Hi Ben Ma
Many thanks for the comprehensive information.
I measured my Nutube in the working right channel. Zenerdiode was 9,34 V with only one tube drawing current. As I remember it was lower when both heaters were drawing current. Filament Voltage was spot on 0,7 V. Assuming the heater wire on the left side is not totally different from the right side I have no rational explanation for the failure. There is even a picture of a glowing heater wire with 25 mA on it. Glowing but intact.
I found about nine to ten reports in this and in another thread about broken Nutubes in a B1 (may be there are even more reports).
In one case the side was not specified in all other cases the wire in left side broke. I did not find any case were the right wire broke.
As both heaters get the power from the same Zenerdiode via 1% 475 Ohms resistors to me it seems there is a QA /QC problem with the left channel of the Nutube. It is definitly not a function of the circuit or stupid Diyers.
Many thanks for the comprehensive information.
I measured my Nutube in the working right channel. Zenerdiode was 9,34 V with only one tube drawing current. As I remember it was lower when both heaters were drawing current. Filament Voltage was spot on 0,7 V. Assuming the heater wire on the left side is not totally different from the right side I have no rational explanation for the failure. There is even a picture of a glowing heater wire with 25 mA on it. Glowing but intact.
I found about nine to ten reports in this and in another thread about broken Nutubes in a B1 (may be there are even more reports).
In one case the side was not specified in all other cases the wire in left side broke. I did not find any case were the right wire broke.
As both heaters get the power from the same Zenerdiode via 1% 475 Ohms resistors to me it seems there is a QA /QC problem with the left channel of the Nutube. It is definitly not a function of the circuit or stupid Diyers.
Alright, well I'm doing one more pass at this (no pun intended, sorry). I ordered another nutube, and the antivibration kit. I have been running a passive preamp, which is not bad at all, but I do miss the sound of the B1, and I like to have the buffer option if I want it. Are there any lessons learned here about how we run the preamp? Maybe any differences in leaving it on all the time vs. turning on and off? Any environmental factors that could be at play besides just factory QC? As always, thank you to everyone who responds and helps with these posts.
Thanks Papa. I'll let you know how it goes. Much appreciated.Goes out on Monday.
I'm not a fan of leaving audio equipment ON all the time, I even added an On / Off switch to the remote power supply for my Threshold FET 10HL preamp and Threshold FET 10Pe phono preamplifier.
I built the B1 Korg before the kit was available, I lined the inside of the enclosure with automotive sound deadening, suspended the PCB using rubber mounts and placed foam under the Nutube with a couple drops of hot glue before I soldered the tube leads. I did the same to the Balanced B1 Korg I also built, which has two Nutubes in it. 5+ years later, still works fine. Never had a problem with microphonics or the high pitch noise others have had.
If you look at how fine the wire is for the filaments, let alone the the connection of that wire, I would think vibration control would be VERY important. Then again, I'm no Electrical Engineer, I am however a Mechanical Engineer with 42 years of QC and failure analysis experience with three Automotive Manufacturers.
My opinion for what it's worth.
elwood, that's really helpful. I will try something similar. The PCB was already mounted on thick rubber washers, I will add the anti-vibration mount, as well as sound deadening for the chassis where I can. Though it might be easier to line the outside of the box. I guess it could be that you just have to be extremely gentle with this item. It makes you appreciate what kind of beating a 12ax7 can put up with, and probably why they were in basically everything for 50 years.
Vibration for the tube really should better pretty soft. A hard rubber or even soft silicone rubber might be good for a base on which stack foam or something like that. Then you have those leads that are soldered right to the circuit board. I found that Pete Millett's isolation and damping product takes most every chance for vibration to enter the tube.
There is no need to fully line the inside, ignore the vertical surfaces, the horizontal surfaces only need 50% coverage MAX. I use the NAPA equivalent of Dura-Max/Liner, no more than 25% more than the PCB area top and bottom panels. Your just adding weight to the panels to change the frequency they vibrate at.
The rubber mounts for the PCB are from a hobby shop for either helicopter or drone motor mounts (3mm threaded).
