Comment by sosomoxie
6 hours ago
CRTs are peak steam punk technology. Analog, electric, kinda dangerous. Just totally mindblowing that we had these things in our living rooms shooting electric beams everywhere. I doubt it's environmentally friendly at all, but I'd love to see some new CRTs being made.
There's a synchronous and instantaneous nature you don't find in modern designs.
The image is not stored at any point. The receiver and the transmitter are part of the same electric circuit in a certain sense. It's a virtual circuit but the entire thing - transmitter and receiving unit alike - are oscillating in unison driven by a single clock.
The image is never entirely realized as a complete thing, either. While slow phosphor tubes do display a static image, most CRT systems used extremely fast phosphors; they release the majority of the light within a millisecond of the beam hitting them. If you take a really fast exposure of a CRT display (say 1/100,000th of a second) you don't see the whole image on the photograph - only the most recently few drawn lines glow. The image as a whole never exists at the same time. It exists only in the persistence of vision.
> The image is not stored at any point.
Just wanted to add one thing, not as a correction but just because I learned it recently and find it fascinating. PAL televisions (the color TV standard in Europe) actually do store one full horizontal scanline at a time, before any of it is drawn on the screen. This is due to a clever encoding used in this format where the TV actually needs to average two successive scan lines (phase-shifted compared to each other) to draw them. Supposedly this cancels out some forms of distortion. It is quite fascinating this was even possible with analogue technology. The line is stored in a delay line for 64 microseconds. See e.g.: https://www.youtube.com/watch?v=bsk4WWtRx6M
At some point, most NTSC TVs had delay lines, too. A comb filter was commonly used for separating the chroma from the luma, taking advantage of the chroma phase being flipped each line. Sophisticated comb filters would have multiple delay lines and logic to adaptively decide which to use. Some even delayed a whole field or frame, so you could say that in this case one or more frames were stored in the TV.
https://www.extron.com/article/ntscdb3
I only knew about SECAM, where it’s even part of the name (Système Électronique Couleur Avec Mémoire)
The physical components of those delay lines were massive crystals with silver electrodes grafted on to them. Very interesting component.
All PAL TVs had a delay line in them? Crazy.
It doesn’t begin at the transmitter either, in the earliest days even the camera was essentially part of the same circuit. Yes, the concept of filming a show and showing the film over the air existed eventually, but before that (and even after that, for live programming) the camera would scan the subject image (actors, etc) line-by-line and down a wire to the transmitter which would send it straight to your TV and into the electron beam.
In fact in order to show a feed of only text/logos/etc in the earlier days, they would literally just point the camera at a physical object (like letters on a paper, etc) and broadcast from the camera directly. There wasn’t really any other way to do it.
Our station had an art department that used a hot press to create text boards that were set on an easel that had a camera pointed at it. By using a black background with white text you could merge the text camera with a camera in the studio and "super-imposed the text into the video feed.
"And if you tell the kids that today, they won't believe it!"
>>> The image is not stored at any point.
The very first computers (Manchester baby) used CRTs as memory - the ones and zeros were bright spots on a “mesh” and the electric charge on the mesh was read and resent back to the crt to keep the ram fresh (a sorta self refreshing ram)
Yeah it super weird that while we struggle with latency in the digital world, storing anything for any amount of time is an almost impossible challenge in the analog world.
You should check out:
- Core memory - Drum memory - Bubble memory - Mercury delay line memory - Magnetic type memory :P
And probably many more. Remember that computers don't even need to be digital!
I was on a course at Sony in San Mateo in the 1980s and they had a 36" prototype television in the corner. We all asked for it to be turned on. We were told by the instructor that he was not allowed to turn it on because the 40,000V anode voltage generated too many X-rays at the front of the picture tube.
:-))))
One summer odd-job included an afternoon of throwing a few dozen CRTs off a 3rd floor balcony into a rolloff dumpster. I'da done it for free.
People pay for that these days in smash rooms.
What do you mean "had"? I just turned mine off a minute ago. I am yet to make the transition to flat screen TVs but in the mean time, at least no-one's tracking my consumer habits.
Not through your TV, but they see you driving to the last Blockbuster tho
The shadow mask system for colour CRTs was a huge improvement that thwarted worries about ''beams everywhere'':
https://en.wikipedia.org/wiki/Shadow_mask
Extra dangerous aspect: On really early CRTs they hadn't quite nailed the glass thicknesses. One failure mode was that the neck that held the electron gun would fail. This would propell the gun through the front of the screen, possibly toward the viewer.
Likewise, a dropped CRT tube was a constant terror for TV manufacturing and repair folks, as it likely would implode and send zillions of razor-sharp fragments airborne.
My high school science teacher used to share anecdotes from his days in electrical repair.
He said his coworkers would sometimes toss a television capacitor at each other as a prank.
Those capacitors retained enough charge to give the person unlucky enough to catch one a considerable jolt.
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I remember smashing a broken monitor as a kid for fun, hearing about the implosion stuff, and sadly found the back of the glass was stuck to some kind of plastic film that didnt allow the pieces to fly about :(
I can't still get over how we used to put them straight in our faces, yet I never knew of someone having an accidental face reshaping ever.
I don't know, "Killed by electron gun breakdown" sounds like a rad way to go. You can replace "electron gun" with "particle accelerator" if you want.
With CRTs, the environmental problem is the heavy metals: tons of lead in the glass screen, plus cadmium and whatnot. Supposedly there can be many pounds of lead in a large CRT.
This thread makes me realise that the old Telequipment D61 Cathode Ray Oscilloscope I have is worth hanging on to. It's basically a CRT with signal conditioning on its inputs, including a "Z mod" input, making it easy to do cool stuff with it.
We're getting awfully close to recreating CRT qualities with modern display panels. A curved 4:3 1000Hz OLED panel behind glass, and an integrated RetroTink 4K with G-Sync Pulsar support would do it. Then add in a simulated degauss effect and electrical whine and buzzing sounds for fun.
>1000 Hz
This sounds like a brute force solution over just having the display controller read the image as it is being sent and emulating the phosphors.
still can't play duck hunt on it though.
Yes you can, see https://neslcdmod.com/
It basically mods the rom to allow for a bit more latency when checking the hit targets
And perhaps peak atompunk too when used as RAM. [0]
[0] https://en.wikipedia.org/wiki/Williams_tube
Damn, what I wouldn't give to be able to look at my computer and see the bits bobbing in its onboard ram
Like the MegaProcessor? [0]
[0] https://www.youtube.com/watch?v=lNa9bQRPMB8
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The 1940-1990 era of technology can't be beat. Add hard drives and tape to the mix. What happened to electromechanical design? I doubt it would be taught anymore. Everything is solid state
Solid state is the superior technology for almost everything. No moving parts means more reliable, quieter, and very likely more energy efficient since no mass has to move.
Do modern hdd's last as long as the old platter ones? For me, when the SSDs fail it's frustrating because I can't open it up and do anything about it--it's a complete loss. So I tend to have a low opinion of their reliability (same issue I have with old versus new electronic-everything cars). I don't know the actual lifetimes. Surely USB sticks are universally recognized as pretty crappy. I can leave those in the same location plugged in and they'll randomly die after a couple of years.
Also, I believe precursors to CRT existed in the 19th century. What was unique with television was the creation of a full CRT system that allowed moving picture consumption to be a mass phenomena.