US2937305A - Ruggedized electron tube - Google Patents

Description

y 1960 P. A. DE BACKER 2,937,305

RUGGEDIZED ELECTRON TUBE Filed June 26, 1958 1 I :z I I 11 i I. u

INVENTOR. L umzn PA. Dr: BHEKER BY jaw cathode.

2,931,305 RUGGEDIZED ELECTRON TUBE Lucien P. A. De Backer, Bloomfield, NJ., assignor to Radio Corporation of America, a corporation of Delaware Application June 26, 1958-, Serial No. 744,831

1 Claims. (Cl; 313-247).

This invention relates to electron tubes, and particularly to an electron tube having a relatively rugged structure for preserving a prees'tablished spacing between a cathode and a grid.

One type of electron tube in which the invention finds particular utility is the so-called pencil tube. A pencil tube comprises a structure including an elongated envelope having metallic end portions and an intermediate portion made of insulating material such as glass or ceramic. A metallic disc having a central opening is sealed across the intermediate portion. I

In a triode type of pencil tube, 'a tubular grid is sup ported on the metallic disc with an end portion of the grid extending through the opening in the disc and fixed to the walls defining the opening. The grid thus extends towards one end portion of the envlope. 'A tubular anode is supported in the aforementioned end portion and surrounds the grid in concentric relation therewith. A tubular cathode is supported in the other'envelope end portion and extends intothe grid in concentric relation therewith.

It will be seen from the foregoing that the three tubular electrodes are supported at one end portion thereof, with the other end portion free of support. In this situation, there is likelihood of vibration of the free end portions when the tube is subjected to impacts. Such vibration produces adverse effects, such as microphonics in the cut put of a system in which the tube is used.

In the structure aforementioned the anode is relatively massive and extends only slightly from its supported region. Therefore the anode is elfectively restrained from a vibrational response to impacts. However, the

- free ends of the grid and cathode extend an appreciable distance from their regions of support and are relatively light in structure. Suchlight structure, while reducing the burden imposed on the support elements, such as the disc and an end portion of the envelope, is incapable of providing adequate support for the free end portions of these electrodes in certain circumstances. (For example, when the grid and cathode are extremely closely spaced in ultra high frequency applications involving impacts of appreciable magnitude, the free end portions of these electrodes may respond to the impacts in vibrations having an amplitude suflicient to bridge the spacing between .the electrodes.

In attempting to meet the foregoing problem, it .has been found impractical to utilize the anode in a'support system. This is because the anode is usually operated at a relatively high voltage difference with respect to the grid and cathode. Consequently, an insulating support utilizing both the anode and the free end portions of the grid and cathode would give rise to current leakage between the anode and one or both of the grid and It is therefore an object of the invention to support the free end portions of a tubular grid and cathode in a pencil type tube.

. Afurther object is to support ruggedly free end por- 2,937,305 Patented May 17, 1960 ICE tions of two relatively closely spaced electrodes by a support element disposed between the electrodes and having a larger transverse extent than the normal spacing between the electrodes.

An embodiment of the invention, selected for illustrative purposes, and in which the foregoing objects and purpose are realized, comprises a pencil type tube wherein a tubular cathode and grid are supported at one end portion only, and free end portions of these electrodes extend in telescoped relation into a tubular anode. For supporting the free end portions of the grid and cathode, a ring shaped support member which may be made of a ceramic, is snugly interposed between the cathode and grid free end portions. However, since the normal spacing between the cathode and grid may beso small as to render the use of such spacing member impractical, pro- ;vision is made, according to the invention, for'enlarging 'the spacing between the cathode and grid free end portions referred .to, without modifying the spacing between the grid free end portion and the anode. To this end, the free end portion of the cathode is reduced in transverse extent to a value smaller than that of .the active portion of the cathode. extent results in desired enlargement of the annular space between the free end portions of the cathode and grid, and permits utilization of a support member of convenient handling size. p

This manner of engagement of the free end portions of the cathode and grid provides a relatively rugged support of such free end portions. Appreciably contributing to such ruggedness is the axial displacement of the supported ends of the enode and cathode. This displacement results from the fact that the disc to which the grid is supported, is closer to the free end portions of the cathode and grid, than the envelope end portion to which the cathode is supported. Consequently, vibration of the free end portion of the cathode will occur through' arcs of longer radius than vibrations of the free end portion of the grid. When both end portions vibrate simulintroduces a component of motion axially of these electrodes. However, theinsulating member snugly engaging the free end portions of the cathode and anode contributes to a restraint of the aforementioned component of motion.

