US3138733A - Support and spacer assembly for electron discharge tubes - Google Patents

Description

June 23, 1964 E. K. SMITH 3,138,733

SUPPORT AND SPACER ASSEMBLY FOR ELECTRON DISCHARGE TUBES Filed June 29, 1961 E'NTOR. E. K. SMITH HIS ATTORNEY United States Patent M 3,138,733 SUPPORT AND SPACER ASSEMBLY FOR ELECTRON DISCHARGE TUBES Earle K. Smith, West Orange, N.J., assignor to General Signal Corporation, a corporation of New York Filed June 29, 1961, Ser. No. 126,781 7 Claims. (Cl. 313-256) The present invention relates to electronic discharge devices, and more particularly to an improved insulative supporting and spacing assembly for the electrodes of vac uum or gas discharge tubes.

In the construction of vacuum or gas discharge tubes, it is often necessary to connect two or more electrodes together mechanically to provide mutual support and maintain accurate spacing therebetween. Because of the different voltages applied to the separate electrodes of the tube, it is necessary that these supports and spacers, which mechanically connect the electrodes, are members having the proper electrical insulating characteristics. The internal elements of a tube, such as the heat shield can, for example, and various other supporting elements and connections are preferably made of metal such as nickel; and during construction of these tubes, these metallic parts are subjected to high temperatures, which are necessary to carry out a degassing process and treatment for the emissive coating of the cathode. During this treatment there is a certain degree of vaporization of the metallic parts which tend to deposit minute quantities of a metallic conductive material on the surfaces of any insulating element inside the tube. Also, because of electronic or ionic bombardment during operation of the tube, there is a certain amount of sputtering of the conductive material from the anode and cathode, which accumulates on the surfaces of any insulating elements that may be used in the tube. It is evident that accumulations of this conductive material shortens the life of the tube by forming a continuous conductive path between the electrodes.

In an attempt to lessen the effect of these metallic deposits, which cause a breakdown in the tube because of surface leakage, it has been proposed to provide insulating members having a distinctive configuration, which tends to prevent the formation of a continuous film of conductive material over the surface area. In forming and mounting such an insulator in a tube, consideration must be given to lateral spacing inside the tube, which is limited, and yet the insulating member must have the proper volume to prevent electrical conduction therethrough. Also, the insulating member must be so formed and mounted that accurate spacing of the electrodes can be maintained, even under shock and vibration.

In tubes where an insulating member is placed between two parallel plane surfaces, an electrical insulating member, which effectively prevents volume conductivity therebetween, yet provides a surface configuration that tends to delay the formation of a continuous film of conductive material, and yet provides and maintains accurate spacing between these surfaces, is a cylindrical member of ceramic material, such as steatite, for example, which has a plurality of axially spaced annular recesses in its surface.

Because it is understood that the evaporated or sputtered material tends to follow a direct and approximately straight line path in its movement from its source, the material does not readily reach the inner portion or base of the recesses, thereby preventing an early breakdown of the tube because of the presence of a continuous conductive path formed by the metallic deposits. Therefore, it is apparent, that an insulating member of this type is most effective where the ratio of the depth to width of each recess, is at a maximum.

However, in the construction of vacuum and gas discharge tubes; horizontal space considerations limit the Patented June 23, 1964 maximum outside diameter of these insulating members; and it follows, that this, together with the necessity of providing insulation offering sufficient resistance to volume conductivity limits the maximum depth of the recesses. Moreover, because of the limits of ceramic fabrication, there is also a limit to the minimum width of each of these recesses that is feasible. Thus, heretofore, lateral space considerations, volume conductivity, and the feasible limits of ceramic molding and/ or machining prevented the construction of a tube where the insulating member had recesses of suflicient depth to width ratio to prevent after a time breakdown of the tube because of surface leakage.

