I had one for Xmas in the early 60s. I think my Dad bought it from The Army and Navy Store, the headphones looked military like with a black metal headband, Bakelite ear cups and khaki coloured wire which attached to two terminals on a wooden box with a speaker like grill on the front , though it emitted no sound! I couldn't understand how it could work, having no power supply and was even more confused when I took the back off to reveal a couple of soldered wires and what looked like a glass filament. The only connection to the box as I recall was a wire which was attached to a earthing rod outside in the garden? I think he bought them for my cousins too and later made one for himself, though this one was powered by a small battery, maybe this was an early attempt at making a transistor radio?Before I could stretch to a transistor radio, as boy I made myself a crystal set from parts bought from a shop in town, whose name I can't remember. Having soldered the few components in accordance with a circuit drawing I had, and spread a thin wire around my bedroom ceiling to act as an aerial, I could twiddle with the little tuning device and sit up late at night listening to Radio Caroline and other stations on my little bakelite headphones. Does anybody else remember their crystal set?