US2996637A

US2996637A - Electron tube construction

Info

Publication number: US2996637A
Application number: US339002A
Authority: US
Inventors: Lloyd P Garner; William N Parker
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1953-02-26
Filing date: 1953-02-26
Publication date: 1961-08-15
Anticipated expiration: 1978-08-15

Description

1 P. GARNER Er A1. 2,996,637

ELECTRON TUBE CONSTRUCTION 2 Sheets-Sheet l n p 5.,/ 0 J Z f M* Q e. F I1. 1 1 A41 11 1 t 1.7.1 1 2 1 1 -l 1 y 11 /W W11 11 1 1 11H 1 1 111 1 1 1 1 d I/ d. 7. l f H n ZV1# f. z z

Aug. 15, 1961 Origmal Filed May l2, 1948 BY omav Aug. 15, 1961 P. GARNER ET AL 2,996,637

1 ELECTRON TUBE CONSTRUCTION Original Filed May l2, 1948 2 Sheets-Sheet 2 INVENTORS LL wn P. EAHNEH X/ WILLIAM N. PARKER BY www @rates 16 Claims. (Cl. 313-265) This invention relates to electron discharge devices capable of relatively high specific power output at ultra high frequencies and more specifically to methods of constructing such devices.

This application is a continuation of our pending application Serial No. 26,696, and tiled May`12, 1948, now abandoned.

A principal object of the invention is the provision of an electron discharge device in which functional and constructional features are coordinated to produce an improved design of such a device which operates more eiciently because of the precision methods or modes of assembly employed in the fabrication of the resulting tube structure.

Another object is the provision of improved mechanics made available and/or employed in the technique of constructing an electron discharge device, more particularly of the character herein contemplated whereby a superior and/or improved vacuum tube is achieved.

Another object of the invention relates to providing a method for manufacturing an electron discharge device having the component parts and/or units thereof closely spaced to produce greater efficiency in the performance of the device, said improvement in performance being attributable largely to the use of instrumentalities not heretofore available for obtaining precision work but made available and constituting features of the technique contemplated herein.

A further object is the provision of a RF. high power tube fabricated by a technique which permits dispensing with common prior art expedients such as spot welding, ceramic internal spacing members, non-rigid high inductance supporting leads, etc., whereby a superior and simplitied tube structure is obtained.

A still further object is the provision of sub-.assemblies which are provided with leads that are capable of functioning as supports and/or jigging surfaces in the consolidation of the various sub-assemblies, said leads being capable of accurately supporting their respective electrode constructions upon jigging means during the joining of said assemblies and in relation to a common reference surface, these leads serve also as sub-assembly consolidants in the joining of sub-assemblies.

More special and specific objects of the invention relate to the provision of an electron tube structure cornprised of a plurality of sub-assemblies which may be pre-fabricated and can be consolidated into a composite unitary structure with accurately aligned and spaced active surfaces which may incorporate parts of a jigging means integral with an active surface; forming said subassemblies with concentric cylindrical electrodes accurately juxtaposed in concentric spaced relation and supported by rigid lead structures of low-electrical impedance, which leads may be of a thermal conductive character for cooling purposes or a thermal isolation character to conserve heat as a given construction may dictate; adapting the sub-assemblies to a mechanized operation in producing the main assembly which operation follows a sequential arrangement of the component critical parts by using one component as a common reference surface in connection with a jig and/or mandrel;

i arent Patented Aug. 15, 1961 utilizing metal-to-metal joints or seals for certain of the active surfaces and employing R.F. induction for sealing and for welding operations for consolidating the separate sub-assemblies; maintaining symmetrical any strains produced during the general assembly of the tube parts; making the terminal lead a continuous surface of revolution; and employing other novel features of construction and arrangement of parts which will manifest themselves as the description proceeds.

Referring to the accompanying drawings:

FIG. l is an axial section of a completed tube of the triode type embodying the invention;

FIG. 2 yis an axial section of the anode and envelope sub-assembly;

FIG. 3 is an axial section of the grid and cathode sub-assembly;

. FIG. 4 is an axial section of the heater unit sub-assembly;

FIG. 5 is a perspective View of parts of the mount sub-assembly shown in FIGURE 3, said parts being illustrated in an exploded relation to show the sequence and method of assembly operations;

FIG. 6 is a cross-sectional View showing the basic assembly procedure, more particularly with respect to illustrating the R.F. induction welding or joining of the metal tubular leads and electrode support members; and

FIG. 7 is a perspective view of the jig device including support mandrels used in joining the sub-assemblies into a composite assembly.

According to the present invention the vacuum tube construction comprises a plurality of sub-assemblies which are consolidated into a main assembly by the use of precision means employed in accordance with a method that produces a completed structure having the various components thereof precisely arranged with respect to one another. By being enabled to accurately control the alignment of the various sub-assemblies with respect to a common reference surface the design of the tube assembly is such as to position the component parts in very close critical relation and therefore makes it possible to obtain a tube construction not heretofore obtainable.

Broadly speaking the components or sub-assembly parts of the tube comprise 1) a cathode-heater subassembly; (2) a grid-cathode sub-assembly; and (3) an anode-envelope sub-assembly. It is to be appreciated that each of the sub-assemblies are fabricated from various elements which in themselves may involve careful assembly; furthermore certain of these elements are believed to embody novel features which will be set forth hereinafter.

The precision technique which our invention contemplates may be reduced to comparatively simple terms when the invention is stated in its broadest aspects. These essential features are namely the provision of a basic jigging means, which as noted above, employs an assembly operation performed with a jigging device designed to utilize a single reference surface, and preferably embodying a basic metal joining means consisting primarily of a radio frequency induction welding apparatus. A thirdl feature relates to the sequence of the assembly operations.

