US2732510A - Electron - Google Patents

Description

Jan. 24, 1956 M. J. ZUNJCK ELECTRONEMITTER Filed March 13, 1952 Mun gm MN m W H m2 IIU I L E 0. Mwm

.l-Illlll] United States Patent 2,732,510 ELECTRON EMITIER Michael J. Zunick, Greenfield, Wis., assignor to General Electric Company, a corporation of New York Application March 13, 1952, Serial No. 276,313

' 12 Claims. c1, 313-37 The present invention relates in general to electronics, and has more particular reference to electron emitters, the invention pertaining especially to an improved support structure for filaments of the sort commonly employed as electron emitting cathodes in electron flow devices, such as X-ray generating tubes and the like.

X-ray generating tubes commonly comprise an anode and an electron emitting cathode element enclosed in a sealed and evacuated envelope, X-rays being generated at the anode as the result of impingement thereon of electrons emitted by the cathode element. The electron emitting element is commonly mounted in a cathode structure embodying a cup adapted to aid in directing, toward the anode, electrons emitted by the cathode element. Such cathode structures have comprised a multiplicity of components, secured together, as by means of screw fastening elements, and hence necessarily formed with threaded sockets for receiving such elements. As a consequence, conventional support structures for electron emitters have been relatively expensive and diflicult to assemble. Furthermore, the formation of threaded fastening elements and corresponding threaded sockets in the components to be joined, as well as the application of threaded elements in position securing components together, commonly results in the production of small metal particles, scraped or otherwise detached or loosened from the components of the structure, which, if accidentally allowed to remain in situ, may deleteriously affect the operation of an elec-' tron flow device .in which the emitter and its support struc ture are assembled. Such conventional support structures, of course, require manual assembly of the components, entailing undesirable handling thereof during the assembly operations.

An important-object of the present invention is to pro,- vide an improved support structure for electron emitters,

comprising a minimum number of componentparts of relatively simple, inexpensive form and adapted to facilitate the assembly of the support structure at low cost.

Another important object is to provide a support structure for electron emitters embodying parts adapted for automatic assembly, as by applying the parts in a suitable jig, thereby minimizing the necessity of handling the parts during the assembly operation withconsequent reduction of handling contamination thereof.

Another important object resides'in providing a support structure of the character mentioned having a minimum number of component parts adapted to be secured together by welding, thereby avoiding the employment of fastening screws and inhibiting the formation of loose metallic particles in the support structure.

Another important object is 'to provide a structure of the character mentioned'including a component comprising a cathode cup element having a transverse groove formed in a face thereof :and channels or ducts'communieating the bottom of the groove with the opposite face of the cup .element, and including stem supporting means located in seats formed in said ducts for accurately locating and securing emitter supporting stems in said ducts.

Another important object is to provide improved means for mounting and insulating an emitter support stern in a cathode cup element of the character mentioned; a further object being to employ a block of suitable insulating material sized to fit snugly in a seat formed in the cup element, the block being formed with a support channel therein and sized to snugly receive an emitter support stem in accurately mounted position in the cup element.

Another important objectis to employ'a formed block of insulating material comprising magnesium oxide, lava, glass, porcelain, or the like, for mounting an emitter support stem in a cathode cup structure; a further important object being to provide improved means for mounting and retaining the block of insulation in mounted position on the cathode cup element, saidmeans comprising a shelllike housing adapted to retain the block in operative position to support and insulate an emitter carrying stem mounted therein, even though said block may become cracked in service. I

Another important object resides in the provision of improved means for mechanically and electrically connecting an electron emitting filament on a support stem.

Another important object is to provide improved and simplified means whereby a filament support stem may be mounted and secured in precisely adjusted position in a stem supporting member, such as a cathode cup element.

Another important object resides in providing a cathode structure of the character mentioned including improved means for mounting the structure in rigid fashion on a mounting base adapted to form a portion of the evacuated envelope of an electron flow device, to thereby provide the cathode structure and its mounting base as a sub-assembly unit adapted for incorporation with envelope means, in building an electron flow device embodying said cathode structure in operative position therein.

The foregoing and numerous other important objects, advantages, and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawings, discloses preferred embodiments of the invention.

