We found this circuit in a 1957 Raytheon transistor publication. The circuit can be assembled with more modern transistors with minor changes. The handset must be high impedance magnetic.
This circuit generates a sinusoidal signal with only -80 dB THD. The circuit was found in a 90's...
Suggested by a 90’s Radio Electronics, this circuit automatically activates the recording switch of an...
Found in American documentation from the 90s, this circuit triggers a buzzer with a Sonalert-type...