US2906912A - Cathode assembly for electron discharge devices - Google Patents

Description

c. v. I ITTON 2,906,912

cATHoDE AssEMBLY'EoR ELEcTRoN DISCHARGE DEVICES Sept; 29, 1959 Fild Nov. 15, 1954 ad lull.;

IN VEN TOR.

N@ mm cATnoDE ASSEMBLY Eon ELEc'TRoN DISCHARGE DEVICES Charles V. Litton, Grass Valley, Calif., assigner to Litton Industries, Inc., Beverly Hills, Calif., a corporation of Delaware Application November 15, 1954, Serial No. 468,956 3 Claims. (Cl. 313-344) This invention relates to a cathode assembly for electron discharge devices, and more particularly to a telescoped cathode assembly of great rigidity which employs a filamentary cathode. Although, in general, the cathode assembly of the invention may be employed in various types of vacuum tubes, it is particularly useful in multicavity magnetrons which employ a lamentary cathode of the biiilar type, and the preferred embodiment of the invention will therefore be illustrated and described in connection with a vacuum tube of this type.

Filamentary cathodes of the bifllar type are in general well known to the electron art, and are employed to serve several useful functions. Firstly, utilization of two counter-energized helical filaments substantially eliminates the extraneous magnetic eld which is normally generated by a single helical wound filament. Secondly, a biiilar iilamentary cathode provides a S-terminal centertapped cathode assembly the central terminal of which may be employed for modulating the ow of electrons emitted from the cathode.

Although bilar filaments have heretofore found extensive use in the vacuum tube art in general, their use in the magnetron art has been complicated heretofore by several factors. For example, the 3-terminal cathode assemblies utilized in the prior art for mounting filamentary cathodes are unusually lengthy and bulky owing partly to the requirement that all three of the cathode terminals of a magnetron be well insulated and spaced from the main housing assembly which constitutes the anode terminal, and partly from the fact that each of the three terminals must be spaced axially from the other two terminals in order to facilitate the making of electrical connections to the terminals. -In addition, the utilization of a bilar flamentary cathode with its concomitant lengthy terminal assembly intensities the problem of maintaining the cathode in a rigid position relative to the associated magnetron anode.

In the prior art one significant advance has been made which offers at least a partial solution of the problem set forth above. This prior art structure involves the use of a pair of concentrically mounted conical frustrums for supporting the cathode, the frustrums being so shaped at their apical ends to present a pair of complementary semicircular terminals for respectively connecting to the two windings of the cathode. This particular form of cathode assembly is disclosed in U.S. Patent No. 2,474,263, issued June 28, 1949 to Charles V. Litton.

Although the aforementioned prior art cathode assembly has been successful in proving the utility of employing bilar ilamentary cathodes in magnetrons, it is nevertheless limited by several inherent disadvantages. Firstly, the resulting cathode assembly is still relatively lengthy owing to the fact that the three cathode terminals are axially spaced from each other by relatively large distances. Secondly, each of the terminals includes a threaded collar to provide a terminal surface which may be engaged by the corresponding connecting terminals of an associated tube socket. Thirdly, the iilamentary cath- States atent 2 ode is still 'susceptible to vibration owing to the relatively large overall length of the cathode assembly.

The present invention, on the other hand, obviates the above and other disadvantages of the prior art cathode assemblies by providing a relatively short 3-terminal cathode assembly of exceptional rigidity and 011e in which electrical connection is made directly to the terminals without the utilization of additional components. According to the basic concept of the invention, there is provided a unitary cathode assembly in which the terminal subassembly includes three concentrically mounted and axially spaced annular terminal members which are telescoped so as to be connectable directly to the elements of an associated tube socket without employing any additional collars or sleeves.

More particularly, according to the invention each of the three annular terminal members is of a different size and includes first and second sleeve-like end regions having different diameters, the end regions being separated by an S-shaped central region which telescopically interconnects the two end regions. The iirst or largest terminal member is coupled at its large end to the magnetron anode housing through a iirst glass sleeve, and is coupled at its smaller end to the large end of the second or intermediate terminal member through a second glass sleeve. Similarly the smaller end of the second terminal member is coupled to the large end of the third or smallest terminal member through a third glass sleeve, the smaller end of the third terminal member being enclosed to define in combination with the other terminal members and the associated glass sleeves a hermetically sealed cathode terminal assembly.

