US2950406A - Precision cathode-ray tube assembly - Google Patents

Description

Aug. 23, 1960 G. F. BARNETT ErAL 2,950,405

PRECISION cATHoDE-RAY TUBE ASSEMBLY 5 Sheets-Sheet 1 Filed May 10, 1954 ila Il 0 Aug. 23, 1960 I G. F. BARNETT' ETAL 2,950,406

PRECISION cATEoDE-RAY TUBE ASSEMBLY Filed May 1o, 1954 5 Sheets-sheet 2 /A/YE/V MRS.

ug- 23, 1960 G. F. BARNETT ETAL 2,950,406

PRECISION CATIFODE-RAY TUBE ASSEMBLY Filed May 1o, 1954 5 Sheets-Sheet 3 ug- 23, 1969 G. F. BARNETT ETAL 2,950,406

PRECISION CATHODE-RAY TUBE ASSEMBLY Filed May l0, 1954 5 Sheets-Sheet 4 1N VEN TORS. 60)/ F. EAK/V577 GO/PDON A?, SPE/VCE@ Wurf/ff .SALGA/0257- Aug. 23, 1960 G. F. BARNETT ErAL 2,950,406

PRECISION cATEoDE-RAY TUBE ASSEMBLY 5 Sheets-Sheet 5 filed May lO, 1954 s aten Zidfidd Patented Aug. 23, lt)

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PRECISION CATHODE-RAY TUBE ASSEMBLY Guy F. Barnett, Roslyn, Gordon R. Spencer, Perlrasie, Walter F. Baghurst, Sonderton, and George W. Pratt, Ambler, Pa., assignors to Phiico Corporation, Philau delphia, Pa., a corporation of Pennsylvania Filed May 10, 1954, Ser. No. 428,744

19 Claims. (Ci. 313-69) This invention relates to electron beam tubes and more especially it relates to cathode-ray tubes having a plurality of separately controllable electron beams.

A principal object of the invention is to provide an improved organization of elements which constitute a plural-beam electron gun having the utmost precision as regards dual-beam control, dual-beam spot size as well as stability and accuracy of dual-beam deflection, and dual-beam trajectories.

Another principal object is to provide an improved organization of elements which enable a dual-beam electron gun to be manufactured and assembled so that the finished gun has optimum mechanical strength consistent with optimum precision whereby such guns may be made in large quantities with uniform characteristics.

Another principal object is to provide an improved dual-beam electron gun for use in so-called color television picture tubes and the like.

The art of cathoderay tubes has reached a comparatively high state of development and has enabled such tubes to be used satisfactorily in the fields of oscillography, black and white picture reproduction, radar scopes and the like. However, in certain highly specialized fields of use, amongst which may be mentioned color television reproduction, the structures and assemblies which are used in conventional black and white cathode-ray tubes, have not been found entirely successful. One of the serious problems which has thus far faced the color television picture tube art is that, for a given neness of picture detail, the beam spot must be focused to a much smaller size on the screen, as compared with the black and white spot. This is an unavoidable concomitant of color television systems since each elemental area of the subject matter must be separately scanned in three subdivisions or so-called tri-color elements, whether these elements be in the form of tricolor dots or tricolor strips. Another problem which exists in the color picture tube art is that for a given intensity of color brightness, as compared with black and white tubes, the transducing action of the electron beam in converting its electron energy into visible color brightness on each screen element, is sustained for only onethird of the time as compared with black and white screens. This, therefore, requires a more intense electron beam in the color television tubes as compared with that in the black and White tube. Ordinarily, such a rf quirement would not be serious where a single beam of scanning electrons is used. However, when two or more beams are used, it is necessary to maintain the same deflection for both beams, and it is necessary to make sure that the beams do not intermodulate each other. The last mentioned problem increases enormously as the beam intensity increases. `It is of no importance where the beam intensity is extremely low, for example in the order of a few micro amperes, but it becomes a difiicult problem where beam currents of the order of hundreds of micro amperes are necessary.

As a result of the stringent conditions color television tubes must meet, it has not been found possible until the advent of the present invention to manufacture satisfac torily and with the desired uniformity and precision, plural-beam tubes using a single gun for color picture reproduction especially where the two sections of the dual-beam must at every instant be identically deflected. We have found that the order of precision required for such dual-beam tubes is entirely different from that of ordinary black and white cathode-ray tubes.

Accordingly, a principal object of the invention relates to a novel d-ual-beam electron gun wherein the elements of the gun are iuterlocked with utmost precision, and high intensity dual-beams can be developed in close proximity and without undesirable cross modulation therebetween.

Another object is to provide a novel dual-beam electron gun employing respective individual beam intensity control electrodes which are physically as close as possible, in conjunction with a novel construction of electrode supports and spacer means which are specially shaped to reduce the likelihood of current leakage between the electrodes, which leakage tends to result from vaporization or sublimation of cathode material and the like on adjacent parts.

An important feature of the invention, which enables the foregoing objects to be obtained, is the provision of a special and novel single electrode which acts not only to sheld from each other the closely spaced beams emerging from grids from each other so Aas to prevent undesirable beam intermodulation, but also acts as a single beam converging electrode for both beams after they leave their respective control grids. Another important feature of this electrode is that it is positioned in a specially chosen region of the dual-beam trajectory so that it exerts negligible focusing or defocusing action on the two beams and also draws substantially no current from either beam. `Furthermore, the positioning of this composite shielding and conversion electrode, because of its thickness and rigidity, is capable of acting as a rigid backing member to enable the remaining parts of the gun to be clamped or fastened tightly together as a unit without danger of mechanically distorting the parts and especially Without mechanically distorting the dual control grids.

A further feature relates to a novel cathode-ray tube for color television and the like, employing a fluorescent screen composed of adjacent strips of different fluorescent materials of elemental width in the direction in which they are scanned by the color transducing beam, and a novel form of dual-beam electron gun having means to develop in closely spaced relation to the color transducing beam, a separate monitoring beam, with both said beams mutually isolated so far as cross modulation is concerned.

Another feature relates to a novel dual-beam electron gun having a pair of beam intensity control electrodes in lthe form of flat conductive strips mounted in substantially coplanar but spaced array, with the adjacent spaced ends of the strips as close as possible and each strip having a specially shaped beam controlling perforation.

A further feature relates to a ruggedized dual-beam electron gun wherein the parts are fashioned and cut to highly precise dimensions to enable the various parts ofV the gun to be assembled in clamped stacked array without danger of distorting or changing the precise predetermined spacing between the gun electrodes; and without requiring complicated assembly operations.

A still further feature relates to the novel organization, arrangement, and relative location, shaping and interconnection of parts which cooperate to provide an improved dual-beam electron gun, and which renders the 3 gun suitable for mass production even kby automatic machinery, while preserving the optimum of precision in the characteristics of the dual-beams.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed'descriptions and the vappended claims.

In the drawing which shows,by way of example, certain preferred embodiments,

Fig. 1 is a perspective view of a cathode-ray tube according to the'invention, with part'of the enclosing bulb j broken away to show the interior construction more clearly;

Fig. 1A is ra magnified perspective View of a portion of the fluorescent screen of Fig. l;V

Fig. 1B is a sectional View o fFig. 1A taken along the line 1B-1B thereof;

Fig. 1C is a magnified view of part of a cathode subassembly used in explaining the invention; Fig. 1D is a magnified view of part of a cathode coating shaving device;

Fig. 1E is a schematic diagram of a modified cathode;

Fig. 2 is a greatly enlarged view of part of the header of the tube of Fig. l and showing-the gun construction in more detail;

Fig. 3 is a sectional view of Fig. 2, taken along the line Fig. 4 is a'sectional View of Fig. 2, taken along the line 4-4 thereof;

Fig. 5 is a sectional View of Fig. 4, taken along the line 5-5`thereof;

Fig. 6 is a sectional View of Fig. 4, taken along the line 6-6 thereof;

Fig. 7 is an exploded view of the electron gun shown in Figs. 1 to 6;

Figs. 8, 9 and 10 are respective sectional views taken along the respective lines 8 8, 9--9, and 11i-1G of Fig. 7;

Fig. 1l is a sectional view of Fig. 9, taken along the line 11,-11 thereof;

Fig. 11A is a sectional view of Fig. 9, taken along the line 11A-11A thereof;

Figs. 11B, 11C, 11D, 11E are diagrams used in explaining certain features of the invention;

Fig. 13 is an enlarged sectional view of Fig. 10, taken along the line 13-13 thereof;

Fig. 14 is a plan view of one of the clamping or retainer members for the parts of the electron gun according to the invention;

Fig. 15 is a sectional view of Fig. 14 taken along the line 15-15 thereof;

Fig. 16 is a sectional view of-Fig. 14 taken along the line 16-16 thereof;

Fig. 17 is a schematic composite circuit diagram and tube according to the invention.

The invention is in the nature of an improvement on the kind of cathode-ray tube disclosed for example in copending application Serial No. 307,868, filed September 4, 1952, issued as U.S. Patent 2,712,087, and nds its primary utility in cathode-ray tubes used for the reproduction of colored television subject matter and the like. However, as will be apparent from the ensuing description, certain features of the invention are of great utility in other systems where two or more electron beams are used, one of which is a signal transduc'mg beam, and the other of which is a monitoring or indexing beam. The invention also is applicable to other devices lsuch as storage cathode-ray tubes employing a main writingbeam and an auxiliary reading or erasing beam. Since, however, there are certain problems and diiculties peculiar to the dual-beam color televisionY tube, the invention will be described in connection with that kind of tube.

a uorescent screen formed of so-called tri-color dot sets and the excitation of the appropriate dot in each tri-color set at any given instant is determined by the arrival angle of one of three separate beams from respective electron guns, in conjunction with a so-called tri-apertured masking plate mounted :infrontof the fluorescent screen. Apart from the diiculty and cost of manufacture of the tri-color dot tube is the limitation which it inherently possesses in that Vthe peak beam electron quantity actually striking each tri-color dot is physically limited by the size of the aperture in line with each dot, which aperture must be relatively close to the fluorescent screen. Since the color dot selection is a function of the angle at which the beam approaches'the screen, and also Vof the positions of the mask apertures relative to the phosphor dots, itrbecomes increasingly diicult to effect the desired selection as the size of the screen is increased.

The second main category of television color tube employs a screen with adjacent parallel color strips, as distinguished from dots, and a series of deviation electrodes closely adjacent the strips to change the angle of arrival ofthe normally deflected beam so that it strikes the proper color strip. Here again, as in the rst kind of tube, there is a physical barrier in the form of the deviation electrodes just ahead of the screen. Furthermore, in this second type of tube an additional deflection system is required to effect the color deviation, in addition to the usual beam-deflecting system for scanning. Y

The third category of color tube with which the present invention is primarily concerned avoids the disadvantages of both the above two categories. It has the advantage of the adjacent color strips of the second category, but instead of using a single beam which requires conventional beamdeflection and separate beam deviation for color selection, it uses a dual-beam, and both of these beams are always subjected to the same deection. One of these beams is referred to herein as the color transducing beam, the other beam is referred to herein as the monitoring or indexing beam. Y

As indicated in the perspective View of Fig. '1, a tube according to the invention, may comprise any well-known form of evacuated enclosing bulb consisting of the usual glass neck portion 10 which is joined to the funnel-shaped portion 11, this funnel-shaped portion being closed off by the transparent viewing face portion 12.. rl`he opposite end of the neck portion 10 has sealed thereto any well-known type of glass header 13 through which the various lead-in wires'14 are sealed preferably, although not necessarily, in circular array. Supported within the neck portion 1@ in the Ymanner to be described hereinbelow, is an electrode assembly according to the invention. This assembly comprises in general a dualbeam electron gun 15 which will be described in detail hereinbelow, and an'elong'ated tubular anode 16. rhe anode 16, in accordance with one phase of the invention, is of much longer axial length than that customarily employed in black and white cathode-ray tubes, and is supported rmly but resiliently against the inner Wall of neck 11 at a plurality of spaced Vplanes by means of the metal spring fingers to be described.

