'Magic Eye' tuning indicators were used to assist accurate tuning of radios. They were driven by the AVC voltage which goes more negative with increasing signal strength. This example has dual sensitivity. The EM4 had dual sensitivity with one pattern closing at -5 volts and the other at -16 volts; this made it useful over a wide range of signal strengths. 6.3 volt indirectly heated cathode at 200 ma. anode 250 volts.

Physical Description

Tubular glass bulb has been almost completely removed revealing the valve's internal structure. Part of the glass is separate from the object. Base with 8 side contacts (P base). Mounted on display block.

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