[Amps] Alpha PA-77 (not D or S) Questions

[Paul Christensen]

> 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