Abstract:
The in-line type electron gun includes an electron beam generating section for generating and directing plural electron beams along toward a phosphor screen, and an electron beam focusing section for focusing the plural electron beams from the electron beam generating section onto the phosphor screen. The electron beam focusing section includes a focus electrode, at least one intermediate electrode and an anode supplied with a highest voltage arranged in the order named. The at least one intermediate electrode is supplied with an intermediate voltage between the highest voltage and a voltage supplied to the focus electrode. The following relationship is satisfied: 1.55≦D/L≦1.72, and 18.2 mm≦d≦26 mm,where D (mm) is a diagonal length of a usable display area of the phosphor screen, L (mm) is a distance from a center of the phosphor screen to an end of the anode facing toward the focus electrode, and d (mm) is an outside diameter of the neck portion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cathode ray tube, and particularly to a cathode ray tube having its overall length shortened with its deflection angle increased, but without increasing deflection power consumption or degrading display resolution. 
     Cathode ray tubes such as color cathode ray tubes used as TV picture tubes and monitor tubes for information terminals house an electron gun for emitting a plurality (usually three) of electron beams at one end of an evacuated envelope, a phosphor screen (a viewing screen) formed of phosphors coated on an inner surface of the evacuated envelope at the other end thereof for emitting light of a plurality (usually three) of colors, and a shadow mask which serves as a color selection electrode and is closely spaced from the phosphor screen. 
     The electron beams emitted from the electron gun are deflected to scan the phosphor screen horizontally and vertically in two dimensions, by magnetic fields generated by a deflection yoke mounted externally of the evacuated envelope and display a desired image on the phosphor screen. 
     FIG. 16 is a schematic cross-sectional view of a shadow mask type color cathode ray tube as an example of a cathode ray tube to which the present invention is applicable, and FIG. 17 is a front view of a panel portion of the color cathode ray tube of FIG.  16 . 
     In FIG. 16, reference numeral  1  denotes the panel portion forming a viewing screen,  2  is a neck portion,  3  is a funnel portion,  4  is a phosphor screen,  5  is a shadow mask,  6  is a mask frame,  7  is a magnetic shield,  8  is a mask suspension mechanism,  9  is an in-line type electron gun,  10  is a deflection yoke,  11  is an internal conductive coating,  12  is a shield cup,  13  is a contact spring,  14  is a getter,  15  is a stem,  16  are stem pins,  17  is an implosion protection band,  18  is a magnetic beam adjusting device, and  19  is a usable display area. 
     In FIG. 16, a dimension L is a distance from the phosphor screen  4  to the end of the anode on the focus electrode side thereof, of the in-line beam type electron gun  9 , and a dimension d is an outside diameter of the neck portion  2 . In FIG. 17, a dimension D is a diagonal length of the usable display area  19 . 
     The evacuated envelope of this color cathode ray tube is comprised of the panel portion  1 , the neck portion  2  and the funnel portion  3 . Three electron beams (one center electron beam Bc and two side electron beams Bs) emitted from the in-line type electron gun housed in the neck portion  2  is scanned over the phosphor screen  4  two-dimensionally by the horizontal and vertical deflection magnetic fields generated by the deflection yoke  10  mounted around the transition region between the funnel portion  3  and the neck portion. 
     The highest voltage (an anode voltage) to the electron gun is supplied by the contact springs  13  attached to the shield cup  12  via the internal conductive coating  11  coated on the inner surface of the funnel portion  3  from an anode button (not shown) embedded in a wall of the funnel portion  3 . 
     The deflection yoke  10  is of a self-converging type which provides a pin cushion-like horizontal deflection magnetic field and a barrel-like vertical deflection magnetic field to converge a plurality of electron beams over the entire phosphor screen. 
     The electron beams Bc, Bs are modulated in amount by modulating signals such as video signals supplied via the stem pins  1   6 , are color-selected by the shadow mask  5  disposed immediately in front of the phosphor screen  4 , and impinge upon the phosphors of the corresponding colors to reproduce a desired image. Color purity of the reproduced color image and static convergence of the three electron beams are adjusted by the magnetic beam adjusting device  18  mounted around the neck portion  2 . 
     In color cathode ray tubes of this type, a large-diameter non-axially-symmetric lens formed between an anode and a focus electrode are extensively used as a main lens system of the electron gun to provide sufficiently small electron beam spots over the entire phosphor screen. 
     FIG. 18 is a schematic side elevation view of a prior art electron gun employing the large-diameter non-axially-symmetric lens system viewed in a direction perpendicular to the in-line direction of the electron beams. In this electron gun, an electron beam generating section is comprised of a cathode  21 , the first grid electrode  22  and the second grid electrode  23 , and an accelerating and focusing section is comprised of the third grid electrode  24  serving as a focus electrode and the fourth electrode  25  serving as an anode. The cathode and electrodes are fixed on a pair of insulating rods  26  made of glass in the predetermined order and the predetermined spaced relationship. 
     The contact springs  13  are attached to the front end of the shield cup  12  which in turn is attached to the anode  25 . The highest voltage is applied to the anode  15  by the resilient contact springs  13  pressed against the internal conductive coating  11  on the inner wall of the funnel portion  3 . 
     FIG. 19 is a plan view of the third grid electrode  24  viewed from an anode side thereof and FIG. 20 is a cross-sectional side view of the third grid electrode  24  viewed in a direction perpendicular to the in-line direction of the three electron beams. Reference  31  denotes an electric field correction plate having three vertically elongated electron beam apertures with their minor diameters in the in-line direction of the electron beams and disposed within the third grid electrode  24 , and reference numeral  32  denotes an electrode having the configuration of the outer periphery of a racetrack shape (hereinafter referred to as a racetrack electrode) and formed with a single opening with its major diameter in the in-line direction of the electron beams. 
     FIG. 21 is a plan view of the anode  25  viewed from the third grid electrode  24  side thereof and FIG. 22 is a cross-sectional side view of the anode  25  viewed in the direction perpendicular to the in-line direction of the three electron beams. Reference  33  denotes an electric field correction plate having a vertically elongated electron beam aperture at the center with its minor diameter in the in-line direction of the electron beams and cutouts on opposite sides of the electron beam aperture and disposed within the anode  25 , and reference numeral  34  denotes a racetrack electrode formed with a single opening with its major diameter in the in-line direction of the electron beams. With such an electrode structure, an effectively large-diameter electron lens is formed between the grid electrode  24  and the anode to provide a high definition image display. 
