Twenty-eighth operational CT-100 screen shots...

[old_tv_nut]

Pete,

A great picture! Keep at it.

Getting a precise gray scale setting is difficult without a color meter, but IF the bias and drive controls do not interact too badly you can usually get a pretty good result by eyeball. It really helps if the controls can be rocked back and forth through the correct point - you can go for decreasingly obvious misadjustment as you rock the control back and forth, and zero in on a good point. The ideal is to be able to set the lowlights and the highlights separately, doing the blacks/dark bars first - but not all sets will let you do this. Looking at the CT-100 schematic, if the DC clamping is working OK, you should be able to set the lowlights close and then set the drives for proper white. Then touch up the lowlights for precise tracking, and go back and forth from highlights to lowlights again if necessary.

Because of differences in phosphor spectra, a filter colorimeter may be slightly off in its readings. The Zenith optics lab had to use a master spectroradiometer to calibrate filter-type colorimeters to the current phosphor set - the colorimeters would then have a multi-positon switch for different calibrations. The spectroradiometer was calibrated against a NBS traceable standard lamp, and then the color was calculated from the measured spectrum using the CIE standard obsrerver curves. (These curves have been shown to have some errors, but that's another story). I believe that nowadays there are better ways to calibrate than a standard lamp, using power measurements of laser sources, but I haven't kept track of what optical instrument companies are actually doing.

The best white point setting (for one observer) can be made using a split-screen D65 lamp. This device has a window that is half open to the CRT and half mirrored to reflect the D65 lamp. The view is of the screen gray bar immediately adjacent to the lamp gray, with no intervening frame line. Any one person can get a near perfect match (for him/her self) of monitors having any phosphors by using this. However, other individuals likely will see the match as slightly off due to normal color vision variations. I and one of the older engineers always disagreed on how much blue drive produced a match. (He needed more blue.) Now that I am older and slowly developing cataracts, I probably need more blue than I used to.

The colorimeter substitutes its filtered spectral responses for the human eye, which is reasonable but not as accurate as a spectroradiometer, hence the need for multiple calibrations depending on the phosphor characteristics. I would guess that the colorimeter will be fairly correct for the different greens, both of which have smooth spectra, but may show errors due to the difference between the CT-100 red spectrum and the spikey rare-earth red spectrum of a modern tube.

So - if you get a colorimeter, and the two sets don't end up looking like the same gray scale, you may have to trust your eyes.

[frenchy]

Just do that old psychology trick I read in one of my old tv repair books - hire somebody to set the greyscale for you and tell them to ask YOU when they have it white : )
They said repairman should do that to prevent the customer from a callback complaining "this thing is green", because they are the one that decided it was white to begin with, heh heh.

[Pete Deksnis]

I have been experimenting with the relative setting of the G2 grids. The attached photo is with a low-brightness grey G2 setup (didn't upload for some reason; musta been too big. Substituted an ad c.u.). It is fairly decent and still viewable in the morning light. When a brighter grey is obtained with a relatively greater G2 setup, the resulting picture will lack adequate red phosphor output, an effect that is particularly noticeable where green is an element of the color being reproduced (as in that odd hue in the background of the GMA-set).

A low G2 grey setup provides greater G1 (control grid) response; a high G2 (brighter grey) setup delivers a brighter picture. With the greater G2 setup, I was able to watch the set during a bright sunny day with just the blinds closed.

So far, I haven’t been able to have it both ways.

Next step is to backup farther and readjust the red purity, which has deteriorated since set up weeks ago, as discovered last weekend during G2 adjustments. This will be at least part of the solution.

[Steve D.]

Hey Pete,

I have been following your restoration efforts with great interest. Seems there's no end to the technicial issues in trying to achieve the perfect image on a CT-100. As you, and the rest of us CT-100 owners have learned, this set is very high maintenance, and a bit temperamental. And, while it's fun, for a while, to tweak this control and that, you may just want to walk away for a time. Sit back and watch the beautiful results you have achieved. Enjoy the fruits of your labor. I love the photo of your CT-100 sitting in the corner purring away and displaying it's magnificent living color picture.

