US3558965A

US3558965A - Cathode for television tube and method of making

Info

Publication number: US3558965A
Application number: US672272A
Authority: US
Inventors: Laszlo Javorik; David Y Stowell; Dennis M Healy
Original assignee: National Video Corp
Current assignee: National Video Corp
Priority date: 1967-10-02
Filing date: 1967-10-02
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26

Abstract

Cathode for television tube and method of making wherein a generally circular ceramic body is employed to support a cathode disc in predetermined relation to the G-1 control grid.

D R A W I N G

Description

United States Patent Inventors Appl. No.

Filed Patented Assignee CATI-IODE FOR TELEVISION TUBE AND METHOD References Cited UNITED STATES PATENTS FOREIGN PATENTS Canada 313/27OX 313/270X 313/270X 3 l 3/337X MAKING Z'QZQYJFLESZZ 0 D I F. 3 Claims 7 rawmg Artgrney-Dawson, Tilton, Fallon & Lungmus US. Cl 313/270, 313/337 Int. Cl H0 lj l/94, ABSTRACT: Cathode for television tube and method of mak- HOlj 19/48 ing wherein a generally circular ceramic body is employed to Field of Search 313/270, support a cathode disc in predetermined relation to the G 1 337 control grid.

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CATI IODE FOR TELEVISION TUBE AND METHOD OF MAKING SUMMARY OF INVENTION The invention has particular application to impregnated cathode discs. These ordinarily include a sintered tungsten matrix impregnated with the usual electron emissivc compounds of aluminum, barium, calcium, strontium, etc. A number of problems are encountered in fabricating assemblies of this type. Such include maintaining a small fixed distance from the top of cathode and the bottom of the -1 control grid; firmly fixing the cathode in place to prevent microphonics, and thirdly, to effectively utilize the head quanta involved-such as minimizing losses, maximizing the use of electrical current input, etc.

Conventionally, cathodes are mounted on relatively long cylindrical sleeves which are heated throughout their entire length, producing big heat losses through radiation and through conduction through associated mounting means, not withstanding the fact that only the small top portion of the cathode is the part utilizing the heat for electron emission. Such a design possesses another disadvantage in that the main means of heat flow from the filament to the cathode sleeve is by radiation, requiring higher filament temperatures with the attendant disadvantages of less life for the filament and longer warmup time. Such a construction makes difficult the maintenance of the critical cathode to grid distance by simple mechanical means. With cathodic discs of the character referred to, gas poisoning is substantially minimized but the possibility of metal poisoning is present so that relatively exotic metals are required for association with the cathode material-such as molybedenum and tantalum. The invention avoids the foregoing difficulties and disadvantages and provides a novel and efficient cathode mounting.

The invention is described in conjunction with the accompanying drawing in which:

FIG. I is a fragmentary sectional view through a cathode ray tube gun portion constructed in accordance with the teachings of this invention;

FIG. 2 is a top-plan view of the structure seen in FIG. 1 with portions broken away and shown in section;

FIG. 3 is a fragmentary sectional view of a cathode in the process of fabrication according to the teaching of the inventlon;

FIG. 4 is a fragmentary sectional view showing apparatus for constructing a modified fon'n of cathode;

FIGS. 5 and 6 are fragmentary section views of cathode mounting means embodying the teachings of the invention; and

FIG. 7 is a fragmentary enlarged view of FIG. 3.

In the illustration given and with reference to FIGS. 1 and 2, the numeral 10 designates generally the G-l control grid which is seen to be a cup-shaped metal body. This necessarily includes a base 11 and cylindrical sidewall 12. The central portion of the base 11 is apertured as at 13 to provide for the electron emission.

The electron emission comes from an impregnated cathode disc 14 (seen in FIG. I immediately below but spaced from the base 11 of the rib 10). The means for supporting the disc 14 includes a ceramic element generally designated 15.

