The Radio ClearaTuner is attached to the Arial Wire to give you greater distance, more volume greater selectivity, less static, better tone quality and less interference. It is an interesting accessory for crystal radio users, because the ClearaTuner attaches to the crystal radio; to make it a two tuned circuit. There is also special fixed condenser, that is mounted to the ClearaTuner; that tunes your Aerial, with the the coil slider.
There is a antique type capacitor; that is connected between the two vintage copper Fahnestock Wire Clips. The original coil tuner knob was replaced, on the ClearaTuner Crystal Set.
Radio History TimeLine - spartaotr.com
ClearaTuner Crystal Set - oldradios.co.nz