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Old 15th September 2003, 09:23 PM   #1
Bricolo is offline Bricolo  France
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Default Hum problem, but on the tweeter (!?)

Whao, that's my 1st post on the tube forum


I'm asking this question for a friend (maybe that's why I never posted here: I don't have any tube amp)
He has a tube amp (don't remember exaclly which one, but I think the question can be answeared without knowing this)


The problem is that on one channel, he has a hum on the speaker? Strangely, this noise comes from the tweeter, and not from the woofer. It's definitely not a 50 or 100hz hum, and goes away after 20 minutes of use.

I'm wondering where this hum can come from, since it's not 50/100Hz.

Does one of you tube specialists have an idea?


Thanks
Alex
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Old 15th September 2003, 09:55 PM   #2
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It could come from power supply noise. Does it use a SS rectifier, or tube?

Tim
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Old 15th September 2003, 10:24 PM   #3
SY is offline SY  United States
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Quote:
Originally posted by Sch3mat1c
It could come from power supply noise. Does it use a SS rectifier, or tube?

Tim
Unlikely if it goes away after 20 minutes. Sounds like something is thermalling, probably a cap or a solder joint. What I'd do is warm the amp up until the noise goes away, then use freeze spray on the caps and resistors one by one until the thermally-intermittent component is located ( DON'T use the freeze spray on the tubes!)
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Old 15th September 2003, 10:30 PM   #4
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Hi,

Quote:
Sounds like something is thermalling, probably a cap or a solder joint.
Indeed, I'd vote for the bad solder joint and look at the PSU first.

Quote:
then use freeze spray on the caps and resistors one by one until the thermally-intermittent component is located ( DON'T use the freeze spray on the tubes!)
Eeeek...I've never felt comfortable with that on tubed circuits...maybe I'm just paranoid...

Cheers,
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Old 15th September 2003, 10:33 PM   #5
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I once worked in a repair company where freeze spray was mostly used to spray on cockroaches that were living in brought-in VCR's and decided to take a walk into the building.

Saved the company from having the whole firm gassed to kill the insects.
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Old 15th September 2003, 10:38 PM   #6
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Hi,

Quote:
I once worked in a repair company where freeze spray was mostly used to spray on cockroaches that were living in VCR's and decided to take a walk into the building. Saved the company from having the whole firm gassed to kill the insects.
And the crickets were still humming happilly ever after....in the tweeters.

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Old 15th September 2003, 10:40 PM   #7
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We used hammers on those. There isn't a tone control on amps for nothing, isn't it ?

Of course I have a "be nice to animals" sticker on my car
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Old 15th September 2003, 10:48 PM   #8
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Hi,

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There isn't a tone control on amps for nothing, isn't it ?
Tone controls? Cricket controls you mean?

Those have been banned ages ago...

They're only accepted on hot long Summers when temperatures rise way above 35 degs. C and cockroaches want to wander...

Maybe we should take a trip to Rio and I'll show you real cockroaches?

LOL...
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Old 15th September 2003, 10:50 PM   #9
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I stepped on a very big one in Kathmandu once that just continued its walk, amazing !

But there must be nicer things to see in Rio, Frank

What was the subject again ?

\JP knows when it goes to far
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Old 15th September 2003, 10:59 PM   #10
SY is offline SY  United States
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Quote:
Eeeek...I've never felt comfortable with that on tubed circuits...maybe I'm just paranoid...
I got my first job 35 years ago repairing TV sets, 99% of which were tube. And every repair shop used freeze spray.

Quote:
I stepped on a very big one in Kathmandu once that just continued its walk, amazing !
I did a stint at University of Pennsylvania, an Ivy League school in the slums of Philadelphia. We had an amazingly hardy and diverse set of cockroaches inhabiting the Chemistry building; maybe it was mutations... Figuring out ways to kill them became sport in our lab. A CRC Handbook dropped from one meter is insufficient. Placing them in a flask and evacuating to 50 microns of pressure stunned them, but they could be revived with mouth-to-mouth (well, actually, pipette-to-mandible). I can personally attest that exposure to arsenic pentafluoride is ineffective unless an admixture of arsenic trifluoride is made in a 1:4 ratio.
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