H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
H03F3/38—DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers
H03F3/40—DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers with tubes only