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RE: Oscillation

I replaced all 4 of the power tubes, not just one, because I had no way to know which one of the 4 was arcing. Furthermore, the tubes I replaced were "old", in terms of use. This amp appears to use something like the Futterman "totem pole" topology with two tubes on one side and two tubes on the other side of the PP output. Each of the two tubes, one per side, that receives the signal from the input stage at its grid has a 1K ohm stopper, so far as I recall. (There is no sign of the 150kHz ACV on the stopper resistors, either side.) This is also per the original Beveridge schematic, which I have here (but not in front of me at the moment). There are also 7.5M ohms feedback resistors between the front end and the output stage, which is where there can be trouble with oscillation. However, the 150kHz ACV is not seen on the feedback resistors, either.

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