"K7ITM" wrote in
ups.com:

Actually, the comparison of a grounded-cathode and a grounded-grid
amplifier is a good illustration of how the plate source impedance and
the optimal load impedance are unrelated. The change between those
two types, for a given tube and given plate voltage, has a minor
effect on optimal load impedance, and a major effect on plate source
impedance.

Tom,

A good point!

I am playing around with a model of 4 x 811A in GG followed by a PI
coupler into a nominal 50 ohm load to explore the small delta dynamic
source resistance, and the common cathode configuration would be an
interesting contrast. The interesting thing in modelling the GG triode
class B config is that the changing driver load as Ia changes (ie the
feedback) will vary in effect depending on the equivalent source
impedance of the driver. Again another variable that mitigates against
the accidental "conjugate match".

Owen