US2282392A - Electron discharge device - Google Patents

Description

May 12, 1942. c. A. BIELING ELECTRON DISCHARGE DEVICE Filed June 6, 1941 2 Sheets-Sheet l "mum M llllulm ATTORNEY May 12, 1942. c, A BIEUNG 2,282,392

ELECTRON DISCHARGE DEVICE x Filed June e, 1941 2 sheets-sheet 2 F/G. 4 v e F/c. 5

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Patented May 12, 1942 2,282,392 ELECTRON DISCHARGE DEVICE Carl A. Bleling, Westileld, N. Telephone laboratories,

J.. allig-nor to Bell New York, N. Y., a corporation of New York Application June 6, 1941, Serial No. 396,851 13 Claims. (Cl. 25o-27.5)

This invention relates to electron discharge devices and more particularly to such devices operable at frequencies corresponding to wavelengths in the centimeter range.

The operating characteristics of ultra-high frequency electron discharge devices of the type to which this invention pertains are dependent to a large extent upon the interelectrode spacings inasmuch as these spacings are largely determinative of the interelectrode impedances. In order that a particular device may have predetermined operating characteristics, it is necessary that the interelectrode spaclngs be accurately established during the fabrication of the device. Also, in order that the operating characteristics may be constant it is necessary that the interelectrode spacings be maintained constant during operation of the devices inasmuch as, the spacings being extremely small, changes of small absolute magnitudes therein result in relatively large variations in the interelectrode impedances and correspondingly large variations in the operating characteristics. The necessity of obtaining small interelectrode impedances requires the use of small electrodes which are difiicult to space accurately and the dimensions of which may undergo relatively large variations with the temperature variations to which the electrodes are subjected during the outgassing treatment and the operation of thedevice.

One object of this invention is to maintain the spacing of electrodes in an electron discharge device substantially constant during the operation thereof.

More specifically, one object of this invention is to preserve the form of the electrodes and to maintain xed the position of the effective portion or surface thereof while allowing expansion and contraction of the electrodes with temper ature variations therein.

Another object of this invention is to enable the expeditious mounting of two or more electrodes in accurate, very small space relation.

A further object of this invention is to reduce heat losses by conduction from thermionic cathodes whereby an improved thermal emciency for the cathode is realized.

In one illustrative embodiment of this invention, an electron discharge device operable as an amplier at frequencies corresponding to wavelengths of the order of 15 centimeters comprises a cathode, an anode, a control grid and a screen grid, the several electrodes having substantially parallel effective surfaces in close space relation.

In accordance'with one feature of this invention, the cathode or anode, or both, is so mounted that the eii'ective surface thereof is fixed against displacement with temperature variations while the other portions thereof may expand and contract freely with temperature variations.

In accordance with another feature of this invention, the control grid and screen grid, or both, comprises a support and a plurality of wires having parallel linear portions lying in a common plane and is so constructed that the wires maintain their parallel coplanar relation despite temperature variations therein.

In accordance with a further feature of this invention, the several electrodes are mounted within a cylindrical electrodes in coaxial relation and are spaced from one another by spacers of`vaccurately predetermined thickness, the electrodes and spacers constituting a pile-up of elements within the cylindrical member and being locked in position within the cylindrical member by a single clamping or locking element.

'I'he invention and the above-noted and other features thereof will be understood more clearly and fully from the vfollowing detailed description with reference to the accompanying drawings in which:

Fig. l is a side view mainly in section of a portion of an electron discharge device illustrative of one embodiment of this invention;

Fig. 2 is an exploded perspective view of the electrode assembly included in the device illustrated in Fig. l;

Fig. 3 is an enlarged end view of the cathode and its support in the device shown in Fig. 1;

Fig. 4 is a detail view in section of a modification of the cathode assembly included in the device shown in Fig. l;

Fig. 4A is a fragmentary end view of the cathode and the support therefor included in the assembly show in Fig. 4;

Fig. 5 is an enlarged plan view of the grid assemblies included in the device shown in Fig. 1;

Fig. 6 is a view in section of the grid assembly taken along line 6 6 of Fig. 5; and

Fig. 7 is another view in section along line 1 1 of Fig. 5 of the grid assembly.l

Referring now to the drawings, the electron discharge device illustratedin Figs. 1 and 2 is a tetrode especially suitable for use as an amplifier at ultra-high frequencies and comprises an evacuated enclosing vessel having an intermediate, cylindrical metallic portion I0, for example of copper, and vitreous end portions II and I2 hermetically sealed to opposite ends of the memember which positions the metallic spacing ring 23 Ill. The metallic portion Il) is der I3 and has an integral tubulation I4 hermetically sealed at its outer end by a vitreous cap or body I5.

