If the C2300 is new and breaking in, my advise is to leave it along for a while. If something goes wrong, one of the first questions you will get from any customer service person is "What tubes are you using and where did you get them? ".
12AX7 tubes are also named ECC83. Search both on the web, tons of information out there. Grinnell's posted link above is a great start. Where or from whom you buy from is huge. Keep in mind, New Old Stock {NOS) is hard to prove. Finding the right dealer, someone you feel you can trust is pretty tough. Also, search the audio forums for good tube dealers.
Good Luck!
12AX7 tubes are also named ECC83. Search both on the web, tons of information out there. Grinnell's posted link above is a great start. Where or from whom you buy from is huge. Keep in mind, New Old Stock {NOS) is hard to prove. Finding the right dealer, someone you feel you can trust is pretty tough. Also, search the audio forums for good tube dealers.
Good Luck!