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.
I found this circuit in an old Argentine publication from 1973. The components are no longer...
This circuit has an LED indication of the timing progress, having been found in an old...
This simple signal tracer was found in a Popular Electronics from the 90's. The transistor can be a...