Larry, in my case I used a Lionel smoke unit but its no longer available. I upgraded mine maybe 8 years ago. If you have trouble getting your hands on an MTH smoke unit, the ones used in the Lionel Lionchief engines will fit. You will have to change the resistor. I use 22 ohm 2 watt wire wounds connected to the R2LC. Basically how the existing puffer unit is driven from.
Pete