I Googled it, but it turns out I should have used the search function here first as the first result was a link to a
post here from last year.
Mitica, who has had the entire history of every photo company and camera implanted in his head by the government

, had this to say...
"Pax Ruby was built by Yamato Camera Industry (Japan) around 1950. Came with two distinct lenses on a Synchro shutter. The first one was the Luminar 45/2.8 or 45/3.5 and the other was Color Luna 45/2.8
Yamato was bought by Canon in 1960."
Unfortunately I can't find an online manual for the Pax but I will keep looking. The
Rangefinder Forum may be another good place to ask.