If you are asking these questions, best to go with Audio Research replacement tubes. I was trying to 'get into' tubes and bought an Audio Research SP-10. (15 tubes!) Then I realized that sort of tube-ness was over my head, and bought an Audio Research SP-15 (three tubes) (sold the SP-10) and will buy extra tubes to do just what "newbee" suggests.
The quandries of 'tube rolling' I want to leave to the adventurous.
The quandries of 'tube rolling' I want to leave to the adventurous.