The S-shaped central region of each of the terminal members is so oriented with respect to the large end of the terminal member that a portion of the central region protrudes radially from the magnetron axis a distance larger than the outside radius of the glass sleeve connected to the largerend of the terminal member. In this manner each of the terminals may be engaged by the elements of an associated tube socket without interference from the adjacent glass sleeve.

lit is therefore an object of the invention to provide a 3terminal magnetron cathode assembly wherein the terminals are formed to provide a telescoped terminal subassembly, yeach pair of adjacent terminals being separated by an associated glass sleeve.

Another object of the invention is to provide a relatively short and rigid 3-termina1 cathode assembly in which the terminals are composed of annular members having sleeve-like end regions of diierent diameters and an S-shaped central region to provide a telescoped terv minal assembly in which connection can be made to each terminal without interference from adjacent insulative supporting members.

A further object of the invention is to provide a 3-terminal magnetron cathode assembly including a bilar type iilamentary cathode, the assembly including three concentrically mounted and axially spaced annular members which constitute the cathode terminals, each of the annular members being insulatively supported by an associated glass sleeve and having an S-shaped central region which protrudes radially from the magnetron axis a distance larger than the radial distance from the magnetron axis to the external periphery of the associated glass sleeve.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which one embodiment of the invention is illustrated by wayk of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

With reference now to the drawing, there is shown in the ligure a sectional View of a preferred embodiment of a. cathode assembly, according to the invention, which inludes a hermetically sealed vterminal subassembly, generally `designated 1t), and a cathode support subassembly, general-lv Vdesignated 1 ;2. for rigidly Supporting and providing electrical connection to the bilar lamentary cathode of a cathode subassembly, generally designated 1 4.

According to the invention, terminal assembly 10, ir1-V c lundes three annular terminal members 18, 29 and 22, respectively, which are hermetically sealed to and insu-` lativcly separated by two glass sleeves 24 and 26. In addition, the terminal assembly includes a third glass SlSYe 2.?5 Whifh iS herhetally Sealed at .one end to terminal member 22 and at its other end to a magnetron housing member 30, only a portion o f which is shown.

l VEach of terminal members 1,8, 20 and 22 is preferably constructed of Kovar or a similar alloy whose coeicient of Vthermal expansion closely approximates that of glass, and'includes two sleeve-like end regions of different diameters which are separated by a central region having an S-shapedvcross-sectional conrguration. lt wi-ll be noted that the smaller ends of terminal members Y22 and 251), are substantially identical in size with the large ends of ter: minal members2t) and 18V, respectively, thereby perrnitf` ting the luse of cylindrical glass sleeves for nsllltlatvely ihtrhghhs'ctins the fsrhrlihals.- It will also. be notedV that terr'ninalV member l18 enclosed at its7 smaller end.

Asy shOWlll in the ligure, the 'rshaped central region of, 99h of the'rihihel members is, S0 oriented with Speer i9 its. hSs'Ciateflshd .regions that it promises. railinly beyond theexternal periphery of the glass sleeve which is. aed to the lares?? Qld, Qf the ierrhihal member; In this manner a heb@ s clsst ihslhlihgthree cohceiitriclcylihdrietal arrays Qf Gentech Sprihgfs may he utilized fer mal;- ing electrical connection to Vterminal members 18, and` 2: withopt interferencei from the adjacent glass sleeves, and without the utilization of additional metal sleeves o r Cellars, as rfequiredih theA prior hrt With reference to` the iight?, for example; the is illustrated by three conf nector elements`32, 34 and respectively, how the conlasts. gf e tube Sachet 0f thehove type would engage terminal` members 1 8., ZOand 2,2., respectively.

The lSIP-shaped central regions ofthe terminal members also serves the additional function of telescoping the end regions of the terminal members, thereby materially de,- creasing the axial length of the cathode assembly of the invention. In practice it has been found that Vcathodeassemblies constructed. in accordance to the principles of the invention are. several inches shorter than correspondingv cathode assemblies constructed inr accordance withv the prior ari technique rIfhe glass sleeves employed for insulatively mountingv terminal' members 18, 20 and 22 are preferably composed of relatively hard glass in order to provide a mechanically rugged'structure capable of withstanding4 the relatively hardvacuums established within the chamber defined byterminal assembly 1Q and the associated magnetron housing. The length of glass sleeves 24 and 26 should preferably be such that adjacent terminal membersl are separated by a distance of the order of .050v of an inch after the terminalY members have been sealed to the sleeves.` Glass sleeve 2,3, on the other hand, IIiust be relatively long inv comparison with the otherr glass!v sleeves, since sleeve 28 must be capable of withstandingVV the` relatively high anode;to cathode potential normally anche@ i9 hh operating whahah@ A typical' overall liislh for-@ach 0f Sleeves.- Zlf and 2@ is flic) Of anihsh, while Slew-@.28 is` preferably iB/r inches. le1isth.there. by orcviding.ax` separation between termlrlalmembcr 22'v afllllm'afllh-housingfhffapnrorirhately.- 1V@ taches .Itvvlilllbe'y recognizedhof course, that the` particular dimens sions selected for the various elements of the terminal assembly are determined in view of the desired position of cathode subassembly 14 relative to the magnetron anode and by the dimensions of the elements of cathode support subassembly 12.

