. Bell telephone magazine . been used, to-gether with other very small com-ponents, to make a variety of compactelectronic packages which performa great many of the functions requiredin the modern electronic art. With its virtues there are also somelimitations: the point-contact transis-tor is more noisy in a circuit thanone would like, and its ability to han-dle power Is limited. The noisetencis to restrict Its use to the controlof electrical signals rather than their generation or amplification and itspower capacity limits It to relativelysmall currents. The point-contact transistor, firstme
. Bell telephone magazine . been used, to-gether with other very small com-ponents, to make a variety of compactelectronic packages which performa great many of the functions requiredin the modern electronic art. With its virtues there are also somelimitations: the point-contact transis-tor is more noisy in a circuit thanone would like, and its ability to han-dle power Is limited. The noisetencis to restrict Its use to the controlof electrical signals rather than their generation or amplification and itspower capacity limits It to relativelysmall currents. The point-contact transistor, firstmember of the family, has been joinedby a number of other types whichhave been announced during the fiveyears under review. A photo-tran-sistor Invented by J. N. Shive has al-ready gone Into Bell System serviceIn the card translator used In tele-phone exchanges for automatic rout-ing in toll dialing. The photo-tran-sistor Is a device In which the flow ofcurrent through a point-contact on a 76 Bell Telephone Magazine SUMMER I. A portion of the cartridge casing of a point-contact transistor has been cut away to show, magnified, the two points on the germanium surface small germanium wafer is controlledby a fine beam of light shining on asensitive area of the germanium sur-face. In its telephone exchange useit conserves both space and power. The Junction Transistor Early in the study of transistors,it was predicted by Shockley, on thebasis of theory, that a junctiontransistor, different in structure, wouldhave useful properties. The idea wasto have in a germanium crystal a verythin region of one electrical typeseparating the two adjoining end re-gions of different electrical type. Thetwo boundaries or junctions be-tween the thin region and the two end regions were to serve the samefunctions as the two points in thepoint-contact device. The thing itselfwas simple. Shockleys theory couldpredict the performance to be ex-pected. The problem was to findways to make it. With metallurgists
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