To Cap or not to cap?

[Hella1hella]

Hello everyone. Just wanted some opinions on a matter that has given me much thought. Should old amps be capped just because they are old? I'm not talking about replacing all of the caps, just the ones in the "Dog House" or whatever you technical guys call it . I have had guys say to recap an amp right when you get it, and some guys say do not recap unless you need to. If you plan on using the amp for playing with a band etc, is it a good idea to recap? On the same idea however, I have also heard if you use the amp, less chance a cap is going to leak etc. If I take a vintage amp into my tech (Another guy all for only replacing them if they are bad) and ask him to just do a look over and put in a grounded power cable, is that good enough? Just thought this would be a good topic to post on here, as I know there are probably a lot of people asking this very same question.

[R.G.]

Should old amps be capped just because they are old?

What follows is my opinion, and some of the reasons behind it. The fundamental reasoning is that an amplifier must be able to be used to amplify. If it cannot do this, it eventually becomes a piece of sculpture - that is, it's visually and perhaps emotionally appealing, but serves no other useful function.

I'm not talking about replacing all of the caps, just the ones in the "Dog House" or whatever you technical guys call it .

We call them "electrolytic capacitors". Electrolytic capacitors have a built-in failure mechanism. They will all fail eventually. It's only a question of when.

I have had guys say to recap an amp right when you get it, and some guys say do not recap unless you need to.

Those guys are expressing their opinions. There are two major schools of thought. One is the one I have, that an amp needs to work. The other is that vintage amps are precious museum pieces and replacing any piece, however necessary the replacement may be, degrades it from it's primal perfection. (I did mention that I have an opinion, right? )

The guys who think it has to be able to play (and usually to play reliably) come down on the side of recapping at some interval, maybe every ten to twenty years, which corresponds to a reasonable time where you can count on the caps being good and reliable.

The guys who venerate the amp as an original relic will say to not replace anything until it flatly fails. In fact, they don't like to do it then, but they eventually need to make sound with it. This "originality is everything" position has been heavily influenced by the vintage guitar/amp dealer/collector market.

You will hear stories from the second group who say that changing the caps will destroy its tone. Maybe. It will probably sound different. It will sound more like it did when it was new, and may have substantially less hum. I guess it depends on what the person expressing the opinion likes to think of as "vintage tone".

I guess there is a third group, who thinks that every amp is just a platform for the mod of the week. Sigh.

If you plan on using the amp for playing with a band etc, is it a good idea to recap?

This depend on what the result of a failure at a gig is. If you can say "Oh, well," and let it wait for a repair, you don't have to do preventive replacements. If you will lose a chunk of your livelihood if it fails, you may want to think about recapping every ten to twenty years, counting from date of manufacture. If you have to make &$#@* sure it works, you take a second amp just in case.

On the same idea however, I have also heard if you use the amp, less chance a cap is going to leak etc.

The failure mechanism in electrolytic caps is postponed by regular use. "Closet queen" amps which have not been fired up in 30-40 years often have a cap failure when turned on, no matter how good they look. If they don't, you were lucky. Amps which are used regularly and not *ab*used will have the longest capacitor lifetime.

On the other hand, random failures can happen anytime. But that's the origin of the "use it and it'll last longer" story.

If I take a vintage amp into my tech (Another guy all for only replacing them if they are bad) and ask him to just do a look over and put in a grounded power cable, is that good enough?

It's your question to answer. My personal opinion is that I can't afford sculpture. I think an amp ought to be reliable, so I would try to replace the caps before they fail. There are some failures that can take out your power transformer or the output transformer. If you can afford to have the amp down at any time for a trip to the tech, you can wait til they fail.

Good enough? If it were mine, and had original caps over 25 years old, I'd recap it. The line cord is a safety issue. But it's your amp, and you have to decide if you're willing to live with a failure when it happens.

[Chuck H]

I am ALWAYS a proponent for replacing electrolytic caps over fifteen years old on principal alone. I've heard A LOT of bad sounding vintage amps that were left with the original power supply filters just because "vintage" caps were still "working". I've also seen amps that had original caps FAIL at inconvenient times. And I've seen countless bias supply failures due to old electrolytic caps.

