I was reminded of the remarkable valves of the Third Reich by Ostar Ganz which had 230 Volt heaters. I experienced no trouble with heater/cathode leakage, unlike some later CRTs. The insulation withstood the 326 Volt peak potential difference without complaint.
They used a 7-pin holder, C07, with an earthed plate between heater, cathode and other electrode pins to avoid hum pick-up. With no mains transformer, the result was a very light and simple AC/DC chassis.
The museum has only B5 based Ostar Ganz valves - Ed.