Ok, so I just got down rocking out for a good hour or so after putting in the 6v6s.... and all I have to say is: HOLY SH!T WHAT A DIFFERENCE! I think I have finally gotten it! This is really the tone I have been looking for all along. Smooth, sweet with a little bit of vintage. For anyone who uses there amp for any type of blues driven music (not just blues, but classic rock, jazz, jam band) and you have a mark iv, you should really give these a try. I really need to try them with the band, but first impressions blew me away. I'm not so sure about a metal tone, since I don't play that and I play a Fender, but for a warm sweet blues tone from a strat, this is it! Very happy. I'll post again once I play with the band.