This PUT circuit was found in a 1967 General Electric SCR manual. The basic component is unusual, and the capacitor must be low-leakage.
A circuit for controlling the temperature of a heating element was found in a Mullard transistor manual...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...