Mesa Carbine M6 Bass Amp

[tubby]

Hi,

anybody know the official Mesa Service Center approved mV numbers (across the 0,2 resistors) for biasing the output FETs on the above amp?

[lowell]

I'm an authorized tech for Mesa and there's no schematic on their tech page. They have a pdf that says these amps need to be sent to the factory to be updated though. And I've dealt with this before and they do require it be sent in. Reach out to Rich Duvall Repair Department Manager 707-789-3324.

[tubby]

Thanks lowell for the info and taking the time to check that!

I'm not sure if I wanna go down that route (yet) cause from what I've heard, the whole output section is replaced and this is gonna set me back a couple of hundred bucks.
Thing is, the amp is working just fine, I cleaned the inside and while I had it open I thought I might as well check the bias, just out of curiosity.

In the meantime I've found a schematic of the power amp section in this thread:
https://music-electronics-forum.com/...bine-schematic

In another forum 10mV were mentioned as the value to adjust to. On my amp I measured ~5mV on all FETs.
Out of curiosity I hooked up the scope to the output and 1kHz sine to the input and went through the whole range (0,05 - 35 mV) of the bias trimmer (right in the middle of the supplied schematic).

I couldn't find any crossover distortion on the output signal regardless of the trimmer position. Am I wrong to expect any at the lowest bias settings?