> Can you remember the frequency where the problem occurs?
>
No, but anyone building a solid state amp should always look
at the drain or collector with a scope on every band. It's
particularly important to do this when the device is near
the peak voltage limit in normal operation. The Motorola
boards I've worked with have always needed some
improvements.
Lot's of people seem to only look at the DC rating and think
if that parameter is met everything is OK. It's the peak
voltage that kills the device, and if everything including
the load and drive level is perfect the peak is about twice
the highest dc value. Get a goofy strip line effect by
pacing compensating caps on the transformer and nothing at
the drains (or collectors) or filter leads or construction
that unloads the output device at a harmonic and you can
have some pretty high voltages compared to the drain supply
voltage.
A voltage spike will kill the device instantly, unlike a
thermal issue.
73 Tom
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