US3452242A

US3452242A - Color picture tube

Info

Publication number: US3452242A
Application number: US668373A
Authority: US
Inventors: Senri Miyaoka
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1966-09-17
Filing date: 1967-09-18
Publication date: 1969-06-24
Anticipated expiration: 1986-06-24
Also published as: DE1537375A1; GB1208002A

Description

June 24, 1969 SE.NRI MIYAOKA COLOR PICTURE TUBE sheet ors Filed Sept. 18, 1967 PRIOR ART PRIOR ART INVENTOR.

SENRI MIYAOKA ATTORNEY June 24, 1969 SENRI MIYAOKA COLOR PICTURE TUBE Sheet of6 Filed Sept. 18, 1967 INVENTOR.

A TTO R N E June 24, 1969 SENRI MIYAOKA COLOR PICTURE TUBE Sheet Filed Sept. 18, 1967 INVENTOR. SENRI MIYAOKA ATTORNEY June 24, 1969 SENRI MIYAOKA COLOR P I CTURE TUBE sheet 5 or6 Filed Sept. 18, 1967 INVENTOR.

SENRI MIYAOKA ATTORNEY June 24, 1969 SENRI MIYAOKA COLOR PICTURE TUBE Sheet Filed Sept. 18, 1967 a b C d ZJ 3 ZJ 3 1d 1c 1b 1a INVENTOR.

SENRI M I YAOKA ATTORNEY United States Patent 3,452,242 COLOR PICTURE TUBE Senri Miyaoka, Fujisawa-shi, Japan, assignor to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Sept. 18, 1967, Ser. No. 668,373 Claims priority, application Japan, Sept. 17, 1966, 41/61,340, ll/61,341 Int. Cl. H01j 29/20 US. Cl. 31521 10 Claims ABSTRACT OF THE DISCLOSURE A color picture tube includes at least one electron gun device, a phosphor screen having tri-color phosphors arranged in stripes, and a post-deflection grid device placed between the electron gun device and the phosphor screen and defined by wires in parallel with the stripes of color phosphors. The grid device is biased at an average voltage which is the same as the anode voltage for the phosphor screen and deflects the electron beams emitted from the electron gun device on to predetermined phosphors without post-acceleration or focusing of such beams.

This invention relates to a color picture tube, and more particularly to an improved color picture tube including post-deflection means and a striped color phosphor screen. Heretofore, so-called shadow-mask and Chromatron tubes have been proposed and put to practical use in color television reception. In the Chromatron picture tube an electron beam is post-accelerated and focused by a grid for impingement upon the phosphor screen, and the electron beam transmission factor is six times as great as that of the shadow-mask tube to provide for increased brightness of the reproduced picture. In spite of such a basic advantage, however, the Chromatron picture tube is more diflicult to produce than the shadow-mask tube and is burdened with certain operational difliculties. The production and operational difiiculties encountered with the Chromatron tube include the following:

(1) Since the electron beam is contracted or narrowed within the tube by focusing effect of the grid, the phosphor screen cannot be produced by a mere optical printing of a shadow image of the grid on the screen. If such optical printing was employed, dispersion in the operating characteristics of the finished tubes would result, and hence production of the phosphor screen requires many manufacturing operations.

(2) Due to need for exact reproducibility of the electric fields in the tube, precision of the parts is required to be by far higher than that for the shadow-mask tube, which inevitably increases the cost of the parts.

(3) A large potential difference exists between the grid and the phosphor screen, for example, in the range from about 15 to 16 kv., and this produces sparks or stray emission, which leads to troubles in relation to breakdown voltage.

(4) The contrast of the reproduced picture is decreased due to fog and the like resulting from the presence of secondary electrons or backscattering electrons.

(5) Resolution is decreased due to low mean electric potential in the tube.

I have found that all of the above-mentioned difficulties experienced in the manufacture and operation of Chromatron picture tubes result from the operation of the grid at a potential about A of the anode potential of the phosphor screen for accomplishment of the post-acceleration and focusing of the electron beam. In accordance with the present invention, the described difficulties are all avoided by maintaining the grid at an average or mean potential that is substantially equal to the anode potential "ice of the phosphor screen, and by effecting only post-deflection of the electron beam.

One object of this invention is to provide an improved color picture tube which is provided with a post-deflection grid device.

