Patent Publication Number: US-6707244-B2

Title: Cathode-ray tube apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-158810, filed May 28, 2001; and No. 2002-149517, filed May 23, 2002, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a cathode-ray tube (CRT) apparatus, and more particularly to a CRT apparatus having an electron gun assembly capable of effecting dynamic astigmatism compensation. 
     2. Description of the Related Art 
     In general terms, a color CRT apparatus comprises an in-line electron gun assembly that emits three electron beams, and a deflection yoke that produces deflection magnetic fields for deflecting the three electron beams emitted from the electron gun assembly and causing them to horizontally and vertically scan the phosphor screen. The deflection yoke produces non-uniform magnetic fields comprising a pincushion-shaped horizontal deflection magnetic field  74 , as shown in FIG. 11, and a barrel-shaped vertical deflection magnetic field. 
     An electron beam  63  (B, G, R) that has passed through the non-uniform magnetic fields suffers a deflection aberration, i.e. astigmatism due to the deflection magnetic fields. Specifically, the electron beam  63  traveling to a peripheral portion of the phosphor screen suffers a force as indicated by arrows  a  and  b  by the deflection magnetic field  74 . Consequently, as shown in FIG. 12, the beam spot on the peripheral portion of the phosphor screen deforms to have a vertically elongated low-luminance halo portion  76  and a horizontally elongated high-luminance core portion  75 . Such deformation of the beam spot occurs at peripheral portions of the screen in the vertical direction V, horizontal direction H and diagonal direction D, as shown in FIG.  13 . The deformation considerably degrades the resolution. 
     In order to improve the degradation in resolution, an electron gun assembly has been proposed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 3-93135 and Jpn. Pat. Appln. KOKAI Publication No. 3-95835. In the proposed electron gun assembly, as shown in FIG. 14, a fourth grid G 4  and a sixth grid G 6  are supplied with a dynamic focus voltage obtained by superimposing an AC component E 4  varying in synchronism with the deflection magnetic fields upon a DC voltage E 3 . Thereby, a first quadrupole lens is created between the third G 3  and fourth grid G 4 , and a second quadrupole lens is created between the fifth grid G 5  and sixth grid G 6 . 
     In this electron gun assembly, the first quadrupole lens corrects image-magnifications which differ in horizontal and vertical directions. At the same time, the second quadrupole lens and an ultimate focusing lens, which is created between the sixth grid G 6  and seventh grid G 7 , function to prevent the electron beam  63 , which is ultimately deflected onto the peripheral portion of the screen, from being extremely deformed by the deflection aberration due to the deflection magnetic fields. 
     With the deflection of the electron beams, potential differences vary between the fourth grid G 4  and sixth grid G 6  supplied with the dynamic focus voltage, on the one hand, and the adjacent third grid G 3 , fifth grid G 5  and seventh grid G 7 , on the other. Accordingly, the coulomb force varies between the grids G 3  through G 7 . Owing to the variation in coulomb force, mechanical vibrations occur in the grids G 3  through G 7 . The mechanical vibrations are transmitted to the funnel via insulating supports, which support the grids G 3  to G 7 , and stem pins electrically connected to the grids G 3  to G 7 . Consequently, the funnel vibrates, and abnormal noise is produced from the funnel. 
     The third grid G 3  is a main factor that increases the amplitude of vibration of the funnel. The first reason is that the distance between the third grid G 3  and fourth grid G 4  is narrower than that between the third grid G 3  and second grid G 2 . Thus, the variation in coulomb force between the third grid G 3  and fourth grid G 4  is greater than that between the second grid G 2  and third grid G 3 , and vibration easily occurs between the third grid G 3  and fourth grid G 4 . The second reason is that the third grid G 3  is formed of a plate-shaped electrode. Therefore, compared to a cup-shaped electrode body such as the fifth grid G 5  that extends in the tube-axis direction, the third grid G 3  has a lower flexure rigidity to vibration in the tube-axis direction and tends to vibrate easily. 
