Electrolytic Caps [Good or Bad?]

[Steve Conner]

Look! Rare vintage TOC electrolytics! Low starting bid.

These units have an amazing tone* and will transform** your Fender Twin or similar. Satisfaction*** guaranteed.




*The last sounds they made were Phizzz, Splurt, Sizzle, BANG!
** Transform it into a smouldering wreck.
*** Mine, not yours, sucker!

PS Thanks for the huge post, RG. For what it's worth, I was an audiophile, but I got better. My turning point was a summer job in the radio studios at BBC Scotland. One day my boss asked me to make up some speaker cables for one of the studios. I was like, "Where's the speaker cable", and he replied, "There's no such thing. Use that reel of line cord over there."

I'm thinking of founding the 3dB Club, we refuse to buy anything that makes less than 3dB of a difference to something.

[R.G.]

Originally Posted by guitician

So, for someone to react to the "Perceived" change in a caps sound, there would have to be a real "rustle" or "snap", or then those changes would have gone unnoticed. I find it hard to believe that all these listeners are delusional.

Give the posting a careful read again. Nothing was said about the need for a rustle or snap - only that the ability to form a fully formed image about what might happen from very fragmentary data was a survival advantage. Don't try to read more into it than I said. The people that formed the "delusional" images of being tiger chow were the ones that, on average, reproduced more, as they were not there when the jaws closed.

If you want to say that forming a full image from partial data is delusional, you can; I didn't say that. What I said was that forming a picture from fragmentary data was something that humans do very, very well, and so readily that we're in general unaware that we do it. I can find URLs for you to read up on that if you like.

And I did not say that "all these listeners are delusional". I said, meant, and stand by that they form images which may or may not be accurate based on whatever data their senses give them, plus a whole lot of post processing inside the human brain. Again, I can find you references if you have issues with that.

Hmmm... so the experts never listen to and adjust their designs afterwards?

You really need to read the words I wrote. I didn't say experts didn't listen to and adjust designs.

But I did respond to your comment that good audio systems (presumably most or all by the context) are put together by trial and error. I don't know many experts who put together anything by trial and error. They put them together by design, by intent, by the knowledge learned by training and experience, as opposed to trial and error. The million-monkeys approach to Shakespeare probably is not used by experts. There is a difference, and not the one you are implying.

Of course, that's just your subjective experience ;-)

Of course it is. That's why I said what I did. Wasn't that obvious enough not to need restating?

I once replaced the original silicon diodes in an early 1960s Dynaco SCA-35 with current production soft-recovery diodes, on the theory that the current ones are lower-noise. The improvement in sound was so pronounced, it surprised me. So, I tried the same thing on the bridge of one of my Leslie 122s--no difference whatsoever. I was predicting some change, but I perceived none. Bandwidth limitation in the Leslie or just no difference? I don't have an explanation.

Whereas we now can measure snap-off ringing or lack thereof, in rectifier diodes, and we now know that the specific conditions of diode, wire placement (and therefore inductive and capacitive parasitics) can greatly affect the need for snubbing diode turn off. I don't know that's the explanation, as I'd have to do the examinations on the equipment involved to know, but it could well be that the diodes didn't do snap-off ringing on the Leslies, or that other factors prevented diode turnoff transients from being propagated into the audio path. Mother Nature is very picky about the smallest of Her Laws being followed at all times.

Speaking of bandwidth limitations, I've had my hearing checked a few times, most recently when being fitted for a new pair of on-stage hearing protectors. I can still "objectively" hear to ~23kHz. I do hear things other people don't. Perhaps, psychologically, the denial of the subjective perceptions of some by others is displaced resentment at their inability to perceive things that others do. If you're going to invoke psychological mechanisms, let's open the door to all of them ;-)

Congratulations. I'm all the way open to invoking psychological mechanisms, or other mechanisms of any type whatsoever where the mechanism can be (a) repeated by disinterested observers and (b) at least conceptually measured.

In response to the very soft drive-by comment, displaced resentment is a fine thing to allude to, oh so softly. Sorry, but that's not my issue. You're not the only one whose hearing has been tested. And if we want to allow "displaced resentment" as a mechanism, there are all kinds of things that can cause displaced resentment, and the whole implied chain of responses that theoretically might cause. Shoot, I could conceive of a possible situation where someone concludes the "experts" must always be wrong because one hears things that others do not.

Of course, historically, hearing and seeing things others do not has been a chancy thing to have happen to one.

I would take the bet that I could repeatably distinguish pre-burned-in vs. non-burned-in examples of the same brand of, say, Panasonic ECQP 0.1uF coupling capacitors in the same amp, under conditions where all other factors were controlled under A-B-X testing.

I'd dearly love to take your money.

I've talked to materials experts who say burn-in is reasonable, and you've talked to those who say it isn't. Thus, there seems to be some disagreement about it even among objective scientists.

Yeah. That's why I insist on measurements. Instruments may or may not be sensitive enough to dredge a signal out of noise - as humans do with patterns really there, or sometimes not, as perceived patterns in video-noise snow. Experts' opinions are just that, opinions. They can be deceived or self deceived. 'Course, if you wanted to plant corn and get a big crop, you might be more interested in talking to a practicing corn farmer than a tobacco farmer. Just a thought.

I had someone tell me recently that it was vitally important to install a $30 Jensen copper foil in oil capacitor and cloth-insulated wire inside a Stratocaster for the best tone. I remain skeptical.

I would remain skeptical too. I laughed until tears came to my eyes when I read about the claims of water-jacketed speaker cables. The problem is that there are people who really do believe that stuff, wholesale. And they tell their friends. And they post it on the internet, so it must be true.

In general, I try to maintain some balance between science and subjectivity. One of the things I've written about in my academic career is the appearance of the medical expert in the 19th century. If you want to read some crazy "science," pick up a 19th C. medical textbook and see what was regarded as objective fact by "experts." Or read Charlotte Perkins Gilman's famous short story "The Yellow Wall-paper."

