Electrolytic Caps [Good or Bad?]

[Prairie Dawg]

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]

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]

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]

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.]

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]

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.]

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]

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]

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]

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]

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]

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.