I hotrodded my 800 some.. I use KT-77's. Love the sound and the crunch. Depending on what values you use to hot rod your amp, you might find the 77's accentuate the top end a little too much for your liking. I just back off the presence and treb some though and that sorts it out. Nice tight bottom end. That said, I'm prob going to go to 6CA7's as i think they are a little more forgiving on top. As for reliability, I've used KT-77's a few times and they seem to hold up fairly well.