@jjss49 So true in regard to listener acclimation period with any new component/variable being inserted into system. This especially true when I'm already contented with system sound quality. My comfort zone is upended when something new placed in system, I'm in analytical mode which detracts from that comfort. Over time I can settle back into comfort zone, especially if change is positive. If change is negative, I find it hard to get back to comfort zone, in which case I come to understand that particular change not good.
As for tubes, I find power tubes most sensitive to burn in, found at least 85-100 hours is time of great change. Rectifier tubes sensitive as well, signal tube somewhat less. The fewer the tubes, the more I hear changes. SET, DHT especially sensitive.