Light source display tube

Abstract: A light source display tube as a unit element arranged in matrix form in one plane to constitute a large screen display device, where stray path for electrons emitted from the cathode is eliminated, and concentration of the electric field of the control grid to disturb the electron flowing is prevented, thereby the pseudo light emission is prevented and the electric trouble is minimized in simple constitution.

Description: The invention relates to a light source display tube comprising a vacuum envelope having a light transmissive front panel on a front opening of a rectangular side plate and a back plate on a rear opening thereof being hermetically sealed, a fluorescent display member formed by arranging fluorescent screens in matrix form onto an inner surface of said front panel, an anode electrode group comprising a plurality of accelerating anodes arranged on a periphery of each of said fluorescent screens, a cathode electrode group comprising cathodes for electron emission arranged independently corresponding to each of said fluorescent screens, a grid electrode group comprising a plurality of control grids arranged between said cathode electrode group and said fluorescent display member in a direction of rows (or columns) corresponding to each fluorescent screen of said fluorescent display member and having an electron passing hole for passing electrons from each of the cathodes as a divergent beam, and a back electrode group comprising a plurality of back electrodes arranged at the rear surface side of said cathode electrode group in a direction of columns (or rows) corresponding to each fluorescent screen of said fluorescent display member, wherein the control grids of said grid electrode group and the back electrodes of said back electrode group together constitute a matrix. Such a display tube is known from EP-A-217 003. When a monochromatic display tube utilizing light emission of fluorescent material is made, one picture element and such monochromatic display tubes are arranged in matrix form to constitute a large screen display device, disadvantage occurs in that a space is produced on connecting portion of each monochromatic display tube thereby improvement of resolving power is difficult, and the high resolving power may be accompanied by high cost. Consequently, in the prior art of EP-A-217 003, a light source display tube improving the above-mentioned disadvantage is disclosed in a light source display tube. Such a light source display tube is shown in a front view of FIG. 1, a lateral sectional view of FIG. 2 and an exploded perspective view of FIG. 3. The figures show the case that a fluorescent screen having respective fluorescent materials of R (red), G (green) and B (blue) each made one picture element is arranged in matrix form of 3 x 3 picture elements in number. In these figures, numeral 1 designates a vacuum envelope as a glass tube which is hermetically sealed by a front panel 2, a back plate 3 and a cylindrical side plate 4. On inner surface of the front panel 2 is formed a fluorescent display member 5 which is arranged and coated in matrix form using three-color fluorescent materials R, G, B each made a unit picture element and comprises fluorescent screens 5R, 5G and 5B of the 3 x 3 picture elements. Wherein suffix of the fluorescent screens 5R, 5G and 5B correspond to red (R), green (G) and blue (B) respectively. Numeral 6 designates an anode electrode group comprising a plurality of accelerating anodes 61, 62, ... arranged corresponding to periphery of the fluorescent screens 5R, 5G and 5B of the fluorescent display member 5 respectively, and high voltage is applied to these accelerating anodes 61, 62, ... through an external terminal 16. Numeral 7 designates a cathode electrode group comprising cathodes 711 - 733 for electron emission (713, 723, 731, 732 and 733 being not shown) respectively arranged independently corresponding to each of the fluorescent screens 5R, 5G, 5B of the fluorescent display member 5, and these cathodes 711 - 733 are supported between a pair of supports 17a, 17b. Wherein first and second suffix of the cathodes 711 - 733 correspond to the first - third row and the first - third column respectively. In each of the cathodes 711 - 733, for example, an indirectly-heated cathode where oxide is coated on a nickel sleeve or a direct heated cathode where oxide is coated on tungsten may be used. Numeral 8 designates a grid electrode group comprising control grids 81 - 83 for row selecting arranged between the cathode electrode group 7 and the fluorescent display member 5, and these control grids 81 - 83 are