> Tom, I think you've been fooled all this time about the most common
> failure mode of solid state transistor amplifiers. Again, the main cause
> of failure is excess power dissipation in the transistor due to load
> mismatch, not voltage breakdown. If voltage breakdown were the issue,
> you'd see voltage peak detection circuits in amp finals.
If I was fooled, so was Helge Granburg at Motorola before he died.
Helge, being fooled like me, thought the same thing.
The reason you don't see peak voltage detection circuits is
because by the time the voltage gets there, it is too late. You will
never remove drive in less than a few RF cycles.
That's why you need to measure SWR, and do it while the
envelope is rising....unless you use transistors that have a voltage
rating of several times the working voltage or use a hard clamp that
is very fast.
Of course you could be right, and Helge could have been wrong.
But keep in mind I can measure hundreds of volts on the drain of a
MRF-150 operating at 20 volts with the right load conditions.
73, Tom W8JI
w8ji@contesting.com
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