The jigging device includes mandrels which are of a reciprocal and/ or telescopic construction and having supporting surfaces for the Work parts. The sub-assemblies constitute separate cylindrical elements adapted to form a cylindrical array of the electrodes when the various parts are consolidated into a main assembly. The inside bore of the cathode lead cylinder is used as a base reference surface throughout the entire assembly operation, and is filled with other parts only after all critical assemblies are linished. The invention will be more fully understood as the discussion proceeds.

Referring to FIG. 1 the active electron emitting surface is the outer or peripheral cylindrical surface of an inner short cathode cylinder 1. Though only the relatively short length of the cylinder is used for electron emission the end of the cylinder which is made by a drawing and expanding process is left closed to prevent R.F. currents from being induced in the cathode heater region within the cathode cylinder. The cathode cylinder 1 is so constructed of appropriate metal that only its active electron emitting peripheral surface coating is of larger diameter to provide close radial spacing with respect to its associated electronic electrode, the grid 2. The diameter of the inactive portion of the cathode cylinder and the cathode support member is reduced to a diameter smaller than that of the active cathode cylinder so that an increased radial spacing between the cathode line and grid line is provided in a region removed axially from the electronic functional region. In this way high interelectrode capacities occur only in electronically active regions where electronic advantages accruing to close spacing offset the circuit disadvantages of high capacity.

The cathode cylinder 1 is heated by radiant heat made available by dissipating electric energy in the helical heater 3 extending into the space inside the cathode cylinder 1. Heater 3 is supported on a rod 40 which is connected, as best shown in FIGS. 1 and 4, to one side of a heater support sleeve 22 which is to be described more fully below. In addition to supporting one end of heater 3, rod 40 also serves to carry heater current thereto. The other end of heater 3 is electrically connected to a heater lead 41 which is coaxially carried within the sleeve 22 by a vacuum tight glass bead 42 fused therewithin. Two means are provided for conserving cathode heater energy. One is to reduce or impede radiation of heat away from the enlarged cylindrical emitting region by providing one or more radiation shields 4 as integral parts of the heater structure.- A heat conduction resistive means is provided in the form of a very thin wall tubular section of the cathode support lead member 5. The thin wall tubular support member is made integrally with strong heavier wall portions which serve well to strengthen the support member and facilitate accurate mounting. The thin wall portion of the cathode support member provides in addition to mechanical support for the cathode a thermal conduction resistance. This characteristic accrues to the small metallic cross section of the thin wall tubular member 5. In addition to this tube being made to have thin wall (less than one thousandths of an inch is feasible) it is preferably made of a metal or an alloy which exhibits poor thermal conductivity such as an alloy of Ni-Fe-Co. The cathode support member 5 being made in a continuous cylinder and being joined to the cathode cylinder and other support members by continuous peripheral welds, the support has low electrical inductive reactance. At high frequencies the depths of penetration of electric currents in a metal conductor are small, thus the resistance to high frequency electric conduction along the cathode support member is not substantially impaired by reason of the thin metal wall. This thin wall tubular cathode support member 5 thus offers a new and improved means for supporting cathodes mechanically while also providing improved resistance to wasteful heat loss and improved electric circuit characteristics i.e. low electric impedance.

The cathode support member 5 is made by a mechanical process fully described in a co-pending application led by us March 31, 1948, bearing Serial No. 18,114, now Patent No. 2,610,304, dated September 9, 1952, relating to thinned Wall tubing adapted for example as a cathode support. The support 5 is joined to the cathode 1 at one end and to the cathode lead cylinder 6 at its other end by a process of simultaneous RI. induction welding fully described in a co-pending application Serial N0.

17,824, led by us on March 30, 1948, assigned to the same assignee as the present application, now Patent No. 2,625,637, dated January 13, 1953, hereinafter referred to more particularly.

The cathode lead cylinder or stem member 6 is a metal cylinder of carefully controlled inside bore and diameter. It will be seen from what follows that the inside bore or inside cylindrical surface is used as a reference surface to which each successive crucial assembly joining operation is referred in the mechanized assembly process. By referring each assembly joining operation to the same reference surface and/ or axis, damaging cumulative errors in assembly are minimized. This is one of the several features that contributes to the possibility of machine mounting the present tube. Toward the end of the lead cylinder remote from the active cathode surface is fastened, by suitable means such as brazing, etc., a flange like ferrule 7 of appropriate metal for bonding or sealing the member 6 to a tubular glass or ceramic insulation member or section 8 having an inner diameter larger than the outer diameter of the stem member 6 (see FIG- URES 7 and 3). The seal flange 7 is preferably shaped as indicated so that its sealing surface will be substantially free from distortions and/ or deformations induced by expansion and/or thermal mis-matches between the cathode lead cylinder 6 and the seal flange 7. By using appropriate shapes the seal ange and cathode lead cylinder need not be made of the same material, strain isolation being insured through geometrical shapes.

Electronically associated with the cathode electrode and physically surrounding the cathode is the tubular grid electrode 2. lts characteristic electronic function is to control the electron space current passing through interelectrode space in the active region of the tube.

Since the grid electrode surrounds the hot cathode and is in close space relation thereto, it absorbs heat conveyed by radiation from the hot cathode surface. It is further heated by energy from two other sources. One is the heat energy resulting from electron bombardment due to electron collection which heating was fully discussed above. Another source of heat energy plaguing the grid is heat dissipated in the grid surface metal by its resistance to the flow of Rf". currents resulting from capacity charging or displacement currents.

