All About CRTs

For old-timers, CRTs — cathode ray tubes — were fixtures as kids sat in front of TVs watching everything from Howdy Doody to Star Trek. But there’s at least one generation that thinks TVs and computer monitors are flat. If that describes you, you might enjoy [The 8-Bit Guy’s] coverage of how CRTs work in the video below.

CRTs were heavy, took high voltage, and had a dangerous vacuum inside, so we really don’t miss them. The phosphor on the screen had a tendency to “burn in” if you showed the same image over and over. We don’t miss that either.

The basic idea is simple. An electron is fired at the phosphor behind the screen. An electrostatic or electromagnetic arrangement allows you to hit specific spots on the screen, and, of course, you can turn the beam off. Color CRTs have three different phosphors, and the beams have to fire at the correct color phosphor.

The best part of the video is the part where they tear apart an actual CRT, something you don’t see very often. We were worried about the vacuum, but the tube in question had already vented to atmosphere.

We doubt CRTs will make a comeback like vinyl records have. If so, maybe you’ll settle for a software simulation. It does make retrocomputing simulators feel better.

76 thoughts on “All About CRTs

  1. TFTs and OLED screens also suffer ‘burn in’ though the mechanism is (obviously) different.

    I don’t miss colour CRTs so much now TFTs etc have got so high resolution (though that does present its own problems) but I do miss monochrome CRTs, there’s something special about them and I wish I’d kept a terminal or two.

    1. I did keep 2 terminals as well as a “minitel” to have fancy setup when my old days and free time comes …
      That said, I’m not nostalgic of the weight and desk real estate that came with CRTs but it still took a lot of time to get in similar price category (with inflation) an screen that kind of match the CRT I had :
      When I ditched my cheap 2nd hand CRT (sony trinitron 21′) in the mid 2000′ because I did not take the time to repar it right away (contrast problem fixed by changing a resistor on the ctrl board) I gat a FHD 20′ LCD with a comparable pixel count but much lower refresh rate and contrast !
      Now that I switched to a a color accurate 27’4k I feel the virtual real estate is making up for the still lower contrast and refresh rate but it was not super cheap as my previous screens were!

      PS : my fixed CRT has been happily leaving it’s 3rd life in my home made arcade machine for the past ~20y

    2. Agreed. And let’s don’t forget the dead pixels..
      I’ve got a 5:4 LCD with pivot function and some dead red pixels.

      Also, quite a few flatscreens had died because of failing backgrounds illumination.
      It probably was the inverter for the CCFL bulbs that failed.
      CRT monitors generally lasted longer, I think.

    3. Monochrome CRTs are quite beautiful and relaxing. There is a reason that a lot of artists were working with them in the 60s and 70s.
      I don’t miss the sound of flyback transformers though.

  2. One thing I definitely don’t miss from CRT’s is their bulky size. I have made my desks 100cm (40″) deep and as CRT’s became bigger you still were awefully close as a desk stood against a wall.
    On a normal 80cm desk usually the monitor’s rear was against the wall, and the keyboard right in front of the monitor and the keyboard lined up with the front of the desk.

    But since the LCD age I noticed I didn’t use the space at the back and am now making them 80cm (32″) deep, with space for a sheet of A4 paper ánd a tablet between keyboard and monitor

    1. Ah, the warm glow of having office desking/tables where you got the back end of the person opposite’s 17″ CRT pointing at you (and yours at them), because the tables weren’t deep enough to go back-to-back.

    2. The 200W of heat times 50 desks wasn’t much fun in the summers when the office aircon would’ve been overwhelmed even without the monitors. When CRTs came out the company I worked for upgraded just for the energy savings

      1. Last summer I had to teach a class internally and did most of it standing in front of one of those 2m (6ft) presentation displays. The heat that comes off of those is conciderable!

    3. I remember briefly hearing about “Flat CRTs” about 6 or 7 years into LCDs being very common. And by “flat” I mean “thin” (not just a flat glass surface at the end of the tube). There were just a couple of pictures, devices that were about an inch or two thick. I don’t know what ever happened to it. I assume the technology wasn’t viable for the mass market

      1. Flat CRT’s were edged out by Plasma, which has similar physical characteristics (weight, delicateness) but plasma sets were easy to build and didn’t need to be aligned. They didn’t last as long as CRT’s though, as I recall they burned in like 5x faster, and as soon as TFT’s became practical plasma sets went away too. Unfortunately it was a few years before color rendition was up to what the glass sets would do, but nobody was making those any more.