The expert-of-the-day syndrome is always a danger. Georg Ohm received a lot of guff I understand when he was unraveling how voltage, resistance and current related. The prevailing expert opinion was that voltage was equal to resistance times current raised to some power. Ohm was soundly beaten upon for saying the exponent was unity.

The problem was the crude instrumentation at the time. Measurement was crude, and it was not always possible to distinguish things that closely. Of course, the argument quietly faded away when the instruments got accurate enough to do the measurements to an acceptable degree of accuracy.

Medicine in particular has been the repository of bad science, not least because of the willingness of people to believe what they're told, the placebo effect, and the sheer volume of money available to people willing to lie convincingly to sell something. By contrast, the audio huxters are small potatoes indeed.

Originally Posted by Lord Kelvin

When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science.

Of course

Originally Posted by Einstein

If we knew what it was we were doing, it would not be called research, would it?

[tedmich]

Bravo RG! You are a scientist AND an auditory aesthete, proving these needn't be mutually exclusive.

I think you will find the discussion I linked to previously quite amusing, as one poor empiricist actually tried to quantify capacitor tone and "break in". The poster (spkrdtr) actually passed on the report (here: http://www.polkaudio.com/forums/atta...4&d=1207187391) and got crucified! (You dare to even ask the question blasphemer!)

To quote one dismissive expert (+11k posts vs spkrdtr's 8):
"Another friggen scientist
Please take your head out of your ass. I swear you can hear so much better that way. I don't need charts to tell me what sounds better."

goring sacred cows...what fun!

[guitician]

R.G. the "rustle and snap" quote was taken out of context. I was trying to state that a change in a caps sound is "change" and not "made up". Looking at an optical illusion requires that you "Look" at it, sometimes it will appear to change by itself. This will not happen for everyone the "Looks" at it though. I know that perceived effects in sound are real, and do play a part in the audiophiles experience. If a graphic artist used this mechanism in his art, does it make it not worth as much, because they have left part of the work to our own brain? If it doesn't work for your particular needs, don't buy it.

Sound making devices(musical inst.) were first put together by creative people, not by trained engineers. The first devices for audio production were brought about by inventing minds exploring uncharted areas of the physical world, who mostly used their ears. That's all I was getting at by "trail and error".

I think it's best that the music do the talking...I'll just listen.

[rudutch]

So,

after reading all these posts, I still am not enlightened.

The conclusion:

Some say 'change 'em'
others say
'if it ain't broke (leaking / swelled) don't fix it'.

Is this the whole rosewood Vs maple fender neck debate in a different genre?

I was hoping for a more definitive post as I have 3 amps form '65 to '73 all with original caps (none leaking / swelling / etc.) They all get used 3-5 times a month for an hour or more

You guys do amaze me with your knowledge though

[guitician]

Well that depends if you:

Have the time and money to replace all the e-caps just to have a secure sense that your e-caps are newly replaced and may be more reliable because of it.

or

You play your amps with a backup and can just roll with a failure, should one ever occur.

[R.G.]

Originally Posted by guitician

Well that depends if you:
Have the time and money to replace all the e-caps just to have a secure sense that your e-caps are newly replaced and may be more reliable because of it.

or

You play your amps with a backup and can just roll with a failure, should one ever occur.

I completely agree with that. Old caps may work for a long time. They may also die the next time you turn them on. There's no way to know about one specific cap, so all you can do is play the statistics.

The amps from '65 to '73 have caps that are 36 years to 44 years old. They are clearly at the end of the bottom of the "bathtub curve" for failures, and may in fact be remarkable as survivors. But nothing lasts forever. One day they will fail. The question is - what are you going to do about it?

If I have an application that demands my amp not fail on me during a performance situation where I may not have a backup, I will insist on having the predictably failing parts be within the low-failures part of the reliability bathtub curve.

If I could stand for a cap to fail, and then take it off line and use other things while it was being repaired, I might not insist on the caps being less than ten years old.

What this whole argu... er, discussion, has missed is that aging electro caps also change an amp's tone. This may be in a good way, may be in a bad way. And an aging cap may cause funny problems with amps, like intermittents, oscillation, and ghost noting.

But if you can stand for your amps to fail and wait for them to be repaired, you don't have to preemptively replace them all. You can wait for them to fail, then replace them. I personally dislike the prospect of likely failure, so I'm nearly always on the side of "let's make this reliable". But not everyone needs or wants that.

Bottom line: it's up to you. They *will* fail someday. You just don't know when. If you're OK with not knowing, and letting them fail first, then fixing the amp, so be it. If you need them to NOT fail, or if you're having funny problems with the amp, or you just wonder what the amp sounded like when it was new, you may want to replace them. It's kinda like getting a flu shot. If you can deal with the consequences, you don't necessarily need the prophylaxis.

I deal a lot with people who can't stand for their amp to fail just before a performance in West Bug's Ear, so I advise replacement.

It's worth noting that playing an amp a few times a month for an hour or so is one of the things which should prolong capacitor life. They don't get too hot for too long, and get regular doses of re-forming voltage. Like people eating healthy foods and getting a healthy amount of exercise, it's a good regimen. But then there's Jim Fixx, the late-60's running guru who became famous for promoting running when running for exercise was new. He was healthy and vigorous - until he dropped dead of a massive heart attack at age 52 after his daily run.

It's always something. Figure out what works for you and do it. You know the arguments now.

[soundmasterg]

Hey R.G., if I have some LCR caps and some Sprague Atom caps that are new but have been sitting on the shelf for 8-10 years, should I bother to try to reform them and use them?

Greg

[R.G.]

Originally Posted by soundmasterg

Hey R.G., if I have some LCR caps and some Sprague Atom caps that are new but have been sitting on the shelf for 8-10 years, should I bother to try to reform them and use them?

Greg

I would, if only to make sure that they don't leak and overheat when they're fired up.

Re-forming is a breeze: hook them up to their rated DC voltage, but through a 100K resistor. When the voltage across the 100K drops under 10% of the rated voltage, you can hook up the voltage directly. This may take some hours if the caps have a reparable problem. It may never happen if they are too far gone. Probably good brand name caps will recover fine.

