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PostPosted: Wed Jan 04, 2017 12:49 pm 
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Bottle Rocket

Joined: Wed Jan 04, 2017 12:39 pm
Posts: 15
I traded away my old Dual Recto for a Mark I that seemed to work for a few weeks.


After a few weeks it suddenly developed a loud hum that occurs anytime the amp is on. It hums when no guitar is plugged in, when no effects are in the loop, when I try using a patch cable in the effects loop, and the only way to change the intensity of the hum is to raise or lower the master volume. No other control has any bearing on the hum, including reverb, presence, the EQ, volume 1 or volume 2.

I've tried swapping power and preamp tubes with no change. I have tried plugging it in to an external cabinet to no avail. I've tried different electrical outlets, and different venues and absolutely no change.

Occasionally the amp will turn on and run quiet and I've noticed the tone is substantially better. Then after a bit of time playing the hum will start and the tone becomes noticeably worse. It won't cut through in a band situation well, and it seems to lose the strong midrange punch and the breakup from the amp becomes harsh and non-musical.



I took a short video of what the map is doing that I'll post below. Thank you in advance for any help.


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PostPosted: Wed Jan 04, 2017 12:50 pm 
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Bottle Rocket

Joined: Wed Jan 04, 2017 12:39 pm
Posts: 15
https://youtu.be/1FYLHpbjzyk


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PostPosted: Thu Jan 05, 2017 3:52 pm 
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Mark III
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Joined: Thu Sep 25, 2008 2:55 pm
Posts: 238
It sounds like a 60 Hz ground loop. Have you tried switching the ground switch on the back? Does that make a difference?


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PostPosted: Mon Jan 09, 2017 9:52 am 
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Bottle Rocket

Joined: Wed Jan 04, 2017 12:39 pm
Posts: 15
Unfortunately the ground switch did not make a difference


Two things happened leading up to the noise

It rode in the trunk of my car for a couple weeks and got bumped around

I got a reverb pedal and tried running it through the effects loop



I don't know if I knocked something loose in the car or using the loop for the first time in a while messed a jack up


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PostPosted: Fri Jan 13, 2017 1:57 pm 
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Mark III
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Joined: Thu Sep 25, 2008 2:55 pm
Posts: 238
I don't really have any other ideas. Since it happens in different venues, it must be something wrong with the amp. You may want to take it to an amp tech. Here ais a list I found with some of the potential issues:

http://www.geofex.com/ampdbug/hum.htm

Good luck. Please let us know if you discover the problem/solution.


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PostPosted: Sun Jan 22, 2017 9:16 pm 
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Mark II

Joined: Sat Aug 05, 2006 11:15 pm
Posts: 127
Location: San Jose, CA
time for a cap job :lol:

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PostPosted: Wed Mar 01, 2017 4:57 pm 
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Bottle Rocket

Joined: Wed Jan 04, 2017 12:39 pm
Posts: 15
Just an update...

Picked it up from Slemmons Music today in Dallas, TX


It was the 12at7 reverb driver that was causing the hum, 1 of the power tubes wasn't functioning (the heater element failed) and the other 3 were weak. In addition one of the pots had been replaced with a low quality one. $224 later its back to new condition and working 100%! As it turns out that's better than when I first got it so I'm stoked!

Highly recommend Slemmons for their fast turn around and excellent work


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