     SUMMARY OF THE INVENTION 
     While cathode ray tubes presently used as a monitor tube in the information terminals increases in the size of the viewing screen, there is a demand for reduction of their overall length with a view to improving the efficiency of utilization of the space. 
     The overall length of cathode ray tubes without changing the size of the viewing screen can be shortened by increasing the maximum deflection angle of the electron beams so as to decrease the distance from the phosphor screen to the end of the anode on its focus electrode (the third grid electrode). 
     In this specification, the ratio D/L is used instead of a deflection angle, where D (mm) is a diagonal length of the usable display area of the viewing screen, and L (mm) is a distance from the center of the phosphor screen to the end of the anode on its focus electrode side in a cathode ray tube. 
     A 90° deflection angle is extensively employed in presently-used monitor tubes for information terminals and this corresponds to the D/L of about 1.35. If the ratio D/L is increased without changing the overall length of an electron gun, the overall length of the cathode ray tube decreases correspondingly. 
     If the ratio is selected to be at least 1.55, for example, the overall length of a cathode ray tube having the D of 460 mm (corresponding to a nominal 19-inch diagonal tube) is shortened approximately to that of a cathode ray tube having the D of 410 mm (corresponding to a nominal 17-inch diagonal tube) with D/L being 1.35, and the overall length of a cathode ray tube having the D of 510 mm (corresponding to a nominal 21-inch diagonal tube) is shortened approximately to that of a cathode ray tube having the D of 460 mm (corresponding to a nominal 19-inch diagonal tube) with D/L being 1.35. 
     But, if the ratio D/L is selected to be at least 1.55 for the prior art cathode ray tubes, the deflection power consumption is increased due to the increase beam deflection angle when the outside diameter of a glass tube forming the neck portion (hereinafter referred to as a glass neck tube) is unchanged, and is 29.1 mm, for example, as in the prior art cathode ray tubes. 
     FIG. 23 is a graph showing the relationship between the deflection power consumption (MHA 2 ) and the outside diameter d (mm) of the glass neck tubes with the ratio D/L as a parameter, where D (mm) is a diagonal length of the usable display area of the viewing screen, and L (mm) is a distance from the center of the phosphor screen to the end of the anode on its focus electrode side in cathode ray tubes. In this specification, for simplicity, the deflection power consumption is evaluated in terms of a product of an inductance (mH) of a deflection yoke and the square of a peak-to-peak value of a deflection current (A). The curves (a) and (b) correspond to the D/L of 1.35 (a 90° deflection) and 1.55 (a 100° deflection) and the curve (c) indicates the case of the D/L of 2.25 (a 110° deflection) for comparison. 
     FIG. 23 shows that the deflection power consumption of the cathode ray tube with the D/L of 1.55 increases by about 17% compared with that of the cathode ray tube with the D/L of 1.35 when both the cathode ray tubes use a glass neck tube of 29.1 mm in outside diameter. 
     The increase in deflection power consumption increases load to the deflection circuit, and consequently the increase in the deflection power consumption needs to be limited to about 10% at most, that is, the deflection power consumption needs to be limited to 17.4 mHA 2  at most, so that the cathode ray tubes with the higher D/L ratio are operated at a high deflection frequency comparable to that operable with the prior art cathode ray tubes with the D/L of 1.35. This means that the outside diameter of the glass neck tube needs to be 26 mm at most. 
     The wall thickness of the glass neck tube generally needs to be about 2.5 mm to prevent destruction of the glass neck tube by arcing and consequently reduction of the outside diameter of the glass neck tube results in the reduction of the inside diameter of the glass neck tube which in turn reduces the outside diameter of the electron gun housed in the glass neck tube. 
     FIG. 24 is a graph showing the relationship between the outside diameter of the glass neck tubes and the effective lens diameter of the main lenses formed by the electrodes shown in FIGS. 19 to  22 . In this specification, the effective lens diameter of a lens is defined as a diameter of an equal-diameter two-cylinder lens having aberration approximately equal to that of the lens in question. It shows that the outside diameter 29.1 mm of the glass neck tube provides the effective lens diameter of 8 mm, but the outside diameter 24.3 mm of the glass neck tube provides the effective lens diameter of 5.6 mm, resulting in the reduction of about 30% in the effective lens diameter. 
     This reduction in the effective lens diameter increases spherical aberration, consequently increases the diameter of the electron beam spots and degrades the quality of the displayed images. This has been an obstacle to employing the larger beam deflection angles. 
     The diameter of an electron beam in the main lens has to be optimized to reduce the diameter of the beam spot on the phosphor screen. An analysis by computer simulation showed that the optimum electron beam diameter in the main lens is about 1.3 mm for a main lens of 8 mm in diameter and this minimizes the electron beam spot on the phosphor screen. 
     FIG. 25 is a schematic cross-sectional view of the neck portion for explaining the minimum usable outside diameter of the glass neck tube, reference character N denotes the glass neck tube, M is an electrode of the main lens and A are electron beam apertures in the electrode M of the main lens. In FIG. 25, for simplicity we have omitted a number of features needed for the electrode of the main lens. 
     The electrode M of the main lens is housed in the glass neck tube N of d (mm) in outside diameter. The diameter d 1  of each of electron beam apertures A in the electrode M must be at least 1.3 mm so that the electron beams do not strike the electrode M. 
     When the electrode M (the electric field correction plate  31  in FIG. 19, for example) of the main lens is made of a plate-like component, the thickness of the plate-like component must be at least 0.5 mm in order to provide sufficient mechanical strength, and a spacing S 2  between the opposing edges of the two adjacent electron beam apertures A must be at least 0.5 mm to facilitate punching of the electron beam apertures A by using a punch press. 
     FIG. 26 is a graph showing the relationship between the displacement P of the electron beam spot on the phosphor screen caused by charging of the inner surface of the glass neck tube after the cathode ray tube operation of 24 hours and the distance S 1  from the center line of a path of the side electron beam to the inner wall of the glass neck tube. 
     It is known that the maximum permissible displacement P of the electron beam spot on the phosphor screen after the operation of 24 hours is generally 0.1 mm, and therefore FIG. 26 shows that the displacement P of the electron beam spot after the operation of 24 hours is kept within the maximum permissible limit by selecting the distance S 1  to be at least 4.8 mm. 
     The minimum of the outside diameter d of the glass neck tube N is calculated with the wall thickness S 3  of the glass neck tube being 2.5 mm as follows: 
     