[novosibir]

I don't want to piss onto anyones opinion or experience, just want to tell, what has happened to me once...

... it's been already a few years ago, as one of my customers came with his early 70' Marshall SLP (the one with the six can caps on top of the chassis) and had a prob with a high pitch squealing from time to time. It turned out, that one of the two "+" contacts of the preamp filter cap was loose - the lug/rivet connection was loose and some oxidation already went in between. By wiggling on the contact you could provoke the squeal, or stop it.

If I recall correctly, Erie caps were in this amp, but already about 35 years old, so I've recommended, to swap all six cans with new ones. And because I wanted to do the customer a favor, I've ordered a 'six-pack' of the in HiFi circles highly regarded "Mundorf" can caps. The Mundorf 50+50/500 have the same diameter, just are a bit shorter like the TAD's. I've measured the Mundorf's before swapping in and recognized, that ESR was overwhelming great. Though they were new, I've formed the caps in the amp before first firing up - a 100K in the B+ between the rectifier diodes and the 1-st caps, yellow H.T. CT still disconnected, still no bleeders (the 56K's) soldered back to the screen filters and of course w/o tubes - and surprisingly after less than one hour the voltage drop across the 100K was less than 2VDC, what proofed a negligible low leakage current.

I thought "WOW" by myself and thought, how happy the customer probably will be, because I couldn't notice any ghosting even with the amp set to very high volume!

Two days later the customer called me, said that at rehearsing yesterday he couldn't recognize his amp anymore...

... but no! He wasn't happy! He's been whining like a kid, asked what else I've done to his amp - asked, why it does sound so much different now! He said, that the amp now sounds so polite, so clean and literally like polished - quite like a new amp from the 90' and not like the old British Beast from the early 70' with the nice british dirt in the sound as before!

And after some discussion, where I've affirmed, that I haven't done anything else than only swapped the filter caps including the bias caps, adjusted the bias and still cleaned some ground connections, he begged, to put back his old filter caps again, except the failed one of course, as soon as possible - and still showed up at the same evening, to bring his amp back.

I haven't swapped back his old Erie's in the amp, but six NOS LCR's from 1993, from which I still do have a huge stash. They measured much worse concerning ESR compared to the Mundorf's, they also took about 12 hours forming time after the 100K method and voltage drop across the 100K after 12h forming time has been about 5 volts as opposed to the Mundorf's value of less than 2 volts.

By playing the amp I could recognize some slightly ghosting at higher volume settings, especially the open G string and playing beyond the 7-th fret, but it's been tolerable.

In the evening the customer picked up his amp - and called me up the next day very late, just before midnight..... and he's been sooo happy again He's been so much surprised, that his amp came to life again and got back its 'old sound' like before, just even a bit better and said, that he nearly couldn't stop playing his amp again in the reherasing room, hence his phone call came so late.

Yes, it seems that sometimes the physically regarded worse components nonetheless are the better components for guitar tube amps

Have a nice Sunday!

Larry

[Prairie Dawg]

Originally Posted by novosibir

I don't want to piss onto anyones opinion or experience, just want to tell, what has happened to me once...

... it's been already a few years ago, as one of my customers came with his early 70' Marshall SLP (the one with the six can caps on top of the chassis) and had a prob with a high pitch squealing from time to time. It turned out, that one of the two "+" contacts of the preamp filter cap was loose - the lug/rivet connection was loose and some oxidation already went in between. By wiggling on the contact you could provoke the squeal, or stop it.

If I recall correctly, Erie caps were in this amp, but already about 35 years old, so I've recommended, to swap all six cans with new ones. And because I wanted to do the customer a favor, I've ordered a 'six-pack' of the in HiFi circles highly regarded "Mundorf" can caps. The Mundorf 50+50/500 have the same diameter, just are a bit shorter like the TAD's. I've measured the Mundorf's before swapping in and recognized, that ESR was overwhelming great. Though they were new, I've formed the caps in the amp before first firing up - a 100K in the B+ between the rectifier diodes and the 1-st caps, yellow H.T. CT still disconnected, still no bleeders (the 56K's) soldered back to the screen filters and of course w/o tubes - and surprisingly after less than one hour the voltage drop across the 100K was less than 2VDC, what proofed a negligible low leakage current.

I thought "WOW" by myself and thought, how happy the customer probably will be, because I couldn't notice any ghosting even with the amp set to very high volume!

Two days later the customer called me, said that at rehearsing yesterday he couldn't recognize his amp anymore...

... but no! He wasn't happy! He's been whining like a kid, asked what else I've done to his amp - asked, why it does sound so much different now! He said, that the amp now sounds so polite, so clean and literally like polished - quite like a new amp from the 90' and not like the old British Beast from the early 70' with the nice british dirt in the sound as before!

And after some discussion, where I've affirmed, that I haven't done anything else than only swapped the filter caps including the bias caps, adjusted the bias and still cleaned some ground connections, he begged, to put back his old filter caps again, except the failed one of course, as soon as possible - and still showed up at the same evening, to bring his amp back.

I haven't swapped back his old Erie's in the amp, but six NOS LCR's from 1993, from which I still do have a huge stash. They measured much worse concerning ESR compared to the Mundorf's, they also took about 12 hours forming time after the 100K method and voltage drop across the 100K after 12h forming time has been about 5 volts as opposed to the Mundorf's value of less than 2 volts.

By playing the amp I could recognize some slightly ghosting at higher volume settings, especially the open G string and playing beyond the 7-th fret, but it's been tolerable.

In the evening the customer picked up his amp - and called me up the next day very late, just before midnight..... and he's been sooo happy again He's been so much surprised, that his amp came to life again and got back its 'old sound' like before, just even a bit better and said, that he nearly couldn't stop playing his amp again in the reherasing room, hence his phone call came so late.

Yes, it seems that sometimes the physically regarded worse components nonetheless are the better components for guitar tube amps

Have a nice Sunday!