Mounted within the metallic portion .I and clamped against the seat or shoulder I3 by a ring I6 threaded to the portion I0 is a of elements including a cathode, a pair of grids and an anode mounted in coaxial relation, very` insulated from one another closely spaced and and the metallic portion I0. The anode comprises a metallic rod I1 having a sulating washer or support 20, for example of: mica or silica, in turn seated on the seat or shoulder I3, the anode being clamped centrally to the washer by a lock member 2| threaded thereon, and the washer 20 fitting the internal wall of the portion I0 of the enclosing Vessel to locate the anode coaxally within this portion. Leading-in connection to the anode may be established through a tubular conductor. 22 slidably fitted on the anode rod I1 and sealed through the outer end of lthe vitreous portion I2 of the enclosing vessel.

Bearing against the washer or support 20 is a which has bearing thereagainst, in turn, an annular insulating spacer 24, for example of mica or silica, of accurately predetermined thickness so as to position the screen grid assembly accurately in desired relation to the surface I8 of the anode.

As shown more clearly in Figs. 5, 6 and '1, the

screen grid assembly includes an annular metallic support 25, for example of copper, having in one face thereof a radial recess 26 and having also a raised portion 21 which is tted in a central aperture in an insulating support 28, for example of quartz or mica, fitted within the metallic portion I0 of the enclosing vessel. Seated in an annular recess in the support and secured to the support, as by rivets 29, is an annular metallic member in which there is xed a metallic ring 30. Secured between the members 30 and 30' are a plurality of substantially U-shaped parallel, equally spaced wires 3|. As shown in Fig. 2, the intermediate portions of the wires 3l are coplanar and parallel to the surface I8 of the anode and in immediate proximity thereto. For example, the spacing between these wires and the surface I8 may be of the order of .016 inch.

In order to maintain the position of the intermediate portions of` the wires 3l substantially unaltered during the temperature cycles through which the wires pass during the outgassing treatment and operation of the device, in a particularly advantageous construction the wires 3| and annular members 30 and 30' aremade of particular materials and the assembly is fabricated in a particular manner. Specifically, the wires 3I are made of a material havingahigher temperature coeiiicient of expansion than the annular members 30 and 30' so that, relatively speaking, when the grid assembly undergoes temperature variations the annular members 30, 30' remain substantially fixed in form and dimensions. As specific illustrations, the wires 3l may be of nichrome and the annular members 30 and 30' may be of nickel or iron, or the wires may be of tungsten and the annular members may be of molybdenum. v

In the fabrication of the grid structure, straight wires are secured at their ends and in parallel pile-up plane end face I8 and an integral collar I9 seated on an inannulus is then xedly mounted, the assembly is heated and the wires are formed by a suitable die into the form shown in the drawings; The forming of the wires is carried out at a temperature higher than that to which the wires are heated during the outgassing treatment and operation of the device. Consequently, in the completed grid structure, the wires 3l are constantly under a slight tension and any expansion and contraction of the intermediate portions of the wires 3l during the outgassing treatment and operation of the device is substantially linear, in the direction of the length of the wires, so that these intermediate portions remain effectively in a common, xed plane at all times.

Bearing against the insulating support 28 and fitted within the metallic portion I0 of the enclosing vessel is another insulating support 32, similar to the support 28, which mounts a control grid assembly in coaxial relation with the screen grid assembly. The control grid assembly is the same as the screen grid assembly, is fabricated in the manner described above and includes a support 25a having a radial slot 26a in one face thereof and having also a raised portion 21a tted in the central aperture in the insulating support 32, an annular metallic member 30a seated in a recess in and secured to the support relation between the members 30 and 30'. The 75 25a, and a plurality of parallel, equally spaced, substantially U-shaped wires 3Ia secured at their ends to the annular member 30a.

The radial slots or recesses 26 and 26a extend at the same angle, for example a right angle, with respect to the respective wires 3I and 3Ia. Fitted in these recesses or slots and held therein by the insulating member 24 and a similar mem- `ber 33 are metallic strip conductors 34 having bent portions 35 which provide suiiicient friction between the conductors and the associated supports and insulating members engaged thereby to lock the conductors in position. The conductors are of the same width as the slots or recesses 26 and 26a so that when the conductors are aligned during the assembly of the ldevice, the wires 3Ia of the control grid are positioned in parallel relation to the wires 3I of the screen grid. As shown in Fig. 1, the conductors 34 are sealed in the cap or closure I5.

