Patent Publication Number: US-6222310-B1

Title: Cathode ray tube having one piece electrode plate with inclined and continuous steps

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. application Ser. No. 08/064,639, filed May 21, 1993, now U.S. Pat. No. 6,040,655, the subject matter of which is incorporated by reference herein, in which U.S. application Ser. No. 08/450,707, filed May 25, 1995, now U.S. Pat. No. 5,522,750, is a divisional thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cathode-ray tube and, particularly, to an improvement of an electrode plate which constitutes an electron gun of a cathode-ray tube. 
     2. Prior Art 
     A cathode-ray tube (hereinafter referred to as a color cathode-ray tube) used for color image display is constituted by a panel unit which is an image screen, a neck unit which holds an electron gun, and a funnel unit which couples the panel unit to the neck unit. In the funnel unit is mounted a deflector which causes an electron beam emitted from the electron gun to scan a fluorescent screen applied to the inner surface of the panel. 
     The electron gun held in the neck unit is provided with various electrodes such as a cathode electrode, a control electrode, a focusing electrode and an acceleration electrode. The electron beam from the cathode electrode is modulated by a signal applied to, the control electrode, and is permitted to impinge on the fluorescent screen after having been imparted with a required sectional shape and energy through the focusing electrode and the acceleration electrode. In the course of arriving at the fluorescent screen from the electron gun, the electron beam is deflected in a horizontal direction and in a vertical direction by the deflector provided in the funnel unit so as to form an image on the fluorescent screen (Japanese Patent Laid Open No. 215640/1984). 
     FIG. 16A is a plan view of an electrode (G 3  electrode) which constitutes the electron gun provided in a conventional cathode-ray tube, and FIG. 16B is a sectional view of the G 3  electrode along the line B—B′ of FIG.  16 A. In these drawings, symbol G 3  denotes a G 3  electrode, E 1  denotes a first electrode plate which constitutes the G 3  electrode G 3 , symbol E 2  denotes a second electrode plate which constitutes the G 3  electrode G 3 , symbols H denote beam passage holes. Each of the first and second electrode plates E 1 , E 2  has three in-line beam passage holes H. Symbols S denotes bead supports (supports of bead glass not shown) provided to the first electrode plate E 1 . 
     A conventional G 3  electrode G 3  has been formed by welding two electrode plates together, i.e., by welding together a first electrode plate E 1  having bead supports S and a second electrode plate E 2  having three beam passage holes H. Therefore, the thickness of the first electrode plate E 1  where bead supports S are formed is different from that of the second electrode plate E 2  where the beam passage holes H are bored, developing steps in the boundary between the two. The reason why the plates with different thicknesses are used and a step is formed is to decrease the gap between the G 2  electrode (not shown) and the G 3  electrode G 3  in order to improve the focusing performance without deteriorating the breakdown voltage characteristics. 
     Conventionally, as shown in FIGS. 16A and 16B, since two electrode plates E 1  and E 2  are welded together, the productivity is low and the manufacturing cost is high. Furthermore, when a piece of electrode plate is subjected to coining by press-machining in order to obtain an electrode having a step, there arises a problem that the tools are often damaged due to the lack of sufficient strength. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to produce a one piece electrode plate with a step where a portion having beam passage holes and a portion having bead supports are formed in one body, maintaining a good productivity without increasing the cost of manufacturing, and preventing the machining tool from being damaged, by solving the aforementioned problems. 
     The above-mentioned object of the present invention is accomplished by a cathode-ray tube which has ann electron gun that includes a one piece electrode plate, wherein the electrode plate has a plurality of beam passage holes and bead supports, a portion having the beam passage holes and a portion having the bead supports are formed as a unitary or one piece structure, the two portions have different thicknesses, and steps are obliquely formed along the boundaries between the two portions. 
     Furthermore, a cathode-ray tube of the present invention has an electron gun that includes an electrode plate made by fabricating a metal plate such that a portion provided with a plurality of beam passage holes and a portion provided with bead supports are integrally formed in one piece, the two portions having different plate thicknesses, and accordingly steps are formed along the boundaries between the two portions, by punching the metal plate into a predetermined shape by press-forming, and then further punching the metal plate to make the beam passage holes. 
