For those unfamiliar with the Primitive Line Circuit Diagram art school, Xtal is often used as an abbreviation for Crystal. One art critic suggested that Tjilpi's original lino cut masterpiece had something of the appeal of Mr Magoo or Foo, if the image were rotated 90 degrees counter clockwise. While appreciating this reference, Tjilpi prefers the name Xtalman.
Crystal Radio Sets, the making of which was a popular hobby in the 1930s, used a crystal of galena - lead sulphide - the ore from which lead is obtained, as a detector, or what is now known as a diode, to demodulate the audio signal carried by an amplitude modulated [AM] carrier wave. A "cats whisker" made of metal wire, wound into a coil with a probing tip, was moved around on the crystal of galena until a 'hot spot' was found and a station was heard through the headphones: seen on the right of the diagram looking reminiscent of "Foo" looking over a fence. On the right of the top line is a left-pointing triangle with a rectangular block beside it. This is the symbol for a diode - a piece of electronic trickery originally made using the element Germanium - which replaced the galena crystal. Even when a Germanium diode is used in place of a piece of galena - the radio - which functions without batteries as it only needs the energy gathered by its antenna, is still known as a Crystal Set. A simple radio such as this will receive many stations at once, as it has no means of selecting one from the other. In order to make such a radio selective, a tuned circuit is added to pick out stations operating on different frequencies. The addition of a capacitor, represented by the bright white lines with horizontal bars mid-left circuit, is one way of doing this, and that is why Xtalman has "added capacity" to his original form, which may be seen in a post below.
Rapid changes in technology have not only seen galena suitable for use in crystal sets difficult to obtain, but Germanium diodes are equally hard to find. Tjilpi has fond memories of making crystal set radios with both types of detector when he was a weeaye of about twelve summers, so if anybody is having difficulty wondering what he would like for his birthday: there's a hint.
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