Mounted opposite the control grid and coaxial therewith is a cathode structure which includes an annular insulating support 36, for example of fused silica, iitted within the metallic portion I0 of the enclosing vessel and accurately spaced a predetermined distance from the insulating member 33 by a pair of metallic spacers 31 and 38. Coaxially positioned with respect to the support 36 is a tubular metallic member or support 3S having a flange 40 bearing against the support 36, the member or support 39 being securely affixed to the support 36 by a lock member 4I threaded on the support 39 and bearing against the support 36. The support 36 is slidably engaged by a tubular conductor 42, similar to the conductor 22, which serves as the leading-in conductor for the cathode and is sealed to and extends through the vitreous portion II of the enclosing vessel.

'I'he cathode structure includes also a metallic cup-shaped cathode member 43 the outer surface of the base of which is coated with a thermionic material and which surface is parallel and in immediate proximity to the intermediate portions of the wires 3 Ia of the control grid. The spacing between this surface and these wires may be of is positioned coaxlally within the inner end of the support 3l by three thin wires Il, of a material having low heat conductivity, such as nichrome, arranged tangentially with respect to the cathode member and secured thereto and to the flange 40 of the support Il. Mounted within the cathode member 4I is a heater mament 4l having leading-in conductors 4l extending through the support II and conductor I2.

The cathode structure is ynxed in position by metallic rings Il, one'of which bears against the support ss, which rings are locked in position by the ring I6.

It will be noted that in the device described hereinabover the interelectrode Bpacings are maintained substantially constant during operation of the device so that the interelectrode lm pedances are maintained substantially constant and uniform operating characteristics are realized. 'I'he anode is rigidly mounted by the support in proximity to the surface II so that the position of this surface is fixed. Expansion and contraction of the anode occurs substantially entirely between the support 2li and the vitreous portion I2, such action being permitted freely due to the sliding lit of the anode rod I1 in the tubular portion of the conductor 22. Similarly, the emissive surface of the cathode member 43 is xed in position due to the rigid mounting of this member, by the wires M, in proximity to the emissive surface thereof. Such expansion and contraction of the cathode as may occur during operation of the device takes place between the support 36 and the vitreous portion Il of the enclosing vessel, this action being permittedfreely by the sliding tlt between the support 39 and the leading-in conductor 42. Because of the form and construction thereof, any expansion and contraction of the intermediate portions of the grid wires 3i and 3io occurs in the direction of the length of these portions so that the intermediate portions of the wires of each grid remain coplanar during operation of the device and the position of the common plane remains nxed. The several insulating washers and supports have a very low temperature coeiilcient of expansion and contraction and, hence, remain of substantially fixed dimensions during operation of the device.

It will be noted also that the physical connection between the cathode member 43 and the support 39, although rigid, is very small from a thermal standpoint, because of the thinness and material of the wires M, so that little heat transfer by conduction occurs between the cathode member and the support. Hence, a high thermal efficiency for the cathode is obtainedand, in addition, the support 39 is maintained at a fairly low temperature during the operation of the device.

Electrically, the cathode construction has at least two decided advantages. The support 3s and cathode member 43, it will be noted, have juxtaposed coaxial cylindrical portions of appreciable areas so that the capacitance therebetween is fairly high and, as a result, a low impedance path for high frequency currents is attained, thereby preventing permeation of high frequency currents to the heater system for the cathode. Also, the leading-in conductors 4 6 are within the leading-in system for the cathode so that these conductors are effectively outside of the high frequency neld of the cathode to conyby a high input eiliciency is quency energy thereby is extremely small whereachieved,

Itwillbenotedalsothattheratioofthearea of the emissive surface of the cathode to the total area of the inner end of the cathode structureisclosetounitysothatstraycapacitances are minimized, whereby an optimum control or input emciency is realized. Furthermore. it will be appreciated that the electrode system comprises two sections, one composed of the cathode and control grid and the other composed of the screen grid and anode, which are substantially mirror images of each other and which are coupled only by the electron stream so that the two sections together constitute a coaxial line section having very little discontinuity whereby constant operating characteristics and a high operating eiiiciency are obtained. Finally, it will be noted that the electrodesfmay be assembled expeditiously and the desired space relation thereof obtained accurately and in a facile manner.

In the cathode and support construction illustrated in Figs. 4 and 4A. the cathode member 4I is coaxlally positioned within the cylindrical portion I8 of a metallic support 4l and is secured to this portion by three equally spaced thin wire elements ill of low heat flow. 'Ihe wire elements 50 may be, for example, of 3-mil tungsten welded to the cathode member and the portion j of the support 49. The support is positioned between two insulating annuli Il and 52, for example of quartz or silica, one of which bears against the metallic spacer ring Il and the other of which has bearing thereagainst the metallic ring 41. Leading-in connection to the cathode may be established through atubular metallic conductor 53 slidably fitted within the cathode member the conductor 53 enclosing the leading-in conductors 48 for the heater filament 45, It will be noted that the cathode member I3 is rigidly mounted in position, by the wire elements Il, in immediate proximity to the emissive surface thereof, so that the position of 'this surface is fixed during operation of the device. Buch expansion and contraction of the cathode member as may occur with temperature variations takes place to the left, in Fig. 4, of the emissive surface and is permitted freely by the sliding fit of the cathode member and the conductor Il. 'I'he heat loss from the cathode member due to conduction by way of the wires il obviously is extremely small so that a high. thermal operating eniciency for the cathode is obtained.

After the assembly of the device and prior to its pumping and'outgassing, the outer surface of trol grid circuit and the absorption of high frethe portion Ill is coated with asilver paste or is eiectroplated with silver. This procedure prevents the formation of metallic oxides at the elevated temperatures during pumping and provides good electrical contact to the portion Il in cases where the metallic portion Il is associated with an external circuit or ground.

Although specific embodiments of the invention have been shown and described, it will be understood that they are but illustrative and that various modincations may be made therein without departing from the scope and spirit of this invention as deiincd in the appended claims.

What is claimed is:

1. An electrode for electron discharge devices comprising an apertured support member, and a plurality of wires secured to said support member at their ends and overlying the aperture therein, each of said wires having an intermediate U-shaped portion including an elongated,

linear central part and armsextending from the endsof said linear part and at angles thereto, the linear central parts of said wires being substantially parallel and coplanarm- 2. An electrode for electron discharge devices `in accordance with claim 1 wherein said wires s are of a material having a higher temperature coeillcient of expansion than said support member.

3. An electrode for electron discharge devices in accordance with claim 1 wherein said support member is of molybdenum and said wires are l of tungsten.

4. An electrode for electron discharge devices 3 in accordance with claim 1 wherein said support member is of nickel and said wires are of nichrome.

5. An electrode for electron discharge -devices comprising an annular support, and a plurality lof parallel wires each having an intermediate portion in the form of a`U, the base of which is elongated and linear, said wires overlying the i aperture in said support and having end portions xed to said support.

6. The method of fabricating an electrode for electron discharge devices which comprises securing a plurality of wires at opposite ends and in parallel relation to a metallic support, heating the assembly thus formed to a temperature f higher than that to which the electrode will be subjected when in use, and forming said wires i l while at said temperature into parallel elements having U-shaped sections the intermediate por- 3 tions of which are substantially parallel to the i plane of said support. j 7. A cathode structure for electron discharge g devices' comprising a cup-shaped cathode member having an electron emissive surface, a rigid 1 metallic support having a tubular portion enl compassing and closely spaced from said cathode member, means mounting said support, and a plurality of thin wire elements of low heat conductivity securing said cathode member to said 3 tubular portion.

8. A cathode structure for electron discharge adjacent said surface and to said support adjacent said one end thereof, heater means for said slidably enmember.

10. An electron discharge device comprising an enclosing vessel having an intermediate portion and opposite endv portions, a cathode and an anode within said vessel and having opposed substantially parallel faces, a leading-in system for said anode including a pair of slidably fitted conductors one of which is sealed in one of said end portions and the other of which extends from said anode and is integral therewith, rigid means fixing the face of said anode against movement,

a leading-in system for said cathode including a pair of slidably iltted conductors one of which is sealed to the otherof said end portions and the other of which extends from adjacent said cathode, means rigidly securing said cathode to the other of said cathode leading-in conductors, and means xing said other cathode leading-in 'conductor against displacement at the end thereof nearest said cathode.-

ll. An electron discharge device comprising a hollow cylindrical member, a plurality of electrodes within said member, supports for said electrodes secured thereto and extending transversely of and slidably fitted in said cylindrical member, spacer members between said supports, and means locking said supports and spacer members in said cylindrical member.

12. An electron discharge device comprising an enclosing vessel including a cylindrical metallic portion having a seating surface therein, a cathode, anode and grid within said vessel, annular supports for each of said cathode, anode and grid aflixed thereto and slidably fitted in said cylindrical portion, spacer members between said supports and slidably fitted in said cylindrical portion, said supports and spacer members constituting .a pile-up mounted on said seating surface, and a clamping ring fixed to said cylindrical portion and locking said pile-up against said seating surface.

13. An electron discharge device comprising a cathode, an anode, apair of grid electrodes between said cathode an'd said anode, each of said grid electrodes comprising a support having a slot in one face thereof and a plurality of parallel wires amxed to the support, means spacing said grid electrodes in parallel relation, a pair of leading-in conductors each of which is fitted in one of said slots, and means fixing said conductors in relation to eac'l'iother.

CARL A. BIELING.

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