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).
When S1 is pressed, the circuit allows music to be played from an audio source on the telephone line....
This circuit was found in an Experimenters Handbook of the 1990s. The purpose of this circuit is to...
The action of this circuit, found in a 1977 amateur radio documentation, is like to a delay line....