Are tubes used for high voltage/high power h-bridge circuits?
Mercury Arc devices were often manufactured in multiple anode packages so center tap schemes make sense .Vacuum tubes can and do have very high Anode voltage ratings but the Cathode filament voltage rating of a indirectly heated tube is low .The directly heated tube has a heater cathode voltage rating of zero because the heater is the cathode .Directly heated tubes are more common at high power. Filament power requirements are lower for directly heated tubes         .This means that if you did a vacuum tube full bridge at high power which means high voltage you would have to isolate the heaters .Such heater isolation would be a penalty if say you were dealing with thousands of volts of RF on say a 50Kw AM transmitter.The full bridge produces twice the power as the push pull with twice the number of vacuum tubes .The total cost including skilled hand assembly of a 4 valve full bridge will be more than a 2 valve push pull that used larger valves to make the same power .