Measured VF14 characteristic

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I first tried the ef12k "Archualt" (sorting through 3 tubes) in my original Neumann U-47, and after much tweaking, it was still too bright for my tastes. Then I tried ef14s, and was very happy with the sound. Yes, the noise floor is a little bit higher, but nothing that interferes with my uses. To me it has all the "big" sound of the original set up, which is what I want out of this mic.
Not empirical, totally subjective.
 
Yes , i'm not a big fan of EF12 in U47 microphones.
i find the sound good but a little thin, HIFI...
EF14 in triode is better but a bit harsh in the mid/high
Like i said before, i prefer the EF14 in self bias and suppressor to ground.Closer but still not perfect through.
Now Milan give us another way: the EF13, a remote cutoff pentode version of the ef12
He shows us that there's another way than sharp-cutoff pentodes.
There's a lot of tubes to try now ;)
some ideas ?
Maybe someone's tried the EF11 ?
 
Based on the Moxtone graphs, am I correct in surmising that if you raise the plate voltage, you actually lower Ri plate impedance? It looks as though raising the plate voltage would also raise the mu/gain.

Also, how much anode current is considered "insufficient"?

Thanks so much!
 
Yes raising Va lower Ri and raise gain (a little) and noise
in theory, anode current is insufficient in the non linear side of the curve
regards
Fred
 
Thank you. I am currently using an EF802 in my mic with about 50V on the plate. I'm very eager to try 35V now and see the results. Perhaps I can place a potentiometer in place of R6 to adjust plate voltage.
 
You can experiment with a pot at the anode and another at the cathode, and then find more easily the optimal bias point.
EF8XX are good tubes for mics, i had a Wunder audio CM7GT with one EF844s , it was nice.
But Ri is higher on this tubes, so you may find that 50V is finally not so bad...
 
Good point, granger.frederic. I myself was just coming to the same conclusion that my ideas to experiment with underheating more and lowering plate voltage will likely just raise Ri. Probably resulting in less bass, or even less treble too?

Could still be an interesting experiment.
 
bezen4uk said:
Hi guys,
I had opportunity to make thorough mesuring test of the mint VF14 tube.
Tube is marked with "M", "Bld 00" and "432".
I choosed heater voltage same as in Neumann U47.
I used Fluke 8050A as multimeter and L1-3 tubetester as power supply.
Enjoy the graph.
Also, I made some measurements of amplification factor in original U47 mike, will post later.
So, your graph was created from written static datapoints or graphed by a machine in real time?
Amount of time spent at each point?
Only one voltmeter used?
No measurements for -1.1v grid bias?
Only one tube measured?
 
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
 
Hello David,
The graph was created from static points (5-7sec per point).
The was no drift of points (Up drift was less than 10mV).

I used 2 devices to collect data (plate current and plate voltage).
After measurement I corrected all data to one voltmeter.

The data collecting algorithm:
* set Ug1->increase Up until reach Ip target points (0.1, 0.3, 0.5, 0.7mA).
Constant Ip target points make measuring much faster (recommend).

No -1.1V info, but it can be easily calculated (I can update graph).

The tube was single, very new looking.
Before testing I applied 3 days non-stop burning-in process at Uh=55V, Ug1=-0.1V and Ip=12mA (tube connected as triode).
After that I applied U47 mode for 8 hours and then started measuring.
 
