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MAIN PURPOSE: Build a radio that needs no battery and plays AM stations from the radio waves alone
A radio with no battery, no plug and no power at all: the radio waves themselves drive the earpiece. Wind a coil on the tall tube, screw the aerial, ground, diode and earpiece wires to the six terminal holes, and slide a wire along the coil to tune in. This is how people listened in the 1920s, and how soldiers built "foxhole radios" from razor blades in the Second World War. It is quiet and magical: a voice from far away out of nothing.
Printing notes
74.7 cm³
Volume
92.7 g
Est. weight
7,316
Triangles
Wind about 60 turns of 0.3 mm enamelled wire on the tube; use a 1N34A germanium diode, a crystal earpiece, 20 m of aerial wire and a ground to a metal water pipe. Prints as shown on its floor, no supports.