US2728007A - Cathode ray tube gun structure - Google Patents

Description

1955 D. D. VAN ORMER 2,728,007

CATHODE RAY TUBE GUN STRUCTURE Filed July 1, 1953 2 Sheets-Sheet 1 INVEN TOR.

flaw/ml. Vail firmer 495M LL 9 Dec. 20, 1955 D. D. VAN ORMER 2,728,007

CATHODE RAY TUBE GUN STRUCTURE Filed July 1, 1953 2 Sheets-Sheet 2 5'? g f 4 +2 0 my 1 6 g] 15 5 g a 44 40 fi INVENTOR.

United States Patent Oi CATHODE RAY TUBE GUN STRUCTURE David D. Van Ormer, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application July 1, 1953, Serial No. 355,309

7 Claims. (Cl. 313-82) This invention relates to electron discharge devices of the cathode ray type and particularly to mount structures and means to support electrodes in such devices.

The electron gun structure of cathode ray tubes convcntionally includes a cathode electrode, a control grid, an accelerating screen grid electrode, and a second accelcrating electrode. These electrodes are normally formed of tubular members which are mounted successively along a common axis within a tubular neck portion of the cathode ray tube envelope.

The cathode electrode of such devices consists of a small tubular electrode which is closed at one end and is mounted coaxially within the tubular control grid electrode. The mounting of the cathode electrode is a ceramic disc to which the tubular cathode is fixed through an aperture at the center of the ceramic disc. The combined ceramic disc and cathode are mounted within the tubular control grid by locking the ceramic so that the closed end of the cathode is at a predetermined distance from one end of the control grid. The control grid at this end is closed by a transverse wall portion having a small aperture at its center aligned with the closed end of the cathode. This end of the cathode is coated with an electron emitting material to provide a source of electrons which are urged through the aperture of the control grid The electrostatic fields between these gun electrodes form the electron emission from the cathode into an electron beam directed substantially along the axis of the tubular neck portion of the electron beam path and on the end wall or face plate of a larger bulbous portion of the tube envelope. Defiecting means are normally provided for scanning the electron beam over the fluorescent screen in any desired manner, such as in a rectangular raster, for example.

The gun structure as described above is normally mounted within the tubular neck portion of the envelope by relatively heavy leads welded to the metallic portions of the tubular electrodes and to metal pins scaled through the end of the tubular neck end, which are in turn connected to the base pins of the tube. The structure thus described is of a conventional design and is well-known and is shown and described in greater detail in U. S. Patent 2,496,127 to Joseph Kelar.

Similar structures are used in cathode ray tubes used in television viewing picture tubes. However, with the trend toward television picture tubes of larger fluorescent screen area, the tendency is to also extend the length of the tubular neck portion of the tube envelope. However, the length of the front-to-back dimension ofthe cathode ray tube is limited from a practical standpoint by the size of the television cabinet in which the tube is to be mounted. It is desirable to keep the dimensions of such' cabinets, from front to back, as small as possible so as to enable the cabinet to be passed through apartment-size Patented Dec. 20, 1955 ICC doorways, for example. Furthermore, a cabinet with small front to back dimensions is more desirable from an aesthetic point of view. One solution has been in providing a larger deflection angle of the electron beam. However, another solution would also be to eliminate the spacing between the gun and the stem of the tube, which is occupied by the leads extending from the electrodes to the base pins of the tube.

Cathode ray tubes of the type described also have a relatively inefiicicnt cathode structure. The cathode material on the closed end of the tubular cathode electrodes is normally heated to thermionic temperatures by a double helical filament coil threaded into the open end of the tubular cathode. During tube operation heat radiated from the coil filament heats the tubular walls of the cathode electrode to a temperature atwhich sufficient heat is conducted by the cathode walls to theemitting end wall to provide a copious emission of electrons from the thermionic coating. Thus the cathode coating is indirectly heated by heat conducted to it by the side walls of the tubular cathode. Furthermore, the contact between the tubular cathode wall and the ceramic support disc provides a loss of heat energy so that a cathode structure of the type described uses an excessive amount of electrical energy. Standard cathode filaments used in the tubes of the type described require 0.6 ampere of current at 6.3 voltages or a heat dissipation of 3.78 watts. This amount of energy constitutes a relatively large drain of power from the circuit system of the tube. It is desirable that such heater power he reduced to a minimum.

