This circuit is for old telephones with analog lines. It was found in the May 1988 Radio Electronics magazine. The circuit is powered by the line signal voltaje.
Using the Texas Instruments SN75489P this circuit was found in June 1978 Radio Electronics...
We found this circuit, which should only be used with incandescent lamps. In the Motorola Linear...
Found in Electronics Now from the 1980s, this amplifier can also be seen in commercial amplifiers...