US2507709A

US2507709A - Grid electrode and method of manufacture

Info

Publication number: US2507709A
Application number: US699423A
Authority: US
Inventors: Gronros Warren
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1946-09-26
Filing date: 1946-09-26
Publication date: 1950-05-16
Anticipated expiration: 1967-05-16

Description

May 16, 1950 w. GRONROS 2,507,709

GRID ELECTRODE AND METHOD OF MANUFACTURE Filed Sept. 26, 1946 ZSheets-Sheet 1 Human" FIG. 3 FIG. I?

Y k lfi/ /A 22 20 22 45 INVENTOR WGRONROS BV yW A 7' TORNEV May 16, 1950 w. GRONROS GRID ELECTRODE AND METHOD OF MANUFACTURE Filed Sept. 26, 1946 2 Sheets-Sheet 2 FIG. 9

INVENTOR By W. GRONROS ATTORNEY Patented May 16, 1950 UNITED STATES PATENT OFFICE GRID ELECTRODE AND METHOD OF MANUFACTURE Warren Gi'onros,,New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New YorlnN. Y., a corporation of New York Application September 26, 1946, Serial No. 699,423

9 Claims. 1

This invention relates to electronic discharge devices and, more particularly to methods of manufacture of electrodes for such devices.

In ultra-high frequency signaling systems, including electronic discharge devices, one of the factors enabling short wavelength operation is the small inter-element spacing in the devices which results in a high transconductance to capacity ratio and thereby allows attainment of high efficiency.

When the electrodes or elements'in the device are reduced in size to micro-midget dimensions to attain relatively close spacing,'particular diffi culti'es are usually encounteredin the construction and fabrication of'the gridor control electrode. This electrode is conventionally formed of a continuous wire helix' mounted onupright wire supportsand such a construction is madequate with respect to self-supporting qualities when the components ofth'e' grid and particularly thelateral'wires'are'materially reduced in diameter: In" order'to' achieve"micro-dimensional spacing; thegridmustbe' as'closeas possible to the cathode or emitter and the anode mustclosely surround'the grid to securea symmetrical'mounting ofth'e' elements in the device. Sincethe widthand length of' the elementcompares inmagnitude with the diameter thereof; the micro midgetsize materially "differs from the conventional dimensions of these elements. Forexample-,-a typical grid structuremay-have a'major axis of'.228-inch, a minor axis of .0325:inch ancta usefullength of- .255'inch'. Insuch a small construction; the grid lateral wire or helix'must be of relatively small diameter, e.--g. .0005 inch, to provide a large numberof turns on the =grid-for attaining the desired controlling action. Such fine wire, about equivalent in diameter to a finespider web strand, is substantially devoidofself -supporting characteristics and requires a framework structure: to sustain the'lateralsinuniform and constant -rela-' tionship with the other elements inthe assembly.

An object of this invention is to'facilitate-the manufacture of micro-electrode structures.

Another object of: the invention is to stabilize the space relationof the surfaces ofcooperating electrodes.

A further'object of the'invention-is to reestablish linearity ofthe laterals of the grid-electrode after heat treatment.

Another object of the invention is to overcome loss of tension in thelatera-lsof the grid electrode and to increase the'efiiciency of the controlling action in the flow of electrons in the discharge-space between'the electrodes.

These objects are attained in accordance with features of this invention by'winding the fine grid wireon a hollow metallic frame structure having reinforcing bridging arms at opposite ends of the frame, securing, e. g. brazing, the laterals of the grid to the frame, and finally mechanically stretching the laterals by compression molding of the metal bridging'arms to provide tension in the laterals so that they are realigned in uniform lateral relation on opposite sides of the frame structure.

A feature of this construction is the limited elongation of the bridging arms to take up the slack in the lateral wires due to heat treatment during the brazing operation. This is accomplished by placing a mandrel in the completely wound grid and inserting the assembly between pressure dies which contain embossments to engage the outer surfaces of the bridging arms on opposite sides of the grid structure. Pressure exerted on the dies and the interposed grid assembly causes the metal in the bridging arms to flow at the point of contact of the embossments inthe dies. Consequent elongation of the arms increases the spacing of the side frame portions with resultant tensioning of thegrid lateral wires to align them in uniformparallel relation.

