Filter Cap forming ??

rnau · 11-08-2009, 07:50 PM

I took my amp in for a cap job today, so I'm curious about this. He has a variac so he will be "forming" the caps. Is this necessary? I've read conflicting things. Some say it needs to be done, and some say that new caps are "formed" at the factory. By the way, he installed JJ caps. What do you guys think?

thrawn86 · 11-08-2009, 07:53 PM

Most of the pro's here and DIY gents DO recommend that the caps get formed, not just the 'factory' formation. Look through the threads here and find MajorNut1967's JCM800 build; I believe somewhere in that thread there is a good discussion on it.

Wilder Amplification · 11-08-2009, 10:30 PM

Quote:

Originally Posted by rnau

I took my amp in for a cap job today, so I'm curious about this. He has a variac so he will be "forming" the caps. Is this necessary? I've read conflicting things. Some say it needs to be done, and some say that new caps are "formed" at the factory. By the way, he installed JJ caps. What do you guys think?

It is a great idea to form new caps. Caps are "quick formed" at the factory. However, a "new" cap that is 5 years old or more DEFINITELY should be properly formed. Catch is...without a manufacturer's date code you have no idea how long that cap may have been sitting on the shelf so I say form all of them.

MajorNut1967 had a batch of brand new JJs, and one of them blew up on him during the forming process. So the forming process ensures that they're not gonna blow up upon first power up by "shock charging" a brand new cap that hasn't had its dielectric fully formed.

You have to remember...humans make these things. What's to say that a few somehow skipped the "quick form" process at the factory? Or that it wasn't properly done? Another thing the forming process ensures gets properly done before first initial power up. Just like humans match power valves...yet I've had sets where one valve was drawing considerably less current than the others in the set. They also claim that if you replace valves marked with the same matching numbers don't need to be rebiased...again, bullshit. Humans box and match them and shit gets mismarked all the time...in the world of amps and electronics, NEVER ASSUME ANYTHING! And it is for this reason why we form brand new filter caps.

Some techs use a variac to do it...I myself have a different method that I prefer. Every tech has his own preferred method and they're all correct.

rnau · 11-08-2009, 11:21 PM

Thanks for the great info, he told me it takes about 8 hours to properly charge the caps. The main reason for the interest is at some point I want to build a Metro amp, so I'm trying to gain as much knowledge as I can. I'm excited to hear the amp when it returns. The amp had ITT caps made in the UK in it, I take it that those were probably the original ones. Are there any other cap manufacturers out there besides JJ?

Wilder Amplification · 11-08-2009, 11:28 PM

Quote:

Originally Posted by rnau

Thanks for the great info, he told me it takes about 8 hours to properly charge the caps. The main reason for the interest is at some point I want to build a Metro amp, so I'm trying to gain as much knowledge as I can. I'm excited to hear the amp when it returns. The amp had ITT caps made in the UK in it, I take it that those were probably the original ones. Are there any other cap manufacturers out there besides JJ?

By ITT, are you sure they weren't F & T?

rnau · 11-08-2009, 11:35 PM

I thought it was ITT, but I could be wrong, I don't have the amp here right now.
It seems to be the stock ones that came in an 82 4010 combo.

11-08-2009, 07:50 PM	#1 (permalink)
rnau Member Join Date: Sep 2009 Posts: 55	Filter Cap forming ?? I took my amp in for a cap job today, so I'm curious about this. He has a variac so he will be "forming" the caps. Is this necessary? I've read conflicting things. Some say it needs to be done, and some say that new caps are "formed" at the factory. By the way, he installed JJ caps. What do you guys think? __________________ 1982 JCM800 4010 2008 AS50D

11-08-2009, 11:21 PM	#4 (permalink)
rnau Member Join Date: Sep 2009 Posts: 55	Re: Filter Cap forming ?? Thanks for the great info, he told me it takes about 8 hours to properly charge the caps. The main reason for the interest is at some point I want to build a Metro amp, so I'm trying to gain as much knowledge as I can. I'm excited to hear the amp when it returns. The amp had ITT caps made in the UK in it, I take it that those were probably the original ones. Are there any other cap manufacturers out there besides JJ? __________________ 1982 JCM800 4010 2008 AS50D

11-08-2009, 11:35 PM	#6 (permalink)
rnau Member Join Date: Sep 2009 Posts: 55	Re: Filter Cap forming ?? I thought it was ITT, but I could be wrong, I don't have the amp here right now. It seems to be the stock ones that came in an 82 4010 combo. __________________ 1982 JCM800 4010 2008 AS50D

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