To minimize the heat generated in the grid electrode by electron collection the grid cathode spacing is made small as noted previously. To facilitate the removal of heat or the cooling of the grid electrode it is constructed of high thermal conductivity metal or alloys such as copper and so proportioned that end cooling may be substantial. It is further constructed in such a way as to avoid joints which usually introduce thermal and electrical resistance. The grid electrode 2 is so constructed that each grid wire or bar is made integrally with a heavier or larger cross section tubular supporting lead 9 which holds it in position, leads electricity to it, and conveys heat away from it. The mechanical process by which the grid is constructed is fully disclosed in our Patent No. 2,610,304. The metal is pressed into grooves of a mandrel and the thin connecting webs are etched away, forming a grid structure in which the grid wires are integral with end ferrules.

In making the grid electrode structure the grid wires or bars are orientated substantially parallel to the cylinder axis, though some advantages do accrue to orientating them in a coarse spiral, and made integral with the support tube 9 which is provided with a jigging surface 10 of cylindrical shape also integral with the tube 9. This jigging surface is formed on the grid structure close to the base of the grid wires and on the cylindrical portion of the structure into which the grid wires or bars blend integrally. The jigging surface is shaped and its dimensions xed by the tools on which the grid is made. The rollers that force the metal stock into the grooved mandrel are used to form and locate the jigging surface by opening them out to form a larger cylinder than the grid wire-web cylinder but smaller than the original or unworked blank cylinder. The forming of the jigging cylinder 10 is preferably done immediately after rolling the grid wire-web cylinder and while the grid is still on the forming mandrel.` The mandrel need not even be stopped from turning between these two operations. This minimizes the chances of inaccuracies of axial coincidence between that of the jigging surface and the grid wire array.

The grid structure is provided with a thin spoked or serrated top hat 11 (see particularly FIG. 5) integral with a band 12 into which the grid wires blend at their ends opposite the grid support member 9. The band 12 serves to give mechanical support separation to the grid wires and to support the serrated hat. The serrated hat 11 serves to provide electric shielding between the inactive cathode and anode. The serrated hat 11 is formed in the grid blank before the rolling process and is formed in accordance with any suitable process.

The grid structure 2, 9 is mounted upon and connected with a metal grid support lead member 13. The joining operation is preferably done by R.F. induction welding at 14 (see FIG. 6). The jigs and other features of this operation are subsequently discussed herein. The grid support lead member 13 extends axially away from the grid to provide length for the grid-anode-envelope insulator 15. The grid support lead member 13 comprises a tubular portion joined to the support tube 9, a tubular ange or sleeve 24 of enlarged diameter and a radiallyextending connecting liange 25 which provides a ledge of suitable shape for bonding or sealing the cathode-grid insulation member 8 thereto. The sleeve 24 provides means for attaching or assembling the grid-cathode sub-assembly of FIG. 3 to the anode-envelope sub-assembly as by R.F. induction welding at 16.

Associated with the grid electrode 2 and physically surrounding it but spaced away and insulated from it is the anode electrode 17. The electronic function of the anode is to provide means for maintaining an appropriate electric field for facilitating the movement of and collection of electrons traversing the evacuated space between the various electrodes.

The anode is made of copper for reasons of thermal and electrical conductivity and is in the shape of a metal cylinder, the inside surface of which serves as the anode electrode inside the 'Vacuum enclosure, While the outside of said cylinder is outside the Vacuum enclosure where it may be cooled by air, Water, etc. Made as an integral part of the anode 17 is a metal exhaust tube 18'. The anode and the metal exhaust tube are formed together from a metal slug by a process of cold extrusion. The two cylindrical surfaces (external and internal) of the anode cylinder are made accurately co-axial so that the external surface may be reliably used in mounting or assembling the anode-envelope sub-assembly and the gridcathode sub-assembly. The outside surface of the anode cylinder is used as a jigging surface in connection with final assembly method, an operation discussed hereinafter, which method insures close co-axiality of and uniform spacing between -grid and anode electrodes. Brazed or welded onto the anode cylinder in a Vacuum tight manner is a flange or ferrule 19 suitably shaped to provide means for attaching an insulating member 15. At the opposite end of said insulating and vacuum tight member 15 is attached a tubular metal envelope seal member and grid terminal 20 provided with a suitable surface 21 for sealing in a Vacuum tight manner to the insulating cylinder 15. A cylindrical portion of member 20 is suitable for receiving the sleeve 24 of the grid lead support member 13 for attaching by RF. induction welding at 16 the anode sub-assembly to the grid-cathode subassembling by use of aligning mandrels with the lower edges of member 20 and sleeve 24 in registration. The

6 method and operation of this assembly operation will be subsequently described.

The cathode heater assembly, all of which is mounted within or upon a heater support sleeve 22, is attached 1n place inside the cathode lead support cylinder 6 by RF. induction welding at 23. Since in the mounting of this part there are no critical mechanical requirements of co-axiality the heater support sleeve is R.F. induction welded at 23 to the cathode lead support cylinder 6 without precaution as to position except axial position. That is, the ends of the two telescopic tubes should be in approximately the same transverse plane to insure a vacuum tight weld.

After performing the assembly operation as indicated up to this point, the hermetically sealed tube may be exhausted and processed in a conventional manner after the completion of which the metal exhaust tube 18 may be pinched off in accordance with United States Patent 2,427,597, issued September 16, 1947, to Lloyd P. Garner et al. Said patent discloses a cold welding process in which the weld is accomplished by pressure imparted by rollers. However, a hot pinch welding may be used if desired.

The methods and procedures of assembling the cornponent parts of the representative triode of FIG. l

which methods and/or procedures constitute important features of this invention will presently be discussed more particularly with reference to the several figures. It should be understood that the methods and procedures claimed are not limited to a triode as shown but may be :applied to diodes, tetrodes, etc. to advantage.

