Although new version of IV-18 VFD seems working great, but its luminance is too small compare with first one with same voltage, I've check every thing from high voltage ripple to HV5812 scanning code, but still not found where the problem is.

When I comparing both tubes, it seems to have two types.

first one, I brought cuple month ago, which is military grade type of IV-18

the military mark is at the back of the tube.

second one seems to be civil grade of IV-18

other than the mark at the back, both plate that contain deoxidants and the white paint to cover the mark is less than military grade type of IV-18.

So, I'm thinking that if civil grade needs higher voltage than 30V?

current step-up design can handle up to 40V, so maybe I'll try how it performs on higher voltage.