BA11-D Mounting Box

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The BA11-D mounting box was an early standard hex system unit backplane mounting box. One of the BA11 mounting boxes, they were used to hold mid-series PDP-11/05's and early PDP-11/40's.

They were principally mounted in the H960 series of 19"-wide racks produced by DEC. Those provided 63" of vertical mounting space, divided into units of 10-1/2", which were further subdividable into a pair of 5-1/4" spaces. The 10-1/2" tall BA11-D mounting box was designed for these spaces, and could contain up to 5 standard size (4-slot) system units.

BA11-D's were principally used in 'basic box' roles, not as expansion boxes. The former contained the CPU, and had a front panel.

The system units were mounted longitudinally, facing up; they were generally mounted with the A-row connectors at the back. A pair of cooling fans was mounted at the front of the box, to provide air-flow to the boards; the power supply had its own internal fan, also at the front.

The BA11-D's dimensions were 10-1/2" high, 19" wide, and 23" deep.


The BA11-D came with the H750 Power Supply; it was a separate unit, mounted longitudinally in the box, at the right-hand side. It contained two transformers, and a PCB which supplied +15V (1A) and -15V (8A), and some +5V (20A); an H744 +5V Regulator‎‎ provided the balance (20A).

The power distribution panel (which contained the older 9-pin versions of the standard DEC power distribution connectors) was at the front. A BC05T (110V input) or BC05U (220V) line set controlled the main AC input power.

It 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.

Mounting slides

A BA11-D from the side, showing the mounting slide inner

Like many other PDP-11 boxes, it was rack-mounted using multi-part 'Chassis Trak' slides from General Devices, coated in a zinc-phosphate 'Pakerize' coating. The 'inner' part of the slide (show in the image to the right) is bolted to the box; the 'outer' is attached to the rack. The inner slides into the outer; a releasable latch prevents it being fully withdrawn accidentally.

Many BA11-D units are now found with the inners (above) still there, but the outers have been discarded (often left with the rack they were mounted in). If the inners are there, General Devices still makes another slide whose outers are identical to those used with the BA11-D, and those are readily available (albeit fairly expensive). The General Devices 'Chassis Trak' part number for that is C-230-S-122 (22"); the -124 (24") is sometimes slightly cheaper, and can easily be modified to fit an H960 rack, by drilling two extra holes.