It's a FACT that even most enthusiasts now don't even balk at the idea of new electrolytic caps and a proper three prong grounded AC mains cable. The ONLY reason to f#@k around with old caps anymore is either because of lore perpetuated "mojo" or sheer cheapness.

Electrolytic caps use a liquid goo as an insulator/oxide former. This goo dries up with age. The phenomenon is WORSE is the amp is unused because the aluminum oxides that make the insulator are not rebuilt within the life of the goo.

To be certain there do seem to be some old caps that are still doing their job after 20+ years. This is the exception, not the rule. I promise. And many modern caps are not capable of the same longevity of performance (so it seems). But there are good quality caps available that will absolutely be an improvement over any cap over ten years old.

Keep in mind that an electrolytic cap needs to conform to two criteria to do it's job as intended. ESR would be the series resistance of the cap. This tends to rise with age. That means any feedback loops (negative OR positive) that exist within the power supply rail will be eminently more impressed on the signal path. Then there is the actual uf value, which tends to drop with age. This will dictate how much ripple the cap can control in the HV rail. So a lowering value lends itself to ghost notes (however mild) and extra ripple noise (120Hz hum).

It does seem (to me) that older caps seem to have greater longevity than newer caps. I can't say why. But I can offer an analogy... Lets say that the foundation of your home originally had a moisture barrier of 10 mil plastic. That was 25 years ago and the plastic has a known life of 15 years. The plastic may or may not be bad depending on the specific circumstances. Now, new moisture barrier is only six mil. It has better moisture resistance and overall performance, but, due to the lighter mil thickness only has a life of 10 years. Unless you don't mind your house rotting out from the ground up you need to replace the old moisture barrier with the more efficient but lower life product. The new product may not have the same longevity as the older one, but it will work better than original and certainly better than than the aged installation that is already ten years past it's intended lifespan. Nuff said.

This in mind... There are some really crappy caps out there. None will under perform the old originals, but many may fail within relatively short time. So choose a quality product. It's too f'in bad but most better quality caps are radial lead anymore. This means retrofitting where axial leads or "cans" were originally used. Nichicon and Panasonic seem to be the most highly ranked so far. Time will tell. But it hardly matters as ANY new cap will outperform anything over 15 years old that it replaces initially. Point is that ALL THE OLD ELECTROLYTICS HAVE OUTLIVED THEIR USEFULNESS IN SPADES BY NOW. There's just no getting around it. So pick the best caps you can. Retrofit as needed and hope for the best.

JM2C

[olddawg]

Ya know. I agree with recapping old amps. However I have been running an experiment for some time. I have a 1963 Blonde Tremolux that I acquired around 1981. It is bone stock. The only thing that has ever been changed is the output tubes. I use it every month or 2. It is whisper quiet and sounds great. It has the original power cord and all original caps. I have modernized all of my other amps usually when something else failed. This one just keeps on going and I keep telling myself if it works great why mess with it. Maybe it's the So Cal climate near the beach and the light but regular use?

[Steve Conner]

Well, I've also seen electrolytics with 1956 date codes that were still going strong in 2006. But then I saw some other ones that exploded in a stinky, gooey mess, and might well have started a fire if I hadn't been around to cut the power.

Failure is a random thing. Just because we use 20 years as a rule of thumb, doesn't mean they all die when they turn 20. If electrolytics are kept cool and charged up regularly to "reform" them, they might surprise you with a very long life indeed. Then again, they might not...

Nowadays, for new builds I like to use 105'C rated electrolytics if I can find them. They should last longer than the ordinary 85 degree ones at a given temperature.

[pdf64]

Yes, the 1958 Plessey multi-section can cap in my friend's Watkins Westminster is still going fine.
The amp isn't gigged, each section is working fine and it's used regularly.
I reasoned that given the above, the original would have a fair chance of outlasting anything that I might replace it with (hope that makes sense).
Regards cap life, it's surprising when flipping through the catalogues at the variety in the manufacturer's intended life for electrolytics; from 2000hours at 85C to 27500 hours at 105C. So in a guitar amp used for say 10 hours/week, a RIFA PEG124 series cap should be good for over 5 decades, outlasting how much longer I'll be needing an amp for!
Pete.