The purpose of the present invention is to provide an improved electronic discharge tube which is so constructed that the accumulation of metallic deposits in the tube does not provide a path for surface leakage between the electrodes; also, to provide a tube which may be easily assembled in mass production with accurate spacing between the electrodes; and also a tube wherein the insulating supporting structure prevents Volume conductivity therethrough. Also, the purpose of the present invention is to provide a tube having these characteristics wherein the insulating assembly does not increase the lateral spacing inside the tube. In furtherance thereof,

One of the objects of the present invention is to provide an improved insulating support and spacer assembly for a discharge tube.

Another object of the present invention is to provide an insulating support assembly comprised of ceramic material which permits a surface configuration, having one or more annular recesses of a depth to width ratio which exceeds substantially that which is feasible in the molding or other fabrication of ceramic insulators.

Another object of this invention is to provide an improved insulating support assembly for the electrodes of a tube which has an improved surface configuration to pre vent the formation of a continuous film of conductive material.

Still another object of this invention is to provide an improved tube wherein vibration or shock does not alter the spacing between the electrode or misalign the insulating assembly to affect adversely the depth to width ratio of the annular recesses therein.

Still another object of this invention is to provide an insulating support assembly which presents a surface configuration of spaced annular recesses of a large depth to width ratio, and yet prevents volume conductivity through the material.

A further object of this invention is to provide an improved insulating support structure for the electrodes of an electronic tube which permits an accurate spacing of the individual electrodes in mass production and has a surface configuration which prevents the formation of a continuous film of conductive material between the electrodes.

A further object of this invention is to provide an improved insulating support assembly for the electrodes of a discharge tube which permits the use therein of a relatively inexpensive element made of ceramic material.

Other objects of this invention will become apparent from the specification, the drawing, and the appended claims.

In the drawings:

FIG. 1 is an elevation, partly in section of a tube constructed in accordance with one embodiment of this invention;

FIG. 2 is a sectional view taken in line 22 of FIG. 1, and looking in the direction of the arrows;

FIG. 3 is an enlarged sectional view taken on line 33 of FIG. 1, and looking in the direction of the arrows,

to show an insulating supporting assembly according to one embodiment of the invention;

FIG. 4 is an enlarged sectional elevation of an insulating support assembly constructed according to another embodiment of this invention; and

FIG. 5 is an enlarged sectional elevation of still another embodiment of an insulating support assembly of this invention.

Referring to the drawing, a tube generally referred to at is comprised of a glass envelope 12 that is sealed as by fusing, for example, at its lower end to an annular flange 14 of a glass reentrant stem 16. The upper end of the envelope 12 is also sealed as by fusing, for example, to an outer edge 18 of a glass cap 20.

The cathode of the tube 10, which is enclosed by a conventional cylindrical heat shield can 22 is rigidly sup ported in the envelope 12 by a pair of stiff bifurcated metallic members 24 (one of which is shown) connected at one end to the can 22. The members 24 are fastened as by welding at their other end to a collar 26 that is clamped around the stem 16. Rods 28 are anchored in the stem 16 and are connected to the can 22 at its lower peripheral edge by tabs 30 which are welded to the can.

The upper end of the can is provided with a plane metallic top 34 that is flanged at its peripheral edge and fastened, as by welding, to cover the can 22. The surface of the top 34 is slightly recessed from the upper edge of the can 22. A metallic reenforcing band 36 is attached around the can 22 adjacent its upper edge to increase its structural strength. The top 34 of the can 22 has a central opening 38 to provide communication between the cathode that is inside the can 22 and the other electrodes of the tube. A cylindrical metallic shield 40 surrounds the opening 38 and is attached to the top 34 by tabs 42 which are fastened to the shield 40 and the top 34 as by welding.

Extending inwardly into the envelope 12 from the glass cap is an anode assembly 44, which is supported by conventional heat dissipating plates 46 that are attached at one end as by spot welding to the assembly 44 and are also attached to a pair of supporting rods 48 that extend through the cap 20 to provide an external anode connection 50.

