Behold, R J Carpenter signalled from keyed 4-1000A filament:

Others have mentioned uses for these tubes. What they haven't mentioned
is that you will need a power supply delivering DC somewhere in the 150
to 250 volt range. It is absolutely vital that this supply have a
transformer to isolate you from the 115 V AC mains. Otherwise you'll
likely kill someone or yourself, since on side of the AC line is
connected to ground and the other is HOT with respect to every grounded
object.

Junk boxes all across the world may be full of these transformers, but
you may have trouble finding one. In that case you could use a couple
of 115 to 12-or-so volt transformers. One to go from 115 to 12 V AC,
the other connected "backwards" to go from 12 V AC back to 115 V AC. Now
you have 115 V AC with neither side grounded - much safer.

Just to add, if you only need ~15 watts for your project, bathroom shaver
isolation transformers hooked up in a FW doubler are great for this too.

You can get them from building surplus or second hand stores for 2-$5.

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca