So how did we get reasonable efficiency in plate modulated 160m PA stages,
> where we couldn't use a value as big as .01 uf to bypass the end of plate
> feed RF choke without serious effects on the modulation? Or was it that
> generally speaking, 160m AM tx's didn't cover so much of the HF spectrum,
> and were able to use much bigger plate chokes (1 or 2millihenry)?
It was, indeed, Peter.
Even the National R-175 chokes found on Johnson and many other amps,
including many H.B. projects allowed for getting away with less bypass C
at the base of the choke. It was when 6 band amps started appearing with
strings of filter caps and plate chokes < 90uh that the problems started to
surface. When the FCC opened up 160 meters to QRO, many of us just
added a 180-200 uh choke in series with the original, and mounted it at
right angle to it. I notice that several manufacturers today use two chokes
and switch the big one out for 40-30-20-17-15-10 meter operation. This
is the ideal way to keep RF going where it is supposed to, and prevents
those terrible oders of burning chokes in the ham shack.
>
> I seem to remember a number of professional tx's in those days that used
> push-pull RF stages, and so the problem would be a lot less. STill, not
all
> of them did so.
I still have an old pi-wound choke from an AM BC transmitter that is HUGE!
Must be wound with #18 DCC wire...
(((73)))
Phil, K5PC
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