This may not apply to your setup, but I have individual bias pots for each output tube. There’s a recommended bias range for each tube type . Running the bias toward the lower end of the bias range can supposedly get more life from them. It’s possible that the tube that runs at the lowest bias setting may last longer in general, but don’t know for sure. There’s no guarantee you’ll have optimal SQ with all bias ranges either, but that’s always subjective anyway.
