RI bassman causes tube hum & OT replacing

[Tim Foutris]

Hi,
I have had to replace the stock OT twice & numerous tubes ( Left side only ) have begun humming & eventually need replacing or will blow on a RI bassman . I had work done on it 12+ years ago to cut the bassiness and install a loop( bad idea - I've never used it) Could the loop which was inserted & used 2 of the RCA speaker outputs be causing the Tubes or OT problem? Could it be grounding? It looks like it shares the ground with the speaker outs. The tubes are the bigger issue for me. I understand these stock OT's don't last.
Thanks,
Tim

[stokes]

You say you have had to replace "numerous tubes (Left side only) if you are refering to the power tubes and saying you replaced only one of the pair,it is possible that the output tubes dont match closely enough and would cause hum.Output tubes should be matched within about 5ma's or they will cause hum,with a properly matched pair or quartet of tubes a push-pull output will cancel hum.

[Tim Foutris]

RI bassman hum

Thanks,
I tried to be clear but I wasn't. Its the Power tubes; they start out without hum but eventually start to hum and ultimately they'll blow. I thought the fact that the OT has been replaced twice might give insight.
Can sockets not tight enough cause these kind of problems?
Thanks,
Tim

[stokes]

Sounds more like the tubes are biased too hot.Do the plates glow red before they blow?How long before they blow?What exactly do you mean by "left side only"?Why did you replace the OT twice?Do you check the current draw when you replace the power tubes?If the current draw is too high it will do exactly what you describe.

[Enzo]

Sounds to me also like the one side is losing bias. Monitor the DC voltage at pin 5 of the tubes on that side. If the bias is like -42V on the good side, is it about the same on the bad side too? Does it drift downward? COUld be a leaky cap from the PI. If so, the voltage would sink even without the tube.

Cure your tube problem, and you won't have a transformer problem.