五極管

thumb|upright|Graphic symbol representing a pentode of the indirectly heated cathode class Electrodes, listed from top to bottom: anode, suppressor grid, screen grid, control grid, cathode A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called a triple-grid amplifier in some literature) was developed from the screen-grid tube or shield-grid tube (a type of tetrode tube) by the addition of a grid between the screen