US2443916A

US2443916A - Cathode-grid assembly for cathode-ray tubes

Info

Publication number: US2443916A
Application number: US757633A
Authority: US
Inventors: Kelar Joseph
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1947-06-27
Filing date: 1947-06-27
Publication date: 1948-06-22
Anticipated expiration: 1965-06-22

Description

June 22, 1948, 1 KELAR y 2,443,916

CAIIHODEPGRID ASSEMBLY FOR' A CATHODE RAY TUBE Filed June 27, 1947 mi im y E Gttorneg Patented June 22? 1948 @Arnone-RAY TUBES Joseph Kelar; Lancaster, Pa. assigner to Raafio- Gnrnoration of America, a corporation of Dglaf ware i invention -relates to cathode ray-tubes, and

inpartiularto an electrongungstruturehaving i an improved `c"atl'iode-grid Aunit assembly tor-such tubes.

A conventional type of cathodefraytube has an electron gun'structure comprising a `tubular cath; ode enelosingpa heaterfilament spaced criti` cally from a control grid; Axialllyspacedalong the gun from the control grid is a focusing grid plate, a rst anode cylinder y and a second lanode' cylinder. `These structures when maintained! at appropriate electrostatic potentials form' `a lseries of lai-potential electron- Elenses which tendfto-iorm the electron emission i from kthe cathode. vinto.` :a beam and accelerate and `'ocus the bear-neon a fiuorescent screen at the end of the tube.

`Theconstrnction of the cathode-grid structure of Aa conventional type of electron gun has always involvedthe difficult process of assembling; :by hand operation; 'many smallfparts `the proper relationships. The processl also involves fthefiixing of lseveral subassemblies -in a predetermined spaced relationship involving critical 1distances conforming to smal-l tolerances.

n practica, subassemblies fand spacer elements are found to vary considerably in'theirwcritical dimensions and aresconsequentlymatchiedl'to provide the desired 4cathode grid `spacing.`4 Vfill-1e procedure of matchinglfhas con-'sistemaofsorting cathode ,subassernbglies into several groups, f of which each hgrouypfinludes cathode subassemblies conforming within close -tolerancestola specific dimension. Thecathode-to gri-d ceramic-:spacers are'-;also divided into a vlike-number ofi-groups each of which contains sp acers contormingvvithin closeA tolerances to f -aspeciiic dimension; Each groupof cathode subassembliesisthenfmatched Withoone of-thegroups of lspacers-so that 'when a cathode subassembly `and a s pacer of-I'matched groups are assembledinca-'grid cylinder,v Ythere Will* result a cathode-gridl 'strlictl-irehaving4 a close approximation, of the predetermined ioathodeato grid:#spacingd Such a process of matchingifis time consurn'ingand involves continuous checking which process if does not "lend: "itsel toouantity production;

Conventionallyy the control gridoand: focusing gridare/held in a predetermined'spacedirelationshipby Ia jigandthen:mountedcon .ceramic `aside rods orbyfsupports fused-ina:glass/bead. Suche procedure p1aces,f:-par-ts :of tlfle.l .grida supporting structure under strains, which; When-uponagemoyal of Athe.jig-:cerises a change in the relative ,spacing of the ftwogrids Inacouracies ini this gridfespac.- ing produce variations the. control? -gm'dncut-,

off `vo1tage. It is,necessaryfthat:these cutofi voltages be Within certain limits. A` large variation from the required voltage indicates .a poor gun structure which must be discarded.

v In the conventional design of control gridthe electrode yconsists of a cylinder havingan `aperf tureddi'sc yclosing one end. thereof. This grid cylinder isA used-to `support 1a cathode structure. Also, this grid assembly'presents a large areato theother electrodes in the electron gun, andi thus results-in aflarge input capacitance.- ySuch a large input capacitance is a rserious disadvantage espe,` cially for applications in which a high frequency signal is impressed .on the 4control grid as in televisionV applications.

