The Bally/Stern lamp driver uses SCRs. The replacement for the one fried on your board should be 2N5060.
There are two different types used. One larger, one smaller.
Smaller = 2N5060
Larger = MCR106
Equivalent parts will also work. Just keep in mind that they're SCRs.
http://en.wikipedia.org/wiki/Silicon-controlled_rectifier
There is a good description of how the lamps work in the Bally theory of operation manual. Worth a read.
http://arcarc.xmission.com/Pinball/PDF%20Pinball%20Misc/Bally%20Theory%20of%20Operation.pdf