Good morning PB. I rechecked the black wires and couldn't find anything that was loose, but I resoldered them just in case. I don't have a spare 6080 at the moment so I can't test it. However, my 6080 tube is a bit loose at the base (the metal part at the bottom), if that means anything. Rechecked the voltages and got the same readings at 7 and 9.
On another note, I actually remember hearing a noise the first time I turned the amp on a week ago. I'm not sure where the noise was coming from but it stopped working shortly after that. I had a spare 6080 tube (but later sold an amp with the tube) and tested that but by that time the big board stopped working. Do you think maybe the 6080 tube was the one making noise and is it possible that it messed up the big board?
I will buy a spare 6080 for testing.