Tranz4mr’s KW Page


Replacing the KW Whistle Rectifier Disc with a Diode

Photo #1 - Diode 1N1190AR

All Postwar KW’s use an inexpensive rectifier disc to create the DC that trips the whistle solenoid in pre and postwar trains. In modern trains it activates the electronic whistle. Eventually these discs fail and must be replaced. The best replacement is a stud mounted, anode to case rectifier diode. Model 1N1190AR, available from is a 600V 40 Amp diode with a threaded 1/4”-28 stud mount. See Photo 1. Use the steps that follow to replace the original rectifier disks.

  1. 1.Remove the Cover and Top Plate per the KW Rebuild Page.

  2. 2.Use a small flat bladed screwdriver to pry off the Speed Nut that is holding the old Rectifier Disc in place. Photo 2 & 3.

  3. 3.Remove the old Rectifier Disc, Stud and Fiber Washers.
    Photo 4 and 5.

  4. 4.Install the new Diode to the Bracket in the same hole that the Rectifier Disc was in. The top of the Diode should face in towards the center of the transformer.  Use 11/16” and a 7/16” wrenches to tighten the Diode securely. Photo 6.

  5. 5.Bend the top of the Diode and the Brass Arm gently so that the connector holes match up. Photos 4 - 7.

  6. 6.Use a number 6 brass or steel bolt, nut and lock washer to connect the diode to the brass arm. Photo 6 & 7.

  7. 7.Temporarily reinstall the top plate (don’t bend the tabs to lock the top plate yet). Rotate the roller arm and verify that the screw attached to the diode and brass arm doesn’t touch anything. If it touches bend the top of the diode and brass arm so that it clears. Photo 6 & 7

  8. 8. Reassemble the top plate per the KW Rebuild Page

Photo #3- Pry off Speed Nut and remove Disk, Insulating washers and brass stud.
Photo #2- Rectifier Disc. Photo by Kris Blackwell
Photo #4- Backside showing Brass Arm, Brass Stud and Insulating Washer.
Photo #5- Disc removed. Brass Arm visible through hole. Photo by Kris Blackwell
Photo #6- Diode installed and attached to  Brass Arm .

Photo #7- Check clearance and bend diode and brass arm to adjust.