Another object of this invention is to provide a color picture tube the interior of which is held at substantially a constant voltage to ensure that the electron beam advances substantially rectilinearly, that is, without being contracted or focused by a grid device in the tube.

A further object of this invention is to provide a color picture tube which ensures such rectilinear advance of the electron beam and which is easy to design and facilitates manufacture of the phosphor screen.

Still a further object of this invention is to provide a color picture tube having a phosphor screen with striped color phosphors and which is provided with a postdeflection grid device held at an average or mean potential equal to the anode potential of the phosphor screen.

Still another object of this invention is to provide a color picture tube which includes a post deflection grid device held at an average or mean potential equal to the anode potential of the phosphor screen and which affords enhanced resolution and white balance.

The above, and other objects, features and advantages of this invention will become apparent from the following detailed description which is to be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of a Chromatron picture tube;

FIG. 2 is a fragmentary enlarged schematic diagram of a portion of a conventional Chromatron tube in the vicinity of the grid and phosphor screen thereof, for explaining its operating mechanism;

FIG. 3 is an enlarged view similar to that of FIG. 2 for explaining the present invention;

FIG. 4 is a similar enlarged view illustrating one embodiment of this invention;

FIG. 5 is a schematic diagram illustrating color selection by the post-deflection grid device of the embodiment shown on FIG. 4;

FIGS. 6A, 6B and 6C are schematic diagrams illustrating the accomplishment of color switching operations by a grid device in accordance with another embodiment of this invention;

FIG. 7 is a schematic diagram illustrating one of the ways in which the color switching operations may be effected in the embodiment shown on FIGS. 6A, 6B and 6C;

FIG. 8 is a schematic diagram which illustrates another embodiment of this invention;

FIG. 9 is a schematic diagram for explaining the color selection by the embodiment shown in FIG. 8; and

FIG. 10 is a schematic diagram illustrating color switching operations in still another embodiment of this invention.

In order to facilitate understanding of the present invention, the fundamentals of the conventional type of Chromatron picture tube will first be described with reference to FIGS. 1 and 2. In FIG. 1, reference character T indicates an envelope, G an electron gun, and Y a deflection device. Reference numeral 2 designates a phosphor screen, on the front surface of which color phosphor stripes of, for example, red R, green G and blue B are laid down in a repeating cyclic order. Reference numeral 1 identifies a grid of wires which are disposed substantially parallel with, but spaced a certain distance from the phosphor screen 2 and are adapted to carry out the so-called post-acceleration and focusing of an electron beam when disposed at a potential approximately of the anode potential of the phosphor screen. In such a case, equipotential lines 4 (FIG. 2) are formed in the vicinity of the grid wires 1. The electric fields are each symmetrical with respect to the central axis O-O of an electron beam 5 passing centrally through the space between adjacent grid wires. In the space between adjacent grid wires, the intensity of the electric field increases with increasing distance from the central axis O-O, and such variation of the field acts to deflect the beam toward the center between adjacent grid wires. As a result of this, the electron beam 5 is contracted or narrowed in the direction toward the phosphor screen. The intensity with which the electron beam is thus contracted or focused varies with the ratio of the grid potential to the anode potential of the phosphor screen. When such ratio is A, sufficient focusing is effected. When the ratio of grid potential to the anode potential of the phosphor screen is less than /21, excessive focusing results, and with the ratio exceeding insuflicient focusing is achieved. In the television art, a picture tube having three electron guns is commonly referred to as a three-beam Chromatron picture tube, and a picture tube of the type having one electron gun and in which alternate grid wires are supplied with deflection voltage to post-accelerate and focus an electron beam and to slightly shift it on the phosphor screen for color switching, is generally referred to as a one-gun post-aceeleration-focusing type Chromatron picture tube.

For elimination of the above-described disadvantages experienced in the past with such conventional types of Chromatron tubes, in accordance with the present invention the average or mean potential of the grid is held substantially equal to the anode potential of the phosphor screen, thereby to permit rectilinear travel of the electron beam in the tube and thus avoid the post-acceleration and focusing of the beam. In that case, that is, when the grid and anode potential are substantially equal, the beam width on the phosphor screen 2 is substantially the same as the slit width between adjacent grid wires 1, as shown on FIG. 3.

