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
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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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
)
(I probably got the Nuvistors at the same place you did
)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.....
Mark
Mark
http://www.mif.pg.gda.pl/homepages/frank/short/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.........
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.........
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.
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
Dave
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
John
Mark,
I think you may be confusing microphonics with the ability to survive high impact acceleration. Some nuvistors such as the 7586 were rated for 1000 g of shock that would shatter a glass tube. Inside nuvistors structural masses are small and cantilevers short, so forces would be relatively small - if you dropped one onto a concrete floor for example. But, they still behave like zingy little microphones.
I think you may be confusing microphonics with the ability to survive high impact acceleration. Some nuvistors such as the 7586 were rated for 1000 g of shock that would shatter a glass tube. Inside nuvistors structural masses are small and cantilevers short, so forces would be relatively small - if you dropped one onto a concrete floor for example. But, they still behave like zingy little microphones.
Mark A. Gulbrandsen said:
?
you meant "...high gain situation it would be critical ... to be microphonic."
anyway-comparing to 12B4,that's wimpy tube
been there ,done that...even if I didn't tried 12B4,I tried several others in same league
several yrs ago ,I fiddled with 7586 and 6CW4,along with few pencil toobz from MIG......didn't liked what I get comparing to EC8010 and mighty 7788 (or is it 6688,never know....
) ; all this strictly talking about simple (or "simple") line stage....
I don't have an clear analysis about why Nuvistors tend to be microphonic. The mechanical resonances in the elements of a Nuvistor will be at higher frequencies than the mechanical resonances in larger tubes, and the resultant microphonic sound may therefore be more irritating, even if its magnitude is no higher. My recollection of the sound of the Nuvistors that I played with for audio (mostly 6CW4 if I recall) is that they sounded very “zingy”. Part of that sound might have been due their inherently non-linear nature, but I suspect that it was more the microphonics I was hearing, because a gentle tap with a pencil created related-sounding effects. This is not to say that such a tube can’t be isolated and shock-mounted – they certainly could be, and should be for audio.
In microphones the size advantage of a Nuvistor is just too tempting. I’ll bet most of the tube mikes you’ll see are not intended for hand-held use. Typically studios suspend these kinds of mikes in an elastic suspension. And I’ll wager that the Nuvistor inside is well isolated and shock mounted. I once had an ancient Neumann U47 that had a Telefunken V14 tube inside. This was a large, though squat, metal-envelope pentode wired as a triode. As I recall, even this large tube was suspended in a shock mount inside the microphone’s body.
The site appears to be currently down but the technical library at http://pearl-hifi.com contains an excellent downloadable PDF on tube microphonics which correlates frequency and amplitude with grid. (Real men use acorns anyway. )
)
Brian wrote
'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.'
This is what has always put me off: I have yet to see a nuvistor that's anywhere as linear as a good conventional triode. If you want to go small the 955 and 958A acorns display exceptional linearity.
I think Musical Fidelity used them as a sales gimmick to influence magazine journos who can't read a tube datasheet, much in the same way as Tim de Paravicini did when using parallel 12AX7 as output tubes (my No 1 vote for the most insane circuit of the last century).
pm
'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.'
This is what has always put me off: I have yet to see a nuvistor that's anywhere as linear as a good conventional triode. If you want to go small the 955 and 958A acorns display exceptional linearity.
I think Musical Fidelity used them as a sales gimmick to influence magazine journos who can't read a tube datasheet, much in the same way as Tim de Paravicini did when using parallel 12AX7 as output tubes (my No 1 vote for the most insane circuit of the last century).
pm
Well I recommend them....
I have converted the 6SN7 from end of my GTA SE40s to nuvistors--8203 I think. They are "suspended” on the ends of the resister leads and wires into an adapter socket so that might lessen the microphonics--or make them worse—I dunno. The big problem is the little buggers love to oscillate—use a low value grid resister. I run mine at about 88V and 12 mA/1.5V bias. I suggest trying them ‘cause they sound damn good (better than the 6SN7) and none of my golden eared friend have ever said they are microphonic.
tim
I have converted the 6SN7 from end of my GTA SE40s to nuvistors--8203 I think. They are "suspended” on the ends of the resister leads and wires into an adapter socket so that might lessen the microphonics--or make them worse—I dunno. The big problem is the little buggers love to oscillate—use a low value grid resister. I run mine at about 88V and 12 mA/1.5V bias. I suggest trying them ‘cause they sound damn good (better than the 6SN7) and none of my golden eared friend have ever said they are microphonic.
tim
Nuvistors...
Great little things these....
Sound pretty damnd good too...
Ive used them to good effect in a SE 6C33 and a OTL based on the Allan Kimmel but using 6C33 instead of the PL/EL509 type tubes.... The Nuvistors were used as the first gain-stage wired in 'Mu stage' format, with half of 6SN7 in the top position Other half of 6SN7 used as the driver in the SE and phase-split in the OTL....
Very clean sounding, with excellent detail and low noise if you have a good one...
Michrophonics is definately an issue with them. Some show michrophonics that are intolerable Others seem 'Nearly' immune to it. Ive used both the 7586 and the higher Mu types. The higher Mu types seem slightly Less Michrophonic than the medium Mu types OR maybe its just luck and the Nuvistors I have just work out that way....
Ive found that with the examples I have, that the RCA ones are the worst for Mic. and that Sylvania and Tung-Sol are pretty good.
I have a single example of 7586 made by Tung-Sol, that you can whack with a spoon and shows Nearly No michrophonics-Wish I had a couple more like that one....
(Not that I make a habit of whacking valves with a spoon!)
The Michrophonics of a Nuvistor are quite unique...They 'Ping' at around 1.5-2KHz, quite a pure note, if tapped lightly with a finger-Some are so bad, that just stroking your finger on the top will cause an audible sound....
Great little things these....
Sound pretty damnd good too...
Ive used them to good effect in a SE 6C33 and a OTL based on the Allan Kimmel but using 6C33 instead of the PL/EL509 type tubes.... The Nuvistors were used as the first gain-stage wired in 'Mu stage' format, with half of 6SN7 in the top position Other half of 6SN7 used as the driver in the SE and phase-split in the OTL....
Very clean sounding, with excellent detail and low noise if you have a good one...
Michrophonics is definately an issue with them. Some show michrophonics that are intolerable Others seem 'Nearly' immune to it. Ive used both the 7586 and the higher Mu types. The higher Mu types seem slightly Less Michrophonic than the medium Mu types OR maybe its just luck and the Nuvistors I have just work out that way....
Ive found that with the examples I have, that the RCA ones are the worst for Mic. and that Sylvania and Tung-Sol are pretty good.
I have a single example of 7586 made by Tung-Sol, that you can whack with a spoon and shows Nearly No michrophonics-Wish I had a couple more like that one....
(Not that I make a habit of whacking valves with a spoon!)
The Michrophonics of a Nuvistor are quite unique...They 'Ping' at around 1.5-2KHz, quite a pure note, if tapped lightly with a finger-Some are so bad, that just stroking your finger on the top will cause an audible sound....
I know this is a old thread,but nuvistors high mu type are excellent sounding and in the Ampex MR70 is very very good. Ampex did their homework and put the nuvistors in the line amps which are isolated modules, The preamps use 18 nuvistors total,the line amps use 4 each. I have yet to hear a vacuum tube preamp that comes close. The high mu nuvistor is extremely neutral,with speed,clarity,and dynamics that are exceptional. Too bad Ampex was the only ones that understood how good they could be.
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