Nik sets the bias at the factory. You may just want to check it, but, it should be set.   If the tubes are JJ's they're just fine, unless you're going for a different tone, or, breakup. I'm getting a set of 5881's to try. Larry Carlton uses them. The ground hum with Strats is usually the pickups. Single coils have a tendency to do that, especially the neck and bridge. Your instrument cable and how close you're standing to the amp can have an effect as well as any pedals you may be using. You can always add a layer of aluminum, or, copper foil to the underside of your pickguard and in the routered channel in your guitar. This is agreat way to minimize pickup noise. Enjoy!  Bill