Vic: 1970's and 1980's HF amp designs published by ARRL often included
switched zener bias for class ab and c. What was described by W2RU I
suspect is an adaptation of these designs. I have used the same 27 volt
zener with pairs of 3-500;s operating on cw. Keeps the tubes cut off
nicely. One of course must not forget to switch it back for ssb, which
I assume is why it has never been implemented commercially. A look at
the amp designs on arrl's web site will provide much food for thought.
73 bob de w9ge
Vic Rosenthal wrote:
W2RU - Bud Hippisley wrote:
3. I operate 99% CW, and have added a 25 - 28 volt (50 watt!) Zener in
series with the stock 5.1 volt operating bias Zener when I am on CW. I
originally did this because I run full break-in on CW, and use an
electronic
TR switch on the output of the amplifier, so I needed to cut off all
plate
current to eliminate "hash" in the receiver. Secondary benefits of
this are
that I have no power dissipated in key-up idling current and my key-down
efficiency is probably slightly higher than it would be with the
stock class
B biasing.
I am also primarily a CW operator and would be interested in hearing
about any others who have optimized amplifiers for CW. I've always
felt that it's a shame to waste power by biasing CW amplifiers for
minimum IMD!
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