[sdiy] cap autopsy /Color Codes

[Dave Krooshof]

Colour codes: Are said to be conform the resistor coding.
I'm not sure though.

Tube amp caps, especially the big ones, tend to dry out.
They even where out quicker then the tubes themselves.
Replacing them often refresh the sound, depending on the circuit
and their place in it.
The highvoltage caps are a little hard to find, but stores
that do computer diy electronics often have them, as these
are used in switching power supplies.
Look at the shopowners eyebrows when you say '400 volt'.
An over 1cm raise is not a good sign.

Dried elco's behave wierd, as chemical processes are very
unpredictable. This is a matter of surfaces that got very chaotic
in structure. After some time, the chemical REDOX processes get
things in some order again. This is the same thing that happens in
batteries. I guess you found empty batteries able to give one more
kick after your walkman/mobile phone has been shut off for a while.

So, just replace these old rinkles with nice young juicy ones.

>Just on a side note, apart from 2 of these capasitors which are
>obviously busted, there are many others which seems to have "surface
>cracks". I'm not sure whether this is just the "paint" coat, or
>whether this is a sign that the caps lifespan is coming to an end,
I do not realy think it's such a bad sign, as I have many cracked caps
that function as they should. I did replace caps like those several times,
but with the result of loosing volume (as I posted here before).
I guess it's only the coating that is funky.

If the cracks were a problem, effects would have been more obvious
and it would take less time for the cap to leave the building.

>is this common with these Mullard C280's?
Yes, very much so.

>Would it seem a wise idea to
>replace all these caps with any sign of cracking with fresh
>replacements of some kind?
No, I'd say, only if the apparatus is disfunctional.



Dave


Ps: Capacity is actually a weird concept if you think of it as ability.
You add a certain amount of possibility to hold electrons in a circuit.
nearly a philosofical concept, in a way.

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Dave Krooshof http://www.xs4all.nl/~krooshof
geluidstechnicus @ http://www.ahk.nl/the/theatertechniek_ov.html
webmaster: http://www.popronde.nl
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