This document details how to resolve a slipping drive train (the locomotive chuffs, but doesn't move) on the HO 4-8-2 Mohawk steam locomotive.
This document lists the recommended DC transformers for use with M.T.H. HO locomotives outfitted with Proto-Sound 3.0.
This document details the differences between the various sizes of Marklin C-Track HO Stud Rail curves. The chart includes a mm to inch comparison for each curve's radius.