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)

Output power will not rise for a given anode voltage and a given
excitation (drive). But with a reduced conduction angle the anode input
power will be less. On the other hand you'll need more drive to arrive
at the same anode currrent. But drive power doesn't enter the anode
efficiency calculation, which is rf output power divided by dc anode
input power (the quotient obtained thus multiplied by 100 if you want
it in percent).


I try to explain me better. When I change the grid resistor, I see no chage in
the ratio between RF output power and DC input power, this meaning that
efficiency does not change, I would have exprrcted that, going class-C, I would
have got a higher efficiency (more RF power, or lower DC power, or both).

73

Tony I0JX

When I change the grid resistor, I see no chage in the ratio between
RF output power and DC input power, this meaning that efficiency
does not change, I would have exprrcted that, going class-C, I would
have got a higher efficiency (more RF power, or lower DC power, or both).

So would I. How do you feed the 829B's screen grid?

The screen grid is fed by a dedicated 200V supply, which is very stable (within
the screen current excursion).

73

Tony I0JX

On Feb 6, 9:10*pm, (Edmund H. Ramm) wrote:
In "Antonio Vernucci" writes:

[...]
When I change the grid resistor, I see no chage in the ratio between
RF output power and DC input power, this meaning that efficiency
does not change, I would have exprrcted that, going class-C, I would
have got a higher efficiency (more RF power, or lower DC power, or both).

* *So would I. How do you feed the 829B's screen grid?

* *73, Eddi ._._.
--
* * * e-mail: dk3uz AT arrl DOT net *| *AMPRNET:
* * * If replying to a Usenet article, please use above e-mail address.
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Your not supposed to ask questions like that Eddi !

My point with the grid supply wave form , is that the point of
conduction is set by the voltage .. so depending on th voltage the
sinusodial drive waveform will redue to a pulse train .same peak ..
but lower average ... I think there is some form of operation in
the 'negative' region .. now if the screen is dropper fed, then
its floating and may be subject to secondary emission .. so the
working point of the valve is moving ... may be not if the screen
is stabllised .. but if so . would than not affect the am mode ?

G ..