The deformation of the bridging arms does not materially alter the dimensional limits of the grid structure since the stretching may be only one or-one and a half thousandths of an inch. Furthermore, the elongation is well within the limits of the breaking strength of the fine wire andthe bending limit of the frame material so that no deleterious effects are caused by the stretching operation. On the other hand, the expansion of the arms equalizes the pull on the grid lateral wires so that all the laterals are stretched simultaneously and the stresses set up in the laterals reset the wires in positive linear relation both longitudinally and transversely across the grid frame structure. This construction materially improves the inter-element spacing. in the device and increases the transconductance to capacity ratio in the discharge path.

These and other features and advantages of the invention will be set forth in more detail in the following description which, together with the accompanying drawings, disclose illustrative physical aspects of the invention. In the drawing,

Fig. 1 is anelevational view on a greatly enlarged-scale of one embodimentv of the grid electrode'to which the fabrication methods of this invention a Dper-tain;

Fig. 2 is an edgewise view in elevation of the electrode of Fig. 1;

Fig. 3 is an end plan view of the grid frame structure;

Fig. 4.- is the same as Fig. 1 except that it shows the stretching indentations in the bridging arms of the frame;

Figs. 5 and 6 are side and bottom views, respectively, of a clamping vise assembly utilized in the fabrication of the electrode structure;

Figs. '7 to 9, inclusive, show in enlarged perspective views, various forms of compression dies which may be employed in the vise of Figs. 5 and 6.

Fig. 10 is a perspective view showing the relationship of the grid structure and a mandrel prior to insertion of the latter into the grid;

Fig. 11 is a fragmentary view of the grid and mandrel mounted between a pair of cooperating dies; and

Fig. 12 is an enlarged exaggerated view in cross-- section of a portion of a bridging arm of the frame structure, taken on the lines I2l2 of Fig. 4, to illustrate the deformation in the surface of the arm to achieve the tensioning of the grid laterals on the frame.

The invention is concerned primarily with the fabrication of electrodes and particularly the control electrode or wire wound grid of the symmetrical type employed in electronic discharge devices in cooperation with other electrodes, such as a cathode or emitter and a surrounding anode, all the electrodes being usually mounted in a uni-- tary assembly between top and bottom spacer insulators to maintain the respective electrodes in uniform and constant spaced relationship in 01'- der to realize the desired electrostatic and dynamic characteristics suitable for particular operating functions. The conventional form of grid is usually produced by winding a wire in the form of a flattened helix around a pair of parallel support wires with the lateral turns spaced on the support wires by swaging the lateral turns in notches in the supports or welding the turns to the supports. This form of construction requires that the lateral wire be of sufiicient cross-section to produce a self-supporting electrode assembly.

The conventional type of grid electrode seriously limits the design possibilities of devices employed in ultra-short wave operation. For example, to secure micro-dimensional spacing the diameter of the grid winding wire must be materially reduced but then the wire is not sufficiently rigid to form a self-supporting structure. The swaging or welding methods of securing the grid laterals to the supports limits the spacing of the laterals, and the support rods or wires produce variations in the major and minor axes of the grid so that the assembly deviates widely from the optimum dimensions desired.

In order to overcome these difficulties and to produce elements of micro-midget dimensions, this invention provides a construction of control electrode of the frame type to sustain the fragile wire laterals in constant and uniform spaced relation. Referring to the drawings, and particularly to Figs. 1 to 3, inclusive, the grid electrode is shown enlarged ten times actual size. The dimensions of the micro-midget grid are .228 inch major axis, .225 inch useful length, .333 inch over-all length and .0325 inch minor axis or distance between laterals on opposite sides of the wound grid. The lateral wire for the grid helix is one-half mil or .0005 inch wound at a pitch of 340 turns per inch with a total of 72.5 turns over a length of .213 inch of the grid frame. Of course, other dimensions can be applied to different forms of electrodes depending on the characteristics desired in the discharge device, the above data being given as an example to indicate the minute configurations of the electrodes embodying features of this invention.