Most vacuum tube electron discharge devices, as evidenced by the foregoing description are structurally characterized by several metallic electrodes held in more or less critical space relation by conducting supports which supports are in turn held electrically insulated from one another and pass through a hermetically sealed and vacuum tight enclosure. A further structural characterization of high frequency high power electron discharge device is that the space relation of electrodes is increasingly critical and the size of electrically insulated leads is increasingly large compared with low `frequency devices and the length of electric conduction paths is short from active electrode to region of access outside the evacuated enclosure. These required characteristics are conserved in lthis invention by combining several principles and methods.

Due to inherent physical properties of materials it is substantially impossible to position critically spaced vacuum tube electrodes in a structure through the utilization of a joining means that requires high temperature operation of jigs and iixtures in nominal contact with the electrodes during the joining. Deformations of jigs, lixtures and parts resulting from thermal expansions, strain relieving, and temperature differences are responsible for much of the inherent diiiculty. Aside from inherent difficulties of behavior of materials, are ditiiculties arising from manipulative tedium of such operations. Such operations are also slow and expensive. Such assembly methods frequently rely upon axial and rotational accuracies of complicated machines and the rigidity of weak and clumsy lixtures.

This invention circumvents the limiting or inhibiting characteristics of conventional practice by employing a new method of welding metal joints very quickly `and simultaneously, used in combination with a simple jigging means in such a way that the parts joined except for `a very small region near the weld are not heated substantially above room tempera-ture.

As noted above the R.F. welding apparatus and/or method which We employ in practicing our invention is an important adjunct in that it lends itself to securing precision results. In the aforesaid Patent No. 2,625,637, we have disclosed the details of a high frequency welding apparatus which may be very effectively employed in the 'present tube const-ruction. apparatus has special features of design, its principle of operation and/or application herein may be ybriey described generally. A principal advantage obtained by `the use of our high-frequency welding, is that parts undergoing treatment may avoid contacting or touching the Welding electrodes and the welding may be confined to narrow surface contours of predetermined depths.

The essential elements of the apparatus comprise an applicator coil which surrounds the periphery of the circular work pieces and has a relatively sharp taper facing the work for concentrating the magnetic flux. A further concentration of the flux may be achieved by close spacing between 'the applicator coil and the work pieces. The welding means may be employed for any -type of induction weld between any two or more metals of the same or different melting points. Special atmospheres may be used to surround the welding apparatus, or natural atmosphere at atmospheric pressure may also be employed.

In making a weld there are certain variable factors to be given consideration that are dependent upon the character of weld desired. For example, if the power is relatively high at low frequency, the time duration of the cycle should be relatively short. Again, if the frequency is high a relatively shallow weld may be provided or if the frequency is low a relatively deep weld may be secured. Spacing between the work coil and the Weld location is also a factor to be considered.

It will therefore `be seen that the controlling features of the welding process and/or apparatus may constitute the amount of power and/or frequency used; the time duration of the welding cycle, etc. The selection. or determination of the Value of these factors will depend upon the character of the weld.

With this general understanding of the welding process and apparatus preferably employed in carrying out the present invention, more specific instructions will lbe given in connection with the present illustration of the invention.

We have found that `through the use of this R.F. induction welding process we can effectively use a simple and basically direct jigging means for holding parts in position for joining thus eliminating operator skill or judgment. Since -by R.F. induction welding a substantially minimum amount of heat is required to consummate a weld, parts may be jigged by holding devices which hold the parts relatively close to the weld region without the jigs being heated during the welding process. The value of this advantageous feature can hardly be over-emphasized. It means that the jigging conditions are devoid of the high temperature idiosyncrasies of steels and/or materials used in construction of jigs.

The fact that a R.F. induction weld can be consummated without any welding device touching the parts is of great importance in that no great deforming or displacing forces are imposed upon the parts or jigs during welding. This is a very important feature.

The simultaneous contour deep weld feature is of great importance in that an entire weld is consummated substantially simultaneously with the desirable result that extreme uniformity of thermal expansion and contraction of parts or regions of parts being welded causes a minimum of warping, bending, or puckering deformations. To this same feature accrues the desirable minimum of asymmetrical residual internal strains within the welded parts. This assures a minimum of part and/ or alignment deformations resulting from strain relieving during subsequent heat treatment, etc.

The basic assembly and/ or technique may be discussed with particular reference to FIGS. 6 and 7. FIG. 7 shows in perspective a simple but basically sound mechanical means for supporting jigging mandrels 30 and 31 in accurate coaxiality. The jigging mandrels 30 and 31 have locating surfaces which are of right cylindrical shape and are preferably the same diameter. Such cylindrical man- Although the aforesaid dr'els are made' by grinding the same in a conventionalcylindrical grinder, a widely practiced precision machining operation. It is preferable that all critical surfaces required on such mandrels be ground in one machine set up to avoid inaccuracies due to variations in set-ups. A recommended device of simple construction for holding right cylindrical mandrels of the same diameter in accurate co-axiality is a system of V blocks 32 in which the V notches 33 are ground in the blocks in one grinding operation in a conventional surface grinding machine. This surface grinding operation is also a widely practical art and one amenable to high degrees of accuracy. The right cylinder V block device olers an excellent and simple means for holding cylindrical parts in remarkably accurate icoaxiality.

