There is presented a comparative analysis of MBK and TWT parameters, and their influence on the spectrum of functions, which each of the devices is best suited to fulfill. Devices of different power level (from hundreds of watts to hundreds of kilowatts) and frequency range (from units to tenth of GHz) are analyzed. Most decisive parameters, namely, the cathode and control voltages, efficiency, the amplification frequency band, the noises, harmonic and spurious oscillation parameters, the sensitivity to voltage instabilities, and the mass and dimensions of the devices are considered. In specific fields of operation the vibration‐proof parameters of the device is also of great importance. Interrelations between some of the devices’ parameters and the parameters of radio — electronic systems are discussed. Main requirements are mentioned, which power amplifiers have to meet to satisfy the demands of different types of modern radio‐electronic systems. The degree of satisfying these demands by MBKs and TWTs determine the preferable fields of their application. © 2003 American Institute of Physics