Beam-index tube

The beam-index tube is a color television cathode ray tube (CRT) design, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing mask as developed by RCA. Beam indexing offered much brighter pictures than shadow-mask CRTs, reducing power consumption, and as they used a single electron gun rather than three, they were easier to build and required no alignment adjustments.

Philco led the development of the beam-indexing concept in a series of experimental devices they called the Apple tube. In spite of lengthy development, they were never able to manufacture a cost-competitive indexing tube, and eventually abandoned the concept. The major problem was the cost of the indexing electronics, which in later models required an expensive photomultiplier tube.

New detectors and transistor-based electronics led to the system being re-introduced as the Uniray in the 1970s. It was highly competitive in price terms, but competing against greatly improved shadow mask designs and the new Trinitron. Several Japanese companies used the Uniray for a variety of specialist purposes, the best-known being the Sony Indextron series. The system also saw some military use, due to its low sensitivity to magnetic interference, and in such use in the UK it was known as the Zebra tube.

History

Early color CRTs

In conventional black-and-white (B&W) televisions, the CRT screen has a uniform coating of phosphor that emits white light when struck by electrons. The beam from an electron gun at the back of the tube is deflected (most commonly) by the varying fields from magnetic coils so it may be directed at any point on the screen.