Slow printing on a Durst 138 with a CLS301 head
Our Durst 138 CLS301 is a 5x7 colour head with two 120 volt 300 watt bulbs and a Durst TRA301 power transformer. The formats we use on this enlarger aare 35mm, medium format 645 up to 6x9, and large format 4x5 and 5x7.
In Canada, we use the 110/120volt plug but the transformer also has the European 220/240 volt plug.
Our enlarger doesn't seem slow, compared to our other enlargers.
At the moment we are using a Rodenstock 150mm lens which has F stops ranging from F5.6 (wide aperture - large hole, lets the most light through the lens) to F45 (narrow aperture - small hole allows less light through the lens). The wider F stop, in our lens 5.6, takes less time to get to black than using F45. Some photographers prefer not to use the widest opening of a lens....but to move 2 or 3 stops down. We mostly use F11 or F16.
Check your lenses to see what F stop you are using on each enlarger lens for comparison.
I'm sure others will chime in to help you as well. Wonderful enlargers, aren't they? Good luck with this.