The better capacitors are needed for switching power supplies so there
was not a lot of consumer demand for them back when the 7A13 was
produced. Aluminum electrolytics are a lot better than they used to
be so except in high reliability and wide temperature range
applications, wet tantalums are not really needed except in very high
performance AC coupling applications like oscilloscope front ends and
some low noise circuits.
Even now power supply designers often overlook the ripple current
rating for capacitors leading to short capacitor life.
On Mon, 23 Jul 2012 20:46:03 -0500, "Rob" <rgwood@...>
wrote:
Thanks David, I saw the post but missed the logic on which was good and why.
(as well as 2 of the links via "speed reading" I guess...sigh...)....
Anyway, much appreciated..
I do not remember the ESR and ESL on caps being something to concerns
oneself with back when I worked on consumer electronics 20 years ago.
However, I know that my chosen addiction is a big step above the stuff I
worked on in those days. The education I receive via this forum is
invaluable and I appreciate you taking the time. If/ when I am finished with
the mainframes and plug-ins I don't ultimately want to keep....
I want to be able to tell people what I replaced and why, and hopefully give
them something that will last another decade. This education from time to
time will help me in that goal.
Rob
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of David
Sent: Monday, July 23, 2012 8:17 PM
To: TekScopes@...
Subject: Re: [TekScopes] Adjusting a 7A13, and a few other questions
I mentioned a couple of replacements for this capacitor in my earlier post.
The capacitor in this case is used for bulk power supply decoupling so low
ESR and ESL is important while leakage is irrelevent. The 109D 10uF 50V has
an 8 Ohm ESR and 160 mA ripple current specification at 120Hz.
An organic polymer electrolytic of the same value should be a superior
replacement if its super low ESR does not cause circuit oscillation which
would not be a problem here because of the relatively high wire resistance
from the mainframe power supply.
A very good low impedance aluminum electrolytic would need to be at least
twice as large achieve the same ESR and ripple current rating but would be
half the price of the organic polymer electrolytic capacitor.
On Mon, 23 Jul 2012 19:50:42 -0500, "Rob" <rgwood@...>
wrote:
Forgive me jumping into a post but the question is related and I know
Keith so he won't mind.... (much)....
When choosing a sub for the particular cap referenced here...
Is a standard electrolytic (by standard electrolytic I mean a 'good'
105C,
etc.) an ok sub or must one go with a wet tantalum?
Thanks in advance for answering
Rob aka Keith * smile *
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On
Behalf Of Brad Thompson
Sent: Monday, July 23, 2012 7:14 PM
To: TekScopes@...
Subject: Re: [TekScopes] Adjusting a 7A13, and a few other questions
On 7/23/2012 6:05 PM, keithostertag wrote:
I am just now getting around to looking at my 7A13, bought on eBay
awhile back. I've never used a differential amp. Serial # B236701.
<snip>
I thought I'd show you a cap I found which has visible leaking (C505):
Hello, Keith and the group--
That's a so-called "wet slug" tantalum capacitor. Its clear outer
jacket is yellowed, likely due to overheating.
IIRC, the electrolyte in the wet-slug capacitors is sulfuric acid, so
when you remove the failed capacitor, I'd recommend swabbing the
corroded area with a weak baking-soda solution to neutralize any
remaining acid, followed by swabbing with distilled water to remove any
chemical residues.
Inspect for corrosion damage to all PC-board traces in the area and
repair as necessary.
Wet-slug caps don't like to operate with a reverse bias and are likely
to fail prematurely, so check the circuitry for upstream component
failures that might have back-biased the capacitor.
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David Hess