Krell LBG Pre heat problem?

I just got an older Krell KBL Pre and hooked it up in an enclosed cabinet. It seems to generate a lot of heat which I suspect is abnormal. The power supply is outside the cabinet. It is actually so hot that you cannot keep in contact with your skin without having to remove it for fear of getting burned. When placed in the open it gets warm but never so much as to feeling "hot". How much heat is normal for this unit?