Soviet IV-6 (??-6) is a regular VFD. (In fact, IV-** denotes an VFD, "IV" stands for Russian "Indicator Vacuumnyi" in Russian, no translation is needed, I think
). However there are two or three models that have IV-** marking but are no VFDs, nobody knows why.
Just like any other VFD, IV-6 is operated just like any vacuum triode. Filament voltage is 1.2 V rated, voltages between 1.0 and 1.35 V are permitted. Pins 7 and 8 are filament and directly heated cathode. A positive voltage should be appliet to the grid (pin 9) and anodes (all other pins). Pin 12 is cut and used for a key. Each anode corresponds to a segment, and manipuulating grid voltage can be used for multiplexing.
Rated anode voltage is 27 V (25 to 30 V) and 0.5 mA constant current. But it works even at 12V or less so you may use regular 40xx series ICs with them.
Simpliest usage: apply 1.2 V between pins 7 and 8, connect pin 8 to ground. Apply positive voltage 12...27V to pin 9 and to one or more other pins. You may connect pins 1-6, 9, 10 and 11 directly to outputs of 40xx logic.