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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
Proud Mary wrote ...
Well, it certainly does have a hydrated, water-of-crystallisation look about it, doesn't it?
It would be a total guess on my part, but it sure strikes me as thin wisps of hydrate crystal type stuff.
Keep a camera on it and watch it over a few hours, maybe it will grow?
Lederer, in Contact Potential, Pumps, and Getters RCA, 1940, describes the use of barium-magnesium and barium-aluminium alloy getters, which he says "are brittle at room temperature. It is customary, therefore, to pulverize the alloys and compact the powder into small pellets on a pill press." This description fits the 2X2A case perfectly, as there is a pill shaped pressing on the upper surface of the heat shield above the grill.
As for watching the crystal grow, I have done just that, but not intentionally. I ran a 100 image stack at x1000, which took about ten minutes, but the output image had odd artefacts which you'd only expect to see if the subject had moved during stack compilation. I didn't think that much about it, because it's difficult to avoid vibration altogether at that magnification, making image synthesis problematic for someone with only very basic equipment, and even more basic skills.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Proud Mary wrote ...
Patrick wrote ...
Proud Mary wrote ...
Well, it certainly does have a hydrated, water-of-crystallisation look about it, doesn't it?
It would be a total guess on my part, but it sure strikes me as thin wisps of hydrate crystal type stuff.
Keep a camera on it and watch it over a few hours, maybe it will grow?
Lederer, in Contact Potential, Pumps, and Getters RCA, 1940, describes the use of barium-magnesium and barium-aluminium alloy getters, which he says "are brittle at room temperature. It is customary, therefore, to pulverize the alloys and compact the powder into small pellets on a pill press." This description fits the 2X2A case perfectly, as there is a pill shaped pressing on the upper surface of the heat shield above the grill.
As for watching the crystal grow, I have done just that, but not intentionally. I ran a 100 image stack at x1000, which took about ten minutes, but the output image had odd artefacts which you'd only expect to see if the subject had moved during stack compilation. I didn't think that much about it, because it's difficult to avoid vibration altogether at that magnification, making image synthesis problematic for someone with only very basic equipment, and even more basic skills.
Aye, Patrick, barium hydroxide octahydrate Ba(OH)2·8H2O is a likely candidate for the crystals - an extremely noxious, toxic substance - though I suppose it could be a complex of barium and magnesium, or barium and aluminium, for all I know. I'm more at home with the preparation of goulash than I am with chemistry!
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
plazmatron wrote ...
This is a great thread. I have never seen so may x-ray photons emerge from a tube in Field emission mode!
It seems to be surviving long enough for some decent experiments too.
Les
You're right, Les, that the abundant emission of these Soviet 2X2As is unusual, and that we should try to explain it. A new destructive test suggests itself: running a 'new old stock' 2X2A in field emission mode for, say, 5 hrs, (or until failure, whichever is sooner) followed by micrographical examination of the valve's internal elements. This should show up as pitting, cracking, fissures, melting, etc where the electrons have been impacting, and so reveal the origin of the X-rays.
I'm working up some dosimetry on 2X2A using the Victoreen Rad-Check Plus, and will have something to show for it in the coming week.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Proud Mary wrote ...
You're right, Les, that the abundant emission of these Soviet 2X2As is unusual, and that we should try to explain it. A new destructive test suggests itself: running a 'new old stock' 2X2A in field emission mode for, say, 5 hrs, (or until failure, whichever is sooner) followed by micrographical examination of the valve's internal elements. This should show up as pitting, cracking, fissures, melting, etc where the electrons have been impacting, and so reveal the origin of the X-rays.
Contrary to what you might expect, it doesn't have to be obviously sharp points that are responsible for field emission. Based on what I have seen here, and my own experiments (building field emission cathodes), it may well be the entire inner surface of the anode bell that is emitting electrons in a very uniform fashion.
As I recall, the last American 2X2 I had, had an obviously pressed thin anode bell, with a turned out edge. The surface was very smooth. However, as is evident is Stellas photomicrographs, the entire surface of the Russian anode bell is very rough, and under magnification somewhat crystalline in appearance. All of those tiny points on the surface of the metal may make ideal field emitters.
Of course, this is just a hypothesis, so I will order a couple off fleabay, remove the anodes, and test them in my vacuum rig.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
plazmatron wrote ...
I will order a couple off fleabay, remove the anodes, and test them in my vacuum rig.
Golly, that's very thoughtful of you, Les. Radu will be delighted.
Of course, you're right to suggest that the field emission points need not necessarily be obvious to the naked eye. For the moment, at least, I can't think of any certain means for locating the emission source/s - what I shall call the effective cathode to avoid confusion - but am more confident in finding thermally-induced changes in the micro-topography caused by electron strikes on the effective anode - so long as these aren't so diffuse as to defeat detection with my simple equipment.
If nothing obvious to the microscope appears after a good 'burning in' of the valve - or burning out, as the case may be - then I can etch the surface in the hope of revealing the grain structure and any changes in it, reflection pleochromism under polarised light, and so on. Won't know till we get there.
But it wouldn't be an experiment if we already knew the outcome.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Proud Mary wrote ...
Golly, that's very thoughtful of you, Les. Radu will be delighted.
Not at all, I am every bit as curious as everyone else on here. I have just ordered 4 tubes from Lithuania, so they should be here in a week or two.
Proud Mary wrote ...
Of course, you're right to suggest that the field emission points need not necessarily be obvious to the naked eye. For the moment, at least, I can't think of any certain means for locating the emission source/s - what I shall call the effective cathode to avoid confusion - but am more confident in finding thermally-induced changes in the micro-topography caused by electron strikes on the effective anode - so long as these aren't so diffuse as to defeat detection with my simple equipment.
I will have the opportunity to use whatever anode material I choose. Tungsten will be my first choice, however maybe something with a lower melting point will prove more useful in determining where electron impacts are taking place.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Hi Les,
plazmatron wrote ...
Not at all, I am every bit as curious as everyone else on here. I have just ordered 4 tubes from Lithuania, so they should be here in a week or two.
If you purchased them from Gintaras (Store KWTubes) it might take a while, I also got my tubes from him, he sells a lot of good stuff, but recently he left for a trip in Cambodia, and no news from him since then. Malaria? hope not.
I'd love an uranium anode tube. That would create some very interesting x-rays. Or should I call them Gamma already? Apparently the difference is in the means of producing them, and not the energy.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
radhoo wrote ...
If you purchased them from Gintaras (Store KWTubes) it might take a while, I also got my tubes from him, he sells a lot of good stuff, but recently he left for a trip in Cambodia, and no news from him since then. Malaria? hope not.
Gintaras is a lover of costly Brompton folding bicycles, and travels round the world to folding bicycle conventions and activities.
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Vacuum Rectifiers X-rays report
