an amplifier level - setting apparatus is provided for obtaining the maximum power output and highest efficiency allowable for a predetermined level of distortion . according to the invention , a training signal is applied to the input of the amplifier prior to the desired signal . the training signal level is increased while the output distortion is measured . when the output distortion level reaches a predetermined limit , the corresponding training signal input level is saved . the input signal level is then adjusted to this saved level value , thereby resulting in the maximum amplifier output level possible that is still within the distortion limit .