18-09-2016, 11:12 AM
Thanks, everyone.
I am on some other vintage sites too.
Re: Rod Pentodes.
I got some NOS 1j42a tubes. They are 11.5mA filament like the 1j24b, but are twin control grid like the 1j37a. Unusually they are really 12V max for Anode and g2 and seem to be best about 6V to 8V HT!
I hope to to do a couple of 12V battery radios, one using 1j42a with a Lady cell and 12V A23 HT and one using ECH81 = ECH83 using 12V SLA, perhaps both TRF and superhet.
I've not decided how to do the audio out, though a pair of 1j24b in Push Pull Class B is about 25mA filament and gives good volume using a 3W 110 + 110 to 9V mains transformer, the bias currents cancel, but that needs at least 36V HT. Similarly while either section of an ECH81 can probably be reasonable as Class B push pull in a pair, you'd likely need about 100V HT. The Anode currents of tubes are tiny under 36V. Even 2K headphone or crystal earpiece covert sets needed at least a 22.5V battery and often used two.
I am on some other vintage sites too.
Re: Rod Pentodes.
I got some NOS 1j42a tubes. They are 11.5mA filament like the 1j24b, but are twin control grid like the 1j37a. Unusually they are really 12V max for Anode and g2 and seem to be best about 6V to 8V HT!
I hope to to do a couple of 12V battery radios, one using 1j42a with a Lady cell and 12V A23 HT and one using ECH81 = ECH83 using 12V SLA, perhaps both TRF and superhet.
I've not decided how to do the audio out, though a pair of 1j24b in Push Pull Class B is about 25mA filament and gives good volume using a 3W 110 + 110 to 9V mains transformer, the bias currents cancel, but that needs at least 36V HT. Similarly while either section of an ECH81 can probably be reasonable as Class B push pull in a pair, you'd likely need about 100V HT. The Anode currents of tubes are tiny under 36V. Even 2K headphone or crystal earpiece covert sets needed at least a 22.5V battery and often used two.
