> 5. Should I assume that this amp, with its simple unswitched plate choke,
> will not operate on 12m?
Bob,
I would not run the 77 on 12M unless you update the plate choke. One
possibility is to send the existing choke to Dick Byrd, N4UQ who will
exchange it with a modified B&W 802 type. His choke uses heavier wire and
should also operate better on 160M. Another possibility is a switched
plate choke.
Check the wiring of the 160M modification. There's a hand-drawn diagram on
the Alpha web site that I believe applies to the 77, 70A, and 70V.
Hopefully, the prior owner added more bypass C at the input to the plate
choke as part of the 160M conversion.
Also check for heating of the Centralab doorknob caps when operating on
160M. This may be where a large portion of power is being absorbed. Again,
I would be highly suspect of the 160M conversion as well as any unauthorized
mods, unless it was performed by Alpha.
The QSK circuit in the 77 is a simple voltage doubler, consisting of a few
electrolytic caps and resistors. Your own circuit likely does a better job
of QSK switching.
Paul, W9AC
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