US2228941A - Cathode assembly - Google Patents

Description

Jan. 14, 1941. R. B. AYE R CATHODE ASSEMBLY Filed May- 51, 1940 ill? A 9 INVENTOR RAYMOND B. AYE/2 ATTORNEY Patented Jan. 14, 1941 UNITED STATES CATHODE ASSEMBLY Raymond B. Ayer, Verona, N. J assignor to Radio Corporation of America, a corporation of Delaware Application May 31, 1940, Serial No. 338,189

7 Claims.

My invention relates to cathodes for electron discharge devices, particularly to supports and current supply means for cathodes in such devices.

Transmitter tubes of the type shown in the Zottu et a1. Patent 2,113,671, April 12, 1938, employ a cage type cathode comprising circularly arranged parallel straight filament wires. When these filament wires are of pure metals such as tungsten or tantalum and are operated at temperatures as high as 2000 C. or above, the problem of insulatingly supporting the cathode in fixed spaced relation with the other electrodes is diflicult. If mechanical supports are provided at both ends of the cathode, provision must be made for expansion and contraction of the file.- ment wires, and insulating bushings must be provided to withstand the high operating temperature and yet permit free longitudinal movement for the wires.

An object of my invention is a cathode with improved support means that will accurately fix the cathode in spaced relation with the other electrodes and will permit longitudinal expanson.

A more specific object of my invention is an improved cathode support for transmitter tubes of high power that is easy to assemble and will protect insulating spacers from the high operating temperatures of the cathode.

The characteristic features of my invention are defined in the appended claims and one preferred embodiment thereof is described in the following specification and shown in the accompanying drawing in which Figure 1 shows in section my improved cathode and support mounted in a transmitter tube, Figure 2 is a longitudinal sectional view showing details of construction of my improved cathode support, and Figure 3 is an end view of the assembly shown in Figure 2.

The particular transmitter tube shown in the drawing comprises a water-cooled anode l, coaxial with a screen grid 2, a control grid 3 and cathode 4. The wires of the grids and cathode are straight and parallel, are circularly arranged, and lie in concentric cylindrical surfaces. The filament wires of the cathode are at their lower end 5 bunched together and joined as by arc welding or high temperature brazing.

Hollow lead-in conductors or pipes 6 and I sealed into the upper end of the envelope support the cathode and supply the heating current to the filament wires. On the inner ends of the pipes are carried concentric metal ring 8 and metal plate or disc l0. Preferably the plate is fiat, although the plate may be convexed or concaved, and preferably the rim of the plate lies in the plane of the ring although it may be axially displaced with respect to the ring. The inner periphery of the ring is serrated with radial teeth or extensions 9 interleaved with serrations II on the outer periphery of the disc. The serrations may be rounded as shown, triangular in shape or of any desired configuration which can be easily formed in the ring and disc and fitted together without short circuit. Alternate filament wires 4 of the cathode are joined to the serration 9 on the ring, the other wires being joined to the serrations H on the disc. To join the filament wires to the serrations, it is preferred to bore holes in the serrations normal to the plane of the ring and disc, with the holes arranged in a circle coaxial with the ring. The

ends of the filament wires may then be inserted in the holes and, when brazed or welded in place, stand normal to the plane of the ring and disc and accurately center the cathode in the tube.

According to one of the novel features of my invention, a cooling fluid is circulated in contact with the rear surface of the ring 8 and disc 10, the cooling effect of the fluid being brought to the ends of the filament wires. Since the ends of the filament wires are kept cool the wires will not bow or buckle and the brazed connections at the ends of the wires cannot be softened or loosened by heat. The ring 8 closes one end of a hollow annulus l2 comprising two telescoped and coaxial spaced tubular walls I: and H. The interior of the annulus communicates with the interior of the lead-in pipe 6 and is joined gas and liquid tight to the end of the pipe. Pipe 6 has a central partition l5 that extends into the annulus and abuts liquid tight at its end against the inner surfaces of cylinders l3 and I4 and ring 8. Cooling fluid, such as water, entering conductor 6 on one side of the partition then flows into and around the annulus to the other side of the partition where it re-enters tube 6 and flows out. Pipe 1 is joined gas and liquid tight to the rear surface of disc Ill and is provided with a central partition so that cooling fluid flowing inwardly along one side of the partition is projected against the rear surface of the disc and flows out along the other side of the partition. Alternatively, of course, a small feed pipe could be passed into pipe I and terminated short of the rear surface of the disc It to provide the inlet or outlet passage within the pipe I for the cooling fluid. The inner end of the pipe I and disc I0 is held coaxial with and in fixed spaced relation from the inner cylinder [4 of the annulus by an insulating bushing I6 of refractory insulating material, such as ceramic.

