Color cathode-ray tube apparatus

In an electron gun assembly, electron beams emitted from cathodes are focused in first cross-over and accelerated and controlled by grids along three axes arranged in-line. The controlled electron beams are weakly converged by unipotential lenses and are converged in a vertical plane by a common single electron lens having a lens power which is varied in accordance with a horizontal or vertical deflection of the electron beams. The converged electron beams form second cross-over on the axes which are shifted along the axes are diverged from the second cross-overs. The diverged electron beams are further focused and converged onto a screen by a main lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a color cathode-ray tube apparatus and, 
more particularly, an electron gun assembly for use in a color cathode-ray 
tube apparatus, which dynamically focuses electron beams, thereby forming 
a high-resolution image on the phosphor screen of the color cathode-ray 
tube apparatus. 
2. Description of the Related Art 
FIG. 1 is a cross-sectional view of a color cathode-ray tube apparatus of 
the most common type. As is shown in this figure, the color cathode-ray 
tube apparatus comprises a faceplate 3, a funnel 4, a neck 5, an electron 
gun assembly 6, a deflection unit 7, and a shadow mask 9. The faceplate 3 
has an edge portion 3a. A screen 2 is formed on the inner surface of the 
face-plate 3. The funnel 4 connects the edge portion 3a of the faceplate 3 
to the neck 5. The electron gun assembly 6 is located within the neck 5. 
The deflection unit 7 is shaped like a ring, surrounding the junction of 
the funnel 4 and the neck 5. The unit 7 is designed to deflect the 
electron beams emitted by the electron gun assembly 6. The shadow mask 9 
is held in the faceplate 3 and opposes the screen 2, spaced apart 
therefrom by a predetermined distance. The mask 9 has a number of 
apertures 8 for guiding the electron beams onto the screen 2. The color 
cathode-ray tube apparatus further comprises an inner conductive layer 10 
and an anode terminal (not shown). The layer 10 is coated uniformly on the 
inner surface of the funnel 4 and also on a part of the inner surface of 
the neck 5. The anode terminal (not shown) is mounted on a part of the 
inner surface of the funnel 4. 
Red phosphor, green phosphor, and blue phosphor are coated on the screen 2 
in the form of stripes or dots. The electron gun assembly 6 emits three 
electron beams BR, BG, and BB. The beams BR, BG, and BB are deflected by 
the deflection unit 7, guided by the shadow mask 9, and applied onto the 
phosphor stripes or dots. When excited by these electron beams, the red 
phosphor stripes or dots emit red light, the green phosphor stripes or 
dots emit green light, and the blue phosphor stripes or dots emit blue 
light. 
The electron gun assembly 6 has a beam-forming section GE and a 
beam-processing section ML. The section GE generates three parallel 
electron beams BR, BG, and BB in so-called "in-line alignment," and 
accelerates and controls these beams. The beam-processing section ML 
focuses and converges the three electron beams emitted from the 
beam-forming section GE. The electron beams BR, BG, and BB emitted from 
the electron gun assembly 6 are deflected by means of the deflection unit 
7, guided by the shadow mask 8, and applied onto the screen 2. Hence, the 
electron beams scan the screen 2, forming rasters on the screen 2. 
The deflection unit 7 has a horizontal deflection coil and a vertical 
deflection coil. The horizontal deflection coil generates a 
horizontal-deflection magnetic field for deflecting the electron beams in 
the horizontal direction. The vertical deflection coil generates a 
vertical-deflection magnetic field for deflecting the electron beams in 
the vertical direction. 
When any beam emitted from the electron gun assembly 6 is deflected by 
means of the deflection unit 7, it cannot be correctly converged and thus 
fails to form a beam spot on the target phosphor stripe or dot formed on 
the screen 2. To converge the beam with accuracy, the so-called 
"convergence-free system" is used in the conventional cathode-ray tube 
apparatus. In this system, the horizontal-deflection magnetic field is 
formed into a pincushion-shape, and the vertical-deflection magnetic field 
is formed into a barrel-shape. The pincushion magnetic field and the 
barrel magnetic field act, in concert, on the three electron beams such 
that the beams are correctly converged on the target phosphor stripes or 
dots, respectively. 
Generally, even a magnetic field, which is considered to be uniform in its 
intensity distribution, includes a small pincushion component or a small 
barrel component. FIG. 2A schematically shows a magnetic field including a 
pincushion component. An electron directed to the peripheral portion of 
the screen 2, in particular, is subjected to a relatively prominent 
deflection aberration as the beam passes through this magnetic field. 
Consequently, when the beam lands on the peripheral portion of the screen 
2, it forms a beam spot which is distorted as is shown in FIG. 2B. The 
distorted beam spot consists of a horizontally elongated core having high 
luminance and halos having low luminance, one extending upward from the 
core and the other extending downward from the core. The larger the 
cathode-ray tube apparatus, or the more the beam is deflected, the more 
the beam spot is distorted. 
This distortion of the beam spot is produced due to over-focusing of the 
electron beam in the vertical plane. A method of reducing or eliminating 
the deflection aberration, i.e., the cause of the distortion of the beam 
spot, is disclosed in Television Technology, Vol. 36, pp. 41-55, 1988. 
This method is characterized in that a quadruple lens is incorporated into 
an electron gun assembly, and is driven to emit an electron beam having a 
cross section whose upper and lower portions are more intense than the 
right and left portions. When this method is applied, however, an electron 
beam will have an elliptical cross section extending in the vertical 
direction, and will be subjected to a more prominent aberration. Thus, in 
order to focus the electron beam appropriately, the power of the electron 
lens must be changed greatly. Here arises a problem. The more the power of 
the lens is varied, the greater the changes in the voltage for achieving 
dynamic focusing of the beam, and, hence, the greater circuit load the 
cathode ray tube apparatus requires. 
Further, in the quadruple lens, the electron beam is excessively diverged 
in the vertical plane and the electron beam is excessively focused in the 
horizontal direction. It is therefore necessary to add to the lens some 
elements for correcting this over-focusing of the electron beam, which 
would render the lens more complex in structure. To control such a complex 
electron lens, the circuit for controlling the electron gun assembly needs 
to be complex inevitably. 
Japanese Laid Open Patent Application No. 60-22140 discloses a cathode-ray 
tube apparatus, wherein electron beams are guided to cross twice the axis 
of the electron gun assembly, thereby to achieve a sufficient resolution 
even if the beam current is comparatively small. The gun assembly used in 
this apparatus comprises a three-electrode unit including a first grid G1 
(i.e., the control electrode) and a second grid G2 (i.e., the shield 
electrode), a main lens electrode for forming a main electron lens, and an 
auxiliary electrode G2s. The electrode G2s is interposed between the 
three-electrode unit and the main-lens electrode, and is applied with a 
voltage which is lower than the voltage applied to the second grid G2 and 
changes in accordance with the desired deflection angle of the electron 
beam. 
In this electron gun assembly, the electron beam crosses the axis of the 
assembly twice until it reaches the main lens electrode, and its 
peripheral portion is trimmed by a trimming electrode as the beam travels 
from the main lens electrode to the phosphor screen. The beam, however, 
forms but a distorted spot on the phosphor screen due to the deflection 
aberration, though the image resolution is sufficiently high if the beam 
current is relatively small. This is because the beam is anisotropically 
distorted by the deflection magnetic field, and the anisotropic distortion 
cannot be eliminated since the beam crosses the axis of the gun assembly 
two times while traveling from the cathode to the main lens electrode. 
Moreover, even if the second cross-over is dynamically shifted on the axis 
of the gun assembly, the shape of the second cross-over is changed in the 
horizontal or vertical plane, due to the auxiliary electrode G2s which are 
located between the cathode and the third grid G3, or within the 
beam-forming section of the gun assembly. Hence, the deflection aberration 
cannot be either reduced or eliminated in the cathode-ray tube, wherein 
self-convergence deflection magnetic fields are generated. Rather, the 
deflection aberration increases, and the beam will form an even more 
distorted spot on the phosphor screen. 