     More specifically, the third grid G 3  is a plate-shaped electrode and is supported and fixed by insulating supports at its upper and lower portions. The coulomb force acting between the electrodes is mainly applied to an intermediate portion between the two support points at the upper and lower portions of the third grid G 3  when the third grid G 3  is supported at these two points. Consequently, as shown in FIG. 16, the third grid G 3  flexes in the tube-axis direction and vibrates. 
     The vibration occurring at the third grid G 3  and fourth grid G 4  is modulated while being transmitted to the funnel. The vibration is frequency-modulated or increased by a resonance phenomenon due to the frequency of the dynamic focus voltage and the natural vibration characteristics of the third grid G 3  and fourth grid G 4  in the tube-axis direction. Consequently, the funnel vibrates at audio frequencies (20 Hz to 20 kHz) and produces abnormal noise. The natural vibration characteristics, that is, the characteristic frequency, are determined by the distance between the paired insulating supports that fix the electrode, the thickness of the electrode, the hardness of the electrode material, the electrode structure, etc. 
     In particular, when such a high-frequency voltage as to vary in synchronism with the horizontal deflection magnetic field is applied as the dynamic focus electrode, abnormal noise at a higher level may be produced due to resonance. Moreover, it has been made clear by experiments that the abnormal noise increases as the fourth grid G 4  and sixth grid G 6  supplied with the dynamic focus voltage are disposed closer to the cathodes K (on the stem section side) accommodating heaters. 
     The reasons appear to be that (1) the stem pins are firmly fixed to the stem section by means of welding, and so vibration occurring in each grid may easily be transmitted, (2) the electrode supplied with the dynamic focus voltage is formed of a plate-shaped electrode, and so it may easily transmit the vibration, and (3) the electrode supplied with the dynamic focus voltage is disposed near the heaters, and thus it may easily thermally expand. It is assumed that these factors may be combined in a complex fashion and a large abnormal noise is produced. 
     A dynamic focus voltage including an AC component E 4  of 40 kHz to 100 kHz was applied to the fourth grid G 4  and sixth grid G 6  of the CRT apparatus with the electron gun assembly  64  shown in FIG.  14 . The level of produced abnormal noise was measured. FIG. 15 shows the measured results. 
     In FIG. 15, the abscissa indicates the frequency of the AC component E 4  included in the dynamic focus voltage, and the ordinate indicates the level of sound pressure sensed by humans in 10 grades. Normally, the level of abnormal noise needs to be suppressed to level 2 or less, at which the noise is hardly sensed by humans or negligible as being not unpleasant. According to the measured results shown in FIG. 15, the noise level exceeds level 2 at many frequency bands. If abnormal noise of level 2 or more has occurred, even if good image characteristics are obtained by the application of the dynamic focus voltage, the viewer feels unpleasant, and the product value and reliability of the CRT apparatus are greatly degraded. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above problems, and its object is to provide a cathode-ray tube apparatus which can suppress abnormal noise and has a high product value and reliability. 
     According to an aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, the dynamic focus electrode comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction. 
     According to another aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction. 
     According to another aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, each of the dynamic focus electrode and at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction. 
     According to the cathode-ray tube apparatus, each of the dynamic focus electrode and at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions. Thereby, a flexure phenomenon due to vibration in the tube-axis direction can be suppressed. Specifically, when a dynamic focus voltage is applied, a coulomb force acting between the dynamic focus electrode and the adjacent electrode varies in synchronism with the frequency of the AC component included in the dynamic focus voltage. This results in a tube-axis-directional mechanical vibration of each electrode and a flexure vibration of the electrodes. However, these vibrations can be suppressed. 
     As is shown in FIG. 17, the plate-shaped dynamic focus electrode (G 3 - 1 ) has the recessed/projected vibration-damping portion (X 3 ) in the surface including the electron beam passage hole (X 2 ). When the vibration-damping portion is not provided, the coulomb force acts mainly at an intermediate portion, i.e. the electron beam passage hole, between the upper and lower support fixture points. By contrast, with the vibration-damping portion provided, the coulomb force acts mainly at the recessed/projected vibration-damping portion. At the same time, the coulomb force acting on the whole electrode is dispersed by the vibration-damping portion, and a flexure phenomenon does not easily occur. 
