[BDM]

Ok I'm not up & up on everything radio. So maybe someone can better explain to me the tuned antenna inputs on the back of most 36 through 38 MY sets. Those that are used for the "tuned aerial" antennas they once sold (I have a few factory doublets stashed away). I'm assuming from reading the schematic it's simply switching to tuned coils optimized for doublet antennas (of the manufactures design or perimeters). I was playing around with one of the loop antennas and decided to connect it up to the tuned inputs. Suddenly I could actually use the antenna without tuning the variable cap itself, though when done it would still optimize reception. Of course this brought in plenty more noise and the antenna lost some of it directional characteristics.

[Radioroslyn]

I would suspect that it's just a way to get you to buy a Philco antenna. The older sets just have a single termination for the antenna connection for a longwire. The later set with two connections is set up for an antenna setup being fed with Hi Z ladder line in a dipole configuration. They tend to work a bit better than the longwire, quieter and a little directional.
Terry