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The Western Electric model 500 telephone series was the standard domestic desk telephone set issued by the Bell System in North America from 1950 through the 1984 Bell System divestiture. Millions of model 500-series phones were produced and were present in most homes in North America. Many are still in use today because of their durability and ample availability. Its modular construction compared to previous types simplified manufacture and repair, and facilitated a large number of variants with added features. Touch-tone service was introduced to residential customers in 1963 with the model 1500 telephone, which had a push-button pad for the ten digits. The model 2500 telephone, introduced in 1968, added the * and # keys, and is still in production today by several manufacturers. ==History== The Western Electric 500-type telephone replaced the 300-type which had been produced since 1936. Like its predecessor, the model 500 line was designed by the firm of industrial designer Henry Dreyfuss, the product of several years of research and testing in collaboration with Bell Laboratories and Western Electric. Development started in 1946 and lead to pre-production units in 1948 and field trials with 4000 telephone sets in 1949. AT&T announced the new telephone publicly in 1949, and communicated the first availability of approximately 23,000 sets in the second quarter 1950 to the Bell System operating companies on May 1, 1950. Third and fourth quarter production was estimated at 49,000 and 93,000, respectively. Including 20,000 units of a special purpose set (501B), approximately 183,000 units were produced by the end of the first production year.〔Events in Telecommunications History, AT&T〕 In the following years, systematic replacement of 25 million 300-type telephones commenced because of the much improved electrical and acoustic efficiency of the new model.〔Chapuis, R.J., Joel Jr., A.E., Joel, A.E., ''100 Years of Telephone Switching'', IOS Press, 2003, p. 334〕 This efficiency permitted the new model to be used on long rural loops, which previously required special sets with local batteries to power the transmitter, not just on urban short loops, because it contained a self-adjusting gain control. This also permitted the use of thinner loop wires and thus delivered cost-savings in the build-out of the network. The replacement of 300-series telephones with 500-series sets created large stockpiles of 300-type components that had not reached their intended service life. The accelerating demand for new telephone service in the 1950s created pressure on the manufacturing facilities, which the Bell System alleviated by reusing these older components to refurbish used 302 telephone sets with a new modern housing that had a look-alike appearance to the 500 model, but were electrically identical to the older 302 telephone. This program commenced in 1955, and the converted set was labeled as the model 5302 telephone. It was produced until the mid-1960s in the refurbishing shops of each Bell Operating Company, not on the assembly lines of Western Electric factories. From the 1949 field trials until 1953, only black sets of the 500-type telephone were manufactured. The introduction of telephones in color occurred in several stages until 1957, as manufacturing capability was refined and material selection processes were completed. In the 1960s, after the introduction of touch-tone service in November 1963 in various locations of the telephone network, the 500 was retrofitted with a push-button keypad, creating the model 1500 for the 10-button version and in 1968 the model 2500, having 12 keys. The 1970s brought the conversion to modular cord technology, replacing the hard-wired handset cords as well as the fixed line cords (mounting cords) with cords that were terminated on both ends with 4P4C (RJ-10) connectors for handsets, and 6P4C (RJ-14) connectors for mounting. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「model 500 telephone」の詳細全文を読む スポンサード リンク
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