US2731578A - Electron tube - Google Patents

Description

Jan. 17, 1956 J. A. M CULLOUGH 2,731,573

ELECTRON TUBE Filed April 50, 1951 Sheets-Sheet 1 dual? ,4. ME Cu//ou BY 621 A TTOPNEY Jan. 17, 1956' Filed April 30, 1951 J. A. M CULLOUGH ELECTRON TUBE 3 Sheets-Sheet 2 To E/Ybausf Pam a INVENTOR. Jack AMfiCu/lough ATTORNEY Jan. 17, 1956 .1. A. MOCULLOUGH ELECTRON TUBE 5 Sheets-Sheet 3 Filed April 30, 1951 7b Ex/iaus? Pam 9 INVENTOR. Jack A. Ms Cu/lougfi BY Mg 7 ATTORNEY the general shape of a flat cylinder.

United States Patent C) ELECTRON TUBE Jack A. McCullough, Millbrae, Calif., assignor to Eitel- McCullough, Inc., San Bruno, Califi, a corporaticn of California Application April 30, 1951, Serial No. 223,708

8 Claims. (Cl. 313-245) My invention relates to an electron tube embodying a ceramic construction such as disclosed in the copending application of Harold E. Sorg et al., Serial No. 202,666, now Patent No. 2,647,218, and more particularly to improvements adapted for small tube structures such as those in the receiving tube category.

Receiving tubes as made in the past have served a good purpose but they have left much to be desired in matters of dependability and ruggedness, the shortcomings being largely due to the mechanical construction of the glass tubes which had grown out of the old lamp industry.

It is among the objects of my invention to overcome the above limitations and to provide a tube of compact and rugged construction.

Another object is to provide a tube which is easy to fabricate and assemble.

A further object is to provide a tube of the character described having two electrode assemblies in the same envelope.

A still further object is to provide an improved method of assembling and evacuating the envelope.

'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 to the drawings:

Figure 1 is a plan view of a tube embodying the improvements of my invention; and

Figure 2 is a sectional view of the same taken in a plane indicated by line 2-2 of Figure 1.

Figures 3 and 4 are sectional views showing the tube in a bell jar during the exhaust operation.

In terms of broad inclusion, a twin triode type of tube embodying my invention comprises an envelope having The envelope is made up of ceramic sections including two disk-like end wall pieces and two aligned cylindrical side wall pieces. These ceramic sections have metalized abutting edges which are brazed together to form a vacuum-tight envelope. A cathode, common to both triode units, composes a flat button having a suitable heater and is supported on a transverse metal disk centrally of the envelope, the edge of which disk is connected to the braze between the side wall cylinders. Two disk-like grids on opposite sides of the cathode are supported on metal terminal pins extending through the end walls. The ceramic end wall sections also function as anodes and have their inner faces metalized for that purpose, these metalized areas being connected to the end wall brazes. Terminals for the anodes and cathode are provided by metalized areas on the ceramic envelope adjacent the respective brazed joints.

In greater detail and referring to Figures 1 and 2, my improved tube is shown as a twin triode suitable for tube uses normally classed as receiving tubes. Tubes in this category in the past have been of glass or glass and metal ice construction with electrode assemblies supported within the envelope by transverse insulators such as mica sheets and the like. In my tube no glass or complicated glass and metal construction is employed, and the internal insulators are eliminated.

The improved tube has the general shape of a flat cylinder and does not involve the usual type of socket arrangements. For a tube having a plate dissipation of about 15 watts per anode, the tube would be about onethird the size of that shown in Figures 1 and 2. The envelope is made up of four ceramic sections including two disk-shaped end wall sections 2 and two aligned cylindrical side wall sections 3. The end pieces 2 are of identical shape and the side wall pieces 3 are also shaped alike so that actually there are only two different kinds of ceramic pieces used in making up the envelope.

The envelope sections are fitted together along abutting edges, end sections 2 being preferably recessed at the periphery to receive the side wall cylinders and the central abutting edges of the side wall sections 3 being preferably recessed to provide'a circular groove for purposes hereinafter described. These ceramic sections are metallically bonded together at the joints to form vacuum-tight seals; the side sections being united by a metallic bond 4 and the end sections being united to the side cylinders by the bonds 6. These bonding layers extend along the abutting surfaces between the parts from the inside to the outside of the envelope and also function as lead-in conductors to the electrodes.

