US 3319102 A
Description (OCR text may contain errors)
May 9, 1967 J. H. JOHNSON ELECTRON GUN ASSEMBLY WITH INCREASED COOLING SURFACES Original Filed Aug. 20, 1962 INVENTOR JAY H Jam/501v mm 4% mw-fwam ATTORNEYS United States Patent ()fiice 3,3191% Patented May 9, 1967 3,319,1ti2 ELECTRUN GUN ASSEMBLY WHTH INCREASED COULHNG SURFACES by H. Johnson, Owensboro, Ky., assignor to Kentucky Electronics Inc., Owensboro, Ky., a corporation of Kentucky Griginal application Aug. 20, 1962, Ser. No. 217,790, new Patent No. 3,204,141, dated Aug. 31, 1%5. Divided and this application Nov. 2, 1964, Ser. No. 408,398 8 Claims. (Cl. 31345) This invention relates to electronic discharge devices and methods of assembly, such as a cathode ray electron tube and more particularly to electron gun structures adapted for use therein, and is a division of my copending application S.N. 217,790 filed Aug. 20, 1962, now Patent No. 3,204,141, for Electron Gun.
In electron gun structures itis desirable to provide very closely controlled inter-electrode spacings and to maintain the spacings under various conditions encountered in operation. Conventional electron guns have varying characteristics at different operating temperatures as electrode spacings are subjected to temperature differences. larly critical when low voltage cathode ray tubes are employed in transistor-operated television sets, for example.
It is very difficult to hold the spacings of electrodes Within close tolerances during assembly by conventional methods, and is also almost impossible to gage the tolerances after assembly to determine the spacings without finishing a tube and finding rejects of the entire assembly with poor emission and performance.
Thus, it is an object of this invention to provide, in the structure of an electron gun, accurate means for gaging the initial spacing of the electrodes, and means for maintaining the spacing without substantial change due to thermal expansion of the metallic electron gun parts.
Another object of the invention is to provide a control grid structure which will permit the accurate spacing of the surface of the grid and the surface of the cathode in an electron gun.
It is a further object of the invention to provide an improved control grid structure and a screen grid structure for preventing thermal expansion from varying the critical spacing between the effective surfaces of the cathode, control grid and screen grid.
It is still a further object of the invention to provide an improved construction of cathode, control grid, and screen grid assembly for low voltage cathode ray tubes permitting methods of assembling to accurate spacing tolerances and testing to assure that proper tolerances are attained.
Briefly, this novel electron gun assembly includes a cathode, first and second grids, and is suitable for a lowvoltage, low-current, transistor-operated television picture tube. A low-voltage tube requires close-r spacing of the cathode and grid surfaces of the electron gun, and the closer spacing in turn greatly increases the importance of stability of the spacing. The problem of stability of spacing is not, however, confined to low-voltage tubes. Furthermore, this novel gun incorporates features which enable operation of the gun with greatly reduced current drain. One of these features is the method of mounting the cathode sleeve cylinder and base sleeve in the ceramic disc insulator whereby there is a minimal physical thermal contact between the metal cathode structure and the ceramic insulator disc structure and thereby less heat transfer or loss from the cathode to the disc.
Another feature is the smaller beam apertures in the grids which reduce the size of the beam and the power needed to form and accelerate it. The smaller grid apertures also have the very signifisant incidental benefit of These dimensional tolerances are particuproviding a more well-defined picture through means of the sharper beam of electrons striking the face of the picture tube.
A thinner effective surface is needed on both grids in order to provide the closer spacing and smaller grid apertures necessary for a transistor operated, low-power television set. Also it is advantageous in provision of tools and dies which produce such par-ts to very close tolerances. In the subject electron gun, these surfaces are much thinner than those heretofore used. Conventionally, the walls of the grid structure are about .010 inch thick in order to provide a stable support for the effective surface. One existing method for providing a thinner effective surface is to coin the effective area immediately surrounding the grid aperture to a thinner wall thickness. The grid of the subject gun may have Wall thickness of as low as 001:.00025 which will provide a uniform end wall of that thickness. By reducing the material thickness, the tolerance on the material is reduced 50 percent which results in a more uniform wall thickness. The uniform thinness of the end wall is advantageous for closer spacing between electrodes. This grid may be fabricated from the thinner material with sufficient structural rigidity because of the corrugation around the conical surface.
Thermal stability of the grid structure is provided by the lancing around the end wall with four small equidistant lance webs which permits horizontal thermal expansion in the direction of least resistance and thereby prevents bowing of the end wall due to thermal expansion. This lan-ced grid structure also permits heat fiow from the area which would otherwise be enclosed by the grid.