     According to the present invention, welding is eliminated since the portion having beam passage holes and the portion with bead supports are integrally formed together in one piece which have different thicknesses. Therefore, the productivity is improved and the manufacturing cost decreases. Moreover, since use is made of a one piece metal plate that has a step in advance, no coining is required or the forming rate of coining is small, making it possible to prevent the machining tools from being damaged during the press-forming. Besides, since the step is obliquely formed, the burden of the punching tools can be small and is prevented from being damaged. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a plan view of a G 3  electrode of an electron gun provided in a cathode-ray tube of an embodiment according to the present invention; 
     FIG. 1B is a sectional view of the G 3  electrode along this line A-A 1  in FIG. 1A; 
     FIGS. 2A-2E illustrate the steps for manufacturing the G 3  electrode shown in FIGS. 1A and 1B; 
     FIG. 3 is a sectional view of a color cathode-ray tube of the embodiment according to the present invention; 
     FIGS. 4A and 4B are sectional views illustrating an essential part of the electron gun of the present invention; 
     FIG. 5 is a diagram of characteristics of the electron gun shown in FIGS. 4A and 4B; 
     FIG. 6 is a diagram of characteristics of the electron gun shown in FIGS. 4A and 4B; 
     FIG. 7 is a sectional view showing an essential part of another embodiment of the electron gun of the present invention; 
     FIG. 8 is a sectional view showing essential part of a further another embodiment of an electron gun of the present invention; 
     FIG. 9 is a sectional view showing an essential part of a further another embodiment of the electron gun of the present invention; 
     FIG. 10 is a partly cut-away sectional view showing an essential part of further another embodiment of the electron gun of the present invention; 
     FIG. 11 is a partly cut-away perspective view showing an essential part of further another embodiment of the electron gun of the present invention; 
     FIG. 12 is a partly cut-away perspective view showing an essential part of a yet further embodiment of the electron gun of the present invention; 
     FIGS. 13A-13D show a front view, a side view, a rear view and a plan view of a yet further embodiment of the electron gun of the present invention; 
     FIG. 14 is a partly cut-away perspective view showing an essential part of an example of a fluorescent screen and a shadow mask of the present invention; 
     FIG. 15 is a plan view showing an essential part of another example of the fluorescent screen of the present invention; 
     FIG. 16A is a plan view of the G 3  electrode constituting an electron gun provided in a conventional cathode-ray tube; and 
     FIG. 16B is a sectional view of the G 3  electrode along the line B-B′ of FIG.  16 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be described with reference to FIGS. 1A and 1B and  2 A- 2 E. Here, the same members as those shown in FIGS. 16A and 16B are denoted by the same reference symbols and numerals. 
     FIG. 1A is a plan view of an electrode (G 3  electrode) of an electron gun provided in a cathode-ray tube of an embodiment according to the present invention, and FIG. 1B is a sectional view of the G 3  electrode taken along line A-A′ of FIG.  1 A. In these drawings, symbol G 3  denotes a G 3  electrode, E denotes an electrode plate which constitutes the G 3  electrode G 3 , symbol H denotes three beam passage holes formed in line in the electrode plate E, and symbol S denotes bead supports (portions for supporting the bead glass that is not shown) provided to the electrode plate E. 
     As shown, the G 3  electrode G 3  of this embodiment is made of one piece of an electrode plate E which has a portion in which three beam passage holes H are formed and a portion provided with bead supports S as a unitary or one piece structure, the two portions having different plate thicknesses, and steps being obliquely formed in the boundaries between the two portions. The reason why the thicknesses of the two portions are different and the steps are formed is to reduce the gap between the G 2  electrode (not shown) and the G 3  electrode G 3  in order to improve the focusing performance without deteriorating the breakdown voltage characteristics. 
     In this embodiment, the thickness T 1  of the portion of the plate E where the beam passage holes H are formed is 1.0 mm, and the thickness T 2  of the portion where the bead supports S are provided is 0.7 mm. Further, the angles alpha in the steps are 135 degrees, and the width  1   1  of the electrode plate E is 17 mm and the width  1   2  is 7 mm. 