[Hella1hella]

Wow thanks everybody, great information. I think this will be a great help for newer people to vintage amps when searching online. It seems the general consensus is that it is a great idea to recap! However, this raises the next question? What should you pay for caps? Seems like there is alot of ripping off being done, and what are the best brands? Best quality IMO does not always mean highest price, so what caps are the best for a working musician, that will keep the amp sounding great, while allowing the player to actually be able to afford servicing. Also, what are caps to stray from? Now there is a great possibility I am wrong here, but I have compiled a small list of amps, that range from having alot of caps, to less caps. Many people on forums are asking this hot question "How much will my cap job cost?" Its a very hard question to answer, but I feel that there is a ball park range that could be given, just so people are not shocked when going to their tech. Just the idea of the price is enough to scare some people away, leading to failure.

Here are the amps:
Fender blackface/silverface champ
Fender Princeton
Fender Blackface bassman
Fender Tweed Bassman
Fender Deluxe Reverb/non reverb
Fender Super Reverb
Fender Twin Reverb
Marshall 2203
Marshall JCM 800
Marshall JTM 45

Anyone who feels there should be anything added to the list, feel free. Again, I am not very keen on the technical aspects of things ( I am working on it) but I thought this list would help to offer people what they may be able to expect.

[R.G.]

The caps are often inexpensive, compared to the cost of a good tech's time. The exceptions are where you have to buy some rare, multisection cap made out of refined unobtainium, or where you buy La-De-Da brand caps from Corksniffer's Online. The big questions will be how much tech bench time the amp takes to re-cap, and whether cap substitutions are necessary because of unavailability.

[nashvillebill]

Yes, the 1958 Plessey multi-section can cap in my friend's Watkins Westminster is still going fine.
The amp isn't gigged, each section is working fine and it's used regularly.
I reasoned that given the above, the original would have a fair chance of outlasting anything that I might replace it with (hope that makes sense).
Regards cap life, it's surprising when flipping through the catalogues at the variety in the manufacturer's intended life for electrolytics; from 2000hours at 85C to 27500 hours at 105C. So in a guitar amp used for say 10 hours/week, a RIFA PEG124 series cap should be good for over 5 decades, outlasting how much longer I'll be needing an amp for!
Pete.

Ah but there's a flaw in this approach. The capacitor's life is influenced not only by the hours it's used but also by its mere existence. Electrolytics depend on a tight seal (otherwise the cap will dry out) but it's a fact of life, no seal is perfect. Rubber seals dry out, crimped connections slowly loosen over time. So predicting its life solely on its hours of use fails to take into account this inevitable degradation.

An analogy would be the tires on your car. They may have an expected life of 50,000 miles; so if the car is a museum car and only driven 500 miles a year, the tires ought to last 100 years, right??? But in the real world, the rubber compounds in the tire degrade over time. So 20 years from now the tire may still look like it's holding air, but take the car out on the road and catastrophic failure is possible (in fact probable as the tire gets older).

[R.G.]

There is a concept in various disciplines called the "survivor effect". Survivors are notable *because* they are survivors.

A surviving, good-condition 1958 capacitor is by no means impossible, but it does call for the kind of notability we have for humans that live over 100 years. It would be very, very interesting if it were possible to find out how many of the rest of the caps from that manufacturing run are still functional. If that one is not about nine-sigmas out on the distribution, I want to talk to the designers and manufacturing guys that made it.

There is a con which uses the survivor effect. The con man sends predictions of this week's NFL/NBA/NHL/whatever games to someone, saying which team will win. He's correct. Then the next week, he predicts and is right again. Then the next week, then the next, until he's down to the last game. Con man then offers to bet for the final game for the recipient of all these right guesses, or to tell the recipient the prediction for the final game for a big fee. Recipient figures "Wow! He's been right *every dad-gum time! It's a sure thing. I'll make a killing." and bets/pays. Con man absconds with money.

The con man obviously did not really know the results of a string of 10 (11, 12?) games every time. He sent predictions on both teams to a profusion of marks. Each set of marks that got a wrong prediction was dropped out of the next predictions. Only the remarkably few marks that got by accident 100% correct predictions were worked for the final sting. But those marks were **convinced**.