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Post subject: Blues Junior III Hum
Posted: Sun Jan 01, 2017 7:20 am
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Just recently picked up a used FBJ III and love the sound but I'm getting a hum from the amp.

I'm guessing the topic has been covered before but a quick search didn't turn up anything specific for me

No matter which order I put the 3 'pre-amp' tubes in the hum is always there. and it lessens with the FAT off

If I pull any of V1-2 or 3 the hum goes away.

My local shop only had 2 tubes in stock so I still have 1 older tube in it.

The hum goes away if there is no cable plugged in ???

Just wondering if you might offer some thoughts


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 2:28 am
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You write ;
"The hum goes away if there is no cable plugged in ??? "
No hum when nothing plug in the amp ; it is not the amp

Check your guitar ( ground missing ? ) or what you plug in the amp. They may act like antenna to send noise / hum to the amp.


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 2:58 am
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Thanks for the reply.

I thought that might have been the case too.

I should have also included that it doesn't matter which of the guitars is plugged in. The hum is still there


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 3:54 am
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Did you try guitars with another amp ?
Cell phone, computer... may induce hum by guitars pickups.

If amp do not hum if alone, IMO it can't be the amp or you forget to tel something....


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 4:25 am
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Don't forget, a amp will reproduce what you send it


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 5:45 am
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and to be more clear... :D

Turn amp on and let it warm up - no hum
plug cable into amp (without guitar plugged in) - hum
plug in guitar - still hum
touch metal on guitar - hum goes away.

This is true for any of the three guitars I have.

There is no hum from any of the guitars in my other amp (but its just a small solid state unit)

I thought maybe bad cable but the other amp appears to eliminate that possibility.

Is it possible that there's a grounding issue with the input jack on the amp ?

I'm not so good with electrical issues so I really do appreciate the help & comments


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 5:59 am
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ehencher wrote:
and to be more clear... :D

Turn amp on and let it warm up - no hum Normal
plug cable into amp (without guitar plugged in) - hum Normal it is like an antenna with no guitar plug.
plug in guitar - still hum ; guitar receive interference
touch metal on guitar - hum goes away., you send interference to ground by your body, no more interference go to the amp

This is true for any of the three guitars I have.

There is no hum from any of the guitars in my other amp (but its just a small solid state unit)
IMO , yes

I thought maybe bad cable but the other amp appears to eliminate that possibility.

Is it possible that there's a grounding issue with the input jack on the amp ?
No with what you write


I'm not so good with electrical issues so I really do appreciate the help & comments


Somethings from outside go into the guitars.
Do you have a know good ground at you house outlets ?
Can you test on another room, far from you are ? Or another house ?
Cellphone, computer, halogen bulb, neon bulb are all Off ?


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Post subject: Re: Blues Junior III Hum
Posted: Mon Jan 02, 2017 7:30 pm
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Since the amp makes no hum without any input it appears to not be the amp.
Since another amp with the same cable and 3 guitars also makes no hum ... the next then question becomes:
What is in your signal chain with the BJ3 that might not be in the chain with your other amp?
Whatever the source of the hum, it is more likely in front of the amp and not part of it.

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Post subject: Re: Blues Junior III Hum
Posted: Wed Jan 04, 2017 10:23 am
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Sounds to me like the jack connections have broken loose from the circuit board or a damaged jack.
Its a very common issue with these. The 1/4 plug has enough leverage to tweak and damage the jack when a cord is tripped over. Its probably why the guy sold it.
You probably need a new jack. Maybe a little rework to repair torn traces. I would charge @ $45 for the repair, check the tubes, and resolder. Hope you find a good tech


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Post subject: Re: Blues Junior III Hum
Posted: Wed Jan 04, 2017 4:06 pm
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TimsAudio wrote:
Sounds to me like the jack connections have broken loose from the circuit board or a damaged jack.
Its a very common issue with these. The 1/4 plug has enough leverage to tweak and damage the jack when a cord is tripped over. Its probably why the guy sold it.
You probably need a new jack. Maybe a little rework to repair torn traces. I would charge @ $45 for the repair, check the tubes, and resolder. Hope you find a good tech


+1

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Post subject: Re: Blues Junior III Hum
Posted: Thu Jan 05, 2017 4:33 am
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Thanks everyone for the responses - much appreciate the sharing of knowledge.

I wish I was closer to TimsAudio - he'd have the amp right away.

Since I live in a small town I`m going to have to check and see if there`s anyone who can work on it


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Post subject: Re: Blues Junior III Hum
Posted: Thu Jan 05, 2017 4:40 am
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ehencher wrote:
Thanks everyone for the responses - much appreciate the sharing of knowledge.

I wish I was closer to TimsAudio - he'd have the amp right away.

Since I live in a small town I`m going to have to check and see if there`s anyone who can work on it



With guitar plug in the amp , if you move the jack in the amp plug with amp power ON, you'll hear if there is a bad connection or broken solder or broken plug.


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