On Feb 2, 6:29*pm, "Antonio Vernucci" wrote:
I cannot give you actual values for your set up, but basically, if you
have already provided optimum bias with your fixed bias voltage, then
you will not need to develop any more bias across a grid resistor.

peter

My fixed bias is set for an idling plate current of 10 mA. The only criterion
behind that bias setting was to keep the final tube safe. So, it may not be
optimum with regard to the final stage efficiency.

On the contrary, it is surely not optimum because, without extra bias, the tube
operates class B. More bias is needed (produced by the grid resistor) to have
the tube operating class C.

73

Tony I0JX

With a fixed bias supply , do you really need a grid resistor as
such ? how is the -Ve bias reaching the grid ? ....with the
cathode earthed .. the fixed bias is 'required' .. I would think for
a given drive level ... increasing the -Ve grid bias would reduce
the conduction angle and slide the stage from class b to c as
the peak drive level would need to overcome the bias to allow
the grid to conduct .. thus the conduction angle is reduced ?

G ..