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Bad hum and shock in a twin

 
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tnt



Joined: 14 May 2007
Posts: 2898
Location: Princeton, NJ

PostPosted: Wed Sep 08, 2010 10:24 pm    Post subject: Bad hum and shock in a twin Reply with quote

So we had a bad hum when not touching the strings of the guit plugged into a Fender twin tonight and mild shocks when touching lips to mic, with hands on strings.

We isolated the problem to the amp by swapping it out with another amp.

Is this a 'straight to the service center' issue, or are there some easy things I can look for?

Thanks.
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74 Strat



Joined: 23 Feb 2008
Posts: 5639

PostPosted: Thu Sep 09, 2010 6:18 am    Post subject: Reply with quote

IS it a vintage Twin? Does it still have the 2 prong cord? I had a 1961 Ampeg Reverberocket and I got violently shocked one day when I touched my mouth to a mic. I ended up putting in a 3 prong to stop it from happening. I also noticed that the level of hum would change depending on the outlet used. Try a different wall outlet...Dean
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Travst



Joined: 15 Jul 2008
Posts: 9535
Location: Birmingham, AL

PostPosted: Thu Sep 09, 2010 7:21 am    Post subject: Reply with quote

I also think it's an issue involving the 2-prong cord or an incorrect conversion to 3-prong. I'd try flipping the direction of the cord at the wall outlet first. If that reduces hum and doesn't shock you after, it's probably the culprit.
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I need more practice, not more gear.
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tnt



Joined: 14 May 2007
Posts: 2898
Location: Princeton, NJ

PostPosted: Thu Sep 09, 2010 7:59 am    Post subject: Reply with quote

No, it's a modern twin 2004-05 ish... - three prong plug.

It's plugged into a power strip, then into a correctly grounded wall outlet. which I thought the strip might be the problem. I didn't have my little yellow tester thing with me, but we plugged another amp into the same exact outlet on the strip and the problem went away.

Could it be just a lose ground connection between the cord and the amp?

Is that easily handled? I'm not comfortable opening up amps, but if it's outside of the guts, maybe I can fix it.
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solemn13



Joined: 26 Jun 2008
Posts: 3807
Location: On a lost bound train runnin on Rogaine out of control

PostPosted: Thu Sep 09, 2010 8:08 am    Post subject: Reply with quote

It would be inside the chassis but it could be as simple as the ground wire coming loose from the screw that holds it to the chassis.
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tnt



Joined: 14 May 2007
Posts: 2898
Location: Princeton, NJ

PostPosted: Thu Sep 09, 2010 8:32 am    Post subject: Reply with quote

solemn13 wrote:
It would be inside the chassis but it could be as simple as the ground wire coming loose from the screw that holds it to the chassis.


So, just don't touch the caps or anything....right?
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Travst



Joined: 15 Jul 2008
Posts: 9535
Location: Birmingham, AL

PostPosted: Thu Sep 09, 2010 8:39 am    Post subject: Reply with quote

Right, stay away from all the electronics and just peek at the cord coming into the amp.
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John
I need more practice, not more gear.
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tnt



Joined: 14 May 2007
Posts: 2898
Location: Princeton, NJ

PostPosted: Thu Sep 09, 2010 8:47 am    Post subject: Reply with quote

Thanks.
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