US2866120A - Method of making an electron tube - Google Patents

Description

Dec. 23, 1958 c. M. MORRIS ET AL METHOD OF MAKING AN ELECTRON TUBE Filed Nov. 14, 1955 3 Sheets-Sheet l lmo INI/[NTORS ELIFFDRD MMEIRRIS 4i NIEIHDLFIS EFRYSLHK Dec. 23, 1958 Filed Nov. 14, 1955 C. M. MORRIS ET AL METHOD OF MAKING AN ELECTRON TUBE 5 Sheets-Sheet 2 A l 4. a\\\\\\\\\\\\\\\\\\\ CLIFF-BRO NLMDRRIS & NHIHULHS EPRYSLHK Dec. 23, 1958 c. M. MORRIS ET AL 2,866,120

METHOD O MAKING AN ELECTRON TUBE Filed Nov. 14, 1955 I5 Sheets-Sheet 3 'IIIIIIIIIIIIIIIIIIIIIII" Lg- I ELIFFDRD M.ME1RRIS & NIBHEJLHS EPRYSLRK United States Patent ce METHOD OF MAKING AN ELECTRON TUBE Clifford M. Morris, Hackensack, and Nicholas E. Pryslak,

Summit, N. J assignors to Radio Corporation of America, a corporation of Delaware Application November 14, 1955, Serial No. 546,445

3 Claims. c1. 313 247 This invention relates to a method of making an electron tube structure. Particularly, the invention concerns a method of making and assembling an electron tube structure having apertured elements.

A structure wherein the electrode leads are integral with the envelope thereof is used in electron tubes having relatively small interelectrode spacings. Such a structure, therefore, proves useful at relatively high frequencies. pencil type electron tube wherein the electrodes compise concentric tubular elements. As the interelectrode spacings in pencil tubes are relatively small, the electrodes of the tube must be maintained substantially in exact alignment for desired tube operation.

In order that the assembly of such electron tube structures be facilitated, the apertured elements comprising the structure are usually aligned upon a plurality of assembling mandrels before they are fastened to each other. The separate mandrels must be held directly in line with each other in order that the elements be in proper alignment. Consequently, unless great care is taken in the positioning of the mandrels poor alignment of the elements results. The use of a number of mandrels makes the assembling process a less automatic one. The assembling process then requires a continual inspection of the positioning of the mandrels. The greater number of operations required, when more than one mandrel is used, also tends to increase the rejection rate due to poorly aligned assemblies. Then, too, the greater number of operations increases the cost of producing electron tube structures which employ these assemblies. Consequently, it is desirable that a single assembling mandrel be used to accurately align the elements in registry with each other. If a single mandrel is used the elements must be mounted upon the mandrel in an order such that their transverse extents, that is, their aperture diameters, are each successively smaller. However, electron tubes often require the use of a structure having one apertured element mounted substantially in exact alignment between other elements having larger apertures. Such tube struc tures could not, heretofore, be assembled on a single mandrel.

The reason for using tubes comprising one apertured element sandwiched between other elements having apertures of larger transverse extents will be apparent from the following:

In the mass production of pencil tubes it has proven desirable to utilize tubular envelope and electrode components of drawn construction. By drawn construction there is meant the use of pre-formed tubular stock which has been worked to the desired size by having been drawn through dies. The use of this construction technique effects an economy and a greater ease of manufacture over previous techniques. These advantages are due to the elimination of the relatively delicate, costly, and time consuming machining operations necessary when tube electrodes are shaped by means of cutting tools.

The structure finds use in what is known as a I Patented Dec. 23, 1958 However, in tubes utilizing drawn construction the transverse extent of the aperture in one of the apertured portions of the tube structure must be smaller than that of the apertures in the apertured portions to be assembled on opposite sides of the one portion. A pencil tube triode of drawn construction has an envelope comprising, at one end thereof, an end portion. This end portion is made up of a relatively thin tubular element having a tubular-shaped anode therein. The other end of the envelope includes another end portion. This other end portion has a cathode support cylinder therein. An apertured disc is disposed intermediate the end portions. The disc supports a cyIindrically-shaped grid electrode within the tubular anode. The grid support disc must have an aperture smaller than that in each of the end portions of the tube. The smaller aperture in the end portion adjacent to the anode is necessary in order to support the cylindrical grid within the anode and against the disc walls defining the disc aperture. The support disc must also have an aperture smaller than that in the other end portion, at the cathode end of the tube. This is so because there is mounted, within the aperture of this other end portion, a cathode support member having a diameter greater than that of the grid. Thus the grid support disc must have an aperture smaller than those in both of the envelope end portions. Consequently, a single mandrel could not heretofore be used to assemble an electron tube structure comprising the aforedescribed grid support disc and envelope end portions.

