The Radio Board.org
A makeshift piezo earphone arrangement comprises a stethoscope and a piezo transducer.
Stethoscope
The sound emanating from the transducer is captured by the bell of the stethoscope held against its face.
Piezo Transducer
A Germanium transistor may be configured as a diode, having its forward voltage as low as 0.1 V, by just interconnecting its base and emitter.
Basic Shunt-fed Crystal Radio
It makes for an ideal detector in a shunt-fed crystal radio.
A medium wave broadcast station antenna system generally comprises a ¼ λ vertical element
and earth.
It would not be wrong to infer that such an antenna would be ideal for a crystal radio.
Crystal Radio Antenna Arrangement
However, practical reasons necessitate use of a much shorter element, with a suitable loading
In a ham shack, either half of a 40m inverted ' V ' dipole antenna would come in quite handy
as a usable crystal radio antenna element.
Handy Crystal Radio Antenna
However, a suitable loading coil would be required to make it resonant at the desired frequency.