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Do It Yourself (DIY) paradise for tube and SET project builders.

True, I guess,

but I did not want to be the guy who told the guy to wiggle parts with power on, if the guy got electrocuted.

I have a pair of Beveridge direct-drive amplifiers, which are now 46 years old but which I have owned for about 4-5 years. For the first year or so of my ownership, one of them would tend to oscillate even on the work bench, with no speaker attached. (In fact, you can't practically work on the amps while they are attached to the speakers.) Since those amps develop 3200V in the output stage, I was loathe to do as you suggest. I could only power it up, determine that it was or wasn't oscillating, and then power down and wait for the V to settle before touching anything. Using that approach and with the kind and patient email advice of Steve O, we practically rebuilt the amplifier section by section, as each fix failed to affect the tendency to oscillate. Finally I said to myself that the problem must be something illogical, because we had covered all logical possibilities. At that point, I went around wiggling parts (not for the first time), whereupon I discovered that one capacitor had a bad solder joint that gave way under my second or third wiggle. I had empirically re-soldered most of the joints on the PCB before that, to no avail, among the many other things I/we did. This wasn't a wasted effort, because I learned a lot about the complex Beveridge circuit.


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  • True, I guess, - Lew 10:45:48 07/04/17 (0)

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