Author Topic: How do tubes do that voodoo they do?  (Read 6880 times)

Offline allenzachary

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How do tubes do that voodoo they do?
« on: November 28, 2009, 06:31:33 AM »
Yesterday, with my 14 year-old daughter looking on, I performed a repair on my Audible Illusions Modulus 2D preamp (aka "The Tube Eater" as Carlman likes to call it).  It had developed a wicked 60 cycle hum in the line stage.

The repair was as simple as it could be, a swap-out of the 6922's in the line stage.  Reconnected it and the hum was gone.  My daughter was duly impressed.  She also thought it was cool that the "new" tubes I used to replace the "old' tubes were probably as old as I was (Sylvania 6DJ8...yellow and black box address said "New York, 17" which meant they were at least 40 years old).  

Then the questions came:

How did you know the problem was caused be the tube?

       -I did some simple troubleshooting, such as pulling the input/output cables and tinkering with the switches.  They pointed at the tubes as the problem.  Besides, tubes are usually the cause of the problem. [Easy one.  She has the smartest Dad in the world.]

Then why do use tubes?

      -Because they sound great.  They are also easy to repair.  [Still the smartest Dad.]

What goes wrong with them?

     -Err, um.  Well, they get old....

They get old?

     -Yes.

But you replaced the "old" ones with something as old as you, didn't you? [There aren't many things older than me, you see.]  They worked perfectly and fixed the problem, right?

    -Umm. Yeah.  I guess.... [Her Dad is just as dumb as every other old guy- just weirder.]  They wear out.

What wears out?  [She is holding the old tube and sees there are no moving parts.] Nothing looks worn.  How does it wear out?

    -I guess a little like a light bulb.  

But when a light bulb wears out, you can see a broken filament.  There's nothing I can see that's broken in here....

     -It just does...OK? ["Because I said so"...that's the right parent answer, isn't it?]

Now, she is still a little impressed that I could fix a problem with a strange machine that uses flat black plastic things to make music, just to a lesser degree.  


So here's a topic:  Why do good tubes go bad?  What breaks in over the break in period?  Why do tubes sound the way they do?  

Please answer in plain English...I can read white papers and not understand them all on my own.  

Discuss amongst yourselves.

Thanks



Offline richidoo

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Re: How do tubes do that voodoo they do?
« Reply #1 on: November 28, 2009, 06:47:18 AM »
Electrons fly from cathode to plate in proportion to the input signal applied to grid. When the electrons run out, tube is finito.

Tube can also fail due to mechanical reasons of poor design and construction, in various and sometimes exciting ways.

More detailed explanation: http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

You got a smart kid there Allen, but you already knew that...

Offline Carlman

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Re: How do tubes do that voodoo they do?
« Reply #2 on: November 29, 2009, 04:47:47 PM »
Tubes are a complicated set of man-made objects attempting to control chaos.  Controlled chaos is similar to the creation of music.  How it all comes together takes time to learn.  If she really wants the answer, the info in Rich's link is a great start. 

As to break-in, here's what I think: When a new tube is installed, it starts making microscopic connections and paths for the electrons to flow.. once that process finishes, the tube is 'broken in'. 

-C
I really enjoy listening to music.

Offline tmazz

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Re: How do tubes do that voodoo they do?
« Reply #3 on: November 29, 2009, 11:34:53 PM »
On a real high level the two most common causes of tube breakdown are gas leakage (or the loss of the "vacuum" part of a vacuum tube) and a physical or chemical change in the materials used to make the innards of the tube due to prolonged exposure to the heat, electron flow or magnetism that is part of the normal operation of a tube. Also, these things happen during the operation of a tube, so a properly stored vacuum tube will not age as it sits on the shelf, thus explaining why you can replace a five year old worn out tube with a 40 year old NOS one.

