Pentode suppressor grid

Pentode Vacuum tube with five active electrodes cathode, control grid, screen grid, suppressor grid, plate. 

The suppressor grid of a pentode reduces the effects of secondary emission in the device. This attribute, thus, reduces the requirement to provide a reverse electron flow path for the screen grid power supply. The screen current requirement for a pentode may, however, be somewhat higher than for a tetrode of the same general characteristics. 

Suppressor grid The fifth grid of a pentode electron tube, which provides screening between plate and screen grid. 

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