Hi!  This is my first post on here, but saw it from Twitter.  Depending on the transformer you're using, it may not have enough power to run the older (Post War, for one) Lionel trains.

The best I've had in newer sets is the CW-80 that comes with the last batch of transformer-controlled sets (just before LionChief).

Those tended to have enough power to get my older trains running alongside the newer ones if I don't feel like getting any of my vintage transformers out to run the trains.