OK, so it was tube socket related on that channel. I've got something on that side that is occasionally not happy. The tube had a bent pin, but now it all seems to be ok. Both sides are testing at 75V. I'm running it now and it seems to be doing alright. No C4S yet, but I have to make that upgrade on both of my units. BTW, I never got a manual for the C4S, can that be sent over to me? Working out the bugs now though