>> 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....
How do you plan on doing that on a wideband transformer output amplifier?
Since the Impedance of the collector is equal to Collector voltage squared /
twice the power output and the transformation ratio is equal to the sqaure
of the turns on the transformer, the swr would be changing as the power
output ramped up.
>unless you use transistors that have a voltage
>rating of several times the working voltage or use a hard clamp that
>is very fast.
Motorola rates their Bipolars at 30 to 1 swr over all phase angles, if
operated within spec.
--Toll Free
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