The AM Forum

If you have a large size gassy tube (but other wise ok) I'd like to experiment with restoring the vacuum in one. I have picked up some UHV equipment that was scrapped but functional and it might be interesting.   Large size preferred since I'll have to weld (fuze?) the glass tubing to pull the vacuum by hand, and no matter how much that Bugle Boy 12AX7 is worth, I don't think I could do it. 

PS -I don't expect it to work, I think I am only going to make a mess, but it will be interesting to try.  The real trick would be to figure out how to get some fresh getter material in there and fire it off after restoring the vacuum.

So, got any gassy bottles?

This is a great thing for someone to try.

Probably 50 years from now, if there are any tube experimenters left, this will become common.

I agree.

Are you sure you need a gassy one to start with? Because as soon as you grind a hole in the envelope to connect the tubing, it's going to be gassy all right.

Besides, if you begin with a good tube with a good vacuum (that is, after you first hone your glassworking skills by practicing on some other tubes), you have a reference point. You first build a working circuit with the tube in place. Then, if the tube works after you pull the new vacuum and getter it, you'll know you were successful. If you start with a gassy tube and it doesn't work afterwards, then you won't really know whether it was something you did or the tube was bad to start with.

There's a French ham who made two wonderful YouTube videos about making tubes from scratch. Maybe there's something in there that would help you.
http://www.youtube.com/watch?v=gl-QMuUQhVM
http://www.youtube.com/watch?v=9S5OwqOXen8&feature=relmfu


Anyway, all the power to you as you embark on this project.

http://www.youtube.com/watch?v=oSgVGwqJ2Jk&feature=relmfu

Ron Soyland a ham in Texas makes tubes.  He uses getter rings from old tubes since they often have plenty of material. 

He has demos on making a Deforest Audion tube, Fleming Diode and a couple other things. 

His choice of shirts is rather flamboyant but he gives step by step instructions.

If your pumping tube is large enough you could use some kind of bellows to manipulate a little getter on a rod inside there and flash it, then withdraw the rod and seal off. No idea if it would work but we used long flexible bellows in school to position things inside a vacuum chamber. I hope you will try your experiment!

Interesting. Might be worth seeking the advice of a seasoned glassblower ... could save some trial and error. How would you find and repair the leak that caused it to go gassy in the first place?   

Ed I've got a few 810 bottles that have lost seal between the glass and the ceramic grid cap mount. 
Would they do ?

Is your address good in the callbook ?

Some bottles like the 3-500 and 4-400 have zirconium getters, in the
plate. If you can restore gassy 3-500Z tubes you will be a very popular
person when the Chinese suppliers fold up tent.

Pete

Many here and elsewhere make the mistake of referring to tube gas as an air leak. Almost all TX tubes will outgas from the anode as this is a result of either abuse or storage. The 3-500Z is a prime example of an outgas prone tube that can often be restored by running the anode a bright red at a voltage that wont sustain an arc. That is typically around 1000V with sufficient positive bias to get Ip to a high enough level. Ive recovered many, including Eimac, this way but if the gas is excessive and the remaining getter coating is insufficient then its either junk or use it at a lower voltage until it dies. Ive done this with a few that wont hi-pot at 4KV but run fine in a SB-220 in the 1800V CW position.

An air leak (yes air is a gas but not for this discussion ;D) is a totally different issue and I dont know if an already activated filament can be exposed to air without destroying it. I dont know of anyone that has rebuilt a big glass tube but it may have been done in the 30's??

And then there are those tubes that have a combination of gas and air.

Carl

Be careful with the exhaust of a vacuum pump. Some pumps have mercury in them and outgas a little in the exhaust. Best to vent outside away from people.

Can one still find a "local glassblower" who will make oddball things based on drawings? Many old scientific construction articles recommend those craftsmen for things like a mercury diffusion pump, leading one to believe that it s a simple task for an experienced glassblower. The lack of a diffusion pump (and money!) was one of the things that kept me from trying to build a home made accelerator in high school.