        1. Zenith had a flat tension mask crt which had a shadow mask which was flat and under tension from springs Which enable that to stay flat, even as it was heated during use. This allowed the tube to have a flat front. Unfortunately a flat screen of any size has to be really thick to be strong enough to hold a vacuum, and the zenith CRTs were extremely heavy for their midest size. I think there were some issues with dot pitch because of the way the shadow mask expanded when it got hot. I think they also had a fairly narrow deflection angle, so you fot a flat screen but s really deep box behind it.

          About the same time Sony was selling a folded CRT where the electron beam was curved and scaned the phosphor screen that was parallel with the electron gun and was viewed from the back. I don’t wrmber where the deflection coils were located to keep them from obscuring the image. Maybe it was electrostatic deflection. Anyway for obvious reasons it was monochrome and the tube was relatively large for a smallish image. You still see them in apartment building intercoms from the 1980s and 1990a

          Those are the only “flat” CRTs i can think of and neither was flat in the sense of a flat screen with thin borders without a bulky box behind it

      2. The technologies were called Field Emission Display (FED) and Surface-Conduction Electron-Emitter Display (SED) and I don’t think either were ever mass-produced. This was probably more a matter of not having a market niche worth developing-for since there were prototypes.

  3. I think the “problem” with faithful black/white CRT simulation is that we don’t have true black/white screens anymore.

    All the modern flat panels are based on inferior RGB technology, with e-ink screens being the exception.
    So there are always those annoying RGB sub pixels around that kinda ruin the mood.

    I mean, the human eye not only has receptors for RGB, but also monochrome (brightness, grayscale).
    And it’s the monochrome/grayscale aspect that gets a bit neglected these days.

    Hopefully this wi change for the better once again,
    so we can faithfully enjoy “3D Monster Maze” again or relive the good old Macintosh days. ;)

    1. > I think the “problem” with faithful black/white CRT simulation is that we don’t have true black/white > screens anymore.

      This!! I still remember how nice and crisp were the monochrome monitors on old Macs and Atari (ST series)

    2. I mean, the human eye not only has receptors for RGB, but also monochrome (brightness, grayscale).

      Yes and no. If you are looking directly at something you are only getting RGB. However, if our peripheral vision is purely based on brightness.

      Hopefully this will change for the better once again, so we can faithfully enjoy “3D Monster Maze” again or relive the good old Macintosh days.

      You seem to be delving a bit into the audiophile category of rosy retrospection because nostalgia is a great deceiver. I would suggest actually getting the old hardware and actually relearning what it is that you are missing because anything short the real hardware will measure up to your deceptive memory of it.

      1. “Yes and no. If you are looking directly at something you are only getting RGB. However, if our peripheral vision is purely based on brightness.”

        There’s also night time. That’s when we use our rods.

        “You seem to be delving a bit into the audiophile category of rosy retrospection because nostalgia is a great deceiver.”

        Hm, maybe I do?! 🤷‍♂️
        I’m still tinkering with old stuff. Even stuff that’s older than me.

        For some reason, I find these older things more fascinating than current technology. Generally speaking, I mean. Things like relay circuits or core memory come to mind.

        Not sure why, to be honest. Maybe it’s nostalgia, maybe not?
        But how can I be nostalgic for something that’s older than me and which I have no memories of ? 🤔

        “I would suggest actually getting the old hardware and actually relearning what it is that you are missing because anything short the real hardware will measure up to your deceptive memory of it.”

        “You” in the sense of me or everyone? 🤨
        Personally, I do have a little bit of vintage equipment in the house.
        A couple of b/w TVs, small color TVs, green monitors, a 4.77 MHz PC, a C64, an ZX81, some 20th century Macs etc.
        My “collection” surely is very humble in comparison to real vintage fans, I think. 🙁

  4. How is a vacuum dangerous? When I was a kid we would throw old vacuum tubes we found down by a stream and enjoy the nice anti-pop they made when they imploded. Is a CRT implosion asymmetrical which somehow reflcts some of the implosion into outward movement? That’s all I can think of but still it seems the effect would be relatively small.
    Also you can’t vent a vacuum to atmosphere, the words vent implies something leaving when in fact the opposite would happen, air would get in.

