I tried the EH6CA7 on my Metro Plexi 50 watt and liked them.The amp is currently being modded by David Bray so I'm anxious to see how they sound after he's done with it. On my Marsha I use the original Mullards EL34 and liked them, but then I tried the JJEL34 and it gave me different tone that I also like.I also have the SED's and like them also but I can't get the bias as low as it needs to be, I hadn't had the chance to take it to Dave so he can change the Bias pot so I can use them safely. I can't get the bias lower than 44! The JJ's are tighter and better for metal stuff, but the Mullards are smoother and spongier and has a bit more clarity. I'm going to try the EH6CA7 on the Marsha and see what happens. I just wonder if Dave build his amp with the JJ's in mind and he tweaks them like that or it really doesn't make a difference what tube you use as long as it sounds good to you?