US2288380A

US2288380A - High frequency radio tube

Info

Publication number: US2288380A
Application number: US372867A
Authority: US
Inventors: Jr Arthur K Wing
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-01-02
Filing date: 1941-01-02
Publication date: 1942-06-30
Anticipated expiration: 1959-06-30

Description

June 30, 1942. A. K. wms, JR 2,288,330

HIGH FREQUENCY RADIO TUBE Filed Jan. 2, 1941 iiiiiiiiiiiiiiiiii umuuu!! INVENIOR. I A. K. WING, JR.

I BY m zz.

ATTORNEY.

Patented June 30, 1942 2,288,880 man FREQUENCY more runs Arthur K. Wing, In, Chatham, N. 1., asslgnor to Radio Corporation of America, a corporation of Delaware Application January 2, 1941, Serial No. 372,867

Claims.

My invention relates to electron discharge devices, particularly to transmitter tubes for high frequency operation.

Conventional structures and methods of assembly cannot be used in making transmitter tubes suitable for amplifier operation at high frequency such as in television and frequency modulation transmitters where the frequency may be higher than 30 or 40 megacycles and where the power may be several kilowatts. The close spacing of the electrodes requires accurate alignment and rigid support and the intense high frequency fields require complete electrostatic isolation of the output and input circuits and electrodes. It is desirable to keep the mass of the metal parts of the tube at a minimum.

The object of my invention is an improved radio tube of the transmitter type in which the electrodes are accurately aligned and rigidly supported with a minimum of metal mass, and in which the output electrodes are completely shielded from the input electrodes.

The characteristic features of my invention are defined in the appended claims and the preferred embodiment thereof is described in the following specification and shown in the accompanying drawing in which Figure 1 is a longitudinal half-section of my improved tube, Figure 2 is a sectioned detailed view taken along line 2-2 of Figure 1 showing the cathode support, and Figure 3 is a view along the line 3-3 of Figure 1.

The anode I is of the externally cooled type and encloses coaxial screen grid 2, control grid 3 and cathode 4. The two grids are cylindrical, each comprising a. plurality of parallel grid wires arranged in a circle and held at their ends by collars. The cathode shown comprises a single helix of electron emissive metal such as tungsten or thoriated tungsten supported at its upper end on the central rod 5, the rod being joined at its lower end to the bridge structure 6 which in turn-is clamped at its opposite ends to the two lead-in conductors 1 for the cathode. The control grid lead-in conductors, not visible in Figure l, are of the same size and shape as the cathode lead-ins and are in a plane normal to the plane of the cathode lead-ins. The four bushings 8 for the lead-in conductors comprise, preferably, joined at one end to a metal disc and at the other end to a metal sleeve, which is in turn brazed to openings in the sheet metal header 9.

The rim portion of the header is rolled or pressed with a channel shaped in cross section, and the glassbulb I0 is joined to the outer cylinder of the channel. Flexibility of the outer cylinder in a radial direction minimizes strains in the glass of the bulb at the seal and thermally isolates this seal glass cylinders each hermetically II, substantially ui region from the glass-to-metal seals of the bushings 8.

There are no interelectrode spacers and the header, according to my invention, comprises the sole support for the grid and cathode electrode assemblies, and although the header is made of thin sheet metal it will rigidly hold the electrodes in their position in the tube and will withstand warping caused by heat and at-. mospheric pressure, which pressure may be upward of pounds on a header only 3.5 inches in diameter. I propose, according to my invention, to concave the header inwardly as shown. The re-entrant concavity of the header not only strengthens the header but provides a convenient protecting recess for the lead-in bushings 8. One convenient way to make my novel header is to spin or press the sheet material with a substantially hemispherical or conical portion I2 and with the channel I I along the rim of the hemisphere. Die punches may then be used to flatten seats for the bushings 8 in the bottom portion of the header. The exhaust tube I3 is joined to the center of the bottom of the header, the sheet metal around the exhaust tube being further stiffened by an embossed annular groove around the exhaust tube junction. My header is easily made from relatively light weight sheet metal and without the usual heavy reinforcing metal plate across the end of the tube. The electrodes may be supported directly on the header with no bracing means or electrode-toenvelope spacers and with negligible displacement of the electrodes during manufacture and use. 1

The screen grid is supported at the small end of the metal cone I4 which, at its larger end, is slipped over the rim portion of the header and into the channel I I and spot welded. The screen grid cone is coaxial with the electrodes, and, with the metal header 9, completely encloses the lead-in conductors for the cathode and control grid and shields these conductors from the anode.

The cathode support rod 5 is inserted at its lower end in an eyelet I5 which is held against the upper side of the insulating bar I6 of the bridge structure 6 and is drawn as best shown in Figure 2 in snug contact with the bar by metal strap I'I drawn tightly over the head of the eyelet by thebolt I8 with a tapered head and. tapered washer. As the bolt is tightened the strap is drawn downwardly and into the tapered hole in the ceramic. Opposite ends of the bar I 6 are bolted to clamps engaging the cathode lead-in conductors I just inside the header. The heating circuit for the cathode is completed from one conductor through the heat shield I9, through the support rod 5, through the heating cathode 4 and thence through the other conductor I insulatingly joined to the heat shield by the ceramic bushing 2|. The heat shield I9, being larger in diameter than the small end of the cone, cooperates with the cone to prevent heating, by the cathode, of the bridge structure 6 and or the glass-to-metal seals of the lead-in bushings l.

