gas discharge tube color code

[NiHaoMike]

I have a bunch of gas discharge tubes (from old telephone equipment) that look like big glass diodes (about the size of a grain of rice) with 3 color stripes on them. Is there a standardized color code for them? One (randomly picked) has blue, brown, (larger space) and white stripes.

[ElectronicTonic]

This is purely speculation, but I would guess that the first two bands are one significant figure, then a multiplier.
Blue Brown = 6 x 10^1 = 60 V breakdown voltage. Probably for surge protection.
What are the colors on some of the other tubes?
Can you test them to measure their breakdown voltages and compare that with the color bands?

[calexanian]

If I am not mistaken thats an old ring detector. there was 48 volts DC on the system. The ring signal was 90VAC and the the spark gap would conduct and run current to the bell or ringer. Or they are just protection, but I know I have seen old telephone ringers that worked on that principal.

[minime72706]

90VDC standoff voltage seems quite reasonable in the purview of telecommunications systems. 60V would be valid if there wasn't a high-voltage ring signal. I think "telecommunications" doesn't really imply that you have a system that shares lines with the POT (plain old telephone) system. I just know that telecom stuff uses 48V pretty often. I have a few beefy regulators that run off of 48V and output some sensible digital electronics voltage value that I got at a flea market (MIT Flea). I got some 90V GDTs from Electronics Goldmine as well as some different ones at the same flea market which means that value is common. I got the 90V GDTs from the same seller at the flea market that I just mentioned.

You can also totally just test them if you have a power supply that goes high enough. If you have a few (at least a couple I guess) DC power supplies with isolated output, you could put them in series for higher voltage. Be sure to turn the voltage up slowly and keep the current limit low. I personally tested one for fun by attaching it to the output of a CW multiplier I made. That surely made it glow

The moral is: 90V is a common GDT stand-off voltage for telecommunications and 60V also seems reasonable assuming it's not for POTS. 60V would be better for more sensitive electronics. It would not surprise me if the first reply post is entirely correct.

EDIT: By the way, if you are able to test them, remember that they won't break down at the rated voltage - it may easily need to be 10% more. The rated voltage is the "Stand-off voltage", I believe. This means that it can avoid breaking down at that voltage effectively indefinitely.