Cathode ray tubes of the type described also usev spacer elements between the cathode supporting ceramic disc and the apertured closed end of the control grid electrode to provide the predetermined cathode-grid spacing. These spacers have taken the form of metal eyelets, annular ceramic insulators or the like. If the cathode to grid distance is critical, these spacers must closely conform by a small tolerance to the predetermined spacing distance. This requirement necessitates close inspection of each spacer and a process of matching spacers of a certain size with cathode-ceramic assemblies of a specific size, since there are variations both in the spacers and in the mounting of the cathode within the ceramic. Such a procedure of matching a spacer to a cathode-ceramic member requires careful time consuming work.

It is, therefore, an object of this invention to provide a novel and simplified electrode structure for a cathode ray tube.

It is a further object of this invention to provide a simplified and accurate mounting structure for a cathode grid assembly in a cathode ray tube.

It is another object of the invention to provide cathode ray tube having shorter front-to-back dimension.

It is another object of the invention to provide a cab ode filament unit for a cathode ray tube utilizing a mini mum of power output.

It is a further object of the invention to provide a cathode-grid assembly utilizing a simplified and accurate mounting structure.

The invention is in the structural design of a cathode control grid and accelerating grid assembly. The novel assembly comprises a supporting tubular accelerating electrode in which a pair of parallel disposed support plates of an insulating material are locked in place. Between the supporting plates there are fixed a control grid elec- Figure 1 is a partial sectional view of a cathode raytube in accordance with the invention.

Figure 2 is an enlarged sectional view of part of the gun structure of the tube of Figure 1.

ama qo-v 3. Figure 3 is a cross sectional view along lines 3--3 of Figure 2. v

Figure 4 is a sectional viewl of part of the structure of Figure 1- at right angles. to the section; of Figure 1-.

FigureSisa sectional view of: a simplified gunstruc: ture utilizing a different form. of the invention;

Figure l discloses a cathode ray tube whichmaybe used for-television viewing. The tuheconsistsof an.

evacuated :envelope having a large :bulbousshell orconelike portion. 10. and a. tubular neck portion 12 fixed to the bulbousportion. Within the'tubular'neelc12"is'mounted an electron gun 14- for. forming-and directing-a=beam of electrons substantially alongthe 3 axis of -the neck portion 12-toward a fluorescent screen 16 formed on the-inner' surface of the end-wall face plate 18- of the bulbousenvelope portion 10;

Two pairs of'coils are formed into a neck yoke '24).

mounted on the envelope neck 12 for scanning the. electron beam in any desired'pattern over the surface of the fluorescent screen 16. The scanning coils are conventionally arranged withthe coils of'each pairconnectedin a seriesandmounted on opposite sidesof the tubularv neck 12'; Each pair ofcoils is connected to appropriate sources of saw tooth currents for providing the scanning fieldsto move the electron beam inthe desired raster pattern over the fluorescent screen 16. A focusingcoil 22f may be used to focus the electron beam to a; fine/spot on he. fluor scent Screen u n be. op on.

The electron gun of conventional cathode ray tubes normally consists of a plurality of tubular electrodes. The cathode of the gun comprises a small tubular electrode having. one end closed by asolid wall portion upon which is formed a coating oflelectron emissive material such as arnixtnre of barium andstrontium carbonates.

The .tubular cathode is mounted Within a tubular control grid whichis closedjatone end'by a solidwall'having a small aperture at its center. with the. coated end-wall of the cathode closely spaced from and alignedwith the central aperture of the control" grid, The gun also isnormally formed with a'plurality of tubular accelerating electrodes spaced along a common axis and'having apertures therethrough aligned with the central aperture of the control grid for the,passage therethrough of thelelectrons from the cathode in the formof a beam. Electron guns of this type are shown and de scribed patent'to J; Kelar 2,496,127;

In accordance with. theinvention, however, the'clectron' gun 14 is provided With-a simplified andmovehelectrode arrangement. As shown in Figures 2, 3, and 4; thecathode electrode consists of a tubular member 24 which is mounted on and extends between two parallel sheets" of mica 26: Furthermore, the'tubular cathode 24"is en-' closed in an open ended'box construction 28 having at the box b'y the two mica plates-26.

The mica grid assembly 26 -2 8 -'is; mounted "within a tubular accelerating electrode 32 Ametaidiaphragm or walljportion-34 is fixedby welding, for example; across one end of the tubular accelerating electrodo 32'as shown in Figure 2. The diaphragm 34 iis'spaced' a sutlicient'distance from the'adjacent end oftubular member' 32"to.

pr v de. a ap-l ke. streams.atth tend AS shown in ure. he .mi anl tes. 2.65am. ,i.1m-:n

snedsqtha ti thex arefix sttd th t i nfir ture 28, they will slip tightly into;.thegtuhnlat ,electitode.