     FIGS. 2A to  2 E are diagrams illustrating the process for fabricating the G 3  electrode G 3  that is shown in FIGS. 1A and 1B. FIGS. 2A and 2C are partial plan views for illustrating a metal plate from which the G 3  electrode of the embodiment is to be produced, FIG. 2B is a side view of the metal plate of FIG. 2A, FIG. 2D is a side view of the metal plate of FIG. 2C, and FIG. 2E is a side view of the G 3  electrode G 3  after it is punched. First, the metal material shown in FIGS. 2A and 2B is rolled to obtain a one piece metal plate M having steps that have inclined walls and is continuously formed. The one piece metal plate M of this embodiment is machined into a size of the final product. That is, the metal plate M has a thickness T 1  of 1.0 mm, a thickness T 2  of 0.7 mm, an angle alpha of 135 degrees, a width L of 20 mm and a width  1   2  of 7 mm. Then, as shown in FIG. 2C, predetermined three beam passage holes H and a predetermined outer shape are formed by punching by press to obtain the G 3  electrode G 3 . 
     Here, the metal plate M can be pre-formed in a size which is slightly greater than that of the product, for example, in a size having a thickness T Y  of 1.0+0.1 mm and a thickness T 2  of 0.7+0.1 mm, and the size of the final product can be accomplished by coining during the press forming. 
     The portion having beam passage holes H and the portion having bead supports S of the G 3  electrode shown in FIGS. 1A,  1 B and  2 A- 2 E are formed as a unitary structure even though they have different thicknesses T 1  and T 2 . Therefore, welding is not necessary, and the productivity increases and the manufacturing cost decreases. Moreover, since use is made of a metal plate M that have steps formed in advance, no coining is required or the forming rate of coining can be small, making it possible to prevent the machining tools from being damaged during the press forming. Since the steps can be obliquely formed, the burden of the machining tools is made light and the tools are prevented from being damaged. 
     The aforementioned sizes of the embodiment are only illustrative, and a variety of sizes can be set as a matter of course. In the case of the metal plate M of FIGS. 2A-2E, roughly the sizes are desirably T 1 /T 2 =i to 6, 1 2 /L≦0.8. 
     Concretely described below is a cathode-ray tube to which the present invention can be adapted. 
     FIG. 3 is a schematical diagram illustrating the constitution of an embodiment of the present invention, wherein reference numeral  1  denotes a panel,  2  denotes a funnel,  3  denotes a neck part,  4  denotes a fluorescent screen,  5  denotes a shadow mask,  6  denotes a magnetic shield,  7  denotes a deflection yoke,  8  denotes a purity-adjusting magnet,  9  denotes a magnet for adjusting the center beam static convergence,  10  denotes a magnet for adjusting the side beam static convergence,  11  denotes an electron gun, symbol Bc denotes a center beam, and Bs denotes side beams. 
     The convergence (static convergence) of such a color cathode-ray tube is adjusted by first converging the two side beams Bs, Bs, and then causing the converging points of the center and side beams Bc, Bs, Bs to agree with each other. 
     On the outer surface of the panel  1  is formed, as required, a thin film of a single layer or a multilayer contains SnO 2 , In 2 O 3 , etc. to prevent reflection and changing. Furthermore, though not diagramed, an inner electrically conducting film composed of graphite or the like is deposited on the inner surfaces of the funnel  2  and the neck  3 . The electrically conducting film contains titanium dioxide and the like in addition to graphite to control its resistance. The film is for suppressing arc. The electrically conducting film electrically connects a high-tension terminal (not shown) to the electron gun  11 . 
