PDP-8/A transformer hum

Paul Koning paulkoning at comcast.net
Tue Jun 9 09:18:30 CDT 2020

> On Jun 9, 2020, at 2:59 AM, Josh Dersch via cctalk <cctalk at classiccmp.org> wrote:
> Hi all --
> I'm working on a PDP-8/A I picked up at VCF West last summer.  After a lot
> of cleaning and some power supply repair it's showing signs of life (CPU
> seems to be at least minimally functional, core memory is going to need
> some debugging.)
> The transformer in the power supply is humming quite loudly, however, and
> I'm curious if this is normal for the 8/A (or is typical for an 8/A of this
> vintage).  I'm used to the supplies in various other DEC machines not being
> exactly silent but this is a rather severe 60Hz buzz that you can clearly
> hear over the fans when the machine is in operation.

Assuming these are traditional transformers with laminated sheet iron cores, check if the rivets or screws holding the laminations together are loose.  If yes, tighten or replace the fastener.


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