Nonlinear Amplification

Author: N.H. Crowhurst

Grid voltage/plate current curves are always that - curved. Because of this curvature, the same change in input voltage will not always cause the same change in output current and voltage. For example, a negative change of 1 volt may produce a 2-milliampere change in plate current, accompanied by a 40-volt change in plate potential (using a plate load resistor of 20,000 ohms); a positive change of 1 volt may produce a 2.5-milliampere change in plate current, accompanied by a 50-volt change in plate potential.

The positive half of a wave will thus get amplified more than the negative half. At the input both positive and negative halves of the wave measure 1 volt, but at the output the negative half is 50 volts, and the positive half is 40 volts. This distortion of the wave is due to the curvature or nonlinearity of the tube characteristic.

Nonlinear amplification causes distorted output