franklinh

re-capping
« on: August 18, 2004, 11:33:55 AM »
Hello everyone!

Here's a free for all...

I'm thinking about re-capping some older pieces of gear... a pair of Universal Audio 1108 mic pres and a Melcor CL-20 compressor.  Assuming this is the right thing to do for 30+ yr old gear, are there any brands of capacitor out there that y'all would recommend?  

Also, there are some yellow colored cylindrical shape caps in the 100's of volts range... are these a special type?

Appreciatively,

franklinh


SSLtech

re-capping
« Reply #1 on: August 18, 2004, 12:40:50 PM »
You don't need to replace capacitors just because they're capacitors...

Electrolytics do indeed tend to dry out, depending on many factors, but people don't tend to replace non-electrolytics due to age...

Make sure that you understand the difference before you start ripping out other caps.... :shock:

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

rafafredd

re-capping
« Reply #2 on: August 18, 2004, 12:45:26 PM »
I also have a question about old electros...

If I measure the capacitance and it´s ok, even thought it´s very old, should I just use it?

In my mind, when there is a problem with the caps, their capacitance tends to go down, no?

Or should I just trash those old electros even thought they reads nice capacitance? Will they just "puf" anytime?

I´m asking all those questions because I´ve got a capacitance meter recently and almost all of my old caps even from very old modules measures nice...

Svart

re-capping
« Reply #3 on: August 18, 2004, 01:06:49 PM »
doesn't ESR go up with age?
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

soundguy

re-capping
« Reply #4 on: August 18, 2004, 01:07:37 PM »
whenever this subject coomes up nobody every brings any perspective to the table.  There is a big difference between recapping an outboard mic pre vs. recapping an entire console...  The bad caps in a console will always add up to a much bigger problem than a cap in a single piece of outboard gear that isnt maybe passing as much bass as it should.  I learned the hard way that if the gear sounds good, dont f**k with it, and you can get away with this in a piece of outboard for a long time.  I found that while single channels on my console sounded good, the sum of the whole DEFINITELY benefitted when I finally decided to recap the whole thing.  Had I just had one or two of the eq's in a rack, I never would have and it completely wouldnt have bothered me....  These comments of course do not apply to caps that are obviously bad...

I put bc caps in my 1108's and like them alot.  you can really go off the deepend with caps though, I tried lots of stuff in my 1108's and they all sounded very different.  If you really want to try to change things up you can spend some time playing with different brands for a different sound.  

dave

chips are good with dip...

Rhodes Capacitors
« Reply #5 on: August 18, 2004, 01:11:31 PM »
I purchased a Rhodes 73 suitcase some time ago, which didn?t work, and the problem was a couple of bad caps (Motorola capacitors). I then started measuring all caps in circuit and most readings are extremely high. The keyboards sounds a little fuzzy especially after it heats up and also becomes quite.

 What are the best caps to replace these white Motorola caps (I believe there ceramic) anyone familiar with Rhodes circuit...


 :guinness:

SSLtech

re-capping
« Reply #6 on: August 18, 2004, 02:57:44 PM »
Quote from: "rafafredd"
I also have a question about old electros...

If I measure the capacitance and it´s ok, even thought it´s very old, should I just use it?


It depends. old electrolytics can get prone to leakage and/or breakdown. If they break down they can be like old tantalums and fail short[/u] circuit... In something like a tube HT supply, this can be fairly disastrous... They will often read perfectly good right up to the point of catastrophic failure... though the sound might also not be affected right up to the point of failure. Old 'Lytics might need to be 're-formed' if the device has not been powered up for a long time, to prevent this typr of failure.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

nacho459

re-capping
« Reply #7 on: August 18, 2004, 05:43:05 PM »
I don't just recap stuff because it's old.

Recapping isn't like changing the oil, shocks, or belts on your car. It?s not something that needs to be done regularly regardless of the make of model of the car. Recapping is more like recharging the freon in your air conditioner. It's probably going to need to be done eventually, but it could be 5 of 20 years down the line.

That said, if something is 30 years old, recapping won't hurt it but may not be necessary.

With most gear I'll only recap it if it's noisy or inconsistent. However with tube gear, if it's 30 years old I'll probably swap out the power caps, and test all the polys, If it's got selenium rectifiers, definitely change them out.
Some caps will last forever, while other wear out fast.

Gold

re-capping
« Reply #8 on: August 18, 2004, 05:55:54 PM »
I borrowed an ESR meter to test aluminum electrolytics. So far it has never met a cap it didn't like. I was having problems with some Neumann PEV EQ's . I used the ESR meter to test all the caps (correctly I think). All tested good. I started swapping the coupling caps out one at a time and lo and behold everything got better. Are ESR meters useless? The one I have is by Creative Electronics.

soundguy

re-capping
« Reply #9 on: August 18, 2004, 06:16:09 PM »
paul-

I have the same experience with ESR meters.  Makes me think twice about the techs that swear by them...  I had DC blocking caps that were well within the range of the meter, all tested good, yet audibly were not blocking the DC they were put there to block.  Changed them out and the popping on the switch went away, as I suspected it would.  The old caps tested identical on an esr meter to the new caps...

dave

chips are good with dip...


