This circuit was found in the October 1989 issue of Radio Electronics magazine. It drives an auxiliary relay with the call signal for a possible louder bell.
This amplification stage circuit with a germanium transistor was found in a 1980s documentation. The...
In the figure we have the way to obtain an adjustable constant current source of 2 mA. The...
The circuit is from an old documentation making use of an operational amplifier of the time. The...