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Korg Nutube - sub-sub-miniture twin triode
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Author:  wdecho [ 28 Dec 2017, 15:28 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

I built the Pete Millett designed preamplifier using his board with the Nutube for $55 on Ebay. Simple easy build and it does work and sound really good with a SS amplifier. I had to make one correction to stop oscillation by installing a 1K grid stopping resistor otherwise it would oscillate when the pot was fully off. What peaked my interest with the Nutube was Nelson Pass' talk at the Burning Amp Festival 2017 in November. His circuit varies some from Pete's in that he installed a constant current source for the tubes. Worthy project for anyone interested. Scoped good.

https://www.ebay.com/itm/DIY-PCB-plus-T ... 2749.l2649

Possibly some boards to be made using NP design in the future. Anyone interested in NP talk can find it on youtube BAF 2017 with detailed info on the tube with charts.

https://www.youtube.com/watch?v=sCqAvYDpbKQ

Author:  mwhouston [ 28 Dec 2017, 17:59 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

Good to know. Mines on hold while s finish a Hiraga 8W Class A.

Author:  Geek [ 29 Dec 2017, 02:16 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

Good advice, thanks!

I would not have thought this an issue in a tube of such low Gm. Will keep in mind :D

Author:  wdecho [ 29 Dec 2017, 07:04 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

Geek wrote:
Good advice, thanks!

I would not have thought this an issue in a tube of such low Gm. Will keep in mind :D


I spoke to Pete about the issue after I installed the grid stoppers and he had noticed the same problem on some builds but his fix was a different transistor until I pointed out that grid stopper resistor would solve the problem. Nelson Pass always uses gate stopper resistors in all his production offerings. As he said there is always one amplifier during production that will oscillate if one is not installed. One may try building without a grid stopper resistor because in my view less parts are best and install the gate stopper if you encounter oscillation.

I have not jumped through the hoops to install pictures here but one can find my build on the Klipsch forum.

https://community.klipsch.com/index.php ... utube-6p1/

I strongly suggest that one watch the NP video at the BAF 2017. Even veterans may learn something. People fly in from all over the world to hear Nelson and find out what new project he is working on.

Author:  scafas [ 24 Jan 2018, 10:13 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

in the time that I wait for the korg 6p1 to arrive, I have produced a printed circuit suitable as a line and headphone preamp.
this is my circuit:

Author:  Geek [ 24 Jan 2018, 14:54 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

Nice work, Scafas! :up:

Wdecho - yes, I use grid/gate stoppers as a matter of course. It's inexpensive insurance.

What Nelson will tell you too as he did me is use a carbon comp here - anything else can cause oscillations at UHF, not so much of what they're made of (though metal by nature are little inductors), but how they are made. Even the carbon film are spiral because of laser trimming. That spiral can insert *just* enough nH inductance to make a 400+ MHz oscillator, especially with RF types, like 12AT7, ECC88, etc.

12AX7 by thier construction are usually immune.

Cheers!

Author:  scafas [ 10 Feb 2018, 06:15 ]
Post subject:  Re: Korg Nutube - sub-sub-miniture twin triode

this is the final circuit , i made it with two output mode : line and headphone amp
the ne5534 is an example but it work with my headphone.

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