I know this is a far fetch, but someone has to know...

I had a vacuum tube phase a while back. I was trying to come up with a list of easily accessible versions of materials needed for vacuum tube making. One of those was the getter to maintain high vacuum. I later found out that titanium filament getters are infinitely better than barium for homemade tubes, but before I discovered that, I noticed something very interesting.

I had a bag of 100 neon (erm, penning mix akshully) indicators. I decided to break one apart and smash away all of the glass leaving just the Dumet wires that I could use later for making glass pinch seals (there is a better way to do that as well, don't even get me started). I then laid the two wires (electrodes still attached) temporarily on my workbench. Well I forgot about them for a day or two, but when I saw them again, the electrodes had turned chalky-white. This is completely identical to the behavior of a barium getter when a lamp envelope (or a vacuum tube) takes on air.

Does this mean that neon indicator electrodes are a dirt-cheap easily accessible way to get barium getters? I know you would still need to spot-weld a "c" shaped wire on the ends of the electrode to form a loop that can be induction-flashed (look up "D" style barium getters), but the result should be the same at the end. Also you would probably need multiple of these assemblies since the barium element is so small.

Again, in a home setup, the easiest and best way to have high-vacuum with a getter is to have 2 dedicated electrical feed throughs going to a titanium filament that can be heated to incandescence when the vacuum is getting cruddy, but nothing is cooler than seeing a barium mirror on the glass envelope. I don't have a spot-welder or an induction heater so this really doesn't apply to me but I still wanna know.

Thanks!

PS I sort of have a lot of ideas regarding vacuum tube making so ask away if you wish

This idea just would not work because barium film on the electrodes will oxidize in seconds (as you have seen already) when exposed to the air. And certainly will not survive tube sealing and processing.  A known crude DIY substitute is magnesium strip, if heated in already pumped up tube it will form a getter mirror somewhat working in a barium mirror way. Yes in possible and easy to reuse dumet wires, but beware that tinned part will start to burn if heated in the air, better to use bare dumet from crushed incandescent lamps, I tried and it works OK.

If you want to play with DIY tubes, glow discharge things are much easier to make. Well even a medical syringe can pull enough vacuum temporary to see a low pressure glow discharge! Drill some holes in the syringe and glue electrode wires tightly. Because of how air Paschen curve goes, air discharge won't start at mains 120 or 230V at any pressure, but even better you can easily use some safe low-power HV source like CCFL inverter.

This idea just would not work because barium film on the electrodes will oxidize in seconds (as you have seen already) when exposed to the air. And certainly will not survive tube sealing and processing.  A known crude DIY substitute is magnesium strip, if heated in already pumped up tube it will form a getter mirror somewhat working in a barium mirror way. Yes in possible and easy to reuse dumet wires, but beware that tinned part will start to burn if heated in the air, better to use bare dumet from crushed incandescent lamps, I tried and it works OK.

If you want to play with DIY tubes, glow discharge things are much easier to make. Well even a medical syringe can pull enough vacuum temporary to see a low pressure glow discharge! Drill some holes in the syringe and glue electrode wires tightly. Because of how air Paschen curve goes, air discharge won't start at mains 120 or 230V at any pressure, but even better you can easily use some safe low-power HV source like CCFL inverter.

Aww shucks. It’s just a film? I thought they looked the electrodes might have been made of barium. Too bad.

I have heard of Mg being used as a getter, but as far as I am aware it is mostly only effective against O₂. And it requires an induction heater. Ti and Zr both will absorb O₂, N₂, CO₂, H₂, and H₂O, but Ti is the cheapest even though it doesn’t work quite as well an Zr. I do believe if you heat up the titanium enough it will form a mirror, but I believe it requires very high temperatures. This should be easy enough to achieve if you have a titanium filament instead of an induction ring.

I was wondering about the tinning on the dumet, if maybe it would cause a problem (I guess it does…). I have made soft glass seals with just plain old copper wire though, and I wonder why more people don’t just do that. Is it not as good / reliable? I am just going to make a separate thread about this…

I have also used a syringe with a small tesla coil to make a glow discharge, but I would definitely like to try and make a real glass discharge tube. I haven’t tried it with a CCFL inverter, I might try that. Making vacuum tubes would be cool, and I do have an interest in that, but it definitely is unrealistic for me because of all of the tools required.

