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Post subject: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Fri Mar 24, 2017 9:20 am
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I turned on my Blues Jr III the other day and it let out a pop, then died. Checking inside, it was the 2amp fuse that had blown. I replaced it and turned the unit on. Upon doing so it crackled and the EL-84 tube on the left started glowing really brightly...like a 100 light bulb brightly! I shut it down, made sure the fuse was seated and turned it on again. It did the same thing, but then seemed to calm down. I plucked one string on the connected guitar and it let out a crackle and died, having blown the same fuse again.

Anyone have any insight into what's going on and how it might be fixed?

Thanks in advance.


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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Fri Mar 24, 2017 9:23 pm
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Hi thirteenthirteen,

Remove the output tubes, replace fuse, power on and see if fuse holds. Likely a bad output tube, and possibly fried screen grid resistor. If fuse holds with output tubes removed, check your screen grid resistors and try a new set of output tubes.

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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Sat Mar 25, 2017 9:51 am
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Thanks much for the reply.

Removed the output tubes, replaced fuse, currently have the amp on and the fuse is holding. Which is good...maybe. Well, it's progress anyway.

I have to confess a high degree of ignorance in these matters so I don't know what the screen grid resistor is, much less how to check it.

Could you please elaborate on that? Feel free to dumb it down for me.

Thanks.


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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Sat Mar 25, 2017 10:21 am
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You're in good hands here, 13.
shimmi is great at this kind of thing and we have lots of other folks here who are also very knowledgeable and helpful too.
Pay close attention.
This will be good for you.
I am an old dog and I learn all kinds of new tricks here.
Be patient, though.
Not all the members come round every day.
Hopefully, you'll enjoy the experience so much you'll decide to stick around and participate in other discussions as well.

In the meantime, welcome to our forum.

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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Sat Mar 25, 2017 8:17 pm
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thirteen,
Do you have, and know how to use, a multimeter? Read schematics? If not, you might be limited to a visual inspection. Note that there is high voltage present in the amp, even when unplugged from electricity.

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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Sun Mar 26, 2017 1:14 pm
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First;
The power tube could be short, need some new one with a bias check.
Put two news one.
Reverse power tubes. If the one wich glow bright do the same thing in other socket, it is the tube not the circuit or the resistor . Replace both tubes

Second;
Bad contact with bias circuit ; solders , tube socket pins

Remove the "s" on your title ; there is one tube glowing :lol:

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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Wed Mar 29, 2017 5:55 am
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Ha! Fair enough, stratele; indeed only one of the tubes was glowing like a light bulb. Although perhaps a bit more linguistically elegant, the title of my post was inaccurate. Guilty as charged.

Anyway, here's an update: I purchased a new matched set of JJ Electronics tubes from Amazon for under $25. I replaced them both, along with the blown fuse, held my breath, turned it on and everything worked perfectly!

I'm guessing this means one of the tubes was in some way "bad".

So, problem solved. I am still curious as to why the tube failed when it did. There was no traumatic event leading up to all this and the amp itself is less than eight months old. Is this a normal, common occurrence?

This is my first tube amp, and I can tell you that from now on I'll be bringing a solid-state amp along as a backup when I play out.

At any rate, I appreciate all the help.


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Post subject: Re: Blues Jr III blowing fuse, tubes glowing very brightly
Posted: Wed Mar 29, 2017 6:18 am
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Power tube can fail anytime but this not happend often,
Bias check is a must if you want the better tone and long life to the tube.

Never put news power tubes without checking and ajusting bais .
Or keep new tubes in stock all the time.....

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