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  #31  
Old 05-05-2011, 04:50 PM
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Originally Posted by miniman82 View Post
It's hard to explain. You know how a 21AXP22 normally has a whitish grey look to it, like the CYP tubes do? This one has a slight, I don't know, almost greenish hue to it. You have to have another AXP right next to it to see the difference.
The one in my 4 also has a greenish hue to the screen, as opposed to the greyish color of most other 21AX's. Maybe an early phosphor gamut. Mine isn't really bright, but the color reproduction can be spectacular. See avatar.
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  #32  
Old 05-05-2011, 09:14 PM
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Quote:
Originally Posted by miniman82 View Post
It's hard to explain. You know how a 21AXP22 normally has a whitish grey look to it, like the CYP tubes do? This one has a slight, I don't know, almost greenish hue to it. You have to have another AXP right next to it to see the difference.
Nick,

The only 21AX's that have this greenish color phosphor have been mostly found in CT55's. I also have a very early CTC4 which has a 21AX with a greenish looking face. Another intresting discovery is that, at least on the crt from my 55, which was rebuilt by Hawkeye, RCA was using up the 20 pin stems left over from the production of 15GP22's, rather than using a 14pin stem as would normally be expected. Take a close look at the stem on your tube. See if you can count the number of wires by looking into the end of the neck through the neck glass. The old gun removed from my 21AX was mounted on a 20 pin 15G stem.

All this leads us to believe that the initial production run of 21AX tubes, which were used in the CT55 sets, and which have this greenish color phosphor, may be using the full gamut phosphors like were used in the 15GP22 tubes. Some day we will need to test one of these green faced 21AX tubes with a colorimiter to see if they are indeed full gamut or not.

CT55's are known for having a brilliant color picture. Perhaps full gamut phosphors are part of the reason for this. AFter all a CT55 is actually a CT100 with a 21" crt and a modified HV section. Perhaps the phosphors are also an extension of the CT100 series.

Time and further investigation will reveal the answer.

Bob
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  #33  
Old 05-05-2011, 10:29 PM
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Originally Posted by ohohyodafarted View Post
See if you can count the number of wires by looking into the end of the neck through the neck glass. The old gun removed from my 21AX was mounted on a 20 pin 15G stem.
I just went to look, and from what I can see it has the same number of pins the base does. But this particular tube was made very late in '54, so it's not like it's from the initial run or anything. In fact, the code 4-52 indicates it was made during the last week of '54.

Quote:
All this leads us to believe that the initial production run of 21AX tubes, which were used in the CT55 sets and which have this greenish color phosphor, may be using the full gamut phosphors like were used in the 15GP22 tubes. Some day we will need to test one of these green faced 21AX tubes with a colorimiter to see if they are indeed full gamut or not.

Sounds like another interesting project for a failed tube, obvisouly we would not want to destroy a rebuildable one. What is involved in the testing? Are samples taken of the actual phosphor, or just the light given off by it when excited? The observation makes sense, the screen has the same kind of look that a 15GP22 does with a little bit of sparkle I can't quite put my finger on.


Quote:
CT55's are known for having a brilliant color picture. Perhaps full gamut phosphors are part of the reason for this. After all, a CT55 is actually a CT100 with a 21" crt and a modified HV section. Perhaps the phosphors are also an extension of the CT100 series.

That's what I've always thought, but now the expert has confirmed!
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  #34  
Old 05-05-2011, 10:57 PM
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The gamut has to be measured by the light from an operating tube. Chemical analysis would require smashing the tube - not recommended!

