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  #1  
Old 08-11-2005, 11:46 AM
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Pete Deksnis Pete Deksnis is offline
15GP22 demo @ ETF 2007
 
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Twenty-eighth operational CT-100 screen shots...

It's a good 15GP22 with low hours, a restored CTC2 chassis with a complete set of original RCA peaking coils, and a rooftop antenna picking up a true NTSC color signal. Here's a revisit to 1953 NTSC color via 51-year-old hardware.

http://home.att.net/~pldexnis/CTC2_h...ing_Color.html

Last edited by Pete Deksnis; 08-12-2005 at 06:38 AM.
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  #2  
Old 08-11-2005, 12:19 PM
jroberts500 jroberts500 is offline
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Excellent!

That's beautiful!
Thanks for preserving something from the past!
Sincerely, John
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  #3  
Old 08-11-2005, 05:00 PM
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"page cannot be displayed"??
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  #4  
Old 08-11-2005, 07:19 PM
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That's REALLY somethin'-but stupid question-do roundies all "lose" so much of the picture? Or is that just a peculiarity of the early 15" sets? -Sandy G.
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  #5  
Old 08-11-2005, 07:26 PM
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Eric H Eric H is offline
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Sandy,
That set in the background is a 16:9 set showing a 4:3 picture so it looks like the picture is much wider but if you look closely you can see there are actually black bars on the sides.
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  #6  
Old 08-11-2005, 07:33 PM
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Superb!
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  #7  
Old 08-11-2005, 09:24 PM
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Pete Deksnis Pete Deksnis is offline
15GP22 demo @ ETF 2007
 
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bobgary questions

Simplistically, a 15GP22 is a dud for one of only two reasons: no vacuum and no or low emission. (Maybe that makes three?)

Anyway, the process to rebuild a no/low emission 15GP22 electron gun assembly is perfected and in place. Ditto the manufacturer of glass stems. Basically, rebuilding the gun means replacing the old filament and cathode with new ones.

Recently (the last year or more) effort was extended to connect a stem to an old, dud 15GP22 neck. This has been done although I'm not certain the technique is as reliable as, say, the rebuilding of the electron gun. But the process has been successfully demonstrated.

What's being done now? The archives have yielded a bit of vintage 15GP22 data covering the baking temperature and slew rate of that baking heat. They are different from what is done today. Finding a way to reproduce the vintage procedure is the present challenge.

As to the phosphor in air question, no one seems certain although the current thinking is that since the 15GP22 is aluminized, the phosphors may be protected from the air.

Last edited by Pete Deksnis; 08-11-2005 at 09:28 PM.
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  #8  
Old 08-12-2005, 01:53 AM
Jonathan Jonathan is offline
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Let me say, that is a beautiful picture. Absolutely beautiful. Infact so beautiful it's almost on par with this girl i gave a crush on. :P

I'd love to own a Merril and an RCA prewar set.... Maybe some day...

Jonathan
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  #9  
Old 08-12-2005, 05:28 AM
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OvenMaster OvenMaster is offline
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Who knew that old sets like that could produce such great pix? Gorgeous and well done!
Tom
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  #10  
Old 08-12-2005, 08:59 AM
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I'm thoroughly impressed with the work you are doing. These sets must be preserved, and you are showing that it can be done. Are there many around that just aren't worth trying to restore?
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  #11  
Old 08-12-2005, 10:04 AM
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Is there any possibility of air hurting a non-aluminized phosphor? I thought phosphors are essentially oxides or sulfides (specially formulated rock), so I would guess air is not going to do anything to them. (Moisture might be another issue. Maybe oxygen can hurt the sulfides or sulfur air pollution can hurt the oxides?) Have there been any expert opinions on this? Were old B&W tubes tubes ever rebuilt just by replacing the gun and leaving the phosphor alone, and did this depend on aluminization? This would be a good indication that there is no problem.
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Old 08-12-2005, 10:23 AM
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Pete Regarding the colors on the CT-100 - As I'm sure you realize, the original phosphors will ALLOW you to get correct colors, but there are a lot of matrix adjustments that need to be correct too. (Also, all the tubes in the color section need to be good - a weak tube in one part of the matrix may leave you with "acceptable" but not correct results.) So far, no two CT-100s that I have seen, nor the early Zenith prototype I saw, got the same color reproduction. Have you put color bars in and attempted the matrix adjustments?
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  #13  
Old 08-12-2005, 11:23 AM
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Pete Deksnis Pete Deksnis is offline
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Wayne. Thus far, I've gone by the book aligning the color (all front-panel controls) -- except for the I gain, which is running nearly wide open. Re color bars: gated color bars seem to have a luminance issue when bounced against the same signal displayed on the digital set. Blue bars on the CT-100 appear to be near-saturation in order to view red- and green-hue bars.