provided with holes 91 - 93 for electron passing so that an electron beam 11 from the cathodes 711 - 733 respectively passes as divergent beam in the direction corresponding to each of the fluorescent screens 5R, 5G and 5B of the fluorescent display member 5. Numeral 10 designates a back electrode group comprising stripe-form back electrodes 101 - 103 for column selection, respectively arranged to face to each of the fluorescent screens 5R, 5G and 5B of the fluorescent display member 5, along the column direction, behind the cathode electrode group 7, on the back plate 3 of the vacuum envelope 1, and these back electrodes 101 - 103 are a conductive layer of silver or the like formed on the back plate. Each of the back electrodes 101 - 103 is given negative potential and 0 V or positive potential of several V with respect to the potential of each of the cathodes 711 - 733 so as to control the electron beam 11 emitted from the cathodes 711 - 733. Numeral 12 designates a lead wire as an external terminal to draw each electrode of the cathode electrode group 7, the grid electrode group 8 and the back electrode group 10 from the back plate 3 to the outside. Next, operation will be described. When each of the back electrodes 101 - 103 is at negative potential with respect to the potential of the cathodes 711 - 733, since the circumference of these cathodes 711 - 733 is surrounded by the negative potential, electrons from each of the cathodes 711 - 733 can not flow through the control grids 81 - 83 to the accelerating anodes 61, 62, ... thereby the cutoff state occurs. In this state, if 0 V or positive potential of several V with respect to the potential of the cathodes 711 - 733 is applied to the back electrodes 101 - 103, the electron beam 11 emitted from these cathodes 711 - 733 flows towards the control grids 81 - 83. If the potential of each of the control grids 81 - 83 is negative potential with respect to the cathodes 711 - 733 then, the electron beam 11 cannot pass through the electron passing holes 91 - 93 of these control grids 81 - 83, thereby the electron beam 11 can not flow to the accelerating anodes 61, 62, ..., and each of the fluorescent screens 5R, 5G and 5B of the fluorescent display member 5 does not emit light. If the potential of the control grids 81 - 83 is positive potential with respect to the cathodes 711 - 733, the electron beam 11 passes through the electron passing holes 91 - 93 of the control grids 81 - 83 respectively, thereby each of the fluorescent screens 5R, 5G and 5B emits light. Consequently, each of the grid electrodes 81 - 83 of the grid electrode group 8 arranged in matrix form corresponding to each of the fluorescent screens 5R, 5G and 5B and each of the back electrodes 101 - 103 of the back electrode group 10 are selectively controlled to drive (dynamic drive), thereby only the fluorescent screens 5R, 5G and 5B with both electrodes crossing can emit light selectively. As above described, the fluorescent screens 5R, 5G and 5B composed of the fluorescent materials of the three colors are arranged in matrix form of the 3 x 3 picture elements on the inner surface of the front panel 2 of the vacuum envelope 1, and the cathode electrode group 7, the grid electrode group 8 and the back electrode group 10 are installed corresponding to each of the fluorescent screens 5R, 5G and 5B, thereby the light source display tube of high brightness emission can be obtained. Consequently, when a large screen color display device is assembled using the light source display tube as a unit, a space between each picture element is shortened in comparison to that using a monochromatic tube having only one picture element, thereby the resolving power can be improved and the number of parts and the manufacturing process number can be decreased. Not only the structure can be simplified and the cost can be made low, but also the weight of the display device can be reduced. In the shown example, although the fluorescent screens composed of the fluorescent materials of the three colors, R, G and B are arranged in matrix form of the 3 x 3 picture elements on the inner surface of the front panel 2, the example is not limited to this but a fluorescent screen with one fluorescent material made one picture element may be arranged in matrix form of arbitrary m x n picture elements (where m, n: arbitrary positive integer) within the vacuum envelope, and corresponding to this, the arrangement and constitution of the grid electrode group and the back electrode group can be varied. Also as shown in FIG. 4, a light source display tube is proposed in that each control grid of the grid electrode group 8 is