Loudspeaker Crystal Radio

This is the speaker variant of my series-tuned crystal radio with an alternative detector.

Loudspeaker Crystal Radio
Replacing balanced armature headphones (impedance around a few hundred ohms) with a low impedance speaker required the use of an output transformer.

A power transformer, with its inherent thick conductors, appeared to be the ideal substitute for a low-loss output transformer.

Trials with transformers rated 230V/24V-2A, 230V/24V-5A and 230V/24V-15A proved the last one to be the best.

Series-tuned Loudspeaker 
Crystal Radio - Schematic
Aided by the perfect match offered by my 'Homebrew Horn Speaker' and 60' wire antenna, reception of the lone local 200kW 612kHz AM broadcast station, located 20km away, was excellent.

Performance was also quite good using the parallel-tuned configuration.

Parallel-tuned Loudspeaker
Crystal Radio - Schematic
Related post: Compact Loudspeaker Crystal Radio