Yaqin MC13s issues

Discussion in 'Audio Hardware' started by RonL945, Jul 11, 2019.

  1. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    I just received the Yaqin MC13. It has one AX7 tube missing out of the 4 preamp tubes. I have ordered that.
    I did run it without it thinking that it will at least run one channel. Connected a TT with built in preamp to Mc13. But ran into issues. First was that there was huge music volume out of one speaker (b&w bookshelf pair). Unbearable kind. And volume was still at ‘zero’. So I immediately switched it off. Then without removing the TT input from Aux1 in MC13, I switched the Input at front of MC to AuX2. And Aux2 doesn’t actually have any input connected. Note that the TT is still connected to AUX1. Started the TT and then I hear music from the speaker at very low volume. Still the volume knob makes no difference to volume. Note that increasing volume when input 1 Aux1 was selected does increase the volume a bit from what was too loud for the speaker to handle and it almost destroys my speakers.
    Any idea what is happening to my amplifier and why is it behaving this way? Is the missing 12AX7 causing this problem? I do want to upgrade this as soon as we get this working.
    Thanks for response in advance. I do want to like this amp!!
     
  2. chipcalzada

    chipcalzada Well-Known Member

    I don't think you should ever turn a tube amp on with a missing tube (whether preamp or power), I've certainly never done that. My first tube amp was a Yaqin and it was built like a tank so hopefully, when the new preamp tube arrives it will function properly. Did you buy this brand new? What is the explanation for the missing tube?
     
  3. BIGGER Dave

    BIGGER Dave Forum Resident

    Is this the correct tube complement?

    (4) EL34
    (2) 12AX7/ecc83
    (2) 12AU7/ecc82

    If so, sounds to me you have an 12AX7/ecc83 in a socket designed to take a 12AU7/ecc82. The 12AX7 has a gain factor of five times that of a 12AU7 (100 vs 20). I would double check that you didn’t accidentally plug a 12AX7 in a 12AU7 socket.

    (From looking at some pics on the Internet, it appears the 12AU7 tubes are the two in the middle, and the 12AX7 are on the far left and far right. But if yours is different, go by what’s marked on your amp).
     
    Last edited: Jul 12, 2019 at 1:46 AM
  4. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    Thanks for the response. I did buy it brand new. Missing in the package itself. Will update once I get the tube in.
     
  5. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    The tubes are in the marked sockets and you are right about the location of the two preamp tubes. I have ordered a TungSol 12AX7. Should I change the other 12AX7 also to a TungSol? I will update when I get the tube fixed. Hopefully today.
     
  6. Paopawdecarabao

    Paopawdecarabao Well-Known Member

    Location:
    Los Angeles
    I do have a MC13s but have never tried to power it with a missing tube as well. They say that you should not also power a tube amp without speakers connected.

    Hopefully you sort out your problem and it is a great amp. I just recently upgraded my caps to a russian pio caps and it sounds great with Gold Lions Kt 77 and 12ax7.

    I just found a good deal on a CM ii and put that on my main system but I will keep my MC13s for a while then sell it.
     
  7. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    I just checked again. And guess what! You are a 100% correct. The tube missing is not 12AX7 but 12AU7 and one of the 12AX7 was put in the 12AU7 slot and hence that loud noise and the feedback to all inputs. Your explanation of what the two tubes were got me thinking and I put on my reading glasses and checked the numbers on the tubes again and voila I was shown the true numbers! You are genius! Thanks a ton. All problems solved. Now just need to go and get the 12AU7. And of course keep the 12AX7 for rolling. The amp sounds great! And yes it’s built like a tank.
     
  8. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    Update: I got the tubes in correct sockets and got the missing tube also. Still one side speaker has full volume and other speaker is controlled by the volume knob. So problem persists. Yesterday when I had only one side working , it was working fine. Basically the same side where they put wrong tube is the one having issues of full volume and no control from the volume knob. So I will be returning the amp as I don’t know how to fix it. Did my best. Any ideas what could be wrong in this amp? I did like what came out from it at almost full volume, but it’s loud so can’t be listening at that volume all the time!
     
  9. RonL945

    RonL945 New Member Thread Starter

    Location:
    Texas
    By the way I put Gold Lion tubes for 12AU7. Didn’t notice much difference between them and the one originally sent with the amp. Of course that was only one single tube they sent! Also tried TungSol 12AX7. There also I didn’t notice any difference in the sound quality or the tone. Also to my surprise the sound from my Naim Superuniti is also not lit different. In fact I like it as much as the sound from this MC13 tube amp from Yaqin. Just to let you guys know. I had McIntosh system in same room with B&W 803s and IMO Superuniti is similar in sound quality and tone. Whatever that means! I was playing the Marantz 15TT (clearaudio stuff). So I am guessing I am an ok audiophile for listening experience of over 15 years. I am sad that Yaqin did not workout. Really sad.
     
  10. chipcalzada

    chipcalzada Well-Known Member

    You probably blew a capacitor when you turned it on with a missing tube.
     
  11. fmfxray373

    fmfxray373 Forum Resident

    Location:
    san diego
    Actually nothing should happen to the amp or pre-amp if you run it without a tube in the socket while troubleshooting. You won't get sound but that is about it.
     
  12. chipcalzada

    chipcalzada Well-Known Member

    I didn't know that. Perhaps the amp was defective, I still don't understand how the seller could have shipped it with a missing tube.
     

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