The 'large-particle' method serves as the basis for proposing a numerical cylindrical model of an amplifier with a drift space. The model makes it possible to analyze the interaction processes in the device: buildup of the space charge, formation of the amplification region and stable electron configurations, and processes in the device: buildup of the space charge, formation of the amplification regime and stable electron configurations, and processes in the drift region. The following basic dynamic characteristics of a typical amplifier are calculated: the volt-ampere, operating, and range characteristics. The calculation results are compared with experiment.