EP0198753B1 - Electron gun for a cathode ray tube, in particular for colour television - Google Patents

Electron gun for a cathode ray tube, in particular for colour television Download PDF

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Publication number
EP0198753B1
EP0198753B1 EP19860400661 EP86400661A EP0198753B1 EP 0198753 B1 EP0198753 B1 EP 0198753B1 EP 19860400661 EP19860400661 EP 19860400661 EP 86400661 A EP86400661 A EP 86400661A EP 0198753 B1 EP0198753 B1 EP 0198753B1
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EP
European Patent Office
Prior art keywords
electrode
cathode
potential
gun
electron gun
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP19860400661
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German (de)
French (fr)
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EP0198753A1 (en
Inventor
Jacques Baudry
Olivier Trinchero
Gérard Proudhon
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Videocolor SA
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Videocolor SA
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Priority claimed from FR8504848A external-priority patent/FR2579823B1/en
Priority claimed from FR8512419A external-priority patent/FR2586326B1/en
Application filed by Videocolor SA filed Critical Videocolor SA
Priority to AT86400661T priority Critical patent/ATE49321T1/en
Publication of EP0198753A1 publication Critical patent/EP0198753A1/en
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Publication of EP0198753B1 publication Critical patent/EP0198753B1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/48—Electron guns
    • H01J29/50—Electron guns two or more guns in a single vacuum space, e.g. for plural-ray tube
    • H01J29/503—Three or more guns, the axes of which lay in a common plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/48—Electron guns
    • H01J29/488—Schematic arrangements of the electrodes for beam forming; Place and form of the elecrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2229/00—Details of cathode ray tubes or electron beam tubes
    • H01J2229/48—Electron guns
    • H01J2229/4844—Electron guns characterised by beam passing apertures or combinations
    • H01J2229/4848—Aperture shape as viewed along beam axis
    • H01J2229/4872—Aperture shape as viewed along beam axis circular