When a tube having a plurality of grids is assembled (e. g. a pencil tube tetrode or pentode) the apertures in the grid support discs, going in a direction from the anode end of the tube to the cathode end, must be successively smaller. This means that there must be successively assembled on a single mandrel, first a member having a relatively lar e aperture (one envelope end portion) then members having smaller apertures (the grid support discs) and finally another member having a relatively large aperture (the other envelope end portion).

It is therefore an object of the invention to provide an electron tube structure which lends itself to assembly on a single mandrel, and which includes an element, having a relatively small aperture, mounted substantially in exact alignment between other elements having larger apertures, and an improved method of assembling the same.

Another object of the present invention is to provide an improved electron tube structure of drawn construction and having an electrode with a relatively small aperture mounted in substantially exact alignment between adjacent elements having larger apertures.

Another aim of this invention is to provide an improved method of making an electron tube structure having apertured members of drawn construction and disposed in an order not determined by aperture size.

The foregoing and related objects are realized in an elongated electron tube having tubular end portions and an apertured disc disposed in coaxial relation, and with the disc between the end portions. One of the end portions, serving as the anode, has an aperture or passageway of smaller transverse extent that the passageway in the other end portion, a cathode being supported by this other end portion. The aperture or passageway in the disc has a size intermediate that of the passageways in the two end portions referred to. This permits the two end portions and the disc to be mounted on a single mandrel, and to be fixed in this relation. To permit a grid having a smaller transverse extent than the anode verse extent than that of the passageway in the anode. A tubular grid is fixed within the smaller insert passageway. This permits the grid to havea transverse extent for extension within the anode andin concentric relation thereto. There is mounted within the large passageway of the end portion at the cathode end of the tube, an assembly which includes a cathodes support and a cathode. The cathode is disposed withinthe grid aforementioned; The resultant structure, therefore, includes tube elements (the disc and end portions) having one order of transverse size different for assembly on a single mandrel and, supported on the elements, electrodes having another order of transverse size difference for disposing the electrodes in concentric relation in a different order from the aforementioned one order.

This invention is described in greater detail in connection with the accompanying three sheets of drawings wherein like numerals refer to like parts and wherein:

Fig. l is a partly cut-away elevational view of a pencil tube triode embodying the invention;

Fig. 2 is a sectional view taken on line 22 of Fig. 1;

Fig. 3 is a perspective view of a flexible ring or insert used in the tube of Fig. 1;

Fig. 4 is an exploded view, partly in section, of the tube of Fig. 1;

Fig. 5 is an elevational cross sectional view of a pencil tube envelope assembly, supported on a mandrel, during a step in the manufacture of the tube of Fig. 1;

Fig. 6 is an exploded view of some of the elements of the tube of Fig. 1 and showing the mandrels used in mounting a grid in an envelope assembly;

Fig. 7 is a partly cut-away view of a cathode of the tube of Fig. 1 and showing a mandrel of the type used to mount the cathode within a grid assembly of the tube; and

Fig. 8 is a partly cut-away elevational view of a pencil tube tetrode according to the invention.

Referring to the drawing in more detail, there is shown in Fig. 1 thereof an elongated pencil tube triode which employs the structure of the invention and which has been manufactured in accordance with the novel method of the invention. The pencil tube 10 includes an envelope comprised of two envelope end portions 12 and 14 in the form of tubular metallic members of drawn construction, a disc-shaped envelope and electrode support member 16 intermediate the end portions, andtwo tubular insulating members 18 and 20. The insulating members 18 and 29, which may be made of an electrically non-conductive material such as glass, are disposed each between one of the tubular end portion members 12 and 14 and the disc-shaped member 16. The insulating members serve as insulating spacers between the members 12, 14, and 16. Tubular electrodes, which comprise an anode 22, a grid 24, and a cathode 26, are mounted in concentric relation within the tube, the grid 24 being disposed around the cathode 26 and within the anode 22. Lead-in wires 28 at one end of the tube provide electrical access to some of the elements therewithin. An exhaust or tip-off tubulation 30 is fixed to the end of the tube remote from th lead wires 28 and is shown pinched off after the tube 10 has been exhausted.