Such restraint of axial movement, is in addition to the damping effect produced by resistance to bending of the portions of the cathode and grid engaged by the support member aforementioned. Any vibration of the free end portions of the cathode and grid would involve a bending thereof at the region engaged by the support member. This is because the cathode and grid would extendalong angular-1y disposed axis during periods of vibration,- and the support member would be incapable of preserving a coaxial relation with each of the angularly disposed cathode and grid referred to. However, the material stiffness of the cathode and grid resist the bending thereof required for vibration, and hence contributes to a restraint of vibration.

In addition to the foregoing restraints to vibration of the free end portions of the cathode and grid, impedance Such reduction in transversethe cathode and grid. This is particularly significant in a tube of the type referred to, since in such tube the characteristics thereof are appreciably more dependent on the cathode-grid spacing, than the anode-grid spacing. One reason for this is that in most applications the anode-grid spacing is many times as great as the cathodegrid spacing, so that a given change in spacing is relatively much greater when it concerns the grid and cathode, than when it relates to the grid and anode.

It will be seen from the foregoing, therefore, that incorporation of the invention in a tube structure is accompanied by many advantages.

Further features and purposes of the invention will become apparent as the instant description proceeds.

Reference to the accompanying drawing for a more detailed consideration of an embodiment of the inven tion will reveal that I Fig. 1 shows a longitudinal crossrsection of an electron tube in which the invention is embodied;

Fig. 2 shows a transverse section along the lines 272 of Fig. l; and

Fig. 3 is a fragmentary sectional view of a tube showing a modified embodiment of the invention.

The electron tube shown in Fig. 1 is of the pencil type and includes an envelope formed by two metallic end portions 12 and an intermediate portion formed by tubular members 14, 16 which may be made of glass or a ceramic. Tubular member 14 is sealed to a flange 18 extending from end portion 10, and tubular member 16 is sealed to a similar flange 20 extending from end portion 12. Adjacent ends of tubular members 1 16 are sealed to a metal disc 22 by means of brackets 2-4.. The disc 22 is provided with a central opening 26 defined by walls including a cylindrical portion 28 and a beveled portion 30.

In end portion 10, an anode 32 is supported and is fixed by means of a force fit relation with respect to the end portion, or by being brazed thereto. A cathode support 34 is fixedly positioned in end portion 12 as by a force fit or by brazing. A tubular cathode 36 may be fixed to support 34, in a suitable way as by welding or brazing, either directly or through an intermediate tubular portion of reduced heat conductivity made of a material such as Kovar. A grid 37 of tubular shape is mounted at one end thereof on disc 22, by engaging the wall portions 28, defining the opening 26 through the disc.

End portions 10 and 12 are closed by a pinched exhaust tubulation 38 and a wafer 40 of insulating material, respectively, to preserve a desired vacuum condition with the envelope referred to. Lead-ins 42, 44 are connected to. a heater 45 within the cathode 36.

It will be noted that the aforedescribed mounting of the electrodes, disposes an active portion of the anode 32 partly in end portion 10 and partly in the space between this; end portion and the disc 22. The anode extends a relatively short distance from its region of engagement by end portion 10, and is relatively massive, so that the free end portion thereof is restrained effectually from vibration.

The mounting arrangement described also disposes grid 37 partly in end portion 10 and fully along the space between this end portion and the disc 22. The grid 37, therefore, extends a greater distance from its support than the anode 32. This greater distance, coupled with the relatively light structure of the grid, as will appear more fully in the following, render the free end portion of the grid more responsive in vibration to shocks applied to the tube, than the anode aforementioned.

With respect to the mounting of the cathode 36, it will be noted that one end thereof is fixed to support 34 in a region spaced farther from the anode 32 than the grid supporting disc 22. Consequently, when the cathode is provided with a length so that its free end coincides substantially with the free end of grid 37, such free cathodeendis farther spaced from the region of cathode support than characterizes the spacing between the free end of grid 37 and its support. However, while the cathode has a greater length from its free end to its support, it is inherently stronger than the grid because of its imperforate character. Therefore, the free end of the cathode is less responsive in vibration to tube shocks than the free end of the grid.

