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


    Built a bucking transformer.

    Share

    corndog71

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

    Built a bucking transformer.

    Post by corndog71 on Sun Jun 12, 2016 5:48 pm

    Tallying up the cost I probably spent around $90 but it was a fun / frustrating project.





    Drops the wall AC by around 7.4 volts.

    sKiZo

    Posts : 1308
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Built a bucking transformer.

    Post by sKiZo on Sun Jun 12, 2016 7:31 pm

    Why frustrating? Fairly straight forward project ...

    Great addition to any tube system though, considering today's wall output.



    PS ... mine cost me next to nothing as it was all "crap" that had been collecting dust in the bins.   pirat

    Captain Coconut

    Posts : 213
    Join date : 2009-10-13
    Age : 64
    Location : Great White North

    Re: Built a bucking transformer.

    Post by Captain Coconut on Sun Jun 12, 2016 7:47 pm

    Been there, done that. Got the desired reduction in voltage.

    Bob Latino
    Admin

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

    Re: Built a bucking transformer.

    Post by Bob Latino on Sun Jun 12, 2016 8:14 pm

    The VTA amps will all work fine for any incoming line voltages up to about 122 VAC. Over 122 VAC, the user should consider either a bucking transformer OR a variac. A number of VTA amp customers have used the variacs from Circuit Specialists in Tempe, AZ. The 5 amp model that they sell for $64.95 works fine for the VTA ST-70 or ST-120. The 20 amp model can be used for a pair of M-125's. Set to about 118 VAC, these variacs will give slightly increased tube life. Yes - these are made in China but everyone who has used one says they work fine. The analog meters on these variacs are a little coarse. What I would do is put a multimeter on the unit's AC outlet and turn the knob until your multimeter says 118 VAC.

    Variacs at Circuit Specialists in Tempe, AZ

    Bob

    audiobill

    Posts : 270
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Built a bucking transformer.

    Post by audiobill on Sun Jun 12, 2016 9:18 pm

    Also, some of us have found used, but good condition US made 15-20 amp variacs on craigslist for $100 or so.....

    corndog71

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

    Re: Built a bucking transformer.

    Post by corndog71 on Sun Jun 12, 2016 10:00 pm

    I already have a variac. I just wanted to build one of these for fun and thought I'd show it off.

    arledgsc

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

    Re: Built a bucking transformer.

    Post by arledgsc on Mon Jun 13, 2016 10:01 am

    Congrats... What application is the bucker being used? The Hammond transformer used here is rated 37.8VA on the primary. The transformer core would saturate with the current draw of an ST-70 or ST-120 amp.

    corndog71

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

    Re: Built a bucking transformer.

    Post by corndog71 on Mon Jun 13, 2016 11:36 am

    arledgsc wrote:Congrats... What application is the bucker being used?  The Hammond transformer used here is rated 37.8VA on the primary.  The transformer core would saturate with the current draw of an ST-70 or ST-120 amp.  

    Hmm.. I believe this was the one that Skizo recommended. It's similar to his, 6A secondary. I built it for my ST35.

    deepee99

    Posts : 1332
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Built a bucking transformer.

    Post by deepee99 on Mon Jun 13, 2016 12:52 pm

    How do solid-state devices (CDs, TVs, DVDs etc. react to the lower voltages?

    Dave_in_Va

    Posts : 142
    Join date : 2013-04-02

    Re: Built a bucking transformer.

    Post by Dave_in_Va on Mon Jun 13, 2016 1:04 pm

    I built a simplified version of this one.

    https://robrobinette.com/5e3_Modifications.htm#Bucking_Transformer

    At first I tried to use a smaller box but it just wasn't worth the hassle. This case is approx. 7" x 5" x 3".
    Right now I'm getting 123.3 out of the wall and 115.8 out of the bucker. Close enough for ('60's) rock & roll.

