Joe,
Here's some more threads to help you understand the various Siemens CCa:
http://db.audioasylum.com/cgi/search.mpl?forum=tubes&searchtext=siemens+cca
Here's some more threads to help you understand the various Siemens CCa:
http://db.audioasylum.com/cgi/search.mpl?forum=tubes&searchtext=siemens+cca