[Amps] When does an GG Amp draw current.

[Bill Turner]

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On Tue, 31 May 2016 11:53:10 -0700, Paul wrote:

>When does an GG Amp start to 
>draw grid current? Is it when the peak rf  voltage applied to the 
>cathode exceeds the bias voltage?

REPLY:

Yes, when the grid is driven positive with respect to the cathode at
the peak of the RF cycle. At low drive levels the amp is actually in
Class A mode and only gets into Class AB as drive increases. 

This assumes of course that the amount of bias is set correctly. With
no drive, the plate current should be about 10 to 20 % of the maximum
when driven to full output. For example, my homebrew 8877 draws 800 ma
plate current at 1500 watts out and idles at about 100 mA. The exact
amount is not particularly critical. A higher idle current will give
better linearity but reduces efficiency and wastes power. It is a
compromise the designer must make. No free lunch. 

73, Bill W6WRT