US3560780A

US3560780A - Vacuum tube with coaxial assembly of electrostatic focusing means and electron gun mount

Info

Publication number: US3560780A
Application number: US732218A
Authority: US
Inventors: Johann B Beeli
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; ITT Inc
Priority date: 1968-05-27
Filing date: 1968-05-27
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02

Abstract

The invention comprises an electron gun having an outer cylindrical tube, inside of which a shorter cylindrical tube is positioned. The inner tube is maintained at a different directcurrent potential than the outer tube. The inner tube is positioned inside the outer tube spaced from the ends of the outer tube. Symmetrical electron lenses are then produced at the ends of the inner tube. The use of the outer tube as a mechanical support for the inner tube makes the construction mechanically strong, yet inexpensive.

Description

United States Patent m1 3,560,780

[72] Inventor Johann B. Beeli 2.219,] 1 1 10/1940 Nicoll 313/82 Sylmar, Calif. 2.533.790 12/1950 Grivet 313/82 [2] A pl. No 732,218 2.740919 4/1956 Fleming... 3I3/82X [22] Filed May 27, 1968 3.210.145 l0/1965 Fyler 313/82X [45] Patented Feb. 2. 1971 2248.558 7/1941 Schlesinger 313/82X [73] Assignee International Telephone and Telegraph 2,721,287 10/ l 955 Van Ormer. 3 l 3/82X Corporation 3,2414 1 0 4/1966 Oess 313/82X New York, N.Y.

a corporation of Delaware [54] VACUUM TUBE WITH COAXIAL ASSEMBLY OF ELECTROSTATIC FOCUSING MEANS AND 82BFC, 251, 257

[56] References Cited UNITED STATES PATENTS 2,185,807 l/l940 Gabor et a1. 313/82 Primary ExaminerRoy Lake Assistant Examiner-V. Lafranchi Attorneys-C. Cornell Remsen, Jr., Walter]. Baum, Paul W.

Hemminger, Percy P. Lantzy and A. Donald Stolzy ABSTRACT: The invention comprises an electron gun having an outer cylindrical tube, inside of which a shorter cylindrical tube is positioned. The inner tube is maintained at a different direct-current potential than the outer tube. The inner tube is positioned inside the outer tube spaced from the ends of the outer tube. Symmetrical electron lenses are then produced at the ends of the inner tube. The use of the outer tube as a mechanical support for the inner tube :makes the construction mechanically strong, yet inexpensive.

BACKGROUND OF THE INVENTION This invention relates to electron discharge devices. and more particularly to an inexpensive. high strength electron gun.

In the past it has been the practice to form an electron gun from a cathode and three axially aligned conductive cylinders. all of the cylinders having the same inside and outside diameters. The middle cylinder is then maintained at a potential different from the outer two to form focusing electron lenses at the mutually adjacent ends of the tubes.

Due to the use of this prior art construction. extreme care must be taken to align the tubes. The alignment must also be made with an insulating material. This makes the gun as sembly relatively weak.

SUMMARY OF THE INVENTION In accordance with the device of the present invention, the abovedescribed and other disadvantages of prior art are overcome by providing a fixed conductive tube inside of which a second tube is fixed concentric to the first tube. Conveniently, the second tube is mounted in insulator rings which are in turn held against the ends of the second tube by metal rings that are spot welded to the first tube. The second tube is thus smaller in diameter than the first tube and is spaced and insulated therefrom. The second tube is also centrally located inside the first tube, the second tube being shorter than the first tube.

In accordance with the foregoing, the spot welding of the rings makes it possible to assemble and completely fabricate the electron gun of the invention in a few simple steps. Use of the first tube as the structural supporting member for the second tube makes the unit unusally strong.

In accordance with another feature of the invention, a small hole is provided through the wall of the first tube at a position intermediate the ends of the second tube so that a lead-in wire may be connected to the first tube through the hole. This makes it possible to create uniformally symmetrical electron lenses at ends of the second tube.

The above-described and other advantages of the present invention will be understood from the following description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWING In the drawing, which is to be regarded as merely illustrative: The FIG. is a longitudinal sectional view through a vacuum tube such as a TV camera tube employing the electron gun of the present invention.

DESCRIPTION OF OF THE PREFERRED EMBODIMENT In the drawing a vacuum tube is indicated at having an evacuated envelope 11. The electron gun of the invention is indicated at 12 in the right end tube 10.

Gun 12 comprises an outer cylindrical metal tube 13, having a hat-shaped cathode 14 with an electron emissive coating 15 thereon. Cathode 14 is held against the right end of tube 13 with an insulator ring 16 sandwiched in between. Ring 16 has an axial projection 17, which extends into the interior of the right end of tube 13.

Electron gun 12 also includes an inner metal cylinder 24, which is supported on insulator rings and 26 between metal gs 27 and 28. Metal rings 27 and 28 are spot welded to tube 13.