Referring to the drawings:

Fig. 1 is a diagrammatic view of an electron flow device including a cathode structure embodying the present invention;

Fig. 2 is an elevation view, partially sectionalized, showing a structure embodying the invention;

Figs. 3, 4 and 5 are sectional views taken substantially along ,the lines 3.-3, 4-4 and 5-5 in Fig. 2;

Fig. 6 is a sectional view showing a modified arrangement embodying the invention;

Fig. 7 is a sectional view taken substantially along the line 7-7 in Fig. 6;

Fig. 8 is a greatly enlarged view of the filament connected end of a filament support stem forming part of the structure shown in Figs. 2 and 3 and Fig. 9 is an enlarged sectional view through a stem insulating and supporting device forming a part of the structure shown in Figs. 2 and 3.

To illustrate the invention thedrawings show electron emission means comprising a cathode structure C of a sort well adapted for use in electron flow devices, such as an X-ray generating tube T. As shown, the tube comprises an anode A and the cathode structure C enclosed within and supported on a sealed and evacuated envelope E, which may beof any desired or preferred form and construction. X-ray generating devices operate as such in response to impingement on the anode of electrons emitted by the cathode, such electronic impingement resulting in the generation of X-rays at the anode, whence the enclosing envelope.

Metallic filaments are commonly employed as electron emitters 'in electron fiow devices, such filaments 'be'ing electrically excitable, for electron emission therefrom, as by the passage of electrical current therethrough, from a power source located outwardly of the envelope of the device. Electrons emitted by an energized filament are commonly caused to travel toward and to impinge upon the anode of the device under the influence of an electron driving potential applied between the filament and the anode, as .tlrom a suitable source of electrical power also disposed outwardly of the envelope. In such electron fiow devices, therefore, it is necessary to provide for mounting the electron emitting filament Within the enclosing envelope, and .to provide for electrically connecting the filament not only with an external source of filament energizing power, but also with a suitable external power source for applying electron driving potential bctween the anodeand cathodeof the device.

The present invention provides an improved .rnounting structure for supporting an electron emission filament in operative position within the sealed envelope of an electron fiow device, the structure also affording means for electrically connecting the supported filament with electrical power sources located outwardly of the envelope of the device in which the structure is or may be assembled for use.

As shown 'in the drawings, the electron emission means of the present invention comprises an electron emitting filament 11 and a support structure '12 for mounting the filament'li within the sealed envelope of an electron flow device. The support structure 12 comprises a preferably cylindrical block 13 of any suitable material, such as steel, said block having an outwardly opening slot or groove 14 formed in its front end, the groove 14, in 'the illustrated embodiment, extending diametrically and trans verscly of the block 13 and opening at the opposite sides thereof, thereby facilitating the formation of the groove by a simple milling operation transversely across the front face of the block. The block 13 may also be formed with a pair of parallel, spaced apart, preferably cylini drical channels 15 and 15, said channels each opening at one end upon the bottom of the groove 14, the opposite ends of "the channels opening into enlarged cavities 16 and 16' formed in'and opening outwardly of the rear face of the block.

The filament 11 is supported in the groove 14 with the axis of the filament lying substantially in the medial plane of the groove and at a predetermined elevation between the bottom and open top of the groove, the opposite ends of the filament being mechanically and electrically connected on mounting stems 17 and 17', of suitable electrical conducting material such as molybdenum, supported on the block 13 in position extending coaxially with respect to the channels 15 and 1'5. In that connection, the stems 17 and 17' maybe formedwith tapered end portions '13 and means, extending and secured in the seats 16 and 16', is provided for mountingthe stems 17 and 17' in position on the block '13 presenting the tapered end portions 18 of the stems Within the channels 15 and 15', the filament 11, atthe opposite ends thereof, being formed with mounting extensions 1.9 adapted to be mechanically and electrically secured upon the tapered end portions 13 of the filament-mounting stems.

