US3569768A

US3569768A - Cathode sleeve effecting maximum heat transfer to top of cathode cap and minimum to cap wall

Info

Publication number: US3569768A
Application number: US777571A
Authority: US
Inventors: David Benda
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1968-11-21
Filing date: 1968-11-21
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09
Also published as: BE741953A; DE6944717U

Abstract

A cathode assembly for use in an electron discharge device wherein one end of the cathode sleeve is closed by a cap having electron emissive material exteriorly disposed thereon. The end portion of the sleeve underlying the sidewall of the cap is formed as a shield to provide a space between the sleeve and the cap except for limited seating and bonding contact therebetween at substantially the rim portion of the cap. Since the cathode assembly so formed provides limited heat conduction and radiation between the sleeve and the cap, the emissive cap area receives the major portion of its operational heat by direct radiation from the heater oriented within the cathode sleeve.

Description

I United States Patent 1 3,569,768

[72] Inventor David Benda 3,240,978 3/1966 Krawitz 313/337X Geneva, NY. 3,354,340 11/1961 Almer et a1. 313/82 1 9gp;- 1 5 1968 FOREIGN PATENTS l e ov. [45] Patented Man 9,1971 1,152,794 2/1958 France 313/337 [73] Assignee Sylvania Electric Products Inc. Primary Examiner-Robert Segal Attorneys- Norman J. OMalley, Cyril A. Krenzer and Frederick H. Rinn [54] CATHODE SLEEVE EFFECTING MAXIMUM HEAT TRANSFER TO TOP OF CATHODE CAP AND MINIMUM T0 CAP WALL schims 5 Drawing Figs ABSTRACT: A cathode assembly for use in an electron discharge device wherein one end of the cathode sleeve is [52] US. Cl 313/270, closed by a cap having electronicmissive material exterior), 3 {3,337 disposed thereon. The end portion of the sleeve underlying the [51] Int. Cl H01] l/94, sidewall f the cap is fol-med as a shield to provide a space J 19/48 between the sleeve and the cap except for limited seating and Fleld of Search 31 b di g t t th b l t b t ti lly th i p ti 3374313/270 of the cap. Since the cathode assembly so formed provides limited heat conduction and radiation between the sleeve and [56] References cued the cap, the emissive cap area receives the major portion of its UNITED STATES PATENTS operational heat by direct radiation from the heater oriented 3,085,175 4/1963 Knauf 313/337X within the cathode sleeve.

PATENTED MAR 9197i 37 i 35 l3 mall-m rI'I'I'nIIV/I'I I l INVENTOR. I DAVID BENDA PRIOR ART g d. 5 g ATTORNEY CATl-IODE SLEEVE EFFECTING MAXIMUM HEAT TRANSFER T T0? OF CATHODE CAP AND MINEIMUM TO CAP WALL BACKGROUND OF THE INVENTION The invention relates to electron discharge devices and more particularly to improved cathode assemblies for use in cathode-ray tubes.

Both monochromic and polychromic cathode-ray tubes conventionally employ one or more electron guns having cathodes which utilize heat responsive electron emissive materials as sources of electron beam energy. Some cathode assemblies are in the form of a one piece sleevelike structure having an integrally closed end, while other assemblies comprise a metallic sleeve whereof one end is closed by a metallic cap on which an area of electron emitting material is exteriorly disposed. Heat is supplied to the cathode by a formed heater positioned within the sleeve in a manner to promote efficient use of the heat generated.

It has been found that the cathode structure as a whole and the support means therefor function as a heat sink. The extensive contact areas between the cap and the sleeve, and the sleeve and the support means make up a comprehensive conductive thermal sink which markedly influences the efficiency of the cathode operation. This sink effect not only conducts heat away from the cathode emissive area, but the thermal effects of extremes in operating voltages are also readily conducted to the electron emissive portion. When a rise in heater voltage takes place, for example, from a normal 6.3 volts to a higher than normal voltage such as 7.0, the higher temperature of the heater is conducted from the cathode sleeve to the terminal emissive region which not only deleteriously affects stable cathode operation but also shortens operational life of the tube.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned difficulties and to provide an improved cathode assembly for an electron discharge device wherein changes in heater voltage produce limited effects on cathode emission.

Another object is to provide an improved cathode assembly for an electron discharge device wherein there is limited heat conduction between the electron emissive portion and the supporting structure.