A plurality of stiff rods 52 having a bent portion 54 at one end are spaced angularly about the top 34 of the can 22, and are fastened at their bent ends 54 as by welding to the top 34, and recessed peripheral edge 35 of the can 22 to extend upwardly in parallel relation to each other and parallel to the axis of the can 22. Mounted on each of the rods 52 is a metallic eyelet member 56 which slidably fits on the rod 52 and rests on the rod adjacent the bent portion 54. The bend 54 serves to hold each of the eyelets in proper longitudinal position on its respective rod 52. Each eyelet 56 has a flared out portion 57 which acts as a supporting surface as will be described hereinafter.

A circular grid shield, generally referred to at 58 is supported spaced from the top 34 of the can 22. The grid shield is metallic and has a downwardly extending peripheral flange 60 and a plane top 62. The top 62 has a plurality of openings through which the rods 52 extend when the shield 58 is in position, and a central opening 64 in registry with the opening 38. A grid 67 which is comprised of a plurality of spaced bars covers the opening 64; and they are attached to the top 62 as by welding.

The grid shield 58 is spaced from the can 22 so that its top 62 is substantially parallel to the top 34 of the can. Each rod 52 is provided with an elongate sleeve 66 of ceramic material, such as steatite, which slidably fits on its respective rod to insulate the shield 58 from the rod 52 where it passes through the openings therein. Each sleeve 66 engages at its bottom end a respective eyelet 56 centrally of its flared out portion 57.

The shield 58 is accurately spaced from the top 34 of the can 22 by a pair of cylindrical insulating members 68 and 7 0. These members 68 and 70 are provided with a plurality of axially spaced annular recesses 72 to provide a surface configuration for hindering the formation of a continuous conductive path of metallic particles thereon. The members 68 and 70 are preferably a ceramic material of the aluminum oxide and/ or magnesium oxide type, generally known as steatite. Although it is considered that the limits of ceramic fabrication prevents a recess being smaller in width than in the neighborhood of fifteen thousandths of an inch; in the actual construction of a tube according to the present invention, the width of each of the recesses 72 was in the neighborhood of twenty-thousandths of an inch. Also, the insulating members 68 and 70 having recesses of this width have an outside diameter of approximately twenty-five hundredths of an inch to provide for the limited lateral spacing. The depth of each of the recesses 72 is in the neighborhood of sixty-four thousandths of an inch. A central opening of the insulating members 68 and 70 has a diameter of one-hundred twenty-two thousandths of an inch to slidably fit on the sleeve 66. Thus, the thickness of the continuous portions of the members 68 and 70 is substantially equal to the depth of the recesses to provide strength to the member and provide the proper volume of insulating material. Also, with reference to the cylindrical members 68 and 78 the depth to width ratio of each of the recesses 72 is in the neighborhood of 3 to 1. Although, it has been found that a depth to width ratio of approximately 4 to 1 which is the greatest that is feasible in the molding of ceramic insulating material of this type and size assists in preventing the formation of a continuous conductive path, after a suflicient length of time a conductive path will form on the exterior surface of the members 68 and 70.

Each of the members 68 and 70 is provided with end faces 74 which lie in a plane perpendicular to the axis of its respective member. The member 68 is positioned on the sleeve 66 so that one end face engages against the portion 57 of the eyelet 56 and the member 70 is also positioned on the sleeve axially of the member 68. The top 62 of the grid shield 58 engages against the upper end face 74 of the member 79.

To provide a recess 73 having a greater depth to width ratio than is feasible with present ceramic molding practices, a thin metallic washer 75 slidably fits over the sleeve 66 and is interposed between the members 68 and 70 to engage against the upper face 74 of the member 68 and the lower end face 74 of the member 70. The washer 75 preferably has an outside diameter which is no greater than the diameter of the members 68 and 70, when measured at the base of the recesses 72.

The metallic washer 75, which may be inexpensively cut from thin sheet stock, may be in the neighborhood of one-thousandths of an inch thick to provide the maximum possible protection. However, in the actual tube constructed, as hereinbefore mentioned, a metallic washer five-thousandths of an inch thick provided a recess between the members 68 and 70 which had a depth to width ratio of approximately twelve to one, which successfully prevented the formation of a continuous conductive path, and which is not feasible with present methods of ceramic molding.

