Year ago, between 20-30, I came up with an explanation of why non-push-pull
triode amplifiers are
not grid neutralized. I was wrong.
Later I figured it out. The input capacitance of a tube throws the balance
off. E F Johnson solved this problem
in their little courier amplifier. There is a capacitor across the non-tube
side of the input capacitor equal to the input capacitance
of the two 811a tubes.
At one frequency you can neutralize the amplifier, but as you tune off
that frequency the input ckt's balance is thrown off it the shunt capacitance
is not added on the non-tube side of the split stator capacitor.
There is one other thing that can throw the balance off and that is the
grid loading due to grid current on one side if the split stator.
Not so sure how that fits in.
It would be neat to build a large triode grid driven amplifier with a PI
output some time.
73
Bill wa4lav
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