The Sears Silvertone guitar really made its mark in music history as the unofficial "first guitar" of guitar's icons.
Chet Atkins, Bob Dylan and Jimi Hendrix, among many others, played their first chords on a Sears Silvertone.
During World War II, Sears introduced the Silvertone radio antenna with "stratobeam reception." And to help power the radios, Sears sold Silvertone wind generators.
In the late 1930s, however, Silvertone radios quickly took off in popularity.
The era corresponded with the outbreak of military aggressions in the Pacific theater.
There has also been a conventional wisdom that Harmony did not put serial numbers on their mandolins. A Harmony Model number is generally stamped as XXXHXX.
It appears that the number after the H is the model number and the number prior is the serial of that batch, made in that time period.
In other words, you can't date a Harmony instrument from the serial number alone. It should also be noted that some of the time that stamped number just isn't there.