06-02-2017, 10:11 AM
No offense taken - just wanted to let you know that I've worked on a lot of AMPEGS - but this is my first foray into the VT amps.
Found a spot on the board where there was arcing between the feedback at R48 and the common line going to R22, R19, R6, R5, R7. Cleaned it up and I think that was the problem. I also realized that the previous owner had substituted a 12AX7 for V3 which is specked as a 12DW7. They probably read Aspen Pittmans tube amp book where he says that the 12AX7 can be used in place of the 12DW7 in the VT40, but I'm not so sure considering the unique characteristics of the 12DW7.
Brought up the Amp on a variac with a dim bulb tester - before the arc cleanup I would get a bit of glow on the bulb, now It stays dark - checked voltages seem to be good. Waiting on a new 12DW7 and then I'll be able to test it completely.
Found a spot on the board where there was arcing between the feedback at R48 and the common line going to R22, R19, R6, R5, R7. Cleaned it up and I think that was the problem. I also realized that the previous owner had substituted a 12AX7 for V3 which is specked as a 12DW7. They probably read Aspen Pittmans tube amp book where he says that the 12AX7 can be used in place of the 12DW7 in the VT40, but I'm not so sure considering the unique characteristics of the 12DW7.
Brought up the Amp on a variac with a dim bulb tester - before the arc cleanup I would get a bit of glow on the bulb, now It stays dark - checked voltages seem to be good. Waiting on a new 12DW7 and then I'll be able to test it completely.