[Reece]

A radio of this vintage was made to use a long wire antenna, not a loop. For local use, ten or fifteen feet of insulated wire run around the baseboard, or under the edge of the rug, or up behind the curtain and hooked to the curtain rod, connected to the antenna terminal, will work.

The reason that built-in loop antennas work on later radios is that they were designed to be substituted for the small antenna coil that was used in earlier sets. Since earlier sets have the antenna coils built in, the tuning capacitor already has its coil and any other coil added to it just upsets the capacitive/inductive pair.

It is possible, however, to build a large tuned loop separate from the radio and couple it to the radio's antenna terminal with a one-turn sensing loop wound alongside the tuned loop.