Is this accurate? What type of pump is required to be able to evacuate air on nixie tubes?

[Miles Thatch]

[gregebert]

Several years ago I researched neon signage, and you need a high-vacuum, around 1 micron (10-3 Torr). The books I have didn't get into specific vacuum levels, as there are multiple ways to cleanse the tubes, notably via bombarding. They did not cover nixie tubes.

To get micron-level vacuum, you need a mechanical pump to get around 100 microns, followed by a diffusion pump. There might be other ways to get the required cleanliness without a diffusion pump, but I dont have any details. If you just want to do some experimenting, start with a mechanical pump. I plan to do that soon, as I have a small pump used for evacuating air conditioning equipment.

Some of the reasons I'm not doing neon work are the cost of the equipment, the dangers of bombarding, need for mercury to extend tube life, and I expect it to be difficult to find getter material. All I want to do is get some sort of discharge glow, and play around with easy-to-find gases like argon and helium.

I saw a mention in the Weston book of pressures in the 10-2 to 10-4 Torr, though it covers theory of operation rather than fabrication details.

On Friday, November 22, 2024 at 12:33:28 PM UTC-8 Miles Thatch wrote:

[Instrument Resources of America]

I saw bombarding being done. I sit here now shaking and shuddering from the experience. Here is a fairly detailed video of neon sign manufacturing.       https://www.youtube.com/watch?v=kH635AEawGY          The bombarding process starts at about 12:30. The demonstration that I saw, they deliberately drew a two foot arc just for show. It was impressive, and S-C-A-R-R-Y. This may not help you with your endeavors, but it is interesting, and mentions 'neon' a number of times.

Ira.

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[Miles Thatch]

Not sure why by my messages aren't coming through..

[Anders Mikkelsen]

The ultimate pressure is one thing, but the most critical is the nature of contaminants. Due to the low conductance of the tubulation and the short cycle time on sealex machines used for production, the initial vacuum in receiving tubes is not very good before the getter is fired, but tubes are well pre-cleaned and baked to get rid of organic contaminants and moisture. Then the remaining N2 and O2 is captured by the getter.

From RCAs excellent "Electron Tube Design", pp. 510:

"While a pressure in finished tubes in the region of 10^-5 to 10^-7 mm Hg is expected, this degree of vacuum is attained in present receiving-type tubes only by the use of getters. The pressure range covered on sealex-processed tubes may be from 10 to 500 microns (1 x 10^-2 to 5 x 10^-1 mm Hg} as read on a Pirani gauge, but the actual pressure in the tube is, of course, much higher."

In a nixie tube, evaporable Barium getters are not common, but Zirconium pill getters are very common. I would bet the requirements for evacuation are similar to in receiving tubes, but maybe more relaxed still for a few reasons. Firstly, residual Argon is less of a problem in Nixies as it is already present in the Penning mix, while receiving tubes are very sensitive to residual gas which causes grid current. Secondly, due to the glow discharge there is sputtering, which tends to chemically and physically trap contamination. I've made Neon tubes without cleaning the glass, without firing the electrodes, and without bombarding. If left running for a while, they will eventually clean up to pure red due to self-cleanup.

[Miles Thatch]

Seems pretty straight.

I realize it's high voltage but if the young lady can do it, I don't see why us gentlemen here can't.

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[Miles Thatch]

I'm not sure what is so dramatic about the bombarding process? Sure it's high voltages, as one would expect with this sort of manufacturing but if the young lady can do it with confidence, I don't see why full grown men here can't. 

[gregebert]

It can be done, but it's very dangerous. Bombarding current is on the order of hundreds of mA, and in the kilovolt range. I've heard of incidents where an arc went thru the manifold and into the evacuation pump; if such a path is possible, there are undoubtedly  other paths thru your body, which are fatal at the currents being used. Several people have been killed doing fractal art with a microwave oven transformer, and that's at a lower voltage than bombarding. It only takes 1 small mistake; for me, the reward was nowhere near the risk so I never got into neon art. For others, it's a different story and that's why they jump out of airplanes, URBEX high rooftops and bridges, or spray tags on freeway signs.

