6977 / DM160 Tuning Eye Tube  
Written by AnubisTTP on 2007-10-06  


At a mere 25mm in length, the 6977 is considered by most tube collectors to be the world's smallest eye tube, although referring to this device as an eye tube is not strictly accurate. Though the 6977 has a control grid, the indicator region does not vary in size relative to the control grid input signal. Instead, the control grid simply varies the brightness of the glow. That being said, the 6977 is a unique device, a subminiature triode with a phosphor coating that visually indicates the tube's internal state. The 6977 was originally designed as a logic indicator for early computer systems, but saw nearly as much use as a triode for battery powered radios and similar devices.


The 6977 "magic eye tube" operates at 30 volts.

6977 indicator with US quarter for scale.

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