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Blown Fuse?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Marc Morfei, Apr 13, 2021.

  1. Marc Morfei

    Marc Morfei Friend of Leo's Silver Supporter

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    What is the most likely cause of a blown fuse? Long story that I won't get into, but it blows instantly when the amp is switched on. I dread bringing it to a tech and spending $$, since I was leaning toward selling this amp anyway. But if there is a chance it might be something simple, I am willing to take a crack at it. I know very little about amp electronics, but I can follow instructions, and I can solder.
     
  2. kbold

    kbold Friend of Leo's

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    Sounds very much like a short ..... somewhere.

    1) The first thing I always do is inspect visually ... bad soldering, loose wire, burnt out/damaged component, blown/swollen electrolytic cap.
    2) Try powering up without any tubes fitted.
    3) If no joy, time to get out the multimeter.
    If you can separate the power supply from the other circuitry you can narrow it down.
    Check sections for low ohms that might indicate a short (with the power disconnected and capacitors discharged).
    Components: I would check diodes and capacitors first.

    Except for testing with tubes removed, all other tests can be done with no power. (Did I already recommend discharging cap's first?)
     
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  3. Wally

    Wally Telefied Ad Free Member

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    It would be good to know what amp you have there. That said...
    Pull the tubes...lay them out in order. Install a new fuse and fire the amp up. Does the fuse blow? If so, it is tech ime. If not, install the rectifier...if it has one. Does the fuse blow? If so, you may have a bad rectifier tube....or a problem in the filter section. If the fuse holds, install one of the power tubes. If the fuse blows, try the other power tube in that socket. If the fuse doesn’t blow, the first tube is bad. Get a new set of power tubes. If the power tube installation don’t blow the fuse, Proceed through the rest of the tubes in order from the power tubes to the input. Somewhere along the line, , you will find the problem area. A new tube or tubes may pr may not cure the problem. You may have a bad component in the circuit attached to a tube that causes the fuse to blow.
     
    Last edited: Apr 13, 2021
  4. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Just for clarification, I believe @Wally meant "Pull the tubes... Lay them out in order. Install a new FUSE and fire the amp up".
     
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  5. Wally

    Wally Telefied Ad Free Member

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    Thanks for the heads up on my mistake, Griff, which I corrected.
     
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  6. Telekarster

    Telekarster Tele-Afflicted

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    Definitely sounds like a dead short somewhere, or... have you tried a different wall socket? Anyway, @Wally suggestion is +1!
     
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  7. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    You bet, it's an otherwise very good post.
     
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  8. schmee

    schmee Doctor of Teleocity

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    FIRST: Are you using slo blo fuses?
    Of course we have non idea if it's a stadium 1949 mono block theatre amp or a Fender Champ....
     
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  9. uriah1

    uriah1 Telefied Gold Supporter

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    Think I had a bad pi that took out a plate or screen resistor and then fuse. Been awhile.
     
    Last edited: Apr 13, 2021
  10. Killing Floor

    Killing Floor Tele-Afflicted

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    I had a Peavey amp growing up that always blew fuses. If you stuff aluminum foil or fold a paper clip in the canister it solves the problem. Shhh, yeah, I know. But it worked for years in high school and I didn’t know better. I’m sure that is not recommended.
     
  11. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    @Killing Floor - please don't recommend stuff like that to a user that doesn't have electronics experience and can't tell if you're joking.
     
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  12. Wally

    Wally Telefied Ad Free Member

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    +10000000000.......electrons do strange things when they get out of control. Since we are holding ground in our hands when we play the instruments hooked up to these amps, we would not want those electrons finding a way to course through our bodies while trying to find the shortest path to ground.
    Even if the lack of proper fusing did not expose the user to danger, the equipment is most definitely not operating as it should and therefore does not sound like it should. I had a proud owner of a Vox AC100 talking to me about how the amp had never failed him during his playing days decades earlier. I was pulling the fuse to see whadahey. There it was...a perfectly rolled cylinder of aluminum foil that was in the amp when he bought it long ago...he had never done anything to the amp. He was not phased by the revelation that hotwiring. He also was not phased when I reported to hi: that two of the four EL34s had shorts and one that was not shorted was not working. He had been playing on a single EL34 back then....and thought that because it said Vox AC100 on it that the amp sounded fantastic!!!! All he wanted was some speaker cab connections. I did that for him with the advice that he never even plug the amp in. I did NOT install a new fuse, and I certainly did not reinstall that roll of aluminum foil. He passed some t8me after that..sadly. That amp now lives in Uruguay.
     
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  13. Marc Morfei

    Marc Morfei Friend of Leo's Silver Supporter

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    Fender Bassbreaker 15 head.
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Cool, so with a bassbreaker and no tools, all you can really do is pull the tubes like Wally mentioned to see if the fuse blows. Anything other than that and you'd likely need some tools or take it to a tech.

    If you felt adventurous and you're familiar with working on amps, you could disconnect the secondaries of the PT so only the primary is hooked up and do more testing, but that does involve opening up the amp and sticking a hand in there, which should only be done if you're 100% confident in the safety of the procedure.

    If not, a tech can isolate this problem quickly for you.
     
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  15. Dave Hicks

    Dave Hicks Friend of Leo's

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    What an opportune thread.

    I just blew a fuse (Fender Princeton Reverb II) for the first time that I recall. Do fuses eventually go out with their boots on, or is this a sign of another problem?

    I don't have a replacement at the moment, but I'll get some new fuses and if they pop, try the diagnostics that you all have mentioned above.

    D.H.
     
  16. Wally

    Wally Telefied Ad Free Member

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    Fuses will blow when they are hit with a power surge in the AC supply, when there is excessive current draw from the amp’s circuit...or when a man made fuse decides that it has lived long enough. If two fuses, blow, there is a problem in the amp, ime.
     
  17. Dave Hicks

    Dave Hicks Friend of Leo's

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    Thanks, off to the hardware store, there being no Radio Shack in town any more.

    D.H.
     
  18. Preacher

    Preacher Friend of Leo's

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    So when I was a youngster I had a radio that I added a tape deck to. And every so often it would short out and blow the fuse. I believe it took a 2 or 3 amp fuse and I would just replace it. Then I ran out of 3 amp fuses, and I put in a 5 amp fuse. Soon after I blew that fuse and I think I graduated eventually to a 20 amp fuse. When that one blew it was late at night and dark in the car.
    I knew EXACTLY where the short was by the bright light and could find it in the morning from the scorch on a piece of metal that was rubbing against the hot wire.
     
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  19. Dave Hicks

    Dave Hicks Friend of Leo's

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    Had a car like that once.

    D.H.
     
  20. Telekarster

    Telekarster Tele-Afflicted

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    Back in the day when we had glass fuses in cars, a buddy of mine hotwired a fuse because it kept popping on him. I told him that it was a bad idea and he needed to fig out what was going on in that circuit. 3 days later I ran into him... without a car, at a buddies house. He told me his car caught fire and burned on the side of the road! :eek: It's never a good idea to "rig" an electrical system of any kind ;)
     
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