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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Feb 2018, 10:20 pm   #1
linescan87
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Default Tants

Hi All,

Blue, green and red. Tantalum capacitors come in many colours. Does the colour have any significance?

Just wondering,

John Joe.
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Old 14th Feb 2018, 10:22 pm   #2
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Default Re: Tants

I have learned that anything that isn't yellow and isn't less than about 20 years old should be got rid of quickly. Blue ones are especially nasty.

Yes I know this isn't very scientific.
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Old 14th Feb 2018, 10:31 pm   #3
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Default Re: Tants

I'd concur with the above- and the blues may be nearer toasty brown on occasion.... I think the yellow types may have been Philips (not to be confused with pretty orange colour solid aluminium, a Philips speciality that seem to be very trustworthy with similar applications).
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Old 14th Feb 2018, 10:42 pm   #4
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Default Re: Tants

Found a photo of my least favourite ones. As you can see they have been removed. This was because they became resistors and not very resistive ones. One of which caused my Tek HT to blow the fuse. No sign of any brown there. This is due to the fuse, fortunately.
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Old 15th Feb 2018, 1:47 am   #5
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Default Re: Tants

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Originally Posted by turretslug View Post
nearer toasty brown on occasion.....
I think I replaced failed blue ones (in a commercial oscilloscope, in they which had done some damage) with orange ones, which caused more damage when they failed, shortly after installation. These were replaced with good quality aluminium electrolytics....and happiness ensued.

The point has been made previously on the forum that circuits need to be designed competently to use tants otherwise tants will fail. I think I belong to the school of thought that suggests the best modern aluminium electrolytics are good enough for me.

B
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Old 15th Feb 2018, 2:11 am   #6
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Default Re: Tants

Blue ones have a nasty habit of going short circuit.
Duff ones can be fun if there is plenty of power available.
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Old 15th Feb 2018, 6:46 am   #7
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Default Re: Tants

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Originally Posted by Refugee View Post
Blue ones have a nasty habit of going short circuit.
Duff ones can be fun if there is plenty of power available.
Indeed they can !

I had one blow its top of, which went off like like a rocket, pass over my co-workers head and embed its self as a molten mass into the floor the other side of his bench. This was on new equipment at the back end of the 80s !

If someone’s eye had been in the trajectory path, I shudder to think of the consequences. Be careful out there !
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Old 15th Feb 2018, 10:07 am   #8
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Default Re: Tants

I have found when it comes to replacing the little fire breathing dragons, that it's usually good enough these days to replace them with half decent low ESR electrolytic capacitors of about twice the value. Also usually a larger headroom on maximum voltage then. As tantalum capacitor prices shoot up rapidly for higher voltages, manufacturers tended to push them pretty close to the line. In some Tektronix scopes for example, some wonderful individual decided to use 16v caps on the 15v line. I'd be happier with 35v myself. Thanks to Tantalum being a "conflict mineral", prices have risen to ridiculous levels as well so direct replacements aren't always cost effective.

I will say that the new AVX SMD line at least (TAJ) seems to be indestructible. I have tried over-volting (30v across 16v tant in reverse) and they just get hot. No sign of an explosion or fireball. If they're on a board, they just tend to desolder themselves and fall off if the orientation isn't flat!
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Old 15th Feb 2018, 10:11 am   #9
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Default Re: Tants

I think the crude designation by colour is misleading. There are other blue ones for example, different to those pictured above (darker). These were by Siemens and I have found them to be good.
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Old 15th Feb 2018, 10:22 am   #10
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Default Re: Tants

I'm working on a Skantic TV at the moment that is absolutely littered with them, all the colours of the rainbow and they have already caused quite a bit of bother. I have seen them explode before.

I remember reading an article in Television by Les Lawry-Johns "Beware the blue tants" Think there all suspect now.
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Old 15th Feb 2018, 10:47 am   #11
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Default Re: Tants

Hi.

I think tantalum bead capacitors are not to be trusted and agree that modern low leakage low ESR electrolytic capacitors generally make good replacements. I would have thought that tants are pretty safe in timing circuit applications where there's not a low impedance voltage source available to wreak havoc if the cap should fail short circuit.
It always gets me worried about working on live equipment that has tants connected across supply lines. Maybe they should be issued with a health warning to put on your eye protection! Not just this, but the fire risk is very real.

Regards
Symon.
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Old 15th Feb 2018, 11:27 am   #12
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Default Re: Tants

The main problem is that the spec sheet for the tantalum beads back in the early 80's suggested that 6V ones should be used to decouple 5V rails, 16V ones on 15V rails etc. That is why they were made with such strange voltages. That is now known to be an invitation to disaster. Current guidelines is that they should have at least 30% and preferably 50% higher voltage rating than the rail voltage. So for example 8V on 5V rails, 20V on 15V rails etc.

