Walter, W2DU wrote:
"The internal resistance in Class B and C amps has two parts, 1) the
cathode-to-plate resistance, which is dissipative, and 2) the
non-dissipative resistance established by the V/I ratio within the
pi-network tank circuit -- a high resistance at the input and a low
resistance at the output."

It`s true that a parallel resonant circuit constructed of ideal
inductance and capacitance has high (infinite) impedance and no loss.
The configuration of the high impedance in series with the load limits
output. But, we use imperfect components and we seek a limiting
impedance equat to the 50-ohm load, not an infinite impedance.

My take on the non-dissipative impedance is that it comes from the
switched-off time of the Class B and C amps. During this time in each
cycle, no current flows through the amp to cause loss. Likewise, there
is no current from the amp (actually it is a switch operating on and off
at a radio frequency) to the load or tank circuit. The tank circuit
cleans up the pulse mess, filling gaps in the RF cycle.

Best regards, Richard Harrison, KB5WZI