This circuit was found in an Electronic Engineering of the 80s. The circuit indicates when a telephone line is being used, being useful in case of extensions.
The circuit in the figure is based on two integrated LM108 and its gain is basically determined by the...
Found in a 1968 Ferranti documentation, this circuit can be implemented with modern equivalent...
This amplifier stage was equipped with a Motorola radio from the 70s. The transistors were from...