This is also a good read,
Very large valves of this design were used up through the late 60s for rectification to HVDC for efficient long distance high voltage transmissiion lines. I don't know if any of the valves still exist, since solid state and fiber optically triggered solid state devices may have completely replaced them. The huge powers and voltages (hundreds of kV) there make a great "natural experiment" to exaggerate the possible isotopic shifts seen in fluorescent lamps. But did anyone save even one of those valves? And more difficult: did anyone bother to save the mercury contained therein? The last of those valves I know of were manufactured or at least marketed by ASEA (essentially "the Swedish General Electric Company", If I recall ithe translation and acronym correctly).