     Thereby, a resonance phenomenon due to the frequency component in the AC component and the natural vibration characteristics of the electrode can be suppressed. Accordingly, the frequency modulation of mechanical vibration caused by the electrode due to coulomb force variations and the increase in the tube-axis-directional vibration amplitude can be suppressed. Therefore, the occurrence of mechanical vibration transmitted to the funnel via the insulating support and stem pins can be reduced, and the occurrence of abnormal noise suppressed. Thus, a CRT apparatus with high product values and reliability can be provided. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a partial cross-sectional view schematically showing the structure of a color CRT apparatus according to an embodiment of the present invention; 
     FIG. 2 is a view schematically showing the structure of an example of an electron gun assembly applied to the color CRT apparatus shown in FIG. 1; 
     FIG. 3 is a front view schematically showing the structure of a first segment of a third grid applied to the electron gun assembly shown in FIG. 2; 
     FIG. 4 is a cross-sectional view schematically showing the structure of the first segment shown in FIG. 3; 
     FIG. 5 is a graph showing measured results of abnormal noise produced from the color CRT apparatus according to the embodiment; 
     FIG. 6 is a graph showing measured results of abnormal noise produced from a color CRT apparatus according to another embodiment of the invention; 
     FIG. 7 is a view schematically showing the structure of another electron gun assembly applicable to the color CRT apparatus shown in FIG. 1; 
     FIG. 8 is a front view schematically showing another structure of the first segment of the third grid; 
     FIG. 9 is a view schematically showing the structure of another electron gun assembly applicable to the color CRT apparatus shown in FIG. 1; 
     FIG. 10 is a cross-sectional view schematically showing the structure of the color CRT apparatus according to the embodiment of the invention; 
     FIG. 11 is a view illustrating the state in which an electron beam suffers a deflection aberration; 
     FIG. 12 is a view illustrating deformation of a beam spot; 
     FIG. 13 is a view illustrating deformation of a beam spot on a screen; 
     FIG. 14 shows an example of a prior-art electron gun assembly; 
     FIG. 15 is a graph showing measured results of abnormal noise produced from the prior-art color CRT apparatus; 
     FIG. 16 is a view illustrating a flexure phenomenon due to coulomb force of a dynamic focus electrode; 
     FIG. 17 is a view for explaining the advantage of the color CRT apparatus of the present invention; and 
     FIGS. 18A to  18 E are front views schematically showing other structures of the first segment of the third grid. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A cathode-ray tube apparatus according to an embodiment of the present invention will now be described with reference to the accompanying drawings. 
     As is shown in FIGS. 1 and 10, a cathode-ray tube (CRT) apparatus has an envelope  10 . This CRT apparatus is a self-convergence type color CRT apparatus used in a color TV receiver, a color terminal display, etc. The envelope  10  has a substantially rectangular face panel  11 , and a funnel  12  integrally coupled to the face panel  11 . A phosphor screen  13  is formed on an inside surface of the face panel  11  and comprises striped or dot-shaped three-color phosphor layers that emit blue, green and red light, respectively. A shadow mask  15  is disposed to face the phosphor screen  13  and has many apertures  14  in its inner area. The shadow mask  15  is attached to a mask frame  41 . The mask frame  41  is engaged with stud pins  44  via resilient support members  42 . The stud pins  44  are provided on an inner surface of a skirt portion  43  of the face panel  11 . An inner shield  45  is attached to the mask frame  41 . An explosion-proof band  46  and lug portions  47  for attachment to the housing (not shown) are provided on an outer peripheral part of the skirt portion  43 . 
