US3026438A

US3026438A - Grid-cathode assembly for cathode ray tubes

Info

Publication number: US3026438A
Application number: US740082A
Authority: US
Inventors: Jr Thomas P Warne
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1958-06-05
Filing date: 1958-06-05
Publication date: 1962-03-20
Anticipated expiration: 1979-03-20

Description

March 20, 1962 T. P. WARNE, JR

GRID-CATHODE ASSEMBLY FOR CATHODE RAY TUBES Filed June 5, 1958 IN VEN TOR.

THums P WARNEJR.

United States Patent Ofiice 3,026,438 Patented Mar. 20, 1962 3,026,438 GRID-CATHODE ASSEIVLBLY FOR CATHODE RAY TUBES Thomas P. Warne, Jr., Trout Run, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed June 5, 1958, Ser. No. 740,082

6 Claims. (Cl. 31382) This invention relates to cathode ray tubes, and in particular to a novel structure for controlling electrode spacing and a novel method of assembly of electrodes.

The exact spacing and alignment of a grid electrode aperture with relation to an emitting cathode electrode face is very important because it determines the efiective control of the grid. The grid aperture alignment and spacing from the cathode emitting face must be accurate because it forms part of the first electron lens system by which the beam is formed and focused. Since it is necessary to have precision in the spacing and alignment of the cathode and grid, and because uniformity of the close spacing of these two electrodes in each tube is required in mass production of tubes of the same type, the mechanical design of a grid-cathode unit of an electron gun represents one of the important problems in gun design.

The construction of a grid-cathode structure of a conventional type of electron gun has involved the difiicult process of assembling many small parts in proper relationship. The process also involves fixing several subassemblies in predetermined spaced relationships involving critical distances subject to small tolerances. The distances between parts are generally measured by a micrometer dial ga e and spacing adjustments are made by inserting spacers of various thickness. This method is tedious and time-consuming.

Furthermore, in a conventional electron gun assembly, the heating of the cathode sometimes causes the cathode emitting surface to move closer to the grid aperture. This change in grid-cathode spacing results fi'om the expansion of the cathode cylinder when the heater is turned on. Warping of the grid cylinder due to changes in pressure or temperature may also afiect the alignment and spacing of the grid-cathode.

An object of this invention is to simplify the spacing adjustment between electrodes of a cathode ray tube.

Another object of this invention is to provide an improved structure for accurate control of the spacing from cathode to grid.

Another object is to provide a grid-cathode assembly which is stable under varying operating conditions.

According to this invention electrodes have co-operating means on adjacent surfaces to provide a spiral action with respect to each other upon relative rotation. Spacing of the electrodes is controlled by rotation of one electrode with respect to another electrode.

According to one embodiment of the invention, which is described in detail in the following specification, a grid cathode assembly includes co-operating means which consist of bosses co-operating with ramps. During assembly of the electron gun the bosses and ramps are engaged and a rotation of the cathode with respect to the grid provides spacing adjustment.

The invention is more fully described in the following detailed description when read with the drawing in which:

FIG. 1 is an elevational view partially in section showing the grid-cathode assembly employing the metallic spacer cylinder;

FIG. 2 is a section taken along the line 22 of FIG. 1 showing one form of the bosses, according to the invention;

FIG. 3 is a perspective view of the metallic spacer cylinder showing the ramps;

FIG. 4 is a vertical section showing the grid-cathode assembly employing the ceramic disk and the retainer; and

FIG. 5 is a perspective view of the ceramic disk in corporating the ramps.

The same reference characters are used to denote similar elements throughout the drawing.

FIG. 1 of the drawing illustrates an embodiment of the invention in which a grid-cathode assembly comprises a metallic grid cylinder 1, a metallic spacer cylinder 3, a ceramic disk 5 and a cathode 7. The spacer cylinder 3 and the ceramic disk 5 serve as support structure for supporting the cathode 7 relative to the grid cylinder 1. The metallic grid cylinder 1 has a closed end 9 with a relatively small circular aperture 11 centrally located therein. Three elongated bosses 13 radially positioned 120 apart are formed in the grid endwall 9. The elongated bosses 13 are clearly shown in FIG. 2 of the drawing.

The metallic spacer cylinder 3 is an integral structure having a lower cylinder portion 15, and a smaller diameter tubular portion 17 coaxially positioned and connected by a shoulder or annular section 19. The lower portion 15 fits closely into the grid cylinder 1 to allow rotational and longitudinal motion of the metallic spacer 3 against the grid cylinder Wall. The lower portion 15, which is open-ended, has a pair of spaced slots 21 in the wall adjacent the open end. The smaller tubular portion 17 has a flanged end 23 on which three gradient sections or ramps 25 are formed.

Each of the ramps 25, illustrated in FIG. 3, delineates a 120 arc of the generally annular pattern formed by the flange 23. Each ramp 25 slopes in the same direction along its are at the same angle. Ramps which slope .030 inch in of are have been found to be satisfactory. The flanged end 23 is provided with a large aperture 27 through which the cathode 7 may be projected.

