How much hum is normal from a new tube amp

Might be a lemon set.

i have Lab12 Integre4 MKII, zero hum.

The demo set I auditioned had a slight hum when using XLR input, but none when using RCA input. My brand new set has no hum though at all. Perhaps try switching the inputs first? If it still bothers you just exchange a new one. 

@blue-magoo Less than 2 months. Mine so far is dead quiet. But like I said, the demo set I auditioned had faint hum from the amp itself when using the XLR. Finger-crossed it would not happen to mine because I really like the sound of it.