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
Virtual Valve Amplifier (amplifier class A), to make only one side conduct at a time (class B), or intermediate (class AB). Class A uses more power for the same output (i.e., is less efficient), can produce less output power from the same devices, and produces lower distortion, than classes AB and B. These devices generally consisted of a 12AU7 medium-mu triode driving a single 6L6GC beam power pentode audio output valve or similar. Its effects are distinctive due to convolution of the non-linearity of the triode interacting with those of the pentode, with both devices operating in class-A mode. The 6L6GC is similar