There were a plethora of options and accessories for this enlarger. This includes at least 3 types of original Durst light sources, perhaps more, as well as some aftermarket 3rd party options. The key question here is what's inside the head of your 138. Could you please post a photo?
I think most came standard with the adjustable (3 degrees of freedom) bulb socket that would fit a standard opal bulb. I think this was quite easily converted to the bulb socket for the point source in case you'd want to go that route. Note that in either case, you also need the appropriate sets of condensers. A third option available from Durst was a cold light that slid into the lower condenser socket; since this was a diffuse light source, no condensers are needed. Another option that is fairly common is the Ilford 500 head that plugs into the place where the 45-degree mirror is at the top front of the enlarger head; you lift out the mirror and put the T-shaped 500 light source in its spot. Again, you need the appropriate condensers.
In any case, in general: yes, it's easy to install one of the appropriate light sources in/on this enlarger. It depends mostly on what you've already got, and what can get your hands on.