     FIGS. 4A and 4B show the electron gun  11 , and is a sectional view of G 3  and G 4  electrodes that constitute a bipotential-type main lens in the horizontal direction and in the vertical direction. In FIGS. 4A and 4B, reference numeral  111  denotes the outer periphery of the G 3  electrode,  121  denotes the outer periphery of the G 4  electrode, and  13  denotes a cup electrode. Reference numeral  112  denotes an electrode for correcting astigmatism provided on the inside of the outer periphery  111  of the G 3  electrode, and  122  denotes an electrode for correcting astigmatism provided on the inside of the outer periphery  121  of the G 4  electrode. The electrode plate  112  has an aperture  114  for passing the center beam and apertures  113 ,  113 ′ for passing the outer beams, and the electrode plate  122  has an aperture  124  for passing the center beam and apertures  123 ,  123 ′ for passing the outer beams, all apertures being arranged in line. In this embodiment, the apertures  113 ,  113 ′,  114 ,  123 ,  123 ′ and  124  have oval shapes, and the corresponding apertures of the G 3  electrode and the G 4  electrode have the same shapes and the same sizes. When the apertures  113 ,  113 ′,  123 ,  123 ′ of the outer sides and the center apertures  114 ,  124  have the same shape and the same size, the main lens formed on the outer side exhibits a strong lens converging action in the horizontal direction. Therefore, the diameters of the apertures of the outer sides in the horizontal direction are selected to be greater than the inside diameters of the center apertures in the horizontal direction, in order to equalize the strengths of the converging actions in both the horizontal direction and the vertical direction. 
     FIG. 5 shows the ratio of focal distances in both the horizontal and vertical directions relative to the diameter b 1  in the horizontal direction of the center apertures  114 ,  124  found by computer simulation in the embodiment shown in FIGS. 4A and 4B, where the inside diameters of the outer peripheries  111  and  121  in the horizontal direction are h=20.0 mm, the inside diameters in the vertical direction are v=9.4 mm, the diameters of the center apertures  114  and  124  in the vertical direction are a 1 =8.4 mm, the recess depth of the electrode plate  112  is d 3 =1.5 mm, and the distances from the center axis are S=6.6 mm. 
     Here, the focal distance in the horizontal or in the vertical direction means the distance from the end surface of the G 3  electrode on the G 4  electrode side up to the point where the electron beam crosses the center axis, the electron beam being emitted from a point on the center axis, having passed the horizontal or vertical axis of the center aperture and having focused by the main lens. The distance from the end surface to the fluorescent screen is set to be 340 mm, the outgoing points are found at which the outgoing angle can correspond to the value of 340 mm, and the electron beam is permitted to go out from an intermediate point of the above outgoing points at the same outgoing angle. FIG. 5 shows the ratio of focal distances in the horizontal direction and in the vertical direction in this case. As will be obvious from FIG. 5, when the diameter of the center aperture in the horizontal direction is b 1 ≈5.5 mm, then the focal in the vertical direction and in the horizontal direction distances become in agreement, and the intensities of the converging actions in both directions becomes equal, making it possible to eliminate astigmatism. 
     In this case, the converging action of the lens is equal to that of a cylindrical bipotential lens of a diameter of 8 mm arranged with a gap of 1 mm. 
     This is greater than a limit value of 6.8 mm for the electrode aperture limited by L=h−2×S (where L=limit value of aperture diameter, h=aperture in the horizontal direction, S=the center axis of aperture) when h=20.0 mm and S=6.6 mm. 
     FIG. 6 shows the relationship between the diameters b 2  in the horizontal direction of the apertures  113 ,  113 ′,  123 ,  123 ′ of the outer sides and the horizontal spot movement distance of the electron beam of the outer sides on the fluorescent screen when the sizes are the same as those of the embodiment of FIGS. 4A and 4B. The relationship was found by computer simulation. A voltage of 7 KV is applied to the G 3  electrode, a voltage of 25 KV is applied to the electrode G 4 , and the distance from the end of the G 3  electrode on the side of the G 4  electrode to the fluorescent screen is set to be 340 mm. The electron beams of the outer sides are separate from the center electron beam by 6.6 mm in the horizontal direction. Therefore, the spot movement distance is 6.6 mm that is necessary to achieve STC. In practice, however, the spot movement distance is in most cases designed to be about 6.1 mm to impart freedom for adjusting the color purity. To maintain this movement distance, the diameter b 2  should be 5.8 mm. 
