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


    Is VTA 120 in need of Step down or bucking transformer?

    corndog71
    corndog71

    Posts : 705
    Join date : 2013-03-19
    Location : It can get windy here

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by corndog71 on Wed Aug 13, 2014 4:39 pm

    I live on the north side of Chicago and get a fairly steady 125VAC. I remember getting a solid 120VAC in one of the suburbs bordering the city.
    sKiZo
    sKiZo

    Posts : 1531
    Join date : 2013-04-01
    Location : Michigan USA

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by sKiZo on Wed Aug 13, 2014 4:42 pm

    Yup ... I used to be one of those "end of line" customers - unfortunately, civilization seems to be creeping up on me. A 600 acre centennial farm across the street sold recently and developers were lining up to piece it out. Ah, well ... progress.

    I've got a 5a variac, but I use that on the hobby bench. I figured no sense tying it up for single purpose voltage reduction when a bucker would do. That's a LOT cheaper if you can scrounge up the parts. Outlet strips are real popular as cases, and the only other expense is the transformer.

    You CAN get a "line conditioner" that stabilizes voltage to a certain degree. Even those can't handle a radical power offset from "normal" for any great length of time - they're more built for transients. And in any case, they tend to be uber expensive.

    If your power wanders a lot, I believe Kill A Watt makes a remote display device that you can plug in and keep the readout handy as a quick reference. Set that up in series with a variac and adjust as needed whenever you power up the amp.

    PS ... what's the deal with variacs lately anyway? My 5a cost me $50 shipped a couple years back ... they seem to have doubled in price since I last looked. Should have bought a boatload of those instead of that Radio Shack stock I guess ...  bom

    corndog71 wrote:I live on the north side of Chicago and get a fairly steady 125VAC.  I remember getting a solid 120VAC in one of the suburbs bordering the city.

    Anywhere near Deerfield? I hear they have a fairly consistent zero VAC ... reigning kings as power outage capital of the world. Controlling voltage there would amount to how fast you peddle.

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Soylent-Green-Charlton-He-010

    "Faster old man! I'm trying to listen here!!"
    Pillo69
    Pillo69

    Posts : 171
    Join date : 2012-04-11
    Location : Granada (España)

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by Pillo69 on Thu Aug 14, 2014 5:21 am

    In the diagram below you can see an enlargement of provided by Skizo, where you can adjust the output voltage with a rotary selector, by a voltmeter see the output voltage.
    You can use a transformer to 24v secondary.

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Reductor_de_tensi_n
    Dahlberg
    Dahlberg

    Posts : 122
    Join date : 2016-09-27
    Age : 58
    Location : Sweden

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by Dahlberg on Sat Jan 07, 2017 4:05 pm

    Thanks for the shematic, most helpful Smile
    I've built a bucking transformer today Very Happy Stripped the secondary from a
    300va toroid and rewound it with another 4mm2 wire. Dropped 6V and
    seems to be stable and not getting hot or anything. Ac-voltage have
    differed from 225 to 238v the last days and that doesn't seem to be ok.
    Power transformer goes quite hot and then it hums just to much.

    Each channel of M-125 draws 170w so I figured that 300va would be
    fairly sufficient. I'm building a second one for the other channel as well
    and maybe I will ad some more turns to the secondary to let it drop ~10v.

    Any thoughts about if the transformers are big enough are welcome.
    pichacker
    pichacker

    Posts : 99
    Join date : 2016-08-01
    Age : 55
    Location : Near to London - UK

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by pichacker on Sun Jan 08, 2017 10:22 am

    Dahlberg,

    Your bucking transformer is more than adequate for many M-125s..... Let's try some simple maths for ideal situations. (Ready to be shot down in flames if I make a mistake Smile )

    Watts = Voltage * Current
    Current = Watts / Voltage

    You say that the single M-125 draws 170w and assume your supply voltage is 220V. The amp will be drawing 170W / 220V = 700mA.

    If you wish to drop 10V then the total power for the 10V winding will be:-

    10V * 0.7A = 7W!

    You'd be surprised how small a transformer you can get away with. Obviously the larger the transformer the better the regulation will be but there are sensible limits.

    Hope this helps.

    Steve.
    deepee99
    deepee99

    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Anyone care to build me a bucking xformer?

    Post by deepee99 on Sun Jan 08, 2017 10:54 am

    I have a massive Furman SPR 20i that clamps the output voltage at 121 VAC pretty much regardless of what's coming out of the wall, which is fine for the s/s gear, TV, etc. It would be nice to dial the amp outputs down to 118 or so but there are no adjustments to do so. I lack the parts and/or expertise to build my own bucking xformer, and wondering if there's someone here who might care to build one for me (it would be running a pair of M-125s) and what it would cost. Volunteers? I'd gladly pay you Tuesday for a ham-bucker today. PM or just reply here.
    Thanks,
    David
    Dahlberg
    Dahlberg

    Posts : 122
    Join date : 2016-09-27
    Age : 58
    Location : Sweden

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Diy buck transformer 300va

    Post by Dahlberg on Sun Jan 08, 2017 3:01 pm

    Ended up with two like this, one for each M-125. Drops 10v so I should
    stay below 230v in the future, 218-228v if this weekend is what's normal.

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Bucktrans

    Sponsored content

    Is VTA 120 in need of Step down or bucking transformer? - Page 2 Empty Re: Is VTA 120 in need of Step down or bucking transformer?

    Post by Sponsored content


      Current date/time is Wed Oct 16, 2019 9:59 pm