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Korg florescent tube project (Read 7457 times)
4krow
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Korg florescent tube project
03/20/18 at 22:18:00
 
The Korg 'Nutube 6P1 is a minature florescent DHT (directly heated triode) that has recently been developed. Well, 3 years ago anyway. In spite of the fact that it is a vacuum tube per se, the available power must be amplified and buffered with a transistor follower. This of course, means that it is no longer a tube project, but tube hy-bred project. Non the less, I decided to give it a try. Parts have come in and all I need to do is power it up. Pray for me...

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deucekazoo
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Re: Korg florescent tube project
Reply #1 - 03/20/18 at 23:17:31
 
Good Luck!
That does not look like a tube. Almost reminds me of a digital clock display. Let see some more pics.
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4krow
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Re: Korg florescent tube project
Reply #2 - 03/21/18 at 00:43:13
 
Just hooked up 12v battery to the circuit. Well, it works. Need to adjust the bias so that it is set at 2.5 volts for the filaments. The green glow is pukey looking to me, but it is not bright. When the circuit clips, you can see the tubes 'flash' a bit. I will add a volume control to the input, since a CD player of 2 volts may be a bit much... dunno.

  Yes, you can read about the SP1 at the Korg website. It can tell you a lot more than I can about this product.
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Jeff of Arabica
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Re: Korg florescent tube project
Reply #3 - 03/21/18 at 05:37:28
 
Oh wow!  I read about the Nutube a few months back after seeing a reference to it her in the forums.

How did you get your hands on one 4K?  Super cool!
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Lonely Raven
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Re: Korg florescent tube project
Reply #4 - 03/21/18 at 06:34:57
 
That is very cool - but I'm still a skeptic, even more so once I heard it needed a transistor boost to use it in our audio applications.

I'm eager to see what you think of it though.

I've always wondered how smoothly it clips...does it clip like a tube? If so, I could see chaining these to get the amplification you need and a nice tube distortion for a guitar preamp.
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4krow
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Re: Korg florescent tube project
Reply #5 - 03/21/18 at 14:54:54
 
Jeff,  Yes, you can find the US dealer at eBay. Pmillet has opened a store in association with Korg.

 LR,  I have the same reservations as you about this. So far, I have not gotten past just getting it hooked up and am starting to experiment with the bias setting for the tube. When set at the recommended 2.5 volts, it is in clipping and of course, that just sounds bad. It clips hard at that bias setting, so I moved the voltage to 2.04 volts and so far, that seems decent. This is all using a 12 volt battery. I intend to try out an 18 volt battery, since the spec sheets show lower distortion characteristics.
I have to make an enclosure for it, and wire it up for use in my system upstairs. I want to use a pot on the input, as using a CD player seems to be a bit hot for the tube.
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4krow
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Re: Korg florescent tube project
Reply #6 - 03/24/18 at 00:26:10
 
 Moving along here. I increased the voltage to 18 VDC and there is more amplification. I also increased the bias to 2.4 VDC and it will likely remain at that point. Lastly, I  included a 20k pot on the input, padded by 6db, and that also may stay the same, though I will try a couple of others. Soundwise, I am not 100% sure since at this time, I am using the shop system. I will be putting it into an enclosure soon enough, and then try it out in the big system. More later.
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4krow
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Re: Korg florescent tube project
Reply #7 - 03/24/18 at 21:48:24
 
Got this mounted in a small enclosure. Using 2-9 volt batteries for power. Will be testing in the big system soon.

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Lonely Raven
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Re: Korg florescent tube project
Reply #8 - 03/28/18 at 19:42:44
 

It looks perfectly setup for your application! Nice! I was expecting more of a hodge podge, but they designed it to be easily implemented.

