US3254258A

US3254258A - Electron tube

Info

Publication number: US3254258A
Application number: US296575A
Authority: US
Inventors: William R Stuart
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1963-07-22
Filing date: 1963-07-22
Publication date: 1966-05-31
Anticipated expiration: 1983-05-31

Description

May 31, 1966 w. R. STUART ELECTRON TUBE Filed July 22, 1963 INVENTOR. 7 WILLIAM R. STUART ATTORNEY 3,254,258 I ELECTRON TUBE William R. Stuart, San Carlos, Calif., assignor to Eitel- McCullough, Inc., San Carlos, Calif., a corporation of California Filed July 22, 1963, Ser. No. 296,575 4 Claims. (Cl. 313-256) This invention relates to electron tubes and more particularly to an electron tube having an improved electrode alignment arrangement.

Recent requirements have made it necessary for electron tubes to be able to meet new specifications calling for ability to withstand extreme shock and vibration and also requiring improved accuracy in electrode alignment. In the past, a dielectric electrode support pin was often used to hold the electrodes of an electron tube in alignment. However, thehot cathode in such an electron tube expands and contracts out of proportion with respect to the other electrodes which are supported by the dielectric electrode support pin. Consequently, the prior arrangement of providing alignment between the various electrodes of a tetrode tube, for example, was to braze the control and screen grid structures to metallized bands on the dielectric electrode support pin. The cathode structure could not be brazed to the dielectric electrode support pin because of its disproportionate movement with respect to the controland screen grid structure which would, cause the portion of the cathode structure'adjacent the area of the braze to severely warp, and this would finally result in the destruction of the tube. Hence, the procedure previous to this invention was to provide an extremely fine tolerance on the' surface of the dielectric electrode support pin which extended through a precisely formed aperture in the cathode structure to permit the cathode structure to slide along the dielectric electrode support member in accordance with its expansion and contraction characteristics. Providing a fine tolerance on the external surface of the dielectric electrode support pin was expensive and time consuming, but was necessary in prior electron tubes. However, in spite of the great care that was taken in providing the fine tolerance on the dielectric electrode support pin, a large proportion of the number of electron tubes previously made had to be discarded when it was discovered that the space between the aperture in the cathode structure and the surface of the dielectric electrode support. pin was too large causing unwanted noise. in shock and vibration tests. A need existed for an electron tube having an improved electrode support arrangement to consistently 3,254,253 Patented May 31, 1966 "ice ' URE 1, and

FIGURE 3 is an enlarged elevational view partly in section of the cathode and the dielectric electrode sup portpin at operating temperature.

Referring in more detail to the drawing, an attempt will be made to describe first the construction which is either shown in the Drieschman et al. Patent No. 2,472,- 942 or utilized in improved versions thereof prior to this invention. The tube of FIGURE 1 comprises a heater coil 1, a cathode 2, a control grid 3, a screen grid 4 and an anode 5.

The envelope for the tube is formed in part by the inverted cup-shaped metal anode 5. The remainder of the envelope is formed by the metal ring 7, brazed to the bottom of theanode and to the top of a ceramic cylinder 8 which is metallized in conventional manner for this purpose; a metal sealing ring 9 and a metal shell 10 which are sealed together by a final braze or weld 11, with ring 9 being brazed to the bottom of ceramic cylinder 8 which is metallized for this purpose; and a ceramic header disk 12 which has an annular metallized area brazed to shell 10.

As regards terminals for the electrodes, the outer portion of the anode of course serves as its own terminal. The ring 9 and shell 10 can serve as the terminal for the screen grid 4. The remaining terminals are formed by pins sealed in the header disk 12. Eight small diameter pins (only four of which are shown in FIGURE 1) are arranged in a circular array around a large diameter center pin 22. Although eight small pins are employed, only six of them are required as terminal-s. In the construction shown, four pins including pins 14 and 18 serve as cathode terminals and pin 17 serves as heater terminal. Pin 15 is shown in FIGURE 1 as one of the pins not required as a terminal. The center pin 22 is the control grid terminal. The center pin is sealed in the header by metallizing the wall of the aperture in the header and brazing .the pin thereto. In the case of .the small pins the apertures in the header are not metallized but instead an annular area is metallized on the bottom of the header around each pin. A copper Washer 24 is brazed to the meet the high standards required under shock and vibratube having an envelope enclosing cylindrical electrodes including a cathode. A dielectric electrode support pin having a tapered end portion is provided to support the tube electrodes. One of the electrodes other than the cathode is connected to the dielectric electrode support pin. An annular flexible metal member which has an aperture therein is connected to the cathode. The tapered end portion of the dielectric electrode support pin extends through the aperture and engages the annular flexible metal member to maintain alignment of the cylindrical cathode during operation of the tube.