Definitions

  • the invention relates to an electron gun for cathode ray tube, in particular for color television.
  • a cathode ray tube is constituted by a vacuum glass vial having at its front part a screen slab the internal face of which is covered with cathodoluminescent materials (called phosphors) emitting a radiation of visible light when they are excited by a electron beam produced by one (or more) electron gun.
  • the screen is generally made up of triplets of phosphors, one for each fundamental color, usually red, green and blue.
  • three electron guns are provided, each intended to excite a particular color, the perforated mask placed in front of the screen allowing the electron beam intended for a color to excite only phosphors of this color.
  • An electron gun is formed, on the one hand, of a cathode with surface emitting electrons when it is heated by a filament and, on the other hand, of electrodes or grids denoted generally Gi, G 2 , Gs etc the index representing the position relative to the cathode, this index increasing with the distance from the cathode -of which the first two G 1 and G 2 perform a prefocusing of the electron beam and the following G s , G 4 , etc ... form electrostatic lenses for focusing and concentrating the electron beam.
  • the modulation of the electron beam as a function of the intensity of the point to be projected on the screen is obtained by modulating the potential of the cathode or by modulating the potential of the first grid G i (Wehnelt).
  • the electrodes of electrostatic lenses are usually brought to very high potentials, most often of the order of several kilovolts.
  • the invention relates more particularly to a tube of which at least one grid of the electrostatic lenses is, in normal operation, brought to a very high potential, of the order of 25 Kilovolts for example, and which retains a potential of the same order of greatness for a significant time after the power supply to this tube has been cut off.
  • the glass bulb has an internal conductive coating to which said grid is connected as well as an external conductive coating brought to ground potential; the glass bulb thus constitutes, with its coatings, a large capacity capacitor which retains its charge for a long period even after it has been disconnected from its power source; therefore the internal coating and the electrode connected to it retain the high potential.
  • the invention according to claim 1 makes it possible to suppress at low cost the phenomenon of cathode glow appearing when the tube supply is cut off.
  • the opening of this end wall closest to the cathode has a rim or flange, advantageously turned towards the inside of this elongated grid.
  • Another embodiment of the intermediate grid is as in claim 10. It has been found that good results are obtained when the ratio between these diameters is at most 0.92.
  • the example which will be described in relation to the figures relates to an electron gun for color television tube of the mask type, the three beams produced by the (triple) gun being said to be in line, that is to say - say coplanar.
  • Such an electron gun comprises, on the one hand, three cathodes K each having an emissive surface 10 perpendicular to the axis 11 of the tube and heated by a filament (not shown) and, on the other hand, a set of electrodes G 1 , G 2 , Gs, G 4 , Gs and Ge of which the first two, G 1 and G 2 , ef carry out the prefocusing and the following, G 3 to Gs, constitute electrostatic lenses for focusing and concentrating the electron beams.
  • a cathode K is along the axis 11 of the tube, while the axes of the other two are parallel to the axis 11, in the same plane, and in positions symmetrical with respect to this axis 11.
  • the electrodes G 1 , G 2 and G 4 of generally planar shape each have three circular openings centered on the axis of the corresponding cathode to let the electron beam coming from this cathode pass while the elongated electrodes, substantially in the shape of cylinders or parallelepiped, Gs, Gs and Ge have end walls, each of which also includes three circular openings centered on the axis of the corresponding cathode.
  • Figure 1 being a section along the axis of the tube shows only the central cathode and the corresponding openings of the electrodes.
  • the electrodes or grids G 3 and Gs are connected to a terminal 3 receiving a potential of average value, of the order of 8 Kilovolts, while the electrodes or grids G 4 and Ge are connected to a terminal 4 connected to a source of potential of high value, of the order of 25 Kilovolts.
  • the assembly formed by the electrodes or grids Gs, G 4 and Gs constitutes an electrostatic lens of the unipotential type, called Einzel, while the electrodes or grids G 5 and Ge constitute an electrostatic lens called the bipotential.
  • Each of the electrodes is metallic and is formed from a sheet of constant thickness.
  • the elongated part 12 of the electrode G s has the same thickness as the end walls 13 and 14.
  • the openings of the electrode G 4 and of the walls ends of the electrodes G 5 and Gs, as well as the openings in the end wall 15 of the grid G 3 which is furthest from the cathode K all have the same diameter.
  • the openings of the grids G 1 and G 2 as well as the openings of the wall 16 of the grid G s which faces the cathode K, have smaller diameters.
  • the grid G 3 has, like the grid G s , a generally substantially cylindrical or parallelepipedal shape with the same thickness of the cylindrical wall 17 and of the end walls 15 and 16. But at the wall 16, of the same thickness as the wall 15, is welded, according to an exemplary embodiment of the invention, a plate or insert 18 ( Figures 3 and 4) with openings 19, 20 and 21 corresponding to the openings of the wall 16, that is to say of same diameter and same relative arrangement.
  • the plate 18 is welded against the internal face of the wall 16, for example by four welding points in the vicinity of its corners.
  • This welding is carried out before the mounting of the electrodes, that is to say before the two cups 22 and 23 constituting the two parts of the electrode Ga are associated with one another.
  • the assembly constituted by the walls 16 and 18 has a thickness which is approximately three times greater than the thickness of the wall 15; in other words the insert 18 has a thickness which is approximately twice that of the walls of the original grid G 3 .
  • terminal 4 retains a potential of the order of 25 Kilovolts while the potentials of the other electrodes reach zero immediately (ground potential).
  • the limit 25 ′ of influence of the potential induced by the gate G 4 is much further from the cathode K, which considerably reduces the proportion of electrons which will reach the central part of the screen and thus there will be practically no stray glow visible in the center of this screen.
  • the thickness of the front wall of the grid G 3 is of the order of three times the thickness of its rear wall 15. A satisfactory result of eliminating cathode gleams is still obtained when this thickness of the anterior wall is about twice the thickness of the posterior wall.
  • the electrode G 3 is in two parts, the first comprising only the front wall 30 of greater thickness than the rest, 31, of the electrode Gs.
  • This second part 31 comprises the elongated part and the other end wall.
  • the parts 30 and 31 are associated for example by welding.
  • FIG. 6 represents yet another embodiment in which the front wall 16 'of the electrode G s has the same thickness as the other parts of this electrode but the openings of this front wall 16' are all bordered by a flange or rim 32.
  • the advantage of this embodiment is that it involves only a slight modification of the known electron gun.
  • the holes 19, 20 and 21 of the insert 18 have a diameter greater than the diameter of the corresponding holes of the wall 16. But in this case, it is preferable that the thickness of the insert be greater than that which it presents when the diameters are equal. In other words it is preferable that the thickness of the insert increases with the diameter of its opening.
  • the opening of the wall 15 of the grid G 3 has a diameter d 3 less than the diameter d 4 common to the opening of the grid G 4 and to the anterior opening, facing the cathode, of the grid Gs.
  • the ratio ds / d 4 is less than 1.
  • the equipotential line L 2 corresponding to the line 25 in FIG. 2a (or 25 ′ in FIG. 2 b ), intersects the z axis at a point B practically inside the grid Ga. It can be seen that there also, the influence of the high voltage of the gate G 4 is therefore reduced by the reduction in the diameter d a (if we compare with FIG. 2a). It has been found that a d s / d 4 ratio of 0.6875 makes it possible to obtain a good compromise between the quality of the cathode image in image formation and reduction of the parasitic phenomenon of cathode glow when the power supplies.
  • the hole in the wall 15 1 of the grid G 3 has, as in FIG. 1, a cylindrical collar which advances inside the cylinder G 3 .
  • This flange can be obtained during the manufacture of G 3 by extrusion. Its effect makes it possible to reduce the reduction in the ratio d 3 / d 4 necessary for the invention.
  • a ratio d a / d 4 of 0.844 was produced.
  • the invention achieves the desired result by limiting the influence of the high level equipotential lines in the beam forming area.
  • such an effect can be achieved in particular by increasing the dimensions of the holes of the grids following the very high voltage grid.
  • the invention also applies to the case where the grid G 4 is thick, for example made in the form of a cylinder. Its proximity to the filament being unchanged, the problem and the solution of the invention remain.

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  • Electrodes For Cathode-Ray Tubes (AREA)

Description

L'invention est relative à un canon à électrons pour tube à rayons cathodiques, notamment pour la télévision en couleurs.The invention relates to an electron gun for cathode ray tube, in particular for color television.

