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, and an H9273-A 9-slot Q/CD backplane, which could hold quad-sized cards.

The manual says the BA11-N was for PDP-11/03L's, but the LSI-11 used in that machine was only Q16 capable, making the Q18 H9273 backplane superfluous, like that in the BA11-M mounting box. 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, as in the up-rated BA11-S mounting box.

Since the H9273 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 a problem with this 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.

See also

• BA11-M mounting box
• BA11-S mounting box

Further reading

• BA11-N Mounting Box Technical Manual (EK-BA11N-TM-001) - not available online
• BA11-N Mounting Box Illustrated Parts Breakdown (EK-BA11N-IP) - not available online

External links

• microcomputer interfaces handbook - BA11-N is covered on pp. 74-82, 82-90 of the PDF
• Microcomputer Products Handbook - the BA11-M is covered in Chapter 54 (pp. 523-527 of the PDF)
• BA11-N mounting box user's guide (EK-BA11N-UG-001)
• PDP11/23 Field Maintenance Print Set (MP00740) - Contains the BA11-N Field Maintenance Print Set (MP00487) on pp. 32-87)