US3566179A - Cathode and heater constructions and mountings in electron discharge devices - Google Patents

Abstract

The present invention comprises new and useful cathode and heater constructions and assemblies for electron discharge devices, particularly vacuum tubes. The cathode or heater is mounted at both ends to the interior structure of the electron discharge device and, in a preferred form of the invention, is pressed over a pair of bosses which are integral with heat sinks comprising opposite ends of the device. The materials of these bosses and the cathode or heater are so chosen that the coefficient of thermal expansion of the bosses is greater than that of the material of the cathode or heater. In this way, operating temperatures do not reduce, but rather, increase the securement of opposite ends of the cathode or heater to the respective mounting bosses.

Description

United States Patent [111 3,566,179

[72] Inventor Beverly D. Kumpfer 2,212,827 8/ 1940 Etzrodt 313/341X Salt Lake City, Utah 2,342,044 2/ 1944 Foote 313/274 [21] Appl. No. 738,465 2,848,642 8/1958 Wisco et al.. 313/279 [22] Filed June 20, 1968 3,013,180 12/1961 Peters 313/344X [45] Patented Feb. 23, 1971 3,076,122 1/1963 Kumpfer 313/274X [73] Assignee American Microwave Incorporated 3,250,943 5/ 1966 Antonis et a1. 313/344X Salt Lake City, Utah 3,431,448 3/ 1969 English 313/344X [54] CATIIODE AND HEATER CONSTRUCTIONS AND MOUNTINGS IN ELECTRON DISCHARGE [56] References Cited UNITED STATES PATENTS 1,995,702 3/1935 Capicotto 313/337X 3,409,530 11/1968 Locke et a1. 204/196 Primary Examiner-John W. Huckert Assistant ExaminerAndrew .1. James Attorney-M. Ralph Shaffer ABSTRACT: The present invention comprises new and useful cathode and heater constructions and assemblies for electron discharge devices, particularly vacuum tubes. The cathode or heater is mounted at both ends to the interior structure of the electron discharge device and, in a preferred form of the invention, is pressed over a pair of bosses which are integral with heat sinks comprising opposite ends of the device. The materials of these bosses and the cathode or heater are so chosen that the coefficient of thermal expansion of the bosses is greater than that of the material of the cathode or heater. ln this way, operating temperatures do not reduce, but rather, increase the securement of opposite ends of the cathode or heater to the respective mounting bosses.

PATENTEU mm 7 r/ f/// ////M F/GJ INVENTOR. BEVERLY D. KUMPFER HIS ATTORNEY CATEKOEBE AND HEATER CONSTRUCTIONS AND MGUGS EN ELECTRON DISCHARGE DEVICES This present invention relates to cathode and heater constructions for electron discharge devices such as vacuum tubes and, more particularly, to a new improved construction of the type described wherein opposite ends thereof are respectively mounted to and over mounting bosses forming a part of the cathode or heater circuit. In a preferred form of the invention, the outer diameter of these bosses is larger than the inside diameter of the cathode or heater construction, so that a tight, pressed or screwed fit and a gripping engagement therebetween can be achieved, by virtue of the resiliency of the end turns of the cathode or heater.

The mounting bosses in a preferred form of the invention constitute integral portions of respective heat sinks defining ends of the electron discharge device.

Accordingly, a principal object of the present invention is to provide a new and improved cathode or heater construction in an electron discharge device.

A further object of the invention is to provide a new and improved electron discharge device such as a vacuum tube having a novel cathode and heater, and mounting structure therefore, whereby access to the electron discharge device may be easily achieved to maintain or replace interior parts of the tube, including the cathode or heater thereof.

An additional object of the invention is to provide in an electron discharge device an improved cathode heater and mounting structure wherein-a tight fit is insured relative to the cathode or heater and its mounting construction, not only during dormancy, but also during intervals of high temperature use.

A further object of the invention is to provide a cathode construction in an electron discharge device wherein the desired operating temperature of the cathode construction is maintained substantially along its entire length.

An additional object is to improve and, indeed, increase the metal-to-metal contact of opposite ends of the cathode or heater, used in the present invention, with the mounting bosses to which they are mounted.

