二に極きょく真しん空くう管かん

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Meanings

1

Technical term for a two-electrode vacuum tube; in modern contexts often refers to a semiconductor diode as well, but the kanji specifically indicates a vacuum tube diode.

初しょ期きのラジオ受じゅ信しん機きには二に極きょく真しん空くう管かんが使つかわれていた。
Early radio receivers used vacuum tube diodes.