       
           d= 2×(S 1 +S 2 +d 1 +S 3 )=2×(4.8+0.5+1.3+2.5)=18.2 mm. 
       
     
     The minimum usable outside diameter d of the glass neck tube N is 18.2 mm. 
     FIG. 27 is a graph showing the relationship between deflection power consumption and the ratio D/L of a diagonal length D of the usable display area of the viewing screen to a distance L from the center of the phosphor screen to the end of the anode on its focus electrode side in a cathode ray tube for the outside diameters of the glass neck tubes of 18.2 mm and 29.1 mm. The curve (a) indicates the relationship for the glass neck tube of 18.2 mm in outside diameter and the curve (b) indicates the relationship for the glass neck tube of 29.1 mm in outside diameter for comparison. 
     The curve (a) shows that the ratio D/L must be selected to be not more than 1.72 to limit the deflection power consumption to 17.4 mHA 2 . But it has been difficult to shorten the overall length of a cathode ray tube without increasing deflection power consumption or degrading the image quality. 
     It is an object of the present invention to provide a cathode ray tube having its overall length shortened without increasing deflection power consumption or degrading the image quality, by solving the above problems. 
     The following describes the representative structures of the cathode ray tubes in accordance with present invention for achieving the above object. 
     To accomplish the above objects, in accordance with an embodiment of the present invention, there is provided a color cathode ray tube comprising an evacuated envelope comprising a panel portion, a neck portion and a funnel portion for connecting said panel portion and said neck portion, a phosphor screen formed on an inner surface of said panel portion, an in-line type electron gun housed in said neck portion, and an electron beam deflection yoke mounted around a transition region between said funnel portion and said neck portion for generating magnetic deflection fields, said in-line type electron gun comprising an electron beam generating section having a plurality of in-line cathodes, an electron beam control electrode and an accelerating electrode arranged in the order named for generating and directing a plurality of electron beams along separate paths in a horizontal plane toward said phosphor screen, an electron beam focusing section for focusing said plurality of electron beams from said electron beam generating section onto said phosphor screen, said electron beam focusing section comprising a focus electrode, at least one intermediate electrode and an anode supplied with a highest voltage arranged in the order named, said at least one intermediate electrode being supplied with an intermediate voltage between said highest voltage and a voltage supplied to said focus electrode, wherein the following relationship is satisfied: 
     