The electron lens is located in the beam-forming section of the gun 
assembly, in order to make the beam cross the axis of the gun assembly for 
the second time. This electron lens comprises four thin electrodes. These 
electrodes are located so close to one another that their potential affect 
mutually to a degree which depends on the shapes of the electrodes and 
also those of the openings made in the electrodes. Consequently, the 
characteristics of the electron lens fluctuate. Due to the fluctuation of 
its characteristics, the lens can hardly focus an electron beam 
sufficiently in the vertical direction only. Rather, this quadruple lens 
may focus an electron beam more in the horizontal direction than in the 
vertical direction. 
As may be clear from the above, the larger the color cathode-ray tube 
apparatus, or the more the electron beam are deflected, the more the 
resultant image will be deteriorated. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a color cathode-ray tube 
apparatus wherein, although electron beams are subjected to deflection 
aberration, they are focused such that beam spots, distorted as little as 
possible, are formed on the phosphor screen, thereby forming a 
high-quality image on the entire phosphor screen. 
According to a first aspect of this invention, there is provided an 
electron gun assembly having three gun axes aligned in a horizontal plane 
and designed to emit electron beams which are to be deflected in both a 
horizontal plane and a vertical plane and then applied to a phosphor 
screen, said assembly comprising: means for emitting three electron beams 
arranged in-line along the three gun axes, respectively, and accelerating 
and controlling the electron beams emitted from said emitting means; first 
electron lens means for focusing the electron beams, having a lens power 
which is greater in the vertical plane than in the horizontal plane, 
thereby causing the three electron beams to cross the gun axes only in the 
vertical plane and form cross-overs on the gun axes; second electron lens 
means for focusing the electron beams; and cross-over shifting means for 
changing vertical-focusing power supplied to the first electron lens 
means, in accordance with the horizontal or vertical deflection of the 
electron beams, thereby shifting the cross-overs on the gun axes between 
the first electron lens means and the second electron lens means. 
According to a second aspect of the invention, there is provided an 
electron gun assembly having three gun axes aligned in a horizontal plane 
and designed to emit electron beams which are to be deflected in both a 
horizontal plane and a vertical plane and then applied to a phosphor 
screen, said assembly comprising: three cathodes arranged in in-line 
alignment for emitting three electron beams along the three gun axes, 
respectively; control electrode means having three round through holes and 
held at a predetermined potential, for accelerating and controlling the 
electron beams which have been emitted by the cathodes; first electrode 
means including electrodes each having three holes spaced apart in a 
horizontal direction, for guiding electron beams, one of said electrodes 
being applied with a potential changed in accordance with a deflection of 
the electron beam , and the remaining electrode means having one through 
hole for guiding the three electron beams, for focusing the electron beams 
and also converging the electron beams while the beams are traveling 
toward the phosphor screen. 
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 in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will now be described, with 
reference to FIGS. 3 to 8. 
FIG. 3 is a longitudinal sectional view of a color cathode ray-tube 
apparatus according to the invention, taken along X-Z plane, i.e., the 
horizontal plane. FIG. 4 is also a longitudinal sectional view of the 
electron gun assembly incorporated in the apparatus, taken along Y-Z 
plane, i.e., the vertical plane. 
As is shown in FIGS. 3 and 4, an electron gun assembly 100 of in-line type 
is incorporated in the neck 5 of the color cathode-ray tube apparatus. The 
assembly 100 comprises an insulated support rod MFG, three cathodes K, a 
first grid G1, a second grid G2, a third grid G3, a fourth grid G4, a 
fifth grid G5, an auxiliary grid G56, a sixth grid G6, a seventh grid G7, 
an eighth grid G8, and a ninth grid G9. The nine grids and the auxiliary 
grid are supported by the support rod MFG, and are arranged in a line, 
from the cathodes K toward the screen SCN in the order they are mentioned. 
A bulb spacer BS is mounted on the ninth grid G9 and contacts the inner 
surface of the neck 5, thus holding the grid G9 in place. The electron gun 
assembly 100 is fixed to the neck 5 by means of stem pins STP. 
