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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


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    VTA ST 70 16 ohm output to speakers

    Dave_in_Va
    Dave_in_Va


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    Post by Dave_in_Va Tue Oct 26, 2021 4:09 pm

    I'm getting a pair of 16 ohm speakers and just want to double check that I'll be doing this right. I can solder okay but I'm not a tech.

    Bob said...
    "After March of 2017 all the VTA amps have TWO red posts. In most cases the two red posts were set up for 4 and 8 ohms and the yellow (16 ohm) wire is still connected to the NFB eyelet on the driver board. If you have 16 ohm speakers, you should connect the YELLOW (16 ohm) wire to one of the red binding posts and then run a wire from that post to the NFB eyelet on the driver board to still provide negative feedback for the amp."

    So, I plan on snipping those long yellow wires that run from the back of the amp to the front, connect one snipped end to the speaker terminal and from that terminal run a piece of wire back to the other snipped end and splice/solder/shrink tube it so I'll still have a connection to the board (I don't want to get the iron close to the board, just to be careful).

    Is this okay and is 600 volt 18 gauge wire okay to use to connect the terminal back to the yellow wire?
    Thanks for the help.
    ps I now have the three terminal connectors on my ST70. So I'll have 8ohm and 16 ohm outputs.

    VTA ST 70 16 ohm output to speakers JRJSYgy
    Bob Latino
    Bob Latino
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    Post by Bob Latino Tue Oct 26, 2021 6:35 pm

    For others that have VTA amps from before March of 2017 with a pair of TWO post binding posts (one BLACK and one RED post), you can can get a pair of THREE post binding posts (two RED and one BLACK post) with a new 3 hole backing board from the web page at the link below. They are about 1/2 way down the page on the right.

    http://www.tubes4hifi.com/ST70.htm

    Bob

    Dave_in_Va
    Dave_in_Va


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    Post by Dave_in_Va Tue Oct 26, 2021 6:45 pm

    Bob, Is my 18 gauge 600 volt wire okay to use?
    Bob Latino
    Bob Latino
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    Post by Bob Latino Tue Oct 26, 2021 7:11 pm

    Dave_in_Va wrote:Bob, Is my 18 gauge 600 volt wire okay to use?

    Yes - that wire would be fine ..

    Bob
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    Seamus


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    Post by Seamus Fri Oct 29, 2021 9:30 am

    There is no magic in the FB routing shown. You should be able to simply cut the yellow 16Ω lead at a suitable position to reach the 16Ω terminal and join two leads at the terminal.

    One could argue that a more direct route, rather than right next to the power transformer might benefit.

    VTA ST 70 16 ohm output to speakers St70fb10
    Dave_in_Va
    Dave_in_Va


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    Post by Dave_in_Va Fri Oct 29, 2021 10:01 am

    I'm going to try and keep the wiring looking pretty much as it is. The amp is dead quiet and I'd hate to change that (just in case).
    To tell the truth, I hate fooling with it all but it'll be better to feed the new speakers with the correct tap.
    Dave_in_Va
    Dave_in_Va


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    Post by Dave_in_Va Fri Oct 29, 2021 12:59 pm

    More work than it should have been (I'm not a tech) but it came out okay.
    The speakers won't be in for another month but at least I'll be ready ;-)

    VTA ST 70 16 ohm output to speakers JSlbQV9
    Dave_in_Va
    Dave_in_Va


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    Post by Dave_in_Va Fri Oct 29, 2021 1:02 pm

    Man...it would be SOOO much easier to mess with stuff like this if the speaker connection posts had holes for the wires to go through.
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    Seamus


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    Post by Seamus Sat Oct 30, 2021 12:28 pm

    Chaps, induction is reduced as the square of the distance.

    As built, the feedback passes right next to the transformer, say ½" from the core.
    Moving the lead 2" away reduces the induction by a factor of 16.

    One channel FB passes directly along the twist 120v for about 3", the other directly parallels the untwisted 120v for ≈1"


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