating, and to receive broadcast you must be on the verge of oscillation. You should have the description in the "Guide" as you may now be getting a certain amount of hum. We know of no better . ac circuit. You should have used a coupon. oJ ACKO (Auckland) : I want to replace the yalyes in my four valve B.D. What do you adyise me to use? A.: You ean still keep using the A609 in the radio stages. Koz the detector try 615 Philips, or PM6D Mullard. For first audio any of the following: A609, PM5X, 221A, L610. For the last stage: B605, PM256, UX112, P610. dA, C.B. (Rotherham): Volume has bef come considerably reduced and I have checked over all the connections. HRyerything seems O.K. A.: We regret we cannot help you as you have given us no clue to work on. Contact the dealer who sold you the set, H H. (Christ church) ; Can A and B ® current bet taken from a "B" eliminator? A.: No, the winding on the secondary will not supply enough current. C. D. (Auckland): My set will not oscillate when the aerial is connected to the centre tap of the coil and the earth is on, but when the earth is removed it will oscillate freely. A.: This is due probably to damping effects of the aerial which are countered when the earth is removed. 2. Why does 1ZB come in stronger than 1YA? . A.: Probably your set amplifies frequency in the Feelon of 1ZB greater than ose e near 1Y. ‘A SRLINE (Featherston) : With the detector rheostat on about a quarter turn and the amplifier on full I can get only very weak strength. When I touch the first valve there is a whistle,

A.: This appears to be due to poor emission. ‘The valves are paralysed and should be replaced. ((OILFORMER (Hikurangi): Please design secondary and reactions coils to eover the waveband from 20 to 80 metres. Ribbed formers 2iin. outside diameter secondary wire 22 s.w.g. bare spaced an eighth of an inch, wire 30 dse. tuning condenser ‘0001 slow-motion reaction condenser, 0002, valve A615.

dy Cc. (N.E. Valley): One of your * answers to my queries did not seem to agree with what I had worked out myself, This is in relation to the number of turns on the primary of an r.f. transformer. I worked out to be about 14 and you say 11. Which is correct? A.: Both; the impedance of the valves varies according to the frequency it is receiving, so that anywhere between 11 and 15 turns would be correct. 2. I have a 201A in the last stage of my 6-valve set. The signals do not seem to be as loud as they should do. A.: The 201A should not be in the last stage. Put in a power valve. In respect to the first audio valve see that the primaries are not reversed in relation to the secondary winding. ANGUS (Wanganui): I am troubled with coupling between the rf. and — coils of my 4-valve screen-grid set. A.: Try a imfd. by-pass condenser across the radio and detector battery lead. Do not use a common lead in the "B" battery leads to the s.g. and any other valves. Use separate leads and wiring, otherwise place large radio frequency chokes in leads. This is a common complaint in your type of set. Reduce the grid leak value and look very carefully over your audio side where oscillation is really taking place. 2. Are the signal strengths referred to by Sellens of *phone or speaker A.: Both. If you consult the table which was published a short time back you will notice that some of the higher numbers refer to speaker strength. Others are ’phones. 8. How is the centre tap of the variometer volume control in a 5-valve Stewart Warner neutrodyne connected to the rest of the set? A.: The two grid returns of the rf. valves are brought to the centre tap and the outside terminals go to the "A" battery. C V.N.B. (Feilding) : I find the voltage ® supplied by my home-made charger is correct, but the charging rate is too high. When I bring the voltage down the amperage immediately jumps up. A.: This is quite correct; the higher the voltage tised in charging the lower the amperage and conversely the lower the voltage the higher the amperage when using apparatus of this description. You need a power clarostat (Radio, Ltd., Auckland) or a power rheostat (National Electric Engineering, Wellington). You

might try four yards of 18 gauge nicrome wire in series with your lowest tap. MUSs#Y (Nelson) : When listening to 2YA reception is mushy, more so than any other station. A.: This may be due to your locality, as your set would hardly distort on one station. , K A.D. (Hawke’s Bay): Could you * give me the address of "Crystal and One Valve, Auckland"? A.: Ve cannot make addresses public without the wish of the person concerned, but if "Crystal and Valve" cares to send his address to us we shall forward it on to you.

Band. Secondary. ‘Tickler. 16/27 metres 24 4 27/48 6 44 47/84. 11 8