What will cause my EL-34 filaments to glow differently.

I have a modified Dyna St 70 with a Curcio driver board. My right channel tube filaments glow one brighter than the other. I have checked the filament voltage and it is the same on both sides, left and right. There is nothing in the circuit that I can see that would cause this imbalance. I have moved the tubes around and the condition remains with all combinations.
it is possible for different tubes, esp. tubes from different MFGs or production lots to have subtle differences. if the difference can be compared like a 15watt bulb vs a 300 watt bulb, check voltage, and if possible current draw. if the ghetter has turned milky in the "brighter" tube, the tube may have lost its Vacuum = bad tube. Otherwise need better description of problem.
Swap them and see if the same tube is brighter. If so, it is most likely that the filament (which is what glows) is just sticking up and out a little more from the cathode sleeve it is slid into, which is just a manufacturing variation, is common, and not a single thing to worry about.
It sounds like the bias is off and the plates glowing. Check the bias.