On one of the Facebook model train groups I was in, I read an article about someone who was building a transistorized throttle based upon a design called the “Pacematic”. I did a bit of googling, and found this description. It seems like a relatively simple circuit based upon the 555 timer. I started digging around and also found this page which lists a lot of transistorized circuits for driving model trains:

http://www.circuitous.ca/Throttles.html

I find this kind of stuff fairly interesting. Still, I think these circuits are mostly of historical interest. Now, with the availability of cheap microcontrollers and DC motor drivers, it seems like you can make far more versatile and powerful throttle control circuits. As soon as my new N scale network gets up and running, I’ll have an update of what I’m doing.