An amplifier system. The amplifier system includes a vacuum tube amplifier, an electron source voltage modulation circuit, and a linearization circuit. The vacuum tube amplifier includes an input signal terminal and an output signal terminal. The electron source voltage modulation circuit includes an input terminal coupled to one of the input signal terminal and the output signal of the vacuum tube amplifier, and includes an output terminal coupled to one of an electron source of the vacuum tube amplifier and an interaction region of the vacuum tube amplifier. The linearization circuit is coupled to the input signal terminal of the vacuum tube amplifier. In conjunction with or instead of the electron source voltage modulation circuit, the amplifier circuit may additionally include an electron beam control circuit, including an input terminal coupled to one of the input signal terminal and the output signal of the vacuum tube amplifier, and including an output terminal coupled to the electron source of the vacuum tube amplifier.