US2886733A

US2886733A - Grid structure for electron tube

Info

Publication number: US2886733A
Application number: US548170A
Authority: US
Inventors: Eugene J Naill
Original assignee: Machlett Laboratories Inc
Current assignee: Machlett Laboratories Inc
Priority date: 1955-11-21
Filing date: 1955-11-21
Publication date: 1959-05-12
Anticipated expiration: 1976-05-12

Description

May 12, 1959 E. J. NAILL GRID STRUCTURE FOR ELECTRON TUBE 2 'Sheets-Sheetl Filed Nov. 21, 1955 INVENTOR. EUGENE J. NAILL ATTORNEYS y 12, 1959 E. J. NAILL 2,886,733

GRID STRUCTURE FOR ELECTRON TUBE Filed Nov. 21, 1955 2 Sheets-Sheet 2 {I II In VIII/[1% 5 l &

INVENTOR.

EUGENE J. NAILL ATTORNEYS GRID STRUCTURE FOR ELECTRON TUBE Eugene J. Nail], New Canaan, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application November 21, 1955, Serial No. 548,170

3 Claims. (Cl. 313-265) This invention relates to electrode structures for electron tubes and has particular reference to a novel grid structure wherein a mesh grid is supported in a manner permitting free expansion of the grid with respect to its supporting structure while retaining efiicient electrical contact therewith.

My copending application Serial No. 428,313 filed May 7, 1954, now U. S. Patent No. 2,850,664, shows and describes one method of improving upon known prior grid structures, and the present invention is a further improvement upon a similar electron tube structure.

In the presently described type of electron tube it is desirable to employ a grid composed of a mesh of relatively fine interwoven wires which is positioned in pre determined close-spaced relation to and between a cathode and an anode for controlling flow of electrons from the cathode to the anode. The grid is preferably mounted upon one end of a tubular support to which it is necessarily conductively connected. However, it is essential that the grid be permitted to freely expand, without breaking the electrical connection with the support, when it becomes heated during operation of the tube.

The prior art shows various relatively ineffective ways of mounting mesh grids, but in most cases the grids are not permitted to expand sufficiently to prevent deformation such as produces variations in the interelectrode spacings. In other cases, while the grids may expand, the electrical conductivity between the grids and their supporting structures is inefficient to such an extent that radio frequency currents are not efficiently passed through the structure.

Accordingly, it is a primary object of this invention to provide an improved grid structure for electron tubes wherein a mesh-type grid is supported upon and in efficient electrically conductive engagement with a generally tubular structure in desired spaced relation to an anode and a cathode, the grid being permitted to freely expand with respect to its supporting structure without interfering with the electrical conductivity therebetween.

This objective is accomplished by providing a fiat annulus over the end of the tubular grid support, which annulus supports the marginal areas of the mesh grid. A flanged collar is positioned around the circumference of the end portion of the support and the adjacent outer periphery of the annulus, and the flange thereon engages the outer exposed surface of the grid. The collar is welded or otherwise secured directly to the support whereby efiicient electrical conductivity is assured between the support and the grid. The grid and annulus assembly, however, is not rigidly secured to the collar and thus is free to expand when heated.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein Fig. 1 is a front elevational view partly in axial section illustrating a tube embodying a preferred form of this invention;

Fig. 2 is an enlarged axial sectional view of the grid structure of the tube shown in Fig. 1; and Fig. 3 is a plan view of the structure shown in Fig. 2. Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, the tube shown in Fig. 1 includes a glass cylinder 10 which forms a part of the tube envelope. To one end of the cylinder 10 is vacuum-sealed a tubular anode terminal 11 which supports within it an anode 12;

the active surface 13 of which is directed toward and in predetermined spaced relation to the active surface of a cathode 14. The cathode 14 is substantially planar and parallel to the active anode surface 13 and is mounted on one end of a tubular support 15 by which it is connected to one end of a tubular metal cylinder 16. The cylinder 16 is connected by a ring 17 of dielectrical material to a tubular terminal 18, the support 15, cylinder 16, ring 17 and terminal 18 being substantially coaxial.

The terminal 18 supports therewithin a metal disc 19 to which is connected one end of a filament-supporting rod 20. The rod 20 extends toward the cathode 14 and has attached to it one end of a filament 21 which is positioned adjacent the cathode 14 for heating purposes. The other end of the filament 21 is connected by a conductor 22 to the cylinder 16. One end of a metal tube 23 is secured in encircling relation to the cylinder 16 and extends longitudinally of the device in spaced encircling relation to the first terminal 18. The outer end portion of the tube 23 is sealed to the inner surface of a second tubular cathode terminal 24, thus providing; a complete circuit from

terminals

18 and 24 through the filament 21.

The outer terminal 24 is connected by a dielectric ring 25 to one end of a coaxial cylinder 26 having its other end sealed to an intermediate portion of the inner surface of a coaxial tubular grid support 27. The outer end portion of the grid support 27 is sealed to a tubular grid terminal 28 which is sealed to the adjacent end of the glass envelope portion 10. The grid-support ing structure is thus coaxial with the cathode structure and anode. The inner end surface of the grid support 27 terminates adjacent a plane passing between the anode and cathode surfaces substantially perpendicular to the axis of the coaxial electrodes.

On the inner end of the grid support 27 is positioned a metal annulus 29 whichcarries a circular wiremesh grid 30, the grid spanning the central opening in the annulus and having its marginal portions securely afiixed to the annulus by suitable means such as by brazing while the mesh is maintained in stretched condition.

The annulus 29 having the grid 30 thereon is held in place on the end of the grid support 27 by a flanged collar 31 which fits over the support 27 and annulus 29, with the flange portion 32 thereof overlying the outer surface of the grid 30. In assembling the device, the collar 31 is urged axially in the direction of the cathode terminals to press the flange portion 32 firmly against the grid 30, and then is spot-welded to the support at frequent intervals around its circumference. This method insures efiicient conductivity between the support 27 and collar 31 as well as between the collar 31 and grid 30.

The collar 31 is preferably made of a thin, soft metal which permits it to be welded to the support with light delicate Welds which do not destroy the space relationships between the assembled parts such as might result from distortion occurring during normal methods of welding.

It is particularly pointed out that with a thin collar 31, the collar may be welded to the annulus 29 and the flange portion 32 thereof may also be welded to the grid, and when the grid and annulus are heated during operation of the tube the inherent characteristics of the Ice Patented May 1 2, 1959 thin collar will permit flexing thereof sufficiently to allow relatively unrestricted thermal expansion of the grid assembly.

Since the flange32 is annular in shape, it is apparent that a substantially continuous annular line of contact is made between the grid and flange insuring eflicient passage of radio frequency currents. While a continuous line of contact is not required for eflicient operation of a tube, it is preferred that the area of contact around the grid be substantially continuous, and at least of greator area than that which is provided by spaced contacts.

With the present construction it is also apparent that the supporting structure for the grid does not require the use of movable members which, in order to function efliciently, must be inherently relatively thin and flexible. The grid 30 of the present invention is permitted, with the annulus 29, to expand freely. The flange does not provide any amount of restriction such as would prevent the desired free expansion characteristics and does provide means for obtaining the desired area contact for efficient radio frequency current conductivity.

A further desirable feature of a coaxial tube structure as described lies in the fact that the end of the cylinder 27 may be presented, during assembly of the tube, as a locating surface for the grid. This particular construction permits the end surface of the cylinder 27 to be machined so as to be parallel with and in exact spaced relation to the active surface of the cathode, which desirable method of fabrication cannot readily be performed in other tube structures.

From the foregoing description it is apparent that an improved grid structure for electron tubes has been provided in accordance with the objects of this invention. It is also apparent that various modifications Within the scope of the invention may occur to those skilled in the art. Therefore, it is to be understood that the details of construction described herein shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. An electrode structure for an electron tube, comprising a rigid annular support, an electrode having thermal expansion characteristics positioned on the rigid support and consisting of an annulus having a grid affixed thereto and spanning the central opening therein, and a collar affixed in encircling relation to the support and freely encircling the outer periphery of the electrode, said collar having a flange engaging the exposed surface of the electrode and retaining the electrode firmly upon the support, said flange being characterized by its ability to flex with changes in thermal expansion characteristics of the eleo trode.

2. An electrode structure for an electron tube, comprising a rigid substantially tubular support having one end provided with a continuous planar annular surface, an electrode having thermal expansion characteristics positioned on the annular end of the rigid support and consisting of a relatively flat annulus having one side surface engaging said end of the support and having a circular mesh-type grid afiixed throughout its marginal area to the other side of the annulus and spanning the central opening therein, and retaining means conductively connecting the grid with the rigid support and retaining the electrode firmly upon the annular end thereof comprising a ring encircling the end of the support and the outer periphery of the electrode, the ring being affixed to the support and having an inwardly turned flange overlying the electrode and in firm conductive engagement with the marginal portion of the grid, the flange being relatively thin and capable of relatively easily flexing under the influence of changing thermal expansion characteristics of the electrode.

3. In an electron tube embodying an envelope containing substantially planar cathode and anode electrodes having their effective surfaces in spaced substantially coaxial parallel relation, a grid electrode having thermal expansion characteristics positioned between the effective surfaces of the cathode and anode electrodes and comprising a wire mesh grid aflixed throughout its marginal area to one side of a relatively flat annulus, a relatively rigid annular support encircling the cathode electrode and engaging and supporting the annulus, and a collar conductively connecting the grid with the support and retaining the grid electrode firmly upon the support, the collar being aflixed to the periphery of the support and having an inwardly turned flange overlying and in firm conductive engagement with the marginal portion of the grid, the flange being relatively thin and capable of relatively easily flexing under the influence of changing thermal expansion characteristics of the grid electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,446,271 Eitel Aug. 3, 1948 2,455,868 Koch Dec. 7, 1948 2,467,303 Watson Feb. 8, 1949' 2,714,676 Machlett et al Aug. 2, 1955