Scodiddly

re-capping
« Reply #10 on: August 18, 2004, 07:21:32 PM »
I've had mixed results with my ESR meter.  I've definitely found situations where I ended up replacing tested-good caps and fixing the problem, but I've also had good luck finding the few bad caps in something with the meter too.

There are some other things to look out for, like resistors that have drifted in value.

CJ

re-capping
« Reply #11 on: August 18, 2004, 07:23:12 PM »
If it sounds good, leave it alone as Soundguy says. Sometimes an old cap can have a sound that you will lose when you swap it out. Even in the pwr supply. The "vintage" factor can figure in also. I have a 1964 DeLuxe Reverb that I should probably recap, but the pwr lytics check out fine for leakage and capacity, and recapping woul lessen the "funk factor" as far as resale. If you do not have to worry about the "vintage factor", replace the lytics, starting with the pwr supply, and listen after each replacement. Don't change a million things at once, otherwise, you will not know how to get your sound back. There is nothing worse than making a change for the worst and not being able to get it back. Happened to me on a 64 Fender Mustang. I thought it would sound better if I took out the tone control and cap. Never sounded the same, and I forgot to write down the original way it was wired, which might have been a mod. Tommypiper brought over a pair of V76's one day. One recapped, and one original. I thought the original had a slightly better sound, less brittle on the highend. But their might have been other mods.
New lytics might take awhile to break in. You can speed up this process by putting them on a pwr supply and bringing up the voltage little by little for a few days. You can check to see if new lytics will change anything by hooking them up in  parallel with the old ones via alligator clips. Be carefrul. Discharge the cpas after every try.
cj
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Jonathan Hayward

re-capping
« Reply #12 on: August 19, 2004, 04:13:45 PM »
CJ, how do you measure leakage?
Also, is there anything else that changes with age other than capacitance? is that the reason ESR increases (as someone said)- that capacitance decreases?

Keef, apart from shorting (and catching fire apparently), do similar things happen to old tants (being a form of lytic) making them candidates for routine replacement?

I know, a lot of questions.

CJ

re-capping
« Reply #13 on: August 19, 2004, 05:29:14 PM »
the sencore has a leakage check on it.
or you could use a 100k resistor in series with a cap and check the voltage drop while applying voltage.
also, if your pwr tranny is getting overly hot, that could be a sign of current going thru the caps instead of the tubes.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Scodiddly

re-capping
« Reply #14 on: August 19, 2004, 05:50:39 PM »
ESR shouldn't affect capacitance... or put another way, you can have buttloads of ESR (and mysterious intermittent zapping noises) and not lose any capacitance.

One fun trick I figured out after recapping my brother's old Ampeg B15:  How long does it take for the amp to stop producing sound after you shut it off?  For his amp, it seemed to go on forever.  Maybe a 30-60 seconds?  For a tube amp that's forever.  After recapping it ran down in a few seconds, like most tube amps.  I figured out later that the ESR was high enough to drastically slow down the drainage when the power was off.

Jonathan Hayward

re-capping
« Reply #15 on: August 19, 2004, 06:39:25 PM »
CJ, just to check what you meant...
You connect the pos of the cap under test to a supply, the neg to a 100k, the other end of the resistor to supply ground, and see if there is any voltage at the neg of the capacitor?
Sorry if I'm being obtuse, it's late....

Scodiddly, I meant; given that - all other things being equal - a larger capacitor (in capacitance) has a lower ESR than a smaller one (this scraped from my memory), if an old capacitor seemed to be 'losing' capacitance would that mean that its ESR was changing as a function of that. You're saying that the relationship is more complex than that?
Again, sorry if I'm being obtuse, it's late....

Scodiddly

re-capping
« Reply #16 on: August 19, 2004, 07:15:45 PM »
ESR is really the result of materials, design, and age, and any relation to capacitance seems to be accidental.  At least that's been my experience, although for healthy caps there's a slight difference.

But yeah, I've measured very olde (1950's) filter caps and found full specified capacitance... but the ESR meter showed very high resistance (the scale on my meter ends around 30-40 ohms).

Whether or not to replace a high ESR cap that seems otherwise healthy, in an amp that seems OK, is a judgement call.  My brother's B15, at least according to him, "came back to life" after a recap, although I didn't hear much of a difference.  But I've never been a huge fan of B15s anyway.  I do a lot more guitar amps, there's definitely a difference most of the time.  For me it's when an amp starts getting fun to play through, as I do a guitar check after each major operation.

Steve Jones

re-capping
« Reply #17 on: August 20, 2004, 06:14:24 AM »
Unless the "collector" value of a piece of gear overrides the sonic value, why not replace 20-30 year old electro's? They were never meant to last that long, there is no "voodoo" to old caps, if you put good high quality new caps in and re-calibrate the unit to factory spec then it will as far as the caps are concerned sound like it was meant to when it was built.

I would like to have someone explain to me the technical reasons for the mystique of leaving decades old dried out electrolytic capacitors in a piece of equipment, other than some fluke that makes it sound better as the caps drift out of spec.
Synthesizer technician
Sydney Australia.

http://synthrepairs.com


 

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