After using it for more than a month, I must say that sound quality and construction are excellent. Sound quality has been increasing as the valves have been used. The power transformer is quite heated when its been running for several hours, but according to the instruction manual its normal and Im not worried about it. In my case I have connected a preamplifier to XiangSheng 728A mk3 valves and the sound quality has improved quite a bit, it can regulate the bass and the sharp and adapt the sound to the acoustic conditions of the room, recordings, etc.