       
         1.55 ≦D/L≦ 1.72, 
       
     
     and 
     
       
         18.2 mm≦ d≦ 26 mm, 
       
     
     where D (mm) is a diagonal length of a usable display area of said phosphor screen, L (mm) is a distance from a center of said phosphor screen to an end of said anode facing toward said focus electrode, and d (mm) is an outside diameter of said neck portion. 
     To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a color cathode ray tube wherein in the above embodiment, said focus electrode are subdivided into a plurality of electrode members, at least one first-type electron lens is formed by electrode members of said plurality of electrode members for focusing said plurality of electron beams in one of horizontal and vertical directions and diffusing said plurality of electron beams in another of the horizontal and vertical directions, a strength of said at least one first type electron lens becoming weaker with increasing deflection of said plurality of electron beams, a second-type electron lens is formed by electrode members of said plurality of electrode members for exerting a focusing action on said plurality of electron beams weakening with the increasing deflection of said plurality of electron beams, and a main lens is formed by said anode, said at least one intermediate electrode and one of said plurality of electrode members facing said at least one intermediate electrode for focusing said plurality of electron beams stronger in a horizontal direction than in a vertical direction. 
     The above embodiments provide cathode ray tubes having their overall length shortened without increasing the deflection power consumption or degrading the image display quality. 
     The present invention is not limited to the structure of the above embodiments, and various changes and modifications can be made to the above-explained structures without departing from the spirit and scope of the invention as defined in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, in which like reference numerals designate similar components throughout the figures, and in which: 
     FIG. 1 is a schematic cross-sectional view of a shadow mask type color cathode ray tube similar to that shown in FIG. 16, for explaining an embodiment of a cathode ray tube in accordance with the present invention; 
     FIG. 2 is a schematic side elevation view of an in-line type electron gun housed in a neck portion of the color cathode ray tube of FIG. 1, viewed in a direction perpendicular to the in-line direction of the electron beams; 
     FIG. 3 is a plan view of the third grid electrode taken along line III—III of FIG. 2; 
     FIG. 4 is a cross-sectional view of the third grid electrode taken along line IV—IV of FIG. 3; 
     FIG. 5 is a plan view of an anode taken along line V—V of FIG. 2; 
     FIG. 6 is a cross-sectional view of the anode taken alo ng line VI—VI of FIG. 5; 
     FIG. 7 is a plan view of an intermediate electrode taken along line VII—VII of FIG. 2; 
     FIG. 8 is a cross-sectional view of the intermediate electrode taken along line VIII—VIII of FIG. 7; 
     FIG. 9 is a graph showing the relationship between the voltage applied to the intermediate electrode and the effective diameter of the main lens for explaining an embodiment of a cathode ray tube in accordance with the present invention; 
     FIG. 10 is a side elevation view of an in-line type electron gun viewed in a direction perpendicular to the in-line direction of the electron beams for explaining another embodiment of a cathode ray tube in accordance with the present invention; 
     FIG. 11 is a schematic plan view of an end face of a second member of the third grid electrode on its side facing a first member of the third grid electrode of FIG. 10; 
     FIG. 12 is a schematic plan view of an end face of the first member of the third grid electrode on its side facing the second member of the third grid electrode of FIG. 10; 
     FIG. 13 is a schematic plan view of an end face of the second grid electrode on its side facing the first member of the third grid electrode of FIG. 10; 
     FIG. 14 is a cross-sectional view of the second grid electrode taken along line XIV—XIV of FIG. 13; 
     FIG. 15 is an illustration of waveforms of focus voltages; 
     FIG. 16 is a schematic cross-sectional view of a shadow mask type color cathode ray tube as an example of a cathode ray tube to which the present invention is applicable; 
     FIG. 17 is a front view of a panel portion of the color cathode ray tube of FIG. 16; 
     FIG. 18 is a schematic side elevation view of a prior art electron gun employing a large-diameter non-axially symmetric lens system viewed in a direction perpendicular to the in-line direction of the electron beams; 
     FIG. 19 is a plan view of the third grid electrode of the electron gun viewed from an anode side thereof of FIG. 18; 
     FIG. 20 is a cross-sectional view of the third grid electrode of the electron gun of FIG. 18 viewed in a direction perpendicular to the in-line direction of the three electron beams; 
     FIG. 21 is a plan view of the anode viewed from the third grid electrode side thereof; 
     FIG. 22 is a cross-sectional view of the anode viewed in the direction perpendicular to the in-line direction of the three electron beams; 
     FIG. 23 is a graph showing the relationship between the deflection power consumption (mHA 2 ) and the outside diameter d (mm) of the glass neck tubes with the ratio D/L as a parameter, where D (mm) is a diagonal length of the usable display area of the viewing screen, and L (mm) is a distance from the center of the phosphor screen to the end of the anode on its focus electrode side; 
     FIG. 24 is a graph showing the relationship between the outside diameter of the glass neck tubes and the effective lens diameter of the main lenses formed by the electrodes shown in FIGS. 19 to  22 ; 
     FIG. 25 is a schematic cross-sectional view of the neck portion for explaining the minimum usable outside diameter of the glass neck tube; 
     FIG. 26 is a graph showing the relationship between the displacement P of the electron beam spot on the phosphor screen after operation of 24 hours and the distance S 1  from the center line of a path of the side electron beam to the inner wall of the glass neck tube; 
     FIG. 27 is a graph showing the relationship between deflection power consumption and the ratio D/L of a diagonal length D of the usable display area of the viewing screen to a distance L from the center of the phosphor screen to the end of the anode on its focus electrode side for the outside diameters of the glass neck tubes of 18.2 mm and 29.1 mm; 
     FIG. 28 is a side elevation view of an in-line type electron gun viewed in a direction perpendicular to the in-line direction of three electron beams for explaining a cathode ray tube of a third embodiment of the present invention; 
     FIG. 29 is a front view of the side of the third member  54  of the fifth grid electrode facing the second member  55  of the fifth grid electrode of FIG. 28; 
     FIG. 30 is a cross-sectional view of the third member  54  of the fifth grid electrode  54  taken along line  130 — 130  of FIG. 29; 
     FIG. 31 is a front view of the side of the second member  55  of the fifth grid electrode facing the third member  54  of the fifth grid electrode of FIG. 28; 
     FIG. 32 is a cross-sectional view of the second member  55  of the fifth grid electrode  54  taken along line  132 — 132  of FIG. 31; 
     FIG. 33 is a front view of the side of the second member  55  of the fifth grid electrode facing the first member  56  of the fifth grid electrode of FIG. 28; 
     FIG. 34 is a side elevation view of an in-line type electron gun viewed in a direction perpendicular to the in-line direction of three electron beams for explaining a dimensional example of the third embodiment of the present invention; 
     FIG. 35 is a front view of the side of the intermediate electrode  52  facing the anode  51  of FIG. 34; 
     FIG. 36 is a side elevation view of the intermediate electrode  52  viewed in the in-line direction of the electron beams of FIG. 35; 
     FIG. 37 is a plan view of the cup-shaped electrode  71  of FIG. 34; 
     FIG. 38 is a cross-sectional view of the cup-shaped electrode  71  taken along line  138 — 138  of FIG. 37; 
     FIG. 39 is a plan view of the plate-like electrode  74  of FIG. 34; 
     FIG. 40 is a side elevation view of the plate-like electrode  74  of FIG. 39; 
