I found a note I intended to post but don`t see it so I suppose it was
lost in cyberspace somewhere. I was responding to Owen Duffy.

Owen wrote:
"How could such a transfer characteristic be argued to be linear?"

I responded:
Conditioning.

Class C amplifiers are used lawfully in great abundance. That is proof
enough that they are relatively free from distortion. Pulses in plate
current don`t prevent the output of the Class C amplifier from becoming
a pure sinusoid. Just as an internal combustion engine uses an almost
endless string of exlosions in its cylinders to produce a smooth uniform
rotation of its crankshaft and flywheel, the Class C amplifier uses an
almost endless series of pulses to produce a smooth sinusoid.

I will quote B. Whitfield Griffith, Jr., Principal Engineer (retired) at
Continental Electronics, Dallas Texas, builder of many of the world`s
most powerful radio transmitters. Griffith says on page 500 of
"Radio-Electronic Transmission Fundamentals", that it is important where
you couple the load to the Class C amplifier:
"Figure 56-2 shows how the class C amplifier might look in a typical
arrangement. Many refinements of the circuit, which are necessary for
practical reasons, are omitted here, since we are concerned only with
the fundamental principles of its operation at this time. The plate load
impedance consists of a tank circuit of a type similar ro that of Fig.
15-5; the difference is that the load resistor is in series with the
inductance rather than the capacitance. This is the preferred
arrangement, because the harmonic components of the plate current all
have frequencies higher than the fundamental and quite naturally tend to
follow the capacitive branch of the circuit. By extracting power from
the inductive branch, therefore we can expect to find less harmonic
energy in the output than would be present if we loaded the capacitive
branch. This load resistance may be an actual resistor, if we wish to
feed the output of this amplifier into a dummy load for measurement
purposes, or it may be the input resistance presented by some type of
impedance-matching network so arranged that the loading of the amplifier
can readily be varied. Another common method is to couple resistance
effectively into the tank inductance by means of the mutual inductance
between the tank and a secondary coil which is coupled to it
magnetically, where resistive loads appear in the secondary circuit.

There is also shown in Fig. 56-2 the r-f waveform of voltage and current
which we would expect to find at various points in the amplifier
circuit. No allowance is made in these illustrations for the differences
in potentials of various portions of the circuit; these diagrams are
merely representative of the behavior of the r-f potentials and
currents. Notice particularly that the r-f plate voltage is 180 degrees
out of phase with the r-f grid voltage. The reason for this is easily
understood. When the grid is its at its most positive potential, the
plate current is at its maximum. As the plate current is drawn through
the load impedance, the increase in plate current causes a corresponding
reduction in plate voltage. The plate voltage therefore swings downward
at the moment the grid voltage swings upward. We also see that the
current in the load resistor is lagging the r-f plate voltage by an
angle of a little less than 90 degrees. Correct operation of the tank
circuit requires that the resistance of this load resistor be much
smaller than the reactance of the coil."

Best regards, Richard Harrison, KB5WZI