A further object is to provide an improved cathode assembly for an electron gun of a cathode-ray tube wherein there is radiation shielding and limited contact between the cathode sleeve and the cap portion thereof.

The foregoing objects are achieved in one aspect of the invention by the provision of an improved cathode assembly of a cathode-ray tube wherein the upper sidewall portion of the cathode sleeve, that partially underlies the sidewall of the closure cap, has an exterior diameter that is less than the interior diameter of the encompassing sidewall of the closure cap. In one embodiment, the exterior diameter of the upper sidewall portion of the sleeve is achieve by externally reducing'the thickness of the sleeve material in-that portion. A transition area on the sleeve defines a continuation of the sleeve diameter provided by the full thickness of the material. With the cap fitted over the end of the sleeve in a substantially telescoped manner, the closure portion of the cap is determinately spaced from the open end of the sleeve, and the termination area of the cap sidewall is seated on the transition area of the sleeve and bonded thereto by a plurality of spaced apart welds. Thus, a cathode assembly is provided wherein the cap sidewall is spaced from and shielded by the major portion of the underlying area of the sleeve and only makes limited seating and bonding contact therewith at the transition region on the sleeve. The cathode assembly so constructed exhibits improved stabilization of operating parameters and prolonged operational life.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a prior art view illustrating in section a control grid of an electron gun of a cathode-ray tube with a cathode assembly oriented therein;

FIGS. 2, 3, and 4 are enlarged sectional views illustrating the relationship between the cathode sleeve and the closure cap for several embodiments of the invention; and

FIG. 5 is a graph illustrating the relationship of heater voltage to cathode temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.-

With reference to the drawings, FIG. 1 is a prior art view illustrating a cathode assembly 11 positioned within the control grid 13 of an electron gun of the type conventionally utilized, either singly or plurally, in cathode-ray tubes. The cathode assembly comprises a .cathode sleeve 15 having an upper sidewall portion 17, defining a top open end 18, a lower sidewall portion 19 defining a bottom open end 20, and an intermediate sidewall portion 21 therebetween. The top end 18 of the sleeve is closed by a cathode cap 23 of an electron emission promoting metal with electron emissive material 25 disposed on the exterior surface thereof. Positioned within the sleeve 15 is a formed heater 27 which provides the heat required to produce electron emission from the material 25. The cathode assembly 11 may be supported, for example, by cathode shielding means 29 which is formed for discrete attachment to the lower sidewall portion 19 of the sleeve by several spaced apart welds. The control grid and the cathode assembly support means are affixed to electron gun support beads, not shown, by attachment means 31 and 33 respectively. Thus, the cathode is mounted in a manner that the emissive material 25 is in spaced relationship with the aperture 35 provided in the end wall 37 of the grid 13. During the operation of the cathode-ray tube, the electrons emitted by the material 25 pass through the grid aperture 35 as an electron beam and thence traverse the associated gun elements, not shown, to be directed to the screen of the tube.

It is to be noted in FIG. I that the cathode cap seats on the top end 18 of the sleeve with theperipheral sidewall 39 of the cap making contiguous and extensive contact with the upper sidewall portion 37 of the sleeve thereby effecting a comprehensive heat sink relationship. As the heater 27 warms up, the heat thereof radiates to both the sleeve and the cap thereby retarding the temperature rise of the emissive portion. On those occasions when the heater is subjected to abnormally high voltages, the increased heat therefrom radiates to practically the whole of the cathode wherein it is conducted to the emissive a raising the temperature thereof higher than desired. Such is graphically illustrated in FIG. 5 wherein the temperature variation of the cathode emitting surface is related to the change inheater voltage by curve A. The slope of this curve above the normal 6.3 heater voltage is considered too steep for efficient cathode operation and prolonged operational life.

With reference to FIG. 2, there is illustrated one embodiment of the invention which overcomes the undesired temperature differential evidenced in the prior art. The cathode assembly 41 of this first embodiment is oriented within the control grid 13 in a manner similar to that described for the prior art, but the cathode assembly 41, per se, is markedly different.

The cathode sleeve 15' has the upper sidewall portion 17" of a length y which is formedof a reduced thickness of material to provide an upper portion exterior diameter n. The transition region 43 of the upper sidewall portion has a larger exterior diameter w whereat it integrally adjoins an intermediate sidewall portion 21 having an exterior diameter p. As shown, the diameters w and p are substantially equal, but it is not intended that they be limited to equality.

