Electrolytic caps useful life?

[Groover]

1) Should one just assume that original caps in a '70s Fender are too old and should be replaced, or do I only need to replace them if the amp exhibits problems?

2) I have read some things about re-forming caps. It's not unusual for some of my Fender amps to go unused for a couple of years or more. Should I go through a cap re-forming process before sing one of them?

[ctcpete]

I am an old tech guy but tube amp newbie (experts please correct me if I am wrong). From all I've read electrolytics of that age are way past due for replacement, especially the filter caps in the dog house (Fenders).

I am also working on a refurb of an old SF Twin and am waiting on my caps from Mouser. The other day I was at a Guitar show and got to talking with an amp tech with lots of experience or so he said. He strongly warned me to not power up the amp after swapping the electrolytics without using a Variac or equivelent device as they would fail early. Is this true?

Thanks again for all the great info on this site.

Pete

[izzybell2810]

Hi,
to re-form a cap you need bring up the voltage and current up slowly. Idealy you should bring it up to spec over a few hours with a variac whilst monitoring the current, voltage, capacitence and power factor of the cap. Realisticly, not everyone has this equipment. You could use a light bulb limiter (a light bulb wired in series with the live conductor of the power cord) to limit the current ect.

Dave.

[Groover]

Do new electrolytics (ie new modern as opposed to new old stock) need to be formed? It seems to me that I have seen some yeses and some nos.

[TD_Madden]

No.

[Enzo]

I have been soldering audio circuits over 50 years, and in that time I have never "formed" a cap. And in that time I also have never had a new cap fail on me for lack of forming. Mallory or whoever doesn't send out millions of caps that can't be used without some sort of preparation ritual.

[stokes]

Originally Posted by Groover

1) Should one just assume that original caps in a '70s Fender are too old and should be replaced, or do I only need to replace them if the amp exhibits problems?

2) I have read some things about re-forming caps. It's not unusual for some of my Fender amps to go unused for a couple of years or more. Should I go through a cap re-forming process before sing one of them?

If your amp sits for years without being used,it is likely the filter caps will dry out and would be adviseable to "re-form" them,or in many cases,just change them.As for forming new caps,the debate has gone on for years,as Enzo points out,he has never formed new ones and hasnt had any problems,I on the other hand have never installed new ones with out forming them,just the way I learned,and have always done it,cant teach an old dog....and I havent heard a good argument for not doing it.I am sure the big amp manufacturers dont do it,but if I made thousands of amps at the rate they do,I am sure I wouldnt have the time to do it either,but I've seen more than a few premature cap failures in fairly young amps to keep me doing it.Does forming them make them last longer?who can say for certain,but I havent had a cap job I've done come back to me yet.

[GibsonLover]

If Leo didn't do it, I don't need to. The only thing I use a variac for is "condition unknown" amps.

[cbarrow7625]

Mallory or whoever doesn't send out millions of caps that can't be used without some sort of preparation ritual.

Ding! Ding! Ding! We have a winner! Logic beats out fuzzy magic, myth and misinformation once again.

[insp166]

No do not replace any thing it will lose all of its value.

Now that I got that out of the way some people think they get an old amp replacing anything loses its value.

Ok if you just want to put it on a shelf for the next 50 years ok

Like an old car if you find one you have to install a new battery, tires, wipers, and convertible top if it has one.

Same for an amp Caps are like the battery they go bad with age. Tubes do not just sitting around. Replace the two wire with three wire with ground

What do you mean it will not sound like it did back in 1954 you were not around how would know, O you listened to the 45 record.

You would be surprised what a new speaker does for an old amp.

Old amps are like old cars if you want to run it you have to rebuild it


MY TUBE AMP SITE

[izzybell2810]

Originally Posted by GibsonLover

If Leo didn't do it, I don't need to. The only thing I use a variac for is "condition unknown" amps.

An old amplifier that's been sitting un-powered for 2 years as I believe this has, is in my opinion "condition unknown"

I never have and never will re form a new cap, but I wouldn't full power a 30/40/50 year old amp that's been sitting idle for a couple of years ect!