FIG. 6 shows in some detail the method of holding tube parts for uniting by R.F. induction welding. The jigging surfaces of the two mandrels are designated as 34 and 35. The parts holding Isurfaces 34 and 35 are integral with the respective mandrels. The mandrel 31 with its parts holding surface 34 supports

parts

1, 5, 6, 8 and 13 of the partially completed sub-assembly of FIG. 3 by fitting snugly inside the cathode lead cylinder 6. Mandrel 30 holds the grid 2 by snugly gripping its jigging surface 10 inside the cylindrical recess 35 toward its end. With the mandrels, holding the various parts, placed in and against the V notches of the V blocks (see FIG. 7), the unjoined parts may be brought axially into light contact or in close proximity to one another and positioned within the R.F. induction coil 36 by suitable mechanism. With the unjoined parts 9 and 13 appropriately held within the R.F. coil 36 lan intense R.F. current is caused to flow through said coil which currents induce intense currents in and beneath a narrow surface contour around the contiguous edges of adjacently held parts. This narrowly confined intense rush of R.F. current induced in the unjoined parts causes the metals of which they are made to quickly heat to melting whereupon they are united or welded at 14. As noted above the magnitude and duration of the induced R.F. currents are critical. Obviously the greater the currents the shorter the time required to consummate a weld. It should also be pointed out that timing of current flow is critical and important. If the current is allowed to flow for a long time after melting begins `the liquid metal will be thrown or forced away from the region beneath the induction coil by forces resulting from gravity, the reaction between electric currents flowing in the induction coil 36 and the work pieces being welded, and also by centrifugal forces in the case work rotates. Hence it is important that the welding R.F. current be caused to cease owing at a critical moment in the process. This is preferably accomplished by or through the use of an electronic keying or timing or modulation means (not shown) in conjunction with an electronic R.F. power generator used to supply R.F. power to the induction coil 36. The induction coil is preferably a one turn coil constructed of copper and embodying a suitable means for minimizing lead effects. Simple coils without lead effect precautions may be used to produce satisfactory welds if the work pieces and their mandrel are made to rotate or revolve swiftly about their axes thus moving all sections of the weld contour through all regions of the non-uniformly concentrated R.F. eld within a poorly lead corrected coil.

Rotation of work pieces may be found to have other advantages in such matters as critical coil-work alignment. If the work is rotated less critical alignment will be necessary since each element of the work pieces is periodically exposed to the variously concentrated portions of the R.F. field. It is recommended that the induction coil be so mounted with respect to the Work pieces to be welded that `the plane of the active coil be parallel with the plane of the weld contours, and that it be substantially coaxial with the work pieces, particularly when the coil is well corrected for lead loss and/or produces a uniform RF. iield. The deleterious effects of a poorly corrected coil may be somewhatcompensated for by shifting the axis of the coil so that the spacing between the coil and the work is reduced in regions of weak RF. eld or regions where field concentration by the coil is poor. The width or axial length of the active face of the coil is determined by the axial length over which it is required to heat the work pieces, the material of the work pieces, the radial spacing between the fcoil and work pieces, and the electrical transfer characteristics of the RF. powe generating and transmission system.

It will be seen from the foregoing discussion that in the joining of parts by R.F. induction welding they need not be in contact with each other or in contact with the welding apparatus. They are joined by molten metals iiowing from shallow surface portions of the closelyy adjacent parts, which molten metals intermingle and solidify on cessation of power input to form a welded assembly. In the event the parts to be joined are of metals of different melting points a weld or incipient weld may result if there is a finite mutual solubility between the various metals with one being molten.

Even though the actual welding takes place very rapidly there may be chemical reactions between the metals of the parts and the atmosphere in'which the Welds are made. It may then be desirable to conduct the welding operation in a controlled atmosphere to avoid undesirable reactions such as oxidation. This may be readily done by providing a gas bell within which the welding operation is conducted. For gases that are lighter than air such as hydrogen and helium a bell with its lower end open may be fil-led with gas and lowered over the work pieces jigged in place within the RI". welding coil, etc.

It should be pointed out that in using RF. induction welding as a joining means in the manufacture of power tubes of the type described it is possible to join glassed metal assemblies in which the glass-to-metal seal is less remote from the region of metal-to-rnetal joining than is true or practical in the use of any other joining means. This is a matter of importance in tube manufacture. It facilitates the making of shorter lower inductance structures than can be made using gas or `arc welding or silver soldering, etc.

From a discussion of the present invention thus far, two characteristic basic features have been described, namely (l) the use of a jigging mechanism whereby the several sub-assemblies :are aligned with respect to a given reference surface; and (2) the use of special R.F. induction welding apparatus for uniting or joining metal and/ or glass parts. Another equally important feature of the invention is the sequence of the assembly operations.

FIG. 3 shows a cathode-grid sub-assembly in which the numeral 6 designates 4the cathode lead cylinder, the inside bore of which has a carefully controlled diameter and which inside bore of surface is used as the basic reference jigging surface for all critical assembly jigging. The partially completed sub-assembly consists of the cathode lead cylinder 6, the cathode lead cylinder seal ilange 7', the grid lead-support member 13, :and the cathode-grid insulating member 8 hermetically sealed between flanges and/or ledges as indicated. The sealing operation and fixtures are of the precision type 4and it will become obvious as the assembly sequence is discussed that it is preferable or substantially necessary that smaller diameter innermost parts be assembled first and that intermediate diameter intermediately disposed parts be assembled inthe order of their ascending diameters. We have found this sequence of assembly to be necessary for two reasons: (l) it is the only sequence'which provides a feasible possibility of holding each part in a substantial or rigid jig during joining; and (2) it provides the only feasible means for ready access by R.F. induction welding appurtenances to the joint regions.

