First tube issue...during a gig

Discussion in 'Amps and Cabs' started by 72Telecaster, Jan 26, 2012.

  1. 72Telecaster

    72Telecaster Silver Supporting Member

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    So during rehearsal last night at church my AC15C1 just cut out mid song. Not cool. Luckily the other guitarist runs a stereo rig with an AC15 so I salvaged the set, but I'm wondering if there are ideas on the culprit. I'm a novice when it comes to tube operation so here's the scenario:

    Recently retubed with JJ's across the board - <5 hours on the new tubes.
    Not so good fact: The amp sat in my trunk all day...in MN it was probably 35 degrees outside - black car + sunlight might have warmed it up a bit, but consider 8 hours sitting in ~40 degree temp.

    Brought it into church, sat for 5 minutes or so, fired it up without thinking to let it sit, started playing within another 5-10 minutes. It worked just fine for a good 20 minutes, then dead. The 2nd EL84 from the right (looking at the amp from the back) wasn't glowing when I tried powering it up. Going to check the fuses tonight.

    Would the temperature differentiation have caused this? Or a faulty EL84? Thankfully I have a matched pair at home to swap in, I just want to prevent this in the future...
     
  2. neville5000

    neville5000 Supporting Member

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    Sounds like a bad EL84. If they're going to prematurely die it's usually within the first 48 hours.
     
  3. clothwiring

    clothwiring Supporting Member

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    I don't know the amp so I might be wrong by saying this. It's 90% either the power tubes or rectifier tube (if this amp has one of 'em). If it's the rect tube, also get yourself (a) new fuse(s).

    When gigging tube amps I ALWAYS have a complete set of backup tubes and fuses for the amp. I've never had an issue live but if I do I have no problem switching the power/rect/fuses on first signs of problems.
     
  4. Blue Strat

    Blue Strat Member

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    If there's still one working EL84 the amp wouldn't be silent. A dead preamp tube, rectifier, or something unrelated to tubes is more likely. If the amp is lighting up it's not your main power fuse.

    Plug directly into the amp, no pedals, different cable, and try again. Then, if there's still a problem, backtrack to the original tubes. If all is well, install one of the new tubes at a time.

    It's about the process, not an instantaneous answer which can only be a guess.
     
  5. michael.e

    michael.e Supporting Member

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    Luckily it wasn't during a gig, but a rehearsal. Sucks when it happens under the pressure of performing.
     
  6. 72Telecaster

    72Telecaster Silver Supporting Member

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    I believe it's a solid state rectifier in the AC15.

    I did try plugging straight in a couple times and no sound at all. Usually the amp "hiss" is very audible as you turn the volume and master up but after powering it on and dialing the volumes up it remained silent.

    Blue_Strat - thanks for the pointers, that was my main interest in finding some starting points and things to investigate.
     
  7. tommc

    tommc Member

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    If it's completely dead, do noise at all. first check the fuse(s). If it's blown, go to Radio Shack and buy a handful - they are cheap.
     
    Last edited: Jan 26, 2012
  8. 72Telecaster

    72Telecaster Silver Supporting Member

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    ..found the culprit

    [​IMG]

    tube cracked clear around the base...:(
     
  9. Hwoltage

    Hwoltage Member

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    Did you fire it up directly out of the trunk of your car?
     
  10. 72Telecaster

    72Telecaster Silver Supporting Member

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    it was maybe 10-15 minutes after
     
  11. Hwoltage

    Hwoltage Member

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    That's probably what did it.
     
  12. Avatar Tech

    Avatar Tech Member

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    I've been having horrible luck with JJ EL84's lately. Exact same issue with cracking, usually after less than 10 hours of use. I switched to Sovtek's because the price is similar. I find that I like the tone better too. It's a little warmer.
    Anyway I don't think you did anything because I had to toss 5 of the last 20 JJ's I bought.
    CD
     
  13. 72Telecaster

    72Telecaster Silver Supporting Member

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    Wow, that's disappointing. Thanks for the heads up.
     
  14. Blue Strat

    Blue Strat Member

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    No problems with JJ EL84's here in 100s and 100s shipped.

    Extreme temperature changes are NOT good for tubes.
     
  15. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Probably not, tubes can and should be able to take it. Probably got hit some how. I have left all kinds of amps outside, even 0 degrees all day, and after about two minutes on standby no issues ever.
     
  16. Blue Strat

    Blue Strat Member

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    No, it probably WAS the issue. Nothing is ever 100% consistent. Life is about playing the odds, plus we're talking about EL84s which are more fragile than any of the other types of power tubes.
     
  17. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Sorry but I disagree. As long as the amp isn't immediately turned on and wailed on cold should not be an issue, after all tubes were in car radios at one point. Probably just spotty quality, which is the real cause.
     
  18. guitarjazz

    guitarjazz Member

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    I'm having a flashback to pulling my Mark IIC out of the equipment truck in January 1984, completely frozen. I took the chassis out and held a blow dryer on it for a couple of hours...and it worked fine.
     

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