     An in-line electron gun assembly  18  is disposed within a neck  16  corresponding to a small-diameter portion of the funnel  12 . The electron gun assembly  18  emits three horizontal in-line electron beams  17 B,  17 G and  17 R, i.e. a center beam  17 G and a pair of side beams  17 B and  17 R, toward the phosphor screen  13 . In the electron gun assembly  18 , side beam passage holes in the low-voltage side electrode of a main lens section are decentered relative to those in the high-voltage side electrode of the main lens section. Thereby, the three electron beams  17 B,  17 G and  17 R are converged on a central area of the phosphor screen  13 . 
     An end portion of the neck  16  is sealed by a stem portion  21 . A plurality of stem pins  20  are embedded in the stem portion  21 . The stem pins  20  are electrically connected to the electrodes of the electron gun assembly  18  and supplied with predetermined voltages. 
     A deflection yoke  19  is mounted on an outside part of the funnel  12 . The deflection yoke  19  produces non-uniform magnetic fields that deflect the three electron beams  17 B,  17 G and  17 R emitted from the electron gun assembly  18  in a horizontal direction H and a vertical direction V. The non-uniform magnetic fields comprise a pincushion-shaped horizontal deflection magnetic field and a barrel-shaped vertical deflection magnetic field. 
     In this type of color CRT apparatus, the three electron beams  17 B,  17 G and  17 R emitted from the electron gun assembly  18  are focused on the associated phosphor layers on the phosphor screen  13 , while being self-converged toward the phosphor screen  13 . In addition, the three electron beams  17 B,  17 G and  17 R are deflected by the non-uniform deflection magnetic fields to scan the phosphor screen  13  in the horizontal direction H and vertical direction V. Thus, a color image is displayed. 
     The electron gun assembly  18  applied to the color CRT apparatus is constructed, as shown in FIGS. 1 and 2. The electron gun assembly  18  includes cathodes KB, KG and KR each accommodating a heater. The cathodes KB, KG and KR are arranged in line in the horizontal direction H perpendicular to a tube-axis direction Z at intervals of about 5 mm. The electron gun assembly  18  includes first to sixth grids successively arranged in the tube-axis direction Z from the cathode K side toward the phosphor screen  13 . The third grid G 3  comprises a first segment G 3 - 1  disposed on the cathode K side and a second segment G 3 - 2  disposed on the phosphor screen  13  side. The fifth grid G 5  comprises a first segment G 5 - 1  disposed on the cathode K side and a second segment G 5 - 2  disposed on the phosphor screen  13  side. An intermediate electrode GM is disposed between the second segment G 5 - 2  of fifth grid G 5  and the sixth grid G 6 . A convergence cup CV is fixed to the sixth grid G 6  by means of welding. 
     The first grid G 1  and second grid G 2  are arranged at a very small distance of 0.2 mm or less. The second grid G 2  and the first segment G 3 - 1  of third grid G 3  are arranged at a distance of about 0.5 to 1 mm. The first segment G 3 - 1  and second segment G 3 - 2  are arranged at a distance of about 0.2 to 0.8 mm. The second segment G 3 - 2  and fourth grid G 4  are arranged at a distance of about 0.5 to 1 mm. The fourth grid G 4 , the first segment G 5 - 1  of fifth grid G 5 , the second segment G 5 - 2  of fifth grid G 5 , the intermediate electrode GM, and the sixth grid G 6  are arranged at distances of about 0.5 to 1 mm, respectively. 
     These electrodes are fixed by a pair of insulating supports  22  formed of bead glass. A plurality of contacts  24  provided on the convergence cup CV are electrically connected to an internal conductor film  23  coated on an area extending from the inner surface of the funnel  12  to the inner surface of the neck  16 . A lead line b for supplying voltage to the first segment G 3 - 1  of third grid G 3  and a lead line c for connecting the first segment G 3 - 1  and the segment G 5 - 2  of fifth grid G 5  are connected at diagonal positions of the first segment G 3 - 1 . 
