US3746904A - Cathode-ray tube including a glass envelope with two spaced external conductive coating and a connecting strip of a third external conductive coating thereon - Google Patents

Abstract

A cathode-ray tube including a glass envelope having a forward portion terminating in a viewing screen, a center portion, and a rear portion including an electron-gun assembly having at least one focusing lens therein. A first external conductive coating is on the forward portion of the envelope, and a second conductive coating spaced from the first conductive coating is on the rear portion of the envelope at least over the focusing lens. A longitudinal strip of a third external conductive coating on the center portion of the envelope connects the first and second conductive coatings.

Description

[ CATIIODE-RAY TUBE INCLUDING A GLASS ENVELOPE WITH TWO SPACED EXTERNAL CONDUCTIVE COATING AND A CONNECTING STRIP OF A THIRD EXTERNAL CONDUCTIVE COATING 7/1952 Breeden 313/85 R X 2,771,566 11/1956 Baracket 313/85 R X 2,829,292 4/1958 Krause 313/85 R X 3,614,519 10/1971 Figlewicz 313/85 S X FOREIGN PATENTS OR APPLICATIONS 6,703,723 9/1967 Netherlands 313/85 R Primary Examiner-Robert Segal AttorneyGlenn H. Brustle [57] ABSTRACT A cathode-ray tube including a glass envelope having a forward portion terminating in a viewing screen, a center portion, and a rear portion including an electron-gun assembly having at least one focusing lens therein. A first external conductive coating is on the forward portion of the envelope, and a second conductive coating spaced from the first conductive coating is on the rear portion of the envelope at least over the focusing lens. A longitudinal strip of a third external conductive coating on the center portion of the envelope connects the first and second conductive coatings.

1 Claim, 1 Drawing Figure Patented July 17, 1973 3,746,904

' INVEN'IOR. ALTON J. TORRE ATTORNEY CATHODE-RAY TUBE INCLUDING A CLASS ENVELOPE WITH TWO SPACED EXTERNAL CONDUCTIVE COATING AND A CONNECTING STRIP OF A THIRD EXTERNAL CONDUCTIVE COATING THEREON BACKGROUND OF THE INVENTION The invention relates to a novel cathode-ray tube, for example, to a color television picture tube, including a glass envelope with two spaced external conductive coatings and a connecting strip of a third conductive coating thereon.

One type of cathode-ray tube conventionally comprises a glass envelope having a forward portion terminating in a vewing window with a luminescent viewing screen thereon and a rear portion including bipotential electron-gun assembly having at least one electron gun with focusing lens. Each electron gun projects one electron beam towards the window to excite the screen to luminescence. A deflection yoke mounted on the envelope includes magnetic field producing coils positioned adjacent the envelope to provide for deflection of the electron beams.

The tube includes a first external conductive coating on the forward portion of the envelope or funnel between the yoke and the viewing screen and a second conductive coating, spaced from the first conductive coating, on the rear portion of the envelope or neck at least over the focusing lenses of the electron gun. The second conductive coating is spaced from the first coating to permit mounting of the yoke on an uncoated portion of the envelope. If the yoke were mounted on a conductive coating, it may accidentally become grounded to the coating. In the operation of the tube, the second coating is connected to a ground potential with a spring clip clamped against the coating, which is in turn connected with a ground wire to a convenient ground potential. By grounding the second coating in this manner, a special clip with groundwire is necessary, which increases the cost of equipment necessary for tube operation. In addition, the clip with ground wire results in an increased number of separate external components necessaryfor tube operation. Furthermore, the ground clip may become easily disconnected or may be improperly connected, resulting in decreased operating performance of the tube.

SUMMARY OF THE INVENTION As in the prior art, the novel cathode-ray tube includes an evacuated glass envelope having a forward portion or funnel terminating in a viewing screen, a center portion, and a rear portion or neck including an electron gun therein. The forward portion includes a first external conductive coating, and the rear portion includes a second external conductive coating, spaced from the first external conductive coating, at least around the envelope over the focusing lens of the electron gun. Unlike the prior art, the center portion includes a longitudinal strip of a third external conductive coating connecting the first and second coatings.

