A type of vacuum tube that consists of five elements (hence the name), the cathode, the plate, the screen grid, the supressor grid, and the grid. The pentode solves many problems found in the triode and the tetrode. It was invented in 1926 by Jobst and Telegen, and found application in amplification equipment, just like its predecessors, the triode and tetrode.
The addition of two extra grids reduces the phenomena of secondary emission and stray capacitance. It also smooths out the amplification curve, reducing distortion. Some disadvantages are the increased cost and increased circuit complexity, because five elements have to be connected, instead of just three or four, and the extra noise caused by the extra circuit elements.