All Postwar ZW’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



Use the steps that follow to replace the original rectifier disks.

•Remove the Red and Green lens covers from the ZW.

•Remove the 2 light bulbs.

•Remove the 4 bolts that hold the ZW top cover on.

•Remove the ZW top cover.

•Remove the 2 screws holding down the Whistle Switch Assembly. Photo 2.

Figure #1 - Diode 1N1190AR

Photo #2 - Remove 2 Screws

•Carefully lift up the Whistle Switch Assembly. Photo 3.

•Watch out for the flat piece of insulation under it and the insulation under that with the 4 fingers. See Photos 4 & 5

Photo #3 - Lift Up the Whistle Switch Assembly

Photo #4 - Flat Insulation

Photo #5 - Spring Contact Insulation with the 4 fingers

•Use a small flat bladed screwdriver to pry off the Speed Nut with the black wire that is holding the old Rectifier Disc in place. Photo 6.

•Remove the old Rectifier Disc , Stud and Fiber Washers. Photo 7

•Use a soldering iron to remove the Black Wire from the Speed Nut.  Photos 7 & 8.

Photo #6 - Pry Off the Speed Nut

Photo #7 - Stud, Fiber Washers, Disc & Speed Nut.

Photo #8 - Remove the Black Wire from the Speed Nut.

DO NOT REMOVE THE WHITE RESISTOR WIRE shown in Photo 9 & 10.

Diode Installation 



•Install the new Diode to the Whistle Switch Assembly Bracket in the same hole that the Rectifier Disc was in. Use 11/16” and a 7/16” wrenches to tighten the Diode securely. Photos 9 & 10.

Photo #9 - Install the New Diode.

Photo #8 - Remove the Black Wire from the Speed Nut.

•Insert the Black Wire through the hole in the end of the Diode. Photo 11.

•Solder the Black Wire to the end of the Diode. Photo 12

Photo #11 - Re-attach Black Wire to the Diode.

Photo #12 - Solder the Black Wire to the Diode.

Reassembly 

•Clean the brass Spring Contact and the Shaft with a Dremel wire wheel. Photo 13.

•Apply a light coat of clear teflon grease under the spring contact and on the shaft where it contacts the case. Photo 13.

• Hold the Spring Contact in place for reassembly. Photo 13.

•Install the Spring Contact Insulation with the 4 fingers over the Shaft & Spring Contact. Make sure that the 4 vertical fingers are bent down and go in alongside the shaft. Photo 14.

Photo #13 - B or C Inner Dial Shaft & Spring Contact.

Photo #14 - Install Spring Contact Insulation over the Shaft & Spring Contact.

•Install the Flat Insulation over theSpring Contact Insulation. Photo 15.

•Reinstall the Whistle Switch Assembly . Install and tighten the  2 round head screws. Photo 16.

•Reinstall the ZW top cover.

•Reinstall the 4 screws that hold the ZW top cover on.

•Reinstall the 2 light bulbs.

•Reinstall the Red and Green lens covers from the ZW.

•Repeat everything above for the Diode on the other side of the transformer.

Photo #15 - Install the Flat Insulation over the Spring Contact Insulation.

Photo #16 - Install the Whistle Switch Assembly.