Up until I saw this comment, I thought all 21AX's used the same phosphors as the 15G. There are two defining characteristics of the 15G phosphors: the blue is true NTSC blue (more cyan and less violet than modern tubes), and most important, the green is P1, less yellow than the later sulfide or cadmium sulfide green. (And, of course, the red is not very efficient.) The question is which phosphor or phosphors were changed in the 21AX's that changed the face color. If it was the red phosphor, it might be hard to determine, as most of the red phosphors used over the years fluoresced in about the same color, until the cadmium sulfide red in the all-sulfide tube. This phosphor was strongly colored under ambient light, resulting in a fairly strong green face color, and also its emission turned orangy under high beam current. The all-sulfide tube (including sulfide blue) could not be made until techniques to prevent contamination were developed. Contamination of the blue sulfide by copper would turn it into a green phosphor. The uncontaminated blue is more deep blue than than NTSC specs, and is what we have today.
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Old 05-05-2011, 11:09 PM
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It would be interesting to see the different blends of phosphor used over the years ploted on the color spectrum horse shoe(I can't recall the right name) for comparison.

Tom C.
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  #36  
Old 05-05-2011, 11:31 PM
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Originally Posted by old_tv_nut View Post
The gamut has to be measured by the light from an operating tube. Chemical analysis would require smashing the tube - not recommended!
Interesting. So would I be right in assuming the piece of gear to make such a measurement is quite expensive? I wonder if some university somehwere would have one I can borrow? I currently have both ilk of AXP tube, and I'm dying to put the 'phosphor' debate to rest once and for all!

What I'm really shooting for is to get a light sample from all types of tube, so we have a reference. Currently I have the 2 AXP's, a green FBP, a green FJP (sans lens), and a pair of grey faced CYP tubes for comparison. One of the CYP's is an 'A' version, not sure if that matters or not. That's the reason for the investigation.
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  #37  
Old 05-05-2011, 11:51 PM
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So the greenish (early version) would be the 21AXP22 and the later version (whitish) would be 21AXP22A? This has been eluded to before but it would be good to clear that up.
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  #38  
Old 05-06-2011, 12:33 AM
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So the greenish (early version) would be the 21AXP22 and the later version (whitish) would be 21AXP22A? This has been eluded to before but it would be good to clear that up.
Therein lies the rub.

I've seen 21AXP22 and 21AXP22A tubes that are grey faced, the only difference noted in the data sheets being the addition of a resistive inner coating for arcing protection for the 'A' version. As pointed out by yoda, the early 21AXP22 tubes with greenish phosphor colors on their face are likely related to the 15GP22. It's thought to be the result of RCA wanting the 21" version of set (21-CT-55) to be just like the earlier 15" one (CT-100), though no definitive proof exists to my knowledge. It's all conjecture by the collecting community at this point.

Furthermore, the change of phosphor was likely related to light output. As I understand it, customers complained of dim tubes so RCA set out to make some improvement. Perhaps this is why early AXP's are green like the 15GP22, while later ones are grey? Changes like this continued throughout the roudie's life, eventually leading to the very bright FJP/FBJ line of picture tubes. While they did not produce colors as accurately as the early ones, obvisouly customers were willing to trade off some loss in color fidelity for a bump in brightness. This also explains the changes in circuitry, since there's no point in decoding the NTSC signal exactly if you're not going to reproduce the picture on a tube that gives 'true' colors. Cost was also a big factor in those times, so it's a real chicken vs egg scenario.


In any event, some day I'd like to get my hands on the instrument used to make such measurements. That way I can test all versions of tube, in order to figure out what phosphors were used in which version of tube. Then we can make definitive statements about the tubes, instead of wondering 'why?'
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  #39  
Old 05-06-2011, 08:52 AM
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Originally Posted by miniman82 View Post
Interesting. So would I be right in assuming the piece of gear to make such a measurement is quite expensive?
Nick,

Actually there is a colirimiter that attaches to a laptop. A couple of the collectors have one. I think it was about $200. I would bet Cliff Benham owns one. I would email him and see what he has to say about it.

I believe that Cliff and John Folsom tested a tube at John's house some time back using the device.

Bob
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  #40  
Old 05-06-2011, 10:11 AM
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Quote:
Originally Posted by ohohyodafarted View Post
Nick,

Actually there is a colirimiter that attaches to a laptop. A couple of the collectors have one. I think it was about $200. I would bet Cliff Benham owns one. I would email him and see what he has to say about it.

