PDP 11 gear finally moved

Pete Turnbull pete at dunnington.plus.com
Tue Jul 21 11:43:00 CDT 2015

On 21/07/2015 06:14, Eric Smith wrote:
> On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson
> <RichA at livingcomputermuseum.org> wrote:
>> industry white papers with tables of decay rates for
>> the aluminum electrolytics that indicate that, *no matter what*, they lose
>> capacitance over time, until c. 14 years from manufacturer date they are at 10%
>> of rating.
> That's very interesting. I haven't seen those white papers, but the
> "no matter what" must in fact depend on something, since on the PDP-1
> Restoration Project we found that most of the 40 year old aluminum
> electrolytic capacitors still met their original specifications,
> including capacitance within rated tolerance.

Yep, I find "no matter what" and "10%" very hard to believe for similar 
reasons.  For one example, the aluminium electrolytics I recently took 
out of a 4-decade-old PDP-8/L were fine after reforming.  In fact based 
on my tests I'd say they were well within their stated tolerance.  My 
other PDP-8s, of not dissimilar vintage, are running fine.  As is my 
c.2000 Origin 2000, my several other SGIs (some of which have been in 
regular use since the mid 90s, and two have been running 24/7 with only 
brief interruptions over that period), assorted PDP-11s, ...


Pete Turnbull

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