made channel form with U-shaped cross-section, and a shield plate 18 made of metal projecting laterally is attached to each such control grid, thereby stray electrons from gap between each control grid and the back plate is absorbed by the shield plate 18 and the pseudo emission of the fluorescent screen due to the stray electrons is prevented effectively (for example, Japanese utility model application No. 62-114562). Further, as disclosed in Japanese patent application laid-open No. 62-241256 for example, an electron passing portion formed on each of the control grids 81 - 83 as above described is provided with a dome-shaped mesh portion, thereby electrons emitted from the cathodes 711 - 733 are spread uniformly and can be irradiated uniformly onto the fluorescent screen 5, and the divergent angle of the electron beam 11 can be arbitrarily adjusted corresponding to curvature of the dome-shaped mesh portion. Moreover, a light source display tube is proposed where the larger the curvature of the dome-shaped mesh, the larger the divergent angle of the beam, thereby length of the display tube can be decreased. As shown in FIGS. 4 and 6, when the channel-shaped control grids 81, 82, ... with U-shaped cross-section are arranged on the back plate 3, in order to draw the lead wires 12 for the cathodes 711, 712, ..., the back electrode 101 or the like, notched recesses 13 must be formed on both lateral edge portions of the control grid abutting on the back plate 3. On the other hand, electrons emitted from the cathodes 711, 712, ... are attracted by a voltage applied to the control grids 81, 82, ... and apt to move to both lateral sides of the control grid. Consequently, stray electrons occurs from the notched recess 13 thereby the pseudo emission may be produced. Also if a control grid manufactured by means of etching and press forming is used as the channel-shaped control grid with U-shaped cross-section, when the electric field of 10 8 V/m or more is applied to the control grid, the electron emission is produced due to the field emission phenomenon and the pseudo emission may be produced at the fluorescent display member due to the emitted electrons. In this case, if the control grid is manufactured by drawing and the surface is rounded, the field emission can be prevented, but the working of the dome-shaped mesh portion becomes difficult. Also as shown in FIG. 5, if a getter 16 is attached to a skirt portion of the accelerating anode 61, a getter film 17 is formed in wide area of the inner surface of the side plate due to flash of the getter 16 thereby the electric trouble such as shortcircuit or discharge may be produced between the getter film 17 and the control grid 81. Since the cathodes 711 - 733, the control grids 81 - 83, the back electrodes 101 - 103 and lead wires for these electrodes are installed on the back plate 3 of the vacuum envelope 1, it is difficult to widen the space between each electrode and the space between each lead wire, thereby the electric trouble may be produced also on account of this state. In order that the lead wires 12 for the cathodes 711 - 733, the control grids 81 - 83, the back electrodes 101 - 103 and the like are easily taken to the outside, i.e., to rear side of the back plate 3, as shown in FIG. 7, the vacuum envelope 1 is manufactured in trumpet shape so that the installation area of the back electrodes 101 - 103 becomes narrower than that of the fluorescent screen. In this case, the back electrode 101 and the control grid 81 being next or near the side plate of the vacuum envelope 1, must be installed not just behind the fluorescent screen 5R corresponding to these but on position facing partially to the next fluorescent screen 5B, i.e., position shifted towards the center of the vacuum envelope 1. Consequently, electrons emitted from the cathode 712 are guided towards the fluorescent screen 5R and also may be leaked to the next fluorescent screen 5B thereby the pseudo emission may be produced in the fluorescent screen 5B. Also when electrons emitted from the cathodes 711 - 733 respectively are accelerated by the accelerating anodes 61, 62, ..., a part thereof charges a top end edge portion of the skirt of the accelerating anode extending towards the back plate, and discharge is produced at the edge portion. Consequently, divergent beam may not be irradiated uniformly and efficiently from the cathodes 711 - 733 onto the fluorescent screens 5R, 5G, 5B respectively. From GB-A-21 70 351 luminescent display cells are known which are similar to those as disclosed in EP-A-217 003. But these display cells do not have a back electrode but only a conductive retainer