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A transistor radio is a small portable radio receiver that uses transistor-based circuitry. Following their development in 1954, made possible by the invention of the transistor in 1947, they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s. Their pocket size sparked a change in popular music listening habits, allowing people to listen to music anywhere they went. Beginning in the 1980s cheap AM transistor radios were superseded by devices with higher audio quality, portable CD players, personal audio players, and boom boxes. ==Background== Before the transistor was invented, radios used vacuum tubes. Although portable vacuum tube radios were produced, they were bulky and heavy due to the large batteries necessary to supply the high power consumption of the tubes, and the transformer required to step up the low battery voltage to the high anode voltage needed by the tubes. Bell Laboratories demonstrated the first transistor on December 23, 1947.〔(The Invention of the Transistor )〕 The scientific team at Bell Laboratories responsible for the solid-state amplifier included William Shockley, Walter Houser Brattain, and John Bardeen.〔 page 13〕 After obtaining patent protection, the company held a news conference on June 30, 1948, at which a prototype transistor radio was demonstrated. There are many claimants to the title of the first company to produce practical transistor radios, often incorrectly attributed to Sony (originally Tokyo Telecommunications Engineering Corporation). Texas Instruments had demonstrated all-transistor AM (amplitude modulation) radios as early as May 25, 1954,〔Invention and Technology Magazine, Fall 2004, Volume 20 Issue 2, "The Revolution in your Pocket", Author: Robert J. Simcoe〕〔Book Title: TI, the Transistor, and Me, Author: Ed Millis, page 34〕 but their performance was well below that of equivalent vacuum tube models. A workable all-transistor radio was demonstrated in August 1953 at the Düsseldorf Radio Fair by the German firm Intermetall.〔Article: "The French Transistor", Author: Armand Van Dormael, page 15, Source: IEEE Global History Network〕 It was built with four of Intermetall's hand-made transistors, based upon the 1948 invention of the "Transistron"-germanium point-contact transistor by Herbert Mataré and Heinrich Welker. However, as with the early Texas Instruments units (and others) only prototypes were ever built; it was never put into commercial production. RCA had demonstrated a prototype transistor radio as early as 1952 and it is likely that they and the other radio makers were planning transistor radios of their own, but Texas Instruments and Regency Division of I.D.E.A., were the first to offer a production model starting in October 1954.〔website: www.regencytr1.com, Regency TR-1 Transistor Radio History〕 The use of transistors instead of vacuum tubes as the amplifier elements meant that the device was much smaller, required far less power to operate than a tube radio, and was more shock-resistant. Since the transistor base draws current, its input impedance is low in contrast to the high input impedance of the vacuum tubes.〔 page 32〕 It also allowed "instant-on" operation, since there were no filaments to heat up. The typical portable tube radio of the fifties was about the size and weight of a lunchbox, and contained several heavy, non-rechargeable batteries— one or more so-called "A" batteries to heat the tube filaments and a large 45- to 90-volt "B" battery to power the signal circuits. By comparison, the transistor radio could fit in a pocket and weighed half a pound or less, and was powered by standard flashlight batteries or a single compact 9-volt battery. The now-familiar 9-volt battery was introduced for powering transistor radios. Listeners sometimes held an entire transistor radio directly against the side of the head, with the speaker against the ear, to minimize the "tinny" sound caused by the high resonant frequency of its small speaker. Most radios included earphone jacks and came with single earphones that provided only mediocre-quality sound reproduction. To consumers familiar with the earphone-listening experience of the transistor radio, the first Sony Walkman cassette player, with a pair of high-fidelity stereo earphones, would provide a greatly contrasting display of audio fidelity. 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「Transistor radio」の詳細全文を読む スポンサード リンク
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