For a current of 5A and a supply of 6 V this circuit was found in documentation from the 70s. Transistors admit modern equivalents. Q1 is a PUT uncommon today.
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...