The Gold Lion KT88s are great tubes, but they definitely favor the high end and lean more detailed than warm or rich. I’m using 8 of them at the moment, which I balance out by using 6 vintage Mullard tubes in the preamp section. It’s a great combination. The Gold Lions add back some of those highs that the Mullards lack, and the Mullards do a great job of warming up the Gold Lions and keeping this amp sounding like a tube amp. But be forewarned that with forward or bright sounding preamp tubes, your amp might sound a little cold.