[Amps] 811A vs 572B

[Vic K2VCO]

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
http://www.qsl.net/k2vco/