US2446271A - Electron tube grid structure - Google Patents

Description

Aug. 3, w. W EIT-EL ELECTRON TUBE GRID STRUCTURE FiledJan. 25, 1946' INVENToR WILL/AM W. El EL.

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Patented Ang. 3, 1948 1 2,446.27; nxcrnoh 'runs Gum srnUc'rUns wnum w. nml, Woodside, cuir., assigner u Enel-McCullough, .Inc.,- ,San Bruno, Calif., corporationf Califol'niaE anuuumniinm zsgdsis, serial No. 642,944

solaire.. wisse-215i' Hy invention relates to an electron tube having parallel planmelectrodesi.

One ofthe .principal problems in tubes having planar electrodes with close spacings .isto maintain the grid wiresj'in a commonV plane and pre` vent grid distortion due to warping and sagging of the wires under 'heat during operation of the tube, which deformation alters the electrode spacing: and thereby changes the operating characteristics of tube, causingfrequency drift and other undesirable effects. 'Y The broad oblect of my invention is to provide an improved grid structure in-a tube of the character described,V sothat initial spacings between electrodesare accurately maintained during operation of the tulle.

-A more specific object includes the provision, in a grid having a multiplicity of parallel grid wires, of means for retaining the wires in a commonplane. j

Another object is to provide a grid of the character described embodying improvements whereby problems ofgrid warpage. spot heating and grid emission are alleviated.

A further object is to provide an improved methodof fabricating a grid structure.

The invention es otheroblects and features of advantage, some of which, with the foregoing, will be set forth in the following, description of my invention. It is to be understood :thatI do not limit myself to this disclosure of.: species of my invention-ail may adopt variant embodiments thereof withlnthescope ofthe claims.

Referring to the drawing: f

Figure 1 is an axial sectional view of a tube embodying mylnvention; and

Figure 2 is j. grid, portions of thestructure being omitted for simplicity. l l

Figure 3 is enlarged detail view showing an intersection ofegrid wires.

In terms of-s oad inclusion, my electron tube embodies a gri having a multiplicity of closely spaced main wires lying in a common plane presenting a flat grid surface, and a wire disposed transversely of the -first mentioned wires and lying fiat against the grid surface. In my preferred structure, several transverse wires are provided, spaced rnore widely apart vthan the main grid wires. The transverse wires are preferably bonded to the main.wlres at the 'intersections thereof. Ina .triode having my improvedgrid interposed between an anode and cathode, the grid -is preferably positioned with the vtransverse wires on the surface facing the anode.

plan view looking down at the In greater detail, and referring tothe drawing, my improvements are illustrated by a triode structure comprising an anode 2, grid l and cathode arrangedjwith active surfaces disposed in parallel planes.4 These electrodes are mounted in a" suitable envelope structure, that chosen lfor illustration comprising a body sections of vitreous material. such as glass. sealed at one end to an anode supporting member 1 and at the other -enel to a tubular envelope section l. Anode support 1 'also functions as the anode terminal andcomprises a metal cup having a cylindrical wall l extending from a flange ll to which the glass is sealed. Anode 2 is secured to neck l2 of the support by braze l2.

' The anode is preferably of metal'lhaving good heat conductivity, such as copper, 'with a fiat anode surface presented interiorly of the envelope and having a stem portion I4 extending outwardly of theenvelope. A suitable cooler is 'provided on the anode, preferably comprising a metal core II fitted on stem Il Vand carrying a series of transverse disk-like heat radiating ilns l1 separated by spacing rings Il, the fins and spacers being clamped together by a crimped lip IQ on core ll,

The tube is exhausted through a metal tubulation 2l secured to anode stem Il by braze il and communicating with a passage 22 ported into the envelope through opening 23. After exhaust, the tube is sealed by pinching off the tubulation at tip 24.

Envelope section l at the opposite end of the envelope is a cylindrically shaped metallic mem- `ber having an outturned flange 28 to` which glass body section l is sealed. Section 2 1" is arranged coaxially with the anode and also functions as the terminal for grid l. outer end of tubular section I is open, whereby the' grid and cathode structures may be inserted through this end of the envelope.

Grid 2 is supported on a. sleeve* 21 of metal having good heat conductivity. such as copper, insertable in envelope section 8. l The section l and sleeve 21 are shaped and proportioned to provide limit stops to establish a predetermined spacing between the grid and anode. This is preferably accomplished by an offsetportion 2l on section l providing an annular seat engageable by alllp formed by an offset portion ll on sleeve 2 1.

