[sdiy] A little on capacitors from people smarter than me

[Graham Atkins]

I have seen old ex military radio sets that had a special connector and
plug to reverse bias the electrolytics every so often.

There was a video somewhere on YouTube showing what can happen
if you even marginally apply high voltages to electrolytics. Highly
dangerous without eye protection etc....Not recommended.

Graham

On 29 Mar 2010, at 23:35, cheater cheater wrote:

> Hi guys,
> I was following a recent thread elsewhere on capacitors in the audio
> chain and distortion. I'm sure a lot of people here know all about
> this, but I think it's a relevant topic here especially for beginners
> like me. A lot of the stuff I see (especially modulars) uses
> cheap/old/random caps, or people go with the first part they can find
> in their box, etc. It can and does make a big difference in audio
> quality. I thought I'd forward some materials and interesting opinions
> for anyone who might be interested.
>
> One particular thing that's pointed out is that if the (electrolyte)
> capacitors were shelved for a few years it's good to reform the oxide
> layer on the electrodes by slowly bringing up voltage across the
> capacitor (in the right direction, of course). This lowers leakage
> current. If after reforming the capacitor still has high leakage
> current it's broken. In that case reforming also turns out to be a
> good way to screen capacitors for deficiencies.
>
> The whole process of reforming and testing is easy to set up and can
> be automated, which is important for people who want to manufacture,
> or just don't want to lose time.
>
> Out of curiosity - how many people here have been applying this?
>
> Cheers
> D.
>
> ------------------------
>
> http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
> http://waltjung.org/PDFs/Picking_Capacitors_2.pdf
> http://electronicdesign.com/article/analog-and-mixed-signal/bob-s-mailbox15653.aspx
> http://www.scribd.com/doc/2610442/Capacitor-Sound
>
> on capacitor reforming:
> http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
>
> -------------------------
>
> Please see the technical paper that I wrote entitled "Ceramic
> Capacitors" back in later 1980 or so, basically in response to the
> Jung/Marsh article in Audio Magazine. My paper is on the last page
> (page 8) of my 990 data package:
>
> http://www.johnhardyco.com/pdf/990-2007.pdf
>
> In it I refer to Jung's use of X7R ceramics in his tests. I also make
> reference to AES preprint #1719(D1) entitled "Topology Considerations
> for RIAA Phono Preamplifiers" where Jung expresses a favorable view of
> the COG/NP0 dielectric. I contacted him about the COG/NP0 dielectrics
> after his Audio article, and he must have taken a closer look (first
> look?) at the COG/NPO parts for the AES preprint.
>
> John Hardy
>
> --------------------------
>
> (...) from what I can tell, the oxide
> layer is reformed by current flow, but only in one direction.  In the
> wrong direction, it actually erodes it, which is supposedly why the
> release magic smoke so quickly when the polarity is reversed.
>
> So the idea, is that if they've been sitting for a while, you should
> slowly bring up the current so that the oxide has time to reform.  If
> current doesn't fall to a steady state, then the cap is fubar, and
> must be replaced.
>
> I say if one is worried about reforming the thing in the first place,
> just replace it, but hey.
>
> Cheers,
> Christopher Deckard
>
> ----------------------------
>
>> If I remember to, I'll bring a recap job up on the variac, but more
>> often than not, I just throw the switch, and let 'er rip.
>
> I generally take that approach. After the 1977 blackout in NY City,
> when power came back on at ABC's network headquarters, hundreds of
> pieces of equipment failed to come back up and it was almost
> exclusively power supply capacitors.
>
> So, when I'm working on a piece of equipment, I figure that if the
> caps are weak, hitting them with the startup surge will identify the
> weak ones and then I can replace them.
>
> I may be more circumspect with ancient tube gear, but I don't work on
> that, I think I have only one tube antique here, and I'd probably
> power it up carefully after changing the power transformer as it
> hasn't been on for > 25 years. I do have the replacement power
> transformer in my round toit pile.
>
> Cheers,
>
> Richard
>
> Richard L. Hess
>
> ---------------------
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy