You didn't mention your power tube plate voltage. It's common for these amps to run higher than schematic voltages in modern AC outlets, but yours seems quite high. The resistors going to pins 1 and 6 should be 100k ohms, not 100 ohms. If you've tried the amp and it's working fine then maybe that's just a typo? Otherwise, if the amp is not working fine 100 ohm plate resistor values would explain the high voltage and perhaps part of what's wrong.?. If the plate resistors are actually 100k, do you have a Sovtek 5y3? There was a long run of those tubes that had a much lower voltage drop than should be expected and those tubes have been a problem for a lot of people. If you have another 5y3 (not Sovtek or relatively new Sovtek) you could plug that in and see if those voltages come down.
Regarding the 566 ohm cathode resistor. A lot of users increase to value of that resistor to compensate tube bias for the higher plate voltages due to modern higher AC mains voltage. 566 was probably fine. But then, it was a badly drifting resistor. So probably better to get rid of it.
I don't think the 40/20/20 can or the 5u cathode bypass cap would be stock. Though it's hard to say. A lot of Fender amps left the factory with whatever components they had that would get the orders filled. But I don't imagine they would have had 40/20/20 cans and 5uf caps on hand. More likely someone did a "cap job" on the amp some time in history and those are just the parts they used. Honestly, don't sweat the 40uf for the 5y3. It'll work fine and the amp will have better ripple filtering.
So, what is the power tube plate voltage? Is the 5y3 a Sovtek? Are the 12ax7 plate resistors 100 ohm or 100k? And is the amp working or broken?
Regarding the 566 ohm cathode resistor. A lot of users increase to value of that resistor to compensate tube bias for the higher plate voltages due to modern higher AC mains voltage. 566 was probably fine. But then, it was a badly drifting resistor. So probably better to get rid of it.
I don't think the 40/20/20 can or the 5u cathode bypass cap would be stock. Though it's hard to say. A lot of Fender amps left the factory with whatever components they had that would get the orders filled. But I don't imagine they would have had 40/20/20 cans and 5uf caps on hand. More likely someone did a "cap job" on the amp some time in history and those are just the parts they used. Honestly, don't sweat the 40uf for the 5y3. It'll work fine and the amp will have better ripple filtering.
So, what is the power tube plate voltage? Is the 5y3 a Sovtek? Are the 12ax7 plate resistors 100 ohm or 100k? And is the amp working or broken?
Comment