Barrie,
The first rule of amplifier building after keeping your hands in your
pockets is to know what your plate load resistance is. Without it you
can't know the proper values for C1, C2 and L to maintain the proper Q.
Your friend must first decide what OUTPUT power his amp is going to be
designed for. Then what the input power is going to be with some
reasonable efficiency (usually around 55%) (Pin=Pout/.55). Then,
knowing what his INPUT power will be, use the plate voltage (under load)
to determine the plate current at that voltage (I=P/E). Then use the
formula (RL=Ep/(1.6xIp)) to approximate his plate load resistance. That
will be the value of non inductive resistance to place between the plate
and ground for testing.
Don't fudge on the value of C1 and L. There are several on line tools to
calculate the values of the tank circuit. Stay within reasonable limits
to keep the Q of the circuit between about 12 and 15. Get the Q too
high and tuning will be extremely sharp and things will begin to melt
down because of the high circulating currents. Too low and tuning will
be too broad and you'll have practically no harmonic suppression.
Good luck with your project!
73, Tony W4ZT
Barrie Smith wrote:
> A friend is building a 3CX3000 amp for 6M.
>
> He wishes to ballpark the tuned input circuit by installing
a resistor between the tube input and ground.
>
> What would be the proper value for this resistor?
>
> TIA, Barrie, W7ALW
> _______________________________________________
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