I believe that Cliff and John Folsom tested a tube at John's house some time back using the device.

Bob
Or, you might want a spectrometer like this one which measures the actual intensity vs wavelength rather than giving you RBG values like a colorimeter does.

John
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  #41  
Old 05-06-2011, 05:05 PM
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Quote:
Originally Posted by miniman82 View Post
Interesting. So would I be right in assuming the piece of gear to make such a measurement is quite expensive? I wonder if some university somehwere would have one I can borrow? I currently have both ilk of AXP tube, and I'm dying to put the 'phosphor' debate to rest once and for all!

What I'm really shooting for is to get a light sample from all types of tube, so we have a reference. Currently I have the 2 AXP's, a green FBP, a green FJP (sans lens), and a pair of grey faced CYP tubes for comparison. One of the CYP's is an 'A' version, not sure if that matters or not. That's the reason for the investigation.
I and some others have a Spyder 3 colorimeter, which is fairly good as colorimeters go, but not to be relied on for fine differences in the red phosphors, as their spectra varied the most with different formulations (rare earth vs. non-rare earth, for example). Cliff also has an "Eye_one" or "I1" spectroradiometer, which will give a true reading despite the spiky spectrum of rare-earth phosphors or the variations in bandwidth of the others. I believe the Spyder 3 is in the $200 or so range these days (haven't looked lately), while the spectroradiometer starts at around $1000 and up depending on what software you license with it. Packages range form monitor only to full printer/monitor/scanner workflow profiling and calibration. They keep changing the packages each year. It is also sold by Spectracal with a TV/home theater calibration software package. Used ones sometimes go for as little as half price, but usually more like $800, and are often missing parts of the kit. I would like to have one, but haven't seen one at the price and condition I would like, so I get along with the Spyder 3, which has been just fine for calibrating my computer monitors.
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  #42  
Old 05-06-2011, 05:08 PM
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By the way, when you measure a tube, you get the operational color, not the pure phosphor color, because any imperfections in the color purity settings, light scattering, electron scattering, etc. are all included.
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  #43  
Old 05-06-2011, 10:15 PM
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Originally Posted by ohohyodafarted View Post
Nick, <---> I believe that Cliff and John Folsom tested a tube at John's house some time back using the device.
Bob
We did test several tubes including a 21AXP22. Attached are several different
charts and graphs: The first is the spectrum response of the 21AXP22 taken with the EYE-ONE Pro Spectroradiometer. This is a gray faced tube as I remember. The second and third are both CIE charts comparing the color
coordinates, some measured and some published, of various color sources and
defined colors. Disregard "RX43" in the title of the third one.

Hope this helps answer some of the questions. Cliff
Attached Images
File Type: jpg 15gp22_manual_Folsom-Dexnis.jpg (33.1 KB, 29 views)
Attached Files
File Type: pdf 21axp22 spec .pdf (58.8 KB, 43 views)
File Type: pdf 15GP22-21AXP22 graph .pdf (3.6 KB, 50 views)
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  #44  
Old 05-06-2011, 10:31 PM
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Wow, outstanding work!

Looks like they are pretty close, for the most part. I'd bet the later tubes are farther apart than the early ones, have you tested any of them?
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  #45  
Old 05-07-2011, 12:40 AM
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Originally Posted by miniman82 View Post
Wow, outstanding work!

Looks like they are pretty close, for the most part. I'd bet the later tubes are farther apart than the early ones, have you tested any of them?
Here are the spectrum charts for the 15GP22 and a rare earth Mitsubishi tube at the ETF Museum. Please note that the vertical scale for the 15GP22 is different than that of the 21AXP22 and the rare earth tube. That's why it appears to be very low when in fact it is close to the 21AXP22.
Attached Files
File Type: pdf 15gp22 white screen spec.pdf (52.4 KB, 41 views)
File Type: pdf rare earth red mitsubishi 04-25-10.pdf (57.8 KB, 42 views)

Last edited by cbenham; 05-07-2011 at 01:09 AM.
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