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.
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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.