> In reference to the subject matter. I have an article here written by
> a ham in spain and published by Svetlana several years ago. This
> gentleman built an amp, single 572B, using a home made rf choke and
> input transformer combined, and using a large swamping resistor ,
> about 75 ohms at 40 watts, untuned input..
With low enough swamping resistance it will certainly work OK.
The swamping resistance simply has to be a fraction of the lowest
expected impedance of the load throughout each portion of the RF
cycle. That way non-linearity over the RF cycle and harmonics are
minimized.
There also are cases where you can "get away" without a tuned
input or any special considerations in an amplifier drawing grid
current or a less than 360-degree conduction angle amplifier, but
they are specific to a particular set of circumstances such as
exciter type and cable lengths. The problem is such systems are
not reliably reproduced.
If you want to build a linear GG amplifier (or grid driven amp that
draws grid current) with near optimum IMD performance, you either
better swamp the heck out of the input or use a proper tuned input.
Eimac and others aren't just joking when they suggest a tuned
input or swamping resistance as a good design suggestion. There
is a valid technical reason for their suggestions.
73, Tom W8JI
W8JI@contesting.com
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