Each filament mounting portion 159 may be mechanically and electrically connected with the tapered end portion 18 of its corresponding support stem by applying the end of the mounting portion 19 upon the tapered portion 13 of the stem .on which it is to be attached, wrapping a length of thread-like wire 20 about the pertions 13 and .13, and then securing the portions 18 and 19 and the thread-like binding Wire 20 together by spot welding the same, as at 21.

in order to mount the filament supporting stems 1.7 and 17 accurately in position extending coaxially with respect to the channels 15 and 15 to thereby accurately locate the position of the supported filament 11 in the groove -14, the stems '17 and 17' may be received in preferably cylindrical mounting members 21 and 21 having portions adapted to extend snugly Within the cavities 16 and 16', to thereby accurately locate the stems 17 and 17 with respect to the channels 15 and 15'. In the illustrated embodiment, the :stem :17 is insulated from the block 13, while the stem 17 is electrically connected with the block so that the filament '11 may be energized for electron emission by-electrically connecting the .stem 17 and the block 13 with a suitable source of filament energizing power. It is, of course, within the contemplation of the present invention to electrically insulate both of the stems 17 and 1.7 from the block 13, in which case it would become necessary to provide means for connecting both of the stems with the filament energizing power source.

The mountin'gmember 21 preferably comprises a cylindrical body .of insulating material, such as magnesium oxide, lava, glass or porcelain, sized for snug intertitment at one end in the cavity .16. A cup-shaped shell 22, having an outstanding peripheral rim 23 and formed to snugly receive the portions of the insulating body 21 which extend outwardly of the cavity 16, is provided to support the member 21 in operative-position on the block 13,, the shell being secured on the block 1.3 in any preferred fashion and preferably by welding the rim 23 to the block. The insulating body 21 is formed with an axial channel 24 in coaxial alinement with the channel 15, and fitted with a preferably metal sleeve 25 having a peened portion 26 at one end of the sleeve and formed with a peripheral head 27 medially thereof, whereby to secure the body '21 on the sleeve 25 between the peened portion 26 and the head '27, the sleeve 25, at its end remote from the peened portion 26, extending outwardly of the insulating body through an opening 28 formed in the retaining member 22. The stem 17 and sleeve 25 are formed for snug slidinginterfitment of the stem within the sleeve.

The cylindrical mounting member 21 may comprise a sleeve of electrical conducting material sized to snugly fit at one end within the cavity 16' and formed to snugly, yet 'slidingly receive the filament mounting stem 17', the member 21' being secured in an suitable or preferred fashion on the'block 13.

The sleeves 21" and 25 preferably comprise metal which may readily be weldingly connected with the stems 17 and 17'. .The sleeve 21' and the retaining shell 22 preferably comprise metal adapted to be readily connected, as by welding, with the'block 13. To this end, the sleeves21 and 25 and the retaining shell 22 may be made of nickel or a ferrous alloy of nickel, which is readily connectible by welding either with the steel block 13 or with the molybdenum filament mounting stems or both.

It will be seen from the foregoing that the emission element 11 audits support means, including the mounting stems 17 and 17, maybe readily assembled on the block 13 with -the element 11 located in precisely determined position in the groove 14 with minimum effort and substantially without requiring the parts to he handled. To this end, the block '13may be placed face downwardly in a suitable holding fi ture for the reception of the stem mountings in the sockets 16am] 16'. The stem mounting, comprising the insulating body 21, the retaining she] 22, and the stem mounting sleeve 25, may then be secured in place, as by welding the rim 25 to the block 13; and the mounting, comprising the metal sleeve 21, may also be secured at one end in the socket 16'. The block 13 with attached stem mountings may then be inverted and secured in a suitable holder for the assembly of the stems "and 1.7 and .theemission element 11.

.If desired, theelement 11 may be mounted on the stems .17 and l7' before the same are assembled in the stem mountings. To this end, the stems 17 and 17 may be clamped :in desired spaced relation in a suitable holder and the element 11 attached to the stern ends 18 in the manner heretofore described. 'lhereupon, the stems 17 and 17 may be applied in the stem mountings by employing the holder to aid in applying the ends of the stems 17 and 17 remote from the filament carrying ends thereof, through the channels 15 and 15 and into the ends of the sleeves 21' and 25. The stems may then be axially moved in the sleeves until the ends of the stems 17 and 17 which are remote from the filament carrying ends thereof, project outwardly of the sleeves 21' and 25, the stems 17 and 17' at such stage of the assembly being straight rods of sufficientlength to allow the same to be held in the mountings with the stem ends 18 projecting outwardly of the upper face of the block 13.