It has alsoiibeensthefpractice Vtoller-ing the .ends of the :heater-iilament out through the lower open end Lof .the gun structure :over .the center of the .tube stem. `Due `to itsl'fragileconstructiomthe heater :filament is mounted separately-by welding to :thefstem leads after the rest of `thezvgunstructurehasebeen monntedaon .the tube stem.. Due ,to close .spacingfbetween the l gunand the tube stern; it has been difficult to insert a Weldingtool in this space Vorjoining the lament vto its leads. Furthermore, itiis desirable to mount lthe gun structure close to` the tube stem to provide as short 1a; neckas possible for the -cathode ray tube. Such closefmoimtne of the ,gun .Structure to the tubestem is prevented by the conventional Ifila-l ment mounting..

It is,Y therefore,gan `object of my invention zto pmvidcan .electron gun structure comprising :few par-,ts and whose `dit:lcrisicns are not limitcdiby close tolerances.

It iis also an object of my invention toE provide an. ,electron euri `structure designed for rapid assembla 1t :islaocther obiect of muri-ventina to provide a gun.structurromprsins a plurality :of Subassemblies :of fsirnpliiieddesign .It .is also cb ectzcf ,my ,invention i@ erotic# an electron suo- -structcrecharing :accurate eri@- cathose and'control .grid-.toxicomane.arid spacings.

3 to the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a partial sectional View in elevation of an electron gun structure according to my invention;

Fig. 2 is an elevational view in section of a cathode-grid assembly incorporating the novel structure of my invention;

Fig. 3 is an enlarged partial view of the contro grid subassembly of Fig. 1; v

Fig. 4 is an elevational view of thecathode filament subassembly of Fig. 1, according 'to Vmylinvention;

Figs. 5 and 6 are elevational sectional views ofv a control grid assembly according to modifications' of my invention; and

Fig. 7 illustrates a device for lixing the cathode sleeve to its support ceramic.

Referring to Fig. 1 there is illustrated anv electron discharge tube of the cathode ray type having an envelope 10,preferablyof glass,closedat one end by a stem'press l2. Mounted within the tubular envelope i8 is an 'electron gun structure, to be described, for accelerating and vfocusing a beam of electrons on a fluorescentscreen `Ilv at the otherend I3 of the dischargetube. Such a structure illustrated in Fig. 1 may be incorporated in a cathode ray tube, for example. The end of the tubular envelope may be enclosed in a base element i4 if desired through which extend base pins I8. Sealed through the glass stem l2 of the tube l0 are a plurality of stem leads I8 for supporting the electron gun structure within the tubular portion i0 as well as for forming electrical conductor means between the base pins IB and the respective leads to theelectrodes of the gun structure. Mounted on two of the stem leads I8 are a pair of ceramic support rods 28 and :22. Fixed to the ceramic supports 28 and 22 is a grid support cylinder 24. Also mounted on the ceramic support rods 28 and 22 and spaced axially within the tubular envelope I0 from the support cylinder 24 is a first anode electrode comprising a cylinder 26.

Within the tubular grid support 24 are mounted a plurality of electrodes in a manner disclosed in detail in Fig. 2. As shown in Fig. 2 the upper end of the` grid cylinder24 is closed by a circular plate 38 having an aperture 32 in the center thereof. The apertured plate 38 comprises a grid structure which is utilized as the second or shield grid of the electron gun. The tubular grid 24 has an opening or aperture -25 in the side wall thereof, the purpose of which will be explained below. This opening 25 inthe preferred form shown in Figs. 1 and 2 extends from the lower edge of the tubular electrode 24 to a predetermined distance below the top edge of the electrode. Mounted within the support electrode 24 is a ceramic disc 34 having a peripheral ridge portion 35 extending above the upper surface of the disc 34 and held in abutment against the under surface oi' the apertured plate 38.

