How often should you use your spare amps so the capacitors don't dry up? I hear Krell amps dry up if not used but what about other brands? - AVS Forum
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post #1 of 6 Old 03-09-2013, 08:12 PM - Thread Starter
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Have any of you ever had to deal with your capacitors drying up after not using them in a while? Should I hook the spare amps up once a month, week, to make sure that it doesn't go bad?
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post #2 of 6 Old 03-10-2013, 06:09 AM
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Originally Posted by keyboardcat View Post

Have any of you ever had to deal with your capacitors drying up after not using them in a while? Should I hook the spare amps up once a month, week, to make sure that it doesn't go bad?

If you define "a while" in decades, then yes, one normally sees some drying out of electrolytic caps after a few decades. When equipment runs hot, it often shows up first in the electrolytic caps. There are electrolytic caps in equipment from the 1930s that are still holding their own. This is rare.

About 5 years ago there was a rash of defective electrolytic capacitors that failed very prematurely due to an error in the chemical formula of their electrolyte, and started bulging and failing after just a few months.

I've had components where every electrolytic of a certain kind failed after just a few years. A friend minted some money some years back when this happened to some high end audio consoles that were worth a good chunk of a $million. He painstakingly replaced 100's of parts.

These are exceptional cases. The usual situation is stable operation for several decades.
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post #3 of 6 Old 03-10-2013, 09:30 AM
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Electrolytic capacitors do not "dry up".

An electrolytic capacitor is not like a normal capacitor, which has two metal plates separated by an insulator material of some sort (mylar, polyester, etc.).

An electrolytic capacitor is made MUCH smaller, for its capacitance, by using a single metal plate coated with electrolyte material.

This electrolyte material undergoes a chemical reaction when a voltage of the correct polarity is applied. This chemical reaction forms a microscopically thin layer which acts as an insulator as long as the voltage is maintained, and the rest of the electroltyic material is connected physically to an outer metal can that acts as the negative connection of the capacitor.

When the capacitor is not used for a long time, the chemical reaction that forms the insulating layer may not take place as it should, and the capacitor leaks current or completely shorts out.

How long is too long?

It may be a question of months or years, depending on the age and quality of the capacitor. There are many many variables including temperatures, voltage applied vs voltage rating, etc. which make it hard to generalize
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post #4 of 6 Old 03-10-2013, 10:32 AM
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Originally Posted by commsysman View Post

Electrolytic capacitors do not "dry up".

Interesting claim. Its been a number of years since I last tore an electrolytic capacitor apart. Back in the 1930s electrolytic capacitors did have liquid in them. My recollection that more recent versions used a jelled liquid that was more like a paste.

Wikipedia says:

http://en.wikipedia.org/wiki/Electrolytic_capacitor

"An electrolytic capacitor is a capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types, but with performance disadvantages."

My understanding of how electrolytic capacitors disputes the above.

http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm

"Electrolytic capacitors are capacitors in which one or both of the "plates" is a non-metallic conductive substance, an electrolyte. Electrolytes have lower conductivity than metals, so are only used in capacitors when metallic plate is not practical, such as when the dielectric surface is fragile or rough in shape or when ionic current is required to maintain the dielectric integrity. The dielectric material of electrolytic capacitors is produced from the anode metal itself in what is known as the forming (or anodizing process. During this process, current flows from the anode metal – which must be a valve metal such as aluminum, niobium, tantalum, titanium, or silicon – through a conductive bath of a special forming electrolyte to the bath cathode. The flow of current causes an insulating metal oxide to grow out of and into the surface of the anode. The thickness, structure and composition of this insulating layer determine its dielectric strength.

The above description is actually a little self-contradictory, but corrects itself in the second sentence:

"The dielectric material of electrolytic capacitors is produced from the anode metal itself in what is known as the forming (or anodizing process."

The anode is typically aluminum (hence the use of the word anodizing) or tantalum.
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An electrolytic capacitor is not like a normal capacitor, which has two metal plates separated by an insulator material of some sort (mylar, polyester, etc.).

False. If you tear an electrolytic apart you will find two metal plates which are either aluminum or tantalum. They are separated by a layer that functions something like a wick, mechanically separating the metal plates and retaining and distributing the electrolyte. The actual dielectric is a thin oxide layer related to the material that the metal plates are made out of, IOW either aluminum oxide or tantalum oxide. Either of these materials combine a high dielectric constant with excellent insulating properties in thin layers.

http://en.wikipedia.org/wiki/Tantalum_capacitor

"A tantalum capacitor is a type of electrolytic capacitor, a component of electronic circuits. It typically consists of a pellet of tantalum metal as anode, covered by an insulating oxide layer that forms the dielectric, surrounded by conductive material as a cathode. Tantalum capacitors are the main use of the element tantalum".
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This electrolyte material undergoes a chemical reaction when a voltage of the correct polarity is applied. This chemical reaction forms a microscopically thin layer which acts as an insulator as long as the voltage is maintained, and the rest of the electroltyic material is connected physically to an outer metal can that acts as the negative connection of the capacitor.

Agreed.
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post #5 of 6 Old 03-10-2013, 11:50 AM - Thread Starter
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This is why I was worried about amps drying up and got scared after reading this.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1296341195&openflup&10&4

I have been told that the worst thing you can do is let a big Krell sit in its box for years.I was told the caps all dry out especially if it has not been serviced for 10yrs.I am looking for a KSA 300s but they are all just sitting in the closet then coming out for Big Bucks.Is this not bad for them?


02-02-11: Macrojack
Yes!!! Krell is not at its best unless properly aged in a "Krellar". This is similar to a wine cellar with controlled humidity and temperature. The serious audiophile keeps storage records and carefully monitors his stash so as to not mature the critical Krellulites at too rapid a pace.
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post #6 of 6 Old 03-11-2013, 06:35 AM
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Quote:
Originally Posted by keyboardcat View Post

This is why I was worried about amps drying up and got scared after reading this.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1296341195&openflup&10&4

I have been told that the worst thing you can do is let a big Krell sit in its box for years.I was told the caps all dry out especially if it has not been serviced for 10yrs.I am looking for a KSA 300s but they are all just sitting in the closet then coming out for Big Bucks.Is this not bad for them?


02-02-11: Macrojack
Yes!!! Krell is not at its best unless properly aged in a "Krellar". This is similar to a wine cellar with controlled humidity and temperature. The serious audiophile keeps storage records and carefully monitors his stash so as to not mature the critical Krellulites at too rapid a pace.

If you believe that sort of thing, you're going to be chasing your tail for the rest of your life... ;-)

OTOH, your quote is very funny - a neat piece of fine writing.

As I have mentioned here several times, about 3 years ago my audio club was offered the opportunity to go to Manhattan and clean out two store rooms that had been the property of a well-known audio magazine that was moving their offices for the first time in over 20 years. Their people had supposedly gone over the two store rooms and according to them, it was all not that valuable.

One of the treasures we found under a ton of junk was a ca. 1992 Pass Threshold SA4e. It was with other stuff that related to well known audio personage who died like a decade ago, so it had probably not been powered up for at least that long. It might have been sitting there since 1993.

I took the Threshold SA4e home and put it on my test bench. It met original specs, and with a bullet! We sold it on Audiogon for about $6k and I banked my share of the cash.
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