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#16
07-31-2020, 11:44 PM
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Honestly, the glasswork part of it seems like the easiest part to me. (Or maybe second easiest, behind cooking the tube under vacuum.) Something that you merely need to practice a bit. Not to mention that there are plenty of glass blowers in the world, the skill is very much alive. Building a gun seems more difficult but not impossible, but that skill is largely forgotten.
Now, the real hard part is the equipment like the specialized lathes and glass torches. And materials, like gun cathodes and getters. 
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#17
08-06-2020, 06:24 PM
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I'm not sure why some of you seem to think baking out during applying vacuum is such a big deal. It simply means the tube is in an oven during the time the vacuum is drawn. Having the tube in some sort of enclosure at that stage is a good idea anyway because the tube may implode when vacuum is drawn. Equipment with this arrangement is available, if not common.
One of the major difficulty when re-building CRTs is the gradual heating and cooling of the glass when making a glass-to-glass joint. If not done correctly the glass will crack. A crack cannot be "welded" closed, the cracked section has to be cut off, you can only do that a few times before too much of the original neck is cut off. If the crack happens when the glass "button" on the end of the gun is attached the whole gun assembly probably has to be replaced. There are many glass formulas, they react to heating differently. Most CRT are made of a type of glass that is not the easiest to work. If you will notice, Glassslinger uses Pyrex glass. Pyrex does not expand with heating like most other glasses and so it rarely cracks. You cannot directly join Pyrex with CRT glass. Nick (miniman82) is supposed to retire this year. He will then have time to work on his re-building shop and eventually start rebuilding CRTs.
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#18
08-22-2020, 08:47 AM
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Quote:
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#19
11-16-2020, 03:37 AM
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Pyrex glass is a "hard" glass and therefore quite easy to work with and resistant to thermal shocks. The expansion coefficient is around 33x10 ^ -7. The situation is different with sodium and lead glasses, which are "soft" glasses. The expansion coefficient is 94 ... 106x10 ^ -7. The error in cooling and join will unfortunately break.
I mainly use soft glass to build my electron tubes, so differently to Glasslinger. But let's go back to the regeneration of picture tubes. I have the biggest problem with extending the "necks" of the cathode ray tubes because I do not have a large horizontal glass lathe. I perform this operation in my hands. This is possible for small picture tubes, but it's a problem for bigger. Getters are not a problem for me. I have a lot of this parts, Italian production SAES and Polish (UNITRA ZAP). I have a lot of glass sockets and I can do sockets in laboratory scale. The construction of electron guns for black and white CRTs is possible, especially for simple types of electron guns (triode or tetrode type). In the attachments there are some pictures of the CRT with my electron gun. This is the first cathode ray tube in which I have done almost everything: I replaced the phosphor, replaced the aquadag, and mounted an electron gun of my design. The bad contrast is because the cathode is too close to Wehnelt. Focusing and deflection is magnetic. There is Ion trap (necessary: I have not metallisation of screen). Last edited by AlekZ; 11-16-2020 at 03:43 AM.
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#20
11-16-2020, 09:29 AM
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This is very interesting Alekz. I know a few people who will follow your progress with interest.
Thanks, Peter
__________________
http://www.nostalgiatech.co.uk/Vintagetech.htm https://www.youtube.com/c/PeterScott/videos
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#21
11-28-2020, 04:52 PM
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Thanks to some space above my shop rafters, I have at least 3 dud 21FJP22 for possible delivery to Nick, if he so desires practice CRT's.
One RCA Colorama and two Sylvania RE's fully intact but DOA due to various gun maladies.
__________________
"When resistors increase in value, they're worthless" -Dave G
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#22
12-15-2020, 06:34 PM
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Back in the 70s, we came close to buying a CRT rebuilding system from a company out of what I recall was Chicago. They used to advertise them in the back of Radio Electronics etc.
The only good thing is that if we did buy it, I would have tossed all the equipment and materials twenty years ago.. John
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#25
10-22-2021, 03:09 AM
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I did more tests with heaters. Not having a hydrogen furnace for as high a temperature as necessary, I made a simple glass device. It replaces the hydrogen furnace. Water electrolysis takes place in the vessel on the right. The purest hydrogen is produced by electrolysis of an aqueous solution of potassium hydroxide on nickel electrodes. It is used here. Gas bubbles can entrain small amounts of potassium hydroxide with them, which is detrimental to the heater insulator layer. Therefore, there is a scrubber in the path of the gas, containing water with a small amount of phenolphthalein. This is where the hydroxide particles are absorbed. The pink color means that the water will be replaced soon. The pure hydrogen flows further into the vessel with electrical feedthroughs. The electric current heats the heater and the process can be controlled by regulating it. The used hydrogen flows out through the siphon with the "glass" on the left. This piece of apparatus is also very important. By lighting up the gas bubbles coming out of here, I listen to see if they are shooting. If so, it means that the hydrogen is still contaminated with air and the apparatus still needs to be flushed with hydrogen. Only when the hydrogen quietly ignites, do I start the sintering process of the insulator.
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#27
01-15-2022, 03:46 PM
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#28
02-03-2022, 09:39 PM
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It has been a while since I have been on the site. After my current gig (maybe a few years) this could be rite up my ally. Learning how to weld a new gun on a old tube does not seem like rocket science.
Where do we stand on guns? Is their NOS available for the color roundies? Do the B&W tubes require rephosphor and aluminumizing? How would we deal with toxic chemical disposal? Is it feasible to replace cathodes in guns? Does the cesium alloy degrade on cathodes not under vacuum?
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#29
02-04-2022, 01:10 AM
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One of those questions is easy to answer. The emissive surface of a cathode will be ruined by loss of vacuum. I didn't think caesium was normally used for cathodes but I could be wrong.
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#30
02-04-2022, 09:04 AM
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Quote:
Welding glass tubes is not so much a matter of science but skill, harder to get right than it looks. Note that there cannot be too large a bulge where the joint is on the outside (ID of the yoke) or the inside (sliding in the gun). Also it has to be straight. Some types of guns might be found. There supposedly is a source in Russia. B/W CRT do not always need a new phosphor, I think it would be a good idea but several people that plan to re-gun tubes do not plan to do it because of the added complications. If a tube is not aluminized it requires a different type of gun (older design) and those might not be available. Perhaps in that case the old gun has to be reused and the cathode replaced. It isn't feasible to re- screen color tubes with the state of the art. I don't know about waste chemical disposal. Depending on local regulation a small amount may not be a problem. "The devil is in the details." New cathodes have a combination of carbonates (barium, strontium and calcium?). Our Polish friend would know. After the vacuum is applied the cathode is heated and carbon dioxide (CO2) (and perhaps H2O) is released from the cathode leaving the oxides. If the cathode is exposed to air the cathode absorbs CO2 and H2O but not in the right way so it is ruined. You also have to install a new getter, which I believe contains barium and maybe another metal.
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