A linear amplifier comprises an electron gun assembly having a cathode, and an anode spaced from the cathode. A relatively high voltage potential is applied between the anode and the cathode, and the cathode provides an electron beam in response to the relatively high voltage potential. A control grid is spaced between the cathode and the anode, and is coupled to an input port adapted to receive the input signal. The input signal causes the control grid to density modulate the beam. The control grid is also coupled to a bias voltage source to preclude transmission of the electron beam during the negative half cycle of the input signal. A plurality of collector stages are provided with a respective electric potential thereto ranging between a potential of the cathode and a potential of the anode to efficiently collect the electrons of the beam after passing the anode. A first one of the collector stages is spaced from the anode opposite from the control grid and is further coupled to an output port to provide an amplified output signal therefrom. The respective electric potentials of the collector stages have corresponding voltage values such as to provide near-constant and high efficiency across a power range of the input signal.