     Each of the electrodes has three electron beam passage holes for passing the three electron beams  17 B,  17 G and  17 R in association with the cathodes KB, KG and KR. Each of the first grid G 1  and second grid G 2  is a plate-shaped electrode and has small electron beam passage holes each having a diameter of 0.5 mm or less. The first segment G 3 - 1  is a plate-shaped electrode and has electron beam passage holes each having a diameter of about 1 mm. The second segment G 3 - 2  has, in its surface facing the first segment G 3 - 1 , oval electron beam passage holes each having a vertical dimension of about 1 mm and a horizontal dimension of about 3-6 mm. Each of that surface of the second segment G 3 - 2 , which faces the fourth grid G 4 , the fourth grid G 4 , the first segment G 5 - 1 , the second segment G 5 - 2 , the intermediate electrode GM, and the sixth grid G 6  has relatively large electron beam passage holes each having a diameter of about 3-6 mm. 
     Electron lenses are created between the electrodes by making the electron beam passage holes of the respective electrodes face each other at predetermined distances. Specifically, the cathodes K, first grid G 1  and second grid G 2  constitute an electron beam generating section that generates electron beams. The first segment G 5 - 1  of fifth grid G 5 , the second segment G 5 - 2  of fifth grid G 5 , the intermediate electrode GM and the sixth grid G 6  constitute a main lens section for ultimately focusing the electron beams on the phosphor screen  13 . 
     Quadrupole lenses are created between the first segment G 3 - 1  and second segment G 3 - 2  of the third grid and between the first segment G 5 - 1  and second segment G 5 - 2  of the fifth grid by combining circular, vertically elongated and horizontally elongated electron beam passage holes formed in their mutually opposing surfaces, or by providing screens around their asymmetric electron beam passage holes. 
     The first segment G 3 - 1  of the third grid is constructed, for example, as shown in FIGS. 3 and 4. The first segment G 3 - 1  has a flat electrode plate  31 . The electrode plate  31  has a rectangular shape elongated in the horizontal direction H. The electrode plate  31  has three electron beam passage holes  32  provided in association with the three electron beams arranged in the horizontal direction H. 
     The electrode plate  31  has vibration-damping portions  33  formed to damp vibration in the tube-axis direction Z. Each vibration-damping portion  33  is a recessed/projected portion that is recessed or projected in the tube-axis direction Z. In this embodiment, the vibration-damping portion  33  is an annular recess or projection formed around each electron beam passage hole  32 . The vibration-damping portion  33  is formed by means of drawing, or a so-called beading process. 
     The first segment G 3 - 1  also has a vibration-damping portion  34 . The vibration-damping portion  34  is a recessed portion formed by recessing the entire electrode plate  31  including the vibration-damping portions  33  toward the second grid G 2  side. The vibration-damping portion  34  is formed by a beading process. 
     The first segment G 3 - 1  has embedment portions  36  extending in the vertical direction V. The embedment portions  36  are formed in parallel to the electrode plate  31  with electron beam passage holes  32 , and are displaced relative to the electrode plate  31  in the tube-axis direction Z. The electrode plate  31  and embedment portions  36  are integrally coupled by oblique portions  35 . 
     Each embedment portion  36  has a reinforcement portion  37  for reinforcing fixation to the insulating support  22 . The reinforcement portion  37  is formed by a recessed or projecting portion extending in the longitudinal direction of the embedment portion  36 . The reinforcement portion  37  is formed by a beading process. Alternatively, the reinforcement portion  37  may be formed by subjecting to a beading process the entire embedment portion  36  excluding an outer peripheral portion thereof. 
     Thereby, the flexure rigidity of the first segment G 3 - 1  to vibration in the tube-axis direction Z can be enhanced, and mechanical vibration in the tube-axis direction Z can be suppressed. Specifically, the vibration-damping portions (recessed/projected portions)  33  formed symmetric with respect to the electron beam passage holes  32  of first segment G 3 - 1  can enhance the flexure rigidity of the electrode itself in the state in which the first segment G 3 - 1  is supported by the embedment portions  36  embedded in the insulating supports  22 . In addition, the action of the coulomb force due to a varying dynamic focus voltage applied to the first segment G 3 - 1  concentrates mainly at the vibration-damping portions (recessed/projected portions)  33  which are located closest to the adjacent electrode. Accordingly, the coulomb force does not act at the center of the electrode and is dispersed to the vibration-damping portions  33 . The variation in coulomb force does not convert to flexure of the electrode in the state in which the electrode is supported by the embedment portions  36 . Thereby, it is possible to suppress a frequency modulation and an increase in mechanical vibration amplitude due to a resonance between the natural vibration characteristics of the electrode in tube-axis direction Z and the frequency component in the dynamic focus voltage. Therefore, occurrence of abnormal noise via the funnel can effectively be suppressed. 