The anode may be cooled according to my invention with an air radiator comprising fins II integrally joined to a hub 22 which in turn may be shrink-fitted by diiierential expansion on a sleeve 28. The sleeve 23 is then soldered to the outer surface of the anode to provide a low resistance heat conducting band between the anode and the fins. The radiator fins and hub may be machined from aluminum or other good heat conducting material and the sleeve and anode wall made, preferably, of copper.

The washer-like disc or collar 24 at the upper end of the control grid 3 is provided with a series of holes circularly arranged to receive the ends of the control grid wires. To obviate buckling or bowing of these wires because of unequal I claim:

1. An electron discharge device comprising a cup-shaped anode, a dish-shapedsheet metal header, a glass bulb hermetically joined to the rim of the anode and to the rim of the header, a cathode, a control grid and a screen grid coaxial with and in said anode, lead-in conductors hermetically and insulatingly sealed through the bottom of said header and connected to said cathode and control grid. a metal cone coaxial with said anode and surrounding said conductors, the small end of the cone being joined to one end of said screen grid and the large end of the cone being joined to said header.

2. An electron discharge device comprising an envelope closed at one end with a round sheet metal header, said header being relatively large in diameter and its sheet metal being relatively thin, said header being dish-shaped, the bottom portion and the rim portion of the header being joined by a substantially conical shaped portion heat expansion, the wires are passed freely through the holes in the washer, the washer being held in place by tabs welded to only two or three of the grid wires. A metal or ceramic washer was found unsuitable because of difliculty in obtaining free movement of the wires through the holes in the washer without either binding or excessive looseness. It has been found that a graphite or carbon washer ideally meets the requirements of the spacing collar. Graphite is sufliciently refractory to withstand the high temperatures and willnot bind the grid wires when hot.

The entire tube assembly may conveniently be supported upon a plate 25 with a large central opening to clear the lead-in bushings I. Electrical connection to the header and to its attached screen grid is made by a number of flexible spring fingers 26 fastened as by spot welding to the upper surface of the plate and arranged around the periphery of the header. The header and its connected screen grid is grounded for radio frequency potentials by capacitively coupling the header to ground. A thin fiat insulator 28, approximately coextensive with the rim of the header, separates the plate 2! from the metal plate 21, of the grounded transmitter chassis.

Good results, according to my invention, have been obtained in making transmitter tubes of the type commercially known as the 827R, where the high frequency output power is one kilowatt at 108 megacycles or 1.5 kilowatts at 50 megaoycles. The diameter of the anode is about 1.5 inches, the anode length 2.25 inches, the header outside diameter 8.6 inches, the overall length of the tube 4.5 inches, and the header of commercial .030 inch nickel-iron-cobalt alloy sheet. The filament carries 25 amperes and operates at about 2000 K. The upper part of cone I I, the

grid wires and metal parts adjacent the filament are preferably of tantalum, molybdenum or other highly refractory metal.

The dish-shaped contour of the header materially strengthens the header against flexure and thus holds the cathode and control grid electrodes in place, and the length of the lead-in conductors is reduced without reducing the length of any of the insulating paths. My improved radio tube is easily made, the electrodes are accurately aligned and rigidlysupported, and the input electrodes are completely shielded from the output electrodes.

so that the header can withstand atmospheric pressure without fiexure, lead-in conductors insulatingly sealed in and extending through said bottom portion of the header, a first electrode in and in spaced relation with said envelope, the support for said first electrode being said conductors and the sole support for said header being a hermetic junction between the rim of said header and said envelope, 9. second electrode mounted in spaced cooperative relation with said first electrode.

3. An electron discharge device comprising a cup-shaped anode, a sheet metal header hermetically closing one end of said anode, a cathode and a grid coaxial with and in said anode, leadin conductors hermetically and insulatingly sealed through the bottom of said header and connected to said cathode, a metal cone coaxial with said anode and surrounding said conductors, the small end of the cone being joined to said grid and the large end of the cone being joined to said header, a disc-shaped metal shield supported by said lead-in conductors in the cone and transverselyof the axis of the cone, said disc being larger in diameter than the small end of said cone and extending to but spaced from the wall of said cone.

4. An electron discharge device envelope comprising a header closing one end of said envelope, said header comprising a round sheet metal member, said member being concave'd and reentrant with respect to said envelope, the bottom portion of the member being joined to the rim portion of the header by'a substantially conically shaped portion, said rim portion being formed with an annular channel U-shaped in cross section, lead-in bushings hermetically sealed to said bottom portion of the header and said envelope being hermetically joined to the outer wall of said channel.

5. An envelope, a helical wire cathode in said envelope, two relatively heavy support and current supply conductors through the envelope, a support rod centrally in said cathode, means supporting said rod comprising a bridge structure clamped at opposite ends to said lead-in conductors, said bridge structure being electrically non-conductive between its ends, said rod being clamped to the central portion of said structure, and electrical connections between the terminals of the cathode and said two conductors.

ARTHUR, K. WING, JR.