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 simple toy organ circuit in the February 1968 issue of Radio Electronics magazine. The...
In the figure we have a practical circuit for use with a magnetic transducer. The 20 M ohms...
This circuit was found in a Motorola documentation from the 70s. The components are from the time,...