     FIG. 41 is a plan view of the side of the anode  51  facing the fourth member  52  of the fifth grid electrode of FIG. 34; 
     FIG. 42 is a cross-sectional view of the anode  51  taken along line  142 — 142  of FIG. 41; 
     FIG. 43 is a plan view of the plate-like electrode  76  of FIG. 34; 
     FIG. 44 is a cross-sectional view of the plate-like electrode  76  taken along line  144 — 144  of FIG. 43; 
     FIG. 45 is a front view of the cup-shaped electrode  75  of FIG. 34; 
     FIG. 46 is a cross-sectional view of the cup-shaped electrode  75  taken along line  146 — 146  of FIG. 45; 
     FIG. 47 is a front view of the side of the fourth member  53  of the fifth grid electrode facing the intermediate electrode  52  of FIG. 34; 
     FIG. 48 is a cross-sectional view of the fourth member  53  taken along line  148 — 148  of FIG. 47; 
     FIG. 49 is a plan view of the plate-like electrode  77  of FIG. 34; and 
     FIG. 50 is a cross-sectional view of the plate-like electrode  77  taken along line  150 — 150  of FIG.  49 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a schematic cross-sectional view of a shadow mask type color cathode ray tube similar to that shown in FIG. 16, for explaining a first embodiment of a cathode ray tube in accordance with the present invention. The construction and operation of this color cathode ray tube is similar to those of the color cathode ray tube of FIG. 16, and therefore the explanation of those is omitted here. 
     The diagonal length D of the usable display area of the viewing screen of the panel portion  1  in FIG. 17 is 460 mm in the case of FIG. 1, and the outside diameter d of the neck portion  2  is 24.3 mm. 
     FIG. 2 is a schematic side elevation view of an in-line type electron gun housed in the neck portion of the color cathode ray tube of FIG. 1, viewed in a direction perpendicular to the in-line direction of the electron beams. This electron gun differs from the prior art electron gun shown in FIG. 18 in that an intermediate  27  electrode is disposed between the grid electrode  24  serving as a focus electrode and the fifth electrode  25  serving as an anode. 
     Further, this electron gun is provided with an internal resistor  35  attached to one of a pair of insulating support rods  26  for fixing the electrodes of the electron guns therebetween. The internal resistor  35  has an anode terminal  36  welded to a shield cup  12 , an intermediate terminal  37  welded to the intermediate electrode  27  and a low voltage terminal  38  welded to a grounding terminal of the electron gun or the like. 
     FIG. 3 is a plan view of the third grid electrode  24  taken along line III—III of FIG. 2, FIG. 4 is a cross-sectional view of the third grid electrode  24  taken along line IV—IV of FIG. 3, FIG. 5 is a plan view of the anode  25  taken along line V—V of FIG. 2, FIG. 6 is a cross-sectional view of the anode  25  taken along line VI—VI of FIG. 5, FIG. 7 is a plan view of the intermediate electrode  27  taken along line VII—VII of FIG. 2, and FIG. 8 is a cross-sectional view of the intermediate electrode  27  taken along line VIII—VIII of FIG.  7 . 
     In the color cathode ray tube of this embodiment explained in connection with FIGS. 1 to  8 , the diagonal length D of the usable display area  19  (see FIG. 17) of the viewing screen, the distance L from the center of the phosphor screen to the end of the anode on its focus electrode side, and the outside diameter d of the neck portion are selected to be 460 mm, 292.9 mm and 24.3 mm, respectively, resulting in the ratio D/L of 1.57. 
     The distance L of this embodiment is approximately equal to that of a prior art color cathode ray tube with D being 410 mm and D/L being 1.4 and therefore the overall length of this embodiment is reduced to that of the prior art color cathode ray tube. 
     In addition to this, the increase in the deflection power consumption in this embodiment is limited to about 3% compared with the prior art cathode ray tube, because the deflection power consumption became 16.3 mHA 2  as shown in FIG. 23 by reducing the outside diameter d of the neck portion  2  to 24.3 mm. 
     In FIGS. 3 and 4, reference  39  denotes an electric field correction plate having three vertically elongated electron beam apertures with their minor diameters in the in-line direction of the electron beams and reference numeral  40  denotes a racetrack electrode formed with a single opening with its major diameter in the in-line direction of the electron beams. The electric field correction plate  39  is retracted into the inside of the racetrack electrode  40  from its open end. 
     In FIGS. 5 and 6, reference  41  denotes an electric field correction plate having a vertically elongated electron beam aperture at the center with its minor diameter in the in-line direction of the electron beams and cutouts on opposite sides of the electron beam aperture and reference numeral  42  denotes a racetrack electrode formed with a single opening with its major diameter in the in-line direction of the electron beams. The electric field correction plate  41  is retracted into the inside of the racetrack electrode  42  from its open end. 
     In FIGS. 7 and 8, reference  43  denotes an electric field correction plate having three vertically elongated electron beam apertures with their minor diameters in the in-line direction of the electron beams and reference numeral  44  denote a pair of racetrack electrodes each formed with a single opening with its major diameter in the in-line direction of the electron beams. The pair of racetrack electrodes  44  are disposed to sandwich the electric field correction plate  43  such that the electric field correction plate  43  is retracted from the open ends of the racetrack electrodes  44 . 
     The internal resistor  35  shown in FIG. 2 is attached closely to one of the insulating support rods  26 , its anode terminal  36  is welded to the sidewall of the shield cup  12 , the intermediate terminal  37  is welded to the sidewall of the intermediate electrode  27 , and the low voltage terminal  38  is welded to the grounding terminal of the electron gun to be grounded via one of the stem pins  16 . The internal resistor  35  divides the anode voltage to provide a high voltage lower than the anode voltage to the intermediate electrode  27 . 
     The internal resistor  35  comprises a substrate made of ceramic, for example, a resistive film element made chiefly of ruthenium oxide and printed on the substrate, and an insulating glass coated on the resistive film, and its overall resistance is approximately in a range of 1 to 3 gigaohms. 
     The voltage applied to the intermediate electrode  27  is adjusted to a desired value by changing the ratio (0.55, for example) of a resistance between the intermediate terminal  37  and the low voltage terminal  38  to that between the anode terminal  36  and the low voltage terminal  38 . 
     The contact springs  13  are attached to the front end of the shield cup  12  which in turn is welded to the anode  25 . The anode voltage is applied to the anode  25  by the resilient contact springs  13  pressed against the internal conductive coating  11  on the inner wall of the funnel portion  3 . 
     FIG. 9 is a graph showing the relationship between the effective diameter of the main lens and the potential of the intermediate electrode  27  for an example of a cathode ray tube of the present invention. FIG. 9 shows the relationship between the effective diameter of the main lens and the ratio of a voltage of the intermediate electrode  27  to the anode voltage obtained by computer simulation for an example in which the outside diameter of the glass neck tube is 24.3 mm and the axial length of the intermediate electrode  27  is 3 mm. FIG. 9 shows that application of 50% of the anode voltage to the intermediate electrode  27  provides the effective lens diameter of 8.2 mm, and this effective lens diameter is equivalent to that of the conventional electron guns used for the glass neck tube of 29.1 mm in outside diameter. 
     By this embodiment, the increase in deflection power consumption is reduced greatly, and also the high-definition display image is obtained. 
     The following describes a second embodiment which is useful especially for cathode ray tubes having the usable display area of 510 mm or less in diagonal length D. 
     By selecting the ratio D/L and the outside diameter d of the glass neck tube N to satisfy the following inequalities, 
     
