mr dave

The only time I had a problem like that was due to a blown tube but that was in a combo amp. Did you buy this gear in a store or through a private sale? On the plus side a replacement tube is usually only about $15.

I also don't understand why you're running a speaker lead from the processor loop to the cab. As a loop it normally connects back to the head. The loops (aside from Slave Out) are labeled as Send/Receive on the amp schematic Google provides too. Also, effect and processor loops are usually meant to handle rack based / studio effect units, as opposed to typical stomp boxes.

So... undo that processor loop thing to test it out, just connect the speakers and a straight line from the bass to the amp and if it's still not jiving then I'd be calling my local music shops and finding out if they have other suggestions (and possibly replacement tubes).

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