Capacitor Age and Replacement Guide

[Alonzo]

How about a general guide on what to look for and when to consider replacing the power supply capacitors (or any other stressed component) in our older gear?  I think my eldest is around 6 or 7 years old and none appear damaged, but that's still pretty young for some BH gear out in the wild.  Any guidelines we should follow with our gear?  My amps are on at least 12 hrs a day almost every day.
How about some pictures of good caps and some bulging older ones for comparison?
Alonzo

[Paul Birkeland]

This is a pretty tough question to answer.  For certain older kits (the Paraglow especially), things run really hot under the hood and capacitor lifetime suffers.  The last pair of Paraglows I rebuilt had one electrolytic cap that wasn't visually painful to look at out of both amps. 

When you move into the newer/bigger kits, temperatures are lower, airflow is better, and ultimately we have been using really good caps for quite a while now.  Provided they are available, the electrolytic caps that we put in the Crack are 12,000 hours at 105C with a generous ripple current rating. If we assume that your equipment averages 50C over the 12 hours you operate it, it's completely possible that you'll see 50 years of reliable operation in that position.

For other caps, like the 10,000uF caps in our filament and heater supplies, ripple current is fairly high, but still even our 10,000uF/10V cap is 10,000 hours at 105C and 4A of ripple current. 

Ultimately I think this will be kinda like the synthetic vs. conventional oil situation with cars, where I would definitely change caps that are 15+ years old in vintage components, but if I see a Panasonic TS-ED or Nichicon UCS2 in 20 years, I will be far more hesitant to just throw them away because of how old they are.

There are also some 20,000 hour electrolytic caps appearing on the market, so at some point these components will live longer than their owners.  For example, something like this installed in the  SEX amp in place of the 22uF/450V cap that's there is going to last for a century or two.

[Alonzo]

Okay, that's good to know.  I try to give everything a good dusting and once over every year and keep everything on isolation blocks to allow air flow.
Thanks Paul.

[EricS]

Alonzo - From what Paul posted above, it sounds like this isn't worth worrying about in BH kits. 

More generic and mass-produced consumer gear, though, is a whole different story!  I've replaced tons of bad caps in solid state gear (amps, televisions, preamps, digital pianos, etc).  While there are some clear signs of a bad cap (I've attached some images below) such as bulging and leaked electrolytic fluid, many caps simply fail without any visible signs at all.  If you see anything like in these images, that cap is definitely bad and needs to go.  But, the inverse is not true: a cap with no visible symptoms cannot be assumed to be problem free in a piece of misbehaving equipment.  As far as I know, there's really no definitive way to locate a bad cap while it is mounted in a circuit.  Even removing the cap and subjecting it to measurement with one meter or another is not a definitive test.

My experience in these cases has been failed fuses resulting from dried out PSU caps that shorted the power supply.  Usually, a fuse goes bad.  Figuring it is just from old age or years worth of turn on surges, I replace the fuse for the first time in over a decade.  Then, the new fuse goes bad a few days to a few weeks later.  To me, this is a sure sign of a failing PSU cap.  Though, in equipment that is 10 to 15+ years old, blowing fuses could be a variety of causes...  After repairing a number of items, I've come to be highly suspicious of old electrolytic caps in misbehaving gear.  In a case like this with mass-produced consumer gear, I just do a wholesale cap replacement.  It's only one more step beyond removing the cap to test it...  just drop in a new one.   I start with ALL of the PSU caps first and see if that solves the problem.  In 95% of the cases it does.  If problems persist (like with my digital piano), I go after ALL of the rest of the electrolytic caps next.  This solved my problem.

By the way Alonzo, thanks for leaving one of Mike's TFA-2004 Jr. Mexico pin stripe transformers for me a few years back.  I picked up the one in M4 and am finally getting around to building my amp: https://forum.bottlehead.com/index.php?topic=11749.0.   

Edit: that URL looks pretty messy.  I used the "insert hyperlink" button and just pasted in my URL... How do I insert a nice, clean link?

[Paul Birkeland]

a cap with no visible symptoms cannot be assumed to be problem free in a piece of misbehaving equipment.

I definitely struggle to convince people that this is true!

It's also worth mentioning that while it's easy to find 12,000-20,000+ hour rated electrolytic capacitors, the high lifetime options in surface mount packaging are severely limited.

[EricS]

My uneducated guess on the dearth of long-life surface mount caps is that better and thicker insulators lead to improved lifespan, so the small package is the limiting factor. 

[Paul Birkeland]

Have you had any of the high life surface mount caps die?  There are so few of them that it seems unlikely that you'd ever run into them.

[EricS]

Sorry, Paul - I don't have any experience with the long life surface mount caps.  I've only played with the cheapo ones that mass manufacturers stick on their boards.  With my digital piano, the PSU board had small-can radial lead electrolytics and the digital synth board was all tiny-can surface mount electrolytics, like in the third image I posted above.   I had to replace all 107 caps in order to bring it back to life. 

My first rule of electrolytic caps: don't trust 'em if they are over 15 years old.
My second rule of electrolytic caps: if one is bad, what makes you think the one right next to it (and so on, down the line) is miraculously good?

 

[robertod]

Thanks for the info.  I just recently build the Jagers speakers very good set of speakers and what a difference from my Straight 8.  Which led me to think of either upgrading my M1 audio note integrated amp or upgrade parts.  Also upgrade my wright sound 2A3s mono blocks.  Wondering if the music will improve another level.  The music sounds great with the addition of the Jagers, I'll inspect my equipment and go from there. Any thoughts or opinions.
Thanks again good info.