Useful Tips and Jottings

Radio Record, Volume II, Issue 23, 21 December 1928, Page 28

Useful Tips and Jottings

eral hours in the naphtha or spirit, stirring them frequently. The re.u8 will almost completely dissolve ne liquid, which should then be poured off into a bottle. Before assembling terminals, or components on the plywood panels, give the latter three good coats of the above mix: ture. The panel will then be found to provide a perfect degree of insuon, and its total cost will work out as the merest fraction of that of an ebonite panel of the same dimensions. Battery Connections. BATTERY connections can be made with almost any size wire, provided it is suitably insulated, The B Battery wires carry small amounts of current, but the voltage is as high, and in many cases higher, than the voltage in the electric light wires in your home. Rubber covered wire is de: sirable. Thq A battery wires carry relatively larger amounts of current at much lower voltage. This means that very small wire should not be used. The size should be at least No. 16. While thin insulation is theoretic. ally sufficient because of the low voltage. rubber covered insulation is safe because an accidental short cireuit in storage battery wiring may result in a fire. The special cables sold for connecting the batteries contain a group of wires each of the right size and with the proper insulation. The size of the wire used to connect the loudspeaker is of no importance. CORRESPONDENT wants advice on his receiver. With the aid of his circuit and layout diagram, it was quite easy to diagnose his troyble. The writer considered it of sufficient interest to mention in these columns, and it may help other amateurs, whose sets have similar symptoms. 1. B batteries run down abnormally fast, and when milliam meter connected in B-lead, a current of 3ma, was passing even when filaments cut off. 2. C battery also continually discharging through no apparent reason, 3. Very distorted music when C battery disconnected, and poor with C. battery connected. The circuit under disqussion was a Browning Drake, with

three audio stages. Two impedance, ind one resistance capacity coupling. To find the reason of the B current flowing when filaments turned off, assuming; of course, that no leakage through faulty insulation, the B circuit was followed. The only place that was likely to be fauity was either the large condenser across the B battery, or the coupling condenser in either the resistance or impedance coupling unit. In view of the fact that the C battery ran down yery quickly, it was assumed to be a faulty coupling conhdenser. This is the path the anode eurrent was taking. Through thé anode resistance or choke, through the faulty condenser, to the grid of the following valve, and so on ,threugh the grid leak, or impedance and C battery to B, As the C and B batteries are thus connected in series, both would run down, eve when the receiver was not in use. This is a fault that is always likely to eccur, and those owners of sets suffering from simliar complaints should not fail to test all their condensers with a pair of phones and a dry battery, by the method described this week in the ‘"Beginner’s’ Corner." Substitution with new ones is the only remedy, and only good mira condensers of .006 to .01 mfd. capacity should be used. In the case of some commer: cia] impedance units, the condenser is incorporidted inside. To test this, temporarily disconnect the P, G, B, and F terminals on the unit. and test termin-

ee OO OO NNN OOOO TOOT eee als P and ©, as it is between these two that the coupling condenser is. eonnected, The Trickle Charger. RE your trickle charger for A and B batteries in "Radio Record," Noyember 23. Having built this charger to your specifications hroughout I should just like to know one or two points about connecting up, (1) Can I eharge A battery on its own and also B battery likewise? (2) The charger seems to be working OK, ‘but on testing current on A minus and plus terminals I only get 2 volts + amp., but on bridging B minus and plus I gat 12 volts $ amp. I would like to know if jit is all right to charge A battery on these rates, or is there some fault somewhere? The wiring is OK, the only thing my cell transformer is 8 volts instead of 10-12, as you mention, Would ‘nt make any difference, or could the -charger be made to charge at, say, 2 to 8 amps if wanted. My battery is 4 volts 80 amp. hour, charging rate 3 amps.-B.L.O. (Auckland). a ANSWERS. (1) Yes, a wet B battery can be charged as readily as an A accumulator, but charge one at a time. ~ (2) If the instructions had been followed and a 10-12 volt Bell transformer been employed the voltage would have been 4 volts as required. The charger is meant to charge at. the rate of 4 fmpere per hour. TOR really strong and pure loud- & speaker reproduction it is absolutely essential to use a large power or a super-power valve on the last stage.