Found in a 1964 Electronic Design, this circuit makes use of period components. The components are from the time, and modern equivalents can be used.
This configuration of PWM control with the LM317 was found in a Popular Electronics from the 90s....
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in Signetics documentation from the 90's. The circuit performance curve is...