I came across these following "6 Moons" reviews on Yamamoto 300B and 45 SET amps in my digital library. They include some pretty good detail of build quality and higher grade components. Should provoke some thought and give you something to contemplate.
http://6moons.com/audioreviews/yamamoto2/45.html
http://6moons.com/audioreviews/yamamoto6/a09s.html
http://6moons.com/audioreviews/yamamoto2/45.html
http://6moons.com/audioreviews/yamamoto6/a09s.html