Found in old documentation, this circuit makes use of amplifiers of the time, uncommon today. Next to the diagram, the formula for calculating the components.
This Power supply is intended to Power small loads with currents up to 30 mA. The voltage depends...
This setting appears multiple times on the site from different sources. This is from a 2000 manual...
The transistor in this circuit can be the BC548 or any general-purpose equivalent, and the phone...