The cathode 7 includes a conventional hollow metallic cylinder 29, closed at one end by a cap portion 31. The outer surface of cap portion 31 is coated with an emitting layer 33 of thermionic emitting material, such as a mixture of strontium and barium oxides. This material is well known and is recognized as that which easily emits electrons, when heated to high temperatures. Mounted within the cathode cylinder 29 is a heater filament 35 which is coated with a layer of insulating material. The filament 35 is twisted in a coil formation to provide a unidirectional field when filament 35 is heated with alternating current. The cathode cylinder 29 is supported within a central aperture 39 of the ceramic support disk 5 by peripheral beads 41 pressed out of the wall of the cathode cylinder 29 into contact with opposite surfaces of the ceramic disk 5.

During assembly of the grid-cathode unit, the cathode cylinder 29 and attached ceramic disk 5 are inserted into the grid cylinder 1 so that the disk 5 rests against the shoulder or annular section 19 of the spacer 3. The cathode 29 is so positioned within the ceramic disk 5 so that the cathode emitting layer 33 projects from the relatively large aperture 27 of the spacer. A portion of the wall of the spacer 3 adjacent and below the inserted ceramic disk 5 is then crimped to rigidly fix the ceramic disk 5 within the spacer cylinder 3 against the shoulder or annular section 19. When so fixed, the cathode 7 and the metallic spacer 3 are spaced in insulated relationship.

The metallic spacer cylinder 3 securing the ceramic disk 5 which supports the cathode 7 is telescoped into the grid cylinder 1 thereby engaging the ramps 25 of the spacer 3 with the bosses 13 of the grid 1. Projections 42 of a rubber ended mandrel 43 engage the pair of slots 21 at the open end of the spacer 15. By rotating the mandrel 43 the spacer cylinder 3 rotates relative to the grid end wall 9. Rotation of the spacer cylinder 3 While the ramps 25 and the bosses 13 are engaged allows the spacer cylinder 3 to move along its longitudinal axis and thus varies the spacing from cathode to grid.

The desired spacing between the cathode emitting layer 33 and the grid aperture 11 may be determined by an electric spark method, or an optical method, or any other suitable method. In the optical method, a microscope 45 is positioned above the grid aperture 11 whereby the spacing from the grid end wall 9 and grid aperture 11 to the cathode emitting layer 33 may be viewed and measured. The microscope 45 is so fixed that when the layer 33 is viewed in sharp focus, the desired spacing from cathode to grid has been effected. Alternatively, in the electric spark method, the cathode 7 and spacer 3 are moved axially within the grid cylinder 1 toward the grid aperture 11 until a point is reached at which a predetermined potential applied between the cathode 7 and grid 1 causes an electric spark from the closed end 31 of the cathode to the grid end wall 9.

When the desired spacing is obtained, the cylindrical wall of the metallic grid cylinder 1 and the close-fitting metallic spacer 3 are welded together. A desired spacing and relationship between the grid aperture 11 and the cathode emitting face 31 is fixed in this manner.

Changes in temperature may cause warpage of the electrodes. Since both grid end wall 9 and the spacer flange 2-3 remain in direct contact and respond to warpage as an integral structure, changes in temperature do not effect their spacing. This construction of the grid-cathode unit affords a substantially constant spacing and alignment of the grid aperture 11 relative to the cathode emitter.

In another embodiment of the invention, illustrated in FIGS. 4 and 5, the assembly comprises a grid cylinder 47, a cathode 49, a ceramic spacer or disk 51, and a metallic retainer ring 53. The cathode 49 is substantially the same as cathode 7 shown in the above embodiment.

The ceramic disk 51 has three gradient portions or ramps 55 on one surface. These ramps are similar in structure to the ramps 25 described above, but may be metallize'd to provide a smooth, uniform surface for allowing the bosses 13 of the grid cylinder 47 to slide freely on the ramps 55. The other side of the disk 51 has a pair of spaced slots 57 which in one form may be two rectilinear grooves 180 apart.

The cathode 49 is positioned within a central aperture 59 of the ceramic disk 51 and is supported by peripheral beads 61 pressed out of the cathode cylinder wall into contact with opposite surfaces of the ceramic disk 51. The ceramic disk 51 serves as support structure for supporting the cathode 49 relative to the grid cylinder 47.

The metallic retainer ring 53 is a metallic annulus which snugly fits into the grid cylinder 47, and which may freely be moved against the grid cylinder wall. On one surface, the retainer ring 53 has a pair of protuberances 65 which may be tightly fitted into the slots 57 of the ceramic disk 51 to allow a close engagement of the retainer ring 53 and the disk 51. On the other annular surface of the retainer ring 53, there are two spaced slots 67 into which a tool, such as a mandrel 43, may be inserted.

