In early crystal radios a piece of Galena was mounted in a Wood’s Metal holder. A modern silicon diode could be used, but would not be as efficient as Galena or Germanium. Germanium also has a low band gap and was used in commercial diodes and transistors. Galena has a very low band gap which make it very efficient at converting the AM radio signal into sound. Galena, which is lead ore or lead sulfide, was one of the most common minerals used to make radio detectors. There are many crystalline minerals that can be used to make a point contact diode. The conversion device was called a detector, but in modern terms is a point contact diode. A crystal radio needs a device to convert the amplitude modulated radio signal into a signal that can drive headphones or a speaker.
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