[sdiy] cap autopsy

[Happy Harry]

Hi Alex:

I'll speak for the caps... maybe Eric will mention the tubes.

Usually, electrolytic caps start out dead and improve with
on time.

I don't know about tubes (for sure) as they get older their
emissivity goes down (they get weaker...). But I don't think
that is over a two week period... its more a long term function.
This applies mostly to power tubes... not usually the preamp stages.

Also look for any parts that could go open thermally, it might be
a resistor in the power supply that opens up when hot, etc.

Replacing the caps is usually not a bad idea in an old amp. They will
dry out and become much smaller caps with time !

H^)  Harry


>From: Alex Dickey <Alex at centricitysoftware.com>
>To: synth-diy at node12b53.a2000.nl
>Subject: [sdiy] cap autopsy
>Date: Mon, 29 Jan 2001 09:32:01 -0800
>
>so as i prepare to replace the caps in this tube amp that i was asking
>about, it occurred to me to ask a different question about the
>performance/death of said amp.
>
>when i first got the amp two years ago (at the flea) it worked.  over time
>it slowly lost volume until it stoppped passing signal at all.  i wrote it
>off as dead and stuck it in my friend's gear closet.  over christmas, i
>found the amp again and for kicks plugged it in.  lo! it worked.  but over
>the course of a few weeks of steady use, it stopped working again.
>
>i have no doubt that the fact that the caps are TOAST is a big part of 
>this.
>but what's actually happening?  why does the amp work, then not, then work,
>then...
>
>alex
>
>p.s.-sorry about the MIME shit on my messages.  anyone who has any clue how
>to make outlook 2k do text-only mode (tools>options>mail format>plain text
>isn't enough for some reason) pleeeeese write me.  my IS guy is stumped.

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