US2850664A

US2850664A - Grid structure

Info

Publication number: US2850664A
Authority: US
Inventors: Eugene J Naill
Original assignee: Machlett Laboratories Inc
Current assignee: Machlett Laboratories Inc
Priority date: 1954-05-07
Filing date: 1954-05-07
Publication date: 1958-09-02
Anticipated expiration: 1975-09-02

Description

Sept. 2, 1958 E. J. NAILL GRID STRUCTURE Filed May 7, 1954 4 Sheets-Sheet 1 INVENTUR.

EUGENE J. AILL BY d I 0u.. y

ATTORNEY Sept. 2, 1958 E, J, NAILL 2,850,664

GRID STRUCTURE v Filed May 7, 1954 ,4 Sheets-Sheet 2 INVENTOR.

EUGENE NAI LL SePt'fZ, 1958` E. J. NAILL 2,850,664

GRID STRUCTURE Fileday '1, 1954 4 sheets-sheet s V2'- 20 2' FIG. 6 d WWI f i FIG. 7

l v V FIG. 5

IN VEN TOR.

EUGENE ILL BY ATTORNEY Sept 2, 1958- E. J. NAILL 2,850,664

GRID STRUCTURE V Filed May '1, 1954 4 sheets-sheet 4 INVENTOR.

EUGENE J. NAILL BY M AT ORNEY Unite G STRUCTURE Application May 7, 1954, Serial No. 428,313

3 Claims. (Qi. 313-265) This invention relates to a novel grid structure which is simple yet rugged and which may be cheaply fabricated and easily assembled.

The application of Joseph W. Skehan and Andrew Kudola, Jr., Serial No. 294,884 tiled lune 2l, 1951, describes a device forand a method of making a grid. This grid structure results in a superior grid which will not warp or otherwise deflect from itsV normal plane sufliciently to change the tube characteristics or short to the adjacent electrode. The grid of that application consists of a mesh of ne wires which is brazed to an annular supporting ring. This supporting ring, in turn, has to be supported upon a structure which is sufficiently flexible to permit its expansion but which makes good electrical contact with the active grid surface. Without such a support structure, many advantages of the grid itself are lost.

The present invention provides a support structure which permits free expansion of the grid supporting annulus and at the same time makes good Contact with the active grid. This support consists primarily of a planar mounting deck which may be composed of sheet metallic material satisfactory for user in vacuum tubes. This deck forms a fiat base against which the grid supporting ring may be mounted. The grid is not fixed directly to the planar surface of this deck because such a mounting would be rigid and tend to oppose the tendencies of the grid ring to expand. Instead the grid is held in place by metallic tabs which may be bent over the grid support and which are small enough to be quite flexible so that the expansion of the: grid ring is not impaired. The grid mesh is advantageously on that side of the support ring which isaway from the mounting surface of the mounting deck so that the planar surface of the mounting ring may be used to4 obtain square positioning of the grid structure. Some Contact is, of course, afforded to the grid structure throughthe mounting deck which is made of conductive material.4 However, actual joints occur only between the tabsuandjthe grid mesh. This is particularly advantageous singel the active grid portion is in this manner directly conneted'to thesupport structure.

Accurate spacing between the cathode and grid electrode is also particularly important in most applications employing planar electrodes. The structure of this invention permits very accurate interelectrode spacings by virtue of thev tube construction employed. More specifically, the cathode and stem structure is so mounted that as, an assembly its outside surface is cylindrical.

Thegrid support structure of the present invention consistsof a tubular mounting member which penetrates the vacuumenvelope. Thissupport is advantageously ,connected to a tubular metallic member forming a portion of the envelope.. This grid potential tubular envelope portion is, in turn, sealed to a dielectric ring which is, in turn, sealed to another tubular member. This nal tubular member has a portion which will snugly engage the cathode and stem structure. Since the grid mesh thickness is constant within small tolerances as is the thickness of its mounting ring and the mounting deck, the axial distance arent O f 2,850,664 atented Sept. 2, 1958 between the end of the tubular grid support member and the active grid mesh structure can be predicted quite accurately. The difference of the cathode-grid spacing and the dimension between the end of the grid support and the active grid structure will, of course, be the distance between the end of the active grid structure and the cathode. A fixture is provided which permits the correct relative positioning of the cathode and the end of the tubular grid support before the two tubular metallic members which are in sliding contact with one another are brazed together. Thereafter, the brazing operation may be completed, and then the structure turned upside down and the grid welded in place. The planar grid mounting deckprevents any cooking or other misalignrnent which could introduce inaccuracy.

For a better understanding of the present invention reference is made to the following drawings:

Fig. l is an elevational View in partial section of an electron tube structure employing the present invention;

Fig. 2 is a plan View of the grid mounting structure from above;

Fig. 3 is a side elevational View of the grid structure of Fig. 2 in axial section;

Fig. 4 schematically illustrates the placing of the grid structure assembly on the grid mounting deck;

Fig. 5 schematically shows in section the iixture employed in the first stage of bending the. tabs in place;

Fig. 6 illustrates a second step in bending the tabs into place;

Fig. 7 illustrates a methodk of welding the tabs to the grid structure;

Fig.V 8 schematically illustrates in partial section the use of a fixture with the supports to obtain accurate gridcathodespacing.

