From a bit of googling, they came out of the Pioneer S-A700V, one of the all-in-one home stereos (cassette, LP, speakers). Sears has them labeled as replacement parts, so they appear to be gutted from a nice Sears stereo from the early 80s.
i dont really have anything planned for them. i figure ill hang on to them and build some enclosures for HT use at some point, but ill be sure to show something