wa 47

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

xeawr

Well-known member
Joined
Dec 14, 2016
Messages
160
Location
Germany / Austria
Not a stupid question at all. I do it by performing various measurements. Not quite a walk in the park. If you are going after a clone, it's not the point to get rid of it, but match it instead. This exact point is driving me nuts currently, as im trying to nail a c800 clone, but i'm nowhere near done.

There is a body resonance, there is resonance of the cavity of the body (helmholz resonance), there's resonances and reflections around the capsule, angle of the capsule compared to the perpendicular bar of the grille, upper and lower in case of u47/c800 and such.

Elam is for example easy, the point is to kill all the resonances. I even have a mic which doesn't need any grille/shielding. As complicated as it sounds it's way easier to do.

U87s goal is also to have least resonances and reflections around the capsule. Sleve of the body doesn't resonate at all.

These effects show up in frequency response graphs, and are not subtle, several db of peaks and notches all over the place.

In case of u47 which has fairly microphonic tube (contrary to what many believe), you can replace the capsule with a 50pf capacitor, and listen to just the mechanical ringing of the components (microphonics). You would be surprised how much of a drum kit sound (high spl) the mic would pick up ;)
I hear this over and over again, and - although I want to believe it - I'm having some doubts. The coupling cap alone is so microphonic, that it acts as a microphone (tap that thing and you know what I mean). So it could very well be the cap you install as capsule replacement and/or the coupling cap.

- Not talking about the body resonances, those are obvious, but the VF14M tube being "ridiculously microphonic"...
 

soapfoot

Well-known member
Joined
Dec 27, 2010
Messages
705
Location
LA + Brooklyn
I hear this over and over again, and - although I want to believe it - I'm having some doubts. The coupling cap alone is so microphonic, that it acts as a microphone (tap that thing and you know what I mean). So it could very well be the cap you install as capsule replacement and/or the coupling cap.

- Not talking about the body resonances, those are obvious, but the VF14M tube being "ridiculously microphonic"...

Since the coupling cap is typically soldered to the tube socket, microphonic behavior from tapping the cap might still be a symptom of a microphonic tube

(And while a metallized paper cap can be microphonic to some degree, it seems far less-likely to be noticeably-microphonic than a steel vacuum tube, no?)
 

Bonnie1

Well-known member
Joined
Jan 24, 2016
Messages
58
Since the coupling cap is typically soldered to the tube socket, microphonic behavior from tapping the cap might still be a symptom of a microphonic tube

(And while a metallized paper cap can be microphonic to some degree, it seems far less-likely to be noticeably-microphonic than a steel vacuum tube, no?)
Ummm... all historic Tele/Neumann U47/48 we have worked on, the location for the coupling cap's is on the resistors boards underneath the transformer. Or am I not remembering correctly?
 

tomas.borgstrom

Well-known member
Joined
Mar 11, 2014
Messages
68
I hear this over and over again, and - although I want to believe it - I'm having some doubts. The coupling cap alone is so microphonic, that it acts as a microphone (tap that thing and you know what I mean). So it could very well be the cap you install as capsule replacement and/or the coupling cap.

- Not talking about the body resonances, those are obvious, but the VF14M tube being "ridiculously microphonic"...
Do you mean that all VF14 are very microphonic? That's not my experience.
 

Purplenoise

Well-known member
Joined
Sep 19, 2019
Messages
465
Since the coupling cap is typically soldered to the tube socket, microphonic behavior from tapping the cap might still be a symptom of a microphonic tube

(And while a metallized paper cap can be microphonic to some degree, it seems far less-likely to be noticeably-microphonic than a steel vacuum tube, no?)
This shouldn’t be the case in original 47s since the mp cap is not connected directly to the tube pin but you got a valid point.
 

xeawr

Well-known member
Joined
Dec 14, 2016
Messages
160
Location
Germany / Austria
Do you mean that all VF14 are very microphonic? That's not my experience.

Sorry for not phrasing it properly. I was responding to kingkorg's statement about the VF14M supposedly being "very microphonic":

kingkorg said:
In case of u47 which has fairly microphonic tube (contrary to what many believe), you can replace the capsule with a 50pf capacitor, and listen to just the mechanical ringing of the components (microphonics). You would be surprised how much of a drum kit sound (high spl) the mic would pick up ;)

Something that I have heard many times, but I have difficulty believing.
 

kingkorg

Well-known member
Joined
Apr 15, 2017
Messages
1,804
Location
Norway
The point is not how microphonic it is, the point is that it is microphonic to whatever degree you like to believe, and as such the microphonic component is contributing to it's characteristic signature.
 

tony hunt

Well-known member
Joined
Mar 13, 2014
Messages
132
Location
Frankfurt 230V / 50Hz
Am I crazy, or are microphonic tubes in studio microphones really so naughty?
It's not like they are being hit with pencils all the time, or recording Einstürzende Neubauten every day surely?
If a tube delivers the goods in a studio mic, why should I care if it is microphonic? Am I missing something?
 