       
           D/L≧ 1.57, d≦ 26 mm, 
       
     
     the distance L from the center of the phosphor screen to the end of the anode on its focus electrode side is reduced from 364 mm to 325 mm, as a result the depth of a monitor set can be shortened and the usable space on the desk is increased, resulting in improvement of the efficiency of utilization of the space on the desk. 
     In the case of a cathode ray tube having the usable display area of 510 mm or less in diagonal length, the dimension L becomes 325 mm or less, and consequently the decrease in the dimension L leads to improvement of working environment. 
     FIG. 10 is a side elevation view of an in-line type electron gun viewed in a direction perpendicular to the in-line direction of three electron beams for explaining a cathode ray tube of the second embodiment. In FIG. 10, reference numeral  51  denotes the anode,  52  is the intermediate electrode,  53  is the fourth member of the fifth grid electrode,  54  is the third member of the fifth grid electrode and  55  is the second member of the fifth grid electrode. Reference numeral  56  denotes the first member of the fifth grid electrode,  57  is the fourth grid electrode,  58  is the second member of the third grid electrode,  59  is the first member of the third grid electrode,  60  is the second grid electrode,  61  is the first grid electrode,  62  are the cathodes, and  63  is the stem. 
     Reference numeral  54 A denote four vertical plates attached to the end of the third member  54  of the fifth grid electrode on its side facing the second member  55  of the fifth grid electrode,  55 A are two horizontal plates attached to the end of the second member  55  of the fifth grid electrode on its side facing the third member  54  of the fifth grid electrode, and these vertical plates  54 A and these horizontal plates  55 A form a second-stage electrostatic quadrupole lens therebetween. Reference numeral  64  denotes the shield cup,  65  is the internal resistor,  66  is the anode terminal,  67  is the intermediate terminal and  68  is the low voltage terminal. 
     FIG. 11 is a schematic plan view of the end of the second member of the third grid electrode on its side facing the first member of the third grid electrode, FIG. 12 is a schematic plan view of the end of the first member of the third grid electrode on its side facing the second member of the third grid electrode, FIG. 13 is a schematic plan view of the second grid electrode on its side facing the first member of the third grid electrode, and FIG. 14 is a cross-sectional view of the second grid electrode taken along line XIV—XIV of FIG.  13 . 
     In FIG. 10, the anode  51  is supplied with the anode voltage which is the highest voltage and the intermediate electrode  52  is supplied with the intermediate voltage which is 50 to 60% of the anode voltage via the internal resistor  65 . 
     The fourth member  53  and the second member  55  of the fifth grid electrode and the second member  58  of the third grid electrode are connected with each other within the cathode ray tube and are supplied with a second focus voltage comprised of a fixed voltage of about 25% of the anode voltage superposed with a dynamic voltage increasing with increasing deflection of the electron beams. The third member  54  and the first member  56  of the fifth grid electrode and the first member  59  of the third grid electrode are internally connected with each other and are supplied with a first focus voltage of about 28% of the anode voltage. The fourth grid electrode  57  and the second grid electrode  60  are internally connected with each other and are supplied with a screen voltage of about 500V to about 800V, and the first grid electrode  61  is supplied with a voltage in a range of −50 to 0 volts. 
     FIG. 15 is an illustration of the magnitude of the focus voltages and their waveforms. The second focus voltage (Vf 2  +dVf) is always lower than the first focus voltage (Vf 1 ). But the second focus voltage (Vf 2 +dVf) can be sometimes selected such that it exceeds the first focus voltage (Vf 1 ) slightly at the periphery of the viewing screen. 
     With this structure, the anode  51 , the intermediate electrode  52  and the fourth member  53  of the fifth grid electrode  53  form a main lens thereamong. 
     The shapes of the grid electrodes are similar to those of the corresponding grid electrodes shown in FIGS. 3 to  8 . The shapes of the apertures in the electric field correction plates and the distances by which the electric field correction plates are retracted into the inside of the racetrack electrodes from their open ends are optimized such that the main lens exerts horizontally strong focusing action on the electron beams. 
     The second-stage electrostatic quadrupole lens is formed between facing portions of the third member  54  and the second member  55  of the fifth grid electrode such that the vertically strong focusing action is exerted on the electron beams when the electron beams are not deflected and the strength of the vertically strong focusing action decreases with increasing deflection of the electron beams. 
     Two horizontal plates  55 A are attached to the second member  55  of the fifth grid electrode such that they sandwich the electron beams in a direction perpendicular to the in-line direction of the electron beams and they extend toward the third member  54  of the fifth grid electrode, and the four vertical plates  54 A are attached to the third member  54  of the fifth grid electrode such that they sandwich each of the electron beams in the in-line direction of the electron beams and they extend toward the second member  55  of the fifth grid electrode. The two horizontal plates  55 A and the four vertical plates  54 A form the second-stage electrostatic quadrupole lens. 
     One correction lens for the curvature of the image field is formed between the facing portions of the fourth member  53  and the third member  54  of the fifth grid electrode and another correction lens for the curvature of the image field is formed between the facing portions of the second member  55  and the first member  56  of the fifth grid electrode such that the focusing strengths of the correction lenses weaken with increasing deflection of the electron beams. 
     The first-stage electrostatic quadrupole lens is formed between the facing portions of the second member  58  and the first member  59  of the third grid electrode such that the horizontally strong focusing action is exerted on the electron beams when the electron beams are not deflected and the strength of the horizontally strong focusing action decreases with increasing deflection of the electron beams. 
     The portion of the second member  58  of the third grid electrode facing the first member  59  of the third grid electrode is formed with three keyholes  69  elongated in a direction perpendicular to the in-line direction of the electron beams as shown in FIG. 11, and the portion of the first member  59  of the third grid electrode facing the second member  58  of the third grid electrode is formed with three rectangular apertures  70  elongated in to the in-line direction of the electron beams as shown in FIG.  12 . 
     The side of the second grid electrode  60  facing the first member  59  of the third grid electrode is formed with three circular apertures  71  each superposed with a larger slot  72  elongated in the in-line direction of the electron beams as shown in FIGS. 13 and 14. 
     This structure of the electron gun increases the effective lens diameter of the main lens by about 40% compared with a conventional electron gun which does not employ any intermediate electrodes unlike the present invention, and reduces the diameter of the electron beam spots over the entire viewing screen. 
     At the center of the viewing screen, the second-stage electrostatic quadrupole lens which focuses the electron beams strongly in a vertical direction cancels out the astigmatism of the main lens which focuses the electron beams strongly in a horizontal direction and the first-stage electrostatic quadrupole lens which focuses the electron beams strongly in the horizontal direction cancels out the astigmatism of the second grid electrode  60  which focuses the electron beams strongly in the vertical direction, to provide approximately circular electron beam spots. 
     At the periphery of the viewing screen, the focusing actions of the first-stage and second-stage electrostatic quadrupole lenses weaken and consequently the astigmatism of the main lens which focuses more strongly in a horizontal direction than in a vertical direction cancels out the astigmatism caused by the deflection magnetic fields which focuses more strongly in the vertical direction than in the horizontal direction. 
     Further, the second grid electrode  60  serves to make the beam spots approximately circular. Simultaneously with this, the focusing action of the correction lens for curvature of the image field and that of the main lens weaken to lengthen the focal length such that focusing of the electron beams are optimized even at the periphery of the viewing screen. This effect by the correction lens for curvature of the image field makes possible the reduction of the required magnitude of a dynamic voltage, and suppresses the increase in the dynamic voltage due to the increase in the maximum deflection angle. 
     Therefore in this embodiment also, the increase in deflection power consumption is minimized and the high definition image display is provided. 
     The following describes a third embodiment which is also useful especially for cathode ray tubes having the usable display area of 510 mm or less in diagonal length. 
     FIG. 28 is a side elevation view of an in-line type electron gun viewed in a direction perpendicular to the in-line direction of three electron beams for explaining a cathode ray tube of the third embodiment. The same reference numerals as utilized in FIG. 10 designate corresponding portions in FIG.  28 . 
     The structure of the color cathode ray tube in the third embodiment may be substantially the same as that in the second embodiment, except for the structures of the electrostatic quadrupole lenses formed within the fifth grid electrode. 