Un tube à rayons cathodiques est constitué par une ampoule de verre sous vide présentant à sa partie antérieure une dalle-écran dont la face interne est recouverte de matières cathodoluminescen- tes (appelées luminophores) émettant un rayonnement de lumière visible quand elles sont excitées par un faisceau d'électrons produit par un (ou plusieurs) canon à électrons. Pour la visualisation en couleurs l'écran est formé en général de triplets de luminophores, un pour chaque couleur fondamentale, habituellement le rouge, le vert et le bleu. Dans un tube de visualisation en couleurs du type à masque on prévoit trois canons à électrons, chacun étant destiné à exciter une couleur particulière, le masque perforé disposé devant l'écran permettant que le faisceau d'électrons prévu pour une couleur n'excite que les luminophores de cette couleur.A cathode ray tube is constituted by a vacuum glass vial having at its front part a screen slab the internal face of which is covered with cathodoluminescent materials (called phosphors) emitting a radiation of visible light when they are excited by a electron beam produced by one (or more) electron gun. For color visualization, the screen is generally made up of triplets of phosphors, one for each fundamental color, usually red, green and blue. In a mask type color display tube, three electron guns are provided, each intended to excite a particular color, the perforated mask placed in front of the screen allowing the electron beam intended for a color to excite only phosphors of this color.

Un canon à électrons est formé, d'une part, d'une cathode à surface émettant des électrons lorsqu'elle est chauffée par un filament et, d'autre part, d'électrodes ou grilles dénotées généralement Gi, G2, Gs etc - l'indice représentant la position par rapport à la cathode, cet indice croissant avec l'éloignement de la cathode -dont les deux premières G1 et G2 effectuent une préfocalisation du faisceau d'électrons et les suivantes Gs, G4, etc... forment des lentilles électrostatiques de focalisation et concentration du faisceau d'électrons. La modulation du faisceau d'électrons en fonction de l'intensité du point à projeter sur l'écran est obtenue par la modulation du potentiel de la cathode ou par modulation du potentiel de la première grille Gi (Wehnelt).An electron gun is formed, on the one hand, of a cathode with surface emitting electrons when it is heated by a filament and, on the other hand, of electrodes or grids denoted generally Gi, G 2 , Gs etc the index representing the position relative to the cathode, this index increasing with the distance from the cathode -of which the first two G 1 and G 2 perform a prefocusing of the electron beam and the following G s , G 4 , etc ... form electrostatic lenses for focusing and concentrating the electron beam. The modulation of the electron beam as a function of the intensity of the point to be projected on the screen is obtained by modulating the potential of the cathode or by modulating the potential of the first grid G i (Wehnelt).

Les électrodes des lentilles électrostatiques sont habituellement portées à des potentiels très élevés, le plus souvent de l'ordre de plusieurs Kilovolts. L'invention se rapporte plus particulièrement à un tube dont au moins une grille des lentilles électrostatiques est, en fonctionnement normal, portée à un potentiel très élevé, de l'ordre de 25 Kilovolts par exemple, et qui conserve un potentiel du même ordre de grandeur pendant un temps important après la coupure de l'alimentation de ce tube. Ce potentiel ne disparaît pas immédiatement pour la raison suivante: l'ampoule de verre présente un revêtement conducteur interne auquel est connecté ladite grille ainsi qu'un revêtement conducteur externe porté au potentiel de la masse ; l'ampoule de verre constitue ainsi, avec ses revêtements, un condensateur de grande capacité qui conserve sa charge pendant une longue période même après qu'il ait été déconnecté de sa source d'alimentation ; de ce fait le revêtement interne et l'électrode qui lui est reliée conservent le potentiel élevé.The electrodes of electrostatic lenses are usually brought to very high potentials, most often of the order of several kilovolts. The invention relates more particularly to a tube of which at least one grid of the electrostatic lenses is, in normal operation, brought to a very high potential, of the order of 25 Kilovolts for example, and which retains a potential of the same order of greatness for a significant time after the power supply to this tube has been cut off. This potential does not disappear immediately for the following reason: the glass bulb has an internal conductive coating to which said grid is connected as well as an external conductive coating brought to ground potential; the glass bulb thus constitutes, with its coatings, a large capacity capacitor which retains its charge for a long period even after it has been disconnected from its power source; therefore the internal coating and the electrode connected to it retain the high potential.

On a constaté que le potentiel élevé maintenu sur une grille pouvait provoquer - lorsque la distance séparant cette grille de la cathode est relativement faible - la projection d'électrons au centre de l'écran, se traduisant par une ou plusieurs taches lumineuses visibles tant que la température de la cathode reste élevée. Un tel défaut est quelquefois appelé "lueur de cathode".It was found that the high potential maintained on a grid could cause - when the distance separating this grid from the cathode is relatively small - the projection of electrons in the center of the screen, resulting in one or more visible light spots as long as the cathode temperature remains high. Such a defect is sometimes called "cathode glow".

Pour remédier à cet inconvénient on a proposé de disposer dans le circuit externe au tube des diodes de décharge. Mais cette solution est onéreuse.To remedy this drawback, it has been proposed to have discharge diodes in the circuit external to the tube. But this solution is expensive.

L'invention selon la revendication 1 permet de supprimer à faible prix le phénomène de lueur de cathode apparaissant à la coupure de l'alimentation du tube.The invention according to claim 1 makes it possible to suppress at low cost the phenomenon of cathode glow appearing when the tube supply is cut off.

