Amps will not hold bias.

If you are for sure that your tubes are not bad and the socket which holds these tubes are check and inpected then your answer would be:


There could be two things.

1) Your bias pot are going bad. Clean and do measurement on both channel.  See if you get a reading.  Turning clock wise or counter clock wise will either increase or decrease.  If both has the same reading ( you are good).

Next step. 

2) one of the resistors to ground could be open or bad.

Almarg, where are you? Help needed here.

Hi Zipost  
1) Can I be sure that tubes are good I don't have a tester but seems unlikely that 3 pair would all display the same issue. But can anyone be sure of anything in this hobby LOL.
2) bias pots seem to adjust and track the same from amp to amp although one seems to run out of adjustment before the other. But might clean pots to see if that helps.
3) May pop the bottom off and look to see what I can see re: resistor but getting over my head at that point.

Hi Jim
They are mono amps and yes I agree with your assessment, and that is the big head scratcher. What are the odds that all 3 pair of tubes would have the same issue?

Hi Roxy54 
Ventura CA, You know someone that could help?