[GreenKeys] [External] Re: ST-6 neon lamp part number

[Jones, Douglas W]

From: Dave Horsfall [dave at horsfall.org] -- Tuesday, May 26, 2020 3:48 PM

> What can possibly break down in an NE-2 (apart from mechanical failure of the bulb etc)?

Neon discharge lamps and displays age because of sputtering.  Fast moving ions in the neon plasma bang into the electrodes and knock atoms loose.  Those atoms condense onto surfaces elsewhere in the bulb.  So, a metal film from the electrodes slowly deposits itself on the inside of the glass envelope, turning it dark.  Also, when sputtered atoms redeposit on the surface of the electrodes, they don't restore the original surface, but instead, they form a nano-scale sponge that doesn't conduct as well as the native electrode material.  The result is that the glow starts to get spotty and flicker irregularly.

There are tricks for re-forming the electrodes in glow lamps.  People who are into nixie tubes have pursued these rather aggressively because Nixies are hard to replace.  NE-2 lamps aren't worth trying to re-form, they're still made, and dirt cheap.

The 1965-vintage PDP-8 I'm working on restoring has neon indicator lights on the front and back of the power supply to show it's on.  They flicker irregularly when on.  Not worth fixing.

I've got a Heathkit digital clock that I built in 1976.  It's been running almost continuously since.  The 7-segment neon displays in it are mostly still in great shape, but the most significant digit is starting to have trouble.  The other digits roll through all numbers, but the most significant digit is either off or 1 (since the clock is usually set for 12 hour time).  That 1 is starting to wear out.

              Doug Jones
              jones at cs.uiowa.edu