This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
In the figure we have the typical configuration of a voltage regulator based on an operational amplifier....
Found in 1969 Ferranti documentation, this small font is characterized by its low ripple....
We found this circuit in a 1980s publication on telephony. The circuit uses an integrated...