AaronWil

Thank you both! Appreciate the ideas. Tubes are original, with just a few hours on them. I swapped out the 6550 and 12zx7's with a newer set from one of my HD100's and found same issue. Will try the pots next. Loud & clear on not touching the caps. Thx!

Hello. Have a SV 112 MKII that I bought new years ago, and have used only on very rare occasion. It's in mint condition and has likely seen less than 3 hours of use. Fired it up last night to find it making horrible scratching noises mixed with an overall terrible sound, and big uncontrolled volume swells even with master volume at zero. Tried all the obvious fixes, including a reset. Even tried a different cord & outlet, with and without it's switchboard attached. Let it sit powered up for an hour and found everything to appear normal. No excessive heat, no tube noise, and all the buttons, switches & knobs appear to be normal. If anything, the master volume knob sets off the noises when touched, but not every time I try it. It's a "scratch, scratch, scratch, EXTREMELY LOUD GUITAR, scratch, scratch, SEMI LOUD GUITAR..." sort of thing. And that's with the master volume at ZERO. Have had lots of other tube amps and this initially made me think tubes, but these are so new that I'm doubtful that's the case. Pulled and inspected all four tubes and sockets anyway and saw nothing unusual. Cleaned leads and reinstalled. No improvement. Tried running out to a 4x12 cabinet too. I have HD100 heads that have been used & abused almost daily for years and still work like new. I have no idea why this combo would go mental on me now. When not in use, it's been kept unplugged with a cover. It's never even left the room it's in since I got it. So it's not a handling or power surge issue. I don't live anywhere remotely near an amp repair place, let alone a service center. I'm thinking one of the two main boards has failed. Are spares available? Not wanting to spend a fortune on fixing it, but it's a true shame to let it die. Any suggestions? Thanks! Aaron