Can power tubes make Hiss?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by alanfc, Jun 6, 2005.


  1. alanfc

    alanfc Member

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    hi, I have a question on Hiss,

    My master boost never used to make hiss, on my 1993 Rivera R55-112. On channel 1 Brit channel. But now it does....
    Now once I use the master boost (must have, sounds great) there's alot of hiss.

    I had new SED EL34's installed and biased about 2 months ago.
    I wonder if SED's have problems in general? Unfortunately these were not bought from a rigorous tube-tesing vendor.
    I've traded around preamp tubes, checked my guitars and cords. No change.

    More -
    I tried different guitars, removing different pedals from the lineup, turning off all lights and computer monitor, traded changed new old preamp tubes in all positions. Also tried I through different speaker cabs.
    It always made some normal sounding hiss, but at practice this weekend I found myself having to turn off the boost between songs, never used to need to do that

    thanks
     
  2. Wakarusa

    Wakarusa Member

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    A big source of hiss is "shot noise" (basically the sound of electrons running into something.. like the guts of a resistor... or the plates of a tube). I suppose some power tubes could hiss more than others. Also possible that the fresh tubes, perhaps running at a new bias point, have exposed a stressed resistor.
     
  3. alanfc

    alanfc Member

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    fascinating,
    OK my tubes =are = new. I hope this is not my problem !

    I think I need to test this alot more with all my pedals & everything, to eliminate them first ! And try batteries perhaps.
    thanks
     
  4. Gary Ladd

    Gary Ladd Member

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    Hissing usually indicates a capacitor(s) is going bad....
     
  5. alanfc

    alanfc Member

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    gaaahhh I hope thats not it:( :eek:
     

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