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 circuit was suggested by Siliconix in a 1980s publication. The circuit uses components from the time...
This amplifier with two FETs in direct coupling (cascode) was found in a 90s Popular Electronics. The...
This circuit uses the 7815 regulator to obtain a voltage for motor control num shield for PC. The...