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All about the Lionel KW

The Lionel KW is the second most powerful, and second most popular Lionel transformer of the 1950s and 1960s. If the Lionel ZW was Lionel’s Cadillac, the KW was Lionel’s Buick. It was a 190-watt transformer and Lionel sold it from 1950 to 1965. It replaced Lionel’s 150-watt ZW lookalike, the VW.

Finding original KW instructions or an original KW manual online is a bit difficult, but there’s plenty the original instructions don’t mention.

Lionel KW

The 190-watt Lionel KW was Lionel’s second most powerful transformer of the postwar era.

The KW is just like any other transformer in that you need to check it for safety before you use it. Also, although a lot of people forget to mention this, it’s important to unplug or otherwise disconnect the power when you’re not using it. I have my transformers plugged into a power strip with an on/off switch so I can switch them all on and off at once.

The KW is cheaper today than it was even a decade ago. Modern transformers with higher wattages put a dent in vintage high-end transformers’ market value. That said, the KW is still an excellent transformer. Pair up a KW with one of Lionel’s better postwar locomotives like a 675, and you’ll understand postwar Lionel’s enduring appeal. Reconditioned KWs sell for around $100. As-is or untested KWs can sell for less than $50, depending on what’s missing.

Lights and pinout

The KW has a red light that acts as a short-circuit indicator. It is not a power indicator. Normally you should expect this light to be off.

The KW has six posts on the back. Posts A-U and B-U correspond to the two big handles on each end. U is the common post, which goes to the outer rail.

The remaining posts give fixed voltage outputs. C-D, at 14 volts, is the most useful combination. D-U gives a 20 volt output on earlier models, which is high enough to cause some problems. Post-1956 models provide 19 volts at this output, which is a better voltage for Lionel O22 switches. Lionel O22s can’t handle 20 volts. The U-C combination outputs 6 volts but has no circuit breaker protection, so use an external circuit breaker if you use this output.

Although a KW can run other makes of trains, be very careful with a KW and Marx or American Flyer trains. KWs can output 19-20 volts, which is well above the 15 volt maximum that Marx and American Flyer motors are designed to handle. Use a voltmeter if you’re going to run non-Lionel trains.


The two large handles control your trains. The levers at the bottom controls the whistle. Flip it right to make train A whistle, or left to make train B whistle. Only one train can whistle at a time, unlike the top-end ZW. The buttons right next to each throttle change each train’s direction.

The KW’s relatively low cost makes it a popular accessory transformer, but you should consider one thing before you power accessories with a KW’s throttles. When the carbon rollers never roll, they tend to become brittle. The best way to prevent that is to adjust the voltage up or down a half volt every once in a while. Or you can power your accessories with something else, like an LW, or a PC power supply.

Common repairs

The most common problem I see on the KW is broken binding posts, which cuts off power to one or more of the controls. Fixing this is very similar to fixing binding posts on the ZW. The whistle control can also get a bit wimpy. You can fix that by replacing the old rectifier discs with diodes.


Early KW transformers from 1950-56 had a top voltage of 20 volts.

In 1957, Lionel released a revised version that topped out at 19 volts and provided a 19-volt output from posts D-U. Many experts believe this change was to prevent problems with Lionel’s O22 switches, which work well at 19 volts but burn out at 20.

There is little to no difference in value between the two versions.

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