Pentode cathode

FIGURE 5.6 Four standard grid tube representations (a) triode, (b) tetrode, (c) pentode, (d) beam power, (e) cathode types. 

FIGURE 5.16 Pentode audio amplifier circuits (a) audio amplifier with fixed bias, (b) audio amplifier cathode bias (self bias). 

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

In usual tetrode and pentode structures, the capacitance from screen-to-grid is approximately half the published tube input capacitance. The tube input capacitance is primarily the sum of the grid-to-screen capacitance and the grid-to-cathode capacitance. 

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