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


    New bias recommendations for all VTA amps

    Share

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    New bias recommendations for all VTA amps

    Post by Bob Latino on Fri May 20, 2016 12:06 pm

    After extensive listening at various bias settings for ALL the VTA amps I am now recommending slightly lower bias settings for some of the VTA amps. These recommendations give no changes in the sound quality of the amps but will noticeably extend tube life. The listening was not only done by me but was also done by a number of VTA amp customers.

    VTA ST-70 with EL34 or 6L6 output tubes > recommended bias setting is .40 VDC per each output tube which gives a bias current of 40 milliamps per each output tube.

    VTA ST-70 with KT66 or KT77 output tubes > recommended bias setting is .45 VDC per each output tube which gives a bias current of 45 milliamps per each output tube.

    VTA ST-70 with 6550 or KT88 output tubes > recommended bias setting is .50 VDC per each output tube which gives a bias current of 50 milliamps per each output tube.
    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    VTA ST-120 with 6550, KT88 or KT120 output tubes > recommended bias setting is .50 VDC per each output tube which gives a bias current of 50 milliamps per each output tube.

    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    VTA M-125 with 6550, KT88 or KT120 output tubes USING TWO OUTPUT TUBES PER AMP > recommended setting is .50 VDC per each output tube which gives a bias current of 50 milliamps per each output tube.

    VTA M-125 with 6550, KT88 or KT120 output tubes USING FOUR OUTPUT TUBES PER AMP > recommended setting is 1.00 VDC per each side which gives a bias current of 50 milliamps per each output tube.

    All the user manuals will be changed to reflect the new bias recommendations ...

    Bob

    audiobill

    Posts : 271
    Join date : 2014-03-13
    Location : Philadelphia

    Re: New bias recommendations for all VTA amps

    Post by audiobill on Fri May 20, 2016 12:29 pm

    Bob, I've found no audible difference running my ST-120 with KT88s at .50vdc per tube....agree with your recommendations.

    RockyAM

    Posts : 26
    Join date : 2008-12-14

    Re: New bias recommendations for all VTA amps

    Post by RockyAM on Fri May 20, 2016 1:29 pm

    Bob, in my VTA M-125's I have actually run the bias in both amps at 1.0, 1.10 and 1.20 volts using 4 output tubes. I tried like hell but I honestly could hear no difference in the amps. Of course my wife keeps bitchin' at me "Why don't you just listen to the music instead of fiddling with those things?". I spent another night changing out that front driver tube on both amps and replaying a test track that I use and all I got was "How many times are you going to listen to that damn song!" LOL oh well RockyAM

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: New bias recommendations for all VTA amps

    Post by MontanaWay on Fri May 20, 2016 2:46 pm

    with my variations of the ST120 aka Fats Domino and M125 aka Big Bopper, from the very get go I've been setting bias for the KT120's at 500mV. I too tried various levels, but could not hear any audible differences.
    So why not extend tube life to the max possible!
    Very good suggestion!

    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: New bias recommendations for all VTA amps

    Post by deepee99 on Fri May 20, 2016 3:11 pm

    I have found no audible difference between .5 and .6. Insofar as output tubes are spendy, why not let them loaf a bit?

    WntrMute2

    Posts : 96
    Join date : 2010-11-21

    Re: New bias recommendations for all VTA amps

    Post by WntrMute2 on Sun Jul 03, 2016 8:43 pm

    Will this provide less stress on our poor 5AR4s?

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New bias recommendations for all VTA amps

    Post by Bob Latino on Sun Jul 03, 2016 8:47 pm

    WntrMute2 wrote:Will this provide less stress on our poor 5AR4s?

    Yes - Besides longer output tube life, the rectifier will also be less stressed ...

    Bob

    Sponsored content

    Re: New bias recommendations for all VTA amps

    Post by Sponsored content Today at 8:14 am


      Current date/time is Sun Sep 25, 2016 8:14 am