Tetrode tube amplifiers are used worldwide in both laboratory and EMC testing applications. They are known for their reliability, durability and excellent performance. A tetrode is a vacuum tube having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate.

There are several varieties of Tetrode, the most common being the screen-grid tube and the beam tetrode. In screen-grid tubes and beam Tetrode, the first grid is the control grid and the second grid is the screen grid. In other Tetrode one of the grids is a control grid, while the other may have a variety of functions.