Teletype Corporation Manuals
Info on HAL ST-6 Terminal Unit
This scan removed at the request of Bill Henry K9GWT at Hal Communications. I foolishly forgot that HAL is still very much in business, and happy to provide manuals for their equipment (at modest cost).
Model 28 Reperf
Fundamentals of Page Typer of the AN/FGC-58
Atlantic Surplus Sales Catalog
This is a very useful reference for Teletype machines and parts; page 16 shows the part numbers for the speed gears for Models 14, 15, and 28, for example.