vacuum-type electron tube with five electrodes. Besides the cathode filament, anode plate, and control grid of the triode and the added screen grid of the tetrode, there is still another grid (suppressor grid) placed between the screen grid and the anode plate and maintained at cathode potential. Thus, any electrons emitted from the plate surface by secondary emission (electron tube) are repelled back to the plate. The pentode can be used for almost all purposes for which vacuum tubes are used, including amplification, mixing, oscillation, and pulse generation, and in circuits for timing, control, and counting. Today pentode tubes are primarily used in audio amplifiers (amplifier), because they generate less noise than solid-state components.