The holder may then be removed from the stems 17 and 17' to permit the same to bedrawn through the sleeves 21 and 25, as by gripping the ends of the stems 17 and 17' which project from the block remote ends of the sleeves 21' and 25, in order to draw the filament supporting stem ends 18 into the channels 15 and 15' to thereby support the filament in accurately determined position within the groove 14. Thereupon, the sleeves 21' and 25 may be welded upon the stem portions enclosed therein to secure the same against axial movement with respect to the block 13. After the welding operation, the stem 17 may be cut off opposite the block remote end of the mounting sleeve 21, while the stem 17 may be cut off at a desired distance outwardly of the mounting sleeve 25 and bent to form a connection lug 29, as shown in Fig. 1, for a purpose hereinafter more fully described.

Alternately, the stems 17 and 17', prior to the attachment of the emission element 11 thereon, may be applied in the stem mountings in position with their filament mounting ends 18 projecting above or outwardly of the front face of the block 13. The emission element 11 may then be mounted and attached to said ends of the stems, in the manner heretofore described, after which the stems may be drawn axially in the sleeves 21 and 25 to the position shown in Figs. 1 and 2, and weldingly secured in adjusted position in the sleeves in the manner mentioned supra.

In order to mount the electron emission structure on and in an enclosing envelope, such as the envelope of an X-ray tube, the same may be supoprted upon a pedestal or base 30 adapted to form a portion of the enclosing envelope. The pedestal 30, in turn, may carry a plurality of mounting stems 31 and 32 secured thereon in spaced apart relationship, the stem 32 at least being relatively insulated electrically from the remaining stems 31. As shown, the pedestal 30 may comprise a tubular glass member 130 having a closed end 33, forming a pinch seal in which the stems 31 and 32 are embedded, with the stem 32 and at least one of the stems 31 extending through and on opposite sides of the pinch seal.

Alternately, the pedestal or base may comprise a tubular glass member 130 having an end closed by means of a cup-shaped member 30' of metal, having a rim joined to the member 130' by a glass-to-metal seal. The stems 31 and 32 may be mounted on the member 30' in any suitable or preferred fashion in manner relatively insulating at least the stem 32 from the metal member, as by means of a glass-metal seal 33. In such contraction, the stems 31, if desired, may be weldingly attached on the member 30, or they may be attached thereon as by means of glass-metal seals like the seal 33'. The stems 31 extend upwardly of the base 30 and have outwardly offset upstanding end portions 31' remote from the base in position to supportingly engage the block 13, while the stem 32 is provided with an offset lug 32' in position to register and engage with the connection lug 29 of the stem 17, when the block 13 is in position mountedon the stern portions 31'.

For the purpose ofmounting the block 13 upon the stern portions 31', the block is provided with lateral grooves 34 which, for manufacturing convenience, may

extend from one end of the block to its other end. These grooves are adapted to receive the stem portions 31' snugly therein; and a holding collar 35 may be applied snugly about the sides of the block 13 to hold the stem portions 31 in the grooves 34, and hence mount the block 13 upon the stems. To this end, the sleeve 35 is sized to tightly fit upon the block 13; and the same may be welded upon the block, especially at the stem portions 31', whereby to weldingly secure the stems in the grooves 34 and to secure the sleeve 35 on the stems and on the block 13. When the block 13 is thus mounted on the stem portions 31, the attachment lug 29 will be disposed in adjacent contact with the lug 32', and said lugs are preferably mechanically and electrically secured together, as by welding.

In order to assemble and secure the block 13 upon the stems 31', the block, with emission element 11 mounted and secured therein in the manner heretofore described, may be disposed face downwardly in a suitable jig or holder. The support 30, with stems 31 and 32 mounted in place thereon, may then be applied to the block 13 in order to dispose the stem portions 31' in the grooves 34. The stem portions 31 may then be weldingly connected with the block 13; and the sleeve.

35 may be applied and weldingly or otherwise secured on the block 13, either prior to or after the assembly of the stern portions 31 in the grooves 34.