These and other objects and features of advantage will become apparent from a reading of the following detailed description wherein reference is made to the accompanying drawing in which:

metallizing and the pin, and a kovar washer 25 is brazed to the copper washer and to the pin.

The anode structure is completed by brazing on conventional metal cooling fins 27 and a two-piece metal cover 28 over the pinched-01f exhaust tubulation 29. The

small wires 34 which pass through apertures in the disk and are spot welded at each end to the posts. A conventional getter strip 35 is spot welded to post 32. The grids 3 and 4 are conventional cage-type wire structures, each having an inverted cup-shaped configuration. It will be noted that the screen and control grids and the cathode all have

metal end portions

36, 37 and 38, respectively.

Control grid 3 is supported by means of a metal ring 40 attached to the bottom thereof and having two, down.-

wardly extending projections 41 on its diametrically opposite sides (only one such projection being visible in FIGURE 1). A supporting yoke structure is formed by two U-shaped rods 42 brazed at their ends to the projections 41 and at their center in a slot in the top of the center pin 22. Cathode support ring 44 has four channelshaped legs 45. The channel construction extends along the sides of the pins 14 and 18. This construction is important in order to braze the legs 45 to the pins and makes a much more rigid structure. Continuing with the description of the cathode support members, a very thin metal heat dam 46 is attached to the lower end of the cathode can. The lower end of the heat dam is spot welded to the outer surface of the support ring 44.

The heater posts 31 and 32 are brazed at their lower ends in legs 47 and 48. As in the case of the cathode support legs, and for the same reasons, the heater legs are channel-shaped including the portion which extends over and is brazed to the terminal pin 17. A ceramic rigidifying disk 50 is metallized on its outer periphery and brazed to the cathode support ring 44. The disk 50 is apertured to receive heater posts 31 and 32, and the walls of apertures are metallized and brazed to the posts.

The lower end of the screen grid 4 is attached to a metal cone 52 mounted on a metal support ring 53. The cone is attached to ring 53 by screws 54 (preferably three) which abut the cone and are received in threaded apertures in the ring. Ring 53 has a three-part shape comprising a cylindrical side portion 55 brazed to shell 10, a flat cone-supporting portion 56, and a downturned centering flange portion 57 at its inner periphery. The apertures for screws 54- are so positioned that when the screws are inserted in members 52 and 53, member 52 is centered with respect to flange 57.

Referring to all the figures, a dielectric electrode support pin 60 is shown. Pin 60 is made of ceramic and its periphery is metallized where it passes through the screen and

control grid ends

36 and 37 and is brazed to these ends. In addition, the pin has a large disk portion 61 between the cathode and control grid to reduce the capacitance between these electrodes.

The pin 60 has a tapered end portion 63. The metal end portion 38 of the cathode 2 is a thin annular flexible metal member consisting of Hastelloy B metal, which is the trade name of a nickel based alloy containing small amounts of molybdenum, iron and carbon. Hastelloy B has an expansion characteristic similar to the nickel cathode 2 and still retains its hardness at tube operating and processing temperatures. The metal end portion 38 is preferably 2 mils thick and is spot welded around its outer edge to the cathode 2.

The tapered end portion 63 of the dielectric electrode support pin 60 extends through an aperture in the metal end portion 38. The dielectric electrode support pin 60 has one portion which has a diameter that is larger than the diameter of the aperture in the metal end portion 38 and another portion which has a diameter smaller than the diameter of the aperture in the metal end portion 38. Thus, in operation, as can be seen from FIGURE 3, the cathode 2 expands when hot and moves closer to the disk portion 61 of pin 60. The metal end portion 38 flexes to permit the cylindrical cathode 2 to be kept in concentric alignment with respect to the cylindrical control grid 3. This arrangement eliminates noise when the tube is subjected to shock and vibration applications.

The teaching of this invention may be practiced by utilizing any means at the end portion of the dielectric pin 60 having a surface extending at an angle to the axis of the pin functioning similarly to the tapered portion 63 so as to engage the member 38 of the cathode 2 in order to maintain alignment of the cathode cylinder when the tube is in operation.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall wvithin the spirit and scope thereof.

I claim: 1. An electron tube having an envelope enclosing cylindrical electrodes including a cathode, a dielectric electrodesupport pin mounted between said electrodes, said dielectric electrode support pin having a tapered end portion, at least one of said cylindrical electrodes other than said cathode being connected to said dielectric electrode support pin, and an annular flexible metal member connected to said cylindrical cathode, said annular flexible metal member having an aperture therein, said tapered end portion of said dielectric electrode support pin extends through said aperture and the tapered'surface of said end portion engages said annular flexible metal member to maintain alignment of the cathode during operation of the tube, the tapered portion of said pin having a maximum diameter which is larger than said aperture, and the maximum diameter end of said tapered portion is located along said pin on the side of said flexible member toward said connection between the pin and said at least one other electrode.