As shown in detail in Fig. 3 -the disc 34 has at its center an apertured opening 4| coaxial tothe shield grid opening 32. The under surface of the ceramic disc 34 is machined to forma recess 45 coaxial with the aperture 4I and having a greater diameter than the recess 4I. A control grid is mounted within the apertures 4I and 45 of the ceramic disc 34. The preferred form of the control grid is shown in Figs. 2 and 3. This control grid comprises a grommet or eyelet 44 tted into the aperture 4I of the supporting ceramic disc 34. Eyelet 44 preferably'has a flanged portion fixed by welding to a grid plate 42. Grid plate 42 is preferably a small circular disc having an aperture 43 at its center. Plate 42 is tted into the recessed portion 45 of the ceramic disc and xed to eyelet 44 so that aperture 43 is coaxial to the grid shield aperture 32. A control grid conductor lead 43 is xed to the control grid plate 42 and extends from the grid plate out through the opening 25 in the side of the shield grid cylinder 24 as shown in Figs. 1 and 2.

Fixed immediately below the ceramic support disc`34 is a supporting ceramic cup 36. The ceelectrodey24 so that the lip 39 of the cup is posi-` center.

ramic cup 38 is arranged within the cylindrical tioned in abutment against the lower surface of the ceramic disc34. Through the bottom of the ceramic cup 36is formed an aperture 31 at its Coaxially mounted within the central aperture 31 is a tubular cathode electrode 5D. Cathode tube 58 is fixed to the ceramic support cup 36 by the forming of peripheral ribs or beadings 54 above and below the supporting portion of the cup 33. Beadings 54 are pressed out of themetal wall of thetubular cathode 58 and forced against the adjacent portions of the ceramic 3B so as to tightly lock the tubular cathode 50 to the support ceramic cup 36. The upper end of the cathode tube 50 is closed, as shown in Fig. 1 by a cap portion 52. Fig. 2'shows one form of a possible tubular cathode 58. Howeven it is possible to form the cathode 58 as a cup closed at one end by a drawing operation from a single piece of metal. The upper surface of the cathode cap 52 is usually coated by a mixture of the oxidesof the alkaline earth metals to provide a source of electrons as is well known in the art. This activated surface of the cathode cap 52 is accurately spaced at a predetermined distance from the control grid 42.v A cathode conductor lead 56 is fixed to the cathode sleeve 58 at 58 and extends radially through the aperture 25 in the side wall of the supporting shield grid cylinder 24. Y

To provide the desired amount of electron emission from the activated surface of the cathodefcap-52, the cathode 58 is heated to an appropriate temperature. For this purpose a heater'lament 60 is mounted so as to extend upwardly into the tubular cathode 50. The cathode heater lament `6l) is mounted on a second ceramic cup 38 which is coaxially mounted within the supporting shield grid cylinder 24 in such a manner that the lip 53 of the ceramic cup 38 abuts against the lower surface of the cathode support cup 36. In the center region of the bottom of the ceramic cup 38 are formed two-

apertures

62 and 64 as shown in Figs. 2 and 4. A pair of heater lament leads 66 and 68 extend across the center region ofthe lower surface of the ceramic cup 38. The ends v'lil and 'I2 respectivelyof heater leads 66 and 68 are respectively anchored within recesses 14 in the bottom of the ceramic 38 (Fig. 2). The opposite ends respectively of the heater leads 66 and 68 extend upwardly through apertures 15 and 11 (Fig. 4) within the wall portion of the ceramic cup 38.

To assemble the cathode heater filament within its support ceramic cup 38 the heater leads 66 and 68 are provided with a shape disclosed in Fig. 4. The ends 'I6 and 18 of the heater ilament leads are threaded through the respective openings 15 and 11 in the ceramic cup wall until the other ends 'Ill and l2 are fitted tightly into the Vrespective recesses 14 in the bottom of the ceramic cup 38. The ends 16 and 18 of the laenmarca 5. menu leadsiarenthenrbent sharply4 at1f909 sofas..-to extend ra'diallytaway'ifromfthe :center-aofi the .ce' ramic; cup reim. Grooves. :33; Landrziare provided iristheaipper vsurface of. the ceramic .cup 38 tore-.z spectively' receivewends .la and 18 of: the filament: leads :flushfto` the. upper surfacev of.` the cup :lip:v Theflam'entvends Stand 63 ,of heater filament 60;-.areithreaded respectively through the-Lopeningsafzgfandd inthe .bottom ofthe ceramicnm Theinlament :ends: et `and 63 -may be .thenireay speotively Weldedltothe lamentleads 65 and (58..` This arrangement `iixes the .heaterilament BD betweenvthe'leads. 8 and As shown in Fig.' 4 an;additional groove 1,51. is. formed infthe lip portion -53of the Aceramic oup-38. The-groovet't permits, the passage: therethrough of the cathode lead 563Iand allowsthe lip .surface 53 of the cerarn. icaacupa to tflush'to the under surface of: the rstceramic cup 36.` i

