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    ST 70 PS .02 cap

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    bongoman

    Posts : 6
    Join date : 2011-02-02

    ST 70 PS .02 cap

    Post by bongoman on Mon Feb 25, 2013 5:44 pm

    Hello all; first post and I am wondering if anyone can tell me why we need that little .02 cap on the PS bias strip? The one with three legs grounded through the center leg? I'm using the VTA driver board with a can cap and new PT. I see on the VTA site that he uses two little caps grounded and wired to the PT instead of that three legged disc cap.. Don't know the value of those caps.
    Thanks for any help.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST 70 PS .02 cap

    Post by Bob Latino on Mon Feb 25, 2013 6:11 pm

    bongoman wrote:Hello all; first post and I am wondering if anyone can tell me why we need that little .02 cap on the PS bias strip? The one with three legs grounded through the center leg? I'm using the VTA driver board with a can cap and new PT. I see on the VTA site that he uses two little caps grounded and wired to the PT instead of that three legged disc cap.. Don't know the value of those caps.
    Thanks for any help.

    Those two .022 uF caps are reponsible for grounding the center taps of the two 6.3 volt AC filament lines. Those two green caps on the VTA amps are equal to the "double .022 uF cap" that Dynaco used on the original ST-70. As a side note, I had a customer call me one time saying that those two small green .022 uF caps on his VTA amp "looked a little wimpy". Those green caps supplied with the VTA amp kits are 100 volt caps. The voltage that they look at is 1/2 the 6.3 VAC filament line. IOW - those 100 volt caps look at about 3.15 volts AC. Why put a large 200 or 400 volt cap when there is scarcely more than 3 volts there ? Those original Dynaco "double .022 caps" were only rated at 50 volts anyhow ..

    Bob

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