ATM (automatic telephone manufacturing company) crystal set 48308, c1923 It has the BBC logo on it. A label inside reads…Plug in No. 150 coil for Daventry. For local station insert a short circuiting plug into coil holder.

One hinge is missing, the other is broken. A reason for this damage may be the short-circuiting plug installed at the rear of the set. This plug is too tall to fit in the case with the lid closed. The retaining screws are also missing from main panel, so the entire chassis can easily lift out. Terminal screws are missing from phone 2.

The crystal set was a simple radio receiver which did not need any power to make it work. It only received AM, amplitude modulated, signals. The crystal, with a point contact, called a cat's whisker as that was what was sometimes used, on its surface, created a diode action rectifying the carrier wave so making it possible to hear the audio signal which was modulated onto it.