JPH0562612A - Color picture tube - Google Patents

Abstract

PURPOSE:To provide a color picture tube provided with an electron gun, the main electron lens of which is increased in the diameter at the maximum, while the spherical aberration is minimized, and the generation of the coma is reduced. CONSTITUTION:A three-pole part T comprising an in-line type electron source generating a plurality of electron beams and control electrodes G1, G2 controlling the electron beams, a bipotential type main electron lens Lb comprising a focusing electrode G3 crossing a plurality of the controlled electron beams with each other and an accelerating electrode G4, and electrostatic deflecting plates A, B converging a plurality of the electron beams passing through the main electron lens Lb on a screen S, are arranged in order. At least one intermediate electrode GM is insertion-arranged between the focusing electrode G3 and the accelerating electrode G4 that form the main electron lens Lb, and an electron gun is thus formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color picture tube,
In particular, the present invention relates to a color picture tube which is used for a television, a terminal display or the like and has a small electron beam spot diameter and high resolution.

[0002]

2. Description of the Related Art A color picture tube used for color image display comprises a panel section which is a picture screen, a neck section which houses an electron gun, and a funnel section which connects the panel section and the neck section. Is equipped with a deflection device for scanning an electron beam emitted from an electron gun on a fluorescent screen formed by coating on the inner surface of the panel.

The electron gun housed in the neck portion is provided with various electrodes such as a cathode electrode, a control electrode, a focusing electrode and an accelerating electrode, and an electron beam from the cathode electrode is modulated by a signal applied to the control electrode. The electron beam is made into a required cross-sectional shape through the focusing electrode and the accelerating electrode, energy is applied, and the electron beam is projected onto the phosphor screen. The electron beam is deflected in the horizontal direction and the vertical direction by the deflecting device provided in the funnel portion on the way from the electron gun to the fluorescent screen to form an image on the fluorescent screen.

In this type of color picture tube, in order to make the image displayed on the fluorescent screen highly precise, it is necessary to reduce the spot diameter of the electron beam on the fluorescent screen, which is the electron gun. It depends on the performance of.

As described above, the electron gun generates an electron beam and controls the generated electron beam by a three-pole portion (cathode electrode and control electrode) and an electron beam controlled by the three-pole portion. The main electron lens unit (focusing electrode and accelerating electrode) for focusing, accelerating, and concentrating the light beam is a factor that greatly affects the spot diameter of the electron beam in these configurations. Spherical aberration can be mentioned. If the spherical aberration of the main electron lens can be reduced, the spot diameter of the electron beam can be reduced and a high-definition image can be obtained.
It is well known that the spherical aberration of the main electron lens can be reduced by enlarging the diameter of the electrode forming the main electron lens.

By the way, the main electron lens is usually composed of an electrostatic lens, and the electrostatic lens has a plurality of electrodes each having an electron beam passage hole arranged coaxially. It is formed by applying a predetermined potential to. Conventionally, there are several types of this electrostatic lens depending on the configuration of the electrode, but basically, in any type, the diameter of the electron beam passage hole is made as large as possible to increase the diameter of the electrode. (Japanese Patent Laid-Open No. 59-215640)
Publication).

However, since the electron gun is arranged in the neck portion of the color picture tube having a small diameter, the diameter of the electron beam passage hole is naturally limited. If the diameter of the neck portion is enlarged to increase the diameter of the electron beam passage hole, the deflection power of the deflection yoke arranged outside the neck portion increases,
Increasing the diameter of the neck is not preferred.

Conventionally, as a first means for solving the above-mentioned point, instead of providing three parallel electron lenses on the same plane, this is constituted by one large-diameter electron lens to increase the above-mentioned large-diameter. There is known a so-called 1-gun 3-beam type electron gun in which three electron beams are allowed to cross each other in the central portion of the electron lens so as to maximize the lens performance. No. 5591.

FIG. 7 is a sectional view showing an electrode structure of the electron gun of the one-gun three-beam system.

In the figure, K _R ', K _G ' and K _B 'are red, green,
Three cathodes arranged in parallel corresponding to each blue color, G ₁ 'is the first electrode, G ₂ ' is the second electrode, G ₃ 'is the third electrode, G ₄ ' is the fourth electrode (focusing electrode) , G ₅ 'is a fifth electrode, A', B'is an electrostatic deflection plate, and S is a screen.

