Beam tetrode

A beam tetrode, sometimes called a "beam power tube", is a type of tetrode vacuum tube (or 'valve') with auxiliary beam-focusing plates designed to augment power-handling capability and help reduce unwanted emission effects. These tubes are usually used for power amplification, especially at audio-frequency.

History

The problem of secondary emission from the anode (US: plate) in the tetrode tube was solved by Philips/Mullard with the introduction of a suppressor grid to produce the pentode construction. Since Philips held a patent on this design, other manufacturers were keen to produce pentode type tubes without infringing the patent. In the UK, two EMI engineers, Cabot Bull and Sidney Rodda, produced and patented an alternate design in 1932. Their design had the following features (compared to the normal pentode).