Not that this is very new information, but I discovered, when working on a beautiful sounding '64 super reverb that every plate/slope resistor in the amp was WAY off spec. They are supposed to be 100K and not one measured below 130k.
The amp was super warm and soft to play.
Just made me think even more about how we all seem to hold vintage amps in such high regard, when its always possible that its the out of spec parts that give some of the best magic, and that the reason amp repair tends to "loose the magic" that an amp has might be a clue that replacing parts to the schematic specs may not be the absolute best solution all the time