Elle est caractérisée en ce que, pour éloigner de la cathode l'effet du potentiel élevé restant sur une grille après la coupure de l'alimentation du tube, on interpose entre cette grille et la cathode des moyens de masquage, lesdits moyens de masquage faisant partie d'une grille intermédiaire qui, après la coupure, est portée au potentiel de la masse, ladite grille intermédiaire, qui est de forme allongée avec des parois transversales d'extrémités, est telle que la paroi d'extrémité la plus proche de la cathode est plus épaisse que la paroi opposée. En variante selon la revendication 7 l'ouverture de cette paroi d'extrémité la plus proche de la cathode, présente un rebord ou collerette, avantageusement tourné vers l'intérieur de cette grille allongée.It is characterized in that, to move away from the cathode the effect of the high potential remaining on a grid after the supply of the tube is cut off, interposed between this grid and the cathode is masking means, said masking means making part of an intermediate grid which, after cutting, is brought to ground potential, said intermediate grid, which is of elongated shape with transverse end walls, is such that the end wall closest to the cathode is thicker than the opposite wall. As a variant according to claim 7, the opening of this end wall closest to the cathode has a rim or flange, advantageously turned towards the inside of this elongated grid.

Une autre réalisation de la grille intermédiaire est conferme à la revendication 10. On a constaté qu'on obtenait de bons résultats lorsque le rapport entre ces diamètres est d'au plus 0,92.Another embodiment of the intermediate grid is as in claim 10. It has been found that good results are obtained when the ratio between these diameters is at most 0.92.

D'autres caractéristiques et avantages de l'invention apparaîtront avec la description de certains de ses modes de réalisation, celle-ci étant effectuée en se référant aux dessins ci-annexés sur lesquels :

  • - la figure 1 est un schéma en coupe d'un canon à électrons pour tube de télévision en couleurs à trois faisceaux en ligne comportant le perfectionnement de l'invention,
  • - les figures 2a et 2b sont des dessins encore plus schématiques de canons à électrons du même type que ceux de la figure 1, d'une part sans, et d'autre part avec, le perfectionnement de l'invention et montrant l'effet de ce perfectionnement,
  • - la figure 3 montre une pièce du canon de la figure 1,
  • - la figure 4 est une coupe selon la ligne 4-4 de la figure 3,
  • - la figure 5 représente une grille du canon de la figure 1 pour une variante,
  • - la figure 6 représente une partie d'une grille du canon de la figure 1 pour une autre variante, et
  • - la figure 7 est une vue analogue à celle de la figure 2b mais pour une variante.
Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:
  • FIG. 1 is a sectional diagram of an electron gun for a color television tube with three beams in line comprising the improvement of the invention,
  • - Figures 2a and 2b are even more schematic drawings of electron guns of the same type as those of Figure 1, on the one hand without, and on the other hand with, the improvement of the invention and showing the effect of this improvement,
  • FIG. 3 shows a part of the barrel of FIG. 1,
  • FIG. 4 is a section along line 4-4 of FIG. 3,
  • FIG. 5 represents a grid of the barrel of FIG. 1 for a variant,
  • FIG. 6 represents part of a grid of the barrel of FIG. 1 for another variant, and
  • - Figure 7 is a view similar to that of Figure 2b but for a variant.

L'exemple qui va être décrit en relation avec les figures se rapporte à un canon à électrons pour tube de télévision en couleurs du type à masque, les trois faisceaux produits par le canon (triple) étant dits en ligne, c'est-à-dire coplanaires.The example which will be described in relation to the figures relates to an electron gun for color television tube of the mask type, the three beams produced by the (triple) gun being said to be in line, that is to say - say coplanar.

Un tel canon à électrons comporte, d'une part, trois cathodes K présentant chacune une surface émissive 10 perpendiculaire à l'axe 11 du tube et chauffée par un filament (non représenté) et, d'autre part, un ensemble d'électrodes G1, G2, Gs, G4, Gs et Ge dont les deux premières, G1 et G2, effectuent la préfocalisation et les suivantes, G3 à Gs, constituent des lentilles électrostatiques de focalisation et concentration des faisceaux d'électrons.Such an electron gun comprises, on the one hand, three cathodes K each having an emissive surface 10 perpendicular to the axis 11 of the tube and heated by a filament (not shown) and, on the other hand, a set of electrodes G 1 , G 2 , Gs, G 4 , Gs and Ge of which the first two, G 1 and G 2 , ef carry out the prefocusing and the following, G 3 to Gs, constitute electrostatic lenses for focusing and concentrating the electron beams.

Une cathode K est selon l'axe 11 du tube, tandis que les axes des deux autres sont parallèles à l'axe 11, dans le même plan, et en positions symétriques par rapport à cet axe 11.A cathode K is along the axis 11 of the tube, while the axes of the other two are parallel to the axis 11, in the same plane, and in positions symmetrical with respect to this axis 11.

Les électrodes G1, G2 et G4 de forme générale plane comportent chacune trois ouvertures circulaires centrées sur l'axe de la cathode correspondante pour laisser passer le faisceau d'électrons provenant de cette cathode tandis que les électrodes allongées, sensiblement en forme de cylindres ou parallélépipédiques, Gs, Gs et Ge présentent des parois d'extrémités dont chacune comprend également trois ouvertures circulaires centrées sur l'axe de la cathode correspondante. La figure 1 étant une coupe selon l'axe du tube ne montre que la cathode centrale et les ouvertures correspondantes des électrodes.The electrodes G 1 , G 2 and G 4 of generally planar shape each have three circular openings centered on the axis of the corresponding cathode to let the electron beam coming from this cathode pass while the elongated electrodes, substantially in the shape of cylinders or parallelepiped, Gs, Gs and Ge have end walls, each of which also includes three circular openings centered on the axis of the corresponding cathode. Figure 1 being a section along the axis of the tube shows only the central cathode and the corresponding openings of the electrodes.

