New Electrolytic Capacitor Forming?

[tbryanh]

Should new electrolytic capacitors be formed before using?

[dai h.]

new ones don't need to be formed. Old ones that have been sitting unused--it's a good idea.

[stokes]

I was taught to always form new caps.I have seen a lot of caps with no date code,no idea how long they have sitting on some shelf.It wont hurt and it just insures that the electrolyte is properly formed and the cap will live a full life.

[dai h.]

yeah it won't hurt them but I can't imagine it as being necessary for a new cap and if you read literature on manf. sites they only seem to tell you to form old caps. Take say an electronic device on an assembly line with tens or more alu electros--how much extra time (30mins per cap or maybe group of caps x number of caps with diff. voltage ratings = money) is that going to take to do what seems to be an unnecesary procedure? New ones are ready to be used. If a "new cap" isn't then that would seem to say it's actually not new or something is wrong with it. Life as I understand is matter of how much voltage relative to rating plus heat (less = better) plus what sort of cap it is in the first place (long life, high temp. etc.etc.). Even if you formed two caps the same way the one that has more current going through and is receiving more heat is probably going to wear out more than one that doesn't and is in a cooler area of the amp (so I wonder how much diff. forming would make relative to more conventional life influencing factors). I suppose if you're doing stuff as a hobby though then maybe the time constraint doesn't matter and that makes it perfectly acceptable to engage in non-economical practices, choose really expensive parts, etc, etc. But charging by the hour for repair or on a production line not sure it it would make sense. Also, if you think about it Marshall, Fender, etc. probably didn't when they assembled their (now) vintage amps and it's kind of hard to imagine someone specifically pointing out that some specfic vintage amp had a problem "because the caps weren't formed when they were put in at the factory". One thing I've read though is that subjectively forming can supposely make them sound a bit better but I have no idea if that is true.

[Alex R]

With you on this one, dai... The great divide on this sort of issue is always going to be between those who fit caps in pursuit of their repair/construction business, and those whose time is not so closely related to money. Those who do it for money sometimes tend to be impatient about timeconsuming 'voodoo', partly because it threatens to make their lives more tiresome, and partly because they have plenty of real-world experience, much more than the average hobbyist, and so just know more. So as always you have to look for observer bias, and evaluate competing sources of authority.

It would be very interesting to know the original source of the cap-forming idea. Does anyone have any historical information?

My two-penn'orth is that I have fitted plenty of caps over the years for customers, never took any steps to form any of the new ones, or to re-form older-but-ok caps in amps I was restoring, and I never noticed any problems or had an amp with a new cap I'd fitted failed. Maybe I'm missing some quality issue here, not sure, but, you know, the experience adds up, and I've been out plenty of times to hear amps I've worked on used on stage, and I'm still happy not forming caps.

I had a spell of opening up failed or weakly functioning caps in pursuit of more information in this slightly grey area. Shorts between electrolyte layers are almost always the problem, and are usually very obvious once you unwind them, and even in weak-but-functioning caps I would find evidence of intermittent shorting. Not entirely sure whether forming might defend against this, by far the most common failure mode in electro caps.

I would certainly be patient enough to read a lucid and brief account of what forming achieves inside the cap.

[stokes]

Forming insures the electrolyte is not dried up and that the oxide coating is even.When a cap sits for a long time with no voltage/current applied the electrolyte begins to dry,and the oxide coating begins to get "spotty".How long is too long?I dont know,but as I said I have seen many caps,in fact I have a couple of Spragues I am installing right now with no date code.I have no idea how long they were sitting with no voltage being applied.Where did this all begin?Back in the '70's I saw a tech bulletin from Sprague advising to form caps and to replace them after ten years.My supplier at the time was discarding a bunch of old stock electros,and showed it to me,and even gave me some new ones to keep me from taking the old ones out of the trash,that was convincing enough for me.I know you could argue that caps have improved,but I dont see how,they are still made with the same materials etc.As far as your statement "never took any steps to form any of the new ones, or to re-form older-but-ok caps in amps I was restoring," I have listened to an amp with older caps,then reformed them and noticed an improvement in the bass response,replace them with fresh pre-formed caps and it sounded like a whole different amp.When I do a cap job I order the caps and form them before the customer even gets to me,he doesnt pay anything for that.I always give the guarantee that if the caps are over ten years old,and seem otherwise to be okay, he will see a noticeable improvement in the overall response or the old ones go back in,no charge.I have yet to put any caps back in.I am not looking to argue or convince anybody to do something they dont want to do,if it works for you,then dont form them,but I havent heard an argument that convinces me it is not practical to do it as yet.

[J Martin]

I have always brought up the voltage on new caps slowly with my Variac. Years ago there was an incident when I had just recapped an old Marshall. I was slowly bringing the amp up when I heard a sound like boiling water. I put my ear next to the chassis and determined that the sound was coming from one of the LCR cans and it was getting warm. It had a recent date code and the polarity was correct. I can't help thinking that there would have been a bang if it got full voltage right away. So I guess, even new caps can fail.

[Alex R]

Interesting. So how long is long enough, and at what voltage?

[Bruce / Mission Amps]

Interesting. So how long is long enough, and at what voltage?

I do the same thing that J Martin does.
For repairs I just use the variac to slowly bring up the B+ to see if a cap is bad.
With the primary plugged into my variac, only I use a solid state rectifier in the amp with no tubes.
For the custom builds, I do the same thing but starting with a B+ of around 100vdc, I turn up the variac so the B+ rises in increments of about 20v-30v for 5-10 minutes at a time a time until I hit the E-cap's voltage limits for a few more minutes.
Does it make any real sonic difference? I don't know for sure and would not be so tonally arrogant as to say I really hear a difference.
Some might say that's because I'm not good enough to hear a difference but I just doubt it makes much, if any difference, as long as the E-caps are not really, more then a couple-three years old.
But, at least I know a head of time if the cap is crappy, leaky or bad, ...
and I have found bad, brand new E-caps, including many of mis-fabled Sprague Atom caps.
As a matter of fact I don't really use many of the ATOM caps anymore unless a customer requests them.
I am very partial to the new imported F&T caps but recently I've found TAD 500v caps to extremely good too.
Where are they made? I don't know... they look a lot like F&T caps but I suspect they are SINO.

[stokes]

I never said I hear a difference when it comes to new caps being used without or with forming,I dont and have never installed them without forming first.The difference is very noticeable when comparing old and new caps,or if you have an older amp with original caps,re-forming them will tighten things up some,but is better when they are replaced.I like the F&T's a lot,but still do use the Spragues as well,old habits die hard,I've heard some people say the failure rate has increased as of late,but I havent had any problems yet.The F&t's are great replacements for the 220uf/300v used in most Boogies,but for the rest I like the Sprague 30uf/500v's.I havent tried the TAD's you describe,but since you say they look like F&T's and I think TAD is based in Europe,I would guess they are re-labeled F&T's.When forming I use the variac,of course no tubes and SS rect is a must, and turn it up 10-20v's every hour or so,just the way I learned,but I have read where some people just turn the variac slow and steady over a total of a couple of minutes.Guess it is a "gray area",but like I said I have never heard a good argument for not doing it,and have heard too many stories like J Martins,so until someone can come up with a reason not to...

[Chris - CMW amps]

Afaik:

the TAD Audio (e)caps are F&Ts, the gold caps are chinese made ones (used to be F&T too). The audio-caps (20u/550V, etc.) are great for recapping bf/sf Fenders imho.