Michael Axel , Dec 28, 2006; 08:06 p.m.
I have a Chromega BXL (about 20 years old), and have never had to replace the bulb. As for cooling fans, they don't need them because of a heat sink built into them. You didn't say exactly "when" it blows. When the timer comes on?
I'd put the surge protection before the timer, and not in between. It could be a short in the enlarger or timer, I suppose. How many bulbs have you gone through? Maybe you just got a bad replacement bulb.