Cathode I is mounted on a stem I2 4also coaxial with the anode and arranged to project into the envelope through tubular section I. The cathode stem comprises a pair of concentric stem members including an outer tubular part 33 and an inner rod-like part 34. These stem members During assembly, the

tween rod Il and the lower end of a sleeve Il.

which sleeve is fitted into stem member and secured thereto by braze ll. For convenience in making connection with the inner stem member. a. cup-shaped terminal Il is preferably fixed to the outer end of rod ll and spaced from the outer stem member by-insulator.

The cathode comprises a cylindrical can l2 having a flat top carrying the active coating which may be of the usual oxide type commonly used for indirectly heated cathodes. Can l! is coaxial with and secured to the inner end of stem member Il. The cathode heater comprises a spiral 4I having one end connected to stem member Il lby-bracket M and the other end connected to stem member Il by bracket 4l. l Suitable haines I1 and 4l arranged in can 42 serve to confine the heat and direct it toward the active surface of the cathode.

. The cathode structure is supported from envelope section l by a U-shaped metallic sleeve having an outer flange 4l and an inner flange Il, this cathode supporting sleeve being fitted into section I in nested relation to grid support-a ing sleeve 21. A vitreous `ring 52 is sealed between stem member and inturned lip 53 on sleeve flange il. A shield M on the stem above glass ring 52 serves to direct the latter against heat and material sputtered from the cathode.

Cathode supporting sleeve El is also shaped and proportioned to provide a limit stop to establish a predetermined spacing between the cathode and grid, this being accomplished by utilizing the folded inner end of the sleeve as a lip for engaging the seat provided by offset portion Ii of the grid supporting sleeve. The various p arts are so proportioned that the distance between the upper grid surface and the lip at oifset ll is less than that between the anode surface and the seat at inch and a grid-cathode spacing of .0045 inch have been satisfactorily made and used.

The final closure is made by a fused metallic bond It joining the outer adjacent edges of section l, sleeve 21 and sleeve flange Il. This bond may be formed by welding or grazing to simultaneously join the three edges together.

' While the tube structure above described is preferred, it is understood that my improved grid structure, hereinafter described, may be incorpo- 'rated in any tube having planar type electrodes.

including tubes having more than one grid, the

triode illustrated being chosen for purposes of simplicity.

' As stated earlier herein, one of the principal problems in tubes having planar electrodes with close spacings is to maintain the grid wires in a common plane and prevent misalignment due to warping and sagging of the wires under heat dur-` ing operation of the tube, which deformation alters the operating characteristics of the tube. In the past, grids of this type have been made with straight parallel wires supported at the ends,

these grids being particularly bad because of relative warping between the wires. Grids of mesh construction have also been used. embodying woven wires, but prefabricated'meshes are dim- 4 cult if not impossible to mount on a support and insure uniform tautness of the individual wires in the mesh. A woven structure is also bad because the bends formed in the individual wires of the mesh complicate the warping problem when the structure is subsequently heated.

My improved grid shown in Figures 1, 2 and 3 comprises a multiplicity of straight wires Il lying parallel in a common plane to present a flat grid surface. These main grid bars are of small diameter and are closely spaced, being preferably of a refractory metal wire such as molybdenum or tungsten, the latter being preferred. Main grid wires of .0018 inch diameter spaced .006 inch apart have been satisfactorily used in a tube having electrode spacings of the character described. Grid wires I1 are stretched across and secured to a hat mounting ring Il, preferably of tungsten, adapted for fastening to a ange l on supporting sleeve f1.

A plurality of say three straight tungsten wires Il are disposed transversely of wires i1 to lle fiat against the surface formed by the main grid wires. These secondary grid wires are preferably of the same material and diameter as the main grid bars and are stretched across and secured to mounting ring 5I. Since the main and transverse grid bars are all straight wires they may be positioned across the mounting ring with uniformly applied tension. The transverse wires Il are bonded to each of the main wires Il at each intersection thereof. plished by a metallic coating l2 over all of the lWires, which coating preferably extends over ring [l to simultaneously braze the wires to the mounting ring. Coating 82 is of a metal having lower melting point than that of the grid wires and is preferably of a material, such as gold, acting as a suppresser of electron emission as well as a bonding agent.

