QUESTIONS AND ANSWERS

Radio Record, Volume VII, Issue 14, 13 October 1933, Page 27

QUESTIONS AND ANSWERS

L. H. (Wakefield): There is no output : transformer shown in the cireuit vf the 1933 Night Hawk," described in the "Radio Times" recently. Why is this? A.:. This set is intended to be used with one of the latest permanent magnet speakers, which incorporates tapped output transformers. ; 2. What would the results be if the matching ‘transformer were omitted altogether? A.: Both tone ‘and volume would suffer appreciably. Ifyou have a cone speaker. your best.plan would be to fit a tapped output.choke, as shown in the circuit diagram of the "1932 Ovtspan Four," described in the October, 1932, issue of the "Radio Times." 2194. (--): Full details for winding all types of r.f. coils for both short-wave and broadcast bands are given in the 1933 "Radio Guide.’ m 2. What is the maximum plate voltage I can apply to my one-valve set? _A.: Anything up to 150 volts, though you will find the set will work best with a plate voltage of from 223 to 45 volts ATHS" (Wellington) and others: A three-valve short-wave receiver, ‘employing the. latest type valves, which draws .its plate and filament supply from any ‘type of a.c, broadcast set. will, be described .in. the November: ‘Radio Times," and we advise you to wait for this rather than to build up your-own converters, as these, when home-built. are rarely. satisfactory. D: D. (Dunedin): The article on building ‘a "‘Universal Power Pack" appeared in the last March issue of the "Radio Times," You will have no difficulty in securing a full kit of parts. FB, (Dunedin): Can I replace | the 227’s in'’my set with 56's without any change in the wiring, and, if so,. World it improve the set's perform‘A.: Yes, though whether any marked improvement will be noticed is doubtful. . Will replacing the 227’s with 56’s at a time spoil the. sete perform ance? .

A.: No, not in the least, though it is usually more satisfactory to replace the whole set at once rather than one at a time, "Ruas" (--): I have a midget condenser with plates of the size shown in the sketch. What is its capacity? A.: Approximately .0001mfd, — 2. What would be its approximate tuning range in metres if it were employed as the tuning condenser in a short-wave set? : A.: This. depends upon the size of the coils. Three sets of coils would probably be needed to cover the short-wave band. "7 OLU" (Auckland): See ansaver to 219A, opposite. I S.W. (Wakefield) : I have a five-valve * battery set, operated in conjunction with a 100ft. aerial, 60ft. high. . Is this suitable for dx work? A.: Yes, quite suitable. 2. Where could I obtain the circuit of a two-valve all-wave battery set? A.: In the "Radio Times" dated April, 19338. 3. Is it necessary to hold more than one license if two sets are used by the same owner? A.: No. * AUPIO" (Auckland): My present earth consists of a 4ft. galvanised pipe buried under the house in very. dry ground, as shown in my sketch. How could I improve it? A.: Your best plan would be to drive a 4ft. pipe in the nearest corner of the lawn, and then run a lead under the house and up through the floor to your set. You will then be able to keep this earth damp by pouring a bucket of water, into which a handful of salt has been dissolved, over it every fortnight or so. 2. What is the correct value of gridleak to employ with an A415? A.: Anything from 2 to 5 megs. 8. Does a faulty grid-leak cause intermittent crackling? A.: Yes, though a number of things, such as a faulty earth, loose connections, a defective audio ‘transformer, a-run-down "B" or "C" battery, ete., can also cause distortion. "BEGINNER" (Wellington): My set is not very selective. Where could I find details of a suitable wave-trap? A.: In the July "Radio Times." The circuit you enclose is not of a wavyetrap, but of an aerial tuner, which, from the point of view of sharpening up tuning, is not as effective. GER (Kakanui): We have a six-valve Thermiodyne battery-operated set which is about seven years old. It was working when we switched it off in America to bring it here, but it has refused to-go since. Do you think it is powerful enough? ; A.: This is obviously a case for a serviceman, as there is no indication as 10 where the fault lies. Your set’ would certainly be powerful enough, and though old will give you many years of service yet. Your best plan would be to take it to a qualified serviceman. ; J S. (Wanganui): Replace your valves * with a 280. 247, 235 and q 224A. Wither of the makes you mention would be suitable.

2. I have logged 87 stations. Is this good for this type of set?’ ° A.: Very good, You certainly cannot expect many more. 3. My set has developed a loud hui. What is the cause of this? A.: It is impossible to help you, as hum can be due to so many different causes. It may be due to one of your valves, as judging from your first question these are getting old. H. (Te Puke): How can I connect a microphone to my set? A.: Break the lead to the cathode of the detector valve and insert it there. 2. How can I connect a pick-up to my set? A.: Connect it across the grid leak 3. In the instructions for building the "All-Wave One," described in the 1933 "Radio Guide," the value of the differential condenser is given as .00025 mfd. Is_ this value correct, as I have been unabie to buy one so far? A.: Any value from .0002 to .0003 mfd. would be suitable. KF W.A. (Christchurch) : I have a sixvalve battery set. ‘The tone is inclined to be deep and muffled, and though it is very pleasant to listen to,. articula-| tion is rarely clear. How.can I improve the tone? A.: The high-frequency response would be improved if you removed any tone control condenser which may be present. This would probably be connected from the plate of the output valve to earth. P V. (Te Kuiti) : Your five-valve super- * het. igs quite suitable for dxing. Highty feet is quite sufficient length for your aerial, though you may notice a slight improvement in signal strength if you increase it to 100 and increase the height at the far end to 35 or 40ft. G. H.W. (Hauraki Plains) : About three years azo I made a five-valye Browning Drake from the description in the "Radio Record." It has given very satisfactory service, but it is now rather out of date, and I would like to build an up-to-date set such as the "A.V.C, Superhet." My constructional experience has been limited to t.r.f. battery sets, and I have

Information Coupon {To be used with all requests for information.) Name of set Model" "eee etme eee eeeeeeaeees Name Address FOTO CSS SHESSHSSEOSOAEE SEO OES PSSA SESSESCEESSESESESEOS* "FHSS SHHSSSHSSSOSSHEEHEHOSEOHOSSHSESOSES SEHR TRAE SETHE HESS ESESOEESSESEOYE Nom de plume .........-eeee To be kent in subsequent inquiries Please Note:- * (1) Be specitic ana obriet, tabu lating, if possible. Write legibly and 6p one side of the paper. (8) We do not design circuits . (4) Limit three questions . unless ' I/+ is enclosed. (5) Postal queries limit, 3 questions. Enclose stamped and addressed envelope and 1/- fee.: «2

had no experience either. of superhets or of sereen-grid valves, A.: In the circumstances we do not advise you to begin a.c. construction by , building an A.V.C. superhet, because a certain amount of experience is required before a set of this type can be built successfully. If you would like ‘to comMence with a superhet, build the "Hight Star Five," described in the August "Radio Times." This is a five-valve superheterodyne employing the latest type valyes. Its construction is quite straightforward and is explained in detail in a lengthy article, which is well illustrated with diagrams and photographs. ‘This set is capable of a very fine performance, and we are sure you would be pleased with it,