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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Tube Amp Troubles

Discussion in 'Amp Central Station' started by El Jeffe, Nov 18, 2017.

  1. El Jeffe

    El Jeffe TDPRI Member

    84
    Oct 4, 2009
    Eugene
    I left my Blues Jr. on the bus for a few weeks and the other day found there was mold growing on the laquered tweed, which surprised me, but then I remembered I was on the Oregon coast and it's very damp and the climate here ruins everything. I took the amp inside and plugged it in to run it for a while, figuring it had sat for too long without being ran. After a minute it buzzed into a crescendo and then the little 2 amp fuse blew. I figured there was possibly some moisture at work so I let it chill by the stove for a night and the heater all day. Put a new fuse in, fired it up, and recieved yet another crecendo of buzzing noise. Got a picture of a redplating el84 tube and turned the amp off before it exploded. Ha. My question is- should I spring for new power tubes- is that the likely culprit? Process of elimination to diagnose the problem, right? Tubes go bad. Or is something more sinister afoot in my beloved backup amp? I've burned thru many tubes but have never blown a fuse before. Anyways, thank you for reading, any thoughts and advice are greatly appreciated.

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  2. CV Jee Beez

    CV Jee Beez Tele-Meister

    Age:
    43
    336
    Nov 24, 2016
    Duarte, CA
    Occam's razor. Tubes are the simplest answer so try that. A pair could be about 20-30 dollars. Best of luck.
     
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  3. T Prior

    T Prior Poster Extraordinaire

    Mar 17, 2003
    Charlotte NC
    first hunch is a bad tube as they are both drawing from the same power supply.

    But think of this, tubes are sealed, no moisture, no mold, none of that stuff gets inside a tube. When the tube is not hot and just sitting around it doesn't much care about the environment. The pins do and the socket does.

    before you get a new tube though, swap the tubes in the sockets, the RED should follow the tube, if it doesn't, you obviously have another issue.
     

  4. blues bondsman

    blues bondsman Tele-Holic

    653
    Feb 12, 2012
    Indiana
    T Prior hit it on the head, swap tubes and see if it red plates in the other socket.
     
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  5. El Jeffe

    El Jeffe TDPRI Member

    84
    Oct 4, 2009
    Eugene
    That's a great idea. Why didn't I think of that? Thank you!
     

  6. aerhed

    aerhed Tele-Holic

    Age:
    58
    622
    Dec 24, 2016
    Boulder, WY
    New band name for one nighters: The moldy PCB's
     
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  7. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Worst case scenario....the mold was an indicator of moisture. The amp should have been allowed to dry out before it was put into use. When the electrons were allowed to roam around in that wet circuit, bad things happened. Cross your fingers that you do not have major problems. An amp would be better protected in such environments in a road case with some serious dessicants inside the amp cab.
     
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  8. El Jeffe

    El Jeffe TDPRI Member

    84
    Oct 4, 2009
    Eugene
    True. I'm crossing my fingers
     

  9. JD0x0

    JD0x0 Friend of Leo's

    Age:
    27
    Feb 22, 2009
    New York
    Yeah, almost seems like moisture may have made it into the PCB and cause conductivity in the bias supply, making the bias shoot up, causing the redplate. I've never just seen an old tube start redplating, but I also don't have much experience with failing tubes.
     

  10. El Jeffe

    El Jeffe TDPRI Member

    84
    Oct 4, 2009
    Eugene
    I switched the power tubes around so the redplating tube as seen on the left in the picture is now on the right. The same tube is now redplating on the right side. I had to play a little to make it redplate and quickly turned it off when I saw what looked like a lightning storm in said red plating tube. Gonna order a new pair and take better care of it from now on. Hope it's still okay, but won't really know until I get new tubes in and play it for a bit.
     
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  11. Dacious

    Dacious Friend of Leo's

    Mar 16, 2003
    Godzone
    You've got a cooked grid in the bad tube. The good news is redplating following the tube. But as Wally said, the dampness may have precipitated it. Keep your eye on the replacement. Moisture can also get in the ribbon connectors and corrode combined with heat.
     

  12. T Prior

    T Prior Poster Extraordinaire

    Mar 17, 2003
    Charlotte NC
    all of the above , or maybe it's just a bad tube or tube gone bad ! Who can say. It's speculation.

    It's possible that the RED plating started and was not even noticed. Very glad to hear the RED followed the tube.

    Why did I suggest swapping the tubes to see if the RED follows the tube ?

    45 years experience as a tech in the electronics industry :)

    The first 40 years I didn't swap the tubes in the sockets :( ( just kidding)
     
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