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Pentode
From Wikipedia, the free encyclopedia
A pentode is a multi-grid vacuum tube, which was invented by the Dutchman Bernhard D.H. Tellegen in 1926.
A tetrode could supply sufficient power to a speaker or transmitter, and offered a larger amplification factor than the prior art triode.
However, a tetrode showed secondary emission of electrons from the anode, which caused increased current toward the screen grid, and caused the anode current to decrease with increasing anode voltage over part of the Ia/Va characteristic. Tellegen introduced an additional electrode, called the suppressor grid, which solved the problem of secondary emission.
Pentode valves were first used in consumer-type radio receivers. A well-known pentode type, the EF-50, was designed before the start of the World War II. The EF-50 pentode was extensively used in radar sets and other military electronic equipment. The pentode contributed to the electronic preponderance of the Allies. After WW II, pentodes were widely used in TV receivers. Vacuum tubes were replaced by transistors during the 1960s. However, pentodes (and triodes) are still appreciated by a number of audio enthusiasts for their unique distorted valve sound.