> Subject: [Amps] Bias or Plate voltage change
>
> I've seen many GG amplifiers with a lower working plate voltage for
> CW mode
> than for SSB (for example some 2KV for CW, 3 KV for SSB).
> Others have a fixed plate voltage value and change cathode bias
> instead (7.5V
> for SSB, 27V for CW).
> Why this? and which method works better?. The latter seems to be
> cheaper, but
> is that the only reason?. One can work SSB with CW plate settings (not
> cathode
> bias CW settings), but what about CW at SSB plate settings?. Too many
> questions!, sorry.
I think a lot of this goes back to the old days when power limitations posed
by the FCC called for 1 kw input maximum on cw. I see no reason for
switching HV anymore. Large commercial amps like the Harris RF-110 switch
the bias for cw so as not to have to reduce the drive when going from ssb to
cw mode. (my guess) My rule of thumb when designing a new amp is to design
the tank circuit for the maximum key-down anode voltage and the recommended
anode current for ssb operation at a Q of 6-10. This will give you best bang
for your buck. (efficiency) You can then add a switch to increase bias when
on cw mode if desired. This will reduce resting anode current key-up, and
result in less heat generation in the cabinet. This also usually results in
a cleaner signal, but most amps nowadays are already cleaner than the radios
driving them!
I hope this helps with your query.....
(((73)))
Phil Clements, K5PC
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