US3927341A

US3927341A - Cathode ray tube gun having nested electrode assembly

Info

Publication number: US3927341A
Application number: US179154A
Authority: US
Inventors: Richard Henry Hughes
Original assignee: RCA Corp
Current assignee: RCA Licensing Corp
Priority date: 1969-09-12
Filing date: 1971-09-09
Publication date: 1975-12-16
Anticipated expiration: 1992-12-16

Abstract

A conventional three-gun assembly for a color cathode ray tube is modified by eliminating the usual radial convergence cup, mounting the radial convergence pole pieces on the forward ends of the last focus electrodes, and providing each gun with a combination magnetic shield and electrode support member in the form of an open frame of magnetic metal mounted on the insulator support rods and having one side attached to the last focus electrode, an opposite side shielding the associated pole pieces from the other pole pieces, and two other connecting sides. The last focus electrode may be one of two tubular electrodes of small diameter having outwardly-flared ends adjacent to each other.

Description

' United States Patent Hughes Dec. 16, 1975 CATHODE RAY TUBE GUN HAVING 3,440,468 4/1969 Suzuki et a1. 313/70 c NESTED ELECTRODE ASSEMBLY 3,448,316 6/1969 Yoshida et al 313/70 C X [75] Inventor: Richard Henry Hughes, Lancaster,

Related US. Application Data Continuation of Ser. No. 857,371, Sept. 12, 1969, abandoned.

Assignee:

us. (:1. 313/412; 313/417 1111. c1. H01J 29/51; 11011 31/20 Field of Search 313/69 c,70 c, 77, 84,

[56] References Cited UNITED STATES PATENTS 8/1958 Hughes 313/70 C 7/1961 Hughes 1 1 1. 313/70 C 11/1967 Pappadis 1 313/70 C 6/1968 Kraner et al. 313/70 C X Primary Examiner-Robert Segal Attorney, Agent, or FirmGlenn H. Bruestle; Dennis H. lrlbeck ABSTRACT A conventional three-gun assembly for a color cathode ray tube is modified by eliminating the usual radial convergence cup, mounting the radial convergence pole pieces on the forward ends of the last focus electrodes, and providing each gun with a combination magnetic shield and electrode support member in the form of an open frame of magnetic metal mounted on the insulator support rods and having one side attached to the last focus electrode, an opposite side shielding the associated pole pieces from the other pole pieces, and two other connecting sides. The last focus electrode may be one of two tubular electrodes of small diameter having outwardly-flared ends adjacent to each other.

10 Claims, 4 Drawing Figures CATHODE RAY TUBE GUN HAVING NESTED ELECTRODE ASSEMBLY This is a continuation, of application Ser. No. 5 857,371, filed Sept. 12, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to cathode ray tube guns, and

is particularly directed to a unitary assembly of electron guns disposed side-by-side for projecting and radially converging a plurality of electron beams onto a luminescent screen, as in direct-view color cathode ray tubes of the shadow mask type for home television use.

An example of a unitary gun assembly, widely used in the manufacture of color television tubes, disclosed in my U.S. Pat. No. 3,254,251 issued May 31, 1966, comprises three electron guns, each including a cathode and a series of aligned beam modulating, accelerating and focusing electrodes, mounted in a side-by-side delta array by means of mounting straps attached to the electrodes and to three insulator support rods, and a cup-shaped radial convergence cage having a tripleapertures flat base mounted on the ends of the last gun electrodes and containing three pairs of radiallyextending magnetic convergence pole pieces, with the pole pieces of each pair disposed on opposite sides of one of the three beams and having terminal portions adapted to be coupled through the tube envelope with an external magnet to establish do and dynamic convergence magnetic fields in the path of the beam, and a Y-shaped magnetic shield interposed between the three beams. This gun structure is satisfactory for most of the color tubes now being manufactured, in sizes from 15 inches to 25 inches, and deflection angles up to 90, with conventional 1-7/16 inches O.D. envelope necks in which the gun structure is mounted. However, in designing color tubes with larger deflection angles, e. g., 1 10, and/or in smaller sizes, e.g., 13 inches, it has been found desirable to use a neck of smaller size, e.g., 1 /8 inches O.D., or less. It is difiicult to merely scale the conventional gun assembly with the pole pieces mounted in a convergence cup, down in size to fit in the smaller neck. Moreover, a disadvantage of the conventional gun assembly is the necessity for using elaborate jig means to assemble the convergence cup with its apertures in desired alignment with the electrodes of the three guns. Pappadis U.S. Pat. No. 3,353,049, issued Nov. 14, 1967, discloses a three-gun assembly in which the conventional convergence cup is omitted and the pole pieces for each beam are attached by tabs to one side of the last tubular focusing electrode and extend through slots therein, with the three last focusing electrodes mounted on three magnetic straps which also form a Y shield between the three beams in the region of the pole pieces. This arrangement does not reduce the overall diameter of the gun assembly, as compared with the conventional assembly. One disadvantage of the patent structure is that the extension of the pole pieces into the interior of the last tubular focusing electrode produces severe astigmatism of the focus lens field. Another disadvantage of this structure is that each magnetic strap extends entirely across the gap between the associated pole pieces, and in close proximity thereto, and hence, produces a severe shunting effect on the magnetic field established across that gap, as explained in applicants U.S. Pat. No. 2,991,381, issued July 4, 1961. Moreover, the tabs in 2 the patent do not positively position the inner ends of the pole pieces.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a plural gun assembly, for a color cathode ray tube, whichminimizes the disadvantages of prior gun assemblies.

