Agree with several of your other posters. No need to change the 6AS7 output tubes. Play around with NOS 6SN7's in the first row first. To be honest I've noticed less of a difference with tube swapping in my S30 than most of my other amps. I'm not saying there is not a difference - it's just more subtle. Don't expect night and day difference. The S30 really does sound very nice out of the box.
