I’ve tried a few SS amps, but now using Prima Luna EVO 200 integrated amp on my Cornwall IVs and it sounds amazing! The first thing however is you NEED to use the 4 ohm taps. The EL34’s on the 8 ohm taps are a disaster. The 4 ohm tap is where it’s AT!
Second thing is try bigger tubes. I’m using 6550 EH’s and they sound perfect to me. I also have KT120’s. They sound more controlled in the lows and more dynamic, BUT, they also sound too bright. To be fair, I’ve only got about 24 hours run time on the 120’s so maybe they’ll still smooth out. But for now I’m really loving the 6550’s. I do want to try KT88’s at some point.
Also... big tweak for the Cornwalls was to put them up on 4x4s. Raising them up 3.5" really opened up the lows, and improved the imaging. A game changer for me.