The frame of the grid electrode is preferably formed of molybdenum, to reduce the amount of metal to a minimum and also to provide a material of high tensile strength. Other metals may be used, such as nickel or steel for certain applications. The frame is formed of sheet metal which may be punched and shaped to desired configurations, and as shown, involves two half-sections in abutting relation along the lateral sides to form a hollow rectangular structure. One section has an upright column or portion 20 of arcuate cross-section on one side of the frame and a similar column 2| on the other side, the two columns being connected together by spacing beams or bridging

arms

22 and 23 adjacent opposite ends of the columns. The arms are slightly bowed or extend outwardly beyond the surface of the columns, as shown in Figs. 2 and 3, to bring their inner surfaces in line with the lateral winding of the grid. The other section is also provided with a pair of

cooperating columns

24 and 25 which are spaced by

arms

26 and 21. One of the columns. for example 2|, is provided with an extension 28 for anchoring or connecting purposes in the unitary mount assembly of the other electrodes coupled with the proposed grid electrode. The two sections are accurately formed and assembled to provide a hollow frame having accurately dimensioned surfaces and contours so that the major and minor axes may be held to very definite limits to insure the resultant characteristics desired in the device. The minor axis dimension can be readily fixed by the accurate channel shape of the

juxtaposed columns

20 and 24, and 2! and 25 since the terminating surfaces of the accurate columns are plane outer boundaries on opposite sides of the hollow frame. The major axis dimension may be held constant and within close limits by the bridging arms connecting the columns at opposite ends. Although the proposed frame structure is shown as formed of two half sections, it is possible to construct the frame of a single body if a tubular form is substituted instead of one of sheet material.

In fabricating the bi-part frame of molybdenum, the two sections, after forming. are plated with a noble metal. such as gold. and placed in an oven supplied with a non-oxidizing atmosphere. such as hydrogen, and the two sections are brazed to ether by fusing the gold film over the lon itudinal ioints along the abutting edges of the sections. Since some of the gold film is lost by flowing in the brazed joints, it is desirable to recoat or plate the complete frame to replenish the surface film on the channel columns. This may be performed in a non-oxidizing atmosphere to avoid contamination of the coating and to produce positive adherence of the plating film.

The plated hollow frame is then ready for the winding operating in which very small diameter wire, for example .0005 inch tungsten or smaller, is wound around the columns over a length between the bridging arms at opposite ends of the frame. The winding is performed by rotating the frame on a suitable mandrel and applying the fine wire in continuous rotation around the channel columns at a desired pitch, for example enom-7.09

The

are uniformly spaced over the useful areaof'the grid-electrode and the assembly forms a rec- "tangularcage, with the grid laterals at predeterminedspacing to produce the desired controlling action on the electronstream in the discharge device.

Thegrid lateralsare 'securedto the channel columns by brazing in a hydrogen oven at a temperature of about lllll) degrees centigrade.

In-thisoperation, the excess gold plating flows -over the wire in contact *With' the columns and --a1so fiWs"a10ng'the wire laterals therebygoldplating the fine tungsten wire. This eliminates the necessity for using gold-plated-wireto reduce emission from thegrid during operation of the device. During thebrazing operation, the

' slightly greater expansion of the frame relative to the-tungsten-laterals maintains sufficient tension on the laterals and prevents their sagging during the time the gold film is fluid and thus incipient adherence between adjacent laterals is prevented. After the brazing operation and cooling'of the assembly, the laterals are no-longer under tension, due to looseningproduced by embed- :ding of-the wire turns in the gold'platingand by permanent set in the-wire while under tension atthe elevated brazing temperature.

To restore the grid laterals 29 tothe desired tension to realign them uniformly with the surfaces ofthe channel supports, the major'axis of the frame is increased'one or two-thousandths of an inch by deformation of the bridging arms or beams sothat expansion ofthe channel columns will stretch the wires to their original tension but not/sufficientlyto'causebreakageof the wire or bending of the columns.