Gun 15 is, according to the invention, designed to develop a dual-beam, the two beams being indicated by the numerals 17, 18 (Figs. 1 and 1A). Beanr17 will be referred to herein as the color transducing beam, while beam 18 will be referred to as the monitoring or indexing beam. Surrounding neck 10 is any well-known form of electromagnetic focusing yoke schematically indicated at 19 for focusing the dual- beams 17, 18, as respective minute spaced Yspots on the uorescent screen 2i?. Screen 20 (Fig. 1B) may be attached or deposited directly on the interior surface of face plate 12, for if desired, it can be applied to any suitable light transparent sheet which can be mounted within the tube, in close proximity to face plate 12.

Screen 20 may comprise a series of regularly repeated sets of tri-color strips 21, 22, 23, which extend parallel to one another in a vertical direction as seen in Fig. l. Preferably these strips are spaced slightly from each other, but need not necessarily be. Each of these tri-color sets comprises a strip 21 which, for example, may be of any well-known uorescent material which uoresces blue when struck by the transducing beam 17 strip 22 may be of a material which fluoresces red, and strip 23 may be of a material which iuoresces green. In accordance with well-known color principles, even when the strips of each tri-color set are energized in time succession by the beam 17, the combination of colors because of optical lag and because of the phosphorescent elect, produce a resultant single visual color whose hue will be dependent upon the relative intensities with which the individual color strips in each set are excited by the beam 17. The elemental width of the beam 17 in the direction of the horizontal line scan should not be greater than the Width w of each color strip, and preferably is substantially less than in the conventional black and White picture tube, wherein the scanning beam, for substantially the same picture definition, can have a width approximately three times as wide as the beam 17. Therefore, in the type of tube according to this invention, it is necessary, for image brightness equivalent to the black and white tube, that the beam 17 have a peak intensity which is many times that required in such black and white tubes. Furthermore, it has been found necessary to prevent intermodulation between the dual- beams 17, 13. This intermodulation prevention is achieved by a novel beamconvergence and beam-shielding electrode, which constitutes a very important feature of the invention.

By any well-known magnetic horizontal and vertical deflection yokes represented schematically at 24, surrounding the neck 10, the two beams 17 and 1S are moved synchronously or in unison so as to scan the screen in successive parallel lines extending substantially transverse to the length of the tri-color strips of screen 20.

All the fluorescent strips 21, 22, 23, etc., are provided with a thin electron permeable coating 20a, of low secondary electron-emissivity but -which is electrically conducting and transparent to the beam 17. Typical of such materials is aluminum, magnesium, or beryllium. The coating 20a can be deposited so that it also acts as a mirror to reect the fluorescent light from the fluorescent strips outwardly through the face plate 12 which face plate, of course, should be substantially uniformly transparent to all the desired visible light rays from the screen 20. Suitably deposited on the coating 20a on the side facing the gun 1S are spaced strips 2Gb of a material having a high secondary emissive power or at least of a power which is substantially higher than that of the coating 20a. For example, the strips 20h may be of gold or other high atomic number metal such as platinum or tungsten, or of an oxide such as magnesium oxide or any other equivalent high ratio secondary emitter. The secondary emission strips 20b are applied over the coating 20a but only in registry with fluorescent strips of a particular color, for example the secondary emission strips 2Gb may be applied so as to be in registry over the red uorescent strips 22. By means of the coating 20a, the screen as a whole can be connected to the positive pole of a suitable direct current power supply by means of a conductor sealed through the wall of the cathode-ray tube bulb. For a detailed description of the action of the indexing beam 1S with respect to the secondary emission strips 2Gb, reference may be had to U.S. Patent No. 2,742,531. Suffice it to say for the present that each time the indexing beam 18 strikes one of the secondary emission strips 20h, it produces a pulse of secondary electron current. This pulse can be picked up by a suitable electron collector electrode, such lfor example as a conductive coating on the interior wall of the bulb adjacent to, but spaced from, the screen 20.

We have found that beause of the extremely small Width of the scanning beam and because of the high beam intensity required, conventional gun constructions used in black and white tubes are not feasible for this type of tube. Furthermore, we have found that the parts of the gun must be made with extreme precision and yet capable of assembly in such a Way that in the final assembled unit the desired uniformity of precision is maintained, even between large batches of such guns.

For that purpose, the gun construction such as illustrated in the drawing has been devised and has been found to produce the desired results. Referring to the drawing, the gun 15 includes a cathode sub-assembly 25 consisting of a tubular metal sleeve 26 (Fig. lC) of nickel or the like, which is closed ott at its forward end by metal cap 27 also of nickel which may be welded to the tube 26. The cap 27 may have a dat surface or it may have a rounded or dome-shaped contour, as shown schematically in Fig. 1E. 1f desired, the elements 26 and 27 may be formed from a single extruded metal piece. The cap 27 is of a suicient thickness so that it maintains its close spacing with respect to the adjacent control grids even when it is raised to electron-emitting temperature by the usual heater element (not shown) mounted Within sleeve 26. Cathode sleeve 26 passes through a corresponding central opening in a disc 28 of any non-conductive refractory ceramic such for example as lavite, steatite, etc., and is held irmlypin place in the ceramic for example by peripheral beads 29, 3% (Fig. 5), formed in the body of the sleeve 26 which beads abut against the respective opposite faces of disc 2S.

We have found that one of the important items of precision which enables the gun to produce the desired results, is that the front surface of ceramic 28 must be absolutely free from any undesired surface non-uniformities. For example, in the case of the at surface of ceramic 28 the surface atness should be to an accuracy of .0001 inch because this face of the ceramic forms the basic reference plane upon which the precision assembly of the remaining parts depends. For that reason, ordinary ceramic surfaces should be avoided. For example, as shown in the highly magnified partial view of a conventional ceramic body (Fig. 1C) there may be high and low points and if these surface irregularities occur it may not be possible to maintain the desired precision of location and spacing of the various parts of the gun. As represented by the wavy dotted line surface in Fig. 1C, the usual unground ceramic member would be uneven and would thus provide an irregular reference surface. In order to avoid this diflculty the ceramic 28 is preferably surface ground by any technique well-known in the precision lapping machine art, to provide a perfectly smooth planar reference surface as indicated by the undotted surface line in Fig. 1C. For ex ample, the ceramic may be lap ground in a machine used in lapping the surfaces of piezo crystals and the like so that the atness of the front face of ceramic 28 is within an accuracy of .0001 inch. Therefore, when the cathode sleeve 26 is assembled in the ceramic, the plane of the flat face of cap 27 is parallel to the front face of the ceramic Within plus or minus .0002 inch. It will be understood, of course, that the invention is not limited to a cathode having a flat face adjacent the control grids. If desired, the face or cap on the cathode may be domeshaped so as further to reduce any possibility of substantial change in spacing between the cathode and grids as the cathode is heated.

