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Post subject: Trying to troubleshoot Blues Jr.
Posted: Sat May 16, 2015 5:06 pm
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I'm trying to diagnose an intermittent issue with my 2012 Blues Jr and since the first culprit is usually the pre amp tubes, this is where I began. As was suggested previously, I checked the sockets and everything was snug and tight.

I replaced the stock GT-12AX7 in V1 with a brand new out of the box GT-12AX7. There was no change. I put back the stock tube in V1 and repeated the procedure with V2. Still no change. It appeared that three was indeed the charm because when I put the new tube in V3 the noises were gone and everything sounded as it should.

I played through the amp for about 10 minutes. No issues. Left it on for a couple of hours, then played some more. Everything looked and sounded fine so I turned off the amp and figured I had solved the problem. Fast forward a few more hours and the gremlins returned. This time I recorded the noises in hope that our resident amp gurus can help. Blues Jr. noises The noises are there while playing a low open E. At around 14 seconds the guitar cable is removed and we have other noises until the amp is switched off at 23 seconds.

If it's the tubes I suppose it could be more than 1 pre amp tube but I assumed this to be unlikely. Could it be the power tubes? All tubes had a nice orange glow.


Thanks and Cheers!
BM

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Sat May 16, 2015 6:37 pm
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That sounds like a rattling tube. Do you have another set of output tubes to try?

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Sun May 17, 2015 2:50 am
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shimmilou wrote:
That sounds like a rattling tube. Do you have another set of output tubes to try?



+1


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Sun May 17, 2015 6:55 am
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stratele52 wrote:
shimmilou wrote:
That sounds like a rattling tube. Do you have another set of output tubes to try?
+1
Thanks for the reply, guys.

Is the rattling caused by a faulty tube or by the vibration of the metal cage or power tube stabilizer or something else inside? I don't have another set of output tubes. What I'd like to avoid is bringing the amp in for repair and being told that it's "just a tube".

Cheers!
BM

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Sun May 17, 2015 7:12 am
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You have 2 choice; buy some tubes and try or pay somebody to do for you .......

Spare tubes are always useful if you play with tubes 'amp many years


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Sun May 17, 2015 8:50 am
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If you don't have a pair of power tubes and you suspect one of them, just pull one at a time and listen to the amp with only one in.
If one is quiet and the other noisy, you've found your problem.


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 6:46 am
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stratele52 wrote:
You have 2 choice; buy some tubes and try or pay somebody to do for you .......

Spare tubes are always useful if you play with tubes 'amp many years
Sounds like a good plan, stratele52. If I take the amp in for servicing and it's the power tubes, then I've paid for a set of tubes plus the service fee. If I can rule out the tubes then it would most likely be something under warranty so worst case scenario I've paid for a spare set of power tubes which is always good to have on hand.

For my own curiosity and education, here's a question for the amp techs. A customer brings in his BJr. and tells you he has an intermittent problem and that the amp is making this noise . What steps do you take to diagnose the issue?

Cheers!
BM

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 8:17 am
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First, recreate the symptom with an oscillator to confirm it isn't a buzzing fret or a bad cable. Connect dummy load and an oscilloscope.
Second, wiggle the tubes to see if the socket pins are intermittent and tap on the tubes to look for microphonic tube. Substitute tubes, one at a time
Third, wiggle the input jack and exercise the controls.
Fourth, exercise the speaker plug and run it on a known good speaker to confirm it isn't blown.
If that doesn't smoke it out, pull the chassis. Tap on the board while running to look for intermittents. Pull the board and look for broken solder.


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 8:33 am
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TimsAudio wrote:
First, recreate the symptom with an oscillator to confirm it isn't a buzzing fret or a bad cable. Connect dummy load and an oscilloscope.
Second, wiggle the tubes to see if the socket pins are intermittent and tap on the tubes to look for microphonic tube. Substitute tubes, one at a time
Third, wiggle the input jack and exercise the controls.
Fourth, exercise the speaker plug and run it on a known good speaker to confirm it isn't blown.
If that doesn't smoke it out, pull the chassis. Tap on the board while running to look for intermittents. Pull the board and look for broken solder.
Thanks, TimsAudio. Very informative. Even though I don't foresee myself venturing too far beyond swapping tubes, I do enjoy learning how things work and this forum contains a wealth of knowledge.

Cheers!
BM

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 8:35 am
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If the guitar and cable are in good shape and you are sure it is only the amp , Il would clean the tubes socket contacts and retensioning them .

I 'll check if tubes sockets's solder with the circuit are not broken


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 4:23 pm
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I changed the power tubes and after a 3-hour jam session everything with the amp is normal. I'd say the issue was with the power tubes but I won't in case I jinx something. :lol:

Thanks to everyone for the feedback
Cheers!
BM

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 4:36 pm
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Bluer Monkey wrote:
I changed the power tubes and after a 3-hour jam session everything with the amp is normal. I'd say the issue was with the power tubes but I won't in case I jinx something. :lol:

Thanks to everyone for the feedback
Cheers!
BM



Try old ones and see what happen before you put it in the garbage.

For the new tubes, a bias check is a must and adjust if needed if you want the best tone and long life for you tubes .


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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 4:43 pm
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stratele52 wrote:
Bluer Monkey wrote:
I changed the power tubes and after a 3-hour jam session everything with the amp is normal. I'd say the issue was with the power tubes but I won't in case I jinx something. :lol:

Thanks to everyone for the feedback
Cheers!
BM



Try old ones and see what happen before you put it in the garbage.

For the new tubes, a bias check is a must and adjust if needed if you want the best tone and long life for you tubes .


+1

Tube longevity depends upon a healthy bias voltage.

Arjay

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Mon May 18, 2015 4:43 pm
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Good job Bluer Monkey!

Remember the K.I.S.S principle. With a tube amp, odds are that a great deal of problems will be tube related (tubes, solder joints, sockets, are most common). Tube substitution is the easiest and often best method for troubleshooting, and probably should be the first thing to try when problems arise. With many modern amps, it is a good idea to inspect all solder joints when intermittent problems arise.

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Post subject: Re: Trying to troubleshoot Blues Jr.
Posted: Tue May 19, 2015 4:51 am
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shimmilou wrote:
Good job Bluer Monkey! Remember the K.I.S.S principle. ...
Absolutely! Given my knowledge of the inner workings of a tube amp, the K.I.S.S. principle is the ONLY principle for me. :D

As for biasing, I went with what I had gathered from a sweep of the "Internets" which led me to believe that it is not necessary to adjust the bias when replacing power tubes of the same type and rating. In this case I replaced the stock GT-EL84 rated 4 with a matched pair of the same rating.

Cheers!
BM

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