De Forest Audion
From ETHW
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United States. On 25 October 1906 Lee de Forest submitted a patent application on a "Device for amplifying feeble electrical currents", which included the first form of the 3-electrode Audion. The device and its later improvements became the standard, allowing for inexpensive amplification of wireless voice signals among other amplification uses. It remained in widespread use until replaced by the transistor.
