As many owners know, the average life of electrolytic and tantalum capacitors in the 60's and 70's was very low, a decade or two at most. Since many (all?) B&O products from that era used those types of capacitors, most owners of this vintage equipment will be noticing some strange things, like lots of hum on the outputs, or bass/treble controls not working properly, and things of that nature.

Modern replacement capacitors are generally physically smaller and have a much longer potential life. That's not a really big issue with most PCB-mounted caps, but the offboard caps used in much equipment will be starting to degrade (if they're not already).

The problem is the electrolytic solution inside electros (electrolytic capacitors) dries out with time. That reduces the actual capacitance of the unit, and can also lead to secondary effects, such as internal resistance.

By way of example, I carefully measured a 1962-vintage 2000ųF 50V DC capacitor, and it measured 94 ųF (at 100 Hz), and what's more, it had an internal resistance of about 770kΩ So it wasn't able to do it's job at all well. Most electros of similar ratings have similar problems.

Replacing these physically large electros with modern equivalents can be easier (they're typically less than half the size (1/4 the volume) of the cap they're meant to replace. But without pulling apart the wiring loom and rerouting the connections (which is tricky in this aged equipment due to insulator and wire brittleness), it's not easy to replace the units nicely. And if you love your equipment, even on the inside, modern caps are just boring.

The catch is, the insides of these caps can be a combination of chemicals, none of which are good for you. So there are a couple of options for cleaning the caps first, properly disposing of electrolyte and wax/tar/phenol products, and so on. 

What I've done is documented one fairly simple way of replacing the old metal can type caps with modern replacements. Even better, I've photographed the whole process.

Rather than putting these images and ideas up with no-one to look at them, I thought I'd wait to see if there is any interest in seeing how this can be done.

I realise there are others who have done the same thing, and to be honest, they probably did a better job than I can! But if you're thinking about doing it, and you're not sure where to start, once you've seen a knucklehead like me do it, you'll know anyone can do it.

You're welcome to PM me if you'd like specific details, or else pop a reply in to this thread and I'll set up a blow-by-blow of the process somewhere.

I've done the same thing with the re-belting of the 1600, and that's been on a promise to this forum for some time now - I've culled it down to 20 or so photos, but finding the time... And I figure there might be more interest right now in cap refitting than one model's belts.

I hope this makes someone else happy!

Since I never chuck anything away, (ever!) so I'll have the photos for a very long time (touch wood).

Cheers,

PCPete 

Get'm on Pete!

If you make one person happy, then it's worth it. I for one would love to see a blow-by-blow account of cap replacement.
I haven't tackled it yet, but with lots of older B&O, I'm sure I will soon.

Andy T.

Please post away! It is something that quite a few of us will need to tackle over the next few years as our kit ages.

Simon

Peter,

please go for it and post your cap replacement info.  I'm an electronnics novice and before I break out the blow torch thingy to weld the insides of my failing units, any help is appreciated.  When I first saw a thread on cap replacement, I thought it was a fashion statemement about hats!.  As an aside, I look like a prat in a hat and once reduced a whole shop full of people in the Lake District into hysterical laughter just by trying on hats.

Hi Pete,

I have a Beosystem 7000 hooked up to a pair of Beovox 5000 type 6206 ( with cubes)

 A while ago I went on vacation and turned off the power to the sytem, when I cam back all previous humming from the receiver disappeared.

 To my ear the speakers sound good, do you think that replacing the caps (where) will make a big difference?

Andrew 

Andrew, the problem you describe could have been caused by a number of issues.

But if the problem you experienced did disappear after turning off the unit, then the simple test will be to see if the humming reappears. If it does, then one of the possibilities could be component changes over time.

I'm not sure how old the Beosystem 7000 is... if it's a 60's or early 70's model, then that might suggest components are the cause.

But it could also be due to any number of unrelated issues. (I sound like a politician, sorry about that!). Maybe if other folks have seen the same problem you have (and if the 7000 systems were popular, other users might be seeing the same problem you describe), it would be easier to confirm.

That would include issues with the power in the house, external electrical fields, speaker leads routed in parallel with house wiring, and others more exciting and unrelated. 

Unless the humming reappears, I'd hold off on replacing caps for the time being - it's a reasonably fiddly job to do (even just swapping caps without putting them inside the old ones), and it could just be one or two components at issue, and figuring out which is which could be a bit of a task.

But if the problem reappears, it's one thing you can try!

