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Low-Pressure Gas Thermionic Triodes and Tetrodes

The gas triode contains an oxide-coated thermionic cathode, a control grid, and an anode. Although the grid is called a control grid, it can control the operation of the tube only under certain conditions; for other conditions it loses control.

circuit of a mercury-arc rectifier
Figure 6. Simplified circuit of a mercury-arc rectifier.

In this tube, often called by the trade name Thyratron, the control grid is so designed that for certain anode, or plate, voltages the negative grid is able to block the tube and prevent electron flow from the hot cathode to the plate. If the grid is made less negative or the plate is made more positive than critical values, the grid loses control, electrons suddenly flow to the positive plate, ionization by collision occurs, and the plate passes a current largely controlled by the external resistance in the plate circuit. In the gas tetrode, a second grid is arranged so that the control characteristics can be varied.



Last Update: 2011-05-30