     FIG. 7 is a sectional view illustrating an essential portion of an electron gun in the color cathode-ray tube of another embodiment according to the present invention, and shows the G 3  electrode in cross section in the vertical direction. The apertures  41 ,  41 ′,  42  formed in the electrode  112  have shapes in which the end points of the two arcs are connected together by two parallel lines. The spot shape on the fluorescent screen is not so good as that of oval apertures. However, the apertures which consist of arcs and lines can be formed easily and precisely. Even in this embodiment, the diameters of the apertures in the horizontal direction are smaller than those in the vertical direction. 
     FIGS. 8 and 9 are sectional views illustrating an essential portion of the electron gun of a further embodiment according to the present invention, and show the G 3  electrode and the G 4  electrode in cross section in the vertical direction. The center apertures  52 ,  62  have a symmetrical axis in the vertical direction but the apertures  51 ,  51 ′,  61 ,  61 ′ of the outer sides have no symmetrical axis in the vertical direction. The apertures  51 ,  51 ′,  61 ,  61 ′ of the outer sides each consist of a combination of two ovals having the same major axes but different minor axes. In the outer apertures  51  and  51 ′ of the G 3  electrode, the ovals on the outer sides have minor axes smaller than those of the inner sides. By forming the outer apertures of the G 3  electrode in such a shape, the electron beam can be converged in the center direction more strongly than when the apertures each consist of a single ellipse as denoted by  113  and  113 ′ in FIGS. 4A and 4B. Therefore, the STC can be achieved even when the diameter is further decreased in the horizontal direction. 
     In the G 4  electrode, on the other hand, the outer apertures designated by  61  and  61 ′ in FIG. 9 are constituted by a combination of such two ovals that the oval of the inner side has a short minor axis smaller than that of the oval of the outer side, so that the electron beam is converged toward the center more strongly. 
     Thus, if the apertures of the outer sides are asymmetrically formed with respect to the vertical direction, the electron beam is more converged making it easy to accomplish the STC. When the converging force is too strong, the apertures of the G 4  electrode are formed as in FIG. 8, and the apertures of the G 3  electrode are formed as in FIG. 9 to weaken the converging force. 
     When main lenses corresponding to red, green and blue three colors are arranged in parallel on the same horizontal plane under the limitation of the outer shape of the electron gun, the present invention makes it possible to constitute main lenses having converging action weaker than that of when cylindrical electrodes having maximum diameters are arranged. It is therefore possible to strikingly improve the converging performance of the color cathode-ray tube. 
     Furthermore, the STC can be accomplished by properly selecting the recess amount of the electrode plate and the shapes of apertures formed in the electrode plates without shifting the center axes of the outer apertures formed in the G 3  electrode and the G 4  electrode that constitute main lens. During the assembling, therefore, jigs having the same diameters and the same axes can be used for the G 3  electrode and the G 4  electrode to improve assembling precision. 
     FIG. 10 is a partly cut-away perspective view illustrating an essential part of an electron gun of another embodiment according to the present invention, wherein the electrode plates  133  and  143  have oval apertures  135  and  145  for the center beam like those of the electrode plates of FIGS. 4A and 4B, but have oval apertures for the side beams of both sides that are cut into halves. That is, the apertures have no portion that comes in contact with the outer peripheral electrodes  131 ,  141  at both the right and left ends. The passage for the center beam is surrounded by the apertures  135  and  145  formed in the electrode plates  133  and  143 , and the passages for the side beams on both sides are partly surrounded by the ends of the electrode plates  133 ,  143  and the remaining portions are surrounded by the outer peripheral electrodes  131  and  141 . Such a structure makes it possible to maximize the aperture of the main lenses for the side beams. Moreover, the electrode plates having small areas makes it possible to easily accomplish good flatness. Besides, since oval apertures that require high precision are formed less, the machining can be easily performed. Symbols d 3  and d 4  denote recess amounts which may be the same or different. 
     In the embodiment of FIG. 10, though the apertures are of oval shapes, the astigmatism can be removed even in the case of apertures having diameters in the vertical direction are greater than those in the horizontal direction. 
