The Dynaco Tube Audio Forum

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


    Are Matched Output Tubes Necessary with VTA ST-70?

    avatar
    knotscott

    Posts : 15
    Join date : 2019-12-28
    Location : Rochester, NY

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Are Matched Output Tubes Necessary with VTA ST-70?

    Post by knotscott on Fri Feb 07, 2020 10:49 am

    With the independent bias adjustments of the VTA ST-70 PCB, how beneficial is it to match the output tubes?
    Bob Latino
    Bob Latino
    Admin

    Posts : 2874
    Join date : 2008-11-26
    Location : Massachusetts

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by Bob Latino on Sat Feb 08, 2020 1:29 pm

    knotscott wrote:With the independent bias adjustments of the VTA ST-70 PCB, how beneficial is it to match the output tubes?

    It is always better to use a matched quad of output tubes BUT > A few times I have lost an output tube on my own VTA ST-120 and have replaced the bad tube with another NEW one of the same type > biased it up and listened to the music. I honestly could not tell any difference in the sound of the amp.

    Bob
    avatar
    nmchiefsfan

    Posts : 56
    Join date : 2012-03-21

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by nmchiefsfan on Sat Feb 08, 2020 7:06 pm

    I think it depends how hard you are driving them. At low volumes it should be fine but when you drive them harder you may start to notice when they switch to class AB
    avatar
    knotscott

    Posts : 15
    Join date : 2019-12-28
    Location : Rochester, NY

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by knotscott on Sun Feb 09, 2020 1:06 am

    Thanks guys. Sounds like it's a good idea, but not necessarily a must have. I don't push the volume much these days. My current EL34EH were matched, so I should be good to go for now.
    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 1:40 pm

    I wonder how they match them and what they mean when they say "matched". Color, smell, weight? I just bought two quad sets of matched KT120s from TAD, not cheap. I'm able to monitor each tubes bias current individually. Both sets have one tube that consistently is 5mA under the other three (in any position). In other words, if I set the left and right sides so that their hottest tube is 50mA, three are within 1mA at 50mA the the forth is closer to 45mA. And that's, of course, with the same bias as the other tube conducting 50mA. That's 10% low. Not what I would call matched.

    I think that if the conditions where they select matching tubes is different than we're using them, we may see something less than a good match. Also, I wonder if the match drifts away as the tubes age.

    I think when I buy replacements I'll not bother with paying for matched sets and see what happens.

    Ken
    peterh
    peterh

    Posts : 1251
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by peterh on Fri Feb 14, 2020 1:48 pm

    KenGaler wrote:I wonder how they match them and what they mean when they say "matched".  Color, smell, weight?  I just bought two quad sets of matched KT120s from TAD, not cheap.  I'm able to monitor each tubes bias current individually.  Both sets have one tube that consistently is 5mA under the other three (in any position).  In other words, if I set the left and right sides so that their hottest tube is 50mA, three are within 1mA at 50mA the the forth is closer to 45mA.  And that's, of course, with the same bias as the other tube conducting 50mA.  That's 10% low.  Not what I would call matched.  

    I think that if the conditions where they select matching tubes is different than we're using them, we may see something less than a good match.  Also, I wonder if the match drifts away as the tubes age.

    I think when I buy replacements I'll not bother with paying for matched sets and see what happens.

    Ken

    Matching has primarily 2 components :
    - drawing same current in identical envorinment
    This is essential to avoid DC in the output transformer. This req is possible to fulfill
    at idle with individual adjustments, bet that won't help current balance at more power
    - amplificates equally , Gm, any difference here will make one half of the signal smaller,
    thus creating (primarily 2-tone) distortion. This is reduced by the use of NFB BUT NOT
    TOTALLY

