US2677781A

US2677781A - Electron tube

Info

Publication number: US2677781A
Application number: US297207A
Authority: US
Inventors: Donald F Drieschman
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1952-07-05
Filing date: 1952-07-05
Publication date: 1954-05-04
Anticipated expiration: 1971-05-04

Description

4, 1954 D. F. DRIESCHMAN 2,677,781

ELECTRON TUBE Filed July 5, 1952 IN V EN TOR.

BY M54 A TTOE/V E Y Donald E Uriesc/rman Patented May 4, 1954 ELECTRON TUBE Donald F. Drieschman, Los Altos, Califi, assignor to Eitel-McCullough, Inc., San Bruno, Calif a corporation of California Application July 5,- 1952, Serial No. 297,207

2 Claims. 1

My invention relates to. an electron tube of the type having coaxial terminals, and more particularly to improvements in the envelope structure of such tubes.

It is. among the objects of my invention to provide an improved vacuum tube envelope construction incorporating ceramic parts.

Another object is to provide a simplified stem structure for such a tube.

A. further object is to provide an envelope of the character described for a tube having planar type electrodes.

The invention possesses other objects and features of advantage some. of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodiments thereof within the scope of the claims.

Referring. tothe drawing, the single figure is an axial sectional view of a tube embodying the improvements of my invention.

In greater detail, the triode type of tube illustrated comprises an anode 2, grid 3 and cathode 4 having active surfaces disposed in parallel wardly projecting portion carrying a suitable cooler 6. The anode also carries the metal eX- haust tubulation l which communicates with the envelope through passage 8, the tubulation'being pinched off at tip 9 after evacuation of the envelope.

Cathode 4 at the lower portion of the envelope is of the indirectly heated type and comprises a cup-shaped metal sleeve having a flat upper surface coated with a suitable electron emissive material. The heater II for the cathode comprises a coil disposed within the cathode sleeve and is preferably surrounded by a suitable heat shield l2. Grid 3 is of the disk type having parallel wire bars lying between the anode and cathode.

Coaxial metal terminals, also preferably of copper, are provided on the envelope for the anode and grid, the anode terminal generally designated l3 being cup-shaped and the grid terminal generally designated I t being tubular in shape. These terminals are separated and electrically insulated by a ceramic cylinder l6 metallically bonded at I! to the anode terminal and at [8 to the grid terminal. These ceramic-tometal seals are made by using metalizing and brazing techniques as hereinafter described; The cup-shaped anode terminal which is secured to anode 2 has a cylindrical flange l9 forming a contact surface and has a re-entrant bottom wall providing a recess for receiving the ceramic wall cylinder it. The tubular grid terminal l4 has a contact surface 2| and at the upper end a cupped flange 22 for receiving the ceramic cylinder.

Cathode stern generally designated 23 comprises a cylindrical ceramic stem member 24 coaxial with grid terminal I4 and projecting downwardly from the lower end of the envelope. This stem member is hollowed out at the lower end to provide a cylindrical recess 28 and also has a bore 21 extending from the recess into the envelope. A ceramic supporting ring 28 surrounds the stem member at a point adjacent the grid terminal and is metallically bondedto stem member 24 at joint 29.

The whole stem structure is so designed that the cathode may be completely mounted on the stem and the entire unit inserted into the tube through grid terminal l4. For this purpose the cathode stem includes a metal sleeve 3| which fits the grid terminal. Sleeve 3| is preferably of copper and is preferably U-shaped with an inner edge brazed to ceramic supporting ring 28 at 32 and with an outer edge registering with the lower edge of the grid terminal. Cathode sleeve 4 is fitted over the inner end of stem member 24 for support and one end of the heater coil ll is fastened to the sleeve 4. The other end of the heater is supported by a metal lead 33 which extends downwardly through bore 27 to a mounting button 34.

Cathode terminal 35 is formed by metalizing the outer cylindrical surface of ceramic stem member 24, which metalized area connects with the metallic bond at joint 29 so that the latter serves as a lead-in conductor for the cathode. The metalized area also extends upwardly along the stem member to make contact with the oathode sleeve 4, thus completing the cathode circuit into the tube.

