This circuit needs a a Faraday shield, which is connected to 0V.To make this one wrap a tin foil around the coil.and connect to 0v.Then you can use this circuit for find metal.Tune your mw radio until whistle sound comes.
# This circuit operates with 12V power supply
# IC1d pin 11 needs to be attached to a MW radio aerial, or should be wrapped around the radio
# The prototype used 50 turns of 22 awg/30 swg (0.315 mm) enamelled copper wire, wound on a 4.7"/120 mm former. This was then wrapped in insulation tape.