The 8008 1749

I've seen 40's vintage TVs that used a 25L6 as a 300khz or so oscilltor to bounce the B+ up to 5kv or so, and also light a 1B3 up (not much current there). Heck, flyback systems are like that, effectively.

BTW, the 6.3 volt heater standard came about from car batteries being 6.3 volts and the then growing popularity of car radios. A *lot* of the early RCA octal series tubes were rebased 4-5-6-7 pin designs, too. a 5Y3 and type 80 are the same tube, ditto for a 5U4-5Z3. Only the base is different.

RCA did this with the switch to miniatures after the war, too.

Early early radios used 2.5 volts on the heater-filiment. 5 volts became a briefly used standard, but 6.3 came right afterwards.

Even many 'conventional' tubes will in fact conduct at surprisingly low voltges - most dampers from TV sets will in fact conduct pretty hard at a few volts, and there are even a few triodes that can sort of work at 12 volts. The space charge ones were just designed for it. I suppose NuVistors could, too, but those came way late in the game. A tube the size of a pencil eraser is cool, though.