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Overscan is a behaviour in certain television sets in which part of the input picture is cut off by the visible bounds of the screen. It exists because cathode-ray tube (CRT) television sets from the 1930s to the early 2000s were highly variable in how the video image was positioned within the borders of the screen. It then became common ...
The tube has a perfectly proportioned copy of the test pattern master art (or a modified variant with the station ID replacing the Indian-head portrait, such as those used by KRLD-TV, [2] WBAP-TV [3] and WKY-TV [4]) inside, permanently deposited as a carbon image on an aluminum target plate or slide.
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. [2] The images may represent electrical waveforms on an oscilloscope , a frame of video on an analog television set (TV), digital raster graphics on a computer monitor , or ...
Screen-door effects are more noticeable than LCD when up close, or on larger sizes. [53] New models are no longer produced. Colored sub-pixels may age at different rates, leading to a color shift, although some models will scan pixels to even out wear and prevent this shift. [54] Sensitive to UV light from direct sunlight.
The biggest problem with many picture tubes is the loss of emission or electron production due to contaminated or damaged cathode that surrounds the heater. The 7JP4 was used in the following sets (incomplete list): Motorola VT-71 Motorola VT-73 Hallicrafters 504, 505, T-54 Sentinel TV-400 Sentinel TV-405 National TV-7W Philco 50-T701 & 50-T702
Stray electrons at the edge of the beam were cut off by the mask, creating a sharply focused spot that was small enough to hit a single colored phosphor on the screen. Since each of the guns was aimed at the hole from a slightly different angle, the spots of phosphor on the tube could be separated slightly to prevent overlap.
After being cut off by the mask, the beams would continue forward at slightly different angles, hitting the screens at slightly different locations. The spread was a function of the distance between the guns at the back of the tube, and the distance between the mask plate and the screen.
The tube was mounted vertically in the bottom of the cabinet with the screen pointing downward towards a concave mirror which reflected the image upward toward an angled mirror at the top of the cabinet onto the 25 inch screen, The top of the tube mirror box had a Schmidt lens [e] to correct aberrations. Because the picture had to be magnified ...