The three cathodes K _R ', K _G ' and K _B '
And a first electrode G ₁ ′ and a second electrode G ₂ ′ form a three-pole portion T, and each has a cylindrical third electrode G ₃ ′, fourth electrode G ₄ ′ (focusing electrode), The five-electrode G ₅ ′ (acceleration electrode) constitutes a unipotential type main electron lens Lu. The electron beams emitted from the three cathodes K _R ′, K _G ′, and K _B ′ cross each other at a position satisfying the Fraunhofer condition (condition in which coma aberration becomes zero) approximately at the center of the main electron lens Lu. , then the electron beam is convergence on the screen S by the action of the fifth electrode G ₅ 'electrostatic deflection plates a disposed downstream of (acceleration electrode)', B '.

As described above, in the one-gun three-beam type electron gun, one main electron lens Lu focuses three electron beams, and the main electron lens Lu has only one electron beam passage hole. Therefore, the lens aperture with respect to the limited neck diameter, that is, the diameter of the electrode can be increased.

In addition to the above, a second method for solving the above-mentioned point
As such means, an electron gun is known in which the length of the main electron lens in the tube axis direction is enlarged to form an electron lens called a so-called extended electric field type main electron lens.

FIG. 3C shows a third electrode G ₃ (focusing electrode) and a fourth electrode G ₄ in the extended electric field type main electron lens.
It is sectional drawing which shows the structure of the part of (accelerating electrode).

In the second means, the third electrode G ₃
The distance between the (focusing electrode) and the fourth electrode G ₄ (accelerating electrode) is made wider than the normal distance so that the potential change in the tube axis direction in the main electron lens becomes gentle, so that the main electron lens This is intended to reduce spherical aberration.

[0016]

However, since the first means uses the unipotential lens as the main electron lens Lu, the spherical aberration of the main electron lens Lu is large and the main electron lens Lu is Even if the diameter is increased, there is a problem that the characteristics are not fully utilized.

The second means forms a third electrode G ₃ (focusing electrode) in order to form an extended electric field type main electron lens.
And the distance between the fourth electrode G ₄ (accelerating electrode) is increased,
In the enlarged portion, there is a problem that the electron beam is affected by an undesired electric field in the neck portion. When the second means is to be realized by the 1-gun 3-beam system, the side electron beam is made incident on the main electron lens so as to satisfy the Fraunhofer condition (condition in which coma aberration becomes zero). Even if it does, there is a problem that a large coma aberration is likely to occur due to the deviation of the conditions based on the limit of manufacturing accuracy.

The present invention was devised to solve the above problems, and its purpose is to minimize spherical aberration,
Another object of the present invention is to provide a color picture tube equipped with an electron gun in which coma aberration is reduced and the main electron lens is maximized in diameter.

[0019]

In order to achieve the above-mentioned object, the present invention provides a triode consisting of an in-line type electron source for generating a plurality of electron beams and a control electrode for controlling these electron beams, A bipotential main electron lens including a focusing electrode, a first electrostatic deflection unit, and an acceleration electrode that intersects the controlled electron beams, and the electron beams that have passed through the main electron lens are converged on a screen. In an electron gun in which a second electrostatic deflection section is sequentially arranged, at least one intermediate electrode is inserted and arranged between a focusing electrode and an accelerating electrode forming the bipotential main electron lens to form the electron gun. The first means described above is provided.

Further, in order to achieve the above object, the present invention provides a focusing electrode of the bipotential type main electron lens,
At least one of the intermediate electrode and the accelerating electrode is provided with a second means having a potential distribution that gradually changes on the triode side and sharply changes on the screen side.

[0021]

Since the electron gun of the present invention uses the bipotential type main electron lens formed by the focusing electrode, the first electrostatic deflecting portion, at least one intermediate electrode and the accelerating electrode, it is similar to the conventional electron gun. Spherical aberration can be reduced as compared with the one using the unipotential type main electron lens, thereby making it possible to reduce the spot diameter of the electron beam and obtain a high-definition image.

Further, in the electron gun of the present invention, since at least one intermediate electrode is arranged between the focusing electrode and the accelerating electrode, compared with the conventional electron gun using the extended electric field type main electron lens. As a result, the electron beam is extremely less affected by an undesired electric field (disturbance electric field) in the neck portion. In addition to this, since the spherical aberration of the main electron lens is minimized, it is possible to sufficiently suppress the occurrence of coma aberration in the electron beams obliquely incident on the main electron lens on both sides.

[0023]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a color picture tube according to the present invention.

In FIG. 1, 1 is a panel portion, 2 is a funnel portion, 3 is a neck portion, 4 is a fluorescent screen (screen), 5 is a shadow mask, 6 is a magnetic shield, 7 is a deflection yoke, and 8 is a purity adjusting magnet. , 9 are center beam static convergence adjustment magnets, 10 are side beam static convergence adjustment magnets, 11
Is an electron gun, Bc is a center beam, and Bs is a side beam.

In order to perform the convergence adjustment (static convergence) of such a color picture tube, first the two side beams Bs and Bs are converged, and then the center beam Bc and the convergence point of the side beam Bs are set. I try to concentrate.

On the outer surface of the panel portion 1, a thin film, such as SnO ₂ or In, which prevents reflection and electrification is formed if necessary.
A thin film containing ₂ O ₃ or the like is formed in a single layer or multiple layers. Further, although not shown, the funnel portion 2 and the neck portion 3
An inner conductive film made of graphite or the like is deposited on the inner surface of the, and this conductive film electrically connects a high-voltage terminal (not shown) and the electron gun 11.

FIG. 2 is a sectional view showing an embodiment of the electrode arrangement of the electron gun portion of the color picture tube.

In FIG. 2, K _R , K _G , and K _B are red,
Three cathodes arranged in parallel corresponding to each color of green and blue, G
₁ The first electrode, G ₂ and the third electrode divided second electrode, G ₃ is two (focusing electrode), G ₄ and the fourth electrode (accelerating electrode), G _M is the intermediate electrode, C, D Is a pair of first electrostatic deflection plates (first electrostatic deflection unit), A and B are paired second electrostatic deflection plates (second electrostatic deflection unit), and S is a screen.

Then, the three cathodes K _R , K _G and K _B
The third electrode G ₃ (focusing electrode), the first electrostatic deflection plates C and D, and the intermediate portion are formed by the first electrode G ₁ and the second electrode G _2. The electrode G _M and the fourth electrode G ₄ constitute a bipotential type main electron lens Lb. Also, a third electrode (focusing electrode) divided into two
The first electrostatic deflecting plates C and D are arranged between G ₃ and the second electrostatic deflecting plates A and B are arranged on the screen S side of the fourth electrode (accelerating electrode) G ₄ . The three cathodes K _R , K _G , and K _B emit electron beams B _R , B _G , and B _B , respectively, and these electron beams B _R , B _G , and B _B are the first electrode G ₁ and the second electrode G _2. And are commonly controlled by and.

The electron gun shown in FIG. 2 operates as described below.

The electron beams B _R , B _G , and B _B emitted from the three cathodes K _R , K _G , and K _B , respectively, are well known in their common first electrode G ₁ and second electrode G ₂ . The intensity and the like are controlled, and the light is incident on the arrangement portion of the third electrode (focusing electrode) G ₃ and the first electrostatic deflecting plates C and D that configure the bipotential type main electron lens Lb. In the arranged portion, the center electron beam B _G of the electron beams B _R , B _G , and B _B goes straight, but the two side electron beams B _R and B _B are the first electrostatic deflection plates C, Due to the action of D, the light is deflected so as to be incident near the center of the main electron lens Lb, that is, at a position (arrangement portion of the intermediate electrode G _M ) that satisfies the Fraunhofer condition (condition for making coma aberration zero), , Three electron beams B _R ,
B _G and B _B will intersect. After passing through the position, the center electron beam B _G goes straight on,
The two side electron beams B _R and B _B respectively proceed in a direction away from the center electron beam B _G and pass through the main electron lens Lb, and then these three electron beams B R
_R , B _G , and B _B are incident on the arrangement portion of the second electrostatic deflection plates A and B. In this arrangement, the center electron beam B _G goes straight as well, but the two side electron beams B G
_R, B _B are deflected so as to approach the center electron beam B _G by the action of the second electrostatic deflection plates A, B, 3 electron beams B _R, B _G, is B _B is convergence on the screen S ..

Next, the difference in structure and potential distribution between the bipotential lens used in this embodiment and a lens of another shape will be described with reference to FIGS. 3 and 4.

FIG. 3 is a sectional view showing the arrangement of electrodes in the case of forming lenses of various shapes.
Is an ordinary unipotential lens, (b) is an ordinary bipotential lens, (c) is an extended electric field type bipotential lens, and (d) is the bipotential lens used in this embodiment.

In this case, the unipotential lens (a) is constructed by arranging the third electrode G ₃ , the fourth electrode G ₄ , and the fifth electrode G ₅ side by side. The third electrode G ₃ and the fifth electrode G 5 The applied voltage of G ₅ is both Eb, and E is applied to the fourth electrode G ₄ .
The voltage Ef lower than b is applied. Bipotential lens (b), the third electrode G _3, those composed by close proximity of the fourth electrode G _4, the voltage applied to the fourth electrode G ₄ and Eb, more Eb to the third electrode G ₃ Low voltage E
f is applied. (C) Extended field type bipotential lens is intended to be constituted by arrangement expand the distance between the third electrode G ₃ and the fourth electrode G _4, the third electrode G ₃ to the fourth electrode G ₄ The voltage applying means is the same as in the case of (b). The bipotential lens of this example (d) is
The third electrode G _3, the intermediate electrode G _M, constituted by the juxtaposition of the fourth electrode G ₄ (provided that the first deflection plate C, D are omitted for convenience of explanation) ones, the fourth electrode G ₄ Applied voltage is E
b, a voltage Ef lower than Eb is applied to the third electrode G ₃ , and as will be described later, Eb is applied to the intermediate electrode G _M ,
A voltage Em that is intermediate between Ef is applied.

FIG. 4 is a characteristic diagram showing the potential distribution on the tube axis in the arrangement shown in FIGS. 3 (a) to 3 (d). The characteristics of (1) correspond to the arrangement configurations shown in (a) to (d) of FIG. 3, respectively.

That is, the unipotential lens in (a) is set so that the potentials at both ends are high and the potential in the middle part is low, and in the bipotential lens in (b), the potential on the three-pole side is continuous. It is set so that the potential on the screen side is high and the potential changes sharply during that period. In the extended electric field type bipotential lens of (c), although the potential on the triode side is low and the potential on the screen side is high, the potential change between them is set to be gentle, and the extended electric field bipotential lens of the present example of (d) is used. Bipotential lens
It has a characteristic similar to that of (c), but the potential change on the triode side (low potential side) is relatively gradual, whereas the potential change on the screen side (high potential side). Is set to be relatively steep.

When constructing the lenses shown in FIGS. 3A to 3D, all the lenses shown in FIGS. 3A to 3D are selected so that the inner diameters of the electrodes are the same. Among them, further, the fourth electrode G ₄ in the unipotential lens of (a) has a length in the tube axial direction standardized by the inner diameter of the electrode to be 0.69, and the extended electric field type bipolar of (c). Third electrode G ₃ and fourth in the potential lens
The gap length between the electrodes G ₄ is 0.85 when normalized by the electrode inner diameter, and the length of the intermediate electrode G _M in the bipotential lens of this embodiment in (d) is normalized by the electrode inner diameter. It is chosen to be 0.69.

And, in particular, the bipotential lens of the present embodiment of (d) is between the third electrode G ₃ and the fourth electrode G ₄ when compared with the normal bipotential lens of (b). The gap is widened and, for example, one intermediate electrode G _M is inserted between the gaps. Also,
The intermediate electrode G _M has the average (E _f + E _b ) / 2 of the voltages E _f and E _b applied to the third electrode G ₃ and the fourth electrode G ₄ , respectively.
It intended to provide a more slightly lower voltage E _m, for example, the applied voltage E _f of the third electrode G ₃ 7～8KV, intermediate electrode G _M
The applied voltage E _m of the second electrode G ₄ is about 15 KV and the applied voltage E _b of the fourth electrode G ₄ is about 30 KV.

FIG. 5 is a characteristic diagram showing a situation in which spherical aberration occurs in the lens of FIGS. 3A to 3D, in which the R coordinate of each trajectory in the electron beam of the center electron beam at the lens exit. The relationship between the inclination (dR / dz) of each orbit in the electron beam with respect to the screen (value in the radial direction standardized by the electrode diameter) is shown.

