I just picked up an Ampeg SVT-150H. Now, I have a GK amp, which i usually love, but I sometimes wonder about the other end of the tone spectrum, ampeg. also, this doubles as/ was originally designed as? a guitar head. can't hurt to have an extra one of those about. i found this on CL and snagged it on a whim. I really dig the tone- it sounds remarkably tubey and warm for an SS head. Definitely a decent 'Ampeg' tone. So that's cool. It's kinda loud [It's 150W @ 4 ohms, and ???@ 8 ohms. maybe 75-100?] i'm using my neo112/212 cabs since that's all i've got. they actually sound pretty good. But it's hissy. At all frequency levels. I can EQ out a lot of it but anywhere over like 30% volume there is a noticeable hiss. It doesn't seem to matter if i have less gain/full master or hi gain/less master. It's very pronounced on the top 6 bands of the 9-band EQ. The louder the amp, the hissier the signal. My bass's input seems to make no difference. So, is there anything I can do to fix this, or at least lessen its effect? I figure taking it to a tech would be the best option, but is there a quick n dirty that I could do it? I don't want to incur a huge tech repair bill. I've considered opening it up and blowing some canned air through it. Would that make a difference? I'm no engineer but I'm not unfamiliar with electronics, just don't entirely know what i should do first. What would be the best way to isolate the problem?