On Feb 6, 12:12*am, "Antonio Vernucci" wrote:
* In this case the grid resistor, connected between the rf-bypassed
negative port of the bias supply and the cold end of the grid choke has
to provide the difference between the protective bias (above mentioned
-33V) and the class C bias specified in the valve data sheet. Simple
Ohm's law can be applied. If the grid current is say 2mA and the desired
grid bias is -63V, i.e. a difference of 30V, the control grid resistor
needs to have 15kOhm.

* 73, Eddi ._._.

Yes, Ohm's law is OK, but the my issue was that whatever "desired grid bias" I
take, the final stage efficiency does not change, So, changing the grid resistor
makes almost no difference, whilst I would have expected that biasing the tube
in the class-C region would yield more RF power that when it operates in class B
(i.e. with grid resistor = 0 ohm)

73

Tony I0J

My practical experience is that lowering the grid resistor I always
get more
output power FOR THE SAME GRID CURRENT.

So ... how do you know its the same ...if you use a meter ..
then the shape factor of the grid pulse will change the meter
reading .. wider pulse lower peak will still give the same
reading ?

need to check the waveform .. not easey .. simple way is to
forget the resistor and provide a variable bias psu . and inject
via a low ohm rf-choke ... and add some link to the bias voltage
and the pa plate supply ..no bias no supply .. simple relay ?