As shown.V in:Fig.,2 the ceramic supports 34;". 3d andx38iiare locked together one against :the other-between the screen gridqplate Scand'. a angedaringgdii vwhich is pressed into the openendiof the support cylinder.` 2d and welded `to :the sideszthereof to tightlyhcld the several ceramics in fposi-tionl t v Asshown invFig..2 theicontrolgrid .42 .comprises; a relativeiy small` surface area. In the conventional design for an electron gunl the conitrollgrid was formed as. a `supporting cylinder. similan tothe supporting grid cylinder 24 of Fig. 2u.. Such aisupporting `control -gridcylinder pre'- sented .a large. area to the other electrodes within the gun. and resulted in a large input capacitance.: Aflargepinput;capacitance is aserious disadvan--. tagexesp'ecially. for-applications in whicha high frequency signal is impressed on the control grid as in.televisioniapplications. The eyelet lill and gridfpla'te i2 .of Figs. 2 and 3 present a much smallernsurface area exposed to adjacent electrodes ofthe electron gun structure andthus.- eliminates `the large input capacitance which is such a .disadvantage in conventional gun, structure.

Furthermore, in conventional electron gun construction..itxhaszbeen .a problem to obtain the: cor` rectnspacing. between the control grid and the seconder screen grid to within close tolerances. Inaccuracies in. this control grid-to-screen grid spacing produce variations in thefcontrol grid cutoff voltage. These cutoi voltages are required tobe Within' certain limits and any large variation from therequired voltages will produce a poor=gunfstructure which frequently mustbe discard-ed. The'particular. construction shown in. Fig.: 2` provides ameans and a method vioraccurately. obtaining the required control grid-toscreengrid` spacing. The ceramic disc 3d is preferably. pressed out in a metal die from a pasty ceramic' material. The discs are'then fired'after which they may be machined to provide the required shape. In the construction of the ceramic disc-i3d there may be variations in the height of therib: 35 above the ysurfa-ceoi the disc 34. The rib `35. forms a means for spacing Athe grid plate 42 from the screen gridplate 33. `The variations in the ribs 35 of the Iceramic disc 34 may be compensated for by the depthto which the recess 45. of 'disc 34 is machined out. This recess t5 can be machined very accurately toa depth within plusor minus 1 mil of the desired amount; That iszthedepth towhichthe recess 45 is cutde-` termines thefspacing betweenthe control .grid plate. 42; and the shield `grid plate 30. This structural l relationship v of f grid plates f'and i 4.2.. .-providesr .fa :simple land' accurate. i method Vf or asseiri:d

blingf; the two. grids.'.rel'ative..to eachzother, With.A

the desired spacing. i

Figsn5 :anda :disclosewmodications `in theform ofthe .control grid 'structure disclosedv in' Figs. 2

andt'B.: .Inf'Fig-- ;5,a` fors'instance; the .control gridE takes .thef'formxof an eyeletiimountedonsa ceramic disc "s The eyelet ongrcmmets com prisesfs.. fiangeduportionzrM -which .is fitted into the recess :85 -rnaohinedinto the flower surface of.

supportingdisc v86. v. The. depthto. Whichthe-recess 35 Voffceramicdisc-3 .is machined determines the spacing-,between the controigrid 88 Land its corresponding shield grid. Eyeletf .823 @is rmly fixed to the ceramic supportvdisc 36. Lbygbending over `a lip portion' in contactnwitntheupper.surface ofi` the. disc T86.. This lipjl: ofrtheueyeletwmay beturned over-by La spinning process.. In. this modification.l of Fig; 5 the grid-.eyelet Biis imade fromI solid .stock-and'. is machined to the desired' In Figs avthird-modicationo the control .grid

is.I yshown in which `a flanged eyelet. 9d `is inserted through a central-.aperture-QS. of a supporting.

