US2905848A - Cathode ray tube gun structure - Google Patents

Description

Sept. 22, 1959 Filed Oct. 18, 1957 60/E00/V E. SPENCER United Sttes CATHODE'RAY TUBE GUN STRUCTURE Application October 18, 1957,'Serial No. 691,026

.Claims. (Cl.'313-82) This invention relates ,generally to electron discharge devices, and more particularly to improved electrode mounting means associated therewith.

Conventional cathode ray tubes generally employ an electron gun assembly having a plurality of tubular electrodes mounted in spaced relation along a common axis, the assembly typically including a tubular filamentary type cathode, a control grid, an accelerating screen grid electrode and a high voltage anode, the entire gun structure being mounted in the neck portion of a cathode ray tube envelope.

The type of cathode employed in such tubes is of the indirectly-heated, oxide-coated variety, consisting of a small metal tube closed at one end, usually made of nickel or a nickel alloy, and having on the outer surface of the closed end a deposit of electron emissive material, the material being heated, during tube operation, to thermionic temperatures by a helically wound filament or heater inserted within the cathode sleeve.

Cathode ray tube gun structures made in accordance with standard practice and embodying the general arrangement of electrodes discussed above have been found generally satisfactory. There are, however, certain disadvantages inherent in this type of electrode gun struc ture. These disadvantages, or limitations, are particularly manifest in fields of application where compactness and low power consumption are of principal concern, as for example, in the manufacture of portable television apparatus.

The cathode normally employed in cathode ray tubes, consumes considerable power during operation. Thisis principally brought about by the fact that the electron emitting surface of the cathode must be brought to thermionic temperatures by heat conducted to it through the cylindrical walls of the tubular cathode. This mode of operation, results in considerable waste of energy through both radiation to cooler surroundings and conduction away from the cathode through the supporting structure associated therewith. This thermally ineflicient arrangement results in a considerable loss of power from the tube system and is particularly objectionable, as indicated above, in situations where minimum power consumption is a primary consideration. Moreover, the thermal inetficiency of this type cathode construction is accentuated by the fact that to provide sufiicient cathode end area on which to deposit the requisite amount of electron emissive material necessitates a cathode sleeve of relatively large diameter. This requirement gives rise to use of a cathode having an extensive surface area, a configuration poorly adapted to this type of operation and one whose losses through radiation are excessive. To supply this type cathode with sufficient power to actuate the electron emissive material requires a heater filament of considerable lengthand consequently a cathode of suflicient depth .to receive it, thereby materially increasing the overall length of the cathode ray tube gun structure.

atent Another objectionable feature, arising out of the concentric .telescoping arrangement of the cathode and control grid, is the necessity of using a plurality of auxiliary members to bring about acceptable interelectrode'alignment. To keep the accumulated error of such a composite assembly within acceptable limits requires that the component parts be dimensioned to exceedingly close tolerances. This technique, while producing an acceptable product, isboth expensive and time consuming.

Moreover, accurate axial spacing between the cathode and grid, in contradistinction to axial alignment, is additionally complicated by the fact that the thermal gradients, induced by thermionic heating of the cathode element in the manner discussed, produce corresponding changes in the cathodes length affecting its spacing from the control grid. This variation in spacing results in'a fluctuating cross-over point adversely affecting spot size.

In addition to proper .cathode-to-grid spacing .it is equally important to the proper functioning of the cathode ray tube, that the electron beam apertures of the control grid and its immediately adjacent accelerating electrode be in precise axial alignment. Any deviation from true alignment results in a condition known as coma, seriously impairing the efiectiveness of the electron optical focusing system. The conventional arrangement of electrodes does not admit of a simple method of electrode alignment but on the contrary requires elaborate jigging to obtainthe registration necessary to insure acceptable focusing of the electron Writing beam.

In the television art in general there has been .an increasing demand for more compact television picture tubes of larger fluorescent screen area. This trend, while predicated .in large degree on aesthetics has certain more tangible causes, one of which is the production of a cheaper television set through decrease in the .size of the required television cabinet and other complementary equipment. Attempts to compress the overall length of the conventional gun assembly, in order to reduce costs and create a more aesthetically pleasing product have to date been largely unsuccessful.