assembly for retaining the electrode structure and interconnecting the second control grids. First control grids and second control grids form a matrix. Moreover, US-A-3,532,921 and US-A-4,308,484 show display devices. In the first publication, a mesh grid is disclosed, the main portion of which is curved to be in concentric relation with the cathode in order to obtain a uniform brightness. In the second publication, a flat shadow mask plate is used for passing a beam. These two publications are less related to the present invention as the first two mentioned publications. It is an object of the present invention to provide a light source display tube having simple electric connections and in which pseudo-emission due to stray electrons can be securely prevented. Also, the function of a control grid should not deteriorate and the field emission phenomenon should be prevented. The thermoelectrons emitted from the cathode should be irradiated onto the fluorescent screen uniformly and efficiently. In accordance with the invention, a light source display tube as defined in the preamble of claim 1 is characterized in that a substrate for mounting said cathode electrode group, said grid electrode group and the back electrode group thereon is suspended at a distance from the back plate of said vacuum envelope, that said control grids are of channel-shaped form with a substantially U-shaped cross-section and a U-shaped opening end surface abutting the upper surface of the substrate, and that some sides of the control grid oppose a circumferential surface of the substrate, are in close contact with this circumferential surface and extend to the rear surface of the substrate, and that a lead wire for each of the electrode groups is introduced from a rear surface side of said substrate through a through-hole or a notched portion of the substrate. An advantage of such a light source display tube lies in the fact that stray electron currents are suppressed and the pseudo-emission can be securely prevented. Preferable embodiments are defined in the dependent claims. If a getter is installed on the rear surface of the substrate in floating from the back plate and opposed to the back plate, even if a getter film is formed in wide area on the back plate due to flash of the getter, the distance between the getter film and each electrode group installed on the substrate is not shortened and there is no fear of producing the electric trouble due to the getter film. If a lead wire installed on joint portion between the back plate and a cylindrical side plate and constituting an electric path for any of the electrodes rises vertically along an inner surface of the cylindrical side plate, and the substrate is supported by upper end portion of the lead wire in floating from the back plate, the substrate can be supported firmly without using a special support member. If the control grid is provided with an electrode plate manufactured by means of etching and press forming, and a shield body manufactured by drawing, having a hole fitted to a dome-shaped mesh portion of the electrode plate, is constituted integral therewith, function of the control grid is not deteriorated and the field emission phenomenon can be securely prevented. Further, if the control grid at least on a peripheral portion of the vacuum envelope is slanted so that an electron passing portion is deflected towards the fluorescent screen on the peripheral portion of the vacuum envelope, electrons passing through the electron passing portion collide only on the fluorescent screen of the corresponding peripheral portion, thereby leakage to other neighboring fluorescent screen can be securely prevented. If a flat shadow mask plate provided with a plurality of window holes for passing divergent electron beam, is installed as an accelerating plate in front of the fluorescent display member, the divergent electron beam can be irradiated onto the fluorescent screen of the fluorescent display member uniformly and efficiently. FIG. 1 is a plan view of a light source display tube in the prior art; FIG. 2 is a transverse sectional view taken along A-A line of FIG. 1; FIG. 3 is an exploded perspective view of a part of FIG. 1; FIG. 4 is a transverse sectional view of a light source display tube of another example in the prior art; FIG. 5 is a view illustrating a transverse section from direction different by 90 degrees from FIG. 4; FIG. 6 is an exploded perspective view of a part of FIG. 4; FIG. 7 is a transverse sectional view of a light source display tube of still another example in the prior art; FIG. 8 is a transverse sectional view of a part of a light source