I just received an email from Gary Dews (Border Patrol) saying that new tubes can calm down with use. I will monitor the tube sound.
Border Patrol DAC tube change
I replace the EZ80 tube in my Border Patrol DAC SE USB+SPDIF with an EZ80 GE made in Great Britain. The tube was made for GE by Mullard. The improvements were significant. The DAC now sounds more dynamic and the high frequencies improved. My wife says its more lively.