Smaller Advent woofer

[Pete B]

I don't really want to get into this, BUT, I was one of the people who suggested not replacing

Sprague Compulytics IF they test out okay, BUT do you know how to test them?  Just ESR and

value is not enough, you also have to test for breakdown voltage.

Anyway, I made the suggestion based on the fact that most people probably do not know how 

to select a very low ESR electrolytic cap with similar characteristics.

We are lucky, very lucky when a 20+ year old electrolytic cap is still working.  And actually my gut

feeling is that modern electrolytics might not last as long as the better older ones, due to the push

to make them cheaper/smaller.  There is even the BAD CAPS web page - they don't make them like they used to:

https://www.badcaps.net/index.php

It is not an uninformed blanket statement, rather it is a statement based on the fact that ALL electro's

employ a chemical paste that dries out and degrades over time.

There are also the, IIRC, Carlin types that are 9 out of 10 times bad, they need to be replaced.

 

From the BAD CAPS web site - keep in mind folks that when you work in the field you learn a lot

more than the average Joe doing this in their basement:

How did this happen?
   The reason this problem exists is because of a large-scale industrial espionage foul-up.  Some companies decided to steal an electrolyte formula from another competitor.  Little be known to them, the stolen formula was incomplete and flawed.  They didn't discover this until it was too late and they had manufactured and distributed literally MILLIONS of these flawed capacitors.  It was way too late for any kind of recall, and even today, these crappy components are being used in new boards.  As I mentioned before, I believe this problem runs much deeper than simply an industrial espionage screw-up, as that incident was exposed years ago, and the problem still exists today.  Nowadays, it just boils down to corporate bean counters cutting corners to save money by using shoddy components.

The cause...
   This inferior and flawed electrolyte formula was used by a number of component manufacturers that sold to many different, reputable, and well known motherboard manufacturers.  This problem isn't isolated to one particular brand of motherboard, and not even isolated to motherboards alone.  I won't mention brands, but a VERY popular monitor manufacturer has been plagued with RMA's on some of their monitors that were built using these inferior capacitors.  This problem has been reported in computer motherboards, monitors,  televisions, radios, and stereo equipment.  Through my experiences owning a service center, I've personally seen and serviced a large number of 'high-end' equipment that had prematurely failed capacitors.

More detailed information...
   In more technical terms, this is is what actually happens to the capacitor...in the simplest of terms.  Think of an electrolytic capacitors as a battery.  They are designed to store a charge and release that charge depending on the specific requirements of the circuit.  Inside the capacitor there are two metal plates with dielectric material between them, wrapped in paper, filled with acid (electrolyte), and sealed in its housing or 'canister'.  What happens is the flawed electrolyte prematurely deteriorates and dries up.  When this happens the capacitance value changes, becomes erratic, and can even short completely, which obviously causes the circuit to malfunction.  On your motherboard, this results in system instabilities or complete failure of your board.

   From a physical standpoint, the capacitor can display a number of symptoms and even have catastrophic failures.  Catastrophic failure is a rare phenomenon, but it does happen.  The reason is this...  A capacitor canister is completely sealed and air tight.  When the electrolyte dries it turns from a liquid state into a gas.  This gas expands with heat and builds great pressure inside the canister, the theory is the same as a pressure cooker.  Of course the obvious happens when that pressure builds too much, and the capacitor will vent.  This is what causes the capacitor to 'bulge' or swell up.  In a catastrophic failure, the capacitor may actually burst or explode.  It can sound like a firecracker going off or sound similar to air escaping from a car tire, depending on how high the pressure has built.  A physically failing capacitor has an ammonia-like odor (at least that what I thought it smelled like)...  Capacitors that has swollen up are easy to detect, but one that has burst are even more noticeable.  It will usually blow from the top and spew its innards throughout your computer case.  The innards are mostly paper and any remaining electrolyte, but it sure can leave a mess...  Once again, catastrophic failure is a rare phenomenon...  It's not dangerous either, as long as you practice common sense safety precautions!  If you suspect bad caps, don't put your face near them while the system is powered up, and don't eat the paper or electrolyte that they blow out!
 

[Pete B]

I'm very curious to know the weight of the cone and voice coil if you have a scale.

Also, the length of the voice coil windings.

[ra.ra]

58 minutes ago, Pete B said:

BUT do you know how to test them?  Just ESR and value is not enough,

That's about as far as I can go, so anything more specific regarding voltage and I am clearly unqualified, and I suspect most of the weekend hobbyists like myself are in the same boat.

58 minutes ago, Pete B said:

And actually my gut feeling is that modern electrolytics might not last as long as the better older ones....

I like this statement, too. Pete. We know there are always varying degrees of quality in most any sort of goods produced at any time, and as soon as I wrote my not-fully-informed defense on behalf of more modern caps, I thought to myself, "but I so often prefer the quality of older things over their contemporary replacements".   Compulytics I am willing to try to salvage - - - black/red Callins-Temples maybe not so much - -  in fact, never.

 

[ra.ra]

31 minutes ago, Pete B said:

....the weight of the cone and voice coil ...... the length of the voice coil windings.

If I am able to furnish any of this, I will try. Let me try to find that over-baked woofer first.

[Pete B]

This is a very interesting read, note that new caps are aged with an applied voltage that is higher

than the rated voltage - page 3.  Also note the discussion of expected life and failure modes on 

page 13:   http://www.cde.com/resources/catalogs/AEappGUIDE.pdf

[Pete B]

On 9/16/2017 at 12:17 AM, ra.ra said:

I like this statement, too. Pete. We know there are always varying degrees of quality in most any sort of goods produced at any time, and as soon as I wrote my not-fully-informed defense on behalf of more modern caps, I thought to myself, "but I so often prefer the quality of older things over their contemporary replacements".   Compulytics I am willing to try to salvage - - - black/red Callins-Temples maybe not so much - -  in fact, never.

 

Right,  I think there was more pride in manufacturing and/or fear in losing business in "the old days"

but today the lesser known names will certainly cut corners to meet a price point.

I like Bennic NPE's when I have to use them, most other brands not so much.

Not sure what I'll do to replace low ESR screw terminal type caps - probably back to back snap-in caps.

[Pete B]

On the other hand, if I was restoring a high value classic such as the LS-3/5a I'd probably use

like type caps.  Bennic's for electros of the same DF (ESR) as the original caps.

[Pete B]

On cap testers, see the examples toward the end: