It is always gratifying for "it worked the first time" posts. We too often get a warped view of builds just looking at the problem solving that goes on here.
I admit to helping another Bottlehead with his FP III. We flipped it over and plugged it in, turned it off took out the tubes, made changes, and it went on like that.
Finally I was flummoxed at the problem, we were troubleshooting from the bottom and one side wasn't working. We flipped it over and that tube wasn't in the socket.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FSlapHead.gif&hash=e5c580c3cfdf525c26703ae0328aefb586b04de5)
We went upstairs and listened to it for several hours.