Replace a Lionel RW rectifier disc with a diode

Vintage Lionel transformers activated the whistle using a rectifier disc. These discs tend to degrade over time. You can expect to pay about $5 for a replacement disc. But a modern diode is much cheaper, works better, and is more reliable. Here’s how to replace a Lionel RW rectifier disc with a diode.

First things first: Get a common 6A10 diode. They’re cheap. You ought to be able to get one for about $1.50 or 10 of them for around $5, shipped. If you buy them from overseas, then they can be even cheaper. However, you’ll have to tolerate much slower shipping. People have used other 6-amp diodes in the past, but the 6A10 is the current version of those older diodes. There was nothing wrong with them, but the 6A10 will be easier for you to find today.

Removing the RW’s rectifier disc

replace a Lionel RW rectifier disc with a diode
Desolder or clip the wire the screwdriver is pointing to on the right. On the left, note the rectifier disc and the resistance wire.

Open up the transformer. Remove the screw on the handle if it has one, then pull straight up on the handle. Flip the transformer over and remove the four screws. Flip the transformer back right side up, and lift the cover off.

With the front of the transformer facing you, the rectifier disc is on the left.

Above the rectifier, you’ll see a bare wire wrapped around an insulator with a yellow wire attached to it. Lionel called this a resistance wire. Desolder the yellow wire from the resistance wire. On the other side of the transformer, there’s a black wire that connects to a tab near the whistle button. It’s the lower of the two black wires. Clip or desolder this black wire.

With that done, you can move on to that obsolete, pesky disc.

Lionel RW rectifier removal
Pry off the speed nut with a small screwdriver. Note the disc’s appearance. This disc still works, but not reliably.

Next, pry off the speed nut holding the rectifier disc.

Straighten the four tabs that hold the control board in place on the top of the transformer. Lift up the left side enough that the whole whistle control assembly will come free. Now you can pry off the insulating washer and push out the stud that held the rectifier disc.

Installing the diode

Lionel RW diode placement
The diode attaches to the yellow wire and this copper arm.

After you remove all the old, obsolete stuff, you’ll see a copper arm that the stud engaged.

Flip the copper arm up enough that you can get to it.

Solder the striped side of the diode to the arm. Next, solder the yellow wire to the other end of the diode and then insulate the connection with shrink tube or electrical tape. Finally, put a piece of black electrical tape on the back side of the copper arm. There’s usually plenty of clearance between the copper and the transformer core, but be safe.

Here’s what the finished installation looks like. The striped end of the diode goes to the yellow wire and the other end goes on the copper arm. Be sure to insulate the connection between the diode and the wire.

Check everything for clearance before you snap the whistle control assembly back into place and press the control board back down. Move the diode out of the way if necessary. Twist the four tabs slightly to secure it, then replace the cover and the handle, and secure the handle with the four screws.

Advantages of the diode

With a diode, you’ll find the slightest press of the whistle button starts the whistle with no delay. With a worn-out rectifier disc, there may be a delay and it may not work every time. In the 1950s, that disc was all we had, but we have better technology today. The diode is also about three times more rugged than the disc. The disc has about a 2 amp rating while the diode has a 6 amp rating.

Replacing a Lionel RW transformer rectifier disc with a diode is the best way to get reliable whistle operation. It’s not a difficult upgrade to do and it’s certainly not expensive.

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