Questions and Answers

Radio Record, Volume IV, Issue 23, 19 December 1930, Page 13

Questions and Answers

C H.G, (Oamaru): I have a four-valve «Ye B.D. using G.P, and a B605 power valve. What is the drain on my "B" battery ?-21 m.amps. if properly biased. ' "@& What should be the life of my "B" batttry? ‘The set is in use on an average of three hours daily -Six to nine months. 8. Would a Philips A630 be all right in the radio stage? A.: Yes, but it may cause instability. 4, Will future B.D. articles include a triode as well as a screen-grid circuit? A.: The former has often been published already,

"CAMERON" (Canterbury): Your query’ was answered in our issue dated October 17. A little observation would have saved us time in looking up references. G P.K, (Te Aroha): In what issue was * the "R" method of judging reception volume published?-August 22, 19380. 2. Could you publish a technical in-dex?-We do so annually. 3. When are time signals sent from 2YA?I-At 4 p.m. and 7.30 p.m. "RECORD READER" (Huntly): If have a Mullard four-valve receiver. Where could I obtain short-wave coils? A.: Write Spedding Ltd. Box 462, Auckland. C A.H. (Napier): I wish to construct e the "Guide" screen-gride -shortwave receiver. Oould six-volt valves be used ?-Yes, 2. What alterations will be necessary to the circuit ?-None, 8. Which six-volt valves would be best? A.: One screen grid, a special detector, a general purpose, and a 605 type. 4, Are amperites necessary when using a six-volt accumulator?-No. A B.C. (Waipawa) : Where could I ob- * tain a circuit diagram of a shortwave adapter to use with a commercial five-valve set? A.: In the 1929 "Listeners’ Guide." A further one will be published in the 1931 "Guide." 2. What is the best combination of valves to use with it? A.: The ones you are at present using are quite suitable. Use a special detector, 415 type, in the adapter. " &A UDIO" (Oamaru): Is the shortwave adapter as described in the 1929 "Guide" as good as any for simplicity and efficiency ?--Yes. 2. Where may I procure one? A.: From almost any dealer or Te Aro, Book Depot, Wellington, 8 Is the log enclosed a good one for my set?-Yes, "WACO" (Oamaru) : What would it cost to change my five-valve commercial set into an electric one? ¢ We do not advise it. It would not be worth the trouble. 2. My aerial pole on the house is five feet higher than the one at the bottom of the yard. Would it be better shorter? A.: No, worse. 3. Would you advise me to bring my lead-in to the set as I have indicated? A.: No, your aerial would be much less efficient. H P. (Blenheim) : In a recent issue in ¢ "T.aboratory Jottings’ you say the Marconi pick-up is satisfactory for the average set. Could I get enough volume for a small room from my eight-valve super. het. with two audio stages?-Yes. 2. Could I arrange the pick-up so as to get the benefit of my full eight valves? -Nd, , 8. Who stocks the Marconi pick-up? A.: The nearest agents for these, so far as we know, are Fear and Co., Willis Street, Wellington, and the C.A.S., Wellington.

A $.M. (Fairburns): One of my masts * is much lower than the other because of the slope of the ground, and my lead-in comes in from the top mast. Is that the correct one? A.: Take it from the nearest. Otherwise it is immaterial. "PEP-PUNCH" (Christchurch) ; What valve would you recommend for a one-valve amplifier, using Daniel Cells as "A" supply? A.: In the two volt class use the Radiotron 230 type, in the four volt the 415 type. 2. Using Daniel cells as "A" supply, would it be necessary to use a wet "B" battery ? A,: No, a dry one would be quite suitable. A B.S. (Onehunga): I have a_three- * valve commercial set which I have been using about 15 months. I find now that I cannot get Wellington. I have renewed my valves, but not my bat‘teries. A.: It was probably not necessary to buy a new set of valves, but new "B" batteries are certainly indicated. Af T.S. (Kaitangata): You stated in ® answer to a previous query concerning the Daniel Cell battery charger that the drain of 1.16 amps was a little high for the charging of a six volt accumulator by a nine cell Daniel’s cell charger. Would the addition of another three cells, making a total of 12, be more efficient? A.: It is certainly worth trying. 2. Would the increased voltage have a harmful effect on the accumulator. A,: No, it would be quite safe. "(VRANK" (Wanganui): I enclose a copy of a circuit for a two-valve ali-wave receiver taken from an English magazine. Would this be suitable for N.Z. conditions? A.: Probably not. In a short time we will be publishing a series of excellent all-wave receivers. We would advise you to wait for this. "(IRYSTALITE" (Wellington) : In the issue dated December 14, 1928, there appeared an article entitled "A Crystal with Unusual Volume." I have recently constructed this set for use at a place about 20 miles from Wellington, but ‘cannot get the increased volume referred to. It is just as loud with one detector as it is with two, irrespective

of the manner in which the detectoxs are placed. . A.: In the first place this is merely an experimental set which, however, will do all that is claimed for it if it is working properly. Carborundum erystals are very patchy and though they appear to be matched they may differ electrically. We would advise that you exper ment further until you get two that are properly matched. Forget about full-wave rectification which at the best of times is an experimental hook-up. GARTORIUS (Woodville) : My set has a background noise on the lower numbers of the tuning dial. At 20 it isa roar, and if I detach the aerial it bursts into oscillation. The noises are almost eliminated while it is raining. A.: It appears that there is a leak either in the high-tension wires across the insulators or switches in or surrounding your home is taking place, and

