Fuse blew on Fender DRRI 65 - why would that be?

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PhiltrePhiltre Frets: 4164
edited February 2021 in Amps
I hardly play this amp at all, bought new nearly 3 years ago. Played it for a few minutes then turned it off using the power and standby switches and immediately turned it on again - I think I turned on the standby switch first and then the power switch (the wrong order). Main fuse on the amp is now blown. Could this be a sign of something else? And where do I get a supply of new fuses?

The fuse is a F1AL250V.
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  • ICBMICBM Frets: 71960
    edited February 2021
    Most likely the rectifier valve arced when it was made to suddenly recharge the filter caps when already hot and so fully conducting - normally it warms up slowly so the current ramps up gradually. It may or may not be permanently damaged.

    You can get them easily online, eg - https://www.ebay.co.uk/itm/F-1A-Fast-Quick-blow-Cartridge-Glass-Fuses-5x20mm/182771234596

    I would buy five. If the fuse blows again you also probably need a new rectifier valve - there's also an outside chance it could be a power valve, but much less likely - so you'll need more than one fuse. Even if it was just a one-off and it doesn't blow again, it's a good idea to have a couple of spares anyway.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    @ICBM thanks for that. I'll order some fuses and re-test.

    If it was the rectifier valve is there any visual clue that might show if it is damaged?
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  • ICBMICBM Frets: 71960
    Philtre said:

    If it was the rectifier valve is there any visual clue that might show if it is damaged?
    Not when it's not running. If it is, you might see flashes from inside the valve structure just before the fuse blows.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    Thanks, @ICBM . I think my plan will be to wait for the new fuses to arrive (eBay delivery so next week), pop a new one in and have a look at the power and rectifier valves when powering up. If the fuse does blow again can I pull the rectifier and power valves out and power up to see if it is one of these causing it?
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  • ICBMICBM Frets: 71960
    Philtre said:
    Thanks, @ICBM . I think my plan will be to wait for the new fuses to arrive (eBay delivery so next week), pop a new one in and have a look at the power and rectifier valves when powering up. If the fuse does blow again can I pull the rectifier and power valves out and power up to see if it is one of these causing it?
    Yes. Pull all three, and power up with a new fuse. If it doesn't blow, put the rectifier in next and try again, then if it holds, the power valves one at a time.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    Cheers, @ICBM - I shall try this when the fuses arrive. :-)
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  • PhiltrePhiltre Frets: 4164
    edited February 2021
    Fingers crossed, it seems to be OK. It turns out that my Peavey Classic 20w Mini Head also uses a F1AL250V fuse in it so I popped it into the Fender and it's all working! Must have been a one off, as @ICBM says, from powering up too quickly. Well, at least I hope it was a one off!
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  • ICBMICBM Frets: 71960
    I forgot to mention earlier, but the other thread reminded me - if the amp is still set for 230V ( as they come stock, due to EU regulations) it will be harder on the valves and more likely to do this. It needs to be set for 240V really, which is still the correct UK voltage. This involves swapping two push-connectors inside and is something you can do yourself, but if you’re not comfortable with it, it can wait until you can have a tech look at it, it’s not that critical.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • TeleMasterTeleMaster Frets: 10103
    My 65 DRRI blew a fuse a couple of times. 
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  • PhiltrePhiltre Frets: 4164
    @ICBM I'm happy to make the wiring change if I'm certain which wires to swap. I'll investigate.

    @TeleMaster any reason why?
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  • TeleMasterTeleMaster Frets: 10103
    Philtre said:
    @ICBM I'm happy to make the wiring change if I'm certain which wires to swap. I'll investigate.

    @TeleMaster any reason why?
    No idea. I had a Bassman that did it too. Only Fender amps blew fuses on me. It was rare but I always carried spare fuses with me. 
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  • ICBMICBM Frets: 71960
    I think that one of the reasons is that Fender insist on using fast-blow fuses. This is because they don’t fit adequate secondary fusing, and in order to comply with yet more regulations, a slow-blow (T) fuse isn’t considered safe enough - although in practical terms they’re much better at riding out brief spikes or surges.

    They even have to add an extra component - an inrush suppressor - to stop the F fuse blowing every time you power the amp up. It would be much better to fit an HT fuse and then the mains fuse could be a T.

    I have to admit that if it was my own amp I would fit a T fuse and not worry any more about it! But I can’t really do that in professional work.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    Just blew another fuse on this.

    1. Played amp for 10 minutes or so
    2. Powered down to standby and then power switch off
    3. Turned amp off at mains switch
    4. Put amp power switch on and then standby switch on (mains switch at wall was still off) - blew the fuse at this point

    Seems to be a surge at point (4)
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  • ICBMICBM Frets: 71960
    The fuse blew while the wall switch was still off?

    Or do you mean it blew when you turned the wall switch on with both amp switches already on?

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    edited April 2021
    ICBM said:
    The fuse blew while the wall switch was still off?

    Or do you mean it blew when you turned the wall switch on with both amp switches already on?
    Yep, while the wall switch was off. I could hear a surge at stage (4). After that happened I put all amp switches to off, put mains on at the wall then power switch on amp to on but amp didn't power up so the fuse must have blown at stage (4).

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  • ICBMICBM Frets: 71960
    That's very weird/worrying - the switch on the wall socket should disconnect the live pin of the socket so it should then be impossible for it to blow the fuse in the amp.

    I can't think of any way for it to happen unless the wall socket is wired wrongly.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    The mains switch is OK, just tested it.

    Perhaps there was still some high voltage in the amp circuit that discharged when I flicked the power and standby switches to on?
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  • ICBMICBM Frets: 71960
    Philtre said:
    The mains switch is OK, just tested it.

    Perhaps there was still some high voltage in the amp circuit that discharged when I flicked the power and standby switches to on?
    Not if it's the mains primary fuse. That's between the wall supply and the amp's power transformer.

    Does the amp have a moulded plug on the mains cable or an old-style one with a screw cover?

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 4164
    To be clear, I mean the fuse in the amp blew, not the mains plug (moulded).
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  • ICBMICBM Frets: 71960
    Philtre said:
    To be clear, I mean the fuse in the amp blew, not the mains plug (moulded).
    That's what I expected, but it's still in line between the power cable and the amp circuit, so with the wall switch off - assuming it has disconnected the live and not the neutral - no current can go through the fuse.

    Either the fuse didn't actually blow at that point and it's somehow tricked you that it did, or there is something badly wrong with the wall socket wiring or the amp.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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