A depth of a recess in the order of twelve times its width has been found to represent a suitable relationship for the tube constructed as hereinbefore mentioned. However, for other tube structures a lesser or greater ratio of depth to width may be employed that produces the desired results. For example, with a metallic disc 75 in the order of one-thousandth of an inch thick and of a diameter which is substantially equal to the diameter of the members 68 and 70 when measured at the bases of the recesses 72, a recess 73 is obtained which has a depth that is in the order of sixty times its width; and it should be understood that this invention is not limited to the particular ratios stated, but is intended to embrace all dimensions which afford the desired protection.

Although, the base or root of the recess 73 is metallic and conductive, the walls of the recess 73 near the bottom are adequately shielded from the deposit of conductive material. Any appreciable vapor pressure of the washer 75 could cause condensation of the vapor on the cooler insulator surfaces and being conductive cause surface current leakage. Thus, to insure against the washer 75 itself from contributing conductive material to this region, it has been found necessary only to use a metal having a low vapor pressure, and whose oxides have a low vapor pressure, such as nickel, molybdenum, or tantalum, and give it the usual cleaning treatment satisfactory for vacuum or gas tube parts.

A metallic grid heat shield generally referred to at 80 is generally circular in configuration and is comprised of a plane bottom portion 82 that has an upwardly extending peripheral flange 84. The bottom portion 82 has angularly spaced openings to receive the rods 52. Interposed between the portion 82 of the grid heat shield 80 and the parallel plane surface 62 of the shield 58 and slidably mounted on each sleeve 66 are cylindrical ceramic members 86 and 88 which are similarly configurated, and are similar to the members 68 and 70. Also interposed between each pair of members 86 and 88 is a thin metallic washer 90 similar to the washer 75 to form a recess 92 similar to the recess 73. The top of the sleeve 66 may be coextensive with upper end face of the member 88 for supporting the shield 80 spaced from the shield 58. An ayelet 94 is crirnped on each rod 52 at its upper end to complete the assembly.

It will be noted in FIG. 3, that the end faces 74 of the members 68 and 70 which engage against opposite sides of the washer 75 and the end faces of the members 86 and 88 which engage against the washer 90, have an end surface, the diameter of which is coextensive with the outside diameters of the respective members.

Thus, the evaporated or sputtered material between the cathode can 22 and the grid shield 58 is delayed in providing a continuous path by the recesses 72 of the members, and after a time when a conductive path does form, it is prevented from electrically connecting the top 34 of the can 22 and the surface 62 of the shield 58 by the narrow recess 73, the root of which is the peripheral edge of the metallic washer 75 and the walls of which are the exposed opposing parallel end faces 74. The resistance to volume conductivity of the members 68 and 70 is suiiicient in that the members 68 and 70 each have an integral portion the diameter of which is equal to the diameter of the member when measured at the base of the recess 72 and the thickness of which is substantially equal to the depth of the recesses.

In assembling the tube, a sleeve 66 is merely slipped on each rod 52. A member 68 is then slipped over each sleeve 66, and a Washer 75 then slipped over each sleeve 66. Next a member 70 is positioned to each sleeve 66 so that washer 75 is interposed between members 68 and 70. By merely slipping the shield 58 over the sleeves 66 it is in proper spaced relationship when engaging the end faces of the member 70. Also, the members 86, washers 90 and members 88 are fit on the sleeve 66 to support and space the heat shield 80 in a similar manner.

During operation, it is apparent that any vibration or shock does not adversely affect the spacing of the elements in the tube or the depth to width ratios of the recesses 73 or 92.

Referring to FIG. 4, if it is desired to use a single cylindrical steatite member, such as 100, to space the shields 58 and 80, a thin metallic washer referred to at 102 is interposed between end face 104 of each of the members 100 and the opposing metallic face of the top 62 of the member 58 to provide a narrow recess therebetween. Also, another metallic washer such as 106 is interposed between opposing faces of the bottom portion 82 and the end face 108 to provide a similar narrow recess. Similarly a washer 110 may be interposed between the portion 57 of the eyelet 56 and end face 112 of the member between the eyelet 56 and top 62. FIG. 5 illustrates the manner in which an insulating supporting assembly may be provided with a number of narrow recesses having the desired depth to width ratios by using both the washers 75 and 90, and the washers 102, 104, 106 and 110 in their respective positions.

