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    Howto cut 5V from the mains line

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    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Howto cut 5V from the mains line

    Post by peterh on Sat Nov 22, 2014 2:09 pm

    It seems that us subscribers in general has an higher mains voltage then the
    (old) amps are built for.

    Well, there is a free cure that does not involve external transformers or
    hot varistors.

    The price to pay is to switch to solid state rectifer.

    The unused 5V filament is well isolated, in fact it is designed to isolate 500V from the
    transformer core.

    What is needed is to connect this winding in series with the primary winding. It could be
    connected in two ways, to add 5V or to subtract 5V, the only way is to test either way and
    measure on the 6.3V winding if it increases or decreases. The one that gives a decreased
    voltage is the "right way".


    arledgsc

    Posts : 330
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Howto cut 5V from the mains line

    Post by arledgsc on Sun Nov 23, 2014 11:09 am

    That is a clever way boosting or bucking the line voltage without the need for an external fixed transformer or auto-transformer.

    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Howto cut 5V from the mains line

    Post by corndog71 on Sun Nov 23, 2014 6:05 pm

    Hmm... I could do that on my ST120 since I didn't bother with a tube rectifier. Has anyone tried this yet?

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Howto cut 5V from the mains line

    Post by sKiZo on Sun Nov 23, 2014 7:30 pm

    I got my lil bucker, so not an issue ...

    But ...

    Just checked my line voltage today, and it's down several points vac from usual. I suppose the ultimate solution would be to come up with a variable supply that you could adjust as needed. Just hate to tie up a perfectly good variac for one purpose ... and variacs aren't as cheap as they once were. My 5a has better than doubled in price ... should have invested in those instead of pork bellies I guess ... ;-}


    Pillo69

    Posts : 104
    Join date : 2012-04-11
    Location : Granada (España)

    Re: Howto cut 5V from the mains line

    Post by Pillo69 on Mon Nov 24, 2014 4:44 am

    Here is a schematic of the operation of a transformer voltage reducer.

    http://dynacotubeaudio.forumotion.com/t2298p15-is-vta-120-in-need-of-step-down-or-bucking-transformer

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