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 triac circuit was taken from an article in the July 1970 Radio Electronics magazine. Note the...
Signals ranging from a few millivolts to a few volts can be used to excite a relay with this...
This circuit was found in American documentation from the 90's. The transformer determines the...