Thus, it is apparent that I have provided an improved tube structure wherein the electrodes may be accurately assembled in the proper spaced relation in mass production inexpensively, by using inexpensive molded ceramic insulating members, such as steatite, and metallic washers having a low vapor pressure that are in the order of one thousandth to five thousandths or more of an inch thick; while still maintaining maximum resistance to volume conductivity and having a surface configuration which prevents the formation of a continuous path of conductive material on the insulating members. It is apparent, that although steatite is preferable because it provides good mechanical and electrical properties and offers high electrical resistance at elevated temperatures, any ceramic material having similar properties may be used.

Also, although cylindrical insulating members are used in conjunction with washers which may be cylindrical, it is contemplated that members of steatite and their metallic inserts of any cross-section may be used provided a sufficient depth to width ratio is maintained. Also, the ceramic members themselves may have more or less recesses than illustrated or in some instances no recesses at all.

Although I have shown several specific embodiments of this invention it is to be understood that various modifications and adaptations may be made without departing from the spirit or scope of this invention.

What I claim is:

1. In an electron tube wherein a plurality of elements, each of which has a plane surface portion, are spaced in the envelope so that their plane surface portions are in substantially parallel spaced relation, and each of which constitute sources of vaporized conductive material when heated during fabrication and operation of the tube, and wherein said elements are aflixedly spaced from each other by sleeves of ceramic material extending from the plane surface portions of the elements and substantially normal thereto, each of said sleeves having a plane surface extending parallel to the plane surface portions of the elements and similar plane surface portions of other sleeves, each said sleeve being of such dimension to operatively resist volume conductivity between the elements, the combination of, a thin fiat metallic plate mounted between and in engagement at opposite sides thereof with each of a plurality of adjacent plane surfaces, at least one plane surface of each adjacent plane surface being the end of a sleeve of ceramic material, each said metallic plate being of such perimetral dimension and so positioned between said plane surfaces to form a narrow annular recess with its peripheral edge as the base of the recess and each of the adjacent plane surfaces spaced thereby being the sidewalls thereof, each said recess having a depth to width ratio to effectively prevent a surface leakage path of vaporized conductive material continuous from one element deposited along the exterior of each respective sleeve to another element, without increasing the lateral dimension of each sleeve and without reducing the resistance of each sleeve to volume conductivity.

2. In an electron tube according to claim 1 wherein both adjacent plane surfaces forming the sidewalls of the recess are the adjoining spaced end walls of sleeves of ceramic material.

3. In an electron tube according to claim 1 wherein each said metallic plate is comprised of a metal having a low vapor pressure at operating and processing temperatures to eliminate each said metallic plate as a source of vaporized conductive material when heated during fabrication and operation of the tube.

4. An insulator spacer assembly for the elements in an electron tube envelope wherein the elements have plane surface portions and are supportedly positioned therein so that their plane surface portions are substantially parallel, said assembly comprising a plurality of means supporting the elements in said position, a sleeve of ceramic material through which the supporting means extends, said sleeve having opposite plane end faces contiguous the spaced parallel plane surfaces of the elements, said sleeve being of a predetermined length to determine the spacing between the elements and of a predetermined minimum lateral thickness to provide sulficient resistance to volume conductivity during operation of the tube and having an external perimetral dimension in accordance with the space limitation in the tube envelope, and a thin fiat metallic plate positioned between at least one end face of the sleeve and the contiguous plane surface of the adjoining element and in intimate engagement therewith, said plate being positioned out of contact with the supporting means and positioned and having a perimetral dimension so that its peripheral edge constitutes the base of a narrow annular recess with the end face and contiguous plane surface forming the opposite parallel sidewalls thereof, said recess having a sufficient depth to width ratio to prevent the formation of a continuous conductive path of deposited metallic material extending axially on the exterior surface of the sleeve when the tube is heated during fabrication and operation thereof as caused by sources of vaporized conductive material in the tube envelope.