    (This is the first one I built, the second was neater. I use one for my VTA ST 70, VTA SP 14, PH 14 and ancient Audio Control 520 EQ. I use the other for what I consider more "delicate" '60's guitar/keys gear, like a 1967 Silvertone 1482 amp and a '67 Vox Jaguar organ. I generally don't worry about pro level gear like '60's Fender amps.)





    Last edited by Dave_in_Va on Mon Jun 13, 2016 1:27 pm; edited 1 time in total

    arledgsc

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

    Re: Built a bucking transformer.

    Post by arledgsc on Mon Jun 13, 2016 1:19 pm

    corndog71 wrote:
    arledgsc wrote:Congrats... What application is the bucker being used?  The Hammond transformer used here is rated 37.8VA on the primary.  The transformer core would saturate with the current draw of an ST-70 or ST-120 amp.  

    Hmm.. I believe this was the one that Skizo recommended.  It's similar to his, 6A secondary.  I built it for my ST35.
    I think you are OK.  Sorry for the alarm bells.  Only the current needed to buck 6V is carried through the bucker primary.  The main current for the amp circuits is pulled directly from the wall plug (and carried through the secondary).

    sKiZo

    Posts : 1308
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Built a bucking transformer.

    Post by sKiZo on Mon Jun 13, 2016 1:53 pm

    corndog71 wrote:
    arledgsc wrote:Congrats... What application is the bucker being used?  The Hammond transformer used here is rated 37.8VA on the primary.  The transformer core would saturate with the current draw of an ST-70 or ST-120 amp.  

    Hmm.. I believe this was the one that Skizo recommended.  It's similar to his, 6A secondary.  I built it for my ST35.

    Correction ... 6 VOLT secondary, just to head off any potential confusion.

    And yes, it's also a 6 AMP rating, so it can handle the amplifier easily ... both windings should be the same rating unless otherwise noted on the label. Main thing you lil bucker builders gotta remember is to TEST before using, as it is possible to hook it up backwards and BOOST what the amp sees.

    Also, solid state isn't as vulnerable to out of spec wall voltage as tube equipment - you should be good up to around 125vac even on the classic equipment, but don't quote me on that. I just use the bucker on the ST120 and the Eico HF12a that I use to power a center channel. Everything else is straight out of the wall ... with protection of course.

    corndog71

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

    Re: Built a bucking transformer.

    Post by corndog71 on Mon Jun 13, 2016 5:21 pm

    sKiZo wrote:Main thing you lil bucker builders gotta remember is to TEST before using, as it is possible to hook it up backwards and BOOST what the amp sees.

    Right. That was the frustrating part as the first time I connected the wires I got 129 volts! affraid

    arledgsc

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

    Re: Built a bucking transformer.

    Post by arledgsc on Mon Jun 13, 2016 6:58 pm

    Here's a basic schematic for a bucker with a 10V secondary at 120Vac. 

    I use a battery to figure out polarity of the secondary to avoid 50/50 chance of wiring a booster instead.  Touching (on/off) a 1.5V battery to the secondary produces voltage pulses on the primary.  Mark which end of the secondary is touching the battery (+) terminal produces positive going voltage spikes on the primary and mark it.  In the example below these same polarity sides of the primary and secondary are noted with "dots" near there respective ends.  Then wire up accordingly.  But good idea to smoke test with no load!   Using a battery at the secondary steps up the primary voltage that is easy to measure versus the other way around.  

    tubes4hifi
    Admin

    Posts : 1282
    Join date : 2008-11-30

    Re: Built a bucking transformer.

    Post by tubes4hifi on Wed Jun 15, 2016 11:07 am

    thanks for the schematic arledgsc, for those of us that can read them, they are worth 100,000 words!

    corndog71

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

    Re: Built a bucking transformer.

    Post by corndog71 on Wed Jun 15, 2016 11:44 am

    I would still test your wiring because I tried doing it like that first pic and got a boost in voltage.

    Sponsored content

    Re: Built a bucking transformer.

    Post by Sponsored content Today at 5:33 am


      Current date/time is Sat Dec 03, 2016 5:33 am