display tube as an embodiment of the invention; FIG. 9 is a perspective view illustrating lead wire taking state of FIG. 8; FIG. 10 is a transverse sectional view of a part of a light source display tube as another embodiment of the invention; FIG. 11 is a perspective view of a part of FIG. 10; FIG. 12 is a transverse sectional view of a part of a light source display tube as still another embodiment of the invention; FIG. 13 is a transverse plan view taken along B-B line of FIG. 12; FIG. 14 is an exploded perspective view illustrating a control grid; FIG. 15 is a transverse sectional view of assembling state of FIG. 14; FIG. 16 is a transverse sectional view of assembling state illustrating another control grid; FIG. 17 is a transverse sectional view of a light source display tube; and FIG. 18 is a transverse sectional view of another light source display tube. Preferred embodiments of the invention will now be described in detail referring to the accompanying drawings. In FIG. 8, FIG. 9 where the same parts as those in FIG. 4, FIG. 5 are designated by the same reference numerals, numeral 14 designates a ceramic substrate arranged in floating from a back plate 3, and a cathode electrode group 7, a grid electrode group 8 and a back electrode group 10 are mounted on a surface of the ceramic substrate 14. As a support of the ceramic substrate 14, for example, a lead wire 12 for each electrode group is utilized. Sides 8a, 8b of control grids 81 - 83 to constitute the grid electrode group 8 opposed to a circumferential surface of the ceramic substrate 14 are in close contact with the circumferential surfaces and extended to the rear surface of the ceramic substrate. The lead wire of each electrode group penetrates the ceramic substrate or is introduced through a notched portion (not shown) of the circumferential surface of the substrate to the rear surface of the ceramic substrate, and then introduced through a joint portion between the back plate 3 and the side plate 4 joined by a low melting-point glass 15 to the outside. Depth of notching is defined so that the lead wire 12 is flush with the circumferential surface of the substrate. In FIG. 10, FIG. 11 illustrating another embodiment of the invention, numeral 19 designates a getter mounted on a rear surface of a substrate 14 in floating from a back plate 3 through a mounting plate 20. According to the above-mentioned constitution when the getter 19 is flashed, a getter film 21 is formed on the back plate but the distance between the getter film 21 and each electrode group installed on the surface of the substrate is not shortened and the electric trouble is not produced. The getter 19 may be mounted directly on the rear surface of the substrate, or otherwise as shown in FIG. 11, a shield portion 22 of U-shaped form is mounted on the rear surface of the substrate and the getter 19 is installed within the shield portion 22, thereby spread of the getter film 21 can be suppressed and the electric trouble due to the getter film 21 can be prevented more securely. In FIG. 12, FIG. 13 illustrating a light source display tube as still another embodiment of the invention, a lead wire 12 (Only one side is shown in the example.) installed at least to position near the four corners of the vacuum envelope 1 is grasped by a joint portion between the back plate 3 and the cylindrical side plate 4 of the vacuum envelope 1, and rises vertically along the inner surface of the cylindrical side plate in the vacuum envelope 1. Numeral 14 designates a ceramic substrate supported in floating from the back plate 3 by each lead wire 12, and the lead wire 12 is utilized as a part of lead wires for the back electrodes 101 - 103, the cathodes 711 - 742, the control grids 81 - 83 installed on the surface of the substrate 14. When the channel-shaped control grids 81 - 83 with U-shaped cross-section are mounted on the substrate 14 as shown in the figure, sides 8a, 8b of the control grid opposed to the circumferential surface of the substrate are extended to the rear side of the substrate 14 so as to surround the substrate 14, and the lead wire 12 is fixed to the extended portion 8b and supports the substrate 14. Also the lead wire 12 may be directly fixed to the substrate 14 and support it. In FIG. 14, FIG. 15 show the constitution of the control grid useful for understanding the invention. An electrode plate 23 with dome-shaped mesh portions 24 at substantially regular intervals is manufactured by means of etching and press forming, and numeral 25 designates a shield body manufactured by drawing and having holes 26 bored at substantially regular intervals to be fitted to the