Here is B&W blurb from RCA with some time spent on making tubes, both big & little:

http://www.youtube.com/watch?v=J61hHMjxzC4

73DG

As Carl said, a gassy tube due to outgassing from internal components after running overloaded it typical. A gassy tube from a physical leak is usually no good. If the filament ran with air, it is likely heavily oxidized and ruined. A month ago we were testing a 7835 triode, a very high power tube, and it broke ceramic, up to air as they say. This instantly causes the thoriated tungsten bars to oxidize and deposits a greenish grey coating throughout. Even Burle Industries (old RCA) cannot rebuild the tube once this happens, as it is difficult to clean it again.
If you open a tube to air, then repump it, as long as you can exhaust the tube while elements are hot, you have hope. Doing it cold is a recipe for failure.

You also want a gauge to indicate vacuum level, like an ion pump.

Probably not. However, the type of glassblowing shown in the two Youtube videos I posted above is simple with only a little practice. Somewhere between the 4th and 7th grade, I used to do simple glass working and a little blowing in my grandmother's kitchen, mostly with 1/4" glass tubing. The instructions I went by were from a library book geared to boys my age. If a kid that age can do it, anyone can. It's all about practice, patience, and desire.

Now, what is NOT so simple is keeping larger pieces from cracking as they cool. That French ham used an annealing oven to prevent that.

Many years ago, C. L. Stong published articles in The Amateur Scientist column of Scientific American. I believe some of those had a little glassblowing tutorials. There are certainly tutorials on YouTube.


Me too! In my youthful case, it was a cyclotron. (BTW, it is now a felony to possess a particle accelerator.) You and I are a lot alike. I just love the Bunker of Doom pages. :-)

A federal crime to possess a particle accelerator?  where is that written?

First, I don't have a diffusion pump, which were the mercury based type (now use oils) and don't plan on pumping out an mercury based tubes.  I have a small turbo molecular pumping system and some gauges that I salvaged from some scrap equipment (I am such a scavenger). Should run clean enough to restore tubes that have just leaked by bad seals.  I don't know how healthy the pumps are, The turbo pump spins around 50,000 RPM, and if the oil or bearings are bad, this will be a really short experiment followed by a loud noise as it crashes.

It seems that for tiny amounts of outgassing, there are various ways of cleaning up a tube. All much easier than re-pumping the envelope.  I was thinking of trying tubes that had bad seals that leaked over time and were REALLY gassy.   Anyone wants to donate a dud, I'm good in QRZ.   

There is a place that actually sells materials to folks who want to make their own vacuum tubes. http://electrontubestore.com/  has envelopes, bases, wire to glass seals, and other bits.  Shocking how expensive Thoriated tungsten wire is!!!


P.S. you can have my particle accelerator when you pry it from my cold dead fingers.

I am not sure, but I think I would start with small not large tubes, and indirectly heated ones... less chance of a bad deal with the filament. Then if that works, try some DHT tubes... also small tubes, less vacuum to pull?

                  _-_-bear

I don't remember. I think you need a license from the NRC or something. Obviously, universities, etc. own them and nobody gets charged with a crime.

A few years ago, I was thinking of building a betatron (possibly the world's ultimate negative ion generator, so I thought.). That's where I read --from multiple sources-- that you'd better not try that in your garage, as there are very severe penalties for doing that. That's all I remember.

This is all I could find, from http://www.physicsforums.com/archive/index.php/t-169138.html
"If you're in the US, whatever you end up building (whether a reactor or cyclotron), if it has the potential to produce ionizing radiation, it will require a radioactive materials license which can be quite expensive depending on where you live. The licensing requires that you have a radiation protection program, are qualified by education and experience to possess radioactive materials or radiation producing machines, etc."

"If it produces ionizing radiation, then YES - IT IS ILLEGAL!!!!

You have to be licensed by the NRC to operate an X-ray machine,
an accelerator, or possess a radioisotope.

This is the only way that one can be sure that someone isn't producing
radiation that is irradiating unspecting people because the operator of
the source didn't consider proper shieldig....

If you don't know the laws, please refrain from giving advice to yourg
students who may follow it and get into trouble.

Dr. Gregory Greenman
Physicist"

Having said this, there certainly are an awful lot of stories of people doing this in their garage, with no mention of any legal consequences.

On the subject of particle beams, this guy Burt rides the ragged edge of disaster, but makes really neat items:

http://205.243.100.155/frames/interesting.html and play the first video down.

Not to mention shrunken coins from a mega-dose of electromagnetism and giant Tesla coils.

73DG

While we are moving off topic to particle accelerators, here's some interesting old info about Dr. Lawrence and his cyclotrons.

http://www.lbl.gov/Science-Articles/Research-Review/Magazine/1981/index.html