Cathode Ray Context

A few ways cathode ray tubes were used that you might not have been aware of by simply watching the boob tube.

By Ernie Smith

Today in Tedium: The cathode-ray tube is having a bit of a revival at the moment in the public consciousness, as people who grew up with these screens suddenly see the distinct advantages they hold in certain use cases, often related to the things they display. (Sometimes, though, the CRT becomes a bit of a villain in the story, something that a confused contributor to TechRadar found as he struggled to get his set working because he couldn’t find a compatible remote.) Of course, the electron guns that we brought into our homes by the millions were primarily used as television sets, but they also had other uses—or at least other novel methods of use—worth highlighting. And with that in mind, today’s Tedium highlights inventive and novel uses of the good ol’ CRT. — Ernie @ Tedium

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The year that the cathode-ray tube amusement device, a not-a-video-game device that relied on the placement of physical overlays to function, was first patented by inventors Thomas Goldsmith and Ray Mann. Built before the TV became mainstream, the amusement device functioned by having the device modify the actual cathode-ray beam on the screen. “The game can be made more spectacular, and the interest therein both from the player’s and the observer’s standpoint can be increased, by making a visible explosion of the cathode-ray beam take place when the target is hit,” the patent filing stated.

CRT as RAM: How early optical cathode ray tubes found use as primitive forms of computer memory

As we’ve written in the past, vacuum tubes had an important role in the history of computing, even if that role has evolved somewhat in the modern day.

The CRT had a similar arc of having value in a lot of areas, including in the management and storage of memory. Perhaps the most notable example of this was developed by Fredrick C. Williams and Tom Kilburn, researchers at the British Telecommunications Research Establishment who used the properties of the CRT to store random-access data on a CRT-based monitor, a solution called the Williams-Kilburn Tube. This tube ended up being used by a number of important early computers, most notably the UNIVAC, as a way to store information.

Notably, the way that these tubes worked to store information leveraged features of CRTs that would have been undesirable if you were a television viewer. Essentially, it leverages the fact that electrons will stick to the phosphor of the screen for a short amount of time, allowing data to be stored for a brief period of time as long as the electrons are occasionally refreshed to store the information.

Williams Tube

(Computer History Museum)

To be clear, we’re not talking about a ton of data—at the high end, a single tube could hold 2,048 bits, or 256 bytes of data. But even so it worked, if only for a short amount of time. Williams tubes, despite their wide use, were notoriously unreliable, requiring constant tuning, and were often combined with other types of memory, such as magnetic drums, to allow for multiple, more-reliable memory options.

(Let it be said that degaussing would not be a good idea with a Williams tube.)

The Williams-Kilburn Tube wasn’t alone on this front—RCA had developed a number of competing products (including the Radechon tube, above). Perhaps the most interesting was the Selectron Tube, a vacuum tube and compact CRT that could hold up to 4,096 bits (512 bytes) at the high end. Developed with the help of Russian innovator and early television pioneer Vladimir K. Zworykin, the tube improved on the work of Williams and Kliburn and used different, more reliable methods of data storage.

Zworykin, who developed the tube-based system for distributing television as well as a tube-based system for television cameras to use to properly record material for the format, was the very type of person you wanted developing CRT-based memory, and he definitely pulled through for this one.

Seletron Vacuum Tube Memory

What an expensive-ass RAM module. (via eBay)

One problem: While a better vacuum tube, it was nowhere near as reliable or capable as magnetic core memory, which came out around the same period as the Selectron Tube, and made the idea of storing memory using a CRT obsolete. Just think of it this way—bit for bit, Selectron-based computer memory is the most expensive type of RAM you can buy on eBay.

Ultimately CRT’s use as memory storage was a temporary trend that was quickly innovated past. But it might have been the starting point that got us to our RAM-hungry present.

Five unusual kinds of cathode ray tubes that you’ve probably never seen (or maybe you have, I don’t know your life)

  1. The Magic Eye Tube. This vacuum tube with the built-in elements of a CRT was developed in the 1930s by key television figure Allen B. DuMont, who developed the device as a visual indicator of amplitude—making it a useful tool for tracking the strength of, say, a radio frequency. It’s named for its eye-like shape, created in part because of a filament in the middle that creates the appearance of a pupil. As the website Magic Eye Tubes explains, Magic Eyes found common use as electronic measuring devices in the 1930s and 1940s, even outside of the context of the radio.
  2. The Nimo Tube. This unusual variant of CRT, which was intended to display basic information such as numbers on a small display, is somewhat similar to the Nixie tube, a similar technology that looks like (but isn’t) a vacuum tube. Engineer and YouTuber Fran Blanche said in a 2017 video that the tubes were rare—in large part because of the large amount of energy and complex methods needed to charge the tubes. She got one working, but she noted that “it did turn out to be quite a complicated project.”
  3. Electrostatic printer tubes. Sold by megacorp Raytheon in the 1960s, this technology was intended for high-speed thermal printing of documents. This technology was apparently quite fast; per a 1960 issue of Electronics & Communications it could print more than 20,000 characters per second or 10,000 lines of computerized data per minute. Makes my laser printer sound slow.
  4. The RCA “lollipop” CRT. This experimental attempt at a flat television set, tested by RCA Labs in 1982 and 1983 was one of a handful of flat CRT screens that have been prototyped over the years. This one, per the Early Television Museum, was shut down before it could make any real progress. The technology relied on turning the scanlines on a right angle to display on the screen.
  5. Philips Research Zeus prototype. Only one centimeter thick, the Zeus display technology, developed by Philips Research Laboratories in the 1990s, aimed to develop the theoretical picture-frame television using CRT technology. The technology eventually never made it to market, but is perhaps some of the most groundbreaking research into CRT technology in the past 30 years.