The external face of cap 27 is then coated by any well-known process used in the coating of cathodes for cathode-ray tubes, for example by spraying a mixture of barium and strontium compounds which are eventually broken down in the conventional processing of cathoderay tubes to produce electron emissive oxides.

Here again it has been found necessary to subject the cathode coating to a precise shaving operation. Onemanner'of doing this is to hold the cathode sleeve vWith its coating in-a suitablejigl (Fig. .1D) having agauging surface 32 which can Y.be swept by a l`sharp edged shaving blade 33 so that the coating -24 has a uniformly rgauged thickness. Therefore, when Vthe coated cathode isnssemoled and 'anchored-in ceramic 28, thedistance from .the at forward gauging face-fof that :ceramic to .the surface of coating 34 is held to Ya iixed value plus or minus .0()01 inch. Y

The above-described precision cathode subassembly is larranged to be concentricallyisupported Withinrarcylindrical metal member S5 having a cylindrical .36

Vwhich'is `a close iit around the ceramic 123. Ihe `forward end of lmember 35 is bentrat'right langles 1-to .form aflat annular liange 37 forming Aa central window 38. Wall S6 adjacent the forward end of member -35 .is vprovided with diametricallyopposite cutouts or windows 3:9, .49 through which are arranged to be radially inserted a pair of at metal control grid strips 41, 42. Each of these strips has 'a Aright-angled bent-backportio- n 43, 44, to which respective exible metal connector 4strips 45, 4o, can be welded, 'these flexible strips in turn being welded at their opposite ends lto respective control Vgrid lead-in prongs '47,' 4S, sealed vacuum-tight 'through the glass header d3. Y

' As shown in the greatly enlarged partial '-view of Fig. l2, the control "grid strip 41 has agridlaperture 49 through which beam 17 passes for intensity control. Likewise, grid strip 42 hasV a grid aperture 50 through which the beam 18 passes. While, as shown, these grid apertures are of a shape each having a cylindrical section 51 of predetermined diameter Vjoined to a truetoconical section 52, they may be -of different shapes. Each grid aperture is located lclose to the 'edge of Yits Vstrip so that the Adistance .D between the center lines of the two grid openings is approximately .026 inch. Likewise, when the grid Vstrips are finally assembled -in place, their adjacent edges arespaced apart by aminute gap 53, for example lof '.0015 to .005 inch. VIt has been found thatthis small kgap enables the 'two grids to lbe insulatingly spaced from eachother, and yet it lis fof suflicient narrowness to provide an effective barrier against the passage of electrons therethrough.

However, because of the minuteness of gap 53, Vit has been found necessary to design 'the insulated 'parts which contact the grid and the cathode so that the possibility of conductive current leakage between the grid and cathode is substantially eliminated. Furthermore, it is necessary to 'maintain 4the strips 41, 42, free from mechanical distortion Aand with a minimum `spacing between the grids and cathode. In order to `'insulate and at the same time Y-to space the `control grid strips 41, 42, from the Vnext adjacent dual-'beam Vconvergence and inter-beam shielding electrode 55, there is .provided a at insulator ring 56 of mica vor ceramic having a thickness of .005-.01'0 inch.V Ring 56 has acentral lenlarged circular opening provided 'with diametrically opposite slots 53, 59, and is assembled in place so that slots '58, 59, overlie the gap 53, the said slots being substantially wider Vthan the 'gap 53, 'thus reducing the `likelihood of leakage across Athat gap. From the foregoing it -will Ybe seen that the spacing d1 (see Fig. 13) between the composite electrodeV 'and the flat control grids is only'a small fraction of the distance D between the center llines `of the respective grid openings. ecause of this substantial diiference in relative spacings it is possible lfor the electrode 55 Vto act as an electrostatic shield 'whereby variations in potential of one grid do not cause any modulation of the beam passing through the other grid.

The composite beam convergence and inter-beam shielding electrode 55 which forms a highly important and novel feature of this invention is arranged to seat against the inside vface of flange 37, and therefore `the outside diameter Aof electrode 55 closely ts 'the ins-ide ditimes thicker than the thickness of face 37 of member 35.-

Thus, electrode 55, in addition to performing thevarious electric functions to be described, also Yacts as a solid backing orstiffener for the entire gun. Preferably, the forward marginal'edge ilis roundly chamfered to t snugly Within the corresponding curved inner edge 61 of member 35.

VThe central part of the yforward face of electrode 55 is formed with :a :circular recess 62 having Va depth d of approximately .02 inch.Y The unrecessed thickness of electrode 55 :is provided with two spaced openings 63, i64, symmetrically located ion opposite sidesV of the center line of the :electrode,these two openings being spaced ey the unperforated central portion 65. Openings 63, #64, are spaced apart on centers adistance D which is the same as the spacing between Ithe centers of control grid openings 49, 50 (Fig. l2). Similarly, the openings e3, 64, each has a cylindrical portion 66 and a forward frusto-conical portion 67.V The two beams 17, 18, which emerge through the respective grid openings 49 and Se, would ordinarily diverge away from the central longitudinal axis of the gun. However, by choosing a suitable diameter and depth for the recess 62, and by choosing a suitable thickness for the insulator spacer 56, and by applying the proper potential to electrode 55, that electrode acts as aconvergence electrode for the beams. This causes the beams after they leave their respective control grid apertures to be subjected to a converging action. In the absence Vof such a V-convergence electrode, the

Ybeams after leaving their respective and closely spaced grid apertures would diverge. We have found that -unexpected and novel results are obtained by locating the .said Vcomposite shielding and convergence electrode'' yin a region extremely close to the control grids vand by applying to that composite electrode a potential which is substantially the same as the inherent field position potential at that region. In other words, the composite electrode 55 acts as an electrostatic shield between vthe two closely spaced beams emerging Vfrom the two grids while at the same time it acts to converge the emergent beams, 'and without drawing any beam current, and Without exerting any focusing lor defocusing action on the beams. Thus, the two beams maintain their accurate spaced trajectories so that they can be focused by a common focusing yoke 19 on to the fluorescent screen with the same spacing regardless of the portion of the fluorescent screen Zfisc'an'ned by the beams. Furthermore, the electrode 55 also acts through its central :unperforated portion 65 as an electrostatic shield to prevent crossmodulation between the two beams. lt has been found that in the absence of this central portion 65, the two *beams may undesirably cross-modulate eachother when used in certain types of circuits. To achieve this 'shield- 55 be extremely close to the grid openings 49, Si), .and this also Vminimizes the beam current drawn by it. .Also the electrode 55 is preferably maintained at a potential substantially the same as that of the region in the anodecathode eldin'which it is located, so 4that the configuration of the equi-potential lines is not substantially altered by its presence, and it does not exert any substantial Yfocusing or vdefocusing action on vthe beam. More particularly the face of electrode 55 confronting the .cathode 27 is preferably kept at this potential.

