Building a CRT and bathing yourself in x-rays

For the Milan design week held last April, [Patrick Stevenson Keating] made a cathode ray tube and exhibited it in a department store.

The glass envelope of [Keating]’s tube is a very thick hand-blown piece of glass. After coating the inside of the tube with  a phosphorescent lining, [Keating] installed an electrode in a rubber plug and evacuated all the air out of the tube. When 45,000 Volts is applied to the electrode, a brilliant purple glow fills the tube and illuminates the phosphor.

Since the days of our grandfathers, CRTs have usually been made out of thick leaded glass. The reasoning behind this – and why your old computer monitor weighed a ton – is that electron guns can give off a substantial amount of x-rays. This usually isn’t much of a problem for simple devices such as a Crookes tube and monochrome CRTs. Even though [Keating] doesn’t give us any indication of what is being emitted from his tube, we’re fairly confident it’s safe for short-term exposure.

Despite being a one-pixel CRT, we can imagine using the same process to make a few very interesting pieces of hardware. The Magic Eye tube found in a few exceptionally high-end radios and televisions of the 40s, 50s, and 60s could be replicated using the same processes. Alternatively, this CRT could be used as a Williams tube and serve as a few bits of RAM in a homebrew computer.

You can check out the tube in action while on display after the break, along with a very nice video showing off the construction.

14 thoughts on “Building a CRT and bathing yourself in x-rays

  1. FTA:

    “For Milan Design Week, I teamed up with Super/Collider to create the world’s first handcrafted glass particle accelerator and set it up inside Milan’s poshest department store…”

    World’s first I’m sure, Mr. Blowhard.

    1. they call that Theft Of Patents! this man did NOT invent the CROOKES TUBE… MR CROOKE INVENTED IT!!!

      this man is a thief and any revenue generated is 100% patent theft

      this man will not be accepted by any university or collage in the entire world.


  2. You exceed 21 kV into a vacuum tube, you’re generating X-Rays. 45 kV (yes, 45,000 Volts) generates HARD X-Rays.

    The amount of lead in a CRT is a minor fraction of the glass weight … the front surface can be as much as an inch thick … for mechanical stability, not shielding.

    Early color TVs had tube rectifiers that, while capable of handling in excess of 21.5 kV, had the input (flyback voltage) adjustment to ensure you didn’t turn the rectifier into an X-Ray generator.

    I’ll dig up my old RCA tube manual and send you the details on the magic eye tube theory of operation.

  3. The penetrating power of x-rays is directly related to the acceleration voltage.

    X-rays can be produced at voltages as low as a few kV.

    Crookes tubes typically operate at 10kV.

    I think 15kV is the point at which x-rays are considered to significantly penetrate unleaded glass.

    This “art” exhibit operates at 45kV. Producing x-rays with penetration on par with the old shoe-fitting fluoroscopes; that operated at 50kV and would display a real-time x-ray image of your bones on a phosphor screen.

    The quantity of x-rays are less, and the distances greater. So I think Brian’s right, and for all practical purposes, it’s safe for the typical viewer; though a regulatory agency might not agree.

    But the sheer naivety of the “artist” both for putting an x-ray source in a department store, and falsely claiming it as a world first, is still appalling.

    One can only hope he spends many hours admiring the greatness of his own creation, thus removing another egotistical “artist” from the gene pool.

  4. “Magic Eye” tubes (in all their various configurations) were not limited to a few exceptionally high-end radios and tv’s… they were quite prolific not only in high-end sites, but also in mid-range gear. Sets with them were marketed as being “better” (and they were helpful in getting a look at signal strength/modulation/etc…), but their value to the various TVs & Radios that used them was in the user interface, not in the actual electromechanical functionality of the device (with a limited few exceptions).

    The marketing was very effective, and if you went to a friend’s house and their radio or TV had a “Magic Eye” on it, it has serious Cred. But, they certainly were not rare. They showed up in instrumentation used in a variety of fields (laboratory, industrial, military, audio & video production, art, etc…).

    The website link in the article ( is quite informative and very complete in its scope… worth doing some reading if you’d like to learn more about how things were done back when Hector was a pup.

    1. I visited the site in the link, while he’s got a nice collection, it doesn’t seem to address how they actually work! Sure there’s the diagrams, but how was the beam deflected? And what did that mean? How would you use it to tune in a radio? I’m only curious, but I’d like to know how they actually work and what they do, just for that reason.

  5. – is that electron guns can give off a substantial amount of x-rays.

    Totally not so. Only after they have been accelerated by the HV and hit the target do they produce X-Rays. Higher the voltage the faster they hit the target the more penetrating the X-Ray is.

    Pure tungsten is used in medical X=Ray tubes. The electrons hit the W surface and the X-Ray are emitted. In medical / dental tubes the anode is angled to allow a more uniform intensity field.

    Old Bio Medical Imaging guy

  6. I have an old Grundig three band tabletop radio with a 6E1p¤, 6BR5, 19BR5, EM80, UM80, Y119 type magic eye tube, positioned with the round end down.

    IIRC it’s from around the time when FM radio first started. It also has AM and shortwave.

  7. Every vacuum device operating at voltages in excess of few kilovolts will emit x-rays. Now the thing is how much of these are going to be absorbed by the glass envelope – below 15…20kV i would say most of it. There are exeptions, however – take the russian 2C2S tubes – at 15…17kV they generate insanely intense x-rays which, surprise-surprise, most generic Geiger counters will not detect. So even if you are smart enough to protect yourself by taking some readings around the device, make sure that your instrument is actually sensitive to soft x-rays. Counters sensitive to alpha and beta particles
    are usually much better (because of mica etc window that does not attenuate the rays significantly).

    On the other hand, there are tubes like PD500 by Telefunken (or their counterparts like 6BK4 by RCA or russian GP5) that will not emit anything below 22…25kV because of leaded glass envelope. But once you cross that (and the russian tube is particularly good at high voltages because of favorable physical geometry) the recorded radiation rates rise sharply. Some of these tubes, when insulated properly, can go as high as 70-80kV and will serve as very intense Xray source. But none or almost none of the radiation will be produced at moderate voltages, 20kV or less.

    I was playing with these for quite some time and even managed to obtain decent quality radiographs by using them as a source for x-ray imaging. Do not recommend taking xrays of your body parts with these, though.

    The term “intense” i am using is relative; since these tubes are usually operated in cold cathode mode, most of the energy is turned to heat and only small fraction of electrons hitting the target will be converted to x-ray photons. And this will be just a fraction of capability of a commercial x-ray tube. These experiments can be all lots of fun but one needs to take measures to limit the exposure as much as practical (ALARA; As Low As Reasonaby Achievable). The simplest of them is to keep distance to an operating x-ray source – operate it remotely, take pictures using camera remote or timer, have a Geiger counter handy, use some shielding around the source to narrow the beam. I have successfully used lead shells from an old underground telecommunication cables to make a very effective shielding around the tubes tested.

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