'Ihe cathode is mounted.

greater detail; for example; in the above cited The assembly forms 32 to rigidly hold the mica-grid assembly 2628 within the tubular member 32 and will prevent lateraldisplacement of the assembly within the tubular member 32. A retainer ring 36 is slipped into the open end of the tubular member 32 and into engagement With the adjacent ends of the mica sheets 26 at which point the ring 36 is Welded or locked by other means to support member 32 to hold the grid-mica assembly 26-28 in position and to prevent any axial movement thereof.

Opposite side Walls of tubularmember 32. are cut away: as shownatS S, for example on both sidesandinali'gnment with the ends of the tubular cathode 24. The openings 38 allowthe mounting of the cathode 24- into the mica-grid assembly after the assembly: has been fixed within the tubular accelerating support member 32. Cathode 24 is mounted in openings punched through mica sheets 26 to fit cathode 24 tightly. Also the openings 3.8.permitpassing of lead 40,.toithev cathode 24.. Within the. tubular. cathode 24. there. is positionedv a folded. filae mentary cathodefilament 44.for raising the. temperature.

of. the cathode to thermionictemperatures. The leads 46 of the cathode filament 44 are also broughtout of one.

ofthe. openings 38 in member 32 and ftxedto. appropriate basepins 48 extending through the pressor. closedv end 47 of the tubular neck portion 12., A- lead 42fpasses. through a centralopening in retainer ring 3.6, tothe. con:

trol grid box 28. Cathode andgrid leads. 40and'42 arealso fastened to other base. pins 48 respectively. The pins 48 extendthrough the press 47 and are connected to pins. 49 fixed into the tube base 50.

The outer surface of the, tubular cathode electrode124.

is. coatedjwith electron emitting materialsuchas a mix: ture of barium and. strontium carbonate to. provide. a sOl fce of electrons within the tube. Aligned with a. coatedsurface of cathode 24there is an aperture 52..in. the top of the grid. box 28. to provide passage. therethrough of electronsfrom'the cathode surface. accelerating electrode diaphragm 34 also has formed at its .center an aperture 54in alignment withapertureSZI and the coated cathode surface.

Spaced alongthe axis of tubular member 32-is a second tubular accelerating electrode 56. for providing a high, positive potential gradient in. the beam, path and. to.. accelerate the electrons emitted .from cathode. 24 'to. high velocities. Tubular electrode.5.6is. closed at its opposite. end-by an apertured diaphragm. or: wall portion 58 Mounted. at the edges of thediaphragrnSB are spring fingers or spacers 60 for positioning the end'ofithe. accelerating electrode 56 on the. axis of the tubularneck portion 12; Also the spring fingers 60jmake'electri c'alj contact. between electrode, 56 and a conductive. wall coat; ing 62extending from the end of {electrode v56 to a.ppi nt adjacent the fluorescent screen 16of the tube. i

The operationv of the tube is that in,whi ch current.

passing through filament 44 heats tubular cathode 24' to a temperature at which electrons are freely emitted from the cathode coating. The control grid electrode 28 is normally. operated; at a. range of potentials negative to.

the potentialof the cathode 24. The accelerating elecnode 32, however, isoperated at a potential of'several' hundred volts positive to cathode 24, while electrode 56 is'operated'at .the highest potential inthe order of ',from.

1"to' .18,QOQ volts depending upon the use andi'sizegof' the cathode ray tube. As is well known, thenegativev potential of electrode 28'can be varied until the positive accelerating'potential of electrode 24 will extendthrough aperture 52 and pull electrons emitted from thecathode' coating through aperture 52. These electrons are'a'cceleratedihrough aperture 54 into thetubular electode 56."

The difference in potential between electrodes'32'and' 56 provides electron lens field which aidsij forrning he le tr nsintoa eam. Thebeam electrons, h ve re .dixe g ng in. thei pa ge ro gh the tubular.

' electrode 56;. The field.of.the.focusing,coil,.22.pIOvidea amonuergingaction. onelectrons of the .beamand causes;

The.

them to converge or become focused to a small welldefined beam spot on the surface of the fluorescent screen 16. The voltages shown in Figure 2 represent those which have been applied to the respective electrodes during successful operation of a tube of the type described. However, these values'need not be limiting.

