US2821651A - Grid construction - Google Patents

Description

Jan. 28, '1 958 7 L. c. WERNER 2,821,6 1

GRID CONSTRUCTION Original Filed June 4. 1951 i -Eg.- Jig? 58.

I INVENTOR.

Z. C l s riac r GRID CONSTRUCTION Leo C. Werner, Cedar Grove, N. L, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application June 4, 1951, Serial No. 229,778, now Patent No. 2,648,797, dated August 11, 1953. Divided and this application March 30, 1953, Serial No. 345,596

2 Claims. (Cl. 313350) This invention relates to electron discharge devices, and in particular relates to structures for the control electrode therein, this application being a division of U. S. Patent No. 2,648,797, issued August 11, 1953.

As is well known, the control electrode for electrical discharge tubes usually consists of a cage or grid formed by winding a wire or filament of suitable material helically about two or more upright rods parallel to the central axis of the tube. In most types of tubes, the cathode is positioned within this helical winding, and it is usually necessary to maintain throughout the operative life of the tube a uniform and accurate spacing of the turns of the helix, both between the turns themselves and between the turns and the cathode surface which the helix surrounds. These considerations require some way of fastening the helical winding, turn by turn, to its supporting rods; and such a fastening poses a problem of very considerable difiiculty, particularly in the case of high power or high voltage tubes.

In many such high voltage tubes, the electron emissive cathode consists of a plurality of heated tungsten wires, extending parallel to the central axis of the tube and at uniform radial distance therefrom. The cathode filaments may then be considered as elements of a cylindrical surface. In such cases, the control electrode is usually supported on rods lying on the same radial planes of this cylinder as the respective cathode filaments and at a slightly greater radial distance than the latter. Thus in Fig. 2 of the drawings, the control electrode is a wire wound helically about four support rods which, respectively lie on the same radial plane through the central axis of the tube as do the four vertical filaments which constitute the cathode.

Inhigh power tubes the control electrode usually comprises a molybdenum wire and it might seem simple to spot weld the turns of this wire to the support rods; but it has been found in actual practice that this procedure was unsatisfactory and caused frequent breakage of the molybdenum wire. The above-mentioned practice was accordingly superseded by an expedient shown in Fig. 1 of'the drawings in which the turns 1 of the grid wire were held properly spaced apart along the support rod 2 by a helical wrapping 3 somewhat larger in diameter than the post 2. However, to insure that slight displacements of the grid wire 1 did not permit it to slip past the turnsof the helix 3, it was necessary that the latter should extend radially inward toward the cathode filament for some distance beyond the inner edge of the grid wire 1, as is shown in Fig. 1. This inward projection naturally limits the minimum spacing which was possible between the grid wire 1 and the adjacent leg 4 of the cathode filament and was otherwise found unsatisfactory.

In its general aspect the present invention has for its object an improvement in the supporting structure for the grids of electrical discharge tubes. More particularly, the present invention has for its object the securnited States Patch oing of the grid wire to its supporting posts with greater reliability and less intrusion on the limited spacing between the grid wire and the cathode filament than was possible with control electrode structures of the prior art.

Still another object of this invention is to provide a supporting structure for electrical discharge tube grids which can be made economically and is susceptible of being carried out readily in factory production.

Other objects of the invention will become apparent to those skilled in the art to which it appertains both by direct reference thereto and by implication from the context.

Referring to the accompanying drawings, in which like numerals of reference indicate similar parts throughout the several views: 1

Figure 1 is a sectional view indicating a support structure for control electrodes upon which the present invention improves;

Figure 2 is a view partly in elevation and partly in section of a high power electrical discharge tube having a control electrode structure embodying one form of this invention;

Figure 3 is a plan view of a control electrode embodying the arrangement of Fig. 2 with the grid convolution at the inside of the posts;

Figure 4 is a plan similar to Fig. 3, but with the grid convolution at the outside of the posts;

7 Figure 5 is a perspective view of a post showing portions of convolutions carried by a post;

Figure 6 is a view in elevation of the support post used in the constructions of Figs. 2 to 5, inclusive;

Figure 7 is a perspective view of a modified construction of post; and

Figure 8 is an elevation of a further modified construction of post.