dome-shaped mesh portions of the electrode plate 23. The electrode plate 23 and the shield body 25 are combined by fitting the dome-shaped mesh portion 24 to the hole 26, and integrated, for example, by spot welding or the like at part of the overlaid portion, thereby the control grid is formed. Consequently, the electron beam emitted from the cathodes 711 - 733 is diffused by the dome-shaped mesh portion 24 and irradiated to the fluorescent screens 5R, 5G, 5B, thereby function of the control grid is not deteriorated. Since the shield body 25 is worked by drawing, the bent portions 25a on both sides are made arc shape, and even if voltage of 10 KV or more is applied at the anode, the electric field at the neighborhood of the shield body 25 does not become 10 8 V/m or more and the field emission phenomenon is not produced. FIG. 16 shows another example useful for understanding the invention. The electrode plate 23 has both side portions bent in nearly right angle and constituted into U-shaped cross-section. The electron emission from the cathodes 711 - 733 can be stabilized using the small back electrodes 101 - 103 having nearly the same width as that of the U-shaped opening of the electrode plate 23, and the same voltage from the same power source is applied to both the electrode plate 23 and the shield body 25 and equal potential exists between both members, thereby stray electrons from the electrode plate 23 to the outside can be suppressed and the electron beam passing through the dome-shaped mesh portion 24 can be stabilized. FIG. 17 shows a further example useful for understanding the invention. Channel-shaped control grids 81 - 84 are installed so as to surround cathodes 711-742, respectively. Among these, the control grids 81, 84 on peripheral portions have an inclination of the upper surface so that electrons passing through the control grids 81, 84 are deflected towards the fluorescent screens 5R also on the peripheral portions. That is, a mesh or an opening provided as an electron passing portion on the control grids 81, 84 has the inclination to be opposed to the fluorescent screen at the peripheral portion. If the cathode electrode at the outer circumferential side generates electrons for the fluorescent display, the electrons are within the control grids 81, 84 and do not leak to the outside, and the potential gradient corresponding to the inclination is produced on the periphery of the control grids 81, 84. Consequently, from the electron passing portion 9 opening by this inclination, the electrons are emitted in the perpendicular direction with respect to the inclination and irradiated to the fluorescent screen 5R of the corresponding periphery. Consequently, the electrons are not incident to the neighboring fluorescent screens 5G, 5B as in the prior art, thereby emission in each fluorescent screen can be controlled at high accuracy. Other control grids 82, 83 have similar function and operation to the control grid in the prior art. Although the example has been described in the case that only the control grids 81, 84 at the outermost peripheral portion are given the inclination, other control grids 82, 83 at the inside from the control grids 81, 84 may be given inclination varying gradually and similar effects can be obtained. FIG. 18 shows still another example usefull for understanding the invention. Numeral 27 designates an accelerating anode, and the accelerating anode 27 comprises one conductive plate on which a plurality of window holes 28 to transmit divergent beam from each of the cathodes 711 - 713 are provided. The accelerating anode 27, as a shadow mask plate corresponding to each of the cathodes 711 - 713, is installed between each of the fluorescent screens 5R, 5G, 5B and the control grids 81 - 83, and connected electrically to each of the fluorescent screens 5R, 5G, 5B and an aluminium film (not shown) for preventing the electron reflection provided on the inner surface of the front panel 2. If electrons are emitted from any of the cathodes 711 - 713, through any of the control grids 81 - 83 corresponding to that, divergent beam of the electrons passes through the corresponding window hole 28, and is subjected to the electric field of high voltage and accelerated during passing through the window hole 28, and irradiated onto the prescribed fluorescent screen 5R, 5G, or 5B. In this case, since the accelerating anode 27 as a whole is of flat plate form, the potential gradient to the divergent beam becomes wholly uniform, thereby the divergent beam is not concentrated to a part of the accelerating anode 27. Consequently, the divergent beam is irradiated efficiently to