Can you ID this mystery tube/bulb?

(1/2) > >>


Hi Everyone,

I recently acquired a couple of strange looking tubes.? I would like to get the group’s thoughts on what these could be and what purpose they may have served.? I’ve posted more pictures here:

The tubes measure about 3 inches long and around a half inch in diameter.? One end is open and the glass is ground smooth with a cork placed in the hole.? The filament looks like coiled tungsten and I wonder if this really isn’t a light source of some kind rather than a vacuum tube?? There is what looks like a mica shield mounted below the filament, perhaps a heat deflector?? The four lead out wires through the glass pinch have the same look as Dumet wire.? Two leads go to the filament while the two outboard leads both go to the cylinder element inside the tube.

Can anyone help me ID this odd tube?

Thanks in advance!

Chris W. Millinship:
I don`t know a lot about them but that looks very much like a neon sign tube electrode. The fact that one end is open implies it is meant to be part of something else, and neon signs are all fabricated by hand out of their component parts, shaped and "welded" together with gas torch flame. The end electrodes are certainly pre-fabricated given their relative complexity and attached once the main "body" of the sign/tube is complete.

The coiled filament is the only mystery but possibly it could be for use following or during manufacture as a way of purging the main electrodes of impurities. It appears to be coated in something, could this actually be a getter that is vaporised by heating the coil after evacuating/backfilling the completed tube? Possibly once heated/vaporised, the lead wires are cut off and high voltage electrical connection made to the other two going to the large metal electrode. Maybe could also be used in a similar way to a fluorescent tube as a preheater to aid starting?

Just thoughts really but that`s what it seems to me.


Hi Chris,

Many thanks for your quick response.  I think you may have the answer I was looking for..

Alan Franzman:
I agree with Chris, it's almost certainly a sign tube electrode. Whether the filament is intended to be used only once to flash the getter, or also in normal operation to ease starting I don't know. My experience is limited to the two sign transformers I have, but neither has any filament connections.

I have to wonder just how well the cork protects the getter, and how the sign fabricator is supposed to remove the cork and weld the electrode section to his tubing without spoiling the getter. Is there enough of it on the filament that only a thin surface layer is contaminated, and vaporizing it will release sufficient fresh material to clean up the new sign section and still have some capacity to "get" any more outgassing that occurs as the sign is operated?

I have seen these before they are most defenitly neon sign electrodes they are sealed at each end of the tube
I have seen one operating before at a store


[0] Message Index

[#] Next page

Go to full version