Not sure if the DAC tube will react similarly to the ones in preamps and amps, but usually you can start to tell if you are gonna like it or not within an hour or so. You can roll through tubes and cull the ones that absolutely don't work with your system, then give extended listening time to the ones you like the best. Usually takes several elimination rounds to single out the ones that work with the system, but usually you can tell pretty quickly if the tube has a sound that you like or not.
Brand new tubes are a different story. Seems like they change for the first few hours or so then settle out. I have tried some that i didn't care for at first, but after a little time on them they came around. So don't write a new tube off based on first impressions. Put it in the system some weekend when you can just let the system play and give it some time and then see if it changes tone. Have fun with your rolling.
Mike
Knoxville, TN
