US3393341A - Electron tube joint construction and method of assembly - Google Patents

Description

J. P. POLESE July 16, 1968 ELECTRON TUBE JOINT CONSTRUCTION AND METHOD OF ASSEMBLY Filed June 28, 1965 INVENTOR. JAMES P. POLESE ATTORNEYS United States Patent 3,393,341 ELECTRON TUBE JOINT CONSTRUCTION AND METHOD OF ASSEMBLY James P. Polese, Menlo Park, Calif., assignor, by mesne assignments, to Varian Associates, a corporation of California Filed June 28, 1965, Ser. No. 467,205 7 Claims. (Cl. 313-284) ABSTRACT OF THE DISCLOSURE An electron tube joint construction. The inner peripheries of two sealing rings connected to two tube envelope sections are clamped to an annular electrode support ring interposed therebetween leaving the outer peripheries of the sealing rings spaced apart. The outer peripheries are then bound to each other and bonded together thereby producing residual internal stress in the rings causing their inner peripheries to press against the interposed electrode support to form a good R.F. configuration.

This invention relates to electron tubes and more particularly to joint constructions for forming hermetic seals between adjacent sections of electron tubes wherein an electrode supporting ring is interposed between the envelope sections.

Many electron tubes are designed so that the envelope is formed in two separate sections or subassemblies which must be hermetically joined together in what is usually termed the final seal. In most tubes of this type, one of the envelope sections carries a cathode and the other envelope section carries an anode. The present invention is particularly concerned with the situation where another electrode is present, such as the grid. The problem is to interconnect the two envelope sections in a hermetic seal and also position the extra electrode in its proper place.

The object of the present invention is to provide an electron tube having an improved construction which permits two envelope sections to be hermetically joined together and to position between them an annular support for an electrode.

A further object of the invention is to provide a tube construction of the type described wherein said electrode support is not brazed or soldered to sealing rings on said envelope sections and yet said electrode support is connected to said sealing rings with a connection which has low electrical resistance and high mechanical strength.

Another object of the invention is to provide a tube construction of the type described wherein the relation between said electrode support and said sealing rings serves automatically to align the two envelope sections with respect to each other and the electrode support.

A related object of the invention is to provide a tube construction of the type described which is adapted for obtaining precise spacing between the electrode carried by the annular support and adjacent electrodes carried by the envelope sections.

An additional object of the invention is to provide a tube construction of the type described which provides a good RF circuit configuration.

Briefly described, a tube construction in accordance with a preferred embodiment of the invention comprises two envelope sections having facing sealing rings projecting outwardly thereform. One of the envelope sections carries an anode and the other section carries a cathode. An annular electrode support, or ring, carries a grid located between the anode and cathode. The radially inner faces of the sealing rings abut the grid ring, and the sealing rings are designed so that when the inner portions abut the grid ring, the outer portions are spaced apart.

3,393,341 Patented July 16, 1968 In order to form the final seal, the outer portions of the sealing rings are forced toward each other and are sealed together with a heliarc bead. The internal stress thus formed in the sealing rings holds the grid ring clamped tightly between the sealing rings. The sealing rings are provided with cylindrical abutment surfaces which cooperate with the periphery of the grid ring to automatically align the two envelope sections and the grid.

FIGURE 1 is a view of an electron tube made in accordance with the invention. The joint construction is shown in section and the center portion of the tube is shown in elevation;

FIGURE 2 is an exploded cross-sectional view of the joint construction of FIGURE 1 on an enlarged scale;

FIGURE 3 is a cross-sectional view of the joint structure showing the parts placed in assembled position but before the final seal has been made. FIGURE 3 is on a scale intermediate the scale of FIGURES 1 and 2; and

FIGURE 4 is a view on the scale of FIGURE 3 showing the sealing rings being forced together by pressure cylinders and showing the final seal bead formed while the sealing rings are forced together.

