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I'd like to improve the color tracking a little more if I can. What I've noticed is that the color is quite good if the overall scene is dark, but on brighter scenes, the red becomes weak. What is peculiar to me is that the red becomes weaker in a bright scene than it is in a dark scene. For example, if there is some red lettering or a red object on the screen, and the rest of the scene shifts from darker to lighter, the red stuff actually gets dimmer. Likewise, a face that looks normal if the background is dark loses its red content if the background gets lighter, even though the brightness of the face is unchanged.
I'm wondering if there is a problem in my DC restoration circuitry (particularly for red), or if the DC restoration circuitry is having trouble dealing with the difference between the guns in my CRT?
I've got the red screen at max, blue and green screens much lower, and both the blue and green drive below their original minimum settings (resistors modified). The red background with low brightness is too high, even though green and blue background are set at max. In general, the brightness control does not have the correct range -- it basically always needs to be fully clockwise, and still the image is a little dark, although not bad.
Here is the data on the CRT (see pictures below: #1 red, #2 green, #3 blue). All three guns test with very high emission. Key difference is the cutoff bias:
Red cutoff bias: -51.5 V
Green cutoff bias: -66 V
Blue cutoff bias: -67 V
I also checked the screen voltage during the emission test on my CR-70:
Red screen: 259 V
Green screen: 188 V
Blue screen: 225 V
So although all three guns are capable of high emission, there are significant differences between them in terms of bias and screen current/voltage.
Should the set be easily able to handle these differences within normal control ranges?
Any indication of something not quite right in the video amplifiers or DC restoration circuits?
If it's merely a matter of the set not being able to handle the gun differences within normal design range, I'd like to modify things to work better with the CRT in its current state, if I can figure out what would work.
Since many of you have far more experience with color sets than I do, I thought one of you might have some ideas.
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