[Amps] When does an GG Amp draw current.

[jeff millar]

The grid draws current when it is positive compared to the cathode.  This
occurs on the positive peaks of the drive voltage.   Tubes are very
different in the relationship between grid voltage and plate current.  The
GS35 is known to operate with very high grid current compared to other
tubes.  The 8877 wants very little.  Some tubes like 4cx250 operate without
grid current.

The negative bias voltage sets an idling plate current and the drive causes
the plate current to vary.  The drive will cause the tube to swing between
plate current cutoff and maximum plate current.  The grid current also
swing between zero and some peak set by the drive.

To achieve maximum power output, the positive portion of the drive needs to
force enough plate current to cause the plate voltage to drop to nearly
zero.  The amount of drive required depends on the tube, plate loading, etc.

The GS35 should pull up to several hundred mA of grid current when driven
to full power output.

jeff, wa1hco

On Tue, May 31, 2016 at 2:53 PM, Paul Baldock <paul at paulbaldock.com> wrote:

> My 2 x 3-500Z amp starts to draw a few mA of grid current with about 1
> watt applied. Bias is about 8V.
>
> My home brew GS35B amp  starts to draw a few mA of grid current with about
> 15 watts applied. Bias is about 40V.
>
> Is my GS35B amp behaving as it should? 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?
>
> Thanks
>
> - Paul  KW7Y
>
>
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