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  #196  
Old 05-18-2018, 09:53 PM
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Originally Posted by old_tv_nut View Post
Just had a thought - the blue DC restorer may be weak. This would cause the blue background to drift the opposite of the dominant color and possibly vary over the height of the picture. You wouldn't see this on a grayscale pattern.
We played with the background controls a lot. I don’t have professional test equipment, so I used the blue filter with the Video Esentials disk to calibrate. I know this is not the best way, at a disadvantage without proper tools.
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  #197  
Old 05-18-2018, 09:54 PM
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Your last comment duly noted.
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  #198  
Old 05-18-2018, 09:59 PM
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We played with the background controls a lot. I don’t have professional test equipment, so I used the blue filter with the Video Esentials disk to calibrate. I know this is not the best way, at a disadvantage without proper tools.
This technique should be fine if the DC restoration is good or bad, because the usual test patterns (gray scale or color bars) have constant average current in the three guns. But, on regular video, when a scene has a lot of one color in the highlights, the DC restorers have to work to counter the change in average currents between the guns; so when you have a face and yellow hat filling much of the screen, the tracking gets pushed towards blue if the DC restorers are weak. I think replacing that tube would be worth a try.
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  #199  
Old 05-18-2018, 10:08 PM
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Great suggestion. In case you don’t know, Mike Doyle restored this set. He lives about 50 miles NW of me. When he comes in to town, he will call to see if the sets need adjustment. What is the tube number. I can check that.
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Old 05-18-2018, 10:10 PM
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Confession...I started this comparison to see the colors on this great movie on the set. My curiosity was to see the dark brown/black costumes to see if they are reproduced in phosphors. The pastel Technicolor is spectacular as usual. I do see the blue and added a similar still from the original and a brown/black scene for reference.
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File Type: jpg vlcsnap-2018-05-18-23h00m19s721.jpg (50.4 KB, 26 views)
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  #201  
Old 05-18-2018, 10:12 PM
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Great suggestion. In case you don’t know, Mike Doyle restored this set. He lives about 50 miles NW of me. When he comes in to town, he will call to see if the sets need adjustment. What is the tube number. I can check that.
SAMS calls it V36 (a,b,c), a 6BC7 triple diode.
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  #202  
Old 05-18-2018, 10:19 PM
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Confession...I started this comparison to see the colors on this great movie on the set. My curiosity was to see the dark brown/black costumes to see if they are reproduced in phosphors. The pastel Technicolor is spectacular as usual. I do see the blue and added a similar still from the original and a brown/black scene for reference.
Do you mean you see the blue background shift? If so, maybe the DC restorer design is not perfectly stiff. It would be interesting to see if substituting a known good tube changes it. The kind of test pattern that would really check this is something with most of the top half of the screen a saturated color (say the upper right 80%) and the rest of the screen black. Repeat for each primary and secondary color and see if the black area shifts color. The closest thing on a test CD I know of is the large square color window in the center of the screen that some test CDs have. If you have that, play each primary and secondary color and the white window and see what happens to the black background. Turn up the brightness a little if necessary to see some light in the black area.
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  #203  
Old 05-18-2018, 10:19 PM
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Dave, I can take a shot of the second scene. Posted that first shot.

Your shots look like they are from a flat panel?
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  #204  
Old 05-18-2018, 10:20 PM
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SAMS calls it V36 (a,b,c), a 6BC7 triple diode.
Thank you.
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  #205  
Old 05-18-2018, 10:24 PM
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My stills are from a download of the original movie and captured by VLC Media Player. Pure movie.

I have to find the K Greyson closeup to compare the blueish in your screenshot.
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  #206  
Old 05-18-2018, 10:28 PM
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I will change the tube with a new one, if I can find one. Mike may have one. Will see what happens.
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  #207  
Old 05-18-2018, 10:34 PM
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By the way, the CTC-5 super chassis has DC coupled demods instead of DC restorers, and they bypass part of the resistor network, giving less than 100% DC restoration; so the background definitely drifts opposte the dominant color. I'm guessing they did this to reduce the effects of demodulator bias drift or differences with tube replacements, but it bothers me enough that I have considered snipping out the caps. The DC restoration of the chroma signals in the RCA X/Z demod scheme is much superior, although in those sets the luminance DC coupling is less than 100%.

The individual DC restorers on R,G,B should be best if they are stiff enough, but maybe they would have to be pulse gated to get there and what's seen is due to them not being 100% effective, something I hadn't considered until looking at these pics.

Solid state diode clamps are usually quite stiff enough, but maybe tube diode impedances are too high to work 100% without pulsed gating.

Looking at the TM21 monitor manual, I see they used a pulse-driven feedback clamp circuit.
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  #208  
Old 05-18-2018, 10:57 PM
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Three screen grabs from a video I made of the 2018 Rose Parade. The first two show differences in green between the two sets. It varies from scene to scene. The third shows a problem I’d like to eliminate. Is this ringing?







Video: https://vimeo.com/250371760
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Last edited by etype2; 05-18-2018 at 11:03 PM.
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  #209  
Old 05-18-2018, 10:59 PM
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Don't see the third shot?
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  #210  
Old 05-18-2018, 11:04 PM
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Just posted.
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