It is accordingly an object of the invention toprovide a cathode ray tube gun structure of considerably shorter length than conventional assemblies, thereby permitting the fabrication of a more compact cathode ray tube.

It is another object of this invention to providea unique cathode ray tube gun structure facilitating the alignment of the electron beam apertures of the control grid and first accelerating electrode.

It is a general object of this invention to provide a novel electrode mounting structure which overcomes the limitations of prior art devices.

The aforesaid and other objects within contemplation will be more readily understood by reference to the following detailed description and drawing, in which:

Figure 1 is a fragmentary elevational view of the neck portion of a cathode ray tube embodying structure of the present invention;

Figure 2 is an exploded view of a portion of the gun assembly depicting the interrelation of the parts;

Figure 3 is a perspective showing of the compactly integrated electrode assembly;

Figure 4 is an illustration of one form of apparatus adapted for use in bringing about axial alignment of the electron beam. apertures; and

Figure 5 is a phantom showing of the cathode-grid module depicting certain structural innovations.

This invention, stated generally, relates to novel electro'cle mounting means facilitating precise interelectrode registration and permitting the incorporation, within a cathode ray tube, of a cathode disposed in a plane transverse the tube axis. The accurate spacing required between cathode and control grid is insured by the simple expedient of inserting the cathode sleeve and pre-formed vtab portions of a box-like grid into suitable aligned apertures punched in sheet-like insulating support members .design still further provides means for varying tube transconductance through a unique method of grid spacing.

Still another aspect of this invention relates to means for axially aligning the electron beam apertures of the control grid and first accelerating electrode (screen grid). This is accomplished in a manner unique to the television art and comprises punching a set of orienting holes, conveniently of equal diameter, into the electron beam apertured plate of each electrode, the hole pattern in each case being identically positioned in relation to its respective electron beam aperture.

This technique facilitates a simplified assembling procedure, which consist of merely slipping the orienting holes of each member over appropriately disposed prongs of suitable diameter which serve to impale the members in precise registration. To insure minimal deviation from true axial alignment the orienting prongs may be slightly tapered in order to compensate for slight deviations in the diameter of the orienting holes. Once located, the electrodes are maintained in precise oriented relation by being joined to the cathode-control grid module, as for example by spot welding.

Now making detailed reference to the drawing, Figure 1 shows a cathode ray tube gun assembly 9 comprising a high voltage anode 10, screen grid 11, and the cathodecontrol grid module 12, the high voltage electrodes 10 and 11 being mounted in conventional fashion on the glass beading 13. This invention relates to unique electrode mounting structure comprising the screen grid 11 and its cathode-control grid appendage 12.

To facilitate a clearer understanding of this composite assembly the exploded perspective shown in Figure 2 has been employed, which in conjunction with Figure 3 clearly depicts the relative disposition and interrelation of the parts of the assembly.

This assembly comprises the insulating mica support members or plates 14 disposed in parallel spaced relation and adapted to support, by means of suitable positioned apertures, a tubular cathode 15, a box-like control grid 16, and channel shaped side rails 17. To aid in installing the cathode, the tubular sleeve is dimpled in regions 18 and 19, these prominences serving to provide a locating stop when inserting the cathode into the supporting aperture 20. The cathode is retained in this oriented position by later spot welding a conductor strap 21 to that portion 22 of the cathode sleeve projecting beyond the outer surface of the mica support member 14, the cathode when completely installed being freely suspended between the mica support members 14 in a plane transverse the electron beam axis of the cathode ray tube. The cathode is aligned in back of the grid aperture 23, with the electron emitting surface 24- of the cathode in confronting relation thereto. Embracing the cathode is the box-like control grid 16, this member being located in accurate spaced relation to the cathode by positioning the grid locating tabs 25 within their respective mating apertures 26 in the insulating support members 14. This structure is desirably of box-like configuration to increase its structural rigidity. Moreover, because of the tendency of the knife-like edge portions of the tabs to cut into the mica support, it is desirable, in order to prevent dislocation of the grid structure, to have flat portions of the positioning tabs 25 and 25a in spaced opposed relation as shown in Figure 3. The preferred box-like configuration of the control grid conveniently provides this desired orientation of tab members.

