Possible Clues:

• Public platform
• Sort out spirit platform
• Platform for orchestra conductor
• Where one may go up to speak, or turn up to beat out the music
• Spirit appears after Jack's topped off stage
• The Da is here. Must Orr be here too?
• Strange sort occupying strange platform
• The Da is, or he's going to turn up and beat it at last
• Public speaking area
• Radio operator initially to play guitar on the platform