Determine the oscillation freq. If it's VHF then perform all of the
Measures' measures. (Pun intended).
From: Jon Ogden <firstname.lastname@example.org>
To: Amps Reflector <email@example.com>
Date: Saturday, February 06, 1999 7:40 PM
Subject: [AMPS] Stability Question
>I am finally at the point in putting my amp back together where I can run
>some stability tests. And I have come up with a question/problem.
>Here's how I am testing:
>Key up amp, no RF, Ctune at min, Cload at max, open circuit on output
>(ie: no antenna or dummy load - no coax attached). I figured this would
>be worst case.
>What happens is I seems to have a housing based resonance problem with
>one of my tubes. When the cover is off, every thing is fine. However,
>when I put the cover on and bring Ctune close to its minimum value, the
>plate current starts to rise. I must have a resonance in the tank
>I tried adding a 10 pF vacuum cap in parallel with Ctune as some have
>suggested to improve stability in the past. On paper you would think it
>would work. Effectively, you'd be raising the value of Ctune by 10 pF
>and hopefully, it will never get low enough then to set the amp in to
>oscillation. Well, no such luck. The amp still oscillates even with
>this cap in place.
>So, what have you guys got for ideas? Should I add some "walls" inside
>the housing to try to break things up?
>BTW: My plate voltage is about 5.5 KV on the 4-1000A.
>Any help is appreciated.
>http://www.qsl.net/ke9na <--- CHECK IT OUT! It's been updated!!!!!
>"A life lived in fear is a life half lived."
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