I do think securing the Nutube with foam BEFORE you solder the pins makes the biggest difference. I used a small plastic clamp to hold the Nutube to the foam when I solder the pins. (Make sure you use something like an eraser or more foam on top of the Nutube when using the plastic clamp. Think sandwich)
I've been following this thread since almost the beginning, my compliments to all the members who have posted good photos of the filament wire failures. If my memory is correct, I've only seen one incident where the filament wire had a blob of solder on the end. This I believe was caused by a poor solder connection by KORG's supplier, this should/would be considered a failure which the seller should warranty. This would mean DIYAudio Store would have to step up, the chance of them collecting from KORG is slim to none.
All the other failures I've seen from members, have the wire disconnected before the solder point. Since there is no indicator of excessive heat from current flowing through the wire, you would expect to see a slight discoloration of the wire at the solder point/ broken end. This leads to vibration as the root failure cause, every time the wire vibrates, small cracks occur inside the wire at the solder connection point (the weakest link). It continues to vibrate and more and bigger cracks occur inside the wire until a disconnection failure.
What I'm very curious about, is if this product is used by KORG for use by live concert performers using their equipment, how does KORG handle the vibrations of their equipment by concert sound levels/vibrations?
I forget how many of the Korg tubes that I have used over the years, quite a few, I'm sure of that. Maybe 3 had issues that weren't solvable, but as it turns out, only one had a broken filament. The two others? I really couldn't tell you. When I replaced them all was well.
For the sake of numbers, I bet that I have built more than a dozen units, probably more. I just don't keep track.
For the sake of numbers, I bet that I have built more than a dozen units, probably more. I just don't keep track.
I received the Nutube thanks Papa a couple of weeks ago. Thank you again for your generosity. I took the opportunity before it arrived to replace the standard caps with the Cornell Dubilier film caps recommended by ClaudeG. I've probably put about 100 hours in and am really enjoying the amp. Very punchy with little better high end detail compared to my vintage Sansui. Thanks again!Goes out on Monday.
Hi Gwam, Hi ClaudeG
I have read your comments with great interest. I am thinking to take the risk to buy a new Nutube. Can you please tell me which Cornell Dubillier caps are recommended?
And which vintage Sansui did you compare the Nutube to? It would be helpful to get an idea were to put the nutube soundwise. At the moment I am using a passive preamp which sounds very clean. With my Nutube I got more midrange at the expense of some noise.
I have read your comments with great interest. I am thinking to take the risk to buy a new Nutube. Can you please tell me which Cornell Dubillier caps are recommended?
And which vintage Sansui did you compare the Nutube to? It would be helpful to get an idea were to put the nutube soundwise. At the moment I am using a passive preamp which sounds very clean. With my Nutube I got more midrange at the expense of some noise.
Hallo,
I went for CD940 caps.
In order, from input to output, the DC decoupling caps I used were:
5984-940C6P22K-F
598-940C6W1K-F
598-940C6W3P3K-F
The 3rd one can be much smaller, depending on the following device's input impedance. I went safe with this big cap as I intented to use this board also for test purposes with various units, enabling 5Hz cut off frequency into 10k, which in practice is quite a worst case already. Obviously having the next stage at 20k or 50k or even 100k instead of 10k input impedance reduces this 3rd cap "capacity value need" by the same factor. Same if your speakers can't handle 20Hz...
I do not own a Sansui, so guess that question is not for me. However, I use the B1K in a special pre amp of my own, the one I use every day and that enables quite a lot of things, such as volume control either by resistor network, or by potentiometer, or none. It enables also direct comparisons between passive preamp (I use that one more frequently for simplicity), B1K tube preamp, or any other preamp of my choice I want loop in.
All these volume control and preamp options can be crossed, without any audible loss, mainly for comparison purposes, at the end in my system while simply listening to music I use the 2 best options depending on music.
Passive preamp, used with my "strong sources", gives the most puristic approach and without any real dynamic loss due to the sources being able to drive anything including for some at levels up to 10V RMS, whereas my gain chain enables me to drive my LS at high levels with 1V already. B1K, as I use it, is biased 'less syrupy' and with my tweaks. It is really transparent, dynamic and without any low bass or high treble attenuation, quite close to passive or good active. That's what I wanted in mys sytem. It is quite neutral but adds still some euphonic obviously, which is the intend anyway. Means in my set up a less acurate than passive re soundstage and location, accuracy and also timbres. BUT it gives such a charisma to music, so much flesh ans sensuality... Let's say at mine it is passive for tests, passive for classic & Co, but depending on my mood and with a glass of wine it is defo B1K for Jazz, Golspel, Soul, Blues
I am glad I have both options at the flick of a switch, and while both are still quite neutral and close from a sonic perspective, they are still different (and accurate enough) enough to justify their existence in my main system... while not justifying an other preamp (air is thin inbetween these 2 options really) as long as they work.
