| Electronics > Projects, Designs, and Technical Stuff |
| Electron gun - salvage or build |
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| LaserSteve:
Zinc Orthosilicate Phosphor, Zn2SiO3:Mn Two Moles Zinc Oxide One Mole Silica add .5 to 1.25% Manganese Oxide or Manganese Chloride by weight as the activator. (No activator, no Glow) A slight excess of silica is desired. Potassium chloride or Sodium Chloride (15% by weight, added to basic mixture) may be used as a flux. Fire at 1000'C or higher for green. Add an excess of silica (2 MOLS or more, instead of one) and fire at 850'C to make the amorphous excess silica form that is medium persistence yellow. Grind or Ball Mill the ingredients together as fine as possible, without the KCL, or NaCl, the reaction can take a full 15 hours, with the flux, firing time is 40-60 minutes. You may find the need to fire, regrind, and fire again for the green form. Fire in Air, which is unusual for a Phosphor. Test under 256 or 365 nm illumination. From Dr. Gorton Fonda's recipe.. Otherwise just buy ZNS:CU There are plenty of facile synthesis or sol-gel synthesis of Phosphors on line, especially for ZnS:Cu. Yen and Weber, The Phosphor Handbook, is interesting for Chemists. YMMV as purity and particle size of the ingredients REALLY matter, ie start with Cabosil if you can. |
| Circlotron:
--- Quote from: ChristofferB on May 21, 2020, 04:01:38 pm ---I need something to use it for... --- End quote --- Team up with someone who makes vacuum tubes at home for the audio crowd but hasn't got a pump. You would also need an induction heater for de-gassing during evacuation. |
| BreakingOhmsLaw:
Hi, Used to work in a Philips picture tube factory. Evacuating CRT was done like this: Step 1: Piston Pump to about 50mbar. Step 2: Turbomolecular pump like the one you have in your setup. Step 3: Diffusion Pump while heating the CRT to 200C. After that, CRT was sealed. Step 4: Barium getter pill evaporated with an external RF Field. Heating the CRT was essential to achieve full vacuum, otherwise many molecules stick to the internal parts. |
| ChristofferB:
--- Quote from: LaserSteve on May 22, 2020, 03:06:31 am ---WE try to avoid soft solder in vacuum, but for you, the green or grey GOST standard parts with the hermetic glass are a winner. I'm assuming you do not want to pay 250-350 USD for a commercial feed in KF or other flange. Silver solder is OK. If you want to permanently seal your device, other means must be taken, but for a beginning high vacuum person, they are probably far better then anything you can make, short of Kovar to Aluminosilicate glass or Tungsten to 3320 to Pyrex. . Avoid thermal shock to the seals. They will limit your anode voltage, but for the grids, cathode, etc, not too shabby. If this is an older turbo, you might want to ensure it has the proper lubricant. A manual for the Turbo is a must, as is the proper cooling. J. Melson is right, a screen over the turbo is a very good idea, because otherwise your setup has to be perfectly clean with no broken parts ever. One thing I insist on is a TC or other gauge right at the roughing pump feed on the turbo. I watch mine in real time and have an alarm set up. You'll hear the turbo "load up" if there is a leak, and if the controller is any good it shuts the Turbo down if it senses drag. Suddenly loading the Rotor is not a sound I like to hear, so be careful. There are a couple of types of electron gun, some need much tighter tolerances, some need amazing curved shapes, and others sacrifice spot size for ease of building. Enjoy,... Video gets better at the middle: https://youtu.be/jHGAnJjnNY0 Video CRT https://youtu.be/MsMsZaSz3Fk For an experimental unit there are other ways without the specialized materials. PS, Please skip the Hf , RF, and PbO steps in the above videos if you try this... ::) You don't need low melting glass rods to hold your gun together, either. One other thing for a beginner, never ever trust your glass, always have a tough screen around it to protect you during an implosion. I've seen a few glass things do a pretty good impression of a grenade if mishandled. Always do some stress calculations on that glass, the amount of pressure per unit area when under vacuum is amazing. Applied Science has some videos you may be interested in. I imagine you want to do something like Auger analysis? Or you'd just like to see a beam? Steve --- End quote --- It's a pretty new pump, an EXT255H from 2012, I think it's "as-new". And i have a pirani gauge on the foreline with a set point output to trigger an alarm / emergency pump shutdown etc. I plan on doing as little glass blowing as possible, I've spent a lot of time on it so far, and I have never produced anything I'd risk my turbo on ;D I really like the idea of using the solderable soviet surplus feedtroughs, maybe using 2mm stiff copper wire, and let that be the entire support. That, or some blind holes tapped in a blind flange. All the tips on phosphor mixing are great! Do you know how to bind the phosphors to a surface? I've also seen people having success with using automotive spark plugs as high voltage vacuum feedthroughs, by the way. Might be good for anode voltages. |
| 1sciguy:
450kV power supply for my electron gun at work. I designed the pressure vessel so it can be filled with SF6 insulating gas. We use GaAs photocathodes that are laser driven. I designed the laser system. 50ps pulses at 500 MHz by gain-switching laser diodes and then amplifying with fiber lasers. I actually combined three of these lasers with 120 degree phase shift for a 1.5Ghz pulse train. This was all at a National Lab and I have retired. I would not attempt such a project on my own without serious funds. Photocathodes are cool because all you have to do is bias your cathode at HV and hit it with a laser to get the electrons off. Of course there is chemistry involved to process the cathode in vacuum to lower the work function so it will spit off electrons based on light energy striking it. Thermionic guns are pretty simple, so yes, you could easily take these items from a CRT if you have a means to float your drive electronics at high voltage. |
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