ORRESPONDENTS must attach this coupon to all queries sent to the Technical Hditor (Box 1032. Wellington). Questions arriving without it are likely to go astray or be delayed. Name of set ceseercocaccccccccccce Number of ValeS .ccococcescoc00ce Name PeoCH2S7ASSSHOBOSBAO0D00600090 Address 020000000000000000009000000 COSOSCHLLCONDOASHOOOOHOODOOOTOBOSO0OD20000 COSHH OTT LOOASOHOOTOOASOOODODSGD90G0009 Nom de plume ..coccccccevccovece To be kept in subsequent inquiries. Date cvorccccccccec cece ccoeeee Please Note:(1) Be specific 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.

. ‘ that when it is raining, the leakage is momentarily earthed. As the set goes into oscillation the noise is considerably increased, and more so as the high frequencies are approached, hence the roar. Disconnect the aerial if the noise ceases, connect the aerial up again, and tune the set to its loudest roar. Then switch on every electric switch in the house except that of the set. If there is a defective switch the roar will cease when the switch is cut off. If you locate the defective switch an electrician will fix it uP, for you. Will a set using two 112A’s satiswork a speaker ? : No, you will need at least 171’s. L622 (Christchurch) : Yes, your connections are quite in order. The resistance R3 would be 5000 ohms if you connected it from the point you have shown. You could use 3000 if it were taken from the centre point ‘of a power valve filament. LAMspA (Wellington): What is the correct bias resistance for two 171A’s in push-pull with 180 volts on the plate? -2000 ohms. 2. The residual hum in the push-pull stage is quite audible in the loudspeaker. you suggest a remedy? A.: Only the use of a potentiometer across the a.c. filament supply and adjusted for minimum hum. 8. What value of resistance for volume control should be used in the push-pull stage? A.: A volume contro] should be connected as is shown in the recent deseriptions of the Loftin-White. Value should be about 200,000 ohms. [ -~.

4, Would you comment on my diagram fox screen grid detection on A.: Connect the screen to 90 yolts and by-pass it with a quarter of a megohm to earth, but we do not advise the use of such a circuit. It would be advisable to spend money and time on 245’s in the audio stages instead of screen grid detec-: tion. ‘5. Do you think a vertical aerial such as in the enclosed sketch would be any value for shortwave? A.: For experimental shortwave transmission it would be interesting but very little can better a 70 to 100ft.straight aerial, except two such aerials in opposite 6. What do you think of my rectifying system ? A.: We do not like the aluminium and lead rectifiers, and the Government dislike them to the extent that they prohibit their use, A S.H. (Auckland) : Do you know who * happens to be the agent for Mohawk sets? A.: We regret we do not, If any reader happens to know we shall forward the address on to you, VERTONE" (South Island): Is the audio amplifier of my set inferior to the Loftin White and could it be in- corporated in the set? A.: A little, yes, but unless you have a very true ear for music, particularly in the upper registers, you will not appreciate the difference. It could not practically be incorporated in your set. It is superior on the reproduction of records provided a good pickup and good speaker is used,

2. What is meant by the super exact ‘balancing of all parts giving true clear tone? A.: It means that the impedances are carefully matched and this is done in every good set. ‘ . 8. Is it.an illusion that. tone sounds. better to me through- my receiver than on any. others? _A.: While we would not go so far as to say that the tone of your. set is any better than that of any other good model receiver, we. would add that it isa long way in advance of many, . 4. The L.W. I understand amplifies up to 10,000 cycles in a straight line. I was told that this was of no use, since the New Zealand ‘stations do not. broadcast above 6000. A.: Quite so, hence the practical ‘limitations of the L.W. If frequencies above 6000 are put out blasting takes place. 5, Would the L.W. give more music per note on records or broadcast reception? i: A.: If you are looking for the overtone and: want real brilliant upper reproduction then the L.W. is the amplifier you are looking for.’ Record reproduction is really splendid. True, it is a tone to which one must be educated before it can be properly enjoyed, W.D. (Invercargill) : I constructed ¢ a kit set, but I cannot make the rf. stages oscillate. . I wound 70 turns. of d.s.c. wire on a Qin. former. : It is as well for your neighbours that you cannot make your r.f. stages oscillate. The detector is the oscillating valve and the r.f. must be perfectly stable before good reception is possible. You do not state the gauge of wire used in winding your coil so we cannot tell you if you have enough turns or not; 70 is the correct number for 26 d.s.¢. wire. Try increasing the detector voltage. 2. How can I stop the speaker from rattling? A.: By slackening the diaphragm, but in doing this’ you will make it more or less insensitive. Speakers of this nature will not handle a great deal of volume without distorting. 3. I have left out the by-pass’ condensers because I am running on: batteries. A.: They would be better in because they tend to stablise the set. "SHORT" (Temuka): When tuning short-wave coils the set ‘reacts -at a certain point, depending on the frequeney, and then goes out of oscillation. . A.: Oscillating on short-wave takes place in a manner something like this; but examine your reaction condenser and see that it is quite in order and try a new gvid-leak. If necessary, a grid condenser, "(NROMDALE" (Otago): I have plenty of room for a multi-aérial system, What do you advise? ’ A.: Try two Beverage aerials, one running north-west to Australian stations and the ‘other north-east to -the American, Such an aerial was fully described in the "Radio Record": a little while back. Arrange a switching device so.that you can have either one at will. If you want to use the. ordinary type aerials, tun them in the same directions and for local reception one in line with either 3 or 4YA, whichever comes in: the best, and about 20 feet from the ground. af B.B. ‘(New Brighton): Does my re- * ceiver contain two r.f., one detector and three andio? A.: As far as we know, -yes. 2, What valve do you recommend for each stage? A.: For all but the last stage, UX 201A’s or .221’s and a power valve of the 171A, type in the last socket. B 8.D. (Wanganui): Only one: filament * of the resistance lamp in the A and-B charger .in the 1930 "Guide" glows. _

