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
Pentode to give the sought-after "sonic qualities" of a triode power amplifier. A resistor may be included in series with the screen grid to avoid exceeding the screen grid's power or voltage rating, and to prevent local oscillation. Triode-connection is a useful option for audiophiles who wish to avoid the expense of 'true' power triodes. Pentode A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid amplifying vacuum tube (thermionic valve), which was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode consists of an evacuated glass envelope containing five