Yummy!
http://www.korg.com/us/news/2015/012212/#
That thing looks pretty awesome. I thought it was going to be another one of those solid state tube replacement things.
I can't wait to see a datasheet and how much they cost. I'm very curious about the sound, there's all sorts of pedal based tube stages that sound super fun in applications where it just wasn't cost or space effective to use tubes.
Very curious as to how these work. I remember years ago reading about (TU Delft, I believe) a solid state tube that actually *did* use a cathode/grid/heater construction, but made on a chip-die with modern etch/mask procedures. The cathode wasn't heated, but sprayed electrons because it was shaped into a microscopic spike. Insulating layer on top, on top of that a conductive layer with a hole in it for the grid...you get the idea.
Never heard anything about that anymore...
Quote from: Mike Burgundy on January 28, 2015, 02:22:08 PM
Very curious as to how these work. I remember years ago reading about (TU Delft, I believe) a solid state tube that actually *did* use a cathode/grid/heater construction, but made on a chip-die with modern etch/mask procedures. The cathode wasn't heated, but sprayed electrons because it was shaped into a microscopic spike. Insulating layer on top, on top of that a conductive layer with a hole in it for the grid...you get the idea.
Never heard anything about that anymore...
I saw some displays done like that where laser pulses were used to blast tiny diamond cones out of a carbon target. They were field emission cathodes with no cathode heat, using the extremely high field intensity around a point to achieve several hundred cones per pixel. The display had a grid and used a zinc oxide phosphor that ran at 60 volts. They also used a grid for multiplexing.
The Korg tube appears to be small signal only, suitable for a preamp but nothing with more power than that. I am looking for a future with carbon nanotube cathodes with a negative work function for small signal amplification. There was work being done on low-temperature and room-temperature cathodes, but it all got swept away in the semiconductor juggernaut. I would like to see the noise figures for the Korg tube. If it is running in a temperature-limited rather than space-charge limited regime, the noise will be higher and a triode just might act like a pentode.
Quote from: frequencycentral on January 28, 2015, 01:09:13 PM
Yummy!
http://www.korg.com/us/news/2015/012212/#
So hang on .... am I understanding this right? This thing could change everything? We can run our tube amps at lower voltages and in more compact designs with less heat as well? :o
Unless I misunderstood something (or they turn out to be super expensive) THIS COULD BE A HUGE DEAL!!!
> Very curious as to how these work. ... a microscopic spike
> blast tiny diamond cones out of a carbon target
> appears to be small signal only, suitable for a preamp but nothing with more power
> am I understanding this right? This thing could change everything? We can run our tube amps at lower voltages and in more compact designs with less heat as well?
> THIS COULD BE A HUGE DEAL!!!
Move on. Nothing to see here. This is all VERY old-old-stuff.
It is Noritake's vacuum fluorescent display (VFD). We all know VFDs. They are/were a favorite in microwaves, VCRs, DVDs, and car-audio 1980s-2010. They were expensive but it cost very little to have special words, symbols, logos built-in. My 1994 truck heater has a VFD with little hands/feet/windshield icons. The present DVD machine here has a VFD with the counter/time and symbols for the too-many types of DVDs/CDs it can play. The X-Plod radio in the car is an eye-popper with every type of EQ (jazz/classic/rock/easy), a blazing waterfall (I guess) for volume indication, etc.
A VFD _is_ a vacuum triode, plus some glow-stuff, and recently they put dozens or hundreds of triodes in the bottle.
The main difference between an amplifying vacuum triode and a VFD (aside from the glow-stuff) is that a VFD needs very little current or gain. The geometry is optimized for low-low cost and silk-screen design, not to be an amplifier.
The original VFD is from 1959, the DM-160 from Philips (http://www.mif.pg.gda.pl/homepages/frank/sheets/009/d/DM160.pdf). That one made you diddle the control grid directly. The up-surge of many-object VFDs in the 1980s was due to integrating a digital controller to allow a few lines to control a hundred objects (you can't diddle the grids).
You don't have to get the memos to suspect the VFD business is on a decline. New toys use LCD/Plasma displays so they can put up ANY image, not just built-in images. Cheap new toys (my 2013 microwave) fall back to digit-only green LED (to make the fancier color LCD models look better). VFD is in the crack, and the crack must be narrowing.
So some guy from Korg was crying in his beer (sake?) about the high cost and poor life of 12AX7 and similar devices. And some guy from Noritake was under the same table crying about the fade-out of VFD production and his job. Each heard the other say "vacuum", and after swapping a few curves they realized that Korg could use the mature but going-out-of-style VFD foundry to make low-performance vacuum triodes at going-out-of-business prices.
While the digital decoder would be left out, VFDs usually have a "high"(ish) voltage converter inside which avoids one issue.
It is what it is. A small to very-small vacuum triode of poor perveyance (low conductivity) but "the right curves" and proven long life (with declining brightness/current). Small bent signals should be (are) very easy. The fact that the foundry machinery now has capacity to spare is a big economic bonus.
Fair enough, cross that one off the "things to be excited about" list 8)
As said, modern VFD product does not have the grids available for play (you talk to an onboard chip which decodes to the right segments).
So I am forced to guess from the data on the DM-160 of 1959. (As the Korg puff says, very little new has happened in the West since then.)
The Mu(gp) of a DM-160 is about 30. The saturated plate resistance is around 120K. With 50V supply, practical plate resistor, and reasonable audio load, the in-circuit voltage gain is about 10 or 15, the maximum RMS output may be 3V to 5V.
Of course 3V-5V is more than enough to slam ~~1V amp inputs (or if not, we have 19 cent opamps to boost weak tubes).
The maximum operating zone of a DM-160 is much much less than a 12AX7. 65V plate, 0.75mA current. (12AX7 can stand 330+ V and around 3mA.)
DM-160 curves in pink plotted over 12AX7 curves:
(http://i.imgur.com/9pItkxA.gif)
The dot far-right is roughly the op-point of a 12AX7 in a Fender or copy-cat.
DM-160 curves are very much "triode". However we love our 12AX7, perhaps because its curves depart from classical triode: the zero-grid line bends up due to electron velocity.
Are modern VFD triodes different from DM-160? Sure, but IMHO maybe in a direction of "smaller", lower amplifier performance.
OTOH, you can get 69 or more segments in one VFD. If Korg is just asking for two "segments", they can be equivalent to many single segments. So I will not be shocked if it turns out that Korg's devices run dozen-K impedance at over 1mA each.
The VFD "cathode" is directly-heated oxide-coated filament. DH/OC filaments are darling among some audiophiles. OTOH, these filaments are more like the ones in battery power beach-radios than the robust cathode of a WE 300B. And for VFD use, the filaments are run as cool as possible so the constant glow does not detract from the clever segments. For non-display use the filaments could be run hotter, but that very soon shortens the life down more like a beach-radio tube; and long-life is one of Korg's promises. So I think the filaments won't glow much. Also they will not have the high electron velocity of our beloved 12AX7. Of course it "has to glow", so Korg probably retains the phosphor glow-stuff of a VFD. That glow has nothing to do with thermionic amplification, but it is more honest than putting LEDs under glass.
I've manipulated Korg's image so we can see the working part.
The overall package is a hollow glass slab with pins. If you bust-open some old car-radio or VCR you will find a similar thing behind the display bezel.
I have pink-outlined the working part.
(http://i.imgur.com/brkv7VO.gif)
The horizontal white hair is the filament. Compared to traditional tube assembly, it is very simplified. No bends, spot-weld tabs, etc. In part because in a display system, filament power is a small part of total radio/VCR power, so thrift is not needed.
Under the filament is a hexagonal screen which is the control grid. They probably stamp this out by the acre, instead of hand-turning on a winding lathe as in traditional amplifier tubes.
The grey and blue area below that is the plate. The blue area is phosphor (glow stuff) and I suspect the grey area is bare metal.
All micro-stampings and spot-welds. Much smaller than a car-body, but not so small the workers need real magnification.
As an amplifier----
The grid-plate right under the filament hair has fair conductance, but there is a lot of grid-plate which only "sees" the filament at an angle and a long distance.
Some of the grid area and all of the grid support stamping has no control of the electrons, yet has capacitance to everywhere. This is dead-weight which reduces the gain-bandwidth. (But since "optimized" medium-Mu triodes have GBW far above the audio band, and a music flavor amplifier often wants to limit excess treble, this may be entirely fine.)
I just noted they suggest battery operation. This being a VERY teeny triode of efficient construction, that is practical. But who uses batteries today? And this is far-far from a power amp, you still need a power-plug to make a big sound.
The VFD technology, specific fabrication details, and Noritake's process, are VERY mature. The changes to bring-out K-G-P pins are trivial. So device reliability should be much better than today's perverted market for bottom-bid Chinese audio tubes, and very near the very best Golden Age vacuum tubes. We all have VFDs soldered into our lives and that would not be true if they were not incredibly reliable.
This is a win-win for Korg and Noritake. Real triodes at over-run prices.
If you know vacuum-tube amps, you know it isn't just the tubes. The VFD is not a conventional tube. Amps using different conventional tube-types tend to sound different. Heck, amps that use the same tube types and steal circuits from each other will sound different. There is a lot of tweaking and serendipity in a good guitar amp. Just throwing a triode in doesn't ensure musical happiness.
Korg of course is the kind of people who will probably do the tweaking. They've stayed too near the top of a competitive heap too many decades to be skimping the tweaking. This will be a musically useful product with "a magic feature" at a fair but not-cheap price and good distribution.
Of course if it sells a truck-load, B-ringer will find some VFD machinery and copy-cat it. Or even collect VFD rejects to dress-up a cheap DSP pedal.
A Guide to Fundamental VFD Operation
http://www.noritake-elec.com/vfd_operation.html
This suggests that modern VFDs are operated in the positive-grid area. This gives more plate current (glow), but is usually avoided in small-signal amplification because positive grid means "large" grid current instead of very low grid current. The grid current is not large enough to bother digital semiconductors but would be a major impact on another vacuum triode driving this grid.
All of which can be sorted by clever design of device and circuit to suit audio amplification instead of glowing displays.
Fig 10 suggests the electron flow is not thermally limited.
Crikey Paul you never cease to amaze me with your knowledge! A bigger question is - how do you get an iphone to read a flash drive???
Quote from: PRR on January 29, 2015, 01:41:14 AM
... mucho deep stuff ...
Or even collect VFD rejects to dress-up a cheap DSP pedal.
First things first. Imho.
Quote from: StephenGiles on January 29, 2015, 03:02:15 AM
A bigger question is - how do you get an iphone to read a flash drive???
Get an Android :P
I have an old battery tube portable AM-FM radio made by Philips that uses a DM71 tuning eye tube as the paraphase inverter for the push-pull output stage. It is quite possible to use tuning eye tubes as amplifiers with a µ of about 15.
Tuning eye tubes are usually limited in life by darkening of the phosphor and the zinc oxide phosphor only needs 60 volts for an acceptable output, so they are restricted to these lower voltages. It is quite possible to eliminate the phosphor or change it to P4 so the plate voltage can be raised to 250 volts and more output generated. And the single wire cathode can be folded back on itself several times to look like the cathode on the original Audion triode to get more current. I see this as viable - it just depends on whether anyone has the will to continue on with the development.
Quote from: StephenGiles on January 29, 2015, 03:02:15 AM
Crikey Paul you never cease to amaze me with your knowledge!
Ditto. Thanks, Paul - extremely helpful and informative.
Quote from: StephenGiles on January 29, 2015, 03:02:15 AM
Crikey Paul you never cease to amaze me with your knowledge!
This! Very informative and insightful PRR.
Regardless of whether or not THIS is the next big thing, I do like the fact that this sort of thing is being researched.
> How did I miss this???? (http://www.diystompboxes.com/smfforum/index.php?topic=109952.msg1006732#msg1006732)
You should read a forum hosted by some guy named "Aron". Many good things there.
> impede the production of tubes in North America, or anywhere outside former Iron Curtain countries was the cost of compliance with environmental regulations, given the materials that vaccuum tubes normally employ
I'm not sure this is true.
Tube demand and production sagged VERY badly in the early 1960s, when "environment" was just being talked-about, and fingers were pointing at broad-scale pollution such as the LA Smog which rotted your spare-tire in a couple years. Many tube makers got out of the business knowing that the end was nigh, they should move their capital to semiconductors.
Yes, later some of those former tube-plants became problem-sites. FWIW, there was a mid-1960s stink about the semiconductor plants pouring toxins on the ground.
And it may be related that the last receiving-tube plant in the US, GE's KenRad, which worked military types into the 1990s, was in Kentucky which is not a high labor-cost area and tolerated massive coal-mile pollution for a century.
Of course tube production had a very long tail. Many of the US and EUR machines had already been moved to East Europe for lower labor cost and closer access to the probable long-tail customers, as well as for diplomatic reasons, and perhaps because dumping was not a problem.
> I'm curious about whether this technology is able to sidestep both the production costs and the environmental risk.
First, I would really bet these are made in China now. China's coal-smog spews heavy metals much better than any tube plant could. Tube (VFD) production is high-value, the pollution is very local, China won't care for decades.
Second... these are very teensy and low-performance. The materials are mostly not very exotic. The rare-earth oxide coating is very small even by beach-radio standards. And being used straight-line, it is probably a continuous dip instead of the spray-gun sometimes used for large folded heaters. The grid and plate are simple punchings. The bottle is mostly glass, not even a high-temp glass. Getter metals are expensive and must be worked semi-air-tight, probably not much waste there. Frankly this may be nicer to live near than a junk-auto business. (My other neighbor starts a car-fire about every month, torching out gas-tanks before selling the scrap iron.)
Costs.... the plant is in-place, the mortgage is paid-down, local enforcers have been paid, and demand is declining. Factory cost of VFDs (or a product with minimal changes from VFD) is as low as it will ever get.
Finally: KORG is not going to sell these to DIY guys, that's not what KORG does. I bet they pay Noritake $2 a bulb, put it in a "NuTube Pedal" listing for $99. Plenty of mark-up for KORG and the rock-shop which sells them. If sales are large, B-ringer will find bulbs for $1 and sell the pedal for $49, still with plenty mark-up.
I suspect the tube is so specialized (lame for general tube work) and that Korg will tweak the pedal-product so very-fine, that it will not make sense to buy a $99 pedal to extract a bulb when better tubes are readily available for $19. And that all else inside will be SMD so not moddable with my old eyes and fat fingers (the more clever folks sure will find mods to do).
> Finally: KORG is not going to sell these to DIY guys, that's not what KORG does
Hahaha. I asked my contacts for a tube. Haven't heard back yet. :-)
Quote from: aron on February 02, 2015, 03:54:03 PM
> Finally: KORG is not going to sell these to DIY guys, that's not what KORG does
Hahaha. I asked my contacts for a tube. Haven't heard back yet. :-)
I don't know, opening products up to DIY has been one of the things they've been doing lately... free crowdsourced development. You never know.
http://www.korg.com/us/products/dj/monotribe/page_5.php (http://www.korg.com/us/products/dj/monotribe/page_5.php)
A colleague dug this up: http://hackaday.com/2010/04/22/vfd-as-a-sound-amplifier/.
Also this:
http://www.hpfriedrichs.com/radioroom/vfd/rr-vfd.htm
> Also this:
Interesting.