-In order to support the grids in their predetermined precise closely spaced planar relation with respect to the cathode, 'there .is provided Lan annular ceramic ring 168 (see Figs. 5, 6, and '9-l1).. Furthermore, its opposite hat faces are ground, Vfor example, by lap-,grinding to perfect smoothness and .ilatness This ringfis specially shaped and cutto :reduce ithe possibility of yleakage. be-

9 tween the cathode and the grids. One of the chief causes of such leakage is the sublimation or vaporization of conductive material from thecathode and adjacent metal parts, which material when deposited tends to destroy the desirable characteristics of the gun. In accordance with a feature of the invention, the ceramic ring 68 has its forward flat face 68a undercut with a pair of radially extending notches 69, 70, each of which has a tapered or inclined bottom wall 71, 72. The rear at face of ring 68 is annularly recessed to form an inclined shoulder 73. The inner peripheral face of ring 68 is also provided on diametrically opposite sides thereof With a pair of somewhat tangentially extending slots 74, 75. The particular angle of these slots is not critical so long as the slots do not extend substantially radially with respect t the cathode sleeve 26. The various slots and notches are specially cut and arranged as shown so as to cast shadows Where sublimation or Vaporization of conductive material would be likely to deposit. In other words, .these shadowed areas break the continuity of any conductive vsurface which might otherwise tend to form on the interior of the ceramic ring 68 and on the surface of the cathode ceramic ring 28. The explanation of this protective shadowing will be clear from the schematic views of Figs. 11B-11E. If a completely unnotched insulator ring 76 (Fig. 11B) were used to space the cathode 26 from the grids 41, 42, cathode material, Whether in the form of emission material or other conductive material vaporized from the cathode, would be ejected therefrom in all radial directions against the full height of the internal wall of ring 76, and would also be ejected over the face of ceramic ring 28 as indicated at the stip# pled areas in Fig. 11B. The continued deposition of this material would eventually produce a continuous conductive leakage path between the cathode and the grids.

On the other hand, by forming the downwardly inclined shoulder 73 on the ring 68, according to the invention, and as shown in Fig. 11C, there is always a shadowed area in the corner junction between the ring 68 and the ring 28, and this area is positively protected against deposition of conductive material. Similarly, in the case of a simple unnotched ceramic spacer ring 76, as shown in plan view (Fig. 11D) conductive material could be vaporized or sublimated in all radial directions and might eventually completely coat the entire inner wall of ring 76. By providing the ceramic spacer ring With one or more non-radially directed notches such as notches 74, 75 (see Fig. llE) it is not possible for the deposited material to form a continuous conductive surface since that surface is always shadowed against deposition by the non-radial notches.

lt should be observed that if simple radial notches were provided on the interior face of ring 76, as compared with the non-radial notches 74, 75, the desired discontinuity could not be prevented since the material would eventually deposit within the radial notch. Furthermore, as will be seen from Fig. llC, the forward face of the cathode ceramic ring 28 is also provided with a relatively narrow annular recess 77, which, as shown in Figs. 5, 6, and ll, lies under the shadowing notched shoulder 73. This further `decreases the likelihood of formation of a continuous conductive deposit on ring 28.

Furthermore, by precision lap-grinding of the forward flat surface 68a of ring 68, the desired precise close spacing between the cathode coating and the hat grids 41, 42, is permanently maintained. It has been found practical with this arrangement, therefore, to provide a spacing between the cathode and grids of as little as .003 inch plus or minus .0004 inch, while preserving the necessary freedom from deposit leakage.-

'Ihe manner of assembly of the various parts of the gun is as follows, referring to Fig. 7. The single composite beam-convergence, anti-cross-modulation electrode and stiener element 55 is inserted into member 35 until it seats against ange 37. Mica disc 56 is then inserted. The two grid strips 41, 42, vare then inserted from opposite radial directions through windows 39 and 40. Mica disc 54 is then inserted into member 35 until it rests against the ygrid strips. It should be noted that disc 54 takes no part in spacing the cathode from the grids ybut is merely used to insulate the ring 78 from the grids. Then, a steel retainer ring 78, having an annular bowed top 79 is inserted into member 35 Iand sprung against mica disc 54. Ring 78 should be made of very thin metal stock, for example of .O08 inch thickness and with its outside diameter a close iit to the internal diameter of member 35, so that the ring 78 can be sprung into place and pressed tightly against disc 54. Thereupon the peripheral wall of ring 78 can be Welded to the cylindrical wall 36 of member 35 at a plurality of spaced points around the periphery. The diameter of the circular opening in the top 0f ring 78 is slightly greater than the central opening in mica disc 54. Ring 68 is next inserted into member 35, and is centered therein by engagement with the edge of the central opening in mica disc 54. T his is to increase the leakage path between the two control grids, which would otherwise `be only the thickness of mica disc 54.