The adjacent ends of electrodes 32 and 56 are cut at an angle to the common axis of these electrodes, as shown in Figure 2. This has the effect of tilting the lens field between electrodes 32 and 56 so that the beam electrons passing into this field are bent from their axial beam path in the direction of the axis of the tubular envelope member 12. A magnet 66 mounted on the tubular neck portion 12 provides a magnetic lens field for bending the beam back onto the axis of the neck 12 and to direct the beam through the apertured diaphragm 58 at the end of the tubular electrode 56. The arrangement provides a means for trapping the negative ions formed within the electron beam. This does not constitute a part of the invention and is more fully described in the copending application of L. E. Swedlund, Serial No. 130,775 filed December 2, 1949. Furthermore as part of the ion trapping arrangement, the electrodes 32 and 56 mounted on a common axis are inclined at a small angle to the axis of the tubular neck portion 12.

The novel electrode mounting arrangement, as described above and consisting of electrodes 24, 28 and 32 provides an assembly which can be both simply and ac curately made. Mica can be accurately cut and punched to very close tolerances. Accordingly, mica plates 26 can be accurately cut to provide the correct spacing between cathode 24 and the control grid aperture 52 to Within very close limits. Furthermore, the spacing between the control grid aperture 52 and the accelerating diaphragm 34 can be accurately maintained from tube to tube and within the required limits. Thus the assembling of the electrodes 24 and 28 to the mica spacer elements 26 can be done easily and accurately. The mounting of this cathode grid assembly within the accelerating electrode support 32 can be accomplished easily and without any loss of accuracy in electrode spacing.

By bringing the leads 40 and 46 of the respective electrodes through the side wall of support electrode 32, it is possible to mount the electron gun 14 closer to the press 47 of the tube. This results in a shorter tube neck, which is of an advantage in large tubes where the screento-stem dimension becomes critical.

An additional advantage of the structure described is the ability to use a filamentary folded heater within the cathode 24 in place of the reverse wound coil heaters conventionally used. The difficulty of using a tubular cathode having the emitting surface on a closed end of the cathode, as described above, is the necessity of using an excess amount of power in order to raise the temperature of the tubular cathode sufiiciently high to heat the coating at the closed end to thermionic temperatures. However, the structure shown in Figures 2 and 4, for example is that in which the filament 44 is in direct con tact with the cathode Wall upon which is coated the thermionic material. This provides a much more ei'ficient manner of heating the electron emitting coating and enables the use of a much less power. Furthermore, there is little loss of heat to the mica supports 26, as was true with the conventional type cathode mounted in a heavy ceramic near the emitting end thereof.

The electrode 28 may be formed as a single piece and wrapped around to form its boxlike structure. The bottom of the box or the side 29 of electrode 28 opposite from the grid aperture 52 forms a light shield to prevent a light from the heated cathode 24 from being directed onto the glass surfaces of the press 47 and in turn being reflected down the tube neck 12 onto the fluorescent screen 16. Grid 28, however, need not be made from a single piece wrapped into the desired shape, but may be made of a plurality of metal sheets if desired.

Figure 5 shows an adaptation of the invention of Figure 2 in which some features of the invention can be used in a triode type cathode ray tube. In Figure 5, the mica sheets 26 are locked together by metal plates 68 and 76 on the top and bottom respectively and by side plates 72, of which only one is shown. The tabs 74 corresponding to tabs 30 of Figure 2, for example, extend through the micas 26 from each of the electrode plates 68, 70 and 72 and are bent or twisted to rigidly lock the plates 6S, 7% and 72 to the mica sheets 26 to form a rigid box structure. A cathode 24 of the type described in Figures 2 and 4 is mounted in a similar manner through the mica strips 26 and has its outer surface coated with an electron emitting material. The coated surface of cathode 24 is mounted in a predetermined spacing from an aperture 76 in plate 68. This cathode-grid-mica assembly is mounted on base pins 48 by welding the pins 48 directly to the plate structures of the assembly and also by the leads 75 which extend from the filament 44, the cathode 24 and plate 68 to the several base pins 48. The accelerating electrode of the tube of this type consists merely of wall coating 60 which is extended down the neck 12 of the tube envelope to overlap the grid plate 68. The operation of the tube is of the type disclosed in the above cited application to L. E. Swedlund.

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 is claimed is:

1. An electron gun for a cathode ray tube, said electron gun comprising, a tubular electrode, a pair of support members of electrically insulating material supported within said tubular electrode, a tubular cathode electrode supported Within said tubular electrode transversely to the axis of said tubular electrode and by said insulating support members, and an apertured plate electrode supported by said insulating support members within said tubular electrode and adjacent said cathode electrode.