Thisis accomplished, in accordance :with a feature of this invention, by a compression molding operation in which the surface of the beams or arms is distorted sufficiently by cold fiow to expand the frame and realign the grid laterals on the frame. 'This. pressing or squeezing step isperformed in a vise, impression fixture or jig, shown in Figs. and 6. The Vise comprises a hardened metal frame 35) having an internally threaded head 3! and a solid terminating head or jaw'32' at opposite ends of the frame to form an L! -shaped "structure. "with anelongated slot 33 to form a sliding' track for a movable head or. jawt lwhich is secured to the frame by a plate 35attached to an'extension The frame is also "provided of the movable head. projecting through the slot 33. The movable head is actuated by a lead screw 35 extending through head 3! and controlled by knob 3'! on the screw. The jaws 32 and 3 are provided with cooperating hardened dies 38, shown more clearly in Fig. '7, the dies being removable to accommodate various shapes and configurations of electrodes to be compressed in the jig.

The pressing die of Fig. '7 is for-med with limit projections 39 to embrace the width of the grid frame assembly and a bearing surface area or land 40 between the projections to form a seat for the grid frame. The central portion of the land 40 is provided with an integral elongated embossment 4| of convex contour. As a typical example ofthe dimensionsof the principalsurfaces of the die for-forming. gridsofthe-micro-midget type heretofore mentioned,- theheight ofthe projections 39 above the land-40:.is approximately 015: inch,- the radius of the convex embossment is 4025 inch and the-embossment-extends .002 inch above-the surface of the landfill.

-A somewhat different die construction is-shown in Fig. 8 in which the embossment 'istproduced by embedding a hardened wire--42: in the base of thesland 491withonly a segment of the curved surface of -the wire projecting above the-land surface. Thesame effect, although of different configuration, may be produced by the dieshown .-in Fig. -9 in which integral beads-43 are formed 0n the central: land'surface but at opposite-ends mandrel-t lde inserted in the grid-frame.

. to-face 1 relationship. :assembly-is placed between the cooperating dies, as shown in Fig. 11, the embossrnents M of the to engage'the bridging arms on the gridframe when'place'd in the vise.

' Prior to placing the-grid assembly in the. vise between the cooperating dies, a hardened. steel This mandrel has beveled edges to fit into the channel columns of the frame and opposite planesurfaces to engage the bridging arms of the frame in face- The frame and mandrel dies being in contactwiththe outer surfaces .of

. the arms '22, 23, and QL-and thegrid frame is located between thevprojectionstfi on opposite dios. "In thisposition; the projections 39 onfthe dies are slightly spaced apart asshown in Fig.

:llg-xduetothe thickness of -thearms-on the frames. Whenpressure-is applied tothe dies byt'nescrew advancing K the: movable jaw- 34, the embossments A l-simultaneouslyare forced into the outer metal surfaces'of-the bridging arms and the metal at "the point-of contact flows under the impact to spread or expand the arms; thereby increasing the major taxis dimension of the columns :by. a

- slight amount, approximately one or two-thousandths of an inch.

The'resulta'nt pressure forms annindentation 'in the arms, asshoWnin-Fig. -andmore clearly -in'Fig. 12; land since-the force is-exerted only on the =outer i surfaces :of the-armsand acrossthe columnsso that tension is restored in the laterals *and'wthey; are realigned in uniform spaced relationship on opposite sides of-the frame assembly. --Asi'de from the major functioncfthe frame in supporting thegrid laterals, this form I of construction is hadmi-rablysuitedto meet the close .limits required for the space relationship of the electrodes. :This "is particularly true when. the

electrodes 1 :are reduced- :to micro-midget dimensions since the: rigid molybdenum frame -can be accurately shaped to define the major and minor axes and 1 thereby: insure definite interelectrode spacing while securing reduction of the capacity values between the elements in the electrode assembly.

