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I pulled the main board and all the solder joints looked healthy. Ya for ribbon cables!
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Replaced the ribbon cables with separate wires. Assembled and retested and I'll be dipped, it still does it when sprayed. I'm getting back to my original theory that the board is funky. When sprayed, I get the sizzle and crackle and now there is an oscillation that I can control with the pre pot. Sounds like the outer limits.Comment
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It's not the ribbon cable but the pins or contacts on the mating PC board connector(s). Assuming it's tin (and it's cheap) the connector is not making good contact. Oxidation can happen overnight. I had a $2000 preamp from a European company called Electrocompaniet, and it exhibited the same type of problem. I was listening to Mozart and then all of a sudden it sounded like Nine Inch Nails. Why any electronics designer would use a digital cable for an analog signal is beyond me. I just said screw it, and soldered each connection separately. There are a number of ways of doing this depending on what the PC board connector looks like. Mine consisted of pins spaced apart by 0.1". We are at the mercy of these modern production techniques with ribbon cables and plastic connectors. They are all doomed to fail unless the connections are gas tight. Plastic outgasses.Comment
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Thanks for the input Mark, but the ribbon cables are soldered directly to the boards on this amp. I finally ended up replacing the coupling caps for the first 2 tubes and it seems to have cleared up. Thanks to Jazz for his assistance with this!Comment
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