Les électrodes ou grilles G3 et Gs sont connectées à une borne 3 recevant un potentiel de valeur moyenne, de l'ordre de 8 Kilovolts, tandis que les électrodes ou grilles G4 et Ge sont connectées à une borne 4 reliée à une source de potentiel de valeur élevée, de l'ordre de 25 Kilovolts. De façon en soi connue l'ensemble formé par les électrodes ou grilles Gs, G4 et Gs constitue une lentille électrostatique de type unipotentiel, dite de Einzel, tandis que les électrodes ou grilles G5 et Ge constituent une lentille électrostatique dite bipotentielle.The electrodes or grids G 3 and Gs are connected to a terminal 3 receiving a potential of average value, of the order of 8 Kilovolts, while the electrodes or grids G 4 and Ge are connected to a terminal 4 connected to a source of potential of high value, of the order of 25 Kilovolts. In a manner known per se, the assembly formed by the electrodes or grids Gs, G 4 and Gs constitutes an electrostatic lens of the unipotential type, called Einzel, while the electrodes or grids G 5 and Ge constitute an electrostatic lens called the bipotential.

Chacune des électrodes est métallique et est formée à partir d'une feuille d'épaisseur constante. Ainsi la partie allongée 12 de l'électrode Gs a la même épaisseur que les parois d'extrémités 13 et 14. Dans l'exemple, pour faciliter la fabrication du canon à électrons, les ouvertures de l'électrode G4 et des parois d'extrémités des électrodes G5 et Gs, ainsi que les ouvertures de la paroi d'extrémité 15 de la grille G3 qui est la plus éloignée de la cathode K ont toutes le même diamètre. Par contre les ouvertures des grilles G1 et G2, ainsi que les ouvertures de la paroi 16 de la grille Gs qui est tournée vers la cathode K, ont des diamètres inférieurs.Each of the electrodes is metallic and is formed from a sheet of constant thickness. Thus the elongated part 12 of the electrode G s has the same thickness as the end walls 13 and 14. In the example, to facilitate the manufacture of the electron gun, the openings of the electrode G 4 and of the walls ends of the electrodes G 5 and Gs, as well as the openings in the end wall 15 of the grid G 3 which is furthest from the cathode K all have the same diameter. On the other hand, the openings of the grids G 1 and G 2 , as well as the openings of the wall 16 of the grid G s which faces the cathode K, have smaller diameters.

La grille G3 a, comme la grille Gs, une forme générale sensiblement cylindrique ou parallèlépipédique avec une même épaisseur de la paroi cylindrique 17 et des parois d'extrémités 15 et 16. Mais à la paroi 16, de même épaisseur que la paroi 15, est soudée, selon un exemple de réalisation de l'invention, une plaque ou insert 18 (figures 3 et 4) avec des ouvertures 19, 20 et 21 correspondant aux ouvertures de la paroi 16, c'est-à-dire de même diamètre et de même disposition relative. La plaque 18 est soudée contre la face interne de la paroi 16, par exemple par quatre points de soudure au voisinage de ses coins.The grid G 3 has, like the grid G s , a generally substantially cylindrical or parallelepipedal shape with the same thickness of the cylindrical wall 17 and of the end walls 15 and 16. But at the wall 16, of the same thickness as the wall 15, is welded, according to an exemplary embodiment of the invention, a plate or insert 18 (Figures 3 and 4) with openings 19, 20 and 21 corresponding to the openings of the wall 16, that is to say of same diameter and same relative arrangement. The plate 18 is welded against the internal face of the wall 16, for example by four welding points in the vicinity of its corners.

Ce soudage s'effectue avant le montage des électrodes, c'est-à-dire avant que les deux coupelles 22 et 23 constituant les deux parties de l'électrode Ga soient associées l'une à l'autre.This welding is carried out before the mounting of the electrodes, that is to say before the two cups 22 and 23 constituting the two parts of the electrode Ga are associated with one another.

Dans l'exemple l'ensemble constitué par les parois 16 et 18 présente une épaisseur qui est environ trois fois plus importante que l'épaisseur de la paroi 15 ; autrement dit l'insert 18 a une épaisseur qui est environ deux fois celle des parois de la grille G3 d'origine.In the example, the assembly constituted by the walls 16 and 18 has a thickness which is approximately three times greater than the thickness of the wall 15; in other words the insert 18 has a thickness which is approximately twice that of the walls of the original grid G 3 .

Comme expliqué ci-dessus à la coupure de l'alimentation du tube la borne 4 conserve un potentiel de l'ordre de 25 Kilovolts tandis que les potentiels des autres électrodes atteignent presque immédiatement la valeur zéro (potentiel de la masse).As explained above, when the power supply to the tube is cut off, terminal 4 retains a potential of the order of 25 Kilovolts while the potentials of the other electrodes reach zero immediately (ground potential).

