Hi You do not need the transformer, only the battery. Using the lead wires that go to the locomotive touch them together momentarily and you will get the actual chuff sound. If the wire has the plug on the end use a small jumper wire to insert in the plug and you will get the chuff sound. Jay is correct the locomotive has a chuff sensor on it and when the lead wire from the tender is plugged into the locomotive and you run the locomotive you will get the chuff chuff sound.
Here is a link to my article on the loco and tender, scroll down to the so the sound troubleshooting paragraph for more details. https://www.bachmanntrains.com/home-usa/board/index.php/topic,30394.msg224039.html#msg224039
Have fun, Loco Bill
Here is a link to my article on the loco and tender, scroll down to the so the sound troubleshooting paragraph for more details. https://www.bachmanntrains.com/home-usa/board/index.php/topic,30394.msg224039.html#msg224039
Have fun, Loco Bill