This adjustable circuit from 0 to 200 nA was found in a 90's EDN. The components can still be found relatively easily, as they are CMOS.
This circuit appears in several versions in publications of the time and can be modified by...
This configuration with FET and Unijunction can be found elsewhere on this site. The JFET admits...
We found this circuit in a Popular Electronics from the 90s. It operates at a frequency of 15 kHz....