[R-390] AGC question

[Barry]

When listening to a moderately strong station in the 15mc band, if I switch
to AGC, the signal drops significantly from the MGC position, regardless of
the AGC speed.  With a signal generator as input and the RF gain all the way
CW, I can adjust the signal generator to get -10V on the Diode Load in MGC.
Switching to AGC, the Diode Load drops to about 3.4V to 4V (depending on the
AGC speed position).

I assume this is an AGC problem and if I check the AGC voltage, I'll see
it's generating too much AGC voltage, right (I didn't check this last night
but will)?  If this is the case, where do I start debugging this?  I assume
checking tubes, pin voltages and resistances is the right place to start?

Thanks,

Barry - N4BUQ