• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hum problem, but on the tweeter (!?)

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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
 
Sch3mat1c said:
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 :)att'n: DON'T use the freeze spray on the tubes!)
 
diyAudio Senior Member
Joined 2002
Hi,

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.

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...:goodbad:

Cheers,;)
 
diyAudio Senior Member
Joined 2002
Hi,

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.:cannotbe:

Cheers,;)
 
diyAudio Senior Member
Joined 2002
Hi,

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...;)
 
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.

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.
 
psu problem ?

Hello Alex,

perhaps you have a problem with psu capacitors. When you power on the amplifier there is a "pic" of voltage that the capacitor can't accept and capacitors "cry". Try to bypass psu capacitors, for example, if you have 400V capacitors, try to bypass them with 0,1µF 630V non polarised.
An other thing to do is to verify all solders (soudures in french).

Cordialement.

Pascal.

http://ptsoundlab.free.fr
 
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