The possibility to amplify waves in the waveguide or strip line penetrated by a transverse electron beam has been considered. Electrons can be emitted by FEAS or an extended thermionic cathode located along the line. The structure using FEAS is similar to the microtriode amplifier, but the input signal is supplied into the anode line instead of the cathode one. Wave amplification along the waveguide or line can be achieved due to the well-known effect of negative conduction of electron beam, used formerly in oscillating monotrons with cavities. If the transit angle of electrons drifting across the waveguide or line is 2π <θ <2.8π, the electrons at an average give the energy to the electromagnetic field, and if the current density is sufficient, it becomes possible not only to compensate losses, but to amplify the signal in the frequency band. The amplifier designed on the basis of this principle may be called a polytron. The analyses of polytron has shown that the amplification of millimetric waves is possible for the existing current densities being provided by thermionic cathodes or by FEAS. For example, minimum current densities Je,min providing the loss compensation in copper waveguide are Je,min =73 A/cm2 when λ=2 mm; Je,min =13 A/cm2 when λ=4 mm; Je,min =2.3 A/cm2 when λ=8 mm. The value of amplification depends on the difference between the working current density and the minimum one and the required distance between wide walls of the waveguide or between strip-line conductors makes up 10’s to 100’s of microns. The conducted analysis has shown the proposed principle of amplification in vacuum microelectronics to be promising.