Tube Question

Critical changes occur with tube age. Almost any tube will need to burn off metal oxides. The difference in sound is usually a less strident sound. When the tube goes through this initial process they tend to provide a nice plateau if its the right tube for you for a long time and then go through a period of real mellow musical bloom. But nothing lasts forever and the tube starts to announce its death with crakles and pops or just blows all at once.

With small tubes you should have an excellent idea of the tubes ultimate sound with 24 hours of use, even less. There might be some change after that but it will be very minor. Power tubes are a different matter.

Yes tubes do have a very real burn-in time. It will vary with each tube type and how old it is. I would say that tube burn in is significantly more real than with cables.