Measured VF14 characteristic

[granger.frederic]

Dear Ricardo,

the anode voltage is around 35v= normal Va
the ef13 has an automatic variable mu, the command grid is physically built to achieve this...
So you can't avoid a compression effect, even if in triode mode this effect should be limited

My Psu is not genuine but the U47n is original (capsule k47, nuvistor, transformer, caps, resistors) in a Flea body because of the original body degradation.
Don't worry for solder/unsolder, i'm very delicate.

I've made the Ef14 conversion for some reasons (my nuvistore was a little noisy) and when i have some free time, i like to experiment with various studio gear (mics,preamps,monitors,ext....)

i'll report here after an experiment with a bunch of 13CW4 that i've just bought...
Cheers

 

[granger.frederic]

Dear misha

i can tell you that Flea body quality is as good as Neumann, it's quite impressive.
high impedance board and logo were conserved, but acryl or plexiglass have between 10*17 and 10*19 ohms/cm volume/surface resistivity/insulation, thus good enough for mics...
please check the material specs before posting : http://www.builditsolar.com/References/Glazing/physicalpropertiesAcrylic.pdf
http://www.plexiglas.com/export/sites/plexiglas/.content/medias/downloads/sheet-docs/plexiglas-general-information-and-physical-properties.pdf

i don't want to resell it, just want to record with it...

are you working for/with Andreas Grosser?
regards

 

[granger.frederic]

regarding to the high di-electrical insulation of the acrylic, i doubt that your leakage was due to this material, dirt is the most probable issue.
the acrylic takes the isopropyl alcohol very well, which is the standard for microphones cleaning.
However, i see in various forum posts, some high impedance circuits soldered directly on the epoxy board, and i know that the leakage will be inevitable with time, when the moisture will contaminate the board.
i have tested a K47 capsule from Flea skinned by Mr Thiersh and the result was less than good for my taste.
i prefer a Neumann K47 by far, it's a more detailed and neutral capsule.
just my opinion ...

 

[marcus4audio]

Flea uses acryl for high impedance boards. This material is not good enough for high impedance schematic.

Excuse my ignorance, but what material is used in the original Neumann u47? I know that this question is off topic but I'm really curious.

 

[nielsk]

There is a small phenolic turret board by the transformer and a clear plastic piece that has bracket tabs crimped in under the capsule mounting plate (I do not know material formulation) in the original, that is it.  You can see it clearly in the photo of my EF14 version, which, by the way, does NOT sound "heavy-muddy"... and yes, I auditioned many output caps, including the original.
I have access to 12 mint U-47s for comparison, and I preformed the EF12k mod exactly to Andreas's circuit with his help and it was a bit thin and bright sounding in comparison. The EF14 was not, across the spread of how perfect original ones sound it was right in line. No difference in high SPL response, is there any empirical data to support the presumption that the EF14 distorts and "compresses" before the VF14?
All data from the tube manufactures states that EF14 and VF14 are identical  except for the heater arrangement, with the EF14 having a separate heater.
The change to nuvistor was influenced by it being of available manufacture at the time, and all the old guys I know who have made many, many hit records and used all of these mics since inception are not fond of it, but I have no experience with it. I am tempted to try one in a clone and compare.
Has anyone done this?

 

[lampas]

I have access to 12 mint U-47s for comparison, and I preformed the EF12k mod exactly to Andreas's circuit with his help and it was a bit thin and bright sounding in comparison.

Did you use his transformer for EF12k version too, or did you use original BV8 ?

Thanx.

 

[granger.frederic]

Dear Marcus,
In a U47, the boards near the transformer are low impedance circuits .You can use simple epoxy.
The high impedance is point to point on a plexiglas (or equivalent), you can improve it with Teflon pins if you have background noise issue.Don't use varnish like Andreas Grosser,the varnishes have their proper electrical conductivity and often higher than the board.
This section is critical and must be very very clean.Don't tough anything with your fingers, you must use gloves.Same advices with the capsule.Clean everything with isopropyl alcohol,a lot of cotton tips (no toothbrush), and a lot of time....

i've use my U47n with an EF14 during few years with happiness.But i've noticed, in fixed bias, that the sound with loud sources is not distorted but less relaxed than a VF14 or even EF12.The other issue is the noise with the heather, you must use a separate voltage supply and it's quite difficult to achieve a perfectly stiff and noiseless voltage at 5V. With a LM317 and RC after, it's usable but noisier.That's why i use it in self bias, quieter but transients are faster..............EF12 is too thin for me too,it looses the U47ness.........never ending........
i'm curious to experiment again with the nuvistor which was considered by famous techs, like fabulous tubes.
cheers
Fred

 

[micaddict]

Interesting post again, Misha. Thanks.

