I've just received a copy of a book called "Tuba Views" by Mark S. Chalabala. It is a collection of over 200 full page photos of Tubas and Tuba Players dating back to the early 1800's. It encompasses Helicons, Sousaphones, Ophecleides, OTS(Over The Shoulder) Tubas as well as the more familiar ones that we see and use today. The quality of the images is first class and this book is currently being limited to a run of 750 copies. I obtained my copy via Ebay and cost $51, well worth it if you're interested in old tubas.