Winker using 3 6977 (aka DM160) magic eye tubes. These tubes are different from common eye tubes, like the 6E5, or EM81. Common eye tubes have a 'real' amplifying triode, which makes a winker circuit simple. The triode on the 6977, is the display element itself. A 6977, is like a segment on a VFD display, and the triode is not intended to be used for amplification. That's why 3 are needed (at the absolute minimum) to make a (barely) sustainable phase shift oscillator.