US2918597A

US2918597A - Electron tube

Info

Publication number: US2918597A
Application number: US567129A
Authority: US
Inventors: William W Eitel; Jack A Mccullough; George F Wunderlich
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1956-02-23
Filing date: 1956-02-23
Publication date: 1959-12-22
Anticipated expiration: 1976-12-22

Description

Dec. 22, 1959 w, w, rr ET AL 2,918,597

ELECTRON TUBE Filed Feb. 23; 1956 IN V EN TORS Will/am W. E/fe/ Jack A. M. Cu//oug/1 Geo/ye f? Wander/1th BYM CAP ATTORNEY United States Patent "ice ELECTRON TUBE William W. Eitel, Woodside, Jack A. McCullough, Millbrae, and George F. Wunderlich, Burlingame, Calif., assignors to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Application February 23, 1956, Serial No. 567,129

Claims. (Cl. 313---242) This invention relates to electron tubes and more particularly to improvements in internal shielding structures and cathode supporting structures.

An important requirement for electron tubes is that they have a long life. As is well known by those skilled in the art, there is a tendency for the glass or other insulating material in the tube envelope to deteriorate under the influence of heat and bombardment by electrons and ions, so that after a period of time the insulating material is weakened to the extent that it admits air to destroy the tube vacuum. 1

Accordingly, an object of the invention is to provide an improved shielding arrangement for protecting the insulating material in the tube envelope from the destructive effects of heat and bombardment by electrons and 10118.

An additional object is to provide an electrostatic shielding arrangement for protecting the insulating material in the tube envelope from bombardment by electrons and 10118.

A further object of the invention is to provide a tube of the type described having an improved arrangement for supporting a cylindrical cathode.

Another object is to provide in conjunction with the improved cathode support an improved terminal arrangement whereby the cathode support and the terminals are grouped compactly around the tube axis so as not to interfere with the positioning of the shielding structure.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims.

Referring to the drawings:

Figure 1 is essentially a vertical sectional view on the center line of a diode embodying the improvements of the invention and shows a portion of the lower end of the tube in elevation.

Figure 2 is a bottom view of the improved tube; and,

Figure 3 is a sectional view taken on the line 33 of Figure 1.

Referring in more detail to the drawings, it will be seen that the tube comprises a header 2 of insulating material such as glass forming the bottom of the tube envelope. A side section 3 of the envelope is positioned above the header and is also made of insulating material such as glass. The upper end of the envelope is formed by an external anode 4 in the shape of a cup inverted above side section 3. The header 2 is joined to the side section 3 by means of a sealing ringunit 5 which is made up of a lower metal ring 6 and an upper metal ring 7. The inner edge of ring 6 is sealed in the header 2, and the inner edge of ring 7 is sealed in the lower end of side section 3. The

rings

6 and 7 are shaped so that their outer edges are in contact, and these edges are joined by a weld indicated at 8. Anode 4 is joined to the side Patented Dec. 22, 1959 section 3 by means of a metal ring 10 having its outer edge sealed in the upper end of side section 3 and its inner rim brazed to the side of anode 4. The top of the anode is provided with an exhaust tube 11 which is pinched off in the usual manner. In order to dissipate heat from the anode, it is provided with cooling fins 12. Each of the fins 12 is generally channel-shaped in cross section to form an inner tab 13 and an outer tab 14. The fins are secured in place by soldering the inner tabs 13 to the anode as indicated at 15 in Figure 1.

A plurality of

terminal pins

17, 18, 19 and are sealed in header 2.

Pins

17 and 18 serve as leads for a getter 21. Pin 19 serves as a support for a cylindrical cathode unit 23 and for this purpose is extended upwardly and bent inwardly so that its upper end is coaxially positioned within the tube. At the upper end of cathode unit 23 is the actual cathode cylinder 24. The

side walls of cylinder 24 form the emitting surface, which -is preferably of the oxide coated type. A thin ring 25 of material such as kovar is brazed to the bottom of cylinder 24 to act as a heat dam, and a tubular metal skirt 26 is brazed to the bottom of ring 25. A bottom piece 27 is brazed to the end of skirt 26, and the upper end of terminal pin 19 is brazed to the bottom piece to support the entire cathode unit. The cathode is pro vided with a heater coil 28 having its upper end 29 spot welded to the top of cathode cylinder 24. The lower end 30 of the heater coil is extended downwardly through an insulating plug 31 and spot welded to terminal pin 20. The heater coils 28 are coated in the usual manner with insulating material to prevent electrical contact with cathode cylinder 24. It will be seen that with the described arrangement pin 19 serves as a terminal for both the cathode and one end of the heater, the other end of the heater being served by pin 20.

The improved shielding structure is formed partly by anode 4, which is extended downwardly at 33 into the tube to a point well below the lower end of cathode cylinder 24 and the upper end of side section 3. There are several reasons for this arrangement, one being to prevent straight line travel of electrons from any point on the cathode to any point on the side section 3. Another reason is to prevent heat radiation from the hot cathode structure to the side section 3, particularly at the seal between the upper end of the side section and ring 10. Thus, a major portion of the radiant heat which would normally strike side section 3 will be picked up on the anode extensions 33 and dissipated through fins 12.

In order to complete the arrangement for shielding side section 3 from heat and bombardment by stray electrons and ions, a lower metal shielding ring 34 is provided. It will be seen that by using the pin type terminals 17-20 and the pin type cathode support, shielding ring 34 can be spaced around all of these elements and yet have a relatively small diameter which is substantially equal to the diameter of. anode extension 33. An outwardly extending metal flange 35 is brazed or otherwise attached to the bottom of shield 34 with the periphery of flange 35 being clamped between the

metal rings

6 and 7. In this manner the sealing ring unit 5 serves as a terminal for shield 34, and the shield is completely insulated from all of the tube electrodes. Thus, the shield 34 may be connected to a voltage having a relatively low value compared with that of the anode so that a voltage gradient can be estab ished across the annular gap between the upper end of shield 34 and the lower end of the anode extens on 33. Thus, the

shielding elements

33 and 34 not only form a physical barrier throughout their lengths, but by virtue of the voltage grad ent form an electrostatic trap which further prevents passage of electrons and ions outwardly to the side section 3. As stray electrons and ions attempt to pass through the electrostatic field between

shielding elements

33 and 34, the electrons will be deflected toward the shielding element which forms the more positive side of the field, and the ions will be deflected toward the shielding element which forms the less positive side of the field.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. An electron tube comprising an anode, a cathode, a metal shield and insulating means separating said shield from said anode and cathode, said shield being positioned in the tube so as to prevent direct passage of electrons from said cathode to said insulating means, said shield having one end axially spaced from said anode and having a diameter at least equal to said anode to form within the tube a gap between said anode and said shield, and a terminal for said shield projecting outside of the tube whereby an electrostatic field may be established across said gap.

2. An electron tube comprising a plurality of electrodes, including an anode and a cathode, an envelope for said tube comprising a side section of insulating material, said anode being cup-shaped and inverted over said side sec tion to form the upper portion of said envelope, means sealing said anode to the upper end of said side section, a metal shielding ring positioned below said anode and having a diameter at least equal to the inner diameter of said anode to form an annular gap between the upper end of said ring and the lower end of said anode to prevent direct passage of electrons from said cathode to said side section, insulating means including said side section separating said shield from all of said electrodes, and a terminal for said shield projecting out of the envelope whereby an electrostatic field may be established across said gap.

3. An electron tube comprising a plurality of electrodes including a cathode and an anode, an envelope for said tube comprising a side section of insulating material and a header of insulating material, a metal sealing ring unit joining said header to said side section, and a metal shielding ring inside the envelope and terminating adjacent said anode to form a gap between the anode and shielding ring, said shielding ring being connected to said sealing ring unit and insulated from all of said plurality of electrodes, said metal shielding ring having an inside diameter at least equal to the inside diameter of said anode wherein said metal shield prevents the direct passage of electrons from said cathode to said side section, whereby said sealing ring unit serves as a terminal for said shielding ring and an electrostatic field may be established across said gap.

4. An electron tube comprising an envelope having a header of insulating material at the lower end, a side section of insulating material positioned above said header, and a cup-shaped anode inverted above said side section and forming the upper end of the envelope, a cathode positioned within said anode, means joining said anode and the upper end of said side section, the side walls of said anode projecting downwardly a substantial distance below the upper end of said side section and spaced inwardly therefrom, ,a sealing ring unit joining said header and the lower end of said side section, said ring unit comprising a first metal ring having one end sealed in said header and extending outwardly therefrom, said ring unit further comprising a second metal ring having one end sealed in said side section and "extending outwardly therefrom, a metallic bond joining the outer ends of said first and second rings, a generally cylindrical metal shield positioned within the lower end of said side section and spaced from said anode, said shield having an inner diamter at least equal to the inner diameter of .said anode wherein said shield prevents the direct passage of electrons from said cathode to said side section, said shield having an outwardly extending metal flange at its lower end, the outer portion of .said .fiange being secured between said first and second rings whereby said ring unit serves as a terminal for said shield so that an electrostatic field may be established across the space between said anode and .said shield, and supportingmeansforssa'id cathode positioned within'said shielding ring.

5. An electron tube comprising an envelope having a header of insulating material at the lower end, a side section of insulating material positioned above said header, and a cup-shaped anode inverted above said side section and forming the upper end of the envelope, means connecting said anode to the upper end of said :side

section, a connecting ring unit joining said header and the lower end of said side section, said ring unit comprising a firstmetal ring having one end joined to said header and extending outwardly therefrom, said ring unit further comprising a secondmetal ring having one end joined to said side section and extending outwardly therefrom, a metallic bond joining the outer ends of said first and second rings, a generally cylindrical metal shield positioned within the lower end of said. side section and spaced inwardly therefrom, said shield having an outwardly extending flange at its lower end, the outer portion of said flange being secured between said first and second rings, the upper end of said shield terminating adjacent the lower end of said anode, said shield having an inner diameter at least equal to the inner diameter of said anode wherein said shield is positioned to prevent direct passage of electrons from said cathode to said side section, a cylindrical cathode and a heater for the cathode both positioned concentrically within said cup-shaped anode, terminal pins for said cathode and heater sealed in said header radially inwardly of said shield and projecting downwardly out of the envelope, one of said pins extending upwardly into said anode, and means supporting .said cathode on the upper end of said one pin.

References Cited in the file of this patent UNITED STATES PATENTS 1,929,369 Found Oct. 3, 1933 2,236,859 Vandegrift Apr. 1, 1941' 2,471,005 Norton -a May 2-4, 1949 2,644,907 Drieschman et al July 7, 1953 2,726,346 Busby et al Dec. 6, 1955 2,727,178 Dailey-et al Dec. 13, 1955