Another object is to simplify the structure and method of manufacture of a plural gun assembly.

Still another object is to provide a plural gun assembly that can be made in a size suitable for use in smaller necks than conventional gun assemblies.

In accordance with the present invention, the conventional three-gun assembly of my U.S. Pat. No. 3,254,251 is modified by eliminating the conventional convergence cup, replacing the three mounting straps for the three last focusing tubular electrodes and the Y shield by three combination magnetic shield and electrode support members, each consisting of a single piece of magnetic metal mounted on the insulator support rods and having a first portion spaced axially from the associated pole pieces and attached to the last electrode, and a second portion extending between the associated pole pieces and the pole pieces of the other guns in a region located beyond the last focusing electrode. The axial width of this second portion of each member is preferably small compared to the axial length of the pole pieces, to minimize the shunting effect thereof on the magnetic field between the pole pieces. The pole pieces are mounted on the guns in substantially the same location relative to the last focusing electrode as in the conventional assembly. Preferably, the forward end of each of the last focusing electrodes is reduced in diameter, and the pole pieces for each beam are attached at one end to opposite sides of this forward end and the major portions of the pole pieces extend along the beam path in the region beyond the last focusing electrode. The last focusing electrode of each gun may be a part of a novel two or three electrode focusing lens structure comprising two elongated tubular electrodes having outwardly flared portions at the adjacent ends thereof, or part of a conventional lens structure.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front end view of a three-gun assembly embodying the present invention.

FIG. 2 is a longitudinal section view of the assembly of FIG. 1, taken on the line 2-2 thereof.

FIG. 3 is an elevational view, from line 2-2 of FIG. 1, of the combination shield and support member of FIGS. 1 and 2.

FIG. 4 is a view similar to FIG. 2 of an assembly having adifferent kind of focusing lens structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1, 2 and 3, the invention is illustrated as embodied in a unitary three-gun assembly 1, for use in a direct-view color cathode ray tube of the shadow mask type having an envelope neck 3, shown in dashed lines in FIG. 1, in which the assembly is adapted to snugly fit, like the assembly shown in my U.S. Pat. No. 3,254,251, referred to above. The assembly 1 comprises three substantially identical electron guns 5 dis- Bfid @{hl'metrically about a central longitudinal axis in an qlii ateral triangular (delta) array.

Each of the three guns 5 comprises a cathode assembly 7, a control grid 9, a screen grid 11, a first focus electrode 13, a second focus electrode 15, and a third or final focus electrode 17, all of which are mounted in axially aligned spaced relationship along three insulated, e.g., glass, support rods 19. As shown in FIG. 1, each of the rods 19 are disposed alongside a different two of the three guns 5 outwardly therefrom. Two of the rods 19 and the one gun 5 disposed therebetween are shown in FIG. 2. The cathode assembly 7, control grid 9 and screen grid 11 of each gun are separately supported from the rods 19 by integral strap-like tabs 21 embedded in the rods, in the manner disclosed in US. Pat. No. 3,254,251. The first and

third focus electrodes

13 and 17 of each gun are generally tubular and are supported by

metal straps

23 and 25, respectively, each having its ends embedded in the two adjacent rods 19 and an arcuate middle portion fitting and attached to the focus electrode on the side facing the central axis of the gun assembly, as shown in FIG. 1 for the straps 25. Each second focus electrode is a centrally-apertured sector-shaped plate having its outer ends embedded in the two adjacent rods 19. All of the structure described thus far is conventional, except for the design of the

focus lens electrodes

13, 15, 17, which will be described later, the fact that the straps 25 are made of magnetic material to serve as a partial Y shield between the three beams, and the overalldiameter of the gun assembly.