The sub-assembly of FIG. 3 is built up or assembled as follows: the partially completed sub-assembly is mounted on the jigging mandrel 31 with its parts holding surface 34 engaging the inside bore of the cathode lead cylinder 6 as indicated in FIG. 6. The jigging surface of the mandrel 31 is mounted in the V-block yas indicated in FIG. 7. The cathode is mounted within a cylindrical recess in the end of another mandrel functionally similar to mandrel 30 of FIG. 6. This cathode supporting mandrel is likewise supported in a V-block like mandrel Sil in FIG. 7. The mandrel jigs holding their respective parts are moved axially along the V-blocks until the parts undergoing assembly are brought together or into close proximity and properly positioned within a RJF. induction welding coil functionally similar to coil 36 in FIG. 7. With the jigged work pieces held in place within the coil and an appropriate controlled atmosphere provided, if air is undesirable, the R.F. induction weld 26 (see FIG. 6) is made. The weld `is made by causing critically timed intense RiF. energy to llow through the coil (which does not touch the work) said energy inducing currents in and/or within the two unjoined pieces in a relatively narrow region radially within the inner surface of the coil.

The frequency of the RF. energy is not delicately critical but is chosen -to cause and/ or permit R.=F. energy to be induced in substantial magnitude, within a rind of the work thickness, preferably less than the thickness of the tubular wall of the metal parts to lbe welded. The reason for this is that if a very high frequency be chosen or used the induced energy will generate heat in only a very thin rind or surface lm with the result that 4the weld will be very shallow or the heat will have to be slowly conducted from that sur-face lm into metal beneath it according to heat conduction laws. Welds relying upon heat conduction are not recommended for such applications. If, however, -a lower frequency be used it is possible to directly induce heat energy within -metal of substantial depth thereby speeding up the heating and consequent welding Iprocess. If a sufficiently low frequency be used it is obvious that heat would be generated throughout the entire wall thickness thereby causing the entire metal region lbeneath the coil to heat and melt throughout its thickness. It will therefore be seen that the choice of ,frequency must be made to depend upon -the results desired. -If a thin or shallow weld is desired it may be found desirable from consideration of control to use higher frequency R.-F. energy than if deep welds are desired. It should be pointed out that shallow welds are usually more easily controlled than welds of full depth. It is obvious that in welds of the type indicated a yfull depth weld is precarious in that there is no simple means for supporting the liquid metal inside the tubular members while in the case of a shallow weld the metal constituting the linside rind of the tubular members does not melt until heat is conducted to it from outside and hence supports the liquid metal entering into the weld. Since heat conduction is far slower than R.F. heat generation, the control problem is less severe when higher frequency energy is used to produce shallow Welds. Considerations of weld depth are rather involved and it is not impossible to achieve shallow welds through the use of lower frequencies but control becomes difficult.

After completing the smaller diameter weld 26 of the cathode electrode member, the cathode holding mandrel is withdrawn from the cathode by sliding the mandrel jigging surface along the V-block so that no bending forces are exerted on the cathode.

The next step is to mount the mandrel holding this partially completed sub-assembly in a V-block fitted with a larger RF. induction coil for making the grid weld 114 in the manner described above. After the weld 14 is consummated, as in the case of the cathode weld, the jig is withdrawn axially from the* grid to Iavoid damage, etc.

The next step in the assembly of the triode given for purposes of illustration, is that of uniting or combining the sub-assembly just discussed which is the sub-assembly of FIG. 3 with the anode sub-assembly of FIG. 2. Again the mandrel 31 holding the sub-assembly of FIG. 3 is placed in a set of V-blocks fitted with an appropriate R.F. coil for the envelope weld 16; the anode 17 of the anode-envelope sub-assembly is fitted or placed in a cylindrical recess in the end of another mandrel co-axial with the mandrel 31 4and holding the anode-envelope subassembly; the anode-envelope sub-assembly is moved along the V-notches until the envelope seal yfiange 20 (FIGURES l and 2) is in place around the grid lead flange or sleeve 24 in close spaced relation but out of contact therewith; and the two mandrels are moved along their V-notches, while maintaining said close spaced relation, until the two concentric weld portions are properly spaced from a welding coil arranged to bead weld the registering end edges of the two metal weld flanges at 16, FIG. 1. With this weld completed the cathode lead jigging mandrel 31 is withdrawn from cylinder 6 and the anode jigging mandrel now holding the assemblies of FIGS. 2 and 3 is placed in another V-block fitted With a R.F. induction coil appropriate for making the cathode heater assembly weld 23, FIG. l. The heater sub-assembly (FIG. 4) is placed inside the cathode lead cylinder 6 and moved axially until the concentric tubular member ends are flush, then the mandrel holding the anode is moved in its V-block until the two concentric tubular members are appropriately spaced from the R.F. coil. On the completion of the weld 23, the tube is completely assembled and ready for vacuum processing. In making the cathode heater weld no great mechanical precautions are necessary because its function is not electronic and no great mechanical accuracy of positioning is required, other than the proper depth of insertion of the heater sub-assembly within the cathode lead cylinder which is automatically determined by the length of these leads the end of which are coplanar. This simple expedient avoids assembly problems which might otherwise arise.

I-t should be appreciated that the inside bore of the cathode lead cylinder is used as a base reference surface throughout the entire assembly operation and is filled with other parts only after all critical assemblies are finished. This is an important, distinguishing feature of the invention.

It should be obvious to one skilled in analogous mechanical jigging operation that many variations from the described basic example may be used without departing from the scope and intent of the invention.

The cathode heater sub-assembly of FIG. 4 is of conventional form and should be clear to one skilled in the vacuum tube art.

The sealing of the insulating member (FIG. 2), which in the present illustration is of glass, may be accomplished by mounting metal flange part Ztl and the anode 17, with seal flange 19 attached, in a suitable glassing fixture which positions the metal parts in proper axial and concentric relation. The glass member 15 is sealed at its ends to seal lianges as shown, the heat for sealing being applied by R.F. heating.

