On Aug 25, 2012, at 9:40 AM, Dr. David Kirkby wrote:
> I think one might struggle with tube amps, as any tuning adjustments on the
> input or output are likely to change the phase of the signal at the output of
> the amps. Unless the two signals arriving at the combiner are in phase, you
> are
> not going to get the desired effect.
>
> I might be wrong - I have never tried it, but I suspect it will not be quite
> as
> simple as one might like.
>
> Dave
Yes.
I remember RCA made an AM broadcast rig called the "Ampliphase"
that used two tubes 90deg out of phase and obtained AM by phase-
modulating one of the tubes' RF input to 0 deg or 180 deg compared
to the other tube and it had a reputation for the phase drifting and was
a bear to tune. This was in the broadcast band. 10 meters with tube
amps combined , worse even than 2 tubes in one box, might be very
difficult to keep stable. Maybe 160?
-- Jim , W2XO
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