Measured VF14 characteristic

[moamps]

Do these operating points really tell us anything about sound, or do they just help us pick a relatively linear operating point for a tube? Also, I noticed that the EF13 amplifies many more volts when the signal swings positive than when it swings negative. From what I understand, this significantly increases THD. The other tubes look much more even in that regard.

The transfer (i.e. output) characteristic of any tube tells you an awful lot about that tube, such as its gain, transconductance, plate resistance, available power etc., as well as its harmonic distortion (THD) for the chosen operating point and output voltage swing. In this case, the operating point of the VF14 is not in the most linear part of its characteristic; rather, it is at the knee of the characteristic, as I said earlier. In this area, even the slightest shift in operating point may change the value of Ri and transconductance to a considerable degree. THD may change significantly, as well.

The EF13 is not less linear in the area shown in the graph compared to the rest of the tubes. I'm afraid you have misread the graph.

Also, can we really trust these tube graphs to be indicative of the tube in the actual circuit? Isn't the grid resistor in the mic a much higher value than is typical for these graphs, and that can throw things off, or have I misunderstood?

Output characteristics do not change considerably with different implementations. So, yes, the graphs are indicative of the tube in the actual circuit.

I am using an EF802 in my U47 right now. It's underheated to about 5.6V, and plate voltage is 50V. I wonder if I should adjust that plate voltage down with another resistor, or if that would also effect output impedance?

Since the total output impedance in this case mostly depends on plate resistance (Ri), which is about 10 times smaller that the value of the plate resistor, small changes in the value of the resistor cannot have a significant effect on the total output impedance. So, you can adjust the plate resistor as you see fit.

Regards,
Milan

 

[moamps]

With EF12 tube you may just correct the mode a little bit. It is not necessary to use different x-former. Different anode resistor, different anode currenr, different operation point. And its very close to VF14 ( closer than EF14, inspite of diff. curves). Especially in highs and middle freq-s. I'm sure.

This is a tricky business. There are a lot of things that can be done with the EF12. However, it is not that great in the low frequency part of the spectrum when used with a suboptimal transformer. I'm afraid a 6:1 ratio transformer (with too low primary inductance) won't get you very far (low?) with the EF12, IMO.

Regards,
Milan

 

[granger.frederic]

to me 60% of the U47 is the capsule, 20% the transformer and 20% the tube.
I've experimented with ef12 too, with that same feeling about  low-end.
I'll test the ef13 soon.
I actually quite satisfied with a U47 (K47) modded with an ef14 at 6V , with self bias (100uf) and suppressor to ground.
Fixed bias sounds fine too but i like how self bias reacts with transients .
It's no more  a U47, but it sound very close to an original .

 

[moamps]

I'll test the ef13 soon.

I'd say go for it. In my opinion, the EF13 is underrated. I get the feeling most people shy away from it just because it is a remote cutoff pentode but, with enough TLC, one can get very good results with it. It's not expensive to try out, either.

Regards,
Milan

 

[o3misha]

I have U47 with VF14 . Believe me: low end is not the main thing. Dynamic in middle freqs is more interesting. And EF12 is much more useful than EF14 in many cases. With self bias you have totally different microphone. You have better transients (more stable bias) but you have absolutely different sustain on long notes and colored Hi-Fi -ish sound. I thing that weakness  of self bias is not stable anode current and inflience of the cathode cap.

 

[granger.frederic]

i've already bought a cheap nos Ef13, and i will experiment asap.
Milan, could you tell us how you set it : heather , bias , V anode , etc ..?

o3misha, did you try to ground the suppressor in a EF14 , the sound changes a lot after, much relaxed ...

regards
Fred

 

[o3misha]

with supressor to grid sound became softer but...sluggish. Anyway , EF14 has too much highs, and recorded files need de-esser very often.

 

[granger.frederic]

Sluggish ...ok, that's why i recommend self bias with suppressor to ground on an EF14.
this produce a good compromise, try it if you have time...No de-esser needed...No HiFi sound...
cathode 2,7kohms decoupled with 100uf  nichicon 6,3v is fine for me.

 

[o3misha]

I rejected Ef14 after 2 years of experiments with all possible biasing ways,-this is not the best tube. Self bias may give you good result , especialy with good cathode cap ( I used 200uF red Black Gate) but it is not U47-sh sound at all. With Ef12 I 've got the best result in first day. But I've got good advices from Andreas Grosser and very good transformer (much better than popular AMI). With EF12 sound is U47-ish, but you have to find right operating point.

 

[granger.frederic]

I agree AMI are perhaps a bit overrated
I prefer a T14 by HAUFE than an AMI for example
My transformer is an original HAUFE BV8
biasing is one thing but did you really put the suppressor to ground? or did you try in the  triode mode?

 

[moamps]

i've already bought a cheap nos Ef13, and i will experiment asap.
Milan, could you tell us how you set it : heather , bias , V anode , etc ..?

Better yet, I can show it to you:
http://moxtone.com/ConMic.html

Mind you, the microphone in the article is based on a 'generic' tube mike schematic, with self-bias. I played with different plate and cathode resistor values to get the best sound (to my ears, that is). I'd recommend you start with the values given in the article and go from there. I'm sorry the article is not available in English but I hope the most important stuff in it is self-explanatory. Anyway, if you should have any questions, just let me know.

Regards,
Milan

 

[o3misha]

I agree AMI are perhaps a bit overrated
I prefer a T14 by HAUFE than an AMI for example
My transformer is an original HAUFE BV8
biasing is one thing but did you really put the suppressor to ground? or did you try in the  triode mode?

Yes, Haufe is the best one. And yes, I tried to solder supressor to ground. A bit better (because of less dynamic in lows, btw).
But I don't like highs of EF14.

 

[granger.frederic]

Thanks a lot Milan !
just one thing, the schematic is ok but the desired V anode is missing.
with your graph i read 30v right ?

 

[moamps]

Thanks a lot Milan !
just one thing, the schematic is ok but the desired V anode is missing.
with your graph i read 30v right ?

The starting anode voltage value was around 40V, if I remember correctly (the project is almost 2 years old now).
I believe I settled at around 35V.

Regards,
Milan

 

[granger.frederic]

Thanks Milan,
please read this before KH delete it :http://repforums.prosoundweb.com/index.php/topic,36453.0.html
it's unbelievable!
especially the last post!
this is crazy, he has closed the thread, we're back in the 60's with the Berliner Wall
please everybody read that

 

[bezen4uk]

That's shame to say quasi-science on the objective data.
Middle Age  :-\

 

[moamps]

Thanks Milan,
please read this before KH delete it :http://repforums.prosoundweb.com/index.php/topic,36453.0.html
it's unbelievable!

That guy apparently has a considerable problem understanding and interpreting technical data. He got everything wrong, from the beginning to the end of that post (and thread). I cannot understand for the life of me where he got the idea that the U47 power supply I designed must not be used with the VF14 when the whole project revolves around the VF14. Even if he doesn't understand tech-speak, there are plenty of pictures in the article showing the VF14 that I used in the project.

The claim that I manufacture power supplies for the market is likewise produced out of thin air because I don't. Then he goes on to attack the entire AES, science, whatever...  Oh boy.

Anyway, if I understand correctly, this Klaus makes a living from selling the VF14 and he apparently does not gladly allow talk of alternatives on his forum. So he makes up some wild claims and shuts down the thread, just because he can. I'm afraid that really is reminiscent of the Berlin Wall mindset. In retrospect, given his track record, I guess nothing better could be expected from him.