La distance L séparant la cathode K de l'électrode G4 étant relativement faible, de l'ordre de 1 cm dans l'exemple, l'influence du potentiel de cette électrode G4 peut alors se faire sentir au voisinage de la cathode K et provoquer la formation indésirée d'un faisceau d'électrons selon l'axe du canon, ce qui engendrera une lueur parasite au centre de l'écran. C'est ainsi que, sans le perfectionnement de l'invention, comme le montre la figure 2a, la surface équipotentielle 25 (de 3,5 à 5 Volts), constituant la limite de la zone d'influence du potentiel induit par l'électrode G4 se trouve au voisinage de la grille G2 ; une proportion non négligeable d'électrons atteint alors la région centrale de l'écran. Par contre avec le perfectionnement de l'invention, comme le montre la figure 2b, la limite 25' d'influence du potentiel induit par la grille G4 est nettement plus éloignée de la cathode K, ce qui diminue considérablement la proportion d'électrons qui atteindront la partie centrale de l'écran et ainsi il n'y aura pratiquement pas de lueur parasite visible au centre de cet écran.The distance L separating the cathode K from the electrode G 4 being relatively small, of the order of 1 cm in the example, the influence of the potential of this electrode G 4 can then be felt in the vicinity of the cathode K and cause the unwanted formation of an electron beam along the axis of the barrel, which will generate a stray glow in the center of the screen. Thus, without the improvement of the invention, as shown in FIG. 2a, the equipotential surface 25 (from 3.5 to 5 Volts), constituting the limit of the zone of influence of the potential induced by the electrode G 4 is located in the vicinity of grid G 2 ; a significant proportion of electrons then reaches the central region of the screen. On the other hand, with the improvement of the invention, as shown in FIG. 2b, the limit 25 ′ of influence of the potential induced by the gate G 4 is much further from the cathode K, which considerably reduces the proportion of electrons which will reach the central part of the screen and thus there will be practically no stray glow visible in the center of this screen.

Des expériences ont montré que, sans le perfectionnement de l'invention, avec une paroi 16 d'épaisseur 0,25 mm et une tension nominale d'alimentation du filament de cathode K de 6,3 Volts la lueur parasite est visible lorsque la tension sur la grille G4 atteint 12 Kilovolts. Par contre avec le perfectionnement de l'invention, l'épaisseur de la paroi antérieure, tournée vers la cathode, de la grille Gs étant de 0,75 mm, la lueur parasite n'apparaît que si la tension d'alimentation du filament de la cathode est de 9 Volts et si l'électrode G4 est portée à un potentiel d'au moins 32 Kilovolts.Experiments have shown that, without the improvement of the invention, with a wall 16 of thickness 0.25 mm and a nominal supply voltage of the cathode filament K of 6.3 Volts the stray glow is visible when the voltage on the grid G 4 reaches 12 Kilovolts. On the other hand, with the improvement of the invention, the thickness of the front wall, facing the cathode, of the grid Gs being 0.75 mm, the stray glow only appears if the supply voltage of the filament of the cathode is 9 Volts and if the electrode G 4 is brought to a potential of at least 32 Kilovolts.

Dans cet exemple l'épaisseur de la paroi antérieure de la grille G3 est de l'ordre du triple de l'épaisseur de sa paroi postérieure 15. Un résultat satisfaisant d'élimination des lueurs de cathodes est encore obtenu quand cette épaisseur de la paroi antérieure est environ le double de l'épaisseur de la paroi postérieure.In this example, the thickness of the front wall of the grid G 3 is of the order of three times the thickness of its rear wall 15. A satisfactory result of eliminating cathode gleams is still obtained when this thickness of the anterior wall is about twice the thickness of the posterior wall.

Dans la variante représentée sur la figure 5, l'électrode G3 est en deux parties, la première comprenant seulement la paroi antérieure 30 d'épaisseur plus importante que le reste, 31, de l'électrode Gs. Cette seconde partie 31 comprend la partie allongée et l'autre paroi d'extrémité.In the variant shown in FIG. 5, the electrode G 3 is in two parts, the first comprising only the front wall 30 of greater thickness than the rest, 31, of the electrode Gs. This second part 31 comprises the elongated part and the other end wall.

Les parties 30 et 31 sont associées par exemple par soudage.The parts 30 and 31 are associated for example by welding.

La figure 6 représente encore un autre mode de réalisation dans lequel la paroi antérieure 16' de l'électrode Gs a la même épaisseur que les autres parties de cette électrode mais les ouvertures de cette paroi antérieure 16' sont toutes bordées par une collerette ou rebord 32. L'avantage de cette réalisation est qu'elle n'implique qu'une faible modification du canon à électrons connu.FIG. 6 represents yet another embodiment in which the front wall 16 'of the electrode G s has the same thickness as the other parts of this electrode but the openings of this front wall 16' are all bordered by a flange or rim 32. The advantage of this embodiment is that it involves only a slight modification of the known electron gun.

Dans une variante de la réalisation représentée sur la figure 1, les trous 19, 20 et 21 de l'insert 18 ont un diamètre supérieur au diamètre des trous correspondants de la paroi 16. Mais dans ce cas, il est préférable que l'épaisseur de l'insert soit supérieure à celle qu'il présente lorsque les diamètres sont égaux. Autrement dit il est préférable que l'épaisseur de l'insert croisse avec le diamètre de son ouverture.In a variant of the embodiment shown in FIG. 1, the holes 19, 20 and 21 of the insert 18 have a diameter greater than the diameter of the corresponding holes of the wall 16. But in this case, it is preferable that the thickness of the insert be greater than that which it presents when the diameters are equal. In other words it is preferable that the thickness of the insert increases with the diameter of its opening.

