Not that long ago

June 24, 2019
 by Paul McGowan

While looking at a replacement woofer for a friend of mine I noticed its huge magnet and metal encasing shield. Ah yes, I thought, the magnetic shield that was all the rage a few years ago.

That shield was needed to protect cathode ray tubes which use magnetic steering to position their controlling electron beams. Those electron beams had to be pointed at precise locations to light up different colored phosphors.

Ray tubes! What Buck Rogers technology was this?

Of course, I am referring to the old style television tube known as the CRT: big glowing vacuum tubes that grew in color range and size over their 75-year reign. The largest commercially available model was about 45 inches and weighed several hundred pounds. Larger TVs were technically possible but not marketable as the depth, weight, and cost made them difficult to sell. A 50-inch TV would require a 38-inch picture tube and even larger casing, making it near impossible for the TV to fit inside a standard door (let alone be hefted by mere mortals).

CRT televisions were finally phased out as late as the 2000s and replaced by plasmas, LCDs, OLEDs, LEDs, etc. The newer technologies are insensitive to magnetic fields, and thus, the need for magnetically shielded speaker drivers has vanished in little more than the blink of a technological eye.

Still, does any technology sound more high tech and futuristic as a fricking Ray Tube?

Buck would probably shed a tear for the passing of ray tubes into the boring of Light Emitting Diodes, so too would his contemporaries: Flash Gordon, Tom Swift, Brick Bradford, Don Dixon, Speed Spaulding, and John Carter.

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24 comments on “Not that long ago”

  1. SawI’ve changed quite a few CRT’s (Cathode Ray Tubes) in my time in both TV’s Radars and oscilloscopes. Quite ‘space age’ in their time but even Buck Rodgers would get a belt if he didn’t discharge that capacitive effect of CRT’s first before removing it.
    They were very tough at the screen end but very fragile at the gun end, needed a steady hand when replacing large radar tubes as they were also quite heavy.
    Also allied to CRT’s was the LOPT (Line OutPut Transformer that produced that jolt producing EHT. Components and terms that are quickly disappearing from our vocabulary.

  2. Minor correction. The electron beam in a CRT is steered by electric fields created by the voltage across the plates in the rear of the gun, not magnetic fields. Since a moving charge creates a magnetic field, it can be deflected by external magnetic fields. I had to pull my AR9s halfway across a room to satisfy myself that there was nothing wrong with the picture tube in my TV set.

    In a project built in 1993 for Bellcore we bought 3 45″ Mitsubishi television sets. I think Sony had a much larger one called a “Jumbotron.”

      1. TV sets use magnetic fields, oscilloscopes used electric fields. From Wikipedia;

        In oscilloscope CRTs, electrostatic deflection is used, rather than the magnetic deflection commonly used with television and other large CRTs. The beam is deflected horizontally by applying an electric field between a pair of plates to its left and right, and vertically by applying an electric field to plates above and below. Televisions use magnetic rather than electrostatic deflection because the deflection plates obstruct the beam when the deflection angle is as large as is required for tubes that are relatively short for their size.

  3. While growing up with Cathode Ray Tubes from a few inches to 32 16by9 (a friend was pleased to beat me at 36 inches but it took 4 folk to carry it!) I’ve been fascinated with the technology. After seeing several fixed in the home as a kid they initially frightened me (cracks, sparks and smell of solder) and then, as I grew up and started to understand basic electronics, amazed me. From the limited knowledge I gained I was impressed how the ‘rays’ could be guided by magnets to draw straight converging lines to hit the small red, green and blue phosphor dots. When they ended up in the last versions with almost flat front screens I could forgive them not being able to draw completely straight lines especially near the edges.

    For me, however, being the owner of the best if not largest picture I’ve ever seen in homes, my awe is now with Organic Light Emitting Diodes – OLEDS. The phrase “organic light emitting” when applied to a machine is awesome to me, as “cathode ray” was when I was a kid. No more compromises with LED backlighting or flickering caused by moving mirrors on a projector. Just ultra high definition with perfect colour and it can draw perfect straight lines, when the recording light transmission lens allow… 🙂

  4. After defeating today another one of those miserable captcha’s ….
    “I wonder how many of your readers have no reference for any of the names you referenced in this post ?”
    No many (if any) I think, since most persons on audio sites are greybeards, and thus grew up with CRT.

  5. In the 50’s I was the proud owner of a 9″ TV i my bedroom. The family unit was a whole 14″. Roll forward 30 years and it was a massive 36″ colour unit. That lasted for quite a while, and we then skipped plasma to get our first flat panel LED TV. They are much more capable now. My biggest beef is that there seems to be a hole in the range of screen sizes between 32″ and 40″. Our current 38″ screen fits very neatly between two windows, and replacing it when it dies is not going to be easy.

  6. In the years I was a wire service photojournalist, we had some Buck Rogers-class equipment, the most “James Bond”-like was the Leafax color negative transmitter. Built into a stainless steel Zero Halliburton case, the lid had a keyboard, and the main body featured a pop-up CRT screen to do minor editing, cropping and captioning before converting the negative into analog tones for 2-wire telephone transfer. I got #775 in early 1992, and that whole technology was mostly obsolete by the first AP2000 digital platforms in the mid-’90s. Reuters would not pay the freight to ship the carcass back to them, so I kept mine. Most folks gutted them, to have a new Zero Halliburton case. I finally gutted it recently, and there was that little pop-up screen, spring loaded.

