[AMPS] Question about neutralizing

[Bill Turner]

Something has always puzzled me about neutralizing, so I wonder if
someone on this reflector could answer my question.

With a conventional triode in grounded cathode configuration, the
plate voltage is 180 degrees out of phase with the grid, yet the books
say the cause of instability is capacitive coupling from the plate to
the grid.  How can this be a cause of instability if they are 180 out?
I would think any coupling would be degenerative, not regenerative.  

Even if you allow for phase shift from the reactance of the plate-grid
capacitance, the result should still be degenerative within the 0-90
degree range and would only become regenerative if you went beyond 90
degrees.  In an RC circuit the maximum possible phase shift is 90, so
what's going on?  Any ideas?

73, Bill W7TI


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