SB-200 Grid current controls

[Jan sluchak]

I have been working on this SB-200 now for a while. This group has been
helpful on other issues of this amp. So now this is the status.
I have new 572's from RF parts.  3 months ago, this amp stopped putting
out grid current according to the meter on the amp.  I was tuning and
saw a small puff of smoke I think and the grid current is virtually no
deflection during transmit.  The input power just goes through the amp.
For instance 80 watts in and 80 watts out.  I have checked resistors and
everything for charring. As the interior of this amp is very clean, any
damage would be apparent.  It keys ok and ther is 2300 HV. Plate current
reads a little low though too.  I suspect even though the tubes are lit,
they are not being utilized to amplify the signal as they dont get hot
like their working real hard. They just stay warm.
Question.  What component could I have cooked that controls the grid
current to the finals? I have the book but it doesn't isolate that
specific question or topic.
Thanks for any help. Also 10 meter input is lousy but all others are
good and I test on 20 meters into a dummy load anyway.
Again, thanks
Jan KG6EEE

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