I recently played a televised gig using my mid-1970s Ampeg B-15N, which has been and continues to work fine. The sound engineer plugged a 1/4 cable into the Extension Speaker input on the back of the amp's head, immediately turning a great sounding amp into a no-power fuzz pedal; when the cable was removed the amp returned to its normal self. The cable was not going to another speaker, but to the television station's sound board This has me wondering about a gig next week with the same amp. I'll be using two passive Fender basses and was planning on keeping both plugged in for the duration of the three-hour gig, likely having one in the Bright channel and the other in the Normal channel. Here is the question: Since the amp didn't like having something plugged into the extension speaker, might it not like having two basses plugged in at the same time? Is there any relationship between the two sections of the amp to be concerned about? I have bench-tested and all seems fine, BUT the test was for 10 minutes and not 3 hours. At this age (40+ years) , do these amps mind having multiple instruments plugged in simultaneously?