U47 with an ef86

[nielsk]

Just checked the post, I'm working on it...my scanner is dead, I wil get it scanned out there somewhere. Is there anyone I can email it to that will post it?
How about the VF14 tube data to compare w/ the EF12K (nice link...)

 

[rafafredd]

just click the email button below, and send it to me, and I´ll put it online.

 

[burdij]

I have made some frequency response and gain measurements on the EF86 I am using in a U47 clone circuit. The mike uses a triode connected EF86 (with screen, suppressor and plate connected together as in the U47, tube is a strong used unit manufactured by Mullard) and a Cinemag CM-2461NiCo as the output transformer. I used a prototype dual-DOA servo-balanced preamp using a Cinemag CMMI-3.5C for input and a Cinemag CMOB-1L output transformer. The preamp measures essentially flat from 50Hz to 100KHz and is down -3db at 170KHz and 20Hz.

The mike preamp measures:

20Hz -3db
50Hz -1db
1KHz 0db
22KHz -1db
43KHz -3db

The EF86 is operating at +24.5db (or ratio of 10.7) gain and the transformer has a loss of -23.5 db for a net gain in the mike preamp of +1db.

 

[b2]

Hi,Why not put an EF14?? :green:

She's got the similar data, you have to change the heater voltage (lower than the vf14, 6.3v if I remenber.).May be she will sound pretty good :grin: .

Best regards,b2.

 

[burdij]

The EF12 varies in more than filament voltage and current from a VF14. The VF14 suppressor grid is a seperate connection on the socket. In the EF12, the suppressor is internally connected to the cathode.

 

[nielsk]

I sent the EF12K schematic to rarafred, & aAC701 as well. If he would please....
anyone know of a source for an EF14?

 

[smallbutfine]

Well actually from all i read the EF14 is not as good as the VF14s neumann used... essentially because of poorer specs you have to choose out of a lot to get one that is good enough in this application. RFT would be even worse than TFK here...
Mr Wagner is using EF12k (EF12spez should do as well) - a less microphonic and lower tolerances EF12 (I guess they were just selected after measurement from EF12 production).
However, those prices have gone up alot for a while for these Stahlröhren. I tried to find a good EF12 but in my opinion prices are a bit silly with everyone trying to find VF14 like tubes.
The G7 is a very fine mic concept and may be the better choice... or maybe a direct u67 clone...
Strange but originally the u47 was very known for unpleasant sensitivity for movement, beeing running too hot and using a tube that wasn't really up to date for audio application :razz: , but at least it seems that the higher temperature protects the m7 from condense water...
Is it really that essential to stay by the original (while the originals may even differ a lot soundwise due to age) except for the m7 (or clone) that may be the most essential part of the mic anyways?
How much influence on sound does the bv8 have really?
Sometimes i think that the original tubes and trannys (or clones of them) are mostly bought for fixing originals that might be in nice condition otherwise...
Correct?

Kind regards,
Martin

 

[rafafredd]

Here´s the AC701. The ef12 is pretty unreadable, but I´ll see what can I do...

http://img.photobucket.com/albums/v172/rafafreddy/701.gif

 

[rafafredd]

OK, here it is:

http://hps.infolink.com.br/rafafredd/EF12%20K.pdf

 

[Gus]

-2.2V , 47K and 75V don't look like it will sound like a vf14 at all.

 

[burdij]

The AC701 circuit appears to be set up at -2.2 volts on the grid, also. In fact, there are some other issues with this circuit. There is also a cathode resistor that will affect the bias voltage on the grid. This will develop 1.2 volts on the cathode. The net cathode to grid voltage would be about 1v. I think the .1uf output cap is a bit small too. The 1Kpf capacitor in series with the capsule is un-necessary, too.

 

[burdij]

I guess I read the 120K as a 420K. That makes it even more bizarre. Now with respect to the cathode, the bias will be negative on the grid by .14v.

 

[Gus]

Lets work out the fil voltage

2.2v across 8.2K for .269ma

.269ma times 15K for about 4.02V

about 6.2VDC fil voltage.

 

[smallbutfine]

:grin: Well, that's slightly under the 6.3V spec in the datasheet....
btw , thanks Rafa, for the schems, i did not have them before...
Rest of my post i put in the brewery to not disturb this nice and interesting discussion.
I sincerely appreciate this thread really much....
Kind regards,
Martin