21CT55 Screen-Shot Test

[Tomcomm]

I bought this TV in 1964 for $50 not working. Once I got it operational I decided to keep it in the garage TV shop area. I modified the consul cabinet into a table model by rotating the chassis from horizontal to vertical to take up less room in the cramped garage, also make chassis modification and repair much easier. Yes, in 2007 it became direct composite video input only. Reactivating the RF/IF portions seemed unnecessary since I had good DVD players and the 21CT55 was never intended as a restoration item.

[lnx64]

Wow that third screenshot, looks so sharp and defined! I thought this was S-Video modified for a second.

[Pete Deksnis]

Loved the llama shot.

Pete

[stromberg6]

Beautiful pics as usual, Tom. Thanks for sharing!
Kevin

[benman94]

Would the 19VP22 be NTSC correct also? It was my understanding that they were, but I could be mistaken. That set is looking amazing Tom!
-Benny

[old_tv_nut]

Originally Posted by benman94

Would the 19VP22 be NTSC correct also? It was my understanding that they were, but I could be mistaken. ...
-Benny

Unknown to me. However, a working one could be measured.

--

Here's a laugh: the original patent on the sulfide phosphors touts not only their brightness, but claims that the restricted color gamut is an advantage because the tube cannot make extremely wrong colors! In other words, if you don't correct the reduced saturation (which everyone WOULD do by turning up the color), you can't see variations in transmission so clearly.

Also, there is a story behind the NTSC blue vs. the modern blue. RCA experiments with the triniscope used very pure primary colors, including a blue nearer to present sulfide blue. But sulfide blue is very sensitive to copper impurities, which turn it green. Therefore, RCA chose a different blue phosphor that was slightly toward cyan, but doesn't change due to presence of copper during the processing of the CRT. There is a futher confusion, in that it is not clear that RCA intended the cyanish blue to go into the NTSC specs - the color coordinates that ended up in the FCC rules look suspiciously like a typo.

[lnx64]

While my Samsung isn't a roundie, I have found it's reds to be seriously awesome. It's greens seem a little "wrong" in my opinion though. Blue looks ok but doesn't look at all like your blues.

This is the color test my TV performed with a colorimeter.

[zenithfan1]

Hontou ni? Ore wa Samusung no taikutsu

[colorfixer]

Originally Posted by zenithfan1

Hontou ni? Ore wa Samusung no taikutsu

nihongo ga sukoshi dake dekimasu...

[lnx64]

I have no idea what language that is.

[wa2ise]

Originally Posted by lnx64

I have no idea what language that is.

Neither did Google translate.

Only thing I can say for sure that it's not English. As I'm a single language white trash American.

This gamut shows colors better:

[lnx64]

It must be modified for standard composite video input, I see no RF distortion AT ALL.

If it is RF, I am highly surprised.

[Username1]

That is a really good picture, and very good convergence..... Nice job....
And really good pictures....

[Username1]

Inx64;

Your color "gamut ICE " graph is wrong, in the green by a lot..... Someone here did those measurements and posted them on one of those 15gp's and another tube, and while people maintain the 15g's had better "full"gamut, the graph they posted showed a smaller triangle, than the other tube. I would sure be interested in seeing the response of your tube again, once you figure out what is going on with the green.... Also, try it and be sure that when the screens are turned down, the tube goes into cutoff. I have no idea how the test is run, but I find this testing interesting...

[old_tv_nut]

Originally Posted by Username1

Inx64;

Your color "gamut ICE " graph is wrong, in the green by a lot..... Someone here did those measurements and posted them on one of those 15gp's and another tube, and while people maintain the 15g's had better "full"gamut, the graph they posted showed a smaller triangle, than the other tube. I would sure be interested in seeing the response of your tube again, once you figure out what is going on with the green.... Also, try it and be sure that when the screens are turned down, the tube goes into cutoff. I have no idea how the test is run, but I find this testing interesting...

??
Not sure I follow what you said.

Inx64 did not explain his colorimeter software, but I believe what the CIE gamut display is showing is:
The light colored triangle and square boxes are the aim points for REC709 (HDTV) or sRGB monitors. The circles are the measured points for his set.


edit: bottom line, his green is not wrong, but is fairly typical for all tubes with sulfide green, which is all tubes after the 15GP22 and 21AXP22 (don't recall what green was in the 21CYP22 at the moment).


You can see that the triangle made by the RGB points for his set is slightly smaller than the REC709 spec because the green is slightly yellower.

The magenta is far off from the aim point towards red, and this has to be because of the demodulator gains and angles in his set, since moving the green primary towards yellow causes the magenta to move towards blue in order to keep the white point within spec (which it is). This error in magenta is not necessarily a bad thing, since it helps to prevent purple faces when there is an error in burst phase, and there are few recognizable magenta/purple objects (except maybe Barney the dinosaur). 2nd edit: it also compensates for the movement towards blue of magenta caused by the yellowish sulfide green, making the magenta a closer approximation to NTSC magenta.

A 15GP22 or 21AXP22 CRT has a green that is much less yellow, so the triangle is larger on the cyan side; but the blue in those CRTs is less violet and more cyan, so the triangle is smaller in the blue/purple area.