Actually, that is not the problem. In the Helix, I had the preamp set to use the Helix instead of the DT Pre in the output settings. When I switched the preamp back to DT and unhooked the link, the amp worked again. Apparently, the internal setting the DT received from the Helix didn't change back with an amp reset of a flash re-install, but could only be done by the Helix. I think the tubes probably only have 20-30 hours on them, so I hope they don't need to be retubed. I know the amp is 8 years old, but it hasn't seen much use since I got the Helix.