Questions about forming new filter caps in an amp

FleshOnGear

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I found one on Reverb for like $60, but it’s pretty simple to assemble one. It’s just electrical parts from the local hardware store. You should be able to find schematics and guides if you just Google light bulb limiter.
 

KraftyBob

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+1 for Matthews post - new caps don’t need to be formed. However, if you’ve done a lot of work and want to bring the amp up slowly I prefer a variac with an ammeter like the one you referenced over lightbulb limiters. With the variac if the ammeter spikes you can quickly dial back the voltage.
 

Delicieuxz

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With shipping costs, the lightbulb limiters on eBay would cost me at least as much as the variable voltage regulator on Amazon. I guess the voltage regulator is more capable, and I could use it for sound experimentation, too, under-volting (or slightly over-volting?) an amp.

When is the time to form caps? If I haven't powered up an amp in 5 months, should I be doing that? I have a bunch of amps and some of them often go many months, possibly at times even well over half a year, without me powering them on. The new Ars caps that I've installed in my JCM 800 are dated 2021 12, I guess meaning December 2021. Does that make them akin to caps that have been sitting an amp that's been unused for almost a year, and therefore could use forming?

And to form them, is gradually bringing the amp up to normal voltage over 20 seconds doing it right?
 
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Matthews Guitars

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Definitely DO NOT experiment with running HIGHER than line voltage into your amp. No, no, no!!! Even a few volts over will seriously degrade tube life and may push plate voltages beyond the tolerance of tubes or the transformers.

Don't worry about trying to reform caps if they have been powered within let's say the last two years.
All the manufacturers say that their caps have a 10 year operating life, 5 year shelf life. So up to 5 years without power should not be a problem.

A proper variac power-up for the purpose of reforming caps takes several MINUTES, not 20 seconds.
 

Delicieuxz

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Definitely DO NOT experiment with running HIGHER than line voltage into your amp. No, no, no!!! Even a few volts over will seriously degrade tube life and may push plate voltages beyond the tolerance of tubes or the transformers.

Don't worry about trying to reform caps if they have been powered within let's say the last two years.
All the manufacturers say that their caps have a 10 year operating life, 5 year shelf life. So up to 5 years without power should not be a problem.

A proper variac power-up for the purpose of reforming caps takes several MINUTES, not 20 seconds.
Great info. Thanks!
 

Pete Farrington

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I guess the voltage regulator is more capable
Not really, a limiter works automatically, and reacts quicker if there’s a fault than a variac can be twiddled.
I use my variac once in a blue moon, light bulb limiter at least several times a day on bench days.
Don’t get a variac that doesn’t have in built current and voltage metering.
 

william vogel

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With shipping costs, the lightbulb limiters on eBay would cost me at least as much as the variable voltage regulator on Amazon. I guess the voltage regulator is more capable, and I could use it for sound experimentation, too, under-volting (or slightly over-volting?) an amp.

When is the time to form caps? If I haven't powered up an amp in 5 months, should I be doing that? I have a bunch of amps and some of them often go many months, possibly at times even well over half a year, without me powering them on. The new Ars caps that I've installed in my JCM 800 are dated 2021 12, I guess meaning December 2021. Does that make them akin to caps that have been sitting an amp that's been unused for almost a year, and therefore could use forming?

And to form them, is gradually bringing the amp up to normal voltage over 20 seconds doing it right?
The time to bring up an amp slowly with current and voltage limitations after storage or parts replacement is at an interval that makes you comfortable and assures you that you are following a proactive procedure to ensure minimal collateral damage. Truth is that amps can remain dormant for years without any risk of damage upon initial power on but unless you actually date label the amp upon storage, you can loose track of time and the mystery will be present. Also realize that $150 worth of equipment you can use for other purposes will give you confidence and convenience for protecting valuable electronics, testing electrical components and adjusting voltage for just about anything you want to dim or slow down.
 

FleshOnGear

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@Delicieuxz just to clarify, the light bulb limiter isn’t really for forming the caps, it’s just to protect the amp in case you somehow accidentally create a fault in the amp while wiring it up. Like Matthews said, new caps don’t really need to be formed.
 

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