Hello,
I'm wondering if it's a good idea to replace both coupling caps when one goes bad. Recently, the right coupling cap in my 300b amp blew. The amp is probably 5-6 years old, moderate usage. The caps are Jensen copper foil/paper/oil 0.22, 630V. I'm wondering if this is the end of their normal lifespan. Or if it's not a lifespan issue, would there be better sonic balance between the two channels if both caps were the same age?
Thanks.
TR
I'm wondering if it's a good idea to replace both coupling caps when one goes bad. Recently, the right coupling cap in my 300b amp blew. The amp is probably 5-6 years old, moderate usage. The caps are Jensen copper foil/paper/oil 0.22, 630V. I'm wondering if this is the end of their normal lifespan. Or if it's not a lifespan issue, would there be better sonic balance between the two channels if both caps were the same age?
Thanks.
TR
I don't know if those caps are unreliable, or whether they were stressed in his amp,
but you wouldn't want that to happen again. The 300b tubes aren't cheap, either.
I've never had a coupling capacitor short in any equipment that I've worked on.
Coupling capacitor leakage yes, in really old waxed or molded paper Black Cats.
I've seen over a volt across the output tube grid resistor, which really messes with the bias.
The first time I saw that back in the 70s, it really puzzled me until I lifted one end
of the coupling capacitor, when the voltage across the grid resistor went away.
After that, I took those crappy things out of every piece of equipment I saw them in,
mostly Dynas.
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Hi Ray,
I don't either, but my reasoning was the same as yours.
On average, odd capacitors (not industrial) don't have the benefit of what you would find with a more common capacitor. Paper in oil isn't known for reliability, and the copper foil prevents the short from being burned away (self-healing) that you would normally see.
I would try a film capacitor from Kemit, Cornell Dubilier or another quality industrial capacitor. Go for a Polypropylene dielectric and that should at least equal the best capacitor for sound quality, except it will be a lot more reliable.
-Chris
I don't either, but my reasoning was the same as yours.
On average, odd capacitors (not industrial) don't have the benefit of what you would find with a more common capacitor. Paper in oil isn't known for reliability, and the copper foil prevents the short from being burned away (self-healing) that you would normally see.
I would try a film capacitor from Kemit, Cornell Dubilier or another quality industrial capacitor. Go for a Polypropylene dielectric and that should at least equal the best capacitor for sound quality, except it will be a lot more reliable.
-Chris
Exactly right.
The amp is the Cary 300b integrated. The Jensen caps were standard as part of the "SE" edition (or F1, as they called it). I would assume that the Cary engineers knew what they were doing, but what do I know? Do you think that the Jensens are a bad choice in this configuration?
Something I wonder about: I had been using the amp with a pair of relatively inefficient speakers (i.e. 87db) for about six months. I had always wondered whether this was putting undo stress on the amp, even though I always ran it at low volume (9 or below on the dial).
I doubt it was your or your speakers' fault. I'd like to know what Cary knows about that amp's reliability.
Maybe you could call them and mention this event, and ask if it's happened much before.
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Hi trentero,
Most often engineers are told what parts have to be used by the marketing department.
Paper in oil capacitors are an old technology, and industry moved to better capacitors as they were developed. At no point were they used for better sound quality. When I service an old radio, I normally run into wax paper or paper in oil capacitors. They are basically foil separated by paper soaked in oil or wax. They aren't reliable. I will replace them on sight when restoring a radio, hifi or test equipment. They are trouble.
Any of the "plastic" (poly-) capacitors today outperform them while also being more reliable. The capacitors I suggested to you are what I use for very high quality rebuilds or when I'm building a new amplifier for someone. I test capacitors using a Hewlett Packard 4263A LCR meter that measures dissipation as well as capacitance (ESR isn't the important spec). I often test capacitors at both 1 KHz and 10 KHz. This meter was thousands of dollars when I bought it new. So far the dissipation reading has agreed with subjective opinions.
I should explain what dissipation means in the context of capacitor characteristics. Dissipation is the amount of energy lost in the dielectric of the capacitor. In other words, distortion. When you lose energy in a coupling capacitor, you have altered the signal, which is the definition of distortion.
As Ray said, your tubes are too expensive to sacrifice on the altar of audio fashion. These will outperform the types that came with your amplifier as well.
-Chris
Most often engineers are told what parts have to be used by the marketing department.
Paper in oil capacitors are an old technology, and industry moved to better capacitors as they were developed. At no point were they used for better sound quality. When I service an old radio, I normally run into wax paper or paper in oil capacitors. They are basically foil separated by paper soaked in oil or wax. They aren't reliable. I will replace them on sight when restoring a radio, hifi or test equipment. They are trouble.
Any of the "plastic" (poly-) capacitors today outperform them while also being more reliable. The capacitors I suggested to you are what I use for very high quality rebuilds or when I'm building a new amplifier for someone. I test capacitors using a Hewlett Packard 4263A LCR meter that measures dissipation as well as capacitance (ESR isn't the important spec). I often test capacitors at both 1 KHz and 10 KHz. This meter was thousands of dollars when I bought it new. So far the dissipation reading has agreed with subjective opinions.
