Very low hum in tube amp

[sjeesjie]

Hi, I have this Line Magnetic tube amp. It has a switch for output to speakers or output to headphones. If I choose headphones, there’s a clearly audible hum going on. I think it’s a 50hz hum, it sounds low.
Is this normal for tube amps? It doesn’t have a grounded power cable or anything so it can’t be a ground loop right? Can it be faulty tubes then?

 

[sergeauckland]

Could be but unlikely if it's in both channels.
I think it's more likely to be the inherent noise of the amp. The amp is a single ended EL84 amp, and those are likely to be noisy into reasonably sensitive headphones. The amp claims 87dB S/N ratio A weighted, so hum could well be audible.

S