Cheers,

PCPete 

Wow. Sounds like this is an interesting issue for some people.

While I can't really help with cap replacement in terms of millinery (sorry davefarr ), I can hopefully do something for electronic 'hat' replacement.

I'll post an update in a day or two (I have to find a way to post images as well as write some text). Please bear with me, I'm flat out in my day job (audio/video repair/recovery), but this will be first on my spare-time list. (You could say I have low capacity, but that would be a terrible pun ).

Stay tuned!

PCPete 

Nice post but I tend to disagree a bit with you regarding PCB mounted caps;
I've repaired thousands of B&O things and it's my experience that PCB mounted caps
are just as prone to failure, and maybe even more so, than the large aluminum cans.
Especially the red and orange cylindrical ones that B&O have used heavily are
given candidates. Also some of the "japanese"-type of PCB mounted caps can give
problems, I'm thinking of the ones found in f.e. Beogram CD X where a large number
of 22uF caps provide many hours of repair fun.
Also the tiny, mostly green, ones found in the Beocenter 2100/2200/4000 range are prone to failure,
here the pins seem to oxidate off, presumably because of leakage of the electrolyte fluid.
I don't do many VCR's or TV's but also here the PCB mounted caps easily count for
the majority of faults.
Die_Bogener posted a wonderful thread about the VX5000 machine and the volume of caps problems found here.
That famous capacitor used in many B&O CD decks also springs to mind - and here it
will actually have to be the correct brand and type of cap to make it work.
Fitting a modern component with "far better specs" won't do.

The large cans can be faulty, of course, but it's my experience that it's not quite
as often as many people think, at least when it comes to B&O audio stuff from
the 70's and 80's. Of course they should be checked when restoring the set and any
bad readings or signs of leakage is of course a good reason to replace them.
Large caps, well electrolytic caps in general, from the 1940's and 50's are a completely different issue though. The same goes for the wax-coated paper type that
are practically always leaky.
I like to replace them all on sight as a matter of cause.

To preserve the original look, it's indeed possible to fit a modern component inside
the emptied shell of the old one but it's a fiddly job and really only worth doing
in rare, old or specifically valuable sets.
The paper wrapping of wax/paper caps can be scanned and wrapped around
modern components to keep the innards looking original the same way.

Tantals will develop the odd fault but are generally very good components.
The pattern seems to be that if one tantal fails in a set, the others will probably
also be bad or at least marginal so it's either all stay or all go (Beogram 4002 and 4004).

Ceramic caps and polyester caps are generally very reliable components and I wouldn't
dream of replacing any of them unless physically damaged or otherwise proven faulty.
Besides, many caps of this nature works in carefully adjusted circuits and a replacement
will often require readjusting of the circuit, a waste of time and completely
unnecessary unless of course the actual component was indeed faulty.

We like photos, so please go ahead and post some.

Martin

I think this is a very informative thread especially for people like me who really enjoy trying to do their own repairs. Firstly though I know what an electrolyte capacitor looks like and I can replace them but i have never heard of a tantalum capacitor? Maybe someone could post a pic of an old one and what a new replacement would look like?

Thanks

Found this excellent picture on Google.
There's really no signs of age to a tantal so an old and a new looks pretty much the same.
B&O tend to like using red and green ones, not that the color matters though but different brands may use different colors.

Sizes vary from apprx 3 - 6mm in diameter and height. The shown cap is 4,7uF 35V with positive lead lowest in the picture.

Martin

As a bit of an aside - I recently replaced the crossover electrolytics in my RL60's after twenty odd years (mine from new).

I was gutted to hear no marked improvement nor, afterward, no measurable differences in the capacitors, old or new. I must admit to being completely flumoxed, I had assumed they would have slowly deteriorated over the years without me noticing and I would hear a bright, new top-end. - I certainly wouldn't advise anyone buying old speakers to assume the crossovers might be OK - if you aren't sure, change them anyway, it isn't a huge job.

The details are HERE. - look for the pdf attached to my post.

It just goes to show you never can tell (and you certainly can't assume).

Wow.

Thanks to everyone who found time to respond to this thread!

To help clarify some very good points raised, here's a summary of the ideas I really want to cover in the guide:

There will be pictures. Lots of pictures! So for newcomers who don't know an electrolytic capacitor from a constipated elephant, it should be very easy to identify, check, and replace faulty or "tired" components. (Hint : a constipated elephant is much larger and less shiny than most capacitors! I hope that helps! )

The cap stuffing (or potting) is only really suggested for large offboard metal-can type caps. It's fairly fiddly, and definitely time-consuming (compared with replacing board-mounted caps, which are a piece of cake to replace), and you don't want to be potting away with no audible result.

