The arrows on the ICs connecting the preamp to the amp should point to the preamp. The preamp AC cord should be grounded, but the amp should not (it's grounded through the ICs and the preamp) and you should use a "cheater" plug on the amp's AC cord plug so that you are only plugging two prongs into the wall, not three.
Try those two things, and see if the hum doesn't go away.
Try those two things, and see if the hum doesn't go away.