Questions and Answers

Radio Record, Volume VI, Issue 11, 23 September 1932, Page 10

Questions and Answers

"DUZZLED" (Berhampore): What. is the best erystal circuit to separate 2ZW and 2YA? A.: The "Rejecta 2," described in the "RR," dated June 19, 1931, 2. What. are thé. coil specifications. using a Sin. former and a .00025 variable condenser? A,: As given in the article describing this set. . 3. My aerial is 60ft. long and the earth 80 feet. Would I get better results with a shorter earth, and is the aerial long enough? . A.: Short earth connections: are-always tLe best; 60 feet is long enough for your aerial if it is efficient. If not, crystal re-. ception would he greatly improved by using 100 feet. "TNORMO" (Papakura): Does static injure a radio set? A.: No. , 2. My set hag a statie control. Is it advisable not te use this except when static is bad? A salesman told me that when this control was full on only five valves are -working. A.: Your static control is merely a tone control, which’ reduces the intensity of static by cutting off the high frequencies. It certainly does not cut out any valves. 3. In the event of American valves not being available after the Ottawa Conference, what make would you advise for my set?

A.: We.do not think the Import of yalyes will be in any way influenced by the Conference. However, if. you wish to use English makes, American equivalents are available in nearly all of them-Cos-sor, Osram, Philips, Mullard, ete. R L. (N.P.): Why does my four-valve * "Neutron" set (less shielding) go very much better minus: the grid leak, which is in parallel with the grid condenser, except when oscillation, which is hard to vontrol,; commences with a violent ndise like an exhaust from a motor? The volume is excellent. A.:, Your. grid leak is probably defective. We occasionally find samples marked 3 megs, which on test with an ohmmeter show as much as 10 megs. Keep only to the better makes. The instability is easy to. understand in that. the grid, without the grid leak is more or less up in the air. Your set still operates with the grid leak out because there is always a certain amount of leakage. in the valve holder and through the grid condenser, and perhaps through the grid leak holder. 2. My wavetrap made according to the 1931 "Radio Guide’ and using a .0004 fixed condenser in conjunction with the ,001 compression condenser, is absolutely useless for tuning out 2YB. A.: Reduce the number of turns on the coil by ten or so. 3. Where could I get directions for making up the "Outspan Five’? A.: Unfortunately we are completely sold out of the issue in which the description of this set appeared. However, in the next "Radio Times" the "1932 Outspan" will appear. Briefly, it is a fourvalye battery set using two stages f s.g. vf, s.g. detector, with pentode output. The stages have been ganged successfully, even though reaction is ineorporated. Altogether it is, in our opinion, one of the best dx battery sets we have ever described. | "(XEIMIST" (Auckland): I have made .up the "Outspan Five,’ and it is not too selective. A.: Reduce the number of turns on the , aerial coi] to 16 and also insert, if it is ’ still too unselective for your needs, a 0001 fixed condenser in the aerial. 2. What are the: lowest numbers of turns on the primary coils, using 1fin. . formers inside 2in, formers?

A.: We. do not know quite what you mean by "lowest." The’ practical minimum would be one turn, but you would hear nothing but locals. Try 16 on the aerial primary and 25 on the r.f., and 25 the detector; lin, formers would be of no advantage. The turns are close wound, the bottom primary turn and bottom secondary turn are approximately opposite. N. Zi. 37W (Shannon) : Could you give me the specifications for an 80 mn.h. r.f, choke? . A.: An lin. diameter wooden rod, with 5 slots 1-Sin. wide, tin. deep, and ‘1- Sin. apart. Wind 200 turns 36 d.s.ec. in each slot, making a total of 1000 turns. 2. Could you give me the number of primary turns for an inter-stage primary in a sereen-grid r.f. stage? The former is ‘1din. diameter. A.: 40 turns of 30 d.s.c. would be quite satisfactory. UEERIB" (Balelutha): I have a t.r.f, all-electric 7-valve comyercial set. When the volume is turned toward maximum the set oscillates and bangs when the dial is turned. Valves are O.K. When the dial is stationary the set is all right.

