Colourful Parallel-tuned Air-core Coil Crystal Radio

This is a colourful version of my Crystal Radio with Air Core Coil.

Crystal Radio with Air Core Coil - Schematic
The coil is 75turns of hook-up wire, close-wound on a 2 ⅝" diameter plastic bottle, with a tap at 35 turns.

The 35 turn primary series-tunes the capacitive 60' wire antenna to resonance at 612kHz (frequency of the lone 200kW local AM broadcast station). The secondary is parallel-tuned using a 500+500 pF PVC gang condenser.

Crystal Radio with Air Core Coil
The plastic bottle serves as the coil former cum enclosure. A screw-type terminal strip is used to connect antenna, earth and headphones.

Reception, using sensitive balanced-armature headphones, is quite good. Headphone current, measured using a 1mA FSD 60 Ω meter, is 400 μA.