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


    PA060 No Load secondary HV tolerances

    avatar
    BCROW

    Posts : 5
    Join date : 2015-09-28

    PA060 No Load secondary HV tolerances Empty PA060 No Load secondary HV tolerances

    Post by BCROW on Fri Mar 06, 2020 6:47 am

    Hello,

    Does anyone know the acceptable tolerance for the high voltage secondary portion of the PA060 type power transformer in no-load condition?

    I see specs show 360 55 0 360 but mine is measuring 345 65 0 355 with the specified primary voltage.

    How critical are these voltages in the ST-70 and if so what should I watch out for?

    All the low voltages are spot on.

    Any suggestion/schematic for a load condition test that would somewhat replicate loads in the ST-70?


    Thanks!
    PeterCapo
    PeterCapo

    Posts : 755
    Join date : 2008-12-05

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by PeterCapo on Fri Mar 06, 2020 6:01 pm

    Is your AC mains wandering while you are taking measurements?  Which version of the PA060 do you have?  Older originals had a 117VAC primary, later ones may have had 120VAC primaries.  Some of the newer reissues could have 117, 120 or 122VAC primaries.  The voltage across the primary winding should be measured directly, not by using the dial or meter on a variac.
    avatar
    BCROW

    Posts : 5
    Join date : 2015-09-28

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by BCROW on Fri Mar 06, 2020 6:06 pm


    Hi Peter,

    AC Mains is stable @231V. The power transformer is a 230 volt model from a supplier here in Europe.
    PeterCapo
    PeterCapo

    Posts : 755
    Join date : 2008-12-05

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by PeterCapo on Fri Mar 06, 2020 6:21 pm

    So, no load you are getting 345 65 0 355?  I'm not clear on how much the secondary should vary with no load vs. load.

    I suppose you'd have to find the Thevenin or Norton equivalent, or something like that, of what the secondaries "see" in-circuit.  However, I am not aware of any figures anyone has worked out.

    Do you intend to use it in an actual Stereo 70?  If so, you might just hook it in and see what your readings are.  You might start out running the primary a little lower, using a variac.  If you can safely get it up to full primary voltage, then the voltage chart in the Dynaco manual will tell you if your secondary readings are good or not.  I believe the original readings should stay within 10% of the reference values in the chart.  But, I have had them much closer than that https://www.dynakitparts.com/wp-content/uploads/Dyna-ST70.pdf
    avatar
    BCROW

    Posts : 5
    Join date : 2015-09-28

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by BCROW on Sat Mar 07, 2020 4:03 am

    Thanks, Peter

    Yes, that was the plan.

    Maybe someone has a PA060 laying around or still unbuilt that could post their no-load readings but will proceed with the build and see how it goes. Smile
    avatar
    BCROW

    Posts : 5
    Join date : 2015-09-28

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by BCROW on Sat Mar 07, 2020 10:09 am

    From one of Bob Latino's posts about testing iron:

    1. For the power transformer ... Connect the two BLACK wires to a 120 volt AC power source ..
    Measure the AC voltage across the two RED wires > 700 - 760 VAC
    Measure the AC volatge across the two GREEN wires > 6 - 7.5 volts AC
    Measure the AC voltage across the two BROWN wires > 6 - 7.5 volts AC
    Measure the AC voltage from the RED/BLACK wire to the RED/YELLOW wire > 55 to 60 volts AC
    Measure the AC voltage from the BROWN/YELLOW to the RED/YELLOW - 3 to 4 volts AC
    Measure the AC voltage from the GREEN/YELLOW to the RED/YELLOW - 3 to 4 volts AC

    So guess pretty close, a bit high on the 50-60V but that should drop when there's a load.

    PeterCapo
    PeterCapo

    Posts : 755
    Join date : 2008-12-05

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by PeterCapo on Sun Mar 08, 2020 7:50 pm

    Just to be sure, are the figures given in Post n°6 loaded or unloaded?
    avatar
    BCROW

    Posts : 5
    Join date : 2015-09-28

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by BCROW on Mon Mar 09, 2020 1:23 am

    Peter,

    Here's the source thread. Looks like unloaded to me.

    http://dynacotubeaudio.forumotion.com/t2111-testing-st-70-iron?highlight=transformer

    Sponsored content

    PA060 No Load secondary HV tolerances Empty Re: PA060 No Load secondary HV tolerances

    Post by Sponsored content


      Current date/time is Fri Apr 10, 2020 8:20 am