The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    sds cap board st 70 mod

    Share

    Dave
    Guest

    sds cap board st 70 mod

    Post by Dave on Sun Jun 06, 2010 10:19 pm

    I have an st 70 that has been modified output trannys hammond 1650n, VTA board, 6l6 ouyput tubes, and SDS cap board. I use the VTA to its max, no mixing bias or anything from the SDS board. The SDS board is set up using
    1st section 100/100 to rectifier
    2nd section 390/390 to trannys
    3thrd section 100/100 to B+
    4th section 100/100 to no where

    the first thing I would like to do is swap out section 3 to section 4 for B+. In turn make section 3 as an added capacitance for the output trannys. I just am unclear if I can just tie this section to section 2 with a jumper wire or is a resistor needed? What would the max capacitance be acceptable for this section if more can be added .....how much?

    The second thing I would like to do is add esl caps , im not sure how do figure this one

    thanks for any input
    Dave

    Bob Latino
    Admin

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

    Re: sds cap board st 70 mod

    Post by Bob Latino on Mon Jun 07, 2010 6:19 am

    Dave wrote:I have an st 70 that has been modified output trannys hammond 1650n, VTA board, 6l6 ouyput tubes, and SDS cap board. I use the VTA to its max, no mixing bias or anything from the SDS board. The SDS board is set up using
    1st section 100/100 to rectifier
    2nd section 390/390 to trannys
    3thrd section 100/100 to B+
    4th section 100/100 to no where

    the first thing I would like to do is swap out section 3 to section 4 for B+. In turn make section 3 as an added capacitance for the output trannys. I just am unclear if I can just tie this section to section 2 with a jumper wire or is a resistor needed? What would the max capacitance be acceptable for this section if more can be added .....how much?

    The second thing I would like to do is add esl caps , im not sure how do figure this one

    thanks for any input
    Dave

    Hi Dave,

    To add section 3 to section 2 just run a jumper wire between section 2 and 3. You can use almost any amount of capacitance after the choke. Keep in mind though that the amp will only use just so much capacitance and then anything over that will be useless. With the VTA driver board you then run a 2200 ohm (1 or 2 watt) resistor between the 3rd and 4th sections. The purpose of the resistor is to drop the B+ about 20 to 30 volts to the main B+ input eyelet on the driver board.

    ESL capacitors are bypass capacitors that are used to break up resonances in a large capacitor bank. Just using the SDS board as you have IMHO you don't need ESL capacitors.

    One other thing. The SDS board is set up with each pair of capacitors in series. When you use capacitors in series the effective capacitance is cut in half while the power handling is doubled. The 100/100 section in series gives you an effective capacitance of 50 uF, the 390/390 section gives you 195 uF etc.

    Bob

    Dave
    Guest

    sds cap board st 70 mod

    Post by Dave on Tue Jun 08, 2010 9:23 pm

    Hi Bob, i added the extra caps today big difference in the sound, by the way this amp has the webber WZ68. im going to play with this and probably add some more. it made a big difference on the overall sound . I run this out side on 2 EV12l with 2 horns. Drivers cut off at 4200hz and the horns starting at 550 hz . just with the extra 50 uf i noticed the highs were more crisp and the bass was a bit more pronounced. and the power transformer seemed a bit cooler i will be spending more time with this as the week goes on when I can spend a few hours running it checking choke and tranny temps

    Dave

    Sponsored content

    Re: sds cap board st 70 mod

    Post by Sponsored content Today at 10:06 am


      Current date/time is Tue Dec 06, 2016 10:06 am