The cathode cap 23' is fabricated as a substantially cupshaped member having a closure portion 45 with a peripheral sidewall 47 integrally formed perpendicular thereto. The termination of the cap sidewall 47 defines the height x thereof which is greater than the length y of the upper sidewall portion 17 of the sleeve. The cap is formed to have an interior sidewall diameter m which is greater than the exterior diameter n of the upper sidewall portion 17'. Thus, when the cap 23' is fitted over the upper sidewall portion 17 in a substantially telescoped manner to a predetermined distance to provide a terminal space 2; between the top open end 18 of the sleeve and the closure portion 45 of the cap, the upper sidewall portion also provides a continuing shielding space s between the upper sidewall portion 17' and the cap sidewall 47. With the cap so fitted on the sleeve, the termination area 49 of the cap sidewall is in limited overlay relationship with the upper transition area 43 whereat at least two spaced apart jointure bonds or welds are made to provide attachment and limited contact between the sleeve and the cap.

Electron emissive material 25 is disposed in a conventional manner on the exterior surface of the closure portion 45 of the cap, and a heater 27 is positioned within the sleeve to provide the necessary heat. The cathode assembly is suitably supported as aforedescribed to properly relate the cathode emissive material thereon with the aperture 35 in the control electrode 13.

It has been found that the upper sidewall portion 17' provides both conduction and heat radiation shielding for the cathode cap. Since there is only limited contact between the cap and the sleeve at only the termination and transition areas, 43 and 49 respectively, there is also limited heat conduction between the cathode sleeve proper and the cap. By this construction, the extensive heat sink effects, so prominent in the prior art, are drastically reduced. With reference to FIG. 5, curve B illustrates a much reduced temperature change for the same variation in heater voltage. The invention changes the heat sink affect on the emitting surfacesince the cap receives most of its emitting heat as direct radiation from the heater and a much less amount as conduction from the sleeve. Such is evidenced from curve B, wherein it is noted that the cap heats up more quickly initially since the loss of heat therefrom to the cooler sleeve is limited, and conversely, at extreme operation conditions the hot sleeve does not pump additional extra heat into the cap.

A second embodiment of the invention is illustrated in FIG. 3 wherein the upper sidewall portion 17' of the sleeve has an exterior diameter which decreases in a sequentially symmetrical manner from the upper transition region 43' to a value of n at the top open end 18' of the sleeve. The cap 23 is substantially as shown and described for the first embodiment. While the spacing s between the cap and the upper sidewall portion is of diametrical increasing value it joins with terminal spacing z to provide the beneficial limited contact between the cap and the sleeve at the terminal area 49.

A third embodiment of the invention is shown in FIG. 4. The cathode sleeve is substantially like that illustrated in FIG. 1 whereof the exterior diameter of the upper sidewall portion p is substantially equal to the exterior diameter w of the sleeve transition area 44. The cap portion 24 has a sidewall 47' with the interior diameter m being greater than the sleeve exterior diameter p to provide the space s therebetween. The termination 49' of the cap sidewall is formed as an interiorly protruding rim having an interior diameter w of a value to provide seating and limited bonding of the rim on the exterior surface of the sleeve transition area 44.

As a modification of the third embodiment, the cap sidewall termination 49 is modified and formed as a plurality of interiorly protruding symmetrically arranged rim elements. These several protrusions provide an effective interior diameter w of a value to effect limited seating and bonding contact of the rim resultant limited heat conduction and radiation between the sleeve and the cap minimizes the effect of heater voltage variations on the cathode temperature thereby greatly enhancing cathode operating parameters and lengthening operational life. v I

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Iclaim:

