Hey All,
I'm trying to fix in amp in one day for a touring band coming through. It's a music man 2475 HD-120 (with 12ax7 phase inverter). Any shots in the dark would be helpful seeing as I'm on a time limit.
http://www.thetubestore.com/lib/thet...-Schematic.pdf
Came in pulling lots of current from my limiter, no signal. Turns out one of the 'snubber' caps (plate to ground) was shorted out, when I removed it the signal returned and the current stopped being pulled. It had destroyed the flyback diode and the -16v supply (1n4003 diode and a cap on the bias board was fried, the 150uf electrolytic) The filter caps are out of spec but the voltages are pretty strong, high is about 550 on the limiter. (Can't remember exact and I'm not at the shop...)
Preamp signal seems strong, crank it up and the tubes saturate the way you'd think. Just low overall volume, like a stereo on medium/low output.
16v and -16v have been repaired, snubber caps and flybacks out of circuit for now. Suspect phase inverter, replaced all film caps one by one and measured resistors on the driver board. At this point, I'm guessing OT??? what else could cause low volume, possibly something I missed from working a 12 hour day in here with a fuzzy head??
Thanks so much.
I'm trying to fix in amp in one day for a touring band coming through. It's a music man 2475 HD-120 (with 12ax7 phase inverter). Any shots in the dark would be helpful seeing as I'm on a time limit.
http://www.thetubestore.com/lib/thet...-Schematic.pdf
Came in pulling lots of current from my limiter, no signal. Turns out one of the 'snubber' caps (plate to ground) was shorted out, when I removed it the signal returned and the current stopped being pulled. It had destroyed the flyback diode and the -16v supply (1n4003 diode and a cap on the bias board was fried, the 150uf electrolytic) The filter caps are out of spec but the voltages are pretty strong, high is about 550 on the limiter. (Can't remember exact and I'm not at the shop...)
Preamp signal seems strong, crank it up and the tubes saturate the way you'd think. Just low overall volume, like a stereo on medium/low output.
16v and -16v have been repaired, snubber caps and flybacks out of circuit for now. Suspect phase inverter, replaced all film caps one by one and measured resistors on the driver board. At this point, I'm guessing OT??? what else could cause low volume, possibly something I missed from working a 12 hour day in here with a fuzzy head??
Thanks so much.
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