Pi`he cathode sub-assembly 25 is then inserted into member 35 until the cathode ceramic ring 28 abuts against lthe ceramic ring 68. Then the cathode sub-assembly retainer ring 8i) of any suitable design is inserted. Merely for illustration, ring 80 is shown in Figs. 14-16 as comprising an annular metal member having an outer wall 81 which is provided With six slots 82 spaced sixty degrees apart and with an inner wall 83 which defines a central opening 84 of much larger internal diameter than the diameter of cathode sleeve 26. The wall 83 has two diametrically opposite struck-out lugs 85, 86, leaving a pair of windows 87, 88. The iiat face 89 has twelve punched-out holes 90 formed by punching out 4the metal stock leaving four vertically extending triangular pointed lugs 91 around each hole. The retainer ring, therefore, provides sufficient frictional gripping to retain the various elements in their stacked position. However, before finally welding the retainer ring 80 in place it is necessary to adjust the gap 53 and to align the grid openings 49 and 50 with the corresponding openings 63, 64, in the composite electrodes 55, and it is also necessary to position mica disc 56 so that the slots 58 and 59 are in alignment with the gap 53. For this purpose, the composite electrode 50 may be provided with two additional holes 92, 93, which are diametrically opposite to each other so that by inserting appropriate rods carried by a suitable jig (not shown) and extending through the opening 38 in member 35, and thence through the openings 92, 93 and slots 58, 59, the proper alignment of these parts can be obtained. This jig may also include an additional pair of parallel rods which extend through the openings 73 and 74 and thence through openings 49 and 50 so as to align the said grid openings. When this alignment has -been obtained the retainer ring 88 is forced tightly against the ceramic ring 28 so as to clamp all Ithe stacked parts together with suicient clamping pressure, whereupon the retainer ring Sti can be welded to member 35.

Arranged to be mounted in coaxial alignment with the dual-beam gun is the anode 16 which may consist of an elongated metal tube having the end facing the gun beaded or turned back on itself, as indicated at 94 (Fig. 2). A rst set of three rigid radially extending metal lingers 95 are welded to the anode 16 and a second similar set of rigid radially extending metal fingers 96 are also welded to the anode 16. Likewise the gun cylinder 35 has welded thereto a iirst set of three rigid radially extending fingers 97, and a second similar set of three rigid radially extending metal fingers 98. The anode 16 is assembled so that the radial lingers thereon are in alignment with the corresponding ngers 97, 98, on the gun, and by means of a suitable gauge and jig (not shown), the anode cylinder V16 can be aligned coaxially with the gun 15 andjwith the proper spacing between the ange 37 and the adjacent end of the anode 16,Y whereupon the gun and anode 'can be rigidly united by means of a set of three rigid parallel glass canes 99, 100, 101, which can be softened by heat atrthe regions where they engage the radial' fingers.

In orderY to mount the gun and anode, assembly rigidly with respect to'the header 13, the gun cylinder 36 has welded thereto lat equally spaced pointsv three rigid metal angle - brackets 102, 103, 104, `which are located in alignment with andV welded to corresponding metal pinsV 105, 106, 7 in header 13. This avoids bending of the stem leads or pins, and prevents them from buckling :as they would otherwise tend to do when the guml and anode assembly is inserted into the neck 10 of the gla'ssbulb. We have found that it is important to support the gun and anode assembly with great precision in the neck 10 and for this purpose there is fastened to the forward end of the anode 16 a metal ring 108 carrying a set of six reversely bent -metal spring fingers 109 which are adapted to resiliently press against the interior of neck 10. A similar metal ring 110 is'welded to the anode ,16 approximately half way along its length and this ring also carries a set of three or more bent back resilient metal spring fingers 111 which also resiliently press against the inner face of the neck 10. With this construction considerable force is required to insert theY gun and anode mount within the neck 10. Therefore, in order to prevent planar distortion of the grids 41 and 42V during this insertion operation, the connector members 45 and 46, which connect the said grids to their corresponding lead-in pins 47, 48, are in the form of thin metal ribbons, which are bowed or bent outwardly intermediate their ends so as to provide suicient exibility which prevents grid distortion during the insertion of the mount.

When the header 13, which carries the mount including the gun and the anode 16, is sealed to the lip of the neck portion 6, the bulb is subjected to the usual exhaust, bombarding and gettering processes well-known in the art, the exhaustion taking place through a suitable exhaust tubulation (not shown) forming part of the header 13. This tubulation is in the well-known manner sealed of when the processing has been completed. A conductive coating 112 extends internally along the neck 10 and part of the funnel-shaped portion of the bulb and is contacted by the lingers 10S to form a continuation of anode 16. For a detailed description of how such a tube can be used to reproduce a color subject matter on the screen under control of received tri-color video signalsapplied to grid 41, reference may beV had to application Serial'No. 242,264, filed, August 17, 19'51, issuedas US. Patent 2,742,531.

Y Prom Vthe foregoing, it will be seen that there is provided a cathode-ray tube having the desired minuteness of cross section in the transducing beam 17 and in the monitoring or indexing beam 18, while maintaining the requiredy beam intensity for peak color excitation and also while preserving the fixed space relation between the two beam trajectories without cross beam intermodulation. It has been found that the desired conductive electrical isolation of the extremely close grids is obtained without danger of leakage, and it is possible to reduce the iluorescent vspot by asmuch as ve times that obtainable with ordinary cathode-ray guns. Furthermore, these advantagesV are obtained by using relatively simple electrode structures and assembly operations. It has also been found possible with the tubeas disclosed to produce high definition colored television picturesY with utmost brilliancy of` hues.

While in the foregoing the grid strips 41 and 42 are arranged with the` lineY joining the grid openings parallel tothe length of the tri-coior strips of screen Z0, it will be understood that .those grid openings may be oriented at any other angle with respectto the tri-color strips so long as the grid apertures are maintained in the same plane and are maintained the same distance with respect to the cathode emission surface.

As explained in said U.YS. Patent 2,7 42,5 3 l, the beam 18 acts as an indexing beam which, each time it strikes the secondary emission strips 2Gb, causes a pulse of secondary electrons to be emitted therefrom. This pulse then serves as an indication of the position of the transducing beam 17 with respect to the particular set of tri-color strips being scanned thereby; and thisV pulse can be used to overcome any non-homogeneity or non-linearity in the horizontal deection scanning field, or it can be used to overcome any non-uniformity in the width of the color strips. This indexing pulse can also be used as described in'said Patent 2,742,531', to compare the time phase relation between the received tri-color video signals andthe special phase between the transducing beam 17 and the respective tri-color strips which it is scanning.

While the tube hereinabove described is capable of use in a wide variety of circuits, a typicm circuit is schematically shown in Fig. 17, wherein the tube parts which have been already described are designated by the corresponding numerals. The metal coating 20a for the screen 20 extends beyond the margin of that screen and is provided with a suitable external metal contact button 114 for/connection to a suitable potential tap 115cm a direct current power supply represented schematically by battery 116. For example, tap 115 may be approximately 25 kilovolts.