It will be seen from the foregoing that the electronemission structure may be built as a sub-assembly unit comprising the block 13 with the emission element 11 supported thereon, and the support base 30 including the tubular or skirt-like portions thereof. The entire structure may be assembled substantially without requir ing the handling or touching of the elements forming the cathode head. The glass skirt portions of the base 30, of course, allow the same to be sealed in an envelope opening, such as is formed at an end of the envelope of a conventional X-ray generating tube, to thereby form the base 30 as a re-entrant envelope portion supporting the cathode structure in operative position within the X-ray generating tube.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. An electron emitting cathode structure comprising a block of metal forming a head and provided with a groove opening upon the front face of the block, an elec.

tron emission element and mounting means for supporting the same on said block in position disposed in said groove, means forming a support base, and a plurality of supporting stems secured on and extending from said base, said stems being secured to said head to mount the same on the base, at least one of said stems being electrically insulated from said head and comprising electrical conducting means connected with said emission ele-.

ment for electrically energizing the same.

2. An electron emitting cathode structure comprisinga block of metal forming a head and provided with a groove opening upon the front face of the block, an electron emission element and mounting means for supporting the same on said block in position disposed in said groove,vmeans forming a support base, and a plu rality of supporting stems secured on and extending from said base, said stems being secured to said head to mount the same on the base, at least one of said stems being electrically insulated from said head'and connected with said emission element for electrically energizing the same, said head being provided with lateral grooves for receiv-' ing others of said stems, and means for securing the stems in said lateral grooves.

3. An electron emitting cathode structure comprising a block of metal forming a head and provided with a groove opening upon the front face of the block, an electron emission element and mounting means for supporting the same on said block in position disposed in said groove, means forming a support base, and a plurality of supporting stems secured on and extending from said base, said stems being secured to said head to mount the same on the base, at least one of said stems being electrically insulated from said head and connected with said emission element for electrically energizing the same, said head being provided with lateral grooves for receiving others of said stems, such groove received stems being \veldingly secured to said -head in said lateral grooves.

4. An electron emitting cathode structure comprising a block of metal forming a head and provided with a groove opening upon the front face of the block, an electron emission element and mounting means for supporting the same 'on said block in position disposed in said groove, means forming a support base, and a plurality 'of supporting stems secured on and extending from said base, said stems being secured to said head to mount the same on the base, at least one of said stems being electrically insulated from said head and connected with said emission element for electrically energizing the same, said head being provided with lateral grooves for receiving others of said stems, and a sleeve-like collar secured on said head in position snugly embracing the sides thereof and overlying and enclosing the groove mounted stems.

5. An electron emitting cathode structure comprising a block of metal forming a head and provided with a transverse groove opening upon the front face of the block and having opposite ends extending to and opening at the opposite sides thereof, a sleeve-like collar snugly embracing the sides of and secured to said block in position enclosing the opposite ends of said transverse groove, an electron emission element and mounting means for supporting the same on said block in position disposed in said groove.

6. An electron emitting cathode structure comprising a cylindrical block of metal forming a head, electron emission element supported on said head, a support base comprising a shell structure adapted for integration in an envelope structure to form a part thereof, and means for mounting said block upon said base comprising a plurality of mounting stems of electrical conducting rnaterial secured on and extending from said base, at least one of said stems being electrically connected with said emission element and insulated from said head, said block having spaced mounting grooves formed in its sides in position to receive and to make mechanical and electrical connection with others of said stems, and a collar snugly enclosing the sides of said block and covering the stems in said mounting grooves, whereby the groove mounted stems may support said head on said base.

7. An electron emitting cathode structure comprising a cylindrical block of metal forming a head, an electron emission element supported on and electrically connected with said head, a support base comprising 'a shell struc-' ture adapted for integration in an envelope structure to form a part thereof, and means for mounting said block' upon said base comprising a plurality of mounting stems of electrical conducting material secured on and extending from said base, said block having spaced mounting grooves formed in its sides in position to receive and to make mechanical and electrical connection with said stems, a collar snugly enclosing the sides of said block and covering the stems in said mounting grooves, whereby .the groove mounted (stems may support said head on said base with the stems electrically connected with said head, a connection stem secured on and extending from said base, insulated means for mechanically securing said connection stem on and electrically insulating the same from said head, means for electrically connecting said emission element with said connection stem, and means extending on the side of the shell structure remote from said head for electrically connecting said connection stem and at least one of said groove mounted stems with a source of emission element energizing power.

