US2481202A - Electron discharge device and method of manufacture - Google Patents

Description

Sept. 6, 1949. w. c. DALE 2,48l202 ELECTRON DISCHARGE DEVICE ANID METHOD OF MANUFACTURE Filed NOV. 26, 1946 Jo Z1 My, l Bu mmm 62M@ 0mm Q7 (Ittorneg Patented Sept. 6, 1949 ELECTRON DISCHARGE DEVICE AND IMETHOD OF MANUFACTURE William C. Dale, Livingston, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 26, 1946, Serial No. 712,267

5 Claims. 1

My invention relates to electron tubes, and more particularly to such tubes in which the electron stream is required to traverse at least two grid members, and to their manufacture.

The employment of a plurality of grids in elec-- tron tubes between the cathode and anode is associated with diliiculties which must be overcome in order to prevent impairment of tube characteristics. Thus in tetrodes, for example, where a screen grid is interposed between the anode and control grid, there is a tendency for the electrons emanating from the cathode to be absorbed by such screen grid and produce undesired current therein.

It has heretofore been recognized that the most effective way to shield certain grids in an electron tube from primary electrons is to align the grid closest to the cathode, such as the control grid, which is usually biased slightly negative With respect to the cathode, with the turns of the other grid or grids following the control grid. To accomplish such alignment it has been the practice to first mount one grid upon its support and then mount the other grid or grids upon their supports, after iirst manually adjusting their longitudinal positions so that their turns are in line in the direction of the electron travel from the cathode to the anode. However, such manual adjustment is not entirely satisfactory for the reasons, among others, that it involves an undesirable time expenditure and is dependent upon the operators faculties which may not always be reliable. The lack of reliability of such manual adjustment is more pronounced in the manufacture of small sized tubes where the parts are comparatively small and require a more or less precise positioning.

It is, accordingly, the principal object of my invention to minimize absorption of electrons by one or more of a plurality of grids in an electron tube, where such absorption would result in impairment of tube characteristics.

It is a more particular object of my invention to align the transverse grid wires of a plurality of grids in an electron tube in directions normal to the cathode, in an accurate manner and with a saving of time.

A further object of my invention is to support a plurality of grid members in an electron tube in such a manner that the support is accomplished (Cl. Z50-27.5)

only when the grid members are in a predetermined longitudinal position required for alignment of their transverse grid wires in directions normal to the tube axis.

Further objects of my invention will suggest themselves as the description proceeds.

While the scope of my invention is pointed out particularly in the appended claims, it may 'best be understood from the following detailed description of an embodiment thereof, taken in connection with the accompanying drawing', in which Figure 1 shows an elevation partly in section of an electron tube having two grids made in accordance with my invention with the turns thereof automatically aligned in assembly;

Figure 2 shows an elevation of one of the grids employed in the tube illustrated in Figure l;

Figure 3 shows an elevation of the other of said grids which has larger lateral dimensions than the grid of Figure 2, permitting it to be placed over and surround said grid in coaxial relationship and at a predetermined distance therefrom;

Figures 4, 5, 6 and 7 show one way of making the grids illustrated in the previous gures; Figure 4 showing the cutting of the rods to suitable length; Figure 5 depicting the manner in which lateral extensions or swages are provided on the rods; Figure 6 illustrating the completed rod; and Figure 7 showing the step of applying transverse grid wires to two of such rods and clearly indicating the function of the swages in determining the longitudinal position on the rods of the first transverse grid wire,

Referring now to Figure 1, there is shown an electron tube having an envelope It enclosing an electrode mount including cathode I I, flattened elliptical anode i2, shown in cross section, two grids I3, I4 and two insulating spacers I5, I8 between which the electrodes are supported. The tube is also provided with external contact pins I1. Grid I3 has a pair of grid side rods I9 and grid I4 includes grid side rods 2D. Grids I3, I4 are shown in Figures 1, 2 and 3 as having an accentuated linear pitch for purposes of illustration.

In accordance with my invention grid side rods I9, 20 are provided with swages I8, each of which is provided with an upper and lower surface as viewed in Figure 1, normal to the side rods. The

first turn on each of grids I3 and I4 is applied to one of each pair of said side rods I9, 20 beginning at a portion thereof longitudinally spaced a predetermined distance X from the lower surfaces of swages I8. The grid-wire-turns on each of the grids referred to start at a common side of cathode I I as shown in Figure l and observe a corresponding linear pitch. The lower surface of each of swages I8 abuts against the upper surface of insulating spacer I6. Since this surface of spacer I6 is planar the lower surfaces of swages I8 lie in a common, plane. Since the distance X represents longitudinal spacing of the point of beginning of the grid-turns on each of grids I3, I4 from the lower surfaces of swages I8, these points of r beginning of said grid turns lieh in a common plane. Since the turns of each gridarecharacter- ,ized by a corresponding linear pitch it follows that when grids I3, I4 are mounted in such -a manner that the lower surfaces of swages t8 abut the upper surface of spacer I6, the grid turns of -one of the grids are in line with the grid turns of the other grid substantially in `planes parallel to the direction, of the electron flow from the cathode to the anode.

