Walt, W2DU wrote:
"Rp is a non-dissipative resistance, not a tesisTOR with physical
characteristics."

To nit pick a little, I think some dissipative resistance is found in
the output impedance of a Class C amplifier when you average over an RF
cycle.

Although rp (dynamic plate resistance) is defined as the change in plate
voltage divided by the change in plate current when an increment of
plate voltage produces an incremantal change in plate current, plate
resistance goes down as plate current goes up.

Rp can be very low but not zero when a tube biased beyond its cut-off is
pulsed on heavily duting the RF cycle. In saturated conduction the
voltage drop actoss the tube can be very low and any change in plate
voltage would result in insignificant change in plate current.

When a Class C amplifier is switched into heavy conduction by its grid,
its DC resistance is low and its power suppy may be low in resistance
too. During the conduction part of the RF cycle, the impedance looking
back into the amplifier`s putput is low also. During the switched-off
part of the amplifier`s cycle, the impedance looks like an open circuit.
Over an entire cycle, the tube`s output impedance has an average value.

A pi-network is an impedance transformation device which does not
completely isolate its input from its output, so a tube on its input has
its shunt impedance transformed to some value across its output. Its
resonance can linearize the signal.

Best regards, Richard Harrison, KB6WZI