>Peter, what have you done? You've awoken the undead!
>Prepare for at least six weeks of mayhem and misquotation...
Yup.
>
>
>I used to think that the Q of a parasitic suppressor had some meaning.
>having looked at the problem in detail, I don't believe that any more.
Ditto.
>
>The basic question is: will my HF amplifier oscillate at VHF?
>
>That depends on three things:
>1. Existence of a parasitic VHF resonance - we know that does exist,
> due to unavoidable stray inductance between the tube and C1 of the
> Pi(L) tank.
>2. Existence of a feedback path from output to input of the tube.
>3. Sufficient gain at the VHF resonance to permit oscillation.
>
>Note: ALL THREE of those requirements must be met, or else the amp will
>not oscillate.
>
>The parasitic suppressor operates only on #3 and #1. But in fact the big
>unknown is #2, because it depends on the individual design and
>construction. That's why you always have to develop the suppressor by
>cut-and-try methods.
>
This is so true. You might not even need a typical RL parasitic
suppressor in the anode. It all depends on the design of your circuit.
If someone doubts me then how I was able to stabilize my 4-1000A at 6KV
and make it stable? I have just a single turn (1.5" dia) coil and NO
resistor in my anode. My stability problems were solved at the input of
the tube. Would my design work successfully in someone else's PA? Maybe
or maybe not. Lots of factors have to be taken into account. Yet I know
two of us on the reflector who have 4-1000A amps with no parasitic
resistors. NO one single way is right for all cases. This I have
learned.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
--
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