I have the 50 watt EVH head and 212 cab. The last couple of times I turned it on I would hit the stand-by and there would be no sound. So I went through the process again and still no sound with the volume up. Then all of a sudden BOOM. A loud crack and then it was on. Almost like a bad connection at the guitar jack or the amps input jack. But both of those are OK. I let it warm up for a cuple of minutes too every time. What could this be?