This circuit was found in an old American documentation. It can operate with signals from 40 Hz to 50 Hz and the input voltage range is from 0 to 200 mV.
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...