This circuit was found in a 1967 General Electric manual. It shows a SCR control with unijunction and zener diode. The triac depends on the controlled load.
This interesting adjustable power supply uses the transistors themselves as controllers and...
The operating system used in this circuit of the 1994 Linear Applications Handbook by National...
Found in Unitrode documentation from the 1980s, this circuit makes use of PUTs, currently common...