@SteveH posted:My understanding of the 1.5 Ohm resistor is that when the whistle lever is advanced into the hold position, it drops the voltage from the starting position to keep the whistle motor running on PW tenders.
Actually, the 1.5 ohm resistor is connected across the rectifier. That reduces the DC offset, but also boosts the voltage a few volts for to compensate for the voltage drop due to the current for the whistle tender motor.