The anode coating 112 is likewise provided with an external contact button which is connected to a suitable` tap 121, for example of 30 kilovolts. The negative terminal of source 116 may be connected to the cathode sleeve 2e and grounded. The control grids 41 and 42 may be suitably biased with respect to the cathode 26 by respective potentiometers 122, 123, for example to potentials in a range from 75 to 20G-volts. The composite shielding and convergence electrode 55 can be connected to a suitable potential tap 124, for example of 600 volts, corresponding, as hereinabove mentioned, to the potential of the region of the anode-cathode eld in which it is located. The screen 20v is coupled through a suitable coupling condenser to indexing circuits 126 from which indexing signals are derived and supplied to color signal control circuits 129 to control the application of color signals from tri-color signal source 130 to grid 41 as described in said U.S. Patent 2,742,531.

As described in said'U.S. Patent 2,742,531, grid 42 is supplied with a high ,frequency modulating signal om index beam control circuits 131.

By this arrangement it is possible therefore to keep the color transducing beam 17 and the monitoring beam 1S always at the proper spacing and with the desiredV minuteness of spot size on the screen 20, and accuracy of registration between the transducing beam 17 `and the correct color strip isassured at all times.

Various changes and modications may be made in the disclosed embodiments without departing from the spirit and scope of the invention. For example, while reference is made herein to the ceramic disc 28 having a at surface, it will be understood, of course, that the desired precision spacing may be obtained by using an unground ceramic disc which canbe provided with three or more integral surface projections, the outer faces of which,

, however, are ground at so as to provide the necessary accuracy of abutting contact. Furthermore, if desired, the ceramic disc 278 and the ceramic ring 68 may be made in one piece and the upper edge 68a of ring 68 can be ground to the desired atness andy accuracy.

What is claimed is:

1. Cathode-ray tube apparatus for developing a plurality o'f discrete cathode-ray beams, comprising in combination, a cathode sub-assembly including an electron emittingY cathode having an emissionV surface and a support member fastened to saidY cathode, said support member having a face serving as a precision spacing reference, a plurality of electrically discrete apertured grid electrodes extending radially outward with respect to said cathode with each grid aperture located at a predetermined xed distance from the emission surface of said cathode, an apertured backing electrode member, a single rigid insulator member in contact with said face of said support member and with said grids and serving as a spacer gauge to determine solely the spacing between said emission surface and said grids, and means to clamp said support member, said insulator member and said grids as a stacked unit insulatingly against said backing member.

2. Cathode-ray tube apparatus for developing a plurality of discrete separately controllable cathode-ray beams from a single cathode, comprising in combination, a cathode sub-assembly including an electron emitting cathode having an emission surface and an insulator support member fastened to said cathode with the cathode extending centrally and perpendicularly from said support member, said support member having a precisionground spacing reference face, a tubular rigid insulator having one end in abutting relation with said reference face, a plurality of electrically discrete beam-defining apertured grid strips extending radially outward with respect to said cathode, each of said strips having a minute beam-defining perforation and said strips resting on the opposite end of said tubular insulator, said tubular insulator having a length correlated with the length of said cathode whereby said perforations are held in fixed minute spacing with respect to said emission surface, a composite beam convergence and intermodulation shielding electrode having a plurality of openings in alignment with said perforations, and means to hold said cathode, said grids and said composite electrode together as a rigid unit.

3. A dual-beam gun for cathoderay tubes and the like, comprising cathode sleeve means extending longitudinally of the gun and having emission material from which dual discrete beams are to be developed, a pair of iiat metal strips each having a respective perforation and forming a respective discrete beam control electrode, said strips being mounted in substantially co'planar array with their adjacent edges closely spaced to form an inT sulating gap both for leakage currents and for electron emission therethrough from said emission material, and means rigidly holding said strips in precise closely spaced relation to said emission material, the last mentioned means including a ceramic disc fastened to said cathode sleeve means, said disc having a precision-ground flat on its face, a cylindrical ceramic member having the opposite ends thereof precision-ground, one end being in abutting contact with said ilat and the other end being in direct abutting contact with said metal strips, and means to hold said cathode sleeve means,'said insulator members, an apertured convergence electro'de positioned at a predetermined precise distance from the sides of said strips remote from said cylindrical ceramic member, and said grids together as a rigid unit.

4. Cathode-ray tube apparatus for developing a plurality of discrete cathode-ray beams of close trajectories substantially free from cross-beam intermodulatio'n, cornprising in combination, cathode means, a plurality of discrete control grids each having a beam-defining and control opening, insulator means for supporting said grids in closely spaced relation to' said cathode means adjacent an end thereof, said grids extending transversely to the said beam projectories, and a composite beam convergence and anti-intermodulation shield electrode having a plurality of spaced apertures each in alignment with a corresponding grid opening, the portio'n of said beam convergence electrode between its apertures serving as said antiinter modulation shield.

5. Cathode-ray tube apparatus according to claim 4 in which the apertures in said beam convergence electrode are of the same order of size as the grid perforations, said beam convergence electrode having a single cylindrical recess in its surface o'n the side away from said grids to form a common convergence electrode for both beams.

6. Cathode-ray tube apparatus comprising means including cathode means, accelerating anode means and a pair of control grids, said grids having respective grid openings to develop a plurality of discrete cathode-ray beams, electrode means mounted in closedly spaced relation to said grids, said electrode means having a pair of openings in alignment with said grid openings and also having a portion common to bo'th beams to overcome the tendency of each beam to diverge, and lead-in means for applying to said electrode means a potential corresponding to the free space potential existing at the region of the beam trajectories at which said electrode means is lo'cated, whereby said electrode means shields said grids against cross modulation while effecting beam convergence.

7. Cathode-ray tube apparatus for developing a plurality of discrete cathode-ray beams of close trajectories substantially free from cross-beam intermodulation, comprising in combination, cathode means, a plurality of discrete control grids each having a beam-defining and beam-control perforation, said grids extending in end-on relation with a minute gap between adjacent ends and with said perforations adjacent said gap, insulator means to support said grids in closely spaced relation to said cathode means, and a single electro'de mounted in closely spaced planar parallelism with said grids, said single electrode having a central unperforated portion in alignment with said gap to form an electrostatic shield between said grid perforations for the purpose of preventing crossbeam inter-modulation by said grids, said single electrode also having a cylindrical walled section symmetrically surrounding both beams and forming a single dualbeam convergence electrode for both beams.

