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 Post subject: Gamut of color CRTs
PostPosted: Sep Wed 22, 2021 3:54 pm 
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I'm looking for information on the history of the gamut of color CRTs, starting with the 15GP22 tube and progressing with tubes through the 1980s or so. I seem to recall, once upon a time, reading an article about the development of the various phosphors and how good their emissions were relative to various colors (wavelengths). Anybody know of a good resource for this type of information?

Many thanks.

Dave


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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Wed 22, 2021 4:21 pm 
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RCA did have a booklet which had a lot of that information, but I don't know how widely they were distributed. Someone may still have a copy of it though. I got mine in the mid-1970's when our local RCA distributor sponsored an all day bus trip to the CRT factory in Marion, Indiana for technicians from some of the larger service agencies they provided support for.

While I already had some ideas about the cleanliness required for that sort of assembly, I was quite surprised to see many workers in clean room settings wearing white clothing. Our tour guide, and the booklet, mentioned they were clean at the level of an operating room with air filtration down to small micron levels.

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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Wed 22, 2021 6:12 pm 
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You might try contacting the folks at Early Television Foundation Museum.
https://www.earlytelevision.org/

I watched their recorded Zoom meeting this week where some members went on for over three hours just on TV cameras!
Actually that Zoom recording missed a good part of the beginning of the meeting where they would have covered other subjects.

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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Thu 23, 2021 6:46 pm 
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Two other definitive sources would be EIA and SMPTE. I don't know what their online presence may be.

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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Fri 24, 2021 6:27 am 
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Attachment:
TPM-1508A_RCA_Phosphors_Oct61.pdf [2.33 MiB]
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The P22 phosphors had a color gamut different from the SMPTE C phosphors that were common in the CRT TV monitors at my first TV station. Matching the two would have involved much more than just adjusting the drive and screen controls. One would have had to change the color decoding in the monitor. This was just about the time that everyone purchased a Sony Trinitron. I recall the yellow on the trinitron as being YELLOW when the same color bar was close to green on the Conrac with SMPTE C phosphors. Videotek and others modified Sony TV sets with video inputs for use as utility monitors in broadcast. Back then we had a policy of using only monochrome monitors in the control room, because color monitors on all the cameras would look different from the program monitor. Even then, we tried to use monochrome monitors with phosphors displaying 6500 degrees K (D65). So you will have your work cut out for you in chasing down all the variants that would have affected the displayed color gamut, I think. I dug up an old RCA text off the interweb and attached it here. Maybe it will help.


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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Fri 24, 2021 2:17 pm 
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Thanks for the suggestions. I'll reach out to the Early TV Museum folks and see if they can help.

jfleetwood: Thanks for the info and flyer. Your comment about green on the Trinitron being more yellow gets at exactly what I'm looking for. I've been told that many TVs of that era started shifting the greens to more gold and the reds to more orange. I'm looking for some confirmation of this.

Dave


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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Fri 24, 2021 3:47 pm 
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I can't provide any numbers, but the first color CRTs had a red phosphor that was really red. But they were not very bright and you needed to use the TV in a dimly lit room. I remember that they were called sulfide phosphors.
Somewhat later, I don't have a date, they came out with rare earth phosphors. They were much brighter but the red was somewhat orange. I don't think that any change in the decoding could really compensate for that. But these phosphors were considered an improvement as you no longer needed to watch TV in a darkened room.
I expect that there were further changes made to the phosphors but I don't know what or when.

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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Fri 24, 2021 11:55 pm 
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From what I understand the original NTSC spec phosphor (15GP22 and 21AXP22) had the blue 3X as efficient as the red with green falling approximately between the two, then they designed the 21CYP22 they improved brightness and efficiency balance between phosphors by narrowing the color space and shifting the primaries slightly, then for the 21FBP22 and later CRTs they had close to an even efficiency balance but again slightly different primaries.


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 Post subject: Re: Gamut of color CRTs
PostPosted: Sep Sat 25, 2021 3:56 am 
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Dave, it occurs to me that I might be able to put you in contact with the guy who was the colorimetry expert in the RCA camera group when I worked there in the 1970s. He spent a LOT of time measuring and comparing pickup tubes, beam splitters & CRTs and perhaps even more time explaining to customers and salespeople why various monitors looked different from each other, and real life. He helped design a module called, I think, Chromacomp for RCA cameras which could vary the colorimetry widely without affecting the gray scale, which some customers wanted to deal with the colors they were seeing. It was all beyond me, though I know he tried to explain it to me a few times. PM me if you want his email.

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