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 circuit, which operates between 7 and 30 MHz, was found in Radio Electronics from the 1980s....
This circuit was found in an old American magazine for radio amateurs. The circuit is based on a...
This low current circuit allows the regulation of voltages in the range of 0.5 to 30 V. We find it...