8. Cathode-ray tube apparatus according to claim 7, in which the spacing between said single electrode and said grids is smaller than the distance between the centers of said grid perforations.

9. Cathode-ray tube apparatus for developing a dual cathode-ray beam, comprising in combination, cathode means, a pair of flat metal grid members mounted in endon spaced relation to each other and radially with respect to said cathode means, said grid members having their adjacent ends closely spaced to form a conductivity insulating and electron isolating gap therebetween, each of said grid members having a beam-defining and control perforation adjacent said gap, each of said beams tending to diverge upon emergence from its grid perforation, and a single metal electrode having a pair of peorations respectively in alignment with said grid perforations, and an unperforated portion in alignment with said gap for the purposes described.

10. Cathode-ray tube apparatus for developing a dual cathode-ray beam, comprising in combination, cathode means, a pair of flat grid strips mounted in end-on spaced relation with respect toeach other and radially with respect to said cathode means, said grid strips having their adjacent ends closely spaced to define a conductivity insulating and electron isolating gap, each of said grid strips having a beam-defining and beam intensity control perforation, the beams emerging from said grid perforations tending to diverge, a metal electrode acting as a composite beam convergence and cross beam intermodulation shielding electrode, and means to hold said grids and said metal electrode in closely spaced parallelism with each other, the last mentioned means including a pair of annular members between which said cathode, said grids, and said electrode are clamped.

11. Cathode-ray tube apparatus according to claim l0, in which said metal electrode is of rigid metal stock, and `the last mentioned means also includes :a metal cylinder having an lannular flange at its forward end to receive said metal electrode, said -cylinder Vhaving a pair of diametrically opposite Windows through which said `grid strips insulatingly pass, means to insulate said grid strips from said metal electrode, `andrneans to insulate said cathode from said grids'and including a tubularinsulator spacer member surrounding said cathode and having at least one shadowing notch on its internal surface to prevent the formation of a continuous Yconductive deposit between the cathode and grids.v

12. A cathode-ray tube particularly vdesignedior color television reception, comprising in combination, an evacuated envelope having adjacent the 'viewingrend thereof a screen including a plurality of tri-color'strips "each strip being of elemental Width, an'electron Vgun at Vthe opposite end of Vsaid envelope for developing -a color transducing beam vand a Vseparate but closelyY adjacent monitoring beam, said Vgun including cathode means, la pair of electrically discrete lgrida'one 'ofjsaid-grids havingan openingY to dene said transducing beam, theother grid'having an opening to deiine said monitoringbeam, and electrode means mounted closely adjacent to-said grids and inspaced parallelism therewith for shielding said beams lagainst cross-beam intermodulation and for opposing the tendency 'ofsaid kbeams to diverge when emerging from vtheir Arespective grid openings. g

.13. A cathode-ray tube according vto claim l2, in

Vwhiclrthe last mentioned electrode means comprise a single metal Velectrode having a `pair of yseparate'laut-closely 'adjacent perforations in alignment with and `facing `said grid perforations, said electrode having a vcylindrical recess on the lsiderernote trom said grids, said recess having a diameter and depth correlated with said beams and forming a common convergence electrode for Vboth beams. y 14. A cathode-ray tube according to claim 12, vin whichV said grid openings and the perforations in said convergence electrode are oriented in planar alignment with the length of said tri-color grid strips, each set of tricolor grid strips being provided with a secondary elect-ron emitter for developing a current pulse each time it is traversed by said monitoring beam. l

:15. An electron gun assembly for a cathode ray l'tube comprising, a cathode sub-assembly including an electronemitting cathode having an emission surface, a support member fastened to said surface and having efface serving as a precision spacing reference, a plurality of apertured grid electrodes, an insulating member between said reference face and said grid electrodes which solely determines the spacing between said emission surface and the apertures of said grid electrodes, and a multi-apertured electrode positioned close to said grid electrodes for determirn'ng the point at which beams passing through it cross over one another, said last-named electrode also being constructed and arranged to shield the beams passing through said grid electrodes from modulating one another. Y

16. An electron gun'assembly according to claim 15, in which said .grid 'electrodes are mounted between said kmulti-apertured electrode and the cathode.

-17. An electron -gun assembly Vaccording to claim 15, in which said grid electrodes are mounted between said multi-'ap'ertured electrode land the cathode, and said multi-apertured electrode has a central hollowed .out portion on the Yside thereof which `does not Vface the said grid electrodes.

V18. Electron gun apparatus for a cathode ray tube -comprising a cathode having an electron-emitting area thereupon, A.a plurality Yof ydiscrete control grids -each having Va beam -fdelining and beam controlling",.perforation, said grids being substantially coplanar but with a. minute gap between adjacent ends .and with the said perforations adjacent said gap,tsaid grids vbei'ng'mounted with their respective perforations in a 'iixed spatial relation to said emitting yarea, andan Aelectrode positioned closely adjacent -to said grids Vhaving 'aV-plurality of apertures each in alignment with a corresponding one of said grid Lperforations, .the spacing vbetween'said Velectrode and said grids being smaller vthan the distance between 'the center'sof Said perforations to control the relative positions of the electron beams passing through 'said perforations Tand to-shield1said beams -rorn undesirable cross-modulation.

19. Electron gun apparatus for a cathode -ray tube l'having an anode at a givenpo'sitive potential comprising, a cathode having an electron-emitting area, a 'plurality of apertured grids'mounted 'at a predetermined distance from said emitting area, and a multi-apertured electrode -in -a given region Ibetweenesaid grids Vand said 'anode to which a potential approximatingthe free-space potential of said region of ysaid tube'is -applied thereby to cause electron beams passing through said multi-apertured electrode to cross over at a predetermined point, the portion of said electrode intermedi-ate saidvapertures Yalso serving to prevent beamsp'assing through the apertures of said electrode lfrom intermodulating one another.

References Cited in the -iile of this patent UNITED STATES lPATENTS

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