From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specification for two standard coils and their applicable date ranges and drawing numbers.
| Identifier | ExFiles\Box 69\1\ scan0289 | |
| Date | 3rd January 1930 | |
| X8710 3.1.30. Standard coil D.71650 up to Dec. 2nd as drawing D.70759. Standard coil D.71650 from Dec. 2nd to Dec. 30th as drawing D.72428. EFC/HEW. | ||