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Old 21st September 2010, 05:26 PM   #1
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Default Tube amplifier chassis damping

I currently have on the bench an amplifier whose chassis literally rings like a bell.
At power up the tubes really ring also.

I was thinking of using PL9000 to damp the chassis and transformer covers. Has anyone else tried this approach? It's really easy to work with and dirt cheap compared to more "hifi" options.

As for the tubes themselves ringing at startup, I think that is a circuit issue. I can't help but think that tube life will be diminished with that kind of hammer blow every time I turn the amp on.

Any thoughts would be helpful.

The amp is a Yaqin MS-300C
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Old 21st September 2010, 05:45 PM   #2
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I have no idea what PL9000 might be.

However, a wood case or any sort of solid mounting for the chassis should reduce the Q of the metal. Or a brace. No, a circuit can't ring due to its configuration. Again, something is moving physically and causes a signal to be generated, perhaps a ceramic capacitor or other piezoelectric component.
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Old 21st September 2010, 05:49 PM   #3
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I use perforated aluminium, it does not ring like a flat steel.

http://wavebourn.com/forum/download.php?id=478&f=7
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Old 21st September 2010, 06:09 PM   #4
ChrisA is offline ChrisA  United States
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A recently was testing a guitar amp I build with a resistive dummy load. I had a signal generator on the input and I could hear the signal. I'd spin the frequency dial and clear hear the pitch track the dial. At first I was baffled because there was no speaker, just a huge ceramic tublar resisor sucking up power. Then I noticed the sound has comming from the output transformer. The steel end bels were acting like speakers. The sound wa not loud but just enough to hear.

I bet you have something going on like that, there is maybe a transformer or a choke that is transmitting vibration intothe chassis. So,... kill the problem at the source. Isolate the transformer with rubber bushings. Even if the transformers is not the source it's mass and the rubber bushing can soak up some of the energy.

The PL900 idea was OK but the stuff is not nearly strong enough. The stuff to use is made by 3M and called "5200". It is like an ultra-quality pl9000 and in the amount you need the cost is not to bad. Use this stuff to glue on a length of aluminum angle or a even hardwood like oak or maple. Make the section as tall as you can.

Shop 3M: 3M Marine Adhesive/Sealant 5200, 05203, 3 oz, White

This stuff is unbelievable. it can even be used by divers underwater to make permanent bonds. It cures to a kind of plastic this is used to make "super balls".
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Old 21st September 2010, 06:27 PM   #5
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Remember to get the fast setting 5200 the slow setting stuff can take month's to cure fully!
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Old 21st September 2010, 06:29 PM   #6
SY is offline SY  United States
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Old 21st September 2010, 06:43 PM   #7
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by ChrisA View Post
The PL900 idea was OK but the stuff is not nearly strong enough. The stuff to use is made by 3M and called "5200". It is like an ultra-quality pl9000 and in the amount you need the cost is not to bad. Use this stuff to glue on a length of aluminum angle or a even hardwood like oak or maple. Make the section as tall as you can.

Shop 3M: 3M Marine Adhesive/Sealant 5200, 05203, 3 oz, White

This stuff is unbelievable. it can even be used by divers underwater to make permanent bonds. It cures to a kind of plastic this is used to make "super balls".
I would get an insulated probe "multimeter" and rub each component You will hear the microphonic effect some will be louder than others!

This might give you an idea. I have used bluetack or whitetack under components. Also some types of hot glue gun adhesive helps.

I have also had interaction with heaters and supplies!

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M. Gregg
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Old 21st September 2010, 06:47 PM   #8
M Gregg is offline M Gregg  United Kingdom
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If you can try feeding your heaters from a different supply see if it makes a difference!

Just a thought.
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Old 21st September 2010, 06:50 PM   #9
45 is offline 45  Italy
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Quote:
Originally Posted by Wavebourn View Post
I use perforated aluminium, it does not ring like a flat steel.

http://wavebourn.com/forum/download.php?id=478&f=7
Nice!
Where do you buy it?

Cheers,
45
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Old 21st September 2010, 06:53 PM   #10
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Order Aluminum 3003 Perforated Sheet in Small Quantities at OnlineMetals.com
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