Found in a Raytheon transistor manual from the 1950s, this circuit uses one of the first commercially available transistors, the CK722. The circuit is for using a small speaker as a microphone.
This circuit can be used in alarms by activating a relay or a current load that depends on the...
The circuit given below was found in the National Semiconductor Linear Applications Handbook. The...
The current of this circuit is determined by a PNP transistor. The circuit is suggested by Texas...