[Prcmaker]

Really it's both ways in terms of required current. The thermionic effect requires filament heat, which since being a filament, take some amount of current, often around half an amp, some more some less. A filament could, in theory, be run at any current though so long as the power through the filament stays the same and the voltage is kept low enough not to arc to adjacent parts. There is likely also a minimum current requirement (since you need a source for those free electrons), which often then implies some non-linearity at the low end.

As others have mentioned, the 200amps of this case could be reduced substantially by running filaments in series (can be done with 6.3v heaters as the error from a common 5v or 9v supply is more than if you pair them up and use a 12V supply) though this introduces the failure mode of old Christmas tree lights.

Source: I make vacuum tubes.