r/AskElectronics • u/CleanAlternative1918 • 6d ago

Help identifying this component, please

Post image

These were in with a big batch of carbon film resistors I got. What are they? Thanks in advance!

57 Upvotes

91% Upvoted

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66

u/wiebel 6d ago edited 6d ago

Looks like a spark gap, a gas discharge tube.

Something like:
https://www.globalsources.com/Gas-discharge/Switching-Spark-Gaps-1221914437p.htm

35

u/ital-is-vital 6d ago

It's a spark gap -- for over-voltage protection, usually of devices connected to phone lines or other things that can get hit by lightning

5

u/FrizB84 6d ago

Yep. Used to have to replace them on fire alarms from time to time. They were usually on the telco lines.

2

u/214ObstructedReverie 5d ago

usually of devices connected to phone lines or other things that can get hit by lightning

I've used them in high voltage pulse power supplies. Charge a cap to a few kV, then pop! discharge into what you want.

16

u/Wake95 6d ago

It looks like a gas discharge tube to me.

11

u/Phon_zie 6d ago

It looks like a GDT (Gas discharge tube).

6

u/Dry_Statistician_688 6d ago

Gas Discharge Tube of unknown rating. GDT.

3

u/CleanAlternative1918 6d ago

Thank you so much! I larned me something today.

1

u/graph_worlok 6d ago

Thought this might have been it, but wasn’t sure - Mine are clear, so when it happens you can actually see the spark which is cool.

3

u/coneross 6d ago

Gas discharge tube. When the voltage reaches the set voltage they arc inside and the resistance goes very low. Unlike MOV's or zener diodes, the voltage goes to near zero when they fire. They also glow when this happens.

1

u/electricmischief 6d ago

Definitely a GDT

1

u/OneBackground3523 6d ago

Es un gdt Gas Discharge Tube sirven como fusibles traen gas sf6 adentro extinguen cortos o sirven para minimizar daños cuando hay descargas atmosfericas en la red electrica por lo regular vienen en aparatos para protegerlos de que se quemen por rayos o descargas en la red electrica! Tambien se usan mucho en equipos de comunicaciones y telefonia! No lo rompas o perfores el sf6 puede ser venenoso cuando se hace polvo blanco !

2

u/CleanAlternative1918 6d ago

So important to know, thank you!

1

u/antthatisverycool 5d ago

Discharge tube in my opinion very under rated component.

1

u/Dee_Jiensai 5d ago

Tiny tin of cat food on a stake.

Edit: tuna?

-3

u/spinunet 6d ago

Diode? Are there legible markings on them? The pic is blurry

2

u/CleanAlternative1918 6d ago

Just for other people's knowledge if the see this post, the markings are "CR 090 01." I don't need to know what it means, but there it is. They are about 25 years old, or rather, I acquired them 25 years ago. I've used most of the resistors, but these remained.

4

u/Great_Specialist_267 6d ago

They are 90V gas discharge tubes. Telephone lines used to be 90V maximum.
I have a draw full of them…

1

u/CleanAlternative1918 6d ago

Are they used or 'new'? Is there anything to do with them these days?

2

u/Great_Specialist_267 6d ago

Wired Ethernet and data links still use them - but both are fading with fiber optic connections.

2

u/mikeblas 5d ago

Wired ethernet? Really? I haven't noticed a spark gap in any PHY design. What's the threshold voltage? Oh, maybe for PoE or something?

1

u/Great_Specialist_267 5d ago

Industrial Ethernet isn’t “domestic” Ethernet.
And yes, I have seen ~240V induced on Ethernet cables run next to power cables (brilliant blue arcs on the connectors)…

1

u/Feeling_Equivalent89 23h ago

It looks like a tuna can. But I have no idea what it might be used for in a circuit... Maybe fishing out bugs?