I just bought the Engl SE this past week. Plugged it in today to give it the first test drive and no sound. Actually, if I crank the channel and master volumes on any channel there is a very low volume sound. As soon as I push the tube driver button (feature that is part of the preamp section) the sound cuts off all together. Any thoughts or suggestions? Does that sound like a preamp tube issue or a power amp tube issue? I have tried different cables and guitars and nothing has worked. By the way, it is the EL34 version. Thanks in advance!