In FIG. 3, reference character S designates the pitch of the grid wires 1 (or of the slits defined therebetween), W is the diameter of the grid wires 1 and P is the pitch of color cyclic units of the phosphor stripes making up the phosphor screen. The color cyclic unit mentioned herein is an assembly of adjoining phosphor stripes of one cycle of the repeating cyclic order of the stripes. The slit width is equal to (S W) and the beam width on the phosphor screen is also approximately equal thereto. However, since the beam width must be smaller than that of each phosphor stripe, it is required in the tri-color tube that the slit Width (SW) P/3. In the example of FIG. 3, since P-S, it follows that 2S/3 W, and therefore that the diameter of the grid wires 1 must be greater than of the pitch of the grid wires. This reduces the beam transmission factor to less than A (33%), and it is further reduced to 20 to 25% by consideration of practical manufacturing tolerances, so that the brightness of the reproduced picture is substantially the same as that obtainable with the shadow-mask tube.

Referring now to FIG. 4, it will be seen that the brightness of the reproduced picture may be increased in a tube embodying this invention by providing a grid device therein formed of two sets of

parallel wires

1a and 1b disposed in pairs opposite to each color cyclic unit of red, green and blue phosphor stripes laid down on the phosphor screen 2. The alternately arranged first and

second wires

1a and 1b are connected to terminals t and t through lead wires 31: and 3b respectively, and an electron beam passing between adjacent grid wires 1a-1b, 1b1a, la-lb, etc., is slightly deflected, as indicated at 0, by applying a potential difference between the terminals t and t2.

A DC voltage is applied between the terminals t and t of the grid by a DC power source 6 in such a manner that the electron beams 5 passing through the grid at .4 opposite sides of each of the grid elements or wires which are positively biased are overlapped on the phosphor screen 2. The line deflection voltage is referred to as V and the anode voltage is referred to as Va in this specification. The voltages fed to the two terminals t and t relative to the ground, are determined by a potentiometer 7 to be (VzH-Vf/Z) and (VaVf/2), respectively, so that the mean or average potential of the grid is equal to Va. Thus, rectilinear travelling of the beam in the tube is ensured and the beam width on the phosphor screen 2 becomes substantially equal to the slit width (S-W). In the tri-color tube this beam width is required to be smaller than /3 of the pitch P of the color cyclic units on the phosphor screen, as described in the foregoing, that is, the condition (SW) P/3 must be satisfied. However, P=2S in the embodiment of FIG. 4 and hence it follows that W S/ 3. Thus, in this embodiment it is only necessary that the diameter of the grid wires 1 exceed /3 of the pitch thereof. This inevitably reduces the beam transmission factor to less than (or 66%). In spite of the possible further reduction of the beam transmission factor by reason of manufacturing tolerances, such factor can be maintained at approximately 40 to 50%. Accordingly, it is possible to obtain a reproduced picture which is 2.5 to 3.5 times brighter than that obtainable with the shadow-mask tube.

In FIG. 4, reference character D indicates the distance between the grid and the phosphor screen. Accordingly, the aforementioned line deflection voltage V is approximately given by the following formula.

In the case where D is 15 mm., S is 0.3 mm., and W is 0.125 mm. (the beam transmission factOrZSS /Zw), it fol lows that Vf=l.42 l0 Va. If the anode voltage is 20 kv., the line deflection voltage V is approximately 280 v., which is so small that the problem of discharge can be neglected in practice. Even where the line deflection voltage Vf is greater, it is suflicient only to consider the withstand voltagebetween the lines, since the voltage is a DC voltage and therefore is merely added electrostatistically. FIG. 4 illustrates the case where the electron beam is directed perpendicular to the grid, but in practice the incident angle of the beam to the grid is increased as the beam moves away from the center of the screen to its periphery. The deflection sensitivity increases with an increase in the incident angle, and hence the optimum value of the line deflection voltage Vf becomes correspondingly smaller. However, suitable selection of the distance D between the grid and the phosphor screen in accordance with the horizontal curvature of the grid and the curvature of the glass plate of the phosphor screen makes it possible to obtain substantially the same deflection of the beam over the entire area of the phosphor screen with a constant line deflection voltage.