The cathodes K each contain a heater H each, and emits three electron beams 
BR, BG, and BB when the heaters H generate heat. The first grid G1 and the 
second grid G2 have three, relatively small holes each. The three holes of 
either grid guide the electron beams BR, BG, and BB. The third grid G3 is 
a hollow, thin member made of two parallel plates which are spaced apart 
for a short distance and connected together at both ends. The plate of the 
grid G3, which opposes the second grid G2, has three beam-guiding holes, 
which are larger than those of the second grid G2. The cathodes K, the 
first grid G1, the second grid G2, and the third grid G3 constitute an 
electron beam-forming section GE for controlling and accelerating electron 
beams. 
As is illustrated in FIG. 5A, that plate of the third grid G3, which 
opposes the fourth grid G4, has three, relatively large beam-guiding holes 
121. The fourth grid G4 is a hollow, thin member made of two parallel 
plates each having three beam-guiding holes which have the same diameter 
as the beam-guiding holes 121. The fifth grid G5 is also a hollow, thin 
member made of two parallel plates. The plate of the fifth grid G5, which 
opposes the fourth grid G4, has three beam-guiding hoes having the same 
diameter as the holes 121 of the third grid G3. The plate of the fifth 
grid G5, which opposes the auxiliary grid G56, has one hole 122 for 
guiding the three electron beams BR, BG, and BB. As is shown in FIG. 5B, 
the beam-guiding hole 122 is elongated in the X direction. The fifth grid 
G5 has projections PT extending in the Z direction in the electrode 
structure. The auxiliary grid G56, the sixth grid G6, and the seventh grid 
G7 have one beam-guiding hole each, which is elongated in the X direction 
like the hole 122 of the fifth grid G5. The auxiliary grid G5 also has 
projections PT extending in the Z direction in the electrode structure. 
The eighth grid G8 is a hollow, thin member made of two parallel plates, 
both having one beam-guiding hole which is elongated in the X direction. A 
hollow cylinder LCY 8 is connected to that plate of the grid G8 which 
opposes the phosphor screen. An electric field control plate ECD is 
located in the hollow cylinder LCY, dividing the interior of the cylinder 
LCY into two portions. As is shown in FIG. 5C, the plate ECD has three 
rectangular beam-guiding holes extending in the Y direction, i.e., a 
center hole 123 and two side holes 124 larger than the center hole 123. 
Two projections VIS extend in the Z direction from those portions of the 
plate ECD which are located at the upper end lower edges of either side 
beam-guiding hole 124. 
The ninth grid G9 is a large hollow cylindrical electrode LCY 9 which 
surrounds the eighth grid G8. An electron lens LEL is formed between the 
eighth grid G8 and the ninth grid G9. The bulb spacer BS is mounted on the 
front-end portion of the ninth grid G9. The spacer is electrically and 
mechanically contacts a conductive layer 10 coated on the inner periphery 
of the junction between the funnel 4 and neck 5 of the cathode-ray tube 
apparatus. A high anode voltage is applied to the ninth grid G9 via the 
layer 10 and the bulb spacer BS from an anode terminal (not shown) mounted 
on the funnel 4. Predetermined voltages are applied to all other grids 
from the external voltage sources PS through the stem pins STP. 
As evident from FIG. 4, the cathodes K, the grids G1 to G9, and the 
auxiliary grid G56 are secured to the insulated support rod MFG. As is 
shown in FIG. 3, a deflection yoke 7 is mounted on the junction of the 
funnel 4 and the neck 5. The yoke 7 comprises a horizontal deflection coil 
and a vertical deflection coil The horizontal deflection coil deflects the 
electron beams BR, BG, and BB emitted from the gun assembly, in the 
horizontal direction. The vertical deflection coil deflects the beams BR, 
BG, and BB in the vertical direction. A multi-pole magnet PCM is mounted 
on the neck 5 and located close to the deflection yoke 7, for adjusting 
the paths of the electron beams BR, BG, and BB. 