Cathode support subassembly 12 includes three supporting members 38, 40 and 42 for electrically interconnecting terminal members 18, 20 and 22, respectively, with cathode subassembly 14 and for rigidly maintaining the position of the cathode relative to the associated magnetron anode, not shown. Supporting members 40 and 42 are preferably two conical frustrums constructed in accordance with the principles disclosed in the aforementioned Patent 2,474,263 to Charles V. Litton, and are so disected to provide at their apicalends two spaced, conjugate, semicircular supports which are connected to the left hand end of the cathode subassembly, as viewed in the ligure. Supporting members 4l) and 42 are preferably constructed of molybdenum or a similar material having a relatively low coefficient of thermal expansion, and are aflixed at the periphery of their larger ends to terminal members 20 and 22, respectively, as by brazing, for example. Supporting member 38 is preferably composed of a hollow rod of molybdenum or a similar material, and is brazed at one end to terminal member 18, the other end of supporting member 3S having a shouldered hole bored therein to provide a recess for receiving a cooperating element of cathode subassembly 14. The holes 44 and 46 bored through supporting member 38 are provided to insure that the interior of the member is also evacuated when the magnetron employing the cathode assembly of the invention is outgassed or exhausted.

Cathode sub-assembly 14 includes a bililar type filamentarycathode having two helical windings which are designated 50` and 5:1, respectively, the right hand end of each winding, as viewed in the-ligure, being' electrically and mechanically connected to a common connecting memberSZ. This connecting member is, in turn, xedly attached as by welding or brazing, to a center rod 54 which is composed of tungsten, for example, the center rod being seated in and rigidly held by the central supporting member 38. As shown in the ligure, connecting member 52 may be grooved to improve its heat-dissipating properties.

The other ends of cathode windings 50 and 51 are respectively connected to two semicylindrical connecting members 56 and Sil-which, in turn, are brazed to the api# cal ends of supporting members 40 and 42, respectively. Connecting members 56 and 58 are preferably constructed of molybdenum and, as shown in the ligure, arev spaced from center rod 54 and from each other by finite distances in order to prevent short circuiting of the cathode windings.

Connecting member 56 also includes a shoulder 60 which is utilized for lixedly supporting an annular endhat member 62, the end-hat member being spaced from connecting member 58 and including a flanged end 64 for restricting to a predetermined region thel electron emission into the magnetron interaction chamber. The left hand end of` connecting member 52, as shown in the ligure, is also llanged to provide a second end-hat for restricting the effective region of emission at the other end of the cathode. Both end-hat 62 and connecting member 52 are preferably constructed of zirconium coated molybdenum with a platinum coating over their flanged portions.

It will be. recalledzthat connecting members 56 and 58 are spaced from each other and from center rodi54 in order to,l prevent short circuiting of 'one or both of the cathode windings. It has been found that during operation ofthe magnetron there may be a tendency for free electrons` to pass through the slot between connecting members 56 and 58` and energize structural parts of the magnetron other than the anode, thereby tending to generate oscillations atan undesired frequency. Accordingly, the left-handvendof end-hat memberA 62; as viewedl in the figure, is extended axially along connecting mem'- bers 56 and 58 a distance suicient to prevent the emission of electrons from the slot therebetween.

As set forth hereinabove the cathode comprises two lamentary windings S and 51 which are so mounted and enengized as to constitute a biilar filament. The windings are preferably constructed of carburized thoriated tungsten and are energized so that current in adjacent turns lows in opposite directions with the result that the magnetic field produced by the cathode current is substantially neutralized. Accordingly, if alternating current is applied to energize the cathode, -as is often the case in practice, the small amount of residual alternating flux produced by the cathode is insufficient to appreciably modulate the electrons emitted from the cathode.

In operation power for energizing the lamentary cathode is applied to terminals 20 and 22 to energize the two cathode windings in series. It will be recognized, therefore, that terminal 18 and its associated supporting and connecting members constitute a cathode center tap which may be utilized, if desired, to modulate the electron emission from the cathode windings.

