PDP-8/A transformer hum

Toby Thain toby at telegraphics.com.au
Tue Jun 9 09:34:26 CDT 2020

On 2020-06-09 10:27 a.m., Anders Nelson via cctalk wrote:
> Related question: Is there any reason, other than historical accuracy and
> cost, to not replace the power supplies in vintage computers with modern
> switching power supplies?

3) If it ain't broke, don't fix it

> --
> Anders Nelson
> On Tue, Jun 9, 2020 at 10:19 AM Paul Koning via cctalk <
> cctalk at classiccmp.org> wrote:
>>> 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.
>>         paul

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