The first envelope end portion 12 serves as a mount for a cathode support sleeve 32 which engages the inside wall of the first end portion 12 in a snug fit, the cathode support sleeve 32 supporting the cathode 26 within the tube. The cathode is in turn provided with a heater 34 having leads 36. The cathode 26 is provided with a passageway 38 therethrough affording a communication between the space inside the cathode support sleeve 32 and other portions of the tube. During the evacuation of the tube, when the various elements of the tube have been assembled, the gases from the space inside the cathode support sleeve 32 flow through the passageway 38 and toward theexhaust tubulation 30 and out of the tube.

The secondenvelope end portion 14 serves as an anode support and engages the anode 22 in a snug fit. The anode 22 and second end portion14 are assembled before the envelope elements are sealed together and together form an envelope end member. The envelope elements, when sealed together, form an envelope or bulb assembly 40. The second envelope end portion 14 is provided with a re-entrant portion 42 having an aperture 44 therethrough. The re-entrant portion 42 provides a surface for snuglyengaging the tip-off tubulation 30.

According to the invention, there is provided a ring or apertured insert 58 which has an outer transverse extent or diameter such that the outer walls of the insert engage the walls of the disc 16 defining the disc passageway. The insert 58 also has a passageway or opening which has substantially the same transverse extent as the transverse extent of the grid 24 in order that the grid 24 engage the insert 58 for support thereon. Thus the electron tube It: is provided with a bulb assembly 40 which has members (namely the first envelope portion 12, the grid support disc 16, and the envelope-anode member 50) which have passageways having transverse extents of one order of size difference; and at the same time the tube has other members, namely the tube electrodes, which have another order of size difference.

As shown in Fig. 4, the cathode support sleeve 32, together with the cathode 26 supported therein, are inserted into the first envelope end portion 12 after the envelope members or elements are sealed together to form the bulb assembly 40 and after the grid 24 has been mounted within the anode 22. A getter 46 is also mounted within the cathode support sleeve 32. This getter location prevents getter material from being deposited on undesired surfaces within the tube. The heater 34 and getter 46 constitute a sub-assembly formed on a glass button-like stem 48 whichis eventually sealed into the free end of the first envelope end portion 12. The assembling and sealing of the envelope elements will be described below.

Envelope assembly The assembly procedure is as follows: After the second envelope end portion 14 and anode 22 are assembled to form an integral envelope-anode member 50 (Fig. 5), the envelope or bulb assembly 40 is prepared. The bulb assembly 40 .comprises the first envelope end portion 12, the grid support disc 16, the envelope'anode portion or member 50, and the glass insulators 16 and 18. These parts are joined together by metal-to-glass seals while being held in accurate axial alignment on a single turned metal mandrel 52. The mandrel is preferably of the type having circular symmetry about its long axis for ease in the manufacture of the mandrel. Radio frequency heating equipment, indicated schematically by coils 54 and 56, is used to make the seals. The cathode 26 and grid 24 (Fig. 1) are not in place at this time so these parts are not exposed to the sealing heat.

As illustrated in Figure 5, the assembly of the envelope members is achieved by first positioning the first envelope end portion 12 around the mandrel 52 and in radial engagement with a first mandrel surface 63 which is substantially cylindrical and is coaxial with the axis of the mandrel. The lower end of the envelope end portion rests on a lower surface 60 of the mandrel. Next, one of the insulating spacers 20 is placed around the mandrel with a lower edge of the spacer engaging an upper edge of the envelope'end portion 12. The spacer 20 does not itself engage the mandrel 52. Then the disc-shaped member 16 is placed on the spacer plate 20, a lower edge of the member 16 resting on an upper edge of the spacer. The passageway 62 of the member 16 radially engages an intermediate or second mandrel surface 64 with the walls defining the passageway 62 engaging the mandrel surface 64. The second mandrel surface is also substan tially cylindrical and coaxial with the axis of the mandrel. Thus, the disc-shaped member 16 is maintained in axial alignment with respect to the first envelope end portionv 12. A second insulating spacer 18 is then positioned on the mandrel and on the disc-shaped member 16, the lower edge of the spacer 18 resting on an upper surface of the member 16. Finally, the integral envelope-anode 'mem ber 50 is disposed on the mandrel 52 and in radial engagement with a third or upper surface 66 thereof, the third surface also being substantially cylindrical and coaxial with the mandrel axis. The lower edge of the second envelope end portion 14, of the integral member 50, rests on the top edge of the second spacer 18 while portions of the anode 22 defining the passageway therein engage the substantially cylindrical upper mandrel surface 66. The last named engagement axially aligns the integral envelope-anode member with the disc-shaped member 16 and the first envelope end portion 12. While the three coaxial curved mandrel surfaces 63, 64, and 66 have been described as substantially cylindrical, it will be realized that they may instead be tapered and in the form of truncated cones.

