Pentode

A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube (thermionic valve), which was invented by the Dutchman Bernhard D.H. Tellegen in 1926. Pentodes (termed "triple-grid amplifiers" in some early literature) are closely related to beam tetrodes, and an improvement over conventional tetrodes, which were themselves a development of triodes.