However, I do agree that all likely caps should be measured and replaced if they are causing audible problems. That includes tantalums (the older style tantalum caps, in the little plastic drums, are definitely a problem 40+ years on), and even some greencaps and MKTs or polypropylene caps in more recent equipment. (I'll help identify which are which).

The important thing to note (and Puncher raised this point recently) is that you don't always want to just swap out caps unless there is a really clear need to. Electrolytics tend to dry out over the decades, but not all electros do, and some never do. It can sometimes be related to a particular batch, but sometimes, you get lucky, and the caps are OK. In that case, it might be more of an aesthetic repair, where one particular component on one channel is stuffed, but the other isn't, in which case it's entirely up to you.

And if you do intend to swap out caps willy-nilly, it's probably best to be able to identify the most likely suspects before digging out a soldering iron, or you could be in for a long and tedious repair. Again, I hope I can help identify the worst offenders.

In any case, there's a lot of information to cover, and there's more than one way to pot a capacitor (pardon the pun), so hopefully I'll be able to help identify the usual suspects, as well as helping to give some users the confidence to understand which components may need replacing, how, and with what.

I'm not an engineer or a rocket surgeon, but I hope I can cover most of the excellent suggestions and requests. Keep 'em coming!

I also do a little photography, and I know a pixel from a popsicle (the popsicle is the cold yummy thing, right? ), so hopefully the guide won't be a huge, pixellated monster filled with boring text.

Thanks again to all who have made suggestions, and if you're an interested lurker, please do ask if you'd like to see something not mentioned here addressed.

This is such a cool forum. Thanks to everyone who's taken the time to respond. Keep them coming!

And stay tuned!  

Dillen:

Found this excellent picture on Google.
There's really no signs of age to a tantal so an old and a new looks pretty much the same.
B&O tend to like using red and green ones, not that the color matters though but different brands may use different colors.

Sizes vary from apprx 3 - 6mm in diameter and height. The shown cap is 4,7uF 35V with positive lead lowest in the picture.

Martin

 Thanks...I always wanted to know what those were!!   Never thought of replacing them.....might be the solution to some of my problems on a particular BM1900!!!

The single most useful tool to assist in identifying bad capacitors is called an ESR Meter.

It measures the ESR - Equivalent Series Resistance - of a capacitor - in-circuit, so you do not have to unsolder the capacitor to measure it.

Google "EVB ESR" to get to a super, affordable meter made in Portugal, by a gentleman who offers superb after-sales service. This unit is made under licence from the original ESR meter by *** Smith in Oz.

EVB sells fully assembled units, as well as kits, for those of us who like to have fun with a soldering iron.

Menahem

Hi,

i would like to add some comments...

Tantal caps were used a lot in the 50-70th, then they were replaced by the cheaper electrolyth types. Today they are still used in power supplys, very often as a smd part.

Tantal is very reliable, even for a very long time, they are still very good in power supply's, they have a low ESR and very good filter characteristics. They have almost no trouble with aging, since there is no electrolyth, they can resist heat and mechanical vibrations. So, it sounds like the ideal capacitor. But there is more...

If not used for a very long time (10-20 years...! ) they tend to burn and explode when used again. I found several of these exploded tantals in computer mainboards of the early 80s, just the 2 pins remained, the rest was gone... and i saw it live, it started to burn on the top and ignited more and more. It was a real fire, that was no fun at all.

I could test and reproduce this effect. If you use an old tantal ( i.e. 4.7uF 16V) and start at once with it's maximal rating 16V, it will burn like a candle.  So, never start old hardware without watching it...

The next thing is: Tantal has a very bad filter character used in the signal path for audio applications. I had some old tape decks (B&O and Telefunken) for repair, the owner wanted to play and hear his own old records. I repaired the mechanical deck, replaced all other caps and the sound was original again, but so bad, it was hardly to understand, there was almost no treble and way to much bass. That's the way it was 40 years ago...

The reason was, that there were some tantals used in the sound path. I replaced them by MKS Wima polystyrene types and the sound was perfect, way beyond it's original specification when these decks were new.  The sound was clear, loud and almost like todays equipment.

So, if you find tantals in the the sound path, replace them by modern types. Ok, you change the sound, it does not sound like original, but it sounds fantastic for this old hardware.

Martin