how do you replace one of these?
EDWARD C A
It's easy. The flash tube is protected by the removable pyrex glass protector and you have to remove the glass protector first. There are two wire clips that hold the glass in place: First, push the clips (one at a time) toward the glass to release them from the holding screw. No tools needed to do this. You'll see a two holes in the glass base where the other end of the clips are anchored. When your re-assemble the glass and clips, you'll know where the end of the clips go.
Next, remove the flash tube by pulling up near the flash tube metal pins. I usually use cotton gloves so I don't leave any oils on the surface of the tube. Take caution not to bend the metal wires that encircle the flash tube. Firmly insert the new tube's pins into the base, re-assmble the glass protector with the 2 pins and fire away! Simple.