Hi Sam, Thanks for providing the diagrams for the KTUs (I traced down the BSP # and found the complete documents). Luckily, there are 6Bs on ebay, and I just ordered them. Can't wait to test and compare their operation to the 18D I have on another line. Since I'm only looking for the line-in-use indicated via A-Lead, the 6B may be the ticket! I'll post my results. Thanks for helping. Jim