In operation, a cutoff voltage of 150 kV is applied to the cathodes K, and 
video signals are also supplied to the cathodes K. The first grid G1 is 
maintained at the ground potential, whereas a voltage of 500 V to 1 kV is 
applied to the second grid G2. Voltages of 5 kV to 10 kV are applied to 
the grids G3, G5, G6, and G8; a voltage of 0 V to 1 kV is applied to the 
fourth grid G4; a voltage of 0 V to 3 kV is applied to the auxiliary grid 
G56; and a voltage of 15 to 20 kV is applied to the seventh grid G7. A 
voltage of 25 kV to 35 kV, which is equivalent to an anode voltage, is 
applied to the ninth grid G9. 
When the various voltages, specified above, are applied to the grids of the 
gun assembly from the power supply PS, an electron lenses are formed as is 
shown in FIGS. 6B and 6C. FIG. 6A illustrates only the grids of the gun 
assembly, more particularly showing the arrangement of these grids. FIG. 
6B shows the positions which the electron lens assume in the horizontal 
plane, i.e., the X-Z plane. FIG. 6C shows the positions which the electron 
lens take in the vertical plane, i.e., the Y-Z plane. Further, FIG. 6D is 
a perspective view of the system comprised of some of the electron lenses 
shown in FIGS. 6B and 6C. 
The cathodes K generate electron beams BR, BG, and BB in accordance with a 
video signals supplied to them. These electron beams are focused by the 
grids G1 and G2, thereby crossing gun axes ZR, ZG, and ZB at first 
cross-overs CO1. The beams are focused a little by prefocusing lenses PL 
formed between the grids G2 and G3, and is supplied to the third grid G3. 
The electron beams BR, BG, and BB pass through the third grid G3 and 
focused by unipotential lenses ELS as they pass through the fourth grid 
G4. They are further focused by a single electron lens LEL, as they pass 
through the grids G5 to G9. The electron beams BR, BG, and BB, thus 
focused, are deflected by the yoke 7 in both the horizontal direction and 
the vertical direction and applied to adjacent red, green and blue 
phosphor stripes or dots formed on the screen SCN. 
As other video signals are supplied to the cathodes K, one after another, 
the electron beams BR, BG, and BB scan the phosphor screen SCN, forming a 
color image thereon. Whenever the deflection yoke 7 deflects the beams 
toward the peripheral portion of the phosphor screen SCN, each electron 
beam has a deflection aberration. The characteristics of the main electron 
lens LEL are changed to cancel out the deflection aberration, thereby to 
impart high quality to the color image. 
The unipotential lenses ELS are defined by the round beam-guiding holes of 
the fourth grid G4, the beam-guiding holes of hat plate of the third grid 
G3 which opposes the grid G4, and the beam-guiding holes of that plate of 
the fifth grid G5 which opposes the grid G4. The lenses ELS focus the 
electron beams BR, BG, and BB, which are travelling from the first 
cross-over CO1 and passing through the third grid G3, a little in both the 
horizontal direction and the vertical direction. 
The elongated beam-guiding hole of the auxiliary grid G56, the elongated 
beam-guiding hole of that plate of the grid G5 which faces the grid G56, 
and the elongated beam-guiding hole of that plate of the grid G6 which 
opposes the grid G56 define a single electron lens VL1. This lens VL1 
focuses the electron beams BR, BG, and BB more in the vertical plane, 
i.e., the Y-Z plane, than in the horizontal plane, i.e., the X-Z plane. As 
is shown in FIG. 6C, the beams cross the gun axes in the vertical plane in 
the middle portion of the sixth grid G6, thus forming second cross-over 
CO2. The beams diverge from the second cross-over CO2 toward the seventh 
grid G7. 
The elongated beam-guiding hole of the grid G7, the elongated beam-guiding 
hole of that plate of the grid G6 which opposes the grid G7, and the 
elongated beam-guiding hole of that plate of the grid G8 which opposes the 
grid G7 define a single electron lens VL2. This electron lens VL2 focuses 
the beams a little in the vertical plane and applied to the single 
electron lens LEL which is defined by the grids G8 and G9. The electron 
lens LEL focuses the beams BR, BG, and BB in both the horizontal plane and 
the vertical plane onto the center portion of the phosphor screen SCN. As 
the electron beams land on the screen SCN, they form small beam spots. 
