[sdiy] Restoring vintage HP voltage supply.. original electrolytic caps questioning..

[Dave Brown]

That power supply was built sometime after 1966 if my information is
correct.  I don't know how old it is, but just say 40 years.  I restore
radios back to the early 1920s.  My philosophy is that if a capacitor has
survived 40+ years, it must be a good one.  I have no reason to believe the
capacitors I replace it with will last 10 years, let alone any longer.  But,
one that has survived 40+ years seems to me to have a better chance of
surviving another 10 and possibly more.  Of course I have never tested this
empirically ...

We see a lot of specific capacitor failures when restoring vintage Tektronix
stuff, but they tend to be related to brand.  There are a lot that we just
leave and they work fine.

Dave

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
> Jean-Pierre Desrochers
> Sent: Sunday, October 16, 2016 11:44 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Restoring vintage HP voltage supply.. original
electrolytic caps
> questionning..
> 
> Hi everybody,
> I just bought a vintage HP 6291A power supply on eBay.
> I received it and it is working fine with some recalibration to be done.
> But before doing so I have a question about the inside electrolytic caps..
> Have a look here of a part of the inside circuit:
> http://www.arcenson.com/public/HP_6291A_power_supply.JPG
> 
> There are about 10 or so electrolytic caps inside this supply.
> They are all originals and about 50 years old but working.
> In fact only 3 of them are 20 to 46% off specs (to be replaced).
> All others are around 6 to 15% of uF values, and their ESR values are OK.
> Since there are many 'differing thoughts' about changing all of them or
not
> I'm asking you what would YOU do in my situation ?
> Some say if it's not broken don't replace anything..
> others say don't bother and replace ALL the electrolytics you see..
> 
> By the way, ALL the electrolytic caps are very good quality Sprague.
> If they are to be replaced I would use Sprague ATOM type.
> 
> Your suggestions are very welcomed.
> JP