[AMPS] Grid current "drift"

[KA2YKC@aol.com]

Good Evening.


I have been noticing on my 2x3CX800 amp that if I tune up for legal limit, I
get the following readings which are within spec - Ip=1000ma, Vp=2000v,
Ig=40ma.

However, if I unkey, wait a few seconds, then rekey, my Ig is up around 60ma
or more. As I hold the key down, the Ig will slowly drift back to 40ma or so. 

Where this becomes a problem is when I am on SSB. I will transmit for a minute
or two, then pass the qso over to the other party, then when i re-key an start
to modulate, the grid current will trip the over-current circuit. I have to
speak softer or lower my mic gain the keep this from happening, then 30
seconds or so into the transmission, I can speak at the normal level again,
and the Ig seems to settle down.

Same results with 2 set of tubes, also the RF ouput seems to stay stable on
the Bird 43 while the current drifts downward when testing this in CW mode.
Happens on 20, 17, and 10m.

BTW, the antenna system checks good (very low swr, no change on Bird while the
grid drifts). Is this normal (I wouldn't think so) ? 

Is is possible that there is some heating taking place in the output network ?


TIA for your comments..........

73
Eric


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