If the electron beams focused by the lens LEL ar deflected by the 
deflection yoke 7 generating a magnetic field of the self-convergence 
type, they will be focused excessively in the vertical plane as has been 
mentioned earlier. To prevent such an over focusing of the beams, the 
potential of the auxiliary grid G56 is increased as is illustrated in FIG. 
7 in accordance with the voltage applied to the auxiliary grid G56 from 
the power source PS. When the potential of the grid G56 is increased, the 
vertical-focusing power of the cylindrical electron lens VL1 decreases as 
is indicated by the broken line in FIG. 6C, and the second cross-over CO2 
shifts to position CO2(D). As a result, the distance between the lens LEL 
and the objective point, measured in the vertical direction, becomes 
shorter, thereby preventing the over-focusing of the beams. Therefore, the 
beams are focused appropriately onto the peripheral portion of the screen 
SCN. In other words, dynamic focusing is achieved by changing the 
potential of the auxiliary grid G56. 
Although only the center beam BG is shown in FIG. 6C, the side beams BR and 
BB are dynamically focused in the same way as the center beam BG. As can 
be understood from FIG. 6C, when the beams being applied to the peripheral 
portion of the screen SCN are dynamically focused, the diameter they have 
in the deflection start plane decreases from D to Dd. By virtue of the 
small diameter Dd of the beams, the beams have little deflection 
aberration. Hence, the dynamic focusing helps to form a high-quality image 
on the phosphor screen SCN. In this embodiment, the second cross-over may 
be formed at a position between the lens VL2 or LEL and the screen to 
obtain a same advantage. 
FIG. 6D is a perspective view showing the major electron lens which act on 
the center beam BG. The electron lens VL1, which is defined by the grids 
G5, G56, and G6, focuses the beam BG more in the vertical plane than in 
the horizontal plane. As a result, a line-like second cross-over CO2 is 
formed, where the beam BG crosses the gun axis in front of the electron 
lens LEL. The lens VL1 is designed to focus three electron beams to the 
same degree. More specifically, the lens VL1, which is a planar 
unipotential lens, is formed by the three electrodes identical to the one 
shown in FIG. 5B, which are incorporated in the grids G5, G56, and G6, 
respectively. The elongated beam-guiding hole of each electrode consists 
of one straight portion having a height av and a width aH, and two 
sector-shaped portions having a height bv and a width bH. Assuming that 
the three electron beams are spaced apart at intervals sg, the heights av 
and bv and the widths aH and bH have the following relationships: 
EQU aH&gt;2 sg+av 
EQU bv&gt;1.5 av 
EQU bH&gt;av/2 
If the heights av and bv, the widths aH and bH, and the interval sg had 
other relationships, the potential of the end portions of each electrode 
would focus the electron beams in the horizontal plane, and the side 
electron beams, in particular, would be deflected. 
The relationship specified above are products of the three-dimensional 
analysis and experiments the inventors hereof have performed and 
conducted. It is required that the grids G5 and G6 be spaced apart from 
the auxiliary grid G56 for a distance longer than 1.3.times.av. If an 
electrode similar to the one shown in FIG. 5A were located within a 
distance of 1.3.times.av, an electric field should leak through the holes 
made in those plates of the grids G5 and G6 which oppose the auxiliary 
grid G56, inevitably focusing the electron beams in the horizontal plane. 