Larry

My take on reforming is that it's only necessary if the capacitor has been sitting on the shelf unused for a number of years. I recently tried this with a couple of new old stock FP types that were pretty old. What I did was connect them to a Sprague capacitor bridge that'll let you test for leakage at working voltage. The drill is to set them up, and never let the leakage current exceed .5 ma. As the capacitor reforms you can come back every few hours and recheck your applied voltage and raise it until you reach the .5 ma limit. After about 8 hours the capacitor sections will take full working voltage while leakage is nice and low.

I'll get to put my project in practice and see whether it was worth doing when I finally decide to quit screwing around and put my Princeton Reverb back together. If I've got a new capacitor I might check it for leakage and it it's below the figure for leakage it's formed well enough for me.

[Prairie Dawg]

Originally Posted by rudutch

So,

after reading all these posts, I still am not enlightened.

The conclusion:

Some say 'change 'em'
others say
'if it ain't broke (leaking / swelled) don't fix it'.

Is this the whole rosewood Vs maple fender neck debate in a different genre?

I was hoping for a more definitive post as I have 3 amps form '65 to '73 all with original caps (none leaking / swelling / etc.) They all get used 3-5 times a month for an hour or more

You guys do amaze me with your knowledge though

It's a reliability item as RG says. They're all at least 35 years old. Can't be expected to last forever and if you were able to test them for leakage or you gave them a really close visual examination you'd see my point

Here's some electrolytics in a 1960 Pro amp. What do you see?

[novosibir]

Originally Posted by Prairie Dawg

What do you see?

Bubbles, where the exhaust valve (correct word? I'm a German!) is sitting under the coating. A sign for a bad cap, what even might explode under extreme circumstances.

Larry

[Prairie Dawg]

Originally Posted by novosibir

Bubbles, where the exhaust valve (correct word? I'm a German!) is sitting under the coating. A sign for a bad cap, what even might explode under extreme circumstances.

Larry

Correct. The amp sounded fine and the person who was the former owner (it is now in my custody) had gotten skinned by a local "tech" for a couple hundred bucks to "replace the electrolytic capacitors". Definitely not a long term good thing. Of course the old ones are stashed in a plastic bag somewhere.

But I guess the point is first you have to be able to understand what you're seeing, and the significance of it-which you did. Sometimes that bulge is very slight. They were more or less ready to let go at some inopportune time.

I have a Marshall 4104 in work-it's one of my own amps-and I removed the Daly cans from it. They have leakage deluxe and one even started doing the snap-crackle-pop routine on the test rig.

Here's a shot of the reforming thing I was doing.

[booj]

Quote:
Originally Posted by booj
Exactly. I've replaced 40 - 50 year old caps in amps and checked them with a cap checker only to find out they are absolutely perfect. No leakage, no change in value, although they generally read OVER the rated value.
If the amp is used occasionally, theres no telling how long they will last.
This is just an opinion, of course, since I've only been working on amps for 40 years or so.

Good opinion. I defend your right to have it. However, I also defend my right to think it's incorrect.

What you typed is factually correct.

Quote:
If the amp is used occasionally, theres no telling how long they will last.

There is, literally no telling. It may be 50 more years, it may be five minutes, or the next power-on surge. The statement is literally correct, but not true in the semantic sense that it implies. The only way to tell is to look at the sum of the usage conditions and the statistics for that type/brand/lot number of caps and then ... guess. Caps on a shelf go bad. That's why they're a shelf life item. Using them with a voltage in the upper third of their specified voltage tends to keep the oxide layer repaired by leakage currents electrochemically where shelf sitting would make it degrade more. The occasional use also mitigates against short life by having few power on/off cycles and less overall hours of thermal stress. It's like heaven on earth for a cap.

But musicians want to PLAY these things, and working musicians want them to work every time. That's a little different.

Quote:
This is just an opinion, of course, since I've only been working on amps for 40 years or so.

I've been working on amps on and off for only about 35 years, and haven't made a living at it. I made a living designing and supporting manufacturing of power supplies, so I've seen a LOT of caps used in power equipment, and I've had to understand the math and producers' data on projected lives of power components. I've also talked to a lot of other techs who repair amps, and I get a lot of agreement with doing recap jobs where an owner wants reliability.

I've also had a lot of feedback from owners who took my advice to have the amp recapped. Very often the comment is that the amp sounds amazingly better. Old caps, even ones that don't leak, have drifted values and high internal resistance. That changes the power supply impedance and the sound of the amp. Changing the caps out restores the power supply operation to the way it was when the caps were newer.

I recommend you borrow or rent an ESR meter. It's pretty easy to pick out which caps will make a big difference in sound by testing ESR, not capacitance or leakage. Old caps have higher ESR even if they don't leak and have the same capacitance. It makes a difference.

No one can predict exactly which cap is going to live for another decade. But if you want your expectation that the next time you turn on your amp it's going to play just fine, and the time after that, and the time after that, it makes sense to replace parts which have a built-in failure mechanism, *as admitted by the makers of those parts* every so often so you don't have to have the unpleasant opportunity to play air guitar in front of a crowd.

One of my favorite paraphrased proverbs runs "The race is not always to the swift, nor the contest to the strong; but that's the way to bet."

I gotta switch brands of beer before posts!
I do have an esr meter, in the form of a BK Precision 878A
I DO make a living doing repairs. (I pull a lot of all-nighters)
Most commonly, the customer is happy that he came in to get his input jack fixed and got it back with the input jack fixed. Oh, I tell 'em you should get a cap job done, and the answer is "Thanks for the info".
I don't know what the average income of your coustomers is, but most of mine don't even get basic repairs done until they run out of bubble gum and bailing wire.
I leave it up to the customer. However with all this cool information on this thread, maybe I can conjour up visions of "cap nightmare" scenarios complete with haunting thoughts of PCB vapor inhalation and acid dripping from the chassis.
NOW it's time for that beer.

[R.G.]

Originally Posted by booj

Quote:
I gotta switch brands of beer before posts!

Good idea! I switch brands from time to time just to stay loose!

