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 Post subject: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:13 am 
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Hey All,

I been seeing various posts that the yellow caps shouldn't be used in grid and coupling circuits for output tubes. This is concerning since I have amps that use 7591 and 7868. Do I change these caps out?


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:03 am 
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Location: Clearwater, KS
I've used them for years without any issues. I test them on my cap tester and match pairs and quads. Some purists don't like the sound.


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:32 am 
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Location: Long Island NY
What is the issue? That the caps will break down and ruin the tubes, or that the sound quality is not to somebody's liking?

If it is the former, well, any capacitor has the potential to break down and cause damage. It's in the nature of things. If you buy no-name caps from fly-by-night sellers online you are more likely to run into trouble eventually than if you buy name brand caps from reputable dealers. Of course the parts also have to be used within their specs. But it would be foolhardy to condemn all yellow caps as a class of components based on experiences with one of them or a few.

If it is the latter, some people have very imaginative hearing.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:45 am 
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Location: Boston, Massachusetts
maybe they don't like the color. LOL

I understand that most caps made in China are junk.Taiwan seems to have better quality control.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 7:54 am 
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That if the speaker shorts out or becomes disconnected, the field collapses, the cap shorts out, causing a backfeed and destroying both the tube and the audio output transformer.


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 2:52 pm 
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That issue is only for caps connected across the primary of the audio output transformer. (or transformer primary to ground)

Not the coupling or cathode bypass.

I've yet to have any issue with the yellow caps I've bought from various vendors such as Sal, Bob Piekarz, Mark Oppat, Radio Daze or Antique Electronic Supply.

-Steve

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:00 pm 
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Location: Clearwater, KS
Artcurus wrote:
That if the speaker shorts out or becomes disconnected, the field collapses, the cap shorts out, causing a backfeed and destroying both the tube and the audio output transformer.

If the "yellow" cap is a good quality unit from a reputable seller AND has the correct specs for its use, the cap will be the least of your worries. Audiofiles have this huge marketing game. Elitism and snobbery are rampant.


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:09 pm 
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There are people who won't use those yellow caps for coupling, instead they seek out and install vintage Sprague Black Beauties with the stripes, because they claim that the sound is warmer, whatever that means. What I think they are experiencing as far as "warmer" is the smell of output tubes overheating, melting the tar or wax in expensive output and power transformers because those caps are leaky.

I have yet to see any technical proof such as scope waveforms, frequency response curves, distortion figures, that show any difference in how a capacitor would alter the sound. It should be very easy to document with lab equipment. The fact that no one has done so gives you the real answer.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:16 pm 
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Hate to be the one telling you this but Taiwan caps, US caps, Japan caps, Korea caps are all made in China! :lol: Seriously, because there are only a few sources for the raw materials that go into making capacitors, it doesn't matter where they are assembled, there's gonna be some Chinese content somewhere.

As for speakers becoming disconnected or shorted, there's a huge difference. Momentarily shorting the output of a tube amplifier doesn't hurt it. There is no collapse of the magnetic field in the output transformer and little or no voltage spike. But open-circuiting the speaker leads can result in a voltage spike high enough to puncture the primary insulation of the transformer and ruin it. Look at the derivative formula for inductance, vl = L*(di/dt) where vl is the instantaneous voltage across the inductor, L is the inductance, di is the change in current at that instant, and dt is the length of time under consideration. The inductance of the primary depends on the construction of the transformer minus the reflected load from the secondary. If the speaker is suddenly disconnected from the transformer secondary, the primary inductance jumps up and the current drops. With a very small number for dt (cannot be zero because the magnetic field in a real world transformer doesn't change instantaneously) in the denominator, di/dt is going to be very large and that in turn will be multiplied by a bigger L. This also explains why briefly shorting the speaker leads of a tube amplifier is usually not harmful. That would decrease L and increase di so there would be far less of a spike in vl, if any. However, one would not ordinarily want to leave a tube amplifier connected and running with the output shorted as it would be burning the tubes and heating up the transformer for no purpose.

The exact opposite is true of solid state amplifiers, BTW. Short the speaker wires and you will most likely blow the output stage, but open circuits can usually be tolerated without harm.

In any case, the only place a yellow capacitor would make a difference is if it was connected across the primary of the output transformer. Where used, they were called "critical resonance capacitors." Any practical transformer or inductor has a tendency to "ring" or resonate if shock excited and aside from the distortion this creates in the audio, it can lead to high voltage swings that might break down the transformer insulation. The capacitor returns energy at the critical frequency to cancel such resonances and minimize the ringing. Normally a high voltage cap is used in this application.

If a capacitor was used that broke down at too low a voltage, it could damage the output transformer. But it would depend on how the capacitor was connected in the circuit. If it was connected from the plate side of the primary to B- it could burn out the output transformer primary if it shorted. If it is across the primary (plate to B+) it would actually to tend protect the output transformer if it shorted out, though that would depend on the capacitor failing before the transformer was damaged. Obviously if the cap is connected from the plate to ground you need to make sure it has adequate voltage rating and is from a legitimate manufacturer with good quality control, otherwise you are taking a gamble. Quality capacitors are cheaper than output tubes and transformers.

That's not to say a failed capacitor couldn't cause damage in a grid coupling circuit or a bypass circuit. Anybody who has worked on enough tube entertainment equipment has seen melted plates in tubes, charred resistors, and yes open output transformers due to such caps that shorted. But shorting or opening the speaker would not change anything in such cases.

