Short answer is Yes, the arcing happens in both channel.
for the 5C3S, at the beginning, I don’t think they arc. Then after a month, both tubes arc. For the RCA, they both arc right the way. For the TungSol, so far, only one arc. And when I switch the tube, same behaviour.
maybe as you say I have bad luck, but the percentage seems too high, 50% or 3 out of 6 pairs arc. That’s why I think could it be a me doing something wrong which cause this. But there is only one button, I can’t think of anything except I didn’t wait long enough when restarting the amp.
is it very common for 5U4G to arc? I only have two amps that use 5U4G, and I didn’t roll the tube in my previous amp.