BA11-K mounting box
The BA11-K mounting box was for many years the standard hex system unit backplane mounting box for the H960 series of 19"-wide racks produced by DEC, the BA11 mounting boxes. It could contain up to 5 standard size (4-slot) system units.
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 10-1/2" tall BA11-K mounting box was designed for these spaces.
BA11-K's were used in both 'basic box' and 'expansion box' roles. The latter was used to hold extra devices, and had a blank front panel. The former contained the CPU, and had a front panel of some sort - either a programmer's console, or an operator's console.
In the PDP-11/04 and PDP-11/34 (the models which used this mounting box to hold the CPU) the front panels were the KY11-LA Operator's Console and the KY11-LB Programmer's Console (the same for both CPU's).
The system units were mounted longitudinally, facing upward (unlike the BA11 mounting box, where they had been facing down); they were generally mounted with the A-row connectors at the back, next to the power distribution panel.
The BA11-K came with the H765 Power Supply. The supply was a separate unit, mounted transversely at the rear of the box. It contained up to four DEC standard modular regulators. Cooling fans were mounted at the front of the box; the air was then passed through the power supplies by fans mounted in the H765.
The BA11-K's dimensions were 10-1/2" high, 17-1/8" wide, and 17-1/4" deep without the power supply; with the H765 added, it was 26-1/2" deep, and weighed 87 lbs (without and backplanes or boards).