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EM81 MULLARD TUNING INDICATOR or MAGIC EYE, 1960's

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EM81 MULLARD TUNING INDICATOR or MAGIC EYE, 1960's

Mullard EM81. The tuning indicator tube, or "Magic Eye" as it is was called when introduced by RCA in 1935, was used to display the optimum signal tuning point of a tuner/receiver, or the peak signal level of a preamplifier or tape recorder,this is Mullard's 1960's version. 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 reflective arched disc inside called the target. 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 shown has an arched disc inside that is illuminated on the sides of the bottom edge as the signal is increased the two illuminated edges move towards each other in an arc until they touch at full signal.

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