US3070724A

US3070724A - Electron discharge device

Info

Publication number: US3070724A
Application number: US30868A
Authority: US
Inventors: Harold W Herbert; Robert J Walsh
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1960-05-23
Filing date: 1960-05-23
Publication date: 1962-12-25
Anticipated expiration: 1979-12-25

Description

1962 H. w. HERBERT ETAL 3,070,724

ELECTRON DISCHARGE DEVICE Filed May 25, 1960 scram; Patented Dec. 25, 1962 hoe SJWhfiZd ELECTRON DEC' E iR GE DEVICE Harold W. Herbert and Ro s-est .l. Walsh, Emporium, Pm,

assignors to Syivania Electric Products line, a corporation of Deiaware Filed May 23, 196i), Ser. No. 30,368 Claims. (6i. 313-293) This invention relates to electron discharge devices generally and more specifically to a support for a cathode employed therein.

A need for an electron discharge device of increased reliability and ruggedness resulted in the development of the type popularly known as stacked tubes. In this construction the various electrodes are threaded upon insulative side rods in a predetermined order. The spacing or separation between adjacent electrodes is controlled to a large degree by the thickness of the insulating spacer elements or washers placed on the side rods intermediate the electrodes. After assembly, the parts are clamped together on the insulating members and the assembly is joined to the lead-in pins of a stem. Subsequently, the stem is joined to an enclosure which is then evacuated and sealed in the conventional manner.

The above-described construction was entirely satisfactory when relatively large parts and electrode to electrode spacings were involved. When the tube size and electrode spacings were reduced the parts became smaller and increased problems were encountered. One of the foremost problems was the decreased length of the leakage path between adjacent electrodes due to the thinness of the spacer employed to obtain the proper electrode separation. Therefore it is an object of this invention to increase the length of the leakage path between electrodes while still allowing close spacing to be obtained between adjacent electrodes.

As the spacer thickness became smaller and smaller, an increasing number of tube assemblies were rejected because of the mechanical failure of the insulating spacer when the entire mount was subjected to clamping pressures as a final stage in the assembly operation prior to being joined to the stem. Accordingly, it is a further object of this invention to reduce the rejection rate of stacked tube mounts due to spacer failure caused by compressive stresses set up during the assembly operation.

l-ieretofore, the support and electrical connections to the rectangular cathode sleeve employed in certain varities of stacked tubes have been made by welding the supports to the surfaces of the sleeve which were normal to the coated face. While this is a satisfactory mode of construction for some purposes, the relatively small areas presented to the operator resulted in missed or improper welds which in turn were responsible for the rejection of the cathode-support assemblies. Poor welds were also responsible for the failure of the mounts while under vibration. Therefore, it is yet another object of this invention to provide a mount structure which reduces these failures by allowing the cathode supports to be aiiixed to maior faces of the cathode tubes while maintaining close cathode to grid spacings.

The foregoing and other objects and advantages are achieved in one embodiment of the invention by the provision, in a mount, of a cathode support comprising a pair of pins, tubular insulating members about the pins, and a pair of insulating washers on each of the tubular members. A cathode sleeve, rectangular in cross section, coated with emissive material on one face thereof, is held by a pair of loop supports affixed in opposed relationship to one another on the exterior face of the sleeve opposite the coated face. The loop supports are looped over the tubular members and held in position between the first pair of washers and a succeeding pair of washers. The thickness of the Washers positioned between the cathode loop support and the subsequent electrode is made equal to the sum of the cathode sleeve dimension along the mount axis, plus the thickness of the emissive coating, plus the spacing between the subsequent electrode and the emissive coating.

For a better understanding of the invention reference is made to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevation view in partial section of a stacked tube mount embodying one aspect of the invention;

FIG. 2 is a fragmentary elevation view in partial section of the structure of FIG. 1, shown on a greatly enlarged scale; and

FIG. 3 is a simplified plan view showing the cathode mounting taken along the line llllll of FIG. 2.

Referring to the drawings and more particularly to FIG. 1, the stern wafer it) is preferably fabricated from ceramic material such as alumina, zircon or steatite and has a plurality of conductive lead-in pins 12 passing therethrough. Two of the pins 14 are bridged by a cross bar 17 to which the assembled mount 18 is affixed. Mount 13 comprises a number of electrodes and spacers assembled and clamped together on a pair of metallic pins 29. The pins 2-1 are insulated from the various electrodes by ceramic tubular insulating members 22 and the electrodes are spaced from one another by various spacers. The mount illustrated in the drawings is a triode and is composed of a shield 24 cathode assembly 26, grid 28, and anode Ell.