     As shown in FIG. 11, furthermore, the astigmatism can be removed even by curving the electrode plates  133  and  143  and by continuously changing the recess amounts of the electrode plates. In this case, the diameters of the apertures  135  and  145  in the vertical direction need not necessarily be greater than those in the horizontal direction. When the electrode plate  133  of the G 3  electrode is convexed toward the G 4  electrode as shown, the converging force can be increased in the horizontal direction. Conversely, when the electrode of the G 4  electrode is convexed toward the G 3  electrode, the converging force can be increased in the vertical direction. 
     As shown in FIG. 12, furthermore, the astigmatism can be corrected by providing protrusions  137  and  147  around the apertures  135  and  145  and by adjusting the height of the protrusions. Even in this case, the diameters of the apertures in the vertical direction needs not be greater than those in the horizontal direction. 
     In the embodiments of FIGS. 11 and 12, the astigmatism can be corrected with apertures of true circles offering an advantage that parts can be matched and the electrodes can be assembled more easily than the cases of apertures of non-circular shapes. 
     The above embodiments make it possible to remove halo that generates toward the inner sides of side beams, to sufficiently increase the effective aperture of main lenses in the electron gun, and to strikingly improve the converging performance of the color cathode-ray tube. Furthermore, the mutually facing electrodes have small areas in the main lens making it easy to accomplish good flatness during the machining. In addition, the shaping is easily done since relatively small portions need machining. 
     The electron gun of the present invention can be applied to the main lens of the above-mentioned bipotential type and of any other types, as a matter of course. In the above description, furthermore, the invention is adapted to both of the pair of electrodes constituting the main lens. However, the same effects can be obtained even when the invention is adapted to either one of the electrodes. 
     FIGS. 13A-13D includes a front view, a side view, a rear view and a plan view of an electron gun having first to sixth grids of a further embodiment, wherein reference numeral  1111  denotes a first grid,  1112  denotes a second grid,  1113  denotes a third grid,  1114  denotes a fourth grid,  1115  denotes a fifth grid,  1116  denotes a sixth grid, and reference numeral  1119  denotes a cathode. This electron gun uses a plurality of main lenses to obtain good focusing performance. To obtain an image which is bright and has a high resolution, the anode voltage Eb must be high and is usually from 25 to 35 KV. A focusing voltage Ec 3  is about 30% of the Eb, a voltage Ec 2  of about 400 to 700 V is applied to the second grid  1112 , the first grid  1111  is grounded, and a signal voltage Ek of smaller than 200 V corresponding to the brightness of each pixel is applied to the cathode  1119 . Reference numeral  1127  denotes a third grid feeder line and  1128  denotes a fifth grid feeder line. As shown in FIGS. 13B and 13C, one end  1127   a  of the third grid feeder wire  1127  is fixed to the third grid  1113 , part of the intermediate portion  1127   b  is a bent portion  1127   c  that extends nearly in parallel with a plane perpendicular to the tubular axis, the bent portion  1127   c  passes through between the back surface of a bead glass  1120  and the wall surface (not shown) in the neck tube within the full length  1  of the third grid  1113  in the direction of the tubular axis, and the other end  1127   d  of the feeder wire  1127  is connected to a stem lead that is not shown. Thus the third grid feeder wire can serve as a shielding wire. As shown in FIGS. 13A and 13B, one end  1128   a  of the fifth grid feeder wire  1128  that connects the third grid  1113  to the fifth grid  1115  is fixed to the third grid  1113 , the other end  1128   d  of the wire  1128  is fixed to the fifth grid  1115 , part of its intermediate portion  1128  is a bent portion  1128   c  that extends nearly in parallel with a plane perpendicular to the tubular axis, the bent portion  1128   c  is arranged symmetrically to the above bent portion  1127   c  within with the tubular axis interposed between the two bent portions  1127   c  and  1128   c  the full length  1  in the direction of the tubular axis of the third grid  1113  on a plane perpendicular to the tubular axis, and the bent portion  1128   c  passes through between the back surface of the bead glass  1120  and the wall surface (not shown) in the neck, in order to obtain the same action as the shielding wire. That is, since the feeder wires  1127   c  and  1128   c  are symmetrically arranged on the same plane perpendicular to the tubular axis, and sandwich the tubular axis therebetween, an excellent effect of suppressing the arc discharge over the whole periphery in the neck tube is exhibited compared with those in which the shielding wire is arranged on one side only. 
