> So the RF voltage swing on the plates of the tubes is always the same, and
hence
> the stress on those capacitors is always the same.
Not really.
While the normal peak operating voltage with the tank properly tuned into a
load is less than the dc plate voltage of the amp, the voltage across the
capacitors can vary a great deal with loading and tuning. If the tank is
under- loaded (loading control too far open) or if the load somehow faults
(even for a millisecond) voltages can reach extreme values!
This is by far the most common problem causing switch arcs and tank
component failures (like you have) in amplifiers.
You can see a working demonstration of this at:
http://www.w8ji.com/demonstation.htm
You can find causes and cures explained in detail at:
http://www.w8ji.com/Amplifiers.htm
along with some stuff about selection of components.
73 Tom
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