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Old 16th April 2006, 05:38 PM   #1
Ryssen is offline Ryssen  Sweden
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Default Hum in Speakers

I have a 6B4G SE amp with DC heaters,and i thought the hum came from the heaters,so I removed all the tubes and dissconnected the separate filaments transformers and switcht the HV transformer on,and the hum is still there! Itīs not much hum but itīs still there.The output trafos are about 3 inches away from the HV transformer,it must come from there.Is there a way to filter this out?
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Old 16th April 2006, 05:54 PM   #2
poobah is offline poobah  United States
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Try rotating either of the transformers 90 degrees... or any angle that eliminates the noise.

Also you should have iron-based shields over the windings...

Steel chassis have also been said to create unwanted coupling... although I suspect this is a very minor effect...

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Old 16th April 2006, 06:12 PM   #3
Giaime is offline Giaime  Italy
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Quote:
Originally posted by poobah
Steel chassis have also been said to create unwanted coupling... although I suspect this is a very minor effect...

I think that is the problem of the incurable hum in my preamp. I've used a 1mm steel sheet, alluminium is unobtainable here where I live.
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Old 16th April 2006, 06:21 PM   #4
Ryssen is offline Ryssen  Sweden
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I have a 14x14" steel plate and wood frame,and no there is no iron-based shields over the windings...maybee Iīll try to rotate first...
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Old 16th April 2006, 06:21 PM   #5
poobah is offline poobah  United States
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Aluminum = Unobtainium ?

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Old 16th April 2006, 06:26 PM   #6
poobah is offline poobah  United States
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It is often best to have one transformer laying "flat" and the other "standing up"...
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Old 16th April 2006, 06:34 PM   #7
Ryssen is offline Ryssen  Sweden
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You mean to make iron-based shields in aluminum,that I could do,or make a new 14x14" chassie,that I wont do to muuuch work.
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Old 16th April 2006, 07:10 PM   #8
Giaime is offline Giaime  Italy
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Quote:
Originally posted by poobah
Aluminum = Unobtainium ?

Here at least, absolutely. You can only find in metal surplus places sheets 1mm thick (too little) and 6 meters x 4 meters, and they won't cut it for you, you have to buy the whole sheet (obviously at an insane price).

The best I've found is 1mm steel, 50cm x 25cm, 5 euro each, and with this I've built my preamp.
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Old 16th April 2006, 07:14 PM   #9
poobah is offline poobah  United States
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The windings should have covers made of steel or iron.

An aluminum chassis plate may help. But it may not be the only problem.

Lay one transformer so the laminations are horizontal... the other transformer so the laminations are vertical. That is often best.

Try rotation BEFORE you make a new chassis!

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Old 16th April 2006, 07:16 PM   #10
poobah is offline poobah  United States
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Giaime,

Just a little hint... street signs are made of aluminium...

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