Each of the various sub-assemblies involving insulation members may be cleaned after installing the insulation member and before critically spaced electrodes are added.

From the foregoing description it will be obvious that the assembly of the Villustrated tube is accomplished throughout without taxing the digital dexterity or manipulative skill or judgment of operators. `In fact every assembly operation is performed with tools and fixtures and by processes which are functionally and operatively coordinated and sequenced to facilitate and/or make possible mechanization of assembly. This mechanization of assembly not only eliminates the necessity for but precludes the possibility of manual readjustment of parts during assembly and thereby guarantees a more uniform product. It should also be obvious that the loading of 12 parts onto jigging mandrels may be done manually or by' automatic loading devices.

It should be further obvious that the placing of loaded mandrels 30 and 31 in V-block guides 32 need not necessarily be manual operations but may be mechanized to execute the insertion and translatory movements between limited axial positions thereby positioning the electrodes with respect to associated electrodes and/or the respective support members Ito which they are to be welded, and to positioning the unjoined but properly held parts within the R.F. induction welding coils.

Various other modifications of the invention `may be made in its application to various types of devices bu-t the ones described and/ or suggested may be regarded as illustrative of the scope of the invention which is only limited by the appended claims.

What is claimed is:

l. An electron device, comprising at least two electrodes, means supporting said electrodes in close spaced apart relation and including a pair of tubular metallic conductive members in close spaced telescopic relation, and a fusion seal formed directly between said spaced conductive members, said fusion seal forming the sole mechanical connection between said spaced electrodes.

2. An electron tube, comprising an envelope, at least two spaced apart electrodes in said envelope, said envelope including two tubular metallic members in close spaced telescopic relation, and a fusion seal formed directly therebetween, and said fusion seal forming the sole mechanical connection between said spaced electrodes.

3. An electron tube, comprising an envelope, cathode and anode electrodes having cylindrical active surfaces within said envelope and in spaced apart relation, a pair of close spaced concentric tubular metallic members each forming a portion of said envelope and each joined coaxially to one of said electrodes, a fushion seal formed directly between peripheral portions only of said spaced tubular members, said electrodes being mechanically connected solely through said tubular members and said tubular members being connected solely through said fusion seal.

4. An electron tube, comprising an envelope, coaxial cathode, grid and anode electrodes, a tubular metallic member joined to said anode and forming part of said envelope, a second tubular metallic member forming the sole lead-in and support for said grid and also forming a portion of said envelope, said second metallic member being joined at a portion removed from the periphery thereof to said cathode, said tubular metallic members being in close spaced concentric relation one to the other with their edges in registration at one end thereof and joined solely by a fusion seal formed directly between said spaced metallic members at said edges only, and said grid and anode being mechanically connected solely through said fusion seal.

5. A composite grid and cathode unit comprising a metallic cylindrical grid base, a grid joined to one end of said base and forming a cylindrical grid surface coaxial therewith, a tubular metallic grid supporting ring of larger diameter than said grid base having an inwardly extending metallic flange joined to said base with the exterior surface of the supporting ring coaxial with said grid surface, a cylindrical cathode, a metallic cathode supporting tube having one end joined to the cathode with the cathode supporting tube coaxial with the cathode, a metallic ange joined to the cathode supporting tube near its other end and an insulating cylinder having an inner diameter larger than the outer diameter of said cathode supporting tube sealed between said flanges with said cathode positioned coaxial with said grid surface.

6. An electron discharge device comprising a cathode sub-assembly including a cathode element which is conductively joined to a support lead, the junction of said cathode element and support lead consisting of a supporting member of low radio frequency reactance and high thermal resistance to afford thermal isolation between the cathode element and the radio frequency conductor, a grid sub-assembly comprising a one-piece grid element of high electrical and effective thermal conductivity, a support member integrally formed with said grid element and constituting a continuous low reactance thermally conductive grid lead and terminal, said grid terminal and lead being a continuous surface of revolution, an anodeenvelope sub-assembly comprising an anode electrode having an exhaust tube integrally formed therewith, said subassemblies being mounted concentrically and aligned with respect to one another with the inside of the cathode lead constituting a reference surface for purposes of alignment and spacing of the severa-l electrodes and sub-assemblies, and a Aheater sub-assembly closing the discharge device by a vacuum-tight joint between fthe cathode lead and the lheater lead.

7. A composite anode-grid-oathode assembly unit comprising a cylindrical anode having coaxial external and internal cylindrical surfaces, a radial flange joined to the external surface of said anode at one end, a metal ring having a radial flange, a glass ring -between said flanges and sealed thereto, a grid contact ring joined to said metal ring, a slotted cylinder forming Ian integral grid structure, a grid supporting cylinder joined to said slotted cylinder, said supporting cylinder having a base of larger diameter than the surface of said grid surface and joined to said grid contact ring, a cathode cylinder having a cylindrical inner surface and a thermoactive outer surface at one end, a flange on the other end of the cathode cylinder, .a glass cylinder between and sealed to the base of said grid supporting cylinder and the flange of said cathode cylinder with the inner cylindrical surface of the cathode cylinder positioned parallel to said grid surface, said grid contact ring being positioned in said metal ring with the grid surface spaced from the inner surface of said anode and the cylindrical inner surface of said cathode cylinder positioned coaxial with said inner surface of said anode, whereby the inner anode surface, the grid surface and the cathode thermoactive surface are coaxial, said grid contact ring having a vacuum tight joint with said metal ring.