The lancing also permits accurate spacing between the end wall of the first grid and the coated surface of the cathode upon assembly by the insertion and withdrawal of a precision spacer gauge.
Another feature is the corrugated surface of the grid which provides a greater surface area and, therefore, a means of greater themal radiation. It also povides gaps where the frustoconical structure is secured to the cy lindrical portion of the first grid, allowing heat flow out of the area which would otherwise be enclosed by the first grid between the end wall of the first grid and the cathode ceramic disc. Further, the corrugated surface of the grid provides structural rigidity to resist movement of the end wall due to thermal expansion.
Still another feature is the temperature control of the cathode which is provided by the use of the base cathode sleeve as a heat sink with control of the cathode temperature by means of the length and thickness of the base sleeve, alloy material used in the base sleeve as stainless steel, coating of base sleeve as by carbonizing, or by addition of flanges, ribs, grooves, or dimples to the base sleeve; and the reduced heat loss, through conduction from the cathode to ceramic disc, resulting from the minimal thermal contact between ceramic disc and cathode.
. These and various other objects and features of the invention will be more clearly understood from a reading of the detailed description in conjunction with the drawing in which:
FIG. 1 is a view in section of an electron gun including cathode, control grid, and screen grid embodying the invention;
FIG. 2 is an enlarged view in section of a portion of the illustrative electron gun of FIGURE 1 as taken along lines lI-II of FIGURE 3;
FIG. 3 is a plan view looking into the control grid of an electron gun constructed in accordance with an embodiment of this invention; and
FIG. 4 is a fragmental view in section of FIGURE 2 illustrative of the spacing methods afforded by this invention.
Referring now to FIGURES l and 2, there is depicted one illustrative embodiment of this invention in which the cathode 4-0 is supported by a cathode base sleeve 42, which base sleeve contacts ceramic disc 44- in a very limited surface area contact to reduce the heat transfer from the cathode to the ceramic disc :4 which was norrnally experienced in prior art devices. Tie ceramic disc is enclosed by a cylindrical member 46 and the disc 44 is held in position by means of an annular ring 48 which is oined to the cylinder 46 by any convenient means, such as by brazing. Advantageously, the base sleeve 40 is fabricated from a non-emitting or low-emitting material such as stainless steel, or the outer surface of the base sleeve is coated with a non-emitting material to prevent the deposit of short-circuiting paths across the adjacent surface of the ceramic ring 44. A first control grid 52 engages the outer surface of cylinder 46 and has a surface substantially parailel to the cathode emitting surface. This first grid is corrugated except for surface ltiZ as shown in FIGURE 3 and has one or more small apertures to permit the passage of electrons therethrough. A second screen grid '54 is a combination cylindrical and frustoconical structure and is corrugated similar to the first grid with the conical portions of the two grids facing in opposite directions. Grid 54 is supported from support rods 56 and '58 by means of supporting straps 60 and 62. Similarly, cylinder 48 is supported from the support rods by means of straps 64 and 66. The corrugated frustoconical surfaces increase structural rigidity of both grid members, allowin the effective surfaces to be made with simpler dies to closer tolerances out of extremely thin and uniformly thin material permitting closer spacing and smaller apertures. On grid 52 it also increases heat radiation.
In FIG. 2, which shows to an enlarged scale a portion of the gun assembly of FIG. I, is to be noted that the cathode at has an enlarged cylindrical portion 82 and a reduced cylindrical portion 84 connected thereto by means of an inturned flange portion 85 and the reduced portion 84 terminates in a flat electron emitting end wall 87. The cathode base sleeve 42 is made of non-emitting or lowemitting material or has a non-emitting surface 43 on the enlarged cylindrical portion 38. The other end of the base sleeve has an inturned shoulder 90, a reduced cylindrical portion 92 and an out-turned lip 94. The combination of the shoulder 9d and the out-turned lip 94 engages the reduced inturned flange 96 of the ceramic ring 44. It is to be noted that aside from these limited cylindrical areas of contact between the base sleeve 42, the base sleeve is spaced from the ceramic ring 44'. It is also to be noted that the reduced cylindrical portion 84 of the cathode 44 is spaced from the portion of the base sleeve 42 which engages ceramic ring 14. Thus the conductive path for heat between the cathode 4t) and the ceramic ring 44 is very limited. Consequently, the cathode may rapidly achieve a rise in temperature in response to the energization of the heater coil, not shown, thereby permitting emission from the emitting surface 87 in a minimum of time.
