I have been thinking, the last few days, that I should clear off a spot on the
desk and put my spectrum analyzer and amp on a clean desk and make some tests
to see what the input circuit does.
I have an old Swan Mark II, which did not come with tuned input. I added it
underneath, with small relays and toroids and an additional switch deck. Since
it runs 2 x 3-400 tubes, it would be similar to many of the amps out there. It
would be relatively easy to switch in and out the input circuit.
As I began thinking about that, it occurs to me that any meaningful test would
not be that easy. As soon as I remove the tuned input, the load for the
exciter changes substantially, which means impedances and drive changes. Those
things alone could change the imd sufficiently in the exciter to show a few db
difference in the imd of the amplifier.
That would imply that a lot more testing would be required to understand what
is being tested. Perhaps one of those class A transceivers would be useful as
a driver.
Maybe I should just wait until evening and open a beer and forget the whole
thing. A test run poorly is not as good as a beer drunk poorly.
73, Colin K7FM
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