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.
We found this circuit in an old American documentation. The circuit is suitable for motorcycles and...
Found in a 90’s 303 Circuits, this circuit uses components that are still common and has a common...
The interesting circuit shown in the figure can have its gain digitally controlled and have two...