Referring now to Fig. l there is illustrated an electron tube of coaxial construction, commonly called an inverted lighthouse tube. Within the vacuum envelope of this tube are three active planar electrodes; the anode 10, the grid 11 andthe cathode 12; The anodeis advantageously the bottom of a cup member 14 which has a large diameter tubular skirt which is engaged by and brazedy to a terminal 15. Within the cup member 14 is aiiixed a highly conductive block member for the purpose'of-rernoving heat from the anode surface where it is generated by electron bombardment. An exhaust tubulation 16 may be affixed to the anode block and terminated in a duct through the anode block and cup member il, as described in Patent No. 2,667,593 to Howard D. Doolittle. After exhaust of the completed vacuum tube, this exhaust tubulation, which is advantageously composed of copper, may be pinchedoff with pliers having rounded jaws in order to make a permanent vacuum tight seal.

The grid terminal 1S is a tubular member arranged coaxially with anode terminal` 15. Grid'terminal 18 is joined vacuum tight to anode-terminal 15 by a dielectric ring member @which is sealed vacuum tight between them. Grid'terminal 18` is sealed directly to and supports grid support-member 17 which is also a tubular coaxial member. Thel end of tubular grid support member 17 is closed by a grid mounting deck 2d.' Grid mounting deck 20I is provided withy tabs 21 which are arranged to engage the active'E gridrstructure 11 which isvsupported on annular mounting ring 22.

The active cathode is preferably an oxide coated disk 24 which is indirectly heated by a heaterfmember (not shown). Disk 24 is advantageously directly supported by a high heat flow impedance tubular support member 25. High heat ilow impedance member 25 is, in turn, con-r nectedV to tubularcathode support 26. Tubular cathode support 26-has'cylindrical side walls which snugly engage tubular cathode terminal member 27.

The support between tubular cathode terminal member 27 and tubular grid support 17 is provided through grid connector member 28 which is advantageously a tubular member sealed at one end to grid support member 17 and at its other end to dielectric ring 29. Dielectric ring 29 is, in turn, sealed to the end of cathode terminal member 27.

It should be noted that a tubular flange 30 is provided on grid mounting deck to provide increased capacitive coupling between the grid and cathode members.

The grid structure shown in Figs. 2 and 3 is particularly advantageous. As has been previously mentioned, the Skehan and Kudola invention has provided a method of obtaining extremely tight grid structures which will not sag or buckle upon heating due to expansion effects. The mounting annulus 22 on which the grid structure is secured by brazing, however, should also be free to expand in order to insure that there will be no buckling or sagging at the grid wires. Since this is to be the case, it is not desirable to fix the ring 22 rigidly to the planar grid mounting deck 20 by welding or some similar relatively rigid means. Instead, support of the grid is accomplished through flanges 21 which may be quite narrow and exible and which are easily formed during the fabrication of the grid mounting deck when tubular portion 3i) is formed. These tabs are easily cut out of the sheet forming the deck and bent to a vertical position (see Fig. 4). By use of the tab members 21, a mechanically secure support with sufcient exibility to permit expansion but suihcient rigidity to maintain accurate position is provided. It should be noted that the uniform spacing requirements are attained by mounting the annular mounting ring 22 against the grid mounting deck instead of putting the grid thereagainst. This arrangement has the added advantage of permitting the ends of tabs 21 to be brazed to the grid structure as will hereafter be described. This joint at the end of the tabs will not greatly reduce the flexibility of the structure and will secure improved electrical contact between the grid structure 11 and the planar mounting deck 20 through tabs 21. It is possible to make a joint at this point between the grid and the tabs 21 using low current spot welding because the brazing solder which attaches the grid 11 to ring 22 may be caused by the process to ow and wet tabs 21.

The mounting of the grid mounting ring, with the grid in place, on the planar mounting deck is illustrated in Figs. 4-7. Fig. 4 shows how the ring is put in position. When the ring 22 is in position on the mounting deck 20, the mounting deck may be positioned on anvil member 35 as shown in Fig. 5. A hole is provided in anvil 35 to receive tubular member so that the deck 20 lies iiat against the planar surface of the anvil. An opposed anvil member 36 having a frusto-conical surface 37 at the radius of the tabs 21 is then brought axially down toward the anvil member and against the tabs 21. This action may be facilitated by placing

anvils

35 and 36 in some sort of a press. After removal of anvil 36, the tabs assume the positions shown in Fig. 6. Then an anvil member 38 having a planar contact surface 39 is substituted for anvil 36. Axial downward movement of anvil 38 will cause planar surface 39 of said anvil to flatten tabs 21 against the grid as shown in Fig. 7. Then the assembly may be put in tubular xture 41 for ease in rotation and rotated between the

electrodes

42 and 43 of a spot Welder. The spot Welder will produce a ow of the brazing material holding the grid to its ring 22 and cause a brazed joint to occur between the grid 11 and the tabs 21 as indicated by numeral 45.

