Boulos and I switched everything we could think of while trying to troubleshoot the problem (300Bs, EL84s, input cables and output cables). But it was always between channels. I'm really mad at myself for not suggesting we try another pair of 300Bs.
It would have been the easiest thing to do and would have saved us a lot of time! I should have known it was not Boulos' meticulous and beautiful build as you can see in the photo above! Thanks Boulos!
Gerry