[Ericus Rex]

Connected between G and K of the phase inverter in my tube amp. Seems to function as a current limiter as they only flash at power on and go dim after a few seconds. But what are they called other than glorified Christmas bulbs?


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[mgalusha]

They are neon bulbs and are used to limit the grid current until the tube is warmed up. Some designs use diodes for this purpose. I have worked on a few devices that use those, most recently some Quicksilver gear, they were in both the preamp and the power amps.

[dwmaggie]

Neon bulbs were nicknamed nixies back in the 70's.  They were also used to display numerals in a desktop calculator the size of an IBM Selectronic typewriter.  I have also seen them used in speaker circuits for protection.

[Ericus Rex]

Great!  Thank you, guys!  It's a really great idea, but I'm guessing only needed for diode rectification?

[mgalusha]

Great!  Thank you, guys!  It's a really great idea, but I'm guessing only needed for diode rectification?

If it has tube rectification and they are not slow warmup, then it's still a good idea. Some rectifier tubes will come up very fast, especially directly heated tubes like a 5Y3-GT.

[Ericus Rex]

Thanks, Mike!  Good info there. Do you think these are NE-2? That seems to be the ubiquitous size.

BTW, I still have your old Meadowlarks!