MTH Smoke Unit for WBB 773 Hudson

Not a resistor, but rather some diode pairs.  I normally use a couple of bridge rectifiers connected as diode pairs for this job.  3A models are sufficient for this task.  refer to the diagram below, if you connect the + and - leads together and connect the wire to the motor in series with the bridge using the AC inputs ~, it'll insert about a 1.5V drop in the motor voltage.  If you use two bridges in series, it'll drop the voltage around 3V.  This will assist the smoke and also tame the engine at higher track voltages.  You can put addition al bridge rectifiers in series if necessary for even more voltage drop.

3A Bridge Rectifier

Thanks Gunner, I appreciate the  tip. Do you have parts name and a source?

Gunner, my apologizes--you included source for parts in a link in your response. My bad.

I have some older MTH fan units that I bought to go in my Williams Scale Hudson. What issues, if any did you run into when installing the MTH smoke units? Were any frame or shell mods necessary?

Thanks,

Mike, it was straightforward. I took off the boiler front to see how much room I had and then checked the available MTH smoke generators available that would fit the space. I'd give you the dimensions, but as usual, if something works, I pitch the dimensions. I'd ball park the width as no more than 1 and 1/2" , and the depth  at about 2". I used an electronic caliper to get the readings, and it was dead on. I did have to buy 9/32" brass tubing to make an extension for the smoke generator to extend through the stack. I separated the road gearing from the boiler assembly, keeping the parts in a plastic tray ( a hard-earned lesson). Once disassembled, I removed the Slueth board and heating unit to free up space for the MTH unit. I connected the MTH power leads to the power pickup and frame leads at the bottom of the frame  itself. It was extremely helpful to use what was in place. I added some shrink insulation to one side of both leads before soldering and  slipped it over the solder on the leads and heated it in place. I also added  a micro slide switch to  one lead and used 5-minute epoxy to secure it  where it could be reached so that I could run the engine without the smoke unit operating,  and it turned out to be pretty much unnoticeable once in place. To secure the MTH smoke unit unit in place, I did something unorthodox. I used 5 minute epoxy and a small shim of balsa underneath the unit to keep everything snug.

I still have some work to do however; my WBB 773 will move at a good clip at about 6-8 volts on my layout. The MTH really kicks out smoke at about 15 v. I can't run that high and stay on the rails.  I suggest you look in this forum at the comments of Gunrunner John, as he gave me the first directions on how to try this and he also has a suggestion for the voltage issue. He proposed using bridge rectifier(s) to reduce voltage  to the motor, causing it to require higher voltage to maintain speed.  But since the smoke unit is NOT connected to the rectifier(s) this results in sending higher voltage to the smoke unit, creating more smoke but at a speed that keeps the 773 on the rails. I have the rectifiers on order.

Be sure to refer to Gunrunner John's posts on this subject, since you are definitely getting it from me second hand. He has photos of the boiler casting open with a new unit inserted and  a source for the rectifiers, plus a diagram. 

A heck of a lot of information, but if I can do it, you can to.

Thanks for giving me some detailed info. I like the switch idea. I never thought of that when I was planning my upgrade.

One thing to keep in mind is making sure the smoke unit is removable for maintenance.  It's not if, but when it'll need some work, nature of the beast.