Advantageously, this gun assembly includes means for establishing testing the spacing between grid 52 and cathode 34 as illustrated in FIGURE 4 by the calibrated shim 8'9 inserted in the grid holes 108 to permit positioning cathode surface 87 an exact distance from grid surface 102. Further means for testing the spacing after assembly includes holes such as 95 in the cathode base sleeve 42 above the shoulder of cathode 82. When the gun subassembly is assembled, and before mounting into a complete tube, a measured quantity of air is pressed through holes 95'. Since the air flow path is affected by the gridcathode spacing, this given flow of air is gaged to assure that the spacing between grid 52 and cathode 84 is correct, and rejects can be culled out without the expense of completing an entire tube first to test the assembly.
As seen from FIGURE 3, the control grid 52 has fiat surface portion 102 substantially parallel to the cathode emitting surface '87 and this fiat cylindrical surface is raised or partially separated from a circular shoulder surface area 106 by means of a plurality of spaced lancing or lacing webs 108. These lacing webs permit the escape of heat the-rebetween such that the heat from the cathode 40 may escape without causing undue expansion of the first grid 52. The frustoconical section 110 of the grid 52 has a corrugated surface which extends into the cylindrical section 112. The corrugated cylindrical portion 112 engages the supporting cylinder 46 only at spaced intervals, while providing a series of heat passages between these two members more adequately to ventilate the area around the cathode and thereby further reduce thermal expansion and movement of the members.
Having therefore improved the state of the art, I describe features illustrative of the nature 'of the invention with particularity in the appended claims.
What is claimed is:
1. In an electron gun assembly, the combination comprising an annular support ring, an annular ceramic ring supported by said supporting ring or the inner surface thereof, said ceramic ring having an inner flange of reduced thickness including a pair of substantially parallel sides, a cathode base sleeve within said ceramic ring and having an out-turned lip which engages one of the substantial'ly parallel sides of said inner flange, said cathode base sleeve having a shoulder which engages the other of said parallel sides whereby the conductive heat transfer between said cathode base sleeve and said ceramic ring takes place only at said out-turned lip and said shoulder of said base sleeve, and a first control grid having a cylindrical portion, a frustroconical portion connected to said cylindrical portion and a planar portion connected to said frustoconical portion, said planar portion having an aperture in the center thereof and being spaced from and substantially parallel to said emitting surface, wherein said cylindrical portion of said grid is corrugated, the inner surface of said corrugated grid portion being connected to said support member whereby heat outlets are provided at said corrugated portion.
2. In a gun assembly as defined in claim 1 wherein said planar portion includes a second section positioned in a plane substantially parallel to said first section and a plurality of webs spaced about said first section and connecting said first and second sections whereby heat escapes from said cathode between said Webs.
3. In a gun assembly as defined in claim 1, the combination further comprising a second grid mounted in spaced relationship to said first control grid, said second grid including a cylindrical portion, a frustoconical portion and a planar portion wherein the frustoconical portion slopes toward said first control grid.
4. In a gun assembly as defined in claim 1, the control grid having both said cylindrical and said frustoconical portions corrugated.
5. In an electron gun assembly the combination of a planar electron emitting cathode mounted in a ceramic disc, and a control grid com-prising a frustoconical surface, a planar surface "and a cylindrical surface, the cylindrical surface registering over said ceramic disc to hold said planar cathode and planar surface of the grid in spaced relationship, said cylindrical and frustoconical control grid surfaces being corrugated.
6. The control grid assembly defined in claim 5 wherein :air flow vents are provided between said frustoconical surface and said planar surface, permitting the entry of a cathode-grid spacer shim for adjusting the electrode spacing and further providing an escape path for heat from said cathode.
7. The control grid assembly defined in claim 6 further comprising air vent apertures through said cathode- ,ceramic disc assembly communicating with said air flow vents in said control grid to permit the passage of an air flow stream through said air vents as a measure of the cathode-grid spacing.
8. The method of checking the assembly tolerances of an electron gun with a planar cathode mounted in a ceramic disc and having a grid with a cylindrical surface mated with said dis-c to establish grid-cathode spacing before final assembly of the tube comprising the steps of providing air vent apertures of known configuration in the cathode mount and said grid to provide a restricted air flow path dependent in part upon cathode-grid spacing adjusting the cathode-grid spacing to partially restrict air flow in said path, passing air through said path, and measuring the extent of restriction of said air flow in the path to ascertain correct grid-cathode sepacing.
References Cited by the Examiner UNITED STATES PATENTS Kirkrnan '29--25. 16 X 'Kelar 31138 2 'Burnside -2925.16 X
'Pohle 31 3-25( Beck '31382 Santis 3 13-101 Benda 31382 Benway 3 13-82 Johnson 313--33'1 15 JAMES W. LAWRE'NCE, Primary Examiner.
C. R. CAMPBELL, Assistant Examiner.