Dans la réalisation représentée sur la figure 7, l'ouverture de la paroi 15 de la grille G3 présente un diamètre d3 inférieur au diamètre d4 commun à l'ouverture de la grille G4 et à l'ouverture antérieure, tournée vers la cathode, de la grille Gs. Autrement dit le rapport ds/d4 est inférieur à 1.In the embodiment shown in FIG. 7, the opening of the wall 15 of the grid G 3 has a diameter d 3 less than the diameter d 4 common to the opening of the grid G 4 and to the anterior opening, facing the cathode, of the grid Gs. In other words, the ratio ds / d 4 is less than 1.

La ligne équipotentielle L2, correspondant à la ligne 25 de la figure 2a (ou 25' de la figure 2b), coupe l'axe z en un point B pratiquement à l'intérieur de la grille Ga. On constate que, là aussi, l'influence de la haute tension de la grille G4 est donc diminuée par la diminution du diamètre da (si on compare à la figure 2a). On a constaté qu'un rapport ds/d4 de 0,6875 permettait d'obtenir un bon compromis entre qualité de l'image de cathode en formation d'image et réduction du phénomène parasite de lueur de cathode à l'extinction des alimentations.The equipotential line L 2 , corresponding to the line 25 in FIG. 2a (or 25 ′ in FIG. 2 b ), intersects the z axis at a point B practically inside the grid Ga. It can be seen that there also, the influence of the high voltage of the gate G 4 is therefore reduced by the reduction in the diameter d a (if we compare with FIG. 2a). It has been found that a d s / d 4 ratio of 0.6875 makes it possible to obtain a good compromise between the quality of the cathode image in image formation and reduction of the parasitic phenomenon of cathode glow when the power supplies.

Cependant, le trou de la paroi 151 de la grille G3 présente, comme sur la figure 1, une collerette cylindrique qui avance à l'intérieur du cylindre G3. Cette collerette peut être obtenue à la fabrication de G3 par extrusion. Son effet permet de réduire la diminution du rapport d3/d4 nécessaire à l'invention. Dans un exemple de réalisation pour un compromis comparable à celui obtenu précédemment on a réalisé un rapport da/d4 de 0,844.However, the hole in the wall 15 1 of the grid G 3 has, as in FIG. 1, a cylindrical collar which advances inside the cylinder G 3 . This flange can be obtained during the manufacture of G 3 by extrusion. Its effect makes it possible to reduce the reduction in the ratio d 3 / d 4 necessary for the invention. In an exemplary embodiment for a compromise comparable to that obtained previously, a ratio d a / d 4 of 0.844 was produced.

L'invention obtient le résultat visé en limitant l'influence des lignes équipotentielles de niveau élevé dans la zone de formation du faisceau. Dans d'autres technologies que celle décrite ci-dessus un tel effet peut être réalisé notamment par un accroissement des dimensions des trous des grilles suivants la grille de très haute tension.The invention achieves the desired result by limiting the influence of the high level equipotential lines in the beam forming area. In other technologies than that described above, such an effect can be achieved in particular by increasing the dimensions of the holes of the grids following the very high voltage grid.

L'invention s'applique aussi au cas où la grille G4 est épaisse, par exemple réalisée en forme de cylindre. Sa proximité du filament étant inchangée, le problème et la solution de l'invention restent.The invention also applies to the case where the grid G 4 is thick, for example made in the form of a cylinder. Its proximity to the filament being unchanged, the problem and the solution of the invention remain.

Claims (17)

