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  #16  
Old 08-12-2005, 05:12 PM
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Pete Deksnis Pete Deksnis is offline
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Wayne,

Thanks for all the info.

I thought that I might in be trouble without an NTSC generator because, as you confirmed, of the constant luminance factor. But I hadn’t made a connection to the ‘blue filter’ setup procedure, or using a scope to check luminance of CT-100 RGB channels. Thanks for that tip. I’ll use an S-video VCR and a DVD player to generate a color bar signal, and then scope the RGB channels…

Last edited by Pete Deksnis; 08-12-2005 at 08:22 PM.
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  #17  
Old 08-12-2005, 10:23 PM
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Pete, it may help to use a ture NTSC color bar signal source (foff air or from a generator), instead of the gated rainbow generator, which does not control luminance.

How is the red? you photos seem to show only blues and greens...?
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  #18  
Old 08-13-2005, 11:18 PM
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Where's the red?

Actually John, over-the-air programming with a lot of red was tougher to find than the predominately blue or green samples. I did find some fair examples of red from an ABC movie this evening and added a series of five pictures to the link.
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  #19  
Old 08-14-2005, 06:07 AM
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Congratulations Pete! That picture looks wonderful. I had always wondered if decent convergence was possible on a 15g. That is amazing. Even perfect at the far edges.

John
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  #20  
Old 08-14-2005, 01:09 PM
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Ctc2/ct-100 Matrix Issues

quote from Wayne: "...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."

Checked this out and added material at the bottom of this link under 'CTC2/CT-100 MATRIX ISSUES,

This is a new link.

http://home.att.net/~pldexnis/CTC2_h...r__matrix.html
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  #21  
Old 08-16-2005, 01:41 PM
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CTC2/CT-100 Matrix Issues -- more data...

Calibrate this tweak that: realigned the color and added some screen shots of NTSC color bars that should look better than previous examples on your computer monitor.

See the "CTC2/CT-100 Matrix Issues -- more data... " section at the end on this page:

http://home.att.net/~pldexnis/CTC2_h...r__matrix.html
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  #22  
Old 08-16-2005, 08:57 PM
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Pete,

Great work in setting up the matrix!

As I understand it, your digital camera brightens the blues on the CT100 but not on your modern set. Interesting. I found that some blue/violet neon tubes do the same thing to my digital camera - had to underexpose considerably to get the color even close.

Does the gray scale also look bluer in the photo than to the eye? If your camera allows manual white balance, you could try balancing on the gray scale, and then take pix of the color bars and regular material.

-Wayne
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  #23  
Old 09-05-2005, 01:29 AM
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New matrix alignment

Spent another three hours on the CT-100 color alignment challenge this Labor Day weekend, spinning around a bucket full of variables, including discovering how fine-tuning affects matrix performance, and came up with an improved screen shot of color bars at the bottom of the link.
http://home.att.net/~pldexnis/CTC2_h...r__matrix.html
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  #24  
Old 09-05-2005, 09:55 PM
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Blue only

Once you get to the blue only stage, you should be looking for equal blue luminance visually on the cyan and magenta bars. The tint control will set this. This should be your ideal tint point...for bars.

Modern monitors have a blue only switch for quick setups. Modern NTSC bars are also split field with a smaller sub-set of bars through the middle. With these bars, the larger cyan and magenta bars are tint set as before, but now the sub-set bars (also cyan and magenta, but about 135 degrees out-of-phase) should also be luminance equal (but backwards) to the point that their luminance visually matches the bar above it. Rotate the tint until the upper chip matches the lower chip and all four should match.

This is the quick way to set analog sub-carrier phase from multiple sources through a switcher.

Never having setup a CTC-anything this way, it seem like setting the tint to center and adjusting the innards with this as a reference point would be something to look at.

Hope I did not add more hours to your scope time Pete.

Dave A
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  #25  
Old 09-05-2005, 10:03 PM
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I just wish I knew HALF of what you fellas have forgot about this stuff...History & stuff like that ,I know...This stuff, forget it. I'm all thumbs. I'm in awe...-Sandy G
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  #26  
Old 09-06-2005, 12:27 AM
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Quote:
Originally Posted by bobgary
Are you just adjusting background and screen controls, combined with convergence, to produce accurate NTSC color reproduction? Or are you working farther back in the color sync and demod-phase inversion stages?
Let me first say, there is a vintage procedure for adjusting the matrix that requires I and Q signals from a generator. I have not tried this procedure. I do not have a generator that can supply the appropriate signal, although DaveA has kindly offered to lend me his vintage generator, and so I can perform the procedure sometime in the future.
----------------------------------------------------------------
To begin, color sync and the quadrature transformer and the color burst signal path adjustments must be successfully completed. The set must be able to decode and provide a stable chroma signal to the matrix before it can be tweaked.

Next, purity and gray-scale tracking are set up, basically as published in vintage documentation, which I’ll annotate below, or at least my version. Grey scale tracking is relatively easy to accomplish and has been stable in this CT-100 (B8000194) once set.

Purity setup is similar to early commercial service procedures: move the yoke back, B and G screens down, R screen up full and make adjustments including to the color purity and field neutralizing coils, move the yoke back to standard position, etc.

For grey-scale setup, a CT-100 has RGB screen controls, G and B background controls, and in addition, B and G gain, which consists of a pot on the appropriate 12BH7 circuit boards (not a PC board in the CT-100). These initial adjustments are accomplished with a b&w signal; I simply turn down the Color control. An over-the-air mono transmission (no burst) is hard to find!

