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.
We found this circuit with an operational transconductance amplifier in the Motorola Linear...
Originally the circuit in the figure is indicated by National for the control of an electronic car injection...
This small two-transistor amplifier was found in the April 1994 issue of Electronics Now magazine. This...