This powerful sound emitter used in defense to intimidate people was found in a 90s Popular Electronics. The circuit produces a strong modulated tone of 3 kHz. The modulation is 10 Hz.
This sound relay or Vox was found in 70s RCA documentation. SCRs can be common types today and...
We have here a very interesting project found in a 1982 publication. By the operation of the...
This circuit was found in a European publication from the 1980s. The operational amplifier is not...