Color crt question???
 

The ctc4 I just picked up has a fairly decent 21axp22 in it. The only types of 21axp22's I am familiar with have always had a sort of light gray color phosphor when you look at the crt when not operating.

The 21axp22 crt in the ctc4 I just got, has the typical olive green color phosphors when the set is not operating.

Does anyone have an explanation as to why the phospors would be olive green instead of light gray?

Is it possible that late era 21axp22 replacement crt's from RCA were made with the newer type olive green phosphors that we are all familiar with on most round color crt's?

Inquiring minds need to know!

Bob

It is said that early 21AXP22's have the same 1953NTSC color gamut as a 15GP22, but the later 21AXP22's do not. I do not know the answer, but you may have hit on some real evidence. Can you find a date code on your tube?

Hi Pete,

Where would I look for the date codes?

Also the gray phosphor tube is in the newer ctc5 and is coded as a 21axp22a, (I believe it to be the original) where as the olive green crt is in the ctc4 and is coded as a 21axp22. I suspect that the ctc4 has had the original crt replaced at some time, because my first ctc4 that I had back in the 70's had the original factory crt and it had the gray phosphor.

I wish the gray phosphor crt was the good one, because there is a big difference in the way the color looks on a tube with the gray phosphor. the colors seem more vibrant to me. That is what I remember most about my original ctc4 that had the original crt.

Here's hoping that I can find a used gray faced 21axp22 to restore the ctc4 to it's original state.

Even if I could find a dud with the gray phosphor, I would be willing to pay Hawkeye the $700 he wants to do a rebuild on one with the new long heat up and cool down oven cycle, utilizing the oven cams that John Folsum commissioned.

We could use it to test out the new long cycle protocall for rebuilding the 15gp22 crt's

TTYL,
Bob

The 21AX in my now working CTC-4 appears to have a slightly greenish tint to the screen. It is a rebuilt without the "A" suffix, and produces excellent color, deep reds, brilliant blues and greens and will converge ok after all other minor cabinet repairs, etc, are done and it is in a more permanent spot. Perhaps it is one of the earlier tubes with a proper color gamut, as Pete notes.
I am trying to reduce the size of my screen shots so I can post a couple on the forum, but so far no luck. I will keep on, though.
Enjoy your 4! I am having a ball watching mine. Let us know how the re-cap goes.
Kevin

My -5 has a definite gray screen; I don't remember if the tube is an "A" or not. I am pretty sure it was replaced way back, though, as the markings on the base say "RCA Service Company" which I assume might mean warranty? The next time I pull that set out from the wall I'll check the numbers.

OK Pete, here is what I found,

Olive Green phosphored 21AXP22, SN: AA60243, No date code

Gray phosphored 21AXP22A, SN: AC28825, Date code 57-4

Hope this helps,
Bob

The serial number on my 21AX (no "A") is CM13643. It is a "Monogram"-labeled rebuild, and the number is on the socket of the replacement gun assembly. It has a green tint to the phosphor screen, though slight. The "A" tube I have originally was from the 4, and it has a grayish screen. It is not a rebuild.
Kevin

a timeline of some display developments from SId

http://www.sid.org/archives/0%20-%20...xhibit%206.pdf

shows rare-earth vanadate red introduced in 1964 and rare-earth oxysulfide in 1967.

I'm thinking that the olive-colored screens might be all-sulfide tubes. I'm ordering a 1993 paper from SMPTE on the history of TV display phosphors that may shed some light on this (no pun intended!).

A paper by Larach and Hardy of RCA in the July 1973 Proceedings of the IEEE lists 10 different red phosphors that had been tried up to that time in various color CRT applications. It states that the zinc orthophospate:manganese NTSC red was replaced by all-sulphide tubes for a period of 4 years (1961 -1965), after which the rare-earth red was introduced. The sulfide red was more orange than the NTSC red or current rare-earth reds.

I have not been able to find a reference to the screen color of these variations, although the article says the body color of the sulfide red was originally orange, and this was fixed along with some screen deposition problems before the sulfide red went into use.