Bounding the control grid 16, but electrically insulated therefrom, are the side rails 17, these members preferably being made of electrically conductive material and supported by the mica members 14 in a manner similar to that described for the control grid 16. By the simple expedient of bending or off-setting certain of the locating tabs 28, to prevent their withdrawal from the mica support plate 14, these members serve to lock the assembly into a composite unitary structure. The side rails are then joined to the screen grid 11, as by spot welding, after alignment of the electron beam apertures by means hereinafter described.

The spacer plate 27 facilitates juncture of the cathodecontrol grid-module to the screen grid. electrode and also provides accurate, simplified means for varying the spacing between the screen and control grids thereby providing a convenient method of varying tube transconductance. This plate is desirably configured to bridge the modular assembly in such manner that the screen grid 11, on which the plate is mounted, as by spot welding is suspended from the upper flanges 29 of the side rails 17, in spaced relation to the control grid 16, the axial spacing between these members being accurately determined by the thickness of the spacer plate 27.

The next step in fabricating the electrode assembly is to bring the electron beam apertures 23 of the screen grid 11 and control grid 16 into precise axial alignment.-

7 Both these members are provided with orienting holes 30 punched into their confronting surfaces, these holes preferably being punched by the same die used in piercing the electron beam apertures. The box-like grid structure 16 has an additional pair of holes 31, shown in Figure 5, punched in its lower surface 32 to facilitate insertion of the orienting prongs 33 into and through the box-like structure. A preferred method of assembly is to first position the module 12 on the orienting prongs 33 in the manner shown in Figure 4, followed by similar impalement of the screen grid 11. -Once positioned on the orienting prongs 33 the electron beam apertures 23 are automatically brought into alignment. With the members thus aligned the spacer plate 27 is spot welded to the flanges 29, producing a composite unitary electrode assembly. Screen grid 11, prior to alignment of the control grid 16, may be conveniently staked, along with the high voltage anode 10, to the insulating beads 13, the cathode-grid module being subsequently appended to this high voltage electrode assembly in the manner described.

The orienting prongs 33, in order to insure proper alignment, should be of sufficient thickness to resist distortion during assembly. This requirement dictates the diameter of the orienting holes and often necessitates the use of a relatively large size hole as compared to the diameter of the electron beam aperture. Under certain tube operating conditions electron leakage through these holes results in poor picture definition and in severe cases produces what is knownrin the television art as ghosts. To prevent this phenomenon, orienting hole shields 34, of the general configuration shown in Figure 5 may be employed. These shields are mounted against the inner surface 35 of the control grid side walls and effectively insulate the orienting holes 30 and access holes 31 from the electron stream while permitting full utilization of the holes for purposes of orientation. This shielding may of course be accomplished in a number of ways, for example, by plugging the orienting holes after assembly, but the most satisfactory technique, from the standpoint of both cost and ease of assembly, is that described. 3 a g It has been found expedient in certain applications, from both the standpoint of structural stability and ease of making electrical connections to the electrode assembly, to employ a reenforcing strap 35 (Figure 5) positioned against the under surface of the assembly 112. The strap is spot welded to the side rails 17 and maintained in spaced relation to the control grid 16, the upstanding terminal portions 36 providing convenient means for electrically connecting the screen grid 13 to the connecting pins 13, in the manner clearly shown in Figure 1.

While a preferred embodiment, illustrative of the apparatus of the present invention has been depicted and described, modifications may be made therein Without departing from the scope of the present invention. It will be understood, therefore, that such changes and modifications are contemplated as come within the purview of the appended claims.