Turning in detail to the drawings, Figure 1 has already been described in sufiicient detail above. Referring to Figure 2, an electrical discharge tube referred to generally by the reference numeral 11 is of the general type shown in U. S. Patent No. 2,398,608, issued April 16, 1946, to the present applicant and H. I. Bailey and assigned to applicants present assignee. Since this tube is fully described in the aforesaid patent, it is only necessary to state here that it comprises an anode 12, a pair of tungsten cathode filaments, each of hairpin form, supported with their legs 4 parallel to and equi-distaut from the central axis of the anode 12, and a control electrode comprising a molybdenum wire 18 of helical form supported on four molybdenum posts 19 which are in the same radial planes of the anode 12 as are the four legs of the cathode filaments 4. The cathode filaments 4 are held at their lower ends in vertical posts 5 which are supported in turn from brackets 6 affixed tovterminal posts 7 which are sealed vacuum-tight through a glass bowl 8 to which the anode 12 is likewise sealed. There are two terminals 7 which are respectively connected through their brackets 6 to one end of each of the pair of cathode filaments 4, so that when the brackets 7 are respectively connected to the two sides of a heating circuit current flows up one side of each cathode filament 4 and down the other side to the other bracket 6 and terminal post 7.

The support posts 19 for the control electrode wire 18 are rigidly based on an annular member 13 which may be supported from a post 14- at the center of the bowl 8 by a suitable bracket 15 which, for the sake of simplicity, in the drawing, is shown broken away in Fig. 2, since it forms no part of the present invention.

The upper end of the four posts 19 may be fastened to a top plate 16 to brace them rigidly. The upper ends of the hairpin filaments 4 are held spaced rigidly apart by a member'17 which is so thin'and light as to require no outside support.

The invention contemplates the alternatives of gridsupporting posts 19 either at the outside of. the grid-wire convolutions 18, as in Fig. 3, or at the inside thereof as in Fig.4. In both constructions, each post 19 is provided with a series of substantially chordal grooves spaced at proper intervals along its length to correspond with the spacing desired between the convolutions of the control electrode. The four posts 19 thusgrooved, and cut to length so that the distances of the grooves from the support member 13 are sequentially proper to position the helical grid 18 relative to member 13, have the winding 18 installed in proper position in the manner which will be described more fully below. The grooves constitute ledges which receive, space .and support. the convolutions of the grid at each crossing of the grid wire to the several posts. The grid wire 18 is then locked in position in the grooves 20 by a helical binder 21 which may be preformed and slipped into position on the post 19 with a rotary movement like a screw being threaded into position. The helical binder 21 may be considered a convenient example of retaining means for retaining the convolutions of the grid wire upon its above-mentioned ledge.

In the first instance, of the construction of Fig. 3, to install the grid wire 18. in position, it is first woundinto a helix with desired spacing and internal diameter on a suitable mandrel. grooves 20, are then respectively positioned at points spaced 90 apart on this mandrel with the convolutions passing through said grooves and with the oifset lower portions of the posts positioned in radial planes passing through the axis of the helix. The support member 13 may then be attached to the lower ends of the support rods or posts 19. The mandrel may then be withdrawn and the binders 21 rotatively slid downward into position on the four posts 19. The top plate 16 may then be attached to the upper ends of the posts 19.

