Series-tuned Ferrite Loopstick Crystal Radio

This series-tuned, shunt-fed crystal radio is housed in a plastic pencil box.

Series-tuned Ferrite Loopstick 
Crystal Radio
It has 2 windings of 30 SWG enamelled copper wire on a 6" long, 3/8 " diameter ferrite rod. The primary has 10 turns and the secondary 90, both close-wound.

Series-tuned Ferrite Loopstick
Crystal Radio - schematic
The primary series-tuned circuit, which includes the 200μH moulded inductor, the 3600 pf capacitor and the capacitance of the 60' wire antenna, is resonant at 612 kHz (the frequency of the local 200 kW station, located 20km away). The secondary is also series-tuned using a 500pf PVC variable capacitor. The detector, a germanium transistor with its base and emitter connected, shunt-feeds sensitive balanced-armature phones.

Series-tuned Ferrite Loopstick
Crystal Radio - inside view
Reception of the local station is quite good with headphone current being 625 μA (measured using a 1mA FSD 60 Ω meter).
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