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Author Topic: Can we discuss the Nuvistor please?  (Read 6020 times)

Offline J.J. Blair

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Can we discuss the Nuvistor please?
« on: March 27, 2006, 05:04:51 pm »
I'd like to be educated by some of you on this tube.  What made it so popular with designers at one time?  Are there any specific sonic characteristics associated with it, and why is it frowned upon now?  (I am assuming that it's frowned upon, based on the fact that mics using the Nuvistor fetch lower prices than the same model using an AC701, or other tubes.)  
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They say the heart of Rock & Roll is still beating, which is amazing if you consider all the blow it's done over the years.

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Offline Martin Kantola

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Re: Can we discuss the Nuvistor please?
« Reply #1 on: March 27, 2006, 05:14:34 pm »
Only had a very brief close encounter with one (in a U47). Sounded terrible to me, but I would also very much like to know more about why...

Martin


Offline Arf! Mastering

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Re: Can we discuss the Nuvistor please?
« Reply #2 on: March 27, 2006, 05:23:01 pm »
They sound just fine in my C12a's.   U47's with nuvistors were conversions done when VF14's started getting hard to find.  Nuvistor 47's are not a good way to judge the tube itself.
“A working class hero is something to be,
Keep you doped with religion and sex and T.V.”
John Lennon

"Large signals can actually be counterproductive.  If I scream at you over the phone, you don’t hear me better. If I shine a bright light in your eyes, you don’t see better.”
Dr. C.T. Rubin, biomechanical engineer

Offline Klaus Heyne

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Re: Can we discuss the Nuvistor please?
« Reply #3 on: March 27, 2006, 05:40:46 pm »
At some point, there should be a Primer started in the stickies about the Nuvistor.

In brief: the mid-Nineteensixties saw the first wide-scale commercial application of the transistor. Those companies who were not ready to radically redesign their audio equipment to the new kid on the block were relieved when RCA introduced a sub-miniature, metal enclosed tube they named the Nuvistor (very clever double entendre!), which was to compete head-on with the transistor.

This tube was made available in penthode, triode, and specific models were designed for pre- and line amp amplification gain.

AKG and Neumann, realizing rather few changes were necessary for the adaptation of their existing models to these new tubes, jumped on it, and revamped the entire lines of their previously AC701 (or VF14) equipped mics, in the hope to fend off the impending transistor revolution.

What they did not realize early enough was that Nuvistors had some nasty habits which made them objectively inferior to tubes in their role as impedance converters:

1. Almost always audible ringing of the closely spaced filaments inside the tube (i.e.microphonics)

2. Almost impossible noise selection- few samples were quiet enough, and lasted long enough, to eventually avoid the wrath of the consumer.

3. Many of the mics' original transformers (optimized for specific tube types) were not altered to accommodate the different impedances of the Nuvistor.

4. AKG specifically tried to circumvent some of the inherent problems of the Nuvistor by re-designing their processors as cathode followers, and copied the circuit from the recently introduced sub-miniature C60 (AC701.)

The mating of Nuvistors with a cathode follower has not been particularly successful for the preservation of timbre or personality of tube mics.


In consideration  of the above, one if not the main reason why a Neumann U47 Nuvistor will fetch considerably less in the collector's market can be explained with the three issues I cited above.
The Nuvistor's impedance mismatch in particular renders the formerly full low end of the U47 mic anemic, constricted and nasal.

A slightly off-topic P.S.:
I was for many years the pround owner of two Ampex MR 70 Nuvistor-equipped master tape recorders, which were later equipped and modified by Paul Stubblebine Mastering with Tim De Paravici 1/2" two-track heads.

This was one of those magical matings of machinery and tubes: I have never heard a finer sounding tape recorder before or after.
(Except for the constant pain of maintenance, especially, noisy and frequently failing Nuvistors.....! )
Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Offline volki

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Re: Can we discuss the Nuvistor please?
« Reply #4 on: March 27, 2006, 05:50:58 pm »
The nuvistor was the most advanced stage of developement in terms of miniaturization - it wasn't exactly bigger than some of the early transistor packages at the time. Some people accuse nuvistors of being notoriously microphonic and noisy, but I believe that this can be overcome by careful selection just as it is necessary with other tube types, too. The nuvistor U47 I used last year had no such problems, anyway.

Edit: Klaus, I wasn't noticing your post before I sent off mine. Since you obviously have come across more nuvistor mic's than I have, I will gladly stand corrected  Very Happy
In any case, do you really find the sonic differences of, say, VF14 and nuvistor U47's to be that radical?
Volker Meitz

Offline Klaus Heyne

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Re: Can we discuss the Nuvistor please?
« Reply #5 on: March 27, 2006, 06:08:06 pm »
volki wrote on Mon, 27 March 2006 14:50

... do you really find the sonic differences of, say, VF14 and nuvistor U47's to be that radical?


