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Post subject: 1983 Fender Concert Hum problem
Posted: Thu Jul 01, 2010 6:17 pm
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I recently changed the 10 inch speakers on my '83 Concert. I had read how this amp was really improved with a speaker change. I replaced the factory speakers with Eminence Rajun Cajuns. The amp sounds great but now when I turn the master volume (clean channel) past 4, a hum generates that grows louder if I continue to turn the amp volume up. This happens even when my strat volume is off. What did I do to my amp? Or could this be a tube problem? None of the tubes are sputtering when I tap them. Any ideas?


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Posted: Thu Jul 01, 2010 9:15 pm
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Winston, if the speaker connections are the same as before the swap, I don't see how you could have caused the problem. These are solder connections? If so, they might be worth a recheck. The amp did not do this before the speaker swap ? One more question; will the amp hum if nothing is plugged into it ? Welcome to the forum and I hope we can be of some help. Art

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Posted: Thu Jul 01, 2010 11:59 pm
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A 1983 pedigree pegs this amp at 27 years old -- it's possible that it's time for new power supply and bias caps.

HTH

Arjay

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Posted: Fri Jul 02, 2010 8:17 am
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aclempoppi wrote:
Winston, if the speaker connections are the same as before the swap, I don't see how you could have caused the problem. These are solder connections? If so, they might be worth a recheck. The amp did not do this before the speaker swap ? One more question; will the amp hum if nothing is plugged into it ? Welcome to the forum and I hope we can be of some help. Art


+1 Especially check the ground connections.

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Posted: Fri Jul 02, 2010 10:57 am
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Hey guys, thanks for the input. I had to turn one of the cajuns sideways to about 10 o'clock so the speaker wire could reach the connector points. Maybe I connected them improperly. I have not unplugged the guitar from the amp yet to see if it hums without the guitar. If it does not hum, what would that mean? Your responses are a great help.


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Posted: Fri Jul 02, 2010 11:01 am
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Also, the amp never hummed before the swap. The wires have connectors that slide right onto points on the speaker. No soldering. I put all ground wires back into place exactly like they were on the stock speakers. Below 4 there is no humming.


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Posted: Fri Jul 02, 2010 11:21 pm
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Winston, my concern would be that all of the spade fittings and wire connectors have a good tight sliding connection. Are the new speaker's spade fittings the same size as the original speakers ? And I'd like to make sure that the tubes are all snug in their sockets. Art

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Posted: Sat Jul 03, 2010 3:49 am
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I'm very surprise that a bag connections to a speaker do some hum !

Bad connection= weak soud or no sound but hum ? I can see why.

Maybe you touch a tube, it move and bad connection on socket like said Aclempoppi.

Better to clean socket pins on tubes


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Posted: Sat Jul 03, 2010 1:31 pm
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Make sure your new speakers are the same impedance as the old.
Try disconnecting each speaker in turn to see if the hum disappears
when one is disconnected. Maybe you have a rogue ragin cajun.
It might just be possible too that your new speakers are very
detailed and your hearing sound that you couldn't before which
might be the caps as suggested before.
Good Luck,
Barry


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Posted: Wed Jul 07, 2010 5:32 am
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I will check the impedence to make sure they are the same, and also unplug one speaker at a time. The fittings are very snug. I have checked the tubes and no extra noises are made. When you turn it up the hum is brutal, its not a light noise you could overlook. It sounds like a freaking horn blowing.


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Posted: Wed Jul 07, 2010 1:29 pm
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Like horn blowing ! Could be a tube, or speakers impedance is wrong and make negative feedback is unbalanced.

But I'm not sure of that


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Posted: Wed Jul 07, 2010 6:47 pm
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Ok, I,m going with a positive feedback condition. The amp sounds like it is feeding back on to itself. Usually this will happen if the output trans or power tube sockets have been changed and the plate wires have been connected to the wrong side of the push-pull circuit (aka reverse drive). But that is on the primary side of the trans. To be honest, I've never reversed the lines on the secondary side(speaker) of the trans, but as Stratele brought up, that surely would mess up the negative feedback circuit's job. So I guess that the hook up wiring and each speaker must be checked. With the amp turned off and no guitar plugged in, I'd hook up one speaker, at a time and turn the amp on(standby in play mode) and test. If the problem persists or changes when the guitar is plugged in, then the problem is elsewhere. Art

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Posted: Thu Jul 08, 2010 2:57 am
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+1 aclempoppi

Wintston21 are you sure this problem was not there before you change speakers ?

Or you do any modication in the circuit WHEN you replace speakers ?


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Posted: Tue Jul 27, 2010 1:25 am
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Have you tried it without anything plugged in yet ? That would be the first thing I would do .


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Post subject: 1983 Fender Concert Hum problem
Posted: Sat Jul 31, 2010 8:42 am
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I found the problem. When I switched the speakers I accidentally hit the ground switch and did not realize it. I switched it back to the middle position and the hum disappeared...or at least I have not heard it hum since. Thanks for everyone's reply.


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