![]() If the code on this PCB is either JCM2-60-00 or JCM2-60-02, then it is likely you already have been, or soon will be, confronted with this problem. That is the big PCB where all the valves are. The primary cause of the Marshall JCM2000 Bias Drift is to be found in the main printed circuit board (PCB). Here are our kitsįor matched pairs – 50 watt amps: JJ E元4, Electro Harmonix E元4EH, Tung Sol El34Bįor matched quads – 100 watt amps : JJ E元4 II, Electro Harmonix E元4EH, Tung Sol El34B The Tung Sol El34B is a very good replacement. When this phase has been reached the E元4’s are usually defective and are now ready to go in the trash can. Due to this drift the bias current of the output valves will gradually increase, and keep increasing, until the E元4 glow bright red/orange ( “red plating” and this can also be bad enough to blow the HT fuse. 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. These are nice amps and I have one myself The early (1997-2003) Marshall JCM2000 DSL50, DSL100, TSL100 and TSL122 amps are often troubled by an unstable bias (drifting bias).
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