in manufacture, the ceramic disk 51 supporting the cathode 49 is interlocked with the retainer ring '53 by meansof the disk slots 57 and the corresponding retainer protuberances 65. The cathode 49 and ceramic disk 51 are inserted into the grid cylinder '47 with the cathode emitter 63 facing the grid aperture. The retainer 53 is next inserted into the grid cylinder 47 so that the protuberances 65 engage the slots 57 of the ceramic disk 51. The metallized ramps 55 of the ceramic spacer 51 engage and grid bosses 13. The mandrel 43 is linked with the retainer slots 67 and rotated slowly, thus rotating the retainer ring 53 and the attached structure which includes the ceramic disk 51 and the cathode 49. The same methods of measuring the grid to cathode spacing, as described above, may be employed. The rotation of the ceramic disk 51 while the ramps 55 contact the bosses 13 moves the ceramic disk 51 with the cathode 49 towards or away from the grid aperture 11 depending-upon the direction of rotation. The spacing from cathode to grid is thus adjusted to a desired distance. The metallic grid cylinder 47 and the metallic retainer ring 53 are then fastened, as by welding, to permanently fix the cathode 49 with relation to the grid 47 I According to this invention, a fully adjustable control of grid to cathode spacing during assembly is provided. A cathode assembly is provided which is free floating with respect to the grid aperture. The simplified design and construction lends itself readily to automatic assembly, with a resultant saving in manufacturing time and cost. Better operating efiiciency of the grid-cathode assembly in an electron gun of a cathode ray tube is also provided.

It should be understood that the scope of the invention encompasses the use of any number of grid end wall bosses for engagement with a corresponding number of ramps for space adjustment. Three ramps and corresponding bosses, as illustrated, insures proper alignment. The gradient portions need not be in ramp design, but may take another form, such as studs of varying height. The bosses, described as elongated in the above examples, may be dimples which are circular or rectilinear.

What is claimed is:

l. A cathode grid assembly for an electron gun including a tubular cathode closed at one end and having an emitting surface on said closed end, a tubular grid having an apertured transverse wall adjacent said emitting surface, and tubular supporting means insulatingly supporting said cathode within said grid, said grid and said tubular supporting means having co-operating means on adjacent surfaces thereof for providing a spiral action relative to each other upon relative rotation for adjusting the spacing between the emitting surface in said cathode and said apertured transverse wall.

2. A grid cathode assembly for an electron gun comprising a grid cylinder with an apertured end wall, a cathode having an emitting face adjacent the aperture in said end wall, and means supporting said cathode within said grid cylinder, said supporting means having a number of ramps, said grid end wall having a number of spaced bosses in engagement with said ramps whereby upon relative rotation of said cathode with respect to said grid cylinder the spacing between said cathode and said grid dome is adjusted.

3. A grid-cathode assembly for an electron gun com prising a grid cylinder with an apertured end wall, a cathode having an emitting face, and a spacer cylinder supporting said cathode within said grid cylinder, said spacer cylinder having a predetermined number of ramps on one surface, said grid end wall having a number of spaced projections corresponding to said ramps, said spacer cylinder being adapted to be rotated with respect to said grid cylinder to provide spacing adjustment between said grid end wall and said cathode emitting face.

4. A grid-cathode assembly for an electron gun com prising a grid cylinder with an apertured end wall, a spacer with an annular end, and a cathode assembly, said cathode assembiy being supported by said spacer and insulated from said grid cylinder, said end wall having a number of bosses therein, said annular end having a number of ramps, said ramps and said bosses being capable of slidable engagement, means to rotate said spacer and said cathode assembly with respect to said grid cylinder when said ramps and said bosses are engaged thus displacing said spacer and said cathode assembly with respect to said grid end wall, and means to fasten said spacer in relation to said grid cylinder when a desired grid-to-cathode spacing has been effected.

5. A grid-cathode assembly for an electron gun comprising a metallic grid cylinder, a metallic spacer cylinder which closely fits into said g id Cylinder, a cath q s bly including an emitting face, and a ceramic disk having a central aperture wherein said cathode assembly is positioned, means for fastening said ceramic disk and said cathode assembly within said spacer cylinder, said grid cylinder having a closed end with a number of spaced bosses, said spacer cylinder including a flanged end, having a number of ramps, said ramps engaging said bosses, and slot means for rotating said spacer cylinder within said grid cylinder to adjust the distance between said grid aperture and said cathode emitting face, and means for fastening said cylinders in fixed relationship.

6. A grid-cathode assembly for an electron gun including a grid cylinder, a cathode, a ceramic disk and a retainer; said grid cylinder having a closed end with an aperture therein, said closed end having a number of spaced bosses, said ceramic disk having an aperture wherein said cathode is fixed, a surface of said disk having a number of gradient portions, said number of gradient portions corresponding to said number of bosses; said disk and said cathode being joined and movable as an assembly, said assembly being telescoped into said grid cylinder whereby each of said gradient portions engage a corresponding one of said bosses, said assembly being adjustably rotatable with respect to the grid aperture to vary the distance from the grid aperture to the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,157,718 Mutscheller May 9, 1939 2,345,642 Varian Apr. 4, 1944 2,380,946 Cooke Aug. 7, 1945 2,476,060 Moss July 12, 1949 2,481,648 Dehn Sept. 13, 1949 2,658,393 Woods Nov. 10, 1953 2,717,974 Wihtol Sept. 13, 1955 2,808,527 McKenzie Oct. 1, 1957 2,810,851 Johnson Oct. 22, 1957