6505+ 120 Head shuts itself off after 20 minutes of playing

Discussion in 'Gear & Equipment' started by TheBlackBard, Jun 5, 2021.

  1. TheBlackBard

    TheBlackBard SS.org Regular

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    Basically in the thread title. It shuts itself off, doesn't come back on unless I give it a few minutes and then it comes back on. It's done this twice now and I don't know enough about tube amps to really diagnose them. Tubes are two years old or so with not much playing (couple of hours a month if that).
     
  2. TheBlackBard

    TheBlackBard SS.org Regular

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    Pulled a fuse out of the back. It's gray, and I'm pretty sure they're supposed to be clear, yes?
     
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  3. c7spheres

    c7spheres GuitArtist

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    Have you checked the fuses? If not, unplug amp and check the fuse. Sometimes a fuse can half-blow and cause problems like this. It can sometimes blow but not fully, then it heals itself by basically welding itself back together again. It can also make your amp sound like it's thin and crackly.
     
  4. c7spheres

    c7spheres GuitArtist

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    Haha, Looks like we were typing at the same time! Also, only replace the fuse with the same exactly spec it should be. Don't put something like a slow blow where a fast blow should go. Doing this will normally work just fine, or for awhile, but it can also cause you to blow tubes or fry the amp instead.
     
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  5. TheBlackBard

    TheBlackBard SS.org Regular

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    I can replace the fuse no issue. My thing is, fuses normally blow for a reason, do they not?
     
  6. c7spheres

    c7spheres GuitArtist

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    - It could be the fuse is old from power surges or spikes and nothing is wrong with the amp. It could also be something wrong with the amp or a tube starting to fail pulling more power etc..
    - The only way to know is to put a new one in and see, or take it to a tech to fully diagnose it etc.
    - If you have a tube that's hot plating this can cause it. Basically everything will work normal but as the tube heats up it hot plates causing the fuse to blow then eventually the tube will blow.
     
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  7. USMarine75

    USMarine75 Colorless green ideas sleep furiously Contributor

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    Maybe your amp is trying to tell you something? ;)

    Seriously though... when you say amp turns off... no power (lights off?) or just no noise coming out?
     
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  8. TheBlackBard

    TheBlackBard SS.org Regular

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    Amps shuts off completely. No lights, no nothing. The last time it did it was last week which was when I last played it. After a few minutes, I turned it on, played for a bit, no changes in tone or anything like that and continued to play for 20-30 minutes. Today I fired it up, played for 20 minutes, did it, has not come back on. Pulled the fuse from the back and saw it's grayed out. Other than that, I wouldn't know where to begin and I'm not an amp tech, so I won't be digging around the amp. I know better than that.
     
  9. USMarine75

    USMarine75 Colorless green ideas sleep furiously Contributor

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    Do you have a multimeter? Put it on resistance check (ohm symbol) or diode tester and see if it shows open / zero (bad fuse), or if it shows infinity (good fuse). Otherwise just bring to local store and ask for replacement. They can match. But usually once a fuse goes it goes. Shouldn't be on and off.
     
  10. Spaced Out Ace

    Spaced Out Ace $$60,000,000,000

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    Fast blow fuses are put where they are, typically, because they are used in specific spots to protect mission critical portions of the amp. The reason using a slow blow instead of a fast blow is a bad idea is the fast blow was picked for a good reason. Instead of popping at the faintest idea of an issue, the slow blow requires the issue to persist for some time before going. Meanwhile, the portion of the Amp the fuse is meant to protect is subjected to dangerous voltages or other operating situations, and the key components are destroyed, resulting in a very costly repair. Replace same for same, not similar for work "alike."
     
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  11. budda

    budda Do not criticize as this Contributor

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    Tech time.
     
  12. HeHasTheJazzHands

    HeHasTheJazzHands SS.org Regular

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    If it comes back on then wouldn't that mean the fuses are fine?
     
  13. HeHasTheJazzHands

    HeHasTheJazzHands SS.org Regular

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    Probably a ceramic fuse or something. Don't see them in amps a lot, but they are a common fuse. You need a multimeter or something to check continuity just to make sure, but I'm positive the fuse is fine.
     
  14. Spaced Out Ace

    Spaced Out Ace $$60,000,000,000

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    I'm curious if maybe there is overheating gong on, causing some solder points to fail or something? Not sure.
     
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  15. HeHasTheJazzHands

    HeHasTheJazzHands SS.org Regular

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    That's something I was thinking about as well. Probably a cold/broken solder joint on or near a tube socket.
     
  16. TheBlackBard

    TheBlackBard SS.org Regular

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    Didn't come back on this time.
     
  17. TheBlackBard

    TheBlackBard SS.org Regular

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    I think I'm going to just go ahead and take it to a tech.
     
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  18. TheBlackBard

    TheBlackBard SS.org Regular

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    So my wife brought up a point. Before it did this last week, I accidentally left my tube amp on all night long. Probably about 12 hours. Could it be related?
     
  19. USMarine75

    USMarine75 Colorless green ideas sleep furiously Contributor

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    As long as it was plugged into a speaker cab you're fine. Eddie used to turn an amp on 10 and place guitar next to cab and let it feed back for a month to test an amp lol.

    If the power goes completely off it's not anything to do with a tube or socket. You could have a bad solder joint that finally went or a component. But it's in your power section not anywhere else. Check your power cord too and make sure it's not damaged. But best is to just bring to a tech. Power issues are the easiest and cheapest to fix provided it's not the power stepdown transformer.
     
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  20. TheBlackBard

    TheBlackBard SS.org Regular

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    I looked at the wires coming out of the transformers and it looks like there's some slight bubbling on them. Either way, I'm hoping it's not too expensive of a fix.

    FWIW, the amp still isn't coming on after a few hours of the last incident.
     
    Last edited: Jun 5, 2021

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