This circuit is from Popular Electronics from March 1991. It can still be assembled with the original transistors or BC548 in place. FILT1 is a 455 kHz ceramic filter, which can be found on some old transistor radios. L1 is the exploration coil and is formed by 10 turns of wire 26 in a plastic form about 10 cm in diameter. The circuit is powered by a 9 V battery and the adjustment made in the variable C9, obtained from an old transistor radio.
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