    1. Oh great – what next, denying that dark suckers are a thing…? Even in the early days of the internet, people already knew we don’t actually generate light when we want the darkness to go away – we simply use a dark sucker to get rid of it…

    1. Noticed that first off. The crt’s vacuum was opened to atmosphere. If a spacecraft loses a window…are you sucked into or blown into space? Sorry for the “tomato, tomaato” semantics discussion.

    2. Naw semantics if fun. Though I think the original is correct enough- vented “to” instead of “into” just means the two are in communication, not necessarily the direction of flow.

      1. Nah, the vacuum was removed from the atmosphere when the CRT was manufactured. Balance is restored to Nature when the vacuum is once again freed!

      2. Before I go to bed I turn up the dark.

        IIRC I stole that from an early Pink Floyd song.

        Ladies of HackaDay:
        FYI. If I turn the dark up far enough, I look just like Brad Pitt (or anybody else).

    3. Working with high vac that’s a pretty common way to say it even though, of course, it is air coming in. However, you might also consider saying you are putting beers in the fridge to remove the heat from them. You do say that, right? ;-)

    4. “Vented to atmosphere” isn’t correct, but it’s how electronics tradesman came to refer to the event from the early days when vacuum tubes were only used as rectifiers and amplifiers for radio sets. I think the ideas was that once the catastrophe settled, you could fly your improbably small science fictional spacecraft from the open air of the outside world into the no longer enclosed interior of the tube; thus, a vent had been created (a hole you could pass through) which led to the atmosphere.

  5. If you’re into retro computing, and especially gaming, owning a CRT still makes sense. I have a few, one specific to each platform (PC, Amiga, Spectrum (which really just needs a TV), Macintosh). Games, in particular game sprites, were drawn in such a way that the slight unsharpness of the CRTs was a part of the design. They don’t look as good on an LCD screen (desktop software does look better though…). While there are upscalers which do the “unsharping” on an LCD screen for you (like OSSC, Medusa, etc.), and they do a pretty good job, there are still elements of the experience that are being missed, such as the loud click sound of the CRT starting up, the electrostatic discharges when you changed resolution or contrast, the smell when the monitor heats up, the cracking sounds it makes when it cools down, and the unique adventure of degaussing!!!

    1. +1

      That’s why a Commodore 170x or 1064 monitor looks so different. Dot pitch was about 0.40mm to 0.60mm.
      The original IBM PS/2 monitors were similar (0.40 mm).
      VGA monitors of the 90s were 0.2x mm by contrast. Way too good already.
      That’s why 320×200 games looked so ugly in the late 90s.

    2. Raster-intercept-based light gun/light pen technology also requires a raster scan to work correctly, and even simple hit-detection light guns (like the NES zapper) get thrown off by the slight latency increase of most flat-panel displays.

  6. I urge the staff of this site, and the community as well, to re-search about SED/FED/TDEL monitors; the best of crt with all the possitives of lcds (lcds for me where one step forward and two backwards at the same time). It would be nice to see a diy approach on these technologies.

  7. “dangerous vacuum”

    What the…. ???
    OMG outlaw them already !~’@#%*$%!!

    Because I’ve never know anyone, ever, telling a story about CRT’s spontaneously imploding. In an office/factory/home anywhere. Or this even being “a thing” on the internet when everyone used one because there were no other choices. Or people that had TV’s either.

    I do recall myself and others hurling them with great force at pointy metal objects and not being able to smash the screen.
    And in my working life I’ve know people drop them – hell I got an amazing deal on a 21″ trinitron monitor back in the day cos someone had dropped it and merely damaged the case.

    Maybe the ones I/we tried to destroy were just stronger. Or maybe it wasn’t a problem…

    1. The glass is mighty strong (which is why CRT’s are so heavy). I’ve never seen one implode, but as an urban explorer I’ve seen many a smashed TV screen. Usually they don’t completely break like you’d expect of a glass object, but just have a big hole in the view part, like they’re made of plastic.
      There are two dangers with them.
      1. If they implode while you are at a distance, the collision of the glass might send some tiny glass fragments which won’t do much harm except in eyes.
      2. If they implode while you are handling them (especially the neck), they might suck your hand in, along the sharp edges which can cause conciderable cutting.

      1. 3. You can be cut by sharp glass pieces when cleaning up the range.

        Truth. Drives are better targets. Especially very old ones that would start spinning when powered and open.

    2. Modern CRTs (late 70s or 80s onwards) had a protective shield for this scenario.
      The implosion would still happen, but no shattered glass on front of the CRT tube anymore. Speaking under correction, though.