The rigid frame also provides a broad bearing area for the support of the grid electrode in mica insulators so that misalignment of the grid with respect to the other electrodes is minimized. Further, the gold plating facilitates the relatively close spacing of the fine wire laterals and decreases secondary emission from the grid under high temperature operation. The substantial surface area of the frame also affords greater heat dissipation so that the grid is maintained cooler during operation and the inductance is reduced by avoiding supplemental flexible conductors between the electrodes and terminals of the device. The rugged construction of the grid provides less hazard in the handling and assembly of the device and protects the laterals from distortion. Finally, the uniformity of the grid laterals and their close planar relation insures high transconductance to capacitance ratio at ultrahigh frequencies.

What is claimed is:

1. An electrode for electronic discharge devices, comprising a metallic frame including parallel side channel portions and intermediate bridging portions adjacent opposite ends connecting said channel portions, a plurality of lateral wires extending along said frame and secured in uniform spaced relation to said channel portions parallel to and between said bridging portions, and indentations on said bridging portions for stretching said laterals on said frame.

2. An electrode for electronic discharge devices, comprising a metallic frame including parallel side channel portions and intermediate bridging portions adjacent opposite ends connecting said channel portions, said bridging portions extending outwardly beyond the surface of said channel portions, a continuous helix wound on said frame, lateral portions thereof spanning the space between said channel portions, and central depressions formed in the outer surface of said bridging portions, to tension said lateral portions between said channel portions.

3. An electrode for electronic discharge devices, comprising a metallic frame including parallel side channel portions and intermediate bridging portions connecting said channel portions, and a continuous helix wound on said frame, lateral turns of wire thereof spanning the space between said channel portions and affixed thereto, and said bridging portions having limited sections reduced in thickness to expand said frame and tension the lateral turns of wire.

4. A grid electrode for electronic discharge devices, comprising a metallic frame including parallel side channel portions and intermediate bridging portions connecting said channel portions, and a continuous wire helix wound on said frame including spaced laterals extending across the space between said channel portions, said bridging arms having expanded portions to ap-- ply tension to said laterals extending between said channel portions.

5. The method of tensioning an electrode having a metallic frame including channel side portions and bracing arms at opposite ends connecting said portions, which comprises winding uniformly spaced wire laterals on said frame, affixing said laterals to said side portions, and tensioning said laterals by compression forces applied to said arms.

6. The method of fabricating a grid electrode having a metallic frame including channel side portions and bracing arms at opposite ends connecting said side portions, which comprises coating said frame with a noble metal layer, winding a continuous wire helix on said frame, heating said electrode to afiix said helix to said side portions, and flowing the metal of said arms by compression to tension the helix laterals between said side portions.

7. The method of forming a grid structure including a metallic frame having channel side portions and bridging arms spacing said side portions, which comprises gold-plating said frame, winding a continuous helix about said side portions, embedding said helix in said gold-plating, inserting a mandrel into said frame, placing said frame between forming dies, said dies having embossments engaging said arms, and forcing said embossments against said arms thereby to expand said arms to tension said helix between said side portions.

8. The method of forming a grid structure including channel side portions and bracing arms at opposite ends connecting said side portions, which comprises winding a continuous helix about said side portions, affixing the turns to said side portions, inserting a mandrel into said frame, placing said frame between forming dies, said dies having embossments engaging said arms, pressing said bridging arms between said embossments and mandrel, and tensioning said helix by the expansion of said arms.

9. The method of forming a grid structure including a frame having channel side portions and spacing arms at opposite ends of said portions, which comprises winding a continuous helix about said side portions to span the space encompassed by said arms and side portions, embedding said helix in said side portions to anchor the spaced lateral turns of said helix, inserting a mandrel into said frame, placing said frame between forming dies, said dies having projections in contact with said arms, and squeezing the outer surface of said arms simultaneously against said mandrel to flow the metal by elongation whereby tension is imposed on said helix affixed to said side portions.

WARREN GRONROS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,919,934 Murphy July 25, 1933 2,255,906 Umbreit Sept. 16, 1941 2,310,822 Wheeler Feb. 9, 1943 2,397,233 Bingley Mar. 26, 1946 2,413,689 Clark et al Jan. 7, 1947