I currently prefer a Had single ended tube amp with a massive 12wpc (efficient speakers) and the thing is very revealing of tube differences, and since there are only 2 power tubes it's relatively inexpensive to mess around with. I've enjoyed KT150s, 120s, 88s (including Gold Lions and others), and 6550s...the Lions were my fave for a while (came with the amp). I then tried a pair of JJ KT77s and they sounded pretty bad and ruined the KT77 experience for me (poor, poor me, but the JJs are cheap)..until I bought a pair of Gold Lion KT77s and raved about those...a great tube...replaced by my current fave new version Tung Sol 7581A tubes...amazingly coherent and "perfect for my tastes with this amp." These tubes aren't expensive and have a nice blue fluorescence I enjoy at night, possibly indicating a low threshold of tube glow enjoyment...in any case the 7581A is currently on the top of the power tube heap around here.