Well, I found a short article that talks about why bulbs are used in these circuits, as opposed to fuses. The bulb acts less like a fuse and more like a compressor. Interesting read:
TA Speaker Topics: Vent FAQ's
Thanks, Jerold. Somebody had mentioned a 24v elsewhere, but was uncertain. Like many others, I bought this cabinet used, without a manual. After digging all over the Internet, I figured out, based on the parallel locking pins, the size of the bulb's base and the single contact, it's style is known as BA15S (Bayonet, 15mm diameter, Single contact). Still, I could find nothing that specified wattage.
I just placed an order on eBay for 10 of these cheap. Hope it works!