We found this circuit in an Australian publication from 1991. It is a kit of the time with input for a guitar pickup. The range is a few tens of meters.
This circuit for the power grid was found in the June 1969 Radio Electronics magazine. The SCR and...
This circuit for a commercial compact digital multimeter was found in the March 1979 issue of...
The circuit presented generates short pulses. This configuration was found in a publication from...