With self bias you have better "attacks" at the starts of notes - because of stable anode current, but not "natural" behavior at the sustain area of long notes ( you loose "body" of U47), because of floating of operation point when signal amplitude is changing , I think. Also, there is influence of the cathode cap.  Excess cap in signal path affects on sound. Thats why M49 and M49c are different in sound for example. But, of course, self biasing method has it's own benefits: less noise, for example. Better transients are very good for recording of percussion sounds, for speach, for ambience. 

More body in the fixed or filament biased version is exactly what we found when poctop built both M49 versions.
Same for M269(b) versus M269c.
Not sure if the difference is as noticeable in KM54 versus KM54c. 

 

[o3misha]

Yes. I have long dealt with the problem of different behavior of the tubes with self-and fixed bias. Thank you responded, I am pleased that my findings coincided with the opinion of someone else. 8)

 

[scott_humphrey]

I've seen cracks propagate in acrylic when I tried cleaning with alcohol. Don't do it!

Instead, clean with soap and water, then use gloves when assembling.

 

[granger.frederic]

Dear Misha,

what's wrong with you...
i'm not agree with you.that's all.period.
why are you upset, i just share here my humble experience with my beloved microphones...

i have an original stunning neumann vintage brass KK47, sorry.But i would easily change it for an actual k47/K49, without fear...

your explain about self biasing is not accurate, the moot point with the transients, is the way/time the coupling cathode cap is charging/discharging...etc
i'm not saying that self bias sounds like fixed bias.
i say that ef14 with self bias and suppressor to ground is a good compromise.and if you read my previous posts , you'll see that i use it at 6v.
but i'm not completely satisfied with that, that's why i still experiment...without certainties..

acrylic should be good enough,check the electrical properties (if you want...) and isopropyl alcohol can't destroy it just for a cleaning.But again i don't sell acrylic and i don't even use it....
I would avoid soap which contains grease perhaps some TEEPOL if you want, but alcohol is better.

varnish by definition is crackling with time and heat , especially in a u47,remember the dropping resistor...
i don't see why, if the  highZ parts are clean, the leakage would magically disappear with a varnish.

PLEASE DO NOT USE VARNISH IN A U47!!!!I can tell you that because i've done that with cheap mics, and it was a disaster.You could ruin your mic.
i've never seen varnish in a U47, only in cheap mics like rode NT1 because the highZ is directly on epoxy...

i have a lot of good mics like M367, C414EB, M49c, M149, etc, etc and i have 2 ears...like you i suppose...

MY 2 ears are telling me that an EF12 is not good enough in u47.I loose the U47 sound.period.
VF14er is probably a 407a in parallel (not sure), which i don't like also.

Your post reminds me Klaus Heyne in another Forum, if you know what i mean...
Sorry to be in disagreement with you
just my 2cents

kindest regards
Fred

 

[nielsk]

All with original BV8, as you can see in the photo...

 

[ricardo]

I'm not sure exactly what various people mean by acryl but I think it is http://en.wikipedia.org/wiki/Acrylic_glass.

This is EXACTLY the same as Perspex (UK) and Plexiglas (US).  It is an excellent material to make the insulating parts of condensor capsules.  I used it in some experimental Calrec capsules circa 1980.  It is far better than the epoxy in FR4 for HiZ stuff.

I think also o3misha is mistaken about Andreas applying 'several coats of varnish'.  If you have to do this to cure some fault, something is seriously wrong with your HiZ circuit and its unlikely more varnish will help.

Is Andreas on this forum?

 

[granger.frederic]

yes this topic is about V14 and substitutes
if someone have something interesting about that, then we are open....

just few words about the varnish: urethane and others loose their di-electric insulation with time and heat, and in a U47 the dropping resistor R4 is around 100 °C (like my EF14..........).That heat is surely one part of the U47 sound.

I add, that if the surfaces are not perfectly clean (hard to obtain without a clean room) , you have dirt or even moisture forever inside the varnish.
I'm asking me why Neumann (they must have a clean room) have not put any varnish, in any famous Neumann mic that i have ?

I'm not sure...no, i'm sure, that for a DIY project, it is not a very good advice to use it in a microphone, unless you want to kill it.

For those who are sleeping when reading this topic, we're talking about the electrical insulation of the high impedance parts of a mic.
if the parts are not perfectly insulated or dirty, the risk is to have some serious background noises (like ocean waves for ex.) and major modifications of the frequency response.
the parts are : capsule including mount and wires, command grid , high value polarization resistors and capacitors on it, pad and polar pattern switches .

My humble advice is: point to point on teflon, or glass, or plexiglass or ... , and clean everything several times, it will work fine for several years.

