I've owned these for years and always held onto them because they are something special. In my Vibro Champ these tubes just SING. They have amazing, ringing musical sustain unlike modern tubes I've tried. The tone is extremely balanced and ideal for guitar; not too trebly, not super bass-y, just gold. They have slightly less edge than 12AX7's so they are a perfect match for a practice amp. Tried years ago in a Blues Jr. and they were a huge improvement over the stock tubes. Not a great fit for my Bassman where I want the extra gain and bass response. The reduced gain leaves distortion tones a little lacking for heavy rock music, but perfect for a sweeter 'clean' distortion tone.