    3. The trick is to put the CRT in a pit, then stand back a good ways and throw bricks into the pit.

      My brother and I blew up (imploded) several CRTs that we found in a dump that way.

    4. Was with a colleague when he inadvertently cracked a CRT somewhere near the cathode. A few seconds of hissing and increased heart rate while the tube re-pressurized were the only effects.

      1. Yeah, that’s the correct place to break them if you want to dispose of the vacuum. I usually just tapped with a small hammer the little glass nipple at the very end of the cathode, the same place they used to evacuate the tube in the first place. Hisses for a second or two, really not a serious hazard at all. Sea level is 14 psi; you need a pretty big volume for that to begin to be worrisome.

        1. It really was an issue. It was a common TV shop repair to replace the CRT and bad CRTs had no value, so unless taken care of they were dangerous outside the TV sets they were mounted in. The danger was the fragile neck.

          Typical process to make them safer was to clip (with wire cutters, gloves, eye protection) the tube socket vacuum seal, just as you say. I knew a TV repair shop owner that would take them behind the shop and plink them from a safe distance with a 22 rifle.

    5. It was very common for CRT’s made in the 1960’s thru 1980’s to implode if dropped onto a hard surface. They didn’t have all the fancy protection newer ones do, and being small they also had relatively thin front glass. I’ve seen it happen several times, and usually the entire front of the tube would implode. When the shards hit the back of the tube they would rebound spraying fine sharp glass fragments far enough to reach all the corners of a typical room.

    6. Yeah this was only really a problem on the very old CRTs. Like pre-1950s. Especially the larger ones, those held enough potential energy to really go off like a bomb and didn’t have any internal safety features yet.

      But in the 80s and 90s? Moms around the country threw a brick through the TV when you watched it too long (or at least mine did…) and nothing bad happened. Well, nothing implosion-related. Glass did not fly. And I’ve used some old monitors for target practice before, as well as doing the little trick of unsealing the vacuum relatively slowly by snapping off the little nipple at the back of the electron gun.

  8. I won’t ever miss them.

    The only thing I remember about them is the headaches. I grew up (beginning in the late 80’s) with a computer in the house and although I loved to play games on them, I remember the headache I got every single time I sat behind it. Within 5 minutes I started to get a headache. My parents got an TFT display very early on and that solved the headaches. The last time I saw a CRT was probably 15 years ago in a factory I worked at and I had to fix an issue they were having on DOS. The first thing that happened was the headache.

    The only fun thing about CRT’s I remember was the weird button that made that sound and turned the screen all wonky for a few seconds.

      1. Probably hard to do on a DOS system.-Unless it has VGA/VBE graphics. There used to be refresh rate utilities for DOS/Windows and OS/2 when VESA VBE got more popular.

        On really old systems, it’s best to use a mono CRT with long persistent phosphor.
        A green monitor with a long afterglow, so to say.

        It’s the analog solution to the slow refresh. Really works nice for still images and word processing and control software.

        Only problem is burn-in. A screen blanker utility (proto screen saver) would have been needed to prevent this.
        Lowering the brightness via knob helped, too.

      1. I loved that button. Then one day my dad bought an UPS that didn’t tolerate the sudden current draw and caused the computer to reboot if I pressed degauss. It was hard to learn out of that habit..

    1. The CRT coil whine was because of 15 KHz sync, which was still in human hearing range.

      VGA monitors, by contrast, operated at ~31 KHz and didn’t cause a headache anymore. Except to dogs and bats, maybe.

      Atari ST (mono hires, SM124), Hercules and EGA monitors used higher than 15 KHz sync, as well.

      Professional Amiga users had used a scan-doubler/flicker-fixer and a VGA, monitor.

      So it’s not like CRT whine was inevitable.
      It were mainly TV grade monitors and toy computers (C64, Amiga 500, Famicom) that suffered from cheap companion monitors. ;)

    2. “The last time I saw a CRT was probably 15 years ago in a factory I worked at and I had to fix an issue they were having on DOS. The first thing that happened was the headache. ”

      Probably a machinery with CGA graphics.
      CGA was pretty obsolete but it had the advantage that it supprted ordinary video monitors through composite video.
      So a bog standard TV or surveillance monitor from the 1960s could be used, even!