A power supply 29 connected to a cathode lead 30, to a lead 31 to outer tube, and to a lead 32 to inner tube 24. Lead 32 extends into envelope 11 and through a hole 33 in the sidewall of tube 13. Hole 33 is positioned intermediate the ends of tube 24 so that electron lenses at the ends of tube 24 are symmetrical about the axis of thegun.

In accordance with the foregoing, it WlII be appreciated that the gun 12 may be a stacked construction which is easy to assemble and to fabricate. The jaws of a spot welder may be easily inserted into the interior and over the exterior of tube 13 to spot weld rings 27 and 28 thereto. The electron gun 12 therefore, may be manufactured at low cost. Yet, the gun will have considerable mechanical strength because of the use of unitary tube 13.

Envelope indentations 20 and 21 hold cathode 14 against tube 13. lndentations l8 and 19 support the central portion of tube 13. lndentations 22 and 23 support tube 13 and hold it firmly against cathode 14.

It is also an advantage of the invention that the small hole 33 does not reduce the mechanical strength of tube 13 substantially. whereas this enables lead 32 to project therethrough into contact with tube 24. This arrangement makes it possible to produce electron lenses at the ends of tube 24 which are symmetrical about the axis of gun l2.

Notwithstanding the foregoing, it will be appreciated that any mounting means for tube 24 and cathode 14 may be employed other than those shown and described. Further, hole 33 may be omitted and any other convenient connecting structure may be provided, if desired.

Many other changes and modifications will suggest themselves to those skilled in the art. The invention, is therefore, not to be limited to the embodiment selected for this disclosure, the true scope of the invention being defined only in the appended claims.

Iclaim:

1. A vacuum tube having an evacuated envelope, an electron gun mounted in said evacuated envelope and comprising: a first conductive tube fixed in said envelope, said tube having two open ends; a cathode; first means to fix said cathode in said envelope in a position to supply electrons to one end of said first tube; a second conductive tube open at both ends; second means to fix said second tube inside said first tube coaxially therewith and in a position insulated therefrom, and spaced from the ends thereof, said second tube being smaller in cross section and shorter than said first tube; and third means for maintaining said tubes at different direct-current potentials, said third means including a conductor, said first tube having a hole therethrough between the ends of said second tube, said conductor extending through said hole in a position insulated from said first tube but in contact with said second tube, said second tube having a length sufficiently great and a location such that a radial projection of the crosssectional area of said hole on the outer surface of said second tube is completely intercepted by said second tube, the entire cross-sectional area of said hole thereby lying between the ends of said second tube, said tubes being thin, concentric cylinders, said cathode including a hat-shaped, metal base having an electron emissive coating thereon, said base having a radial flange, said first means including a first insulator ring extending over said one end of said first tube, said envelope having indentations to hold said base fiangetight against said first insulator ring, said envelope having indentations to support said first tube and to prevent movement thereof away from said cathode, said second means including second and third insulator rings to fii snugly inside said first tube, said second tube ends lying on said second and third insulator rings, said second and third rings having radial flanges, extending over the ends of said second tube to retain the same therebetween, said second means including a pair of metal rings on the outside of said second and third insulator rings respectively, said metal rings being fixed to said first tube in a position to hold said second and third insulator rings snugly against the corresponding ends of said second tube.

Claims

1. A vacuum tube having an evacuated envelope, an electron gun mounted in said evacuated envelope and comprising: a first conductive tube fixed in said envelope, said tube having two open ends; a cathode; first means to fix said cathode in said envelope in a position to supply electrons to one end of said first tube; a second conductive tube open at both ends; second means to fix said second tube inside said first tube coaxially therewith and in a position insulated therefrom, and spaced from the ends thereof, said second tube being smaller in cross section and shorter than said first tube; and third means for maintaining said tubes at different direct-current potentials, said third means including a conductor, said first tube having a hole therethrough between the ends of said second tube, said conductor extending through said hole in a position insulated from said first tube but in contact with said second tube, said second tube having a length sufficiently great and a location such that a radial projection of the cross-sectional area of said hole on the outer surface of said second tube is completely intercepted by said second tube, the entire cross-sectional area of said hole thereby lying between the ends of said second tube, said tubes being thin, concentric cylinders, said cathode including a hatshaped, metal base having an electron emissive coating thereon, said base having a radial flange, said first means including a first insulator ring extending over said one end of saiD first tube, said envelope having indentations to hold said base flangetight against said first insulator ring, said envelope having indentations to support said first tube and to prevent movement thereof away from said cathode, said second means including second and third insulator rings to fit snugly inside said first tube, said second tube ends lying on said second and third insulator rings, said second and third rings having radial flanges, extending over the ends of said second tube to retain the same therebetween, said second means including a pair of metal rings on the outside of said second and third insulator rings respectively, said metal rings being fixed to said first tube in a position to hold said second and third insulator rings snugly against the corresponding ends of said second tube.