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Thread: fuse of vintage JBL

  1. #1
    Senior Member pyonc's Avatar
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    fuse of vintage JBL

    Hi friends,

    I need a new fuse for JBL SG520 preamp. According to the manual, it says "a Slo-Blo fuse. A 3/10 AMP. fuse is required for 110-120 volt operation.' I'm not familiar with this kind of fuse. On ebay I see lots of fuses that look like this one, but I can't find the exact match. I appreciate it very much if you can let me know (hopefully a picture), or send me a link to any auction site on the right slo-blo fuse.

  2. #2
    Moderator hjames's Avatar
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    Quote Originally Posted by pyonc View Post
    Hi friends,

    I need a new fuse for JBL SG520 preamp. According to the manual, it says "a Slo-Blo fuse. A 3/10 AMP. fuse is required for 110-120 volt operation.' I'm not familiar with this kind of fuse. On ebay I see lots of fuses that look like this one, but I can't find the exact match. I appreciate it very much if you can let me know (hopefully a picture), or send me a link to any auction site on the right slo-blo fuse.
    You do need to know what the actual fuse is, not a generic description like you listed.

    Size (length) is going to be critical to actually fit the fuseholder ...
    Should I gather you have the original fuse in hand??
    If its a Buss brand fuse, (or something like that)
    it should have a part number stamped on one of the silvery bands ...
    3AG or something similar ...


    Try an actual electronics outfitter like Capital Electronics in Gaithersburg, MD -
    instead of the auction site ...
    You should be able to get a box of Slow Blow fuses for $5 or so ...
    https://www.capitaltristate.com/
    or maybe someone like
    https://www.suburban-electronics.com/





    http://www.jblproservice.com/pdf/Vin.../JBL-SG520.pdf

    On page 22, it says - 4Amp 120 volts slo blo
    on page 28, it says 3/10 Amp slo blo
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  3. #3
    Senior Member pyonc's Avatar
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    Quote Originally Posted by hjames View Post
    You do need to know what the actual fuse is, not a generic description like you listed.

    Size (length) is going to be critical to actually fit the fuseholder ...
    Should I gather you have the original fuse in hand??
    If its a Buss brand fuse, (or something like that)
    it should have a part number stamped on one of the silvery bands ...
    3AG or something similar ...


    Try an actual electronics outfitter like Capital Electronics in Gaithersburg, MD -
    instead of the auction site ...
    You should be able to get a box of Slow Blow fuses for $5 or so ...
    https://www.capitaltristate.com/
    or maybe someone like
    https://www.suburban-electronics.com/





    http://www.jblproservice.com/pdf/Vin.../JBL-SG520.pdf

    On page 22, it says - 4Amp 120 volts slo blo
    on page 28, it says 3/10 Amp slo blo (3 to 10 amps?)

    Thanks so much for your useful information!
    I think I have to take the old fuse out first to check it as you suggested.
    Also, thanks for the info on Capital Electronics in my area, too.

  4. #4
    Senior Member pyonc's Avatar
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    By the way, what is this 3/10 AMP. here? Is it any slo-blo fuse rating from 3 ampere fuse to 10 ampere fuse?
    In other words, exceeding 3 ampere fuse rating but less than 10 ampere fuse rating? Just confused...

  5. #5
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    NO!

    ( 3/10 ) is the same as ( 3 divided by 10 ) is the same as ( 3 over 10 ) which is just another way of saying the previous 2.

    = 0.3 amps

    Take the fuse out and measure it, there are a few sizes present in electronics equipment.

    Hopefully it's 1.25"Long x .25"Diameter


  6. #6
    Senior Member Baron030's Avatar
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    Hi Pyonc
    Looking through the manual, your amp has two fuses. Since, you are living in the state of Maryland. I can assume that you are running this amp with 115 volts. So, the 3/10AMP fuse is referring to 0.3 amps, as in 3 tenths of one amp. My guess is that it is a 3AG sized fuse. And 3AG refers to the physical size of the fuse and not it current rating. The other fuse is for the switched outlets and is most likely a 3AG – 2 amp Slo-Blo fuse.

    Name:  Concealed_fuse.jpg
Views: 409
Size:  31.4 KB

    Best of luck
    Baron030

  7. #7
    Senior Member pyonc's Avatar
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    Quote Originally Posted by Earl K View Post
    NO!

    ( 3/10 ) is the same as ( 3 divided by 10 ) is the same as ( 3 over 10 ) which is just another way of saying the previous 2.

    = 0.3 amps

    Take the fuse out and measure it, there are a few sizes present in electronics equipment.

    Hopefully it's 1.25"Long x .25"Diameter

    Thanks so much! This is the way I learn from JBL guru like you.

  8. #8
    Senior Member pyonc's Avatar
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    Quote Originally Posted by Baron030 View Post
    Hi Pyonc
    Looking through the manual, your amp has two fuses. Since, you are living in the state of Maryland. I can assume that you are running this amp with 115 volts. So, the 3/10AMP fuse is referring to 0.3 amps, as in 3 tenths of one amp. My guess is that it is a 3AG sized fuse. And 3AG refers to the physical size of the fuse and not it current rating. The other fuse is for the switched outlets and is most likely a 3AG – 2 amp Slo-Blo fuse.

    Name:  Concealed_fuse.jpg
Views: 409
Size:  31.4 KB

    Best of luck
    Baron030
    Yes, that slo-blo fuse, 3/10 amp. (as attached in the pic). And there is another fuse 1 amp fast blow (second pic) for a different purpose. Thanks so much for your valuable tip, JBL guru!
    Attached Images Attached Images   

  9. #9
    Senior Member pyonc's Avatar
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    Today I put in the right fuse with correct rating (3/10AMP), but still it doesn't power up.
    Clearly there is another issue. What could it be? Any idea?
    Before I take it to the tech shop nearby, I'd like to ask for your comment.
    Thanks a lot.

  10. #10
    Senior Member grumpy's Avatar
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    Personally, I would start with power supplies and related stuff, switches, and relays (if any).
    This is an old piece of gear, so there could be many issues, but if there is no power... (or the power lamp is burned out), it’s a good starting point. Sounds like a job for the test bench.

  11. #11
    Senior Member pyonc's Avatar
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    Quote Originally Posted by grumpy View Post
    Personally, I would start with power supplies and related stuff, switches, and relays (if any).
    This is an old piece of gear, so there could be many issues, but if there is no power... (or the power lamp is burned out), it’s a good starting point. Sounds like a job for the test bench.
    Thanks for your feedback, grumpy.
    It's in like mint condition, though.
    Let me get back when I get the report from the tech.

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