Holy cow, I did not expect this much help! Looks like I'm not breaking up with this girlfriend (you, my friend, are an enabler) any time soon. Too much for me to process in one go, but I changed out the 500 ohm trimmers for idle current--that was it, nothing else. It was producing clean sound in both channels immediately prior to this, uh, upgrade. I've been using the SM from Hi Fi Engine (good call--that place is truly awesome) but am not as knowledgeable as you. I'm afraid that I changed the setting on the original trimmers so that's out. Aforementioned, I turned the both re-installed original trimmers back to zero (full clockwise) but the girlfr--amp--won't behave and keeps blowing that 250v/4A fuse in the back immediately. I haven't built a DBT but I do have a variac-type thing that I could use. So, just trying to understand what happened on the electronic level, the new trimmers must have been jacked up way to high, which shorted out something permanently in the audio and/or power path, resulting in this sad state of affairs (I had it working; I swear! After seven years I had it working!). By the way, you are either eminently proficient at hi-fi repair or take very good notes (both?) to recall everything with such detail. I really, really thank you for taking the time to help me, poor old sod (I'm the sod, not you). I'm taking a break from this thing for a few days anyway but will report back.