     By symmetrically arranging the two folded portions  1127   c  and  1128   c  within the full length of the third grid in the direction of the tubular axis and by interposing the tubular axis therebetween as in this embodiment, furthermore, the number of times of the occurrence of arc discharge can be decreased to be a fraction of conventional one and the dark current can be decreased to be one-several hundredth or less. That is, the bent portions are preferably provided in positions close to the electrode to which the anode voltage is applied from the standpoint of shielding the bead glass and the tubular wall of the neck from the anode voltage. However, this arrangement might result in local concentration of electric field at places where the feeder wires are bent, contrarily causing arc discharge easily. When the bent portions of the feeder wires for applying the focusing voltage are too close to the second grid electrode, on the other hand, the focusing voltage which is high next to the anode voltage is very likely to develop arc discharge between the bent portions of the feeder wires for applying the focusing voltage and the electrode for applying a low voltage such as the second grid electrode. 
     Extensive experiments concerning the effect of suppressing the occurrence of arc discharge, effect of suppressing the dark current and the operability of assembling electrodes teach that the bent portions of the feeder wires for applying the focusing voltages should best be provided at places that face to the side surfaces of the third grid within the full length  1  thereof in the direction of the tubular axis. 
     According to this embodiment in which both ends of the feeder wires are fixed to the electrodes or the like, the feeder wires are not the source of stray electrons making it possible to prevent the occurrence of arc discharge and to suppress the dark current. 
     FIG. 14 illustrates in detail the fluorescent screen  4  and the shadow mask  5 , wherein the fluorescent screen  4  formed in the inner surface of the panel unit has a number of light-absorbing strips  224  that extend continuously in the vertical direction and are arranged in the horizontal direction. Among the light-absorbing strips  224 , a plurality of fluorescent strips  225 R(red),  225 G(green),  225 B(blue) that emit light of different colors and that continuously extend in the vertical direction in a predetermined order in the horizontal direction are provided. On the inner surface of the panel, furthermore, the curved shadow mask  5  is correspondingly arranged to face the fluorescent screen  4 . The shadow mask  5  has a number of through slits  228  that are long in the vertical direction in correspondence with the fluorescent strips  225  continuously extending fully in the vertical direction, divided in the vertical direction via bridges  229 , and arranged in the horizontal direction at predetermined pitches in columns. 
     FIG. 15 illustrates another embodiment of the fluorescent screen  4  which has dot-like fluorescent spots  226 R(red),  226 G(green),  226 B(blue), and a light-absorbing film  227  with which the surroundings of the spots are filled. 
     The shadow mask  5  is made of steel plate and invar material having a small coefficient of thermal expansion. Though not diagramed, the shadow mask  5  can be covered with bismuth or the like to suppress the thermal expansion. It is allowable to form circular through holes instead of the through slits  228 . 
     The invention is in no way limited to the above-described embodiments only, but can be modified in a variety of other ways without departing from the gist and scope of the invention. In the embodiment shown in FIGS. 1A and 1B, for instance, the portion having beam passage holes H has a thickness greater than that of the portion having bead supports S. The invention, however, can be adapted even to the opposite case. In the steps shown in FIGS. 2A-2E, furthermore, the one piece plate from which the one piece metal plate M is formed can have the size of the final product, or the one piece plate can have a slightly larger size which can then be reduced to the size of the final product through the coining of the one piece metal plate M at the time of press forming. As in the embodiment of FIGS. 2A-2E, furthermore, the outer shape of the G 3  electrode G 3  and the beam passage holes H can be simultaneously punched from the one piece metal plate M during the press forming. When they are not simultaneously punched, either one of them can be punched first. Moreover, the step portions need not necessarily be formed inclinedly. 
     In the one piece electrode plate constituting the electron gun in the cathode-ray tube of the present invention as described above, the portion having beam passage holes and the portion having bead supports can be formed as a unitary one piece structure easily and highly accurately, eliminating the conventionally employed process of welding, and enabling the productivity to increase and the manufacturing cost to decrease. Moreover, since use is made of a material having steps formed in advance, the productivity increases and the machining tool is prevented from being damaged during press forming.