As the tube input impedance in GG is non-linear, the input circuit also helps
in reducing phase distorsion caused by non-linear loading of the driver stage.
This is elaborated in some detail in chapter 11 and 13 of "Single Sideband
Principles and Circuits".
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: <sm0aom@telia.com>; <amps@contesting.com>
Sent: Tuesday, January 24, 2006 5:23 PM
Subject: RE: [Amps] Tuned input
> Thanks Karl-Arne, very informative!
>
> Someone mentioned putting a capacitor directly at the cathode as part of the
> tuned input network to alleviate the inductance problem on 10 meters. It
> seems that would be fine on 10 meters but would not help the situation on
> other bands if a remote tuned (antenna tuner) input circuit was used.
>
> 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.
>
> 73
> Gary K4FMX
>
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> > Behalf Of sm0aom@telia.com
> > Sent: Tuesday, January 24, 2006 3:17 AM
> > To: garyschafer@comcast.net; amps@contesting.com
> > Subject: [Amps] Tuned input
> >
> > The reason for short-circuiting the harmonic currents in the cathode
> > circuits
> > is that they would cause voltage drops over the cathode circuit if not
> > bypassed.
> >
> > As the cathode and plate circuits effectively are in series, these
> > voltage drops
> > may influence the slope and shape of the plate load line,
> > depending on their phase and amplitude relationships with the
> > fundamental current.
> >
> > This can cause decreased power output and efficiency, in a similar way
> > as insufficient Q in the plate circuit.
> >
> > If the impedance of the cathode circuit becomes real at some harmonic
> > frequencies,
> > power will also be dissipated in the circuit.
> >
> > Bill Orr's reommendation of capacitance in the cathode circuit comes
> > from the
> > recommendation to have a circuit Q of about 3, and for a 100 ohms
> > input impedance
> > the resultant Q in a resonant circuit has this value with a
> > capacitance of
> > 13 pF/m. Values of around 20 pF/m were used in circuits with lower
> > input impedances.
> >
> > 73/
> >
> > Karl-Arne
> > SM0AOM
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>
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