This article also lists 5 variations in green phosphor and 3 in blue.

I know that when a B&W CRT faces the sun for years, it turns yellowish. Maybe a similar thing with the color tubes???

Charles

Correction:
I re-read the 1973 paper , and it shows the sulphide red slightly on the more orange side of NTSC red; the vanadate rare earth red (that was used for a short time) slightly less orange; and the yttrium red the most orange of all. The modern value for sRGB primaries would indicate that the latest version of the yttrium red is somewhat less orangy, but also slightly desaturated, at least as practically used in a tube.

Still no info on screen color when the tube is off.

Does the color of the screen actually have anything to do with the phosphors or is it the tint of the glass that makes them the olive green color?

My CTC7 has a 21CYP with a 1960 date code and it has a light gray face.

I am just taking a guess, but here it goes. up until about the early 60's as near as I can remember, after the period when they were making 21cyp22's, the color of the phosphor compounds deposited on the screen became olive green in color. I don not have any idea why this is or what it relates to or even if there is any significance in what the phosphor compounds were made of. All I remember is that the earlier crt's typically had a grey color to them. I do not believe that there is any relationship to the color of the glass faceplate. I am fairly certain the faceplates are clear or very nearly clear.

When you think about it, the probable reason they went to the olive green color phosphor compound was to increase contrast. When the phosphor was not excited, an olive green color is darker than a gray color phosphor. I guess the ultimate color phosphor would be black, provided it wouldn't inhibit the emission of light when excited.

As I recall there were other methods of increasing contrast too. There was a black stripe crt in which there was some sort of configuration where there was a stripe of black between the phosphors to increase the contrast. There may have even been a method where they deposited black between the color phosphor dots, but my mind is foggy on that and maybe I imagine it.

Perhaps some of the other guys around her with a better memory can enlighten us about using black to improve the contrast.

It would be nice if the phosphor reflectance could be made dark independent of its light-emitting properties, but that's just not the case. CRT faceplates have always used a neutral tint if any in order to improve the contrast (except for the very earliest experimental tubes, some of which needed filters to help get a decent red and suppress the much more efficient blue and green). Some modern tubes use a different colored pigment on each phosphor to reduce its reflectance while letting its primary color through.

One possibility, which I have not heard mentioned, is that when going from NTSC phosphors to sulfides, a darker faceplate was used - so a slightly greenish appearance just became darker. The 1973 paper also says that the green phosphor went from silver-acivated zinc-cadmium sulfide to copper-activated zinc sulfide in 1968, which had "a more nearly white body color". However, I think I recall that Zenith-Rauland was using cadmium up until the 1970s. Manufacturers eventually eliminated cadmium because of environmental restrictions.

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.

The early tubes had positive guard band - that is, the holes in the shadow mask were smaller than the phosphor dots. If the beams didn't approach the screen at quite the right angle, there was still some room for them to be off center and still hit the right phosphor dot. However, this could lead to white-field impurity if the dots were not uniformly efficient. When black matrix was added, someone got the idea of making the holes in the black matrix smaller and the holes in the shadow mask bigger. Thus, the electrons hit all of the dot and some of the surrounding black matrix, and their aim can be off more without causing part of the dot to be unlit or wandering onto the wrong color dot. This makes the purity adjustment have a larger tolerance - purity tends to stay good up to the limit of misadjustment and turns bad more suddenly at the extreme.

Combining negative guardband with in-line guns that don't care about vertical displacement of the angle, allowed the introduction of self-converging deflection yoke/tube systems that did away with all the convergence circuits and need for setup in the home. This was a big part of keeping the price of a TV constant or falling in current dollars (and always falling compared to inflation).

I read the above and realized I slipped a cog in a few places - please re-read as edited!

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.

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crt tube
 

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

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?

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?

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.

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.

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.

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

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.

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!

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.

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.