Most notable is the low-low-low current up to 40 Volts on the plate. I wonder if there is a mis-interpretation of the data. The wobbliness of HPF's curves is also curious; we expect small "contact potential" offsets and possible saturation, but not a lot of inflections.
Also the data extends far into the Positive Grid range. In conventional tube work this is a No-No for small-signal amplifiers. Yes, we can bend this rule, especially if we know the grid current and if we have powerful drive (19 penny opamps?).
Assuming "large" plate voltage and non-Positive grid, I get numbers like:
Mu about 20-30 (HPF gets ~15, noting it depends on op-point)
Transconductance about 1V/0.16mA = 160uMho = 0.16mS
Plate resistance near 160K
Plotting a loadline like 140V, 140K resistor, I squint a swing like 105V-135V or 30V p-p with a 2.5Vpp input, or gain near 12 into infinite load.
Certainly a useful Audio Amplifier. But we have these, cheaper. Is it a Tube Amp? Technically yes, but the data does not allow any guess of distortion or grid-blocking to say if it has "the mojo". If I smooth HPF's curves I do get the expected ~~5% THD near clipping; oddly if I use the raw data it looks like very low THD. And there is more to a tube than plate clipping, grid clipping, and 5%THD curvature.
Cool. Do you think they'll make a pentode version? ;)
The NuTube 6P1 is available to buy online now on eBay and www.nutube.us. It should be an interesting part...
Good to see you here, Pete.
I think your link got clobbered in the innernet. (";" s/b ".")
Seller site: http://www.nutube.us/
More links--
eBay store: http://stores.ebay.com/nutubeusstore
KORG site on NuTube: http://korgnutube.com/en/
Quite complete datasheet: http://www.nutube.us/downloads/Nutube_Datasheet_31.pdf
More app-notes: http://korgnutube.com/en/guide/
I guess all of you already seen this? :D
And the first VOX amps using Nutubes are here
http://www.voxamps.com/MV50 (http://www.voxamps.com/MV50)
Quote from: potul on January 16, 2017, 06:24:34 AM
And the first VOX amps using Nutubes are here
http://www.voxamps.com/MV50 (http://www.voxamps.com/MV50)
The store I work at is a Vox dealer and we just put in an order for a few of these. Eager to hear how they sound (and open one up so I can see these things) in person.
Hi,
did you heard it?
Quote from: vince76 on February 02, 2017, 04:14:18 AM
Hi,
did you heard it?
Not yet. Vox says they won't ship until the end of the month :-\
Those datasheets look really badly made. For example several plots have conflicting title and axis label. :icon_redface:
Guys, I got some news that Nutube is on sale in Japan.
Here are addresses of these shops.
http://korgnutube.com/jp/dealer/
BTW, what is the relation between the nutube 6p1 and the Chinese 6p1?
Welcome.
> what is the relation between the nutube 6p1 and the Chinese 6p1?
Probably none at all. The NuTube is really a display tube. Used as an "amplifier" it would be too pathetic to put into production. However Noritaki has excess production capacity, and KORG likes it, so it is being offered.
That link is Japanese and seems to be Japanese shops. I know I have seen a US/EU sales site but am not finding it now.
http://www.nutube.us/ - which has a link to an eBay store for sales.
Spotted these amp kits which may be of interest to some - schematics are included.
https://www.tindie.com/products/microwavemont/nutube-amp-kit-a-vacuum-tube-in-new-century/
https://www.tindie.com/products/microwavemont/nutube-based-15wx2-amplifier-kit-with-class-d-amp/
Quote from: PRR on March 14, 2017, 10:50:52 PM
Welcome.
> what is the relation between the nutube 6p1 and the Chinese 6p1?
Probably none at all. The NuTube is really a display tube. Used as an "amplifier" it would be too pathetic to put into production. However Noritaki has excess production capacity, and KORG likes it, so it is being offered.
That link is Japanese and seems to be Japanese shops. I know I have seen a US/EU sales site but am not finding it now.
nutube.us is the English site, and it is expensive a bit.
I will try to buy one the next time I go to Japan.
Just received in the post 2 samples of KORG NuTube 6P1 triode for a DIY guitar preamp project:
(https://4.bp.blogspot.com/-PcNB7cgMPy8/WR85wwhJSUI/AAAAAAAAMd4/RvdVNnGVQTYDHEyEp-3RAPjBIvZOHrpjgCLcB/s640/Phone%2B059.jpg)
According to the Application Notes (http://korgnutube.com/en/guide/) the gain is 14dB at 12V and 17dB at 30V, I would like to make a boost channel guitar preamp with some cranked distorted output. I plan to cascade two of them at 24V, should I add additional gain? Opamp or JFET amplifier? Where to place the additional amplification, before, after?
Quote from: rezzonics on May 19, 2017, 03:23:14 PM
According to the Application Notes (http://korgnutube.com/en/guide/) the gain is 14dB at 12V and 17dB at 30V, I would like to make a boost channel guitar preamp with some cranked distorted output. I plan to cascade two of them at 24V, should I add additional gain? Opamp or JFET amplifier? Where to place the additional amplification, before, after?
