Questions and Answers

Radio Record, Volume VI, Issue 4, 5 August 1932, Page 10

Questions and Answers

PRS IRELESET (Nelson).-I get 2ZR all over the dial. What can I do? A.: Instal a wavetrap, such as was described in the "Radio Guide’ for 1931. ABRENGA (Waikato)-I intend building the 1931 superhet. adaptor described in the "Guide" to attach to my 45H. Can I use batteries for suppiying the plate current of the 227 valves? A.: Yes, but why go to that trouble when you can draw the power from your set? ~ 2. How would I derive the power from my set? A.: By making a connection on the set side of the field coil of your dynamic speakey and taking this through a 20,000 ohms yariable resistance to the adapter.. If you intend to construct the adapter build it on a metal chassis and place as many of the components as possible underneath. GNORANT (Waikato)-About 15-3 minutes after my set is switched on it fades to about half strength, but after about 9.30 p.m. the set behaves quite satisfactorily. A.: You leaves us in a maze. Frankly, we cannot help you. Your trouble may be in the set or outside it, and without instruments diagnosing the trouble is hopeess. -D*414: (Kingsland).-Do I use more power by using an inside aerial than an outside one? A.: No; your set uses the same amount of power irrespective of the amount of signal picked up.

Moru (Hinui)-Can water from a concrete tank caught off an iron roof be: used for the Daniell cell charger? A.: It: may be all right, but a better plan would be to collect it in an earthenware vessel. 20 (Dunedin).-I recently replaced the valves of my Radiola 20 with Phillips 4 volts, and had the set re-neutralised, The set oscillates more readily than before, and is apparently less selective, Is this any fault Ay: This is due to the newer valves being more efficient. Reduce the voltage on the detector valve to about 223. The set is less Selective for the same reason. 2. Would a six-valve set with two dials convert to a single dial successfully 7-Yes. . A R. (St. Leonards).-A four-valve * WHammarlund Roberts set was fully described in the 1930 "Radio Guide." T P. (Nelson).-My set distorts although * TI have had new valves and batteries. A.: Probably the bias is wrong. With 605 and 90 volts "B" you should have about 124 volts. Your valves appear to be correct, but it is impossible to get at the root of the trouble without using measuring instruments

TTHANKFUL (Oamaru): The "Outspan" goes well if one of the coils is uncovered, but it will not oscillate if it is covered. Would it do so if I added a few more turns to the tickler? A.: Probably. The coil can is introducing a certain amount of damping. ~ 9. Could I use enamelled wire instead of. d.s.c. without altering the number 0: turns?-Yes. . of A.H. (Wellington): How many turns * need I put on the coils of a regenerative set with a erystal detector? . A.: Using a Qin. former, with 26 d.s.¢. wire, you require 72 turns on the secondary, 80 on the primary, and with a ee reaction condenser 20-25 on the ickler, (Rcuir (Christchurch).-Apparently ’ your battery is connected correctly, and its seems as though the meter ter-minalg-have been réversed, |

its 2, When I switch on there is sometimes a low roar in the speaker, which grows in volume every second, When I change the detector valve it does not happen. A.: A microphonie detector. Hither put a lead cap or an internally padded cocoa tin over the valve. 3. What is the best way to tune in a station that one has not the numbers for and can I use one dial instead of two? A.: Your best plan is to look up the known station near wavelength of the wanted station, and search in the vicinity. The two condensers can be ganged, but it requires certain internal altera-tions-maybe new condensers. It would not be inexpensive, B S. (Wanganui R.): Is a 3 x 2tin. * former suitable for the "Outspan Five’? .. _ A.: Do you mean for the coils? If so, is a little big, if you have to use coil cans, ; 2. What is the size of wire and how many turns should I use for .00035 -coydensers, and .0002 differential condensers? A.: The’ secondaries require, using 24 d.s.c. wire, 60 turns. Primary, aerial coil, 20 turns; r.f. coil, 30-35 turns; re- action coil, 15-20 turns. 3. We regret we cannot supply the wiring diagram. It will be the same as that published,

H P, (Matakana): Are the following * yalyes suitable for a four-valve Courier: A425, A415, B406? A.: Leave B406 in the last stage, but this valve in the second last stage is entirely wrong, in that it is a power valye. which draws a large current and is liable to saturate the primary of the last transformer, This valve should be replaced by A409 or a similar valve. Similarly A425 is a high gain valve, and is liable to introduce instability into a set of that type. UPERHET. (Te Kauwhata): K. Frazerhurst, Whakatane, Bay of Plenty. W H.G. (Swanson): I can take a Bev*erage aerial either between two hills or down in the gully and up. Which is correct? A.: It will be quite in order to stretch it between the two hills. It is not an ideal situation, as a Beverage aerial should be low to avoid static and atmospherics, but by dipping it in the gully it would be shielded. DON. ,.CWairoa). : When I tune in a station the squeal is greatly magnified by our next door neighbour’s seyenvalve set. How can I stop this? .: You are not tuning: in correctly, for you should never let your set squeal. (Continued on page 22.)

Information Coupon (To be used with all requests for information.) Name of set seer eeesocoeeseeseoese Model COOH SEH ee esES EHEC DORE EESO® ‘Name SeOPeeedeecesseseseeeessees: Address tees eeeeaseseereveneaccescescnesonss Nom de Plume ....... ee To be kept In Please Note:-- ° (1) Be specitic and briet, tabu: lating, if possible. (2) Write legibly; and on one side of. the paper. (3) We do not design circuits, (3) We do not design circuits, (4) Limit three questions, unless 1/- is enclosed. (5) Postal queries limit three questions, Rnlose stamped envelope and 1/- f ;

Questions and Answers.

(Continued from page 10.) ‘Keep it always on the verge of oscillation, and as soon as you hear the slightest trace of a whistle, bring the reaction back and stop ‘it, and gradually work up again to the oscillation point. You are committing an offence by allowing your set to be heard by your neighbour. B S. DA. (Wanganui): Can I build *the 1932 "Advance" as a long-wave machine only, using .0005 condensers and push-pull pentodes? cele A.: Yes, it would be a good — 2. What voltages would the of the power transformer need to be to deliver 270 volts through a 280 recti-fier?-A.: 325. a 3. As far as we can see the specifications for type "G" are correct. Al M.S.N. (Hornby): I have a sevenGe vyalye superhet. Can I use headphones? : A.: Full details were given in- the "Radio Record," August 7, 1931. S G. (Auckland): I cannot fst results * from the "Sparrow Hawk’ one. A.: You are just a little unfortunate. A few copies got out with the theoretical diagram shown incorrectly. (We are amending yours and returning if. O, (Wketahuna): What alterations * should be made so that I can use my commercial coils for the short-wave screen-grid three designed for the 1930 Handbook? A.: As we neither have particulars of the coils, nor did we design the circuit, we are not in a position to tell you the alterations that you could make. 2. I have a two-valye receiver, which works well, although it oscillates loudly on the 80-metre band. . A.: There are too many turns on the tickler of this coil. Take them off one at a time until oscillation is smooth. Smooth oscillation can be had by taking the grid return to a potentiometer shunted acrosg the A battery. EK J.A. (Orini): Can a pick-up be at- * tached to an eight-valye superhet.? A.: Yes, but it is not easy for an amateur to do, for it is a simple matter to throw the intermediate coils out of line. 2. Is is possible to use a battery shortwave set and use the pick-up circuit as the amplifier ?-Yes, 8. Is electric interference picked up from a gramo-electrie motor installed three feet from the set? A.: If the motor is of the inductance type, no. If of the spark type, yes. Most of them are of the former type. , a =