@aldnorab You are right of course. Probably the tubes (not sure yet), but these are not very old. NOS from Brent Jessee. Supposed to be tested and matched. I have the original tubes that I can stick back in to see, but it is such a pain to do: have to disconnect everything, pull the unit from the cabinet, unscrew about a dozen screws to remove the entire housing.
Re the amp: I'm done for now. Staying with the Voyager. My initial impressions seem to be consistent with ongoing performance, so not much more to say. It is an excellent amp and a bargain at the retail price.