I have recently acquired some very rare Nixie neon numeric digital display tubes, Burroughs number B-7032. They are about 5.5 inches (140mm) tall overall with a 14-pin bakelite base 2.25 inches (57mm) diameter, displaying digits 2 inches (50mm) tall. Unfortunately they are rather blackened (though still functional) from either long use or excessive current.
I got an idea that sand or similar abrasive introduced into the tube may be used to clean the blackened glass (long story -- see below.) Several technical questions remain, some of which may need to be answered experimentally:
1. Would it be possible to use a torch to open a hole in the Nixie tube envelope without cracking it or damaging the internal elements or the bakelite base?
2. Would opening the envelope to the atmosphere harm the internal workings of the tube due to oxidation, etc?
3. Would there be any harm in leaving sand inside the tube when it is sealed up again?
4. Is the gas inside a Nixie similar enough (pure neon, or some kind of a mixtue?) to that used in neon signs that its function would not be altered?
5. How critical is the gas pressure to the Nixie's proper operation, and could a neon sign shop achieve the correct pressure? What exactly is the pressure inside a Nixie tube anyway?
TIA for any input you have.
The long story of how I got the idea:
Recently I toured a museum in the Los Angeles/Hollywood area -- not sure which one it was now, perhaps the Hollywood Entertainment Museum, or the Museum of Radio and Television -- where they had on display a very old piece of film or television studio equipment, a lightbulb cleaning machine. It is a large spidery looking machine which operated somewhat like an amusement park ride, having several arms which spun around in various directions. The ends of the arms held old high-powered studio incandescent lightbulbs, 500 or 1000 watts as I recall, with large spherical glass about 8 or 12 inches in diameter. These bulbs tended to blacken quite quickly when in use, so they were made with a small quantity of sand inside. At the end of each days work, the bulbs would be placed into this contraption and spun around slowly in all directions overnight and the sand would clean the black deposits from inside the glass, leaving the bulb looking shiny new again for the next day's shooting!
Recalling this gave me the idea that a similar process could be used to "un-blacken" the insides of my Nixies.
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Alan "A.J." Franzman
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