An additional object is to provide in an electron discharge device an improved cathode/heater construction and mounting structure therefor, and this wherein the mounting structure may serve optionally as pole-piece receptacles and/or heat sinks.

An additional object is to provide a cathode/heater construction and mounting structure therefor in an electron discharge device, such that the cost of construction and assembly of the device is measurably reduced from that incurred in conventional manufacturing techniques.

An additional object is to provide in an electron discharge device one of a variety of cathode/heater constructions all of which improve metal-to-metal contact of the cathode or heater to the bosses to which they are mounted and, consequently, improve the circuit-path conductivity.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following drawings in which:

FIG. 1 is an elevation, shown principally in vertical section, of an electron discharge device incorporating the principles of the present invention.

H6. 2 is a fragmentary view illustrating a first alternate construction for a cathode as well as its mounting to opposite cathode mounts.

LII

FIG. 5 is substantially similar to FIG. 1, is a fragmentary view, and illustrates that in a preferred form of the invention the cathode or heater structure has an inside diameter which is slightly less than theoutside diameter of the cathode or heater boss to which the former is secured.

FIG. 6 is a view similar to FIG. 5 but illustrates the cathode or heater construction as taking a helically-wound ribbon form.

FIG. 6A is a transverse cross section of a turn of the wire forming the cathode or heater of FIG. 7.

FlG. 7 is similar to FIG. 6 illustrates a cathode or heater as being formed of a conductive wire having an inside tangential character resembling a flat plane, this for increased surface contact with the cathode or heater boss of the mounting structure.

In FIG. I electron discharge device 10 includes annular wall 11 of insulative material generally formed of glass. Disposed through and sealed through the annular wall 11 is an anode terminal 12 which is interiorly connected to anode 13. The opposite, annularly-configured ends of electron discharge device 10 preferably take the form of a cathode/heater mount 14 and also cathode/heater mount 15, both being made of a metal known by the trade name Kovar and joined to annular wall 11 in a glass-to-rnetal seal in a conventional manner. In the case of cathode/heater mount 15, the same is joined to end flange 16 by means of heliarc or nonoXidation type weld 17. End flange 16 will be joined to the annular wall 11 by means of a conventional glass-to-metal seal as at M.

Cathode/heater mounts 14 'and 15 are preferably frustoconical in shape to accommodate the opposite poles of a magnet where such is employed with the tube design. In any event, the invention contemplates that the cathode/heater mounts l4 and 15 will be provided with cathode/heater mounting bosses '18 and 19 preferably comprising molybdenum plugs. The latter are brazed or spot-welded to respective ones of the mounts 14, 15.

Grid 20 is conventional in form and is electrically and physically connected to grid terminal 21, the latter being disposed through insulated plug 22 inserted in Kovar cathode mount 15. A glass-to-metal seal 23 is provided to seal the grid terminal 21 in place.

A signal source 24 may be coupled between grid terminal 21 and a source of grid bias voltage 25. The opposite terminal of the grid bias voltage source 25 is connected to junction 26. End flange 16 in the embodiment shown is maintained at the same reference potential as junction 26, includes junction 27, and is connected thereby to one terminal of cathode/heater voltage source 28. The opposite terminal of cathode/heater voltage source 28 is connected to cathode/heater mount 14 in the manner illustrated. Plate voltage source 29 is connected between terminal 26 and plate terminal 12 in the manner shown.

The grid and plate and their mountings may take any conventional form as indicated. Also, any suitable support structure as needed may be incorporated in the two. This is all conventional. Of great importance, however, is the inclusion of cathode 30. In the embodiment shown in FIG. I cathode 30 takes the form of a helix the turns at the opposite ends of which are preferably touching and directly mounted upon the opposite mounting bosses 18 and 19. The cathode will be formed of conventional material such as tungsten or thoriated tungsten. It will be understood that where a magnet is employed, then the grid 20 may be omitted from the design.

