cctalk Digest, Vol 13, Issue 24

Michael Thompson michael.99.thompson at
Fri Jul 24 12:37:15 CDT 2015

> Date: Thu, 23 Jul 2015 15:27:04 -0600
> From: Eric Smith <spacewar at>
> Subject: Re: PDP 11 gear finally moved
> There's no artifact safety issue for the PDP-1 power supplies.  They
> use a ferroresonant transformer, rectifiers, and filter capacitors.
> If any of those fail, the machine won't work properly, but it won't be
> damaged.

The AC capacitor attached to the ferroresonant transformer can have a
spectacular failure mode where it hisses, sparks, and sprays (probably PCB
laden) oil on everything.  As you said, all that will happen is the output
voltage goes low and it probably blows a fuse.

Michael Thompson

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