The envelope end portions 12 and 14 are then heated, as by radio frequency energy through coils 54 and 56. This heating softens the spacers 18 and 20 to a degree sufiicient to cause them to seal to the envelope end portions 12 and 14 and the disc-shaped member 16. After being cooled, the bulb assembly 40 thus formed is moved in an upward direction off of the mandrel 52 and is ready for further processing.

Electrode assembly Reference is now made to Fig. 4 which illustrates that after the bulb assembly 40 has been; manufactured, an assembly comprised of the grid 24 and the insert 58 is inserted into the bulb assembly 40. A cathode assembly 26 and 32 is then fixed to the bulb assembly after which the stem assembly, comprising the heater 34, the getter 46 and the stem 48, is fixed to the bulb assembly 40. Finally, the exhaust tubulation 30 is inserted through the passageway 44 in the second envelope end portion 14 and is fixed to the end portion and the tube is ready to be evacuated.

Referring to Figure 6, the grid 24 is fixed to the insert 58 to form a grid insert assembly, the lower portion of the grid being secured against the walls of the insert 58 defining the passageway therethrough. The grid-insert assembly thus formed is mounted within the bulb assembly 40 by first placing the grid-insert assembly on a pronged first grid alignment mandrel 68, the pronged portion 70 of the mandrel extending through the passageway in the grid 24 and the insert 58 nesting on a first surface 72 of the pronged mandrel 68. A second grid alignment mandrel 74, having a mandrel prong receiving passageway 76 is inserted into the passageway of the anode 22. The first mandrel 68 is inserted into the first envelope end portion 12 and with the prong 70 thereof mating with the prong receiving passageway 76 of the second mandrel 74. This action forces the insert 58 into the passageway 62 of the disc-shaped member 16. The prong 70 and prong receiving passageway 76 insure that the grid-insert assembly is axially aligned within the bulb assembly 40. The insert 58 is positioned a predetermined axial distance within the disc-shaped member 16 by virtue of a second mandrel surface 78 which engages the lower edge of the first envelope end portion 12 at the desired relationship between the insert 58 and the member 16. When the mandrels 68 and 74 are removed from the bulb assembly 40, the grid 24 is maintained in the desired coaxial relation within the anode 22 by virtue of the force fit (described below) between the insert 58 and the support member 16.

Referring to Fig. 3, the insert 58 may be maintained in the desired position within the disc-shaped support member 16 for the normal life of the tube by a force fit, the insert being adapted to be flexed against the walls defining the passageway 62 in the member 16. The insert is cup-shaped, that is, having a mouth at one end and a closure portion 88 at the other end. The closure portion 88 is apertured, having walls defining a passageway 90 through the portion. The cup-shaped insert 58 is tapered radially outwardly at its mouth. This taper provides the portion of the insert 58 adjacent to its mouth with a larger maximum cross-sectional extent than the cross-sectional extent of the portion of the insert adjacent to the closure portion 88. In addition, the insert 58 has a number of embossments 61 extending radially inwardly therefrom. The portions of the insert between adjacent embossments are adapted to engage the support member 16 in a relatively secure force fit. This provides the insert with a greater radial flexibility than that which would exist in the absence of the embossments. The embossments also allow the insert 58 to sustain a relatively great amount of fiexure within the support member 16 Without substantially deforming the contour of the passageway 90 in the insert. 7

Referring to Fig. 7, the cathode 26 is then positioned with the bulb assembly 40 and in coaxial relation with the grid 24. This is accomplished by first fixing the cathode 26 to the cathode support 32, such as by welding the two elements together. The assembly 26 and 32 thus formed is placed on a pronged first cathode mounting mandrel 80 which is similar to the first grid mounting mandrel 68. A pronged portion 82 of the first cathode mounting mandrel 80 is inserted into the passageway 84 in the cathode 26 and the mandrel 80 is inserted into the lower end of the first envelope end portion 12 as described with respect to the mounting of the grid in Fig. 6. A second cathode mounting mandrel (not shown), similar to the upper mandrel 74 of Fig. 6, is inserted into the anode passageway and the upper part of the prong 8-2 mates with the prong receiving portion of the cooperating second mandrel. Since the lower edge of the cathode support member 32 rests on a first surface 86 of the first cathode mounting mandrel 80, the cathode support member 32, and thus the cathode 26, is disposed the desired axial distance within the bulb assembly 40. The two cathode mounting mandrels are then withdrawn from the bulb assembly, and the stem assembly and exhaust tubulation are fixed to the bulb assembly. The tube is then evacuated and then the exhaust tubulation sealed off.