The manner in which color selection is effected in the tube of FIG. 4 will now be explained with reference to FIG. 5 in which reference characters R G and B indicate electron beams corresponding to the red, green and blue colors. These electron beams may be separately emitted from three electron guns or they may be beams emitted from one electron gun and suitably deflected in accordance with the colors to be displayed, and, in either case the three kinds of electron beams are directed to the grid and the phosphor screen with different angles of incidence, as depicted. As is apparent from FIG. 5, the three electron beams R G and B are directed to the same slits between adjacent grid Wires at a small angle of A0 relative to one another, so that the centers of the beams, if not deflected by the wire grid, would be relatively displaced by AHXD on phosphor screen 2. Color selection can be accomplished by making the displacement A0 D equal to P/3, that is, by making A0=P/3 D.

FIGS. 6A, 6B and 6C will now be referred to in connection with the description of a color picture tube embodying the principles of this invention for accomplishment of color switching by the use of a deflecting grid, that is, a tube in which an electron beam emitted from a single electron gun is selectively deflected by the grid for color switching. As shown on FIG. 6A, first grid wires 1a, and

second grid wires

1b and 1c which together constitute three groups are connected respectively to terminals t t and t through

lead wires

3a, 3b and 3c in such a manner that they are sequentially arranged in a repeating cyclic order of 1a, 10, 1b and 1c, that is, with three second grid wires between adjacent first grid wires 1a. The present example will be described in connection with a socalled double red phosphor screen. In this case, the red, green and blue phosphor stripes R, G and B are laid down on the phosphor screen in parallel with the grid wires at those areas respectively confronting the

grid wires

1c, 1b and 1a, whereby each cycle of the phosphor stripes consists of stripes B, R, G, R, in that order. Voltage fed to the terminals t t and t are indicated by V V and V the anode potential of the phosphor screen is Va and the deflection voltage is V With the above arrangement, all the electron beams are made to impinge upon the green phosphor stripes to produce the green color, as depicted in FIG. 5A, when the voltages V V and V are as follows:

V Va+1.5 Vf

It will be noted that, with such selection of the voltages V V and V the mean electric potential of the grid is equal to the anode potential Va of the phosphor screen to ensure rectilinear travelling of the beams. When the voltages applied to terminals t t and t are as follows:

all of the electron beams impinge on the red phosphor stripes R to produce the red color, as shown on FIG. 6B. In a similar manner the blue color is obtained, as illustrated on FIG. 6C, by selecting the voltages as follows:

Since the voltage V is always constant at Va+0.5Vf when producing the red, green and blue colors, it is suflicient to merely bias the terminal t by a DC current and there is no need to apply a color switching voltage to this terminal.

FIG. 7 illustrates the manner in which color switching may be effected in the embodiment of FIGS. 6A, 6B and 6C by applying a color switching voltage, at a frequency of, for example, 3.58 mc., to the grid terminals t and 1 Such color switching is accomplished by feeding an AC voltage Vs, having a peak-to-peak value of 8 V), to bias the mid-point P between terminals t and t while applying the DC voltage V to the terminal t The application of merely the DC voltage V to the terminal t enables the color switching operations to be carried out in the same manner as in the conventional one-gun Chromatron tube. However, in the case illustrated by FIG. 7, the grid potential is greater than that in the conventional Chromatron tube, from which it would appear that the switching sensitivity is reduced to A that in the conventional Chromatron tube. However, the pitch of the grid wires is /2 that in the conventional Chromatron tube and consequently the switching sensitivity is improved about two times, with the result that the sensitivity is at least /2 that of the Chromatoron tube. Accordingly, the color switching can be accomplished by the use of a voltage Vs having a peak-to-peak value of approximately 500 to 2000 v. which is fully practicable. The lower portion of FIG. 6 graphically illustrates the color switching sequence as a function of time t.