In the embodiment shown there are several advantages present. This will be understood with reference to the operation of the tube. In the first place, the tube ends composed of mounts 14 and 15 serve as heat sinks, both by virtue of their mass and also by virtue of their contiguousness with the outside atmosphere at their exterior surfaces. An efficient heat sink is needed where, in certain specialized tube designs, the operating temperature of the cathode may approach 2200 CB. (The term CB in the art refers to the bright" temperature of a heated cathode as measured by an optical pyrometer.) As to cathode operation, it is much preferred that the cathode operate substantially at the same temperature along its entire length. This is achieved in the present invention since the turns are designed in a uniform cross section and evenly spaced. it is noted that the very few (two or three) turns used to mount the cathode on the molybdenum pluge l8 and 19 will reduce the temperature at these points. ln practice, the inventors tube design has indicated a temperature reduction to about 406 CB at the cathode mounting boss. The temperature gradient present has been found not to be deleterious relative to the cathode as the same progresses from its opposite mountings toward the center of the cathode structure.

H6. illustrates that in a preferred form of the invention the molybdenum mounting boss has slightly larger outside diameter than the insidediameter of the cathode. In practice, it is designed that the inside diameter of the cathode or heater be about .005 inches undersized relative to the outside diameter of the cathode mounting boss. There will be sufficient resiliency in the cathode such that the end turns of the cathode can be literally screwed on to the cathode mounting bosses. Then, when current is applied, the molybdenum boss (by its greater coefficient of thermal expansion relative to that of tungsten of the cathode) will tend to increase its tight fit relative to the cathode. That is to say, the cathode mounting boss expands a greater degree for a given temperature than the cathode. l-iencc, operating temperatures serves not to loosen the connection between the cathode and its mounting bosses, but rather to tighten the same.

it is to be noted that such is accomplished without the need of conventionally known securement techniques such as platinum brazing. This vastly simplifies the cost of manufacture of the tube relative to the cathode and actually improves the cathode connection. Note is to be made that both alignment and a secure mounting characteristic are achieved, owing to the relationship of the cathode to the cathode mounting bosses upon which it is, literally, screwed.

A further element to consider is the method of providing a good current path for electrons proceeding through the juncture composed of the cathode mounting bosses and the cathode itself. Tangential contact of a normally round piece of wire against the surface of the cathode mounting boss causes some restriction for current flow. it would, of course, be advantageous to increase the area of contact of each turn of wire as it engages the surface area of the respective cathode mounting bosses id and 119. Such an increase can be accomplished through use of a cathode formed of a ribbon wire as illustrated in MG. 6 or of a cathode helix having a representative turn a cross section of which is illustrated in H6. 6A wherein one side, perhaps a third of the surface area of the wire of which the cathode is formed, is ground or otherwise made flat as at surface 3'11 of cathode 30B.

in FIG. 2 cathode mounts CM are slightly different in configuration. Nonetheless, the same principle applies, with the molybdenum mounting bosses being spot welded or brazed to the Kovar cathode mounts. Kovar is ideally used because of its adaptability for glass-to-metal seals and its advantageous temperature properties.

In FIG. 2. cathode 32 includes an elongate central cathode length 33 having'at its opposite ends 1% and 35 one or more turns of the cathode for mounting upon respective cathode mounting bosses CM. The structure in FIG. 2 may well be employed where a low temperature operating range is contemplated and where a high electron density about the cathode is not required.

H6. 3 illustrates a tubular cathode mesh 36 the ends of which are pressed over the cathode mounting bosses 37 and 38 in a manner heretofore described in connection with FIG. l. The mesh 36 may raise the form of a Chinese fingers grip" and in such form may be easily mountable over the cathode mounting bosses.

MG. 45 illustrates the situation of an indirectly heated cathode wherein member 39 is pressed over molybdenum mounting bosses db and 4t and serves as a heater for directly heating cathode sleeve 42. in the situation of FIG. d, the

sleeve will generally be composed of nickel coated with a rare earth oxide, such as barium or strontium oxide. in such even the heater will be tungsten or molybdenum coated with aluminum oxide. The nickel sleeve can be brazed or spot welded to one of the mounting bosses as at W in H6. d.

