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Nobsound 6N8P+6P3P

Discussion in 'Tube Audio' started by circlefx, Mar 17, 2018.

  1. circlefx

    circlefx Member

    Messages:
    82
    Location:
    Brooksville ME
    Hi folks. I've seen a few threads about these NOBSOUND amps. I've got the kit, the parts look pretty quality, not high end, but should be good enough for me. I've got a technology club and a couple of students and I are going to put this together. I've taught them to read and follow a wiring diagram, and we've built a few kits, including a waveform generator, but this is next-level for us. I'm feeling pretty good about our progress, and the wiring diagram is ok, but worries me is that the 'instructions' are in Chinese and I have a feeling there's something in there that may be important that we may miss. Anyone who can point us at an English version of the directions for this kit would be our hero! Here's the link to where we bought it on Amazon https://www.amazon.com/gp/product/B01MA2XASK

    [​IMG]

    [​IMG]
     
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  2. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,135
    Location:
    Philly area
    Can't help you on the translation, but I was reading coincidentally about Chinese gear and they are frequently provided with 110V or 220V power transformer primaries, instead of 120VAC/240VAC respectively. This means that your output voltages many run high, and particularly your filament voltages. The latter can shorten the life of the tubes. I see in the last picture that the PT is 110V 50 Hz. Check yours in the kit. Also, if you don't have English instructions for the wiring, be sure to follow good practice for AC wiring (twisted pairs, switch wire parallel and close to chassis, keep away from signal wiring, etc). You can find guidance on line.

    Not sure what to do if you see high voltages in the PT output--bucking transformer maybe? Nice looking amp, though.
     
  3. Dandy

    Dandy Super Member

    Messages:
    4,508
    Location:
    North West, UK
    A bucking transformer would drop the voltage, but would not fit easily into that small chassis. If you like the sound, and your students plan to keep these amps, the next lesson could be 'replacing the power transformer with one with the right primary voltage'. Or if you are buying a lot, maybe Douk could replace all your PTs? Douk Audio seem to make some nice kits.
     
  4. thorpej

    thorpej AK Subscriber Subscriber

    Messages:
    1,657
    Location:
    San Francisco, CA
    ...but, of course, should check the transformer, first, rather than assuming right out the gate that it's wrong.
     
  5. IPADave

    IPADave Which one's Pink? Subscriber

    Messages:
    4,177
    Location:
    Massachusetts
    I can't help you with your issue, but kudos to you for exposing your students to hands on learning. :thumbsup:

    -Dave
     
  6. circlefx

    circlefx Member

    Messages:
    82
    Location:
    Brooksville ME
    I'm like a dog with a bone... I emailed the guy who sells these on Amazon, and it looks like someone in China took the time to do a DIY instruction PDF with a lot of good pictures which he sent me... but of course all the text was in Chinese again! SO, I took the time today and used Google Translate and copied/pasted like crazy to come up with this English version. Some of the photos still have Chinese text that I couldn't translate and that makes me a little nervous, but.. I'm a heck of a lot closer now than I was. I only hope that this document finds its way to other wannabe tube amp kit builders and is helpful. And thanks for the kudos Dave! I am always happiest as a teacher when I can do projects like this with my students, knowing it's going to be a great benefit to them down the road. I wish someone had done this with me in middle school!! :)
    https://drive.google.com/open?id=1_k47LjHySDs_LD-By1eDNZwIilLA-z4T
     
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  7. circlefx

    circlefx Member

    Messages:
    82
    Location:
    Brooksville ME
    RE the transformer... there is an additional document that came with the kit that shows correct wiring for 110/220. It looks as though it can do either/or.
     
  8. Dandy

    Dandy Super Member

    Messages:
    4,508
    Location:
    North West, UK
    Yes, it can do 110v. The issue is that most US line voltages today are higher than this; the nominal voltage is 120v. But as thorpej says, let's see, e.g. what the filament voltage measures.

    BTW, other users report other English translations on the web. Your students may track these down.
     
  9. circlefx

    circlefx Member

    Messages:
    82
    Location:
    Brooksville ME
    I wasn't able to track down the English version of the instructions, although I did see people referencing them, and I really looked! If anyone on AK has them, please share! Thanks!
     
  10. Lavane

    Lavane AK Subscriber Subscriber

    Messages:
    7,384
    Location:
    northern cal.
    You could add dropping resistors for the heaters, no? Thats my main gripe with these Chinese kits, those 110/230 power tranys. I have noticed higher heater voltage in a phono preamp I have. Easy fix, a 5 watt resistor for the signal tubes and a few more resistors for the rectifier. But you shouldn't have to drill holes and cut traces for something new.
     
