Recently, the production data was found and there is no longer any need for guessing.
This information is being compiled, organized and edited into a soon to be released book that details all sorts of production and manufacturing information, including tables showing serial numbers and their date of production.
In the example shown, 190-7215 was made in the 15th week of 1972.
Earlier Leslie motors have a stamped four digit code.
All available information must be taken as a whole, and, combined with some general tips and observations provided below, a narrow range of probable production years can be arrived at which in many cases will be accurate enough for most people's desires.
One thing to remember in this chronological quest is these instruments were built to be played, not (in most cases) to become museum pieces.
Some specific examples are cited that can be used to provide assistance in identifying the production date of similar components. Tung-Sol 6550 tubes have the following format: XXXYYWW, where XXX is the EIA manufacturer code, YY is the last two digits of the year and WW is the number of the week in that year.
285642 would be a Rola speaker made in the 42 week of 19x6 (you have to figure out which decade using other information).
For additional speaker manufacturer codes, see Ted Weber's listing at Weber Speakers.
Thanks to the Electronics Industry Association (EIA) code conveniently placed on them by the manufacturer, many individual components can be dated to the year and week of production.
Due to Hammond and Leslie purchasing components in large quantities, using these codes as definitive signposts will not produce an accurate "born on" date.