On Jun 3, 4:30*pm, "William Sommerwerck"
wrote:
"Smarty" *wrote in ...
As a newcomer to this group, I hesitate to be a contrarian
or appear to be in any way argumentative or disagreeable.

You didn't hesitate to do it to me. Don't pretend to be "diffident, modest,
and shy", because you aren't.

I don't have as much experience servicing TVs as others in this group. But I
have noticed that impurity is less visible with a monochrome signal than a
color one. Clearly, the visibility will vary with all the factors stated, and
possibly some we've missed.

I can understand your confusion about this point, and it is a point of
confusion I share. But I must remind you of what Sherlock Holmes said, that to
speculate without data weakens the mind.

To argue about what is or is not theoretically visible is a complete waste of
time, when a simple experiment would resolve the issue. (And if anyone reading
this thinks I will slide the yoke on my 13" Trinitron to see what happens --
they are mistaken.)

There are two things present that have to be understood. There is
convergence, which is making sure the 3 electron beams hit the same
spot/area at the same time. There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.

Assuing that the convergence of the three images is correct, and only
purity is bad, it will take a trained eye to tell that there is a
purity problem on a B+W picture. But, as soon as a color picture is
presented, colors will be noticeably "off".

I taught color TV servicing at an out-of hours course at Bell
Laboratories 50 years ago and have kept my hand in repairs ever
since. Getting good convergence and purity was/is always a
challenge. Taking tv's on a swivel base and maintaining pruity as the
set is rotated through 120 degrees was always a challenge. The new
flat-screen non-crt tvs are a blessing!!!