Personally, I'd breadboard this one and see what it sounds like. That way you can try all the things you would normally do with a twin triode, for example: series for more gain, parallel to see if it gets that jumpered Marshall sound (plus 30% more gain and lower output impedance), cathode follower for lower output impedance... you get the picture. Then I'd probably throw a Fetzer valve on the breadboard with it and see how it sounds before and after.
That's what I would do if I ever had the time for such things.
In Korg's application circuit schematic, I like how they use JFETs to give their device "tube" tone. Cool! :icon_twisted:
Isn't it just a buffer that let pass everything?
Quote from: rezzonics on May 23, 2017, 02:31:29 AM
Isn't it just a buffer that let pass everything?
Yes, but it's a MAGIC buffer, like found on a Boss MT-2 Metal Zone input, or on Rat pedal output.
They're just buffers, nothing magical in them. And yes, they are pretty much "transparent" unless you try to drive too low-impedance loads (e.g. less than 1K) or simply drive the bufferl with too hot signal. Both would cause the buffer to distort but that should not happen in usual operating conditions.
What folks need to realize about these NuTubes is that they are not your generic 12AX7's. The transconductance is low, B+ voltages failry lowish, and overall impeance levels moderately high-ish, for a vacuum tube circuit. These things are also pretty much operated in grid current region, which is why buffering is even needed in the first place. That alone will change operating characteristics into something different than those of circuits that are not operated in grid current region. IMO, I don't see a gigantic difference to "starved plate" circuits in general. I'm quite sure a plain gain stage is charcteristically closer to Butler "Tube Driver" circuit (and alike) than generic single-ended 12AZ7-based gain stages.
Not that it wouldn't mean one could't squeeze some nice clipping distortion out of these circuits.
Also, the directly-heated cathode can be a nuisance considering schemes such as cathode followers or schemes that utilize cathode loads.
Quote from: teemuk on May 23, 2017, 11:03:20 AM
They're just buffers, nothing magical in them. ...
No magic allowed, eh? :)
Bummer. I wanted to believe the hype!
JFETs are magical, and if you use a TL07x for your buffer, you get TWO per op amp! :icon_wink:
You also get something called an epi-FET, whatever the hell that is (must be amazing)! :icon_lol:
(Not trying to be mean. Just goofing off.)
Quote from: EBK on May 24, 2017, 06:15:30 PM
You also get something called an epi-FET, whatever the hell that is (must be amazing)! :icon_lol:
I believe that is the antidote for sudden allergic reactions to BJT or op-amp based pedals.
Quote from: aron on November 05, 2008, 08:11:51 PM
With very few exceptions, every circuit that I love and use has a JFET in it. ... the JFET rules for me.
Quote from: aron on May 24, 2017, 06:09:17 PM
Bummer. I wanted to believe the hype!
If you are refering to jfet buffers then perhaps you are conflicted about "Magic". ;) Or did the "Ministry" get to you too? (Harry Potter reference.) :icon_mrgreen:
If you are referring to Nutubes then I agree about the hyperbole.
Does anybody know of some liable, proven "starved tube" schematics used for overdrive or distortion? Valve Caster?
I've read that Spice models are not usable for starved tube circuits, but Koren proposed a method to approximate tube model parameters from real measured curves. Could not these parameters be recalculated on the starved region?
Mi idea is to compare simulations of NuTube with "an equivalent" starved tube circuit.
There are some here...
http://revolutiondeux.blogspot.com/2012/04/dean-markley-overlord-to-b-k-butler.html (http://revolutiondeux.blogspot.com/2012/04/dean-markley-overlord-to-b-k-butler.html)
Quote from: teemuk on May 23, 2017, 11:03:20 AM
They're just buffers, nothing magical in them. And yes, they are pretty much "transparent" unless you try to drive too low-impedance loads (e.g. less than 1K) or simply drive the bufferl with too hot signal. Both would cause the buffer to distort but that should not happen in usual operating conditions.
What folks need to realize about these NuTubes is that they are not your generic 12AX7's. The transconductance is low, B+ voltages failry lowish, and overall impeance levels moderately high-ish, for a vacuum tube circuit. These things are also pretty much operated in grid current region, which is why buffering is even needed in the first place. That alone will change operating characteristics into something different than those of circuits that are not operated in grid current region. IMO, I don't see a gigantic difference to "starved plate" circuits in general. I'm quite sure a plain gain stage is charcteristically closer to Butler "Tube Driver" circuit (and alike) than generic single-ended 12AZ7-based gain stages.
Not that it wouldn't mean one could't squeeze some nice clipping distortion out of these circuits.
Also, the directly-heated cathode can be a nuisance considering schemes such as cathode followers or schemes that utilize cathode loads.
Very interesting. I will try to generate SPICE models from NuTube 6P1 datasheet curves and starved 12AX7 curves from this study (http://www.valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf) and compare the response of both.
I will post the results here.
Stay tuned!
Vox appear to like nutubes.
http://www.voxamps.com/MV50
Is there any Pentodes too? Cause having an output Pentode tone before a SS PA would be amazing...
I have published on my blog the calculated Spice models with curves from a starved 12AX7 and a Korg Nutube:
Korg NuTube 6P1 vs 12AX7 starved tube / valve: SPICE models (http://rezzonics.blogspot.fr/2017/05/korg-nutube-6p1-vs-12ax7-starved-tube.html)
Starved 12AX7:
(https://3.bp.blogspot.com/-C7icMSNDsTk/WScl5aXJhTI/AAAAAAAAMfA/1mle3jZ_BScd91C2ySk1tkOX4a8FiPc6QCLcB/s640/12AX7_starved_curves.png)
Korg Nutube 6P1:
(https://3.bp.blogspot.com/-tD29OMGO5qA/WScy4BxXrcI/AAAAAAAAMfU/0mKc6_6Okeg3JcY2RnjRYypoW88_sB6RwCLcB/s640/nu6p1_starved_curves_spice.png)
I will try to make a comparison of frequency response with a basic circuit.
I have published on my blog the gain and frequency response comparison at +24VDC of a NuTube 6P1 triode and a starved 12AX7 tube:
Korg NuTube 6P1 vs 12AX7 starved tube / valve: Gain and frequency response (http://rezzonics.blogspot.fr/2017/05/korg-nutube-6p1-vs-12ax7-starved-tube_26.html)
I am a bit surprised by the results because, if the simulation models are correct, the starved 12AX7 tube has more gain than the NuTube 6P1 triode, 24.6 dB of gain for the 12AX7 compared to 17 dB of the NuTube.
The NuTube requires plate resistors 8 times higher than 12AX7, NuTube maximizes gain with 400K load and 12AX7 with 50K load (in starved mode). NuTube requires bypass capacitors 15 times higher than 12AX7 in order to have a similar response at low frequencies:
The following figure shows the gain and frequency response with bypass capacitors from 10nF to 10uF for 12AX7 (in green) and for NuTube from 150nF to 150uF for NuTube (in blue)
(https://1.bp.blogspot.com/-Q29jBM-hE0Q/WSdXmb-cFtI/AAAAAAAAMgI/ncseiDVOSrAPPCdaqgG5TOX5r9JntJL8ACLcB/s1600/nu6p1_vs_12ax7_freq_cbyp.png)
> I am a bit surprised
Why?
12AX7 is a HIGH-gain device.
NuTube is a display panel. Never meant to have electronic gain at all.
Are you modeling the HIGH grid current the NuTube needs in most of its "good" operating range?
Quote from: frequencycentral on May 25, 2017, 02:13:04 PM
Vox appear to like nutubes.
http://www.voxamps.com/MV50
So they're selling a 50W amplifier paired up with a 25W speaker?
Recipe for success!
Quote from: thermionix on May 26, 2017, 12:27:34 AM
So they're selling a 50W amplifier paired up with a 25W speaker?
Recipe for success!
It's a solid state class d amp that puts out 25W into an 8 ohm speaker, and 50W into 4 ohms. So the speaker in question is most likely 8 ohms.
Quote from: PRR on May 26, 2017, 12:20:18 AM
> I am a bit surprised
Why?
12AX7 is a HIGH-gain device.
NuTube is a display panel. Never meant to have electronic gain at all.
Are you modeling the HIGH grid current the NuTube needs in most of its "good" operating range?
I am surprised because 12AX7 is a high gain device when operated at +350VDC, but I was expecting a huge degradation at +24VDC and NuTube is based on a display technology but it has been designed to work as an amplifier.
I added a current source in the simulations to model grid current, typical grid current is 6uA, max is 30uA.
Quote from: BubbaFet on May 26, 2017, 03:12:50 AM
Quote from: thermionix on May 26, 2017, 12:27:34 AM
So they're selling a 50W amplifier paired up with a 25W speaker?
Recipe for success!
It's a solid state class d amp that puts out 25W into an 8 ohm speaker, and 50W into 4 ohms. So the speaker in question is most likely 8 ohms.
I saw this demo comparing Vox MV50 to AC15 using the same speaker and I was quite convinced by the results, at least with overdrive pedals, maybe not so much with the fuzz:
Quote from: BubbaFet on May 26, 2017, 03:12:50 AM
Quote from: thermionix on May 26, 2017, 12:27:34 AM
So they're selling a 50W amplifier paired up with a 25W speaker?
Recipe for success!
It's a solid state class d amp that puts out 25W into an 8 ohm speaker, and 50W into 4 ohms. So the speaker in question is most likely 8 ohms.
Hadn't noticed that. Still, a little safety margin is advisable. Perhaps they're exaggerating the amp's output power a bit, a pretty common practice.
> I was expecting a huge degradation at +24VDC
Oh, OK.
Gain of a tube stage does not fall off very much with B+.
Here's 12AX7 data for 300V to 90V supply. Take the Fender-typical 100K Rp and 220K load (0.1Meg and 0.24Meg). At 300V, 50. At 90V, 38. A 70% reduction of battery voltage gives a 24% reduction of gain. Or 10.5dB less battery is only 2.4dB less gain.
(https://s21.postimg.org/r6hzg0iz7/12_AX7-gain.gif) (https://postimg.org/image/r6hzg0iz7/)
(Maximum output level *does* decrease nearly with supply voltage, actually faster.)
This is true as far as it goes. There is around +/-1V uncertainty in effective grid bias due to "contact potential". With a tube of amplification factor of 100, supply voltages much under 100V may not bias consistently in mass production. The usual rule for no-trouble design was Mu < B+. 12AX7 types (as diode-triode radio tubes) were widely used near 90V, so the makers made some effort to be consistent in that application. Of course 24V is way lower (at 9V you are outside any B+ zone generally contemplated). The AX seems to be quite linear down to dozen-volts, with of course very low current and probably reduced gain.
