[Arran]

Apparently, it's called an "intermediate" AKA E17 base. It's a little bigger than a candelabra base. It hangs down below the chassis to illuminate the speaker so I don't think heat will be much of an issue.

Lots of options here: http://www.bulbtown.com/Intermediate_Scr..._s/312.htm

According to Wikipedia, assuming it's correct, a an E17 is the same base as a C9 Christmas bulb, it's 17 mm in diameter. The night light style candelabra bulbs are a C7 or E12 which is 12 mm in diameter, the same base used for 120 volt Christmas lights.

http://en.wikipedia.org/wiki/Edison_screw

Here is a site on old fashioned Christmas lights of the series string variety which used C6 bulbs. Very interesting evn though I'm not a light bulb collector.
Regards
Arran