Tantalum filter caps?

[Matthias]

Hey folks,
Need to replace a few electros in this MM-130. all 5 of the 150uF/50vdc.
2 are the bias supply filter, which are really the ones that need replacing.

I went to the local surplus and picked up a handfull of what I thought were regular aluminum's.
But, when I got home and went to test 'em I realized they were much heavier than your average Aluminum type. starting to think they are Tantalum.
They are in an axial package and obviously appear Identical to regular electro's
I know that tant's hate revese voltage and are also very sensitive to over current situations. but what else?
So, If they are tantalum, are they suitable for ps filter apps?
I forgot to add that While looking it up on google I got conflicting information.

[Matthias]

well,
after checking these out with the esr meter I realized that one of my test leads had gone intermittent. replaced the lead and what do you know....the old caps are still kickin'.
But the question remains...
What are your thoughts on tant's in a filtering app.?

[zhyla]

I've heard discussions about various cap types in the signal chain but for just power filtering I think it would be tough to convince me it mattered. How do they compare price wise to electrolytics?

[dai h.]

I think the failure mode for a tant is mostly a short, so for a bias filter in say a 5F6-A/Marshall type pi filter bias circuit would seem to be a bad situation IF a failure did occur. Seem to be used sometimes in a gtr. amp though. IIRC my Boogie .22+ had some for cathode bypass caps.

[Matthias]

Hello Dai,
Pricewise....well, it's not a fair comparison. I got 8 of these along with 4, 13v1A Zeners and 4 ohmite 5W620 Ohm resistors for $3 usa....$5 with gratuity.....
I found pretty much what you said....when they fail it's pretty much a short to ground, so I decided against it...

[dai h.]

nice. Surplus is great isn't it? Maybe you can still use them for something else though. Somewhere you ordinarily wouldn't get to (due to the expense ordinarily of a tant that big).

[Matthias]

The whole point is reduce, reuse, and recycle.....and save money.
You would think among all the Students, Service people, tinkerers, prototypers, and audio-philes, they would be doing business like gang busters. Yet whenever I go there, the place is empty.
I guess in a selfish manner it's ok....More for me.

[jrfrond]

I refuse to use tantalum caps in anything but low-voltage timing circuits. Their reliability sucks.

[Enzo]

When I see them in amp circuits, I replace them with other types.

[tedmich]

Tantalum...
amp people dislike them greatly, although I've seen one in an Egnater cathode bias... Valve Wizard has no such dislike and they work great in linear regulator circuits...

I will try in my cathode bias; the actual voltage is <<10V so real low values can be used..

Amp heads LOVE tantalum resistors (~$7 each!) go figure....

[Enzo]

I think the concensus concern among techs who hate them is not about how well they might work, it is about how often they fail. And how totally unable they are to withstand any sort of trauma.

[6267]

Junkyard or scrapyard is good for free motor run caps, generally film caps with 660v AC ratings, so they'll take a bit of ripple . I wasn't impressed with tantalums in the tone stack, and if you read up on the situation behind coltan ore in the Congo, it's not really encouraging ethically either.

[tedmich]

I think the concensus concern among techs who hate them is not about how well they might work, it is about how often they fail. And how totally unable they are to withstand any sort of trauma.

Dual edged sword here, Audiophiles HATE then due to "audible distortion" of dubious origins; a few articles showed specific coupling applications which had distortion up to ~0.2% at 35Hz for tants of unspecified Mfg.

one "cork sniffer's" opinion:
http://www.geocities.com/Area51/Nebu...rove_audio.txt

"tantalum capacitors _stink _for audio use: they should never be used in any signal-carrying circuit. They sound tubby in the bass, harsh and gritty in the top end, and compressed in their dynamics"

(NOT a double blind I expect)

as to reliability:

http://my.execpc.com/~endlr/reliability.html

"NASA, for example, does not allow them (Alum Electrolytic caps) to be used in flight hardware because of the risk of failure and outgassing. Tantalum capacitors can be used instead."

(but this is for proven circuit designs)

As to audio application and distortion, this shows Tant AOK for audio coupling applications

http://www.digikey.com/Web%20Export/..._tantbench.pdf

they DO require temp de-rating and short circuit failure results in self ignition (MnO2->O2!) which is very nasty and usually craters the PCB.

The have near infinite shelf life, are small and don't require "reforming" ; until I can hear the difference (or get burned!) I'll continue to try them in my circuits.

[Enzo]

The sealed tin can that is an aluminum e-cap would be a prime candidate for boiling off in the vacuum of outer space where NASA goes. The solid little tantalums won;t do that. In guitar amps however, most of the vacuum is confined inside the tubes. The caps don;t get exposed to it much.

One also wonders if NASA orders their tantalums right off the shelf at Mouser or if they spec military grade parts.

[jrfrond]

I've worked in mil-spec and aerospace electronics. Anything used in these applications get put through torture testing before being used, hence the inflated cost.

As for me, I've been a tech since '75, and as far as I am concerned, you can keep your tantalums. They are an accident waiting to happen.