In operation, a deflection yoke having two pair of magnetic field producing coils, each coil having a window, is mounted on the center portion of the novel tube. The yoke is positioned over the center portion with at least one of the windows formed by the inner pair of coils positioned over the strip. The novel tube eliminates the clip with ground wire and utilizes an external strip of conductive coating to connect the second coating to the first coating. The connecting strip connects the second coating to ground potential since the first coating is normally connected to a ground potential during the use of the tube. Since the first, second and connecting strip of a third conductive coating can be simultaneously applied using existing processes at a cost substantially equal to the cost of only the additional coating material, and the clip with ground wire is eliminated, an economy results in the manufacture and use of the novel tube. In addition, the elimination of the clip with ground wire reduces the number of separate external components required for the operation of the tube. Furthermore, replacing the separate mechanical ground connection with an integral ground connection in the form of a strip of conductive coating provides more assurance that the second coating is always connected to ground potential during the operation of the tube. Also, the novel tube can be installed in equipment not previously provided with a mechanical ground, thereby resulting in increased tubeoperating performance without requiring a receiver modification.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is a partially broken away top elevational view of the novel color television picture tube and associated magnetic deflection yoke illustrating the external strip of conducting coating thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT The novel color television picture tube 10 with an electromagnetic deflection yoke 11 positioned thereon is illustrated in the sole FIGURE. The tube 10 comprises a glass envelope 12 including a forward portion or funnel 13 terminating in a panel 14 having a viewing window 15, a rear portion or neck 16 terminating in a stem assembly 17, and a flared center portion 18 connecting between the funnel l3 and neck 16. The inside surface of the funnl 13'includes an internal conductive coating 19. An anode connection 20 is provided through the funnel 13 for connecting a high voltage to the internal coating 19. A luminescent viewing screen 21 comprised of a multiplicity of phosphor dots is supported on the inside surface of the viewing window 15, and an aperture-mask assembly 22 is positioned in the envelope in front of the screen 21. An electron-gun assembly 23 is positioned in the neck 16 for projecting three electron beams 24 red (r), blue (b), and green (g) towards the aperture-mask assembly 22 and the screen 21.

The electron-gun assembly 23 includes three electron guns 25 (only one of which is partially shown in the sole FIGURE). The electron-gun assembly 23 includes a first grid G-l (not shown), a second grid G-2 (not shown), a third or focusing grid G-3 designated 26, and a fourth grid or anode G-4 designated 27. A convergence assembly 28 is coupled to the three electron guns 25. A spacing B exists between the third and fourth grids 26 and 27. The third grid 26 is at approximately 5,500 volts, and the fourth grid 27 is at approximately 25,000 volts. The spacing B" and potential difference produce a lens-like configuration of equipotential field lines resulting in the formation of one of the three electron beams 24. The lens-like configuration having the spacing B" is therefore generally designated a focusing lens of one of the three electron guns 25. For an electron-gun assembly 23 comprising three electron guns 25, there are three focusing lenses 29 in substantial alignment.

The tube includes a first external conductive coating 30 on the external surface of the funnel 13. The first external coating 30 covers substantially the entire external surface of the funnel 13 except for an area surrounding the anode connection 20. This is to prevent current leakage from the anode connection to the first external coating 30. The internal conductive coating 19, the glass funnel l3, and the first external conductive coating in combination provide voltage regulation in the operation of a color television receiver, as is known.

The tube 10 also includes a second external conductive coating 31 on the neck 16. In the preferred embodiment, the second external coating 31 comprises a band around the neck 16 positioned substantially centered over the focusing lenses 29 of the electron-gun assembly 23. The second external coating 31 is believed to equally distribute electrical charges accumulating on the inner surface of the neck 16 over the focusing lenses 29, thereby reducing convergence shift of the electron beams 24 caused by the prior nonuniform charge distribution. Referring to the sole FIGURE, it is preferred the the band of second external coating 31 is approximately 0.75-inch wide.

A longitudinal strip of a third external conductive coating 32 on the center portion 18 of the envelope 12 parallel to the axis A-A of the tube 10 connects the first and second external coatings 30 and 31 respectively. In the preferred embodiment, the third external coating 32 is a longitudinal strip on the top of the surface of the envelope 12 approximately 0.25-inch wide. In this description, the top of the envelope 12 is defined to be that portion of the envelope which is uppermost when positioned in a television receiver.

In the opeation of the novel tube 10, an electromagnetic deflection yoke 11 of the well-known saddle type is positioned on the envelope 12 adjacent the center portion 18 of the envelope 12. The yoke 11 is conventionally positioned on the envelope to produce a deflection field for deflecting the electron beams 24 from the electron-gun assembly 23 to horizontally and vertically sweep the screen 21 scanning a rectangular raster at the screen 21 in a known manner. The yoke 11 includes a set of saddle-type vertical deflection coils 33 and a set of saddle-type horizontal deflection coils 34. The usual convention is to position the horizontal deflection coils 34 inside the vertical deflection coils 33 and in close proximity to the envelope 12.

The horizontal coils 34 each have two spaced groups of active side conductors 35 and 36 extending generally along the longitudinal axis A-A of the tube 10 (only one coil is shown in the sole FIGURE) and spaced from one another circumferentially of the tube 10. The spaced groups of side conductors 35 and 36 are joined at their ends by groups of connecting front and rear end conductors 37 and 38 respectively extending traversely of the tube 10. The groups of side conductors 35 and 36 follow the contour of the envelope 12 on the center portion 18, flaring up at their ends to join the groups of front and rear end conductors 37 and 38, which are spaced from the tube 10. The groups of front and rear end conductors 37 and 38 are usually flared up and spaced from the envelope 12 to prevent their generating a field which interacts with the desired deflection field. The open center space between the two spaced groups of side conductors 35 and 36 and the connecting groups of front and rear end conductors 37 and 38 is generally defined to be a window 39.

It is preferred that the longitudinal strip ofa third external coating 32 which is positioned on the center portion 18 of the envelope 12 not contact or be positioned under the two spaced groups of side conductors 35 and 36 of the horizontal coils 34 to prevent grounding of the third external coating 32 by the shorting of the insulation on the coils.

