Unless an amp is made specifically both for headphones and speakers (i.e., it only has speaker taps), there will generally be some hum on headphones....for even the very best amps. I have a speaker amp to headphone adapter and, while there is some hum, the amp sounds brilliant through the adapter on headphones. This is because it is a brilliant amplifier, a Fi Audio 2A3/45 set of monoblocks. I mainly play the type 45 tube.
I also own the Stratus. It is dead-quiet and lovely to listen to. The 2A3 tube and type 45 tube do not sound the same, which is why I have the adapter and i also use it together with an Audio Note 300B power amp, the Conqueror Silver. There is also some hum with this amp through headphones, but again, it sounds brilliant on headphones.