    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 1:57 pm

    peterh wrote:
    Matching has primarily 2 components :
    - drawing same current in identical envorinment
     This is essential to avoid DC in the output transformer. This req is possible to fulfill
     at idle with individual adjustments, bet that won't help current balance at more power
    - amplificates equally , Gm, any difference  here will make one half of the signal smaller,
     thus creating (primarily 2-tone) distortion. This is reduced by the use of NFB  BUT NOT
     TOTALLY

    Makes sense. I have no idea how far different non-matched tubes can be from each other. Maybe they can be 20-30mA off and 5mA is considered close.
    corndog71
    corndog71

    Posts : 725
    Join date : 2013-03-19
    Location : It can get windy here

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by corndog71 on Fri Feb 14, 2020 2:02 pm

    Here’s an interesting take about power tube matching.

    http://www.ramlabs-musicreference.com/virtues.html
    peterh
    peterh

    Posts : 1251
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by peterh on Fri Feb 14, 2020 2:04 pm

    KenGaler wrote:
    peterh wrote:
    Matching has primarily 2 components :
    - drawing same current in identical envorinment
     This is essential to avoid DC in the output transformer. This req is possible to fulfill
     at idle with individual adjustments, bet that won't help current balance at more power
    - amplificates equally , Gm, any difference  here will make one half of the signal smaller,
     thus creating (primarily 2-tone) distortion. This is reduced by the use of NFB  BUT NOT
     TOTALLY

    Makes sense.  I have no idea how far different non-matched tubes can be from each other.  Maybe they can be 20-30mA off and 5mA is considered close.  

    Tubes are in general +-25% and this is also how it was in "the good old days". It's small
    mechanical builds assembled by hand at low cost. Engineers in the "good old days" knew
    how to design and use tubes with spread parameters and still have the final product
    to be well spec'ed and consistent. The need for matching anything but powertubes was
    the exception. In addition many products needed trim-pots and coils at the final assembly.
    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 2:17 pm

    corndog71 wrote:Here’s an interesting take about power tube matching.

    http://www.ramlabs-musicreference.com/virtues.html

    Wow, that certainly talked me into buying matched sets. Thanks
    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 3:42 pm

    Moved to correct thread


    Last edited by KenGaler on Sat Feb 15, 2020 12:08 pm; edited 1 time in total
    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 3:45 pm

    Moved to correct thread


    Last edited by KenGaler on Sat Feb 15, 2020 12:09 pm; edited 1 time in total
    KenGaler
    KenGaler

    Posts : 76
    Join date : 2019-10-11

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by KenGaler on Fri Feb 14, 2020 3:51 pm

    Moved to correct thread


    Last edited by KenGaler on Sat Feb 15, 2020 12:10 pm; edited 1 time in total
    avatar
    knotscott

    Posts : 15
    Join date : 2019-12-28
    Location : Rochester, NY

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by knotscott on Fri Feb 14, 2020 5:21 pm

    corndog71 wrote:Here’s an interesting take about power tube matching.

    http://www.ramlabs-musicreference.com/virtues.html

    That's an interesting read.....a little beyond my understanding, but still interesting!

    I never really gave much thought about what tube matching meant. I just assumed it meant that they had similar measurements on a tube tester. I have no other way to check beyond the subjectivity of just listening to them.
    peterh
    peterh

    Posts : 1251
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by peterh on Fri Feb 14, 2020 5:26 pm

    knotscott wrote:
    corndog71 wrote:Here’s an interesting take about power tube matching.

    http://www.ramlabs-musicreference.com/virtues.html

    That's an interesting read.....a little beyond my understanding, but still interesting!  

    I never really gave much thought about what tube matching meant.  I just assumed it meant that they had similar measurements on a tube tester.  I have no other way to check beyond the subjectivity of just listening to them.
    And the very important issue is that the readings are done at approximative same voltages
    and loads.

    Sponsored content

    Are Matched Output Tubes Necessary with VTA ST-70? Empty Re: Are Matched Output Tubes Necessary with VTA ST-70?

    Post by Sponsored content


      Current date/time is Thu Feb 27, 2020 11:10 pm