The ceramic used in making up the envelope may be of any suitable ceramic-like material, such as the alumina or zircon type ceramic bodies commercially available. Metallic bonds 4 and 6 forming the vacuum-tight seals may be made in several ways, utilizing known metalizing and brazing techniques. For example, the opposed surfaces of the ceramic pieces may be coated with finely divided molybdenum powder, or a mixture of molybdenum and iron powders or the like, and then fired in hydrogen to a temperature of about 1500" C. to sinter the metal powder to the ceramic surface. This produces a thin metallic layer firmly bonded to the ceramic. Such metallized surfaces may then be brazed or soldered together with silver solder or brazing alloys such as silver-copper, or goldcopper or the like. The brazes are readily made by fitting the metallized ceramic pieces 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 in a suitable furnace.

In the planar electrode tube illustrated having an indirectly heated cathode, the latter comprises a flat buttonlike cathode 7 of a metal such as nickel having parallel surfaces coated with an electron emissive material such as the conventional barium-strontium oxides. This cathode is supported by metal ring 8 in which the cathode button is inserted, the ring being engaged along its periphery by the circular groove formed by the recesses previously mentioned in the ceramic side wall sections 3. The interfitted relationship of these parts also provides means for coaxially aligning the side Wall sections when these wall sections are assembled. When the parts are bonded together at the braze 4 the latter provides the cathode lead-in conductor through the side wall of the envelope.

Cathode terminal 9. on the envelope is preferably formed by a metalized area on the ceramic sections connected to the lead-in braze 4. Thus, when the edges of ceramic sections 3 are treated, as by molybdenumsintering, to metalize the region adjacent the joint, the metalized areas are preferably extended over the outer surfaces to provide a metal band around the body of the envelope to form the terminal 9.

The heater for cathode 7 preferably comprises a flat spiral of heater wire 11 embedded in a suitable insulating material 12 within the cathode button. One end of the heater coil is connected to the cathode and the other end brought out through a metal lead 14 brazed in a .side Wall section 3.

Control grids 15 of :the .twin-triodeiillustratedrarepreferably disk-shaped [grids having parallel wires fastened to retaining rings 17, these grids .being disposed unopposite sides of cathode and parallel therewith. Grid rings 17 are supported on metal leads .28 extending through and brazedrto thezceramic. end walls .2.

ably threeof these supporting-leads for each of the grids. The holes through which the leadsrextencl .are preferably rmetalized land :the leads secured by =ceramic-to-metal brazes.

In my improved tube. the end wall sections ;2 of the envelope alsoserve as the :anodes, Ltheionerfaces .Cdthe ceramic sections being 'rnetalized, as by .molybdenum 'sint'eringto provide .theactive anode surfacesfi. Ceramics such 'as'thealumin'a type ceramicbodies are. quite good heat "conductors and will zadequately dissipate the heat in small tubes having relatively low anode dissipation ratings. The areas around-thegrid .leadsarenot .metalized so as to iusulate the anodefrorn th'e grids. A-convenieut way to do thisis'to provide recesses Zlaround leads 19 and metalizc 'only the flat faces of the ceramic anodes.

.Brazcs function'asthe anode lead-in conductors and anode terminals 22 are preferably formed by metalized areas on the ceramic envelope. Thus when the ceramic pieces are treated, asby molybdenum sintering, tometalize the regionsadjacent the joint, the metalized areasare preferably extended over the outer surfaces to provide metal bands around the body of the envelope to form the terminals 22.

The brazes at'the joints and metalized areas are shown as having appreciable thickness for convenience of illustration. Actually, these are quite thin metal layers, say

of the order of 0.062" totLOOS" thickness, and appear as films or metal skins on the surfaces of the ceramic. If desired, silver, copper or the like may be-electrop'lated or flowed over thesintered'areas to further improve the electrical conductivity. Copper "01' silver plating on the sintered areas, forexample, make-excellent terminal surfaces and is ideal for brazing together at the joints'either wither without the use of additi-ve brazing material.

