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Author Topic: Which Tube Would Come Close To The Sound Of A VF14?  (Read 11424 times)

soapfoot

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Which Tube Would Come Close To The Sound Of A VF14?
« on: March 11, 2011, 09:33:30 pm »

It's well-known that the opinion of the best ears and experts is that there is no substitute for the VF-14M in a U47-style microphone circuit.

However, the fact that those tubes are in extremely limited supply has prompted many builders to use various alternate tubes (certainly with various results).

Since there's such a knowledge pool here, it would be great to see some experts weigh in, subjectively (based on first-hand experience, of course) about the sound and relative timbral qualities of these tubes in that circuit (assuming the necessary external heater voltages and other necessary changes have been made for each tube).

Here's a list of tubes that have been used as substitutes, off the top of my head.  I'm sure it's by no means comprehensive, so feel free to add your own.  Please do comment on any or all to let us know how you feel about their sound/function in this circuit--either compared to the correct VF-14M, or just in general.  If some work poorly with minimal modification but work very well with more extensive re-working of the circuit, that would be good to know.  I'm interested in synergy with the BV8 transformer, M7 or K47 capsule, and headbasket design (in particular).

Here's my (incomplete) list, in no particular order (ignoring the 13CW4 nuvistor, since we've all heard the opinions of that one):

UF14
EF14
EF12(k)
EF12 spez
EF13
EF42
UF42
EF80/800
EF802
EF804/6F40
EF86/806
EF91
EF94
PF86
407A
5840

Thanks in advance.
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klaus

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If we can limit the discussion to the genuine Neumann U47 product whose only variable is the tube (and all necessary circuit/component alterations) then I can tell you from my 30-year personal experience:

1. None of the alternatives you mention will recreate the magic of a VF14 mated to the existing U47 circuit/capsule. And the reason is quite obvious: all the tube you cite are cheaper and more readily available than a VF14. That is the ONLY reason anyone has ever looked at any of these alternatives, not because they would yield superior audio, regardless how you define superior.

2. UF and EF 14, while somewhat related to the VF14 in construction and outline, have an overheating handicap which is only overcome by feeding a second voltage into the mic- a major mod. While these tubes can theoretically be biased in a similar way as the VF14 (fixed) the less noisy option-cathode biasing- will yield a substantial deviation in sound- thinned out, glassy, quite transparent, yet leaning towards body-less.

3. As soon as you exit the steel-tube world and look towards some of the high quality Telefunken designs like EF86/806/804 etc. you get into trouble with the existing transformer configuration: a bad match.

I gave up after these and similar kinds of experiments, and realized that the U47 and VF14-combination is a match made in heaven, and should be left alone. There ARE enough VF14 out there, but an increasing number of U47 seekers feel a five figure price is too steep for their pocket book (understandable), and are lured to substantially cheaper supposed alternatives by posters who claim authority- sometimes individuals with a vested interest (not understandable, in my book).

I do not wish to devalue the role U47 copies, re-interpretations, etc. can play for buyers who simply are not in a position to shell out five figures for a fifty year old microphone- some of these U47-inspired mics are quite nice in their own right- but I caution anybody who is after "that" sound not to fall into the trap discussed by hobbyists and eternal U47 wannabes: there is no substitute for the VF14. Period.
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duskb

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There ARE enough VF14 out there, but an increasing number of U47 seekers feel a five figure price is too steep for their pocket book (understandable), and are lured to substantially cheaper supposed alternatives by posters who claim authority- sometimes individuals with a vested interest (not understandable, in my book).

It's almost pointless to even consider "available" VF14s as a viable replacement at this point because they're either stupid money or were most likely rejected by Neumann at one point anyways.

The whole discussion is moot IMHO. The VF14 is an endangered species and every U47 requires one to make it work. Until someone decides to put the VF14M back on the market owners can either watch their (expensive) microphone sit on the wall or put it back into service with whatever substitute they can muster up.

In the not too distant future even ($x) won't put a VF14 into a U47 so we may as well have the discussion now rather than later. These things won't last forever and the mic's they go in actually might.

Dusk Bennett
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Bubba--Kron

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #3 on: March 17, 2011, 06:57:24 pm »

I have the BeesNeez T1 here which is a fantastic mic with the NOS EF12.   Its very warm and sweet, and seems to have a bit slower attack and slower transient response than a U47.    Its nothing that good compression cant fix, but it does not have that Roger Waters authority to it that only a real U47 seems to have.

Its still a great tool and I am very happy with it, but it makes me realize why the real ones are so expensive.  I still plan to rent a U47 for certain tracks on my own album.  That being said, the T1 is a incredible mic and has its own style and uses that can be taken advantage of!!!!!!

Cheers
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Kai

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2. UF and EF 14, while somewhat related to the VF14 in construction and outline, have an overheating handicap which is only overcome by feeding a second voltage into the mic- a major mod. While these tubes can theoretically be biased in a similar way as the VF14 (fixed) the less noisy option-cathode biasing- will yield a substantial deviation in sound- thinned out, glassy, quite transparent, yet leaning towards body-less.
I've build a mic using the M7 and EF14.
I used fixed bias and underheating proportional (powerwise) to the VF14.
The circuit is exactly the same like in the U47, except for the resistor values in the heating branch, and of course I used a separate heating supply voltage.

Another difference is a fixed cardiod/variable pattern switch similar to the one in the U48, but with variable (external) biasing voltage for the capsule backside.
Switched to cardiod (on the head basket) this is out of circuit.

There is no noise problem with this mic, and none of the above mentioned soundproblems.
I don't have an U47 for comparison, so I can't tell how far they are apart.

I have lot's of other highclass mic's, and this one is at least on par with them.
Sound character is warm and transparent.
It can take quite an amount of treble boost when necessary without becomming grainy or sibilant.
It's very easy to handle in the mix.

Regards
Kai Schluenz
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #5 on: March 18, 2011, 07:52:21 pm »

Good to hear. Would be nice for you to be able to do a side-by-side comparison with a genuine VF14-U47.

I found the VF14- proportional underheating of the EF14 not only problematic in terms of timbre and dynamics, but also in terms of premature caking up of the cathode.
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Mojave

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #6 on: October 27, 2011, 12:45:38 am »

Im not an authority by any means but I am an owner of a Telefunken USA U47 with their VF-14k and it sound excellent. I also see the tube by Wagner called the VF-14W.
Klaus, Can you comment regarding these two varieties of VF-14 vs. VF-14k or VF-14W?
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Victor Mason
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #7 on: October 27, 2011, 04:41:13 am »

Yes,
I can comment that, despite repeated promises by representatives of Telefunken/USA, I have not received a tester of their glass tube-in-a-metal jacket they call "VF14k". I can therefore not make any statements what such a tube would sound like.
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Mojave

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There ARE enough VF14 out there,…..

Would you mind sharing where to look? I can only find one or two. I assumed mainly to look overseas.

Thanks
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Victor Mason
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #9 on: November 06, 2011, 04:54:18 pm »

Victor,
Jus as in your world of vintage Marshall amps, there is a collector's network out there which rarely becomes visible to the uninitiated, but, suffice it to say, the vast majority of remaining VF14s resides with these people (as probably do the vast majority of remaining Plexis!)

EBay.com or eBay.de is a more accessible source. So is Gearslutz classifieds (post a "wanted" ad) also scan all of craigslist via a Google search.
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Mojave

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #10 on: November 07, 2011, 10:45:35 pm »

Of course,
Thanks much
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Victor Mason
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #11 on: November 12, 2011, 07:16:09 pm »

One more thought:
The recent surge in the quest for tubes to sound like a VF14 seems to coincide with the recent surge of copy mics available on the market. Manufacturers of these mics, in order to be profitable, cannot  sell them at the price point of a genuine U47.  Therefore they need to calculate carefully what parts go into these mics, in order to make them financially attractive. With other words, a mic which wholesales for $2k cannot be equipped with a tube that costs $2k, or a capsule (were it available from Neumann at quantity) that costs close to $1k.

As it is generally agreed that three core components in a U47 (capsule, tube, transformer) determine its sonic signature- probably more than all the other components in that mic combined- it seems reasonable that manufacturers of copy mics try to circumvent the cost of these components by suggesting that their alternatives are perfectly acceptable.

Then often comes the time when the owner of such mic seeks to improve its sound (why, must I ask, if the copy mic is that good, would one do that, unless a deficiency is perceived?), but does not wish to do what the manufacturer also did not do: spend the money for the vintage component upgrade. 

That brings us to the Catch 22 where we are today: mic lovers want the sound of the vintage original. They figure that, if they could swap out one or two magic ingredients of their copy mic, it would get them there. But they are often hesitating to spend the money for these parts, then seek the internet for alternatives, of which plenty are advertised, with plenty of promises to that effect, only to end up where they started (minus the money they had spent): still desiring the sound of the vintage original.

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soapfoot

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #12 on: November 12, 2011, 07:49:05 pm »

Klaus,

While I agree with what you're saying, I do feel that there is another category of person who might be interested in answers to this commonly-posed question--

The microphone enthusiast who is interested in building microphones--and is trying to learn about the various tubes available that could be experimented with for their build project in order to subjectively evaluate the sound and character of each (learning in the process) or even so that they may weigh out the pros and cons and do a cost/benefit analysis of the choices--may be most interested of all. 

The elegant simplicity of the U47 head amp probably makes it an appealing platform or jumping-off point for people just exploring tube condenser microphones. For those less interested in attempting an exact copy than they are in taking inspiration from the essential simplicity of this most iconic design, the information about possible tube alternatives would be most welcome indeed.

Best regards,

--brad
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #13 on: November 12, 2011, 10:54:54 pm »

Good point, and certainly a (small) section of the buying public I overlooked in my diatribe.
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Klaus Heyne
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Piedpiper

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #14 on: November 14, 2011, 12:15:52 pm »

That brings us to the Catch 22 where we are today: mic lovers want the sound of the vintage original. They figure that, if they could swap out one or two magic ingredients of their copy mic, it would get them there. But they are often hesitating to spend the money for these parts, then seek the internet for alternatives, of which plenty are advertised, with plenty of promises to that effect, only to end up where they started (minus the money they had spent): still desiring the sound of the vintage original.

There are also many of us that are less attached to the exact idiosyncracies of the original than we are in something similar that is very good, and maybe even from some standpoint "better". I, for instance, have preferred in some ways Andreas Grosser's glass tube alternative to all other options.

Also, I personally, have no resistance to paying for what I want to hear.

Cataloguing the differences of the different options would be useful from a number of standpoints.
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If we can limit the discussion to the genuine Neumann U47 product whose only variable is the tube (and all necessary circuit/component alterations) then I can tell you from my 30-year personal experience:

1. None of the alternatives you mention will recreate the magic of a VF14 mated to the existing U47 circuit/capsule. And the reason is quite obvious: all the tube you cite are cheaper and more readily available than a VF14. That is the ONLY reason anyone has ever looked at any of these alternatives, not because they would yield superior audio, regardless how you define superior.

2. UF and EF 14, while somewhat related to the VF14 in construction and outline, have an overheating handicap which is only overcome by feeding a second voltage into the mic- a major mod. While these tubes can theoretically be biased in a similar way as the VF14 (fixed) the less noisy option-cathode biasing- will yield a substantial deviation in sound- thinned out, glassy, quite transparent, yet leaning towards body-less.

3. As soon as you exit the steel-tube world and look towards some of the high quality Telefunken designs like EF86/806/804 etc. you get into trouble with the existing transformer configuration: a bad match.

I gave up after these and similar kinds of experiments, and realized that the U47 and VF14-combination is a match made in heaven, and should be left alone. There ARE enough VF14 out there, but an increasing number of U47 seekers feel a five figure price is too steep for their pocket book (understandable), and are lured to substantially cheaper supposed alternatives by posters who claim authority- sometimes individuals with a vested interest (not understandable, in my book).

I do not wish to devalue the role U47 copies, re-interpretations, etc. can play for buyers who simply are not in a position to shell out five figures for a fifty year old microphone- some of these U47-inspired mics are quite nice in their own right- but I caution anybody who is after "that" sound not to fall into the trap discussed by hobbyists and eternal U47 wannabes: there is no substitute for the VF14. Period.

Dear Klaus,

What is the special inside of this tube or its Q bias point inside the U47 for be imposible to mimic with another tube ?......Could be its plates, Filament high voltage, the metal case......What kind of tube could be at least a little similar to its tone (at least!!) ??

Opacheco.
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #16 on: April 25, 2016, 01:23:41 am »

If anyone could figure out the special sauce that makes a VF14 so tasty, it would already have been copied and marketed.

The sound of a tube, even in the seemingly relatively uncritical application as impedance converter, is an amalgam of voltages, input and output impedances, current consumption, mechanical construction, thermal conditions, cathode doping, filament arrangements and hook-ups, and so on.

If you cannot afford a genuine Telefunken VF14, you will get there halfway (that word should be underlined!) with some of the derivatives: EF14, UF14, EF12 etc. but they all need careful integration into the circuit, often requiring rewiring, with special attention paid to supply voltages and biasing.

I also tested the "VF14ME" solid state version made in England by Grove Hill Audio a few months ago. It is available now on eBay and Amazon (try getting it even cheaper by buying direct). I thought it was not a bad sounding VF14 copy getting you three-quarters of the way towards the sound of a VF14; besides, it's direct plug & play- no voltage adjustments necessary. Though Grove Hill may have given up manufacturing and pursuing this tack further, there may still be a few of them out there to grab.
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J.J. Blair

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #17 on: April 30, 2016, 08:58:18 pm »

The VF14ME is available on reverb.com. 
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Koen

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #18 on: May 01, 2016, 04:46:02 pm »

How strange, the device is only available at Amazon US. Unable to locate  a dealer in Europe. Moreover, the company is based in Washington. Why the 'made in Europe' pitch I ask myself? Could this be a copy of Andreas Grosser's FET-replacement?
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #19 on: May 01, 2016, 07:18:22 pm »

The British company was or is represented by an individual enthusiast located in Seattle. Contact the company directly, as I suggested.
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Koen

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #20 on: May 02, 2016, 06:52:59 am »

Hello again,
that's what I was aiming at: I can find no mention whatsoever on the web about such company in the UK. Does any of you here have a URL or contact of the actual company in Britain?
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #21 on: May 02, 2016, 12:01:05 pm »

Sending you email contact of the owner. Please check your PM.
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #22 on: May 02, 2016, 06:08:08 pm »

Klaus, all things being equal, would you choose the VF14ME over a Nuvistor?  (Regardless of the circuit conversion needed for the Nuvistor.)
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #23 on: May 03, 2016, 01:19:16 am »

That's like asking: "Klaus, all else being equal, would you rather have your left ring finger or your right middle finger cut off?"

Both choices have significant shortcomings. The Nuvistor lacks heft, the ME lacks resolution. If you were to remove the associated RF suppression circuitry from the Nuvistor, I probably would go for that in a pinch.

There!
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #24 on: May 03, 2016, 10:07:07 am »

"If you were to remove the associated RF suppression circuitry from the Nuvistor, I probably would go for that in a pinch."
None of the schematics I have for the U47N shows any 'RF suppression circuitry'. The 6.8 pF capacitor between anode and grid provides negative feedback and prevents oscillation. In conjunction with the 60 MΩ grid resistor the corner frequency of around 390 Hz makes this feedback effective rather broadband and results in a gentle equalization for low frequencies. Since the considerably different internal construction of the VF14M and circuit layout results in considerably larger inter-electrode capacitances this external feedback was not necessary, and some U47 and U48 versions with the VF14 feature a functionally equivalent 'gimmick' capacitor of a short pair of twisted wires or twin lead between grid and anode terminals. The length of which (= capacitance) was then custom trimmed to achieve the desired frequency response and gain for the specific tube/circuit/transformer combination. Many other similar tube microphone circuits, for example the M49,  specify the capacitance as 'SELECTED'.
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #25 on: May 03, 2016, 01:33:49 pm »

Never seen the "twin wires" in any of the U47 I have worked on, but interesting concept, nevertheless.
I regard the global feedback capacitor like any other such device in this position of a mic circuit as detrimental to good sound, whatever other positive functions it theoretically may have.

By the way, I was not referring to the feedback capacitor, but the choke coil on the Neumann-made plug & play "Nuvistor Kit" in my comment about RF suppression.

Best,
KH
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #26 on: May 04, 2016, 02:50:44 pm »

With a value of 100 µH for the choke in in series to the grid terminal of the (long obsolete) Neumann AR47 conversion kit and 60 MΩ for the grid resistor the resulting corner frequency of nearly 38 kHz does place any effects well above human audible perception. In addition to the feedback capacitance between anode and grid this choke adds in the prevention of the circuit to oscillate at high (radio-) frequencies. Suppression of (external) RF-interference at best is an unintended benefit. With the effective Faraday cage construction of U47/48 and its transformer output configuration it is highly unlikely for any RF-interference to be picked up anyway.
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #27 on: December 14, 2016, 04:53:21 am »

Yes,
I can comment that, despite repeated promises by representatives of Telefunken/USA, I have not received a tester of their glass tube-in-a-metal jacket they call "VF14k". I can therefore not make any statements what such a tube would sound like.

Klaus, did Telefunken USA ever send you a tube? What do you make of this graph ? I find it interesting how close it seems to be but the loss of a few DB's in the lower part of the scale no doubt make a difference. And we know it can't be as quite as a VF14, the good ones I've heard are non existent.

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #28 on: December 14, 2016, 12:30:38 pm »

Telefunken North America has not sent me a tube for testing, but I have had access to several of them through clients through the years. So far, every one of them was too noisy to allow for more critical listening tests.

But if you have followed the lengthy discussions on many forums about the construction details of this VF14 copy, even if you don't have access to the conversations I had with the inventor of the"VF14k", little doubt remains that even under the best of circumstances it cannot approach the unique timbre of a VF14.

Regarding the graph you provided.
If you venture into the scientific world by producing a graph to try to prove something, you should play by the rules scientists have established for the advancement of good scientific knowledge, where careful sourcing and critical evaluation of the information is required: Who made the graph? What were the exact circumstances of its making? Was its creation peer-reviewed?
As long as I don't have that information, the graph is not useful as a basis for any discussion, in my opinion.

 For the rest of us, I am happy to form an opinion in the realm where it really matters-listening
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soapfoot

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #29 on: December 15, 2016, 11:38:26 am »

Something else I notice about the graph--

It seems like the overlay was done in a manner that minimizes as much as possible the low end discrepancy in two ways--

Firstly, the calibration point between the two traces seems almost arbitrary (about 180 cycles?). Notice that the trace for the new tube is about a dB louder than the other at most frequencies. This has the net effect of making the low-end discrepancy psychologically appear to be about a dB not-as-bad. If the two traces were calibrated to be the same at, say, 1k, the deviation in the low end would look even more pronounced.

But more importantly, the scale shown on the graph is a massive 10dB per division-- there's absolutely NO reason to have a resolution that coarse on this graph, except that it makes the two traces "look" more similar and close together. If the resolution were 2dB per division, both traces would still fit on the graph entirely, but the low end discrepancy would be about a division-and-a-half at 50 cycles... which would LOOK much more serious.

Consequently (and also considering the source) that graph appears to me to be marketing material, rather than a study of the relative behaviors of the two tubes. Its objective is NOT to give you an honest idea of the relative behaviors of the two tubes.

Remember also that the principal measurable difference in performance between a VF14 and a 13CW4 Nuvistor is also in the bottom couple of octaves, just like we see here... and that the low end is where much of the U47's signature lies.
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #30 on: December 15, 2016, 08:19:00 pm »

Soapfoot, I think the 10 dB/division scale was chosen because this is the frequency response of the entire microphone, including the capsule, to acoustic signals. If the electronics had been measured separately, a finer vertical scale could easily have been chosen and the rather obvious smoothing could also have been much less. But a graph of the complete microphone's response answers the question that some people would inevitably raise (and justifiably in my opinion), which is how the tube behaves in the context in which it would actually be used, i.e. not driven by a test signal from a relatively low-impedance oscillator, but via a capacitive capsule that has high impedance at low frequencies and low impedance at high frequencies.

--best regards
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #31 on: December 15, 2016, 09:35:50 pm »

I agree with the theory as David explained it. The practical value of this particular graph is still not addressed: how exactly were both mics measured (if they were measured at all) to arrive at what can only be termed excellent results for the copy tube, and, more relevant: how well could even the most honest graph reveal sonic differences in the dynamic (i.e. real life) behavior of tubes?
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soapfoot

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #32 on: December 16, 2016, 01:07:46 am »

Thanks David and Klaus, your points are well-taken
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broncoblair

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #33 on: December 19, 2016, 06:42:29 pm »

So should I bid on this VF14? I guess I could sell my plate... ! Or would I be better off with a nuvistor ? http://www.ebay.com/itm/Telefunken-VF14-VF-14-Tube-for-Neumann-U47-Microphone-Vintage-/262756917429?hash=item3d2d8860b5:g:0KQAAOSwojRYTCUs
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #34 on: December 19, 2016, 08:40:01 pm »

The seller makes returns easy by not attaching any conditions. At this price for a non-M- stamped VF14 version, I would still have the tube authenticated and tested for health by a third party.
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broncoblair

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #35 on: December 20, 2016, 05:47:55 am »

The seller makes returns easy by not attaching any conditions. At this price for a non-M- stamped VF14 version, I would still have the tube authenticated and tested for health by a third party.

Who's best to test the tube ?
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Timjag

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #36 on: December 22, 2016, 01:46:34 pm »

I thought you lot might like this - the BBC's research department assessment of the new Neumann U47 - seems that it wasn't quite up to the mark for Aunty Beeb!

http://downloads.bbc.co.uk/rd/pubs/reports/1954-23.pdf

Nevermind I'm sure they changed half the circuitry anyway!

Happy Christmas everyone!


Tim
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #37 on: December 22, 2016, 02:26:44 pm »

One can sum the report up with these three conclusions:

"In the omnidirectional condition the microphone is of no special interest" I agree.

"These tests confirmed the impression gained when using the U 47 that it gives the best tonal quality of any condenser
microphone we have yet tested"
No objections there, either.

"However, it is considerably larger than the Philips, and Telefunken omnidirectional microphones, and therefore not suitable for certain purposes, such as the Royal Festival Hall" They want good sight lines for the audience and orchestra. If that is the main criterium, I understand their downgrading the U47.

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Timjag

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #38 on: December 22, 2016, 09:20:52 pm »

the price of microphone including cables and mains unit is Ł100 that would be Ł1834($2252) - pretty reasonable I think, although the Beeb probably got a discount.
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gtoledo3

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #39 on: January 01, 2017, 10:30:19 pm »

Klaus, am I correct in remembering you having mentioned some U47s that have been running consistently by the original purchasers, without having been turned off for decades now?

(...Or was that someone else?)
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #40 on: January 02, 2017, 12:12:46 am »

That was me. I worked on two U47 (owners unrelated) which had been left on continuously in excess of 10 years (!) with no ill effect to the tubes or the mic, aside of dried up rubber components inside the amp cavity.
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mbrebes

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #41 on: January 03, 2017, 11:22:45 am »

One of the hardest things on electronics, especially tubes, is heat up and cool down.  Ten years of leaving the power on is much less stressful on electronics than ten years of powering them off and on for the same period.
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #42 on: January 03, 2017, 01:51:14 pm »

..but that may be a simpler suggestion for CERTAIN impedance converter tubes to make. The "always on" rule would be certified stupid and destructive for high-current / amplification tubes.

Differing opinions, especially those accompanied by a solid scientific explanation are welcome.
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Kai

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #43 on: January 03, 2017, 05:55:42 pm »

The most reasonable explanation might be that the VF14 in the U47 is largely underpowered, so there is almost no wear on the filament even when always on.
Opposed to that, every power cycle puts mechanical stress to all parts by thermal expansion.
This would not work on an AC701 e.g., which runs on full power.

One has to mention, that the VF14 is one of very few tubes that can be used underpowered without negative effects on the tube life.
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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #44 on: February 03, 2017, 12:16:58 pm »

An interesting graph and recorded comparison between the VF14M and VF14K is at this site:  http://www.foxaudioresearch.ca/VF14.htm. My Tele U47 #375 is original except for replaced power supply caps, but the original VF14M tube has developed low gain and distortion, so is pretty well shot. The price of the only "original NOS" VF14M I can currently find is $2750!! It resides in Mexico and who knows if it had the discreet Neumann "reject" marking or not. I'm guessing not because the vendor hasn't mentioned it. The VF14K looks pretty good on the graphs in the link for $2000 cheaper. Who knows definitively until using it in the studio? Of course I'd rather have an NOS VF14M that Neumann accepted but somehow got lost, and that a guy in Germany found in his GrossePapa's forgotton workshop and he doesn't have any idea how much it's worth. Dreeeeeam, dream, dream, dream..........
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soapfoot

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #45 on: February 03, 2017, 12:39:27 pm »

I'm not sure "looking good on the graphs" is a good way to judge ANYTHING musical.
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klaus

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Re: Which Tube Would Come Close To The Sound Of A VF14?
« Reply #46 on: February 03, 2017, 02:47:52 pm »

I was just about to respond the same, after reading the link. There is ample empirical evidence with the VF14K dual-glass tube by now to allow for a fairly good opinion, even short of hearing it.

Pumplng static sine waves into a mic amp and recording that on a graph just does not tell the story of how a mic or its components sound.
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