> > One factor that apparently
> >increased the Warrior's VHF instability was so-called
> "So-called" is correct. According to the schematics, it consisted of a
> feedback capacitor from the output end of the pi-tank, back to the
> cathode. This will produce feedback of variable amplitude and phase,
> depending on the settings of the bandswitch and the tuning and loading
> controls. It's hardly surprising that the amp was more liable to
> oscillate at some frequency.
That is NOT correct Ian. Bad enough that Rich says things without
being fully aware what is going on!
The feedback in the Warrior is from the anode, through a capacitor,
through a phase inverting transformer, to the filaments.
The tuning of the tank has a very minimal effect on phase shift.
This is a simple modified bridge system.
I think you are wrongly confusing it with the system in a Yaesu
572B amplifier where feedback is taken AFTER the output tank,
which of course WOULD shift phase with tank tuning and
destabilize the amplifier at HF with some tank settings.
> >Heath did not use neutralization in its subsequent models of GG
> A wise decision, since it never could possibly do what it was intended
Wrong again Ian. The circuit works fine because the feedback
capacitor is taken from the SAME POINT as the stray capacitance
in the tube. Both start with the same point, both have the same
capacitance, and both terminate at the same point. One path is
inverted 180-degreees, the added path, by a broadband transformer
(a third winding over the filament choke).
> >Gonset also used neutralization in their 4, 811 amplifier.
> I'm not familiar with that schematic: would that be real
> neutralization, or more of the bogus kind?
Before you say "bogus", you should look at the system. It works
very well in Heath's amp and other amps. It has nothing to do with
VHF oscilations, it is to stabilize the amp at upper HF.
Collins is about the only one who did not do that, and THEY have
problems with stability on 15 and ten meters in the 30L1. You can
take a Warrior and unload the input and output, rotate the controls
through all settings, and NOT have it oscillate. The same will not
happen with the 30L1 and other amps that do not neutralize.
Let's not feed people trying to learn misinformation Ian!
73, Tom W8JI
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