Aiqin/Oldchen Tube Amps

Discussion in 'Tube Audio' started by bubba42, Jun 9, 2016.

  1. datafone

    datafone Super Member

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    Bris', Australia
    Deleted

    Never mind.
     
    Last edited: Oct 23, 2017

     

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  2. Morten T

    Morten T New Member

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    Hi Poultrygeist
    I totally agree with you, ewer since I saw Scott Faller´s OB´s in a thread at Audiocirkle I have wanted to do something similar.
    http://www.audiocircle.com/index.php?topic=119928.0
    As it is very difficult to get hold of the propper Altec 416A drivers, I could maybe do with something like this.
    http://jazzman-esl-page.blogspot.dk/2011/01/ripole-subs-are-underway.html

    Steven
    I hope you can view this.
    The original question was: what is this 10 Ohm resistor doing between ground and leg 2 on the EL34.
    IMG_1953 tekst_resize.jpg
     
  3. datafone

    datafone Super Member

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    Pin 1 is G3 is it not?

    Maybe that resistor is from pin 2 (filament) to ground?

    Difficult to see in that pic.

    Anyway, I wouldn't connect anode to pin 4 (G2) with just a wire link, yeah it will work but I understand It's better to use a resistor of between 100ohms - 1kohms, this is to prevent parasitic oscillations.
     
  4. Morten T

    Morten T New Member

    Messages:
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    Location:
    Denmark
    Yes, Pin 1 is G3.
    And yes, I can see now the 10 ohm resistor is from filament to ground, but why?
    And the Triode mode connection, I have seen the use of a 100 ohm resistor in the Boyuu EL34 A9 Tube Amp, which is almost similar, I will try that.

    There is quite a lot of difference from the original schematic´s to my amp.
    I have made a new drawing of the schematic´s of my amp, maybe som of you guys will take a look and tell me your opinion.

    This is the original
    Oldchen EL34 tube amplifie Single-ended Class A.jpg

    This is my amp
    OldChen EL34 Class A SE Triode mode.jpg
     
    Last edited: Oct 24, 2017
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  5. datafone

    datafone Super Member

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    2,303
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    Attachments aren't showing for me.

    I think that resistor to ground is not uncommon, but I can't say why as I'm a novice with circuit stuff especially when it differs from my own

    I used a 2 watt 520ohm resistor when my circuit was being done, as I understand it there will be a subtle difference depending on the value. In a lot of literature I have seen it advised to use 1k. I think it is at the discretion of the designer. I have seen used half watt and 1watt and 2watts, and anything in that 100ohms to 1k range.

    Edit: found this with a google search that might be of interest http://www.audiodesignguide.com/New2A3/ETF06TS.pdf
     
    Last edited: Oct 24, 2017
  6. datafone

    datafone Super Member

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    2,303
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    Yeah, quite different, but as of an opinion....... as a novice I rather leave that to the more knowledgeable with tube circuits.

    Heh, the popular 6p3se tetrode :cool:
     

     

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  7. FatDonny

    FatDonny New Member

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    Just ordered mine! WOOT! Thank you all for the information. My first tube amp!
     
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  8. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
    Bris', Australia
    Just noticed something.
    The first filter cap after your rectifier is 100uf? I would check with a tube guru to make sure that is not too high a value for the first cap after the rectifier tube in use.

    Edit: I could be wrong of course, but I think that first cap should be around 40uf, so the original 47uf value might have been more suitable.
     
    Last edited: Oct 25, 2017
  9. Morten T

    Morten T New Member

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    Location:
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    Yes it is 100uf, I am confused too
     
  10. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
    Bris', Australia
    Last edited: Oct 25, 2017
  11. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
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    OK, looking at someone on diyaudio with the same amp, he had 100uf too and said It's way too high and replaced with 33uf cap.
    http://www.diyaudio.com/forums/tubes-valves/298496-el34-single-class-tube-amplifier-kit.html

    It makes sense seeing as the 5U4G is a direct replacement and It's data sheet states 40uf.
    It's in this Sylvania data sheet for the 5U4G, see where it says 'filter input capacitor'
    http://www.r-type.org/pdfs/5u4g.pdf
     
    Last edited: Oct 25, 2017

     

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  12. datafone

    datafone Super Member

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    A lot of different values there and the operating points will be very different than the original schematic, I noticed also that the amount of GNFB will be much greater with those lower value resistors, why they have done this I don't know......more is not always better, unless they increased it for stability reasons, assuming that they know what they are doing.
     
  13. Morten T

    Morten T New Member

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    Location:
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    Hi Datafone
    I just realized, my amp came with a 5U4G
     
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  14. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
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    Hi, Morton

    That's a bonus possibly if the reliability issues of the Chinese and Russian rectifiers are correct.

    I'd be replacing the 100uf/450v cap with a 42uf/450v Panasonic or other quality cap, preferably from a reliable source. Something around 40uf anyway, and no lower in voltage.

    That's about the limit of what I can advise to someone.
     
    Last edited: Oct 31, 2017
  15. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
    Bris', Australia
    @Morten T

    Actually, If it were me I would use a Solon PB series film cap if it can fit OK, 36uf / 400VDC, PB Series, 40mm D x 53mm L.

    They are around 12usd each.

    As you measured 305vdc there 400vdc is OK. That's if I'm reading the schematic correct, I have no experience with tube rectification.
    Edit: I'm not a fan of these caps in the signal path but they work well in power supply duties. I used these feeding the small signal tubes in my custom EL34 amp.

    Edit: just to mention that I found out how well those Solon caps work in the PS was from someone else, as is everything I know of what i do for the most part.
     
    Last edited: Nov 1, 2017
  16. datafone

    datafone Super Member

    Messages:
    2,303
    Location:
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    Is the GNFB needed once the EL34's are triode strapped?

    My understanding is that It's main purpose is for the UL design, when the tubes are run as pseudo triodes this crates local NFB so the global is redundant.

    Be nice if someone else could chime in on this.
     

     

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  17. FatDonny

    FatDonny New Member

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    Just got mine today. Tubes are 2 EL34-B 2 6H9C and 1 5U4G.

    I see good reviews on the 6H9C. Anybody know the difference from the Psvane EL34 and EL34-B?
     
  18. Matthijs89

    Matthijs89 New Member

    Messages:
    2
    Hi!

    So I came across this amp on the internet and, apart from looking really nice, I am glad it preforms good as well. I have an (amateur) quetion. If I want to connect my turntable to the amp, would I be needing a phono pre-amp as well, r can it just go directly into the amp?

    Thanks in advance!
     
  19. Poultrygeist

    Poultrygeist Lunatic Member

    You will need a phono preamp and many like the U-turn or Schiit Mani are quite good and affordable.
     
  20. Matthijs89

    Matthijs89 New Member

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    Thanks for the quck reply! :)
     

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