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Post subject: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 1:32 pm
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Hi folks - I have a strange problem with my Blues Jr. I just put in a pair of JJ tubes and found that only the first tube powers up. Switching tubes around proved the same thing. I then put the original GT's back in - same thing. No glow on tube 2. Last time I used the amp it was fine. Any ideas on what's going on here? Bad socket maybe? Thanks in advance.


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Post subject: Re: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 2:05 pm
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Hi Jead,

It could be the socket, or a broken solder joint or circuit trace, or (insert guess). Do you have a meter and are you handy with it? Since it is only one tube that doesn't light up, it might be easy to trace the problem. :idea:

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

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Post subject: Re: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 2:15 pm
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shimmilou wrote:
Hi Jead,

It could be the socket, or a broken solder joint or circuit trace, or (insert guess). Do you have a meter and are you handy with it? Since it is only one tube that doesn't light up, it might be easy to trace the problem. :idea:


+1

That'd be the first place I'd look. If you're comfortable working with an open chassis, remove it from the cab and perform a continuity check between the traces on the circuit board and the pins of the suspect tube socket. Your DVM should show a dead short on each one of them. If not, then either one of those traces is fractured or you have an open (cold) solder joint between the trace and the socket pin. From your description of the symptoms, it sounds like the filament for that tube is not receiving the requisite voltage.

HTH

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: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 2:30 pm
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WOW! Thanks for the fast responses. After a little reading I figured I'd start by re-tensioning the socket. That did the trick. :D I can now see why the circuit board mounted sockets are considered to be a weak link. They're not particularly sturdy. FYI - I did discharge the amp before poking around in the socket with a screwdriver. :lol:

I really couldn't figure that something spontaneously went wrong. The amp hadn't been moved at all in weeks - all I did was take out the power tubes and replace them. It did'nt exactly inspire a great deal of confidence in me to find that could cause a tube to not power on. I assume since it's working fine again that I shouldn't need to explore any further. Would you folks agree? -and thanks again!


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Post subject: Re: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 2:53 pm
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Good job Jead! Sounds like you got it. That has to be some kind of speed record for repair, congrats. :)

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: BJ el84 doesn't fire up
Posted: Fri Mar 18, 2011 3:24 pm
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shimmilou wrote:
Good job Jead! Sounds like you got it. That has to be some kind of speed record for repair, congrats. :)


+1

OUTSTANDING!

Monitor the situation and always use caution with these types of PCBs.

Rawk on!

8)

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: BJ el84 doesn't fire up
Posted: Sat Mar 19, 2011 6:00 am
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If i remember those amps tubes sockets are mounted to the board. It's might have a broken joint on the board where the tubes is at. I would open her up and take a look


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Post subject: Re: BJ el84 doesn't fire up
Posted: Sat Mar 19, 2011 1:35 pm
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If you're coverd under warranty Fender has a great 5 year warranty, one of the best in the business. If the PCB is weak pushing in a tight fitting tube could do some damage.


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