help?

[Baconator]

My cherished Mark IIC+ has developed a nasty illness. When notes are played hard within a tone or two on either side of A (at least the first two octaves) there's a nasty sound that I can only describe as sounding almost like a really nasty raspy sound that fades back to a normal tone. It happens on both channels. I seem to recall reading something some time ago about what certain notes crapping out might indicate, but I can't for the life of me remember what it would be. These amps are a bit of a bitch to work on due to the fact that there are a few circuit board jammed in there IIRC and I don't have a schematic (not would I attempt the repair unless I was given VERY explicit instructions by someone that really knew what they were talking about. I'm just trying to get an idea of what the problem might be and what I'm looking at in general costs to know if I'm going to need to sell something.

[torndownunit]

I don't have the tech expertise that some of the users on here have, and I am sure some of them will give you some tips soon. I usually just start with the simplest approach though, and that is to check for bad tubes.

[Scottone]

Is the sound definitely coming from the speaker or could it be a mechanical buzz?

[kellythebastard]

Could be bum tubes, could be a bum diode, could be speaker problems. tubes and speaker you can check your self. the other has to be done by a tech

[Baconator]

Well, I'm not a complete idiot, but close. I posted here and the gear forum in my initial panic. Somebody at the gear page directed me to another similar thread pointing out the obvious troubleshooting steps: cheack the speaker, check the power tubes, then preamp tubes. It was the speaker, which I had assumed could never be the problem since it seems like it's built like the proverbial masonry lavatory. Plugging into the only other 8 ohm cab I own seemed to solve the problem. I've been toying with the idea of trying a different, less efficient speaker anyhow so now I guess I have the perfect justification for it. Anybody have suggestions for a good 8ohm 50 watt speaker?

[Scottone]

Anybody have suggestions for a good 8ohm 50 watt speaker?

I really like the Eminence Private Jack that I have loaded in a 1x12 cabinet..you may like that.