     FIG. 29 is a front view of the side of the third member  54  of the fifth grid electrode facing the second member  55  of the fifth grid electrode, FIG. 30 is a cross-sectional view of the third member  54  of the fifth grid electrode  54  taken along line  130 — 130  of FIG. 29, FIG. 31 is a front view of the side of the second member  55  of the fifth grid electrode facing the third member  54  of the fifth grid electrode, FIG. 32 is a cross-sectional view of the second member  55  of the fifth grid electrode  54  taken along line  132 — 132  of FIG.  31 . FIG. 33 is a front view of the side of the second member  55  of the fifth grid electrode facing the first member  56  of the fifth grid electrode. 
     The third-stage electrostatic quadrupole lens is formed between facing portions of the third member  54  and the second member  55  of the fifth grid electrode such that the vertically strong focusing action is exerted on the electron beams when the electron beams are not deflected and the strength of the vertically strong focusing action decreases with increasing deflection of the electron beams. 
     Three pairs of horizontal plates  55 A are attached to the second member  55  of the fifth grid electrode such that each pair of the horizontal plates  55 A sandwich each of the electron beams in a direction perpendicular to the in-line direction of the electron beams and they extend into a respective electron beam aperture  54 A formed in the third member  54  of the fifth grid electrode. The electron beam apertures  54 A are of the shape of a keyhole with its major diameter in a direction perpendicular to the in-line direction of the electron beams. One of the keyhole apertures  54 A and an associated pair of horizontal plates  55 A form a respective third-stage electrostatic quadrupole lens. 
     A correction lens for the curvature of the image field is formed between the facing portions of the fourth member  53  and the third member  54  of the fifth grid electrode such that the focusing strength of the correction lens weakens with increasing deflection of the electron beams. 
     The first-stage and second-stage electrostatic quadrupole lenses are formed between the facing portions of the second member  58  and the first member  59  of the third grid electrode, and between the facing portions of the second member  55  and the first member  56  of the fifth grid electrode, respectively, such that the horizontally strong focusing action is exerted on the electron beams when the electron beams are not deflected and the strength of the horizontally strong focusing action decreases with increasing deflection of the electron beams. 
     The side of the second member  55  of the fifth grid electrode facing the first member  56  of the fifth grid electrode is formed with three keyholes  55 B with their major diameter in a direction perpendicular to the in-line direction of the electron beams as shown in FIG. 33, and the side of the first member  56  of the fifth grid electrode facing the second member  55  of the fifth grid electrode is formed with three circular apertures, to form a second-stage electrostatic quadrupole lens between the second and first members of the fifth grid electrodes. 
     The side of the second member  58  of the third grid electrode facing the first member  59  of the third grid electrode is formed with three keyholes  69  with their major diameters in a direction perpendicular to the in-line direction of the electron beams as shown in FIG. 11, and the side of the first member  59  of the third grid electrode facing the second member  58  of the third grid electrode is formed with three rectangular apertures  70  elongated in to the in-line direction of the electron beams as shown in FIG. 12, to form a first-stage electrostatic quadrupole lens between the second and first members of the fifth grid electrodes. 
     The side of the second grid electrode  60  facing the first member  59  of the third grid electrode is formed with three circular apertures  71  each superposed with a larger slot  72  elongated in the in-line direction of the electron beams as shown in FIGS. 13 and 14. 
     This structure of the electron gun increases the effective lens diameter of the main lens by about 40% compared with a conventional electron gun which does not employ any intermediate electrodes unlike the present invention, and reduces the diameter of the electron beam spots over the entire viewing screen. 
     At the center of the viewing screen, the third-stage electrostatic quadrupole lens which focuses the electron beams strongly in a vertical direction cancels out the astigmatism of the main lens which focuses the electron beams strongly in a horizontal direction and the first-stage and second-stage electrostatic quadrupole lenses which focus the electron beams strongly in the horizontal direction cancels out the astigmatism of the second grid electrode  60  which focuses the electron beams strongly in the vertical direction, to provide approximately circular electron beam spots. 
     At the periphery of the viewing screen, the focusing actions of the third-stage, first-stage and second-stage electrostatic quadrupole lenses weaken and consequently the astigmatism of the main lens which focuses more strongly in a horizontal direction than in a vertical direction cancels out the astigmatism caused by the deflection magnetic fields which focuses more strongly in the vertical direction than in the horizontal direction. 
     Further, the second grid electrode  60  serves to make the beam spots approximately circular. Simultaneously with this, the focusing action of the correction lens for curvature of the image field and that of the main lens weaken to lengthen the focal length such that focusing of the electron beams are optimized even at the periphery of the viewing screen. This effect by the correction lens for curvature of the image field makes possible the reduction of the required magnitude of a dynamic voltage, and suppresses the increase in the dynamic voltage due to the increase in the maximum deflection angle. 
     Therefore in this embodiment also, the increase in deflection power consumption is minimized and the high definition image display is provided. 
     The following explains the configuration of an in-line type electron gun, the dimensions of the major electrodes and the voltages applied to the electrodes of the in-line type electron gun in a cathode ray tube having a neck portion of 24.3 mm in outside diameter in accordance with an embodiment of the present invention, whose plan view viewed in a direction perpendicular to the in-line direction of the electron beams is shown in FIG.  34 . The same reference numerals as utilized in FIG. 28 designate corresponding portions in FIG.  34 . 
     The following are axial lengths of the major electrodes: Anode  51 =5 mm, Intermediate electrode  52 =3.5 mm, Fourth member  53  of the fifth grid electrode=5.5 mm, Third member  54  of the fifth grid electrode=2 mm, Second member  55  of the fifth grid electrode is 11 mm, First member  56  of the fifth grid electrode=2 mm, Fourth grid electrode  57 =0.5 mm, Second member  58  of the third grid electrode=2 mm, First member  59  of the third grid electrode=1.8 mm, and Shield cup  64 =9.6 mm. 
     The following are interelectrode spacings: Anode  51 −Intermediate electrode  52 =0.6 mm, Intermediate electrode  52 −Fourth member  53  of the fifth grid electrode=0.6 mm, Fourth member  53 −Third member  54 , of the fifth grid electrode=0.5 mm, Third member  54 −Second member  55 , of the fifth grid electrode=0.6 mm, Second member  55 −First member  56 , of the fifth grid electrode=0.4 mm, First member  56  of the fifth grid electrode−Fourth grid electrode  57 =0.6 mm, Fourth grid electrode  57 −Second member  58  of the third grid electrode=2 mm, and Second member  58 −First member  59 , of the third grid electrode= 0 .3 mm. 
     The anode  51  is supplied with an anode voltage Va of about 27 kV, and the intermediate electrode  52  is supplied with a voltage of about 55% of the anode voltage Va via the internal resistor  65  of about 2 GΩ. The fourth member  53 , the second member  55  of the fifth grid electrode and the second member  58  of the third grid electrode are internally connected with each other within the cathode ray tube and are supplied with a voltage Vfd of about 25% of the anode voltage Va superposed with a dynamic voltage dVf of about 500 to 800 volts increasing with increasing deflection of the electron beams. 
     The third member  54  and the first member  56  of the fifth grid electrode and the first member  59  of the third grid electrode are internally connected with each other and are supplied with a voltage Vfc of about 28% of the anode voltage Va. The fourth grid electrode  57  and the second grid electrode  60  are internally connected with each other and are supplied with a screen voltage VG 2  of about 600 volts. 
     FIG. 35 is a front view of the side of the intermediate electrode  52  facing the anode  51 , and FIG. 36 is a side elevation view of the intermediate electrode  52  viewed in the in-line direction of the electron beams. The intermediate electrode  52  comprises a pair of cup-shaped electrodes  73  and a plate-like electrode  74  sandwiched between the pair of cup-shaped electrodes  73 . The axial length of the intermediate electrode  52  is 3.5 mm. 
     FIG. 37 is a plan view of the cup-shaped electrode  73  and FIG. 38 is a cross-sectional view of the cup-shaped electrode  73  taken along line  138 — 138  of FIG.  37 . The cup-shaped electrode  73  is formed with a single opening elongated in the in-line direction of the electron beams which is 15 mm in major diameter and 5.8 mm in minor diameter with semicircles of 2.9 mm in radius at the left and right sides. The axial length of the cup-shaped electrode  73  is 1.4 mm. 
     FIG. 39 is a plan view of the plate-like electrode  74  and FIG. 40 is a side elevation view of the plate-like electrode  74 . In FIG. 39, the center electron beam aperture is an ellipse represented by the equation (1), 
     
