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.
This 1.5 A source for FM transmitters was originally intended for the transmitter described in...
This circuit is from the 80's component manual itself, but can be applied to more modern...
We find this circuit in an American 1980s documentation. Integrated circuits are uncommon today as...