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Post subject: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Tue May 07, 2013 6:31 am
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Hi, I plugged my American made Blues Jr. amp into a wall outlet during a gig, and there was a power surge, being the building was very old. It clearly blew my fuse, as the glass was burnt and the wire was severed in the middle. The glass fuse read 2 amps/ 250 volts, and then the number 312, whatever that means. I went to a local hardware store and found a very similar fuse, 2 amps/250 volts, about the same length, maybe off a milimeter(about 1-1/4 inch). However the new fuse did not have the 312 on it. Putting the new fuse in, I turned the amp on and got some sound. I then turned the volume up and the first power tube lit up like a lighthouse, and the amp turned off, blowing the new fuse. Can someone explain to me what I did wrong? I'm guessing I got a different fuse than the one needed, because it lacked the 312 label. Thanks for the help!


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Tue May 07, 2013 7:15 am
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I beliete that he "312" is a manufacture's code and not critical for your use. However, a bright glowing output tube, followed by a blown fuse could indicate a shorted tube or bias way out-of-whack.

Do you have access to a tube tester?


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Tue May 07, 2013 7:19 am
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No but the tubes are brand new.


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Tue May 07, 2013 2:00 pm
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mikeph0210 wrote:
No but the tubes are brand new.


Brand new tube could be bad very soon .

Do you check / adjust bias when put these new tubes ? If not ,too hot bias = life shortened .

If you want to try another fuse ; remove those tubes , and put new fuse . If fuse stay good , problem in tubes.

If it blow , could be many thing.


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Wed May 08, 2013 1:56 pm
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stratele52 wrote:
mikeph0210 wrote:
No but the tubes are brand new.


Brand new tube could be bad very soon .

Do you check / adjust bias when put these new tubes ? If not ,too hot bias = life shortened .

If you want to try another fuse ; remove those tubes , and put new fuse . If fuse stay good , problem in tubes.

If it blow , could be many thing.



+1

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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Wed May 08, 2013 4:14 pm
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mikeph0210 wrote:
No but the tubes are brand new.


Those were new tubes. Right up to the power surge. Stratele is right, pull the power tubes, put in a new fuse and turn it on. If the fuse doesn't blow, it is in the power "amp" but not necessarily the tubes. If it does blow, it is somewhere else and I would suspect the power supply circuitry.

Art


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Thu May 09, 2013 5:30 am
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If that Blues Jr is made in America, it's probably due for some maintenance like filter caps and some resister value checks. New tubes can be bad, but if the bias drifted too hot, they could be red plating and that would kill your new tubes. I'd take it in and get it checked out.

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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Fri May 10, 2013 4:07 am
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mikeph0210,

You may wanna try one thing, first. LIGHTLY spray some contact cleaner (like DeOxit D5 or GN5) onto the pins and into the sockets of those 6L6GCs. Work the tubes in-&-out a few times.

Replace the fuse with proper value (which you already have). See if the tube red plates again. If so, turn amp off. Don't use amp until fixed.

Good luck!


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Post subject: Re: Replaced a fuse in my Blues Jr, and blew the new fuse!
Posted: Mon May 13, 2013 4:54 am
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BMW2002Ti wrote:
mikeph0210,

You may wanna try one thing, first. LIGHTLY spray some contact cleaner (like DeOxit D5 or GN5) onto the pins and into the sockets of those 6L6GCs. Work the tubes in-&-out a few times.

Replace the fuse with proper value (which you already have). See if the tube red plates again. If so, turn amp off. Don't use amp until fixed.

Good luck!


Blues Jr. amps have EL84(6BQ5)tubes,...not 6L6 tubes. I should know,...I had a Blues Jr. amp years ago and it didn't have 6L6 tubes in power section.

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