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Unread 03-28-2010, 03:17 PM   #1 (permalink)
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When to Change Filter Caps ???

I have read so much about changeing the filter caps on amps since I have become a member here that it prompts the following question.

When looking to buy an older head, or otherwise. How will I know that the filter caps need changed ?

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Unread 03-28-2010, 03:30 PM   #2 (permalink)
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Re: When to Change Filter Caps ???

Good Question. I'd like to know too.
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Unread 04-04-2010, 09:32 PM   #3 (permalink)
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Re: When to Change Filter Caps ???

bump
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Unread 04-04-2010, 09:44 PM   #4 (permalink)
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Re: When to Change Filter Caps ???

If I buy an amp and the caps are over 20 years old, AND I plan to play the amp - I replace all of the electrolytics. This includes the power supply filter caps, the bias supply filter caps, and the cathode bypass caps. Although there are lots of caps out there made in the 60's and 70's that are working fine, the failure rate is very high. 20-25 years is pretty much where the failure curve goes significantly North...

If an amp has sat in a closet or basement for many years and has not been powered on, the insulator in the caps can dry out and fail. On the other hand, if an amp has been played regularly, the caps will last longer as the warm-up/cool-down cycles actually keep them in good working condition.

This seems counter-intuitive but is true.

A lot of folks just wait and replace them when they go bad. I personally don't want to wait for them to go bad because that will surely happen at the most inopportune moment. And there's nothing worse that seeing smoke pouring out of your amp while it makes a fizzling sound and goes quiet in the middle of a gig.

If we're talking about a "Collector" amp, I would try not to replace them unless they are visibly swollen or leaking. I will power it up slowly on a Variac (over a period of 3-4 hours) and watch them closely to make sure that they are OK.
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Unread 04-05-2010, 01:00 AM   #5 (permalink)
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Re: When to Change Filter Caps ???

10 years is the average life expectancy of filter caps.
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Unread 04-05-2010, 01:04 AM   #6 (permalink)
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Re: When to Change Filter Caps ???

thx Jon!

Btw, loved the DC 1st part
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Unread 04-05-2010, 03:02 AM   #7 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by Wilder Amplification View Post
10 years is the average life expectancy of filter caps.

Yup, I'd agree, and preventitive maintenance is good guys.
If your amp is coming up to it's 10nth, and you don't fancy weird shit happening during gig, then go ahead and have them replaced, even if the amp is working fine. You don't wait for your tyres to go thread-bare and skid into a ditch do you?

However, I'd just advice people that if your amp gets a bit noisier than normal, is loosing a bit of punch, making stange noises as a note fades out etc. then don't rule out the filter capacitors simply because the amp is "less than 10 years old".
Don't forget that if it looks like a duck, quacks like a duck and waddles like a duck, then it is probably is a duck!!
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Unread 04-05-2010, 04:09 AM   #8 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by PaoloJM View Post
Yup, I'd agree, and preventitive maintenance is good guys.
If your amp is coming up to it's 10nth, and you don't fancy weird shit happening during gig, then go ahead and have them replaced, even if the amp is working fine. You don't wait for your tyres to go thread-bare and skid into a ditch do you?

However, I'd just advice people that if your amp gets a bit noisier than normal, is loosing a bit of punch, making stange noises as a note fades out etc. then don't rule out the filter capacitors simply because the amp is "less than 10 years old".
Don't forget that if it looks like a duck, quacks like a duck and waddles like a duck, then it is probably is a duck!!
Just to clarify what Paolo is saying regarding the "noisier than normal, loosing punch, making strange noises" statement (only because the way it was worded was way too easy to have it taken literally to the extreme)...this does NOT mean that this is ALWAYS indicative of filter caps. Valves going bad exert those same symptoms. However, if it's a situation where you've got known brand new valves that have been tested in another amp and the amp in question still has the above listed symtoms, then filter caps is another possible cause to consider at that point regardless of their age/actual service life.

Sorry Paolo...just figured I'd "remove the blanket" from the blanket statement.
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Unread 04-05-2010, 04:52 AM   #9 (permalink)
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Re: When to Change Filter Caps ???