I should explain what dissipation means in the context of capacitor characteristics. Dissipation is the amount of energy lost in the dielectric of the capacitor. In other words, distortion. When you lose energy in a coupling capacitor, you have altered the signal, which is the definition of distortion.
As Ray said, your tubes are too expensive to sacrifice on the altar of audio fashion. These will outperform the types that came with your amplifier as well.
-Chris
Then Cary should be willing to repair the amps for free, including shipping, whether in or out of warranty.
In a tube phono preamp I built about 100 pieces of, back in the 70s, I used a certain Dale metal film resistor
on the input tube's plate. After a few months of use, those resistors all developed a moderate level
of random noise. I recalled all of the preamps sold, and replaced the bad (or soon to be bad) parts for free.
Dale said it was probably due to someone at the factory touching the bare resistor elements with their hands.
They seemed to already know about it, and weren't surprised, and made no excuses.
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ha-ha. The Jensen caps are not the first issue I've had with this amp (though they may have been related). I've figured out that Cary's service department is a key piece of their business model. As frustrating as it is, here we are.
OK, so if anyone is familiar with this particular amp, can you recommend a better choice? Cary also recommends the Mundorf Supreme Evo, silver-gold at 22 and 2% at 1000VDC, but . . .
Hi trentero,
I made specific suggestions for you. Alternatively, you can buy whatever your heart desires in audiophile approved parts.
I started doing professional (paid for) audio service in the 70's and am extremely familiar with this topic. The parts I would recommend are available from all the usual vendors. They aren't always inexpensive, but at least you're getting what you paid for.
News flash for you. The foil material isn't important. Silver, Gold, Copper or Aluminium doesn't matter. It needs to be conductive. What is important is the dielectric and how consistent the wind tension is. That rules out hand wound parts. Same for transformers, coils and phono cartridges. You also don't need a 1 KV voltage rating. 630 VDC is more than sufficient and is a popular rating.
So what is it you worried about?
-Chris
I made specific suggestions for you. Alternatively, you can buy whatever your heart desires in audiophile approved parts.
I started doing professional (paid for) audio service in the 70's and am extremely familiar with this topic. The parts I would recommend are available from all the usual vendors. They aren't always inexpensive, but at least you're getting what you paid for.
News flash for you. The foil material isn't important. Silver, Gold, Copper or Aluminium doesn't matter. It needs to be conductive. What is important is the dielectric and how consistent the wind tension is. That rules out hand wound parts. Same for transformers, coils and phono cartridges. You also don't need a 1 KV voltage rating. 630 VDC is more than sufficient and is a popular rating.
So what is it you worried about?
-Chris
Hi Anatech,
No worries at all. You obviously know what you are talking about.
You mentioned Kemit and Cornell, but can you point me to the exact piece? I've done a google search, but those brands only come up on Mouser, and I don't see 360VDC.
Hi trentero,
Okay, instead of the odd voltage rating, try looking for 400 VDC and 630 VDC. Those are industry standard voltage ratings. Look for your capacitance and I'm pretty sure that almost all the disty's will carry them. So that means Digikey ($8 shipping to Canada), Mouser and Newark. There are other national distributors out there as well.
So, 0.22uF, 630VDC
Digikey: Film Capacitors | Capacitors | DigiKey
Mouser : Polypropylene (PP) 0.22 uF 630 VDC 5 % Bulk Film Capacitors | Mouser Canada
Newark : http://www.newark.com/w/c/passive-components/capacitors/film-capacitors?capacitance=0.22uf&voltage-rating=630v&capacitor-dielectric-type=pp-polypropylene-
You can choose axial leaded (each end) or radial leaded (one side for both leads). If you go radial, check the lead spacing and if axial, look at the maximum dimensions. These capacitors will typically be smaller than the originals (perfect!).
Those links are just my quick searches to the point where you can specify more characteristics.
-Chris
Okay, instead of the odd voltage rating, try looking for 400 VDC and 630 VDC. Those are industry standard voltage ratings. Look for your capacitance and I'm pretty sure that almost all the disty's will carry them. So that means Digikey ($8 shipping to Canada), Mouser and Newark. There are other national distributors out there as well.
So, 0.22uF, 630VDC
Digikey: Film Capacitors | Capacitors | DigiKey
Mouser : Polypropylene (PP) 0.22 uF 630 VDC 5 % Bulk Film Capacitors | Mouser Canada
Newark : http://www.newark.com/w/c/passive-components/capacitors/film-capacitors?capacitance=0.22uf&voltage-rating=630v&capacitor-dielectric-type=pp-polypropylene-
You can choose axial leaded (each end) or radial leaded (one side for both leads). If you go radial, check the lead spacing and if axial, look at the maximum dimensions. These capacitors will typically be smaller than the originals (perfect!).
Those links are just my quick searches to the point where you can specify more characteristics.
-Chris
What was the failure mode? Am curious.
There are probably a million and one different replacement parts available.
I have a pile of the .22uf Wima MKP10, sound pretty good for the very modest price.
Parts connexion has some close out deals on the audiophile ones, got some of the ClarityCap MR recently.
There are probably a million and one different replacement parts available.
I have a pile of the .22uf Wima MKP10, sound pretty good for the very modest price.
Parts connexion has some close out deals on the audiophile ones, got some of the ClarityCap MR recently.
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