BA11-N mounting box

The BA11-N mounting box was the a mounting box used for QBUS PDP-11's from DEC. It included an H786 power supply (which provided 22A of +5V, and 11A of +12V, although some sources say 15A and 8A respectively); and an H9273-A 9-slot Q/CD backplane, which could hold quad-sized cards.

The H9273-A was a Q18 backplane, but it is relatively easy to upgrade it to Q22.

The manual says the BA11-N was for PDP-11/03L's, but this seems odd, since the LSI-11 used in that machine was only Q16 capable, making the Q18 backplane superfluous. Once the PDP-11/23 appeared, BA11-N's could be used with it (and perhaps the BA11-N was looking forward to this machine) - but after the A revision of the /23's KDF11-A CPU (Q18 only), later revisions really were better off with a Q22 backplane.

Since it was a Q/CD backplane, dual-width QBUS cards could only be placed in the left-hand slots, and quad QBUS-only cards had to not use any pins on the right-hand C/D connectors. (The only DEC card with this limitation seems to have been the MMV11-A.)

It was available both with a front panel with a bezel (with 'Boot', 'Halt' and 'LTC On' switches, and power and run status indicators); and also with a blank front panel (for use as an expansion box).

It was a 5-1/4" tall mounting box, for the H960 series of 19"-wide racks, one of the BA11 mounting boxes. The H960 racks 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 5-1/4" tall BA11-N mounting box was designed for these spaces.

For rack mounting purposes. it did not use external slides (as all the other BA11 mounting boxes did); instead, it was housed in an external 'skin' *termed a 'logic box cover' in DEC documentation, the base unit being called a 'logic box') into which it is slid; the cover would be bolted to the rack.

The backplane was mounted vertically, facing backward (unlike the BA11-M mounting box, where they had been facing forward). Cooling fans mounted on the side of the BA11-N passed air both over the boards, and through the power supply.

The BA11-N's dimensions were 5-1/4" high, 19" wide, and 22-3/4" deep, and it weighed 44 lbs (without any boards). The rack mounting was 26-3/4" long.