File:Bell telephone magazine (1922) (14569601589).jpg

Identifier: belltelephonemag12amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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erfect if the cumulative effects of the distortions and insta-bilities which they introduce are not to be excessive. For example, in the New York-Los Angeles circuit referredto earlier, there are employed over 200 vacuum tubes; aboutone-half of these are used when the man in New York speaksto the man in Los Angeles and the other half are called intoplay when the Los Angeles man replies. Altogether there are,say, 25 times as many tubes in the circuit as in a good radioset. The failure of any one of these tubes would interruptthe conversation. The likelihood of burning out or suddenfailure from any cause should therefore be only one twenty-fifth as great for each of the tubes used on the telephone cir- 245 BELL TELEPHONE QUARTERLY cuit as for each of those in the radio set, if the circuit is to beat least as reliable as a radio set. Of course, an effort is madeto avoid service failures of the tubes on the telephone circuitby regular tests and inspections, but long tube life is neverthe-
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FiGURE 3. 101 F Vacuum (Type L ) Tube. less of vital importance to this end. For this reason thevacuum tubes for telephone use are designed to have averagelives which are much longer than those usually considerednecessary for other services. The present L and V tubes haveaverage lives in the Bell System Plant of about 18,000 and 246 THE VACUUM TUBE IN TELEPHONE COMMUNICATION 70,000 hours (two and eight years) continuous use, respec-tively, and this in spite of very rigid requirements for deter-mining when a tube must be replaced. The average life ofthe tubes used in radio receiving sets is only a small fraction

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