A.: Do you mean tuning dial or. yolume contro] dial? If.the latter then your volume control is defective and should be cleaned and tightened or replaced. If the former, the rotor‘of the ganged condenser is probably. not efficiently earthed, Solder a pigtail connection between rotor and chassis. Keep leads from eaps of s.g. valves well separated, L. S. (Christchureh) : Is it of any bene~« fit to shield coils and valves in battery set? . A.: It depends on the ciréuit you are using. If the set ‘is perfectly-stable without shielding, it is of course not necessary. But with modern s.g. sets, however, shielding will be found essential. 2. Is "A416 suitable for detector, first and second audio? .: Substitute second audio, with a B409, and do not forget appropriate bias. O.K, 3. What New Zealand stations could I get on:a 3-valve set at fair speaker strength ‘with ‘battery, aerin} and location all.in the set’s favour? A.: At, present you should get all New Zealand stations and the main Australians at fair speaker strength. EST" (Hokitika): What is the best combination of valves to use in a 5-valve Fada neutrodyne? Till now I (Continued on page 23.)

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s cmpeeeanememnal y Questions and Answers ; (Continued from page 10.) have been using 201’s in the r.f., B.T.H. detector, and 201A’s in the audio. The combination has not worked too well, and I substituted the r,f. valves’ with 609’s. This has improved things, but the set oscillates: badly and there is mushiness in reproduction. A.: Thé 609 is suitable for detector and first audio. Use 201A’s in the r.f. stages, and a 605 in the power stage, If your set still handles badly it needs re-neutralis-ing. "QCREEN-GRID" (Woodville) : I wish to make up.a set of rf. transformers to be used with 224 valves, How many turns of 88 gauge enamelled would I require on a lin, former for the prim- _ aries? A.: 45-50 for interstage primaries and about 25-30 for aerial primary. 2.. With 100 volts on the plate of a power detector, what is the correct value of the bias resistance? . A.:.15-20,000 ohms. ‘A W. (Wellington) : What is the cause ** of 2YA breaking through at several{ points on the dial lately? Until about a fortnight ago I could tune him out. outside 700 to 740. Now it comes’ in between 680 and 800. A.: We believe that 2YA has increased . power appreciably lately and this. would account ‘for the apparent lack of selectivity in your set. Reduce the effective length of your aerial with a .0001-.0002 mfd. fixed condenser. 2. Is the 750 ohm. resistance between one end of the Béverage aerial and earth essential? A.: It depends on the aerial, Some dxers find this resistance an advantage, while others report increased sensitivity when it is cut out. 8. The device: you mention will increase selectivity, but not power. N.B.-We have noted your suggestion re an article on aetials and this will appear at a later date. yp 5Mo (Picton): Where could I obtain @ commercial 280 yolts d.c. "A" eliminator? A;: Communicate with Fear and Co., Willis Street, Wellington, or Johns Ltd., Auckland, M. H. (Canterbury): I cannot _ hear * 2ZW during the day on my 7-valve super het. Jt comes in quite well at night, _. A.: This is obviously due to your locality, and we cannot help you. "CURIOUS" (Huntly): I have an 8-valve commercial set which has developed a loud hum. The mains trans-formet-and speaker are O.3C, A.: Ten to one the trouble lies in a ' defective bias resistor or in one of the powerpack" condensers, Your best plan is Ea in a qualified serviceman. ‘D NGO" (Auckland): Can I use a ~~ battery operated shortwave adaptor with an 8-valve all-electric set? A.: Quite easily, though why not use an a.c, adaptor and plug into the detectot socket for the power? 2. What batteries would I need for the aboye adaptor? A.: A 60 volts "B" battery and a 2, 4, or 6-volt "A" battery, depending on the valves you are using. 3. What results should I get with the above? A.: At Jeast all the principal shortwave stations of the world, F A. (Christchurch) : I wish to store.an *. "A" battery for two months. What shall I do? A.: Charge the battery fnlly. Empty the battery of the liquid and rinse it out with distilled water. The batteries can then be stored for six months or so without detriment,