H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
H04B1/06—Receivers
H04B1/16—Circuits
H04B1/20—Circuits for coupling gramophone pick-up, recorder output, or microphone to receiver
Poste telephonique comportant un preamplificateur a courant porteur, un interrupteur de coupure de micro et un dispositif de signalisation de cette coupure