My point was that, series modulation does work, best at low power levels because of the inefficiency involved. If you were going to do high level PWM ala Harris's MW-5, et all, thats a different story. High level PWM does work very well, and even today's solid state MW and SW transmitters under 6KW use this principle. To my knowledge, the only domestic manufacturer of high level tube PWM transmitters is continental electronics. They have a 50KW "Solid state modulator" which is essentially 48 750V power supplies individually series modulated with PWM and wired in series to get 10KV average B+ for the final tube. The benefit; no modulator tubes, high efficiency, and lower operation costs. The custom plate transformer which rolls on railroad track by the way, must be a pricy one. Never mind the fiber optic drive system.
+-RH