2. An electron tube having an envelope enclosing cylindrical electrodes including a cathode, a dielectric electrode support pin mounted between said electrodes, said dielectric electrode support pin comprising an elongated ceramic member having a tapered end portion and at least one metallized surface portion, at least one of said cylindrical electrodes other than said cathode being connected to the metallized surface portion of said dielectric electrode support pin, and a thin annular flexible metal member connected to said cylindrical cathode, said thin annular flexible member having an aperture therein, said tapered end portion of said dielectric electrode support pin extends through said aperture and the tapered surface of said end portion engages said thin annular flexible member to maintain alignment of the cathode during operation of the tube, the tapered portion of said pin having a maximum diameter which is larger than said aperture, and the maximum diameter end of said tapered portion is located along said pin on the side of said flexible member toward said connection between the pin and said at least one other electrode.

3. An electron tube having an envelope enclosing cylindrical electrodes including a cathode, a dielectric electrode support pin mounted between said electrodes, said dielectric electrode support pin comprising an elongated ceramic member having a tapered end portion and at least one metallized surface portion, at least one of said cylindrical electrodes other said cathode being connected to the metallized surface portion of said dielectric electrode support pin, and a thin annular flexible metal member connected to one end of said cylindrical cathode, said thin annular flexible member having an aperture therein, said tapered end portion of said dielectric electrode support pin extends through said aperture and engages said thin annular flexible member, said thin annular flexible metal member having an aperture therein, said tapered end portion of said dielectric electrode support pin having one portion having a diameter larger than the diameter of said aperture and another portion having a diameter smaller than the diameter of said aperture, said thin annular flexible metal member consists of Hastelloy B metal.

4. An electron tube having an envelope enclosing cylindrical electrodes including a cathode, a dielectric electrode support pin mounted between said electrodes, said dielectric support pin comprising an elongated ceramic member having a tapered end portion and a pair of metallized surface portions, a cylindrical control grid connected to one of said pair of metallized portions, a cylindrical screen grid connected to the other of said pair of metallized portions, and a thin annular flexible metal member connected to said cylindrical cathode and in engagement with said tapered end portion of said dielectric electrode support pin, said thin annular flexible metal member having an aperture therein, said tapered end portion of said dielectric electrode support pin having one 5 7 portion having a diameter larger than the diameter of said aperture and another portion having a diameter smaller than the diameter of said aperture, said thin annular flexible metal member consists of Hastelloy B metal.

References Cited by the Examiner UNITED STATES PATENTS 6 2,939,988 6/1960 Culbertson et a1 313-250 3,132,274 5/ 1964 Kendall 313363 JAMES D. KALLAM, Acting Primary, Examiner.

JOHN W. HUCKERT, Examiner.

A. J. JAMES, Assistant Examiner.

Claims

1. AN ELECTRON TUBE HAVING AN ENVELOPE ENCLOSING CYLINDRICAL ELECTRODES INCLUDING A CATHODE, A DIELECTRIC ELECTRODE SUPPORT PIN MOUNTED BETWEEN SAID ELECTRODES, SAID DIELECTRIC ELECTRODE SUPPORTED PIN HAVING A TAPERED END PORTION, AT LEAST ONE OF SAID CYLINDRICAL ELECTRODES OTHER THAN SAID CATHODE BEING CONNECTED TO SAID DIELECTRIC ELECTRODE SUPPORT PIN, AND AN ANNULAR FLEXIBLE METAL MEMBER CONNECTED TO SAID CYLINDRICAL CATHODE, SAID ANNULAR FLEXIBLE METAL MEMBER HAVING AN APERTURE THEREIN, SAID TAPERED END PORTION OF SAID DIELECTRIC ELECTRODE SUPPORT PIN EXTENDS THROUGH SAID APERTURE AND THE TAPERED SURFACE OF SAID END PORTION ENGAGES SAID ANNULAR FLEXIBLE METAL MEMBER TO MAINTAIN ALIGNMENT OF THE CATHODE DURING OPERATION OF THE TUBE, THE TAPERED PORTION OF SAID PIN HAVING A MAXIMUM DIAMATER WHICH IS LARGER THAN SAID APERTURE, AND THE MAXIMUM DIAMETER END OF SAID TAPERED PORTION IS LOCATED ALONG SAID PIN ON THE SIDE OF SAID FLEXIBLE MEMBER TOWARD SAID CONNECTION BETWEEN THE PIN AND SAID AT LEAST ONE OTHER ELECTRODE.