A common question is whether transformers for vintage American Flyer, Lionel, and Marx are interchangeable, and what to do if a transformer won’t work.
The simple answer is, yes, a train from one of those makes will run on a transformer from any of the others. They all ran on 0-24 volts AC.
There are two caveats.
Many Lionel transformers deliver about 6 volts on their lowest setting. Marx and Flyer trains run pretty fast at even 6 volts. The maximum setting of 18 volts on most Lionels is more than a Marx or Flyer needs, if you intend for the train to stay on the track. As for 24 volts, present on some Lionel transformers? Let’s not think about that. So, with a Lionel transformer, keep a light hand on the throttle.
And in the 1970s and 1980s, Lionel shipped a few cheap starter-type sets with small DC transformers. In a pinch, you can run an earlier train from all three makes on that. But don’t try to run a Lionel train expecting DC with an AC transformer. They won’t run, and eventually the AC will damage that locomotive. Lionel stopped this practice somewhere around 1984 or 85. If the transformer has a black plastic case with printing molded on it and the direction switch is a sliding switch that locks in place rather than a pushbutton, there’s a pretty good chance it’s DC.
If you need a dead transformer serviced, a hobby shop dealing in prewar and postwar Lionel trains may be able to fix it. Another possibility is a small appliance repair shop, if you can still find one of those. Outright replacement is simpler, though potentially costlier. But in this case, beware. The least expensive Lionel transformer available for separate sale is the infamous CW-80. Unfortunately it’s impossible to get any good information online about the CW-80. Early CW-80s had a big problem with premature failure–my first one died after about 30 minutes of use, literally. Lionel redesigned it, and my replacement has lasted several years, albeit with light use. Mention the CW-80 on a train forum, and people pile on–mostly those who believe Lionel is incapable of doing anything wrong and those who believe Lionel is incapable of anything right. Few of those who speak up actually have any significant experience with current production CW-80s, since most hobbyists use larger, higher-wattage transformers on their layouts. Lionel did unquestionably cut some corners with the CW-80–it doesn’t produce a pure AC sine wave, which can under some circumstances cause odd behavior.
I suggest avoiding the CW-80, simply because comparable transformers made by Model Rectifier Corporation, such as the MRC AC-1301, have a good track record and are usually less expensive. MRC has been making transformers for decades, and it’s all they do.