I have a 23cm four tube 7289 grounded grid cavity amp. The four tubes are
commonly biased. It is generating good output. The strange thing is that on
key down for a couple of seconds, the grid current starts at a reasonable
value then goes to zero. At zero, I still have full output. I realize its
thermal changes that are varying the grid current, but dont understand full
output with no grid current. Also, if the amp is miss tuned, the grid
current will go "negative" (grid meter reads pinned below zero the wrong way).
How can this be??
W4AF
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