     In addition, by the beading process for forming the vibration-damping portion  34 , the electron beam passage holes  32  in the electrode plate  31  of first segment G 3 - 1  can be made closer to the second segment G 3 - 2 . This increases the lens intensity of the quadrupole lens created between the first segment G 3 - 1  and second segment G 3 - 2 . Moreover, if the other part of the electrode plate  31  is made away from the second segment G 3 - 2 , the coulomb force between the electrodes can be decreased. 
     Within the neck  16  of the above-described CRT apparatus, a resistor R is provided to extend in the tube-axis direction Z. As is shown in FIG. 2, the resistor R is provided, for example, on that surface of the insulating support  22 , which is opposite to the surface provided with the electrodes. One end A of the resistor R is connected to the convergence cup CV, and the other end B thereof is led out of the tube and grounded. An intermediate point C of resistor R is electrically connected to the intermediate electrode GM. 
     In the electron gun assembly  18  with the above structure, the three cathodes KB, KG and KR are supplied with a voltage of about 100 to 150 V. The first grid G 1  is grounded. The second grid G 2  and fourth grid G 4  are connected within the tube and supplied with a voltage of about 600 to 800 V from a power supply E 1 . 
     The first segment G 3 - 1  of third grid G 3  and the second segment G 5 - 2  of the fifth grid are connected within the tube. These electrodes are supplied with a dynamic focus voltage obtained by superimposing an AC component supplied from an AC power via a capacitor C 1  upon a focus voltage (reference voltage) of about 6-9 kV supplied from a power supply E 3 . This AC component varies in synchronism with the deflection magnetic fields. 
     The second segment G 3 - 2  of the third grid and the first segment G 5 - 1  of the fifth grid are connected within the tube. These electrodes are supplied with a focus voltage of about 6-9 kV from a power supply E 2 . The sixth grid G 6  is supplied with an anode voltage of about 25-30 kV from a power supply E 5 . The intermediate electrode GM is supplied with a voltage from the intermediate point C of resistor R, which voltage is about 50% to 70% of the anode voltage supplied to the sixth grid G 6 . 
     In the above structure, a first quadrupole lens section is created by the first segment G 3 - 1  and second segment G 3 - 2  of the third grid G 3 . The first quadrupole lens section controls the incidence angles of the three electron beams  17 B,  17 G and  17 R, which enter the main lens section comprising the electrodes from the first segment G 5 - 1  of fifth grid G 5  to the sixth grid G 6 , in synchronism with the deflection magnetic fields. At the same time, a second quadrupole lens section is created by the first segment G 5 - 1  and second segment G 5 - 2  of fifth grid G 5 . The second quadrupole lens section can alter its own lens action in synchronism with the deflection magnetic fields by the application of the dynamic focus voltage. Thus, the horizontal deformation of the beam spot can be improved, compared to the electron gun assembly supplied with no dynamic focus voltage. Moreover, the three electron beams  17 B,  17 G and  17 R can be appropriately focused on a peripheral portion of the phosphor screen  13 . Therefore, a moire, etc. can be suppressed at a peripheral portion of the screen, and good focus characteristics can be obtained over the entire screen. 
     The first segment G 3 - 1  of third grid G 3  is provided with vibration-damping portions  33  and  34  formed by applying a beading process to a peripheral portion of each electron beam passage hole  32  and an outer peripheral portion of the electrode plate  31 . Thus, the flexure rigidity of the first segment G 3 - 1  can be increased, and the flexure vibration in the tube-axis direction Z can greatly be suppressed. Accordingly, the amplitude of vibration propagated to the funnel  12  is remarkably suppressed, and the amplitude of vibration of the funnel  12  decreased to an negligible level. As a result, occurrence of abnormal noise can be prevented. 