The dimensional features of the present embodiment will be detailed as 
follows: 
Interval (sg) between cathodes: 4.92 mm 
Diameter of holes of G1 and G2: 0.62 mm 
Diameter of holes of G3, G4 and G5 faced to the grid G4 : 4.52 mm 
Height/width of holes of grids G5, G56, G6, G7, and G8: 5.52 mm/15.0 mm 
(Height/length of sector-shaped portions: 8.0 mm/2.5 mm) 
Diameter of hole of grid G8 faced to the grid G9: 15.0 mm 
Diameter of hole of grid G9: 18.0 mm 
Lengths of electrodes: G3=1.1 mm; G4=4.4 mm; G5=9.2 mm; G56=8.0 mm; G6=21.0 
mm; G7=4.4 mm; G8=37.0 mm; G9=40.0 mm 
In the embodiment shown in FIG. 3, which is a color cathode-ray tube having 
a 32-inch screen and a deflection angle of 110.degree. , the optimum 
voltages of the grids for focusing the electron beams onto the center 
portion of the screen SCN appropriately are: 
8 kV for the grids G3, G5, G6, and G8 
1 kV for the grid G4 
3 kV for the grid G56 
15 kV for the grid G7 
25 kV for the grid G9 
To focus the beams appropriately onto a peripheral portion of the screen 
SCN, it suffices to increase the voltage of the grid G5 by 500 V only, to 
3.5 kV, whereas it is required to increase the voltage by about 1.0 kV in 
the conventional color cathode-ray tube. In other words, the color 
cathode-ray tube apparatus of this invention needs but a relatively low 
dynamic-focusing voltage. This means that the circuit for driving the 
apparatus need not include a high dynamic-focusing voltage source, and can 
therefore be made at low cost. 
In the embodiment described above, the lens VL1 of a plane type for forming 
the cross-over CO2 is formed by the electrode which has one elongated hole 
122 for allowing three electron beams to pass therethrough. However, it is 
not limited in this embodiment. In the modification, the electrode G5 may 
be provided with three elongated holes 123 to form the electron lens, as 
shown in FIG. 5D. It is preferable in this modification that the aperture 
ratio between a lateral dimension aH to a longitudinal dimension aV of the 
hole 123 set to be relatively large value or quadruple lens is formed to 
apply a divergence force to the electron beams in the horizontal plane, as 
described below, since the electron beams are not focused only in the 
vertical plane but also in the horizontal plane. 
In the embodiment described above, the electron beams BR, BG, and BB are 
focused excessively in the vertical plane, inevitably because of the 
deflection aberration of the beams, caused by the magnetic field generated 
by the deflection yoke 7. Nevertheless, this excessive focusing is 
eliminated. Usually the horizontal-deflection aberration of an electron 
beam is so small that it need not be reduced or eliminated at all. If 
necessary, however, the horizontal-deflection aberration can be 
eliminated. For example, that plate of the grid G5 which opposes the grid 
G4 may be lengthened, and that plate of the grid G5 which opposes the 
auxiliary grid G56 is shortened, whereby a quadruple lens is formed 
between the grid G5 and the auxiliary grid G56. This electron lens has a 
small beam-focusing power. When the electron beams are deflected toward a 
peripheral portion of the screen SCN, the voltage of the auxiliary grid 
G56 is increased to decrease the focusing power of the quadruple lens 
formed between the grids G5 and G56. As a result of this, the electron 
beams are focused also in the horizontal plane and weakly focused in the 
vertical plane relative to that in the horizontal plane or diverged in the 
vertical plane. Since the quadruple lens is much more sensitive than a 
lens, its focusing power remains sufficiently great even if the potential 
of the auxiliary grid G56 fluctuates by several hundred volts. Hence, the 
electron beams directed to a peripheral portion of the screen SCN are 
focused in the horizontal plane, a little too much. This excessive 
horizontal focusing of the beams is suppressed by the deflection 
aberration which the beams have due to the magnetic field generated by the 
deflection yoke 7. Therefore, a electron beam being applied to any portion 
of the phosphor screen SCN can be properly focused in both the vertical 
plane and the horizontal plane. 
As is illustrated in FIG. 6C, the cathode-ray tube apparatus has, among 
other things, the electron lens VL1 for focusing the beams BR, BG, and BB 
mainly in the vertical plane, thereby forming a second cross-overs CO2 
extending in the horizontal direction, and the electron lens LEL for 
focusing these beams, supplied from the cross-overs CO2, onto the phosphor 
screen SCN. As can be understood from FIG. 6B, the lens VL1 does not focus 
the beams in the horizontal plane, thus forming no cross-overs in the 
horizontal plane between the lens VL1 and the lens LEL. 