The number of models that Sony made of its Watchman line of portable television sets, which were produced between 1982 and 2000. While the series eventually moved to LCD, some of the earliest models actually were based on unusually-shaped CRTs, with the tube pointing downward into the set, helping to create the device’s handheld shape. While the most famous kind of pocket TV, examples of pocket TV sets date to at least the mid-1960s.


(Brett Payne/Flickr)

Jumbotrons—the kind you saw in sports stadiums—used CRTs, but not in the way you might think

So, you might remember a while back, in my piece on dots vs. pixels from 2018, that billboards actually required a lower dot density than a traditional sheet of paper might, because you’re located so far away from it that you won’t pick up imperfections, and that this concept also applied to pixels on a screen?

So what if I told you this was essentially the theory on which giant CRT monitors were predicated in the days before the LED? And when I say giant CRT monitors, I of course mean the flashing lights of Sony’s Jumbotron or Mitsubishi’s Diamond Vision, two types of massive screen technologies that dominated in settings like Times Square and large sports stadiums alike.

But when broken down, these massive video walls, in their original mega-CRT form actually used CRTs in a way not unlike how LCD screens break down color. To give you an idea of what I mean, here’s an image of an LED screen up close:

HD TV up close

(Wikimedia Commons)

Now compare that to what the numerous bulbs of an early Jumbotron-style screen look like:

Jumbotron CRT

The Futaba TL-3508XA flood beam CRT. (via Industrial Alchemy)

And for completeness’ sake, what a shadow mask looks like on a standard CRT monitor up close:

Shadow Mask

(Wikimedia Commons)

Essentially, Jumbotrons—which also took cues from Sony’s Trinitron line of TV sets—were effectively recreating what modern OLED or Micro-LED screens do. They excel at lighting up individual pixels, or small clusters of pixels based on the specific image—except by doing so with individual pixels that were larger than a a quarter in size. The result is that the earliest variants of the screen, while massive, had a resolution (240x192) comparable to that of a Colecovision (256x192), while also being smaller than an original NES (256x240).

While mega-sized screens using LCD technology are possible, even successor technologies that didn’t utilize CRT technology took a more roundabout path to displaying pixels. For example SmartVision, a technology put to use in baseball stadiums the world over starting in the 1990s, worked similarly to Jumbotron, utilizing clustered LED “pixels” of red, green, and blue light.

These massive screens were very much a product of the 1980s, with the very first one, a Mitsubishi Diamond Vision screen, first appearing in at the MLB All-Star game at Dodger Stadium in 1980. Hilariously, the technology got a mixed review in its first outing from Los Angeles Times sportswriter Richard Hoffer, who wrote:

The Dodgers’ $3 million score-board was finally unveiled Tuesday night, to the apparent delight of those fans who confirm their reality through the television experience. There really was an All-Star game, and you could ask the 50,000 or so at Dodger Stadium; it was on television there.

That apparently is the function to be filled by the Mitsubishi screen, 560 square feet of something called Diamond Vision. Because, its various and wonderful capabilities not-withstanding, it didn’t do much but remind folks that they had become part of the biggest home-entertainment system in all of America.

In many ways, the jumbo displays were a key element of the great “screening” of global culture, a screening that continues in our pockets to this day. Suddenly, large concerts would evolve from having to lean on laser light shows alone, minimizing the fact that most people could barely even make out the band on the stage, to having big screens that everyone could see.

And not everyone loved that, of course. In a 2011 article for The Post Game, writer Michael Kruse suggested that the Jumbotron effectively ruined sports-going experiences as venues increasingly programmed for the massive TVs.

“It has blurred the lines between those who are watching and those who are being watched. It has blurred the lines between sports and entertainment and between information and advertisement. It has blurred the lines between what’s real and what’s not,” he wrote. ”At stake is our continued ability to tell the difference.”

The most iconic example of the cultural shift enabled by the Jumbotron might be the Jumbotron at One Times Square, which originally appeared with a Sony logo starting in 1990. The massive sign became an icon of NYC in its own way, most famously in 1995, when David Letterman, whose show had access to the sign, used it to display a new slogan for the city: “We can kick your city’s ass.” (The image is sullied by Rudy Giuliani, but admire it all the same.)

The original Jumbotron left in 1996 (and Sony itself quit the jumbo screen market in 2001), but it nonetheless shaped the way that Times Square eventually evolved. And while LED-based jumbo screens eventually became the standard, the roots of this approach were ultimately born of a more novel, obscure technology—a bunch of tiny CRTs that added up into one massive screen that could be viewed from far away.

The thing that I sort of think is important to highlight with this piece is the fact that it is all too easy to take for granted the technology that helps to drive the things we do daily.

When one form of an object like a cathode ray tube becomes so dominant, it can be easy to take for granted it is the only form in which we see it. And the truth is, this basic, fundamental technology appeared in lots of shapes and forms, even directly in our faces.

Everywhere, every day, our world was being made better by this device that shot electrons into our faces so we could see things, but that wasn’t the only way we were using these crazy tubes.

We take CRTs for granted today, but they were damn innovative devices and more versatile than we give them credit for.

Now excuse me while I try to find $8,500 to buy 256 bits of Selectron Computer Memory on eBay.


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Ernie Smith

Your time was just wasted by Ernie Smith

Ernie Smith is the editor of Tedium, and an active internet snarker. Between his many internet side projects, he finds time to hang out with his wife Cat, who's funnier than he is.

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