Fun With Tiny CRT

When we took apart the big old rear projection television, the same family also had an old VHS camcorder from the 1980s slated for disposal. [mle_makes] took it off their hands and merrily started taking it apart for fun components. First component to be brought to our weekly SGVHAK meetup was the viewfinder’s tiny CRT. I brought the box of Sony KP-53S35 salvaged RPTV parts on the same day so we could place the two picture tubes side by side with a ruler between them.

Tiny CRT 1 - Side by side with RPTV tube

While the big tube had 21 years of TV watching burned in to the surface, the little CRT looks to be in good shape. (Also, the RPTV tube was likely driven far harder to generate the necessary brightness.) And since the little tube was part of a battery-powered device (12 volt lead-acid!) the picture tube flickered to life with a DC power supply.

Viewed from the top, we are reminded how much of a space savings modern LCDs gave us. Both of these tubes are far longer than their picture’s diagonal size.

Tiny CRT 2 - Length comparison with RPTV tube

The little tube’s image was remarkably crisp and bright when viewed in person, a fact extremely difficult to capture in a photograph. The 525 scan lines of a NTSC signal meant this little tube was pushing 600 dpi of resolution!

Tiny CRT 3 - tape measure

All of these images on the tube were generated from an old video conference camera, which had a composite video output port that was wired to the tube’s control board. Here’s one of the test setups, using a scrap piece of paper and a simple smiley face drawn on it with a Sharpie marker.

Tiny CRT 4 - camera test setup

The best picture taken of the tube was when I narrowed the aperture to get a longer field of depth, so the camera is free to focus on something other than the actual picture and still get halfway decent results. (I think it is focused on the edges of the glass here.) An admirable amount of paper texture was conveyed on this tube.

Tiny CRT 5 - camera test image

A few weeks after this initial tiny CRT demo, it became the centerpiece of this Freeform Mini CRT Sculpture on instructables.com.

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