agpthng, a lot of good information above. I have a 66-16 that is just a few years older. A more direct link to the manual would be to go to
http://www.singerco.com/support/instruction-manuals and type in 66 and click on search. About half way down the page you will see three listings for 66, one is for the treadle, one for 66-16 and then 66-18. The 66-18 would be similar but has a different finish on it. You can find many model descriptions at
http://ismacs.net/singer_sewing_mach...sses-1-99.html Something to note is, that while Mickey2's link to the AJ serial numbers indicates a date of March 27 1950, it is highly unlikely that your machine was actually made on that date. It simply means that is the date that the serial number would have been
allocated to that model of machine.
Have fun with your "new" machine. Wipe down with sewing machine oil and be sure to oil the machine as indicated in the manual including the sewing hook wick (should be a what looks to be red felt as shown on page 8 of the pdf). They are good straight stitch machines and fairly easy to maintain.
Janey, Neat people never make the exciting discoveries I do.