BA11-E Mounting Box

The BA11-E mounting box was one of the two earliest earliest standard system unit backplane mounting box produced by DEC, along with the BA11-C Mounting Box.

One of the BA11 mounting boxes, it was used in the expansion box role with the early PDP-11's, particularly the PDP-11/20 (hence the -E variant suffix). In that role, it was used to hold extra core main memory systems (each in their own custom system unit) and other devices, and had a blank front panel.

It came in two variants, the rack-mounted BA11-ES (including Tilt and Lock chassis slides), and the table-top BA11-EC. The rack-mounted ones were usually mounted in the H960 series of 19"-wide racks, which provided 63" of vertical mounting space, divided into units of 10-1/2". The 10-1/2" tall BA11-E mounting box was designed for these spaces

A BA11-E could hold up to six standard size (4-slot) system units; these were mounted transversely, facing down. They were generally mounted with the A-row connectors at the left-hand side.

A set of four cooling fans was also mounted at the left-hand side of the box, to provide air-flow to the boards and power supply. Since the fans intruded into the space 'above' the backplanes, the latter could not hold hex cards, only quads, plus a single extended length card.

The BA11-E came with the H720 Power Supply; it was a separate unit, also mounted transversely in the box, at the back. It contained a transformer, and a PCB which supplied -15V (10A), and +5V (22A).

Later versions of the H720 had a pair of connections to the standard DEC Remote Switching Control Bus, so it could turn other units off and on with its power switch.

The power harness ran along the left-hand side; it contained a number of single-width stub cards, which plugged into the power supply slot in the system units (generally the A connector in slot 3).

The BA11-E's dimensions were 10-1/2" high, 19" wide, and 23" deep; it weighed roughly 100 lbs (including some backplanes and boards).