This circuit was found in a 1966 General Electric book. The triac and the day are from that time and can be replaced by modern equivalents depending on the load.
We found this good power amplifier with the LM12 integrated circuit in the March 1989 issue of...
This simple circuit produces a tone when triggered by any vibration picked up by the sensor. The...
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...