H777 Power Supply

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The H777 Power Supply is the power supply unit for the BA11-L mounting box from DEC. It provided DC current at voltages of +5V, +15V and -15V, with optional +20V/-5V for use with core memory. A later variant (used for the PDP-11/24 in the BA11-L box) also provided +15V/-15V for use by its RS232 asynchronous serial lines.

An optional H775A Battery Backup Unit allowed provision of power to MOS main memory units mounted in the BA11-L, allowing their contents to be retained during brief power outages.

A combination of up to 3 modules, composed of boards with integral heat sinks, provided different combinations of output voltages:

  • +5V Regulator - DEC part number 70-11073 or 70-12909 (all configurations had to include one of these)
  • MOS Regulator, +/- 15V, +5VB - 54-11601
  • Core Regulator, +20V, -5V - 54-11599

There are a large number of different models of the H777, but they boil down to a combination of three (later four) options:

  • 110V or 220V AC input
  • The optional +20V/-5V core supply
  • An upgraded +5V power supply (70-12909) which produced 32 amps instead of the 25A of the original (70-11073)

The fourth option is the 'communication regulator', 54-13764, which provides +15V/-15V.

The models are:

Model Input Regulators
-AA 115 25A +5V, MOS and core
-AB 230 25A +5V, MOS and core
-BA 115 25A +5V, MOS only
-BB 230 25A +5V, MOS only
-CA 115 32A +5V, MOS and core
-CB 230 32A +5V, MOS and core
-DA 115 32A +5V, MOS only
-DB 230 32A +5V, MOS only
-UA 115 32A +5V, MOS, communication
-UB 230 32A +5V, MOS, communication

The H777 does not use a power harness; rather, it has a 'power distribution board' built into one end panel, which holds the usual DEC power distribution connectors; the backplane(s) mounted in the BA11-L plug in there.

The power distribution board also holds a connector for the usual DEC Remote Switching Control Bus; this could be used either as an output (on boxes which contained a front panel) or an input (for boxes used as expansion boxes).

It was mounted longitudinally, at one side of mounting box, and included its own cooling fan.

External links