The alignment of the turns of one grid with the turns off one or more other grids in a common vdevi-ce is achieved according to my invention to the extent that inherent :possibilities for such alignment exist in a given structure. When planar grids are involved, which .are rectilinearly displaced, an actualalfignment of the turns thereof in pla-nes parallel to the direction of lelectr-on travel is accomplished. However when the grids are circular `or elliptical or -of flattened elliptical cross 'section and -are -concentrically disposed actua-l alignment of the turns of several such grids throughout their :lengths is inherently -impossible unless special recourses are availed of such as modifying the epitch -of the turns in some of the grids in proximity tothe grid Aside -rods to balance the variation that such-structure tends to produce in the-grid turns -of several grids. However, while my invention as applied to vcircular or elliptical grids results in-a crossing of the grid turns of one grid by the grid turns Iof Yano-ther grid, -such-crossing takes :place substantial-ly midway between the two side rods where the value of the electron ystream vis "at v a maximum. The crossed turns describe sharp angles =as they diverge tow'a-rd the side --rodssuch divergence being rela.tively-slight yand being :at a minimum where alignment 'of the turns is-most needediand at a maximum where such alignment is -less significant. For shielding purposes, therefore, the alignment :produced -by my `invention is effective for grids =of any type.

In carrying out ymy -inventionanydesired number of grids for use -in-a common tube are -iirst prepared. Figures 2 .and A3 show two of such grids vhaving cross sections of such shape that the narrower gri-d of Figure 4itis-adapted to -be -received within the wider grid of Figure 3. Although --for purposes of illustration grids -of such cross sectional area to per-mit concentric `relationship therebetween are `describedlhe-rein, it will be 'understood that my invention is equally well adapted for use in "connection with -planar grids or grids of any cross sectional Yshape which employ side `rods for-supporting the grid turns. -As shown in Figures 2 and 3 notwithstanding -the diierence in cross section normal to the longitudinal axis between the grids, the -longitudinal displacement along the `side rods fofY .the l:point of beginning of the lfirst fgr'id turn from the lower surfaces 2| of the swages I8, is represented by a similar value X for each of the grids. Moreover the linear pitch of the turns of grid I3 corresponds to the linear pitch of the turns of grid I4. This linear pitch may be uniform as shown in Figures 2 and 3. It may also be non-uniform as for variable mu applications. However, such non-uniformity of linear pitch must correspond in each of the grids, the turns of which are to be aligned.

As will be apparent from the foregoing, an important element in my invention is the provision of swages I8 which provide a convenient datum means for determining the location longi- -tudinally on the rods of the start of the rst grid turn thereon. In the instant embodiment of my invention a plurality of similar grid side rods, one of which is shown in Figure 6, are prepared as shown in Figures 4 and 5. Use is made of two cutting vmeans. '33, 34 shown in Figure 4 suitably spaced from each other by a bar 35. This permits the successive cutting of a plurality of rods having equal lengths. The cut rods are next subjected to a swaging operation shown in Figure 5. This may be accomplished by square ended members 35,31 suitably spaced by rod 38. Instead of two swages, one swage may be'applied to each rod without impairing its usefulness in carrying out the purposes of the invention. During the swfaging step the rod is held against movement by members 3&3, 'ili and is pressed by members 36, 3l, by actuating means not shown, against anvils 4I, t2 which are each provided with a rectangular recess having a length greater than the diameter of the rod and a width substantially equal `to that of yone'of said members 35, 3l.

Although the steps of cutting and swaging the side -rods shown in Figures'fi and v5 result in identical dimensioned grid side rods, this similarity of the rods is not essential for operativeness ofthe invention. For example, the rods 4may be of unequal length and the swages may be applied at differently spaced longitudinal locations on Vseveral rods. The only critical dimensional requirement of the Arods is that they possess a length from the llower 4surface 2l on swages AI'8 to the far ends -of the'rods -suii'icient for bridging the axial displacement of the insulating spacers I6 and I'I shown in Figure 1 and for support by said spacers.

The 'grids shown in Figures 2 and 3 owe their property of automatic alignment when mounted in a device such as is illustrated in Figure l, to the novel structure thereof according to the invention. As shown in Figure 7, this structure permits thestepfof winding a grid wire on the previously prepared grid side rods to provide eachof the gridsdepicted in Figures 2 and 3. Side rods I9 yare supported in iiixed spaced relationship by chucks 22, v23 which are ,provided with suitable recesses for receiving the -ends lof the rods. Chucks Y22, 23 may eac-h be provided with two or more pairs of such recesses for accommodating grid rods successively in a plurality of diierent spaced relationships for a plurality of differently cross-sectioned grids Aor a plurality of chucks of the character of 22, 2.3 may be used, each having a pair of recesses differentlyspaced. The ends I9 are-so vpositioned that swages I8 thereon `abut planar-surface -24 of chuck 22. Chucks 22'and 23 areso disposed that they hold rod I9 perpendicular to the planarsurface 24. Although additional swages 25 are shown on rods I9 at the ends thereof remote Yfrom the ends on -which swages I8 are applied, such additional swages may be omitted without .departing Afrom the invention.

