Grid leak resistance isn't only some discrete resistor, there's
also your bias supply to be considered. Is your bias supply able to
sink current, or does its output voltage rise with grid current?

The bias supply is a zener-stabilized -33V supply. I have verified that the
supply voltage stays constant independently of grid current. So the effective
grid resistance coincides with the grid resistor.


[...]
Where has the class-C efficiency advantage gone?

There was a rule of thumb for optimum anode efficiency, which went
along the lines of "when the anode voltage at its lowest swing equals
the control grid voltage" IIRC.

Thanks for tip, though not immediate to measure.

73

Tony I0JX