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EM84 MULLARD TUNING INDICATOR OR MAGIC EYE, 1960's
The Mullard EM84 front viewing tuning indicator. The tuning indicator tube, or "Magic Eye" as it is was introduced by RCA, in 1935. It was used to display the optimum signal tuning point of a tuner/receiver, or the peak signal level of a pre-amplifier or tape recorder. This is Mullard's latest version
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The main benefit in tuning reception was for FM tuners where the exact tuning point was harder to determine than for AM. The indicator tube is a standard thin glass tube envelope with a fluorescing strip inside just beyond the target anode. The electrode structure is based on a double triode with common cathode. The anode of the second triode is called the target and within the electron stream is a deflector electrode designed to alter the path of the electron beam, it would normally be connected to the anode. The tube has a white strip inside mentioned above that is illuminated on the ends as the signal is increased the two illuminated edges move towards each other until they touch at full signal.
The Museum can demonstrate several different "Magic Eyes"