Running tube with lower heater voltage

[Electron Tornado]

Can a tube that lists a heater voltage of 35V, for example, be run with a more common 6.3V?

[pdf64]

Heater voltage linits are typically specified as +/-10% of nominal.
So you’re a million miles off. 

[Latole]

Can a bulb light list for 120 volts be run ( a give a good light ) with 20 volts ?

[Electron Tornado]

Can a bulb light list for 120 volts be run ( a give a good light ) with 20 volts ?

Nope. Kind of what I figured.

[PRR]

You are trying to boil electrons. Same as boiling pasta. Fire too low, never cooks. Fire too high, pot boils over.

There are "alternatives". A 6V:35V transformer. A 120V:20V transformer, backward, 3.5X oversize. The world now has DC-DC converters and you might find a 7V-35V somewhere.

But I can't think of any 35V tube worth the trouble. 35L6 is not a funny 6L6 but a much smaller tube, and readily available as 6Y6. There are a couple old telephone repeater tubes for series working, with marginally better Gm/hiss than average tubes, but still silly (get a proper 35V supply).

[Latole]

But I can't think of any 35V tube worth the trouble. 

I agree