THD Univalve Class A 15 Watt HeadNotes Telefunken Germany 12AX7 installed in both preamp slots Tone gets very squelchy when volume is turned all the way up. Sounds very good until amp reaches that spot on the volume knob. A THD Univalve Class A 15 Watt Head in Very Good condition! At Evolution Music, we attempt to highlight cosmetic defects (if any) by picturing every angle of every piece of gear so you know exactly what you are getting. We always picture any and all accessories too.