Note: We now have a new, superior solution to Marshall JCM2000 bias drift issues. Find the details here. The early (1997-2003) Marshall JCM2000 DSL50, DSL100, TSL100 and TSL122 amps are often troubled by an unstable bias (drifting bias). These are nice amps and I have one myself This can be difficult to diagnose correctly, as it can take half an hour or more of testing and/or playing before this Marshall JCM200 bias drift shows up. […]