Tetrode - definition

The tetrode is a four-element electron tube, which is a structural development of the triode, used mainly in radio technology, amplifiers and high-frequency systems. Its construction is based on the presence of four electrodes: a cathode that emits electrons, an anode that collects charge, and two grids - a control grid and a shield grid - placed between the cathode and anode. An additional grid, called a shielding grid, has been introduced to eliminate unwanted electrostatic interactions between the anode and the control grid, which significantly improves the operating stability and amplification performance of the tetrode compared to triodes.

The shielding grid, located between the control grid and the anode, is usually connected to a positive potential and acts as a barrier to limit the influence of the anode's electrostatic field on the electron flow control area. This reduces the phenomenon of feedback, which in triodes can lead to oscillations and deterioration of amplification linearity. This design allows tetrodes to achieve higher voltage gain and operate at higher frequencies.

However, tetrodes are not free from disadvantages. The most serious of these is the phenomenon of secondary electron emission - a situation where electrons striking the anode knock secondary electrons out of the anode, which can be attracted by the shielding grid. This leads to the phenomenon of the so-called 'dynatronic region' in the characteristics of the anode, manifested by non-linearity and a decrease in the anode current when the anode voltage increases. For this reason, tetrodes have been replaced in many applications by pentodes, which contain an additional grid to prevent secondary emission.

Although semiconductor components have displaced electron tubes in most applications in modern electronics, tetrodes are still used in specialised areas such as broadcast technology, high-end audio amplifiers, or military and laboratory equipment, where their characteristics are still valued.

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