BA11-A mounting box

From Computer History Wiki
Jump to: navigation, search

The BA11-A mounting box is a 10-1/2" mounting box; the terminal variant letter 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 also provided +12V/-12V DC, used for the MS11-M MOS memory's MOS memory chips.

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:

Model Input Memory voltages
-AA 115 +12V, -12V
-AB 230 +12V, -12V
-DA 115 +12V, -15V
-DB 230 +12V, -15V

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

The H7750 Battery Backup Unit, which provided refresh power during brief power outages to MOS memory mounted in the BA11-A, was an option.

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' (DEC part number 54-13815) mounts to the bus bars and provides the needed connectors.

External links