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Post subject: Re: Death of a blues junior
Posted: Fri Jul 18, 2014 9:35 am
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It's the scratched tracer that concerns me...it actually looks like sabotage.
How does thy happen except on purpose? Wouldn't that scratch cause problems?


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Post subject: Re: Death of a blues junior
Posted: Fri Jul 18, 2014 10:00 am
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It is a trace, and it looks burnt to me, as a result of the damage. This trace is connected to one of the ribbon cables. A tracer is a bullet coated with phosphorous that glows showing the path when fired.

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Post subject: Re: Death of a blues junior
Posted: Sat Jul 19, 2014 10:22 am
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Unsurprisingly the board has burned around pin 7, the plate connection for an EL84. You can't "jumper" that or wire past it because the carbon deposit on the PCB is conductive and will short out and burn further when you apply HT voltage to it. You'd have to entirely junk that board and replace it (or cut part of it away and make a point to point section of the amp).

The reason why it's failed is blindingly obvious, it was badly underbiased and has drawn too much current. The guy who biased it hot didn't know what he was doing. Bias isn't a tone control, you don't bias the amp where it sounds good. You measure the HT voltage, look up the tube's rated power dissipation and set it the bias voltage at a point where the tube is running and idle current well within the maximum dissipation. I'm not surprised it failed when it was first used on a gig, it probably ran just fine for the 10 minutes the repair guy spent checking it.

Soldering one resistor across another is a horribly lazy fix. It doesn't take much effort to remove the factory fitted resistor and replace it. Hanging a component in mid air like that is asking for trouble.

tl;dr - the guy knows nothing about setting up tube amps.

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Post subject: Re: Death of a blues junior
Posted: Sat Jul 19, 2014 11:04 am
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GilgaFrank wrote:
Unsurprisingly the board has burned around pin 7, the plate connection for an EL84. You can't "jumper" that or wire past it because the carbon deposit on the PCB is conductive and will short out and burn further when you apply HT voltage to it. You'd have to entirely junk that board and replace it (or cut part of it away and make a point to point section of the amp).

The reason why it's failed is blindingly obvious, it was badly underbiased and has drawn too much current. The guy who biased it hot didn't know what he was doing. Bias isn't a tone control, you don't bias the amp where it sounds good. You measure the HT voltage, look up the tube's rated power dissipation and set it the bias voltage at a point where the tube is running and idle current well within the maximum dissipation. I'm not surprised it failed when it was first used on a gig, it probably ran just fine for the 10 minutes the repair guy spent checking it.

Soldering one resistor across another is a horribly lazy fix. It doesn't take much effort to remove the factory fitted resistor and replace it. Hanging a component in mid air like that is asking for trouble.

tl;dr - the guy knows nothing about setting up tube amps.


+1. On all counts.

That PCB is toast.

Arjay

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Post subject: Re: Death of a blues junior
Posted: Mon Jul 21, 2014 7:13 am
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Shimilou,

Check out picture that says "scratched by a gremlin?" It's on the main board not the tube board....exposed area is the size of a grain of rice.....
I should have specified...it's on the other side of r33


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Post subject: Re: Death of a blues junior
Posted: Mon Jul 21, 2014 9:29 am
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Yes, that's the one, it looks like a very small burn spot at the edge of the trace.

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Post subject: Re: Death of a blues junior
Posted: Sun Aug 03, 2014 9:37 pm
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Glender wrote:
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.


People have been asking for that for years but fender never has done it. sucks


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Post subject: Re: Death of a blues junior
Posted: Sun Aug 03, 2014 10:08 pm
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agdtec wrote:
Glender wrote:
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.


People have been asking for that for years but fender never has done it. sucks


And I'll bet they won't either, the Head version would obviously be even less expensive (no speaker and smaller cabinet requirement) in the lineup, plus once people started running the heads into various cabs, larger 1x12, 2x12 etc and hearing the results of doing so, I suspect it would pose a fair threat to the next size larger, more expensive amps in the lineup. The cab size and particle construction is one of the primary issues holding back what can be a very nice sounding (and louder) amp through a bigger cab, but in doing so I think it keeps the BJr just where Fender wants it in their amp line performance wise. I could be way off in thinking that too. :lol:

I hardly used mine until I did this, sounds WAY better than it used to and still very portable:
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A couple of other forum members have done similar with a head version and multi speaker/larger combo cabs.


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Post subject: Re: Death of a blues junior
Posted: Mon Aug 04, 2014 9:22 am
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^^^Yep!
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