Tube amp problem: loud pops and thumps noise!

Discussion in 'Audio Hardware' started by DoF, Sep 11, 2019.

  1. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    Hi, I have Yaqin MS-30L tube amp. It's been working fine until last few days. When I turn on the amp, after 30 secs later, it starts to produce some sort of popping and thumping like a machine gun, and after another 20 secs it stops.

    Hear the recording: Vocaroo | Voice message

    During the playback there are pops and thumps from time to time. The problem occured two days ago. I've never experienced this before. I thought it's the additional gear, but second time it happened when all was off, the preamp, TT, and subwoofer.

    I've noticed that when the amp is on and no music is playing, very rarely, here and there a pop happens.

    Should I change EL34B tubes? I changed preamp 6J1 tubes lately because one has died...

    Thanks, Adam
     
    Last edited: Sep 11, 2019
  2. Rick Bartlett

    Rick Bartlett Forum Resident

    I can't really help, but that is the sound some refer to as 'motor boating'.
    Could be a number of things including tubes, filter capacitors or a bad transformer.
    If you replace the tubes and it's still happening, you know there's an internal problem somewhere...
     
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  3. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    Thank you.
     
  4. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
  5. Rick Bartlett

    Rick Bartlett Forum Resident

    Hmmmm, interesting.....
    That sounds a lot different to the first sound.
    Silly question, have you cleaned the tube sockets with contact cleaner?
    Also has the possibility of being some cold solder joints somewhere.....
    When it makes that noise, does the noise minimize or go away by tapping around on the amp?
     
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  6. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    I've cleaned them with vacuum cleaner, both sockets and pins. I did not clean preamp tubes though.

    I don't know, outside it looks intact

    No, now the noise is constant, tapping around does not help.
     
  7. Rick Bartlett

    Rick Bartlett Forum Resident

    Always good to have some good spray electrical contact cleaner.
    'De-oxit' is a favorite of many, but it is expensive, but there are some cheaper versions
    which are effective as well.
    These direct surfaces oxidize over time, leaving not particularly great contacts on the
    pins and/or the tube sockets.
    Spray the tube sockets, and the tube pins with it.
    Some use a small wire brush to gently run over the tube pins, then gently wiggle in and out
    with the tube into the tube sockets a few times.
    It may not be the source problem, but it's a cheap way to eliminate if that is a possibility.
     
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  8. Have you measured the mains voltage?
    A large voltage sag can cause motor boating too.
     
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  9. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    I can try. I have 'De-oxit', but I am afraid to spray it into the sockets, won't that cause a short circuit? Should I dry the spray in the sockets?
     
  10. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    No, never.
     
  11. Rick Bartlett

    Rick Bartlett Forum Resident

    You only need a little bit, a quick squirt. It will evaporate ( a few minutes? some say overnight?) so I'm reading, but it will be still
    coated because it is also a lubricant, so it will seem a bit wet.
    I've always gone with a few minutes myself, but I use the solution lightly, and massage the pins in the sockets
    in and out, also allowing some breathing time for the solution to dry.
    Of course, you will need to be confident enough to do it, I don't want to give bad advice either....
    :rolleyes:
     
  12. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    i'll do it, also with those small tubes
     
  13. The only time I have heard motor boating was at an audio meet up.
    In the UK we have AC voltage of around about 230VAC +10% /-6% (ie it's normally around 240VAC), and when we heard the motor boating start someone who had brought his DMM measured the voltage and found it to be 216VAC.

    If you're not comfortable measuring things don't do it.
     
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  14. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    How to do it? PS. there are some bias holes for adjustment I guess.
     
  15. Rick Bartlett

    Rick Bartlett Forum Resident

    As people will say, a little bit of De-Oxit goes a long way, you don't need much.
    A less than half a second quirt into the tube sockets, then massage the tubes in and out a few times.
    The tube pins should appear 'shiny' anyway, but if they are not, that's where a wire brush will come in handy.
    That condition is normally found in vintage amps though, where they have sat for 50 years in a garage somewhere
    to the conditions of weather.
    Measuring AC is dangerous! You will need a multi-meter set to the right settings, or it could be fatal
    to the device or yourself!
    Most certainly research and watch some youtube video's before attempting that.
     
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  16. Rick Bartlett

    Rick Bartlett Forum Resident

    I doubt the Bias has anything to do with your problems, unless you know how to calibrate the Bias procedure for the tubes,
    I'd leave those pots alone.
     
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  17. DoF

    DoF Less is more... Thread Starter

    Location:
    Poland
    What's your best guess?
     
  18. Is the mains cable captive or IEC?
    If it's IEC pull the lead out of the amp and insert the probes.
    As has been pointed out, you need to have the settings correct on the meter, and if you do things wrong there is a danger of death.

    If you're not sure of what you're doing don't do it.
    The same with the amp - if you don't know what you're doing take it to someone who does.
     
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  19. Rick Bartlett

    Rick Bartlett Forum Resident

    Well, I'm no expert, just trying to diagnose some simple things that it could be....

    What concerns me, if the tubes are all fairly new, and/or in good condition, and if the sockets and pins
    are cleaned, it could be another problem further within.
    I go back then to 'cold' solder joints as a possibility.
    As you said before 'I don't know, outside it looks intact'.
    That means you have to get inside and open the amp and inspect for 'cold' solder joints.
    If there are any, then you have to pretty equipped with a soldering iron too and know exactly
    what to look for to make any corrections.
     
  20. Rick Bartlett

    Rick Bartlett Forum Resident

    Yes!
    Don't go probing around into a tube amp if your not sure what your doing.
    There are some even higher voltages lying within, like 500 Volts potentially! even with the amp turned off and unplugged.
    Very dangerous territory if we are discussing these issues at this point.
     
  21. Jeez yeah!
    Charged capacitor discharge from getting your fingers in the wrong place is going to hurt one helluva lot!
     
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  22. Rick Bartlett

    Rick Bartlett Forum Resident

    Hell yeah!
    Gosh, when I was a kid, I even removed a fuse from an amplifier once with it turned off, it grabbed me for a micro
    second then pushed me off the amp.
    Heart was racing like crazy.
    Lesson: Never disrespect electricity and it's stored potential!
     
  23. I think a good starting place for learning about electrics is to learn this.

    [​IMG]
     
  24. jea48

    jea48 Forum Resident

    Location:
    Midwest, USA
    Motor boating.

    Possibly could be caused by a leaky/bad coupling capacitor. But the problem just recently started in both channels?

    What is usually common to both channels is the DC power supply.
     
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  25. Rick Bartlett

    Rick Bartlett Forum Resident

    Interesting thing is in my mind, it's not an old amplifier, so things like solder joints and bad
    coupling caps wouldn't seem likely at this point.
    I do say 'likely', because I don't know anything about this amp and it depends on the solder
    and construction of the unit too.
    The reviews are pretty good on it overall.
    Looking at some of the pictures are a bit concerning internally though.
    US $538.67 17% OFF|YAQIN MC 30L EL34 Push Pull Tube Amplifier HIFI EXQUIS 6CA7 Lamp Integrated Amp with Headphone Output Remote MS 20L-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
    Being a hybrid and using 'unknown' components is a bit frightening.
    Gosh, what are those capacitors used within?
    Those are not even common appropriate capacitors at all.
    That really could be a big problem here......
    The external construction looks quite nice, internally looks a bit dubious.
     
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