Q - How can I date my Harmony guitar from the serial number ?
A - Usually you will find two stamps inside your Harmony guitar. They always are on a place easy to read, ie near the f-holes on a archtop. The larger one is the serial number, and the part after the "H" letter is the model number. For example, on the photo below this guitar is without doubt a H22 (You can type a model number, with the H, on the search box on top of this page). The first part of the serial number has no precise meaning relative to the date of production. It seems Harmony reset these numbers in every batch of the model, so a "6690H22" can be older than a "123H22" for example. Tip : on many guitars (easy to check on flat top acoustics), Harmony stamped the top of the guitar as well as the back, so if the number on the back is difficult to read, use a mirror and check under the top (near the neck)
The other smaller stamp is the date stamp and indicates the year of production. It's said that the letter at the beginning indicates the period of the year, like "F" for "Fall" or "S" for "Spring". That was before Ed, a former worker from the Harmony factory, said : "The company closed down production every July for two weeks. During the last two weeks of June an effort was made to finish as many orders as possible and not start any new orders. The last days of June, we had a complete inventory. I believe the "F'" and "S" may have stood for first and second half of the year."