Here are the images of the Klingon D-6 created by Tobias Richter. The D-6 is the state of the art ship before the D-7s are launched. In "Axanar" the D-7 (like the Constitution Class) is the dreadnaught of their day. There is an arms race to get the respective ships off the line and into battle. So the D-6 is the main ship of the line for the Klingons.
Hope you enjoy them.