We found this circuit in an old documentation, but it is still current. General purpose transistors can be used, and the SCR can be the TIC106. The bell is a transducer with an oscillator (buzzer).
This simple receiver was found in a book on transistors from 1954. The coil determines the...
This configuration, quite common and found in other sites, is from European documentation from the...
The figure shows a simple way to obtain a negative voltage from a common source configuration. The circuit is...