The cathode assembly 26 includes a sleeve or tube 32, rectangular in cross section, coated on one exterior face with electron emissive material 34. Sleeve 32 is supported by loop supports 36 to which electrical connection is made through tab 33. The substantially rectangular cross-sectioned sleeve 32 has emissive coating 34 applied to one major surface while the loop supports 36 are affixed to the opposite major surface. The coated face is posi tioned opposite to, and parallel with, the grid 28 while the uncoated minor faces are substantially parallel to the axis of the support pins 20. The cathode is heated to its operating temperature by heater filament ill which is positioned within the sleeve 32. The size of the sleeve is determined by the desired electrical characteristics of the tube in which the mount is used and is fixed within each tube type.

Loop supports 35 are fabricated from round conductive material having the desired electrical and thermal characteristics. These loops may be fabricated from an alloy comprising approximately 40% nickel with the balance substantially iron. The individual loops may be described as each comprising a bifurcated member having a bight portion 42 adapted to surround the tubular member 22. A part 44 of the bight 42 lies parallel to the longitudinal axis of the sleeve 32. The ends 43 of legs 46 of the support are opposedly formed, and are flattened to provide a greater uniform contact area for welding the legs 46 to the sleeve 32. The flattening also serves to increase the rigidity of the supports 36 at the point of contact with the sleeve 32.

Planar grid 28 is typical of those normally employed in stacked mounts and comprises a molybdenum frame 52 with tungsten lateral wires 54 atfixed across the aperture 56. It has been found that forming grid frame 52 to reduce the grid-cathode spacing is not readily accomplished in a stacked mount because of the brittleness of the molybdenum. At the present state of the art, molybdenum is used because of its excellent mechanical and electrical properties at high temperatures. Due to the close electrode spacings and the smallness of the parts, sharp bends would be required in the frame within a short distance of one another. These bends coupled with the low ductility of molybdenum preclude the use of a formed grid.

After being joined to the sleeve 32, the loops 36 are adjusted to lie in a common plane. A cathode support bent to position the cathode closer to the grid than allowed by the thickness of the spacer between the cathode support and the grid is not believed to be presently feasible for several reasons. For example, in order to provide a formed cathode support sufficiently rigid to maintain the cathode in position when heated to its operating temperature, it would be necessary to use relatively heavy material in fabricating the support. Use of such heavy material, however, would increase the heat loss from the cathode and drop the cathode temperature below normal useful operating levels.

Anode 30 is positioned adjacent aperture 56 in alignment with the emissive coating 34 on the cathode sleeve 32. Shield 24 is provided to protect the stem 10 from deposition of conductive material during tube aging and operation. Getter 60 is secured to standard 62 affixed to the anode.

The mount 13 is assembled by threading shield 24 over the pins 20 and securing it thereto by conventional means which do not form a part of this invention. Next, a tubular member 22 is placed over each of the pins 20. First insulating spacers or washers 64 are then placed over each tubular member 22. These lowermost washers s maintain the cathode supports 36, which are next positioned in the assembly above shield 24. The bight portion 42 of the loops 36 rests upon the washers 64 and surrounds the tubular members 22. The cathode assembly 26 is positioned with the face bearing the emissive coating 34 opposite the grid position.

A second pair of insulating spacers 66 are then placed about tubular mem ers 22 each coming to rest upon the cathode supports 36. As set forth hereinbefore, forming either the grid or the cathode supports to control the gridcathode separation is not feasible. Therefore, the thickness of the spacers 66, measured along the tubular members 22, determines the grid-cathode spacing since the grid will rest against these spacers.

Prior to this invention, when cathode sleeves having their supports afiixed to the center of the minor faces were employed, it was necessary to use a thin spacer to achieve the desired electrode spacings. As an example, when a mount having the following parameters was fabricated, a spacer 66 of .015 inch thick would be required:

Inch Cathode sleeve minor .030 Emissive coating thickness .002 Grid-cathode coating separation .003 Loop upport wire diameter .010

The thickness of the spacer 66 required was calculated by use of the following formula:

/2 cathode sleeve minor support wire diameter emissive coating thickness the grid to cathode coating separation.

Heretofore, when the grid-cathode coating separation was reduced to .001 inch, the spacer 66 thickness required was then .013 inch. However, it was found that ceramic spacers of this thickness failed when subjected to the required mount clamping pressure of 20 pounds. Mounts employing .013 inch thick spacers were consistently rejected due to this mechanical failure. .The critical thickness for a steatite spacer 66, when subjected to a clamping pressure of 20 pounds, is .015 inch. Additionally, spacer less than .015 inch thick provided a minimal path for grid-cathode leakage currents.

When a cathode support 36 embodying one aspect of this invention is employed, absence of mechanical failure 4 of spacers 66 is assured. With the supports 36 formed and attached as shown in the drawings. it is possible to use a spacer .033 inch thick with a grid-cathode coating separation of .001 inch. This spacer thickness is calculated by adding, as in the mount example above:

cathode sleeve minor cathode coating gridcathode separation; or .030 inch plus .002 inch plus .001 inch equals .033 inch.