Guys , talk to Andreas Grosser about tube substitute of Vf14. He made Vf14er based on miniature Russian triod. If you prefer more heavy-muddy sound and if you don't like more leaner sounding Ef12, then you will be happy with vf14er. Its sound very close to Vf14. As for Klaus Heine - I will never listen to guy , who does not respect faсts and prefer  woodoo dances around his idol VF14. I was removed from all forums where Klaus Heine is a resident because I was not agree with him and just asked him to prove his point. All he could say, my ears tell me this and that. blah-blah-blah. He prefer to talk about tubes differences than to work with microphones in studio. That explaines everything he says. And his business, of course. I do not trust the so-called experts who are engaged in repair microphones without understanding what is the correct calculation of tube amplifier circuit . For which to delete the messages, dispels myths and shedding light on the truth, it is easier than to prove the opposite. This disease is called purism, and it is very contagious.
    I'll tell you more about all despised nuvistor that everyone (especially on forum of Klaus Heine ) considered bad for U47 -  it's great tube for U47. Neumann's engineers made ​​a mistake in mode with nuvistor. The value of the cathode resistor is not optimal , because of what has changed with the correct matching transformer. Andreas proved it when he was approached for help with nuvistor U47 owners. Simple selection of the cathode resistor causes that nuvistor U47 sounds great. Andreas can help you in this . Just get in touch with him. Hi has unique knowledge and ears. He is a musician in the past. Do not forget this .
BTW: what biasing method you used for Ef12? It is very important to use right value of the anode resistor to get perfect low end. Andreas use this tube for replacement in old U47s (with usual BV08 transformer 6:1 or 6.5:1) many times for different clients. Many of his clients were very scrupulous in matters of sound. And none remained dissatisfied. If you think that the sound with EF 12 is too thin, it is likely that you made mistakes in setting up the microphone. It is necessary to choose the right all the components and modes in microphone. There is a small difference in the bass with VF14, it's true. But it should not be so much that you could talk about the subtle sound. EF12 is much softer and more comfortable than the EF14 sounds, it is not only a comfortable bass - mic with EF12 may work with higher SPL. Serious underheating leads to failure of 90% of the lamps, if at least every 3-5 years not to regeneration. At EF 14 filament, single,  and not double like a VF14. Therefore, the cathode warms less evenly. The cathode material  prone to failure with underheating  more than VF14. In addition, the EF14  -very microphonic tubes. Very hard to find a decent lamp. If you are lucky - work with EF14 , it is not bad tube. But I repeat: it has a completely different set of harmonics, unlike the VF14. This EF14 sounds very unpleasant and harsh with big SPL.  8)
 
Call Andreas, it's his stuff and his work. The trick of VF14er is - operation point. He used different tubes for VF14er  with good results. At the moment he use fantastic russian miitary triod produced in early 70s. Andreas uses this tube for replacement in U47 for clients who suppose  to find VF14 as time goes by, and who want to keep original mode of their U47. But in all other cases Andreas strongly recommends to use EF12 with proper PSU and modulation or his VF14EF ( for clients who don't care too much about the real tube ).
 
o3misha said:
.... But in all other cases Andreas strongly recommends to use EF12 with proper PSU and modulation or his VF14EF ( for clients who don't care too much about the real tube ).
Or 13cw4 as you mentioned before. People often tend to ignore that little guy. With proper arangement it has the same bass response and more important the right K² distortion point. Only disandvantage is the lover noise than VF14M ;)
 
Hi,
i couldn't find better words for Klaus Heine.Thanks.
I'll try to tweak again with load and Ef12 ...
I thought that the 13cw4 had a higher output impedance : http://gwagner.50webs.com/u47.htm

 
I am very glad to have found like-minded here. Now it is very rare. Thank you. Yes, nuvistor has a different output impedance. And therefore needs to be adjusted by simply changing the cathode resistor. It's amazing how such hard-nosed and supposedly educated people like Klaus could not check it for so many years! I wrote about this in several forums, but I immediately stopped and said that all my words,- nonsense, and that's not even worth trying. VF14 is an icon???Do we all need to pray for VF14 now?
 
It would be a dream if a tech can make several tests on VF14 (other than curves...but it was very interesting), like harmonic distortion K2, K3...SNR,etc... in a U47 headamp off course...and compare it to the principle alternatives like EF12,EF14,13CW4,EF13,EF802,etc...
but it's a lot of work... :'(
 
Andreas did many tests of different VF14s. Especially in the matter of its k2,k3,k4 distortions, noise, and all dynamic characteristics. Then he has builded his VF14EF which produces all harmonic distortions and low end exactly as the best of tested VF14s. He also compared VF14s with other tubes. He is a genius, believe me. You better contact Andreas.
 
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