Is this a bad output tube?

Recently replaced the 845 output tubes in my Nagra VPAs. The replacements are PSVane WE845.

The concern I have is that I have noticed the filament in one tube is brighter than the other three. This is looking down in from the top so not a filament height issue. The bias voltage is spot on with the meter and the plate is not red when I shut down. Sound appears balanced across the two channels as well. They have 15 hours on them now.

Would you regard this as a bad tube that should be exchanged?