5. In an insulator spacer assembly according to claim 4 wherein the contiguous plane surface of the adjoining tube element forming one sidewall of the recess is the end face of a sleeve of ceramic material positioned on the supporting means to space another tube element.

6. An insulator spacer assembly according to claim 4 wherein said metallic plate is comprised of a metal having a low vapor pressure at operating and processing temperatures.

7. An insulator spacer assembly according to claim 4 wherein said sleeve has a plurality of molded axially spaced annular recesses having a depth to width ratio less than said first mentioned recess and wherein said metallic plate has a central opening, and further includes a second sleeve of ceramic material interposed in the first mentioned sleeve surrounding the supporting means and extending through the central opening in the metallic plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,082,474 Van De Graaff June 1, 1937 2,455,851 Beggs Dec. 7, 1948 2,500,153 Cork et al Mar. 14, 1950 2,633,550 Stieritz Mar. 31, 1953 2,860,268 Edwards et a1. Nov. 11, 1958

Claims (1)

1. IN AN ELECTRON TUBE WHEREIN A PLURALITY OF ELEMENTS, EACH OF WHICH HAS A PLANE SURFACE PORTION, ARE SPACED IN THE ENVELOPE SO THAT THEIR PLANE SURFACE PORTIONS ARE IN SUBSTANTIALLY PARALLEL SPACED RELATION, AND EACH OF WHICH CONSTITUTE SOURCES OF VAPORIZED CONDUCTIVE MATERIAL WHEN HEATED DURING FABRICATION AND OPERATION OF THE TUBE, AND WHEREIN SAID ELEMENTS ARE AFFIXEDLY SPACED FROM EACH OTHER BY SLEEVES OF CERAMIC MATERIAL EXTENDING FROM THE PLANE SURFACE PORTIONS OF THE ELEMENTS AND SUBSTANTIALLY NORMAL THERETO, EACH OF SAID SLEEVES HAVING A PLANE SURFACE EXTENDING PARALLEL TO THE PLANE SURFACE PORTIONS OF THE ELEMENTS AND SIMILAR PLANE SURFACE PORTIONS OF THE OTHER SLEEVES, EACH SAID SLEEVE BEING OF SUCH DIMENSION TO OPERATIVELY RESIST VOLUME CONDUCTIVITY BETWEEN THE ELEMENTS, THE COMBINATION OF, A THIN FLAT METALLIC PLATE MOUNTED BETWEEN AND IN ENGAGEMENT AT OPPOSITE SIDES THEREOF WITH EACH OF A PLURALITY OF ADJACENT PLANE SURFACES, AT LEAST ONE PLANE SURFACE OF EACH ADJACENT PLANE SURFACE BEING THE END OF A SLEEVE OF CERAMIC MATERIAL, EACH SAID METALLIC PLATE BEING OF SUCH PERIMETRAL DIMENSION AND SO POSITIONED BETWEEN SAID PLANE SURFACES TO FORM A NARROW ANNULAR RECESS WITH ITS PERIPHERAL EDGE AS THE BASE OF THE RECESS AND EACH OF THE ADJACENT PLANE SURFACES PACED THEREBY BEING THE SIDEWALLS THEREOF, EACH SAID RECESS HAVING A DEPTH TO WIDTH RATIO TO EFFECTIVELY PREVENT A SURFACE LEAKAGE PATH OF VAPORIZED CONDUCTIVE MATERIAL CONTINUOUS FROM ONE ELEMENT DEPOSITED ALONG THE EXTERIOR OF EACH RESPECTIVE SLEEVE TO ANOTHER ELEMENT, WITHOUT INCREASING THE LATERAL DIMENSION OF EAC SLEEVE AND WITHOUT REDUCING THE RESISTANCE OF EACH SLEEVE TO VOLUME CONDUCTIVITY.

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