i have 2 gibson ga79rtv amps. they both sound excellent. however, one runs considerably hotter than the other. what could cause this?
thanks,
thanks,
Moved to Instruments and Amps per forum policy. More likely to get an answer here anyway. 🙂Classic Amps: The 1961 Gibson GA-79RVT
Although oscillation is not impossible, it would sound fuzzy or funny.
I'd cast my vote for different biasing=different tube current/dissipation.
I'd cast my vote for different biasing=different tube current/dissipation.
Consider yourself VERY lucky for owning 2 of those beauties. If someone wants to part with a GA40..I would be happy most happy to oblige. Long story of a lost love....
Yes, that's quite possible. Check the voltages at the output tube grids, which should be close to zero.
If one or more grids are at some significant positive voltage, replace the coupling capacitors.
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thanks to all. it looks like i'll check and possibly replace the coupling caps.
thanks again,
play music!
thanks again,
play music!
thanks to all, i've replaced the coupling caps and the amp doesn't run nearly as hot.
thanks again,
mikeB.
thanks again,
mikeB.
From 1961 it's probably still within the range of crap quality capacitors, that used to leak 😀
With 'modern' ones it's rarely a problem, but back in the 70's it was a VERY common fault with any older valve equipment.
Great, I've only found leaky coupling capacitors a few times in all the old amps that I've worked on, but when it happens, they all should go.
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