I’m just going to copy the notes I made for myself as a guide to this gray-scale task:

CONTRAST AND BACKGROUND DOWN (CCW)
BRIGHTNESS NEAR MAXIMUM
R, G, B SCREEN (GRID 2) SET LOW-LEVEL WHITE RASTER — NO VIDEO

W/MONO SIGNAL SET BRIGHTNESS AND CONTRAST FOR NORMAL

B, G GAIN SET NORMAL-LEVEL WHITE RASTER

SET BRIGHTNESS LOW

R MASTER, G, B BACKGROUND SET TRACK WHITE RASTER LOW-TO-HIGH VIDEO

Once the tracking setup gives a b&w picture that doesn’t add a hue to any setting of the brightness and contrast controls, I crank up the color control and assess the damage.

To review, the purity is set, the grey-scale tracking is set, the color burst amp, color AFC, quadrature transformer, color subcarrier level, burst takeoff transformer, and whatever, are all adjusted BEFORE the matrix is tackled.

There are no matrix controls to speak of. Everything is fixed. During restoration, each matrix resistor was checked and found to be in tolerance. So what gets tweaked and what do you look for? I feed an NTSC color bar into THE SET on channel 4. I do not tweak the screen controls. Ditto the background controls. With a modern dual-trace scope monitoring the green and red 15GP22 control grids and a blue filter to observe the color bars, tweaking consists of a combination of the hue control, the brightness control, the contrast control, and ever so slight touch-up of blue and green gain. I recently discovered that, on this set at least, the fine tuning plays a roll in the matrix drive signals, mostly the blue. There is no red gain because in a CT-100 that gain runs wide open to compensate for the low efficiency of the red phosphor.

[You may recall the earlier scope photos and elation over the red signal being twice the amplitude of the green. That’s because to get the same brightness from the inefficient red phosphor, it is driven with about twice the voltage as the more efficient green (and blue) phosphors. Vintage documentation predicted the modern scope display.]

What I haven’t detailed is how to interpret the scope and filter data into effective tweaking. DaveA has provided a rundown in an earlier post for modern video equipment. Basically with the CT-100, the scope display is used to monitor the amplitude, or height, of the color bars for equal amplitude. Complementing that is the blue filter that’s used to visually balance the intensity of color bars. Blue filter use is a common technique, but it assumes that the matrix for the red and green is okay. I have red and green filters on order. When I get them, I’ll be able to check the matrix for all three colors and tweak as needed.

Of course, all this assumes one is not color blind, although I guess one so afflicted could adjust a matrix fairly well using the scope technique. Sorta thinking out loud here…

The fact is, once set up, any little tweak of any operator control, let alone service controls, will throw off the matrix alignment. That’s why I used the ‘…bucket full of variables’ phrase. It’s frustrating in theory, but in practice, if the ambient light changes and the picture requires more contrast, you can crank up the contrast control a little. Although you are technically no longer aligned, for practical purposes the picture still looks absolutely great. You’ll still have no problem appreciating the wide 1953 gamut.
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  #27  
Old 09-06-2005, 02:44 AM
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Awesome TV!!!!!!

Those screen shots of ct-100 converged properly are simply amazing as expected!!!

I really do wish there were more of these sets with extra CRTs readily available. I'm hoping a lost stash of CRTs will some day show up. I have given up on wanting one of these since CRTs or replacements not available. I'll keep you in mind if ever come across extra 15" CRT.

I just read a review on a Dell Plasma TV for $2599 dollars in newspaper & said set could not decode colors completely accurately. It's amazing what people are paying for crap these days.

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  #28  
Old 09-06-2005, 09:03 AM
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Bobgary, I believe the waveforms you posted correspond to an old Hickok generator, which had full field bars, but not in the modern order according to luma level. Also, once things are reasonably close, it's much easier to check if these color difference signals are exactly correct by looking at the R,G,B waveforms (if available) or looking at the picture through colored filters, or turning off two guns at a time. (Professional monitors will send the blue-only signal to all three guns so you can see blue as monochrome.)

Pete, I don't have a schematic in front of me, but you said the matrix is all fixed resistors. I thought I recalled an "I gain" adjustment in there somewhere?
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  #29  
Old 09-06-2005, 09:24 AM
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Isn't this how the modern sets do...the chroma and luminance signals are mixed before they get to the CRT? Seems like in most of the tube type sets the mixing actually occurs in the crt itself with the chroma at the grids and the luminance at the cathodes.
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  #30  
Old 09-06-2005, 10:44 AM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by old_tv_nut
Pete, I don't have a schematic in front of me, but you said the matrix is all fixed resistors. I thought I recalled an "I gain" adjustment in there somewhere?
You're right about the I gain of course, it was set weeks ago and has never seemed to require further tweeking. And I probably shouldn't have thought of the matrix as only the nine discrete 1/2-watters that combine the +/-IQ and Y.

I wish you could all experience the actual video: There's a commercial playing for a Lilo&StitchII (sp?) DVD. The bug-eyed character in the commercial on the CT-100 has bright, intense, large lime-green eyes that pop off the screen at you. Interestingly, in an A-B comparison between the CT-100 and my 38-in. widescreen CRT HD set, there's no similiar effect on the HD set, although there may be setup issues to consider. Just came back from seeing the DVD at Target. The eyes in the print version were pale blue and didn't even appear to have been designed to draw attention --nothing like the TV ad to my eyes anyway. Now I'm wondering what the DVD image would look like on the Merrill. Na. Not worth the fifteen bucks to find out.
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