Color crt question???

[bgadow]

I'll note that many color tv sets of the early/mid sixties have a green screen bezel which closely matches the picture tube color. So they looked like that when new. I've noticed that rectangular era tubes are always some shade of gray; older/cheaper tubes are light gray up until the black matrix era. And then there is the blue GE Neovision, which must not have offered any real benefit because nobody seemed to have ever copied it.

[andy]

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[radotvguy]

I believe have two of those 21axp22 in my attic , i will look tonight if i still got them .

[old_tv_nut]

A search for phosphor body color led to
http://www.espi-metals.com/technicaldata.htm#P
If you scroll down to P for phosphor, they list a number of color TV and other phosphors and state the body color. None of the color TV phosphors appear to be highly colored. However, there is a reference to a cadmium containing phosphor that is colored.

This leads me to think that the green-face tube were indeed the all-sulfide tubes, with cadmium used in at least the green phsophor.

Can someone with a green-faced tube do some investigation with a strong magnifier/microscope?

1) - Tube off - Are all 3 phosphors the same body color?
2) - Tube on, if the three phosphors are different with tube off - which emission color has which body color?

[bgadow]

When I read old tv nut's post yesterday I thought, eh, he is full of hot air! All the phosphors are going to be the same color!

So last night I took my little 8x magnifying glass and did a survey:

21AXP22(A?) I couldn't get close enough, with the safety glass, to use the magnifier but with the naked eye it is pretty clear that all three are uniformly light gray

21FJP22 (various, all olive green) The 3 phosphors are 3 different colors! I never looked close enough to notice this before. One is gray, one is olive green (perhaps a little lighter) and the third is a darker green, sort of a mustard color. That one appeared to have some impurities to it, colorwise.

21" rectangular in a Motorola (late sixties) 2 of the phosphors are gray and one is light olive

Older GE Portacolor with dot matrix crt-2 are gray and one is a pale grayish green.

18" GE & RCA & newer Portacolor-all gray

1990 Sylvania 20"-you can actually see the colors-one stripe is reddish, another bluish, the third a grayish green

I also took a look at a dud Philco RE21FJP22 (rare earth phosphor) that I have in the attic. Tough to see because of cataracts but it looks all gray. And then there is the tube in my Zenith 25MC33; a mid-70s Zenith branded but Sylvania EIA rebuilt tube. All light gray.

I have not tried to figure out which is which as of yet. It makes me crosseyed enough already! I guess if I can focus on one set of phosphors while working the brightness control I can figure it out. I'm guessing the mustard color is the red?

[old_tv_nut]

Bryan, Thank you! There is nothing like a real experiment!

I don't know if I would hazard a guess about which colored dot is which, but it's fun to guess. Now if you could fire up one, you would find out for sure.

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The 1990 tube has pigmented phosphors - each one has a pigment coating of the same color as the emission, to improve contrast.

[old_tv_nut]

This reply received from Chuck Prazak, former VP Engineering at Rauland:

Yes. The cadmium sulfide red phosphor was a strong, deep yellow color. The zinc-cadmium green was light yellow and the zinc sulfide blue was white.
Even after the rare earth red was introduced, the screen color was still slightly yellowish due to the color of the green phosphor.
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I think that's definitive! The olive-green appearance would be the combination of the phosphor colors and the dark (neutral) faceplate tint.

[bgadow]

All very interesting! I confirmed this last night with a set switched on. Not easy to see, but there it was: mustard=red, green=green, light gray=blue.

[old_tv_nut]

Here's an interview with an old hand at RCA - has some words about how the CRT production process had to be cleaned up so it would not spoil the sulfide phosphors, which were more sensitive to contamination than the older oxide phosphors.

http://www.ieee.org/portal/cms_docs_...everenz027.pdf

[ohohyodafarted]

That was an incredibly fascinating interview. What a fantastic base of scientific knowledge this man had. Considering the early state of technoligical development at the time this gentleman was doing his basic research, the things they accomplished were nothing short of miraculous.

Thanks for posting this. I thoroughly enjoyed reading this interview.

[bgadow]

I had to sit here and read that whole thing. A very good history...I'm glad it was preserved. That gentleman came up with some amazing things that have really changed this world, yet still sounds just like the guy next door.

Man, the internet is a wonderful thing!

[Kiwick]

The Philips delta shadowmask CRTs used in almost all 60s and 70s color TVs here in europe had uniformly white phosphor dots, surrounded by a very reflective aluminium matrix, this combination made for an extremely reflective screen

Early (1975 to 1979) Philips 20AX series in-line CRTs had the same white phosphors and the same reflective aluminium matrix of their delta shadowmask tubes (and they also still needed convergence adjustments)

some later (1979) Philips 30AX series "self-converging" in-line CRTs had the phosphors stripes tinted in pale but very distinct red, green and blue, with the same aluminium matrix

Philips used this combination of pale tinted phosphors and reflective aluminium matrix until the early 90s when they finally switched to darker phosphors and black matrix.

[old_tv_nut]

While googling around, I came across an old thread here (2003) about red phosphors (can't figure out how to find it). Someone said that he heard you could judge the quality of the red (too orange or not) by looking at the yellow color bar.

I want to point out that this is not the case. Due to the rules of color mixture, if the bars are demodulated in the standard NTSC way (that is, red and green are driven to the same level as white), then the yellow bar color will be determined by the blue phosphor and the white point setting. This is because the yellow and blue must add up to make white.

There is an additional fly in the ointment, in that the color demodulators may be designed to have different gains and phases from the standard NTSC in order to partially compensate for non-standard phosphors. In this case, one or both of the red and green guns may be overdriven or underdriven on the yellow color bar, and the blue may be overdriven as well (driven below black). SO, there are many other effects which change the color of the yellow bar, and the color of the red phosphor is a relatively minor part.

[frenchy]

Originally Posted by old_tv_nut

Regarding black matrix tubes, this was one of the big inventions fo the mid-70's. All tubes use the black matrix technique today to reduce the screen reflectivity. Along with this came the concept of "negative guard band" for better purity.

How was 'black matrix" done? What physically was done to the tubes for this?

[old_tv_nut]

As usual, Google finds something:
http://www.achesonindustries.com/doc...20Brochure.pdf