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Re: [Amps] 811A vs 572B

Subject: Re: [Amps] 811A vs 572B
From: Vic K2VCO <>
Date: Mon, 14 Feb 2011 12:40:52 -0800
List-post: <">>
How do you know it was a VHF parasitic?

What were the circumstances of the event?

On 2/13/2011 7:44 PM, Hal W5GHZ wrote:
> My AL811H just went into VHF parasitic oscillation and took out a brand new 
> set of
> 811A's, plate choke, several capacitors and a couple of resistors and the 
> fuses.  This
> is the second time this has happened.  Guess it is time to rebuild this amp 
> from the
> ground up with all of the new parasitic supression techniques and an enhanced 
> power
> supply (six filter caps instead of four).  I will also be putting in the 
> 572B's.
> I have an old Heathkit SB200 and with new tubes and it easily puts out 900 
> watts into a
> 50 ohm dummy load with the currents all in spec.  However, I run it at 600 
> watts.  The
> AL-811H used to run 800 watts until it started acting like a two meter MPO.
> Hal W5GHZ

Vic, K2VCO
Fresno CA
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