Regards,
Milan

 

[granger.frederic]

Yeah Milan !!
You're so right.
I've done a Ctrl+C before he delete it:


Hello everybody,
i know this subject has been discussed many times but did you see this article ?

http://www.moxtone.com/mU47_U47_part3.html

i think that this kind of method is more reliable than purely subjective feelings...
what's your opinion ?
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soapfoot
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Brad Williams

Re: VF14 measurements vs substitutes
« Reply #1 on: February 01, 2014, 08:00:33 am »

I disagree with this position! At least I do when the exact goal is to select a device that creates a "good subjective feeling!" Analogously, I would not let my opinion be swayed by a test designed to "prove" that a given banana tasted better than another variety. To me, the ultimate and most elegant and reliable test would be to simply taste both and choose my favorite. For our interests of choosing which device is best to listen to, I find that the most reliable method of test is to actually listen to it.

Ultimately, such empirical tests give us an indisputable baseline of numbers and figures to argue about, and that's interesting. But as my dad used to say, "figures lie and liars figure."

Applying the scientific method to subjective listening matters quickly turns cumbersome, inelegant, and inconclusive because the number of variables to isolate and measure becomes impracticably large-- In order for such a test to be definitive, we have to be certain that every relevant variable was isolated, tested and accounted for. It's hard to even find consensus on which known variables matter, not to mention any yet-unanticipated or yet-unmeasurable variables worth considering. When thinking of all the possible variables in a device as complex as a vacuum tube, tests like the one to which you linked begin to look very crude indeed, and may not "prove" anything-- particularly when human perception is such a widely variable moving target.

Appealing sound-- like appealing taste and appealing appearance-- is a sensory/sensual experience. When we attempt to reduce it solely to a debate between sets of empirically collected data, something inevitably gets lost in translation. This is why we don't select art, wine, or lovers using the scientific method!
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Jim Williams
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Re: VF14 measurements vs substitutes
« Reply #2 on: February 01, 2014, 11:05:53 am »
"Trust, but verify"  ~ Ronald Reagan
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klaus
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Re: VF14 measurements vs substitutes
« Reply #3 on: February 01, 2014, 01:20:11 pm »
I only glanced at the comparison treatise. (Can someone please make an argument why I should read every damn graph and exposé about microphones and take it seriously, just because it's on the interwebs?)

The testing methodology is faulty, even on a cursory read: It is claimed that in U47-like applications, the EF14 usually is heated with a max of 5VDC. That is not my understanding and my experience. It is usually heated with 6.3VDC. Grossly underheating any tube has its audible artifacts.

If you argue that, as basis of comparison, underheating a specific tube with significant differences in construction to its comparator tube should be the basis of comparison, you've lost me.

Garbage in = Garbage out
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Klaus Heyne
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Re: VF14 measurements vs substitutes
« Reply #4 on: February 01, 2014, 02:13:33 pm »
Klaus, as you said, you only glanced at the article so please allow me to correct you on some points.

For all tubes in the test sample, you have their output characteristics for several heating voltages, as can be seen in the graphs. The heating voltage of 6V is also given for the EF14. The measurements show that the output characteristics of the VF14 for the heating voltage of 35V are the same as the output characteristics of the EF14 when heated with slightly under 5V. What is claimed is that in order to get the same output characteristics as in the normally underheated VF14, the EF14 should be also underheated, with 5V. What is also stated (in 2 places) in the article is that the underheated EF14 is usually prone to microphonics. This is it, no more and no less.

The idea of substituting the VF14 with the EF14 underheated with 5V has been discussed by others on this forum, such as in this thread: http://repforums.prosoundweb.com/index.php?topic=5513.0 . You may be familiar with the implementation proposed by forum member Oliver Archut: http://www.tab-funkenwerk.com/id68.html

To sum things up, the article deals with the measurements of steel tubes and their output characteristics for different heating voltages and how their electrical properties compare with the VF14. It is a strictly technical article. Raw data, if you will. The testing methodology is perfectly fine for the purposes stated in the article.

Milan



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granger.frederic
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Re: VF14 measurements vs substitutes
« Reply #5 on: February 02, 2014, 10:40:50 am »
Thanks Milan,

i tired to read ( from only few "authorized" people ) that this tube, or capsule, or caps ... doesn't sound good...it's too subjective.

we must do some measurements and after we can debate ...
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soapfoot
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Brad Williams

Re: VF14 measurements vs substitutes
« Reply #6 on: February 02, 2014, 11:19:52 am »
or we can all listen, and then debate.

Of course it's 'subjective.'  It's art we're talking about capturing/creating. Microphone choice often straddles that region between 'capture' and 'sound design.'

Why is subjectivity a bad thing?
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granger.frederic
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Re: VF14 measurements vs substitutes
« Reply #7 on: February 02, 2014, 03:07:22 pm »
subjectivity is not a bad or good thing...
we're talking about rare tube substitution in order to have the closest sound of the original.
here, someone has done some measurement with VF14.
he (or we) could do the same with AC701.
I think that measurements/graph with tubes are very reliable.
A tube doesn't have its own sound.
It's the way it reacts with the components around.
If you find two different tubes with the same datasheet/graph, in the same application, the chances that they sound close are good.
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klaus
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Re: VF14 measurements vs substitutes
« Reply #8 on: Yesterday at 12:20:56 am »
Quote from: granger.frederic on February 02, 2014, 03:07:22 pm
A tube doesn't have its own sound.
That statement, to put it politely, is a hypothesis which would need to be backed up to be credible, or it would need at least to come from someone with credibility in the field of microphone development, audio analysis and perception, or deep musical background.

My experience has shown that every tube employed as impedance converter in a condenser microphone has its own sound, even if used in the same application, same microphone, same everything. You substitute one EF86 Phillips with another one in a U67 or Brauner KHE, for example, and you will notice a different timbre, every time.

I used the variance in tube performance/timbre to better match and fine tune KHEs for pre-order clients before they would be sent off.
Try to graph THAT!

I have found it unproductive to argue the same old point of view, that not everything we hear can be expressed in an objective quantification. We are not there yet with analytics (and computing power seems to be concentrated these days more on tasks like buying behavior analytics, rather than esoteric audio queries which make no money for anyone).
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Klaus Heyne
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Re: VF14 measurements vs substitutes
« Reply #9 on: Yesterday at 08:36:02 am »
Dear Klaus,
With respect, off course you have different sound with different tubes even in the same brand and even with the same reference.
only matched pair have the same sound.
their graphs are different and the way it reacts with the component around is different.
Tubes are hand made, so it's nearly impossible to have perfectly matched tubes, in a sample of 10 for example(i've read somewhere that Nagra reject 990 tubes of 1000).And that's why they sound different.
An electron field in a pair of VF14 doesn't have "a sound" but it can be different depending how the inner structure/components are built.it's not something "esoteric", if it doesn't sound the same, you can measure why.(if you know what you have to measure)

We all know your position about rare tube replacement (see my previous post about my M367), but i think we can debate:i've seen last week, on EBay, a VF14 at 1200 euros....with no return possible, no comment...(did you said no money ????)
Obviously, the time has come to find an alternative !
I just prefer experiment/make efforts/do some measurements/debate, than saying it's impossible.(Andreas Grosser, for example, has done that and now sells some alternatives...).Period.
Sorry if it's impossible here , i'll find another forum.
Regards
Fred
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klaus
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Re: VF14 measurements vs substitutes
« Reply #10 on: Yesterday at 01:31:13 pm »
By all means, please find another forum if your main goal is that others agree with you.

You make an absolute statement ("a tube doesn't have its own sound"). I challenge that statement. Then you respond over a whole paragraph that you agree with me ("off course you have different sound with different tubes even in the same brand and even with the same reference") and then... I am getting confused.

I will respond in detail in a day or two to the link you posted. In the meantime, please remember that, through I don't know a single audio professional with access to genuine VF14 who would voluntarily choose a substitute, I warmly invite reports from users of alternatives to expensive, obsolete tubes like Telefunken's VF14.

Users, not posters of unexamined claims or graphs. I am highly skeptical of supposed proof of sound similarities of tubes, as we all know that most who use graphs in audio use them to bend reality towards a specific outcome, rather than find truth by starting out from a position of neutrality, and the few who actually have experience with the subject matter, are not the target audience.

I recommend to you "Proofiness", a book that details the easy entry of "objective" numbers, graphs and statistics into our brain's centers of credulity. 
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Klaus Heyne
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Re: VF14 measurements vs substitutes
« Reply #11 on: Yesterday at 02:00:41 pm »
Dear Klaus,
first, i don't what to convince you or anyone.
i wanted some opinions, i now have yours.
you're skeptical, fine, but i'm not alone in quest of a vf14 substitute : see the multitude of post in various forums including this one, and see the famous mic techs like Grosser/Wagner, see the famous manufacturers like Telefunken/Flea, etc,etc,etc ....
i don't voluntary choose a substitution, it's exactly the opposite.But i/we need one or multiple alternatives, even if it upsets you .
I just don't what to spend a week of studio work with a supposed new old stock rare tube which doesn't work for mic application (like i did before...)
i just don't want to be "le dindon de la farce" anymore.
Please read my posts again, and you'll understand what i mean by "no sound"
(the quotes are important), i tried to be didactic (with examples) but perhaps it was too abstract...
Thanks at all the people who post here
Good luck
Kindest Regards
Fred
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klaus
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Re: VF14 measurements vs substitutes
« Reply #12 on: Yesterday at 10:04:33 pm »
Today I went to the site the OP refers to (http://www.moxtone.com/mU47_U47_part3.html), where it is claimed, in so many words and graphs, that there is no measurable difference between the VF14 tube and "comparable" tubes.

But I wanted to understand the larger context of the article, so I started on page 1, rather than page 3 referenced in the opening post. Here, the author introduces us to a dual-output voltage power supply he manufactures ("Moxtone")*, that can be used for any aftermarket U47 (copy or DIY) mic, as long as it is NOT powered by a VF14, which his supply is not designed to power.

Reading page 1, it became clear to me that the purpose of page 3's conclusion (no difference in performance between a VF14 and EF14), was to condition the reader to his sales pitch with credibility, and sufficiently supported by "scientific" material:

"Hopefully, you will find the data presented in this article a sufficiently valuable contribution to the relatively scarce body of knowledge on the VF14 and a significant help in designing microphones, particularly in understanding and evaluating different options once the VF14 wears out and fails, which it most certainly will."(italics and bold are mine)

This is a common tactic I found during introductions of new products at AES seminars: first, prepare the audience with sufficient techo-babble and test arrays that are hard to impossible to reproduce, then lead them to the inevitable conclusion that only THIS product will solve the problem.

The article should be understood as a sales for the DYI crowd, and, to put it bluntly, has no merits for the readers of this forum, is self-serving, unscientific, with questionable methodology, and only worth reading, in my opinion, as part of a dissertation on (self-) deception.

I keep telling my 12-year old son: if at first you don't understand the purpose of something pitched to you, just follow the money.

Thread closed, and only kept up for the reader as an example of quasi-science in service to peddling product.



* I make no claims as to the product's quality or lack of for its intended application.
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[Moby]

That guy apparently has a considerable problem understanding and interpreting technical data. He got everything wrong, from the beginning to the end of that post (and thread). I cannot understand for the life of me where he got the idea that the U47 power supply I designed must not be used with the VF14 when the whole project revolves around the VF14. Even if he doesn't understand tech-speak, there are plenty of pictures in the article showing the VF14 that I used in the project.

The claim that I manufacture power supplies for the market is likewise produced out of thin air because I don't. Then he goes on to attack the entire AES, science, whatever...  Oh boy.

Anyway, if I understand correctly, this Klaus makes a living from selling the VF14 and he apparently does not gladly allow talk of alternatives on his forum. So he makes up some wild claims and shuts down the thread, just because he can. I'm afraid that really is reminiscent of the Berlin Wall mindset. In retrospect, given his track record, I guess nothing better could be expected from him.

Regards,
Milan

Milan, don't waiste your time and energy on this guy. Just keep on your research! Cheers!

 

[Melodeath00]

That's a disappointing outcome.