In the embodiment of the posts located internally of the grid-wire convolutions as in Fig. 4, the grooves 20 in the support posts 19 which contain the helical grid wire 18 and form ledges therefor, are located in the radially outward faces of the latter. In this case, the support rods or posts 19 may be assembled with the support member 13 before the helical winding 18 is put in place. A mandrel having an outside diameter equal to that desired for the internal radius of the helical grid and provided with four suitable grooves to receive the posts 19 may then be slipped into position through the central opening in the support member 13. The wire 18 may be wound as a helix fitting in the grooves 20 in the posts, after which the mandrel is withdrawn. A helical binder wire 21 may then be rotatively slid downward into place on each of the support posts 19 in the same manner as has been described above, and again constitutes a retaining means for retaining the convolution of the grid wire seated upon its ledge in assembled condition.

In accordance with a modification of the invention, the-support post may be made of semi-tubular material of the form illustrated in Figures 7 and 8 and designated by'numerals 25 and 26 respectively. At intervals equal to'the desired spacing for the grid convolutions, thesupport posts 25, 26 may be punched to strike out projecting tongues 27 which are bent into an L-shape, as shown in Fig. 7. The outwardly projecting portions of .these tongues constitute ledges for the grid wire where the convolutions thereof cross the posts. After the posts 25 The rods or posts 19, having chordal or 26 are mounted on the support members 13 in a manner similar to that described for the posts 19 in Fig. 2, a mandrel provided with suitable longitudinal channels for the posts 25 or 26 and having a diameter equal to that desired for the internal diameter of the helical con trol electrode 18 may be'placed in position and the grid wire 18 wound in helical configuration. Then the posts can be slid onto the mandrel in the channels thereof substantially vto place and spread to engage therespective-convolutions of thegrid in the L-shaped tongues 27 and upon the ledges formed thereby. The four support rods 25 or 26 will, of course, have to be cut'to length properly to that the tongues .27 are each.positioned at the correct distance from the support members 13 to sequentially engage the convolutions of the helical wire 18 properly. After the .gridwire 18 is thus placed in position, the L-shaped tongues 27 may be bent back over the wire 18 thereby constituting a retaining means for the convolution where located on the ledge to hold it firmly in position. The mandrel may then be removed from the structure and the grid completed and installed in the discharge tube in the same way as in Fig.2. Where the spacing between convolutions is sufficient,- the tongues may be aligned 'one above another longitudinally of the post as shown in Fig. 7.

Fig. 8 shows a support rod 26 of the same shape in cross-section as that described in connection with Fig. 7, but in which the tongues 27 are required to be so closely spaced lengthwise of the support rod to accommodate the axial-spacing of the grid wire 18, that.tongues 27 would interfere with each other, if they extended parallel to the longitudinal dimension of the support rod. Hence in Fig.8, the tongues 27 are punched at an angle to the longitudinal axis of the support rod, but as above described, said tongues again each constitute a ledge and a retaining means for the grid wire convolution where crossing the post.

I claim:

1. A support post for the control electrode of an electrical discharge tube comprising a linear member having L-shaped tongues struck up therefrom, said tongues having portions constituting ledges and having portions constituting retaining means extending substantially parallel to the longitudinal central axis of said member, and said ledges being spaced apart along said member to receive successive turns of wire constituting said control electrode.

2. A support post for the control electrode of an electrical discharge tube comprising a linear member having L-shaped tongues struck up therefrom, said tongues having portions constituting ledges and having portions constituting retaining means inclined in a direction circumferentially of the electrode at a substantial angle thereto and to the longitudinal dimension of said member.

ReferencesfCited in the file of this patent UNITED STATES PATENTS 1,432,411 Payne Oct. 17, 1922 1,654,899 Schwerin Jan. 3, 1928 1,792,219 Grebel Feb. 10, 1931 1,957,223 Murphy May 1, 1934 1,976,522 Rose Oct. 9, 1934 1,994,307 Flaws Mar. 12, 1935 2,188,906 Lackey Feb. 6, 1940 2,686,885 Bailin Aug. 17, 1954 FOREIGN PATENTS 85,420 Austria Sept. 10, 1921 192,592 Great Britain Feb. 8, 1923

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