Volker,
Regarding selection for Nuvsitors quiet enough to be used in mics (7586 and 13 CW4 are the most widely used ones):
My failure rate is about 7 in 10. This is a statistical average compiled over the years,  every time I had to replace one. I have a good stock, which I bought early on, because I noticed the exceptionally poor noise quality of these devices for mic applications.

Regarding sonic differences: substantial.
But funny how clients get used to a mic's tone, and how they can make the best of it: I have a major L.A. studio client who has several VF14-U47s and several 13CW4- U47s (all well restored and fully functional.) That studio's clients often prefer the Nuvistor model, because of its aggressive, more "modern" timbre.
Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Offline J.J. Blair

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Re: Can we discuss the Nuvistor please?
« Reply #6 on: March 27, 2006, 06:08:27 pm »
Thanks, guys.  I wan't so much asking about Nuvistors in U47s.  I mean, if U47 afficianados prefer the VF14 to an EF14 or the BLUE EF86 mod, it would seem obvious that the Nuvistor would be less desired in a U47, simply because most U47 lovers consider the VF14 integral to that mic's sound.

My main questions were based on mics like the C60 vs. the C61, or the C12 vs. the C12A, C28 and that Nuvistor version, etc. in terms of desirability.  

Also, is there any conversion option for Nuvistor mics?
studio info

They say the heart of Rock & Roll is still beating, which is amazing if you consider all the blow it's done over the years.

"The Internet enables pompous blowhards to interact with other pompous blowhards in a big circle jerk of pomposity." - Bill Maher

"The negative aspects of this business, not only will continue to prevail, but will continue to accelerate in madness. Conditions aren't going to get better, because the economics of rock and roll are getting closer and closer to the economics of Big Business America." - Bill Graham

Offline Klaus Heyne

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Re: Can we discuss the Nuvistor please?
« Reply #7 on: March 27, 2006, 06:26:03 pm »
Quote:

C60 vs. the C61, or the C12 vs. the C12A, C28

You mention models that, with all due lack of respect, are by and large termed "dogs' in our industry. You further mix up genres when you compare the C12 with the C12A, as the processor in the C12A is a cathode follower (see my earlier comments on that.)

The notable exception to the "dog" category being the C28A and B, (the "C' version was the one with the Nuvistor!): At least all three versions still had plate pick up of the signal, rather than being cathode followers.

But the C28 A/B vs. C models are a good example of what kind of sound the Nuvistor impinges on the timbre of otherwise unchanged mic model circuitries (similar to the comparison between a Neumann KM64 (AC701) and U64 (7586 Nuvistor):

To me, Nuvistors in mics sound unmusical and the all-crucial mid frequencies sound false. The lows are almost always either underrepresented or undefined, and the highs often have a metallic resonance to them.
Klaus Heyne
German Masterworks
www.GermanMasterworks.com

Offline Martin Kantola

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Re: Can we discuss the Nuvistor please?
« Reply #8 on: March 27, 2006, 06:46:02 pm »
Thanks for some seriously good answers... I can fully agree with the observations Klaus has, since I have a test recorded with a few microphones (all using the same type of capsule), and one of them Nuvistor-based. To me, the Nuvistor sounds pretty much like Klaus describes it!

Sorry if I'm going on a sidetrack here, but cathode follower circuits were mentioned. There doesn't seem to be a lot of popular mikes in that camp, do you think it's only because there are not enough good (native) designs, or is there a basic problem with that approach (soundwise)?

Martin

Offline maxdimario

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Re: Can we discuss the Nuvistor please?
« Reply #9 on: March 28, 2006, 02:34:19 am »
.....they suck in mics, and most other audio stuff.
never heard the ampex, though.


Offline Arf! Mastering

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Re: Can we discuss the Nuvistor please?
« Reply #10 on: March 29, 2006, 11:26:21 am »
When I got my C12a's, I was advised to buy a large batch of 7586 Nuvistors and carefully select.  At the time, the tubes were around $10 each and I grabbed 30 of them.  Fortunately, there were enough  winners in the batch to equip my 3 C12a's.   I guess I was very lucky, these mics have gotten stellar reactions from some very  picky singers and musicians.  The reject rate Klaus mentioned - 7 in 10, about matches my experience.
“A working class hero is something to be,
Keep you doped with religion and sex and T.V.”
John Lennon

"Large signals can actually be counterproductive.  If I scream at you over the phone, you don’t hear me better. If I shine a bright light in your eyes, you don’t see better.”
Dr. C.T. Rubin, biomechanical engineer

Offline Mike Cleaver

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Re: Can we discuss the Nuvistor please?
« Reply #11 on: March 29, 2006, 02:26:21 pm »
The only gear with a nuvistor that I've ever experienced was the original CBS Audimax.
The second generation all transistor models sounded much better.
It's a long time ago but IIRC, the nuvistor did increase the noise level and didn't sound quite right when compared to the second generation equipment.
Mike Cleaver Broadcast Services
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