The lower plate voltage was used for CW on amps that were made when the
old rules only allowed 1kw DC input power. Now that the rules allow 1500
watts output power there is no need to lower the plate voltage (unless
you just want to run lower power) as the amp is now tuned the same for
CW as it is for SSB. Same power levels.
As far as the changes in bias, 7.5 volts for SSB and 27 volts for CW,
the 7.5 volts allows for higher zero signal plate current that is
necessary for the amp to remain linear for SSB. For CW the 27 volts will
probably completely cut off the zero signal plate current. This saves on
plate dissipation. The tube does not need to be linear for CW so this
works out fine.
73
Gary K4FMX
GGLL wrote:
> 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.
>
> Thanks in advance
> Best regards
> Guillermo - LU8EYW.
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>
>
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