[Instrument Resources of America]

I do have to hand out much credit to her. To be able to bend glass like that, is a real art form.

Ira.

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[Mac Doktor]

On Nov 26, 2024, at 2:36 AM, Instrument Resources of America <IRACO...@HUGHES.NET> wrote:

I do have to hand out much credit to her. To be able to bend glass like that, is a real art form.

My instructor in neon school was an ace, a real natural and amazing to watch. She made mouthpieces as well. It was a surprisingly complex exercise.

She had all of the latest (circa 2001) gadgets. Digital meters, glass manifold, even a diffusion pump that she never got around to hooking up.

I still have a tall pile of books and thick binders full of stuff taken from everywhere. Fortunately, that came with the tuition so I didn't' have to wait in line at the college bookstore.

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com

"I’ve seen things you people wouldn’t believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near Tannhäuser Gate. 

"All those moments will be lost in time like tears in the rain."— Roy Batty, Blade Runner

[Mark Moulding]

>  Several people have been killed doing fractal art with a microwave oven transformer

Those transformers are dangerous as hell, because one side of them is ground (plus nearly a full amp or so available current - 1 kW, right?) - super easy to get a path through YOU to ground.  I've done "fractal art" (nothing to do with actual fractals, of course), but I used a neon sign transformer - isolated, and only around 15 mA of current - and switched it with a momentary foot pedal.  It would still have been an exceedingly bad day to get across it, but I probably would have survived.  I was extremely careful...

[Mac Doktor]

On Nov 26, 2024, at 3:15 PM, Mark Moulding <urro...@att.net> wrote:

Those transformers are dangerous as hell, because one side of them is ground (plus nearly a full amp or so available current - 1 kW, right?) - super easy to get a path through YOU to ground.  I've done "fractal art" (nothing to do with actual fractals, of course), but I used a neon sign transformer - isolated, and only around 15 mA of current - and switched it with a momentary foot pedal.  It would still have been an exceedingly bad day to get across it, but I probably would have survived.  I was extremely careful...

For those who aren't aware, neon sign transformers are current limited using shunts. Also, the secondary is center tapped to ground so the potential from one wire to ground is only half that of the full secondary. Or something like that. 8D

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com

“...the book said something astonishing, a very big thought. The stars, it said, were suns but very far away. The Sun was a star but close up.”—Carl Sagan, "The Backbone Of Night", Cosmos, 1980

[Miles Thatch]

In the neon sign video, they mentioned that bombardment is meant for dislodge any impurities stuck to the glass. Is that the only reason for it?

[Mac Doktor]

On Nov 29, 2024, at 6:23 PM, Miles Thatch <milesan...@gmail.com> wrote:

In the neon sign video, they mentioned that bombardment is meant for dislodge any impurities stuck to the glass. Is that the only reason for it?

Two things happen. First, the glass gets very hot and the impurities leach out. Second, the cathodes get hot enough to reduce the oxides in the emission coating to elements. Full vacuum is applied to remove the leftover oxygen etc.

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com

"Every kid starts out as a natural-born scientist, and then we beat it out of them. A few trickle through the system with their wonder and enthusiasm for science intact."—Carl Sagan, Psychology Today, 1996

[Mark Moulding]

Well, Terry, that was very interesting.  I just went out to the shop and measured the resistance of the secondary of my neon sign transformer to ground, and sure enough it was definitely non-infinite (about 50k from one side, and greater than the 2M maximum of my cheap garage DVM on the other).  I personally was still using it safely, because I clamped one side of the secondary directly to the workpiece, and the other I held at the end of a 14" plastic rod - but still...

What do you mean by "shunt limited"?  I always believed that the current limiting was by virtue of the inductive impedance of the many turns in the secondary - basically the same as a fluorescent lamp ballast.  Is there some other mechanism at work?

[gregebert]

I believe there is an air-gap in the core that limits the maximum flux (amp-turns) of the transformer.

Be aware that bombarding is done at much higher current than the typical output of a neon-sign transformer.