"1. Output device failure followed by the opening of one DC rail fuse meant that BOTH channels went full rail DC, ie 78 volts. "

Only ONE of them, I think the negative. and it was not full current. you owuld read that on a meter or whatever, but it was not putting out all the current it can.

Yes, they are bad in that respect. That is why I used MJ15024s in mine.