:ceramic disc Si). The flangedfpcrtionio the eyelet 34-is welded either beforeor.` after its insertion inthe'aperture .25 toa gridplateiZfy corresponding to plate -i2i.oFigsf.. 2 and.. The gridplate' 32 iits intoithe recess 9| machined to the desireddepth.

depth lproviding;:the .required spacingzzbetween;

size ofthesspacer members.asvveil-as'variations in the rrelative position of'y the .cathode sleeve .to its supporting ceramic.. disc produce nonuniform.`

cathode-control. grid spacing...

Thef'structure foi. Fig 2 shows ani improved method for mountingfa cathodesleeve `iill-1-elative to\ awcontrolgrid structurefli.-` Ity is desirable thatthe spacing between the top` ofthe cathode electrode and the control grid .conform-to .a pre1 determinedtamount and: Within ratherv small tolerances.:` In the constructionshownin Fig. 2

theiceramiccup 35-formsboth an `insulating support .for the: cathode tube 5l!v as `Wellas a means for spacing the cathodeelectrodefrom. the `control grid 42; Withithe construction of Fig.:2,.the i ceramic cup, 36 .need :not be .formed with any great accuracy; The cathode-tofccntrol.grid

spacing 2-is `determined by the relative position of thefcathode` sleeve' 53ste the ytop ysurface :33 of. the

ChIP-lim.y Thisspacingibetvveen:thewactivatedfsura ama-oie facezof th'e.cathode cap 52'and the top surface 39 of the cup lip may be accurately: formed by the method shown in Fig. 7.

In Fig. 7 the cathode sleeve 50 may be assembled to the ceramic cup 33 by first inserting the open end of the cathode cup 50 through the aperture 30 in the bottom of the cup. The cup together with the cathode is then turned upside down n a polished metal surface 98 so that the lip 39 of thecup is flush with the surface 98. A spacer block I 00 is placed between the cathode cap 52 and the polished surface 9B. A tool inserted into the upper open end of rthe cathode sleeve 50 as shown in Fig. 7, forms the expanded peripheral rib 54 in the metal wall of the cathode tube. This tool consists of a sleeve |02 in which is slidingly mounted a pin |04 having at its lower end a T-shaped head |06, Between the head |06 of pin |04and the end of sleeve |02 is positioned a rubber ring or washer |03. The tool is inserted into the open end of the cathode cylinder 50 until the lower end of the sleeve |02 is approximately ush with the inner surface of the bottom of the ceramic cup 35 as is shown in Fig. 7. The T-headed pin |04 then is moved in an upwardly direction as indicated by the arrow while the sleeve |02 is maintained in position. The upward movement of pin |04 causes the T-shaped head |06 of the pin to compress the rubber washer |00. The rubber washer |08 is of such resiliency that the compression forces the sides of the cathode tube 50 outwardly in a radial direction to form a peripheral rib 54 which determinesthe position of the cathode sleeve 50 relative to the surface 33 of the lip of the ceramic cup 36. This relationship between the cathode sleeve 50 and the ceramic cup 3E can be varied to any desired amount by the use of another spacer block similar to block |00 having a different dimension. To accurately lock the cathode sleeve 50 to the ceramic 36 the tool may be Withdrawn a suicient amount away from the cathode sleeve 50 and another rib 54 pressed outwardly from the surface of the cathode tube 50 on the opposite side of the ceramic 36 so as to firmly lock the cathode sleeve 50 to the cup 36 and prevent any relative movement axially therebetween. Fig. 2 shows this arrangement.

