Abstract A cathode-ray tube, particularly an index-tube, having a narrow, elongated spot. The electron gun of the tube comprises an astigmatic lens, since its grid has a narrow, elongated opening. In order to avoid S-shaped deformation of the spot upon simultaneous deflection of the electron beam in the horizontal and vertical directions the anode of the electron gun is provided with an opening which widens up in the direction towards the target plate on the side remote from the cathode in planes parallel to a plane going through the axis of the electron gun and the direction of length of the spot produced by the electron beam at the centre of the target plate. The anode opening preferably has an elongated sectional area in planes at right angles to the axis of the electron gun the longitudinal direction of said area intersecting substantially at right angles the direction of length of the grid opening in order to reduce the dependence of the width of the spot upon the beam current.
A cathode-ray tube comprising an electron gun having, axially aligned, a cathode having substantially rotational symmetry, a grid, an anode and an acceleration electrode for producing an electron beam, said cathode-ray tube further comprising an electron focusing lens and a target plate comprising stripes of electro-luminescent material oriented in a first direction, said grid having a narrow, elongated opening that extends in said first direction and forms an astigmatic lens for producing an electron beam wherein electron paths lying in an imaginary plane extending in said first direction are focused at a point located at a given distance from said target plate on the side of said electron gun and electron paths lying in an imaginary plane at right angles to said first direction are focused substantially on the target plate, said anode comprising an elongated opening that has a major axis extending at substantially right angles to said first direction and that has a minimum width dimension exceeding the width of said grid opening, said anode opening intersecting the first anode face facing said grid so as to form a first aperture and intersecting the second anode face removed from said grid so as to form a second aperture, said second aperture being wider than said first aperture so that said anode opening widens in step-wise manner from said first face to said second face, said anode opening being substantially rectangular at said second anode face.
Claim 2
Dependent Claim
237 words
A cathode-ray tube comprising an electron gun having, axially aligned, a cathode having substantially rotational symmetry, a grid, an anode and an acceleration electrode for producing an electron beam, said cathode-ray tube further comprising an electron focusing lens and a target plate comprising stripes of electro-luminescent material oriented in a first direction, said grid having a narrow, elongated opening that extends in said first direction and forms an astigmatic lens for producing an electron beam wherein electron paths lying in an imaginary plane extending in said first direction are focused at a point located at a given distance from said target plate on the side of said electron gun and electron paths lying in an imaginary plane at right angles to said first direction are focused substantially on the target plate, said anode comprising an elongated opening that has a major axis extending at substantially right angles to said first direction and that has a minimum width dimension exceeding the width of said grid opening, said anode opening intersecting the first anode face facing said grid so as to form a first aperture and intersecting the second anode face removed from said grid so as to form a second aperture, said second aperture being wider than said first aperture so that said anode opening widens in step-wise manner from said first face to said second face, said anode opening being substantially rectangular at said second anode face.