When the electron beams are deflected by the magnetic field of 
self-convergence type, the vertical focusing power of the lens VL1 is 
decreased in proportion to the deflection angle of the beams. The second 
cross-over CO2 is thereby shifted toward the electron lens LEL, 
appropriately focusing the electron beams BR, BG, and BB onto the 
peripheral portion of the phosphor screen SCN. 
The electron beams BR, BG, and BB have virtually no deflection aberration 
in the horizontal direction, or are under-focused in the horizontal plane. 
Hence, the lens VL1 should better be designed to focus the beams at all or 
slightly over-focus them in the horizontal plane, when its 
horizontal-focusing power is reduced in proportion to the deflection angle 
of the electron beams. At least, the lens VL1 should focus the beams to 
form cross-overs at positions very close to the electron lens LEL. In view 
of this, it is desirable that the electron lens LV1 be a lens which 
focuses beams in the vertical plane only. More specifically, the lens VL1 
must have such an electrode as is shown in FIG. 5B, which has one hole 122 
elongated in the horizontal direction for guiding three parallel beams 
spaced apart in the horizontal direction. As has been pointed out, the 
beam-guiding hole 122 consists of a straight portion and two sector-shaped 
portions 122', and the electrode has two projections PT extending in the X 
direction from upper and lower edges of the straight portion of the hole 
122. Having this specific configuration, the electrode shown in FIG. 5B 
focuses the three beams BR, BG, and BB to the same degree in the vertical 
plane only. 
The embodiment described above has other electron lens PL, ELS, and VL2. 
These lenses are used to adjust the focusing of the beams and to enhance 
the efficiency of the electron gun assembly, thereby forming small beam 
spots on the center portion of the phosphor screen SCN. 
FIG. 8 illustrates a color cathode-ray tube apparatus, which is another 
embodiment of the invention. In this figure, the same reference numerals 
and symbols are used to designate the same components as those shown in 
FIG. 3. As can be seen from FIG. 8, this embodiment is characterized in 
two respects. First, the electron gun assembly has no component equivalent 
to the auxiliary grid G56. Second, the fifth grid G5 is maintained at a 
low potential of 1 to 3 kV, thus forming an electron lens LV1 between the 
fifth grid G5 and the six grid G56. This lens VL1 focuses electron beams 
BR, BG, and BB mainly in the vertical plane. Hence, the electron lens 
system is, after all, the same as that of the first embodiment. 
The potential of the fifth grid G5, which is relatively low, is increased 
in proportion to the deflection angle of the electron beams. As a result 
of this, the vertical-focusing power of the lens VL1 is reduced, and the 
horizontal-focusing power of the cylindrical unipotential lens ELS, formed 
by the grids G3, G4, and G5, is increased. The increase in the 
vertical-focusing power of the lens ELS increases the degree of horizontal 
focusing of the beams which is insufficient because of the deflection 
aberration imparted to the beams by the self-converging magnetic field 
generated by the deflection yoke 7. The electron beams are thereby focused 
appropriately also in the horizontal plane. 
Either embodiment described above has an electron gun assembly which has 
large electron lenses used for focusing three electron beams. 
Nevertheless, this invention can be applied to a color cathode-ray tube 
apparatus wherein three identical large electron lenses are used in place 
of each of such lenses, for focusing the three electron beams, 
respectively. Moreover, according to the present invention, the electrode 
shown in FIG. 5B can be replaced by three electrodes, each having an 
elongated hole, for focusing three electron beams, respectively. 
As has been described in detail, the present invention can provide a color 
cathode-ray tube apparatus, in which three electron beams set in an 
in-line alignment are focused such that they form a high-quality image on 
the phosphor screen, despite of the deflection aberration the beams have 
as they are deflected in the horizontal and vertical directions. In 
particular, since it suffices to apply a low dynamic voltage to reduce or 
eliminate the deflection aberration of the beams, the apparatus needs no 
drive circuits which includes a high-voltage source and is therefore 
expensive. Furthermore, since the electron lens for reducing or 
eliminating the deflection aberration of the beams is a cylindrical one, 
not a quadruple lens, which need not be controlled to adjust its 
horizontal-focusing power and which is easy to operate and design. 
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 devices, 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.