Internally tanatlums look like a sponge where their
charging surface area is exposed in 3-dimensions, whereas electrolytics are a
couple of wound, flat pieces of foil.
Due to their inherent structure, tanatalums
charge very quickly as the 3-D surface gets easily flooded with electrons,
whereas for electrolytics, the electrons have to spread around the plate to be
saturated. That takes time.
So, tantalums are very good for high frequency cap
duties, like on the crystal (clock) circuits. For
power rails, electrolytics are fine of course, but for anything that's a high
frequency circuit, I'd stick with a tantalum if was spec'ed that way to begin
with.
Tantalums are very unfogiving of overvoltage which
is what usually kills them. Once they're saturated, the slightest voltage over
their rating will do them in, where they melt into a short. They work
great when used properly in a circuit where the probability that they'll
ever see a spike is nil. Replacing a tant with one with a larger rating will
slow down the saturation time, so again, I'd just replace it with the
original rating component. I like the Vishay brand which is what we use in the
aviation industry where I work.
I'm no expert (I'm a mechanical engineer however),
but I spent a few hours researching the ins-and-outs of tants one day right
before I did a full recap on my OB-Xa. If it was tantalum, it stayed that
way.
Scott in Ohio
----- Original Message -----From: Daniel ForróSent: Monday, April 08, 2013 11:01 AMSubject: Re: [vintagesynthrepair] Recapping
Thanks for your explanation and the link. So can I take it as a rule of thumb and change all tantalum (in PSU, logic circuits or audio circuits) for low ESR electrolytic? Or is there some case where to change just old tantalum for new one? Could for example using of tantalum rated for higher voltage serve as a sort of better protection against possible fail?I had this fire problem with two ceramic disk caps in the PSU of one old Russian instrument which was not in use for few years. Fortunately I could see the fire, it started immediately after switching on, so I just switched off. It was enough to change those caps and instrument is OK, but I will do complete recapping.Daniel Forro
On 8 Apr, 2013, at 11:32 PM, Alexis V. Rogers wrote:
Tantalums were used due to size and lower ESR. You can get low ESR electrolytics these days. The problem with tantalums is that they close (short) when they fail. When used in a power supply situation, I've seen tantalums burst into flame and end up looking like burnt marshmallows.I've never added capacitors to the IC power lines unless I was replacing with a different IC whose datasheet called for it.