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soapfoot

Ruby Baby

Posts: 7,318 Member Since:04/02/2011

#1 [url]

Dec 31 15 3:04 PM

thank you for the PSA. I remember seeing that page some years ago and cringing at the thought that even one person might do that.

brad allen williams

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bockaudio

Platinum Blonde

Posts: 1,537 Member Since:02/02/2011

#2 [url]

Dec 31 15 3:11 PM

I understand that in 1980 the fashion for vacuum tubes was gone and this seemed like a logical solution (sorry even then it wasn't). Hell, there was a company that took Neumann transformers OUT of U47's and put off the shelf Jensens in, and charged a premium for it!

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Mickeyrouse

Silverado

Posts: 131 Member Since:05/11/2015

#3 [url]

Jan 1 16 4:10 PM

Not that I'm likely to ever be confronted with such a problem, but which is the "Not" procedure-
The fet conversion?
The nuvistor conversion?
Peter Drefahl's VF14 rejuvenation?
Incidentally, I have no experience regarding Peter's U47 service, but I purchased one of his power supplies for my C12A about 12 years ago. It has been extremely reliable and stable. I also sent that C12A to him for routine service a couple years ago and am quite pleased with his work.
Incidentally, could you point me to a source of comparison of the C12 and the C12A? I know they have the same capsules, and C12 is tubed by a glass tube while a C12A uses a 7586 nuvistor. Transformers? Basic circuit concepts? Power supply requirements? Production runs, etc.- inquiring minds want to know.

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bockaudio

Platinum Blonde

Posts: 1,537 Member Since:02/02/2011

#4 [url]

Jan 1 16 7:59 PM

The fet conversion is the primary "NOT".
Oddly the Nuvistor, sanctioned by Neumann, didn't really seem to be thought through. Tube/transformer mismatch = loss of bass. We do not advise.
I have no experience with Drefahl so no comment either way.
BTW a power supply should last and be reliable!
C12 questions posted in new thread.

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soapfoot

Ruby Baby

Posts: 7,318 Member Since:04/02/2011

#5 [url]

Jan 2 16 9:43 AM

Strangely, I've heard a U47 or two with the nuvistor that didn't sound that bad. It does roll off the bass, as you mentioned.

I wonder how many studios have U47s with nuvistors and nobody noticed? I have one very good anecdote that I won't share because I have not personally opened the studio in question's U47s to verify.

brad allen williams

Last Edited By: soapfoot Jan 2 16 9:49 AM. Edited 1 time.

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bockaudio

Platinum Blonde

Posts: 1,537 Member Since:02/02/2011

#8 [url]

Jan 2 16 10:49 PM

gtoledo3 wrote:
Any thoughts on the dual 408a/6028 in a legit U47? Curious if anyone here has heard that....

Using two parts of a triode, using a jfet with a tube, those I get, but when you put two tubes in a mic, I shut down and don't take it seriously. Even with the most robust of builds these mics are fragile and placing two tubes in such a small space is asking for unnecessary problems and lower reliability. I would cite the SM2 as an example of the undue heat, but most of their (SM2) problems are in the cabling.
I'm pretty sure you can acomplish your microphone goals without two tubes (in a mono mic).

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bockaudio

Platinum Blonde

Posts: 1,537 Member Since:02/02/2011

#9 [url]

Jan 2 16 10:54 PM

soapfoot wrote:
Strangely, I've heard a U47 or two with the nuvistor that didn't sound that bad. It does roll off the bass, as you mentioned.

I wonder how many studios have U47s with nuvistors and nobody noticed? I have one very good anecdote that I won't share because I have not personally opened the studio in question's U47s to verify.

Well it still is  most of a U47 with a great capsule, xfmr, psu & fixed bias circuitry.
The Neumann nuvistor mod sounds great if you change out the transformer (and don't throw the old one out!) for a higher turns ratio device with the same aspect ratio and construction technique (like one you may have salvaged from an M49 image), better matching the tube.
When I worked at Hyde Street Studios in San Francisco in the mid-late 1980's I never liked our U47. Found out years later it was Nuvistor.

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gtoledo3

Aqua Marine

Posts: 4,116 Member Since:23/10/2013

#11 [url]

Jan 2 16 11:07 PM

What is your opinion on submini tube vs the EF8X substitutions, sonically?

There are the obvious convenience differences between socketed and soldered tube, and the fact that less percentage of subminis may pass burn in (?). I have never heard the same basic mic, with that aspect altered (and whatever needed parts). But I have heard "U47 style" builds with either that I have thought sounded very nice.

Hopefully this isn't off topic from the greater discussion of U47 tube "substitutions" which seems to be relevant to this thread.

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