I claim:

1. In cathode ray tube gun structure, a pair of sheetlike support members of electrically insulative material having pre-punched apertures in which an array of electrode elements are supported in predetermined fixed orientation, said array including an elongated cathode element disposed transverse the electron beam axis of said structure; an electroniapertured, box-like control grid encircling said cathode element; and a pair of spaced electrically conductive side rails insulated from said cathode element and grid, said side rails spanning said sheet-like members and having end portions mounted in the latter, and said side rails forming an interconnecting bridge between the mentioned cathode-grid assembly and accelerating high voltage electrode means, said high voltage electrode means being carried by said side rails in spaced confronting relation to said grid to form a rigid, unitary gun structure of reduced length Whose intere'lectrode spacing is fixed by said apertured support members.

2. In cathode ray tube gun structure, a pair of sheetlike support members of electrically insulative material having pre-punched apertures in which an array of electrode elements are supported in predetermined fixed orientation, said array including an elongated cathode element disposed transverse the electron beam axis of said structure; an electron-apertured, box-like control grid encircling said cathode element; and a pair of electrically conductive, generally C-shaped side rails insulated firom said cathode element and grid and forming an interconnecting bridge between the mentioned cathode-grid assembly and accelerating high voltage electrode means, said high voltage electrode means including a spacer plate fixedly attached to side rails and spaced in confronting relation to said grid to form a rigid, unitary gun structure of reduced length Whose interelectrode spacing is fixed by said apertured support members.

3. In cathode ray tube gun structure, a pair of sheetlike support members of electrically insulative material containing a pro-punched pattern of apertures captively supporting an array of electrode elements in predetermined, fixed alignment, said array comprising: a tubular cathode sleeve disposed in a plane transverse the electron beam axis of said structure; an electron-apertured, box-1ike control grid encircling said cathode sleeve,

spaced therefrom and electrically shielding said cathode from extraneous positive voltage gradients; and a pair of electrically conductive channel members flanking said grid and cathode, insulated therefrom and bridged by a centrally apentured, electrically conductive, plate-like, electrodeespacmg member on which there is mounted an accelerating electrode having a centrally cup-shaped portion extending through said central aperture into confronting spaced relation with said grid, the composite assembly forming an extremely compact, unitary electron gun structure in which interelectrode spacing is rigidly fixed by said pie-punched support members.

4. In cathode ray tube structure, a pair of sheetlike support members of electrically insulative material having pro-punched apertures in which an array of electrode elements are supported in predetermined fixed orientation, said array including an elongated cathode element disposed transverse the electron beam axis of said structure; an electron-apertured, box-like control grid encircling said cathode element; and a pair of electrically conductive side rails insulated from said cathode element and grid and forming an interconnecting bridge between the mentioned cathode-grid assembly and an accelerating high voltage electrode, said high voltage electrode being mounted on a separately formed electrically conductive plate-like member carried by said side rails and supporting said electrode in spaced confronting relation to said grid to form a rigid, unitary gun structure of reduced length whose interelectrode spacing is fixed by said apertured support members.

5. In cathode ray tube gun structure, a pair of sheetlike support members of electrically insulative material having pre-punched apertures in Which an array of electrode elements are supported in predetermined fixed orientation, said array including an elongated cathode element disposed transverse the electron beam axis of said structure; an electron-apertured, box-like control grid encircling said cathode element; and a pair of electrically conductive side rails insulated from said cathode element and grid and forming an interconnecting bridge between the mentioned cathode grid assembly and an accelerating high voltage electrode, said high voltage electrode being anchored to an electrically conductive plate-like member secured to said side rails and supporting said electrode in spaced confronting relation to said grid to form a rigid, unitary gun structure of reduced length whose interelectrode spacing is fixed by said apertured support members.

References Cited in the file of this patent UNITED STATES PATENTS 2,174,853 Bowie Oct. 3, 1939 2,508,979 Van Gessel May 23, 1950 2,608,744 Starre et al. Sept. 2, 1952 2,728,007 Van Ormer Dec. 20, 1955 2,773,212 Hall Dec. 4, 1956 FOREIGN PATENTS 707,064 Great Britain Apr. 14, 1954 753,507 Great Britain July 25, 1956

Images