This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
This circuit is from an 80's publication. The basic components indicated are of the time, mainly...
This circuit is from an 1977 American publication. The coil consists of 30 + 70 turns of 28 AWG...
The circuit shown in the figure is indicated for alternative sources of energy, such as those...