It's so simple that you don't need a circuit. The parts you need are as follows:
* Tinned copper wire - about 30cm long for sense antenna
* Germanium diode as used in crystal sets (eg 1N34A, OA95 etc)
* Disc ceramic capacitor - anywhere from 1nF to 100nF
* Analogue meter movement - anywhere from 50 uA to 1mA full scale deflection
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