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 multiple thermostat circuit in July 1980 Radio Electronics magazine. It uses...
Other operational amplifiers can be used on this unit gain amplifier. The circuit is from the 1993...
This interesting circuit with an indicator tube powered by a transistor inverter was found in...