In FIG. 5, the straight line m shows the relationship when the spherical aberration is 0, that is, when there is no aberration.
It is shown that the spherical aberration of the lens becomes smaller as it approaches.

As shown in FIG. 5, the bipotential lens of FIG. 3B has considerably smaller spherical aberration than the unipotential lens of FIG. 3A, and the bipotential lens of FIG. The spherical electric field aberration of the extended electric field type bipotential lens of FIG. 9C is considerably smaller than that of the potential lens, and further, the present embodiment of FIG. It can be seen that the spherical aberration of the bipotential lens is smaller.

By the way, when the extended electric field type bipotential lens of FIG. 3C and the bipotential lens of the present example of FIG. 3D are compared, as shown in FIG. Although there is not much difference between the advantages and disadvantages of the above, the extended electric field type bipotential lens has a wide gap between the third electrode G ₃ and the fourth electrode G ₄ due to its structure. Is affected by an undesired electric field (disturbance electric field) in the neck portion, whereas the bipotential lens of the present embodiment also has a gap similar to the gap, but the intermediate electrode G _M is further present in this gap. Are inserted and arranged, the electron beam passing through the gap is not affected by the undesired electric field (disturbance electric field). In addition, in the bipotential lens of the present embodiment, the average (E _f of the applied voltages E _f and E _b of the third electrode G ₃ and the fourth electrode G ₄ on both sides of the inserted intermediate electrode G _M is calculated. By giving a voltage E _m slightly lower than + E _b ) / 2, as shown in FIG. 5, it is possible to improve the spherical aberration characteristic as compared with the extended electric field type bipotential lens.

As described above, particularly in the one-gun three-beam type electron gun, since the two side electron beams are made to enter obliquely with respect to the tube axis, coma aberration is caused in these electron beams. Occurs. This coma is
When the electron beam is passed near the center of the main electron lens so as to satisfy the Fraunhofer condition (condition for reducing coma aberration to zero), it becomes zero, but the unipotential lens of FIG. 2) and the extended electric field type bipotential lens in FIG. 7C, due to a slight deviation from the Fraunhofer condition (condition for reducing coma aberration to zero) due to the limit of manufacturing accuracy, a large coma aberration is generated. May occur.

On the other hand, in the bipotential lens of this embodiment shown in FIG. 9D, as described above, the potential distribution on the tube axis, that is, the third electrode G ₃ , the intermediate electrode G _M , and the fourth electrode G 4 Electrode G
Each applied voltage E _f of _4, E _m, select properly the E _b, spherical aberration is set to be minimized. By the way, between the spherical aberration and the coma, when the spherical aberration coefficient is Csph, the coma coefficient is Ccoma, the focal length of the lens is fo, and the position where the side beam crosses the tube axis is Ze, (dCcoma /
It is known that there is a relationship of dZe) =-(Csph / fo) (for this point, M. Born and Wolf, "P
rinciples of Optics, 4th ed ”Pergumon, New York
1970, Chap. This relation shows that the smaller the spherical aberration coefficient Csph, the smaller the change in the coma aberration coefficient Ccoma with respect to the change in the position Ze where the side beam crosses the tube axis.

By the way, since the bipotential lens of the present embodiment minimizes the spherical aberration, that is, the spherical aberration coefficient Csph, the change amount of the coma aberration coefficient Ccoma due to the change of the position Ze where the side beam crosses the tube axis. Becomes extremely small. Therefore, since the coma aberration becomes zero, that is, Ccoma≈0, even if the position Ze where the side beam crosses the tube axis slightly changes due to the limit of the manufacturing accuracy, the occurrence of the coma aberration accompanying it is suppressed. There is also the effect that you can.

FIG. 6 is a sectional view showing another embodiment of the electrode arrangement of the electron gun portion of the color picture tube.

In FIG. 6, G _M1 is the first intermediate electrode, and G _M2
Is a second intermediate electrode, R is a resistance, and the same components as those shown in FIG.

