> > The auto tuner being discussed for an input tuner, mounted near the
> tube,
> > would suffer a similar problem even if a fixed capacitor was used for 10
> > meters. If the auto tuner indeed is an L network then there would be
> > insufficient capacitance on the lower bands.
> >
> > It would seem that the tuned input circuit is more important from the
> > standpoint of supplying a clean series path for the plate circuit signal
> > than it is for supplying a constant load to the exciter.
If one wants to depart from the traditional Pi input network a parallel
L/C configuration can be utilized. A tapped fixed inductor from the
cathode(s) to ground, shunted by 300 pf Arco trimmers for each band. This
seems to cover all bases, is easy to construct, install, and tune. This is
the scheme utilized in the Alpha 77 series amps that results in a clean
signal and a happy exciter.
I have seen several posts on this thread that indicate a misunderstanding
of how a tuned input works and what it is supposed to accomplish. If the
tuned input assembly is not in close proximity to the cathode and
connected to it with bus wire or strap, an optimum condition probably does
not exist. A low input vswr is not the only consideration, and certainly
not the primary one.
(((73)))
Phil Clements, K5PC
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