Here's a wonderfully interesting little four inch reel of tape that arrived with a lot of other media tapes that I bought somewhere, a few years ago. This seems to have been the property of a jingle company, rather than a radio station, because there are jingles and ads for four stations and eight products (well, not all of them are products - one ad is simply a jingle encouraging folks to cook their food using electricity instead of gas). More than one customer seems to be represented here, perhaps (based on the radio stations involved) all in the Northwest US.
These jingles - which range from a few seconds to a minute (the sixteen of them total about seven minutes) - may or may not have ever seen the light of day on any radio stations. The box makes it clear that these are demos, labeling them as "audition only" in two places. It looks like a company called SRP was responsible for them.
As for the stations involved, only one has an identified location within its jingles: KRLC, in Lewiston-Clarkston, Washington. This station still exists, still at 1350 AM. As for the other stations, KYTE was in Pocatello, ID, KIMA was at 980 in Yakima, WA (where the call letters still exist as a TV station), and I KZUN was at 630 on the dial in Spokane, WA.
My guess is that this is from about 1957-58 - the style of the ads, and in particular the one which uses a calypso setting ("Bogie Brothers Bread") would seem to put them in that range.
I love everything about these ads and jingles - the musical styles, the peppy vocals, the thick echoes - actually, I wish radio still sounded like this.
As a bonus track, here are the complete contents of another tape from this batch of tapes, in this case, a group of sound effects people spend about ten minutes gathering sounds for a TV or radio show (probably TV, judging from the other tapes of this sort that I've found in this haul). They start with breaking glass, then go on with some atmospheric recordings (this section is quite soft - they seem to be trying to get a realistic ambient sound of the background noise heard while in an apartment building - then we get into some slamming doors and other sounds.