8. A composite grid and cathode sub-assembly adapted to be telescoped with and joined to an element of another sub-assembly, said grid and cathode sub-assembly comprising a metallic cylindrical grid base, (a grid joined to one end of said base and forming a cylindrical grid surface co-axial therewith; a tubular metallic grid supporting ring of larger diameter than said grid base having an inwardly extending metallic iiange joined to said base with the exterior surface of the supporting ring co-axial with said grid surface, a cylindrical cathode mounted within said cylindrical grid structure with its emissive surface presented to said grid, a metallic cathode supporting tube having one end joined to the cathode, said cathode supporting tube being co-axial with the cathode, -a metallic flange joined to the cathode supporting tube near its other end and an insulating member sealed between said iianges with said cathode positioned co-axial with said grid surface.

9. An electron discharge device including an anodeenvelope sub-assembly and 1a grid-cathode-envelope subassembly, said grid-cathode-envelope sub-assembly comprising a metallic cylindrical grid base, a grid joined to one end of said base and Aforming a cylindrical grid surface co-axial therewith, a metallic grid supporting ring of larger diameter than said grid base having an inwardly extending llange joined to said base with the exterior surface of the supporting ring co-axial with said grid surface, a cylindrical cathode mounted within said cylindrical grid structure with its emissive surface presented to said grid, a metallic cathode supporting tube having one end joined to the cathode, said cathode supporting tube being co-axial with the cathode, a metallic flanged joined to said cathode supporting tube near its other end and an insulating member sealed between said flanges with said cathode positioned co-axial with said gridsurface; said anode-envelope sub-assembly comprising a hollow cylindrical anode electrode having an outwardly extending ilange joined to an insulating cylindrical envelope member, and a metallic member joined to said last mentioned envelope member and having a cylindrical surface telescoped with and joined to said grid supporting ring of said grid-cathode-envelope subassembly.

10. The method of constructing an electron tube comprised 'of a plurality of sub-assemblies including metal members embodying cylindrical surfaces designed to telescope one another, said method comprising jigging at least two of said sub-assemblies and telescoping said surfaces in close spaced relation, eifecting yaccurate coaxial'alignment of said jigged sub-assemblies; and uniting said jigged sub-assemblies by a fusion weld between said spaced surfaces.

ll. The method of constructing an electron tube comprised of a plurality of sub-assemblies including metal members embodying cylindrical surfaces designed to telescope each other, said method comprising supporting one of said sub-assemblies on a first jigging mandrel, supporting another of said sub-assemblies on a second jigging mandrel, effecting accurate coaxial alignment of said jigged sub-assemblies while maintaining said surfaces out of contact, moving said surfaces into telescopic close spaced relation, and joining said sub-assemblies by forming a fusion Weld between said spaced surfaces.

l2. A composite grid and cathode unit comprising a cylindrical grid base, grid wires joined to one edge of said base and `forming a cylindrical grid surface coaxial therewith, a tubular grid supporting ring of larger diameter than said grid base having an inwardly extending flange joined thereto with the exterior surface of the supporting ring coaxial with said grid surface, a cathode cylinder, a cathode supporting tube having its wall thickness reduced near one end, said end being joined to the cathode cylinder with the internal surface of the cathode supporting tube coaxial with the external surface of the cathode cylinder, `a metallic cathode flange joined to the cathode supporting tube near its other end and a glass cylinder having an inner diameter larger than the outer diameter of said cathode supporting tube between said flanges and sealed thereto with the inside surface of said cathode supporting tube positioned coaxial with said grid surface.

13. An electron tube comprising an envelope, electrodes in the envelope including a grid and a cathode, a tubular metal grid terminal on said envelope, a cathode stem comprising a metal stem member coaxial with said grid terminaba metal supporting sleeve having an edge registering with one edge of said grid terminal, a ceramic Section interposed between said stem member and said supporting sleeve, said ceramic section having an inner diameter larger than the outer diameter of said stem member, means sealing said ceramic section to said stem member and sleeve in vacuum-tight relation, and a metallic bond uniting the registering edges of said sleeve and grid terminal.

14. An electron tube as claimed in claim 13, wherein said means sealing said ceramic section to said stem member includes a metallic flange joined to said stem member and to said ceramic section.

l5. The method of constructing an electron tube cornprised of a plurality of tubular elements adapted to telescope one another, one of said elements comprising a cathode, a second element comprising a grid, a third element comprising an anode, each of said elements comprising a metallic tubular support; said method comprising inserting the cathode element Within the grid element and utilizing the cathode support as a reference surface for joining said elements coaxially with insulating material to form Ia first sub-assembly, joining said anode coaxially to a metallic tubular envelope member with insulating maten'al to form a second sub-assembly, assembling said rst sub-assembly with said second sub-assembly with said tubular grid support close spaced from and within said tubular envelope member, and joining said spaced grid support and said envelope member while holding said cathode and said anode in accurate coaxial relation.

16. An electronV tube comprising an envelope, electrodes in the envelope including an anode and grid and cathode, va tubular metal grid terminal on the envelope, a cathode stern comprising a metal stem member coaxial with the grid terminal, a metal supporting sleeve having an edge registering with the lower edge of the grid terminal, an insulating Section interposed between the stem member and said supporting sleeve, said insulating section having Ian inner diameter larger than the outer diameter of the stem member, means sealing said insulating section to said stern member and sleeve in vacuum-tight relation, and a metallic bond uniting the registering edges of said sleeve and grid terminal.

References Cited in the file of this patent Y UNITED STATES PATENTS Hull et al Feb. 8, 1938 Kallman et al Feb. l0, 1942 McArthur May 26, 1942 Chevigny Apr. 4, 1944 McArthur July 18, 1944 Nergaard Nov. 18, 1947 Chamberlin June 29, 1948 Stone July 13, 1948 Beggs July 27, 1948 Drieschman Aug. 3, 1948 Watson Feb. 8, 1949 FOREIGN PATENTS Great Britain NOV. 5, 1937