I turned my Pittbull 45 on this morning and it immediately made a REALLY loud sound. I turned it off and unplugged everything. Then I turned it back on and it’s still making the same loud sound – kinda like a super loud hum. One of the EL84s is not lighting up like the others, so I’m thinking that it might be that, but I don’t really know.
Any advice? Should I take it into Fryette for service?
Hi EI
I think you found the problem - put in a new set of tubes. Ideally a matched set.
Regards
Dan
Doesn’t the amp need to be biased when changing tubes? I don’t know how to do that. Should I take it to an amp tech, or is it better to bring it to Fryette?
We recommend biasing when the power tubes are changed, especially if it’s been a while. Any amp tech worth his salt can do the bias.
Dave
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What happens if you do not bias the power tubes, I got a 45 with new unbiased power tubes… 
Not an expert by a long shot, but I think if the bias is off one way or the other (too hot or too cold) the tone can suffer. If it’s too hot, I think it can also wear out the tubes prematurely.
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Hello @Planetguitar yes @ElFug is right.
Bias refers to the circuit not the tubes, so once you put the tubes in they will be become biased. The biasing point can be fine tuned to make sure the tubes are operating in the designed range for power dissipation and for minimal cross over distortion. I’d recommend sending the amp to a local tech to do the biasing for you, if it needs it.
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Thanks you guys. I read this thread in the middle of the night and probably could’ve googled it, but my brain was mush at the time. You FRYETTE people are so awesome. Rock on!!
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