Rich, W3HWJ wrote:
Make a desk lamp out of it?
It would make a really nifty light dimmer, but would be rather large.
Sell it in the Radio Classifed section?
2.5V 25A filament ! That's 63W ! 0.1ohm, hot !
Unless you've got a boat anchor of 2.5V transformer lying around, a desk lamp ain't gonna happen. Then again, if you got an old unused PC sitting in a back corner, you might be able to light it up. If it has an ATX type supply, you might be able to open it up and tweak the 3.3V supply down to 2.5V. A 0.032 ohm 50W series resistor is an alternative to tweaking the supply. PCs suck serious juice. 30A or more, available on the 3.3V rail, is normal.
Easiest solution is just to sell it. Don't know the demand on this particular tube. If you had one of its cousins, an ignitron, then you'd have something. A lot of metal shops around here still use spot welders, with those in them.