02-16-2016, 06:25 AM
The PCB layout may be contributing but I would expect the results to be more consistent from amp to amp. That said, Ampeg's PCB layout is pretty close to textbook except that they obviously couldn't twist the pairs. They did run them side by side on the PCB except directly across the tube socket.
If I don't come up with a better solution, I might sacrifice a PCB and convert the V1 filament to twisted pair. I'm also wondering if some 12ax7a are less susceptible to filament hum than others? Maybe the right tube fixes it? I don't remember hum being an issue when we used these new in the 70's and I doubt Ampeg could produce them in large numbers with hum problems.
I don't know if it is a gain difference but the second triode in the same tube with the same filament wiring seems quiet in both V1 and V2. First I'm going to try changing v1, v2 pairs with some NOS tubes and see if the hum gets better or not.
If I don't come up with a better solution, I might sacrifice a PCB and convert the V1 filament to twisted pair. I'm also wondering if some 12ax7a are less susceptible to filament hum than others? Maybe the right tube fixes it? I don't remember hum being an issue when we used these new in the 70's and I doubt Ampeg could produce them in large numbers with hum problems.
I don't know if it is a gain difference but the second triode in the same tube with the same filament wiring seems quiet in both V1 and V2. First I'm going to try changing v1, v2 pairs with some NOS tubes and see if the hum gets better or not.