Tube rolling for C 220


Hello, I want to try to use different tubes for my Macintosh C 220. I unscrewed but still cannot open the case. Can anyone let me know how to open the case ? And I would appreciate if you could share your experience with tube rolling for C 220. Thanks.
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The C220 uses only 12AX7's, 2 for the line stage, and 2 for the phono stage. The C2200 uses 12AX7 and 12AT7. I think Matt's recommendation for Mullard is good, although there is many different ones, depending on vintage and some made for military. Have a few friends that like Telefunken, also some variety, in their MAC gear. Here is a link with lots of information on 12AX7's from another reputable dealer.

http://www.audiotubes.com/12ax7.htm
Thanks a lot Mattmiller. Your realistic explanation was awesome. I did remove it exactly same way you described. I tried with my telefunken tubes but still don't like phono section. I will try GL or mullards. Thanks again.