US2950411A

US2950411A - Power tubes for operation at high frequencies

Info

Publication number: US2950411A
Application number: US737968A
Authority: US
Inventors: Anthony G Nekut; Merrald B Shrader
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1958-05-26
Filing date: 1958-05-26
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. 23, 1960 A. cs. NEKUT ETAL POWER TUBES FOR OPERATION AT HIGH FREQUENCIES Original Filed May 2, 1955 I VE TORS Twin i) I POWER TUBES FOR OPERATION AT HIGH FREQUENCIES Anthony G. Nekut and Merrald B. Shrader, Lancaster,

Pa, assignors to Radio Corporation of America, a corporation of Delaware (Zontinuation of abandoned application Ser. No. 505,388, May 2, 1955. This application May 26, 1958, Ser. No. 737,968

2 Claims. (Cl. 313-250) This invention relates to power electron tubes for operation at high frequencies and particularly such tubes characterized by a stacked construction of the component tube parts.

The instant application is a continuation of our application Serial No. 505,388 filed May 2, 1955, now abandoned.

in electron tubes designed for high power operation, especially at high frequencies, good heat dissipation from the foraminous portions of the grid and anode electrodes is highly desirable. Where such a tube must also be compact for reason of specific installation, conflicting design considerations result. This is especially true with regard to the grid electrodes which are conventionally provided as internal electrodes mounted on pin or disk lead-ins.

Accordingly, it is an object of this invention to provide a novel, compact, and rugged power tube for ultra-high frequency purposes.

A further object of this invention is to provide a novel and improved electron tube structure which is compact and yet which permits efiicient heat dissipation by certain of the tube electrodes.

Another object of our invention is the provision of a novel and improved electron tube structure permitting simplified, and consequently economical, parts fabrication and assembly thereof.

Briefly, according to our invention an electron tube is provided with a novel base structure made up of flat annular ceramic discs acting as insulators between the electrodes. In this regard, each electrode is provided with a flat annular metal flange with certain of said electrodes comprising jointless, completely integral units including such flanges. The electrodes are cylindrical, nested, and coaxially arranged with their flat flanges interleaved with the ceramic discs and vacuum sealed to the flat surfaces only thereof. As such, the electron tube can be fabricated by simply stacking up the electrodes and ceramic discs and vacuum sealing them together in a single jigging and furnace brazing step.

The invention will be described herein as embodied in a tetrode tube, but it will be understood that the invention can be equally well used in triodes, or any other multi-grid tubes for example pentcdes and the like. Accordingly, in the drawing,

Fig. 1 is an elevational view, partly sectional, of a tube embodying the invention;

Fig. 2 is a sectional view of Fig. 1, taken along the line 22 thereof, and viewed in the direction of the arrows.

The particular tube that is illustrated in the drawing comprises an electron emitting cathode 10, a control grid 11, a screen grid 12, and an output anode or plate electrode 13. A suitable heater element, for example in the form of a coiled heater wire 14, is located within the cathode it The anode 13 constitutes the enclosing bulb of the tube and it may be provided at its upper end with a metal exhaust tubulation 15 which can be pinched states iiatent Q off and sealed, after the tube has been evacuated, and processed in the conventional ways. The electrodes referred to each have an electron-active portion which is in radial register with the electron emitting portion of the cathode. In accordance with the invention the tube is closed ofi at its lower end by a base construction comprised of flat

annular insulator discs

16, 17, 18 and 1?, to which are directly sealed the flat annular flanges Ztl, 21, 22 and 23, of the respective electrode tubular skirts or extensions.

Further, in accordance with the invention, the discs 16-19 are preferably of ceramic. And since it is their opposite flat faces only that are sealed to the electrode flanges, only those flat faces need be accurately ground to flat form to enable them to be directly and vacuumtight sealed to their adjacent respective electrode flanges. In order to effect such seals, the ground flat faces of each ceramic disc are metallized and brazed to the electrode flanges as indicated in Fig. l, by any well known brazing operation, for example in a hydrogen atmosphere using a eutectic silver-copper brazing alloy. Preferably, the ceramic of which the discs are made is of the high alumina content kind. Merely by way of example, the ceramic discs may be metallized on their opposite flat faces only, by painting thereon in the required sealing region, a mixture of extremely fine tungsten and iron powders with a binder, and then hydrogen-firing the ceramics at approximately 1400 degrees C. After this fiting or sintering operation, the metallized areas may be wire-brushed to remove any loose powder, and then the metallized surface may be lightly plated with a copper or other metal to promote solder flow when the electrode flanges are brazed thereto.

It will be readily appreciated that unlike prior art tubes, only flat surfaces are utilized as sealing surfaces throughout the entire tube. Such construction avoids the necessity of accurately finishing cylindrical ceramic surfaces to selected sizes for fit to a mating cylindrical electrode surface. And equally important, such construction avoids the necessity of metallizing cylindrical ceramic surfaces. The fact that only flat surfaces are utilized as sealing surfaces permits much simpler and more economical machining of the annular ceramic discs since no close size tolerances need be imposed except on the flat surfaces where machining is much easier. In fact, no finish machining need be performed at all on any cylindrical ceramic surface. And since metallizing is applied only to flat ceramic surfaces, the necessary jigs and procedures are greatly simplified.