Last but not least, I also use the B1K to drive my HP. Note it is a high impedance (650R) studio device with high efficiency, so no problem here, especialy given I went for a mod at the B1K board as to of course extract sound before the last output cap (which wouldn't have been suited to HPs obviously).
I hopoe this helps
MFG
Claude
I went for CD940 caps.
In order, from input to output, the DC decoupling caps I used were:
5984-940C6P22K-F
598-940C6W1K-F
598-940C6W3P3K-F
The 3rd one can be much smaller, depending on the following device's input impedance. I went safe with this big cap as I intented to use this board also for test purposes with various units, enabling 5Hz cut off frequency into 10k, which in practice is quite a worst case already. Obviously having the next stage at 20k or 50k or even 100k instead of 10k input impedance reduces this 3rd cap "capacity value need" by the same factor. Same if your speakers can't handle 20Hz...
I do not own a Sansui, so guess that question is not for me. However, I use the B1K in a special pre amp of my own, the one I use every day and that enables quite a lot of things, such as volume control either by resistor network, or by potentiometer, or none. It enables also direct comparisons between passive preamp (I use that one more frequently for simplicity), B1K tube preamp, or any other preamp of my choice I want loop in.
All these volume control and preamp options can be crossed, without any audible loss, mainly for comparison purposes, at the end in my system while simply listening to music I use the 2 best options depending on music.
Passive preamp, used with my "strong sources", gives the most puristic approach and without any real dynamic loss due to the sources being able to drive anything including for some at levels up to 10V RMS, whereas my gain chain enables me to drive my LS at high levels with 1V already. B1K, as I use it, is biased 'less syrupy' and with my tweaks. It is really transparent, dynamic and without any low bass or high treble attenuation, quite close to passive or good active. That's what I wanted in mys sytem. It is quite neutral but adds still some euphonic obviously, which is the intend anyway. Means in my set up a less acurate than passive re soundstage and location, accuracy and also timbres. BUT it gives such a charisma to music, so much flesh ans sensuality... Let's say at mine it is passive for tests, passive for classic & Co, but depending on my mood and with a glass of wine it is defo B1K for Jazz, Golspel, Soul, Blues
I am glad I have both options at the flick of a switch, and while both are still quite neutral and close from a sonic perspective, they are still different (and accurate enough) enough to justify their existence in my main system... while not justifying an other preamp (air is thin inbetween these 2 options really) as long as they work.
Last but not least, I also use the B1K to drive my HP. Note it is a high impedance (650R) studio device with high efficiency, so no problem here, especialy given I went for a mod at the B1K board as to of course extract sound before the last output cap (which wouldn't have been suited to HPs obviously).
I hopoe this helps
MFG
Claude
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Nice response from Claude. I have a modest setup, and my vintage preamp is a Sansui AU-317 which was recapped last year. Let me have a listen on the weekend and give you some comparison feedback. The B1K is my first build so there was some emotional involvement when everything was working and sounding good! It will be interesting to have a listen back to back with the Sansui now that some weeks have passed. I'll keep you posted.
BTW I used exact same caps as Claude
BTW I used exact same caps as Claude
Hi Claude
many thanks for the type of the caps. I wil l order them to try them out. At the moment I use a Khozmo passive attenuator (shunt with naked Vishay resistor) followed by a Yamaha MX-2 ad vintage Altec Santana 879a. Very transparent and dynamic. With the Nutube I had the impression of more flesh in the midrange. So I am thinking about building a tube buffer or invest into a new nutube.
many thanks for the type of the caps. I wil l order them to try them out. At the moment I use a Khozmo passive attenuator (shunt with naked Vishay resistor) followed by a Yamaha MX-2 ad vintage Altec Santana 879a. Very transparent and dynamic. With the Nutube I had the impression of more flesh in the midrange. So I am thinking about building a tube buffer or invest into a new nutube.