All of these explanations are overly simplistic, but I think they contain enough information to satisfy you daughters curiosity.
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Offline bmr3hc

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Re: How do tubes do that voodoo they do?
« Reply #4 on: November 30, 2009, 05:44:18 AM »
No technical expertise at all with tubes. I am certain they just sound better, to me. Man. wish I was as smart as your 14 yr old daughter, when I was 14. I would certainly be able to understand the workings of tubes, technically, by now.

Henry

"If music be the food of love, play on."  Shakespeare

Bigfish8

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Re: How do tubes do that voodoo they do?
« Reply #5 on: November 30, 2009, 05:12:47 PM »

Offline bmr3hc

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Re: How do tubes do that voodoo they do?
« Reply #6 on: November 30, 2009, 09:08:28 PM »
Found this:  http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm



Thanks Ken. Good reading. I still cannot explain to anyone "why" tubes sound better, to me.

Henry
"If music be the food of love, play on."  Shakespeare

Offline tmazz

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Re: How do tubes do that voodoo they do?
« Reply #7 on: November 30, 2009, 09:43:15 PM »
Actually, why tubes tend to sound better than solid state devices is a fairly easy question to answer. When tubes distort they more heavily distort the even harmonics as opposed to solid state devices which more heavily distort the odd harmonics. To the human ear, odd harmonics are much more annoying than even one (noise of fingernails on a blackboard is very heavily composed of odd harmonics). Secondly, when a solid state divice runs out of gain it sharply shuts off  kind of like the top of a square wave, this is called clipping (additionally when driven to clipping a transistor gives out a kind of high frequency cry of pain - this is why it is easier to blow a speaker by over-driving a small SS amp than by overloading it with too much clean power from a larger one.) On the other hand when a tube approaches the top end of its gain capacity it just gradually decreases its gain until it can't give any more, kind of like looking at the top of a sine wave. So basically tubes tend to sound better because when they distort harmonically they do so in a way that is less offensive or noticeable to our ears and when the misbehave on a amplitude basis they behave in a more "polite" way than SS divices. It's late, so I hope this makes sense.
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Offline BobM

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Re: How do tubes do that voodoo they do?
« Reply #8 on: December 01, 2009, 05:34:47 AM »
I've often wondered about the breakdown of a tube. Most often I have found that my small signal tubes (preamp and phono stage) develop a microphonic characteristic. Usually a low, intermittant whistle that eventually gets louder and more persistent as time goes by. Tube dampers don't have any effect on this and it doesn't manifest immediately, it takes time (1-2 hours) for the tube to warm up and get to a hot enough temperature I guess.

I'd love to know exactly what is whisteling inside there. Anyone know?
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Offline tmazz

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Re: How do tubes do that voodoo they do?
« Reply #9 on: December 01, 2009, 06:57:56 AM »
I have never experienced a whistling in my tubes, that's a new one on me, but if I were to guess I would think is was a sign of gas leakage which usually shows up a noise.
However microphonics in general are caused by a structural weakening of the interior elements of the tube When new (and well designed and constructed) the elements of the tube (plates screens, grids etc.) are rigidly held in place with respect to one another. As the tube ages this structural integrity begins to loosen up and the various elements become more free to move around. Now if we remember that tubes operate by streaming electrons from an anode to a cathode, if the distance between those two elements is not constant, the time it take the electrons to make the trip will change from moment to moment and thus that changing distance will impart its own signature onto the output signal. This is all going on on a microscopic and nanosecond basis, but it ends up making a difference. Remember, the elements are very close together to start with so any movement among then can cause a significant change in distance on a percentage basis. While this may be is a very simplistic explanation (the details get into the realm of quantum physics), it does get across the general idea.
Remember, it's all about the music........

• Nola Boxers
• Sunfire True SW Super Jr (2)
• McIntosh MC 275
• ARC SP-9
• VPI HW-19 Mk IV/SDS/SME IV/Soundsmith Carmen Mk II ES
• Pro-Ject Pre Box S2 DAC/Rasp Pi Roon Endpoint
• DigiBuss/TWL PC&USB/MIT Cables