I have no idea if they have a US equivalent, or what it would be. But they are fairly common in the UK.I don;t own any computing equipment that uses them, but I have the plugoard-programmed controller from some kind of spectrometer instrument that has a row of these indicating the current status, I also have various arrays of them removed from other equipment (not by me, I hasten to add). I've probably got about 30 'spares' in the junk box. They're about the size of a 3AG fuse, but without the metal end caps (obviosuly). They have 4 wries coming out of one end and the seal-off tip at the other. if you find one, you can identify the wires as follows : 1) find a pair of wires that have a low DC resistance to each other. These are the end of the filament. The other 2 wires test as infinite resistance to these (and to each other) 2) Conenct about 1.5V between the filament wires (a single dry cell is fine). Now connect the -ve side of a 30V (24V, whatever) supply to one end of the filament and the other end to each of the other wires in turn. One of them will get the thing glowing grren, that's the anode. 3) With it glowing, connect the +ve side of a 3V supply to the end of the filament connected to the -ve side of the 30V supply. Connecting the -ve end of this 3V supply to the remaining wire should cut off the device and stop it glowing. -tony