Joe, believe it or not, those installations were quite typical. We have a fairly large law firm that is a customer with a similar arrangement.

Prior to about 1976, the norm was 23" racks with multiple 584 panels (13 line card slots each). The panels eventually were modified to permit a single interrupter to operate lamps in other panels, resulting in synchronized lamp flash/wink rates, along with ringing cadence.

At the bottom of these racks, the power supply and ring generator resided. In particularly large installations, there were multiple power supplies.

Around 1975, Western Electric developed the 620 series of modular wall-mounted panels. Each 620A panel had eight line card slots and a Burndy connector that plugged into modular power supplies. There were two power supplies available, one with four power output connectors and the other with ten. These power supplies were unique in the fact that they included the interrupter and ring generator.

These panels were designed to align with the Bell System standard for backboard layouts. They literally took the place of the red field of KSU blocks. The footprint is equivalent to that of a typical half backboard. In essence, with appropriate power supplies, these panels could be stacked side-by-side forever. The only limit was wall space. Since they weren't designed for vertical stacking, horizontally was the only way to grow. Still, with integrated 66 blocks in the unit, they were very space-efficient.

640- series panels were also a part of this family. They included an integral yellow 66 block field for optional services, such as intercoms, tie line circuits, paging interfaces, etc.

The system was quite impressive and offered amazing flexibility. The panels were all plastic, so installation was a breeze. They were lightweight and only required a few screws. Even the power supplies had a back plate that was mounted to the wall and then the actual unit itself would hang on keyhole slots. A single screw secured it to the mount.

Ed Vaughn, MBSWWYPBX