km1h@juno.com wrote:
>
> I remember somewhere back in the 80's an article by Ulrich Rhode that
> described a 1.8 to 30 MHz network.
> Has anyone tried such a circuit?
Hi Carl,
Remember the input circuit serves the function of an RF path for cathode
currents, and there are harmonics generated in the tube.
If you don't use a system that provides a low impedance to ground,
especially for odd multiple harmonics, efficiency and IMD can suffer.
You might very well find the circuit handles matching quite well, but
the PA then suffers IMD and efficiency problems.
A tuned input that provides a low impedance for high order harmonics
isn't always necessary, but it is usually a good idea. Heathkit had a
pair of 3-500's that suffered efficiency problems on ten and fifteen
meters that was traced to this problem. It also shows up in the
AL-1200-82-1500 amps.
73 Tom
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