8. An electron emitting cathode structure comprising a block of metal providing a head having front and back faces, said block being formed therethrough with a pair of spaced channels opening upon the front and back faces of the block, an elongated electron emission element, support means for mounting said element on said head in accurately determined relative position with respect to the front face of the head, said support means comprising a pair of mounting stems of electrical conducting material extending 'coaxially in said channels, said emission element being mechanically and electrically connected on said stems in position extending therebetwecn, and mounting means for securing a said stem on said head comprising a mounting sleeve sized to snugly yet slidingly receive the stem therein, said sleeve comprising material capable of connection with a said stem by welding, whereby the stem may be welded in accurately adjusted position in and axially of the mounting sleeve.

9. An electron emitting cathode structure comprising a block of metal providing a head having front and back faces, said block being formed therethrough with a pair of spaced channels opening upon the front and back faces of the block, an elongated electron emission element, support means for mounting said element on said head in accurately determined relative position with respect to the front face of the head, said support means comprising a pair of mounting stems of electrical conducting material extending coaxially in said channels, said emission element being mechanically and electrically connected on said stems in position extending therebetween, and mounting means for securing a said stem on said head comprising a mounting sleeve sized to snugly yet slidingly receive the stem therein, said sleeve comprising material capable of connection with a said stem by welding, whereby the stern may be Welded in accurately adjusted position in and axially of the mounting sleeve, said head being formed with a seat in its back face, in concentric relation with a said channel, for receiving the mounting means on said seat in position with said sleeve in coaxial alinement with said channel.

10. An electron emitting cathode structure comprising a block of metal providing a head having front and back faces, said block being formed therethrough with a pair of spaced channels opening upon the front and back faces of the block, an elongated electron emission element, support means for mounting said element on said head in accurately determined relative position with rcspect to the front face of the head, said support means comprising a pair of mounting stems of electrical conducting material extending coaxially in said channels, said emission element being mechanically and electrically connected on said stems in position extending therebetween, and mounting means for securing a said stem on said head comprising a mounting sleeve sized to snugly yet sliding'ly receive the stem therein, said sleeve comprising material capable of connection with a said stem by welding, whereby the stem may be welded in accurately adjusted position in and axially of the mounting sleeve, said head being formed with a seat in its back face, in concentric relation with a said channel, and said seat being sized to snugly receive an end of the mounting sleeve to accurately position the sleeve on the head.

'11. An electron emitting cathode structure comprising a block of metal providing a head having front and back faces, said block being formed therethrough with a pair of spaced channels opening upon the front and back faces of the block, an elongated electron emission element, support means for mounting said element on said head in accurately determined relative position with respect to the front face of the head, said support means comprising a pair of mounting stems of electrical conducting material extending coaxially in said channels, said emission element being mechanically and electrically connected on said stems in position extending therebetween, and mounting means for securing a said stem on said head comprising a mounting sleeve sized to snugly yet slidingly receive the stem therein, said sleeve comprising material capable of connection with a said stem by welding, whereby the stem,may be welded in accurately adjusted position in and axially of the mounting sleeve, said head being formed with a seat in its back face, in concentric relation with a said channel, a block of insulation sized to snugly fit said seat and having an axial channel formed concentrically therein, said channel being sized to snugly receive the mounting sleeve, means to secure said sleeve in said channel and means to secure said block of insulation on said head in said seat.

12. An electron emitting cathode structure comprising a block of metal forming a head provided with a groove opening upon the front face of the block, said block being formed therethrough with a pair of spaced channels opening in said groove and on the back face of the block, an elongated electron emission element, support means for mounting said element on said head in comprising material capable of connection with said stem by welding, whereby the stem may be welded in accurately adjusted position in and axially of the mounting sleeve, means forming a support base for said cathode structure, a plurality of stem-like members forming support rods secured on and extending from said base, certain of said stem-like members being secured directly to said head to mount the same on the base, at least one of said stem-like members being mechanically and electrically connected with one of said mounting stems.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,646 Juthe et a1. Apr. 2, 1935 2,200,115 Lessmann May 7, 1940 2,250,323 Atlee July 22, 1941 2,471,298 Atlee May 24, 1949

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