Excellent, thanks Bob.
I did find the second site, but the first one you listed was the info I needed.
Seems the 913 tube was introduced in 1936, and the National CRM scope must have been produced right after.
I'm doing a piece on the National CRM series of scopes for Electric Radio, but have found little data, so thanks for the leads.
I have four of them fun lilttle scopes and they are most buzzardly.
I currently use one with my HRO station, black crackle and green phosper, real boatanchor glowage.