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    Is it okay to parasitically use some power from the ST70's PA060 transformer?

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    Ed Rosenberger

    Posts : 16
    Join date : 2014-10-23
    Location : Gilboa, Ohio

    Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by Ed Rosenberger on Fri Dec 19, 2014 10:11 pm

    I am using a built-in (4-channel input to 1) source switch in my VTA ST70 amp because I do not
    want to use a pre-amp or at the same time do not want to continually change source wires.
    This switch requires an input power of 5-12Vac, uses about 15mA and should arrive in January.
    This ST70 also has the optional stepped attenuator volume control and the octal driver board.

    The following wire pairs on the PA060 power transformer has these approximate output
    values between 117 to 120Vac line input:

    Across the two RED      wires > 700 to 750 volts AC (300mA)
    Across the two WHITE  wires > 5 to 6         volts AC (4A)
    Across the two GREEN  wires > 6.0 to 7.0   volts AC (5A)
    Across the two BROWN wires > 6.0 to 7.0   volts AC (5A)

    So to power this switch with its 5V relays, my thought is to tap off of either the two Green or
    Brown transformer wires using their 6-7Vac.....and hopefully not blow something up.

    My question is:
    Would it work and isn't it better if I pulled 5V equally from both channels, one Green wire
    and one Brown wire?
    Not sure at this point which Green or what Brown wire.....or even if it makes any difference.

    Thank you,
    Ed

    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by MontanaWay on Fri Dec 19, 2014 10:27 pm

    I would just tap into ONE set of the 6.3VAC filament winding. The loading of the switch is so small, it will not cause you any problems.
    For a while, I used a the same filament winding to run my chassis cooling fan supply, which draws 200mA, and it worked just fine!
    These days I use a separate small 12VAC transformer, as the 6.3V were just not enough for the cooling fans, otherwise I'd keep using it.

    Ed Rosenberger

    Posts : 16
    Join date : 2014-10-23
    Location : Gilboa, Ohio

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by Ed Rosenberger on Fri Dec 19, 2014 10:33 pm

    Great....someone who has already done it!
    Can't ask for a better answer.....thank you MontanaWay!

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by peterh on Sun Dec 21, 2014 11:43 am

    The ST70 manual states ( p.2 )
    Two power takeoffs with independent heater windings to eliminate interaction. Each 6.3 volts 1 amp, 350 volts dc 10 mao Dynakit pre- amplifiers plug in directly without modification.

    I have  found no layout of the front octal sockets however,this is extracted from the build instructions
    ( it might be in error )
    1 and 2 _might_ be 6.3V
    3 is ground
    5 B+
    8 bias test


    Last edited by peterh on Sun Dec 21, 2014 11:55 am; edited 1 time in total (Reason for editing : spelling)

    Ed Rosenberger

    Posts : 16
    Join date : 2014-10-23
    Location : Gilboa, Ohio

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by Ed Rosenberger on Sun Dec 21, 2014 2:57 pm

    Good point peterh....I guess in the past pre-amps did suck power from the power transformer through the two front mounted sockets.
    I was more concerned with pulling an un-equal current from the two 6.3V winding's.
    I understand now that the small amount of added current flow from one of these winding's won't affect the music's channel balance.

    The only place I could find good voltage/amp information on the PA060 output wires was at the very end of Triode's outstanding instruction manual.
    http://site.triodestore.com/NEWST70Instructions.pdf

    Three pages up from the last page is information on socket voltages on pins 1 thru 9.
    At this point I'm not sure if those values on the first two columns would be correct with a VTA driver board.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by tubes4hifi on Tue Dec 23, 2014 7:38 pm

    if you have a VTA70 driver board V2 & V3 (the right channel) are connected to one set of 6v windings and V1 is connected to the other pair of 6v windings,
    so if you want to pull a few ma of 6v might as well use the left channel windings

    Ed Rosenberger

    Posts : 16
    Join date : 2014-10-23
    Location : Gilboa, Ohio

    Re: Is it okay to parasitically use some power from the ST70's PA060 transformer?

    Post by Ed Rosenberger on Wed Dec 24, 2014 1:24 am

    Thank you Roy; using the L/H 6.3 volt channel winding's makes sense.....that's what I'll do.

    Ed

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