Why is my fuse blowing when I use "Standby"? Manual for Quinn Sweet Thunder anybody?

Discussion in 'Amps and Cabs' started by michael.e, Apr 18, 2015.

  1. michael.e

    michael.e Supporting Member

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    So this is even more strange than that.

    I run the amp, runs fine, it is noisy/crackly though at times. The fuse does not blow when the amp is on. Not when I use it or even if I leave the amp on. As a test, I have been letting the amp run for a number of hours today. I turned it off with the power switch, not using the "standby" and it powered up just fine.

    It is a Fendery type head.

    Last night, I was swapping preamp tubes and I was using the "standby" switch. There is a loud pop when I use it. So, I finish playing it and shut things down for the night not touching the standby switch. This morning I come in to power it up and no go. No light, fuse dead.


    This has done this since I got it second hand here about 3 months ago. The amp did come with a problem in that it drops in power and begins to distort, though run, if I put boost boxes of any sort. Even if it is a unity gain boost.

    Really scratching my head. Amp sounds beautiful tho!
     
    Last edited: Apr 20, 2015
  2. Fenderosa

    Fenderosa Member

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    I had this problem. I was using quick blow fuses instead of slow blow fuses. problem went away after I switched to slow blow.

    Also, some times an older electrical outlet or older power strip have been culprits.
     
  3. michael.e

    michael.e Supporting Member

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    I believe these are supposed to be quick blow in here. I have had no other issues with other amps in this area. Very strange.
     
  4. Vox66

    Vox66 Member

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    Because it needs the money... ?
     
  5. soulsurfer

    soulsurfer Member

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    I'm unclear at some things...
    you've changed the blown fuse and it still blows them using the standby?
    you've gone back to the original tubes and it still blow fuses?

    I'm trying to find out "what changed" and eliminating random "I just had to take a shyt now" type of thing with fuses/tubes whatever.

    My thoughts are- change one thing at a time. do the same thing every time you make a change. (how you start/stop the amp/volume/type of signal/ etc).
    Basically fixing one thing at a time and eliminating any random happenstance type fubar.
     
  6. michael.e

    michael.e Supporting Member

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    Thanks,
    The amp did the same thing with the original tubes that I got it with. I have swapped out all tubes and it still does it.

    The amp has been blowing fuses in this manner since I got it. It does not do it directly when using standby. I have totally stopped using the standby switch. During the time when I was using it, I would play it for the evening, power down either using standby at that time, or not using it. It did not matter.
    The next morning I come to power it on and it is dead. Fuse blown

    I have not used the standby switch for about a month now and the fuse has not blown.
    This changed last night when I was swapping some more tubes for tonal differences. I would place the amp on standby, change the tube and turn it back on and play. It worked fine all night. I powered down using only the power switch as well. I came out this morning to a dead amp. I changed the fuse and it is working just fine.

    Further,
    On an inconsistent basis, the amp lowers slightly in volume and gets distorted and a bit muddy. I switch over to my Marshall for a bit [clean/dirty rig], and then switch back to the clean amp after a few minutes and it has cleaned up and running at full power again.
    I think it is something in the circuit.
    The amp is a Quinn Sweet Thunder.
     
  7. wyatt

    wyatt Member

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    What amp make and model. You say Fender-y.

    Mains fuses in tube amps are usually slo-blo/delay because there is often a temporary large current draw that will blow a quick-acting fuse.
     
  8. Tylenol Jones

    Tylenol Jones Member

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    Fender amps use "slo-blo" fuses. Not the regular kind. Make sure you have the right type.

    Also, make sure you have the correct manufacturer-recommended amps for the fuse.

    Bought a vintage amp and the fuse blew. After looking at the glass, it was a 3 amps one even though 2 amps is what is supposed to be in there.
     
  9. Paully1

    Paully1 Member

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    Yup, that's why it blows 😀
     
  10. Sweetfinger

    Sweetfinger Supporting Member

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    If you power the amp up on standby, does it blow- or does it blow when switching?
    Switches can go bad.
     
  11. Diablo1

    Diablo1 Member

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    No surprise here. A quick blow fuse + using the standby switch + hot tubes is a recipe for blowing fuses. When you flip the standby switch, the main filter capacitors are absorbing lots of current to charge them up and the hot tubes also instantly draw lots of current. You need a slow blow fuse of the correct value in the amp, or need to avoid using the standby switch.
     
  12. zenas

    zenas Member

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    Blowing fuses and drops volume and gets muddy sometimes. Take it to a tech.
     
  13. DRS

    DRS Member

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    What brand is the amp?
     
  14. Blue Strat

    Blue Strat Member

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    I don't think so. Try a slow blow and see how that works. All Fender amps require slow blows.

    Another possibility is if the amp has a tube rectifier, there may be too much capacitance on the far end of the standby switch which will cause the rectifier to arc and take out the fuse...if not the rectifier itself.
     
  15. Nelson89

    Nelson89 Member

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    Most importantly here, we have no idea whether this amp has a rectifier valve. Valve rectifier + standby switch can be chaos. Had an old fender pro sonic which presented the same issues, what fixed it was swapping out the rectifier valve (which was faulty by that stage) and stopped using the standby switch.

    Edit: Ah damn, blue strat just beat me to the chase by a minute haha.
     
  16. TheoDog

    TheoDog Silver Supporting Member

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    Rectifier tube?
    Usually when an idling amp gets noisy, power tubes are the culprit. The OP only mentioned swapping pre amp tubes.

    Also, slo-blo I the right choice.
     
  17. Nelson89

    Nelson89 Member

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    The amp is blowing fuses, a bad rectifier valve can do that. Also, I'm no amp tech, but last issue I had with another amp which presented the other issues the OP mentioned, i.e. Pop noises, muddy, drop in volume when hitting with boost pedals, ended up being a dodgy preamp valve in the phase inverter position, I figured as well that it'd be power valves, but they weren't the issue that time.

    I'm just presenting stuff from my experience, whilst power valves are probably more likely, they're not the only cause of these symptoms (annoyingly). I usually start with power valves first then work my way through preamps phase and rectifier, after that I take it to a tech.
     
  18. Blue Strat

    Blue Strat Member

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    Yes, for the fuse blowing issue. Noise is probably something else but will be hard to troubleshoot until he stops blowing fuses.
     
  19. swiveltung

    swiveltung Member

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    Not uncommon for old amps to have bad switches. If it is popping when you switch that is a often a worn out switch. However, it shouldn't blow a fuse unless the switch is really toast. You need slo blo fuses in most vintage Fender amps.
     
  20. michael.e

    michael.e Supporting Member

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    Thanks all for the replies. I appreciate it. In my last post, I mentioned that the amp was a Quinn Sweet Thunder. Kind of a mix between a Super Reverb and a Bassman. The amp has a SS rectifier. I had also mentioned prior that I swapped all tubes. That means power and preamp.
    I am mostly a Marshall guy. I did not know that the mains fuse is supposed to be a Slo-Blo. I figured that is what was in there and I did not want to start putting Slo's where I didn't think they belong. That scenario makes sense. I will swap it.

    I am going to drop the amp off at Sebago and have him give it a going-through.
     

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