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RE: Thanks and a further thought..

The amps do not oscillate when in proper operating condition, but they are always a threat to oscillate, because you have a low voltage solid-state front end feeding a very high voltage tube output stage. So, everything has to be copacetic. I am not about to put in any sort of output filter, in any case. That's way above my skill-set. But Harold Beveridge has a low pass filter built in to the input and driver stages. So very hf stuff that might get into the amplifier from the preamp and cause oscillation, does not get there. Like I said, first it remains to be seen that the amp IS oscillating. Then, if it is oscillating, the most likely cause is a bad solder joint in the high voltage section or perhaps a bad NOS power tube or etc. (As you know better than I, finding the cause can be difficult.)

That's what I did last time, made a coil of wire and attached it to my scope probe and just held it near to the HV section of the amplifier without touching it. Oscillation was easy to demonstrate on the scope. I did find some HV probes for Tektronix, at around $1000, for 5kV.


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  • RE: Thanks and a further thought.. - Lew 13:19:38 06/05/20 (0)

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