The ceramic element 15 is also cup-shaped having a base 16 and generally cylindrical sidewall 17, being telescopically received within the cup-shaped control grid 10. The portion of the base 16 of the ceramic element 15 is recessed as at 18 for receiving the previously referred to cathode disc 14. In the illustration given, the base 16 of the ceramic element 15 is equipped with a plurality of upstanding annular ribs or spacer means 19 (see particularly FIG. 2) for maintaining the base ll of the grid 10 to a spaced distance away from the cathode disc 14. Current to the cathode 14 is provided by means of a molybdenum or like refractory metal lead 20 which is seen to extend through an opening 21 (see FIG. 2) in the ceramic element 15. Further, the ceramic element 15 is provided with a hollow interior as at 22 (designated only in FIG. I) for the receipt of a heater generally designated 23 and which is encapsulated or glued in place immediately under the cathode I4 by means of a suitable cement 24. Such a material may be aluminum oxide disposed in a nitrocellulose carrier which is used to advantage in certain instances to insulate the filament.

In the structure just described, the assembly of the ceramic element l5, cathode l4, and heater 23 is inserted into the control grid I0 after which, ledges or tabs 25 are developed from the interior sidewall I2 of the grid 10 to provide both a support and stabilizing function for the ceramic element I5. It will be appreciated, for example, that the ceramic element 15 itself may be equipped with circumferentially spaced apart ribs or even an annular flange as at I26 in FIG. 3 so that the tabs 25 of FIG. I may assume the configuration designated 125 in FIG. 3. It will also be appreciated that the upstanding rib I9 in FIG. I and 2 may be made in the form of separate spacers as contrasted to being integrally formed with the ceramic body 15. Still further, it is within the purview of the invention to provide depending prongs or tabs from the base 11 of the rib 10 to effect the same spacing function provided by the ribs 19. In any event, there is provided axially oppositely acting means in the form of ribs 19 and tabs 25 which serve to both support and immobilize the ceramic body carrying the cathode I4 within the grid 10. Also, we provide means either in the form of the tab portion 26 or the integral ribs 126 to laterally stabilize, i.e., in a radial fashion the ceramic body 15 within the grid 10.

In the development of the assembly made up of elements l4, l5 and 23, we utilize to advantage the structure pictured in FIG. 3. In FIG. 3 the control grid is used as a support surface or jig for arriving at the proper distance between the cathode and grid. A fixture generally designated 127 is put on the inner face llla of the base 111 of the grid. The fixture 127 is itself a disc carefully dimensioned and equipped with a stem portion 128 which extends through the aperture electron emission opening 113. In the process for developing the cathode assembly of FIG. I, the fixture 27 is first installed within the grid 110. Thereafter the cathode disc 114 is mounted atop the fixture 127 and the ceramic body generally designated 115 is mounted as shown in FIG. 3. Thereafter the heater 123 is supported by means (not shown) within the cavity I22 and further the necessary cathode lead is threaded through the opening 121 and also supported in the condition seen in FIG. 3. Thereafter the cement material is poured into the cavity 122 and by virtue of passing through the aperture 121, enters the space 129 to integrate the

elements

115, 114 and 123. If, as in contemporary practice, the spacing between the top of the cathode disc 14 and the underside of the base 11 of the grid 10 is to be 0.006 inches, it it possible to achieve this by using a fixture having a disc portion of that dimension and without having to carefully control the height of the ribs 119. Once the assembly depicted in FIG. 3 is achieved, the tabs 125 can be folded back into conforming relation with the sidewall 112 of the rib 110 after which the integrated assembly can be removed from the control grid body 110. Thereafter the fixture 127 is disassembled from the control grid I10 and the control grid once again ensleeved over the ceramic body 115 and the tangs I25 returned to the condition pictured in FIG. 3.

With the construction just described, it will be apparent that not only are heat losses minimized by the use of the

ceramic body

15 or 115 as the case may be, but also that the heating element is positioned in the most advantageous place for effecting efiicienttransfer of heat to the cathode 14. Further, by virtue of using, in effect, a floating cathode means of fabrication, we avoid previously encountered difficulties in the fabrication of the overall cathode-grid assembly.