While the anode 32 is relatively massive and is ruggedly supported, it has not been found practical to support the free end portionsv of the cathode 36 and grid 37 thereon. This is because such support will involve the use of an insulating member engaging the anode and one or both of the grid and cathode. Such engagement would be objectionable in that it would lead to current leakage across the insulatingmember, in view of the relatively high voltage difference between the anode on the one hand and the grid and cathode on the other, usually req red d r op ation o h tube.- 7

c r ng e t e i ent o t e prob m of v bratie of the. free end portions of the grid 37 and, cathode 3.6 is met, by interposing an insulating ring shapedmember 46, between the free end portions of the cathode and grid. For enlarging the space between the end portions referred to, the cathode 36 is preferably of reduced diameter at its free end portion, as shown at 48 (Fig. 1;). This permits use of an insulating member 46 of desired size for convenient handling. In addition, the reduction in the transverse extent of the cathode free end portion provides a longer leakage path from the cathode to the grid, and reduces the area of engagement between the cathode and the insulating member 46, to reduce heat drain from the cathode. While the voltage difference. between the cathode and grid in operation of a tube of the type referred to is relatively small, the tolerable spacing between the cathode andv grid is so smalL that some current leakage is likely between the two, across a spacing member therebetween, if the spacing member bridges the relatively small normal spacing between the cathode and grid.

The insulating member 46 may be made of a ceramic such as. aluminum oxide and has an outer diameterfor snugly engaging the inner wall of the free end portion of grid 37. For convenience in practicing a method feature of the invention to be described, the grid 37 may have a structure comprising'a plurality of parallel side rods 50 disposed in a circular array (Fig. 2) and turns of lateral wires 52 fixed to the outer sides of the side rods in the aforementioned array. In this way the inner sides of the side, rods will provide tracks along which the snugly fitting insulating member may be slidingly moved to the free end portion of the grid. However, a grid having the laterals on the inner sides of the side rods may be used provided the grid turns are spaced to a lesser degree than the thickness of the insulating member 46.

Before the insulating member 46 is positioned in the grid 37, it is first fixed to the turned-down end portion 48 of the cathode. The fixing is accomplished by a tight fit of the insulating member around the cathode end portion, and by an outward flare 53 in the cathode end. The turned down cathode portion 48 is of such length that the insulating member 46 is wedged between a shoulder 54 on the cathode and the aforementioned fiare53.

In practicing the method aspects of the invention, the grid 37 is fixed as by welding to disc 22, with an end portion of the grid engaging the wall portions 28, 30, defining opening 26 through the disc. Thereafter an assembly comprising support 34, cathode 36 and insulating member 46 fixed as aforedescribed to the turned-down free end portion 48 of the cathode, is extended first through the open end portion 12, with the cathode leading. Continued extending'movement of the assembly causes the insulating member 46 on the leading end of the cathode to be guided into grid 37 by the bevelled wall por-. t-ion 2'6of the disc 22. This permits theinsulatingmemher to enter the grid even though the member fits relatively tightly in the grid. Further'extension of the assembly causes the insulating member 46 to slide on the inner side of side rods 50 of the grid to a position in engagement with the free end portion of the grid. At the same time cathode support 34 is moved to a predetermined position, in which it is fixed, as by brazing, to the inner wall of end portion 12, for completion of the mounting operation.

Instead of turning down a portion of the cathode to provide the free end portion 48 (Fig. l) the cathode may comprise a sleeve 56 (Fig. 3) to which is fixed as by brazing or welding a relatively small tube 5-8 of smaller diameter than the cathode. The end portion of the cathode engaging the tube 58 is preferably turned in as at 60 to provide a flange meeting a flange 62 on the tube 58. The cathode end portion referred to defines an opening 64 to provide communication between the interior of the cathode and the tube envelope for the purpose of evacuation. Insulating member 46 is fixed to tube 58 by being wedged between flange 62 at one end of the tube, and an outward flare 66 in the other end of the tube.

A cathode assembly including the tube 58, insulating member 46 and cathode support 34, may be mounted in relation to grid 37, in the same way as the cathode assembly including cathode end portion 48, as previously described.

I claim:

1. An electron tube having first and second elongated tubular electrodes, said electrodes being disposed in telescoped relation with one group of adjacent ends terminating substantially in common plane, said electrodes having another group of adjacent ends spaced axially of the electrodes, support means adjacent to said another group of ends fixedly engaging said last named ends, an envelope for said tube, said support means being fixed to said envelope, and means engaging said one group of adjacent ends only, for restraining relative movement of said ends, said means being disposed solely between said one group of ends and constituting the sole support for said ends, one of said one group of ends being deformed to enlarge the transverse dimension of the annular space between said one group of ends, said last named means comprising a spacing member disposed solely in said space.