The particular construction of the cathode assembly shown in Figs. 2 and 7 eliminates the use of several parts. Furthermore, this form of cathode assembly does not require the tedious process of matching a, spacer to the particular cathode assembly conventionally used in order to provide the required cathode-to-grid spacing. Furthermore, as pointed out above the ceramic cup 36 need not be made to any close tolerances since the spacing between the activated surface of the cathode and the control grid plate is determined by the relative position of the activated surface of 52 to the surface 39 of the cup lip. This spacing is accurately obtained by the operation of assembling the cathode sleeve 50 to the ceramic cup 36 as disclosed in Fig. 7.

In the conventional type of electron gun construction the heater filament is usually mounted after the cathode grid assembly has been mounted on the glass stem of the discharge tube. Since the cathode heater filament is rather` fragile the ends of the filament are welded or fixed to their respective leads after the cathode grid assembly has been. mounted within the tube. Welding of the ends of the filament to their respective leads requires the inserting of a welding tool into the center portion of the tube stem between the cathode grid assembly vand thesurface of the. stem. The spacing of the gun parts during this opera.- tionis so close that the welding procedure is difiicult. Furthermore, it also necessitates the vpositioning of the cathode grid assembly far enough above the surface of the glass stem so as t0 permit insertion of the appropriate welding tools.

In theparticular `construction shown in Figs. 2 and 4 the cathode filament may be assembled to its lead structure and to its supporting ceramic cup 38 separately before the gun structure shown in Fig. 2 is mounted on the tube stem l2.

The several electrode subassemblies shown in Fig.V 2 are eachv assembled prior to their insertion in the supporting cylinder 24. After the grid plate 32 is mounted in the desired position in one end of the screen grid cylinder 24, the control grid assembly is positioned within the cylinder such that the rib portion 35 abuts against the lower surface of the grid plate 30. The ceramic'cup 3B with the cathode electrode 50 accurately positioned therein is next inserted into the open end of the cylindrical electrode 34. Next, the second ceramic cup 30, with the cathode heater filament mounted thereon, is inserted into the cylindrical electrode 34 so that the cathode heater lament is positioned within the cathode sleeve 50. The second ceramic cup 38 is positioned so that the surface 53 of the cup lip is iiush against the bottom surface of the first ceramic cup 36. The flanged locking ring 40 is then pressed into the open end of the support cylinder 24 and is forced against the bottom surface of the second ceramic cup 38 where it is welded to the inner wall of the support cylinder 24 to rigidly lock the three

ceramic supports

34, 36, 38 Within the screen grid cylinder 24.

rIhe several electrode subassemblies are inserted into the support cylinder 24 so that the electrode leads extend through the opening 25 in the side wall of the support cylinder. Furthermore, ceramic cup 3S is positioned within the support cylinder 24 so that the groove 47 in its upper surface 39 will lit over the control grid lead 46 and permit the lip surface 39 of cup36 to lie flush with the bottom surface of the control grid support disc 34. Likewise, the second ceramic cup 38 is positioned so that groove 5'! will fit over the cathode lead 55 and allow the lip surface 53 of the cup 38 to lie flush against the bottom surface of the rst ceramic cup 36.` When the several parts of the cathode grid assembly of Fig. 2 have been fixed together as described above, this cathode grid assembly cylinder 24 may be mounted onthe

ceramic side rods

20 and 22 in the desired position. Since the electrode leads 46, 56, 'l5 and 'I8 extend laterally from the supporting grid cylinder 24, this cathode grid assembly may be mounted closer to the glass stem portion l2 of the discharge tube. This provides for shorter envelope l0 which is desirable for certain installations.

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What I claim as new is:

1. A cathode-grid assembly for an electron discharge device, said assembly comprising a tubular support member having an apertured wall portion, an apertured shield electrode structure mounted within said support member at one end thereof providing a shield grid, a control grid unit including an insulator` support within said tubular support member and an apertured'control elec-l :andere trodeiiixedthereto i and spaced:from said apertured shield electrode, a lhollovv cathode electrode,

`insulatingirrieans mounting f said i cathodenwithin said-,tubular support-:member adjacent said .con-

-ztrol electrode,V a cathode heater filament mounted l .Within saidv cathode, leads fixed tothe ends. of said lfilament and vextending :through said .apertured Wall'iportionof said support member.

