Bizzare problem with my 6505+ Post knob

[Sinister Mephisto]

So I just turned my 6505+ on for some reamping today and discovered a bizzare problem, my post knob doesn't control volume it now controls a weird combination of gain midrange and it sounds like it's going in and out of phase or something. Maybe someone who knows a little about amps can help me out, I'm clueless! Here's a clip of me turning my post know from 0 to 6 and back. You can hear it starts really honky and low gain sounds like it goes out of phase, and then comes back ultra distorted and scooped around 4 with no real difference in the volume the whole time. WHAT'S GOING ON.

By the way this is straight to the amp from my interface no pedals etc. Also, the crunch channel sounds different to me as well but it's not as obvious, it sounds like there's a clean sound mixed in with the dirty sound. Pretty strange.

http://dl.dropbox.com/u/899440/Misc/6505ProblemClip.mp3

Sorry if this is something obvious, I just can't think what it could be. Thanks in advance!
-Fred

 

[Nebulous]

6505 problems- always sounds like new tubes are needed when other people have asked throughout the years.

 

[Wolfeman]

Probably a bad filter cap. I know on the 5150 it was C37 causing the issue, I don't know if it's numbered the same on the 6505+. Do your tone controls work fine?

 

[Sinister Mephisto]

I hope it's the tubes because that's something I could swap out myself at least. My amp is only about 8 years old I think, is that old enough to have a bad filter cap? The tone controls actually do nothing that I can hear, but presence and resonance work. By the way thanks for replying!

 

[Wolfeman]

Yeah, hate to tell you but it's probably a cap, or something else affecting that area of the ground. It's simply passing the signal around the tone stack and volume control.

 

[Sinister Mephisto]

Ah well thanks so much. I'll bring it in and have it looked at.