I was looking at the antenna hook-up diagram for my 1936 Silvertone Model 1970A, and it looks like there are three wires (red, black, green) that can be hooked up in two different ways: either the black and red hooked to a cold-water pipe and the green to a long wire, or the black alone to a water-pipe ground and the red and green twisted together and attached to a "doublet antenna".

First off, exactly what is a doublet antenna, and what are the comparative advantages of a "doublet" versus a long wire?

Second, were there any after-market loop antennas made that would work well with this set, along the lines of a Zenith "Wave Magnet"? For that matter, how hard would it be to build a rotating loop to fit inside the cabinet, and how would I hook it up?

A doublet is a dipole. These were usually center-fed through twisted pair, sometimes with a matching transformer incorporated at the feed point and another transformer at the radio.

Advantage is lower noise pickup.

Okay, now what about adding a loop to this set? Feasible, or should I just run a wire antenna and ground indoors if I want to avoid an outdoor antenna? I live with my parents (can't afford otherwise) so drilling holes in the walls for lead-ins is pretty much out of the question...

I have also heard of something called a Silvertone Allwave Antenna here (I believe this radio belongs to a forum member):

http://home.comcast.net/~skbrothers/site/?/page/Silvertone_4586_Console_Radio_%28est._1936%29/

Anybody know anything about this device?