Quote:
Originally Posted by Tomcomm
Its most likely a "rare-earth" 21FBP22A as I always suspected and stated in my posts. So is that good or bad from a Picture Quality standpoint? Are the saturated reds of the rare-earth 21FBP22s more like the 15GP22s and 21AXP22s then the more numerous olive-green screen sulfide 21FBP22s? All I know is my 21FBP22A reds are obviously more "RED" then my 13in Sony Pro monitor which has SMPTE-C phosphor and my 27in Sony comb-filtered monitor. Both Sonys are orangeish-red in comparison. I was told the SMPTE-C reds make the reproduction of flesh-tones more natural?
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All rare-earth reds are less orange than the zinc cadmium/sulfide red, especially as the sulfide red shifts even more orange at high beam current. Rare earth reds can vary somewhat among them, but not as orange as the sulfide. The big difference in all tubes after the 21AXP22 is the sulfide green, which is much more yellow than P1; and to some extent the sulfide blue, which is a deeper blue (less cyan) than the 15GP22. Other differences you see in your Sony and other sets can be due to the color matrixing, which was adjusted to get reasonably natural flesh tones. Depending on how much matrix redesign was done, you could also get a sort of auto tint action that reduced the variation in flesh tones to some degree.
You may recall that in some cases when an earlier CRT was replaced with one with more efficient red, there was a change made to the cathode drive to reduce the red Y drive. But the R-Y gain was not reduced. The reason is that the new tube also had a yellower sulfide green. This was like adding some red into every green color, so the high R-Y amplitude tended to compensate by turning off red harder on greenish colors. This corrected the range of hues from red to orange to yellow to green, but also lit up reds too brightly. This compromise was subsequently built into all consumer NTSC sets to some degree, and a SMPTE-agreed amount was built into professional monitors, but with a matrix on/off switch.
Some of the impression of "redder" reds with the older tube comes from the contrast with the P1 green but also is due to the not-overly bright reds (even if they are slightly orange) and/or due to not having a matrix that was fudged to reduce flesh tone variations.
By the way, if you want an example of "how red" NTSC reds should be, note that red traffic signals are outside the NTSC gamut, but incandescent car taillights are not. Most rare-earth tubes are actually close to NTSC red - it's the greens that are way off.