Or just use low ESR electrolytic. Which is what Tektronix did on later versions of equipment that previously had the exploding tant syndrome.

But when they are used in signal level circuitry they are just fine. It is just applications where they get surge voltages and currents (ie power rails) that they are a problem.

Craig
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Old 15th Feb 2018, 11:41 am   #13
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Default Re: Tants

Yes indeed. There are literally only two tants in my Tektronix 2225. Rest of the entire thing is electrolytics. Then again they decided to put Philips axials in there which was a bad idea as they were all bad!
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Old 15th Feb 2018, 11:46 am   #14
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Default Re: Tants

I have seen a trail across the inside of the bottom panel on a bit of equipment where the fire ball had rolled around as it cooled off.
I had to fix the equipment to get money to live on.
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Old 15th Feb 2018, 12:12 pm   #15
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Default Re: Tants

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Originally Posted by MrBungle View Post
Yes indeed. There are literally only two tants in my Tektronix 2225. Rest of the entire thing is electrolytics. Then again they decided to put Philips axials in there which was a bad idea as they were all bad!
Looked at in the context of product that was made from 1987 to 1992 - so about 30 years ago - it is not surprising that component gremlins need to be exorcised
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Old 15th Feb 2018, 12:25 pm   #16
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Default Re: Tants

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Originally Posted by Philips210 View Post
I think tantalum bead capacitors are not to be trusted and agree that modern low leakage low ESR electrolytic capacitors generally make good replacements.
I would totally disagree with this....unless the electrolytics you are referring to are radial through hole parts or axial parts. Most modern electros are surface mount now, in most modern gear. This is a very big problem.

I would rather a board was populated with 50 vintage Tant bead capacitors, either through hole parts or surface mount Tants, than even one surface mount electrolytic !

When a Tant fails (photo attached of a supposed reliable yellow one that recently smoked in one of my SG503 generators) it announces its presence a lot of the time with smoke & that familiar smell. Or it just goes electrically leaky.

When the surface mount electrolytics leaks electrolyte, its a game changer (as they ALWAYS do if you wait long enough) the faults they cause are diaboloical and complex with inter-track leakage, corroded films in surface mount resistors and corroded tracks.

With inter track leakage, you end up with what amounts to a new unique circuit configuration. Because of this, fault characteristics can appear impossible or bizarre and not relate to the circuit architecture of what you are trying to repair. This can make fault finding much more difficult and time consuming. I know, I had inter track leakage issues due to leaking electrolytics in a Tek scope and a video monitor, it is not a good party.

Whenever I see surface mount electros I replace them with Tants, and I'm happier with that and more confident, even knowing that Tants (especially vintage ones) can fail as they do and smoke up the room, but generally they fail destroying themselves, not causing gross destruction to many square centimeters of PCB and parts around them.
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Old 15th Feb 2018, 12:33 pm   #17
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Default Re: Tants

I think we're mostly talking through hole here. When it gets to SMD, the tants are extremely reliable. I don't think I've had a bad one.

I don't think I've actually seen any SMD electrolytics in the real world yet. I've avoided Tek digital scopes because of them so far however, knowing how bad they can be. Everything seems to confine TH electrolytics to the power supply side of things an then SMD tants on the actual equipment. Cheap and reliable!

Wonder if aluminium polymer caps will make this problem one of the past one day...
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Old 15th Feb 2018, 12:39 pm   #18
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Default Re: Tants

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Originally Posted by MrBungle View Post
Wonder if aluminium polymer caps will make this problem one of the past one day...
I hope they do.

One of the main reasons why 1970's vintage automotive electronics was so reliable was that companies like Motorola & Lucas, designed it with no electrolytic caps or Tants. With the under bonnet temperatures, they decided it was an " unfit environment for electrolytics or Tants". Looking at the designs of items like alternator regulators, they were devoid of such parts, most of these vintage designs still work. Unlike a lot of commercial / domestic electronics from that era, where the electrolytics have taken down the function of the device.
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Old 15th Feb 2018, 12:46 pm   #19
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Default Re: Tants

I don't normally go in for wholesale capacitor replacement, but I have just replaced all the tantalum capacitors in an EAI1000 analogue computer with modern aluminium electrolytics. I had a couple of the tants short, one killed the -15V supply (not enough current from said rail to cause the tant to explode) which did little damage. The other shorted the +8V to -8V rail, causing at least one IC to die with it. I did not what a repeat performance so I changed the lot.
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Old 15th Feb 2018, 12:47 pm   #20
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If there was one across both rails that sounds like a design flaw.
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