Referring in more detail to the drawings, FIGURE 1 shows an electron tube 1 having an anode structure 2 and a cathode structure 3. The anode has an electronreceiving surface 4, and the cathode has an electronemitting surface 5. The cathode is preferably of the indirectly heated type and therefore carries an internal heater (not shown). In a preferred embodiment the anode and cathode structures include threaded portions 6 and 7, respectively, for connecting the tubes in associated cavity resonators (not shown).

The anode structure 2 is carried by an annular dielectric envelope wall section 10. The envelope section 10 is preferably made of ceramic and is metalized in the usual manner so that it can be brazed to the side of the anode structure 2 and can also be brazed to a sealing ring 11. Similarly, the cathode structure 3 is carried by an annular dielectric envelope wall section 12. The envelope section 12 is also preferably made of metalized ceramic and is brazed to the cathode structure and to a sealing ring 13. Thus, the tube is made in two sections or subassemblies; namely the anode section and the cathode section.

Intermediate the anode section and the cathode section is a grid electrode 16. The grid electrode comprises a conventional wire mesh grid disk 17 brazed to an annular support, or ring 18. The grid ring 18 is preferably made of tungsten, and as shown in the enlarged FIG- URE 2 is coated with a gold layer 19 where it abuts the sealing rings 11 and 13. The reason for the gold layer is to provide a good electrical connection between the sealing rings and the grid ring and because of the good diffusion properties of gold, as will be hereinafter discussed in more detail.

The sealing ring 11 is provided with a cylindrical abutment surface 22 which abuts the periphery of the grid ring 18 to center the anode section 2 with respect to the grid. Similarly the sealing ring 13 is provided with a cylindrical abutment surface 23 which abuts the periphery of the grid ring 18 to center the cathode section 3 with respect to the grid. Since the anode and cathode sections are both centered with respect to the grid they are automatically centered with respect to each other. As shown in FIGURE 3, the sealing rings 11 and 13 are shaped so that when the radially inner portions of the sealing rings abut the grid ring 18, the radially outer portions of the sealing rings will be separated by a space 24. The sealing ring 11 is preferably made of a core 25 of Kovar coated with a layer of copper 26. Similarly, the sealing ring 13 is preferably made of a core 27 of Kovar coated with a layer of copper 28. The reason for the copper coating 26 and 28 is to provide a low resistance path for RF current and because copper diffuses readily with gold, as will be hereinafter discussed in more detail.

It will be understood from the preceding description that the electron tube 1 is made in two separate sections; namely, the anode section 2 and the cathode section 3, With an intially separate grid 16 interposed between the two sections. In order to complete the tube and make the final seal, the two tube sections are brought together with the grid interposed therebetween, all as shown in FIG- URE 3. A pair of pressure cylinders 30 and 31 surround the tube and are forced together as shown by the arrows in FIGURE 4. Any suitable machinery (not shown) can be used to provide the force represented by the arrows. The requirement is that the force must be sufiicient to deflect one or both of the sealing rings 11 and 13 to provide an internal stress in the rings which will provide a postive and continuing force clamping the inner portions of the sealing rings against the grid ring. In the preferred form of the invention both of the sealing rings are designed to curve or bow toward each other. After the sealing rings are bent until their outer portions touch or nearly touch, the final seal is formed by forming a heliarc bead 32. The outer portions of the sealing rings could alternatively be brazed together.

It will be noted that the sealing ring 13 has a portion 33 which is thicker than the sealing ring 11. The reason for making the inner portion of ring 13 thicker is to avoid any possible deflection thereof as a result of the force of cyilnders 30 and 31. The reason for avoiding deflection is that the grid 17 is very close to the cathode surface 5 and the grid-to-cathode spacing must be within very close tolerance. It will be noted that the described construction makes it easy to obtain exact interelectrode spacings because the surfaces of the cathode, and grid if necessary, can be ground with respect to the face of their respective sealing ring to provide an exactly dimensioned subassembly. Since the thickness of the grid ring and grid is easily controlled, the desired spacings are assured. In order to compensate for the thick portion 33, the outer portion of ring 13 is preferably slightly thinner than the ring 11 so that ring 13 will bow substantially the same amount as ring 11 under the force of the cylinders 30 and 31.

When the pressure cylinders bend the sealing rings 11 and 13 toward each other considerable force is applied at the abutment between the grid ring and sealing rings. Since the sealing rings are deformed, the force remains after the bead 32 is formed and the pressure cylinders 30 and 31 are removed. This abutment force insures a good electrical and mechanical contact between the grid ring and the sealing rings. Such contact is further enhanced by interdiffusion of the metal surfaces of the grid and sealing rings. It is for this reason that the abutting metal surfaces are selected to diffuse readily. For example, the gold-to-copper surfaces disclosed herein have good diffusion properties.

It should be noted that the described construction provides a relatively straight path for RF current from the sealing rings to the grid ring. It will be understood by those skilled in the art that after the final seal is made at 32, the tube is normally pumped out through a tubulation which is then pinched off. In the construction shown the tubulation is on the cathode section 3 and is covered by a protective cylinder 34. It is of course possible that the final seal between the sealing rings 11 and 13 could be made while the entire tube is in a vacuum chamber and in such case a conventional tubulation would not be required. Also, the seal between the sealing rings could be a conventional non-melt pressure seal instead of a heliarc or braze seal.

Although specific details of the present invention have been shown and described herein, it should be understood that the invention encompasses all changes and modifications coming within the spirit and scope of the appended claims.

What is claimed is:

1. An electron tube comprising a hermetically sealed envelope containing electrodes, said envelope being formed in two sections, a hermetic sealing structure connecting said two sections, said sealing structure comprising a first sealing ring connected to a first one of said two sections andprojecting' outwardly therefrom, a second sealing ring connected to the second one of said sections and projecting outwardly therefrom, an annular support for one of said electrodes clamped between said sealing rings adjacent the inner periphery of the rings, said sealing rings being bonded together adjacent their outer peripheries, and said sealing rings having internal stress therein pressing the rings against said annular support for said one electrode.

2. An electron tube as claimed in claim 1 in which each of said sealing rings has a cylindrical abutment surface thereon in engagement with the periphery of said annular support for said one electrode.

3. An electron tube as claimed in claim 1 wherein said electrodes are planar in shape and include an anode and cathode in addition to said'one electrode, said one electrode being a grid, said anode being mounted on said first section, said cathode being mounted on said second section, said grid being closer to said cathode than to said anode, and the radially inner portion of said second sealing ring being thicker than the facing portion of said first sealing ring.

4. An electron tube as claimed in claim 1 in which the abutting portions of said electrode support and sealing rings have metal surfaces which diffuse one into the other.

5. An electron tube as claimed in claim 4 in which said metal surfaces comprise gold and copper.

6. An electron tube comprising a hermetically sealed envelope formed in two sections and containing planar cathode, grid and anode electrodes, a hermetic sealing structure connecting said two sections, said sealing structure comprising a first sealing ring having said anode mounted thereon, said first sealing ring connected to a first one of said two sections and projecting outwardly therefrom, a second sealing ring having said cathode mounted thereon, said second sealing ring connected to the second one of said sections and projecting outwardly therefrom, an annular grid support clamped between said sealing rings adjacent the inner periphery of the rings, said grid being closer to said cathode than to said anode, said sealing rings being bonded together adjacent their outer peripheries with at least one of said sealing rings being bowed toward the other of said sealing rings, and the radially inner portion of said second sealing ring being thicker than the facing portion of said first sealing ring.

7. An electron tube as claimed in claim 6 in which said bowed sealing ring is residually stressed as a result of said bowed configuration.

References Cited UNITED STATES PATENTS Re. 23,735 11/1953 Olson 313284 2,162,234 6/1939 Thomas 313281 2,388,289 11/1945 Ronci 313283 X 2,423,066 6/1947 Gibson 313-284 2,445,237 7/1948 Stone 313-288 2,514,976 7/1950 Stivin 313317 X 2,726,349 12/1955 Wing et a1. 313281 X 2,857,663 10/1958 Beggs 313317 X 3,193,920 7/1965 Culbertson 313-284 X FOREIGN PATENTS 975,461 12/1961 Germany.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

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