  11. BrokenHill

    BrokenHill Well-Known Member

    Messages:
    761
    Location:
    Newhall Pass CA.
    I recently bought a Nobsound preamp from the same manufacturer from DoukAudio, when I
    checked the heater voltages I measured 6.6 volts and my AC voltage test at 118 volts so yes
    the transformers do run a little high on the heater voltages at the tube.

    Heater voltages do have some tolerance that are acceptable, if the tubes that your Nobsound
    Amp uses are expensive to replace then it might be worth getting the heater voltage spot on for
    tube longevity, in my Nobsound preamp it uses 12AX7 tubes and they are easy to come by so
    I am not concerned about the 6.6 heater voltage I have.

    That's a nice kit you got, enjoy.:thumbsup:
     
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  12. gusaudio

    gusaudio AK Subscriber Subscriber

    Messages:
    23
    Thinking of getting one of these for a father daughter project. If the voltages are going to run~14 percent high, we ought to be able to calculate a resistor value to lower the voltage, no?
     
  13. jake

    jake New Member

    Messages:
    30
    6n8p 6p3p.jpg
    I am following this thread since I also bought this kit just a few weeks ago. I am wondering though how the grounding should be best laid out so that humming can be avoided. Hope someone can help.
     
  14. Tubby Tube

    Tubby Tube New Member

    Messages:
    14
    Just bought this kit on ebay. Any more thoughts on the finished amp? Voltages? A CL90 might reduce them slightly? Hum?
     
  15. Tubby Tube

    Tubby Tube New Member

    Messages:
    14
    Bueller?
     
  16. gusaudio

    gusaudio AK Subscriber Subscriber

    Messages:
    23
    Well, halfway through building this and the attached document appears to be pretty worthless. The schematic does not appear to match the pictures, or the components provided. I was hoping to clean up the bad english and post it, but now I am stuck .

    first the kit does not come with the solder lugs pictured in the instructions, so I had to fab something, annoying, but if radio shack were still with us...

    second on the page marked 'teaching amplifier circuit', where there are yellow green and red parts of the schematic circled, there is no 50uF 100v cap supplied, there is no 100uF 50v cap supplied, there is no .22 uF 250v cap supplied. There is a a pair of large tantalum caps 474 400 volt, should be .47 uF, right, shown in the pictures, circled in green, not on the schematic in the area circled in green

    irritating,

    even in China one needs accurate instructions

    am I to just guess at what the values are?

    The pictures above match more or less what I have in the kit but the schematics are incorrect, so I am
     

     

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  17. gusaudio

    gusaudio AK Subscriber Subscriber

    Messages:
    23
    finally the website is back responding

    in the linked pdf, the cap in the circuit from pin 8 of the 6p3p is called 50uF 100 volt, in the posted circuit above [post 13] it shows as a 680uF 25V, so I guess that must be correct[?!]

    in the linked pdf on the schematic there is a .22uF 250 volt from pin 4 of the 6n8p, in the pictures it is the big tantalum. In post 13 it is wired completely differently

    in the linked pdf the schematic shows a 100uF 50v volt cap on pin 3 of the 6n8p parallel with a 2k resistor, I cannot define a value in the pics. in the schematic above it is wired very differently
     
  18. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

    Messages:
    2,721
    Location:
    Terra, 21st century CE
    Really, one would hope that people would have read all the warnings about these kits from China. They should be prepared to accept the poor quality control on parts list? I am guessing that all the audio forums have these stories of some missing parts or the Power trans being incorrect. And spending extra money, time, and work arounds, to get these amps working or functioning.
    You do realize that the factories are probably run by the government and so they can just offer these items with no concern for customer service.
     
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  19. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    52,767
    Just a thought. I would think that the "best" thing to do might be to get (or work up) a good design for the basic components and use what you can to build a good amplifier. You've got transformers (PT and OPTs), sockets, a chassis, and basic hardware. Passive parts are generally cheap for "standard goods". One would not even be tied to using the driver and output tubes used in the "kit".

    As a person who is terrible with prepping a chassis, to me that wouldn't be a bad way to salvage value out of a "kit" supplied in the condition described.

    EDIT: Even if the specifications of the PT and OPTs aren't known, it's fairly straightforward to work out what you've got with a DMM and a little ingenuity (and/or a little googling or searching at sites like www.audioasylum.com or www.diyaudio.com)
     
  20. Tubby Tube

    Tubby Tube New Member

    Messages:
    14
    Incredibly helpful!
     

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