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If you look at a the shadow mask of a color CRT, you can have a pattern like this:

enter image description here

Most TVs were purely analog and had knobs to move the picture horizontally and vertically. How does the green gun stay aligned with the green phosphor in an analog world? it the deflection done by steps instead of continuously? (if that's the case this is probably not linear on flat screens?)

More confusing to me is that these TVs also have image size settings and then I wonder how it worked since, I remember these knobs beings just pots and I don't understand how the guns' beams could still be aligned with the mask.

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    \$\begingroup\$ There is a shadow mask with holes just before the phosphor layer which lets through the electron beams. Look at wikipedia: en.wikipedia.org/wiki/Cathode-ray_tube \$\endgroup\$ – Oldfart Feb 21 at 12:06
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    \$\begingroup\$ I went through it before; the mask is on the screen itself, so I don't understand how adding a minute offset to the deflection doesn't make a beam hit the wrong phosphor \$\endgroup\$ – Thomas Feb 21 at 12:11
  • \$\begingroup\$ @Thomas That thing you call a shadow mask (with the 3 color dots, on the screen itself) is not the shadow mask. \$\endgroup\$ – Harper - Reinstate Monica Feb 22 at 13:33
  • \$\begingroup\$ Yes, after understanding through the two answers, I realized I didn’t have the terminology right. \$\endgroup\$ – Thomas Feb 22 at 16:57
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Refer to @Briandrummond's answer for the original question. As to how the phosphor gets into the exactly correct locations (below from Phosphor Handbook 2nd Edition):

enter image description here

enter image description here

The slurry process is the typical process used for manufacturing mosaic screens. Figure 22 shows the steps in the process: A suspension is prepared by dispersing phosphor powders in an aqueous polyvinyl alcohol (PVA) solution. An aqueous dichromate solution is added to the suspension to make the mixture photosensitive. The mixture is called a slurry; hence the name of the process. A glass panel is set face-down in a spin-coating machine. The slurry is dispensed onto the panel while the glass is rotated slowly with a small tilt angle. The slurry is allowed to spread evenly on the inside surface of the panel without bubbles and using a minimal slurry volume. The panel rotation is then increased to obtain the desired screen thickness on the panel. Any excess slurry is recycled. The coating on the panel is dried with an infrared heater.

The panel is then exposed to light after an appropriate shadow mask (or an aperture grill) has been placed within the panel. The exposure system is equipped with an ultraviolet (UV) light source (mercury-arc lamp) at the site corresponding to the deflection center of the electron gun of the cathode-ray tube to be finished; the system is equipped with a lens that equalized the light beam path to that of the electron beam trajectory, and with a shader plate that controls the light intensity distribution along the panel surface. Generally, a pattern size (dot diameter or stripe width) increases with light intensity for a given exposure time. Therefore, the distribution of the light intensity along the panel surface has to be controlled by employing the shader plate, which corrects the intensity of light from the arc lamp. After exposure, the coating is developed by spraying hot water to wash out phosphors in unexposed areas.

The PVA-dichromate system works here as a negative photoresist. The slurry process, in a word, is photolithographic, employing a shadow mask as a photomask. The only difference between the slurry process and other photolithographic processes is that a given shadow-mask cannot be used to expose other individual panels, whereas a general photomask is repeatedly used to reproduce the same patterns on many substrates.

Note: Also mentioned are a Dusting Process which uses dry phosphor dust and PVA-dichromate and Phototacky process as well as several other processes. Available in the book, which is worth having on your shelf.

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    \$\begingroup\$ very interesting, thanks! \$\endgroup\$ – Thomas Feb 21 at 16:04
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The shadowmask is not on the screen but a carefully controlled (small) distance behind it. Looking from the green gun through any shadowmask hole, you'll only see a green phosphor spot. As you tweak the size control the green beam moves to different spots ... all green, thanks to the shadowmask.

enter image description here

Image source and further reading here

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    \$\begingroup\$ ok, I get it now! thanks! \$\endgroup\$ – Thomas Feb 21 at 14:38
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    \$\begingroup\$ +1 I once wondered how they managed to manufacture and align the shadow mask with the dots so precisely over such a large area. It turns out that the shadow mask was used as a kind of stencil to deposit the three colours of phosphor on the inside of the screen. \$\endgroup\$ – Spehro Pefhany Feb 21 at 14:46
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    \$\begingroup\$ @SpehroPefhany: I had speculated about that, but was never able to find any actual documentation. Do you have any links? It leaves a couple of questions, however. How did they deal with all of the excess phosphor (all three colors) deposited on the back of the mask? Wouldn't that create a rather bright glow inside the CRT if not removed or covered up in some way? Also, one of the big innovations back in the day was to improve contrast by adding a black mask between the phosphor dots on the inside of the glass. How was that accomplished, presumably AFTER the dots had been deposited? \$\endgroup\$ – Dave Tweed Feb 21 at 15:23
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    \$\begingroup\$ It's a photoresist process with the shadow mask as the stencil. I'll add it as an answer as it's pretty long. \$\endgroup\$ – Spehro Pefhany Feb 21 at 15:28
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    \$\begingroup\$ And yes, this means that the CRT's efficiency is actually kind of low, and most of the time the electrons are hitting the back of the shadow mask and heating it up, instead of going through and lighting up phosphors. One of the advantages of Trinitron (aperture grille) CRTs is that they have less "dead area" than shadow mask displays, and can get more brightness for the same gun output. \$\endgroup\$ – hobbs Feb 22 at 1:36

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