In accordance with the present invention, the conventional radial convergence cup in which the convergence pole pieces and Y-shield are usually mounted is eliminated, and two substantially radial pole pieces27 of magnetic metal are attached, as by welding, at one end to the exterior of opposite sides of the forward end 18 of each tubular focus electrode 17, with the major portions of the pole pieces extending along the beam path in a region located beyondthe end 18. Each magnetic support strap 25 is made an integral part of a combination magnetic shield and support member 29 in the form of an open frame having one side constituting the strap 25, an opposite side or strap 31 axially spaced from the strap 25 and extending across the gap between the associated pole pieces 27 and between the latter and the pole pieces 27 of the other two guns in the region beyond the forward end 18 of the tubular focus electrode 17, and two axially-extending sides 33 connecting the two

opposite sides

25 and 31. The sides 31 of the three members 29 form a Y-shaped magnetic shield between the three pairs of pole pieces. The width of the sides 31 in the axial direction is made less than half the axial width of the pole pieces 27, in order to minimize the shunting effect of the magnetic shield on the magnetic fields established between the pole pieces in the operation of the tube. The optimum width represents a compromise between the amount of shielding required between beams and the amount of shunting of each field that can be tolerated. As shown in FIG. 1, the pole pieces 27 comprise conventional flanged terminal portions 27 adapted to snugly fit within the glass neck 3 of the cathode ray tube for coupling to external convergence magnets. Three metal leaf springs 35 are attached, as by welding, to flanged ends 31' of the sides 31 of members 29 to center and support the forward end of the gun assembly in the tube neck. The springs 35 also connect the focus electrodes 17 and members 29 to the high voltage funnel coating. The other end of the gun assembly is mounted on a conventional stem (not shown). By eliminating the conventional convergence cup and scaling down all of the parts in size somewhat, the resulting compact gun assembly can be inserted in a somewhat smaller tube neck.

Three

focus electrodes

13, 15 and 17 form an improved unipotential (Einzel) lens providing optimum electric fields for the electron optics. Each of electrodes'l3 and 15 comprises a major tubular portion 37 of relative small diameter merging smoothly with a relatively-short outwardly-flared or bell-shaped portion 39 increasing in diameter to an inner diameter at the end adjacent to the focus electrode 15 about twice that of the portion 37. The diameter of the aperture 15'. in electrode 15 should be at least as large as, or greater than, the small diameter portion 37. The two

end electrodes

13 and 15 of the focus lens are electrically connected together to operate at the same high voltage by a connecting wire 41, and the middle focus electrode is connected by a connecting wire 43 to one of the lead-in terminals of the stem (not shown) for applying a low or ground potential thereto, as shown in FIG. 2. The purpose of flaring the ends of the

tubular electrodes

13 and 15 is to reduce spherical aberration in the focus lens. The use of a focus electrode 17 having a small diameter makes it possible to mount the pole pieces 27 directly on the outer sides thereof with the desirable relatively close spacing of the pole pieces, thereby obtaining accurate positioning of the pole pieces with respect to the beam axes of the three guns.

FIG. 4-shows a modified three-gun mount assembly 45 substantially identical to assembly 1 of FIGS. 1-3, except :for the substitution of bi-potential or two-electrode focus. lenses for the three-electrode unipotential lensesof the first embodiment. Each focus lens comprises two

tubular focus electrodes

47 and 49 mounted on insulator supportrods 19 by-means of straps 51 and 53, respectively. Each .of

electrodes

47 and 49 com- 1. In a unitary plural gun assembly, each gun comprising a plurality of axially-aligned electrodes mounted in spaced relation along elongated insulating support means for projecting an electron beam along a beam path in a forward direction, and a pair of magnetic pole pieces disposed primarily in a region beyond the forward end of the forwardmost electrode and on opposite sides of the beam path through said gun; the improvement wherein said pole pieces of each gun are disposed entirely outside of the last electrode, the major portions of said pole pieces extend along the beam path in the region located beyond said forwardmost electrode, and each gun includes a combination magnetic shield and electrode support member com-. prising a single piece of magnetic metal mounted on at 1 least one of said support means and having a first portion attached to said last electrode, and a second por-- tion spaced axially from said first portion, disposed in, said region and extending between said pole pieces of that gun and the pole pieces of the other gun or guns for partially shielding the pole pieces of adjacent guns from each other.

2. In an assembly of three electron guns disposed side-by-side in delta array, each gun comprising a plurality of axially-aligned electrodes including a final tubular focus electrode mounted in spaced relation along insulating support means for projecting an electron beam along a beam path in a forward direction, and a pair of substantially radial magnetic pole pieces disposed on opposite sides of the beam path therethrough; the improvement wherein said pole pieces of each gun are disposed entirely outside of said tubular electrode, the major portions of said pole pieces extend along the beam path in a region located beyond the forward end of said tubular electrode, and each gun includes a combination magnetic shield and electrode support member comprising a single piece of magnetic metal mounted on at least one of said support means and including a first portion attached to said tubular electrode, and a second portion spaced axially from said first portion, disposed in said region and extending between said pole pieces of that gun and the pole pieces of the other two guns for partially shielding the pairs of pole pieces of the three guns from each other.

