This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very high frequencies. These are not currently easy to obtain components.
This power supply, found in an Argentine publication from the 1970s, uses a wire potentiometer of 25 W or more...
This circuit was found in a 1968 EEE and can be implemented with any current general-purpose transistor....
The transistors of this 12 V x 150 mA power source can be BC558 for PNP and BD135 for NPN. The...