The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    quad bias control ?

    Share
    avatar
    dmagazz

    Posts : 140
    Join date : 2018-06-20
    Age : 50
    Location : new fairf, ct

    quad bias control ?

    Post by dmagazz on Tue Jun 26, 2018 3:45 pm

    anyone have this installed?
    im referring to this  dynakit  2x2 bias adjustment add on at
    dynakitparts.com shop bias-balance-control-kit

    is there any notable differences between tubes that are supposed to be matched?
    and if they are not matched- is there usually a notable difference?
    personally i like the idea of the kit.
    also id like to know,outside of bias voltage, is there another voltage that varies as the amp is running that you might want to "monitor" with a gauge or a indicator light. to be able to avoid calamity if possible. if you were the kind of person who pushes your amp?
    such as, i am that guy Smile
    avatar
    PeterCapo

    Posts : 561
    Join date : 2008-12-05

    Re: quad bias control ?

    Post by PeterCapo on Tue Jun 26, 2018 4:36 pm

    Funny you should ask... just been having a discussion along these lines over at DD forum.  My take, as of this moment, is that if you are going to use mismatched power tubes, the individual bias adjust (four pots) should help to a point.  But, with well matched power tubes, it's looking to me like an open question, pending further input, though it's also looking like the original, single cathode resistor per channnel Biaset scheme is a better choice in this case.  If I am on the right track here, I think what's missing is a sense for how to quantify the degree of mismatch in power tubes before it would make sense to give up the benefit of the original single cathode resistor Biaset scheme for the four pot scheme.  And I don't think we're very likely to find out.

    If you have a look at the following thread and its sub-threads, you should see interesting discussion on the subject: https://www.audioasylum.com/forums/dynaco/messages/1/17327.html
    avatar
    dmagazz

    Posts : 140
    Join date : 2018-06-20
    Age : 50
    Location : new fairf, ct

    Re: quad bias control ?

    Post by dmagazz on Tue Jun 26, 2018 7:00 pm

    ok so its a fixed resistor evening voltage voltage x 2 thing that keeps transformer voltage in check?
    i was thinking the 4 way bios// sorry.bias may be beneficial in using two different but cross referenced tubes for getting a "best of both worlds thing"like for the liking of 2 different tubes that sound different in the amp, -blending.
    ..now...say your resister is 1.56! as i understand it the bios setting revolves around this because of the resistor that is suppose to have that value. because of ohms law.ie.it takes 1 volt to get 1 ampere through a 1 ohm resistor? so what if that resistor is not spot on 1.56. what if it were 1.49 . would you then set the bias to 1.49?


    edit,-in my haste id forgotten 1.56 is the old battery reference voltage at the 10k ohm right?
    so i re-ask..if the resistor was not quite 10k, say it was 9.6k, would i set the bios to 1.49 ?


    Last edited by dmagazz on Tue Jun 26, 2018 11:22 pm; edited 2 times in total
    avatar
    PeterCapo

    Posts : 561
    Join date : 2008-12-05

    Re: quad bias control ?

    Post by PeterCapo on Tue Jun 26, 2018 7:31 pm

    dmagazz wrote:ok so its a fixed resistor evening voltage voltage x 2 thing that keeps transformer voltage in check?
    i was thinking the 4 way bios may be beneficial in using two different but cross referenced tubes for getting a "best of both worlds thing"like for the liking of 2 different tubes that sound different in the amp, -blending.

    My apologies, but I am not quite sure what you are getting at.  Could you rephrase?

    I think part of what you are asking about is blending different brands of power tubes in the amp.  This could work, but you would still want them to be matched, if possible.  For sonic consistency, have the exact same mix of power tubes in each channel.  If you always use tubes that are not matched, regardless of whether they are the same brand or not, the four bias pots may be a better choice.  But, if the power tubes are mismatched too severely, even the four pots might not help.

    dmagazz wrote:..now...say your resister is 1.56! as i understand it the bios setting revolves around this because of the resistor that is suppose to have that value. because of ohms law.ie.it takes 1 volt to get 1 ampere through a 1 ohm resistor? so what if that resistor is not spot on 1.56. what if it were 1.49 . would you then set the bios to 1.49?

    There's a margin of error on all parameters: the value of the resistor, the accuracy of the meter, etc.  It would be worthwhile measuring the value of the resistor with an appropriate meter to make sure it is in-spec.  Check both of them.  If they are in-spec, then just set the bias to 1.56.  The small margin of error would be inaudible, anyway.
    avatar
    j beede

    Posts : 469
    Join date : 2011-02-07
    Location : California

    Re: quad bias control ?

    Post by j beede on Tue Jun 26, 2018 7:43 pm

    FYI:

    BIOS: Basic Input Output System. This is the code that some computers use to establish fundamental operation at power-on, before the operating system is loaded.

    bios: plural form of the informal word sometimes used in place of "biography".

    bias: Usually refers to a dc voltage or dc current used to set the zero-signal operating point of an amplifier.

    Individual bias potentiometers in a stereo push-pull tube amplifier reduces the amplifier's dependency on complementary tube pair matching. Note that two tubes that produce matching cathode currents with identical bias applied may or may not be matched at other operating points along their characteristic curves.
    avatar
    dmagazz

    Posts : 140
    Join date : 2018-06-20
    Age : 50
    Location : new fairf, ct

    Re: quad bias control ?

    Post by dmagazz on Tue Jun 26, 2018 8:10 pm

    i know this beede, thanks, i am more computer literate than tube audio literate. i was use to the word/sounlike bios because of my familiarity with firmware/software. lol i realised what i was doing earlier today. infact. the start of this thread i spelled it correctly. Wink
    and yet i still misspelled it afterwards. lol, go figure

    Sponsored content

    Re: quad bias control ?

    Post by Sponsored content


      Current date/time is Wed Nov 14, 2018 3:50 am