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 Member (and VTA ST-120 owner)

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    tfm55x

    Posts : 7
    Join date : 2016-01-07

    New Member (and VTA ST-120 owner)

    Post by tfm55x on Fri Jan 29, 2016 11:08 am

    I just finished building and biasing my new VTA ST-120 yesterday evening, and wanted to thank Bob for all his time and effort spent in the creation of such a fine product. The instructions and pictorials were clear and concise, and reflected a high attention to detail. I've built many kits but I found this one to be the most fun to assemble. I think I probably drug the assembly process out a bit, realizing "I'll never get to assemble this again." What to do? I dunno, maybe assemble a stack of these amps for my home theater :: grin ::

    tfm55x

    Posts : 7
    Join date : 2016-01-07

    Re: New Member (and VTA ST-120 owner)

    Post by tfm55x on Fri Jan 29, 2016 11:11 am

    I went ahead and did the diode rectifier mod after reading the thread about it. Thanks to all of you for posting that info. I used some Vishay GP15s instead of 1N4007s, mainly because I had the GP15s on hand.

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: New Member (and VTA ST-120 owner)

    Post by arledgsc on Fri Jan 29, 2016 11:59 am

    Congrats on your successful ST-120 build and welcome!  The fun is not over as it will require several months of run-in plus tube rolling to find what you like best.  Also if you are "jonesing" for the smell of solder flux check out the tubes4hifi preamps or a couple of mono block amp kits.

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: New Member (and VTA ST-120 owner)

    Post by deepee99 on Fri Jan 29, 2016 1:00 pm

    TFM55X,
    Welcome to Tommy's Holiday Camp. Never mind the weather, the holiday's forever Smile. I built a pair of Bob's VTA M-125 mono-blocks and he was hugely helpful while I stumbled through the process and pestered him nearly to the breaking point. No flaws in the directions, just brain-phartes on this end.
    Yes, as arledgsc says, you'll want to roll a few tubes through your 120 till you find just the right flavour. But leave things be for a month or two, let the capacitors settle in, and keep an eye on the bias. Assuming you've got Russian high-quality Gold Lion KT88s or Tung-Sol KT120s for outputs, they will serve you well. So when you get OCD, try different driver tubes out. IMHO, they have more influence on the sound than the power tubes do.
    And when you begin suffering from lead-fume withdrawal, indeed build an SP-13 or -14 line preamp from Roy at tubes4hifi.
    Have fun. That's what this is all about.
    Cheerio,
    DeePee



    Tube Nube

    Posts : 641
    Join date : 2008-12-06
    Age : 53
    Location : Calgary, AB

    Re: New Member (and VTA ST-120 owner)

    Post by Tube Nube on Fri Jan 29, 2016 4:08 pm

    Indeed, welcome. Though the joy of the build is behind you, the fun is only just begun! Even if youre far from a novice, I wager you'll learn a lot here. "Dealer support" and involvement here is outstanding, and there are quite a few members with all kinds of expertise to contribute.

    I second DeePee Dave's recommendation about the sp14 pre amp. Without exaggeration, it is achingly good. But before going there, there are tubes to roll, and recommendations on dozens of subjects to be considered, discussed, implemented, cursed, complained about back here of course, and then refined. Like how to position your speakers, high pass your mains from your subs, etc.

    Plus, this is a fun forum to hang out. Dont think I've ever seen an unkind word or snarky post. So get stuck in.

    sKiZo

    Posts : 1309
    Join date : 2013-04-01
    Location : Michigan USA

    Re: New Member (and VTA ST-120 owner)

    Post by sKiZo on Fri Jan 29, 2016 5:00 pm

    tfm55x wrote: I've built many kids but I found this one to be the most fun to assemble. I think I probably drug the assembly process out a bit, realizing "I'll never get to assemble this again."

    Nice typo ... I think of my little projects as children as well ... clown

    My ST120 is well beyond newborn, but still one of my favorite things in the world ... you can look forward to many happy years of listening pleasure ...

    tfm55x

    Posts : 7
    Join date : 2016-01-07

    Re: New Member (and VTA ST-120 owner)

    Post by tfm55x on Fri Jan 29, 2016 9:48 pm

    One question: how warm should the power transformer get (either whittle idling or while playing?) This is the longest I've had the amp on since completing assembly, and the transformer seems awfully warm. Bias is spot-on for all tubes, and I'm not seeing any red-plating.

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: New Member (and VTA ST-120 owner)

    Post by deepee99 on Sat Jan 30, 2016 1:11 am

    tfm55x wrote:One question: how warm should the power transformer get (either whittle idling or while playing?) This is the longest I've had the amp on since completing assembly, and the transformer seems awfully warm. Bias is spot-on for all tubes, and I'm not seeing any red-plating.

    They can get pretty hot after an hour or three. That's quite normal. Lotsa variables, like the speaker load, but if they're not blowing fuses or emitting any magic smoke, you're OK.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New Member (and VTA ST-120 owner)

    Post by Bob Latino on Sat Jan 30, 2016 12:16 pm

    tfm55x wrote:One question: how warm should the power transformer get (either whittle idling or while playing?) This is the longest I've had the amp on since completing assembly, and the transformer seems awfully warm. Bias is spot-on for all tubes, and I'm not seeing any red-plating.

    Over the past few years we have had a number of posts about tube amps and heat. Tube amps do get pretty warm if they have been left on for a few hours. Nothing to worry about ... They are supposed to run warm ... This is more noticeable in summer when the inside temperature of your home may be warmer .. See link below for an earlier May 2011 forum post about the heat from tube amps ...

    The heat from tube amps

    Bob

    tfm55x

    Posts : 7
    Join date : 2016-01-07

    Re: New Member (and VTA ST-120 owner)

    Post by tfm55x on Sat Jan 30, 2016 2:11 pm

    Thanks, Bob. I wanted to clarify that I was talking about the power transformer in particular. I wasn't terribly worried, since the amp overall was behaving perfectly and sounding terrific, but I wanted to double check, since the transformer was approaching the almost uncomfortably hot to the touch" range.

    tfm55x

    Posts : 7
    Join date : 2016-01-07

    Re: New Member (and VTA ST-120 owner)

    Post by tfm55x on Sat Jan 30, 2016 2:14 pm

    Just read your referenced post. Thanks for the context!

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: New Member (and VTA ST-120 owner)

    Post by tubes4hifi on Sat Jan 30, 2016 9:05 pm

    Bob photo with temps on it shows 122 degrees, that like pretty warm but not what I would call too hot to touch.
    About 2/3 of that heat is actually heat the transformer is absorbing from the tubes all around it. Consider the amp a 150w heater unit.
    Great in the north winter, not so great in Phoenix in the summer . . .

    vtshopdog

    Posts : 69
    Join date : 2015-07-11
    Location : UT, USA

    Re: New Member (and VTA ST-120 owner)

    Post by vtshopdog on Tue Feb 02, 2016 1:45 am

    tubes4hifi wrote: Consider the amp a 150w heater unit.
    Great in the north winter, not so great in Phoenix in the summer . . .

    In a note of irony, my M-125's have actually been making the house cold this winter.  One amp is situated a few feet from my thermostat.  It generates enough heat that the furnace tends to not run because air near thermostat is several degrees warmer than in rest of house.

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: New Member (and VTA ST-120 owner)

    Post by corndog71 on Tue Feb 02, 2016 11:18 am

    I use a larger aluminum Hammond box for my ST120.  Spreading the tubes out helps cool things down a bit.  The right power tube is cooler than the others because it's dying.


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