11-09-2021, 08:35 AM
(11-09-2021, 07:48 AM)BusyBee Wrote: the translated Russian documents mention that there can be massive variation of the characteristics of individual valves of each type. They point out that this is the reason for using a potential divider for g2. This may well explain the variation of results obtained with circuitry.
Not only a potential divider, but an adjustable one at that!
I've got an AF circuit using two 1j24b's, from same filament supply and same HT. Each has a 270k anode load. Each has grid-leak returned to 0V so zero bias (and measuring with a DVM it really is zero.
But to get the same 45V quiescent anode voltage, one needs 23.6V on g2 and the other 36.4V.
I'm sure I could run them from the same potential divider but then I'd need to provision adjustable bias for g1.
I haven't tried any other specimens, unfortunately it's a soldered-together circuit!
I'm just accepting that I'll have to have several trimpots.