FIG. 8 illustrates an embodiment of the invention employing a grid device in which there are three

grid wires

1a, 1b, 1b disposed in front of each color cyclic unit R, G, B. The embodiment shown in FIG. 4 is based upon the concept that the two electron beams passing between adjacent grid wires at opposite sides of each wire 1b are focused on one place, while the embodiment presently being described is based upon the concept that three beams are focused on one place and is, for the purposes of this disclosure, referred to as having three-set grid wires. As shown on FIG. 8, every third grid wire 1a is connected to a terminal t and the remaining grid wires 1b are connected together to a terminal t so that the grid wires are sequentially arranged in a repeating cyclic order of 1a, 1b, 1b and 1a. When biasing the terminal t positive relative to the terminal t the beams passing between the adjacent

second grid wires

1b and 1b are not deflected, while the beams passing between the

grid wires

1a and 1b and between the

grid wires

1b and 1a are deflected in such a direction as to be pulled together. In this manner, the beams passing between the

grid wires

1a and 1b and between the

grid wires

1b and 1a can be overlapped on the intermediate beams passing between the grid wires 1b and 111 so as to all impinge on a common area of the phosphor screen. By applying voltages such as to the terminals t and t respectively, the focusing action mentioned above can be carried out while at the same time maintaining the mean potential of the grid equal to the anode potential Va, thereby to ensure that the beams travel rectilinearly, that is, are not contracted within the tube.

Since the beams are not contracted, the beam Width on the phosphor screen becomes substantially equal to the slit width (S-W) of the grid. In the tri-color tube the beam width must be less than A of the pitch P of the color cyclic units of the phospher screen, that is, (SW) P/3. However, P is equal to 3 S as depicted in FIG. 8, and hence it follows that any value of W 0 will sufiice. In this case there is no limit to the diameter of the grid wires. The space on the screen corresponding to the diameter of each of the grid wires is an allowance for slight variations in the position of the beam landing on the phosphor screen. However, since the pitch of the grid wires is required to be less than /3 of that in a usual Chromatron tube and the diameter W of the grid wires cannot be made too small, the beam transmission factor (SW)/S is less than that obtainable with the usual Chromatron tube. However, it is possible to produce a grid device of the type shown on FIG. 8 with transmission factor ranging from 50 to 60%, so that the brightness of the reproduced picture can be more than 3 to 4 times that obtainable with the shadow-mask tube.

The deflection voltage V) in this embodiment is approximately several hundred volts as is the deflection voltage in the embodiment shown in FIG. 7, and consequently difficult problems are not presented in practical use.

The manner in which color selection is effected in the embodiment of FIG. 8 in dependence on the incident angle of the electron beam will be readily understood from FIG. 9, particularly when compared with FIG. 5 the advantageous features of the embodiment of FIGS. 8 and 9 are as follows:

(1) A monochrome picture can be displayed by making the line deflection voltage Vf equal to zero. Therefore, this example is particularly adapted for use in a one-gun three-beam tube, since monochrome picture reception can be effected merely by stopping the color switching operation.

(2) In the manufacture of the phosphor screen the the red, green and blue color phosphor stripes can be sequentially applied on the inner surface of the panel of the phosphor screen by the steps of printing a shadow image of the grid on the inner surface of the panel to provide guard bands and exposing the areas between the guard bands to light directed through the pattern of a printing mask from the front. This facilitates the manufacture of the phosphor screen while at the same time enhancing the contrast ratio of the reproduced picture to increase color purity.

When at least three electron beams are to be focused on each phosphor stripe, color switching by means of the grid (in a one-gun picture tube) becomes complicated as it requires four terminals and in such case a first grid wire and five second grid Wires are sequentially arranged in a repeating cyclic order of 1a, 1b, 1c, 1d, 10, and 1b, as depicted on FIG. 10.

FIG. schematically illustrates the color switching operation in the case of a grid device having three-set grid wires, that is, two sets of three grid wires disposed opposite each color cyclic unit, and in which electron beams emitted from one gun are selectively switched in accordance with colors desired to be displayed. In this case the grid wires are sequentially arranged in the aforementioned repeating cyclic order. These grid wires are connected respectively to terminals t t t and t through

lead wires

3a, 3b, 3c and 3d similarly to the manner described above with respect to FIGS. 6A, 6B and 6C. By applying suitable voltages to the terminals, color switching can be effected for the same reasons as given above in describing the embodiment of FIGS. 6A, 6B and 6C. In a similar manner, color switching is possible with a grid device having sets of four-, fiveor more grid wires, that is, a grid device in which at least four, five or more electron beams are focused on each phosphor stripe of the screen. However, manufacturing and, practical difficulties increase with increases in the number of the grid wires, and hence no description will be given thereof in this specification.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it will be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

What is claimed is:

