I love the pre-amp tubes. Think everyone should have a few lying around to swap out now and then. If you are getting a little tired of an amp, I find that just by switching V1 to something else can sometimes bring the amp back to life for me again. I have been using a Groove Tube 12ax7C happily in my JCM 800 2204 for a few years now. Today I thought I would try out a JJ Ecc83S I had on the shelf. For some reason I thought I wouldn't like it with this Marshall, but I may like it better. Of course next month I will probably change my mind again. Who has found a tube they really love with Marshalls?