I just described the heaters I made a couple of years ago to a friend and got to thinking I should maybe share the info and photo with tweeters. So, here is the build description:

Cut both ends from a large fruit (or tomato) juice can.
Bend some two pieces of wire with a hook on one end and a loop on the other
Make the wires so the can will hang about 1/2? below bottom of feeder and pop rivet in place
Using a clamp light (such as the one in the link below) notch and bend the upper part of shade to fit inside can
Pop rivet in place so the off/on switch on socket is just inside the bottom of the can
(I had to pinch the shade slightly to get it to hold onto socket firmly)
Wrap in reflective insulation such as shown in link below
Use nothing bigger than a forty watt bulb or it will melt the feeder bottom

http://www.homedepot.com/p/HDX-75-Watt-Incandescent-Clamp-Light-CE-200PDQ/100354513#.UqUsB-LLKF8

http://www.homedepot.com/p/Reach-Barrier-2-ft-x-10-ft-Air-Double-Reflective-Polyethylene-Insulation-Roll-DD24010/204476650#.UqUttuLLKF8

Photo is here: http://upload.pbase.com/image/153703506

Joseph Higbee
Spanaway, WA
Mailto: jvhigbee at hotmail.com