A,: You appear to have it connected up incorrectly, The 16 volts should each go to the extremes of the resistance such . as you have shown diagramatically 32. sketch B, From what you say it: appears that: the terminals ‘on your. valve have heen wrongly marked. . Use the valve in the position it appears to go best. A cross over like this, although . unusual, is not impossible. D. M.M. (Dunedin) : Would less than 6ft. between a double aerial be satisfactory? It is unlikely that less than 6ft. would be any improvement over. the single wire aerial. 2. What is the cause of motor-beating and bubbling in trying for distant stations? A.: It is probably due to: the detector valve or the grid-leak. Try another. 5. Is-a pentode valve suitable in my set? . -A,: Rather than a pentode we wobld advise one of the new type of high gain power valves, such as B406, which, by the way, is a four-volt yalve. ICK-UP" (Auckland): When I turn the volume control of Loftin-White full on the set whistles. A.: You do not state at. what volume, relatively speaking, the set overloads. We presume you have tried reversing the connections and using a different pickup. Furthermore, another screen-grid valve may help. Are «you using the resistances described in the’ most recent description of the L,W.? 2, When I attempt to work the amplifier after a erystal set the output howls adly A.: For local station use the amplifier should be preceded by a tuned: coil such as shown in: the recent series, "PE ANUT" (Christchurch) : Where can .. I obtain a circuit and specificstions for an-a.c. short-wave adapter ‘to use with a screen-grid detector on my set? A.: A super-het. would probably be quite. in order, though if you used R, the W, Two plugged into a gramophone jack ° you would be much more certain of results. A suitable circuit for the gramophone jack will be described in the 1931 "Guide." "WAIKATO" (Taupivi) : I have made certain alterations in the ILR. a.e. set deseribed in the 19380 "Guide." I want to use this for short-wave a,c. .A.: We think a much better plan would be to wait until the 1981 :‘"Guide" and make the special a.e. set that will be’ described therein.

2. On which turn will it be necessary to get the tapping for L3? A.: Halfway. ; 8. Where could I get a suitable circuit for a power pack for this set? A.: The 1931 "Guide,’? which is now in preparation, . "DUNG" (Waikato): I have been using bare copper wire on my aerial, and after a few weeks I noticed that I did not get the same results as before, so I replaced it with enamelled copper wire, which has made a vast improvement. Would corrosion make thir difference? A.: In all probability, yes. 2. How would I connect a condens in series with my aerial to improve short waye reception? a.: Connect the aerial to one side of the condenser and the lead to the sei on the other. : 8. Could I improve the volume by inereasing the B voltage? A,: Yes, With such a valve as B405 in the last stage you would. need 1385 volts B with 124 volts bias for best results, 4. I notice on certain nights blue flashes can be seen on the poles of the high-tension wires that run past my place. How can my reception, which is suffering as a result, be improved? A.: This is a definite case where you should consult the district radio officer, ‘who will probably be, able to do something for you. 5. Is the enclosed sample of insulated wire suitable for a lead-in?-Yes. " NH" (Nelson): Where should I connect the tone control in my set? A.: Between the output terminals and the loudspeaker, providing, of course, you have an output transformer or choke and. condenser output. 2. What is the value of the condensers jv the enclosed circuit? _ 4.A.: Approximately .001 mfds, 3. hich is the best system of tone control? A,: A 10,000 ohms variable resistance in series with a .6 mfd. condenser across the secondary of the last audio transformer. 4, Is a power detector satisfactory for the Browning-Drake? If so, can you give me the circuit? _A.: It is quite satisfactory, and the circuit was given in last week’s "Radio Record." (Continued on page 30.)