I recently acquired an old EM80 magic eye tube. It seemed cool just to play around with it and maybe even make a nice sound level indicator - the thing it was made to do.The filament was OK, so I made a nice little bit of electronics around it.
The high voltage (250V) is generated by a voltage doubler and a transformer used backwards.
Here's the schematic (click for better resolution):
Pictures of the eye in action:
Darkness (long exposure):
And here's what's inside of it: