About Changing Tubes

This video made me totally change my mind. Enjoy

https://youtu.be/VaO7MmghoqA

It makes a lot of sense really...I think it's a bit like the "better opamp than____" discussions that get bandied about...theres a certain point that the technology in question centers around...a tube and an opamp are generally made to amplify signals NOT alter the frequency of them...they may amplify certain aspects of the frequency better or worse depending upon tube design but as the video shows once a tube is designed it pretty much works or does not work...changing the tube/opamp is NOT changing the design of the circuit (unless you are trying to do that with an ill fitted device for effect) you are possibly only changing the volume of the design based upon the tube itself.

Human hearing is so subjective...my dad used to tell me "You only hear what you want to hear"

Excellent myth busting video.

Cheers

Ian

Be wary of taking advice from people trying to sell you something.

Changing tubes in guitar amps is easily audible.  Try it for yourself and make your own decisions.

john12ax7 said:

Be wary of taking advice from people trying to sell you something.

Changing tubes in guitar amps is easily audible.  Try it for yourself and make your own decisions.

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The video never claimed that changing tubes did not create an audible difference in the amp, he basically claimed it did not make a frequency difference in the amp...his findings showed that basically the frequency response was the same its just that the volume point (or tube break up point) was different...the frequency response appeared to be identical curves just at different volume set points...in real life this would make you hear a difference...and he was not selling anything.

iomegaman said:

and he was not selling anything.

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Granted I didn't watch the whole video.  But in previous ones he's made claims about cheap gear being just as good,  and of course then had affiliate links to buy said cheap gear.  So I don't view it as a credible source of information.

I prefer to get information from professional guitarists,  professional recording engineers,  and professional electrical engineers

Edit : I skipped to the comparisons and heard clear differences,  so don't get the original premise,  other than to generate views.

You can also just look at things logically.  An opamp in its linear region,  employing large amounts of negative feedback will be heavily influenced by the feedback network so will minimize differences.

A guitar amp is much different.  Negative feedback is much lower and non-linearity, often intentionally, is much higher.  On top of that the manufacturing spread of tubes is higher.  Expecting there to not be measurable or audible differences doesn't make a whole lot of sense.

Where exactly was the methodology in error, and why would it show a difference you claim to be there?

?
There was no nulling in the null tests. This means they were all different. Lol.

I think what would have been better to say is, "yes there are differences between different tubes, but they will be very subtle between brands and a little less subtle between types". "Most importantly, the difference is subjective and buying more expensive tubes, doesn't necessarily get you a better sound".

Regardless, I don't see the big crime in buying different tubes for your guitar amp and changing them around. Nobody is loosing they're house over it. And its fun! But so was making the video obviously.

I have boxes of tubes vintage and modern. Sometimes I'll "voice" a friends amp by swapping out different tubes. I don't care what brand they are, modern or vintage. But swapping a 12AX7 with a 12AU7 gets you a totally different tone because the whole gain structure of the amp changes. Maybe in the end with a whole band playing on 11 the change is minor in the over all picture, but that's no reason for not doing it. Perhaps the player gives a better performance being more confident about his tone, regardless of anyone else even caring. 

But dude should really at least match the volumes of the guitar tracks he's trying to null so you actually hear a null, or the least amount difference possible. Which would be mostly distortion...Which is the DIFFERENCE.

P.S.
Most people really don't care. This video makes it seem like all guitarists are being hoodwinked by the evil guys in evil guitar forums... Just like "most people" don't care about this post ;D
P.P.S
1997 called and wants its music back...

bluebird said:

?
There was no nulling in the null tests. This means they were all different. Lol.

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Yup

I'm too lazy to watch the video, but if it keeps somebody from spending their money on expensive "NOS" tubes, then it must be good. I don't know what the situation is today, but there used to be quite a few people selling "NOS" tubes at stupid expensive prices for guitar players. Often they claimed that the tubes sound better and last longer. Usually these "NOS" tubes had darkened pins and the glass near the pins was darkened too. That usually happens to tubes that I have used for years, but maybe that happens when tubes are stored in a warehouse for decades or maybe they came out of the factory that way.

Back when I was involved in the world of guitar amps I remember a few times when a customer had bought some "NOS" 12AX7 tubes from the internets that were pretty much unusable. It always went the same way. Angry customer calls that their amp sounds like crap and then they bring it in and I start trying to figure out what the problem is. Of course they never told that they had changed the tubes. I just change the original tubes in that the amp came with and the amp starts sounding great and the customer is amazed that how can this be. There must be people selling some way too low gain and highly microphonic reject pile 12AX7 tubes that should have been destroyed 70 year ago. 12AX7 should last "forever" unless it's abused pretty heavily.

bluebird said:

But dude should really at least match the volumes of the guitar tracks he's trying to null so you actually hear a null, or the least amount difference possible. Which would be mostly distortion...Which is the DIFFERENCE.

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I commented and basically said the same thing. I asked if he adjusted the gain on the files to try to achieve the most nulling and he gave an answer that didn't address my question.

But there was no huge difference in the sound of each tube to my ears, so as long as you're buying a good quality tube, like a JJ, you're fine. I put JJ's in all of my tube gear.

He definitely could have done a better job with the test, but it was enough to convince me the difference isn't big enough to even be worth discussing.

Same with opamps.

Same with cables.

john12ax7 said:

You can also just look at things logically.  An opamp in its linear region,  employing large amounts of negative feedback will be heavily influenced by the feedback network so will minimize differences.

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Exactly.... you can use negative feedback to linearize tube circuits also. Without NF the accumulated frequency response errors from telephone network repeaters, would make long distance phone calls unintelligible. 

A guitar amp is much different.  Negative feedback is much lower and non-linearity, often intentionally, is much higher.  On top of that the manufacturing spread of tubes is higher.  Expecting there to not be measurable or audible differences doesn't make a whole lot of sense.

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I am old enough to remember unplugging all the tubes and riding on my bicycle down to the drug store to test them with the public tube tester. Weak, bad tubes could be identified and replaced.

This is a major difference between glass and solid state... Solid state devices generally work well until they fail outright. Tubes are like car tires, they start good and slowly degrade.

JR

There was a very audible difference in the null tests (that's where I skipped to).

I don't know much about tubes, especially not in guitar amps, but from my experience testing converters, op amps and grounding schemes you can often get to null these much better than in these examples, and the difference between great and meh is usually very audible. And they built up to something much more audible with whole mixes and processing.

In the Behringer LA2A and Pultec clones better tubes made a massive, easily audible difference.

Myth? I don't think so.

I thought guitar amps and ancient preamps lacking NFB were the most obvious places to hear differences, until I started trying different tubes in a U67.  Wow.  The capsule is directly affected by the NFB path, so there’s a very obvious symbiotic relationship that rearranges with swaps, all minute differences are amplified. 

EmRR said:

I thought guitar amps and ancient preamps lacking NFB were the most obvious places to hear differences, until I started trying different tubes in a U67.  Wow.  The capsule is directly affected by the NFB path, so there’s a very obvious symbiotic relationship that rearranges with swaps, all minute differences are amplified.

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If there is only modest loop gain margin (amount of open loop gain more than closed loop gain) changes in open loop gain, like we see routinely between new and old tubes, can cause easily measurable and audible differences.

This is why op amps can start with more than 100 dB open loop gain.

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Null tests don't like phase shift or simple delays that can compromise null test depth with digital gear and some audio paths.

The classic lesson about null testing occurred decades ago when a skilled amplifier designer bet an audiofool rag editor that he could make a solid state amplifier indistinguishable from the expensive industry icon in blind testing by using null testing to reduce differences in transfer function. As I recall he won the bet.  8)

JR

JohnRoberts said:

The classic lesson about null testing occurred decades ago when a skilled amplifier designer bet an audiofool rag editor that he could make a solid state amplifier indistinguishable from the expensive industry icon in blind testing by using null testing to reduce differences in transfer function. As I recall he won the bet.  8)

JR

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Bob Carver vs. the Marantz 9.

I'm Curious how they conducted that null test.

Ricardus said:

Bob Carver vs. the Marantz 9.

I'm Curious how they conducted that null test.

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I don't recall the details but logically to get a representative read for a power amp null test you need to drive them with music and load them similarly to loudspeaker impedances. Drive amplifier A and amplifier B with inverted polarity signals. Load each amplifier with a 4-8 ohm resistive (?) load (they on't have to be pure resistive but must be identical). Then connect the two load - leads together, but floating. A null should exist at that common load - node. I suspect the two amplifier grounds can be connected together so amplifier power supply currents have a simple return path.

JR

 

JohnRoberts said:

I don't recall the details but logically to get a representative read for a power amp null test you need to drive them with music and load them similarly to loudspeaker impedances. Drive amplifier A and amplifier B with inverted polarity signals. Load each amplifier with a 4-8 ohm resistive (?) load (they on't have to be pure resistive but must be identical). Then connect the two load - leads together, but floating. A null should exist at that common load - node. I suspect the two amplifier grounds can be connected together so amplifier power supply currents have a simple return path.

JR

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They did it by playing a digitally recorded signal through the amp before and after the change of tubes. It is easy to line up the resultant digital recordings, invert one and null them.

To me, all this talk about changing tubes is mostly nonsense, especially the part about expensive NOS tubes being the 'best'. Most tubes' manufacturing tolerances result in about a 10% variation in many parameters. It would therefore be interesting if someone repeated these tests but with two sets of tubes from the same manufacturer. I guitar amps with no negative feedback I bet the nulls would be little better than you get with the same type tubes from different manufacturers.

Cheers

Ian


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JohnRoberts said:

This is a major difference between glass and solid state... Solid state devices generally work well until they fail outright. Tubes are like car tires, they start good and slowly degrade.

JR

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In a solid state device, if it doesn't completely fail usually there is an increase in noise if the device is going south, this is true for transistors, specially if the emmiter base junction gets reverse biased, the thing will still work but it will display increased noise and lower hFE. I've also replaced opamps that work perfectly but had much higher noise than usual.