noun
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.
初期のラジオ受信機には二極真空管が使われていた。
Early radio receivers used vacuum tube diodes.
ダイオード is the common loanword for semiconductor diodes, while 二極真空管 specifically refers to a vacuum tube diode and is more technical/historical.
Compound of 二極 (two electrodes) and 真空管 (vacuum tube). The term directly describes the device's structure.