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Last edited by Chris108 on Sep Wed 29, 2021 3:56 pm, edited 2 times in total.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:25 pm 
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A lot of audiophiles tend to base many of their opinions on herd mentality, biases, prejudices, hearsay, and sometimes snake oil technologies. Unless you have a $40,000 speaker system that can bring out the difference in sound quality between a generic Chinese made yellow capacitor and a "Jantzen" brand audio coupling capacitor, I think you'll be safe with the yellow caps. Me, I've done my McIntosh MC-60s and Graysen Stadler 162ks (McIntosh MC-40s) with 630v Sprague orange drop capacitors and they sound just fine.

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Last edited by Indiana Radios on Sep Wed 29, 2021 3:37 pm, edited 2 times in total.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 3:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6386
Location: Minneapolis, MN USA
Artcurus wrote:
Hey All,

I been seeing various posts that the yellow caps shouldn't be used in grid and coupling circuits for output tubes. This is concerning since I have amps that use 7591 and 7868. Do I change these caps out?


Please show us some of these posts.


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:00 pm 
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The only issue I've ever heard of with the yellow caps is that they just sound yellow. :mrgreen:

Seriously use the orange ones. They sound orange. The black ones are neutral. The mustard colored "tone caps" you've heard so much about are to be eaten in a bun, with ketchup.

Ok, all joking aside, the only "yellow" caps in recent history that I've heard discussed negatively, are batches that may have been mismarked at the factory and somehow found their way into the supply chain. go figure. If you're using one with enough of a working voltage safety margin, they will not only outlast all of us, but perhaps the next generation will be keeping them without replacing them 50 years from now.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:16 pm 
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Joined: Feb Wed 04, 2015 12:26 am
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Dale Saukerson wrote:
Artcurus wrote:
Hey All,

I been seeing various posts that the yellow caps shouldn't be used in grid and coupling circuits for output tubes. This is concerning since I have amps that use 7591 and 7868. Do I change these caps out?


Please show us some of these posts.


Thanks all Chris answered my question. This isn't about audiophile caps, this question about making sure that what I was using couldn't inadvertently damage an irreplaceable transformer or a very expensive output tube. Especially 7868. Those have enough problems as it is. And yes, a good portion of the audiophile stuff is hogwash ;-)


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:24 pm 
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Joined: Feb Wed 04, 2015 12:26 am
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Barry H Bennett wrote:
The only issue I've ever heard of with the yellow caps is that they just sound yellow. :mrgreen:

Seriously use the orange ones. They sound orange. The black ones are neutral. The mustard colored "tone caps" you've heard so much about are to be eaten in a bun, with ketchup.

Ok, all joking aside, the only "yellow" caps in recent history that I've heard discussed negatively, are batches that may have been mismarked at the factory and somehow found their way into the supply chain. go figure. If you're using one with enough of a working voltage safety margin, they will not only outlast all of us, but perhaps the next generation will be keeping them without replacing them 50 years from now.


thumbs up


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 4:37 pm 
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Artcurus wrote:
Barry H Bennett wrote:
The only issue I've ever heard of with the yellow caps is that they just sound yellow. :mrgreen:

Seriously use the orange ones. They sound orange. The black ones are neutral. The mustard colored "tone caps" you've heard so much about are to be eaten in a bun, with ketchup.

Ok, all joking aside, the only "yellow" caps in recent history that I've heard discussed negatively, are batches that may have been mismarked at the factory and somehow found their way into the supply chain. go figure. If you're using one with enough of a working voltage safety margin, they will not only outlast all of us, but perhaps the next generation will be keeping them without replacing them 50 years from now.


thumbs up
Double thumbs up. So much of that Phoolery stuff is rubbish… actually just about all of it.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 7:26 pm 
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Here is some interesting reading...Jung and Marsh, "Picking Capacitors"


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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 8:17 pm 
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Extremely interesting!! Also, not light reading lol. More than you ever wanted to know, or thought you would have to know, about capacitors.

Walter Jung also wrote the Op Amp Cookbook, one of my pals during my early electronics years.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 8:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Boston, Massachusetts
Barry H Bennett wrote:
The only issue I've ever heard of with the yellow caps is that they just sound yellow. :mrgreen:

Seriously use the orange ones. They sound orange. The black ones are neutral. The mustard colored "tone caps" you've heard so much about are to be eaten in a bun, with ketchup.

Ok, all joking aside, the only "yellow" caps in recent history that I've heard discussed negatively, are batches that may have been mismarked at the factory and somehow found their way into the supply chain. go figure. If you're using one with enough of a working voltage safety margin, they will not only outlast all of us, but perhaps the next generation will be keeping them without replacing them 50 years from now.


Guess they won't be listening to this song: https://www.youtube.com/watch?v=jQG0gWyTup8

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 10:42 pm 
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The Jung/Marsh paper is what opened up the whole "sonic qualities of capacitors" craze. The thing a lot of people did not realize is that in that paper, they operated the capacitors under conditions of voltage and current that almost never occur in real world audio equipment. This was done deliberately to exaggerate the nonlinearities that were being discussed so people could see them with ordinary test equipment. At normal signal levels those nonlinearities are so subtle they cannot be measured outside a lab with custom, specialized test gear.

Do the nonlinearities in components matter? Well, if you are trying to design an instrumentation amplifier with 0.00001% distortion, you will run into them head first. Even in a modern audio amplifier with 0.001% distortion you may have to put some real effort into your component selection and application if you want to make the spec, since the nonlinearities in the components are additive. But it simply isn't practical in most cases to get the distortion of a tube amplifier much below 2% or 3% without burning up the output transformers, and it is going to be connected to a speaker that will add a minimum of at least another 0.5% distortion. So who cares if you use yellow, orange, green, red, or blue capacitors? Whatever distortion they add will be completely masked by other distortions in the system.

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 Post subject: Re: Question about yellow caps and audio output
PostPosted: Sep Wed 29, 2021 11:52 pm 
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I wonder how the color yellow was selected by most manufacturers?

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