U47 with an ef86

« **on:** May 24, 2007, 06:55:07 PM »

does anyone have the schematic or know where I could find the schemaic for the ef86 moded U47s. I've looked around the forum and can't seem to find it. If I missed a nudge in the right direction would be helpful.
Thanks

« **Reply #1 on:** May 25, 2007, 03:58:40 AM »

I have not ever seen a modification including an EF86 for the U47. That tube most probably won't be able to drive enough low frequencies through the original transformer.

Jakob E.

« **Reply #2 on:** May 25, 2007, 07:56:32 AM »

it must be possible

http://recforums.prosoundweb.com/index.php/m/46767/0/#msg_46767

« **Reply #3 on:** May 25, 2007, 09:12:21 AM »

Possible in what way?

Yes, it will surely be possible to make it work - but it won't be u47-like in sound.

Klaus sums it up nicely - the post starting "Neither rocket science nor.."

http://recforums.prosoundweb.com/index.php/m/46767/0/#msg_46413

Jakob E.

« **Reply #4 on:** May 25, 2007, 10:15:33 AM »

A colleague has two ORIGINAL U47s with the original "Stahlrohren" tubes in them.

Another local chap has a 'Blue engineering' U47 with the EF86 mod.

You Simply Will Not Believe How much poorer the EF86 Version Sounds.

Seriously.

No no no no no.

It is NOT a god way to go.

It will NEVER be a U47 with this mod.

It's midrangey and it 'barks' at you.

Don't do it.

No.

-If you like, I can be firmer with my advice, but it involves cursing.

But seriously. It's NOT a U47. The G7/Lundahl circuit would beat it EVERY time.

Keith

« **Reply #5 on:** May 25, 2007, 11:25:11 AM »

Strange.....the BLUE U47/EF86 does not sound as good to me as a stock U67/EF86 (which is quite nice).

It's not just the tube, but a bad or good marriage of (synergy between) components.

What does make the VF14 so special?

« **Reply #6 on:** May 25, 2007, 03:23:36 PM »

This might be a bit of guessing but what I could glean from VF14 specs is that it has quite a high gain (59), quite low output impedance (around 8.5k). But that is at its nominal test condition which is not where Neumann operated it.
Interestingly enough, the AC701 has the same output impedance but a gain of only 23. A 6CW4 (close to the 13CW4) has a gain of 62 and an output impedance of around 6.3k. Looks close to a VF14 but they don't sound right.

« **Reply #7 on:** May 25, 2007, 04:02:39 PM »

Oh yes... I have a U67 myself. It rocks the balls off the Blue u47.

Keith

« **Reply #8 on:** May 25, 2007, 04:08:46 PM »

I did a lot of looking into the Nuvistor sub for the VF14m and the info I came across claimed that the original transformer was kept, and the Nuvistor had issues driving it; hence the much-discussed loss of low-end when Nuvistor mics are compared with VF14-equipped ones.

I have several associates (pros who won't be unfamiliar to the group) who use the Nuvistor U47 versions and they tell me that it's actually preferable to the VF14 for *some* applications. I also saw some posts at other audio groups to this effect.

An associate of mine recently refurbished a Nuvistor version and was telling me how stunning it now sounds...

FWIW...

Justin

« **Reply #9 on:** May 25, 2007, 06:28:38 PM »

OK

Lets get to the bottom of this dynamic plate R thing.

Anyone that owns a working real u47 with a vf14 want to do some simple measurements to find out what the real dynamic plate R is in a good vf14 u47?

I don't own one to do this.

« **Reply #10 on:** May 25, 2007, 06:36:45 PM »

Sorry Kieth but this post is hurting my brain... :?
-probablt because I have 2 mic bodies waiting to be stuffed and no tubes yet.

« **Reply #11 on:** May 26, 2007, 05:36:18 AM »

Bit off topic, but, maybe you'll find it useful:
http://www.proharmonic.com/recent.htm
scroll down, to the middle of the page...
U47 clone...
I have no experience with this mic, but, I have nothing but
respect for Proharmonic, and I believe it is worth looking into
it...

« **Reply #12 on:** May 27, 2007, 11:30:02 AM »

I have a schematic for a EF12K version U47 if you can find one of these tubes......

« **Reply #13 on:** May 27, 2007, 12:13:02 PM »

Quote

I have a schematic for a EF12K version U47 if you can find one of these tubes......

I do have a pair of these tubes myself. Can you post the schem?

« **Reply #14 on:** May 28, 2007, 09:32:25 AM »

send me ef12 schem!!! please!

« **Reply #15 on:** May 28, 2007, 10:14:48 AM »

If you can,please post it here. this thread will be going to the mic meta. it will be available to the entire forum. thanks

« **Reply #16 on:** May 28, 2007, 10:26:05 AM »

People who know something about simple tube stages should be able to figure it out for themselfs.

« **Reply #17 on:** May 28, 2007, 11:03:22 AM »

i can't find a data sheet for the ef12. does anyone have a link? or can someone provide info on the proper voltages for the tube.

« **Reply #18 on:** May 28, 2007, 12:01:40 PM »

Quote from: "seavote"

i can't find a data sheet for the ef12. does anyone have a link? or can someone provide info on the proper voltages for the tube.

Here you go : EF12 Datasheet

« **Reply #19 on:** May 28, 2007, 12:04:07 PM »

franks
note G3 to cathode

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