Bought from a thrift shop because it was cheap and I wanted another machine to pull apart as practice before I open up the 1515-4 below.

The 1500, 1515 and 1515-4 are virtually identical to look at and almost identical inside. The 1500 is the base model (I don't have one) and is monoaural. The 1515-4 plays 4-track stereo. This 1515 is an in-between: it plays 2-track stereo, which was an early stereo format that didn't catch on.

If you want to impress your friends or win bar bets, there's a quick way to tell these apart just by looking at them. The 1500 says WOLLENSAK on the carrying handle and has no stereo badge. The 1515 says WOLLENSAK on the handle and has a Stereo badge. The 1515-4 has the stereo badge and says WOLLENSAK 3M on the handle.

Inside, the 1500 and 1515 are the same except for the heads and an additional pre-amplifier section inside; to play back in stereo, one track plays through the machine's internal speaker and the other goes out to a jack in the back; you line that out into an external amplifier/speaker system that has an AUX input. Some radios, some televisions, and most stereo systems had them, or you could buy just an audio amplifier and a speaker and go that route.

Pulling this thing apart was a nightmare. Actually—pulling it apart was easy, it was reassembly that was miserable. The Old Man was saying how much he liked them because they're modular inside, and you could work on the electronics without disturbing the deck, and vice-versa. Putting it back together should have been easy but that secondary, add-on pre-amp was jammed hard against the speaker and wouldn't seat the way it was originally, and we couldn't get the body back together; I have no idea how it ever got assembled in the first place.