Audio Aero Capitole - 6021W subminiature tube ??

I would appreciate hearing from someone who can explain the performance of these tubes in the Capitole, including the typical life of the tubes, whether they are susceptible to becomming microphonic or noisy, and how to purchase or change them if necessary. I believe I read these are really small (like the diameter of a pencil) and that they are soldered onto the board. If that is true, is it then necessary to send the player back to the distributor or manufacturer if they need replaced, or are these readily available and set up for user installation? How many years is typical for the tubes to perform in the Capitole before replacement is necessary? Thanks.