In the preferred embodiment, the third external coating 32 is on the tube 10 substantially centered under one window 39 between the two spaced groups of side conductors 35 and 36 (shown in the sole FIGURE) when the yoke 11 is positioned on the tube 10. The width C of the strip of third external coating 32 should not exceed the width of the narrowest portion of the window 39. If the width C of the strip of third external coating 32 is greater than the narrowest width D of the window, it would be under and in contact with the horizontal coil 34, which as previously described, is not desirable.

In the operation of the tube 10 with yoke 11, one window 39 formed by one of the horizontal coils 34 is centered over the top of the envelope l2, and the other window (not shown) formed by the other horizontal coil (not shown) is positioned opposed from the first window 39 centered over the bottom of the envelope 12. In a 25VABP22 color television picture tube, the anode connection 20 is located on the bottom of the funnel 13. Since the third external coating 32 does not extend near the anode connection 20 as previously described, a longitudinal strip of a third external coating 32 would not directly connect with the first external coating 30. It is therefore preferred that the third external conductive coating 32 be positioned under the window 39 on the top of the envelope 12 as previously described.

The first, second and third external coatings 30, 31 and 32 respectively are deposited from a colloidal graphite suspension such as, for example, Aquadag." It is preferred that the dry coatings are about 0.001- inch thick and have a low resistance such as, for example, ohms per linear inch. It is preferred that the coatings are applied as one continuous layer of suspension, rather than as separate abutting or overlapping layers, to provide uniform thickness and resistance.

The coatings are preferably applied by spraying, which is well known.

In the preferred method of applying the coatings, a spray shield (not shown) is positioned over the envelope 12. The shield closely fits against and substantially conforms to the contour of the envelope 12. The shield has cutouts or openings over the portions of the envelope 12 corresponding to the desired position of the coatings 30, 31 and 32 on the envelope 12. The coatings are then applied by spraying onto the unshielded portions of the envelope 12.

Although, in the preferred embodiment, the third external coating 32 is a strip about 0.25 inch wide, the coating width may be narrower since there is substantially no current flow in the coating, The only requirement is that the coating width be sufficient to maintain the second coating 31 at ground potential.

Although the third external coating 32 is described as a strip of a uniform width, it may be of varying width limited only by the width of the window 39 as previously described.

Although particular shapes for the first and second coatings 30 and 31 respectively are described in the preferred embodiment, other shapes can be used such as, for example, the second coating may cover the entire surface of the neck 16.

Although it is described that the horizontal coils 34 are positioned in contact with the envelope 12 and contain a window 39 under which the third conductive coating 32 can be positioned without contacting the spaced groups of side conductors 34 and 36, the vertical coils 33 may alternatively be positioned in contact with the envelope 12. The vertical coils 33 are similar to the horizontal coils 34 and similarly contain a window which would be positioned over the sides of the tube and under which the third conductive coating 32 can be positioned without contacting spaced groups of side conductors of the vertical coils 33.

I claim:

1. In combination, a cathode-ray tube including a glass envelope having a forward conical portion terminating in a viewing window, a center yoke receiving portion, and a rear neck portion having therein a plurality of electron guns in a delta array, each of said guns having a focusing lens, said tube comprising a. a first conductive coating substantially covering the external surface of said conical portion, except for a portion surrounding the anode connection, b. a second circumferential band of conductive coating on the external surface of said neck portion substantially centered over said focusing lenses of said electron guns, and c. a longitudinal strip of a third conductive coating on the external surface of said yoke receiving portion of said envelope connecting said first coating and said second coating; and a saddle yoke comprising at least two inner opposed magnetic field producing coils, each coil having a window which is formed by two spaced groups of side conductors and two connecting groups of end conductors, said yoke being positioned over said yoke receiving portion, with at least one of the windows formed by the inner pair of coils positioned over said strip, said longitudinal strip being of a width less than the space between the two spaced groups of side conductors forming one of said two windows and capable of maintaining said first and said second conductiv'e coatings at the same potential.

Claims (1)

1. In combination, a cathode-ray tube including a glass envelope having a forward conical portion terminating in a viewing window, a center yoke receiving portion, and a rear neck portion having therein a plurality of electron guns in a delta array, each of said guns having a focusing lens, said tube comprising a. a first conductive coating substantially covering the external surface of said conical portion, except for a portion surrounding the anode connection, b. a second circumferential band of conductive coating on the external surface of said neck portion substantially centered over said focusing lenses of said electron guns, and c. a longitudinal strip of a third conductive coating on the external surface of said yoke receiving portion of said envelope connecting said first coating and said second coating; and a saddle yoke comprising at least two inner opposed magnetic field producing coils, each coil having a window which is formed by two spaced groups of side conductors and two connecting groups of end conductors, said yoke being positioned over said yoke receiving portion, with at least one of the windows formed by the inner pair of coils positioned over said strip, said longitudinal strip being of a width less than the space between the two spaced groups of side conductors forming one of said two windows and capable of maintaining said first and said second conductive coatings at the same potential.

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