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Post subject: Blues jr amp problem
Posted: Sat Jun 10, 2017 9:32 pm
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New to forum, hope you can help. I have a three year old Fender Blues Jr. Just changed the tubes for the first time two months ago, probably way over due. Playing a gig, both gain and volume at 6-7, and amp blew, loud dirty hum. Any ideas?


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 1:30 am
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New output tubes always need to check and adjust bias.
Did you ? Sure not.

Amp may have now many issue.


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 2:40 am
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stratele52 wrote:
Amp may have now many issue.


+1

Filter cap, bias-supply cap, runaway tube, the possibilities are endless.

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: Blues jr amp problem
Posted: Tue Jun 13, 2017 2:56 am
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Retroverbial wrote:
stratele52 wrote:
Amp may have now many issue.


+1

Filter cap, bias-supply cap, runaway tube, the possibilities are endless.

Arjay


+1 Endless....


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 9:05 am
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Thanks for reply, don't know how to adjust the bias, any hints?


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 11:14 am
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Need some electronic skill and tools.

Lethal voltage in tubes amp can kill you


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 4:06 pm
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If you still have the old tubes, put em' back in there and try it.

UN


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Post subject: Re: Blues jr amp problem
Posted: Tue Jun 13, 2017 4:28 pm
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IIRC the Blues Jr doesn't have an adjustable bias pot. Thus, altering the idle bias requires some real tech work.

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: Blues jr amp problem
Posted: Tue Jun 13, 2017 6:58 pm
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New tubes are not exempt from blowing.
Start by removing all the tubes. Turn it on. Does it buzz?
If not put in one power tube. Let each tube warm up for 5 minutes. Does it buzz?
Add the other power tube . Does it buzz?
Add the preamp tubes one at a time.
When it starts buzzing, the tube you just added is probably the culprit. Try a different one.
If no tube fixes it, its an internal problem. Good hunting.


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