Measured VF14 characteristic

[granger.frederic]

thanks, i will surely do that.
i'll tweak a bit with ef12 and ef13 before

http://www.voxorama.com/service/detail/andreas-grosser-vf14ef.html

 

[bockaudio]

http://prorecordingworkshop.lefora.com/topic/19403754/Hoping-to-find-a-schematic-of-the-251E-that-I-can-read#.UvU7CPiYPpQ

 

[bockaudio]

Why would you do a 1,1V measurement ?
There's 1V and 1,5V, count the lines, it's not quantum mechanics, just microphones, oups :-X

cuz if you are already there with your DUT and gear setup, why not be specific?

 

[granger.frederic]

Dear o3misha,

i've just found the 13CW4 that was originally installed in my U47
i want to test it again with your advices
could you please explain how you load it ?
cheers
Fred

 

[bezen4uk]

Why would you do a 1,1V measurement ?
There's 1V and 1,5V, count the lines, it's not quantum mechanics, just microphones, oups :-X

cuz if you are already there with your DUT and gear setup, why not be specific?

Hi David,
I made this graph.
I don't have DUT now.
I'll update graph with calculated -1.1V.
Next time I'll measure more specific.
Cheers.

 

[Moby]

Dear o3misha,

i've just found the 13CW4 that was originally installed in my U47
i want to test it again with your advices
could you please explain how you load it ?
cheers
Fred

Dear Fred, Sorry because i answer instead of Misha but here is my advice about U47nu mod. If I understand correctly you own original U47N. Am I right? If yes, than :

VF 14 current is 0,55 mA (lower impedance)

13CW4 current isc only 0,3mA (higher impedance)

1. put R3 a resistor with 27 Ohm parallel

2. change R2 from 60 M Ohm to 100 M Ohm

thats all and you have the same sound as the best VF14 tube

if you like to have the same output level than change the 6,8pF capacitor
between the grid and the anode to 3,3pF 500V highest quality
or you can put it also out no problem.

Cheers, Sergio

 

[granger.frederic]

thanks Sergio,

1. that's 14 ohms on the cathode,instead of the neumann original 20 ohms (29+68), right ?

2. 100MOhms to cut lower i suppose

but i doubt that will lower the output impedance a lot.

why couldn't we lower the anode resistance R5 ?

schematics: http://www.filmsoundsweden.se/backspegel/neumann-u47.html

 

[gary o]

Great link ..... whats the inductor on the grid ? I seen other U47N schematic without inductor ....

 

[granger.frederic]

it's a RF filter but it can be useless, it depends of your environment

should i lower R5 ?

 

[Moby]

thanks Sergio,

1. that's 14 ohms on the cathode,instead of the neumann original 20 ohms (29+68), right ?

2. 100MOhms to cut lower i suppose

but i doubt that will lower the output impedance a lot.

why couldn't we lower the anode resistance R5 ?

schematics: http://www.filmsoundsweden.se/backspegel/neumann-u47.html

No, something's wrong with your calculator. 29/68/27=11.597 ohm. Try it first then respond here. Cheers, Sergio

 

[granger.frederic]

ok
i've done 29+27=14
thanks for explain
i'll try that asap

cheers

 

[Moby]

ok
i've done 29+27=14
thanks for explain
i'll try that asap

cheers

No problem. One more thing. With R2 don't go over 250 M Ohm because the tube is not stabile with high pressure level.
With 100 or 200 M Ohm all is fine
And if you don't mind I would like to see the pic of your mod job Cheers, Sergio

 

[o3misha]

Thanks Moby. You did it. 

granger.frederic , In thanks for the advice, please describe your results here. This is very important in a political sense. 

 

[granger.frederic]

thanks for info
i have both 100 and 200Mohms in stock
i'll report back asap (a week or two)
i have a U47n (neumann K47 never reskinned) which was modded to ef14...
if possible i'll post some shootouts with my U47 EF14/EF13/13CW4 vs my M367 all original...

cheers

 

[bezen4uk]

Added graph with calculated -1.1V curve.

 

[Moby]

Thanks Moby. You did it. 

granger.frederic , In thanks for the advice, please describe your results here. This is very important in a political sense. 

U welcome mate

 

[granger.frederic]

hi guys,
i've just tested the EF13 in fixed bias 1V, heater 5V, Va 35V
it sounds very close to an EF12, very pleasing...
the mids/highs are deep and soft, but it's a little low-mid/bass shy
however the mic has a lot of headroom...

the difference vs an EF14 is not so big when set in self bias Rk=2,7kOhms/100uF/Vh 6v/suppressor grounded, the EF14 has more low mid/bass but has strangely less headroom, the sound is more distorted with very loud sources.

i'll test 13CW4 asap and report my feelings
maybe some shootouts, but it's quite difficult, as the takes are not done in the same time.

cheers
Fred

 

[granger.frederic]

Hi,

i've mounted two different ef13 (philips and tfk) in my U47N with fixed bias 1V
the sound is quite fine but the mic reacts like it has a compressor inside
the sound is compressed with loud sources and is very detailed with quiet sources
this is normal for a remote cutoff pentode ...
after all, this tube was used inside RF receivers to limit the fading effect, and has an automatic variable slope.

i'll abandon this tube for some reasons and will experiment with 13CW4 asap (but the psu needs some mods ...)

cheers

 

[ricardo]

the sound is compressed with loud sources and is very detailed with quiet sources

When you change tubes or biasing, you need to check Anode voltage is near what it was on the original.  Otherwise you'll have early overload which sounds like compression.

 

[o3misha]

hi guys,
i've just tested the EF13 in fixed bias 1V, heater 5V, Va 35V
it sounds very close to an EF12, very pleasing...
the mids/highs are deep and soft, but it's a little low-mid/bass shy
however the mic has a lot of headroom...

the difference vs an EF14 is not so big when set in self bias Rk=2,7kOhms/100uF/Vh 6v/suppressor grounded, the EF14 has more low mid/bass but has strangely less headroom, the sound is more distorted with very loud sources.

i'll test 13CW4 asap and report my feelings
maybe some shootouts, but it's quite difficult, as the takes are not done in the same time.

cheers
Fred

You mentioned that initially you have U47N with nuvistor. What is wrong to use original PSU with your U47, with nuvistor or Andreas Grosser's replacement tubes for your U47N? You have an original U47, so Andreas may help you with replacement tubes. I think it's is not good idea to solder and re-solder old mic...