At rehearsal the other day my amp lost serious power. I could barely hear it. This happened all of a sudden. I was tuning with my rack tuner on mute. When I took it off mute, I had like a quarter of the volume. I narrowed it down between my Alembic FX-1 and QSC PLX-1202 after bypassing everything. Swapped out all cables except the speak-ons ( Don't have spares) Tried a passive bass. Still a faint signal... Since the QSC LED's were barely lighting up, I changed the tube in the Alembic thinking maybe that was the problem. No dice. Then after a couple minutes, the volume came back. I don't understand. Any ideas?