Sprague Forming Info
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Capacitors
Sprague Forming Info
Sprague Forming InfoFrom tjto--(at)--est.net Wed Jan 10 16:36:13 CST 1996
From: tjto--(at)--est.net (Tom Phillips)
Newsgroups: alt.guitar.amps
Subject: Re: Forming Filter Caps ?
Date: Tue, 09 Jan 1996 23:36:22 -0700
> Jon Steele (Jon_Steel--(at)--binc.com) wrote:
> : Amp Techs -
> : How crucial is this business of gradually ramping up the voltage
> : after replacing filter caps? I don't have a variac.
>
> : Thanks in advance if you find the time to respond.
>
Well guys, here goes... Opening the bag of controversy about ³forming² or
³conditioning² electrolytic capacitors.
Here is a quote from appendix C of the 1990 Sprague electrolytic capacitor
catalog.
³When aluminum electrolytic capacitors were first developed,
deterioration ³on-the-shelf² was a major problem and frequent
replacement of stock parts was necessary. Additionally, use of capacitors
for extended periods at small percentages of rated voltage permitted the
dielectric oxide film to ³deform², just as it would ³on-the-shelf². Both
problems were solved in the early 1950¹s with the introduction of
high-purity aluminum foil. Oxide film stability was greatly enhanced and
today aluminum electrolytics can be used after storage, and at any
percentage of rated voltage, without loss of capacitor quality².
Now my personal opinion:
Much of the opinion today about forming electrolytic caps stems from the
days when it was more necessary. Note, however, that Sprague said the
³Oxide film stability was greatly enhanced². They didn¹t say ³perfected².
Therefore, even though they imply that forming not necessary, I do it on
the amps I work on. In may situations there is ³accepted practice² and
³better² or ³best² practice. Think of forming as insurance or that extra
edge.
Bottom line - It¹s probably better to form your new electrolytic caps but
not as necessary as it was in the early days. The longer they have been in
storage before installation, the greater the benefits of forming. If you
don¹t have a variac and you use fresh parts you will be OK. That is, you
won¹r ruin the caps. You will certainly be much better off than you were
with 20+ year old filter caps in your amp.
One last point. Sprague publishes application note number 3499.1 titled
³Reconditioning Procedures for Sprague Aluminum Electrolytic Capacitors².
Therefore, they are admitting that, under certain circumstances,
reconditioning is beneficial.
Hope this helps.
Tom Phillips
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