It will be recognized from the foregoing description that the present invention provides a rigid 3-termina1 magnetron cathode assembly which is relatively compact and in which electrical connection may be made directly to each of the three terminals without the utilization of additional components. In addition, it will be recognized that the utilization of a telescoped terminal subassembly foreshortens the entire cathode assembly and functions to materially increase the rigidity of the overall structure while simultaneously decreasing the sensitivity of the cathode assembly to temperature changes.

What is claimed as new is:

l. A cathode assembly for an ultra-high frequency electron discharge device, said cathode assembly cornprising: a biilar lilamentary cathode including rst and second helical windings each having first and second ends; a terminal subassembly including iirst, second and third annular terminal members having a common axis, rst and second insulative sleeves insulatively interconnecting and concentrically mounting said rst and second terminal members with said second and third terminal members, respectively, and a third insulative sleeve insulatively interconnecting said third terminal member with the housing of the electron discharge device, each of said terminal members including two end regions of diierent diameters interconnected by a telescoped S-shaped central region a portion of which reverses direction with respect to said common axis, the smaller ends of said second and third terminal members being substantially equal in diameter with the llarger ends of said first and second terminal members, respectively, said S-shaped central region of each of said terminal members protruding radially from the common axis of said members a distance larger than the outside radius of the glass sleeve which is connected to its larger end region to provide a protruding annular contact surface adopted to engage a contact member of an associated tube socket; and means connected to said terminal members and to said lilamentary cathode for mechanically mounting said cathode and electrically interconnecting said cathode windings to said terminal members.

2. In a cathode assembly for utilization in a vacuum tube generator of ultra-high frequency electrical signals, a terminal subassembly for providing external electrical connection to an internally mounted cathode, said terminal subassembly comprising: rst, second and third annular terminal members, each of said membersI including a large end region and a small end region telescopically interconnected by a central region said central region having an S-shaped cross sectional configuration a portion of which reverses direction with respect to said end regions, the larger ends of said rst and second terminal members having diameters substantially equal to the diameters of the smaller ends of said second and third terminal members, respectively; first and second glass sleeves insulatively interconnecting the larger ends of said rst and second terminal members to the smaller ends of said second and third terminal members, respectively, and a third glass sleeve insulatively interconnecting the larger end of said third terminal member to the housing of the vacuum tube generator, said terminal members and said glass sleeves being concentrically mounted about a common axis and said S-shaped central region of each of said terminal members protruding radially from said common axis a distance larger than the outside radius of the glass sleeve which is connected to its associated end region to provide a protruding annular contact surface adopted for engagement by a terminal of an associated tube socket.

3. A cathode assembly hermetically sealed to the anode housing member of a magnetron, said cathode assembly comprising: a cathode element having first, second and third terminals for receiving electrical energy; a terminal subassembly hermetically sealing the anode housing member and providing external electrical connection to said cathode element, said terminal subassembly including r.lirst, second and third annular members, each of said terminal members including a large end region and a small end region telescopically interconnected by a central region, said central region having an S-shaped cross sectional configuration a portion which reverses direction with respect to said end regions, the larger ends of said rst and second terminal members having diameters substantially equal to the diameters of the smaller ends of said second and third terminal members, respectively, rst and second glass sleeves insulatively interconnecting the larger ends of said rst and second terminal members to the smaller ends of said second and third terminal members, respectively, and a third glass sleeve insulatively interconnecting the larger end of said third terminal member to the anode housing member, said terminal members and said glass sleeves being concentrically mounted about a common axis, the portion of said S-shaped central region adjacent the larger end of each of said terminal members protruding radially a distance larger than the outside diameter of the 'glass sleeve connected to said larger vend to provide a protruding annular contact surface adapted for engagement by a terminal of an associated tube socket; and rigid supporting means connected between said first, second and third terminal members and said rst, second and third terminals ofsaid cathode, respectively, said supporting means txedly maintaining the position of said cathode relative to the anode housing member and being electrically conductive whereby the application of electrical signals to said terminal members electrically enengizes said cathode.

References Cited in the tile of this patent UNITED STATES PATENTS 2,455,381 Morton et al. Dec. 7, 1948 2,471,424 Glauber May 31, 1949 2,474,263 Litton June 28, 1949 2,542,639 De Walt Feb. 20, 1951 2,609,522 Hull Sept. 2, 1952 2,634,384 Ford et al. Apr. 7, 1953 2,705,294 Shrader Mar. 29, 1955

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