Need help on a old circuit - early Lafayette amp

[Reece]

John beat me to it on the AC line to the speaker plug. That's what it is: there'd be a jumper in the plug to keep you from frying the tubes without the load of the speaker connected. The push-pull output transformer was on the speaker, too, and the screen line runs over there to it. Maybe studying some other push-pull output circuits would help to get a handle on it.
Reece