I discussed this with Leonard a number of years ago when I sent my CD7 in for the upgrade. The upgrade at that time was free if I remember correctly. I was told that the reason for the power supply being upgraded was that there were problems with some of the 6H30 tubes aging differently. This could cause reliability issues as well as other problems in the power supply. That is why the 2 6H30 tubes were replaced with a single 5881. The reason that the 5881 tube was chosen instead of a 6550 like in the CD8 was space. There was concerns that there would not be sufficient clearance for ventilation using a 6550. This could cause heat issues as well as the possibility of shortened tube life.
