So a few years ago I sponsored a contest on another electronics forum, and issued this challenge-Build a single-channel audio amplifier using ONLY dissimilar section tubes, and you must use all sections. No dual triodes, no single pentodes, etc-each section must be different.
Tim, as he usually did at the time, decided Class A wasn't good enough, so built the Borg. And he won the contest, handily.
https://www.seventransistorlabs.com/tmoranwms/Elec_Compound2.htmlTube based PWM generator and class D output...in tubes. Gets reasonably close to mosfet performance, too. Maybe applicable to Class D AM transmitters, if you really wanted to go the difficult route!