Seems like the best "upgrade" for tube amps....

With solid state gear if you want it to really sound right it probably has to be left on all the time- especially preamps.

Our amps seem to get to 99% of where they are going in about an hour- two hours they are totally there. In the old days it took more like three. I credit component improvements for the shorter time these days.

First you do the circuit design.

Next is to see how much it is affected by materials. Some areas in the circuit will be sensitive and other areas nearly immune.

3rd to to sort out what the best materials/parts are and install them.

4th- the 3 most important things in audio: listen, listen, listen.