As much as we could continue following this around, I think you should post some build photos. Specifically it would be good to see the area where the 47uF cathode bypass cap connects, as well as the cathode resistors.
The possibilities I see for what's wrong are:
1. The 47uF cathode bypass cap isn't properly connected.
2. The secondary wiring on the output transformers wasn't done correctly (in the manual where it says "to wire for 8 ohms, do blah blah blah).
3. One of the wires going to terminal 5 or 10 on the output transformer is loose or missing.
-PB