Is the Nuvistor Better Than The 12B4 For A Line Stage - diyAudio
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Old 17th August 2006, 03:33 PM   #1
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Default Is the Nuvistor Better Than The 12B4 For A Line Stage

I have a number of toobe Tektronix scopes that use the 7586 Nuvistor in the front ends. These are unique toobes and among the very last toobes designed and manufactured... even while transistors were taking over to a large degree. Ths nice thing about Nuvistors is that they operate on relatively low DC voltages, are metal cased, more noise immiune, and are less microphonic than almost any other type of tube ever made. That was what made them so ideal for use in the verticle amp front ends of many high end oscilloscopes.

There have been a number of pieces of audio gear built with Nuvistors... The Musical fidelity NuVista line wasone and Conrad Johnson and others also used this unique toobe. It would seem that this type of toobe would be a good candidate for a line stage and it would allow the use of lower voltage transformers and as such making finding surplus trannys easier and also less expensive to aquire. It my well be possible to also use a solid state current source as was done with the 12B4 line stage keeping the current through the tube constant through out its 50,000 hour rated life span..... yes.... 50K hours!

The down side of Nuvistors is they they are somewhat hard to locate and the special sockets they require are even more difficult to locate than the acutal toobes themselves.

While doing a Google search on Nuvistors I turned up the TNT PreAmble N line stage that uses the 7586 Nuvistor. This inexpensive line stage seems like a worthy place to begin experimenting with these most unique of all toobes.

Any comments or feedback would be helpful and appreciated!!

Mark
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Old 17th August 2006, 03:51 PM   #2
SY is offline SY  United States
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Less microphonic? That's totally at odds with my experience and the Nuvistors' reputation. I played with them for a while and finally gave up- the extraordinary measures I had to take to get out the mechanical ringing just weren't worth the small gain in efficiency because of the lower B+ requirement.

(I probably got the Nuvistors at the same place you did )
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Old 17th August 2006, 04:20 PM   #3
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Don't know why a toobe that is supposed to be so anti microphonic would exhibit that problem... they are designed with extremely low microphonics in mind and my TEK scopes certainly don't exhibit any of that problem nor did the designer of the PreAmble N have that problem.... Now I definately HAVE to build it and see.....
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Old 17th August 2006, 04:23 PM   #4
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Gee, I dunno.... most Tek tube 'scopes have so much mass that you'd have to whack them awfully hard to see any vibration make it's way to the tubes...

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Old 17th August 2006, 05:05 PM   #5
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My experience with Nuvistors would completely jib with SY's.

Around here we say "wicked" as in " that danged nuvistor is wicked microphonic"
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Old 17th August 2006, 05:05 PM   #6
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http://www.mif.pg.gda.pl/homepages/f...001/7/7586.gif


think of that tube as a smaller 6DJ8

even if S is on high side,that tube is somewhat wimpy for line preamp-if you ask me.

regarding 12B4 reamp-I didn't fooled you in anything I told you


I see that you didn't tried choke load or VOT configuration yet.........
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Old 17th August 2006, 05:08 PM   #7
kevinkr is offline kevinkr  United States
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In regards to the TEK front ends that used them like the 1A series, they are used to interface voltage amplifier SS circuitry to the distributed vertical amp or equivalent and at the amplitudes and gains involved microphony isn't much of a problem.
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Old 17th August 2006, 07:12 PM   #8
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I agree with others that these tubes are often very microphonic. The 7586 was often used in test equipment in a bootstrapped CF configuration where it offered extremely high input impedance. I have several vintage Tek and HP items with nuvistors in the input stages. Microphonics just wasn't an issue with scopes and meters. As FETs got better, they began to be used instead. Nuvistors are typically not as linear as their noval-based brethren. The mu of a 7586 can easily vary by 2:1 over signal swing, where a 6DJ8/6922 will vary by less than 1.25:1 (rough figures). They're cute, but I would generally choose a glass tube instead.
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Old 17th August 2006, 07:55 PM   #9
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I tried building a MM phono pre many years ago using nuvistors (6DW4 I think they were) and they were cheap then so I bought a bunch of them thinking I would find uses for them. They turned out to be to microphonic and variable to use and I never got the phono preamp to where I thought it was atually usable so I gave up. I had much better luck with the submini missle guidance/hearing aid sausage tubes (6111 etc)

Dave
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Old 17th August 2006, 11:23 PM   #10
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The reason Nuvistors are so microphonic is the elements are cantilevered from the ceramic base, i.e. there is no support at the top of the cathode-grid-plate structure. This is relatively easy to overcome and is worthwhile for their low distortion at low signal levels and long life. I wouldn't use it for a line stage, though.

John
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