Some extrapolation suggests that 12AX7 at 24V will be gain of 26dB, in sight of your modeled 24.6dB. (May only mean the sim extrapolates about the same as my figuring.)
> I added a current source in the simulations to model grid current
Grid current should rise with grid voltage. But not a linear rise like a resistor (or a resistor with a perfect diode). The amount and curvature of this current will influence distortion, unless very well buffered.
Thanks for your comments, they are very instructive. I plan to add JFET buffers/amplifiers before and after each triode section plus a tone stack. I am starting to have good results in simulations.
I was thinking that maybe I could use similar circuits with NuTube and a 12AU7 "starved" tube to get similar gain on both circuits so that I could compare them.
The store I used to work at is a Vox dealer and I said I would post on here as soon as we got the MV50 in and totally forgot :P I even opened one up and got gutshots (see below) for the sake of science. But frankly between the 3 different voices of amp the AC model hands down is the best. The "Rock" sounds really grainy overdriven and the clean just doesn't have much flexibility. I'm not a huge hybrid amp advocate but I really dig the sound and especially the flexibility the AC offers though. Plus a $200 price tag isn't bad 8)
(http://i.imgur.com/8l2fxjB.jpg)
(http://i.imgur.com/LAOEU4q.jpg)
(http://i.imgur.com/LjiCdN3.jpg)
Quote from: vigilante397 on June 05, 2017, 12:32:42 AM
The store I used to work at is a Vox dealer and I said I would post on here as soon as we got the MV50 in and totally forgot :P I even opened one up and got gutshots (see below) for the sake of science. But frankly between the 3 different voices of amp the AC model hands down is the best. The "Rock" sounds really grainy overdriven and the clean just doesn't have much flexibility. I'm not a huge hybrid amp advocate but I really dig the sound and especially the flexibility the AC offers though. Plus a $200 price tag isn't bad 8)
Just curious about what speaker you used to compare the three, and if you think that makes a difference to each model. In other words - do you think the clean model would come out better in a review playing through a Fender cab as opposed to a Vox cab?
Quote from: GGBB on June 05, 2017, 08:12:35 AM
Quote from: vigilante397 on June 05, 2017, 12:32:42 AM
Just curious about what speaker you used to compare the three, and if you think that makes a difference to each model. In other words - do you think the clean model would come out better in a review playing through a Fender cab as opposed to a Vox cab?
I tried all 3 through the Vox 1x8 cab, 1x12 cab, and a Blackstar 2x12 with Vintage 30's. Don't get me wrong, none of them sounded bad, but the Clean had a little too much headroom so it was really hard to get it to drive well (desirable for some styles) and the Rock sounded like a 50W metal zone. Grainy high gain distortion with very little option for clean.
Quote from: vigilante397 on June 05, 2017, 04:43:44 PM
I tried all 3 through the Vox 1x8 cab, 1x12 cab, and a Blackstar 2x12 with Vintage 30's. Don't get me wrong, none of them sounded bad, but the Clean had a little too much headroom so it was really hard to get it to drive well (desirable for some styles) and the Rock sounded like a 50W metal zone. Grainy high gain distortion with very little option for clean.
I get it - Clean is all clean and Rock is all rock, but AC gives you some flexibility.
Any thoughts about clean tone comparison between AC and Clean models? I am seriously thinking about one of these but don't have access to demo units yet. I'm partial to Fender tones vs. Vox, and mainly interested in clean settings since I get my dirt from pedals. The lack of ability to get driven tones with the amp alone wouldn't concern me.
Quote from: GGBB on June 05, 2017, 06:51:54 PM
Quote from: vigilante397 on June 05, 2017, 04:43:44 PM
I tried all 3 through the Vox 1x8 cab, 1x12 cab, and a Blackstar 2x12 with Vintage 30's. Don't get me wrong, none of them sounded bad, but the Clean had a little too much headroom so it was really hard to get it to drive well (desirable for some styles) and the Rock sounded like a 50W metal zone. Grainy high gain distortion with very little option for clean.
I get it - Clean is all clean and Rock is all rock, but AC gives you some flexibility.
Any thoughts about clean tone comparison between AC and Clean models? I am seriously thinking about one of these but don't have access to demo units yet. I'm partial to Fender tones vs. Vox, and mainly interested in clean settings since I get my dirt from pedals. The lack of ability to get driven tones with the amp alone wouldn't concern me.
One thing I did like about the Clean model was that you have a treble and bass control, whereas the AC just has "tone," so it's easier to dial in some beef on the clean where you need it. That being said the main difference between the Clean's clean and the AC's clean is the headroom. On the AC with the gain down low you can still get some hair with hot pickups and really digging into it.
Quote
One thing I did like about the Clean model was that you have a treble and bass control, whereas the AC just has "tone," so it's easier to dial in some beef on the clean where you need it. That being said the main difference between the Clean's clean and the AC's clean is the headroom. On the AC with the gain down low you can still get some hair with hot pickups and really digging into it.
So... do they sound like tube amps to you?
