BA11-A mounting box

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The BA11-A mounting box is a 10-1/2" mounting box; the terminal variant code notwithstanding, it is just about the last in the line of BA11 mounting boxes. It was introduced with the PDP-11/44, and was also used with the PDP-11/24 and VAX-11/730. Unusually for PDP-11s, its integral power supply provided +12V DC, used as that time for MOS memory.

It came with the H7140 power supply, mounted at the rear of the box. There were four main variants, depending on the input AC voltage, and details of the secondary output: the -AA and -DA were 120V input, the -AB and -DB were 240V input.

Maximum power was 1350W with maximum load applied; it could provide 120A of +5V, and 10A of refresh +5V power to MOS memory; 3A of +15V, 3A of -15V; and 5A of +12V, 1A of -12V.

The H7750 battery backup unit, which provided refresh power to MOS memory mounted in the unit during brief power outages, was optional.

Power connections

PDP-11/44 setup

The BA11-A does not use only the standard DEC power distribution connectors; it also provided special connections on bus bars in its power supply, and in some applications (e.g. the -11/44's KD11-Z CPU), the CPU's backplane uses unique Flexprint cables for power, which go to the special connections (see image).

For backplanes which did not have the Flexprint cables (e.g. that of the -11/24's CPU), a special 'Power Distribution Board' (part # 54-13815) mounts to the bus bars and provides the needed connectors.