MG. 7 illustrates the condition wherein a cathode formed of wire material, shown in 6A, is pressed over a respective cathode mounting boss 43 of cathode mount 44.

In summary, the present invention consists principally in the provision of a unique cathode construction in a variety of electron discharge devices. Advantageous use is made of a novel principle incorporated in the invention wherein the mounts for the cathode are formedof a metal the coefficient of thermal expansion of which is greater than the coefficient of thermal expansion of the material of which the cathode/heater is made. Secondly, and most important, the cathode is mounted over the cathode mounting bosses in such a manner as not to require the employment of platinum brazing or other usual means of permanent attachment. Rather, and in a preferred form of the invention, the cathode or heater is simply pressed onto the mounting bosses the outside diameters of which are slightly greater than the inside diameter of the cathode/heater. Heating of the cathode or heater merely increases the degree of retentive engagement ofthe cathode relative to the mount ing bosses. The current path .is improved through use of a cathode at least the end of which are flattened as through the employment of a ribbon wire as in FIG. 6 or a flattened wire as in 6A, so as to increase surface contact of the cathode/heater with the molybdenum mounting bosses.

The structure in FIG. 1 itself is immensely useful in that the cathode or other parts within the tube can be replaced simply by removing the heliarc weld so as to remove the cathode mount 15 and the electrical components attached thereto. This is a marked improvement over prior tube designs.

The invention, as above described, applies both to heater and cathode constructions and their mountings. In the claims appended hereto the term thermionic electron generating means is used to describe generically both a heater and also a cathode, whether the cathode be a directly heated filament or be heated indirectly by a separate heater to heat the cathode to emitting temperature; i.e.', thermionic electron generating means generically refers to an element across which 21 voltage is applied to cause the same to be elevated in temperature and consequently, directly or indirectly, produce electrons.

The electron discharge device ll0 of FIG. 1 will, of course, be evacuated such that a pressure of l X l() mmHg or less exists in the tube. It is most important to note that such a heater or cathode connection is unique and ideally suited to evacuated environments because of the absence of oxidizing gasses; were the same to be used in the presence of air or other oxidizing agents, the simply pressed connections of the cathode or heater extremities to their mounts would soon fail.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects.

lclaim: I

l. in an electron discharge device, a pair of spaced, raised, electrically-conductive cylindrical mounts, means for connecting a voltage across said mounts coupled thereto, and a thermionic, electron-generating means comprising a unitary, electrically conductive, wire element having annularly-configured opposite ends respectively grippingly mounted to and over said mounts, said ends having inner surfaces which are flat, whereby to provide maximum surface contact of said ends with said mounts.

2. Structure according to claim ll wherein said electron generating means comprises a helically wound element.

3. Structure according to claim 1 wherein said electron generating means comprises a tubular, wire-mesh element.

4%. Structure according to claim It wherein said electron generating means comprises a helically wound, flat ribbon element.

generating means comprises a heater for heating an electron emitter to emitting temperature.

8. Structure according to claim 1 wherein said mounts are cylindrical.

Claims (8)

1. In an electron discharge device, a pair of spaced, raised, electrically-conductive cylindrical mounts, means for connecting a voltage across said mounts coupled thereto, and a thermionic, electron-generating means comprising a unitary, electrically conductive, wire element having annularly-configured opposite ends respectively grippingly mounted to and over said mounts, said ends having inner surfaces which are flat, whereby to provide maximum surface contact of said ends with said mounts.

2. Structure according to claim 1 wherein said electron generating means comprises a helically wound element.

3. Structure according to claim 1 wherein said electron generating means comprises a tubular, wire-mesh element.

4. Structure according to claim 1 wherein said electron generating means comprises a helically wound, flat ribbon element.

5. Structure according to claim 2 wherein the inner helical surface of said element is tangentially planar.

6. Structure according to claim 1 wherein said electron generating means comprises an electron emitter.

7. Structure according to claim 1 wherein said electron generating means comprises a heater for heating an electron emitter to emitting temperature.

8. Structure according to claim 1 wherein said mounts are cylindrical.

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