DEC BA11K Fan repair

tony duell ard at
Sat Sep 26 11:25:20 CDT 2015

> >> and you may decide it is better to replace the fan.
> As far as I know, all the old DEC fans, from PDP-8 and
> PDP-11 models, are totally standard size, and can still be
> bought new from Digi-Key, Mouser, etc.  If it is more than a
> few drops of oil needed, then it makes NO SENSE to repair
> windings on a fan you can get for $15.

I'll tell you one that you can't get -- the fan in the PDP11/44. 
That one is a standard outer dimension alright, but electrically
it's plain odd. 35V 70Hz AC or something. It runs from a full-H
circuit from the (possibly battery packed) 36V supply. There have
been suggestions to kludge in 12V DC fans, but I would not do 
that, the fan circuit _is_ part of the design of the PDP11/44 and 
should be preserved.

For the others, well, it may make 'NO SENSE' to you to rewind a 
fan, but I reckon I could rewind at least a DC fan (where insulation
is not a problem) in well under an hour (in fact I did, in one of my
HP9000s). And the wire is not exactly expensive. So it comes down
to the value of my time. Now I believe the value of something like
my time is what I can get for it -- in other words what somebody 
would pay me for an hour of my work. Which in my bitter experience
is close to zero. So it does make sense for me to do it. YMMV.

There is also the issue of keeping the machine as original as possible.
And the fact that a lot of the cheaper (i.e. $15) modern fans are very
poorly made. I think a rebuilt oriignal DEC fan would easily outlast one
of those.


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