2 Tubes in processor should both glow the same

I have a tube processor and one of the two tubes is dimmer than the other. I have rotated the tube to the other socket, same thing. One is always dimmer than the other. Is this normal or abnormal? I played a test CD to check the channel balance and it seemed ok. I'm new to tubes but logically I would think both tubes should be of the same intensity.
It really depends on how they are being used in the circuit and how each one has aged.
The way the filament is setting inside may have something to do with it. If you use a regular bread toaster, look at the heating element inside it while it's toasting. The element will look dimmer if it's leaning a against the insulator. The one tube filament may be touching the cathode more where it looks dim. I'm not saying the tube is good, but all kinds of identical tubes do have a different brightness in the filaments although it's still putting out the same heat.