The setup: (1) both sets adjusted for color picture from over-the-air broadcast. (2) switch from antenna to gated color bar gen. (3) bars on digital set appear normally; blue-direction bars on CT-100 appear normal; red- and green-direction bars very dim. Readjusting contrast and brightness brings up the end hues.

Any thoughts on the color bar anomaly?


I made special efforts to find and use all original inductors, especially those in the demodulator filters, to get as close as possible to factory-original, and was successful except for L42, which I don't think is an important factor anyway (it's in the dc path from the color afc to the reactance tube). Was very fortunately to have gathered a full set of the 'white' inductors, which are very prone to opening up.

My further plans include sweeping the chrom circuits for published specs to help get as close to factory-original as possible.
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  #14  
Old 08-12-2005, 03:25 PM
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Pete,

Using gated rainbow for matrix adjustment can't get you there, because you need each color to have the correct luminance as well as chroma to see if the final R,G,B drives are correct. You can use the gated rainbow to check the phase (and maybe preliminary gain) of I and Q, but not much beyond that If you can get a generator or a DVD with regular color bars (White, Yellow, Cyan, Green, Magenta, Blue, Black), that is best. All is correct when the individual red, green, and blue outputs of the matrix are square waves. All the peaks (max and min) in one channel should be the same amplitude, but the three channels will have different amplitudes depending on how much drive the CRT requires to make white. With non-rare-earth red, this probably means red needs 2 times (or maybe more on the 15G) the drive of green or blue.

Have you ever seen a setup done with a blue viewing filter? This assumes the matrix is correct, and adjusts hue and chroma so all the bars containing blue have the same blue amplitude. If the matrix is not correct, tough! - the red and green will be off when the blue is correct. In the case of the CT-100, it's worthwhile to check all three colors, since you have internal matrix adjustments. You could do this check with red, green, and blue filters. However, if you have full matrixed R,G,B driving the CRT, you can check with a scope. This measurement (and adjustment) is not directly available on later sets that matrixed by putting Y to the cathodes and color differences to the G1's.

Regarding brightness of colors: When a true NTSC tube with nominal NTSC matrixing is used, the reds may be darker than a modern set. This is because the modern set overdrives the R-Y to make up for the smaller difference between the red and green phosphors. In other words, turning on the modern green is like adding a little red to the picture, so the R-Y gain is increased to make the red turn off a little more than normal. On strong red color, this goes too far the other way (because of the CRT gamma), so strong reds come out over-saturated and over-bright. How much of this you see depends on how much R-Y boost the particular manufacturer thought the phosphors should have for best flesh tones and average scene content. On the opposite side of the spectrum, the 15G should show more saturated and brighter cyans. This should be obvious on full color bars along with the more "green" green.

In PAL, and in HDTV, the matrixing at the camera is changed to get the right color-difference signals for the MODERN phosphors with a nominal NTSC electrical matrix. So, reds are no longer overly bright, but of course you can't get the purer green and cyan that you could with real NTSC phosphors.
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  #15  
Old 08-12-2005, 04:56 PM
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Big Dave Big Dave is offline
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Looks good, Pete.
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