Interesting that the Nutubes need some degree of shock protection - rubber grommet mounts. How microphonic are they I wonder?
Read the application notes.
The VFD panel mechanical design is TERRIBLE for stability. Big flat unsupported screens. Unsupported so they do not block-out the display in the original use. Not really something they can engineer-out on a dying product run on existing machinery.
Quote from: BubbaFet on June 05, 2017, 09:29:09 PM
Quote
So... do they sound like tube amps to you?
Kinda :P I'm not going to say they are a mind-blowing sweet tone that I would get to replace all of my tube amps, but for a hybrid it sounds spectacular, and it is absolutely a gig-worthy amp. It has good tone, a lot of power, and it weighs next to nothing. So final answer, it absolutely sounds good enough to keep around as a gigging/practice amp, but don't expect it to become your #1 favorite amp in the world.
Quote from: anotherjim on June 06, 2017, 07:52:35 AM
Interesting that the Nutubes need some degree of shock protection - rubber grommet mounts. How microphonic are they I wonder?
Enough that technical documentation keenly suggests somekind of mounting that does not transfer vibrations. At least one document suggests using a separate circuit board for the NuTube circuitry, which is then mounted on rubber grommets.
Don't know about the NuTube, but in general VFD's are notorious for being very, very microphonic. Obviously it becomes a much bigger concern when the tube is used for audio amplification than when it's used as a display.
That long thin heating filament must pick up a lot of vibrations.
Quote from: rezzonics on June 07, 2017, 09:18:14 AM
That long thin heating filament must pick up a lot of vibrations.
I didn't even think to check that. Could be worth considering, I think I'll ask one of the guys still at the shop to bang on one a bit while he's playing.
Clash of the Titans:
Nutube 6P1 vs 12AU7/12AX7
(https://3.bp.blogspot.com/-xIio0ZEQudI/WTrdojg0IVI/AAAAAAAAMg8/RtVXgRoaeQ8Ycq_6376vwdI2DNGw2Sh7wCLcB/s640/Triodes.jpg)
Who will be the winner?
Same hybrid amplifier circuit with 2 different assembly options:
NuTube 6P1:
(https://4.bp.blogspot.com/-t9aYFPbqck8/WTXUHk2PPeI/AAAAAAAAMgo/-AmtCM6OnIEAKGHttEVYPh_krAdco_pfwCLcB/s640/Tubulator_NuTube_2.jpg)
12AU7 or 12AX7:
(https://3.bp.blogspot.com/-B7xbH96QnGg/WTXUG3dGdZI/AAAAAAAAMgg/RUtA2KWjVks6L7c94KJKVB97vqiP_SMggCLcB/s640/Tubulator_12AU7_2.jpg)
Everything assembled in a 1590J box:
(https://1.bp.blogspot.com/-6cF36vSo6Fw/WTXUGy8ghyI/AAAAAAAAMgk/bxym5g_Oqmgoj89QM31aU2BhQCL_yzLYACLcB/s640/Tubulator_NuTube.jpg)
(https://3.bp.blogspot.com/-xNDngc94XbU/WTXUGpl-9GI/AAAAAAAAMgc/QrhaYJDDz94qgFH6Ew0gSUnwsuo5UYuogCLcB/s640/Tubulator_12AU7.jpg)
PCB has been ordered and I soon will order the components.
I actually moved the speaker output jack to the rear.
Another AC15 vs MV50 comparison, using a Jensen® Vintage 12", Alnico P12Q, 40 watts speaker
So been playing with 6sn7,6sl7,12au7,12ax7 and Raytheon micro tubes for couple of years and having lots of fun. Looking at pentodes now. Started out at +-24v but now everything is +-15v.
Target applications range from reverbs to compressors. Hifi too.
What is confusing is why the tubes do so well at low voltages.
Everything lines up with tube data sheets as far as plate current,bias and so on.
This Haffler dh100 stereo preamp been running for about two months and sounds sweet.
The "dual op amp" is in preamp active tone control, class A output from composite hybrid op-amp.
PP output values are above theoretical values.
The two wires are for heater.
(https://s14.postimg.cc/fh8pfpqyl/A011_EAC0-2828-4_BD4-_AE69-7_B83_CEF364_E1.jpg) (https://postimg.cc/image/fh8pfpqyl/)
What do you mean by "do so well at low voltages"?
IMO, if you look at characteristic curves, a very typical characteristic is that non-linearity gets distinctly worse with lower B+ voltages. This especially with the kind of tubes that are designed to operate at higher plate voltages in general. No, linearity wise the tubes aren't "doing so well", which is why one keeps hearing "tubes must operate at high voltages to sound good" repeated over and over again everytime starved plate circuits come to discussion in one way or another.
That's a "HiFi" design rule though. If the tube is employed for no other reason than to intentionally generate distortion (which is obvious reason of products such as NuTube) then little non-linearity in operation is likely no issue, rather a benefit. So if we have no practical use for the "most linear device ever", which potentially is a vacuum tube triode, we can actually abuse that device in various ways and the output signal still probably sounds like we expect it should sound like: distorted.
Of course those are two entirely dissimilar schools of vacuum tube design. NuTube, and many other "starved plate" circuits cater for the latter but at the expense also perform much, much weaker in respect of the former.