This circuit was found in an American documentation from the 80's. The components are from that time. It provides a variable output of 18 to 30 V with a current of 200 mA.
This is a 1960s amplifier setup found in a period publication. The circuit uses a special driver...
This circuit was found in an American transistor book from the 50's. The indicated transistors are germanium...
In fact, we can say that this circuit found in documentation from the 90s, consists of an intercom...