Suggestions from Correspondents

Radio Record, Volume II, Issue 45, 24 May 1929, Page 34

Suggestions from Correspondents

Combined Circuit "YL CLTIPLYX" (Wellington) suzggests: "I constructed, as a first attempt, the A.C. main crystal and one valve set described by ‘Pentode’ on November 16 last. Using a cheap valve in the rectifier transformer position and a power valve in the audio stage. It works perfectly with a large horn speaker. ‘The 400 ohm potentiometer

across the audio valve makes practically no difference in any position, there being no sign of "hum." The set will not work with the valves in the opposite positions. The grid bias is nine yolts. ’ "Now I consider the one-valve set described on November 80, and decided to combine the two sets, using the November 30 one-valve amplifier with the rectifier transformer part of the November 16 set. I enclose a copy of the circuit I worked out. It also works absolutely O.K., but I should like your advice on the following points :- "(a) Condenser tuning secondary coil. Aerial coil 40 turns, secondary

coil 60. turns, and Wellington tunes in with the condenser plates all out. I tried another condenser in parallel, but had to put it all in and then lost volume compared with only one condenser. Can this be improved? If so, how, please. [Reduce the aerial coil to 20, then, if still tuning with plates out reduce © secondary.] "(b) Tickler coil. I tried 40 turns in ove layer first and found the coil

could be turned in any position or leads reversed without making any difference. I now have 60 turns two layers on, but it still makes no appfeciable difference how I turn it; but it cuts down volume if reversed leads are connected. Why does this coil give me no control? Are still more turns necessary, and if so, how many would you suggest? [Yes; more turns are required.] "The combined set is considerably louder than the A.C. set first published and is absolutely clear and quite loud enough, but I do not feel satisfied on the above points, I have not tried any other station except Wellington.