[ARC5] AM linear amplification

[Jim Haynes]

I'll insert a bit of lore from Loy Barton, who invented the use of a
class-B push pull modulator transformer coupled to the RF amplifier
plate as a way to do AM.  (Replaced the much less efficient Heising
modulation)

He noted that it may be convenient to generate AM at a lower power level
and then amplify it in a linear amplifier.  And pointed out that it is
sufficient for the "linear" RF amplifier to be Class B, because the
tank circuit will turn the half-sinewave pulses into sine waves.  It
is only necessary for the output amplitude to be proportional to the
input.  Which precludes a Class C amplifier but is satisfied by Class B.

Loy E. Barton, "Recent Developments of the Class B Audio- and
Radio-Frequency Amplifiers" Proceedings of the I.R.E., July 1936,
vol 24, no 7, p. 985.