[Amps] Grid neutralized triodes

[Fuqua, William L.]

  Many years ago we discussed plate and grid neutralized triode amplifiers.
Just about all common cathode triode HF power amplifiers used HV split stator
plate capacitors rather than lower voltage ones on the grid.
  Well, I had come up with an complicated explanation and realized now that it was wrong.
I believe the reason that it was so commonly used had to do with imbalance as the capacitance
was varied.
  If you plate neutralize cancel out the plate grid capacitance which also eliminates most of the
plate to cathode capacitance.  So, as you go from max to minimum capacitance there is little imbalance.
And it is unlikely that the amp will go into oscillation when at the extremes of the tuning range.
  However, if the split stator is on the grid one half has the grid cathode capacitance shunting it and the
other has no additional shunt capacitance.
   The Johnson Courier amplifier has a split stator grid circuit, two parallel 811A tubes and a PI network
output. However, a closer look will reveal a shunt capacitor on the stator that is connected to the neutralization
capacitor.
   Look at the BC-375, it has a very complex neutralization method.
Also, although a bit risky, some higher power amplifiers published in the GE notes have MB-150 multiband split
stator tuners on the grids and PI network outputs. I say a bit risky because there is not a shunt cap on one stator.
  That being said, I wish I had time to experiment with some amplifiers and put some of my old big triodes to work.


73
Bill wa4lav