That was a selling point Continental Electronics used back in the 50s. Like Western Electric, Continental never produced a high level plate modulated transmitter. They had a 250 watt rig that used a pair of 4-250s with a combination of control grid and screen grid modulation, plus negative feedback based on audio derived from an RF sample taken at the output terminal and fed back to the speech amplifier. They made it a specific point in the manual to that rig that the total efficiency, comparing power drawn from the a.c. mains to the RF to the antenna, was about the same with low-level (grid modulation or leen-yar) or high level plate modulation, once you calculate in losses in the high level modulator tube plates, modulation transformer, power consumed by the modulator tube filaments, audio driver stage, etc. Some of their higher power transmitters achieved improved efficiency by using the Doherty system, including the Continental transmitter at Border Blaster XERF. Nevertheless, nothing beats the high level plate modulated class-C final for ease and stability in tuning and frequency agility.