each of the fluorescent screens 5R, 5G, 5B respectively. As a result, a picture to be obtained on the color display device can be displayed clearly and brightly. In addition, the window hole 28 can be utilized in arbitrarily selecting round shape, rectangular shape or the like. According to the invention as above described, a channel-shaped control grid with U-shaped cross-section abuts on an upper surface of a substrate and sides of the control grid opposed to a circumferential surface of the ceramic substrate are closely contacted with the circumferential surface and extended to a rear surface of the substrate, and a lead wire for each of the electrode groups mounted on the ceramic substrate penetrates the ceramic substrate or is taken through a notched portion of the circumferential surface of the substrate, thereby stray electrons from portion other than an electron passing portion of the control grid is suppressed and the pseudo emission can be securely prevented. Also, the substrate is installed in floating from the back plate of the vacuum envelope, and various sorts of electrode groups such as a back electrode group, a cathode electrode group, a grid electrode group or the like, are installed on the surface of the substrate, and a getter is installed on the rear surface of the substrate, thereby a getter film due to flash of the getter is formed on the back plate and the electric trouble due to the getter film can be securely prevented. Consequently, flushing of the getter can be performed sufficiently, and the degree of vacuum degree within the vacuum envelope can be highly increased by the getter and the reliability can be improved. Further, a lead wire grasped by joint portion between the back plate and a cylindrical side plate of the vacuum envelope rises vertically along an inner surface of the cylindrical side plate, and the substrate is supported and fixed by upper end portion of the lead wire in floating from the back plate, thereby a special support member for supporting the substrate is not required. Also since the back electrode, the cathode, the control grid and lead wires for these electrodes can be installed utilizing both surfaces of the substrate, the space between each electrode and the space between each lead wire can be widened and the electric trouble can be minimized. Since a control grid is constituted by assembling an electrode plate with dome-shaped mesh portions formed at substantially regular intervals by means of etching and press forming and a shield plate manufactured by drawing and having holes bored to be fitted to the dome-shaped mesh portions, the field emission phenomenon can be securely prevented. Also, since the control grid being at least on a peripheral portion of the vacuum envelope is slanted so that passing electrons are deflected towards the fluorescent screen on the peripheral portion, electrons emitted from the cathode through the control grid to the peripheral portion can be accurately deflected and projected towards the intended fluorescent screen on the peripheral portion. Consequently, the stray electrons to other fluorescent screens can be prevented and high quality displaying becomes possible in the large screen display as a whole. Further, since an accelerating anode of plate form having a plurality of window holes for accelerating and transmitting divergent beam from the cathode is installed, the divergent beam can be prevented from being concentrated to a part of the accelerating anode. Consequently, the irradiation efficiency of the divergent beam to the fluorescent screen can be improved significantly.

Claims: A light source display tube comprising a vacuum envelope (1) having a light transmissive front panel (2) on a front opening of a rectangular side plate (4) and a back plate (3) on a rear opening thereof being hermetically sealed; a fluorescent display member (5) formed by arranging fluorescent screens in matrix form onto an inner surface of said front panel (2); an anode electrode group (6) comprising a plurality of accelerating anodes (61, 62 ...) arranged on a periphery of each of said fluroescent screens; a cathode electrode group (7) comprising cathodes (712-742) for electron emission arranged independently corresponding to each of said fluorescent screens; a grid electrode group (8) comprising a plurality of control grids (81-84) arranged between said cathode electrode group (7) and said fluorescent display member (5) in a direction of rows (or columns) corresponding to each fluorescent screen of said fluorescent display member (5) and having an electron passing hole (91-93) for passing electrons from each of the cathodes (711-733) as a divergent beam; and a back electrode group (10) comprising a plurality of back electrodes (101-103) arranged at the rear surface side of said cathode electrode group (7) in a direction of columns (or rows) corresponding to each fluorescent screen of said fluorescent display member (5), wherein the control grids (81-84) of said grid electrode group (8) and the back electrodes (101-103) of said back electrode group (10) together constitute a matrix, characterized in that a substrate (14) for mounting said cathode electrode group (7), said grid electrode group (8) and the back electrode group (10) thereon is suspended at a distance from the back plate (3) of said vacuum envelope (1), that said control grids (81-84) are of channel-shaped form with a substantially U-shaped cross-section and a U-shaped opening end surface abutting the upper surface of the substrate (14), and that some sides of the control grid oppose a circumferential surface of the substrate (14), are in close contact with this circumferential surface and extend to the rear surface of the substrate (14), and that a lead wire (12) for each of the electrode groups (6-10) is introduced from a rear surface side of said substrate (14) through a through-hole or a notched portion of the substrate (14). A light source display tube as set forth in claim 1, wherein said cathodes (712-742) are indirectly-heated cathodes where oxide is coated on a nickel sleeve, or directly heated cathodes where oxide is coated on tungsten. A light source display tube as set forth in claim 1, wherein said back electrodes (101-103) are conductive layers formed on the substrate (14). A light source display tube as set forth in claim 1, wherein a getter (19) is installed on a rear surface of the substrate (14) so that a getter film (21) is formed on the back plate (3). A light source display tube as set forth in claim 4, wherein said getter (19) is installed through a mounting plate (20) to the rear surface of the substrate (14). A light source display tube as set forth in claim 1, wherein lead wires (12) are installed on a joint portion between the back plate (3) and the side plate (4) of the vacuum envelope (1), and wherein the lead wires (12) within the vacuum envelope (1) rise in parallel to the side plate (4), and the substrate (14) is supported on the upper end portion of the lead wires (12) at a distance from the back plate (3). A light source display tube as set forth in claim 6, wherein the channel-shaped grids (81-84) are mounted on the substrate (14), and wherein sides of the control grids (81-84) opposite to the circumferential surface of the substrate extend to the rear side of the substrate (14), and wherein the extended portions are supported by the upper end portions of the lead wires (12). A light source display tube as set forth in claim 1, characterized in that said control grids (81-84) are each composed of an electrode plate (23) with dome-shaped mesh portions (24) as the electron passing portion formed in substantially regular intervals by means of etching and press forming, and a shield body (25) with U-shaped cross-section having holes (26) to be fitted to the dome-shaped mesh portions (24) and manufactured by drawing to cover said electrode plate (23). A light source display tube as set forth in claim 1, characterized in that the electron passing holes of the control grids (81, 84) in the peripheral area of the vacuum envelope (1) are slanted as a whole relative to the fluorescent screen so that passing electrons are deflected towards the fluorescent screen of the peripheral portion. A light source display tube as set forth in claim 1, characterized in that said accelerating anodes (27) are formed by a flat shadow mask plate installed in front of the fluorescent display member (5), and have a plurality of window holes (28) for passing divergent beams (11) to excite the fluorescent screen.

Inventors: FUTATSUISHI SHUNICHI, HARA ZENICHIRO, ICHIKAWA NORIHIRO, IWATA SHUJI, KAMOGAWA HIROSHI, KOBAYASHI MASAAKI, MASUDA MITSURU, TATSUDA KAZUNORI, TERAZAKI NOBUO, FUTATSUISHI, SHUNICHI, HARA, ZENICHIRO, ICHIKAWA, NORIHIRO, IWATA, SHUJI, KAMOGAWA, HIROSHI, KOBAYASHI, MASAAKI, MASUDA, MITSURU, TATSUDA, KAZUNORI, TERAZAKI, NOBUO, IWATA, SHUJI MITSUBISHI DENDI KABUSHIKI KAISHA, KAMOGAWA, HIROSHI C/O ISE ELECTRONICS CORPORATION, KOBAYASHI, MASAAKI C/O ISE ELECTRONICS CORPORATION, MASUDA, MITSURU C/O ISE ELECTRONICS CORPORATION, TATSUDA, KAZUNORI C/O ISE ELECTRONICS CORPORATION
Applicants: ISE ELECTRONICS CORP, MITSUBISHI ELECTRIC CORP, ISE ELECTRONICS CORPORATION, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: H01J31
IPC codes: H01J31