All Postwar KW’s use inexpensive rectifier discs to create the DC that trips the whistle solenoid in pre and postwar trains. Eventually these discs fail and must be replaced. The best replacement is a stud mounted, anode to case rectifier diode. The Diode needs to be a minimum of 15 amps, 36 volts, 1/4” diameter stud to attach neatly and Anode to Case (R on the end of the part number). There are many 1/4” stud diodes available that meet the above criteria. Model 1N1190AR, or 1N1186AR are 2 that are available online. The 1N1190AR is a 600V 40 Amp diode with a threaded 1/4”-28 stud mount. See Photo 1.

Dissassembly

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

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.

Figure #1 - Diode 1N1190AR

Photo #2- Rectifier Disc.

Photo #3- Pry off Speed Nut and remove Disk, Insulating washers

and brass stud.

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

Photo #4- Backside showing

Brass Arm, Brass Stud and

Insulating Washer.

Photo #5- Disc removed. Brass

Arm visible through hole.

Diode Installation 

4.Install the new Diode to the backside of 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.

Photo #6- Diode installed and

attached to Brass Arm .

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

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.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. Reassemble the top plate per the KW Rebuild Page

Photo #7- Check clearance and

bend diode and brass arm to adjust.