Once the grid is mounted on the planar mounting deck 20, the deck 20 may be welded to grid support 17. The structure previously described facilitates accurate spacing between grid 11 and cathode 12. This is accomplished by completing the sub-assemblies including cathode-disk 24 and

tubular supports

25 and 26 on one hand, and

CTL

cathode terminal 27, dielectric ring 29, grid connection means 28 and grid support tube 17, on the other hand. All of these members in the sub-assemblies are tubular and may be held in accurate alignment during their assembly. The cathode support 26 is a tubular member of such diameter that it is snugly engaged by tubular terminal member 27. The sliding it permits axial adjustment between the two sub-assemblies without misalignment of the mounting edge of tubular member 17 relative to the cathode support structure, and cathode disk 24 in particular. As shown in Fig. 8 a xture 46 provides

shoulders

46a and 46b at axial levels so that the distance between them is the exact spacing between the end of tubular member 17 and cathode surface 12 of disk 24 which is required in order to obtain correct grid-cathode spacing. Therefore, when the assembly is placed on this iixture as shown in Fig. 8, the correct relative position of parts is obtained so that grid 11 will be in exact position when mounting deck 20 is affixed thereto. With iixture 46 in place against the cathode and mounting edge of grid support 17, a brazed joint is completed at the junction 47 between cathode support member 26 and cathode terminal 27. This brazed joint may be advantageously completed by placing the assembly on d its fixture within a bell 48, removing oxidizing gases from the bell and inductively or radiantly heating the region of junction 47 by coil 49 so that the solder placed therebetween will ow and join cathode support 26 and cathode terminal 27 in a vacuum tight joint 47. Thereafter, the structure is removed and the grid mounting deck 20 placed in position on the end of grid support member 17 and welded in place. There is no tubular portion on mounting deck 20 to engage grid support 17, so that there is no opportunity at all for misalignment if the mounting edge of grid support member 17 is square.

A novel grid mounting structure and method of securing the structure in place have been described. Modiications of the structure and the method described will occur to those skilled in the art. All such modifications within the scope of the claims are intended to be Within the scope and spirit of the present invention.

I claim: Y

l. An electron tube embodying an envelope containing planar cathode and anode electrodes in spaced relation, a planar grid structure between the anode and cathode and comprising a stranded active grid and an annulus to which the peripheral portion of the grid is aixed, and means for supporting the grid structure comprising a hollow cylindrical terminal which is a part of the envelope, a hollow cylindrical grid support coaxial with the terminal and sealed adjacent one end to the inner surface of the terminal, the other end terminating in an annular edge, and a capacitive coupling between the grid and cathode which embodies a tubular member positioned between the cathode and grid support and having an outwardly turned flange attached to and supported by the edge of the grid support, the annulus and grid being located upon the flange, the ange having tabs at intervals thereon which are bent around the edge of the annulus and hold the annulus and grid in place.

2. An electron tube embodying an envelope containing planar cathode and anode electrodes in spaced relation, a planar grid structure between the anode and cathode and comprising a planar stranded active grid and an annulus to which the peripheral portion of the grid is aixed, and means for supporting the grid structure comprising a hollow cylindrical terminal which is a part of the envelope encircling the cathode, a hollow cylindrical grid support coaxial with the terminal and sealed adjacent one end to the inner surface of the terminal, the other end terminating in an annular edge, and a capacitive coupling betweeny the grid and cathode which embodies a tubular metal member positioned between the cathode and grid support and having an outwardly extending deck attached to and supported by the edge of the grid sup- 5 port, the deck having tabs at intervals therein which are bent around the edge of and overlie the annulus and hold the annulus in place, the mash being on the side of the annulus away from the deck and adjacent the overlying portions of the tabs.

3. An electron tube embodying an envelope containing planar cathode and anode electrodes in spaced relation, a tubular cathode terminal supporting the cathode and forming a part of the envelope, a planar grid structure between the anode and cathode and comprising a stranded active grid and an annulus to which the peripheral portion of the grid is aiiixed, and means for supporting the grid structure comprising a hollow cylindrical grid terminal which is a part of the envelope encircling the cathode, a hollow cylindrical grid support coaxial with the terminal and sealed adjacent one end to the inner surface of the terminal, the other end terminating in an annular edge, insulated connecting means forming a part of the envelope between the cathode and grid terminals, and a capacitive coupling between the grid and cathode 6 which embodies a tubular metal member encircling the cathode within the grid support and having an outwardly turned flange in which are provided a plurality of flexible metal tabs, the ange attached to and supported by the edge of the grid support, the surface of the annulus opposite the grid being positioned upon the flange and the tabs being bent around the edge of the annulus into overlying relation to the grid and holding the annulus and 2,262,455 Goodloe Nov, l1, 1941 2,323,985 Fausch et al. July 13, 1943 2,402,119 Beggs June 18, 1946 2,425,980 Baird Aug. 19, 1947 2,461,303 Watson Feb. 8, 1949 2,521,545 Shepherd Sept. 5, 1950 2,680,824 Beggs June 8, 1954 2,701,320 Kovach Feb. 1, 1955