picture tube

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picture tube

[′pik·chər ‚tüb]
A cathode-ray tube used in television receivers to produce an image by varying the electron-beam intensity as the beam is deflected from side to side and up and down to scan a raster on the fluorescent screen at the large end of the tube. Also known as kinescope; television picture tube.

Picture tube

A cathode-ray tube used as a television picture tube. Television picture tubes use large glass envelopes that have a light-emitting layer of luminescent material deposited on the inner face. A modulated stream of high-velocity electrons scans this luminescent layer in a series of horizontal lines so that the picture elements (light and dark areas) are recreated.

In a color picture tube (see illustration), the glass bulb is made in two pieces, the face panel and the funnel-neck region. The separate face panel allows the fabrication of the segmented phosphor screen and the mounting of the shadow mask. The two glass pieces are sealed together by a special frit to provide a strong vacuum-tight seal.

The light-emitting colored phosphors on the segmented screen can be either in dot arrays or, now more commonly, in line arrays. Typically, the trios of vertical phosphor lines are spaced 0.6– 0.8 mm apart. Most tubes use a black matrix screen in which the phosphor lines are separated by opaque black lines. This black matrix reduces reflected light, thereby giving better contrast, and also provides a tolerance for the registration of the electron beam with the phosphor lines.

The shadow mask is made of a thin (0.10–0.17 mm) steel sheet in which elongated slits (one row of slits for each phosphor-line trio) have been photoetched. It is formed to a contour similar to that of the glass panel and is mounted at a precise distance from the glass. The width of the slits and their relative position to the phosphor lines are such that the electron beam from one of the three electron guns can strike only one of the sets of color phosphor lines. The shadow mask “shadows” the beam from the other two sets of phosphor lines.

The electron gun for color is similar to that for monochrome except that there are three guns, usually arranged side by side, or in-line. This triple gun has common structural elements, but uses three independent cathodes with separate beam forming and focusing for each beam.

The electromagnetic deflection yoke deflects or bends the beams, as in a monochrome tube, to scan the screen in a television raster. In addition, the yoke's magnetic field is shaped so that the three beams will be deflected in such a way that they land at the same phosphor trio on the screen at the same time. This convergence of the beams produces three images, one in red, one in green, and one in blue, that are superimposed to give a full-color picture. See Cathode-ray tube, Television

References in periodicals archive ?
Allegedly, Chunghwa Picture Tubes has already kicked off cooperation with the Chinese counterpart on back-end production of display modules, with the former supplying about 500,000 units a month to the latter.
Acquisition of Chunghwa Picture Tubes will enable Shenzhen China Star to ramp up capacity of small and medium-sized display panels, especially those for IT (information technology)-based devices, which the Chinese maker is short of now.
From now on, the researchers conclude, color picture tubes "should be considered hazardous waste" and kept out of landfills and municipal-waste incinerators.
He said other major picture tube investments are being made in high resolution computer display tubes.
Chunghwa Picture Tubes will also benefit from the partnership as it has been switching production of small and medium-sized display panels to touch panels over the past years to turn business around.
Chunghwa Picture Tubes has been supplying e-paper displays to PVI since June, and will turn out FFS panels starting in August, industry insiders say.
To quickly build its footholds in the market for small- and medium-sized display panels, Chunghwa Picture Tubes decided to team up with Compal, with the partner holding a 19.
Chunghwa Picture Tubes has been working hard with Compal's reinvested company Toppoly Optoelectronics Corp.
Thomson (Paris: 18453) (NYSE:TMS) announces it has completed its acquisition of Fortune's color picture tube (CPT) assets.
Compounding the issue, picture tube production has moved away from the group's historical home markets in North America and Europe to Asia.
The group is also the only North American manufacturer of aperture masks, a key component in color television picture tubes.
Following this initiative, Thomson will more than double its production of picture tubes originating from the country and will have a worldwide market share of 20% for large and VLS picture tubes.