Of course, there is always the chance that the new bulb you got was either faulty, or someone had got fingerprints on it (which will cause it to burn out quickly).

Based on the info at the back, I think you have model 6730 which is pictured here:


With that model, the necessary transformer and circuitry is built in, and a voltage stabilizer is optional. The available optional Beseler voltage stabilizer is model 6731, and is pictured here:


So it looks to me that your enlarger should work as is, unless something in your setup (electric power source problems or equipment malfunction) gives you electric power that requires stabilization.

Is the timer you are using one that you had before you got the enlarger? I ask, because some timers are such that you need to use stabilization between them and the head.

Hope this helps.