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  1. #1
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    Electron guns, anybody found a source of new unused guns for CRTs?

    There was a thread here about getting an electron gun out of an old TV/monitor picture tube.
    Ideally, I'd like to find a source of new unused, old stock electron guns for my experiments.

    I have obtained guns from old CRTs and my preferred way is to wrap nichrome wire round the neck where I want to cut the tube and arrange to
    pass a current through the wire till its red hot. The tube cracks in a very fine line all the way round. Air leaks in quite slowly,
    so the phosphor isn't disturbed on the screen. I always do this remotely, at a safe distance with the tube covered. Imploding tubes are dangerous.

    I did this recently really as a test of my high vacuum system. This comprises an Edwards EO2 vapour diffusion pump, backed by an Edwards E2M2.
    The system evacuates an 18" high 12" diameter glass bell jar. (Yes it IS behind an acrylic safety cylinder!) The jar is mounted on a thick steel base plate with electrical feed-throughs and there is a large diameter cooled Edwards high vacuum valve between the chamber and the diff pump.

    Once pumped down (which takes about an hour) I turned on the heater and applied an EHT of 1kv. Initially I connected the focus anode to the EHT, so the
    spot I got was about 1/4" in diameter. I was quite surprised that the oxide cathode had survived being back at 1 atmosphere.

    From this experience, it seems that ex CRT guns can be used for experiments, though how long their cathodes will last remains to be seen.
    The particular CRT I used is an old oscilloscope tube with a 4" screen and an unusually open and large electron gun. There is just about enough room
    for me perhaps to be able to fit a replacement directly heated cathode when and if the original one fails.

    I am able to get very reasonable emission from
    nichrome wire that has been coated with a 50/50 mixture of strontium and barium carbonates. These carbonates are not particularly hazardous. I apply the
    50/50 mixture as an aqueous slurry to a slightly heated nichrome wire so it dries quickly and leaves a nice even white coating. Once a high vacuum is established the wire is strongly heated and, although completely dry, a considerable rise in the diff pump's foreline pressure is seen. This indicates the breakdown of the strontium and barium carbonates to their respective oxides, liberating a small amount of CO2 (carbon dioxide). After that, when heated to dull red, the wire is highly emissive and a thermionic voltage can be seen between the wire and an adjacent plate.

    The attached pic is of my ex CRT gun in the bell jar. The glow from the heater is on the left and the bright green spot is the resulting electron beam hitting
    a ZnCdS screen.

    Click image for larger version. 

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    Last edited by Thermionics; 6th February 2012 at 18:05.

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  2. #2
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    Re: Electron guns, anybody sound a source of new unused guns for CRTs?

    I doub't you will find "new unused, old stock" unless you can find a regunnng factory but LCD and plasma technology has put all the ones I know of out of business.

    If you want used but likely to be good ones, contact your local council refuse disposal dept or a local 'waste recycling centre', they usually have a pile of old TV's waiting for disposal and would be only too happy to see them go to a good home. They normally recycle the tube to remove the harmful lead additives in the glass but the tube necks are of no use to them.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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  3. #3
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    Re: Electron guns, anybody sound a source of new unused guns for CRTs?

    Quote Originally Posted by betwixt View Post
    I doub't you will find "new unused, old stock" unless you can find a regunnng factory but LCD and plasma technology has put all the ones I know of out of business.

    If you want used but likely to be good ones, contact your local council refuse disposal dept or a local 'waste recycling centre', they usually have a pile of old TV's waiting for disposal and would be only too happy to see them go to a good home. They normally recycle the tube to remove the harmful lead additives in the glass but the tube necks are of no use to them.

    Brian.
    I've got quite a few old monitors and TVs myself, so I'll salvage guns from all of them before disposing of them. It would be nice to find a stock of guns intended for re-gunning TV tubes. Probably lots were thrown out as re-gunning businesses came to an end.

    Thanks for your reply though.

    C



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    Re: Electron guns, anybody sound a source of new unused guns for CRTs?

    Any real reason why you can't use an SEM filament holder.

    The link below shows filaments and aperatures, but not the holder.

    http://www.google.com/url?sa=t&rct=j...,d.cWc&cad=rja

    I can't seem to find any refernces to a "Weinholt cup" which is what holds the filiment. It's generally cone shaped with a small hole. The filiment is initially centered in the hole with 3 or 4 srrews and then centered later with the electron optics. I think it's also moved vertically.

    Much much stronger filaments can be found in electron beam eveporators. The one i fixed was 30 kW.

    The electron optics consists of aperatures and tubes called the column, focusing and deflection coils.



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    Re: Electron guns, anybody sound a source of new unused guns for CRTs?

    What is the desired effect of your guns? High efficacy NIR emitter?

    I once entertained an emitter using ribbon shaved nichrome embedded in glass in a TO-3 case for a gas analyzer.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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