Keep a lookout for power supplies. I recently bought a Tripp lite PR40 regulated supply from Arrow shipped to my house for $88.00 unbelievable price. I think it must have been a mistake or something because they sell for hundreds of dollars. I use that power supply for my Kl503. Before that I was using a pyramid 30 amp switching supply that was causing him and rfi. This simple switch from supplies fixed the hum.