Bias filters are electrolytic as well i always have them replaced too.
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Unread 04-05-2010, 08:12 AM   #10 (permalink)
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Re: When to Change Filter Caps ???

Filter cap life expectancy varies. Like a lightbulb, an electrolytic capacitor has a finite number of hours in it. Most of the larger can capacitors will last 10'000 hours.

If you used you amp on a regular basis, you can estimate when your filter caps need changing based on the life expectancy of those caps.

The smaller caps, Like in a DSL, will last 5000 to 7000 hours, depending on the model and how it was sized.

For most people, the electrolytic capacitors will last closer to 15 years, maybe more.

There is a method for testing your capacitors but it involves taking them out. If they're already out, you might as well just replace 'em. You can also have a look at the waveforms on an Oscilloscope to get an idea as to how well they're doing their job.
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Unread 04-05-2010, 08:51 AM   #11 (permalink)
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Re: When to Change Filter Caps ???

And that brings another interesting trait about practical electronics (as opposed to theoretical electronics) to light...

Everyone wants "guidelines" to follow but at the same time doesn't wanna feel "locked in" to anything. Yet with electronics, two things hold true -

* There are no absolutes

* There are LOTS of exceptions

It is for these two reasons alone that I am against the whole "power valve swapping movement" that seems to have become ever so popular these days. Unless you're well versed in theory and valve amps and really know what you're doing, there's no absolute guarantee that it will work in the short or long term, and there are way too many exceptions that come into play with each amp model and circuit. Even for those of use who ARE well versed in this field there's no 100% guarantee that things will work, but the odds do seem to be in favor of the tech types getting things to work a lot more consistently than those who just simply follow the advice of others. The difference is that when things go wrong, actual techs know where to look whereas the non-techs would be lost up shit creek without a paddle.
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Unread 04-05-2010, 08:56 AM   #12 (permalink)
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Re: When to Change Filter Caps ???

Quote:
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I am against the whole "power valve swapping movement" that seems to have become ever so popular these days.
Are you against the "Filter Cap Swapping Movement"? Its the new thing. You ain't cool if you're not doing it.
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Unread 04-05-2010, 09:08 AM   #13 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by jcmjmp View Post
Are you against the "Filter Cap Swapping Movement"? Its the new thing. You ain't cool if you're not doing it.
Only if it involves swapping over to the magnetically formed type that use chrome dipped gold irradiated titanum foil plates with the space age cryogenic radiation treated dielectric. Only then will I ever buy into that.
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Unread 04-05-2010, 09:09 AM   #14 (permalink)
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Re: When to Change Filter Caps ???

Can you still get brand new Daly or LCR caps for guys who want the original look? Or can someone suggest a comparable brand X for a standard 50 50 500?
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Unread 04-05-2010, 09:13 AM   #15 (permalink)
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Re: When to Change Filter Caps ???

Quote:
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Can you still get brand new Daly or LCR caps for guys who want the original look? Or can someone suggest a comparable brand X for a standard 50 50 500?
I'd use F&T. They look very much like the LCR 50x50s but are a little bit shorter.

NOS filter caps are a moot point. Just like batteries, they have a shelf life and as such they're a crapshoot and there's no guarantee that they'll be any good.

Unless you have a way to test/measure them prior to installing them it's never a good idea to use caps that are decades old even if they've been sitting in a box all their life.
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Unread 04-05-2010, 09:25 AM   #16 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by Wilder Amplification View Post
I'd use F&T. They look very much like the LCR 50x50s but are a little bit shorter.

NOS filter caps are a moot point. Just like batteries, they have a shelf life and as such they're a crapshoot and there's no guarantee that they'll be any good.

