Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by nemp, Jun 10, 2003.
Do Peavey Classic 30s need biasing? How hard is this?
No. They're cathode (self) biased.
(well strictly, yes you could change the bias if you wanted to, but that would entail replacing the cathode resistor, and there is probably no point anyway - they seem to work reliably with most types of EL84s)
I used to think that too, until I looked at a schematic for one (http://www1.korksoft.com/~schem/newamps/peavey_classic30.pdf), which sure looks fixed bias to me. Am I reading it wrong?
OOPS! Yes, Troy is absolutely right. It's fixed bias.
I have worked on these amps too (admittedly as rarely as I can, they're a complete pain to get into), and I really was sure they were cathode-biased...
You could adjust it, although you'd have to change a fixed resistor (R63 or R64, which are the voltage-divider network for it).
I never have though - I've replaced tubes on these many times too. But that just proves what Randall Smith says, and I agree with - a well-designed amp (which I think the Peavey is, circuit-wise, even though I'm not impressed by the build quality) does not need adjustable bias. Looking at the circuit the bias appears to be -14V, which is quite a conservative (cool) setting at a plate voltage of 332V. I have certainly never had trouble with any type of tubes from the cheapest junk to NOS Mullards.
As long as you don't mind crossover distortion, I agree with you. And FWIW, I'm not even being sarcastic...a lot of people don't realize how much of their amp's distortion is crossover distortion until they get it modded for a bias pot and have it adjusted.
When it comes to the Classic 30--I haven't heard one yet that hasn't sounded good enough to me the way it was.
So that means I have to bias it? When and how do I do this? What if I don't do it will I have problems?
Thanks John, and Troy. Glad to hear that as I don't know what the hell I'm doing when it comes to amp mantainence.
Maybe most Peavey products but a lot of folks (myself included) have a soft spot in their hearts for teh Classic series.
Well its either Peavey C or a Crate TV 60. Help me decide