US2138918A

US2138918A - Cathode

Info

Publication number: US2138918A
Application number: US197757A
Authority: US
Inventors: Cecil E Haller
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-03-24
Filing date: 1938-03-24
Publication date: 1938-12-06
Anticipated expiration: 1955-12-06

Description

Dec. 6Q 1938. Q E HALLER 2,138,918

' CATHODE Filed March 24, 1958 v INVENT CEC/ L E. HALL A TTORNE Y.

Patented Dec. 6, 1938 PATENT OFFICE GATHODE Cecil E. Haller, Bloomfield, N. J., assignor, by

mesne assignments,

America, New York,

Delaware Application March 24,

5 Claims.

My invention relates to thermionic cathodes, particularly indirectly heated cathodes for use in electron discharge devices.

The usual indirectly heated cathode comprises a metal tube or sleeve surrounding a heating element, activated on its outer surface with an electron emitting coating, and supported at its ends by the insulating spacers of the electrode assembly. The metals commercially suitable for carrying the electron emitting coating are not particularly strong at the operating temperature of the cathode, which may suffer deformation caused by thermal and mechanical stresses in use. A cathode. sleeve madefrom a strip of metal rolled into tubular form and closed with a welded or locked seam along one'side of the sleeve bows considerably at its center between its end supports apparently because of the asymmetrical crosssectionofthe sleeve. Seamless tubing of electrolytic nickelsufliciently thin to permit quick heating lacks strength and is particularly diflicult to maintain in close spaced relation to other electrodes in the tube especially when the cathode is long with respect to its cross sectional dimen- 25 sions.

An object of my invention is to make an indirectly heated cathode that is strong and will not bow at operating temperatures, and is easy and inexpensive to manufacture.

A further object of my invention is to make a cathode which is easy to position in the mount, which will remain a fixed and predetermined distance from adjacent electrodes, and which is of thin metal to reduce heating time.

Further objects will appear in the following specification of my invention, a more complete understanding of which may be obtained in the description of specific embodiments set forth in the following specification and shown in the ac- 40 companying drawing in which-- Figure 1 shows an electron discharge device with a cathode embodying my invention,

Figures 2, 5, 6 and 7 are detailed views of indirectly heated cathodes constructed according to my invention, and

Figures 3 and 4 are schematic representations of means for making cathode sleeves according to my invention.

The tube of the beam forming type shown in Figure 1 comprises the conventional parallel insulating spacers l and 2 engaging in perforations the ends of tubular cathode 3 containing heating elements, and side rods of helically wound

grids

4 and 5, anode 6 and beam forming deflection electrodes I positioned parallel to opposite to Radio Corporation of N. Y., a corporation of 1938, Serial No. 197,757

(01. zed-27.5)

edges of the cathode. The electrode assembly is supported upon a re-entrant stem of envelope 8.

Cathode 3 is preferably rectangular in cross section with the sides In and ll of the sleeve activated by the conventional barium strontium oxide coating I2 and parallel to the plane of the side rods of the grids. The uncoated Walls l3 and Id of the sleeve face upon deflecting electrodes 'l, which in the particular beam forming type of tube illustrated serve to direct the electrons laterallyin fan-shaped beams, well-known in such radio tubes commercially known as the SL6. In tubes of this type the cathode is relatively long and slender and when heated to high emission temperatures is apt to deform or buckle at the center. Slight displacement of the cathode sleeve where the cathode to grid spacing is small, often as small as .005 inch, results in short circuitingcontacts between the cathode and grid. It has been proposed to stiffen indirectly heated cathode sleeves by making the sleeve with a relatively heavy lock seam along one side. This seam, however, results in an asymmetrical distribution of metal in the cross section of the sleeve, causing uneven heating of the sleeve after the heating element is lighted, unequal expansions of opposite sides of the sleeve, and bowing or buckling.

