This sound relay or Vox was found in 70s RCA documentation. SCRs can be common types today and transistor a BC558. The circuit is for the 110V power grid.
Found a documentation for PC from 1992, this circuit is indicated for the English power grid of...
September 2017 - Panasonic Dy2L TVS diodes for network applications, security, medical equipment,...
We found this circuit in the May 1996 Electronics Now magazine. The relay must have a voltage...