Found in a radio amateur magazine of the 1980s, this circuit uses components that can still be found easily. The circuit is for NiCad batteries.
This Motorola circuit is from 1965. Collector currents must be 7 and 12 A for transistors....
This low noise circuit was obtained from a 1980s US RF publication. Transistors used are uncommon...
This circuit generates an audio tone whose frequency depends on R1 and C1. See in the math section...