2.A'cathodegrid assembly forv an'electron discharge device,` said assembly comprising a support cylinder, a shield grid electrodecorri-prising` a 'centrally apertured plate-coaxiallyl mountedV Within said support cylinder andY closingone i end thereof,

`a control-grid unit -including `acmetal4 g-rommet iforming' a-control grid electrode'andfinsulating `cylinderlvilith the closedend of said tubularcathode Vspaced from said control grid electrodepn the side thereof opposite from -said shieldHg-rid plate,- a cathodeheaterunit Within said support cylinder vand including a heater filament and insulating means -mounting saidf-iilarnenti-Within said-cathode tube. 1

3..A cathode discharge device comprisingean evacuated envelope, a tubular shield electrode u mounted Within said envelope, a lplate element fixed to and closing one end of said tubular shield electrode, said plate element having la grid aperture therethrough coaxial With said tubular electrode, an annular insulating support disc having a peripheral rib projecting from one surface, said support disc coaXially mounted Within said tubular electrode With said peripheral rib in abutment against said apertured plate element to space said disc surface therefrom, a control grid eyelet xed through the center of said annular support disc, `an insulating cathode support cup coaxally mounted Within said tubular electrode With the lip of the open end of said cup fixed in abutment to said annular support disc, said cathode support cup having an aperture through the center of the bottom thereof, a tubular cathode electrode having one closed end, said tubular cathode electrode coaxially mounted through bottom aperture of said cathode support cup with the closed end of said cathode electrode axially spaced from said control grid eyelet, an insulating heater filament support mounted within said tubular electrode in abutment to the outer bottom surface of said cathode support cup, a plurality of filament lead elements fixed to said filament support, and a heater filament mounted on said lead elements and extending into the open end of said tubular cathode electrode.

4. A cathode grid assembly Ifor an electron discharge device, said assembly comprising a support cylinder, a Wall portion closing one end of said support cylinder, said Wall portion having an aperture through the center thereof forming a shield grid electrode, a control grid unit including a ceramic disc coaxially xed Within said support cylinder and a metal eyelet xed through the center of said ceramic disc and forming a control grid electrode, said ceramic disc having a projection on one side thereof spacing said disc and said control grid eyelet from said shield grid Wall portion, a cathode unit including a first ceramic cup coaxially mounted Within said support cylinder with the lip of said ceramic cup abutting the other side of said ceramic disc, said ceramic cup having :l fing, grid aperture .therethrough coaxial with said -an nperturethrough the center. ofthe bottom thereof, andra tubular-cathode electrode coaxially mounted-throughthe aperture of said ceramic cup :.rvith1one endfof"l said `cathode electrode axially :spacedfromisaid control. grid eyelet, anda cath- :ode` heater ,unitxincludinga second ceramic cup co- 1axiallymounted.Withinsaidesupport cylinder with lthe'zlip ofsaid secondwceramic cupabutting the -bottomvsurfacefof said first ceramic cupwhereby the 'other' yend of V .said tubular cathode electrode iextendswinto ysa-id :second ceramic cup, a pair. of :spacedgconductor `leadsr-.xed to said second cenarniah cupaandfa: heater.r filament. mounted' be- `tween said conductorileads andinextending `into said futher, ,endzonsaid tubular cathode electrode. o5., Ancathodecdischargedevice comprising lan `ovacuatedf-envelope, a. tubular: shield electrode =mountedwithin said envelope, said tubular shield electrode having. anw aperture in `the Wall thereof, anlate element fixedto and. closingy one end oifsaid 'oular shield electrode, said `plate element' `havytubular electrode, `an annularinsulating support disc having a peripheral rib` projecting frornone surface, said I support -ldisc coaxially mounted within-saidtubular electrodevvith saidperiipheral `ribin abutment against said 'apertured'plate` eletm'ent `tospace Ysaid-disc surfacethereif-rom, acori- `trorgrideyelet'fixedthrough the-center of said annularsupport disc, a--first conductor -leadnxed to said grid eyelet and extending through the aperture in the wall of said tubular shield electrode, an insulating lcathode support cup coaxialy mounted Within said tubular electrode with the lip of the open end of said cup fixed in abutiinent to said annular support disc, said cathode support cup having an aperture through the cente of the bottom thereof, a tubular cathode electrode having one closed end, said cathode electrode coaxially mounted through the bottom aperture of said cathode support cup with the closed end of said cathode electrode axially spaced from said control gridl eyelet, a second conduct-or lead fixed to said tubular cathode and extending through the aperture in the Wall of said tubular shield electrode, an insulating heater filament support mounted within said tubular electrode in abutment to the outer bottom surface of said cathode support cup, a plurality of filament lead elements fixed to said filament support, and a heater filament mounted on said lead elements and extending into the open end of said tubular cathode electrode, said lament lead elements having a portion extending through the aperture in the side Wall of said tubular shield electrode in spaced relationship to said first and second conductor leads. i