     Compared to an electrode body provided with no vibration-damping portions formed by a beading process, the electrode body G 3 - 1  with the above structure can have sufficient vibration-suppressing effect and support strength when embedded in the insulating support, even if the thickness of the electrode plate  31  is decreased about 20% to about 0.4 mm to 0.32 mm. It is thus possible to similarly decrease the thickness of the embedment portion  36  of electrode body G 3 - 1 . By decreasing the thickness of the embedment portion  36 , the embedment portion  36  is well supported and fixed in the insulating support  22 . Thus, the support strength of the embedment portion  36  in the insulating support  22  can be increased. The reinforcement portion  37 , which is provided on the embedment portion  36 , further increases the support strength of the electrode body. Moreover, since the weight of the electrode is decreased, the moment of vibration due to coulomb force can be decreased. As a result, abnormal noise can effectively be suppressed. 
     Using the CRT apparatus with the above-described electron gun assembly  18 , abnormal noise was measured by the same method as in the prior art. In this case, the first segment G 3 - 1  of third grid G 3  and the second segment G 5 - 2  of fifth grid G 5  of the electron gun assembly  18  were supplied with a dynamic focus voltage including an AC component of 40-100 kHz. FIGS. 5 and 6 show the measured results. The abscissa indicates the frequency of the AC component included in the dynamic focus voltage, and the ordinate indicates the level of sound pressure sensed by humans in 10 grades. According to the measured results, as shown in FIG. 5, no abnormal noise, which occurred in the prior art, was recognized in all frequency bands. As regards other manufacture lots, as shown in FIG. 6, abnormal noise occurred very rarely in specific frequency bands, but the sound pressure level was not higher than 2. No practical problem was posed. According to the CRT apparatus with the above structure, abnormal noise can remarkably be suppressed. 
     The above-described embodiment is directed to the electron gun assembly  18  as shown in FIG. 2 by way of example. The present invention is not limited to this structure. The electrode structures and the voltages applied to the electron gun assembly  18  may be variously modified. For example, the electron gun assembly  18  may be constructed, as shown in FIG.  7 . In the electron gun assembly  18  shown in FIG. 7, the fourth grid G 4  and intermediate electrode GM are connected, and the voltage applied to the intermediate electrode GM is also applied to the fourth grid G 4 . This electron gun assembly  18 , too, can operate like the electron gun assembly shown in FIG. 2, and can have the same advantages. 
     On the other hand, the first segment G 3 - 1  of third grid G 3  may be constructed, as shown in FIG.  8 . The electron beam passage hole  32  formed in the electrode plate  31  may not be a circular hole, but a slit elongated in the horizontal direction H. With this structure, too, the occurrence of abnormal noise can effectively be suppressed by the vibration-damping portions  33  and  34 . Of course, the electron beam passage hole may have some other shape, e.g. a vertical elongated shape. 
     In the above-described embodiment, the vibration-damping portion  33  is an annular recessed/projected portion formed around the electron beam passage hole  32 . The structure of the vibration-damping portion  33  is not limited to this. For example, the same advantage can be obtained even if the individually formed recessed/projected portion is disposed symmetric with respect to the electron beam passage hole. 
     The first segment G 3 - 1  may have other structures, as shown in FIGS. 18A to  18 E. With these structures wherein vibration-damping portions  33  are formed with the electron beam passage holes  32  interposed, the flexure rigidity can further be enhanced. 
     The vibration-damping portions  33  and  34  and reinforcement portions  37  may be provided on another electrode supplied with a dynamic focus voltage, e.g. the second segment G 5 - 2  of fifth grid G 5 . The kind and number of electrodes to be provided with vibration-damping portions  33  and  34  and reinforcement portions  37  by the beading process are not limited. The structures of the vibration-damping portion  33 ,  34  and the structures of the reinforcement portions  37  may be uniform or combinations of various structures. Needless to say, these structures may be modified where necessary. 
