Chip Owens wrote:
>
> If one uses an hf power amplifier for cw operation only is there any
> good reason to operate it in AB1, AB2, or class B? Wouldn't class C
> operation yield higher efficiency and actually make QSK operation
> easier to implement?
I recently considered the same issue and settled on AB2 (and I don't even know
where my microphone is). I designed my amplifier for 1500 watts out, and
efficiency is irrelevant -- I don't hold the key down long enough to affect my
electric bill. The amplifier generates less harmonic output in AB2, and
reproduces the keying envelope more accurately.
Cathode-driven operation in class AB2 requires a convenient amount of drive
power; in class C, I would need to go to a grid-driven circuit to get enough
output with my exciter. The tubes I'm using do not require neutralization in
the cathode-driven configuration. Bias is supplied simply by forward-biased
diodes; this would be impractical for class-C.
The only reason I could see that QSK would be easier would be that the plate
current would be completely cut off between elements so you could use an
old-style tr switch without noise problems. I am using the vacuum relay QSK
circuit that is on Rich Measures' web site -- it includes an electronic bias
switch to completely cut the tubes off between elements. You can certainly do
this without the vacuum relay if you like tr switches!
> This is my first posting to the reflector. Do I need to put on my
> flak-jacket before reading replies?
Why on earth would anyone think that? :-}
73,
Vic, K2VCO
Fresno CA
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