NORDMENDE SPECTRA CV 630 1.653 J 18 F23-11S CHASSIS ICC7 CRT TUBE VIDEOCOLOR A59EAU25X01 VIEW

The present CRT invention provides an improvement in the appearance of a cathode-ray tube including a rectangular faceplate with an exterior surface having curvature along both the minor and major axes. The faceplate also includes a cathodoluminescent screen on an interior surface thereof. At least in the center portion of the faceplate, the curvature along the minor axis is at least 10 percent greater than the curvature along the major axis. Points on the exterior surface near the ends of the major axis, at the edges of the screen, lie in a first plane which is perpendicular to the central longitudinal axis of the tube; points on the exterior surface near the ends of the minor axis, at the edges of the screen, lie in a second plane which is spaced from and parallel to the first plane; and points on the exterior surface near the ends of the diagonals of the rectangular faceplate, at the edges of the screen, lie in a third plane which is spaced from and parallel to the first plane. The three planes are spaced from the center portion of the faceplate in the order of second plane, first plane and third plane.

What is claimed is:

1. In a cathode-ray tube including a rectangular faceplate with two long sides and two short sides wherein the long sides of the faceplate substantially parallel a centrally located major axis of the tube and the short sides of the faceplate substantially parallel a centrally located minor axis of the tube, said faceplate having an exterior surface having curvature along both its minor and major axes and said faceplate having a cathodoluminescent screen on an interior surface thereof, said tube including an electron gun therein for generating and directing at least one electron beam toward said screen, and wherein, at least in a center portion of the faceplate, a curvature along the minor axis is at least 10 percent greater than the curvature along the major axis; the improvement comprising
points along the major axis on said exterior surface, located at the edges of said screen, lying in a first plane which is perpendicular to a central longitudinal axis of said tube;
points along the minor axis on said exterior surface, located at the edges of said screen, lying in a second plane which is spaced from and parallel to said first plane;
points along the diagonals of said faceplate on said exterior surface, located at the corners of said screen, lying in a third plane which is spaced from and parallel to said first plane;
said first, second and third planes being spaced from a fourth plane, which is parallel to said first, second and third planes and is tangent to the center portion of said faceplate, in the order of said second plane, said first plane and said third plane;
the ratio of the spacing between said second and fourth planes, measured along the central longitudinal axis of said tube, to the spacing between said third and fourth planes being greater than the minor axis dimension of the screen, squared, divided by the diagonal dimension of the screen, squared, and less than one;
the ratio of the spacing between said first and fourth planes, measuredalong the central longitudinal axis of said tube, to the spacing between said third and fourth planes being greater than the major axis dimension of the screen, squared, divided by the diagonal dimension of the screen, squared, and less than one; and
the exterior surface curvature along said minor axis essentially being circular from the center of said faceplate to said second plane, and the exterior surface curvature along said major axis essentially being circular near the center of said faceplate and increasing in curvature near the sides of said faceplate to said first plane.


2. The tube as defined in claim 1, wherein the spacing between said first and second planes approximately equals the spacing between said first and third planes.

3. The tube as defined in claim 2, including said tube having a viewing screen with an approximate 69 cm diagonal and wherein the spacing between said first and second planes is about 4 mm and the spacing between said first and third planes is about 4 mm.

Description:

This invention relates to cathode-ray tubes (CRT's) and, particularly, to the surface contours of the faceplate panels of such tubes.
BACKGROUND OF THE INVENTION
There are two basic faceplate panel contours utilized commercially for rectangular CRT's having screen sizes greater than about a 23 cm diagonal: spherical, and cylindrical. Although flat contours are possible, the added thickness and weight of the faceplate panel required to maintain the same envelope strength are undesirable. Furthermore, if a flat faceplate CRT is a shadow mask color picture tube, the additional weight and complexity of an appropriate shadow mask also are undesirable.
Recently, it has been suggested that spherically-shaped CRT faceplate panels be improved by increasing the radius of curvature of the panels by a factor of 1.5 to 2. Such increase in radius of curvature reduces the curvature of the faceplate panel, thereby permitting more satisfactory off-axis viewing of a tube screen. Although such tubes having increased radius of curvature do provide improved viewing, there is still a need for even flatter faceplates or, alternatively, for tubes that appear to be flatter.
A new faceplate panel contour concept which creates the illusion of flatness is disclosed in three recently-filed, copending U.S. Applications: Ser. No. 469,772, filed by F. R. Ragland, Jr. on Feb. 25, 1983 and now U.S. Pat. No. 4,839,556; Ser. No. 469,774, filed by F. R. Ragland, Jr. on Feb. 25, 1983 and now U.S. Pat. No. 4,786,840; and Ser. No. 469,775, filed by R. J. D'Amato et al. on Feb. 25, 1983 and now abandoned. The contour has curvature along both the major and minor axes of the faceplate panel, but is nonspherical. In a preferred embodiment described in these applications, the peripheral border of the tube screen is planar. In such tubes, it is important to contour the faceplate panel diagnosis so that the differing curvatures extending from the major and minor axes are properly blended. In the above-cited U.S. application Ser. No. 469,774, this blending is accomplished by permitting at least one sign change of the second derivative of the diagonal contour in the center-to-corner direction.
The present invention provides a novel faceplate panel contour which appears flatter than the suggested longer radius tubes and which does not require the use of much thicker glass to maintain tube strength.
SUMMARY OF THE INVENTION:
The present invention provides an improvement in a cathode-ray tube including a rectangular faceplate which has an exterior surface having curvature along both the minor and major axes. The faceplate also includes a cathodoluminescent screen on an interior surface thereof. At least in the center portion of the faceplate, the curvature along the minor axis is at least 10 percent greater than the curvature along the major axis. In the improvement, points on the exterior surface near the ends of the major axis, at the edges of the screen, lie in a first plane which is perpendicular to the central longitudinal axis of the tube; points on the exterior surface near the ends of the minor axis, at the edges of the screen, lie in a second plane which is spaced from and parallel to the first plane; and points on the exterior surface near the ends of the diagonals of the rectangular faceplate, at the edges of the screen, lie in a third plane which is spaced from and parallel to the first plane. The three planes are spaced from the center portion of the faceplate in the order of second plane, first plane and third plane.