The Hawk illuminators use EKE 150W 21Volt bulbs.  These halogen bulbs are only rated for 200 hours! The only way you can get more life out of these bulbs is not to run them at full brightness.

Please see these two links for EKE bulbs from bulbs.com and bulbworks.com respectively:

Ushio 150W 21V Halogen EKE Bulb | EKE (21V, 200 Hrs) | Bulbs.com

Replacement Bulb for Product: EKE, Halogen Lamp (bulbworks.com)