I just purchased a 610 watt Ampeg SVT HLF. It is a restock, however there is no apparent damage and it came it in the original box. Mint Condition. I am in the market for a new head to pair with it. In the mean time I am using my friend's 350 watt Hartke head. It is a tube/solid state combo. When ever I play high up (On the fret board not referring to tone) I get a crackle sound especially when I play an open E and it gets worse as I turn up the volume and the contour. I have been reading that it is probably the tubes going out but I just wanted to make sure its not the cab.