CurtPalme.com Home Theater Forum

[Spanky Ham]

[stridsvognen]

[Spanky Ham]

Um ok. How about a pic of the test pattern with green tube only?

[stridsvognen]

[thewolfman]

[stridsvognen]

Still 180Mhz Green tube only. 03VIM

[stridsvognen]

180Mhz Green tube only 02VIM

[Spanky Ham]

Looking at Craig's green pic and yours, I would say the G90 is better. It will be interesting to see what the results are when you have Craig out to setup your HT.

[stridsvognen]

[Nashou66]

Craig's is definitely Sharper .

[jbmeyer13]

Kurt's is more uniform without the peaking. Hard to tell weather the issue is set up or the camera as all Digital camera's add varying degrees of sharpness. Would be good the see Kurt's once it's all dialed in.

[stridsvognen]

[jbmeyer13]

In my experience tweaking the astig along with the optical and electronic focus will result in improved sharpness but it has no material impact on the uniformity (assuming the set up isn't completely f'd up to begin with). I also experimented with G2/drive settings and they also did not have a material impact on the horizontal (left 1:1 box) uniformity.

[stridsvognen]

[Spanky Ham]

[stridsvognen]

[jbmeyer13]

[Nashou66]

Astig or the CPC magnets are called CPC magnets for a reason. CPC stands for Color Purity Correction magnets. They play a large part in uniformity.


Nashou

[Nashou66]

Convergence and purity in color CRTs[edit]
Due to limitations in the dimensional precision with which CRTs can be manufactured economically, it has not been practically possible to build color CRTs in which three electron beams could be aligned to hit phosphors of respective color in acceptable coordination, solely on the basis of the geometric configuration of the electron gun axes and gun aperture positions, shadow mask apertures, etc. The shadow mask ensures that one beam will only hit spots certain colors of phosphors, but minute variations in physical alignment of the internal parts among individual CRTs will cause variations in the exact alignment of the beams through the shadow mask, allowing some electrons from, for example, the red beam to hit, say, blue phosphors, unless some individual compensation is made for the variance among individual tubes.

Color convergence and color purity are two aspects of this single problem. Firstly, for correct color rendering it is necessary that regardless of where the beams are deflected on the screen, they hit the same spot (and nominally pass through the same hole or slot) on the shadow mask. This is called convergence.[20] More specifically, the convergence at the center of the screen (with no deflection field applied by the yoke) is called static convergence, and the convergence over the rest of the screen area is called dynamic convergence. The beams may converge at the center of the screen and yet stray from each other as they are deflected toward the edges; such a CRT would be said to have good static convergence but poor dynamic convergence. Secondly, each beam must only strike the phosphors of the color it is intended to strike and no others. This is called purity. Like convergence, there is static purity and dynamic purity, with the same meanings of "static" and "dynamic" as for convergence. Convergence and purity are distinct parameters; a CRT could have good purity but poor convergence, or vice versa. Poor convergence causes color "shadows" or "ghosts" along displayed edges and contours, as if the image on the screen were intaglio printed with poor registration. Poor purity causes objects on the screen to appear off-color while their edges remain sharp. Purity and convergence problems can occur at the same time, in the same or different areas of the screen or both over the whole screen, and either uniformly or to greater or lesser degrees over different parts of the screen.

The solution to the static convergence and purity problems is a set of color alignment magnets installed around the neck of the CRT. These movable weak permanent magnets are usually mounted on the back end of the deflection yoke assembly and are set at the factory to compensate for any static purity and convergence errors that are intrinsic to the unadjusted tube. Typically there are two or three pairs of two magnets in the form of rings made of plastic impregnated with a magnetic material, with their magnetic fields parallel to the planes of the magnets, which are perpendicular to the electron gun axes. Each pair of magnetic rings forms a single effective magnet whose field vector can be fully and freely adjusted (in both direction and magnitude). By rotating a pair of magnets relative to each other, their relative field alignment can be varied, adjusting the effective field strength of the pair. (As they rotate relative to each other, each magnet's field can be considered to have two opposing components at right angles, and these four components [two each for two magnets] form two pairs, one pair reinforcing each other and the other pair opposing and canceling each other. Rotating away from alignment, the magnets' mutually reinforcing field components decrease as they are traded for increasing opposed, mutually cancelling components.) By rotating a pair of magnets together, preserving the relative angle between them, the direction of their collective magnetic field can be varied. Overall, adjusting all of the convergence/purity magnets allows a finely tuned slight electron beam deflection and/or lateral offset to be applied, which compensates for minor static convergence and purity errors intrinsic to the uncalibrated tube. Once set, these magnets are usually glued in place, but normally they can be freed and readjusted in the field (e.g. by a TV repair shop) if necessary.

On some CRTs, additional fixed adjustable magnets are added for dynamic convergence and/or dynamic purity at specific points on the screen, typically near the corners or edges. Further adjustment of dynamic convergence and purity typically cannot be done passively, but requires active compensation circuits.

[stridsvognen]