I do have an esr meter, in the form of a BK Precision 878A

Then you know how useful it is in judging the condition of an old cap.

I DO make a living doing repairs. (I pull a lot of all-nighters)

Good!

Most commonly, the customer is happy that he came in to get his input jack fixed and got it back with the input jack fixed.

Yep, that happens a lot. And since most customers are humans, at least nominally, you really can't restore every amp to pristine condition for every repair, as a matter of practicality.

Oh, I tell 'em you should get a cap job done, and the answer is "Thanks for the info".

Yeah. Pesky human customers. They think just because smoke only comes out after two hours that it means that the amp's just old and gets tired after an hour or so.

I don't know what the average income of your coustomers is, but most of mine don't even get basic repairs done until they run out of bubble gum and bailing wire.

I don't have have customers in the sense of amp repairs, but my amp-tech friends do. Yes, the sad state of the non-famous musician is that if he has an argument with his girl friend, he's homeless.

But that shouldn't stop us from giving good advice. As you do. Telling people that their caps are old and may start failing is what should happen. You can lead a horse to water but you can't make him think.

You can't force customers to get preventative maintenance done, and from your note, you don't. But you can advise them. It's a good idea to do preventive maintenance, unlike the start of this discussion where the idea was "never replace a cap preventively, they might last forever."

I leave it up to the customer. However with all this cool information on this thread, maybe I can conjour up visions of "cap nightmare" scenarios complete with haunting thoughts of PCB vapor inhalation and acid dripping from the chassis.

The musicians I know would think "kewl... acid dripping out... "

NOW it's time for that beer.

That's nearly always true.

[Steve Conner]

Originally Posted by Prairie Dawg

It's a reliability item as RG says. They're all at
Here's some electrolytics in a 1960 Pro amp. What do you see?

Looks like you have a case of capacitor nipple!

If I see those "nipples" raised on electrolytics, I tend to prod them gently with a pen while the amp is running, to see if it feels like there's pressure inside. If it feels hard, it's time to turn the power off straight away and replace the caps. If it's soft and squishy, it's probably still time to replace them. If they're actually leaking goop like the ones in the picture, oh my...

I've seen caps where the nipple was raised but they continued to work fine. As RG says, though, how much longer will it work?!

The case study of the player who hated his amp with new capacitors is quite common. They get used to the loose, dirty tone with hum mixed in, because of the crappy old dried-out caps with high ESR and low capacitance. And then you put new capacitors in and it "improves" it out of all recognition. They think the old tone is authentic vintage, but with the new caps it probably sounds more like it did back in the 60s. I'd measure the actual capacitance and ESR of all the old caps in a high-value job and note the info down somewhere.

[R.G.]

Originally Posted by Steve Conner

Looks like you have a case of capacitor nipple!

Tee-hee... kewl, a new syndrome to be publicized, lobbied for, and a telethon or web drive to be done for the benefit of! We could even start a National Institute for the Prevention of Protruded Little End-ie-things (NIPPLE) and with the funds we raise, pay ourselves huge salaries and fund research into where does your capacitor go when it explodes and is it cruel and unusual to shake capacitors with loud audio output. Maybe we could look into lobbying for outlawing combos.

Steve, you're a genius!

That poor guy with the capacitor nipples has a pretty bad case of Leaky Capacitor too, judging by the stains.

The case study of the player who hated his amp with new capacitors is quite common. They get used to the loose, dirty tone with hum mixed in, because of the crappy old dried-out caps with high ESR and low capacitance. And then you put new capacitors in and it "improves" it out of all recognition. They think the old tone is authentic vintage, but with the new caps it probably sounds more like it did back in the 60s. I'd measure the actual capacitance and ESR of all the old caps in a high-value job and note the info down somewhere.

Yeah - and stick in resistors to fake the response. ESR is Equivalent to Some Resistor...

[mdxeng]

Bad electrolytics can result in major damage to the amplifier - blown power transformer, blown output transformer, worn out tubes, capacitor debris leaked into chassis and circuit boards, etc - if not replaced in time. As they dry out they lose their ability to filter, so AC ripple voltage increasing is a symptom which typically isn't audibly detctable as hum in a push-pull amp (which is what most amps are). However, a lack of bass response is also a symptom of bad electrolytic caps. Recapping old amps is needed if the amp gets used. Some old amps still work OK with the original caps, but this is usually due to a lack of use. If the amp is used often, the filter caps are a candidate for failure.

[Prairie Dawg]

Originally Posted by Steve Conner

Looks like you have a case of capacitor nipple!

If I see those "nipples" raised on electrolytics, I tend to prod them gently with a pen while the amp is running, to see if it feels like there's pressure inside. If it feels hard, it's time to turn the power off straight away and replace the caps. If it's soft and squishy, it's probably still time to replace them. If they're actually leaking goop like the ones in the picture, oh my...

I've seen caps where the nipple was raised but they continued to work fine. As RG says, though, how much longer will it work?!

The case study of the player who hated his amp with new capacitors is quite common. They get used to the loose, dirty tone with hum mixed in, because of the crappy old dried-out caps with high ESR and low capacitance. And then you put new capacitors in and it "improves" it out of all recognition. They think the old tone is authentic vintage, but with the new caps it probably sounds more like it did back in the 60s. I'd measure the actual capacitance and ESR of all the old caps in a high-value job and note the info down somewhere.

It's true. I freshened up a Princeton for a guy, it sounded OK when I started but after the electrolytics and some selected resistances were renewed it sounded amazing-touch sensitive, articulate and with clarity-now of which it had had before. He liked it, some people might not, but it's now ready to put in a good solid night's work without getting tired.

[JerryP]

Every cap that failed today was "good" yesterday. I've changed more than a few power transformers because some amp sniffer chose to keep his amp original.
Keeping old caps in an amp is like bragging about picking up a 70 Chevelle with the original oil in it still. Ooh look, an original rod thru the original oil pan!
Jerry

[Prairie Dawg]

Originally Posted by JerryP

Every cap that failed today was "good" yesterday. I've changed more than a few power transformers because some amp sniffer chose to keep his amp original.
Keeping old caps in an amp is like bragging about picking up a 70 Chevelle with the original oil in it still. Ooh look, an original rod thru the original oil pan!
Jerry

Go to the head of the class, as my mother used to say.

