The Lionel TW transformer is an easy to overlook, easily misunderstood transformer from the postwar era. It was designed for single-train layouts with lots of accessories. It contains two transformers in the case, one for the train and one for the accessories.
The Lionel TW provides 175 watts of power and variable voltage of up to 20 volts on its A-U posts, but its main source of appeal is its large number of fixed voltage circuits at varying levels.
Two transformers in one
Since the TW has two transformers in the case, and has two handles, it’s easy to assume it’s a two-train transformer like a KW. It is not. The handle on the left is for blowing the whistle or changing the direction of the train. The TW has only one variable output, the A-U posts. The A post is common, and Lionel labeled it accordingly on the case. On the larger transformers like the KW and ZW, the U post is common.
However, since it’s two transformers, the wattage is split between the train and accessories side. The effective output of the TW transformers is about 65 watts per side. This means the RW or LW transformers can deliver more wattage per handle than the TW, even though they have a slightly lower rating.
Wiring the Lionel TW
When connecting the Lionel TW to track, connect the A post to the outer rail and the U post to the center rail. When phasing a TW with another transformer, phase the A post to the other transformer’s common post, which may not necessarily be A. If you have an early 1953-model TW with a B post, you can wire the B-U combination to the track to get 0-11 volts.
The TW offers several fixed voltages. The most useful are the C-A combination at 18 volts, and D-A at 14 volts. The C-A combination is good for Lionel switches and accessories that need 18 volts. Many American Flyer and Marx accessories expect 14 volts, so the 14 volt combination is more appropriate for them. Use these posts for track-activated accessories that you connect to an insulated rail to activate.
The E-F post offers another 14 volts independent of track power. You can also use the F-A combination for 25 volts, but that’s not very useful as it’s far more voltage than any Lionel accessory needs. It’s really only useful for wiring two sets of lights in series, which you would rarely have any reason to do.
Lionel TW transformers are reasonably plentiful on Ebay.