Two side rods thus supported provide a fixed frame on which grid wire may be wound. The grid winding st-ep may involve the use of a notching wheel 26 for cutting a transverse groove in side rods I9. Grid wire is threaded into said 'groove from a suitable wire source (not shown). Peening wheel 21 is then brought into operative :position to close the groove referred to to embed a transverse portion of the wire therein. To permit .this wire winding procedure, the chucks may be rotatable and the notching and peening wheels 26 and 21 may be supported on xed supports, or the chucks may be xed and the wheels referred to may rotate around the rods I9.

Notching wheel 26 is supported on a structure which includes arm 28, and peening wheel 21 is associated with an arm 29. Arms 28 and 29 are -provided with a critical length from their free ends to adjacent surfaces of wheels 26 and 21. The arms are also provided with planar end surfaces 3l), 3| normal to their longitudinal axis. In operation surfaces 30, 3I of arms 28, 29 abut against a portion of the planar surface 24 of chuck 22. Therefore at the beginning of :a grid winding operation wheels 26, 21 are spaced a predetermined distance from surface 24. The first lturn of grid wire on rods I9 is, therefore, begun at a point on one of the rods which is displaced normally from surface 24 and consequently from surface 2l on swaging member I8, a predetermined distance. The grid winding operation may be continued in known manner until the grid is completed.

It will be apparent from the foregoing that my invention provides an accurate and 'automatic alignment of .the grid turns of a multi-grid structure and eliminates the necessity for manual acljustments. It, therefore, accomplishes a saving in time in the manufacture of a devi-ce employing the grid structure referred to, permitting .ia re- -duction in cost while enhancing the operative eiliciency of the device.

While I have chosen one embodiment for the purpose of illustrating may invention, it is to be distinctly understood that my invention is not limited thereto. Various modifications may be made in the embodiment described without departing from my invention. For example my invention may be employed in connection with grids each having only one supporting side rod. I desire to include these and other modications as may suggest themselves to persons skilled in the art within the scope of the appended claims.

What I claim as new is:

1. An electron tube having a cathode, an anode substantially co-extensive with said cathode, Iand at least two wound grids disposed between and parallel to said cathode and anode, said grids comprising side rods supporting a plurality of turns of grid wire, two spaced parallel insulating plates for supporting said side rods, and uniform lateral projections on said side rods forming planar surfaces normal to said side rods, like planar surfaces on said rods being spaced equally from the nrst turn of grid wire on each grid. the corresponding grid turns on each of said grids having a corresponding linear pitch Iand said like planar surf-aces abutting against a common surface of one of said plates, whereby the turns of one grid are accurately aligned with the turns of the other of said grids in planes normal to the cathode and anode and parallel to the direction of electron travel in said tube.

2. An electron tube having electrodes including a plurality of grids, said grids including side rods.

and at least one insulating plate for supporting one end of said side rods, at least one lateral projection on each of said side rods having a planar surface normal to said rods engaging -a common surface of said plate, the corresponding trans- Verse grid wires on each of said grids having correspondingly linear displacement along said rods, said planar surface :being spaced a predetermined distance from the I'lrst of said transverse grid wires, whereby the grid wires on one grid are effectively in line with the grid wires on another of said grids in predetermined planes, for effective shielding of at least one of said grids by another of said grids.

3. An electron tube having at least a cathode, an anode and two grids, each of said grids including at least one side rod for supporting grid wires thereon, said grid wires being similarly spaced on said grids, like planar means on each of said at least one side rod equally spaced from the rst of said grid wires, and said planar means comprising a swage on said side rod having a planar surface normal to said rod, additional planar mean-s for supporting said rods with said like planar means thereon in the same plane and adjacent each other, whereby the grid wires of one of said grids are effectively in line with corresponding grid wires of the other of said grids in planes parallel to the direction of electron travel from said cathode to said anode.

4. An electron tube having at least a, cathode, an anode, and two grids, said grids having side rods for supporting a grid wire thereon, lateral projections on said side rods forming planar surfaces normal Ito said side rods, said grid wire extending transversely and longitudinally of said side rods and being fixed thereto, the magnitude of longitudinal extension of said grid wire t0- wards one end of said rods -being determined by certain of said planar surfaces, the longitudinal pattern of said grid wire in one of said grids being similar to the longitudinal pattern of said grid wire in the other of said grids, and means for supporting said grids with said certain of said surfaces in a common plane and adjacent each other, .whereby one of said grids eiectively shields the other of said grids from electrons iiowing from the cathode to the anode.

5. An electron tube having a cathode, an anode, at least two grids, and at least one insulating plate for supporting said grids, each of said grids having parallel transverse portions of correspomng longitudinal displacement, stop means on said grids having a planar surface normal ,to the longitudinal axes of said grids and engaging a common surface of said plate, the first of said parallel transverse portions on each 0f said grids being similarly spaced from said planar surrace 0f said stop means, whereby the parallel transverse portions of one of said grids are effectively in line with the parallel transverse portions of the other of said grids in planes parallel to the direction of Itravel of electrons from said cathode to said anode.

WILLIAM C. DALE.

REFERENCES CITED The following references le of this patent:

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