Okay...

Sure, can not tell without doing material analysis, but one can expect barium film on pure iron or nickel plated iron electrodes.

 
As for glass-dumet and glass-copper seals. Ever heard of COE matching? So, you need COE 9 metal to make a reliable seal with soft glass .Platinum or dumet for cheap. Or tungsten with pyrex. Copper does not match but is plastic so you may get *okay* with thin wires. Surface coating/oxidation matters too. Go ahead read some glassblowing books. The craft is old and many excellent books are available for free on archive.org site.

if you are really really serious about making electron tubes, or at least interested in technology, go google this:

Rca1962ElectronTubeDesign

It will show up you a very thorough book on this topic by masters from RCA!

There is also 1940 issue of this book too.

So, you need COE 9 metal to make a reliable seal with soft glass .Platinum or dumet for cheap. Or tungsten with pyrex. Copper does not match but is plastic so you may get *okay* with thin wires. Surface coating/oxidation matters too.

I do anneal my copper wire before using it, and it is pretty thin, probably ~26 AWG if I were to guess. I must say that I have never made a tungsten-Pyrex seal before, though I assume you could probably do the same process except with tungsten instead. They seem more complicated but I may be wrong.

Also dumet wire is only really available in large quantities, and platinum is not really what most people consider “cheap”.

Yes, I have been able to get the proper red-colored oxide stuff on copper in glass. I have (I think) pretty much perfected making copper wires with glass beads sealed to them in this manner, which takes some of the difficulty of making pinch seals out of the equation. All you have to so is pinch the beaded wire into the flare, instead of worrying about getting the copper too hot and having the wrong kind of copper seal. Annealing the glass is probably the hardest part.

if you are really really serious about making electron tubes, or at least interested in technology, go google this:

Rca1962ElectronTubeDesign

It will show up you a very thorough book on this topic by masters from RCA!

There is also 1940 issue of this book too.

I am not really serious about making vacuum tubes. If I had the tools I would totally do it, but I don’t. I am not nearly motivated enough to spend that much money on it. I love glassworking though, and some simple discharge tubes would be cool.

If you have a proper torch, annealing is easy. You turn gas valve to much excess of the fuel, resulting in a bright cold bushy flame. With propane, you will get some soot, with methane just a yellow flame. As you cool the detail in the flame and it gets blackened by soot - it is annealed. If the torch is not easily adjustable - you just brush the detail with working flame back and forth, gradually lowering the temperature. You need to avoid leaving extra thick glass parts, as they stay hot for longer and cause strains when detail is cooled.

Working with Pyrex is much more relaxed, as COE is 3x times lower and risk of cracks is practically eliminated, but you need oxygen torch, good ventilation, and glass-metal seals are more complex to do. Ready-made electrodes are available, though.

My propane torch has a plastic bottom housing and I can't really cover up the air holes effectively to make a sooty flame. I usually just spin the piece slowly in my drill, while (over the course of probably 5 mins) moving the flame back and fourth and very slowly backing it away until I can just turn it off and let it sit.

You *do* need a proper set of torches if you are really serious about glassblowing. No way around. You may adapt, but you end up with poor results and many unnecessary disappoints. For example, neon maker's crossfire handtorch with two fishtail heads allows you to make clean pro looking splices right away with minimum efforts, or a ribbon burner, even small, allows for clean smooth bends. Or a flexible oxygen torch is necessary for working with Pyrex or generally working Euro style. All of these run on gas and air supply, or gas + air + oxy.

5 minutes for annealing in the flame is certainly an overkill, until something is very large/heavy, say the size of the bottle. Usually it happens much faster, some tens of seconds for small things. Complete annealing does not happen this way.









 

The coating used on neon glow electrodes is indeed only a very thin film, and although it has some gettering properties it is typically applied for its electron emission properties.  One of tge most used coatings is barium azide.  It is heated to dull red heat while vacuum pumping to reduce to the metal, releasing nitrogen, but only a few tens of nm thick.

If you wish to experiment more I can send you the proper dumet wires, or automotive grade nickel plated dumet.