This simple metronome, from 1985 documentation uses only transistors and has two settings. For voltages above 6 V, up to 12 V, replace the BC557 with a BD136.
Found in a Popular Electronics from the 90s, this circuit operates up to about 5 MHz input....
This circuit was found in a 1987 edition of the United States' Hands-On Electronics magazine. The...
This circuit that uses potentiometer tuning, was found in a documentation from the 80's. The...