An advantageous increase in the length of the gridcathode leakage current path is also obtained by using this thicker spacer 66. Additionally, the position of the cathode sleeve 32 and supports 36 need not be disturbed once assembled into the mount since the steatite spacers are generally dimensionally stable. If a cathode sleeve i utilized which does not require the addition of emissive materials thereto in the form of a coating, the provision for the coating thickness may be omitted in calculating the spacer 66 thickness.

Grid 28 is next placed over the sleeves 22, an additional set of spacers 68 are added, and then the anode 30 is attached. The stack is compressed by application of 20 pounds pressure to assure that the parts are seated together and to reduce microphonism. The mount is then secured together by clamp means 70 which are not part of the present invention and will therefore not be described in detail.

Getter 60 and getter support 62 are aflixed to the mount 18 and then the entire assembly is then connected to the stem 10. Electrical connections are made between the leads and the various electrodes by means of connecting tabs as for example, tab 38 of the cathode.

By application of this invention it has become possible to fabricate mounts having high inter-electrode leakage resistance and high mechanical strength. These desirable characteristics are obtainable without diminution of other essential features of the stacked mount form of electron discharge device construction.

Having thus described the invention, what is claimed 1. In a mount, a cathode support comprisng a pair of pins, tubular insulating members about said pins, and a pair of insulating washers on each of said tubular members, a cathode sleeve, rectanguiar in cross section, said sleeve being coated with emissive material on one exterior face thereof, a pair of loop supports alfixed to said sleeve in opposed relationship to one another, said supports having flattened cathode sleeve contacting portions, the supports being affixed to the exterior face of the sleeve opposite the coated face at said contacting portions, the loop supports being looped over the tubular members and held between the pairs of washers.

2. In a mount, a cathode support comprising a pair of pins, tubular insulating members about said pins, and a pair of insulating washers on each of said tubular members, a cathode sleeve, rectangular in cross section, said sleeve being coated with emissive material on one exterior face thereof, a pair of loop supports atfixed to said sleeve in opposed relationship to one another, said supports each comprising a bifurcated member having a bight portion adapted to surround said tubular member, said bight portion lying in a given direction in a given plane, the ends of said bifurcated member being flattened and lying in said plane with said ends being opposed and lying parallel to said given direction, the supports being afiixed to the exterior face of the sleeve opposite the coated face at said contacting portions. the loop supports being looped over the tubular members and held between the pairs of washers.

3. In a mount, a cathode support comprising a pair of pins, tubular insulating members about the pins, :1 pair of insulating washers on each of said tubular members, a cathode sleeve, rectangular in cross section, said sleeve being coated with emissive material on one exterior face thereof, a pair of loop supports atfixed to said sleeve in opposed relationship to one another, said supports lying in a given plane and having the end portions thereof formed into flattened sleeve contacting portions also lying in said plane, these supports being affixed to the exterior face of the sleeve opposite the coated face by said flattened portions, the loop supports being looped over the tubular members and held between the pairs of washers.

4. In a mount having a longitudinal axis, a cathode support comprising a pair of pins, tubular insulating members about said pins, an insulating washer about each of said tubular members, a cathode sleeve, rectangular in cross section, aligned with the longitudinal axis of the mount, said sleeve being coated with emissive material of a given thickness on an exterior face thereof, said exterior face lying transverse to the longitudinal axis of said support, a pair of loop supports affixed to the opposite exterior face of the sleeve, said supports being looped about said tubular members and engaging said washer, a second electrode carried by said tubular members, spaced a given distance'from said emissive coating on said cathode face, and an insulating spacer on each of said tubular members engaging the loop supports and positioned intermediate said loop supports and said second electrode, said spacer having a thickness measured along the longitudinal axis of said mount equal to the sum of the cathode sleeve dimension along said axis, the emissive coating thickness, and the spacing between the second electrode and said emissive coating.

5. In a stacked mount structure having a longitudinal axis and including a plurality of aligned electrodes wherein said electrodes are clamped together under a pressure of at least 20 pounds, the combination comprising a pair of pins, tubular insulating members about said pins, an insulating washer about each of said tubular members, a cathode sleeve, rectangular in cross section, aligned with the longitudinal axis of the mount, said sleeve being coated with an emissive material of a given thickness on an exterior face thereof, said exterior face lying transverse the longitudinal axis of said support, a pair of loop supports affixed to the opposite exterior face of the sleeve, said supports being looped about said tubular members and engaging said washer, a second electrode carried by said tubular members, spaced a given distance from said emissive coating on said cathode face, and a steatite spacer on each of said tubular members engaging the loop supports and positioned intermediate said loop supports and said second electrode, said spacer having a thickness of at least .015 inch measured along the longitudinal axis of said mount.

2,064,981 Knoll Dec. 22, 1936 Robinson Jan. 8, 1952 p