Heater terminal 3% is formed by metalizing the inner cylindrical face of hollow stem member 24, which metalized area extends upwardly in the recess to provide a surface to which mounting button 34 can be brazed. A heater terminal is thus provided coaxial with the other electrode terminals so that the tube can readily be plugged into a socket.

Grid 3 is supported by a cylindrical metal mount 31, also preferably of copper, having a skirt adapted for insertion into the grid terminal [4 and lying between the latter and the cathode stem supporting sleeve 3|. The three register-- ing edges are then simultaneously bonded together at braze 38.

The ceramic used in making up the envelope sections may be of any suitable ceramic-like material such as the alumina or zircon type ceramic bodies. I have had good success with the alumina body because it is easy to metalize and has good mechanical strength and thermal resistance properties.

The ceramic-to-ceramic joint 29 and the several ceramic-to-metal joints may be made in several ways using known metalizing and brazing techniques. For example, the ceramic pieces may be coated with finely divided metal powders such as molybdenum or a mixture of 'molybdenum and iron or the like, and fired in hydrogen to a temperature sufficient to sinter the metal powder to the surface of the ceramic. This produces a thin metallic layer tightly knitted to the ceramic. The sintered areas are then preferably electroplated with a metal such as nickel. Such metalized surfaces may then be brazed together or to adjacent metal parts with silver solder or brazing alloys such as silver-copper, goldcopper or the like. The brazes are readily made by fitting the parts together with rings of wire solder adjacent the joints, and then elevating the temperature of the whole up to the melting point of the solder or brazing alloy in a suitable furnace. Another metalizing technique is to paint titanium or zirconium hydride powders on the surfaces of the ceramic parts and fire in vacuum to about 1200 C. after which the metalized ceramics may be brazed with silver solder or the like.

I prefer the sintered and plated procedure of metalizing the ceramics because the plating produces a solid metal face which is excellent for brazing and also ideal for external terminal surfaces such as the

terminals

35 and 36.

My improved tube is extremely rugged and will withstand high temperature operation without failure of the envelope. Where metal terminals are employed, such as the grid and anode terminals, the use of copper brazed to the ceramics provides good electrical conductivity for radio frequency currents. which is usually the complicated part of a tube The stem structure,

of this kind, is considerably simplified in my structure. This comes about because of the use of ceramic parts with metalized surfaces to provide the terminals and utilizing the braze between the ceramics as a lead-in conductor. The simplified stem structure eliminates many metal parts and extra joints.

I claim:

1. An electron tube comprising an evacuated envelope, a cathode in the envelope, a heater in the envelope for the cathode, a cathode stem on the envelope comprising a hollow cylindrical stem member of ceramic, a cathode terminal comprising a metalized area On the outer surface of the ceramic stem member, a heater lead extending into the stem member, and a heater terminal comprising a metalized area on the inner surface of the ceramic stem member, and a vacuum-tight metal partition within the stem member joined to said metalized area and connected to the heater through said lead, said partition being spaced substantially from the lower end of the stem member, said last named metalized area extending below the partition.

2. An electron tube adapted for insertion into a socket comprising an evacuated envelope, a cathode in the envelope, a heater in the envelope for the cathode, a cathode stem portion of said envelope projecting downwardly from the main portion of the envelope and comprising a hollow cylindrical stem member of ceramic, a vacnum-tight partition within the stem member, a heater terminal comprising a metalized area on the inner cylindrical surface of the ceramic stem member below said partition and electrically connected to said heater, and a cathode terminal comprising a metalized area on the outer cylindrical surface of the ceramic stem member and spaced from the heater terminal solely by the intervening ceramic wall of said stem, said inner and outer metalized surfaces providing contact faces for engagement with the socket.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,099,531 Passarge Nov. 16, 1937 2,446,269 Drieschman Aug. 3, 1948 2.461.303 Watson Feb. 8 1949