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[AMPS] 4 1-000 Stability Question

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Subject: [AMPS] 4 1-000 Stability Question
From: (Skip S Isaham)
Date: Sun, 07 Feb 1999 03:23:15 EST
Hi Jon,
I like a quiz...

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 
circuit housing.
...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?

Here's my two cents.  First I'd look around with a broadband field
strength meter and a frequency counter (with RF Pickup Loop) myself, to
confirm it's an actual oscillation, and the relative frequency. That
would only happen if you could safely run the amp with the problem event.

I know it's probably obvious, but I'd confirm the current rise is related
to an RF Oscillation, then the frequency of it. Knowing the problem
frequency would be most helpful.

Coupling a GDO into the cab (power off) with the covers on and off will
also help. If you can determine the frequency shift with the cover
placement, You could then try looking around Inside with the GDO.

That's my first thought...

skipp may   wv6f

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