Bingo! I got fast blow fuses instead of the slow-blow/timed! New heater fuse probably blew as soon as I turned the amp on! D'oh!
Hopefully the right fuses will cure my problem. Times like these I so miss Radio Shack!
Changed R28 and R29 to the stock values. Got sound out of the EL34's, but then the volume went down and up. I decided to hard wire the BR3, thinking the burned traces weren't making good contact. I fired up the amp, and blew Fuse # 5. Turns out I hard wired two wires too close, and it must have...
I replaced the bias trimmer pot. The new one is nice and clean. But it did nothing to fix the problem.
Anyone know what would cause the voltage range at Pin 5 to be very limited when turning the bias pot? There is supposed to be -35 to -50 volts for EL34's, but I am only seeing -39 to -42 volts.
No, these are just plug and play. They plug into the socket, and have internal wiring that converts to the small tube. I think if the socket was bad, it wouldn’t convert to the new tube correctly - so it wouldn’t work. Not 100% sure though.
A bad bias trimmer pot could be part of the problem. If the traces are worn, that would maybe mean bias issues. But, like Peter said, if there’s just low bias, the amp could still sound fine - maybe not great, but not “barely audible”.
I haven’t measured the transformers since it is loud and...
When I connect to pin 5, and turn the bias control, it goes from 39 to 43 or so.
The 2 fuses on the board look fine to me. If they were blown, or the op amp was failing, wouldn’t that kill the sound, even with the Smicz adapters installed?