Just to be clear: Is this a PCS130 without the matching PCS150 light source? Every PCS130 I've seen for sale on eBay has come with a PCS150, which has a light source in the head with three MR11 halogen bulbs and an external control panel that lets you adjust the intensity of the red, green, and blue bulbs. If you've got the PCS150, then you'd probably do better to use it to adjust the contrast of your prints instead of using multigrade filters. Check the Dead Link Removed for manuals and other help with these enlargers.
If you've got only the PCS130, though, with a single screw-in bulb in the head, the filter drawer and multigrade filters are probably the way to go.