In my tube a suitable 'pumpingtubulation (not shown) may be provided 'for evacuating the envelope. Such a .tubu'lation maybe of metal brazed toa wall of the envelope and pinched off in the usual manner after exhaust. With this conventional purnping procedure the ceramic envelope sections would be completely brazed together mall the joints in a suitable furnace before connecting the t ibe ;to a .vaeunm pump.

An improved method of pumping the tube-embodying my invention, :which does not require a tribulation on the envelope, is ilIustrated'in-Figures 3 and 4. case the tube, partially disassembled, is placed in a bell jar 23 seated on a base plate '24 having a duct'z leading to. an exhaust pump. At the stage shown in Figure 3 the tube preferably comprises three subassemblies, namely,

the central assembly comprising cathode 7 mounted on the previously brazed Wall sections 3, and the end assemblies comprisinggrids 16 mounted on anode sections 2. These three units, with the end assemblies separated'frorn the central assemblyyare held by any suitable fixture (not shown) so that the space .between'the tube parts-is evacuated when the bell jar is exhausted. Such fixture .is so arranged that the end assemblies are permitted to collapse together against the central assembly to close thesenvelopeafter exhaust of the bell jar.

When using this exhaust procedure the final brazes betweencerami'c sectionsiand 3 are made in the bell jar. The brazing material, such as silver or copper, is previously applied to the ceramic parts by electroplating or flowing the metal over the sintered'areas as hereiobefore mentioned. The brazing'operation then merely-in- There arepre'ferin this bell jar is first exhausted to a hard vacuum. All the tube assemblies are then preferably heated sufiiciently to outgas the tube parts. This-corresponds tothe usual bake out step; the added advantage in my process being that the tube is open "at this time 'so that the gases-are quickly pumped away, resulting 'in a more "complete outga'ssing of the parts. A simple way of heating the parts forbake out purposes isto .use ametalcylindetuZTiu.the bell jar heated by induction from an external radio-frequency coil 28.

After. outgassing the tube parts the oxide cathode 7 is activated. This is also done while the envelope is in th open position showniinfigure 3. Activation of thc cathodew coating accomplished y heatingtm cathod .withheater ll'zto fllQPI'opGl. forming temperaturein ihfi usual, manner. the heater current in supp e im-my case hrough suitable leads entering the hell iar anticoanected to the heater terminals. llfheadl adadvantagein .mvprocws is that cathode activation takesplace wi h d nger oictmtamimfing the grids and other italpart of the tube. This overcomes a serious 'problem in the making f oxide eoatedtypesofitubes, because ordinarily tube parts such as grids which are closely spaced to the cathodelare vulnerable to contamination by barium and other active agents volatilized from the coating during cathode formation. With my procedure there is much less likelihood of such contamination because ,the gridanode assemblies are further separated from thecalhode; .and the. envelope being open allows the volatile :con- .stituents tobeguicklypumped away.

After the cathode has been formed, the end assembliesare moved into position, against theside :wall-sections to close the envelope :as ishownin Figure-4, and the final brazes are made by bringing the temperature ofv'the metalized ceramicand joints up to the melting .poiutof the metal-to-metal surfaces. Such heating is preferably localized .at.the.-j,oints, :as byradiation.fromadjaeent heater coils .29.. Upon completion :of the brazes the exhaus pumpis ,shuttofif andathecompletcd tube is ready for removal from the bell jar.

I claim:

1. An electron tubecomprising an envelope having a cylindrical ceramic-side wall and-a disk-alike ceramic @Clld wall, the inner .face of the end wall being metalized pr iding an anode, a cathode :carried by the side wall and having aneleflroo :emittingsuriaceiymg parallel with tire-anode,a disk-like .grid interposed between the catho eand auodasupportiugleads to the grid extendi s throug end wall, and .a metallic bond uniting th amic wside ar d-end walls and forming a lead iu connection to the anode.

'2. electron tube comprising an envelope having a cylindrical ceramic side wall. and disk-like ceramic .end walls, said side wall comprising a pair ofaligned sections, the inner :facesofthe end walls ,belngmetalized providing anodes, a cathode supported from the "side wall and having electron emitting surfaces lying parallel with saidanodesa metallic bond uniting the ceramic side wallxsections and forming a lead-in connection to the cathode, disk-like .gt'idsinterposed between the oathode and anodes, supporting leads to the grids extending through-the end walls, .andmetal-lic bonds uniting the ceramic side and end wallsand forming 'leaddn connec- .tions to the anodes.