Purplenoise

Well-known member
Joined
Sep 19, 2019
Messages
465
Am I crazy, or are microphonic tubes in studio microphones really so naughty?
It's not like they are being hit with pencils all the time, or recording Einstürzende Neubauten every day surely?
If a tube delivers the goods in a studio mic, why should I care if it is microphonic? Am I missing something?
It depends on the level of microphonics. The body resonates-reacts to sound especially in the low/low mid area. That energy transfers to the tube through vibration. This is especially evident when you record drums for example.
 

Purplenoise

Well-known member
Joined
Sep 19, 2019
Messages
465
Still, when recording drums, signal is still many orders of magnitude over microphonics..
Isn’t it kind of proportional? I have tested loud perc with microphonic tubes and in some cases the ring/tail was pretty evident…and unpredictable as far as freq. There are cases I have to say that the slight microphony of a tube might be a welcome effect…you might actually prefer the sound with a slightly microphonic tube.
 

doqmemory

Well-known member
Joined
May 9, 2020
Messages
188
Location
Ohio
Isn’t it kind of proportional? I have tested loud perc with microphonic tubes and in some cases the ring/tail was pretty evident…and unpredictable as far as freq. There are cases I have to say that the slight microphony of a tube might be a welcome effect…you might actually prefer the sound with a slightly microphonic tube.
Sounds like a new type of guitar pedal! Try out the new "Slightly Microphonic Tube" pedal!
 

GeorgeToledo

Well-known member
Joined
Mar 3, 2015
Messages
147
We got them like that, were ex-broadcast. Used them like that for years, only recently had a factory-back-conversion done in Berlin.

Actually, I'm pretty sure the VF14 was specified by Neumann for mic use - and there was a very limited amount ever produced. Only something like two or three production runs total, IIRC.
The rumor that it was a common tube comes from the fact that some category of factory rejects were at the time used in an external UHF-band extender for television tuners. I've never seen it used anywhere else.

/Jakob E.

edit/source: TFK Steel Tubes - Tab-Funkenwerk

Related… VF probably stands for verstärker fotozelle, which would roughly translate as photoelectric amplifier.

I think this predecessor family of tubes is probably part of what led to development of VF14 and other tubes with that casing form factor.

 

GeorgeToledo

Well-known member
Joined
Mar 3, 2015
Messages
147
As far as microphonics of VF14, EF12, etc., I have noted it seems that all Berlin or Gefell Neumann models that used steel tube have some form of sponge shockmounting for the tube. Can’t think of any other case they did that.
 

rock soderstrom

Tour de France
Joined
Oct 14, 2009
Messages
1,739
Location
Berlin
Related… VF probably stands for verstärker fotozelle, which would roughly translate as photoelectric amplifier.
I don't think so. The F stands for small signal pentode (in contrast to L= power pentode -->EL84, EL34 or C for triodes as in EC92 or ECC83), the first letter defines the heater voltage.
E=6,3V, like EF86, EF80, EF804, ECC88 etc. Other letters correspond to U=25V (e.g. UF14) or D types (indicate battery tubes). The V stands for Uf 60 Volt / If 0.05 Ampere.
 
Last edited:

GeorgeToledo

Well-known member
Joined
Mar 3, 2015
Messages
147
I don't think so. The F stands for small signal pentode (in contrast to L= power pentode -->EL84, EL34 or C for triodes as in EC92 or ECC83), the first letter defines the heater voltage.
E=6,3V, like EF86, EF80, EF804, ECC88 etc. Other letters correspond to U=25V (e.g. UF14) or D types (indicate battery tubes). The V stands for Uf 60 Volt / If 0.05 Ampere.
Thanks for that! I was feeling a little leery about the F descriptor as I wrote that late at night. I know better! The link I provided about earlier metal tubes coding types had info that jumbled that for me…

Do you have any link on the V standing for 60 volt? No big deal if not.
 

rock soderstrom

Tour de France
Joined
Oct 14, 2009
Messages
1,739
Location
Berlin
Do you have any link on the V standing for 60 volt? No big deal if not.
To be more precise, the V stands for the "Allstrom" series of tubes, which have a nominal heating voltage of 55V(60V) and, more importantly, 0.05A heating current, because they were intended for series connection. The same heater current provides the required equal voltage drop on some tubes in series connection in e.g. a radio set. You don't need a dedicated heating transformer or big load resistors to adjust the B+ voltage for the heater.

It is well described below, unfortunately only in German. Translate it with www.deepl.com


Edit: the whole concept is similiar to the P series TV tubes.
 
Last edited:

GeorgeToledo

Well-known member
Joined
Mar 3, 2015
Messages
147
Thanks! :)

fyi…It is also possible to plug a url into google translate and it will translate the entire page. You can continue to browse through the domain and google will continue translate the site as you click around, as long as you browse through the same tab.
 

Latest posts

Top