Strange Neon Lamp?

Thread Starter


Joined Oct 5, 2006
While taking apart an old electric blanket, I found a neon lamp as part of it's circuitry. It obviously was not being used for its light. It was inside a metal shield. All the other components in the circuit were resistors.

This neon lamp has three electrodes. I was wondering if anyone else has seen this type of neon lamp before. Or, what are these type of neon lamps used for?

I did some searching around online (including wikipedia) and have not found anything yet pertaining to a three electrode neon lamp. I know that ordinary neon lamps are negative resistance devices. This leads me to believe that this lamp is being used in some way as a protective device.

Any ideas? :confused:


Joined Oct 12, 2006
Strange. Are you sure it's a neon lamp and not a rectifier/diode tube? This would seem to fit as you mention the only other components as being resistors. Would have to be a very old blanket, though :S.


Joined Oct 28, 2005
Yes, I think I'ts called a "Flashtube" the breakdown voltage of the gas in the lamp causes it to go "on" , and the lamp's total impedance goes very low as long as the voltage at the lamps terminals is above the rated voltage. This will then bypass some of the circuit for protection, similar to a metal oxide varistor.


Joined Apr 20, 2004

I don't know the "oficial" name for it, but it's the AC equivalent of the gas thyratron tube. As long as the middle electrode keeps the gas ionized, then current will go to the resistance heater strips in the blanket. Seems to me that it might date back to the 1950's. Not sure I'd trust the insulation.

Thread Starter


Joined Oct 5, 2006
I have some info on this device. I hooked up the circuit board to the 120V house voltage. The heater cord got warm. I extracted all of this heater cord from the blanket - a daunting task. I might use it as resistance wire for something else.

The two outer electrodes are line voltage. With exactly 1/2 line voltage from center electrode to each outer electrode. Very little current runs through any electrode during operation. I wish I could draw up a schematic and post it on this forum.

I do not think it is a flashtube. It is not a zenon flashtube. This looks similar to a NE-2 neon lamp.

Anyway, appreciate the feedback. This is an interesting one.

Some links that may be interesting on this: - on memory switches. You'll have to tilt your head to read this one.

I will research further on this myself. I have an interest in old electronics anyway. Kind of nostalgic.

Thank you. :)



Joined Nov 4, 2006
The strange neon lamp device sounds like a control device that uses a bi-metal strip inside to flex with accumulated heat. Thermostats are made with bi-metal strips that bend with temperature. This happens because one metal will expand further and faster than the other, when heated. The different rate of expansion causes curvature in the strip which is often used as a conductor in a control circuit.

Another application of a similar device was used to start fluorescent lamps on a magnetic ballast. These "starters" appear inside those small cylindrical cans that attach to old lamp fixtures if you can find them anymore.

Your device is designed to regulate power to a heating element by switching it on and off at some prescribed rate, controlled by the current limiting resistors that allows the neon gas to achieve various temperatures. This in turn, controls the bi-metal strip bend rate. If you watch it operate, be prepared to watch for quite a while. It is designed to be slow.


Joined Dec 20, 2018
I guess I am resurrecting this thread since there was never a straight answer given.
I have the same blanket that is about 16 years old. I have tested the continuity of the wire throughout the whole blanket and it is good. The blanket has rarely been used so it is in good condition so I would like to fix it.
The only circuitry the blanket has is the board I am posting the picture of. It has an external switch but that has no electronics in it. Just some diodes for the high setting.
So, on the circuit board, you will see this three-pronged bulb protected by a metal shield. It reminds me of a starter bulb for fluorescent light.
I have checked the resistors and they have low resistance. The large one I have never seen before since it is solid black with a bit of texture to it.
In any case, I believe this bulb is the key. It must variate the flow of electricity to the heating wires by turning it on and off by the elements inside heating up and cooling. But I don't know what the type of bulb it is, or where I can get a new one. So if anyone here can enlighten me with these two questions, please do.


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Joined Mar 24, 2008
Please don't post to long dead threads(called necroposting) I have approved your post this time but future necroposts by you will simply be deleted.

It is far better to start a new thread and if appropriate, post a link to this thread in your post. If you need help in navigating this forum software just type @Wendy in your post with your question and I will be tagged to come view it.