Pencil tube. tetrode As illustrated in Fig. 8, the method of the invention may also be used to make an electron tube having a plurality of concentric grids. The pencil tube tetrode 10' of Fig. 8 is similar to the triode of Fig. 1, but with the following differences: (a) the tube 10 includes a second electrode support member 17 mounting a second grid 25, the second member 17 having a passageway which has a cross-sectional extent which is smaller than that of the passageway 62 (Fig. 5) of the first support member 16 and -at least as large as that of the passageway in the anode 22, and (b) a third insulating spacer 19 is positioned between the two grid support members 16 and 17.

In practicing the method of the invention with respect to a plural grid pencil tube, the envelope members are first assembled by successively positioning the following members on amandrel (not shown) which is similar to the one 52 in Fig. 5 but with the exception of an additional mandrel surface (similar to surface 64 of mandrel 52) for coaxially aligning the second electrode support member 17 with'the other tube electrodes. The successively positioned members are the first envelope end portion 12, one of the insulating spacers 20, the first electrode support member 16, a second insulating spacer 19,

. the second electrode support member 17, a third insulating spacer 18, and then the integral envelope-anode member 50. Then, after the members described have been sealed together to form a bulb assembly 40, the second insert 59 and second grid 25 sub-assembly is force fitted above are then fixed to the bulb assembly'and the tube is evacuated and the exhaust tubulation-sealed off.

While the method and structure-of the invention have been described with respect to pencil tube triodes and tetrodes,,it will. be appreciated that the invention may be used to advantage inelectron tubes-having different structural shapesyand dilferentnumbers of electrodes.

What is claimed is :1

l. A method of makingyan; electron; tubexstructure including three members havingpassageways of successively larger transverse-extents,;said method comprising extending a single elongated mandrelthrough said members in an order from the member having the largest passag way extent to the member having the smallest passage.- way extent, fixingsaid members into a-unitary structure, removing said structure from said mandrel, andfixing against the portion ofthe intermediate of said-three members defining the passageway therein an insert hav ing a transverse extentsmaller than that of the passageways inall of. said members.

2. The. method, described. in claim- 1 and wherein said fixing. of said insert comprises, a force fitting only of saidinsert against said intermediate member portion 3. A method of making anelongated electron tube structure including an envelope memben amelectrode support member, an envelopeelectrode member, and; two

$5 insulator members, each of said members having walls defining-a passageway; said method comprising the operations of extending an elongated mandrel, having three coaxial surfaces of successively smaller transverse ex,-

tents, through the'passageway in said envelope member with thenone of said mandrel surfaces having the largest transverse, extent in. radial. engagement with the walls defining the passageway in said envelope member;. disposing one of said insulator members on said envelope memberqandrwiththe walls of said one insulator member around said mandrel; positioning said electrode support member on said one insulator member and with a second of, said. mandrel surfaces in radial engagement with the wallsdefining .the passageways in said support member; disposing the other of said insulator members on said support member and; with the walls of said other insulator member around said mandrel; positioning said envelope-electrodemember on said other insulator memher and with-the third of said mandrel surfaces in radial engagement with the walls defining the passageway in said envelope-electrodemember; fixing said members to each other; removing the. assembly thus formed fro-m said mandrel; and seating against the walls of said electrode support member, defining the passageway therethrough an insert having, a passageway with a maximum transverse extentwhich is smaller than the transverse extents of the passagewaysof all of said members.

References Cited in the file of this patent UNITED STATES PATENTS 1,716,930" Prindle June.11, 1929 2,473;969- Pryslak and McLaughlin June 21, .1949 2,697,796 Eitel Dec. 21, 1-954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,866,120 December 23, 1958 Clifford IVL, Morris 'et al.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 61, for "that" read than column 3, line '7, for "cathodes" read cathode line 60, for "th" read the --u Signed and sealed this 19th day of May 1959,

(SEAL) Attest:

KARL H. ADEINE ROBERT C. WATSON Attesting Oificer Commissioner of Patents

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