Local seller has a head "for parts" at a price that is attractive, and also indicates it doesn't work. I've never biased a tube, although I did wire one of my guitars with pushpulls for parallel/series on each humbucker.
I'm willing to spend the time to do it, but does it require specialized knowledge and/or tools? Anyone know?
Valvestate amps only have a single 12AX7 and it won't require biasing (it's not going to be configured in a bias configuration such as you'd find with a push-pull output tube pair/quad).
As for repair of amps, yes you need some knowledge of amplifier circuits. Unless you're just lucky and happen to find something obviously burnt out and know what to replace it with. I'd guess you have less than a 50% chance of getting the amp working, and that's a guess based on that there might be something simple (wire not hooked up to the speaker etc.) that the guy doesn't notice. Or I guess if the single 12AX7 is faulty...but if it's a dual-channel amp, the clean channel should still work (since the 12AX7 isn't active at all for the clean channel).
OK, thanks. To clarify a couple things, it's just a head, so I doubt the problem is that he hasn't connected any speakers. The tube bias comment was intended to indicate my level of expertise, ie low. I asked the seller about the symptoms, I'll see if he says it's just the dirty channel.
Marshall valvestate repair?
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