The unit is a classic from the early 1920s and uses no active parts. Detection is done using a galena crystal and cat's whisker which must be poked around on the surface of the crystal until detection occurs.
Tuning is not done by varying a capacitor; instead it uses two coils in the form of a variometer. By rotating the tuning knob the inductance is changed thereby moving the resonant frequency of the tuned circuit. For reception of long wave stations, an additional coil was plugged in between two sockets. There are facilities for two antenna lengths (one is coupled by a small capacitor) and two sets of headphones: in the early 1920s it was not uncommon for two people to listen at the same time.
Inside the lid is a white paper instruction sheet showing how to use the unit. The front of the case has the BBC type approval symbol on it.
I connected the receiver to my usual 15m long wire down the garden and managed to receive Radio 5 on Medium Wave at reasonable strength with a pair of SG Brown high impedance headphones connected. Had I played with the cat's whisker a bit longer I might have managed a few other stations. Selectivity was not good, but this is an 85 year old radio remember.
This is the schematic of the receiver.
Gecophone article on the Early Wireless site with schematic and good photos.
Vintage radio web a Dutch site with lots of data on vintage radio including a page on the Gecophone.
A Gecophone copy a Gecophone copy made by a skilled engineer.