I think you mean a 'nuvistor', a metal can type valve, these do have low power heaters, usually about 2volts @ 0.4A, which sounds a lot, but thats only 1 watt, low for a valve heater, you'd have to use a switching reg if you want maximum efficiency from a higher voltage supply.
A 13DE7 might be the sort of thing your after, its a double triode, I dont think they are manufactured anymore but probably still available, as mentioned they were popular in TV front ends, 2 way radios and 'scopes.
This is what they look like, not made from glass, but steel.
Grounded grid operation was technique used to lower the impedance to match a 1/4 wave aerial impedance, a similar manner to a grounded base tranny, I'dve thought you'd also be able to run one in the standard grounded cathode manner just as well.