This circuit was found in documentation from the 1980s. Transistors are general-purpose types like the BC548 for NPN and the BC558 for PNP.
This sensor circuit for currents of the order of nanoamperes was found in an American...
The sensor of this circuit is an NTC of 20 to 50 k resistance at room temperature. The circuit is from a...
This circuit is suggested by Texas Instruments in his Optoelectronics Sourcebook. The transistors...