This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
The setting of this power supply is only 0.1%. We found it in a 1969 US documentation. Transistors...
We found this interesting transistor generator in European documentation from the 1980s. The...
The circuit shown in the figure uses two of the four operational amplifiers found on the LM324...