2. An electron tube having an envelope, two parallel elongated electrodes within said envelope, one group of adjacent ends of said electrodes lying in spaced planes normal to said electrodes, the other group of adjacent ends lying substantially in a common plane, means fixedly supporting said one group of ends, with respect to said envelope, and a spacer member engaging said electrodes only, adjacent said other group of ends thereof for restraining relative movement of said last named ends, said electrodes being spaced a normal predetermined distance from each other, said other group of ends being spaced from each other a distance greater than said predetermined distance, whereby a relatively large annular space is provided between said last named ends, said spacing member being disposed only in said space only and constituting the sole support for said last-named ends.

3. An electron tube having an elongated envelope, two electrodes within said envelope and parallel to the axis thereof, one of said electrodes having an end portion fixed to one end portion of said envelope, the other of said electrodes having an end portion fixed to an intermediate portion of said envelope, said electrodes having active portions mutually spaced a predetermined distance, said electrodes having other and adjacent end portions, said adjacent end portions being mutually spaced :1 distance greater than said predetermined distance, and an insulating member engaging and disposed only between said adjacent end portions and constituting the sole support therefor, for restraining relative movement of said last named end portions.

4. An electron tube having an elongated envelope, a tubular anode supported in one end portion of said en- 6 velope and extending towards an intermediate portion of said envelope, a tubular grid having one end portion supported at said intermediate portion and another end portion extending into said anode, a tubular cathode supported at one end portion thereof in the other end portion of said envelope and extending into said grid end portion, said cathode having an active portion within said grid spaced a predetermined distance from the inner wall of the grid, and an end portion adjacent the other end thereof spaced from said inner wall a distance whereby an annular space is provided between said end portion and said grid, greater than said predetermined distance,

and an insulating member engaging said inner Wall and the outer wall of said cathode end portion and free from contact with said anode and constituting the sole support for said other end of said cathode and said another end portion of said grid, for restraining movement of said cathode and grid with respect to said anode, said insulating member consisting of an annular structure disposed entirely within said annular space.

5. An electron tube having an elongated envelope, a tubular anode supported in one end portion of said envelope and extending towards an intermediate portion of the envelope, a tubular grid having one end supported on said intermediate envelope portion and having another end in a predetermined plane Within said anode, a tubular cathode having one end supported in the other end portion of said envelope and another end substantially in said predetermined plane and within said grid, said cathode including a portion adjacent to said another end thereof of smaller transverse extent than other portions thereof, and an insulating member engaging only the outer wall of said cathode portion and the inner wall of said grid adjacent to said another end thereof, for restraining movement of said cathode and grid with respect to said anode, said insulating member constituting the sole support for said another end of said cathode and said another end of said grid.

6. In an electron tube, a mount comprising a. support, a tubular grid supported at one end on sad support, a tubular cathode supported at one end on said support and extending into said grid, said grid and cathode having adjacent end portions remote from said support, said end portion of said cathode being of smaller tranverse extent than other portions of the cathode for enlarging the transverse dimension of the annular space between said grid and cathode end portions, and an insulating member disposed solely in said annular space and engaging said grid and cathode end portions for restraining relative movement therebetween, said insulating member constituting the sole support for said adjacent end portions.

7. A cathode subassembly for an electron tube comprising a tubular member having opposite end portions of different transverse extents and an intermediate active portion of a transverse extent intermediate said difierent transverse extents, and an insulating member fixed to and engaging sides only, of the end portion of smaller transverse extent and having a transverse extent intermediate the transverse extents of the other of said end portions and said intermediate portion, whereby said other of said end portions is adapted to engage a support for ruggedly supporting said other end portion of said tubular member, and said insulating member is adapted to engage another electrode of said tube for simultaneously spacing and supporting said end portion of smaller transverse extent with respect to said other electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,989,819 Parrott Feb. 5, 1935 2,473,969 Pryslak et al June 21, 1949 2,828,438 McArthur Mar. 25, 1958 2,849,639 Fehr et a1 Aug. 26, 1958 2,866,120 Morris et a1. Dec. 23, 19 58

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