I just read that the old American Flyer locomotives from the 50s and early 60s could use both their standard AC transformers AND any other DC transformer to power the track.
Is this really true?
I always thought that the early American Flyer trains ran on AC only.
All Postwar Gilbert engines can run on DC. Some 332’s (Northerns) and 342’s (0-8-0) were made with permanent magnet fields and will only run on DC.
American Flyer locos with series wound motors will, like their Lionel counterparts, run on AC or DC.
I did not answer the second part of the question. A DC Power Pack needs to have at least a 3A output if it will be used to run a Gilbert steam engine with smoke, choo choo, headlight and pulling a couple of illuminated passenger cars. Some of the dual motored diesels draw even more current pulling the 5 passenger cars. There are some DC Packs made for smaller scales that do not have adequate current supply capability.
Lionel locomotives with universal motors need to have the whistle (or horn) disabled when run on DC, because the DC track voltage mimics the DC normally added to the AC track voltage to operate the whistle relay. This is easy to do by putting a bit of tape between the relay contacts, or just taking the dry cell out of a Diesel. Flyer whistles work on an entirely different principle; and the whistles don’t care whether you use AC or DC.
A Flyer DC-only locomotive’s direction is determined by the polarity of the DC track voltage, while the reversing unit determines the direction of an AC-DC locomotive. But it is easy to modify an AC-DC locomotive to be a DC-only type, and to reverse with track polarity, if you want compatibility among your locomotives.