Amplifier by their physical placement in the signal chain; a preamplifier may precede other signal processing stages, for example. The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors. The first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when the transistor, invented in 1947, replaced them. Today, most amplifiers
Triode limited frequency range and fidelity. It was suited only to a limited range of audio frequencies - essentially voice frequencies. The triode was the first non-mechanical device to provide power gain at audio and radio frequencies, and made radio practical. Triodes are used for amplifiers and oscillators. Many types are used only at low to moderate frequency and power levels. Large water-cooled triodes may be used as the final amplifier in radio transmitters, with ratings of thousands of watts. Specialized types of triode ("lighthouse" tubes, with low capacitance between elements) provide useful gain at microwave frequencies. Vacuum tubes are obsolete