Another very important advantage which stems from flat surface sealing construction is the complete stacking of all of the component tube parts to be brazed and the corresponding single furnace brazing thereof to provide the vacuum envelope. This feature will be more fully described hereinafter.

The cathode 10 is in the form of an inverted cylindrical metal cup having its exterior peripheral surface coated with any suitable electron emission material 24. The cathode cylinder, which carries the electron emissive coating material, is drawn down to an elongated thin walled cylindrical or skirt section 25 which may be integrally formed with or welded to a one-piece self-supporting inverted cup-shaped contact member 26 whose flat flange 2.3 is sealed between the opposed metallized faces of the ceramic thscs 18, 19. If desired, the cylindrical cup-shaped cathode l0 and the thin walled skirt portion 25 and the flanged member 23 may be separate, preformed elements suitably welded together to form a rigid unit. The purposes of the thin walled section 25 is to act as a'heat isolating support between the cylindrical cathode and the ceramic disc 19. The heater element than integral grids according to our invention.

, a 3 14 has one terminal welded to the upper flat top of cathode member 10, and the other terminal is welded to a cylindrical metal rod27 which passes through a central openingin the'cer'amic disc 19. Welded or brazed to rod 27 is a metal washer 28 which is also brazed to the under surface of ceramic disc 19. a a a The control, grid 11 is a' one-piece self-supporting integral unit including a cylindrical foraminous portion 11', a tapered tubular skirt portion 29, a flat radially extending flange 22, and a cylindrical contact extension 30. The foraminous portion 11 of the grid may be constituted by a series of longitudinally extending, circumferentially spaced wires formed by cutting out a series of longitudinal slots in a non-perforate grid blank. The non-perforate grid blank may, forxexample,ihave been previously formed to the desired, contour and wall thickness.

As hereinbefore stated, such integrality of the entire grid 11 results inhighly superior thermal qualities compared to prior art grids fabricated with welded, brazed, or bolted joints wherein separate preformed portions of the grid are joined together to form a composite unit. Moreover, the integral construction, having no welds or other type joints, eliminates losses which frequencies.

The screen grid'12 is of one-piece integral construction similar to the control grid 11 and is provided with an integral flared skirt portion 31 which is also integral with the flat flange 21 and a cylindrical skirt 32. The flange 21 is sealed between the adjacent ceramic discs 16 and 17.

The anode 13 is in the form of an inverted metal cup having an integral flat flange 20 terminating in an upwardly extending cylindrical skirt 33. The flange 20 is sealed to the upper flat face of the ceramic disc 16. The

7 and the insulating spacers are flat, and since the insulating spacers are of ceramic, it will be appreciated that all parts of the tube to be brazed can be stacked, jigged for concentricity, and brazed together in a single, simple step. As such, only one furnace brazing step is required, and no involved machining of electrode or insulator cylindrical surfaces. is required to provide desired spacing surfaces since the desired longitudinal spacing is inherently provided by a simple stacking of the tube parts. Hence, as hereinbefore stated, an economical assembly procedure is provided.

It will be understood, of course, that the invention is not limited to any particular metal for forming the uni: tary or one-piece electrodes. However, in a preferred embodiment the ceramic discs 16-19 are of the high alumina type and the various electrodes are of copper or a high copper conteut alloy having high thermal and electrical conductivity. With such a combination of high alumina ceramic discs and electrodes of a 98% pp between said screen gird flange and said control grid alloy, it has been determined that the temperature drop forexample from the base of the foraminous grid portion to its cylindrical externalcontact skirt portion is of the order of degrees C whereas in prior tubes employing grids of conventional grid alloy compositions and having welded, brazed or bolted joints the temperature drop between the foraminous part of the grid and its external connection may be as high as 700 degrees C. Stated in other words, prior art grids having joined parts may operate 675 C. higher at the foraminous portions thzreof s is well known, high temperature operation of a grid electrode contributes to highly undesirable grid emission.

' Such, of course, is absent in integral grids.

As shown in Fig. 1, the axial length of each of the

ceramic discs

17, 18 and 19, is smaller than the diiference the latter introduces at high semblyr The net result of the structure described is that the particular base structure shown enables the tube to be made extremely short and compact in size. The cost of manufacture is materially reduced since low cost flat ceramic sealing discs can be used'in place of expensive ceramic cylinders. The one-piece electrode structures can be made of copper or similar material to provide excellent electrical and thermal conductivity and heat conduction away from the grid; Finally, the stacked flat ceramic disc and. flatmetal flanged construction provides ready assembly and rugged supports for the electrodes, assuring the maintenance .of their .co-axialalignmentduring and after as- Various changes and modifications may be made in the invention as describedwithout departing from the spirit and scope thereof.