According to my invention the cathode sleeve is providedwith reinforcing means which permit the sleeve to uniformly heat and uniformly expand. Wall l3 of my improved cathode sleeve is joined to contiguous edges of sides l and II by integral folds l and I6. Opposite wall l4 likewise is joined to the sides by folds l1 and H3. The three layers of the cathode sleeve material on walls l3 and M are, in the embodiment shown in Figure 2, pressed tightly together to strengthen the walls. The cross sectional symmetry of the sleeve insures uniform expansion and the thin sides Ill and II permit quick heating of the oxide coated surfaces.

Figures 3 and 4 show means for making the particular cathode sleeve of Figure 2. Seamless tubing l9, preferably of electrolytic nickel, and of the desired length is slipped over a mandrel 20 and pressed between the dies 2| and 22 of a press which flattens the two sides In and H and forms folds l5, l6, l1 and I8, as shown in Figure 4. Folds I5 and I! may then be forced into snug engagement with folds l5 and 18 by forming tool 23, the inside transverse dimension of which is equal to the desired outside dimension of the sleeve. 0

The reinforcing folds may, if desired, be relatively short as shown in Figure 5, the length of each fold preferably being less than one-half the width of walls l3 and I4.

Folds

24, 25, 26 and 21 may be formed by dies similar to those shown in Figure 3 and forced into close engagement with sides l3 and [4 by the dies in Figure 4.

The

folds

24, 25, 26 and 21 may, if desired, remain extended and in a plane parallel to the sides In and H as shown in Figure 6. Walls l3 and M are preferably masked while the cathode activating material is sprayed upon sides In and II and to insure against primary or secondary electron emission from the walls I3 and 14, they may be coated with insulating material 28.

If desired the cathode sleeve may be made of strip material and formed with a conventional lock seam along wall l3 as shown in Figure 7 and provided with folds l1 and I8 along wall [4. While in this embodiment of my invention wall I3 is four layers of the sleeve material thick and wall I4 is three layers thick, the cross sectional configuration of the sleeve is sufiiciently symmetrical to prevent objectionable unevenness in heating. 7 Cathodes constructed according to my invention are strong, will not bow or deform at operating temperatures, are quick heating, and are easy and inexpensive to manufacture.

I claim:

1. A cathode for an electron discharge device comprising a cylinder of rectangular cross section, said cylinder comprising two opposed sides exteriorly coated with an electron emissive material, and two walls joining contiguous edges of said sides, the material of said cylinder being formed throughout its length with integral folds at said contiguous edges for stiffening said cylinder.

2. A cathode for an electron discharge device comprising a metal cylinder rectangular in cross section with two parallel sides exteriorly coated with an electron emissive material and two spaced walls with their edges contiguous to the the edges of said sides, folds in the cathode material along registering edges of said sides and said walls integral with said sides and walls, and a heating element in said cylinder.

3. A cylindrical cathode sleeve for an electron discharge device comprising two opposed side portions of relatively thin metal, means for stiffening said cathode sleeve without increasing the heating time of said side portions comprising a wall integrally joined to two edges of said side portions with folds in said material, said side portions being exteriorly coated with an electron emissive material, and a heating element in said cylinder.

4. A cathode for an electron discharge device comprising a metal cylinder of rectangular cross section, said cylinder comprising two parallel side members exteriorly coated with an electron emissive material, and two spaced parallel walls joining contiguous edges of said side members, means for stiffening said cylinder comprising integral folds throughout the length of said cylinder joining the edges of the side members and walls, the folds being pressed into snug engagement with said walls.

5. A cathode for an electron discharge device comprising a cylinder of rectangular cross section, said cylinder comprising two parallel sides of relatively thin metal, said sides being held in parallel spaced relation by two parallel walls spaced inwardly from the edges of said sides and joined to said sides by integral folds joining adjacent edges of said sides and walls, electron emissive material on said sides and insulating material on said walls.

CECIL E. HALLER.