Quoting Bill Turner <dezrat@outlook.com>:
I agree with Vic's comments 100%.
The only way to neutralize with a pi-input circuit that I know of is
with a coupling coil from plate tank to input tank, which I would NOT
do. Too finicky to adjust and highly dependent on the tuning and
loading of both circuits.
Somewhere, I saw a neutralizing circuit that used a ten turn toroid
between ground and a small pf value capacitor to the output network.
Another ten turns ( 180 degrees out of phase ) on the toroid went
between ground and the input circuit through a small pf capacitor.
Amplitude was controlled with a capacitor from ground to one of the
legs of the toroid. I imagine a variable resistor across either side
of the toroid would do the same thing on a single band amp for six
meters.
But !! If he is using Eimac SK-630 or similar tube sockets with built in
low inductance screen capacitors, there shouldn't be a need for any form
of neutralizing.
Don W4DNR
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