@jjss49 Thanks for your very informative post, it confirmed what I had suspected the changes would be. Of course, actually rolling in a quad would give the definitive answer...
KT66s in place of KT88 tubes
I expect there will be a change in bias, and a reduction in power. But on the basis that lower power tubes generally produce more faithful sound, can one put KT66 tubes in an amp usually requiring two KT88s per channel? I'm thinking about a pair of Quad II/forty push-pull monoblocks.