1. A color picture tube comprising at least one electron gun device; a phosphor screen having a predetermined anode potential and being composed of units of tricolor phosphor stripes sequentially arranged in a predetermined repeating cyclic order; a grid device located between said gun device and said phosphor screen and being disposed substantially parallel to the latter, said grid device including electrically interconnected first grid wires extending parallel to said phosphor stripes and being spaced apart a distance equal to the combined width of said stripes in each said cyclic order unit thereof, and second .grid wires positioned between adjacent first grid wires to define with the latter a group of at least two slits therebetween which correspond with a cyclic order unit of said phosphor stripes; and means for applying to said first grid wires and to at least certain of said second grid wires respective potentials that are always different and serve to direct onto phosphor stripes of the same color in said cyclic order units all of the electron beams from said gun device passing through the corresponding groups of said slits, said diiferent potentials applied to said first and second grid wires being related to each other to provide said grid device with a mean potential that is, at all times, substantially equal to said anode potential of the phosphor screen.

2. A color picture tube according to claim 1, in which said different potentials applied to the first and second grid wires are constant so that selection of the phosphor stripes of the cyclic order units against which the electron beams are directed is determined by the angle of incidence of each of said electron beams with respect to said grid device.

3. A color picture tube according to claim 2, in which one of said second grid wires is positioned between adjacent first grid wires and each said cyclic order unit of the phosphor stripes includes one stripe each of three different colors, and in which said different potentials applied to the first and second grid wires are respectively greater and less than said anode potential of the phosphor screen by substantially equal amounts.

4. A color picture tube according to claim 2, in which two of said second grid wires are positioned between adjacent first grid wires to provide three slits in each said group thereof and each said cyclic order unit of the phosphor stripes includes one stripe each of three different colors, and in which all of said second grid wires are electrically interconnected and said different potentials applied to the first and second grid wires are respectively greater and less than said anode potential of the phosphor screen by predetermined amounts, said amount by which the potential applied to said first grid wires is greater than said anode potential being twice as large as said amount by which the potential applied to said second grid wires is less than said anode potential.

5. A color picture tube according to claim 1, in which the number of said second grid wires disposed between adjacent first grid wires is 211-1-1, in which n is an integer of at least 1, and in which said different potentials applied to said first grid wires and to at least certain grid wires selected from said second grid wires are varied selectively to effect switching of the phosphor stripes of said cyclic order units against which the electron beams are directed in accordance with the variations of said different potentials.

6. A color picture tube according to claim 5, in which three of said second grid wires are disposed between adjacent first grid wires to provide four of said slits in each of said groups thereof, the selectively varied potential for said certain grid wires is applied only to the second grid wire disposed midway between adjacent first grid wires, and the remainder of said second grid wires have a substantially constant potential applied thereto.

7. A color picture tube according to claim 6, in which each said cyclic order unit of the phosphor stripes has one stripe each of first and second colors and two stripes of a third color, with the latter being separated by one of said stripes of the first and second colors, and in which said potentials applied to said first grid wires, said certain second grid wires and said remainder of the second grid wires are related to each other to selectively direct all of the electron beams passing through each said group of slits against a selected one of said stripes of the first and second colors and against said two stripes of said third color in the corresponding cyclic order unit.

8. A color picture tube according to claim 5, in which five of said second grid wires are disposed between adjacent first grid wires to provide six of said slits in each of said groups thereof, the second grid wires closest to said first grid wires are electrically interconnected, the second grid wires located midway between adjacent first grid wires are electrically interconnected and the remainder of said second grid wires are electrically interconnected, and in which different potentials are selectively applied to the variously electrically interconnected second grid wires.

9. A color picture tube according to claim 8, in which each said cyclic order unit of the phosphor stripes has one stripe each of first and second colors and two stripes of a third color separated by one of said stripes of the first and second colors, and in which said potentials applied to said first grid wires and said second grid wires are related to each other to selectively direct all of the electron beams passing through each of said groups of slits against a selected one of said stripes of the first and second colors and against said two stripes of said third color in the corresponding cyclic order unit.

10. A color picture tube according to claim 1 wherein said first grid wires and said second grid wires adjacent thereto are located at substantially the same distance from said phosphor screen.

1 0 References Cited UNITED STATES PATENTS RICHARD A. FARLEY, Primary Examimer. 10 C. L. WHITHAM, Assistant Examiner.

US. Cl. X.R.