Thanks to all for the suggestions on the 77SX, I have the delay
circuit working well now. Rich your comments on the 77 are well taken and
I did look
over your bias system in the January 94 QST, I agree with the RF driven
bias
switch having distortion problems, however I did alot of research on rf
driven
bias switches back in the early 80's and modified a large number of
SB-220's
to rf driven bias switching and there is a way to get rid of the
distortion due to
the turn-on knee of the bias switching transistor that works so well I
use it in
my homebrew 4CX250, the problem is solved by simply installing a 10 ufd
50 volt capacitor across the collector-emitter of the switching
transistor.
The charging of this capacitor provides a path for the cathode current
until
the transistor gets fully turned on. Its simple and it works very well.
I have used this for years and have never had a problem with it, it was
a
great advantage in the 4CX250 amp which idles at 100 ma.!
Mark Graalman
Toledo, Ohio
Callsign: WB8JKR
Member: Society of Telecomunications Engineers
TCBA member # 1399
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