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Hey All,
going over a Peavey Artist VT, that came in with the complaint that it was weak sounding. So, in looking over the power section, I see 500 v on the plates and 496 v on the screens, as per the schematic. I also have -60 volts going from the bias supply to the 220k feeder resistors as per the schematic. Looks ok there, except when I checked each tube with a bias probe to see if there was any with low/hi current draw, I read about 11.5ma on each tube. Now I know that this has a transistor pair driving the output tubes, and I would expect them maybe to be biased a little on the cool side, but 11.5ma??? I haven't had any experience with this particular Peavey circuit, so I don't know if this is normal, or do I need to change the bias resistor to get those tubes working a bit harder, like maybe up around 30-36 ma's?
I also started with the power supply and found the original filter caps to be starting to leak and measuring a low resistance across a couple of them, so I changed all the 100uf/350volt caps and the balance resistors that had drifted way high. I want to get all the voltage rails balanced and just clean up the power supply first.
Another question about this particular amp, is that it has a screen resistor on only one of each output tube pairs, not on each tube as I would expect to see. Of course, that's what the schematic shows as well. So anyone shed any light on that practice (Enzo maybe? lol). So just looking mainly for thoughts from anyone who has been inside these before, as I'm not sure what normal should be. I might throw another set of tubes in to see if maybe all 4 6L6's were just tired, although I would think to have all 4 equally low is kind of weird.
Thanks for any thoughts on this
MattArtist VT schematic.pdf
going over a Peavey Artist VT, that came in with the complaint that it was weak sounding. So, in looking over the power section, I see 500 v on the plates and 496 v on the screens, as per the schematic. I also have -60 volts going from the bias supply to the 220k feeder resistors as per the schematic. Looks ok there, except when I checked each tube with a bias probe to see if there was any with low/hi current draw, I read about 11.5ma on each tube. Now I know that this has a transistor pair driving the output tubes, and I would expect them maybe to be biased a little on the cool side, but 11.5ma??? I haven't had any experience with this particular Peavey circuit, so I don't know if this is normal, or do I need to change the bias resistor to get those tubes working a bit harder, like maybe up around 30-36 ma's?
I also started with the power supply and found the original filter caps to be starting to leak and measuring a low resistance across a couple of them, so I changed all the 100uf/350volt caps and the balance resistors that had drifted way high. I want to get all the voltage rails balanced and just clean up the power supply first.
Another question about this particular amp, is that it has a screen resistor on only one of each output tube pairs, not on each tube as I would expect to see. Of course, that's what the schematic shows as well. So anyone shed any light on that practice (Enzo maybe? lol). So just looking mainly for thoughts from anyone who has been inside these before, as I'm not sure what normal should be. I might throw another set of tubes in to see if maybe all 4 6L6's were just tired, although I would think to have all 4 equally low is kind of weird.
Thanks for any thoughts on this
MattArtist VT schematic.pdf
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