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    Dynaco Mark III VTA and SDS Cap Board

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    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Dynaco Mark III VTA and SDS Cap Board

    Post by stewdan on Sat Feb 12, 2011 5:06 pm

    I am looking for VTA to SDS Cap Board hook up info.

    (1) I currently have a pair of Mark III's ( with Stock Driver Boards ) that I mated with SDS Cap boards. They sound very nice!!!!

    (2) Recently I acquired a pair of Mark III VTA boards and was wondering how to hook them up, since the VTA has caps for setting the Tube Bias. What do I have to avoid using on the SDS Boards??

    Any help would be greatly appreciated.

    Thanks bounce

    Bob Latino
    Admin

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

    Re: Dynaco Mark III VTA and SDS Cap Board

    Post by Bob Latino on Tue Feb 15, 2011 8:41 am

    The bias system on the SDS cap board was designed to be used with stock Mark III bias system. Just ingnore the bias system connection on the SDS cap board and connect the RED/BLACK bias wire from the power transformer to the "- Bias" eyelet on the VTA driver board. The RED/BLACK bias wire will be too short to connect directly to the VTA driver board so you will have to lengthen this wire a few inches.

    Bob

    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Wiring Steps Mark 3 VTA and SDS Cap Board

    Post by stewdan on Sun Feb 20, 2011 10:40 pm


    Hi Bob -- Thanks for responding.

    The version of the SDS Mark III Cap Board that I have uses eight 100 microfarad by 400v caps. So there are 2 caps in series in each section and all 4 sections of the Cap Board have the same capacitance.

    Connection points to the cap board are silk screened on the board for the "4 sections" that basically parrot the Dynaco or some other quad cap.

    I know that I need to make the connections in steps 1-2-3:

    (1) connect the Red/Black wire from the Mark3 Bias line to the BIAS Eyelet of the VTA driver board.

    (2) connect Section 1 of the Cap Board to pin #8 of the GZ34 and one side of the choke.

    (3) connect Section 2 of the Cap Board to the other side of the choke and the red tap wire from the output transformer.

    After steps (1)-(2)-(3), all that I am doing is wiring as per a functional VTAQuapcap as shown in your photobucket../a78/Bob01605/Qyadcapdifferences.jpg

    So now I think I need to do the following:

    (4) connect Section 3 of the Cap Board to one end of a resistor, 2200 ohm 1 watt or some other size? And run a jumper wire from Section 3 back to Section 2.

    (3) connect Section 4 of the Cap Board to the other end of the resistor, and run a wire from section 4 to the B+ eyelet of the Mark 3 VTA board.

    Are my steps correct? What about the resistor size?

    Anything that I missed or did wrong?

    Any and all assistance will be greatly appreciated.

    Stew

    bounce

    Bob Latino
    Admin

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

    Re: Dynaco Mark III VTA and SDS Cap Board

    Post by Bob Latino on Mon Feb 21, 2011 8:36 am

    Hi Stew,

    You are correct.

    Between sections 2 and 3 you run a jumper wire

    Between sections 3 and 4 you run a 2200 ohm resistor. 1 watt will probably work OK. I use a 2 watt resistor here.

    Bob

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