[soundmasterg]

Originally Posted by Prairie Dawg

My take on reforming is that it's only necessary if the capacitor has been sitting on the shelf unused for a number of years. I recently tried this with a couple of new old stock FP types that were pretty old. What I did was connect them to a Sprague capacitor bridge that'll let you test for leakage at working voltage. The drill is to set them up, and never let the leakage current exceed .5 ma. As the capacitor reforms you can come back every few hours and recheck your applied voltage and raise it until you reach the .5 ma limit. After about 8 hours the capacitor sections will take full working voltage while leakage is nice and low.

I'll get to put my project in practice and see whether it was worth doing when I finally decide to quit screwing around and put my Princeton Reverb back together. If I've got a new capacitor I might check it for leakage and it it's below the figure for leakage it's formed well enough for me.

I've got a Sprague Tel-Ohmike also so maybe I'll try that. I was going to try to form them in the amp once I get the amp to that point, but it would be easier to use the Sprague I think.

Thanks also to Enzo!

greg

[Steve Conner]

Originally Posted by JerryP

Ooh look, an original rod thru the original oil pan!
Jerry

Lol

Those TOC capacitors I posted a picture of are from an old audio signal generator. I bought it on Ebay for $20, "tested and working." When I unpacked it and turned it on, as soon as the rectifier tube warmed up there was a horrible fizzing, splattering noise from inside. I opened it, and the guts were covered in sprayed capacitor goop. There's your rod through the oil pan right there! I replaced them with bundles of Taiwan ones, wrapped in electrical tape to make them fit the original clips.

RG: I might be a genius but you sir, are a politician We need to find a cute looking capacitor to be the face of a PETA-style campaign to outlaw combo amps. We can try to ban those Fender doghouses too: insist on free range capacitors!

[guitician]

Originally Posted by JerryP

Keeping old caps in an amp is like bragging about picking up a 70 Chevelle with the original oil in it still.

So, what's the life expectancy of a PIO(Paper-in-Oil) type of filter cap? They are soldered in a can, so they dont dry out. They may age in different ways though.

[mdxeng]

If they're not physically or thermally abused and not overloaded with voltage, they should last a very long time. Lot's of old gear have good coupling caps with this type of construction.

[guitician]

I started looking for "Long Life" caps and found solid polymer caps with as much as 63,000 hours life at 75 degrees Celsius or 167 degrees Fahrenheit. That's 28 years running six hours a day. It didn't see voltages above 63vdc though.

[mdxeng]

The basic thing to remember is that the power supply filter caps, especially the first stage that feeds the output transformer center-tap which 99% of the time are electrolytics, are the ones that work the hardest and the ones that typically need replacing before anything else. The coupling caps that are in the signal flow path don't work nearly as hard and are usually film-type which last very long (but sometimes go bad and are a little difficult to diagnose). So, first step is understand which part of the amp your looking at replacing/upgrading and consider how hard the cap is working. The first stage filter cap in a 50W guitar amp typical values: 450VDC, 70mA @idle, 100-150mA when pushed (rock/metal,etc), typical ripple @idle 2-4VAC. When you see the ripple voltage go up as the amp ages or (approx.) >4VAC @idle, then this may be a sign of an issue. Always look at the filter caps during a service and look for what has been already talked about in this thread. Coupling caps have high voltages, but current levels are small (<1mA) so they are not being worked like the filter caps that are feeding the power tubes with current so the amp sounds good, crisp, loud and nice.

You can hear bad electrolytics. Lack of bass response or audible 60Hz hum are symptoms. Popping sounds, stuff leaking from the chassis, debris inside the chassis like something exploded - these are more obvious symptoms(!).

I've used non-electrolytics (Solen 630V metallized poly) in filter cap positions and I expect they'll last a long time. Sprague Atoms are very reliable for electrolytics, but performance may not be what you're looking for.

[Steve Conner]

Originally Posted by guitician

So, what's the life expectancy of a PIO(Paper-in-Oil) type of filter cap? They are soldered in a can, so they dont dry out. They may age in different ways though.

I've seen paper-in-oil caps go leaky (of current, that is, not oil!) and metallized paper ones too. I just replace them with modern plastic film types.

You really don't want me to service your 1948 TV front Pro.

[tedmich]

Originally Posted by Steve Conner

I've seen paper-in-oil caps go leaky (of current, that is, not oil!) and metallized paper ones too. I just replace them with modern plastic film types.

You really don't want me to service your 1948 TV front Pro.

the association of PIO caps with massive PCB pollution is enough for me to completely avoid them. No audio qualities counterbalance their environmental impact, as they are commonly disposed of improperly. Of course the Mfg were the worst offenders, like GE releasing >500 tons into the Hudson River from their two capacitor manufacturing plants at Hudson Falls and Fort Edward, or Westinghouse in Indiana, or who knows what Soviet era factories today...

I've heard grizzled old techs mutter about how they haven't observed any increased cancer rates but that bad karma has to go somewhere...

[R.G.]

Originally Posted by Steve Conner

RG: I might be a genius but you sir, are a politician

Sir! I am not a member of the government or any other criminal organization!

Originally Posted by guitician

So, what's the life expectancy of a PIO(Paper-in-Oil) type of filter cap? They are soldered in a can, so they dont dry out. They may age in different ways though.

Paper-in-oil is not the way to go. You want polypropylene-in-oil. I have an old textbook on "power capacitors", these being the only caps they could make back in telegraph days, and on into the 1950s. Paper was used because it was the only consistent insulating film they could get before plastics. Oil was used because it made the paper last longer and withstand a higher voltage.