My preferred method of making the grid is to place ring Il on a flat mandrel and wrap a tungsten wire about the mandrel to lay the multi- 'plicity of gridbars 5l over the ring. Secondary lv'vi'res Il are then laid across the mandrel in a transverse direction. A ring-shaped piece of gold wire is then placed over the wires on ring Il and the entire assembly is heated in hydrogen to flow the gold over the wires and mounting ring. The wires are then clipped about the periphery of ring t9 free the completed grid from the mandrel. A series of grids may be made on a single mandrel in this way. If desired, the transverse wires il may be laid on first to underlie main wires I1.

'While three transverse wires il' are'shown. it is understood that more or lessjnay be used, the spacing between the transverse wires being optional and, of course, much wider than that between the main wires. In any event. but few of these secondary wires are required to perform their function of reinforcing and cooling the main grid wires. The transverse wires serve as supporting straps to hold the main wires in a common plane, and also serve as heat conductors to'aid in carrying heat away from the central portions of the grid. Both of these functions operate to prevent grid warpage. Bonding of the wires at the intersections helps from the standpoint of heat conduction as well as lhave no perceptible influence on the electrical characteristics of the grid. Also. since the transverse wires lie flat against the main grid bars the latter are not disturbed from ltheir flat-lying This bonding is accom- :Maan

planar relationship. As a result, the main grid bars present truly fiat grid surfaces to the other electrodes. f

I claim:- j

1. In an electron tube having parallel plane electrodes, a grid comprising a multiplicity of closely spaced parallel wires lying in a common plane presenting a flat grid surface spaced from an adjacent electrode, and a wire dsposed transf versely across the mid-portions of the flrst mentioned wires and lying flat against said surface, said transverse wire having a diameter less than the spacing between the grid and adjacent elec' trode.

2. A grid electrode for an electron tube conrprising a mounting ring, a multiplicity of closely spaced parallel wires extending across the ring and lying in a common plane presenting a flat grid surface, and a plurality of more widely spaced wires extending across said ring in transl.

verse relation to the rst mentioned wires and lying flat against said surface, said wires being bonded to the mounting ring and to each other at the intersections thereof.

3. A grid electrode for an electron tube corri-l prising a mounting ring. a multiplicity of closely spaced parallel wires extending across the ring4 and lying in a common plane presenting a fiat grid surface, a plurality of more widely spaced wires extending across said ring in transverse relation to the first ,mentioned wires and lying fiat against said surface, and a metallic coating on the electrode bonding said wires to the mounting ring and to each other at the intersections thereof.

4. A grid electrode for an electron tube 'comprising a mounting ring, a multiplicity of closely spaced parallel wires of refractory metal extending across the ring and lying in a common plane presenting a at grid surface, a plurality of more widely spaced wires of refractory metal extending across said ring in transverse relation to the nrst mentioned wires and lying fiat against said surface, and a coatingon the electrode of metal having a lower melting point than a 365,303

6 that of the wires bonding said wires to the mounting ring and to each other at the intersections thereof.

5. A grid electrode for an electron tube comprising a mounting ring, a multiplicity of closely spaced parallel wires of tungsten extending across the ring and lying in' a common plane presenting a ,flat grid surface, a plurality of more widely spaced wires of tungsten extending across said ring in transverse relation to the first mentioned wires and lying flat againstsaid surface, and a coating of gold on the elecrode bonding said wires to the mounting ring and to each other at the intersections thereof.

6. In an electron tube having parallel plane electrodes. a grid comprising a 4multiplicity of closely spaced parallel wires lying in a common plane presenting a flat grid surface spaced from an adjacent electrode, and a plurality of more widely spaced wires disposedtransversely across the mid-portions of the first mentioned wires and lying 'ilat against said surface, said transverse wires having a diameter less than the spacing between the grid and adjacent electrode.

The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,472,505 Trimble Oct. 30, 1923 1,892,819 Van Gessel s Jan. 3, 1933 2,045,526 Harries June 23, 1936 2,047,369 Y Hickok July 14, 1936 2,338,036 Gorton Dec. 28, 1943 2,402,119 Beggs June 18, 1946 2,413,689 Clark et al. Jan. 7, 1947 2,415,360 McIntosh Feb. 4, 1947 FOREIGN PATENTS Number Country Date Great Britain Jan. 21, 1932

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