1. In an electron discharge device, a cathode assembly oriented relative to a control grid electrode comprising:

a conductive cathode sleeve having top and bottom open ends defined by upper and lower sidewall portions with an intermediate sidewall portion therebetween;

a cathode cap fabricated as a substantially cup-shaped member formed to fit over the upper sidewall portion of said sleeve in a substantially telescoped spaced-apart manner to provide a closure portion having a peripheral sidewall integrally formed substantially perpendicular thereto with the termination thereof defining a height greater than the length of said sleeve upper sidewall portion, said cap having an interior sidewall diameter greater than the exterior diameter of said sleeve upper sidewall portion to provide a shielding space therebetween, the interior surface of said closure portion being substantially spacedly removed from the exterior surface of said upper sidewall portion and narrowly spaced from the top open end of said sleeve to effect both conduction and heat radiation shielding for said cathode cap, the termination area of said cap sidewall being substantially the only area of said cap in limited overlay contact relationship with said sleeve upper sidewall portion whereat at least two spaced apart jointure bonds are effected to provide attachment and limited contact between said cap and said sleeve;

electron emissive material disposed on the exterior surface of said cap closure portion; A

a heater positioned totally within said sleeve; and

cathode assembly support means formed to provide positioning of said sleeve in a manner that said cathode emissive material thereon is spacedly related to said control grid electrode.

2. A cathode assembly according to claim l wherein said upper and intermediate sidewall portions have an upper transition area therebetween, and wherein the exterior diameter of said upper sidewall portion is less than the exterior diameter of said upper transition area.

3. A cathode assembly according to claim 1 wherein the exterior diameter of said upper sidewall portion substantially equals the exterior diameter of the transition area between said upper and intermediate sidewall portions, and wherein said cap sidewall termination is formed as an interiorly protruding rim having an interior diameter of a value to effect seating and limited bonding of said rim on the exterior surface of said upper sidewall portion at substantially the transition area thereof to provide spacing between the interior of said cap sidewall and the exterior of said sleeve upper sidewall portion.

4. A cathode assembly according to claim 1 wherein the exterior diameter of said upper sidewall portion substantially equals the exterior diameter of the transition area between said upper and intermediate sidewall portion, and wherein said cap sidewall termination is formed as a plura ity of interiorly protruding symmetrically arranged rim elements to provide an effective interior diameter of a value to effect limited seating and bonding of said rim elements to portions of the exterior surface of said transition area to provide spacing terior diameter of said upper sidewall portion decreases in a between the interior of said cap sidewall and the exterior of sequential symmetrical manner from the upper transition area said sleeve upper sidewall portion. between said upper and intermediate sidewall portions to said 5. A cathode assembly according to claim 1 wherein the extop open end. 7

Claims

1. In an electron discharge device, a cathode assembly oriented relative to a control grid electrode comprising: a conductive cathode sleeve having top and bottom open ends defined by upper and lower sidewall portions with an intermediate sidewall portion therebetween; a cathode cap fabricated as a substantially cup-shaped member formed to fit over the upper sidewall portion of said sleeve in a substantially telescoped spaced-apart manner to provide a closure portion having a peripheral sidewall integrally formed substantially perpendicular thereto with the termination thereof defining a height greater than the length of said sleeve upper sidewall portion, said cap having an interior sidewall diameter greater than the exterior diameter of said sleeve upper sidewall portion to provide a shielding space therebetween, the interior surface of said closure portion being substantially spacedly removed from the exterior surface of said upper sidewall portion and narrowly spaced from the top open end of said sleeve to effect both conduction and heat radiation shielding for said cathode cap, the termination area of said cap sidewall being substantially the only area of said cap in limited overlay contact relationship with said sleeve upper sidewall portion whereat at least two spaced apart jointure bonds are effected to provide attachment and limited contact between said cap and said sleeve; electron emissive material disposed on the exterior surface of said cap closure portion; a heater positioned totally within said sleeve; and cathode assembly support means formed to provide positioning of said sleeve in a manner that said cathode emissive material thereon is spaCedly related to said control grid electrode.

2. A cathode assembly according to claim 1 wherein said upper and intermediate sidewall portions have an upper transition area therebetween, and wherein the exterior diameter of said upper sidewall portion is less than the exterior diameter of said upper transition area.

4. A cathode assembly according to claim 1 wherein the exterior diameter of said upper sidewall portion substantially equals the exterior diameter of the transition area between said upper and intermediate sidewall portion, and wherein said cap sidewall termination is formed as a plurality of interiorly protruding symmetrically arranged rim elements to provide an effective interior diameter of a value to effect limited seating and bonding of said rim elements to portions of the exterior surface of said transition area to provide spacing between the interior of said cap sidewall and the exterior of said sleeve upper sidewall portion.

5. A cathode assembly according to claim 1 wherein the exterior diameter of said upper sidewall portion decreases in a sequential symmetrical manner from the upper transition area between said upper and intermediate sidewall portions to said top open end.