Re: caps (was: 8250LP....)

On Mon, Aug 21, 2017 at 4:12 PM,  <silverdr@wfmh.org.pl> wrote:
>
>> On 2017-08-21, at 13:51, Francesco Messineo <francesco.messineo@gmail.com> wrote:
>>
>> sorry to jump into this discussion (I wish I owned either a 1001 or
>> 8x50 myself...), but assuming the leaky capacitors are electrolytics,
>> they can nowadays almost always be replaced with MLCC capacitors that
>> are both tiny and last forever.
>> Of course one should examine the actual circtuit to be sure, but if
>> they're the usual (for the '80s electronics) supply bypass or DC block
>> ones, the MLCC will work even better of the original.
>> I wouldn't dare using an MLCC in place of electrolytic as a switcher
>> output capacitor unless I really checked what I'm doing anyway.
>
> Did they really use electrolytic caps for bypasses in the eighties? I haven't had much experience in the pre 1982 (pre-C64 that is :-) electronics but those I've seen since 1982 were using ceramics for bypasses. DC blocks - yes, I've seen those. As for replacing the aluminium electrolytic ones, I heard about tantalum ones being the best (?) replacement for the aluminium based polarised caps.
>

100nF or 47nF ceramic are ubiquitous close to each digital IC as
supply bypass, but every board has usually a few electrolytics on the
supply rails scattered around or just at the power supply connection
if the board is small. Those are also called "bypass" capacitors (they
just bypass a larger part of the board, not just the IC surroundings).
Tantalum don't leak, but have some other problems (sometimes they
explode or burn for example, and cost more than the MLCCs) and their
ESR is usually quite different from the same capacity aluminum
electrolytic. So you can't just replace a tantalum capacitor for a
regular aluminum one unless you understand that ESR/ESL don't matter
in that application, but when you understand that, then MLCCs are
cheaper and smaller :)

Regards
Frank IZ8DWF

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