Reversing Streetcar voltage

[Joey12]

I bought an ON30 Christmas streetcar without a power adapter.  I have looked at the control board in the house and there is an LM317 voltage regulator which can regulate up to 37v.  I've seen both 7.5v or a 16v adapter for this set.  Does anyone know how to determine the input voltage on this unit?  There is no label on this unit.
Thanks

[Tom_C]

I seem to be late, but 99% sure it will use a 16VAC power supply.