QUESTIONS AND ANSWERS

Radio Record, Volume VII, Issue 46, 24 May 1935, Page 47

QUESTIONS AND ANSWERS

"AMATEUR" (Lawrence): How could I fit a grid bias battery to my set? A.: You have not stated what type of valve you are using in the output stage, and ‘so it is difficult to answer this question. If it is just a matter of replace ment, then connect up a new battery in exactly the same way as the old one. 2. How could I fit a volume control to the speaker when it is away from the set? A.: Connect the two speaker leads from the set to the outside terminals of

a 16,000 or 15,000 ohm _ pontentiometer. Thhn take two further leads from one outside terminal and the moving arm terminal to the speaker. 2. How could I tap 2 volts from a G-yolt accumulator? A.: By connecting the "A-" lead in your set to the "A-" terminal, and the "A+" lead to the cross-bat running from the opposite end of the first cel] (ic, that with the "A-" terminal mounted on it) to the second cell. When this section of the accumulator has run down, transfer the "A-*" lead from the set to the cross-bar where the "A4-" lead is connected, and then transfer the latter lead to the remaining cross-bar. Finally. when the second section is run dowr, the "A-" lead should be advanced to, the second cross-bar, and the "A+." lead to the "A-+-" terminal on the ac-

cumulator. ‘If you eut through the two lead cross-bars with a hack-saw and then fit extra terminals as shown in the accompanying sketch, the accumulator can be connected so that the cells are in series, to give 6 volts, or in parallel, to give 2 volts and three times the amperehou: capacity of the 6-volt accumulator. The lead straps should be cut at K and _L, leaving a gap at least 1-8in. wide, and terminals should be fitted at B, GC, D, and E by boring holes through tbe lead. Also, if desired, terminals can be fitted at A and F by boring across the lead plug and filing a little off each side, as shown in the separate sketch. To use as a 6-yolt accumulator, connect B and C, and also D and I), while for a twovolt A, C, and E should be joined, and also B, D, and F, oJ SLC. (Blenheim) : As far as we know, magnetic bar amplifiers are not nuw obtainable in New Zealand. C R.R. (Queenstown): We do not ad- ®* yise you to use an 82 rectifier in the "Comet Superhet." Even if you have a spare 2.5 volt 3 amp. winding available. In the first place the voltage would be too high, and secondly with this type of rectifier it is always advisable to use choke input to: the smoothing filter: Otherwise the life of the valve ig appreciably shortened. Note: If you have two receivers in locations 80 miles apart, a separate license for each is certainly necessary. "CyCTODE" (Masterton): You could fit ‘an aerovision dial to your set provided it can be mounted on the cabinet without disfiguring. the latter. ‘The chances are that you would not be able to purchase a dial calibrated in kilocycles that would suit your set; hence your best plan would be to buy one with a 0 to 100 scale, G.F. (Mangamahoe): Your set has 2 * cone type of speaker which will not stand more than ordinary room volume without overloading. The fact tbat you ean pick up 2YA and 8YA on the longwave band is probably due to a harmonic in the oscillator beating with the fundamental frequencies of the etations you mention. This does not indicate that there is anything wrong with the set, except perhaps that the oscillator is insufficiently shielded. "N7TIKING" (Christchurch): I intend to build the "Viking Junior," deseribed in the 1934 "Radio Guide." Could I replace the 58 with a 224A and the 56 with a 2A5, as shown in my sketch? A.: You could use a 224A, but with a 2A5 you certainly could’ not connect the ‘phones in the plate circuit as you have shown. Some form of output device would be necessary to keep the plate current from’ flowing through the *phone windings. Incidentally, the screen of the 2A5 should be connected as shown in the circuit on page 40. You have shown it connected to earth "through a fixed condenser, Your best plan would be to use a 56 in the output stage as indicated, as an output transformer would be more expensive to buy than this valve, , Coup the .0001 mfd. condenser across the .00005 mfd. be fixed?

A.: No; by doing this you would greatly restrict the tuning range. The idea of the .0001 mfd. variable. condenser is to give band-spreading and’ make tuning easier. If you use the .00005 mfd. tuning condenser on its own, the following coil details are more suitable :-

4 8. The output of my power pack is about 3800 yolts smoothed. How could I break this down to 250 volts? A.: By connecting a 25,000 ohm voltage divider across the output of the power pack, and taking the "B+-" tap from a point about 4/5 of the way along the divider from the earthed end. "W71C" (Dunedin): My. set. hag .a hum which is distinctly. audible across the room. Could it be.cured? A.: Yes, but as there are so many causes. of hum we do not. advise. you to tackle the job yourself, but to return:the set: to the agents for overhaul. B C.H, .(Milton): The method of as- * sembling a Daniell cell charger is described in the "Radio Record’ dated January 11, 1935,

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