Since the bushing l6 lies between the Watercooled wall of cylinder l4 and pipe 1, and its end is shielded from the filaments by disc l0, its temperature may never rise above the temperature of the cooling fluid, and a tight or drive fit may be made between pipe 1, bushing l6 and cylinder l4 since no provision need be made for expansion of the metal or insulating parts of the cathode support. A heat and electron shield I1 may, if desired, be mounted on the ring 8 to prevent thermal and electron emission from the filament wires to the grid wires.

All metal parts of my improved cathode support may be made of copper, nickel, Monel or other easily machined metal, and because of their mechanical simplicity are easily assembled. Good results have been obtained in making my improved cathode support with the ring 8 and disc ll] of nickel only in thickness. The holes in the serrations of the ring and disc are accurately bored on a drill press or lathe normal to the faces of the ring and disc and the parts then assembled. The filament wires of tungsten, about .05 inch in diameter, are then slightly tapered by caustic etching, inserted in the holes and arc-welded on the under or water-cooled side of the serrations. Preferably the ends of the wires are Pushed through the holes so that their ends appear on the reverse side where they can be arc welded or brazed.

I claim:

1. A cathode assembly comprising a, cylinder with two spaced concentric metal walls, means for circulating a cooling fluid between the walls, a ring, serrated along its inner periphery, in good heat conducting contact with one end of the cylinder, a metal disc serrated along its periphery, in the plane of said ring and coaxial with the ring, the serrations of the disc extending radially outward and between the serrations of the ring, means supporting the disc in insulated spaced relation from the ring, and a filament wire connected to each of the serrations.

2. A cathode assembly comprising an annulus, a metal disc coaxial with the annulus, means for circulating cooling fluid against one side of said disc, a plurality of circularly arranged parallel filament wires, alternate wires being joined at one end to the other side of said disc and the remaining wires being joined at one end of the tubular annulus, said wires extending outwardly normal to the plane of said disc.

3. A cathode comprising a plurality of circularly arranged parallel filament wires, current supply means for one end of the cathode comprising a concentric metal ring and a plate, the outer periphery of the plate and the inner periphery of the ring being serrated with the serrations of the ring and plate interleaved, at least one filament wire joined to each serration.

4. A cathode assembly comprising an annulus with two telescoped spaced tubular walls, said walls being closed at their ends, means for circulating a cooling fluid between said walls, a pipe extending into and coaxial with said annulus, a plate joined to the end of said pipe and fixed in a plane transverse to the axis of said annulus, an insulating bushing between the outer wall of the pipe and the inner wall of the annulus, a filament wire joined at one end to the plate and a second filament wire joined to the end of said annulus, the other ends of the wires being joined together.

5. A cathode assembly comprising a coplanar ring and disc, means for circulating a cooling fiuid against one side of said ring, means for circulating cooling fluid against the corresponding side of said disc, a plurality of filament wires on the other side of the ring and disc, some of the wires being joined to the ring, the remainder of the wires being joined to the disc, the other ends of the wires being connected together.

6. A cathode assembly comprising a concentric ring and plate, a hollow annulus joined to one side of said ring, a pipe joined to one side of said plate, interleaved serrations along the opposing peripheries of the ring and disc, filament wires inserted at one end in holes in said serrations, the opposite ends of said filament wires being mechanically and electrically connected.

7. An electron discharge device comprising a tubular anode and a coaxial cathode, said cathode comprising straight parallel circularly arranged wires lying in a cylindrical surface coaxial with said anode, said wires being mechanically joined together at one end, means for rigidly supporting each wire in said surface comprising two hollow lead-in conductor pipes, a metal ring joined to the inner end of one pipe, a metal plate coaxial with the ring. joined to the end of the other pipe, the other ends of the wires being secured to said ring and disc, and an insulating spacer for rigidly holding said ring and disc in fixed spaced relation.

RAYMOND B. AYER.

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