| 摘要 |
<p>A colour display tube comprising in an evacuated envelope (1) an electron gun system (5) of the "in-line" type to generate three electron beams (6, 7, 8) situated with their axes in one plane, said electron beams converging on a display screen (10) provided on a wall of the envelope and, in the operating display tube, being deflected over said display screen in two mutually perpendicular directions by means of a first and a second deflection field, the direction of the first deflection field being parallel to the said plane, said electron gun system comprising at its ends field shapers (34, 35) for causing the frames described on the display screen by the elctron beams to coincide as much as possible, said field shapers comprising substantially annular elements (34) of a meterial having a high magnetic permeability around the two outermost beams. if in addition two elongate flat strips (35) of a material having a high magnetic permeability are provided symmetrically with respect to the axis (9, 37) of the central beam and the plane through the beam axes, with their longitudinal axis (L) substantially perpendicularly to the said plane, said strips intersecting the said plane, extending with the width axis (B) in the direction of the display screen (10), and having a recess (38) at the level of the beam (7), then it is possible to compensate the horizontal and vertical coma errors more or less independently of each other.</p> |