I look forward to seeing what you think.
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4krow
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Re: Korg florescent tube project
Reply #9 - 03/31/18 at 18:19:24
 
Last night, I used the Korg unit in my big system. In short, I am impressed by certain aspects of the sound. First off, it has about 14db of gain at 18 volts, so I am using a volume control for the input. The net effect is in the bass. Much fuller than without the unit in place. The midrange isn't as forward, but the price paid is, yes, in the presence of the performance. Treble comes out a bit soft, but not unusually so. In fact, I have to factor in my hearing and say that others may find it to be spot on.
I have ordered another kit, so that I may try it in other systems, without taking it in and out for all moves. i like using the two 9 volt batteries, but will try a wall wart affair later on.
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4krow
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Re: Korg florescent tube project
Reply #10 - 04/05/18 at 23:06:09
 
May have a new 'nest' for the Korg project. It is sounding pretty good, and needs a bit more room.
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4krow
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Re: Korg florescent tube project
Reply #11 - 04/07/18 at 00:50:10
 
Next step, getting the RCA jacks mounted.

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4krow
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Re: Korg florescent tube project
Reply #12 - 04/10/18 at 03:22:34
 
Ok, you waited long enough. She is ready to present. I will audition in my big system in the morning.
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4krow
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Re: Korg florescent tube project
Reply #13 - 04/10/18 at 03:24:58
 
A second shot is needed to show the RCA jacks, and the gain control. This allows the unit to be operated with sources that are a bit hotter than others.

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deucekazoo
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Re: Korg florescent tube project
Reply #14 - 04/10/18 at 16:03:37
 
That is cool as sh*t!  8-)

So what do you think of the sound?
Did you ever hear or make the headphone amp using that tube? Seems like that might be a project for me in the future.
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4krow
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Re: Korg florescent tube project
Reply #15 - 04/10/18 at 16:58:38
 
.........Thanks! Let me tell you, these kits are about as easy as it gets. That is due to the silk screening on the high quality boards, a ready made BOM from designer P.Millet (although you may be better served choosing your own choice of capacitors and some other parts), and a parts list that makes populating the board simple. The power supply can either be battery or wall wart. I chose 18 volt battery because it lowers the distortion a bit.
...............Now, on to the sound. To make sure that the input isn't over driven, I have installed a 50k pot. I adjust it so that I don't see the tubes flicker even a tiny bit. Kind of like a VU meter just up to the edge of zero. When this is all done, the sound is pretty damned good. I am sure that it all matters about source, music selection and system synergy, but at this price, get ready to be surprised.
.................The headphone amp is another project that I have taken on, and it is spec'd to run at 24 VDC. For now, I am using the supplied switching power supply. Again same thing applies as far as kit simplicity. Pete Millet has made this easy for us. This kit even has a step by step process. Anyway, I didn't build it that way. I just did my thing. The amp has additional features appreciated by the fact that no one wants a popping sound when the amp is turned on, and so a muting circuit is put into practice here. The sound? Well, here we go again, I really love it. Here is the 'BUT' about it though. I don't care for it with the ORI headphones, or the Hi-Fi Man phones. It is absolutely perfect for the Grado phones though. I almost gave up on them until I heard them through this amp.
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4krow
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Re: Korg florescent tube project
Reply #16 - 04/22/18 at 02:35:45
 
I have sent this unit off to a good customer of mine who is evaluating it. Yup, sometimes a second opinion is the right thing to do. Anyway, here is a version of the same project, but runs on an AC adapter. Ok, before you wince, the volume knob is a joke.
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4krow
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Re: Korg florescent tube project
Reply #17 - 04/22/18 at 02:37:01
 
Next.
Grin

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Re: Korg florescent tube project
Reply #18 - 09/19/18 at 01:24:52
 
I have heard these tend to be microphonic. Was the Nutube quiet?
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4krow
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Re: Korg florescent tube project
Reply #19 - 09/20/18 at 23:46:57
 
Actually, these are the most microphonic tubes that I have ever dealt with. Of course, in headphone use, that tends to be of little concern. This headphone amp has an output as a pre amp, so I tried it out. Let's just say that I am working with that issue, and trying to mechanically isolate the unit.
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