I'm sure going to need help with this one.
This 70s Ampeg chassis came to me last May. It had sat in a barn or something for 12 years, and was dirty as hell. The boards were covered in some kind of film, and there was gobs of old brown flux everywhere. I hit it with a stuff brush and some acetone and then hosed it down. Then I left it in my driveway in hot sunny Florida for the afternoon, and let it set in my shop until parts arrived.
I recapped it, put in a new power cord and fuse holder, sprayed it all out and put it on the bulb limiter. Short story, dead shorted OT. So now we need a replacement. Fliptops has them, but they were on backorder during a pandemic.
Three months later, it arrives. I install it and fire it up again. It powers up OK, and it passes signal, but not nearly enough, with channel two being the strongest. None of the funky echo/afterbeat/tremolo functions work. I don't know yet about the reverb. It is also doing some loud throaty noises when I plug into the ext. speaker jack, which I wanted to do instead of dealing with the XLR plug. And further it either already has, or goes into oscillation when I probe one of the power tube grids or the side of the PI that feeds it. With all these problems, I thought I would just try to get signal flow sorted out with this thread, and start another for other issues for the sake of confusion.
In channel two I get a nice strong wave up to the circled S after the first premp tube V4. (What is that circle S for anyway?) Then it heads off on a wire to the tone control board on the front panel. The signal passes, but is about 8 times less at the treble pot wiper than it is arriving on that wire coming circled S. I have snipped the wire from 470K R61 going to echo switch, no change. I am unsure what to do next. I was hoping I might get advice before I pull the tone control board, which means pulling three rocker switches as well. These are just a bear to service, almost nothing is labeled on the board.
And what is PEC 6470000 in the tone stack?
https://ampeg.com/support/files/Sche...matics%201.pdf
This 70s Ampeg chassis came to me last May. It had sat in a barn or something for 12 years, and was dirty as hell. The boards were covered in some kind of film, and there was gobs of old brown flux everywhere. I hit it with a stuff brush and some acetone and then hosed it down. Then I left it in my driveway in hot sunny Florida for the afternoon, and let it set in my shop until parts arrived.
I recapped it, put in a new power cord and fuse holder, sprayed it all out and put it on the bulb limiter. Short story, dead shorted OT. So now we need a replacement. Fliptops has them, but they were on backorder during a pandemic.
Three months later, it arrives. I install it and fire it up again. It powers up OK, and it passes signal, but not nearly enough, with channel two being the strongest. None of the funky echo/afterbeat/tremolo functions work. I don't know yet about the reverb. It is also doing some loud throaty noises when I plug into the ext. speaker jack, which I wanted to do instead of dealing with the XLR plug. And further it either already has, or goes into oscillation when I probe one of the power tube grids or the side of the PI that feeds it. With all these problems, I thought I would just try to get signal flow sorted out with this thread, and start another for other issues for the sake of confusion.
In channel two I get a nice strong wave up to the circled S after the first premp tube V4. (What is that circle S for anyway?) Then it heads off on a wire to the tone control board on the front panel. The signal passes, but is about 8 times less at the treble pot wiper than it is arriving on that wire coming circled S. I have snipped the wire from 470K R61 going to echo switch, no change. I am unsure what to do next. I was hoping I might get advice before I pull the tone control board, which means pulling three rocker switches as well. These are just a bear to service, almost nothing is labeled on the board.
And what is PEC 6470000 in the tone stack?
https://ampeg.com/support/files/Sche...matics%201.pdf
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