Re: What is it?
I would suggest, that the bottom control with scale, is a variable cap as its travel is only 180 degrees. Yes I know there are pots that do this as well, it still adds up to a null control.
I would be VERY interested to see the circuit. I imagine one valve ( two halves ) will be an oscillator and buffer to reduce impedance, the second pair of triodes will drive the null on the magic eye. Most magic eyes are rather lazy when it comes to sensitivity after all.
Just thinking out while typring.
Joe
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