3. Aurelectron tube comprising 'a generally cylindrical envelope having upper and lower disk-like walls Oi ceramic, a cylindrical sidewall of ceramic "titted to theend walls alongupper an'dlowerjoints, metallic bonds metallic bonds at the upper and lower joints providing lead-in conductors for the anodes, and a cathode in the envelope supported on the side wall and having electron emitting surfaces facing the anodes.

4. An electron tube comprising a generally cylindrical envelope having upper and lower disk-like end walls of ceramic, a cylindrical side wall of ceramic fitted to the end walls along upper and lower joints, metallic bonds uniting the ceramic parts at said joints, the inner faces of the end walls being metalized providing anodes, said metallic bonds at the upper and lower joints providing lead-in conductors for the anodes, a cathode in the envelope supported on the side wall and having electron emitting surfaces facing the anodes, and disk-like grids in the envelope interposed between said cathode and anodes.

5. An electron tube comprising a generally cylindrical envelope having upper and lower disk-like end walls of ceramic, a cylindrical side wall of ceramic fitted to the end walls along upper and lower joints, metallic bonds uniting the ceramic parts at said joints, the inner faces of the end Walls being metalized providing anodes, said metallic bonds at the upper and lower joints providing lead-in conductors for the anodes, said side wall comprising sections fitted together at a joint lying intermediate the end walls, a metallic bond uniting the side wall sections at said intermediate joint, and a cathode in the envelope supported on the side wall and having electron emitting surfaces facing the anodes, said metallie bond at the intermediate joint providing a lead-in conductor for the cathode.

6. An electron tube comprising a generally cylindrical envelope having upper and lower disk-like end walls of ceramic, a cylindrical side wall of ceramic fitted in the end walls along upper and lower joints, metallic bonds uniting the ceramic parts at said joints, the inner faces of the end walls being metalized providing anodes, said metallic bonds at the upper and lower joints providing lead-in conductors for the anodes, said side wall comprising sections fitted together at a joint lying intermediate the end walls, a metallic bond uniting the side wall sections at said intermediate joint, a cathode in the envelope supported on the side wall and having electron emitting surfaces facing the anodes, said metallic bond at the intermediate joint providing a lead-in conductor for the cathode, disk-like grids in the envelope interposed between said cathode and anodes, and supporting leads for the grids extending through the end walls.

7. A stacked ceramic type electron tube comprising an envelope having the shape of a flat cylinder with side and end walls, the side wall comprising metalized ceramic rings sealed in a vertical stack and providing an annular side wall joint between a pair of said rings, a metallic layer uniting the metalized ceramic rings at said joint, one of said end walls providing an anode having an inner anode surface lying substantially parallel with the plane of said joint, a cathode structure in the envelope having an emitting surface substantially parallel with said anode surface, a conductive support for said cathode extending inwardly from said side wall joint, and a terminal on the envelope connected to said cathode support through the metallic layer of said joint.

8. A stacked ceramic type electron tube comprising an envelope having the shape of a flat cylinder with side and end walls, the side wall comprising metalized ceramic rings sealed in a vertical stack and providing an annular side wall joint between a pair of said rings, a metallic layer uniting the metalized ceramic rings at said joint, said end walls providing anodes having inner anode surfaces lying substantially parallel with the plane of said joint, a central cathode stiucture in the envelope having upper and lower emitting surfaces substantially parallel with said anode surfaces, a heater for the cathode interposed between said emitting surfaces, a conductive support for said cathode extending inwardly from said side wall joint, and a terminal on the envelope connected to said cathode through the metallic layer of said joint.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,531 Passarge Nov. 16, 1937 2,167,515 Katsch July 25, 1939 2,200,911 Bowie May 14, 1940 2,351,895 Allerding June 20, 1944 2,371,683 Eitel et al. Mar. 20, 1945 2,422,945 Brian June 24, 1947 2,425,593 Brian Aug. 12, 1947 2,428,610 Beggs Oct. 7, 1947 2,647,218 Sorg June 28, 1953

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