1. An electron gun for a cathode ray tube, more especially for color television, whose electrostatic lenses comprise an electrode (G4) which remains at an elevated potential after cutoff of the supply of the tube, characterized in that in order to reduce the effect on the cathode (K) of the elevated potential remaining at the said electrode (G4) after the cutoff of the supply, the gun comprises means for putting the distance between the cathode and an equipotential surface constituting the limit of the zone of influence of the potential induced by the said electrode remaining at the elevated potential, at a value such that the said elevated potential remaining on the said electrode (G4) after cutoff of the supply has a weak effect on the cathode, said means comprising masking means forming a part of a gun electrode with an intermediate position between the electrode (G4) at the elevated potential and the cathode, and in that the intermediate electrode (Gs) held at ground potential has an elongated form along the axis (11) of the gun with two end walls (15, 16 and 18), the end wall facing the cathode having, in order to perform said masking, a greater thickness than the opposite wall (15).
2. The electron gun as claimed in claim 1 characterized in that the ratio between the thicknesses of the end walls of the intermediate electrode (Gs) is at least of the order of 2.
3. The electron gun as claimed in claim 1 or 2, characterized in that the intermediate electrode (Gs) comprise a main part with the end wall (15 and 16) with equal thicknesses and an insert (18) mounted on the end wall (16) turned towards the cathode.
4. The electron gun as claimed in claim 3, characterized in that the insert (18) is welded in the end wall.
5. The electron gun as claimed in claim 3 or claim 4, characterized in that the insert (18) is mounted on the face of the end wall of the intermediate electrode (Gs) which is to the inside of this electrode.
6. The electron gun as claimed in claim 1, characterized in that the intermediate electrode (Gs) comprises two parts, of which one is constitutes by the thicker end wall (30), and the other (31) is constituted by the longitudinal part and the other end wall.
7. An electron gun for a cathode ray tube, more especially for color television, whose electrostatic lenses comprise an electrode (G4) which remains at an elevated potential after cutoff of the supply of the tube, characterized in that in order to reduce the effect on the cathode (K) of the elevated potential remaining at the said electrode (G4) after the cutoff of the supply, the gun comprises means for putting the distance between the cathode and an equipotential surface constituting the limit of the zone of influence of the potential induced by the said electrode remaining at the elevated potential, at a value such that the said elevated potential remaining on the said electrode (G4) after cutoff of the supply has a weak effect on the cathode, said means comprising masking means forming a part of an electrode of the gun with an intermediate position between the electrode (G4) at the elevated potential and the cathode, and in that the intermediate electrode (Ga) held at ground potential has an elongated form with two end walls (15 and 16'), the orifice of the end wall turned towards the cathode having a rim (32) which is responsible for such masking.
8. The electron gun as claimed in claim 7, characterized in that the rim (32) is turned towards the interior of the intermediate electrode (Gs).
9. The electron gun as claimed in any one of the preceding claims, characterized in that the diameter of the circular orifice of the electrode (G4) placed at an elevated portion is equal to the diameter of the corresponding orifice of the rear end wall (15), opposite to the cathode, of the intermediate electrode (Gs).
10. An electron gun for a cathode ray tube more especially for color television, whose electrostatic lenses comprise an electrode (G4) which remains at an elevated potential after cutoff of the supply to the tube when it is incorporated in the tube and is connected with the internal conducting lining, characterized in that the said electrode (G4) has the highest potential during normal functioning, and in that in order to reduce the effect on the cathode (K) of the elevated potential remaining on at this electrode (G4) after cutoff of the supply, the gun comprises means for putting the distance between the cathode and an equipotential surface constituting the limit of the zone of influence of the potential induced by the said electrode remaining at the elevated potential, at a value such that the said elevated potential remaining on the said electrode (G4) after cutoff of the supply has a weak effect on the cathode, said means comprising masking means forming a part of an electrode of the gun with an intermediate position between the electrode (G4) at the elevated potential and the cathode, and in that the intermediate electrode (Gs) held at ground potential has an elongated form conforming to the axis of the gun with two end walls, the wall which performs the said masking, turned towards the electrode (G4) with the elevated potential having an orifice with a diameter (ds) such that the ratio between this diameter (ds) to the diameter (d4) of the neighboring grid at an elevated potential is substantially less that 1.
11. The gun as claimed in claim 10, characterized in that the ratio of the diameter (ds) of the orifice in the first grid to the diameter (d4) of the neighboring orifice in the second grid is at the most 0.92.
12. The gun as claimed in claim 11, characterized in that the said ratio is of the order of 0.69.
13. The electron gun as claimed in claim 11, characterized in that the said ratio is of the order 0.85.
14. The gun as claimed in claim 10, characterized in that the orifice in the wall of the intermediate grid which is turned towards the electrode or grid with an elevated potential is bordered by a collar directed towards the interior of this intermediate grid (Gs).
15. The electron gun as claimed in any one of the preceding claims, characterized in that in an inherently known manner it comprises a bipotential lens (Gs and Gs) and an Einzel lens (Gs, G4 and G5), the electrode (4) placed at an elevated potential and the intermediate electrode (Gs) together forming two parts of the Einzel lens.
16. A cathode ray tube, characterized in that it comprises an electron gun as claimed in any one of the preceding claims.
17. A color television receiver, characterized in that it comprises a tube as claimed in claim 17.
EP19860400661 1985-03-29 1986-03-27 Electron gun for a cathode ray tube, in particular for colour television Expired - Lifetime EP0198753B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86400661T ATE49321T1 (en) 1985-03-29 1986-03-27 ELECTRON RADIATOR FOR CATHODE RAY TUBE, ESPECIALLY FOR COLOR TELEVISION.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FR8504848A FR2579823B1 (en) 1985-03-29 1985-03-29 ELECTRON CANON AND TELEVISION TUBE USING SUCH A CANON
FR8504848 1985-03-29
FR8512419 1985-08-14
FR8512419A FR2586326B1 (en) 1985-08-14 1985-08-14 ELECTRON CANON FOR CATHODE RAY TUBE, ESPECIALLY FOR COLOR TELEVISION

Publications (2)

Publication Number Publication Date
EP0198753A1 EP0198753A1 (en) 1986-10-22
EP0198753B1 true EP0198753B1 (en) 1990-01-03

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19860400661 Expired - Lifetime EP0198753B1 (en) 1985-03-29 1986-03-27 Electron gun for a cathode ray tube, in particular for colour television

Country Status (6)

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EP (1) EP0198753B1 (en)
JP (1) JP2553468B2 (en)
CA (1) CA1248576A (en)
DE (1) DE3668096D1 (en)
HK (1) HK17495A (en)
SG (1) SG135292G (en)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3374379A (en) * 1964-03-02 1968-03-19 Nippon Columbia Low second grid voltage electron gun
US3873879A (en) * 1972-01-14 1975-03-25 Rca Corp In-line electron gun
JPS5816131Y2 (en) * 1977-09-16 1983-04-01 株式会社東芝 unitized electron gun
NL8102527A (en) * 1981-05-22 1982-12-16 Philips Nv COLOR IMAGE TUBE.

Also Published As

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DE3668096D1 (en) 1990-02-08
JPS61227347A (en) 1986-10-09
EP0198753A1 (en) 1986-10-22
SG135292G (en) 1993-04-16
JP2553468B2 (en) 1996-11-13
HK17495A (en) 1995-02-17
CA1248576A (en) 1989-01-10

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