      Driving a CRT tube directly via RGB pins was possible, too.
      Vintage computer fans still build their CGA-Scart cables these days because of this feature.
      It’s really just TV technology (15KHz, 50/60Hz at 200 lines).
      No wonder it causes headaches. Eye sore wouldn’t be another possible symptom. ;)

    3. “I remember the headache I got every single time I sat behind it. Within 5 minutes I started to get a headache. My parents got an TFT display very early on and that solved the headaches”

      I really think the flickering was part of the problem.
      Because I had experienced similar issues back in the day.
      The noise made by the TV in the living room, by contrast, merely was a bit annoying to me. It caused me slight dizziness, but no headache.

      What caused me headaches, however, was the noise that the PC motherboards in the 2000s made (my old 486 was fine):
      It was coil whine and the HDD noise that caused me headache.
      That’s why I switched to SSDs early on, when they were 16GB in size, still.

    4. Your headaches were likely more due to eyestrain (fuzzy images?) than the properties the CRTs. I’ve used CRTs weekly (vintage computer historian) for 40 years and never got headaches from simply having them on.

      If you watched television back then, did you also get headaches? Exact same tech and refresh rate.

    5. Well, get this: I’m watching YouTube on one daily. No plans to get rid of it as long as it keeps working. Which, at this rate, might exceed the rest of my lifespan. Bonus fun fact: there’s no decent Kodi skin for Standard Definition screen resolution – well, actually, there IS one now…

  9. “CRTs were heavy, took high voltage, and had a dangerous vacuum inside, so we really don’t miss them. ”

    Not always! Ever carried a monochrome TTL monitor? A Hercules monitor, I mean?
    Very lightweight. Could be held by its “tail” (power chord) with a single arm/hand! 😃

    Other monitors like the Atari SM 124 were not much heavier, either.

    What you young guys are thinking of are 19″ VGA CRTs, I guess.
    But their heaviness is also in parts because of their strong power supplies.

    Monochrome CRTs used to be much more modest.
    They could be run off batteries, even.

  10. The 12-year-old me want to turn the ‘electron gun’ from a CRT into a ray gun. Too bad that wasn’t feasible, there were some neighborhood bullies that needed to go away.

  11. Making a x/y visualizer out of a TV back in 1970, or a timebase audio display. The vertical drive becomes the horizontal, audio amped with the sound amp fed into vertical deflection. The horizontal drive has to have similar inductance dummy load. I did it again a few years ago with a little battery TV I found on the curb.

  12. When I was in the US Navy, I was assigned to the telemetry room on the USS Norton Sound, a missile test ship. One of my assignments was to take care of two Ampex 8 channel tape recorders. One of those had a level monitor with a bank of 1″ / 25mm CRTs. When the ship was decommissioned, I grabbed one of those CRTs from spares. I still have it, a cute little thing.

  13. I don’t miss CRTs. I blame them partly for my poor eyesight, I spent my youth on a semi blurry screen in MSDOS. Watched cable TV, still pretty blurry (watchable, but not great fidelity by today’s standards). The retrogamers who insist on CRT use are deluded, that’s like doing a gaussian blur on a document bc the font is pixelated.

    1. The blurry VGA monitors of the late 80s were an intentional thing.
      It’s because of MCGA and 320x200x256 resolution.

      In order to be able to display photographies at this low-resolution and shine by doing so, the CRT *had* to be this blurry.

      The Amiga 1084s monitor and the IBM PS/2 8512 had 0.41m dot pitch, for example.
      The famous Commodore 1701 had 0.64mm, even!

      But by the 1990s, MCGA lost its value and full VGA (640×480) and GUIs like Windows 3 got more popular,
      along with higher resolutions in 256 and more colors.
      That’s when dot pitch changed to 0.28mm or 0.26mm or 0.24mm.
      Previously, CAD monitors had used such resolutions.

      More information on this fine site (we’re not affiliated):
      https://www.dosdays.co.uk/topics/monitors.php

  14. Never mind that – there’s at least one generation that thinks that when you turn the TV on the sound arrives long before the picture, and when you turn it off, the picture first shrinks to a line then to a point…

  15. Fun fact about CRT televisions.
    The first borosilicate color available to artistic lampworkers (glass blowing with a torch) was harvested from CRT televisions. They used borosilicate color glass on the electron guns (I believe to label them and differentiate between different electron guns). Which is why these days these little chunks of glass are referred to as ‘gun mounts’.
    The original colors are referred to as Dwarf colors, for their basic color palette I believe.
    These colors are still made to this day by Origin Glass, but frankly most of these colors are not great to work with. Their white is nice.

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