I have a Philips counter where a Tantalum regularly fails in the oven.
They also failed commonly in transceiver finals in the 80's

--
Raj, VU2ZAP
Bangalore, India.

The history of tantalum failures is wide and varied, but
there are some common characteristics:

1. The tantalum is in a power supply circuit and receives
   a rapid ramp from 0V to operating voltage.
2. The tantalum is spec'd close to its operating voltage,
   very close.... 5V on a 6.3V part, 12.5V on a 15V part...
3. The tantalum is dry slug, and is sealed with epoxy.
4. The instrument has been powered down for an extended
   period.

HP equipment from the 1980's is pretty immune to the problem
because they typically use hermetically sealed mil spec
tantalum capacitors.  Tektronix equipment from the 1980's
is infested with tantalum problems because they used the
cheap epoxy dipped parts.

Tantalum failures are pretty rare in equipment that is
run continuously.  Tantalum has a self healing feature that
corrects any small problems while in operating... Large problems
result in detonation.

Dipped tantalum capacitors of any age are prone to failure.
The tendency can be mitigated largely by never allowing a
tantalum capacitor to see voltage above 50% of its rating.

And finally, powering a tantalum in reverse, will cause instant
and irreparable damage.

-Chuck Harris

Tom Van Baak wrote:

I've seen the butt weld (or crimp) of the wire in hermetic units fail due to corrosion in both HP and Tek gear.  In all cases (about 6), the gear appeared to not have been protected too well from the elements, or was exposed to high humidity for a long time.  The good news is that it fails open and is pretty obvious.

Dave
----- Original Message -----
From: "Chuck Harris" cfharris@erols.com
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, February 8, 2010 6:46:54 AM GMT -08:00 US/Canada Pacific
Subject: Re: [time-nuts] The Smell of Tantalum in the Morning

The history of tantalum failures is wide and varied, but
there are some common characteristics:

1. The tantalum is in a power supply circuit and receives
       a rapid ramp from 0V to operating voltage.
2. The tantalum is spec'd close to its operating voltage,
       very close.... 5V on a 6.3V part, 12.5V on a 15V part...
3. The tantalum is dry slug, and is sealed with epoxy.
4. The instrument has been powered down for an extended
       period.

HP equipment from the 1980's is pretty immune to the problem
because they typically use hermetically sealed mil spec
tantalum capacitors.  Tektronix equipment from the 1980's
is infested with tantalum problems because they used the
cheap epoxy dipped parts.

Tantalum failures are pretty rare in equipment that is
run continuously.  Tantalum has a self healing feature that
corrects any small problems while in operating... Large problems
result in detonation.

Dipped tantalum capacitors of any age are prone to failure.
The tendency can be mitigated largely by never allowing a
tantalum capacitor to see voltage above 50% of its rating.

And finally, powering a tantalum in reverse, will cause instant
and irreparable damage.

-Chuck Harris

Tom Van Baak wrote:

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and follow the instructions there.

While in the US Navy, we had to do equipment inspections.
One quarterly was to examine the capacitors in the power supply of
one piece of equipment.
We were to look for leakage (sulfuric acid) from CL65 type wet slug
tantalum capacitors.
Shortly after that CL65 type capacitors were disapproved for military use.
I never saw one that leaked in that equipment, but, have seen a
number of boards damaged from seal leakage on CL65 capacitors.
Something to look out for.
The CL65 capacitors probably have a pure silver case a sulfuric acid
as an electrolyte.
The seal is Teflon.

We also had an interesting failure mode for ATC ceramic capacitors.
This failure mode will only occur in a sealed environment (submarine.

Just an observation.

73
Glenn
WB4UIV

At 09:46 AM 2/8/2010, you wrote:

My experience is that the plastic ones tend to burn.
The mil grade ones in HP I have never seen fail (As in flame)

On Mon, Feb 8, 2010 at 8:05 PM, Glenn Little WB4UIV <
glennmaillist@bellsouth.net> wrote: