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Two amps, two amp failures, same AC outlet: Faulty power?

Discussion in 'Amps and Cabs [BG]' started by K2000, Apr 28, 2010.


  1. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    Amp troubles...

    My SVT blew a fuse a few weeks ago, so I moved it aside for now, until I can have my tech look at it (my tech is an hour away, and I'll have to rent a car, so I'm just procrastinating). In the meantime I've been using a Plush P1000S (late 60s/70s 100 watt tube amp).

    Tonight when I took the Plush out of standby for the first time, there was a loud feedbacky hum and then the amp shut itself down (it all happened within a split second).

    Here's the fuse, bad pic but it doesn't look like the fuse is broken. However there are a bunch of metallic balls rolling around inside the glass. Perhaps melted bits? I hadn't examined the fuse prior to this.

    fuse1.

    Anyway, two amps, two failures, same AC outlet. Is it possible that the power could be surging/spiking? If it was a problem with power, would that problem happen regardless of whether the amp was in standby? What does the scenario I described indicate, as the source of the problem? Just bad luck, combined with older tube amps? The Ampeg was worked over by Dennis Kager a year ago, and I expected more than a year of trouble free use. I'm not even working these amps particularly hard... I'm not gigging them right now, so they don't even get moved.

    I'm so dejected right now... and I'm reluctant to use that AC outlet again, which will make using my practice space a pain in the ass.

    Comments appreciated.
     
  2. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    Maybe I don't know what I'm looking at... is it the "winding" that is the working part of this fuse (and not the thicker base)? Because the winding is clearly breached.
     
  3. It might be getting not enough/too much voltage. I know some of the ampegs need like 115 volts or something higher than normal.
     
  4. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    One more bit of info... the manager of the space says that amps should be plugged into this particular outlet - the other outlets are for light duty. I didn't know that AC outlets had varied levels of capacity (besides 110 vs. 220 I guess...)
     
  5. padenski

    padenski

    Feb 19, 2008
    Landenberg, PA
  6. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i don't know what the problem with your amp is, but that fuse is most definitely blown.
     
  7. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    a tube amp that is blowing fuses is pulling more current that it was designed to. often, but of course not always, a blown output tube or a 'run-away' bias (bias that isn't stable or supplying enough volts) can cause it to blow.
     
  8. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    I can't say that I'd rule anything out, but it seems unlikely that an AC outlet would blow the fuse on your amp unless the voltage is way too high. Have you used those amps in that outlet before with no problems? It might be worthwhile to get one of those cheap outlet checkers from Radio Shack and check to see that the outlet is wired correctly. It's a good thing to bring to a gig anyway.

    If you have little metal balls rolling around in there you've definitely blown the fuse.

    There is always the possibility, as you say, that it's just bum luck. It seems unlikely, but old tube amps are temperamental and things do go wrong. I agree that you should be getting more than a year of trouble-free service from a recently tuned up amp, though.

    Hopefully, all you've lost is the fuses (and some time). If those fuses did their job, your amp was protected from further damage. Have your tech check them out and give them a clean bill of health, and check that outlet!

    If you're in Brooklyn, NY, have you tried a closer tech? There are some here in the city.

    Best of luck!
     
  9. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    Yes, I've been using that space for over a year. I guess I'm hoping it's the AC, because then it's something I can control/fix, whereas if it's just 'old tube amps' then it's a deeper problem.

    Are those fool proof and easy to use? As you can see, I'm not very savvy with the tech stuff.

    :(
     
  10. Fuses don't really care much about volts - it's the AMPs they pop from.

    If the voltage is low at that particular outlet, then the amps go UP to compensate and the fuse blows.

    BTW:: that's a SLO_BLOW fuse and it's designed to not pop with just a single spike in amps. It can take about 15% more than a SFE or an AGC-type fuse, which will pop almost instantly. That gives you a little grace period before it finally blows.

    I'd run a voltage check on that receptacle and/or it might be old-style aluminum wiring too. Just a guess. But check the voltage for sure!

    An open ground should not cause this problem, although in and of itself, that is a fairly dangerous situation too.

    Even if the receptacle is wired backwards - white and black crossed - it is AC after all, and there's not real polarity issues that can cause this fuse blowing all the time.

    There are some 220V receptacles that LOOK like 120 V ones, but they have an obvious design difference in that the HOT side is perpendicular to the GROUND lug - and that's not to be confused with the ground pin that is semi-round or "D" shaped and used to be on the bottom of the faceplate holes. They are more likely to be on the top of the faceplate now due to NEMA codes.

    This is a 20-Amp duplex outlet:

    electrical-outlet-orientation.

    This and the next are both 220V AC, one is 15 Amp, the other is 20 Amp:::

    61332-electrical-plug-w280.

    61331-electrical-plug-w280.
     
  11. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    They're easy to use and they're relatively foolproof, providing you understand their limitations. They will only tell you if the outlet is wired correctly. They won't tell you if the voltage is too high.

    It would still be a good idea to have the heads checked out by a tech also, just to be safe. I know it's a PITA and it's money out of pocket, but it's best to be sure. I simple fix now might prevent a big, expensive fix later.
     
  12. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    Okay, this may be crazy and/or grasping at straws, but there was a band playing in the room next door at the same time. I wonder if I should do my test when they are playing/not playing, and see if that makes a difference.

    That might help explain why I've used this outlet a lot in the past, with no apparent problem.

    (edit - maybe an outlet tester isn't able to do that)
     
  13. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    I don't expect you'll see a difference, but I suppose it can't hurt to check.

    If you have (or can borrow) a voltmeter, check the voltage at the outlet and see where you stand. You should be pretty safe anywhere from 110 - 125 Volts. Outside of that range is pretty suspect.

    There's a very good chance that a fuse blowing that quickly is a shorted output or rectifier tube. Have your tech check to see if the tube sockets have "arced over", which is a good indication of a short. A short in those tubes can take a transformer with it, but it usually doesn't. Cross you fingers and hope it's just a tube.
     
  14. K2000

    K2000

    Nov 16, 2005
    Brooklyn
    There's no horizontal tines on the AC outlet... standard household configuration.

    Thanks for the good info you guys, I appreciate it.
     
  15. I knew lamps blow fuses like mad, when voltage is low. I'm not surprised that amps do the same.

    Be sure you test voltage, with your gear powered on. Including the band next door, if possible. What the outlet can do at no load is not important; what it does carrying a full load is what matters. FWIW my bedroom outlet drops five volts when I fire up my 2KW Fresnel lamp.
     
  16. Your amplifier should be very happy with just that 15 Amp outlet. That's what they are rated at without the horizontal spades or lugs.

    I still suspect low voltage or just possibly it was time for them to blow - but that's a little far out if you ask me.

    Get/buy a cheap-o digital volt/ohm meter and I'd make sure to check every older building before I ran my equipment on a low voltage setting!

    I test the voltage and the plug/receptacle polarity and for a ground fault (GFCI) if it has one that is!

    GFCI testers are cheap! It'll keep you from electrocuting your lips to the mic some day!

    9610bug-big.
     
  17. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    Unless Ohm's Law has changed recently, lower voltage does not cause a higher current draw. It can't. A circuit draws less current at lower voltages.

    What it will cause, however, is low filament voltage which is very, very bad for your tubes. The tubes will run at a lower temperature than they should and when the high B+ Voltage hits them it will cause cathode stripping.

    Even if none of that were true, the OP's fuses are blowing quickly which would mean, most likely, a dead short and not a voltage issue unless the voltage was WAY out of the normal range.
     
  18. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    Oh, yeah. SurferJoe46's picture is exactly the type of tester I was talking about. Very handy.
     
  19. different voltages require different plug types......if you have access to a multi meter you might want to see if the outlet is wired correctly...if someone has regular duplex outlets wired at 220,you better be in england...they can be bought for as little as a double saw,and would be a good addition to your kit,as well as a ground fault tester@ five bucks
     
  20. There's too much coincidence here to ignore. Two amps pop two different fuses in the same plug. Odd - not?

    I always had low voltage problems at the hospital where I repaired Bio-Medical instruments. Old building that "Grow'd like Topsy" and there were wires and circuits all over the place. Some even ran in loops and tied back to the wrong legs! Home runs even had both fluorescent lights and wall receptacles on them - that's a federal accreditation failure in a medical center!

    The lower the voltages went, the higher the amps draw became until fuses blew and motors stalled. It has a lot to do with heat and since a fuse is AMPS-DRAW related and doesn't care about voltages until they get silly - I claim it's possibly a bad voltage control problem or resistance in an electrical circuit. If it's not in the walls or the distribution panel, a crummy Square-D breaker or from a resistive pole drop (via Edison) or it might be internal draw from the amplifier.

    But SOMEWHERE there is a call for more AMPS - which again, is what a fuse is all about. That's why these fuses are popping.

    The Wattage stays they same - up to a point - but something on the great cosmic teeter totter of electricity has to make up for the voltage differences.

    I've seem household voltages on the end of a run that get to 85-90 VA/C some times. If the wall receptacles are cheap back stab-type, they lose spring tension and the resistance goes up -- and ad-infinitum or until the smoke get so thick you notice it

    Then again, it might be a great big co-inky-dink too.

    Run a clamp on it and check the actual Amps draw for the circuit.
     

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