6. A cathode grid assembly for an electron discharge device, said assembly comprising a support cylinder having an aperture in the wall thereof, a Wall portion closing one end of said support cylinfdeir. said wall portion having an aperture through the center thereof forming a shield grid electrode, 'a control grid unit including a ceramic disc coaxially iixed within said support cylinder and a metal eyelet fixed through the center of said ceramic disc and forming an apertured control grid electrode, said ceramic disc having a projection on one side thereof spacing said disc and said control grid eyelet from said shield grid, a conductor lead fixed to said control grid eyelet and extending through said aperture in the Wall portion of said support cylinder, a cathode unit including a :rst ceramic cup coaxially mounted Within said support cylinder with the lip of said ceramic cup abutting the other side of said ceramic disc, said ceramic cup having an aperture through the center of the bottom thereof, and a tubular cathode electrode coaxially mounted through the aperture of said ceramic cup with one end of said cathode electrode axially spaced from said control grid eyelet, a cathode conductor lead fixed to said cathode electrode and extending through the aperture in the Wall of said support cylinder, and a cathode heater unit including a second ceramic cup coaxially mounted Within said support cylinder with the lip of said second ceramic cup abutting the bottom surface of said rst ceramic cup whereby the other end of said tubular cathode electrode extends into said second ceramic cup, a pair of spaced conductor leads fixed to said second ceramic cup, and a heater lament mounted between said conductor leads and extending into said other end of said tubular cathode electrode, said pair of lament conductor leads extending through the aperture in the wall of said support cylinder in spaced relationship to said control grid conductor lead and said cathode conductor leads.

7. A cathode grid assembly for an electron discharge device, said assembly comprising a ceramic disc having an aperture at the center thereof, a metal eyelet xed through the aperture of said ceramic disc to form a grid electrode, a first ceramic cup mounted coaxial with the ceramic disc andwith the rim ofsaid ceramic cup abutting one face -of said disc, a second ceramic cup mounted coaxially'to said ceramic disc and said rst ceramicY cup and with the rim of said second ceramic -cup'abutting the outer 'bottom surface of fsaid first ceramic cup, means locking together said ceramic disc, said first ceramic cup and said second ceramic cup to prevent relative movement therebetween,l said locking means including a metal plate electrode having an apertured portion, said apertured portion spaced from the other face of saidceramic disc and from said eyelet electrode, said rst ceramic cup having an aperture through the center of the bottom portion thereof, a tubular cathode electrode coaxially xedfin said aperture of said rst ceramic cup with one end of said tubular cathode electrode closelyfspaced from said eyelet electrode and the other 'end of said tubular cathode electrode extending into said second ceramic cup, a pair of heater iilament leads fixed'to said second ceramic cup, each of said filament leads having a portion extending over the outer surface of the center portion of said second ceramic cup, a cathode heater lament lpositioned within said tubular cathode, each end of said cathode lament eX- tending through the bottom of said second ceramic cup and xedly mounted to one of said lament leads.

-V JOSEPH KELAR.