H742 Power Supply

The H742 Power Supply is a modular power supply system from DEC, used in PDP-11/40, PDP-11/45 and PDP-11/70 systems mounted in a BA11-F Mounting Box.

The H740 supplies a modest amount of +15V DC power to various backplanes mounted in the BA11-F, along with a line time clock signal, and AC and DC 'power OK' signals.

It also supplies 20-30V AC to several power regulators (up to five, in spaces numbered 'A' through 'E') mounted in the H742, which provide other voltages such as +5V to the backplanes in the mounting box.

Supported regulators include:

• H744 +5V Regulator (and later versions, H7440 and H7441)
• H745 -15V Regulator
• H754 +20V Regulator

Generally the power wiring harness supports only limited options as to which regulator can be in which spaces; e.g. the later -11/40 harness mandates that A, B and C hold H744's, D holds an H745, and E may hold either an H745 or H754.

Later versions of the basic H742 are the H742A and H7420A; the differences are not yet known.