Grid for colour TV tube - has graded openings near viewing screen to improve contrast

摘要

A colour television tube has a perforated grid positioned inside the tube and at a small distance from the viewing screen. The construction of the grid improves the contrast of the picture obtained on the screen. The grid has a multitude of graded openings (25, 27). The openings are distributed uniformly on concentric rings (29) essentially rectangular. The corners (19) of each concentric ring (29) are rounded. The size of the openings decrease progressively from the centre of the grid to its periphery. The openings are dimensioned to produce a set gradient from the centre outward. The arc at each corner sustain about 20 to 30 degrees. It has part which is essentially circular and two tails which join up the circular part to the linear sides of a rectangle.