PDP 11 gear finally moved
cc at informatik.uni-stuttgart.de
Tue Jul 21 03:30:00 CDT 2015
On Mon, 20 Jul 2015, Rich Alderson wrote:
> 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.
Please excuse me, but this is utter nonsense.
Most electrolytics in our machines are 30 years and older, and they just
work. Those caps that I checked (mostly large filter/smoothing caps), e.g.
those from the LGP-30 (nearly 60 years old) or Mincal 523 (44 years old),
are just fine. Smaller ones don't even have to be bothered with. OTOH foil
caps from the 50s/60s (e.g. ERO/EROFOL/EROID/Wima) tend to lose a bit of
their isolation and become resistive (several MOhm). This can be a problem
with AC coupling in tube circuits. Also problematic are more modern foil
caps in line filters (e.g. X/Y caps), or even oil filled MP caps in power
supply (magnetic constanters, filters) or motor applications (phase
But admittedly I don't know what crappy electrolytics you have encountered
in your "industry grade" machines. Or are we talking of modern
machines (<30 years) ?
>  NB: I am not now, nor have I ever claimed to be, a hardware
> engineer of any stripe, and more particularly not an electronics
> specialist. I am, nonetheless, capable of reading and understanding
> research papers with statistics that back up the claims being made even
> if I could not devise the experiment to test them. I rely on my
> colleagues who are experts to assure me that the writers are not smoking
Statistics... don't believe any statistic that you haven't faked yourself.
Honestly, IMO this doesn't really qualify you as expert in capacitors.
I think those statistics are based on running the caps 24/7 at their
nominal ratings, but surley they don't apply to moderate museum usage.
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