My first attempt at replacing the 6SN7 tubes was to use the 6F8G tubes with an adapter, these sounded great and better than any 6SN7 I ever heard.
After that I discovered the 6J5 tubes, I been using them with adapters for about 3 years now and they sound more linear than the anything I have tried...
Only problem is most are very microphonic, so I am gonna try the 2C22 in the hopes that they will not be as microphonic...