A Look At The Smallest Magnetic Deflection CRT Ever Made

A high-resolution LCD or OLED screen is a commodity component that we can buy on a little breakout board and plug into our microcontrollers without spending more than a dollar or two. We can buy them in sizes ranging from sub-postage-stamp to desktop TV if our budgets stretch that far, and they are easy to drive in every sense of the word. It is not so long ago though that a high-resolution LCD, even a small one, was a seriously expensive component. In consumer electronic devices such as camcorders engineers went to great lengths to avoid those costs, and [12voltvids] recently took a look at one of them.

Inside the viewfinder of a miniaturized Sony camcorder is a CRT. It’s fairly mundane in the scheme of CRTs, in that it’s a monochrome device with no unexpected features. Except that is, for one thing. It’s tiny, with only a 0.5″ inch screen size. Everything else is the same as your vintage full-sized TV, it has an electron gun and a deflection and focusing coil pack, but the entire device has been miniaturized to the point at which the coil pack is larger than the screen it is driving. On the accompanying PCB are all the support circuits, including a tiny flyback transformer and a single IC –  a Rohm BA7149 electronic viewfinder driver that is as near as possible an entire CRT TV on a chip. That’s it, the whole device runs from a single 5 volt supply.

He doesn’t give the date of the camcorder, but given that it looks as though it uses 8mm cassette tapes and has a curved miniaturized design rather than the angular black exteriors that were fashionable earlier we’d guess it to be from some time around the year 2000. To give it some context, at the time one of the hottest pieces of consumer electronics would have been a Diamond Rio MP3 player, and if your desktop PC had the first of the AMD Athlon processors you probably considered it to be about the fastest you could hope to own. The surprise then is that Sony still considered it more economical even at that point to use the CRT and associated circuitry than a tiny LCD. Either way we’d agree with him that it’s a keeper, a fascinating curio for any electronics enthusiast. If we see an old camcorder going for not a lot, we’ll certainly give it a second look after this.

Thanks [Rahul Chawre] for the tip.

33 thoughts on “A Look At The Smallest Magnetic Deflection CRT Ever Made

    1. It was from a 1996 model year CCD TRV11 camcorder. LCD screens were also common back then, but the reason for the B/W CRT viewfinder was for manual focusing.
      Color screens were just not good enough. Even with my current camera, which features an ultra sharp OLED viewfinder they have to include a focus magnifier to aid in focusing. Something that was not needed with a monochrome CRT because the CRT was more than sharp enough for focusing the camera manually under all conditions.
      Hitachi (also sold by RCA) made a small beam index color CRT that was 1.25″ but it was useless to focus with due to it’s low resolution. The cost to make this little CRT in the day was probably higher than a small LCD.
      I currently have 2 digital 8 cameras. One from 1999 and the other from 2000.
      The 1999 model uses the same view finder as in this video, and the next year it had a color LCD.
      The LCD is useless from a focus point of view. Just doesn’t have enough detail so focus the camera.

  1. For anyone wondering: this seems to be the Sony CCD-TRV11. It also had an LCD on the side that you could fold out. Given that the manual has a 1996 copyright, that is likely when it was released. Even in newer Hi8 devices Sony released closer to 2000, they were still using the CRT viewfinder. For example, the CCD-TR3200 my parents bought in I think ’99, also had one.

  2. >”Sony still considered it more economical even at that point to use the CRT and associated circuitry than a tiny LCD.”

    The CRT had no input lag relative to what went into the tape, and it had superior resolution to the LCD, so you could actually see when you’re in/out of focus with the camera. The LCD on the other hand was pixelated which gave the false impression of sharpness, yet when something moved it became ghosted and blurry. LCDs had to become better and cheaper, and the DSPs a whole lot faster (and cheaper) to get you equivalent performance of a tiny black & white CRT.

      1. And for another point, the dynamic range of an LCD was poor compared to the CRT, so the view became washed out and you couldn’t judge the lighting correctly. What you saw on the LCD was not what you got on the TV screen. That’s still the case, but then again the eyepiece viewfinders have dissapeared from cameras almost entirely, so it’s a moot point because nobody’s got anything better.

        1. My sister bought one of the first VHS-C camcorders with an LCD viewfinder. It was absolutely terrible – low resolution being the worst of many complaints. But she *needed* the colour for her use-case.
          Until LCDs came along, I never saw a consumer grade camcorder with a colour viewfinder. I don’t know if even mid-range professional/studio cameras had colour viewfinders.

  3. Also relevant: some newer units had LCD with colour backlights. This only really became practical when blue LEDs did, sometime in late 1998.
    Have a DVD camcorder here which uses this method and kept it around because it does have some use even though long since obsolete thanks to phones with fractions of a GP count.
    Still need to figure out how to convert the drive so it can read full sized DVDs :)

  4. I’ve been looking for a cheap source of tiny TFT displays. Something like 320×240 px with less than 1 inch display size. One can get them as spare parts for viewfinders, but they’re quite expensive.

    1. One I investigated used the viewfinder circuitry to generate H & V sync pulses for the rest of the camera.
      Composite video (presumable from the sensor & processing) to the viewfinder, sync back down to the recoder (tape in those days).
      Why have a separate sync separator when there’s one already there! Problem is, camera wouldn’t work without a functioning viewfinder!

  5. I have one or two around here somewhere. Now to make one into an oscilloscope, to feed stereo audio into the two deflection coils. In small TV’s that I do this to, the flyback has to have an inductive load on it when disconnecting it from the horizontal deflection coil, or no HV. To make the time based display use the vertical as horizontal (rotate the coils 90deg.) Feed audio from a small power amp into the other coil.

  6. Back in the days of CRT dominance, moms would constantly tell their younglings not to sit too close to the TV because it wasn’t good for them. Now imagine strapping a CRT one inch from your eyeball. Getting too many X-Rays seemed possible, but I bet they thought of that and did sufficient remediation.

  7. I ran one of these weekly for the better part of my time in high school. Sometimes multiple times a week filming entire basketball games for the team to review afterward and then during the day for the school “news” segment. Ahh, the dangers of being a nerd. The X-Ray exposure must not be too bad. I’m 33 and still have better than 20/20 vision.

      1. I’ve just got to ask. Does CRT tube size matter with x-ray production? Is the point that small tubes produce less light and so less electrons need to be fired at phosphor to make less glow and so less x-rays? The effect, I suppose, is offset by the fact that it is an inch or so from the eyeball rather than, hopefully, many feet away for a TV. :-) I assume that a CRT that has 100x as many square inches of glowing phosphor would produce 100x as many x-rays but there would be the same yield rate per display surface area. Larger tubes don’t get extra “nasty” as they get bigger, beyond what scaling does. Is that right?

  8. I have both a BW and a color cam corder monitors. Bought the color monitor from a surplus house in 80s to replace BW monitor on my VHS-C camcorder. It worked but sucked power like crazy reducing recording time. Also have just as rare 3 image tube Sony color camera that I dumpster dived for. Someday my family will put it all up on Craigslist for $50….

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