I'm thinking out loud, I guess it's called brainstorming. Just hit DELETE if
it's boring!
I already have just about all the parts for my amplifier, which will use a pair
of 813's,
but before I do too much construction I need to settle on the design :-) Since
I only
operate CW I had decided to go class-C, which would easily produce 750-800
watts from
these tubes.
I had decided to use a conventional grounded-cathode circuit with a
link-coupled
parallel-tuned input.
This means that the drive required will be on the order of 10 watts. No matter
how careful
I am, I can guarantee that the day will come when I hit it with the full 100
watts from my
exciter. So I would want to do something simple to protect the tubes. Should I
use
1) A grid trip circuit that will open the ptt line on excessive grid current,
2) A screen trip circuit, etc., or
3) Something else?
Another possibility is to switch to grounded-grid. I am not sure what the
issues would be
in trying to operate a gg amp in class C. Would I have to do more than just
lift the grids
from DC ground and supply appropriate bias and screen voltages? In particular I
want to
provide a good SWR for my solid-state transceiver, and I don't know what the
input
impedance would look like in class C.
Finally, I could give up on the idea of class-C. In that case I could use a
G2DAF circuit
in which the screen voltage is derived from the drive. This has the advantage
of a simple
swamped input which would provide a good swr to the exciter, and elimination of
the screen
supply. But then I can expect only about 600 watts.
I looked into running a G2DAF or other swamped input amplifier in class C, but
it would
need a very large amount of drive across any reasonable value of swamping
resistance to
get adequate RF grid voltage -- a 1000 ohm resistor would be needed and it
would burn up
about 75 watts just to get the grid swing (and that doesn't include the screen
power for
the G2DAF design).
I'm looking for ideas.
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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