A ‘Magic Eye’ is a specialised vacuum tube that was typically used in old radios as a visual indicator of reception signal strength to aid the user when tuning into a radio station. In the case of the EM81 tube type utilised on the Binson Echorec, visual indication is in the form of green ‘fan’ which close up as the signal level increases, eventually overlapping to indicate overload (see figure 1 below). The green light is caused by a stream of electrons, emitted from the cathode and controlled by the grid, hitting the “target” electrode, which is coated in a layer of phosphor. The phrase “magic eye” became a trade-mark of Radio Corporation of America (RCA) in the mid 1930s, but the device was also known as the “tuning eye” or “cat’s eye” as well as its technical name, the cathode-ray indicator. Occasionally, sceptics would describe the magic eye as the “idiot lamp”, the implication being that radio owners who were not savvy enough to tell if their radio was tuned-in properly using their ears were idiots.
