Over the weekend, I re-activated the electronic bias switch in one of my
PA-70V vapor-cooled amps. Prior to this change, bias was fixed, pursuant to
some information I received from another "vapor" owner of an alleged ETO
service bulletin describing this mod.
Upon reactivating the electronic bias switch, I noticed that grid current
idles slightly negative (below the meter's zero point at about 15-20 mA) in
the high-voltage position. However, grid current is zero in the low voltage
position. This is a grounded-grid, AB1 amplifier using what's essentially a
3CX1000A7 tube.
Does anyone know if this is normal for electronic bias switching and is
there any degradation in performance in allowing this condition to continue?
Thanks!
-Paul, W9AC
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