It is always nice to have a spare set of tubes available to diagnose possible issues with any piece of tube gear, with that said go ahead and get a set for the 12au7 spots in your preamp and I would recommend the Psvane T Series Mark III Premium tubes at about $75.00 a pair, I run a pair in my Lamm LL2.1 preamp and my Jadis tube dac also run the 12 at7s in my VTL amps and the 12ax7 in a ASL headphone amp. I have had nothing but good things to say about the Psvane premium tubes and have settled on them over all the NOS tubes I have tried and have become my go to tubes. Good luck.
