My Blues Jr Just Crapped Out

Discussion in 'Glowing Bottle Tube Amp Forum' started by HotRodSteve, Aug 13, 2019.

  1. PBO Blues

    PBO Blues Tele-Holic

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    Sounds somewhat like a problem I had a couple of years ago (a 2015 Lacquered Tweed BJr, about the same age as yours) that turned out to be a bad screen grid resistor feeding the power tubes. I understand that it's not an entirely unusual failure. I described the problem to my tech like this:

    A loud pop and no power. Fuse burned. I replaced the fuse and restarted. Low hum (louder than normal), then a pop and a louder hum. It does this consistently now, at varying volumes, every time I start it. Hum, pop, louder hum. It does play, though poor quality. Swapped in new power tubes with no change. Swapped in new preamp tubes. (Did a lot of swapping, actually, different combos of new old.) With all new tubes, amp plays but fluctuates. One moment all is well, but seems that as it warms it up it sounds a bit diminished and breaks up very badly in the lower notes. Almost normal in the upper.

    Sound familiar? If so, sounds like it's tech time to me. This is not something you want to tackle.

    Good luck!
     
    Last edited: Aug 19, 2019
  2. HotRodSteve

    HotRodSteve Friend of Leo's

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    Yep, that's the sound I'm getting, buzzy and crackly and almost normal on the treble strings. Sounds like it needs professional help.
     
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  3. PBO Blues

    PBO Blues Tele-Holic

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    Great minds. ;)
     
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  4. JuneauMike

    JuneauMike Friend of Leo's

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    Mine buzzed and oscillated on the notes (don't recall the frequencies most affected) then it eventually started losing volume and then didn't do much of anything at all. It was the filter caps that were the culprit in my case. You are getting to a point where you need a qualified tech to look at it, me thinks. Again, you don't really know why the fuse failed previously.

    The PCB holding the tubes in place (why, hello engineered obsolescence. So nice to meet you) will show signs of damage if it is the culprit. Really you would almost be able to tell at a glance that its burned and scored. Its somewhat obvious. BillM probably has some examples on his website if you look around.
     
  5. HotRodSteve

    HotRodSteve Friend of Leo's

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    I have no idea what caused the original fuse blowout so I'm going to bring it in for repair. This guy looks good and he's only 45 minutes away or so, I'll be calling him to setup an appointment. I'll post how it goes and thanks again to everyone for the advices.

    https://www.ampexperts.com/
     
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  6. Matthias

    Matthias Friend of Leo's Gold Supporter

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    People sell upgrades for the valve PCB on eBay. If mine goes again, I’d consider one of these. https://www.ebay.co.uk/itm/Fender-B...hash=item443ad19722:m:muzAodSy9Ra2Mqrw6p4x51g
     
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  7. jrblue

    jrblue Tele-Afflicted

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    Sorry for your troubles. There must be a reason why that GT tube was put into the amp. I wonder if there was a previous preamp problem. Though my best and most reliable amp is a Pro Junior (first issue, made in USA, played heavily since day one) it has been modded for reliability and is a great amp. But the PJ and BJ are built like crap and there are all too many possible causes for the faults you are experiencing. I do think some PBCB pix would help the forum wizards identify the fault before you see a tech. Some versions of that amp, depending on what needs fixing, are sadly not worth the expense -- depending on the time and parts needed. Good luck. Hopefully it's something small.
     
  8. JuneauMike

    JuneauMike Friend of Leo's

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    Yes, but that is major surgery. And the complicating factor is that you'd have to solder on the PCB board (which is technically more difficult than the garden variety soldering that we do on turret and eyelet boards). I'm good at soldering, but I wouldn't want to take on a job like that.
     
  9. Matthias

    Matthias Friend of Leo's Gold Supporter

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    Oh, I’d get someone else to fit it. I’d likely electrocute myself.
     
  10. Dacious

    Dacious Poster Extraordinaire

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    Noises are never to be ignored.

    The odds are - your old power tubes are cactus.

    That may have caused, or been caused, by a fried resistor in the bias circuit As others have noted it's a fairly common issue with this line of amps, especially once they age.

    If you play a lot i.e. six, seven hours a week or more you may end up replacing tubes once a year in an amp like the BJ. If you have it dimed or are hitting it with overdrive or distortion even moreso.

    Tubes are consumables. Like spark plugs in your car.
     
  11. Commodore 64

    Commodore 64 Friend of Leo's

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    Look for dark burnt resistors and look for similar browning/delamination on the PCB around the power tubes and elsewhere. My first issue Pro Jr fried the traces around the power tubes. I ended up chassis mounting sockets and running flying leads back to the board (instead of the ribbon cables).

    Chopsticking can be of great use in this case to find a dodgy resistor or traces. Once you isolate the location, then it becomes a matter of whether you want perform surgery or not.
     
  12. Tonetele

    Tonetele Poster Extraordinaire

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    My best friend and bandmate changes valves often on his Blues Jr.
    That's what you may get trying English valves ( EL- 34 and EL-84) with a Fender circuit. I don't know, I'm certainly no expert, he is. So I cannot comment further. I sold mine and got a PPRI with 6V6 valves/tubes. Best amp I've owned. JHMHO
     
  13. HotRodSteve

    HotRodSteve Friend of Leo's

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    Got my amp back today and it sounds good again. The problem was one of the resistors (R36) was open. That resistor was replaced and it fixed the problem.
     
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  14. PBO Blues

    PBO Blues Tele-Holic

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    Yep. I believe that's the same one I blew. Glad you're back in business.
     
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