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  1. #1

    Bassman Bias Question

    Can improper bias make the amp sound to boomy? to much low end?

    I popped in 2 Svetlana 6L6's in my RI Bassman and the low end seems a bit much. will biasing properly correct this problem?


  2. #2
    Les Paul Forum Member
    Join Date
    Oct 2006
    SW Virginia

    Re: Bassman Bias Question

    No, it's the circuit as a whole. You could have that modded (lower capacitor values to start with) but then it'll no longer be a bassman to the purists.
    2007 CR8
    2000 Elegant
    1953 J50

  3. #3

    Re: Bassman Bias Question

    If you swapped power tubes without biasing thats a problem, period.

    Not sure about your bass issue but it is a "Bass amp".

  4. #4
    Les Paul Forum Member LeonC's Avatar
    Join Date
    Aug 2002
    Palos Verdes, CA

    Re: Bassman Bias Question

    If an amp was improperly biased, I think you'd notice other things long before you'd notice tonal differences. The feel would be way off and the amp wouldn't sound healthy.

    In the case of really cold bias the amp typically has an overly distorted sound, quite unpleasant. Biased really hot, the amp may sound very squishy and on "the verge of meltdown." If the bias is far enough off, the amp may not even produce sound.

    But too boomy? No, I don't think that's an improper bias. A Bassman, say a 5F6 type circuit, has quite a bit of low end. I typically play it with the bass turned way down.
    Full Disclosure: I built Valclone Amps

  5. #5
    Les Paul Forum Member bluesforstevie's Avatar
    Join Date
    Jun 2002
    Nellytown U. City MO

    Re: Bassman Bias Question

    Overbiasrd will get real spongy and under biased will sound harsh with nasty distortion. It is a bass amp...just like a JTM45 turn bass almost all the way down. YMMV

  6. #6
    Les Paul Forum Member
    Join Date
    Feb 2003
    Lubbock, TX

    Re: Bassman Bias Question

    Imho, it is best practice to know the voltages and bias numbers when new power tubes are installed...and perhaps before. Let’s go ahead and say that it is best to always know what is going on. That way, we have a basis for understanding whatever changes take place whether those changes would be some component failing or just changing power tubes. To answer your question, check the bias so you know what it is. If it is in what most ups consider a usable range and the amp’s Sonics are very different from before, pop the old tubes back in, listen, and take the measurements again to see how those tubes operate in the amp. With all of that information, you will have some idea of why the amp sounds different. If the bias numbers happen to be similar, then the tubes sound very different for each other....and maybe you have to run the tones differently? If the bias numbers are drastically different, then Regina’s the new tubes to the same numbers as the old tubes yielded...what does the amp sound like now?
    This is the only way I know to compare tubes and biasing...and the resultant Sonics.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

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