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Post subject: Death of a blues junior
Posted: Mon Jun 23, 2014 10:02 am
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...my 2001 blues junior died...had it retubed a few years ago....guy said he biased it low to extend my tube life...but I lost some crunch...took it back...re biased hotter...better, but still not as crunchy...couple years go by...playing for average 3 hours once a week...tubes die...same guy retubed....first gig the thing starts smoking after 15 minutes...terrible smell....guy says output transformer blew out the board.....said he's never seen that happen in 40 years....can't even guess how except maybe speaker was connected in footswitch jack in error (but how would the amp still work for 15 minutes if that was the case)....could it have been a Roland single button footswitch was un compatible and ruined my life? It worked as the fat switch for years.
Tech advised me no point fixing it....so I bought the scx2 and will use it to drive the old blues junior speaker....
1/4 mono coupler......
Should new configuration be as loud as old b.j.....same tubes....same speaker...no?


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 10:53 am
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Amps that are underbiased to run "hotter" (i.e. more current through the output tubes) can have more crunch and balls but it sometimes comes at a price. The tubes have to dissipate more power, their anode plates get hotter and may begin to glow orange or red, dramatically reducing their life expectancy.

This extra current also runs through the output transformer and can cause overheating, possibly damaging the internal insulation or causing a short between the windings. Usually the HT fuse should blow before your amp catches fire but it's Sod's law that an £80 transformer will die before a £0.05 fuse blows.

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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 12:14 pm
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Glender wrote:
Should new configuration be as loud as old b.j.....same tubes....same speaker...no?


The Blues Jr uses EL84's while the SCX2 is 6V6-driven.

Apples to oranges.

Arjay

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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 1:46 pm
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Dang! I misread tube specs.
Is there a speaker swap or mod that would increase volume? Or preamp pedal?
Rookie Qs, I know.


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 1:50 pm
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Glender , is the guy is qualified ?

Fix the amp the best way without looking your tone and fry the Output Transformer ?

We can't tell .


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 5:20 pm
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Hmmm, so the amp was working fine (although you say "tubes died" - does this mean they stopped working or the amp just didn't sound like it used to any more, I take it as the latter because you say a couple of years passed - like a normal slow/gradual tube deterioration from use?) until you took it to him, (still working OK just not sounding as good as it used to), for new tubes and a bias adjustment on the new tubes, then it ran for 15 minutes and was irreparably destroyed?

How was he adjusting the bias, has your amp had an adjustable bias pot added to it? Because the Blues Junior in stock form would otherwise require removal of the entire PCB and a resistor change each time the bias needed to be altered. This is not something you would want to be doing very often as continually removing the PCB on that amp flexes/stresses the ribbon cable connections and will cause reliability issues, and repeated soldering/unsoldering and replacing a resistor on that PCB is likely to eventually create an issue with the very thin/delicate traces. The issue could also be from an incorrect adjustment (on the bias pot, if one has been fitted, or an incorrect resistor value) or a loose tube socket that needed re-tensioning has caused a tube to lose it's bias and take out the OT as well.

Maybe seek a different Tech to check the amp over.


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 6:13 pm
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Tubes died: one night after about 2 hours the volume dropped suddenly to half then gradually to crackly mush.....turned it off for a beer and smoke....back on...ok for 10 minutes then volume drop...and mush....
The guy seems qualified and been around for decades.


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 7:55 pm
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Glender,

Sounds like a bias issue (drifting or too hot) or some instability within the output section (like parasitic oscillations).


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Post subject: Re: Death of a blues junior
Posted: Mon Jun 23, 2014 10:33 pm
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At thirteen years old, I'd be reticent to put another dime into the amp.

JMOOC

Arjay

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Post subject: Re: Death of a blues junior
Posted: Tue Jun 24, 2014 1:45 am
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[quote="Glender"
The guy seems qualified and been around for decades.[/quote]


:lol: :lol: :lol:

No proof he is qualified , and look no to me .


Last edited by stratele52 on Tue Jun 24, 2014 1:47 am, edited 1 time in total.

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Post subject: Re: Death of a blues junior
Posted: Tue Jun 24, 2014 1:46 am
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No457 Snowy wrote:
Hmmm, so the amp was working fine (although you say "tubes died" - does this mean they stopped working or the amp just didn't sound like it used to any more, I take it as the latter because you say a couple of years passed - like a normal slow/gradual tube deterioration from use?) until you took it to him, (still working OK just not sounding as good as it used to), for new tubes and a bias adjustment on the new tubes, then it ran for 15 minutes and was irreparably destroyed?

How was he adjusting the bias, has your amp had an adjustable bias pot added to it? Because the Blues Junior in stock form would otherwise require removal of the entire PCB and a resistor change each time the bias needed to be altered. This is not something you would want to be doing very often as continually removing the PCB on that amp flexes/stresses the ribbon cable connections and will cause reliability issues, and repeated soldering/unsoldering and replacing a resistor on that PCB is likely to eventually create an issue with the very thin/delicate traces. The issue could also be from an incorrect adjustment (on the bias pot, if one has been fitted, or an incorrect resistor value) or a loose tube socket that needed re-tensioning has caused a tube to lose it's bias and take out the OT as well.

Maybe seek a different Tech to check the amp over.


+1000


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Post subject: Re: Death of a blues junior
Posted: Sat Jun 28, 2014 12:31 pm
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Superchamp wasn't loud enough to replace BJ....but I don't want to waste the BJ speaker and cab....yarrrrgh.....wish I could get a BJ head only.


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Post subject: Re: Death of a blues junior
Posted: Sat Jun 28, 2014 12:49 pm
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Glender wrote:
wish I could get a BJ head only.


I've seen a few custom conversions on Ebay.

They're not cheap though.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Death of a blues junior
Posted: Sun Jun 29, 2014 10:02 pm
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Disassembled dead BJ....one tube has a sticker on it.....that can't be good right?
[img][img][/img][/img]
Have a pic of said bestickered tube, and the board and it's smokey damage.....but this newbie can't see how to insert pics.


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Post subject: Re: Death of a blues junior
Posted: Sun Jun 29, 2014 10:21 pm
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Your pics must be uploaded to a remote hosting site such as Flickr, Image Shack, or Photobucket. Then you merely post the correctly-formatted link to enable your image(s) to appear within a post. Of the three, I find that Photobucket is the most user-friendly.

Arjay

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