What you have is infact a vacum fluorescent display(VFD) that was used extensively in all sorts of consumer electronic products, mainly stereo's & VCR's. In general, you had a filament pin on either side of the tube assembly that was very much like a vacum tube and HAD to have an AC input(1.5~3.3vAC) from the main power transformer and the rest of the pins were driven by a timer/driver IC.
The two main manufacturer of tubes were NEC & FUTABA and while they were easy to work with, the main disadvatage was the fact that after certain amount of usage, the internal emission would start to decrease which translated in to dimmer segment outputs and often it was not uniform throughout the display. I used to run across many where half or just a section would be dimmer than the rest.
Other than replacing the tube, depending on the configuration of the circuit, you could increase the brightness by increasing the reference zener(segment drive voltage) or increasing the AC but it would rarely be uniformed. If the entire display was rather dim yet working, you could get a much better result but still it would be a matter of a time before having to replace it.