>
>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
[which is actually positive current]
>(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.
If it runs grid current, it's AB2
>
>Does anyone know if this is normal for electronic bias switching and is
>there any degradation in performance in allowing this condition to continue?
>
This sounds unusual to me, however, any RF actuated bias-switching has
built-in "degradation in performance" since it causes the tube to rapidly
switch in and out of linear bias during voice transmission.
>
- later, Paul
Rich. Measures. Web site: www.vcnet.com/measures
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