RCA 21CT55 B8802897 is Alive!

[old_tv_nut]

Originally Posted by ChrisW6ATV

I remember watching rock concert performances on NTSC displays, and noticing massive limitations in resolution of scenes that were mostly black and blue (such as a shot of the drummer when only the blue overhead lights were on), and perhaps other black-plus-color scenes as well. Would this type of programming look better on a wideband-color NTSC display?

The luminance of bright saturated reds is nominally 30% of white, but due to CRT gamma and gamma correction, while the luma SIGNAL is 30% of max, the luminance of the resulting gray is about 0.3 squared or 0.09. The luminance is restored to 0.30 when the chroma signal is turned on and sets the red to 100% (green and blue reduced to zero %). This means that the chroma signal provides 2/3 of the red contrast. When the chroma bandwidth is reduced, it means that details in a red rose, for example, have only 1/3 of the original contrast. Hence, such red objects appear to have reduced sharpness. [Edit - the wideband I channel restores most of this detail contrast.]

Saturated blue objects (with details varying from full blue to black) will have the same type of loss of contrast, with the original 11% of the full black-to-white range changing to only 1%. This may be less or more noticeable than the red problem depending on the over-all content of the scene. If the scene is entirely blue, it will be much more noticeable than if the scene contains full black to white contrast and some blue objects.

If the blue is deep violet-blue or purple, it will be carried in the narrow Q channel, so will not be improved by the wider I bandwidth.

[Sandy G]

It really doesn't matter, in the long run. The MOST IMPORTANT thing is that ANOTHER veteran has been saved, & looks GREAT !

[Tomcomm]

Originally Posted by miniman82

To a point: remember, there are only so many phosphor dots.

This statement suggests the CRT is dot-limited in its ability to display the picture quality improvement of the CTC2B’s wide-band IQ demodulation chassis. The 21FBP22 spec places the distance of adjacent RGB dot clusters at .029 inches. Since the horizontal screen width is 19.25 inches, a maximum TV line without overscan is composed of 664 clusters which will produce 332 line-pairs of resolution. At the accepted TV value of 80 line-pairs per mhz of video bandwidth, the 21FBP22 will support up to 4.15 mhz video bandwidth! This is sufficient for 4.10mhz video of high quality B&W TV and way sufficient for the limited 3.2mhz Color TV luminance video. This CRT easily supports the CTC2B I chroma channel’s 1.3mhz video bandwidth to produce 104 line-pairs of I chroma resolution. This resolution is far greater then the 40 line-pair resolution produced by the .5mhz R-Y, B-Y chroma bandwidths of the CTC4 and later RCA roundys.

Obviously, the quanity of phospher dots can’t possibly limit the ability of a knowable observer viewing a 20in CRT at a distance of less than 40in to determine relative picture quality. The CTC2B’s wide bandwidth I chroma resolution is 260% higher then the CTC4’s and later equi-chroma bw CTV’s resolution. Of course, this difference is most apparent on chroma resolution charts but will certainly be noticeable in any high quality natural scene and will be manifested by obvious reduction in picture quality.

[old_tv_nut]

Tomcomm, you are correct that the triad spacing does not limit the I channel resolution, but your arithmetic and nomenclature are confused.

TV resolution is not specified in line pairs, but in lines (film resolution is specified in line pairs). Furthermore, TV resolution is specified in TV lines per picture height, that is, a distance of 3/4 picture width. So, the correct number is (as you said) approx 80 lines (not pairs) per picture height per MHz, or 80x4/3=107 lines per picture width per MHz. Another way to calculate is the number of half cycles of 4.2 MHz per active scan line (~55 microseconds), or 462 lines of luma resolution. (This is a bit of an overestimate; a good rule of thumb is 440 lines per width or 330 per height.) The spacing of 664 triads per width means that the ratio of spacing to maximum luma frequency (if those sets had comb filters) would be 664/440 = 1.5. Thus, there is little chance of moire' caused by fine detail. In the actual sets with limited luma bandwidth, the ratio is a very generous 2:1. The I bandwidth is 1/2 the limited luma bandwidth, so it clearly can be carried by the screen structure without limitation.

The more important ratio in the 21 inch and later color tubes is the vertical spacing of triads compared to the line spacing, because there is always the possibility of a moire' pattern caused by the scan lines interacting with the triads.

Later smaller tubes, particularly the Portacolors, had insufficient numbers of triads to support full resolution.

[Artie76]

I have an RE21FBP22A that was found in a relative's garage. He used to be a Sears repairman back in the 60s & 70s. Still in the tattered box and unbroken.

[zenithfan1]

Where are you located? I might be interested. Welcome to the forum.

[Artie76]

Long Island, Ny

[zenithfan1]

Oh, that's a bit far as I'm in the Kenosha, WI area. I've had bad luck with shipping things like that. Thanks for letting me know.

[John Folsom]

IF you build a good double wall cardboard box with proper baffles and supports, and ship using Greyhound, you can keep the costs reasonable. I have shipped numerous 15GP22s and 21AXP22s ans 21CYP22s using Greyhound, with NO PROBLEMS!

[KentTeffeteller]

I have gotten my fair share of Roundie CRT, recording consoles, tape machines, etc safely and in one piece by Greyhound. The best way to haul such gear.