DEC 874-A Power Conditioner

J. Blaser oldcpu at
Tue Jan 3 18:01:38 CST 2006

Greetings to all, and here's to 2006!

My first post, though I have skulked for months...still, consider me a 
PDP newbie...

I've recently acquired a fully functional PDP-11/23plus with the idea 
that I'd re-acquaint myself with RSTS/E which happened to be the first 
system I was actually paid to program on.  Trouble is, it was a short 
stint with this local VAR, and it was nearly 30 years ago!  I don't even 
remember what the systems were exactly, though I think they were 
11/40s.  Stangely, these systems were in blue cabinets (did DEC ever do 
blue?), with none of the typical maroon or red PDP-11 signature 
color...that is until the LSI models started showing up in white, which 
is what I've got.

Anyway, I'm now happily in the process of re-assembling the system and 
preparing for my first power up since getting it home.  The 
configuration I have is in a double-wide 40" tall rack unit.  Each rack 
or 'bay' between the three uprights has a 874-A power conditioner / 
power-strip unit that I'm trying to understand.  I haven't been able to 
find any references to this component.  Though I could just replicate 
the configuration that it had before being relocated (switches, wiring, 
etc.), which I have plenty of photos of,  I'd like to understand this 
compenent better.

Since I have a double-wide cabinet, I've got two of these units that are 
linked together with a 3-conductor cable, each end plugged into one of 
the four "Power Control Bus"-labeled sockets.  One 874-A also has 
another connection from a second "PCB" socket to the the 11/23+ 
processor box.  My guess is this line somehow is controlled by the front 
panel AUX ON/OFF switch.

Also, each of the 874-A units has a small 3-position toggle switch: 
'Remote On', 'Off', and 'Local On'.  Before I go much further with 
experimenting on my own, I wonder if anyone here knows these units and 
can offer some info about how these units tie together and what settings 
do what.  Comments?


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