-Steve D.

[old_tv_nut]

Does the CT-100 have any kind of set-up switch that sets the video bias to a fixed value while playing with G2's? If not, you may be walking yourself away from midrange on the G2's and black level (brightness + any other video black level settings if there are any). If you can check the G2's against a service-info value, and/or look at the red video drive with a scope to see if it's clipping, that might help.

The piece of schematic that comes to hand shows R,G,B, drive capacitively coupled to the G1's, each with its own diode DC restorer to set the black level (birghtness) - plus the blue and geen have individual background controls.

I think it goes like this: When you raise the G2 voltage, the tube is harder to cut off, but that means you need more negative swing on the grids, which would not cause the red amp to clip on highlights - maybe the opposite. So, I think it's possible that when you turn up the G2's, you are reaching the max current that the red gun will deliver on the red highlights - just a guess, but if it's true, there's nothing to do but run it at lower settings.

[frenchy]

It's amazing how you can tweak the tint on a black and white picture and it apparently becomes slightly red-tinted... but keep watching it for a minute or two and it eventually just looks like black and white again. Then put it back the way it was before and suddenly it will look green/bluish! Try this one - stare at a test pattern for about 30 seconds, then put it on a program. Wow look at all the pretty colors! : )
All this is probably why I don't spend too much time trying to perfect all the color settings etc., as long as it looks pretty good and people faces are flesh colored, that's 95% of it.

[Pete Deksnis]

Originally Posted by Steve D.

Hey Pete,

Enjoy the fruits of your labor. I love the photo of your CT-100 sitting in the corner purring away and displaying it's magnificent living color picture.

-Steve D.

Matter of fact, last Saturday the set and I had a marathon date lasting 5.5 hours in the morning through early afternoon, then another 3.5 hours of quality time that evening. Tomorrow however the back comes off and the top gets popped in prep for that red purity setup I've been threatening to redo. Before that I'll scope the red gun to check for possible distortion under varying G2 settings. It's all good fun with the only bad thing a hold on the next project, restoring the '56 Philco.

Enjoying retirement,
Pete

[John Folsom]

Pete is correct, retirement IS fun!

[bgadow]

I just wanted to say:

A few years ago the conversations taking place here could have only happened by phone or maybe mail. (assuming that, without this site, folks like Pete & Old TV Nut would even have heard of each other) Half of the phone conversations would have been forgotten. Now, here they are, in writing so you can go back & reread. We can all benefit from the knowledge here, today & hopefully for all time.

[David Roper]

Hear, hear.

[David Roper]

Or should that be: read, read (pronounced red red).

[ceebee23]

The thing that stands out to me in this thread is what a perfectionist will to to make a TV set be as accurate as possible ...just a pity that most programs today are pretty sloppy in terms of color and covered in dreadful station logos.

But then when you watach a film where the colour is part of the whole desing of the movie you realise why getting the best you can out of a TV is worth it.

But then being colour blind means for me getting the colours accurate is rather a subjective thing!

[ceebee23]

and of course ....here in PAL land the colour looks different anyway .... it is interesting how when changing from a PAL source to an NTSC one requires changes to the settings on the set... mainly because the black level is different.

On my Sony the "preset" color, brightness and black level auto-settings are clearly designed for NTSC sources as they are way off for a PAL source ...too dark and contrasty a dn way too much chroma but for NTSC are pretty good.

[Pete Deksnis]

About a week ago I set off to investigate characteristics of the red gun signal. Data from the task has been added to a new Troubleshooting section on the CT-100 site. There are four entries so far; check the one from 11-19-05.
http://home.att.net/~pldexnis/input/...eshooting.html

[Pete Deksnis]

Three weeks ago I readjusted the CT-100 and achieved a better hue match between the 'reference' digital set and the Merrill. It ameliorated my earlier supposition that intense green was a result of wide green gamut. Here's a link to the update page where the 12-9-2005 update appears:

http://home.att.net/~pldexnis/ct-100...tion_log8.html