Re: What replacement for 22uF tantalum beads?


 

How did you measure their ESR?

So far all of the solid tantalum capacitors I have tested using my ESI
250DA impedance bridge had a dissipation (D = ESR/Xc = ESR * 2piFC)
right in line with their specifications whether they were new, NOS
(new old stock), or working parts removed from decades old
instruments.

My hypothesis for the failures of old solid tantalum capacitors is
contamination in the raw materials causing defects in the dielectric
which grow over time. Eventually a large enough defect forms that the
solid tantalum self healing mechanism where heating converts MnO2 to
Mn2O3 fails because of thermal runaway.

On 19 Mar 2016 06:31:10 -0700, you wrote:

Interestingly enough, one of my 485's (SN B142617) had 90% of the 22uf 15V tantalums fail miserably. Their ESR was 4X what it would have been for a cheap-o 22uf 15V. I've been wondering if there was a crap batch of those tants being used around the time of that scope's build date.

I buy almost all of my tantalums off ebay, but the majority of those come from 2 sellers that I trust. I don't know how people feel about sharing seller names here, and I don't want to "advertise" for anyone, but if you'd like to know which seller that is, I can email you the name. I'll post it here if no one speaks up against doing so.

-Brian

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