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    is 400 volt k40y9 .22mfd ok to use in mark iii driver board or need 600 volt

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    daniel a

    Posts : 8
    Join date : 2013-12-26

    is 400 volt k40y9 .22mfd ok to use in mark iii driver board or need 600 volt

    Post by daniel a on Fri Jan 10, 2014 6:50 pm

    Is it ok to use 400 volt Russian k40y9 0.22 mfd capacitor on stock Mark III driver board or is a 600 volt required Ive seen both Thanks

    sKiZo

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

    Re: is 400 volt k40y9 .22mfd ok to use in mark iii driver board or need 600 volt

    Post by sKiZo on Fri Jan 10, 2014 7:42 pm

    It's my understanding the voltage can jump up to 585 volts on startup. Dynaco cut some corners in the original amps ... the quad cap in particular exceeded design voltages every time you fired one up. A slow start circuit can mitigate that, but the 600v components would be a good thing.

    SEE BOB'S NOTE BELOW!

    That said, many of these amps have survived 30+ years of use with no major mishaps or meltdowns. So ... six o'one, etc ...


    Last edited by sKiZo on Fri Jan 10, 2014 8:52 pm; edited 1 time in total

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: is 400 volt k40y9 .22mfd ok to use in mark iii driver board or need 600 volt

    Post by Bob Latino on Fri Jan 10, 2014 8:33 pm

    daniel a wrote:Is it ok to use 400 volt Russian k40y9 0.22 mfd capacitor on stock Mark III driver board or is a 600 volt required     Ive seen both    Thanks

    You can use a 400 volt rated Russian PIO cap on the Mark III. That coupling cap looks at about 250 VDC on one side and about NEGATIVE 50 to 60 VDC on the other side of the cap. This is a voltage swing of 300 to 320 volts. A 400 volt rated cap will be OK here. Also - these Russian PIO caps are said to be very conservatively rated. Mike Samara who posts on the Tube DIY Asylum claims to have used 200 volt rated caps as coupling caps and that they never blew even when looking at probably 100 volts over their rated value.

    What sKiZo has said is correct for the quad cap ... but the Russian PIO's on either a stock Mark III or a VTA ST-120 will never look at that much voltage. By the time the Russian PIO's see B+ high voltage, the voltage has gone through a series of drop down resistors on the quad cap and the driver board.

    Bob

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    Re: is 400 volt k40y9 .22mfd ok to use in mark iii driver board or need 600 volt

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