In this embodiment, two intermediate electrodes are provided between the third electrode G ₃ (focusing electrode) and the fourth electrode G ₄ (accelerating electrode), that is, the first intermediate electrode G _M1 and the second intermediate electrode G. Place _M2 and
The voltage Eb supplied to the second electrostatic deflection plates A and B for convergence is applied to the first intermediate electrode G _M1 and the second intermediate electrode G _M2.
2 is different from that of the embodiment of FIG. 2 in that it is divided by a resistor R and applied, but the other configuration is the same as that of the embodiment of FIG. The operation is the same as that of the example.

According to this embodiment, in addition to the effect of the embodiment of FIG. 2, there is an effect that the number of pins for supplying voltage and the number of power sources can be reduced.

In the above-mentioned two embodiments, one or two intermediate electrodes are inserted and arranged between the third electrode G ₃ (focusing electrode) and the fourth electrode G ₄ (accelerating electrode). However, in the present invention, the number of the intermediate electrodes to be inserted and arranged is not limited to one or two, and three or more intermediate electrodes can be inserted and arranged.

Further, the mode of applying the voltage to the one or two intermediate electrodes is not limited to those of the above-mentioned two embodiments, and any suitable mode can be applied.

Further, when the number of the intermediate electrodes to be inserted and arranged is three or more, the voltage may be applied to the two intermediate electrodes in the same manner as the voltage is applied to the two intermediate electrodes. The effect obtained in this case is similar to the effect obtained when two intermediate electrodes are used.

[0054]

As described above, the color picture tube according to the present invention has the third electrode G ₃ (focusing electrode) in the electron gun.
And a gap between the fourth electrode G ₄ (accelerating electrode),
Since one or more intermediate electrodes G _M (G _M1 , G _M2 ) are inserted and arranged therein, those electrodes G ₃ , G ₄ , G
It is possible to maximize the diameter of the bipotential type main electron lens Lb constituted by _M (G _M1 , G _M2 ) and thereby minimize the spherical aberration of the lens Lb. There is an effect that the coma aberration generated in the side electron beam due to manufacturing accuracy can be almost suppressed.

Therefore, the color picture tube according to the present invention is
There is also an effect that a high-resolution color image with a small spot diameter can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a color picture tube of the present invention.

FIG. 2 is a cross-sectional configuration diagram showing an example of an electrode arrangement of an electron gun portion of the present invention.

FIG. 3 is a cross-sectional configuration diagram showing an electrode arrangement when various lenses are formed.

FIG. 4 is a characteristic diagram showing a potential distribution on a tube axis in the arrangement configuration of FIG.

5 is a characteristic diagram showing occurrence of spherical aberration of a lens in the arrangement configuration of FIG.

FIG. 6 is a sectional view showing another embodiment of the arrangement of electrodes in the electron gun portion of the present invention.

FIG. 7 is a cross-sectional configuration diagram showing an example of an electrode arrangement of a conventional 1-gun 3-beam type electron gun.

[Explanation of symbols]

1 panel 2 funnel portion 3 neck portion 4 a phosphor screen (screen) 5 shadow mask 6 magnetic shield 7 deflection yoke 8 Pyuritei adjusting magnet 9 a center beam static convergence adjusting magnet 10 side beam static convergence adjusting magnet 11 electron gun K _R, K _G , K _B cathode G ₁ first electrode G ₂ second electrode G ₃ third electrode G ₄ fourth electrode G _M intermediate electrode G _M1 first intermediate electrode G _M2 second intermediate electrode C, D first electrostatic deflection plate A , B Second electrostatic deflector B _R , B _G , B _B Electron beam T Tripolar part Lb Bipotential type main electron lens S Screen R Resistance

Claims (2)

[Claims] 1. A triode consisting of an in-line type electron source for generating a plurality of electron beams and a control electrode for controlling these electron beams, a focusing electrode for intersecting the controlled plurality of electron beams, and a first static electrode. An electron gun in which a bipotential type main electron lens including an electric deflection unit and an acceleration electrode and a second electrostatic deflection unit that converges a plurality of electron beams passing through the main electron lens on a screen are sequentially arranged, A color picture tube characterized in that an electron gun is constructed by inserting and arranging at least one intermediate electrode between a focusing electrode and an accelerating electrode constituting the bipotential type main electron lens. 2. The focusing electrode, at least one intermediate electrode, and accelerating electrode of the bi-potential type main electron lens have a potential distribution that changes gently on the triode side and sharply changes on the screen side. The color picture tube according to claim 1, wherein