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Tube amplifier chassis damping

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rastanearian

rastanearian

Member
2009-05-26 6:48 pm
British Columbia
  • #1
    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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    bob91343

    Member
    2010-03-11 10:43 pm
  • #2
    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.
     
    C

    ChrisA

    Member
    2008-01-08 12:22 am
  • #4
    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".
     
    M Gregg

    M Gregg

    Disabled Account
    2010-06-28 11:04 pm
    UK
  • #7
    ChrisA said:
    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".
    Click to expand...

    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!

    Regards
    M. Gregg
     
    W

    woody

    Member
    Paid Member
    2002-01-15 12:57 am
    Tyrone Ga. U.S.A.
  • #13
    I have an old Bottlehead line stage that is a little microphone. So I did an easily reversible damping job. I had block of copper 6" X 2 " X 3/4" that I layed across the top of the aluminum chassis held down with a little blue tack. Then I wrapped each tube with about an oz of 60/40 lead zinc rosin core solder yes the old vintage kind ! Turned out to be a very effective mod that took all of 15 minuets.
     
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