Built on vacuum tube technology, the triode provided the ability to turn an electrical circuit on or off using current flow.
基于真空管技术，三极管提供了使用当前电流打开或关闭一个电路能力。
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In those days the only reliable vacuum tube was the Western Electric repeater triode, and if one needed a variable resistance he wound a lot of wire on a wooden spool.
在那个时候唯一可靠的真空管就是Western Electric 中继器三极管，而如果需要变阻器时，就用金属丝缠在木卷轴上自己做一个。