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

[Michael E Caloroso]

Replacing caps is the general rule with guitar amps.  Note I did not
say absolute.  I bought a british guitar amp that was 40+ years old
and took it to a reputable tech.  He said the caps were fine.

I don't subscribe to the club of blanket replacement of caps.  When I
was restoring my OBX I took before and after scope pictures of the
voltage rails.  Recapping didn't make any difference.

MC

On 10/16/16, Dave Brown <davebr at modularsynthesis.com> wrote:
> 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
>
>
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