3. The improvement of claim 2, wherein the axial width of said second portion of each of said members is less than half the corresponding width of said pole pieces, whereby the shunting effect of said second portion of the magnetic field between the associated pole pieces is minimized.

4. The improvement of claim 2, wherein each of said members is generally rectangular with the central portion cut out to form an open frame having four integrally connected sides comprising one side constituting said first portion having its ends attached to said support means and an intermediate portion extending across and attached to said tubular electrode on the side thereof toward the other guns, a side opposite said one side constituting said second portion of said member, and two connecting sides.

5. The improvement of claim 2, wherein the pole pieces of each gun are attached at one end directly to and supported solely by opposite sides of the exterior of said forward end of said tubular electrode.

6. A unitary plural gun assembly for use in projecting electron beams toward a screen of a cathode-ray tube comprising,

each gun having a plurality of axially-aligned electrodes mounted in spaced relation along elongated insulator support means,

a pair of radial convergence magnetic pole pieces attached to the outer sides of and supported by the electrode of each gun nearest said screen, said pole pieces being entirely outside of and extending beyond said electrode nearest said screen toward said screen,

a combination magnetic shield and electrode support for each gun comprising a single piece of magnetic metal mounted on at least one of said support means and having a first portion attached to the electrode nearest said screen and interconnecting this electrode with said elongated insulator support means, and a second portion extending toward said screen between pole pieces of at least two adjacent guns.

7. The unitary plural gun assembly as defined in claim 6, wherein each gun in axially-aligned order com-, prises, a cathode assembly, a control grid, a screen grid, a first focus electrode, a second focus electrode and a third focus electrode, said third focus electrode being nearest said screen, said pair of magnetic pole pieces being attached to approximately opposite sides of an external portion of said third focus electrode.

8. The unitary plural gun assembly as defined in claim 6, wherein the axial width of the second portion of said combination is less than half the axial width of said pole pieces, wherreby the shunting effect of said second portion on a magnetic field between each pair of pole pieces is minimized.

9. The unitary plural gun assembly as defined in claim 6, including a plurality of metal leaf springs attached to said second portion and extending therefrom toward said screen.

10. The unitary plural gun assembly as defined in claim 6, wherein each combination is generally rectangular having an open central portion and four integrally connected sides, one of said sides constituting said first portion and being attached to said support means, a second side opposite said first portion constituting said second portion, and two other sides connecting said first and second portions.

Claims

1. In a unitary plural gun assembly, each gun comprising a plurality of axially-aligned electrodes mounted in spaced relation along elongated insulating support means for projecting an electron beam along a beam path in a forward direction, and a pair of magnetic pole pieces disposed primarily in a region beyond the forward end of the forwardmost electrode and on opposite sides of the beam path through said gun; the improvement wherein said pole pieces of each gun are disposed entirely outside of the last electrode, the major portions of said pole pieces extend along the beam path in the region located beyond said forwardmost electrode, and each gun includes a combination magnetic shield and electrode support member comprising a single piece of magnetic metal mounted on at least one of said support means and having a first portion attached to said last electrode, and a second portion spaced axially from said first portion, disposed in said region and extending between said pole pieces of that gun and the pole pieces of the other gun or guns for partially shielding the pole pieces of adjacent guns from each other.

6. A unitary plural gun assembly for use in projecting electron beams toward a screen of a cathode-ray tube comprising, each gun having a plurality of axially-aligned electrodes mounted in spaced relation along elongated insulator support means, a pair of radial convergence magnetic pole pieces attached to the outer sides of and supported by the electrode of each gun nearest said screen, said pole pieces being entirely outside of and extending beyond said electrode nearest said screen toward said screen, a combination magnetic shield and electrode support for each gun comprising a single piece of magnetic metal mounted on at least one of said support means and having a first portion attached to the electrode nearest said screen and interconnecting this electrode with said elongated insulator support means, and a second portion extending toward said screen between pole pieces of at least two adjacent guns.

7. The unitary plural gun assembly as defined in claim 6, wherein each gun in axially-aligned order comprises, a cathode assembly, a control grid, a screen grid, a first focus electrode, a second focus electrode and a third focus electrode, said third focus electrode being nearest said screen, said pair of magnetic pole pieces being attached to approximately opposite sides of an external portion of said third focus electrode.