That's perfectly normal for the first minutes, then the hum sort of disappear. It always has a really low hum, but only if you put your ears right next to it. I can't hear it 1 meter from the amp.Try some Russians 6H23P, or Amperex orange globe. But beware on ebay, lotsa fakes going around. Take a look at this thread for more info: http://www.head-fi.org/t/619910/schiit-valhalla-tube-rolling-thread/315#post_11521353Simply a great movie soundtrack, one of the best!