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Blues Jr Needs Help (Nasty sound)

Discussion in 'Glowing Bottle Tube Amp Forum' started by Flat6Driver, Sep 24, 2017.

  1. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs
    So my Blues Junior started making an awful sound last night. It's a crackle sound *similar* to when you plug in a guitar with the amp already on. But it's making the sound with no cable plugged in at all. When amp is nice and warmed up, it just crackles away.

    I bought it used a few years ago and have used it a bunch.

    No maintenance other than keeping the cover on it. Thoughts?
     

  2. JustABluesGuy

    JustABluesGuy Tele-Afflicted

    Age:
    60
    Sep 2, 2016
    Houston, TX
    I don't know where all the experts are tonight. I'm not one of them, but from my limited knowledge "popcorn" or "bacon frying" sounds might mean a bad (cold?) solder joint, or if you're lucky, a loose tube socket.

    If you are unqualified (like me) to work on electronics, you will probably need to see a professional.

    I wouldn't be afraid of re-tensioning the tube sockets, but that's about all I could do.

    Hopefully someone who actually knows something will come along to help you out.

    Good luck with it!
     

  3. Dacious

    Dacious Friend of Leo's

    Mar 16, 2003
    Godzone
    Do you have spare power tubes? Have at look at the tubes in the cutout in the back - is either sparking in sympathy with the sound? Could just be one's had it. Or it could be caused by a bad bias resistor. Does the amp produce sound if you plug a guitar in or just the crackling?
     

  4. Milspec

    Milspec Tele-Afflicted

    Feb 15, 2016
    Nebraska
    You have a loose tube. The BJ amps all have the issue with tubes getting loose in their sockets eventually. Turn it off and see if any of the tubes are loose.
     
    LiteAsh likes this.

  5. Tonetele

    Tonetele Friend of Leo's

    Jun 2, 2009
    South Australia
    I believe Milspec is probably correct. One of my friend "fried" a tube in his BJ and replaced a tube ( valve ) from a Vox he had.
    I believe they are EL-84s.
     

  6. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs
    They didn't appear to be, so maybe it's the socket solder failing. I've fixed other things (my car) but never a tube amp. Is this an easy fix or a major affair (saw someone said it's hard to get apart).

    Should I try new tubes first?
     

  7. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    Yes, Steve, new tubes is first troubleshooting step for me with any tuber amps. Try to be methodical and replace one at a time, moving through the circuit, V1, then V2, etc. If there's no change in tone, put the old tube back. No need to replace unnecessarily.

    If you can wait until Thursday, and I can talk you into driving down to Fredericksburg for the Blues Jam, I have preamp spares a plenty. I am afraid I don't have any el84's though.
     

  8. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs

    Thanks John. I'm not sure I can make it down there this month. Seems pretty easy to swap some tubes, I can start there.
     

  9. Milspec

    Milspec Tele-Afflicted

    Feb 15, 2016
    Nebraska
    I doubt the solder is bad at the sockets, just the socket tension gets weak after awhile....seems to be more common on both of my Blues Jr. than any other amps that I have owned.

    If they are not loose, change the tubes. A Blues Jr. has a fixed bias and do not need re-biased after a tube change (I know people argue about this, but that is the way it was designed). If the noise is still there, check for play in the input jack and work from there.
     

  10. Andy B

    Andy B Tele-Afflicted Silver Supporter

    Mar 16, 2003
    Colorado
    I would suggest that you unplug it, take the back off and inspect the tubes visually. If they look burnt replace them. Blues Jr's bias the power tubes way too hot. Power tubes do not last very long in these amps. Then look at the soldering of all the tube sockets looking for cracked solder joints. . If you don't see anything obvious, plug it in & wiggle the tubes gently & see if the noise goes away or gets worse. See if you can isolate where the noise is coming from.I routinely resolder the tube sockets on every Jr I work on. I also retension the sockets at the same time. I solder a 100k resistor across R37 (green PCB), R51 (creme PCB) to cool the bias down if I am not converting the amp to adjustable fixed bias.
    Pictures are a plus.
     
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  11. alnicopu

    alnicopu Friend of Leo's

    Oct 3, 2009
    georgia
    I agree with both AndyB and Milspec both. Although there is an agrumemt as to whether it was designed to run at around 100% at idle, I would personally drop it down to a safer "range" with a simple resistor. Those things do cook the tubes and in my experience, the smaller bottle tubes cant seem to take the abuse as much as a 6v6 or 6l6, in general.
     

  12. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs
    I don't understand what "bias" means in this context. Can someone explain it?


    I looked a little closer and turned it on with the room lights off. One of them was flickering like a little lightening storm. Gonna get some new ones and see if it's healed.
     

  13. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    You might want to try just removing the tubes and plugging them back in. That will cure issues with minor oxidation forming on the contacts. However, it's good to have some spares on hand for when it is the tube itself.
     

  14. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs

    I did that. Would that have caused the flickering? Wouldn't the flickering mean it's bad?
     

  15. robt57

    robt57 Telefied Ad Free Member

    Feb 29, 2004
    Portland, OR
    And the traces on the PCB are what hold the tube sockets in, so tube swap festing cab tear them up. Buss wire fixed these on HR PCBs a few time myself.
     

  16. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Sounds likely... I just wanted to make sure you had tried reseating them first.
     
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  17. Milspec

    Milspec Tele-Afflicted

    Feb 15, 2016
    Nebraska
    If you haven't purchased the tubes yet, I suggest the JJ or Sovtek brand in those amps. The JJ's handle the hotter bias all day without issue, but I think the Sovteks sound better in my other amp. Not a lot better mind you, but slightly better.
     
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  18. Flat6Driver

    Flat6Driver Friend of Leo's

    Age:
    44
    Jan 14, 2013
    DC Burbs
    Got some new JJ tubes from GC. Seems to have cured the issue. Look how they were packed! IMG_20171003_074440121.jpg
     

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