CRT Construction

Discussion in 'The Projects Forum' started by Sparky49, Nov 18, 2012.

  1. Sparky49

    Thread Starter Well-Known Member

    Jul 16, 2011
    Hi everyone.

    I have begun the quest to build a cathode ray tube. I've made this so that I can edit it, before it goes into the completed projects section. I will polish up the diagrams and such like, as I go along.

    Here is the (probably) final schematic of the CRT. I have modified the accelerating anode from a metal disc to a piece of foil, thanks to shortbus for the link which inspired this change. I decided to use a buchner flask, as althought slightly more expensive than ordinary flasks, it has an arm through which I can draw the vacuum. This is one less point where air can enter, resulting in a more reliable result. Also, if one were to drill a hole through a regular tube/flask, one risks weaken the integrity of the glass. A big mistake when you are creating a vacuum in it!

    Today the glass tubes, aluminium and copper rods, glass flask and bungs arrived. Unfortunately the main bung for the flask was too big so I will have to wait a few days before the smaller size arrives.

    I cut the glass tube so it was about 5 inches long, and inserted the aluminium rod, which will act as my cathode. When the end of the rod was about 2 inches from the end of the tube, I held it in place and expoxied the join so that it was airtight. Once this was dry, I drilled a hole in the smaller bung and pushing the rod through the hole, until the join was in the bung. I then expoxied the ends of the bung to hold the rod and tube in place.


    Meanwhile, I have located a phosphor supplier in China, and I am hoping that they will sell me a small amount. I'll mix this with a little water and pour into the flask. After the water evapourates, I should be left with a thin, even film of phosphor, which will act as my screen!

    At the moment, there isn't much left to do, but once the smaller bung and phosphor arrives, it shouldn't take long for me to finish the project.

    I so excited!

    Last edited: Nov 19, 2012
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    It didn't happen unless there are photos. :)
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
  4. Sparky49

    Thread Starter Well-Known Member

    Jul 16, 2011
    Thanks guys!!!

    I'm not sure how much vacuum I will draw. To save myself some money, I'm going to use the school's vacuum pump, which is used to create a vacuum in a bell tube, so I'm sure it will be alright. :)

    That's a pretty cool website! His designs are quite similar to mine. That's a good thing! I like how he used some foil over the end of the glass tube, so I will try that instead.

    I will get an updated schematic up asap.

  5. Sparky49

    Thread Starter Well-Known Member

    Jul 16, 2011
    Schematic 1 now added.
  6. Sensacell


    Jun 19, 2012
    The epoxy is going to outgass and kill your vacuum?
  7. DickCappels


    Aug 21, 2008
    Do you realize that while what you are doing is very cool, it is also very dangerous? I am thinking about when that flask implodes -will you be wearing safety goggles? Be careful, and when working around high voltages, always keep one hand in your back pocket.

    Just some thoughts if you revise the gun design:
    The work function of the aluminum might be quite high, or impossibly high because of an oxide coating if you don't clean the aluminum right before pumping down the bulb. You might want to consider a G2 to help get the electrons off the cathode. If you put needle points on the end of the rod (sewing machine needles should work), you will get higher current for a given accelerating voltage.
  8. wayneh


    Sep 9, 2010
    I think x-rays are a bigger risk than implosion of the flask, which is designed for vacuum. (Safety goggles still a must.)

    You could spin the aluminum rod in a drill and grind a cone onto the end of it, like sharpening a pencil. Heck, I bet you could use a pencil sharpener.

    When you get your phosphors, I recommend testing your film forming procedure at small scale first, maybe using glass slides. A drop of detergent or Jet-Dri might help reduce surface tension to give a more even film. A problem I see is that the bottom of the flask will not be flat, and you'll get more phosphor in the puddles.
  9. Sparky49

    Thread Starter Well-Known Member

    Jul 16, 2011
    Thanks guys.

    All testing will be done with it behind a plastic screen. Being in a school, we will certainly be wearing goggles and will be very very safe. These flasks are designed to go under very low pressures, so unless I am stupid and crack it, it should be fine. It's only dangerous if you don't know what you are doing. :)

    X Rays will be no bother at such a low potential. Even if any are produced, they'll be so weak that they can't get through the glass.

    I'll try out the phosphor film as you suggest. :)

    Thanks again everyone. :)

  10. KrisBlueNZ


    Oct 17, 2012
    Great line! I'm sure I've seen that on a tombstone somewhere... ;-)