A variation of the jig-fixture arrangement in FIG. 3 is presented in FIG. 4. In FIG. 4, the numeral 227 designates generally a cathodelsupport surface which has a portion 230 formed as a well to receive the conventional tubular cathode support 231. The support or shank 21" may be equipped beforehand with the cathode disc or deposit 214. The distance between the bottom of the well 230 and the surface 227 is carefully regulated so as to develop a precise position for the ceramic support generally designated 215. In the illustration given in FIG. 4, we use a ceramic washer which is placed over the shank 231 and is installed firmly on the surface 227. A metallic collar or washer 232 is then placed over the shank and pressed firmly onto the ceramic washer 215 and it then spot-welded to the shank 231. The unit thus achieved is then removed from the fixture 227 and a second collar or washer is positioned snugly on the other side of the ceramic disc and spot welded to the shank.

A variation in this procedure may be effected by using the arrangement depicted in FIG. 5 wherein the ceramic washer generally designated 315 is provided in two semicircular parts, each part being equipped with a ring fragment 332 having a channel shape in radial section. Additionally, the ring fragment 332 is equipped with prongs as at 333 for frictionally engaging the periphery of the shank331 so as to aid in spot welding or force fitting and substantially reduce conductive heat loss from the cathode.

In still another version, as seen in FIG. 6, the ceramic body 415 is again provided in halves but at least one half is equipped with a pin as at 434 for engagement with the periphery of the shank 431 so as to additionally provide a means for electrical connection as well as stabilizing (pinpointing) the shank relative to the ceramic support.

Finally, to minimize radiative heat losses from either a filament or a cathode shank, cylinders of thin, highly reflecting metal, placed around the filament or shank but not in touch with them, serve very well as radiation shields, returning significant amounts of heat back to the shank or filament and thereby reducing the total power needed to raise the cathode to temperature.

It will be seen that in certain instances a groove 130 may be provided in the ceramic body 115 between the disc 114 and the spacer means 119. Optimumly, this groove is developed on by those skilled in the art without departing from the spirit and scope of the invention.

We claim:

1. A cathode structure for cathode ray tube comprising a cup-shaped metallic grid having a cylindrical sidewall and a flat bottom defining a central aperture; a cup-shaped ceramic body within said grid and having a cylindrical side portion coaxial with the sidewall of said grid, the base of said ceramic body providing a cavity facing said aperture of said grid and adjacent thereto, said base further including integral rib means engaging the bottom of said grid for holding said ceramic body at a predetermined distance therefrom, heater means fixed in the hollow of said ceramic body secured to the base thereof, a plurality of lugs extending radially inwardly of said grid and defining inclined bearing surfaces engaging the lip of said ceramic base for holding the rib means of said body in engagement with said bottom of said grid while holding said body and said grid in coaxial relation; an'electron emitter mounted in said cavity; and conductive means embedded in said ceramic body and contacting said emitter for coupling current thereto; said rib means further cooperating with said interconnecting means for stabilizing said body within said grid.

2. The structure of claim 1 in which each of said lugs has a portion adapted to bear against the cylindrical sidewall of said body to radially immobilize the same.

3. The structure of claim 1 in which said rib means includes a plurality of upstanding ring segments.

Claims

1. A cathode structure for cathode ray tube comprising a cupshaped metallic grid having a cylindrical sidewall and a flat bottom defining a central aperture; a cup-shaped ceramic body within said grid and having a cylindrical side portion coaxial with the sidewall of said grid, the base of said ceramic body providing a cavity facing said aperture of said grid and adjacent thereto, said base further including integral rib means engaging the bottom of said grid for holding said ceramic body at a predetermined distance therefrom, heater means fixed in the hollow of said ceramic body secured to the base thereof, a plurality of lugs extending radially inwardly of said grid and defining inclined bearing surfaces engaging the lip of said ceramic base for holding the rib means of said body in engagement with said bottom of said grid while holding said body and said grid in coaxial relation; an electron emitter mounted in said cavity; and conductive means embedded in said ceramic body and contacting said emitter for coupling current thereto; said rib means further cooperating with said interconnecting means for stabilizing said body within said grid.