The oil was originally mineral oil, later petroleum oils. Such capacitors were a distinct fire hazard, as one of their uses was in line balancing and power factor correction in power stations, and the bigger ones got... HOT. Sometimes they'd boil the oil, or be ruptured by a discharge, and spray hot, atomized oil into the air, producing a fuel-air explosion that might knock down the building. If not, it would burn it down. Special synthetic transformer oils were invented to sidestep the real danger of fire or explosion.

Your oil-and-paper caps would not be that big. However, the power cap industry went to polypropylene film with paper and finally polypro only as soon as it was technically feasible. Paper was never a great insulator. It was impossible in practice to produce paper free of conductive imperfections in some places. As a result, even the best paper had to be used in a dual layer, as the odds of two of these randomly spaced imperfections matching up was incredibly low. Polypropylene films can be made with zero conductive imperfections, so they went to paper plus polypro, then polypro entirely. Modern PCB-free caps are metalized polypropylene film in a non-pcb oil to dissipate heat.

Originally Posted by tedmich

the association of PIO caps with massive PCB pollution is enough for me to completely avoid them. No audio qualities counterbalance their environmental impact, as they are commonly disposed of improperly. Of course the Mfg were the worst offenders, like GE releasing >500 tons into the Hudson River from their two capacitor manufacturing plants at Hudson Falls and Fort Edward, or Westinghouse in Indiana, or who knows what Soviet era factories today...

I've heard grizzled old techs mutter about how they haven't observed any increased cancer rates but that bad karma has to go somewhere...

It's politically correct these days to assume that any oil-bearing capacitor is stuffed with PCBs and dioxin, and that companies like GE were trying to find ways to make the entire planet uninhabitable.

In fact, as I mentioned, PCB bearing insulating oils were developed to try to prevent power station workers and office workers where there were small power plants from being killed by explosion and fires. The guys who invented and used this stuff weren't sadistically evil - at first at least. They honestly could not, for instance, detect dioxin in parts per billion back in the 1950s. Nor was their objective to poison people - PCB build up to toxicity takes a while to happen and it's hard to track it back. PCB oils were so good for what they were intended for, there was an entire industry built up with billions of dollars (back when that was worth more than a casual sneeze) of industrial base, and very little in the way of alternatives when the toxicity was tracked down and analyzed sufficiently.

When they were nailed down, yep, there was some corporate greed to get over, but PCBs were pretty quickly banned, and *every single cap containing insulating oil* since the banning contains oil free of PCBs and dioxins. Guilt by association is always a tricky thing, and it's not much good for caps either. Modern manufacture oil bearing caps are as non-toxic as we can determine any such thing to be, and they're watched well because of the PCB issues.

Originally Posted by mdxeng

The basic thing to remember is that the power supply filter caps, especially the first stage that feeds the output transformer center-tap which 99% of the time are electrolytics, are the ones that work the hardest and the ones that typically need replacing before anything else.

"Worked the hardest" is equivalent to "carries the highest ripple current, and is most heated by ripple current and other hot things nearby". Often that's a rectifier tube.

The coupling caps that are in the signal flow path don't work nearly as hard and are usually film-type which last very long

These things have the advantage of being film construction. This is much more heat-capable than electro caps, and don't have a built-in wear out mechanism like electros. Film caps may be ignored for any kind of regular replacement; replace them when they die.

In fact, no EE worth his salt will use an electro when there is a film which is modestly capable of doing the job. Electros would not exist if anything else could give us the CV product that electros do.

I've used non-electrolytics (Solen 630V metallized poly) in filter cap positions and I expect they'll last a long time.

I've been exhorting people to use motor-run caps for power filter caps for a long time. They have become relatively cheap ($1/uF at 450-500Vdc) and are designed to have huge ripple currents run through them and to dissipate the heat; and they don't have the wear-out mechanism of electros. This is part of my "Immortal Amplifier" that I've been preaching for years. In fact, they do work, and in fact they do last a long time. I rigged up my first amp like this over ten years ago. It's been too short a time to tell much, but ripple and temp rise are exactly what they were when the amp was new. I expect that the amp will work long after I'm dead if tubes can be had for it.

[tedmich]

Originally Posted by R.G.

It's politically correct these days to assume that any oil-bearing capacitor is stuffed with PCBs and dioxin, and that companies like GE were trying to find ways to make the entire planet uninhabitable.

In fact, as I mentioned, PCB bearing insulating oils were developed to try to prevent power station workers and office workers where there were small power plants from being killed by explosion and fires. The guys who invented and used this stuff weren't sadistically evil - at first at least. They honestly could not, for instance, detect dioxin in parts per billion back in the 1950s. Nor was their objective to poison people - PCB build up to toxicity takes a while to happen and it's hard to track it back. PCB oils were so good for what they were intended for, there was an entire industry built up with billions of dollars (back when that was worth more than a casual sneeze) of industrial base, and very little in the way of alternatives when the toxicity was tracked down and analyzed sufficiently.

When they were nailed down, yep, there was some corporate greed to get over, but PCBs were pretty quickly banned, and *every single cap containing insulating oil* since the banning contains oil free of PCBs and dioxins. Guilt by association is always a tricky thing, and it's not much good for caps either. Modern manufacture oil bearing caps are as non-toxic as we can determine any such thing to be, and they're watched well because of the PCB issues


I've been exhorting people to use motor-run caps for power filter caps for a long time. .

The incredible biological persistence of PCBs is why we can still be pissed about the tons GE dumped in NY and Westinghouse dumped in IN. The 1979 ban simply banned US production (after 600,000 tons) but they can still be used in "closed" systems (transformers and capacitors) and there is no plan to actually dispose of the ~1M tons produced until 2025, which is contingent on the so called POPs Treaty ratified by 105 countries....except the US!

Speaking as a biochemist, the health effects of the 200 odd PCB compounds are very scary. They worked well but ideally we shouldn't have to see their environmental impact for the next couple centuries because of some very real corporate dishonesty and greed. See this time line for details:
The History of PCBs - When Were Problems Detected

"quickly banned"? hardly as health effects were seen decades before "ban" and they are still all around us...

