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What are these oscilloscope lightbulbs?

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New Member
I have an analog oscilloscope with no trace. I was checking the problem and found these two "lighbulbs" near the crt socket. I tested conductivity and they are not electrical conductive inside. They dont have visible filament.
Any ideas what are this "lightbulbs"?. Maybe they are burned because they are not conductive inside?. Maybe they are something more sophisticate?

Many thanks!



Well-Known Member
Most Helpful Member
Neon bulb. The meter will read open. There is no filament. It takes about 65 volts AC or 90 volts DC for a spark to jump across the wires in the bulb.

They might not be used to make light. It might be used to keep the voltage at that point from getting too high. Much like a Zener diode. If it is being used to limit voltage you can get them in much higher voltage ratings.

Nigel Goodwin

Super Moderator
Most Helpful Member
Rather than neon bulbs they are going to be spark gaps - so probably filled with something other than neon. It's to absorb any high voltage pulses if the CRT flashes over, to prevent damage to the electronics.
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