Some of the entries on the age list show actual known production dates and can be used as markers to guage the quality of other entries around them.Until this work is published, the Age List will continue to function more or less as it has; a quasi-definitive source of this information and a registry of Hammond and Leslie product owners.However, by examining those components as a group one can determine that the instrument was produced no earlier than the latest date indicated by its component parts.In general, tubes appear to have had the shortest stock life and speakers the longest.Inside each Leslie produced after 1956, on the lower baffle, is a date code (sometimes hidden by the bass speaker).Here's how it works: You have to be able to date the Leslie within 10 years, which should be fairly easy.Just to get started, 21H's are 1951 to 1958, 22H's are 1958 to 1963, 122/142/147/145's are late 1963 and later.
The code typically takes the form of YYWW, where YY is the last two digits of the production year and WW is the production week. All of the speakers in Hammond organs, Hammond Tone Cabinets and Leslie cabinets dating from 1946 forward that I have seen have production date codes stamped on them. The coding scheme is XXXYWW where XXX is the company EIA code (Jensen = 220, Rola = 285, Heppner = 575), Y is the last digit of the production year, and WW is the production week.
Later Leslie motors have a sticker on them indicating their manufacturing date.
The formula is XXX-YYWW, where XXX is the manufacturer EIA code (190 indicates General Instrument in the present example), YY is the last two digits of the year of manufacture, and WW is the week of manufacture.
Even the above is fraught with some risk, as replacement parts used for repair or modification will occasionally skew the overall picture.
Additionally, some organs have been pieced together in order to get one working unit out of many; this will produce inconsistent and unlikely date code ranges.