One of the VF14 important point, is to have (probably on Neuman's demand) a special ultra  high Z inter-electrode insulation , and that's makes the difference in a mic.Idem with AC701 and some Nuvistors.The mount socket used by Neumann is special HiZ too.
Sadly, the EF14 doesn't have the same socket material, nor the EF13/12.That's a bit why, we sometimes loose a lot of magic, with some tube substitutes.

 

[granger.frederic]

I have an M367 (ortf U67) and a vintage U87i , and i can't see any varnish inside on the highZ part. yours must have been modified.Neumann has put the hight Z elements in a closed grey box under the capsule.

however, you probably have (like me) some varnish on the other parts (lowZ) then it's far less critical here.

Change the socket of the EF14 is too risky imho.
the temperature of an ef14 at 5,8v is not dangerous for the tube nor the mic.i've tested that.
Ask Andreas about his varnish, but i can assure you that i wouldn't let him mod my mics , with some varnish in the highZ...
you said military russian triode for the vf14ef...interesting ...
but i can't find such a tube with a heater greater than 6,3v, maybe someone ?

a great link about nuvistor: http://www.r-type.org/articles/art-150.htm

 

[granger.frederic]

"I think Andreas and mr. Thiersh with theirs more than 30 years of experience  know a "little" more than we do (at least more than me)."
ironic, mmm... not sure!

Oh boy, please could we go forward and add something new to this topic

you're happy with EF12 and your eunuch U47 , right, i can sell you a bunch of my stock if you want...

if anyone has something new, like a solid state VF14 emulator attempt (oh, please no more Andreas......), or something else... feel free...

 

[Moby]

Guys, i follow this in silence but I must say that this kind of conversation doesn't move forward this topic. Few details were really interesting but few of them vere really inpropriate. Especially about people who were mentioned here and they don't read this. Can we go back to subject?

 

[o3misha]

You are right, Moby, I have deleted my posts. It was my mistake, to discuss substutes of VF14  and my own problems with acryl parts here. 
I'm sorry , that my advice was not heeded. Probably should create another topic for this, but I sincerely wanted to share my 7-year-old bad experiences with EF14. It made ​​me participate in a topic that others avoid my mistakes, waste their time with that tube, which was not designed for audio( not granger.frederic, of course) and try realy good reliable decisions. I went too far with the pressure. The reason is that I never managed to deeply discuss my real experience with anyone.
But I  would like to see more people are informed by disinterested persons, and not from a commercially-minded professionals like Oliver or Klaus. So have a lot of nonsense and untruths spread about similar characteristics of lamps  EF14 and VF14. Completely different internal design, size and shape of the anode, the filament of the cathode material, the grid current etc. There are few decisions for U47 tube problem, and I tested personally in my own mic a lot of them, so I can talk about subject (thanks to Andreas and my own head). Experts like Andreas never waste time arguing in the forums. This is understandable - they are busy people.

 

[micaddict]

I have deleted my posts.

Well, I do hope you have saved your posts somewhere, o3misha.
I for one would be interested to have a copy.
With off-topic and imperfect bits and all.

I'm sorry , that my advice was not heeded.

Moby suggested that "this kind of conversation doesn't move forward this topic." He might have a point there and he's certainly entitled to his opinion, just like you are entitled to yours.
On the other hand, he's not the original poster nor a moderator and he did say "guys". That's plural.
Hey, hold on guys, I didn't say you should all delete your posts now! 

Yes, another option could be starting your own thread, about VF14 alternatives.
In any case that would make you the original poster, so (within reason and without hurting people) you could say whatever pleases you. 
And I'd be a reader (again) for sure.




Henk

 

[Moby]

You are right, Moby, I have deleted my posts. It was my mistake, to discuss substutes of VF14  and my own problems with Flea parts here. 
I'm sorry , that my advice was not heeded. Probably should create another topic for this, but I sincerely wanted to share my 7-year-old bad experiences with EF14. It made ​​me participate in a topic that others avoid my mistakes, waste their time with that tube, which was not designed for audio( not granger.frederic, of course) and try realy good reliable decisions. I went too far with the pressure. The reason is that I never managed to deeply discuss my real experience with anyone.
But I  would like to see more people are informed by disinterested persons, and not from a commercially-minded professionals like Oliver or Klaus. So have a lot of nonsense and untruths spread about the characteristics of lamps  EF14 and VF14. Completely different internal design, size and shape of the anode, the filament of the cathode material, the grid current etc. There are few decisions for U47 tube problem, and I tested personally in my own mic a lot of them, so I can talk about subject (thanks to Andreas and my own head). Experts like Andreas never waste time arguing in the forums. This is understandable - they are busy people.

Misha, no, no, sorry, the reason I reacted was only to save names who are not in this forum or doesnt read this. All your research comments were usefull same as Granger's. U dont see eye with each other but thats OK, its up to reader to decide who is right