Transistor radio
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 Beginning in the 1980s, however, cheap AM transistor radios were superseded by devices with higher audio quality such as portable CD players, personal audio players, boomboxes, and (eventually) smartphones, some of which contain radios themselves.
Magnetic amplifier
In 1904 radio pioneer Reginald Fessenden placed an order for a high frequency rotary mechanical alternator from the General Electric Company capable of generate AC at a frequency of 100 kHz to be used for continuous wave radio transmission over great distances. The design job was given to General Electric engineer Ernst F. Alexanderson who developed the 2 kW Alexanderson alternator. By 1916 Alexanderson added a magnetic amplifier to control the transmission of these rotary alternators for transoceanic radio communication.