Very simple. Remove 6 screws (3 on each side), 2 back plastic nuts on the back, and the nut on the footswitch. Remove the case, then gently unplug the ribbon cable from the board. Put it back together in reverse order.
I think it needs an adapter. The 12A and ECC are miniature and the socket in which you need to plug it in is much bigger (I may have thought the adapter was the bottom of the tube and thrown it out with the tube--Woops).
I have to admit it's been a few years since seeing inside one of these pedals, but I sure don't remember any adapter. Can you post a pic of what you're seeing?
Hey Bongo, have you by chance tried any other tubes in the MB Compressore? I'm thinking about swapping mine out just to be on the safe side - the comp fell off my 1x12 amp to a concrete floor. Still seems to work fine. Not sure if that is any worse than what happens during shipping. Anyway, the sound man said he was getting hiss from me yesterday. After a little detective work today I found that the compressor does generate a bit of hiss, but it may just be because I was using it to add some gain to my signal (gain on max and volume at noon). It's quiet if I dial it back to unity gain (either with volume or gain) but I don't remember hiss being a problem before, even when using it as a clean boost.
Regrettably I haven't had my hands on a Compressore in years. I also don't know if there's any practical difference between the older and newer models in the particular of how the tube is installed.