       
         (X/2.22) 2 +(Y/2.9) 2 =1  (1), 
       
     
     where the X-axis is in the in-line direction of the electron beams and the Y-axis is perpendicular to the in-line direction, an inner side portion of the side electron beam apertures is a semi-ellipse represented by the equation (2), 
     
       
         (X/1.85) 2 +(Y/2.9) 2 =1  (2), 
       
     
     and an outer side portion of the side electron beam apertures is a semicircle of 2.9 mm in radius. 
     FIG. 41 is a plan view of the side of the anode  51  facing the intermediate electrode  52 , and FIG. 42 is a cross-sectional view of the anode  51  taken along line  142 — 142  of FIG.  41 . The anode  51  is comprised of a cup-shaped electrode  75  and a plate-like electrode  76  which is welded at a distance of 1.3 mm spaced inwardly from the open end of the cup-shaped electrode  75 . 
     FIG. 43 is a plan view of the plate-like electrode  76 , and FIG. 44 is a cross-sectional view of the plate-like electrode  76  taken along line  144 — 144  of FIG.  43 . The center electron beam aperture is an ellipse represented by the equation (3), 
     
       
         (X/2.2) 2 +(Y/2.6) 2 =1  (3), 
       
     
     and an inner side portion of the side electron beam apertures is comprised of a semi-ellipse represented by the equation (4) and a straight line, 
     
       
         (X/2.05) 2 +(Y/3.0) 2 =1  (4). 
       
     
     FIG. 45 is a front view of the cup-shaped electrode  75 , and FIG. 46 is a cross-sectional view of the cup-shaped electrode  75  taken along line  146 — 146  of FIG.  45 . The single opening in the cup-shaped electrode  75  is the same as that in FIG.  37 . 
     FIG. 47 is a front view of the side of the fourth member  53  of the fifth grid electrode facing the intermediate electrode  52 , and FIG. 48 is a cross-sectional view of the fourth member  53  taken along line  148 — 148  of FIG.  47 . The cup-shaped electrode  75  is the same as in FIG.  41 . The plate-like electrode  77  is welded at a distance of 1.3 mm spaced inwardly from the open end of the cup-shaped electrode  75 . 
     FIG. 49 is a plan view of the plate-like electrode  77 , and FIG. 50 is a cross-sectional view of the plate-like electrode  77  taken along line  150 — 150  of FIG.  49 . The center electron beam aperture is an ellipse represented by the equation (5), 
     
       
         (X/2.0) 2 +(Y/2.85) 2 =1  (5), 
       
     
     an inner side portion of the side electron beam apertures is a segment of a semi-ellipse represented by the equation (6) 
     
       
         (X/2.22) 2 +(Y/3.50) 2 =1  (6), 
       
     
     an outer side portion of the side electron beam apertures is a segment of a semi-ellipse represented by the equation (7), 
     
       
         (X/2.06) 2  +(Y/3.50) 2 =1  ( 7 ), 
       
     
     and the inner and outer side portions of the side electron beam apertures are connected by two straight lines. 
     With this structure, the anode  51 , the intermediate electrode  52  and the fourth member  53  of the fifth grid electrode form a main lens thereamong. This main lens is capable of being housed in a glass neck tube of 24.3 mm in outside diameter and provides a large effective lens diameter of 8.3 mm. 
     As explained above, in a cathode ray tube according to the present invention, even if the outside diameter of its glass neck tube is reduced so as to cancel out the increase in deflection power consumption caused by the increase in the maximum deflection angle, the effective lens diameter of the main lens is made approximately equal to that obtainable with the conventional glass neck tube of 29.1 mm in outside diameter, and consequently the present invention provides a high-performance cathode ray tube with its overall length shortened.