Most line level tubes that I've tried seem to take around 50 hours (some more, many less) to stabilize. Chuck certainly has a point. Depending on the surrounding passive components, the preferred tube could be the tubes supplied by the manufacturer. However, in general, I've not found this to be the case with the components that I've owned over the years. Most new production tubes rarely have the sonics that I tend to prefer nor the longevity of NOS. Remember, it's all about synergy. Your tube preferences now can change as other components in your system change. That's what makes tube rolling so much fun. Good luck.
I just installed NOS tubes?
I have just replaced my stock 6922's with some NOS Amperex 7308's green label in my BAT VK-30. How soon should it be before I hear changes in sound quality and what should those changes be if any?