     The present invention is also applicable to an electron gun assembly  18 , as shown in FIG. 9, which adopts a bipotential-focus-type dynamic focus method. In this electron gun assembly  18 , a first grid electrode G 1 , a second grid electrode G 2 , a first segment G 3 - 1  and a second segment G 3 - 2  of a third grid, and a fourth grid G 4  are arranged on the same axis at predetermined distances from three cathodes KB, KG and KR. For example, a voltage of about 150 V is applied to the cathodes KB, KG and KR. The first grid G 1  is grounded. A voltage of about 600 V is applied to the second grid G 2 . The first segment G 3 - 1  is supplied with a voltage of about 8 kV, and the second segment G 3 - 2  is supplied with a dynamic focus voltage of about 8 kV. An anode voltage of about 26 kV is applied to the fourth grid electrode G 4 . The dynamic focus voltage is a parabolic voltage varying in accordance with the deflection operations so as to take a maximum value when the three electron beams  17 B,  17 G and  17 R are deflected onto a peripheral area of the phosphor screen  13  by the deflection magnetic fields. 
     In this electron gun assembly  18 , the cathodes KB, KG and KR, first grid G 1  and second grid G 2  constitute an electron beam generating section. The second grid G 2  and the first segment G 3 - 1  constitute a pre-focus lens section. The second segment G 3 - 2  and fourth grid G 4  constitute a bipotential type main lens section, and focus the three electron beams  17 B,  17 G and  17 R on the phosphor screen  13 . 
     The potential difference between the second segment G 3 - 2  and fourth grid G 4  takes a minimum value when the electron beams  17 B,  17 G and  17 R are deflected on the peripheral area of the phosphor screen  13 . Accordingly, in this case, the lens intensity of the main lens section takes a minimum value. At the same time, the lens intensity of a quadrupole lens constituted by the first segment G 3 - 1  and second segment G 3 - 2  takes a maximum value. 
     The quadrupole lens is designed to focus the electron beams in the horizontal direction H and to diverge them in the vertical direction V. Thereby, when the electron beams are deflected on the peripheral portion of the phosphor screen  13 , the lens intensity of the main lens section is decreased. Thus, the movement of the focal point is compensated as the distance between the electron gun assembly  18  and phosphor screen  13  increases and the image point moves farther. At the same time, with the formation of the quadrupole lens section, a deflection aberration due to the deflection magnetic fields is compensated. 
     In the electron gun assembly  18  with the above structure, the second segment G 3 - 2  supplied with the dynamic focus voltage is formed of a cup-shaped electrode. Compared to the above-described case where the second segment G 3 - 2  is formed of a plate-shaped electrode, vibration due to coulomb force can be lessened. However, if annular vibration-damping portions  33  are formed by a beading process, for example, around the electron beam passage holes  32 , the flexure rigidity of the electrode can be enhanced and abnormal noise can be prevented more effectively. 
     As has been described above, according to the CRT apparatus of this invention, even if the electrode to which the dynamic focus voltage is applied is located near the heaters, or the heat sources, in the cathodes (i.e. even if the first quadrupole lens is situated near the cathodes in order to improve horizontal deformation of the beam spot on the peripheral area of the screen), it is possible to suppress vibration of the electrode in the tube-axis direction resulting from a variation in potential difference between the electrodes due to the application of the dynamic focus voltage. Moreover, it is possible to suppress a resonance phenomenon due to the frequency characteristics of the AC component in the dynamic focus voltage and the natural vibration characteristics (characteristic frequency) of the electrode supplied with the dynamic focus voltage. Thus, the frequency modulation and the increase in amplitude can be suppressed to a substantially negligible level. Therefore, the occurrence of abnormal noise at the funnel due to propagation of vibration from the electrode can be suppressed. At the same time, since the first quadrupole lens can be situated near the heat source, horizontal deformation of the beam spot at the peripheral portion of the screen can effectively be improved. The industrial advantages of these features are very great. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.