Please explain what materials you are using such as paper, graded vs. variable contrast, film etc. I have the same enlarger and get 10-20 second exposures at f5.6 to f11 using Tri-X 120 negatives with Ilford variable contrast filters (usually #1-1/5 to #3) on Adox and Ilford VC papers with the standard enlarger bulb. If I were to print with a fast graded paper and a thin negative I can imagine possibly needing less light. I have flexible neutral density material available if I ever need it. The ND material comes in a roll. You cut a piece to fit into the filter drawer above the negative sandwiched with the VC filter. The ND material is not expensive and should be available at stores like B&H. However, I looked on their website tonight and could not find it. Maybe another member can provide the proper name and where to buy it.
I wonder if your negatives are too thin?