I'm new to model trains so forgive me if I'm going about this the wrong way. I have a Bachmann transformer and speed controller that I am using to power a trolley line that I have running through my Christmas village. I ordered a Circuitron AR-2 to auto reverse the trolley (it should be here tomorrow). From what I understand the board needs a min. of 16V but no more than 18V. I tested my transformer output, it's about 21V. Can I wire in a resistor between the transformer and circuit board or is there another way to step down the voltage?

Speed Controller:
Item number: 46605A

Transformer:
Model: AC1601000
Input: AC120V 60Hz 24W
Output: AC16V 1000mA 16VA