  7. I had a 40″ Trinitron that weighted 320 pounds. You pretty much had to order the matching custom stand that went with it, as it would crush most TV stands. I actually kept it in the family room until 2017. I still worked well, and did hi-def (via component video hookup) better than you would expect. Kudos to the guys from the local affiliate of 1-800-GotJunk who finally wrestled the beast out of here.

  8. We are retro gamers and is really hard to find affordable nice speakers to go with the CRT, so we can play properly N64 or SNES… (in our retro gaming set up)

    Retro consoles and modern speakers don’t get along very well, specially since those were made with the CTR in mind!

    1. If I vaguely remember from my days of reading speaker builder books and magazines, 12 gauge steel might have been the magic number to surround the magnet with, or line the interior of the speaker with, to kill those magnetic fields. Others I believe used an opposing magnet glued to the back of the existing magnet to cancel the field out. It might be possible to retrofit something to an existing speaker, if one isn’t afraid of a little DIY work.

  9. What I disliked about CRTs besides the depth and weight was the geometry of the image on the large flat screens. It was never correct. There were never any straight lines especially close to the viewing edge. The curved screens were somewhat better.

  10. Anything that is cumbersome is destined to be replaced sooner or later if a less cumbersome replacement comes along. So it was with the cathode ray tubes. Technology for the sake of technology is never a good idea. Also many replacements are accepted because they are convenient and cheaper and not because they are better. Here it is a step backwards. So it goes. Regards.

  11. I started watching CRTs before there were color broadcasts. By 1966 we had a 27″ color set, which was as big as they came. I stopped watching TV in 1968, which was healthier for my eyes. When computers became personal I re-discovered monochrome with long persistence green phosphors on Kaypro and Compaq portables, and then moved up to a desktop with a classic IBM 5151 monitor.

    I have used a lot of Tektronix oscillloscopes and I still have a modular portable scope and RF spectrum analyzer, but my last video CRT was the Sony Trinitron 32″ 16×9 flat screen. As they say, by the time it is perfected it is obsolete. The feature of HD CRTs that can’t be duplicated is analog line scan. This enables native resolution of both 720 and 1080 line formats with no digital scaling. They had much better OTA display than plasma or liquid crystal with no conversion artifacts and better blacks. These displays are also natively faster than LCDs, which is why gamers still use them.

    Now everybody is watching streaming and cable which are so mangled from file compression they degrade your vision. Even BluRay is compressed relative to HD broadcast channels – except network distribution is now compressed so the only real HD is live programming on local stations, who pump the color in the studio and compress remote broadcasts like news trucks, concerts and plays.

  12. I wish there were someone who could use the old CRTs, rather than just send them all to a landfill. I have a few perfectly functional CRTs here, including a 27″ that gets used most weekends when one of the kiddos visits. I’d gladly replace it with an LED, but I don’t have room to store it, especially since it will not get any future use. I also have a couple of older TVs, including a 1967 MGA black and white portable (11″ screen, I believe?), and a 19″ color MGA from the 70s. The Salvation Army stores locally I don’t even think will take CRTs anymore–they had a glut, and nobody would buy them.

  13. I just thought I would share another unique piece of history related to the CRT — Shuya Abe and Nam June Paik’s “Wobbulator”. The device was basically a means of using the electromagnetic effect on CRTs for creative/artistic effects. There are still a few of these originals in existence. I have had the pleasure of playing with these crazy devices at the Experimental Television Center and a place called Signal Culture — both in upstate Owego, NY. Here is a link to one in action:


  14. We need to wait till the CRT is actually gone. I use my Sony WEGA 32″ all the time in the basement. Works far and away better than garish cheap LED TV`s. Yes, it weighs 200 pounds.

    When the upstairs Zenith 25″ CRT monitor, with outboard digital tuner, was replaced, we had to go with PLASMA to get around the simply awful LED picture quality. The monitor quality Zenith CRT is superb.

    Plasma went away in the US since no one cares about image quality, just size. Eventually, plasma went away everywhere because of energy compliance standards from what I understand. We still have the Panasonic plasma and nothing new that is affordable comes closed to it. True, it isn’t good in direct sunlight. I’d rather occasionally see a good picture washed out some than a bright, ugly, LED picture all the time, choice to be made.

    Flat screens are JUST now getting decent where most can afford one in spite of no one’s concern over image quality. When OLED gets the reliability down we should be good again. 4K, and worse 8K, have significant BW delivery issues.

    Ignored, is that digital verses analog TV piggybacked the tube conversion and digital is far and away better than analog for image signal stability. Off air I get 720P going to the Sony WEGA with a converter tuner. Digital was the bigger “news” than the change in screen tech, in my opinion.

    PC monitors are similar, my old flat screen Sony Trinitron 21″ was, and still is, superb images and SPEED. Try to buy one used, yep $$$$. The flat screens are again, just getting to be OK.

    New doesn’t mean always better, it means trade-offs, usually. Weight, cost, image quality ETC. Some limits are permanent, and built into the designs. In time we can gain back some of the losses. In the meantime, I’m keeping the big Sony. It reminds me of what new really means. It is best to to wait and see sometimes.

    I bought a 9.7″ Samsung S2 tablet for 200 bucks brand new with an OMLED screen that eclipses the 10″ Apple air iPad we also have. It is like the Apple, but with a Android OS I like far better and with more storage capacity and it was less than half the price. Newest technology? No. A far better compromise? Yes. I finally have a decent screen and OS, both.

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