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previous: pumpstein I just thought of another possibili... -- 8/31/2000 10:22 PM View Thread

Re: Help with motorboating?

9/1/2000 7:11 AM
Steve A.
Re: Help with motorboating?
    My guess is that the motorboating has to do with the grounding of your tone stack... As for the non-isolated jack, you could just remove it from the chassis and add in a ground wire, just to see if that helps things. (If it does then enlarge the hole so that you can use insulated shoulder washers...)  
    But I am concerned about the voltages on the EL84 plates... I think that they are a bit high. You could use 10V/5W zeners in the ground circuit to bring the voltage down to something like 356vdc or 338vdc... Are you using a full wave rectifier or a FWB?  
    Also, you mentioned that your first filter cap was 100uF... that is just a single cap, not a pair of 100uF's in series- right? Having 100uF right after the rectifier could boost the lows enough to cause motorboating but I think it has something to do with the way the tone stack and 12AX7 grounds are wired up...  
--Good luck!  
Steve Ahola