We claim: a

1. A compact, high frequency, high power electron discharge device comprising cup-shaped anode, screen grid, control grid, and cathode electrodes each having a cylindrical electron-active portion; said electrodes being in nested co-axial spaced array in the order named with said anode surrounding the other of said electrodes; said anode having an integral radial flange extending outwardly from the open end thereof perpendicular to the axis of said array; said anode flange having an integral cylindrical extension at the outer periphery thereof coaxial with said array; each of said screen grid, control grid, and cathode electrodes having a tubular support portion extending from its open end away from the cylindrical electron-active portions thereof; the tubular support portions of said screen gird and said control grid being conical and the smaller diameter ends thereof being adjacent the electron-active portions of said electrodes; each of said tubular support portions having a radial flange extending outwardly from the extending open end thereof perpendicular to the axis of said array; each of said flanges of said tubular support portions having a cylindrical extension at the outer periphery thereof coaxial with said array; said cylindrical extensions of said anode, screen grid, control grid, and cathode electrodes being of progressively smaller diameter in the order named; both said screen grid and said control grid electrodes being made of high thermal conductivity metal and being one-piece self-supporting members consisting of their electron-active portions, their conical tubular support portions, their radial flanges, and their cylindrical extensions whereby heat from said grids is rapidly dissipated for' maintaining the temperature differential between the external and enclosed portions of said electrode at a small value whereby undesirable grid emission is substantially prevented; an annular ceramic member having flat end sealing surfaces and a shorter axial length than outer diameter sealed between said anode flange and said screen grid flange on its flat end surfaces only; a first annular ceramic disc having flat end sealing surfaces and a smaller axial thickness than radial thickness sealed asmaller axial thickness than radial thickness sealed be tween said control grid flange and said cathode flange on its flat end sealing surfaces only; a third annular ceramic disc having flat end sealing surfaces and a smaller axial thickness than radial thickness sealed on one of said surfaces only to the side of said cathode flange opposite that sealed to said second annular ceramic disc; said cylindrical extensions being in non-fit relation to the outer edge surfaces of said discs and extending axially at least coextensively-with an adjacent disc, whereby said cylindrical extensions of said screen grid and control grid electrodes define relatively large areas for improved heat transfer to engaging circuit elements; a heater electrode disposed 'within said cathode and comprising a heating element, a support rod, and a sealing flange; said heating element being connected between said cathode and one end of said support rod; said support rod being co-axial with said array and being attached to said sealing flange adjacent its other end; said sealing flange being perpendicular to the axis of said array and being sealed to the flat end sealing surface only of said third annular ceramic disc opposite the surface thereof sealed to said cathode flange; said flanges, said annular ceramic member and discs, and said anode comprising a vacuum tight envelope enclosing said electron active portions of said electrodes and being such that the entire constituent parts of said tube may be assembled, jigged externally of the vacuum envelope, and sealed in a single brazing operation.

2. A compact, high frequency, high power electron discharge device comprising cup-shaped anode, screen grid, control grid, and cathode electrodes each having a cylindrical electron-active portion; said electrodes being in nested co-axial spaced array in the order named with said anode surrounding the other of said electrodes; said anode having a radial flange extending outwardly therefrom and perpendicular to the axis of said array; said anode flange having a cylindrical extension at the outer periphery thereof coaxial with said array; each of said screen grid, control grid, and cathode electrodes having a tubular support portion extending from its open end away from the cylindrical electron-active portions thereof; each of said tubular support portions having a radial flange extending outwardly from the extending open end thereof perpendicular to the axis of said array; each of said flanges of said tubular support portions having a cylindrical extension at the outer periphery thereof coaxial with said array; said cylindrical extensions of said anode, screen grid, control grid, and cathode electrodes being of progressively smaller diameter in the order named; an annular ceramic member having flat end sealing surfaces and sealed between said anode flange and said screen grid flange on its flat end surfaces only; a first annular ceramic disc having flat end sealing surfaces and a smaller axial thickness than radial thickness sealed between said screen grid flange and said control grid flange on its flat end sealing surfaces only; a second annular ceramic disc having flat end sealing surfaces and a smaller axial thickness than radial thickness sealed between said control grid flange and said cathode flange on its flat end sealing surfaces only; a third annular ceramic disc having flat end sealing surfaces and a smaller axial thickness than radial thickness sealed on one of said surfaces only to the side of said cathode flange opposite that sealed to said second annular ceramic disc; said cylindrical extensions being in nonfit relation to the outer edge surfaces of said discs and extending axially at least coextensively with an adjacent disc, whereby said cylindrical extensions of said screen grid and control grid electrodes define relatively large areas for improved heat transfer to engaging circuit elements; a heater electrode disposed within said cathode and comprising a heating element, a support rod, and a sealing flange; said heating element being connected between said cathode and one end of said support rod; said support rod being coaxial with said array and being attached to said sealing flange adjacent its other end; said sealing flange being perpendicular to the axis of said array and being sealed to the flat end sealing surface only of said third annular ceramic disc opposite the surface thereof sealed to said cathode flange; said flanges, said annular ceramic member and discs, and said anode comprising a vacuum tight envelope enclosing said electron active portions of said electrodes and being such that the constituent parts of said tube may be assembled, jigged, and sealed in a single brazing operation.

References Cited in the file of this patent UNITED STATES PATENTS Polese Mar. 21, 1959