From the estate of Adolf Isenthal, an early and unusual form, possibly a prototype, of what appears to be a loose coupler from a crystal radio, constructed on an oak frame, the main large primary coil with copper wire wrapped around small wooden pegs on the outside, the secondary smaller coil constructed similarly but on a helical thread turned via the large wheel at the end, the main winding has a selector with stepped positions on the coil, tubes made of an early plastic material, main supports made from Vulcanite with brass fittings, faults and damage (AF).

Adolf Isenthal, was an electrical engineer who immigrated to Britain in 1889 from Germany. He was an early supplier of X-ray equipment and, in 1898 along with and Charles Potzler set up ‘Isenthal, Potzler & Co.’ at 85 Mortimer Street, London. The company survived until 1925 when it absorbed by the Dubilier Condenser Co. Isenthal also supplied Guglielmo Marconi with electrical equipment.