Unless you have a way to test/measure them prior to installing them it's never a good idea to use caps that are decades old even if they've been sitting in a box all their life.
That makes sense to me. If we're replacing "old" caps, why replace them with "old" caps? Particularly ones that have been sitting unused, as I understand the dielectric goo dries out from non use. Anyway, thanks for the tip. I actually hate this topic because it starts me thinking that I should replace mine based on age alone. The performance isn't an issue but if it has faded over 28 years, you wouldn't know what you've been missing until you popped some new ones in.
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Unread 04-05-2010, 10:14 AM   #17 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by Wilder Amplification View Post
Only if it involves swapping over to the magnetically formed type that use chrome dipped gold irradiated titanum foil plates with the space age cryogenic radiation treated dielectric. Only then will I ever buy into that.

Where can you buy those? I can usually only get standard TAD or F&Ts.

No worries on the blanket clarification. I was just trying get to the people that say "my amp is only 5 years old, it can't be the caps". I've seen it mentioned here once or twice here.

It does kinda seem like vintage collectors, weekend Dumble stock exchange guys, wanna-be internet gurus and people that listen to amps with their eyes and internet forums, have removed a lot of the science from amplifier electronics.
Can you imagine if NASA or Formula 1 worked like that?
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Unread 04-05-2010, 03:57 PM   #18 (permalink)
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Re: When to Change Filter Caps ???

Thank you all for the input and data as it pertains to Caps. From this information I will be better prepared to make sound purchasing decisions. Thanks again.

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Unread 04-20-2010, 09:15 PM   #19 (permalink)
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Re: When to Change Filter Caps ???

How much can one expect to pay to replace caps?
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Unread 04-20-2010, 09:26 PM   #20 (permalink)
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Re: When to Change Filter Caps ???

I don't know how much a tech would charge to do it, but for just the filter caps themselves, a good estimate (in my experience) is $10/each (really like $8 or $9, but this way you don't have to add shipping).
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Unread 04-30-2010, 01:59 PM   #21 (permalink)
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Re: When to Change Filter Caps ???

Just for fun (and because I didn't know where else to put this), I just recapped my own personal Jubilee 2558 combo (and also fixed the heater wiring and the grid resistor leads on the power tubes), and when I was done, I decided to cut open one of the old filter caps to see how they were constructed. I've been curious about this for a while, and it got the better of me, I guess. So here's the inside of a Ruby "GoldCap" 50uf/50uf @500v cap from 2005. Notice how it is NOT two separate caps, but one massive dielectric with taps on it to create the two 50uf sections. Nothing revolutionary or vital here, but pretty neat to see it nonetheless, no?

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Unread 04-30-2010, 03:35 PM   #22 (permalink)
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Re: When to Change Filter Caps ???

Very cool, I always kind of wondered about what was in these
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Unread 04-30-2010, 04:19 PM   #23 (permalink)
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Re: When to Change Filter Caps ???

Cool! You ever see that new show called "Sliced"? It does exactly that but on a big scale. Say take a sawsall to a pinball machine or slot machine or whatever and take a look at how it works. Reminds me of that!
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Unread 04-30-2010, 05:04 PM   #24 (permalink)
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Re: When to Change Filter Caps ???

I may or may not be guilty of doing this on larger objects myself as well...especially my parents' things when I was a kid! :-) That's how you learn how things work, right? Also...Core...thanks for the heads up! I HAVE to look that show up now!
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Unread 05-02-2010, 12:13 AM   #25 (permalink)
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Re: When to Change Filter Caps ???

Quote:
Originally Posted by PaoloJM View Post
Yup, I'd agree, and preventitive maintenance is good guys.
If your amp is coming up to it's 10nth, and you don't fancy weird shit happening during gig, then go ahead and have them replaced, even if the amp is working fine. You don't wait for your tyres to go thread-bare and skid into a ditch do you?

However, I'd just advice people that if your amp gets a bit noisier than normal, is loosing a bit of punch, making stange noises as a note fades out etc. then don't rule out the filter capacitors simply because the amp is "less than 10 years old".
Don't forget that if it looks like a duck, quacks like a duck and waddles like a duck, then it is probably is a duck!!
I guess I get rid of my caps. My amp is 15 and has the original caps, and I've noticed a bit of noise/buzz recently.
And sometimes it has a lot of punch, but others it's a little weak.
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