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

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

In the 60's when we were replacing the round tubes, I always preferred the sulphide (green tube) screen as I always thought they had a richer color to them-much like a Technicolor picture. I remember doing a CTC5 with a sulphide FB and what a picture! There was also a difference in price between the two as the gray screen "rare earth" was about $30 more. In the early 70's I remember the dud allowance being removed on the sulphide as we didn't require a dud on those-just the rare earth. We also sold a lot of Zenith tubes and they didn't require a dud on the roundies so we had a lot of those duds on hand. I wish I had them now!

i like the green too.just has a more pleasing to the eye look. the gray is good,i ll take the green!!

looking at this old thread.

The ctc4 and ctc5 BOTH grey 21AXP22 CRTS while not seeing a ct-100 in person these sets benefit being in subdued light since contrast declines in brighter lighted room. There's a subway commercial I compare my modern tvs green to my roundie sets green. The lettuce is bright green on old and new sets, the green seems lighter on older sets.

In general grass seems light, reds are eye popping, blues slighty subdued is my take from general watching without use of special equipment.


Grey crts seem to have a critical bightness level to them where contrast is good yet screen doesn't appear too dark. The brightnees can be adjusted high where dark areas of screen appear lightened. These CRTS are fun to have but a newer fjp or fbp tube have more contrast. Older CRTS have less contrast in moderate to bright sunlight. These older sets interpret color changes with stations, program material and quality. The NTSC signal from old sets is shown without newer advanced compensating or color balancing circuits, wouldn't these make great station color monitors?


While the novelty of orginal CRT is great why isn't newer tubes considered an upgrade?? The 65' zenith I had was more watchable in daylight and appeared to have greater contrast. brightness seemed less critical to screen quality also. Overall seems upgraded set is more watchable. Using special color meters or other equipment seems overdoing it to prove older tubes have better color .Usually better performance meansan upgrade.


I guess if a newer 15" version of color tube with greater contrast and brightness were available, people would still be chasing those old original tubes.

I watched my set for 6 hours today. The daylight conditions seem to effect grey CRTS pretty much the way room or sunlight has effect on a video projector screen. Light bouncing off crt face and back to viewer. The green screen crts I don't think really aren't that very much brighter you just dont have light bouncing from the room back at you as much. this post updated sice my grey crt had plenty of bightness today which worked actually really well with window opposite of set! but the contrast declined at least some in brighter light conditions. Projector people use the phrase "contrast ratio" older crts must their contrast ratio declined in competing light . My 1996 mitsubishi is much newer and has a black face crt still suffers reflections from the crt glass itself.

I recently came across this patent for an all-sulfide screen.

Interesting that in 1959 -- the date of the application -- the CIE color coordinates for green were still the 1953 NTSC values. Although the author adds the caveat 'most' when referring to color CRTs available then, he does specify both the 21AXP22 and the 21CYP22 as meeting the original NTSC green standard. There is documentation that indicates the 21AXP22 does, but this is the first time I have seen something including the 21CYP22 as well. I suspect the 21CYP22A however does not, as this was touted as a 'brighter' tricolor tube but with greater lag, IIRC.

I found a reference to the color of the sulfide red and vanadate rare-earth red. "The Performance of Color Television Picture Tube Phosphor Screens", Austin E. Hardy, RCA, in IEEE Transactions on Broadcast and Television Receivers, Vol 11, Issue 2, July 1965. Hardy says that the vanadate rare earth red had a constant color practically identical to the NTSC standard. The sulfide red, however, was the same as the vanadate at low current, but shifted toward orange at high current. Both of these red phosphors were used with sulfide green and sulfide blue (which are non-NTSC). I have attached some plots showing NTSC, the vanadate red, and the color shift of the sulfide red for comparison. This shift would be rated "large" on a general color-difference scale, about the same as the change from NTSC green to the yellower sulfide green.

Here's a 1964 ad from Sylvania touting rare earth red phosphor. Note the side-ways reference to the variable color of the sulfide red.

I always liked the pea green face as it was a true sulphide screen and always liked their color as it was more colorful to me and looked very much like "Technicolor". They had a georgeous red.