And as to GE's contempt for the planet, have you watched Conan O'Brien lately?

Oh yes motor start caps are DIRT cheap check these:
50 lot of 20uf for <$20
LOT OF 50 MOTOR START CAPACITORS CBB60 SH 20uF 240VAC - eBay (item 150380267658 end time Oct-20-09 16:11:27 PDT)

[Steve Conner]

Watch out! Motor start and motor run caps are two different things.

Motor start caps are often non-polar electrolytics, not rated for continuous running. I've exploded them before by running a capacitor-start motor off a variac, and I can tell you they smell pretty bad.

Motor RUN caps are great for using in tube amp power supplies, if you have the space in your chassis: they're much bigger than an electrolytic with the same CV product. But as RG says they'll surely outlive the amp builder, if not civilization itself. Wouldn't that be cool, if future archaeologists found your amp in a basement in the radioactive ruins of post-holocaust Manhattan, plugged it in, and it worked

[R.G.]

Originally Posted by tedmich

The incredible biological persistence of PCBs is why we can still be pissed about the tons GE dumped in NY and Westinghouse dumped in IN.

Actually, one can be pissed about almost anything. It's even better if it's a moral outrage, as that keeps the pissing going for long periods of time.

But that's neither here nor there. Cool. If you want to be angry about it and not use small paper and (different) oil capacitors for that reason, that's fine. I don't use small paper and oil caps because there are better, smaller, higher performance alternatives. In either case, neither you nor I use oil and paper caps.

The 1979 ban simply banned US production (after 600,000 tons)

I believe there are disposal requirements which make it almost impossible to dispose of them responsibly as well, some of which are draconian. These have the effect of making people look for ways to dispose of them improperly.

but they can still be used in "closed" systems (transformers and capacitors)

I think that's because of the "no good alternative" thing. I could be wrong, because I don't follow this in detail, but when you heat 50 or 100 gallons of oil inside a high voltage electrical assembly, fire and explosion is a possibility if the container ruptures. Of course, they are "closed" systems. We - and the "good" countries, too, like former Soviet bloc countries, Japan, China, Germany, France, the UK, etc. - also allow the use of enriched uranium in nuclear reactors, which are "closed" systems, encasing stuff more deadly than PCBs.

It's almost like humans can't be trusted with anything more dangerous than cowplop, isn't it?

and there is no plan to actually dispose of the ~1M tons produced until 2025, which is contingent on the so called POPs Treaty ratified by 105 countries....except the US!

Yep, we are the bad guys, all right.

It's funny - there are simple, direct ways to get people to do the right thing. For instance, we have a setup where anyone who is accidentally or otherwise in possession of a PCB bearing capacitor becomes in effect an eco-criminal. This is an incentive to just quietly get rid of the stuff and not be associated with it. Down the drain or dumped in the swamps comes easily to mind, and that's where a lot of the improper disposal comes from. Or we can use waste disposal "companies" that are the commercial arm of organized crime. They have some unusual ideas about how to properly dispose of stuff in general.

I sometimes come up with what I call engineering solutions to social problems. I think that if we took a different approach we could clean up PCBs, with the *help* of the corporate robber barons.

You want to gather up the PCBs for proper disposal? Buy it. Make the price such that people will TRY to find PCB-bearing stuff to turn it in. We have some precedence. The rise in the price of copper to a status as a minor precious metal has created a cottage industry for "copper finders". This involves things like tearing brass kick plates off doors, stripping out the ground wires on electrical poles, etc. If you paid an attractive price for PCB transformer oil, you could buy it up and properly high-temperature incinerate it under controlled conditions like we do with used, worn out currency. This would ensure that the PCBs are sought out with all the ingenuity that humans can come up with. In fact, big corporations would come up with ways to recapture the PCBs that escaped into the environment.

Too much money? Maybe not. We just got "given" a stimulus package which will largely be spent sometime during the next election year (which is neither here nor there - but it makes me angry that I can't be stimulated now when I need it) and which triples the national debt. Wouldn't it make good eco-sense to use some smallish fraction of that to clean up the Spawn-of-the-Devil PCBs that infest our environment? What price clean air and water? A few *billions*, which are down in the rounding error for the stimulus package would buy up all the PCBs and build the high temp incinerators, and make a big start to cleaning up the issue so we could get over it.

But we won't do that. That would reward positive, contributive behavior.

They worked well

They did that.

but ideally

Yep. Sigh. There's a shortage of ideal-ity these days.

we shouldn't have to see their environmental impact for the next couple centuries because of some very real corporate dishonesty and greed.

Yeah. If only we could keep people who are greedy from getting into positions of power to direct organizations... then we could make some progress!!

But seriously - think about what we could do by incenting good behavior.

Oh yes motor start caps are DIRT cheap check these:
50 lot of 20uf for <$20

As Steve notes, motor start caps are not the ticket. These are usually NP electrolytics, and are intended for intermittent use only when the motor starts and then are switched out by a centrifugal switch. They are a very bad alternative to normal electros in DC rectification. Motor run caps are designed for the motor to run with them hooked up all the time.

Sorry. I'm have a bad-coffee day.

[tedmich]

Originally Posted by R.G.

As Steve notes, motor start caps are not the ticket.

Sorry. I'm have a bad-coffee day.

typo, I believe the caps I referenced are PP run caps,

By all means incentive-ise GE to re-procure the 1/2m tons of PCBs it released into the environment that will be asserting their vast array of biological effects for the next several hundred years...As a chemist I simply think we should assume new chemicals to be dangerous until proven otherwise and before they become so profitable and entrenched that the companies can do the harsh math of profits vs suffering. I believe the POPs Treaty is designed to actually remove the toxins from the environment but someone powerful in the US doesn't want to pay to clean up the mess they made...is it you RG? have you been lobbying congress? no I didn't think so...

\This may make you laugh if you haven't already seen it...or even if you have... audiophiles hate scientists/engineers as much as fundamentalists do...perhaps more because they (unfortunately) need them...

Stereophile: Scientists vs Audiophiles 1999