This amplifier for electrometer can work with currents of 0.1 pA in a band of 1 Hz. The circuit is from NASA in a publication of the 60s. Transistors are general purpose types.
This circuit was found in a 1977 publication, but it can be easily assembled, although unijunction...
This alarm circuit was found in a 1982 publication. It uses components that can still be found...
Found in 90s 303 Circuits, this circuit is intended for interfacing analog black / white computer...