This is a Rectify Series drop-in speaker system for Atlas Classic & early-run Master U30/33/36C locomotives. The speaker is a beautiful press-fit between the rear weight and motor mount. No frame/weight/shell modifications are needed! The factory PCB will need to be removed with either a Decoder Buddy installation or a hardwired decoder. Board-style decoders will not work (Soundtraxx PNP, LokSound Direct), as they take up all of the space between the two weights and leave no room for the speaker.
 
The speaker comes fully assembled and tested.