A couple weeks ago I made the plunge, and converted a couple Williams engines to series wiring. It worked really well, and inhanced the slow speed performance remarkably. A nice little side effect of the modification concerns double-heading. Before the mod., when I double-headed engines it worked for a little while, and then one would always go into neutral (usually over a switch). Wiring in series seems to have ended that problem. I am guessing it is because more voltage is applied to the track.
I know this topic has been done to death, but it really does make a difference. I used to think the people complaining about their Williams engines going to fast just weren’t pulling enough cars. I was mistaken!
Another cure may be to buy and use a modern type transformer as they have lower starting voltages than the post war transformers.
So far I don’t have a problem with double heading a couple of powered Williams diesels, I have taken out the reversing feature in two of my SD-45’s and installed a bridge rectifier instead as that allows me only one direction. Might be the bridge rectifier lowers the voltage too not sure on that.
Phillyreading, You are correct. I am currently using a modern ZW with 3 180 watt bricks, command base, and cab-1. This transformer has helped a lot with the slow speed operation of my Williams loco.'s, as the can be kinda “fine-tuned” for speed with this set-up. That being said, the series wiring modification allowed that “fine-tuning” to take place at even a lower speed than before.