Hey amp gurus,
I have been going around and around with a recently rebuilt VHF
amplifier that is refusing to work correctly. To help me think this
through, I want to be sure I am understanding how some portions of
it are SUPPOSED to work, or the theory of them.
I have a 4CX1500B tube. Screen voltage is regulated by a string of
five high power zener diodes with the screen voltage tapped at the
third or fourth zener from the bottom of the series string. I think
I understand how this works with positive screen current but can
someone nudge me in the direction of understanding what happens when
the tube draws negative screen current? My belief is that current
through the zeners (or SOME of them?) INCREASES in by the amount of
negative screen grid current.
Is that correct?
Other than exceeding the power ratings of the diodes, are there any
special concerns here? Is there risk of the thing dropping out of
regulation and allowing voltage on the screen to rise significantly?
I feel sheepish asking this, as I ran this amp for many years with
negative screen current and it obviously worked. But now that I'm
having problems with it I want to understand things better.
I will ask my other question separately as it is not particularly
related to this one.
Thanks,
Paul N1BUG
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