The selected circuit was found in GE's 1977 semiconductor manual. 3N84 is a controlled silicon switch and SCRs support equivalents. The transistor can be a BC558, depending on the supply voltage.
This circuit was found in Radio Electronics from the 90s. The transistor is for general use. The...
We found this circuit in a 2005 Linear Technology application manual. The circuit makes use of a...
This circuit is from 1971 American documentation. Transistors are still common except for 2N2060...