2. An electron gun for a cathode raytube, said electron gun comprising, a tubular electrode, a first apertured metal plate member fixed Within and transversely across said tubular member, a pair of support members of electrically insulating material mounted within said tubular electrode on opposite sides of the axis thereof in contact With said transverse metal plate member, a tubular cathode electrode supported within and transversely to the axis of said tubular electrode and by said insulating support members, and a second apertured metal plate member supported within said tubular electrode by said insulating support members between said cathode electrode and said first metal plate member.

3. An electron gun for a cathode ray tube comprising, a tubular electrode, a first apertured plate member fixed within and closing said tubular electrode adjacent one end thereof, a pair of support plates of electrically insulating material mounted within the other end of said tubular electrode and facing each other on opposite sides of the axis of said tubular member, an edge of each of said insulating support members in contact with said first apertured plate member, a tubular cathode electrode supported within and transversely to the axis of said tubular electrode by said insulating support members, and a second apertured metal plate member fixed within said tubular electrode to said insulating support members between said cathode electrode and said first metal plate member, said first and second metal plate members each having an aperture therethrough on the axis of said tubular members and aligned with a surface portion of said cathode electrode.

4. An electron gun for a cathode ray tube, said electron gun comprising, a tubular electrode, a pair of support members of electrically insulating material supported within: saidtubular electrode, a: tubular cathode electrode supported within: and transversely to the axis oi said tubular; electrode: and by said insulating support members; and? an apertured platev electrode supported withinsaid. tubular electrode by said insulatingsupport-mem hers adjacent said cathode electrode, said tubular electrodezhayingz an aperture in the side Wallthereofiandlead members connected to one of said electrodes Withinsaiditubular member and passing through said-aperture inztheside'wallthereof.

5". electron: gun fona cathode ray tube, said elec-' tron; gum comprising, a tubularelectrode, a first apertured; metaliplate member fixed within and transversely across said tubular: member, a pair ofsupport mernbers of: electrically insulating material mounted within said tubular electrode-on opposite sides of the axisthereof in'scontaet with said transverse metal plate member, a tuhulari cathode electrode supported Within and transversely tOithC axisof said tubular electrode and by said: insulating support members, anda second apertured metakplate-membersupported within said tubular'eleo trode.by saidinsulating support'members between said cathode; electrode andisaid'first metalplate-member, said' tubular electrode having an aperture in the side wall thereof and lead members i connected :to one of said-electrodes within said tubular member and passing-through said aperture in the sidewall thereof.

6. An electrongun for a cathode ray tube'compris inggatubular electrode, a plate member fixed within andclosin'gzsaid' tubulari electrode adjacent one endthereof, said plate member having an aperture therethrough, a pair'of support plates of electrically insulating'material mounted within the other end of said tubular electrode andzfacing. each other on opposite sides of the axis of said tubularmember, anedgeof each of-said insulating support members in contact with said first apertured plate member, a tubularcathode electrode supportedwithin and transversely to the axis of said' tubal-an electrodeby: said insulatingsupport members,- and a second tubularmetal memberfixed within said'tubular 'electr'ode between said insulating support members and enclosing said tubu' larcathodeelectrode, said second tubular member hav ing an aperturetherethrough between a surface" of; saidcatliode electrode and said aperture'in said plat'e member.

7. An electron gun-tor a cathode ray tube, said elec-' tron gun comprising, a tubular electrode, a metalplate' member'fixed within and transversely across said tubular: member," saidplate member havingan aperture there tl1rough,:a pair: of support members of electri'cally insu-' latingmaterial mounted within-said tubular electrode on opposite sides of the axis thereof in contact with said transverse metal plate member; atubular'cathode electrode supported Withinandtransvers'ely to the a'xisof-said tubularelectrode and by said insulatingsupport members, and-a second tubular'metal electrode member supported: within: said tubular electrode between said insulating support members and enclosing said cathode: electrod'e, said second tubular electrode member having-an aperture through thei wall=thereof aligned with said aperture in said metal plate member a-nd a surfac'e'portion of said tubular cathode electrode; said cathode surface portion having a coating of 'therm-ionic emitting -materialthereon.

References Gited inth'e fileiof this-patent UNITED STATES PATENTS 2,194,547 Haines 'Mar. 26; 1940: 2,223,908 Bull- Dec. 3, 1940 2,231,961 Soller -Feb'. 1 8, 1941 2,268,196 Pierce Dec, 30, 1941 2,496,127 Kelar a Jan. 31, 1950 2,516,752 Carbrey July 25, 19'50

Images