6lo4v datasheet/voltages?

[Trumpeter]

Hello all, 

I know it is said the 6lo4v is the same as 6lo1i but I do not believe this is true.  For one thing, the heater requires a different trimming resistor to get it to 6.3v (the resistance of the filament is different between the two).   Also, the display is fairly dim, and in a moderately lit room is almost unreadable.  If I crank the brightness it will get a bit brighter but will bloom.  

I wonder if this could be an issue of voltages or is this just a byproduct of the phosphor type?   I am using Howards board which I believe outputs 300 volts or so.   I really like this little display it would be great if it was more usable.