[GreenKeys] Plantronics tantalums

[John Vendely]

Dipped tantalum capacitors from the late 1970s and early 1980s have a 
particularly poor reputation for reliability, and now fail frequently.  
Comments I've heard from more than one manufacturer suggest there was 
unusually high demand for these parts at the time, and that some 
compromises may have been made that affected longevity.  Later examples 
of this general type of capacitor had considerably improved 
reliability.  Still, even the later dipped tantalums generally didn't 
have the reliability of the metal cased tubular types with glass end 
seals.  These have, with a few notorious exceptions, exhibited good 
reliability.  I think the metal-cased vitamin-Q types you mention were a 
high quality metallized paper capacitor.  I've encountered bad ones from 
time to time, but they're generally fairly reliable, certainly far more 
so than the cheaper molded types of that time.

73,

John K9WT

n 11/13/2010 11:27 AM, David Christ wrote:
> This thread appears to be about dipped radial lead tantalum
> capacitors.  What about the tubular axial lead tantalums in a metal
> case with Teflon ends.  Do they have better durability?  Collins used
> them in a lot of aerospace stuff.
>
> And what about the tubular Vitamin-Q caps also with a metal case but
> with glass ends?
>
> Any guidance on either of these?
>
> David K0LUM
>
>
>
> At 2:09 PM -0500 11/12/10, 73131.3073 at compuserve.com wrote:
>> My experience with Tantalum caps is about the same. However, I have
>> had some luck by bringing up the equipment that contains them with a
>> variac. Starting out at something like 25 VAC for 12 to 24 hours,
>> then upping the voltage by another 25V?for another 24 hours. Keep
>> doing this until you are up to full voltage. Has worked for me. Good
>> luck!
>> ?
>> 73,
>> ?
>> Tim Swarthout, WA5QEG
>>
>>
>>
>> -----Original Message-----
>> From: Geoff Fors<geoff at wb6nvh.com>
>> To: Greenkeys List<greenkeys at mailman.qth.net>
>> Sent: Fri, Nov 12, 2010 12:54 pm
>> Subject: [GreenKeys] Plantronics tantalums
>>
>>
>>
>>
>> Yes, those are radial lead dip tantalums in the Plantronics 1280 modems, and
>> the same thing happened to me when I first got mine.  It usually occurs
>> after long periods of storage, in all sorts of equipment besides the
>> Frederick/Plantronics.
>>
>> I replace them with new ones but rated at least 10 Volts higher, which
>> should still fit.  Common opinion is that the modern electrolytics work just
>> as well, if you can find some that fit.
>>
>> They are used as filters on the various voltage rails in the equipment,
>> which usually (not always) means there is a resistor of about 100 Ohms in
>> series with them, which burns up before they do, after they short.  Without
>> the resistor in the design, they fail most violently and can burn holes
>> through the board, catch fire and send bits of themselves everywhere as
>> miniature projectiles.
>>
>> There's a silver lining in all of this, namely that I have gotten quite a
>> few pieces of high end, expensive test gear for almost nothing because it
>> was "dead," then easily revived by replacement of a few of these shorted
>> tantalums.
>>
>> Geoff
>> WB6NVH
>>
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